Magnetic Hard Disks Photoconductors - Fujielectric · magnetic hard disk currently under development. In order to prevent the depletion of recording bits, tolerance for the size of

Whole Number 198

Magnetic Hard DisksPhotoconductors

The difference in image quality is due tothe difference in photoconductors.Fuji Electric provides a wide range ofphotoconductors for clearer images.

Fuji Electric Photoconductors

The need for clearer imaging continues to increase for copy machines, facsimile machines,printers and other information devices. Demands are also increasing for the application ofadvanced technology to photoconductors, the quality of which determines image quality. FujiElectric has a track record of achieving higher resolutions, faster response speeds andtechnological innovation. We offer a varied product line of photoconductors for copy machineand facsimile applications and photoconductors for printer applications. From a fully automatedintegrated production line that incorporates the latest FA technology and 3 globalmanufacturing bases in Japan, US and China that are under strict quality control, Fuji Electric isable to provide reliable products speedily and with a full range of services.

Automated inspection equipment

Photoconductors for use in printers

Photoconductors for use incopy machines

Cover photo:The hard disk drive (HDD) has

become an essential component ofthe modern personal computer. Theincreasing data storage capacity ofHDDs and their utilization in net-working and AV (audio-visual) infor-mation systems are expected to leadto the development of new markets.

Through the latest technologicaldevelopment, Fuji Electric will con-tinue to provide magnetic harddisks with a leading-edge perfor-mance, as critical components in theconstantly evolving HDD.

The cover photo depicts thebright future for HDDs and showsthe constantly evolving magnetichard disks in combination with vari-ous AV products into which HDDsare expected to be installed in thefuture.

Head Office : No.11-2, Osaki 1-chome, Shinagawa-ku, Tokyo 141-0032, Japan

CONTENTS

Magnetic Hard DisksPhotoconductors

Present Status and Future Prospects for Magnetic Hard Disks 68

Magnetic Layers for Perpendicular Recording Media 73

Magnetic Printing Technology 77

Present Status and Future Prospects for Photoconductors 83

Organic Photoconductors for Printers 87

Organic Photoconductors for Digital Plain Paper Copiers 92

Process Units for Electrophotographic Machines 96

Magnetic Hard Disks

Photoconductors

Vol. 48 No. 3 FUJI ELECTRIC REVIEW68

Nobuyuki TakahashiAkihiro OtsukiTomonobu Ogasawara

Present Status and Future Prospectsfor Magnetic Hard Disks

1. Introduction

In the early 1980s, when computer use transi-tioned from main frame computers used in offices toso-called personal computers for private business andapplications, hard disk drives (HDDs) as externalstorage devices achieved a crucial technological break-through. Under these circumstances, Fuji Electricsucceeded in commercializing thin film magnetic harddisk processed with a sputtering method, and has beensuccessively introducing new products at appropriatetimes as the recording density of HDDs has beenincreasing.

In recent years, recording densities have beenincreasing at an annual rate of 100 %. As a result, theper-bit cost of hard disk has dropped dramatically andhas become lower than that of paper recording media.HDDs, also having a high level of processing capabili-ty, are expected to extend their applications to fieldsother than personal computers.

This paper describes the technological trends thatsupport the future expansion of the market for HDDs,and outlines the present status and future prospects ofFuji Electric’s technology for magnetic hard disk.

2. Trends in Market and Technology for HDDs

Due to their drastic reduction in per-bit cost, aswell as their high capacity and high access rate, HDDsare expected to dominate such new fields as consumerelectronics and IT (information technology) throughoutperforming other storage systems.

Reflecting the continuously increasing recordingdensities, Fig. 1 shows the trend of HDDs’ recordingdensities as demonstrated by research institutesthroughout the world, one or two years ahead ofcommercialization.

In 2001, HDDs equipped with 30 Gbits/in2

(40 Gbytes/platter, 95 mm in size) magnetic hard diskdeveloped by Fuji Electric were commercialized. Inaddition, Fujitsu Ltd. and Seagate Technology success-fully demonstrated 100 Gbits/in2 magnetic hard disk.In 2002, various companies are promoting their devel-opment of commercial 60 Gbits/in2-class HDDs.

The technological development of magnetic headsand magnetic hard disk is crucial for realizing suchsophisticated HDDs as mentioned above. Technologi-cal challenges facing the development of magnetic harddisk, in which Fuji Electric specializes, are classifiedinto the following:™ Magnetic characteristics of thermal stability and

reduced media noise™ HDI (head-disk interface) characteristics of low-

flying stability and high reliability (high durabilityand high environmental resistance)

Figure 2 shows a schematic representation of the

Fig.2 Relationship between elementary technologies andrequested characteristics for magnetic hard disk

Fig.1 Annual trend in recording densities

1992 1996 2000 2004(Year)

0.1

1

10

100200

Rec

ordi

ng

den

sity

(G

bits

/in2 )

Productsshipped

R&D

Magnetic head

Magnetichard disk

(Layer structure)

Lubricant layerProtective layer

Magnetic layerIntermediatelayerUnder layerSubstrate

(Elementary technology)

Magnetic layertechnology(Grain size control)Substrate technol-ogy(Ra,Wa)

Lube and protec-tive layer technol-ogy(Interface to magnetic head)

(Requested characteristics)HDIcharacteristics

Stability of lowhead flyingHigh durable reliabilityHigh resistivityto environmentaldegradation

Magnetic characteristics

Thermal stabilityLow media noise


intricate relationship between elementary technologiesand requested characteristics for magnetic hard disk.

The next chapter outlines the progress of theseindividual elementary technologies.

3. Present Status of Fuji Electric’s Technologyfor Magnetic Hard Disk

3.1 Substrate technologyThe performance of currently-used aluminum sub-

strates directly affects the low-flying stability of mag-netic heads, which is a primary technology thatsupports higher recording densities, and plays animportant role in reducing physical defects of smallrecording bits.

The physical parameters that determine the low-flying stability of magnetic heads are micro-waviness(Wa) and surface roughness (Ra). Reducing Wa requiresapplying an improved grinding technique to the pol-ished substrates, forming NiP plated film with im-proved thermal deformation resistance, and applying ahighly precise polishing technique. The subsequenttexture process greatly affects Ra.

The optimization of processes for the above-men-tioned requirements allowed surface properties (Ra =0.25 nm, Wa = 0.15 nm) as shown in Fig. 3 to beobtained. As a result, the glide avalanche propertyshown in Fig. 4 was obtained and this almost achievedthe low-flying stability required for the 60 Gbits/in2

magnetic hard disk currently under development.In order to prevent the depletion of recording bits,

tolerance for the size of surface defectives is continu-

ously decreasing. The reduction of defects is essentialfor higher reliability when magnetic disk media areinstalled in HDDs, as well as for high yields in themedia manufacturing processes. When mass produc-tion of 30 Gbits/in2 recording media started in 2001,Fuji Electric reviewed items to be improved and ispromoting the advancement of the following:™ Reduction of micro pits and scratches during the

substrate polishing process™ Reduction of scratches during texture processing

and of micro-contamination during washing

3.2 Magnetic film technologyTo realize high recording density, the extent to

which stable recording bits can be made finer is ofprimary importance. Magnetic films for recordinghave gone through several changes since the adoptionof thin films processed with a sputtering method, andwill undergo further change as they are optimized foruse in combination with magnetic read/write heads. Inthe future, it will be important to design magneticfilms that correspond with the development of magnet-ic heads.

This paper introduces a road map for the futuredevelopment of magnetic films.

The crux of the development of magnetic films forlongitudinal recording is to achieve an appropriatebalance (tradeoff) between reduced media noise andthermal stability (smaller thermal decay). In addition,the limited writability of magnetic heads keeps thecoercivity of magnetic media moderate, particularly ina dynamic range. To be specific, low media noise isrealized with magnetically decoupled crystal grainsand finer grains in a magnetic recording layer, andthrough additional measures to secure thermal stabili-ty. The importance of thermal stability was recognizedduring the process of realizing 30 Gbits/in2 magnetichard disk, and requires further improvement. This isthe reason for interest in the AFC (anti-ferromagneticcoupling) structure(1)(2), which was developed in GMR(giant magnetoresistive) elements and is expected to beapplied to magnetic disk media. Figure 5 shows theroad map for development of magnetic films. As shownin Fig. 5, overlapping the development of conven-tional-structure 60 Gbits/in2 longitudinal-recording,

Fig.4 Improvement of glide avalanche properties

Fig.3 Surface properties of magnetic hard disk

+4.0

–4.0

(nm

)

0.71

(mm

)

(mm) 0.9500

05

100

5

10

0

10

20

10 nm

0 nm

5 nm

(nm

)

(µm)

(µm

)

(a) Surface roughness measured with AFM (Ra = 0.25 nm)

(b) Surface micro waviness measured with Zygo (Wa = 0.15 nm)0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.500

1

2

3

4

5

6

AE

sig

nal

vol

tage

(V

)

Magnetic-head flying height (µin)

Conventional 1Conventional 2Newly developed


100 Gbits/in2 perpendicular-recording is being investi-gated.

3.3 Lube and protective film technologyIn magnetic recording, it is important to minimize

clearance between the magnetic recording layer andthe magnetic head element, to make the media surfacesmoother as described in the substrate technologysection, and to make the lube and protective filmthinner to the extent possible.

Future development, however, faces increasinglydifficult challenges for securing flying stability, over-coming interaction between the magnetic head andmagnetic disk in an extremely low flying state, forensuring the required durability in the case that amagnetic head contacts a magnetic disk, and forensuring corrosion resistance of the magnetic layer,which may be required because the film is very thin.

Figure 6 shows the road map for development oflube and protection films.

Since having established CVD technology for 5nm-thick protective films in 30 Gbits/in2 magnetic disks,Fuji Electric is developing thinner protective films andexpects to be able to realize durable and corrosionresistant 2.5 nm-thick films, through securing furtherthickness uniformity and higher film hardening. Inaddition, Fuji Electric is investigating the feasibility ofFCA (filtered cathodic arc) films through using a newdeposition method, to fabricate extremely thin films inthe future.

Fuji Electric is promoting the optimization oflubricant films according to individual HDDs designs.The basic concept for achieving flying stability of amagnetic head lies in forming the lubricant film asthinly as possible on the protective film with surfaceresistivity controlled by a Fuji Electric proprietarytreatment. A thin lubricant film can more easily bedesigned by adopting a lump load system in place ofthe previous CSS (contact start stop) system.

In high-rpm HDDs for server applications, self-recovering capability of the lubricant essential fordurability and prevention of lubricant depletion causedby spin-off must be balanced in the design of a bondinglubricant. On the other hand, lower flying height of a

magnetic head can lead to increased self vibration(instability) of the head itself. This phenomenon is akey factor for magnetic head reliability because it canincrease the risk of accidental trouble in actual severeenvironments. A Fuji Electric study shows that suchtrouble is related to various properties on the mediasurface such as micro–surface-waviness and lubricantthickness. Figure 7 shows an evaluation of magnetic-head flying stability with an AE (acoustic emission)sensor.

According to measurement with an AE sensor,magnetic-head flying stability becomes worse withincreasing lubricant thickness. In addition, moguls areformed on the lubricant surface, and in other words thesurface becomes bumpy. A key factor in the futuredevelopment of lubricant is to prevent moguls frombeing formed.

Based on these conditions, Fuji Electric has devel-oped a proprietary lubricant refining technology SFE

Fig.6 Road map for development of lube and protective film

Fig.7 Evaluation of magnetic-head flying stability with an AEsensor

Fig.5 Road map for magnetic film development

Recordingdensity

Type ofrecordinglayer

Grain size

CoercivityMagneticlayer

<Longitudinal recording>

<Perpendicular recording>

Conventional structure

AFC (anti-ferromagnetic coupling)stucture

CoCr alloy systemMulti layered film system,

hybrid film system

8 to 9 nm 7 to 9 nm 5 to 6 nm 4.5 to 5 nm295 kA/m 334 kA/m 478 kA/m 637 kA/m

CCPB/soft under layer

(Co/M)n/soft under layer

CCPB/AFCCCPB system

60 Gbits/in230 Gbits/in2 120 Gbits/in2 240 Gbits/in2 Recordingdensity

Glideavalanche

Protectivefilm

Lubricantfilm

30 Gbits/in2 60 Gbits/in2 120 Gbits/in2 240 Gbits/in2

6 nm 5 nm 4.5 nm < 4 nm (near contact)

5 nm 2.5 to 3 nm 2 nm < 2 nm (FCA)

Mixture system with additive

New lubricationsystemControl of molecular structure

Design control of molecular weight

<CVD> Surface chemical modification

<PFPE>Improvement of molecular weightdistribution

0 10 20 30 40 50 600

3

6

9

12

15

Magnetic-head flying time (min)

AE

sig

nal

inte

gral

(a.

u.)

(a) Lubricant-thickness-dependence of magnetic-head flying stability

(b) Observation of lubricant thickness change with OSA

1.35+0.2 nm1.55+0.2 nm1.85+0.2 nm

1.35 nm PFPE +0.2 nm lubricant additive1.35 nm PFPE +0.2 nm lubricant additive



1.35 nm PFPE +0.2 nm lubricant additive



(PFPE + lubricant additive)


(supercritical fluid extraction) to perform detailedmolecular weight design according to individual HDDdevelopment programs. In addition, based on thistechnology, Fuji Electric is promoting the study ofnear-contact-recording and contact-recording systemsin their basic research stages.

4. Prospects of Future Technology

As described above, the increase of recordingdensity and cost reduction of recording media arecreating new markets for HDDs.

Along this trend, Fuji Electric has been applyingits originality to find answers to unsolved issues and topromote developments in new fields for recordingmedia. This paper introduces some new technologiesthat show potential for success.

4.1 Glass substrate mediaWith their characteristic advantages of high im-

pact resistance and TMR (track miss registration)resistance, glass substrates are widely used in porta-ble- and server-PCs. Magnetic films formed on glasssubstrates exhibit, however, isotropic magnetism be-cause of the isotropic surface property of glass sub-strates. Their magnetic parametric performance istherefore inferior to that of oriented magnetic filmsformed with Al-substrate media. As a result, futuredemand will be strong for oriented magnetic films onglass substrates. Although there exists a process tosecure oriented magnetism through forming NiP andthen performing the same texturing as Al substrateson glass substrates, this process impairs the advanta-

geous characteristics of glass substrates and increasesthe cost.

Fuji Electric, having developed a repeatable pro-cess to form the same texture lines on glass substratesas on Al-substrates and an original seed layer deposi-tion processes in a vacuum, has optimized the combi-nation of these processes to achieve magnetic-headflying and magnetic parametric performances thatcompare favorably with Al-substrate magnetic media.

In the future, with its high impact resistance, thenewly-developed glass-substrate magnetic media areexpected to be used for various mobile HDD applica-tions in addition to PC applications, while smaller sizemagnetic media are pursued.

4.2 Perpendicular recording mediaIn recent years, applied research for perpendicu-

lar-recording media is increasingly being encouragedbecause the balance among low media noise, thermalstability and magnetic head writability can be de-stroyed in higher-density longitudinal recording media.In the future, attention will be given to the feasibilityof perpendicular recording media with densities great-er than 100 Gbits/in2. Whether or not any one of thevarious media layer structures under development isfinally chosen depends on technological breakthroughsas well as productivity. Fuji Electric is investigatingevery possible development and application related toperpendicular recording media. It is also promotingthe development of longitudinal and perpendicularrecording films simultaneously as shown in the road-map, through setting the demonstration of 100 Gbits/in2

magnetic recording films as a first goal. As digital

Fig.8 Usage development of AV-HDD

Mobilephone

Computer

PC-HDDAV-HDD

Much small AV-HDD

Car electronics(navigation system, etc.)

Digital camera/digitalvideo camera

Video recorder

Videorecorder

Stand alone

PDA

Mobile server(HDD)

Internet(outside network)

In-house network

TV

Consumerequipment(refrigerator, airconditioner, etc.)

Home server (HDD)

i-mode terminalWAP terminal

Network system

Networking of AV device and consumer equipmentin house with home server. Archival management of AV information, operationcontrol of AV devices, and identical control of interface for outside with home server.Mobile server connects directly home server toexchange information with and control the homeelectronic device, as well as connection to internet.

Gameequipment


information technology spreads from PCs to AV (audio-visual) systems, larger-capacity memory will be re-quired, which leads to high hopes for perpendicularrecording media and prompts their development anduse.

4.3 Magnetic printing mediaAfter magnetic hard disk has been incorporated

into an HDD, servo information must be written on themedia to control the magnetic head to realize appropri-ate write and read properties. As recording densitiesincrease, servo writing requires updating of the servowriter and longer times for the servo writing process,resulting in higher cost. With the cooperation of anHDD manufacturer, Fuji Electric has recently estab-lished a process for writing pre-servo informationthrough the use of a contact system, and was the firstcompany in the world to realize mass production of15 Gbits/in2- and 30 Gbits/in2-recording media withinstalled pre-servo information. This technology canbe applied to higher-density recording media in thefuture. It was demonstrated that the servo printingsystem could effectively be applied to perpendicularrecording media. In addition, the servo printingsystem is expected to be widely applied to HDDs forAV applications as a potential means to write securityinformation to disk media, for which PC developmenthas given little consideration in the past.

Figure 8 shows the development of AV-HDD appli-

cations in the future. The technologies described inthis chapter will provide specific solutions for issuesimportant to market development, such as low cost,large capacity and security.

5. Conclusion

This paper outlined achievements of Fuji Electric’stechnological developments and the present status ofmagnetic hard disk. Technological development tomaintain the annual 100 % increase in recordingdensity of recent years is becoming more difficult yearafter year. Nevertheless, it is expected that 60 Gbits/in2

hard disk will probably be realized in 2002 through thecombined efforts of the concerned parties.

Fuji Electric is determined to lead this technologi-cal development and to contribute to the HDD industryin cooperation with other companies as in the case of30 Gbits/in2 hard disk. We hope such efforts lead tothe expansion of the HDD market.

References(1) Abarra, E. et al. Longitudinal magnetic recording

media with thermal stabilization layers, Appl. Phys.Lett. vol.77, 2000, p.2581.

(2) Fullerton, E. et al. Antiferromagnetically coupled mag-netic layers for thermally stable high-density record-ing, Appl. Phys. Lett. vol.77, 2000, p.3806.


Hiroyuki UwazumiYasushi SakaiShunji Takenoiri

Magnetic Layers forPerpendicular Recording Media

1. Introduction

Hard disk drives (HDDs) are recently being incor-porated into video recorders, car navigation devices,family game machines, etc., as devices (AV-HDDs) tostore digital AV (audio-visual) information such asmovies and television programs. Because the AV-HDDhas the features of large capacity, high speed and lowcost, it is suitable for long-time recording, high-speedrandom access and multi-channel simultaneous record-ing and playback. The demand for AV-HDDs isanticipated to increase rapidly in the near future. Inresponse to demands from this new market growing ata rate of 100 % per year, it is necessary to furtherincrease the recording density, which is now at a level of30 Gbits/in2 in mass production.

Present HDDs utilize a longitudinal magneticrecording system in which the recorded magnetizationis aligned in the film plane. If we increase therecording density of this system, the recorded magneti-zation becomes unstable due to the thermal energy atroom temperature, thus creating the problem of ther-mal agitation of magnetization. Recently, a newrecording system suitable for ultra-high density record-ing, i.e. a perpendicular magnetic recording system(1),has been attracting considerable attention, and thisnew system provides greater stability of the recordedmagnetization as the recording density increases.

Figure 1 is a schematic drawing showing the gener-al layer structures and recorded magnetization forperpendicular magnetic recording media. Successivelayers are stacked on the substrate in the order of softmagnetic underlayer, non-magnetic interlayer andmagnetic recording layer for the storage. Because therecorded magnetization is aligned vertically, as op-posed to longitudinally, the film structure and magnet-ic properties are quite different from those of thelongitudinal magnetic recording media. To realizeperpendicular magnetic recording media, it is essentialto redevelop and redesign the film structure, thin filmmaterial and processing techniques.

Of this group, the development of a high perfor-mance magnetic recording layer that retains therecorded magnetization is most important. Figure 2

shows several materials that may be used as the thinfilm material for magnetic recording layer such asCoCrPt alloy film, Co/X multilayer, amorphous filmand FePt ordered lattice alloy film, depending on theapplicable areal recording density. These materialseach have their own characteristic microstructure,physical properties and, particularly, perpendicularmagnetic anisotropy energy Ku. The material mostsuitable for the areal recoding density to be appliedmust be selected for the development of the magneticrecording layer.

From early on, Fuji Electric started the develop-ment of perpendicular magnetic recording media torealize the next generation ultra-high density record-ing media and also initiated active joint research with

Fig.2 Materials for the perpendicular magnetic recording layer

Fig.1 Layer structures and schematic drawing of the recordedmagnetization for perpendicular recording media

Carbon overcoat (< 5 nm)

Nonmagnetic interlayer (< 5 nm)

Magneticrecordinglayer (< 20 nm)

Recordedmagnetization

Soft magnetic underlayer(thickness 100 to 200 nm)

Glass substrate

Areal density (Gbits/in2)

50 100 200 >300

CoCrPt alloy film Composite type media

Co/X multilayer

Amorphous film

FePt ordered lattice alloy film


the Research Institute of Electrical Communication ofTohoku University and the Science & Technical Re-search Laboratories of NHK.(2)(3) In addition to thedevelopment of CoCrPt alloy thin film and Co/Pdmultilayer with 100 to 200 Gbits/in2, which are theimmediate objectives, we are developing amorphousfilm which might be applicable to the ultra-highdensity recording media suitable for densities in excessof 300 Gbits/in2.

In this paper, we will introduce recent results ofthe research by Fuji Electric on high recording densitytechnology, magnetic domain control of the soft mag-netic underlayer and an evaluation technique for themedia, which are essential technologies for the realiza-tion of perpendicular magnetic recording media.

2. Magnetic Domain Control of the Soft MagneticUnderlayer

The soft magnetic underlayer functions to raise thestrength of the writing field of the recording head andthe field gradient applied to the magnetic recordinglayer, and to improve the recording resolution(4). How-ever, the soft magnetic film is liable to have acomplicated magnetic domain structure in which thedirection of the magnetization is grouped in severalmagnetic domains. Because large stray fields will begenerated from the boundaries (domain walls) of themagnetic domains, this will cause high spike noiseduring the read back of signal. Figure 3 (a) shows atypical observed result of the spike noise measured bya GMR head as generated from a CoZrNb alloyamorphous soft magnetic layer with a thickness of100 nm sputtered on the glass substrate. Dark colorareas correspond to the spike generating locations andsuch locations are distributed over the whole area ofthe disk.

Fuji Electric established a layer structure andrelated process technology so as to reduce the spikenoise effectively through adopting magnetic domaincontrol of the soft magnetic underlayer using anantiferromagnetic AF film. In this layer structuredeveloped by Fuji Electric, AF film which consists ofMnIr alloy is sputtered onto a seed layer, and then softmagnetic film which consists of CoZrNb is sputtered.

Ideally, the magnetization of the AF film will bealigned radially from the center of the disk and aradially biased magnetic field will be applied effective-ly to the soft magnetic underlayer, and thus formationof a magnetic domain can be prevented.

However, in actuality, the stray field from thetarget during the sputtering to align the magnetizationof AF film is not always uniform, and the direction ofthe magnetization may change during sputtering of themagnetic recording layer due to heating of the sub-strate. Recognizing the antiferromagnetic characteris-tics of MnIr film vanish at temperatures above 280°C,we undertook the challenge of developing a magneticannealing process to control the direction of magneti-zation of the AF film itself without degrading produc-tivity. In this process, after sputtering of the magneticrecording layer, the temperature of the substrate willbe raised up to about 300°C in the heating chamber ofthe sputtering machine and then will be cooled down toabout 180°C in the cooling chamber where a uniformradial magnetic field will be applied. The magneticfield strength will be about 80 kA/m (1 kOe) and themedia will be retained for about 15 seconds in thecooling chamber. Figure 3 (b) shows a typical observa-tion result of the spike noise generated from mediasubject to the annealing process. The spike noise overthe whole area was eliminated and we were able toreduce the spike noise effectively without degradingthe productivity.

The layer structure and process described aboveare also applicable to any soft magnetic materials. Weare developing new materials with higher saturationflux densities to realize higher density magnetic re-cording systems.

3. Technology for High Density Recording Layer

3.1 CoCrPt-SiO2 granular mediaTo use CoCrPt alloy film as the magnetic recording

layer of a perpendicular magnetic recording system,the following conditions must be realized.q Media noise must be reduced by segregating Cr at

the grain boundary of fine Co alloy grains in orderto reduce the intergranular magnetic interactionsbetween the grains.

w The c-axis orientation of the Co alloy grain normalto the film plane must be improved and a high Ku

value must be induced.Condition q can be realized by increasing Cr

content, as in the case of the longitudinal magneticrecording system. In addition, it is effective to add Taor B, etc., however at the same time, the Ku value isliable to deteriorate. Condition w can be realized bypromoting epitaxial growth to optimize the non-mag-netic interlayer, however it is known that this is liableto limit Cr segregation at the grain boundary.

Fuji Electric has been developing micro-structurecontrol technology consisting of a CoCrPt alloy granu-

Fig.3 Typical observation results of the spike noise

(a) Without AF film (b) With AF film andmagnetic annealing process


lar layer with SiO2 additive for a longitudinal magneticrecording system. With these materials, a high Ku

value can be realized, because SiO2 can be easilyprecipitated to the grain boundary of the Co alloygrains and it is not necessary to increase Cr content oradd elements for reducing the magnetic interactionsbetween grains. Observing such features, we initiatedan investigation of CoCrPt-SiO2 granular media as themagnetic recording layer for a perpendicular magneticrecording system.

Figure 4 shows a TEM (transmission electronmicroscope) image of a CoCrPt-SiO2 granular magneticlayer manufactured by an RF magnetron sputteringprocess using a CoCrPt/SiO2 composite target on an Ruinterlayer. A granular structure can be seen in whichcrystal grain boundaries (whitish areas in the image),composed mainly of the oxide, are formed surrounding6 nm crystal grains. It was verified by X-ray diffrac-tion analysis that the c-axis orientation of Co alloygrains was also excellent. These media have a veryhigh Ku value of 4 × 105 J/m3 which is more than twicethe value of the CoCrPt magnetic recording layer andthe loop squareness is almost 1.

Figure 5 shows MFM (magnetic force microscopy)images of magnetization bits recorded by a single poletype head on CoCrPt-SiO2 granular media with a soft

magnetic underlayer. In Fig. 5 (a), (b) and (c) are thebits recorded at linear recording densities of 20, 28 and31 kfc/mm (500, 700 and 800 kFCI) respectively. Rela-tively clear magnetization switching is observed evenat the linear recording density of (b) which correspondsto a recording density of 82 Gbits/in2. These mediahave excellent thermal stability and the read backsignal decay is almost zero at any recording density.

As mentioned above, the CoCrPt granular magnet-ic layer with SiO2 additive is a promising material formagnetic recoding layers with recording densities of100 to 200 Gbits/in2. We are making further efforts tooptimize the layer structure and composition of thematerial.

3.2 CoTb amorphous composite-type mediaAs mentioned before, amorphous film, consisting of

a rare-earth metal such as Tb and a 3d transitionmetal such as Co or Fe, is a material that holdspotential for realizing the high recording densitybeyond 300 Gbits/in2. Because of the extremely strongexchange interaction in the film plane direction, themagnetization is widely coupled. Therefore, it isdifficult to implement microscopic magnetizationswitching on the order of nanometers.

We investigated a process for realizing the micro-scopic magnetization switching of amorphous film anddiscovered that a composite type media layered withCoCrPtB film, for which the magnetization switchingunit is small, is compatible with both thermal stabilityand media noise characteristics.

Fig.5 MFM images of CoCrPt-SiO2 granular media

Fig.4 TEM image of CoCrPt-SiO2 granular magnetic layer

Fig.6 SNR and time decay of the read back signal as afunction of CoTb layer thickness

CoTb/CoCrPtB (20 nm)Linear density 25 kFCI

CoTb thickness (nm)

CoTb/CoCrPtB (20 nm)Linear density 300 kFCI

Sig

nal

dec

ay(%

/ dec

ade)

SN

R (

dBp-

p/rm

s)

0 2 4 6 8 10 12

CoTb thickness (nm)0 2 4 6 8 10 12

20

18

16

14

12

10

0

-2

-4

-6

-8

22

5 nm

(a) (b) (c)


Figure 6 shows the signal-to-media-noise ratio(SNR) of the composite type media formed from CoTbamorphous film layered on a CoCrPtB alloy film,having a thickness of 20 nm at the linear recordingdensity of 12 kfc/mm (300 kFCI), and the time decay ofthe read back signal measured at 1 kfc/mm (25 kFCI)for the evaluation of thermal stability, as a function ofthe CoTb layer thickness.

At a CoTb thickness of 6 nm, SNR is at itsmaximum value and SNR is improved by 2 dB com-pared with its value in the case without CoTb. Withthe increase of CoTb thickness, the time decay of theread back signal is improved. The time decay is almostzero when CoTb thickness is greater than 6 nm.Excellent SNR and thermal stability characteristicswere obtained from composite type media having alayer structure of CoTb (6 nm) and CoCyPtB (20 nm).

By observation using an MFM, it was verified that70 Gbits/in2 could be realized with this media. Wehope to be able to achieve even higher recordingdensities through combination with granular media.

4. Evaluation and Analysis Technique forPerpendicular Recording Media

In the development of excellent magnetic recordingmedia, evaluation and analysis techniques are indis-pensable. Especially, for quantitative discussions ofthe noise characteristics of high-density recordingmedia, the micro recording bits have to be observedand evaluated directly, and then the causes of noisegeneration must be investigated. For this purpose, weare developing an evaluation and analysis techniquefor the magnetized patterns of perpendicular magneticrecording media using an MFM and are workingjointly with the Science & Technical Research Labora-tories of NHK.(3) In this paper, we would like tointroduce a technique for evaluating and analyzingmagnetic cluster size in an ac erased state, which isconsidered to have a strong correlation with medianoise.

The number of magnetic clusters in the orientedmagnetization can be viewed by observing ac erasedmedia with an MFM. After image processing of theobserved image, we approximated each cluster with acircle and obtained its diameter D and standarddeviation σ. Figure 7 shows the relationship betweenstandard deviation σ of the magnetic cluster andnormalized media noise of the perpendicular magneticrecording media for several magnetic recording materi-als and layer structures. The standard deviation σshows a strong correlation with the media noise andthe media noise decreases with the decrease of σ. It isalso clear that the size of the cluster has a strongcorrelation with the recording resolution.

Such analysis is very effective for quantifying thetarget magnetic cluster size necessary for higher

recording density and lower noise. Therefore, thisanalysis technique is useful for the design of media.Now, we are investigating procedures for achievingbetter resolution of the MFM image, so that an evenmore precise evaluation can be obtained.

5. Conclusion

Fuji Electric is performing comprehensive researchand development of perpendicular magnetic recordingmedia for ultra-high-density recording, including themagnetic domain control and the evaluating analysistechnique. In addition to the development of theCoCrPt-SiO2 granular film magnetic recording layerfor 100 to 200 Gbits/in2, we are developing amorphousfilm which has the potential to realize ultra-highrecording densities of more than 300 Gbits/in2. We areworking toward realization of the high capacity AV-HDD which is expected to become a major sales itemon the market. Lastly, we extend our thanks to Prof.Yoshihisa Nakamura and Prof. Hiroaki Muraoka of theResearch Institute of Electrical Communication, To-hoku University, and to Dr. Takahiro Tamaki, Seniorresearch engineer of the Science & Technical ResearchLaboratories, NHK for their helpful advice.

References(1) Takano, H., et al. Abstracts of the 8th Joint MMM-

Intermag Conference, CA-01, 2001, p.131.(2) Shimatsu, T., et al. J. Magn. Magn. Mater., Vol. 235,

2001, p.273-280.(3) Kitano, M., et al. J. Magn. Magn. Mater., Vol. 235,

2001, p.459-464.(4) Iwasaki, S., et al. IEEE Trans. Magn., Vol.15, No.6,

1979, p.1456-1459.

Fig.7 Relation between normalized media noise and standarddeviation of the magnetic cluster size

70

60

50

40

30

20

10

00 5 10 20 2515

Linear density300 kFCI

Linear density100 kFCI

Standard deviation of the magnetic cluster size, σ(nm)

Nor

mal

ized

med

ia n

oise


Kiminori SatoKazuo NimuraAkira Saito

Magnetic Printing Technology

1. Introduction

Hard disk drives (HDDs) are equipped in mostpersonal computers as peripheral storage equipmentand the worldwide annual production of HDDs isexpected to reach 200 million units (in 2001). In recentyears, HDDs also have come to be installed in so-callednetwork household appliances such as informationappliances and digital home electronic equipment (thelatest of which includes car navigation devices, digitalTVs, and VCRs with built-in HDDs). This trend iscreating another new market equal to or greater thanthe personal computer market. Aiming at thesemarkets, Fuji Electric has been promoting the researchand development project of magnetic disks for HDDssince 1999. Fuji Electric’s projects cover such diversetopics as the development of new material substratealternatives to aluminum, perpendicular recordingmedia for high-density recording, and technology tolower the cost of embedding information into magneticdisks. The above-mentioned last technology aims toembed into magnetic disks such information as servopatterns used in HDDs and security data indispens-able to network household appliances.

As part of the above-mentioned technologies, thispaper will present our servo pattern and the magneticprinting technology, which is a new technique forembedding patterns into magnetic disks, and describethe major practical results achieved by the develop-ment thus far. This magnetic printing technology hasbeen developed for the mass production of magneticdisks, based on research by Matsushita Electric Indus-trial Co., Ltd., and in cooperation with Fuji Electric’scustomer HDD manufacturers.

2. Magnetic Head Positioning Mechanism andServo Pattern

2.1 Magnetic head positioning mechanism in HDDFigure 1 shows a schematic illustration of the

structure of a magnetic head positioning mechanism inthe HDD. The magnetic disk as a recording mediumrotates at a high-speed of several thousand r/min by aspindle motor. When reading or writing data, the

magnetic head flies about 10 nm above the rotatingmagnetic disk with a surfacing mechanism referred toas a slider. The slider is fixed to a rotary positioner viaa suspension and the magnetic head can be moved toand positioned at an arbitrary track on the magneticdisk by a rotating action of the rotary positioner.

2.2 Servo patternIn an HDD, the position information (which is

referred to as the servo pattern) for detecting theposition of the magnetic head relative to the targettrack on magnetic disk is written in advance onto themagnetic disk. As shown in Fig. 2 (a), servo zoneswritten with servo patterns and data zones for reading/writing data are alternately aligned at fixed intervalsin the circumferential direction. Thus, the magnetichead can detect its own position at every fixed timewhile reading/writing data (this method is referred toas the sector servo method and is utilized widely inHDDs.). Figure 2 (b) shows an example servo patternwritten in a servo zone. The servo zone contains aservo clock, an address pattern, and a position detec-tion pattern. The position detection pattern in thefigure is a checker pattern utilized in many HDDs, anddetects the position based on the difference in ampli-tude of a read signal waveform.

Fig.1 Magnetic head positioning mechanism in HDD

Slider

Suspension

Magnetichead

Magnetic disk Spindle motor

Rotary positioner

VCM


As the track recording density increases, thenumber of the tracks increases, and accordingly, theservo writing time also increases. In addition, a higheraccuracy is required for the STW mechanism, since thetrack pitch becomes narrower. Parallel servo writingwith multiple expensive STWs provided in a cleanroom may provide a temporary solution, but imposes aheavy financial burden.

3.2 Servo writing by magnetic printingAs a low-cost and speedy servo writing measure

alternative to the above-mentioned STW, Fuji Electricfocused attention on the magnetic printing technologythat copies magnetic patterns from an original record-ing disk (referred to as the master disk) to anothermagnetic disk in block.(1) to (3) In this magnetic printingtechnology, a reference servo pattern is written inadvance to a magnetic disk, then based on thereference servo pattern, the HDD writes a finer servopattern on itself (this is referred to as self servowriting). The time required for magnetic printing ofone magnetic disk is less than six seconds and is muchless than the STW’s executing time. Since self servowriting can be implemented outside of a clean room, ithas the effect of extensively reducing the investment inclean rooms.

Figure 4 shows the principle of the magneticprinting process. First, an external magnetic field isbrought close to the magnetic disk to magnetize therecording layers of the magnetic disk in one direction(DC erasing). Next, a magnetic field is applied fromabove the master disk in the direction opposite to theDC erasing, while bringing the master disk into closecontact with the magnetic disk. The master disk is asilicon substrate, in which slots of several hundred nmin width are formed corresponding to the servo pat-tern, and soft magnetic material (Co) is embedded inthe slots. In the gaps between the soft magneticmaterial, magnetic flux leaks in the direction oppositeto the DC erasing magnetic field. On the magneticdisk, areas that have been in contact with parts of themaster disk part containing no soft magnetic materialare magnetized in the direction opposite to the DCerasing magnetic field, and the DC erased condition isretained at areas that have been in contact with theparts containing soft magnetic material. Thus, theservo pattern data of the master disk is printed on themagnetic disk. Lastly, contact between the masterdisk and the magnetic disk is released. Figure 5 showsan external view of the master disk.

In mass production, the keys to achieving uniformprinting of signals over the entire disk surface are thetechnologies to ensure good contact between the mas-ter disk and the magnetic disk and to maintain thecleanliness of both disks while in close contact. Theformer technology is achieved by configuring themaster disk to have alternating land parts that formthe servo patterns and groove parts that function as

3. Servo Writing

3.1 Conventional servo writing method by STWIn conventional HDDs, an equipment referred to as

the servo track writer (STW) writes servo patterns (seeFig. 3). After building in the magnetic disk in theHDD, a pushpin is inserted into the HDD case in orderto mechanically hold the rotary positioner in the drive.Based on an encoder in the STW, the STW’s fine rotarymechanism is moved to cause slight movement of theabove-mentioned pushpin and rotary positioner, and tosuccessively write the servo pattern corresponding toeach track. A 20 Gbyte-per-plate class magnetic diskrequires about ten minutes or more for servo writing.

Fig.3 Servo writing by STW

Fig.2 Servo pattern

Magnetic disk

Target track Rotary positioner

Servo zone

Data zone

Servo clock

Servo zone Data zone

Addresspattern

(b) Expanded view of servo zone

(a) Servo pattern written on magnetic disk

Positiondetectingpattern

Magnetic diskHDD

Rotarypositioner

Fine rotary mechanism (with built-in encoder)

STW

Pushpin


air flow channels, for controlling the pressure of the airflow through the grooves. Measures for achieving thelatter technology are as follows:(1) Perform a magnetic disk surface inspection just

before the magnetic printing process.(2) Provide a continuous downward flow of air to

maintain cleanliness in the vicinity of the magnet-ic printing process to below Class 1.

(3) Periodically clean the master disk.Figure 6 shows an example of a servo signal

waveform read from a magnetic-printed servo pattern.It is evident from the figure that a uniform envelope isachieved around the circumference of a track.

4. Practical Results of Development

4.1 Mass production of magnetic printing diskIn July 2001, Fuji Electric started to mass-produce

magnetic disks with servo patterns recorded by mag-netic-printing (hereafter referred to as magnetic print-ing disks). At present, magnetic printing disks withrecording capacity of 40 Gbyte-per-plate class arebeing shipped to HDD manufacturers. These disks arefor use in personal computers and the number of disksshipped in 2001 is expected to reach 2.5 million units.Before shipping, quality checks associated with thecleanliness of the magnetic disks (including the testsfor amplitude stability, ion contamination, corrosion,and organic contamination) are implemented. Theresults have verified that application of the cleaningtechnology described above enables magnetic printingto be performed without causing any damage orcontamination on the magnetic disk surface.

4.2 Application to next generation disksAn experimental trial of magnetic printing for

high-coercivity magnetic disks and perpendicular re-cording disks has been implemented ahead of time.The results of the basic experiment confirmed that themagnetic printing technology could be applied to bothdisks.4.2.1 High-coercivity disk

The recording layer coercivity, Hc, of magneticdisks is increasing year after year and is expected toreach 480 kA/m (6,000 Oe) in 2003. As a result of the

Fig.5 Outer view of master disk

Fig.6 Servo signal waveform from magnetic printing disk(longitudinal recording)

Fig.4 Magnetic printing process (longitudinal recording)

Movement of magnetMagnet for DC erasing

(a) DC erasing process

Recording layer (magnetic disk)

Movement of magnetMagnet for printing

(b) Printing process

Recording layer (magnetic disk)

Magnetic disk

Movement ofmagnet

Soft magneticmaterial (Co)

Magnet forprinting

Magnetic flux

Master disk

Master disk

Coercivity Hc = 320 kA/m, Measured at disk inner diameter

1

A

Top Horizontal axis: Time (2 ms/dev), Vertical axis: Voltage (50 mV/dev)

Bottom Horizontal axis: Time (0.1 µs/dev), Vertical axis: Voltage (37.5 mV/dev)

Disk rotation cycle

Extension


magnetic printing basic experiment for magnetic diskswith recording layer coercivity Hc of over 480 kA/m,it could be verified that a signal output level equal tothat of current media with Hc 320 kA/m (4,000 Oe)can be achieved. Figure 7 shows an example of a servosignal waveform.(4)

4.2.2 Perpendicular recording diskFor areal densities greater than 100 Gbits/in2, the

recording method is expected to shift from the currentlongitudinal recording method to the perpendicularrecording method. The basic experiment of magneticprinting was implemented for the perpendicular re-cording disk. Using an external magnet and a masterdisk equivalent to those used for longitudinal record-ing, the perpendicular components of magnetic leakageflux from the edge of the soft magnetic material on themaster disk perform the perpendicular recording.Figure 8 shows an example of a servo signal waveform.It was verified that a signal output level equal to thatof a longitudinal disk can be achieved. (5)

4.3 Development of next generation magnetic printingequipmentFigure 9 shows an external view of the next

generation magnetic printing equipment developed byFuji Electric. This equipment has newly been devel-oped to support magnetic printing to not only conven-tional aluminum-substrate longitudinal recordingmagnetic disks but also to disks for which demand isexpected to increase such as glass-substrate magneticdisks, perpendicular magnetic printed disks, and mag-netic disks with high-coercivity recording layers. Thisnext generation magnetic printing equipment containsa magnetic disk cleaning and initializing unit with

tape burnishing function for removing particles at-tached to the disks using a burnishing (polishing) tapeand a DC erasing function for magnetic disks, asurface inspection unit for detecting attached particlessmaller than 1 µm in size, a magnetic printing unit forimplementing the magnetic printing while limiting theeccentricity between the master disk and the magneticdisk to less than 10 µm, and a master disk cleaningunit for removing particles attached to the masterdisks with the tape burnishing function. The equip-ment has been designed for ease of maintenance andeach unit can operate independently. By placing themagnetic disk cleaning/initializing unit and the sur-

Fig.7 Servo signal waveform from high-coercivity magneticprinted disk (longitudinal recording)

Fig.8 Servo signal waveform from perpendicular magneticprinting disk

Fig.9 External view of next generation magnetic printingequipment


1

A


Bottom Horizontal axis: Time (0.1 µs/dev), Vertical axis: Voltage (37.5 mV/dev)

Disk rotation cycle

Extension


1

A


Bottom Horizontal axis: Time (0.2 µs/dev), Vertical axis: Voltage (70 mV/dev)

Disk rotation cycle

Extension

Magnetic diskcleaning and initializing unit

Inspectionunit

Magneticprintingunit

Master diskcleaning unit


Fig.10 Structure of track following test function

Table 1 Specifications of next generation magnetic printingequipment

face inspection unit just in front of the magneticprinting unit, the cleanliness of the magnetic disk to beinserted into the magnetic printing unit can be strictlycontrolled. Additionally, the magnetic printing unitensures a cleanliness level of Class 1 by placing themagnetic printing mechanism at the top of the diskhandling mechanism to constantly maintain a down-ward flow of clean air. The main specifications arelisted in Table 1.

4.4 Development of servo testerA servo tester has been developed, incorporating a

servo signal test function that automatically measuresthe servo signal quality of the magnetic printing disk,and a track following test function that, based on theservo signal, performs positioning control of the mag-netic head on an arbitrary track and measures thepositioning accuracy. The former function is helpful asa measure for evaluating details of the signal quality,and the latter function is effective as a measure forcomprehensive evaluating the servo signal.

Figure 10 illustrates the structure of the trackfollowing test function system, which is based on acommercially available spinstand (a specific tester for

magnetic disks and heads consisting of a spindle motorfor rotating a magnetic disk and a stage mechanism formoving and positioning a magnetic head). The systemincludes a rotary positioner for positioning a magnetichead on a target track rapidly, a servo demodulationcircuit for acquiring a position error signal from aservo track, a servo controller (DS1103 made bydSPACE) for controlling the rotary positioner’s posi-tioning based on a position error signal, and a hostpersonal computer. This allows the track followingtest to be performed on the spinstand, for a magneticprinting disk on which a servo pattern has beenrecorded. The VCM (voice coil motor) type rotarypositioner commonly equipped with the HDD is usedhere. Figure 11 shows an example of the magnetichead positioning accuracy measured on a magneticprinting disk. It is evident that the accuracy is within±0.1 µm, which is nearly equal to 1/10 of the trackwidth.

5. Future Plans

Because the HDDs equipped in network householdappliances are expected to be used daily for recordingor replaying movies, greater recording density permagnetic disk will be required as in the case ofpersonal computer use. Figure 12 shows a yearly trendforecast of the track recording density (TPI: Track perinch).

To further enhance magnetic printing technology,Fuji Electric plans to achieve a track recording densityof 150 kTPI (equal to twice the current value) withinthe year of 2002 by promoting the formation of finerservo patterns on the master disk, optimization of themagnet for an external magnetic field using magneticsimulations, and improvement of the servo pattern.

The magnetic printing technology can be appliednot only to the servo pattern, but also to data or

Fig.11 Measured positioning accuracy of magnetic head whentrack-following

Item

Printing throughput

Specification

600 plates/hour

Eccentricity < 10 µm

Magnetic disk size 2.5/3.5 inch

Substrate Aluminum/Glass

Coercivity Hc < 640 kA/m

Recording method Longitudinal/Perpendicular

Setup time < 4 hours

Cleanliness Class 1 (below 0.1 µm)

Master disk cleaning Yes (tape burnishing method andpurpose-built cleaning disk method)

Magnetic disk cleaning Yes (tape burnishing method)

Availability factor > 96 %

Size 3,300 width×1,400 depth×2,000 height (mm)

Servocontroller(DS1103)

Host personalcomputer

GPIB

Servo demodulation circuit

Rotary positioner

Spindle motor

Magnetic head

Magnetic disk

Equ

al t

o ±

0.1

µm


1

Horizontal axis: Time (2 ms/dev), Vertical axis: Voltage (10 mV/dev)


software embedding. Another study is planned intothe feasibility of new applications such as a securitymagnetic disk with security data embedded, which willbecome a key technology in network household appli-ances.

6. Conclusion

This paper has presented a servo pattern forpositioning the HDD magnetic head, its new writingmethod, and magnetic printing technology, and hasreported Fuji Electric’s principal developmental results

and future plans. The magnetic printing technology isreceiving attention from HDD-related manufacturersas a potential technology for extensively reducing thecost of the servo writing process in HDD production.Fuji Electric expects that the number of manufacturersadopting this technology increases and that the tech-nology becomes the de facto standard for servo writingin the future.

References(1) Ishida, T. et al. Demodulation of Servo Tracking

Signals Printed with Lithographically Patterned Mas-ter Disk. IEEE Trans. Magn. vol.37, no.4, 2001, p.1412-1415.

(2) Ishida, T. et al. Printed Media Technology for anEffective and Inexpensive Servo Track Writing ofHDDs. IEEE Trans. Magn. vol.37, no.4, 2001, p.1875-1877.

(3) Saito, A. et al. Optimization of a Magnetic PrintingProcess by Computer Simulation. IEEE Trans. Magn.vol.37, no.4, 2001, p.1389-1392.

(4) Saito, A. et al. Magnetic Printing Technique forLongitudinal Thin Film Media with High Coercivity of6000 Oe. MMM2001, Seattle, HD-02 2001.

(5) Saito, A. et al. A novel magnetic printing technique forperpendicular media. Intermag Europe 2002, Amster-dam, BS-07, 2002.

Fig.12 Trend forecast of HDD track recording density

Tra

ck r

ecor

din

g de

nsi

ty (

kTP

I)

400

350

300

250

200

150

100

50

0

Time (Year)

Master disk pattern exposuremachine updated

Magnet and servo pattern improved

Potential capability ofprinting technology

New lithographic exposure machine introduced

Track density trend

’05(Q3)

’05 (Q1)

’04(Q3)

’04 (Q1)

’03(Q3)

’03 (Q1)

’02(Q3)

’02 (Q1)

’01(Q3)

’01 (Q1)


Haruo KawakamiMitsuru NaritaTatsuo Tanaka

Present Status and Future Prospectsfor Photoconductors

1. Introduction

The improvement in performance of personal com-puters and peripherals and their rapid popularizationhas recently been remarkable. The influence thatdevelopment of these information devices brings intoour lives can be expressed with three keywords:digitalization, colorization and networking. For exam-ple, imaging devices, including cameras and videos, areadvancing at a rapid pace and the transmission of colorimages via internet is already a daily occurrence. It issignificant that these phenomena are seen not only inoffices but also widely in homes.

Under these circumstances, the importance of therole of printers and PPCs, which display and recordthe information and images, is increasing more andmore, and their expected level of performance isbecoming higher.

In this paper we are going to explain the markettrends for printers and PPCs, discuss the trends ofprinters using electrophotographc technology and ofPPCs, and present an overview of corresponding FujiElectric photoconductors and their peripheral devices.

2. Market Trend of Printers and PPCs

Despite the progress of thin model displays astypified by liquid crystal displays, the consumption ofpaper as an information medium continues to growsteadily. The main reason for the increasing consump-tion of paper is thought to be attributable to the factthat, above all, paper combines multiple functions suchas the displaying, writing, storing and transmitting ofdata, and also is a lightweight and very serviceablemedium.

On the other hand, new technologies, includingelectronic books and electronic paper, are being devel-oped as media alternatives to paper. In the mid- andlong-term horizons, the percentage of these electronicmedia relative to paper is estimated to increasecontinuously. For the moment, the increase in infor-mation quantity itself is thought to be due to thesynergistic effect of both media, resulting in thecontinued growth of both media(1).

In computer image output devices, the inkjetmethod is used mainly for personal-use devices and theelectrophotographic method is mainly for office-usedevices. The inkjet method has features of low deviceprice, color printing and good printing quality forcoated papers, and the electrophotographic method hasfeatures low running cost, high printing speed andgood printing quality for plain papers. Figure 1 showsa market forecast for color hard copy devices. Al-though electrophotographic color printers and colorPPCs are only at the beginning of their real popular-ization, future large-scale growth is expected. Theinkjet method and electrophotographic method areexpected to compete with each other and yet tocontinue growing together, benefiting from their re-spective advantages. At present, the ratio of printedsheets by the inkjet method compared to the electro-photography method (including monochrome images)is said to be approximately 1 : 3 (inkjet: electrophotog-raphy).

3. Trend of Electrophotographic Devices

The shipped quantities of electrophotographicprinters and PPCs have in the last several yearsexhibited a trend of saturation, showing only a smallincrease of several percent. But with the progress of

Fig.1 Forecast of shipment amount for color hard copyingdevices

PictographyThermal transferInkjetElectrophotography

’98 ’99 ’00 ’01 ’02 ’03 ’04 ’050

5,000

10,000

15,000

20,000

25,000

30,000

(Year)

Yen

val

ue

of s

hip

men

ts(1

00 m

illi

on y

en)


technologies and change in device composition, a newmarket is now opening up corresponding to the changein business environment represented by the abovemen-tioned three keywords.

3.1 Electrophotographic printerThe introduction of color printing in electrophoto-

graphic printers lagged the development of colorizationin other information devices. Figure 2 and Fig. 3 showthe trends in shipment quantities for monochromeelectrophotographic printers and color electrophoto-graphic printers respectively. In the estimates for2001, the shipment of monochrome printers is about 10million units, while the shipment of color printers isonly 700 thousand units. However, in the last severalyears shipments of color printers have grown by about30 % per year, suggesting rapid growth of the marketin coming years.

As seen in Fig. 3, at present most of the shippedcolor printers are low-speed machines having printingspeeds not higher than 6 pages per minute (ppm).However, owing to the rapid progress of technologicaldevelopment and the ongoing application of thattechnology into products, medium- and high-speed

machines having printing speeds in excess of 15 ppmare expected to become the major products. In thisscenario, the one-drum rotary system which prints 4colors sequentially with a single drum, will be utilizedin low-speed machines, while the four-drum systemwhich prints each of 4 colors with 4 individualphotoconductor drums, will be chiefly adopted formedium- and high-speed machines. The potential forexpanding the market for electrophotographic devicesdepends upon the extent to which products can beprovided at lower prices.

The requested improvements in properties of pho-toconductor drums for color printers are enhancedprinting quality, especially higher resolution, and thestable photo-responsibility necessary for color repro-duction. Of the abovementioned processes, especiallyin a 4-drum system, high dimensional accuracy isrequired of substrates for the purpose of controllingdiscrepancy in colors.

Another new trend is the popularization of on-demand printers with the advance of networking ofinformation. Of the total quantity of printing on papermedia, 70 % is occupied by newspapers, books, maga-zines and catalogs. Offset printing and photogravureprinting are applied at present as the printing methodfor these paper media, of which the on-demand-printertargets small-lot printing or on-site printing. Theirmarket image is not clear in some aspects, but the on-demand printer is a new application that leverages thefeatures of electrophotographic printers, i.e. high-speedand flexibility.

For photoconductor drums used in these applica-tions, high sensibility and high photo response forsupporting the printing speed, durability for achievinga long useful life of the photoconductors, and highresolution approaching the level of offset printing arerequired. Some trials are reported to have achievedimproved resolution by using liquid toner instead ofthe conventional dry toner, and photoconductors corre-sponding to this method are also being developed(2).

3.2 PPCsFigure 4 shows the trend of shipments of PPCs.

Although the total number of shipments has nearlyleveled off, shipments of digital PPCs show a rapidgrowth of 20 % per year, overtaking the lead fromanalog PPCs. Especially multifunction peripherals,which combine the functions of printers, PPCs andfacsimile machines, show a steady increase withmedium- and high-speed types as their main products.On the other hand, it is also estimated that low-speedmachines having an image output speed of lower than10 ppm will gradually be replaced by printers.

The characteristics requested of photoconductorsfor digital PPCs, in addition to high-speed photoresponse and durability, are the realization of photo-responsibility adapted to the printer process includingtonal characteristics for reproduction of half tones.

Fig.3 Forecast of shipment units for color electrophotographicprinters

Fig.2 Transition of shipment units for monochrome electro-photographic printers

12,000

10,000

8,000

6,000

4,000

2,000

01999 2000 2001

(Year)

Sh

ipm

ent

quan

tity

(10

3 u

nit

s)

21 and above ppm15 to 20 ppm7 to 14 ppm6 and below ppm

’98 ’99 ’00 ’01 ’02 ’03 ’04 ’05

(Year)

0

500

1,000

1,500

2,000

2,500

3,000

Sh

ipm

ent

quan

tity

(10

3 u

nit

s)


Table 1 Outline of Fuji Electric’s OPCs

3.3 PhotoconductorsOrganic photoconductors (OPCs), selenium photo-

conductors and amorphous silicon conductors are usedas the photoconductors for electrophotographic print-ers and PPCs. Figure 5 shows the trend of totalproduction of these photoconductors, exhibiting steadyannual increase rates of 6 to 10 %. As was alreadymentioned, the formation of new markets in the futureis expected, including the popularization of colorprinters and on-demand printers, for which furthergrowth is forecast.

The required characteristics for coping with thesenew developments are summarized as follows:(1) For color printers: high-resolution, color reproduc-

ibility and material tube preci-sion

(2) For on-demand printers:high-sensitivity, high-speed re-sponse and durability

(3) For digital PPCs: high-speed response, durabilityand tone

In addition, improvement of various components,including developers, rollers and blades, and improve-

ment in process conditions (low temperature fixing,advanced image-transfer conditions) are being ad-vanced, and application of these improvements toexisting processes is an important task.

4. Overview of Fuji Products

Fuji Electric has established an independent com-pany, Fuji Electric Image Devices Co. Ltd., uniting thebusinesses of electrophotographic photo conductor andrelated areas, and has built up a system to copespeedily with drastic environmental changes. Asproduction bases for photoconductors, in addition tothe domestic Fuji Electric factory in the Matsumotoarea, Fuji has subsidiary companies, i.e. U. S. FujiElectric in USA and Hong Kong Fujidenki in HongKong, and is able to meet worldwide demand effective-ly. Also in the Shenzhen area of China, Fuji has FusuiElectric, a subsidiary company of Hong Kong Fuji-denki, as a production base for various peripheral de-vices including process cartridges and toner cartridges.At present, many printer suppliers assemble printersin the Asian region including China, and we believethat the production of photoconductors in Hong Kongand of peripherals in Shenzhen will provide greatconvenience.

4.1 OPCFuji Electric has the 4 types of OPCs shown in

Table 1 as a product series.(1) OPC for printers

As OPCs for printers (Type 8), Fuji Electric hasvarious products which correspond to a wide sensitivi-ty range from low-speed machines to high-speed ma-chines. Especially for the series of organic materialproducts we provide many kinds of materials (chargegeneration material, charge transport material, etc.)and can satisfy diverse customer requirements. Thecolor reproducibility can also be controlled for a widerange as required by color printers. In addition, thedimensional precision of drums is also enhanced byimproving the finishing method.(2) OPC for PPCs

We have 2 product series of photoconductors, type9 for analog PPCs and type 10 for digital PPCs. We

Fig.5 Transition of production for photoconductors

Fig.4 Transition of shipment units for PPCs

5,000

4,000

3,000

2,000

1,000

01999 2000

Analog PPCsDigital PPCs

2001

(Year)

Sh

ipm

ent

quan

tity

(10

3 u

nit

s)

120

100

80

60

40

20

01999 2000 2001

(Year)

Pro

duct

ion

(10

6 pc

s)Feature

Chargingpolarity

Layerstructure

Type

8 Negative Multilayer

Application

Printer, Facsimile, Multifunction peripheral

9 Negative Multilayer Analog PPC

10 Negative Multilayer Digital PPC,Multifunction peripheral

11 Positive Monolayer Printer, Facsimile,Multifunction peripheral


offer a full range of products to satisfy requirementsfor high-speed response, high durability and tone asrequested especially for PPCs, and we are improvingthe characteristics further by developing and designingnew materials.(3) Positive monolayer OPCs

The realization of positive charging monolayerOPCs, which have low ozone generation, excellentresolution, response and environmental stability, haslong been expected. The layer structure thereof isshown in Fig. 6. As is known well, positive chargingOPCs have the advantage of low ozone generation evenwhen using a charging process with corona charging,and additionally are able to achieve intrinsically highresolution because photo absorption and chargingoccurs on the surface of the photoconductors. Theyhave higher response and environmental characteris-tics than multilayer types and, in addition, requireonly a simple dipping process resulting in a highproductivity. Based upon these advantages, positivecharging monolayer OPCs are being applied to medi-um-speed page printers and on-demand printers, andimprovements in sensitivity are further extendingtheir application range.

4.2 Selenium photoconductorsThe product series of selenium photoconductors is

shown in Table 2. We have 2 types of products, Se-Teand Se-As. Fuji Electric always leads this productarea based upon its abundant experience which in-cludes selenium material technology, selenium purifi-

cation technology and vacuum evaporation technology,and Fuji Electric’s proven track record in meetingcustomer requirements.

4.3 Peripheral productsOn the basis of electrophotographic process tech-

nology cultivated over many years, Fuji Electric devel-ops, designs and manufactures integrated processunits, each of which contains a core photoconductor,and charging, development and cleaning components.Furthermore, we are endeavoring to develop a FujiElectric original unit that realizes small-size and highimage-quality. Many of these products are manufac-tured at the above-mentioned Fusui Electric facility.

5. Conclusion

With the advent of a highly information-orientedsociety, the performance expected of photoconductors isbecoming higher and higher, including clearer imagequality and higher durability. To meet these require-ments, Fuji Electric endeavors to develop the mostattractive products in the world, and to develop themost advanced materials, products and productiontechnology. We are firmly determined to further buildup our technology through concentrated effort by theentire company and all of its groups, and to supplyproducts having high performance and reliability cor-responding to customers’ needs.

References(1) Kipphan, H. Final Program and Proceedings of IS&T’s

NIP17. International Conference on Digital PrintingTechnology. 2001, p.2.

(2) Yagi, H., et al. Final Program and Proceedings ofIS&T’s NIP16. International Conference on DigitalPrinting Technology. 2000, p.246.

Table 2 Outline of Fuji Electric’s Se photoconductorsFig.6 Layer structure of OPC

Charge transport layer (CTL)

Charge generation layer (CGL)

Charge generation + Charge transport layer

Under coat layer (UCL) Under coat layer (UCL)

SubstrateSubstrate

(a) Negative chargingmultilayer OPC

(b) Positive chargingmonolayer OPC

Type Material

4 Se-Te Medium- and low-speed PPC,Laser diode printers

5 Se-As High-speed PPC, Laser diode printers

Application


Seishi TerasakiKoji FukushimaMasahiro Morimoto

Organic Photoconductors for Printers

Fig.2 Layer structure

1. Introduction

With changes in the printer business such as thegrowth of inkjet printers as personal-use low-speedprinters and the arrival of the network age, the marketfor high-speed, MFP (multifunction peripheral) andfull color electro-photographic printers is expected toexpand, and in contrast, the market for low-speedprinters with simple functions will contract as shownin Fig. 1.

In keeping with this market trend, requirements offunctionality and quality for photoconductors as majorprinters components are increasing year by year. FujiElectric has developed and manufactured negative-charging and positive-charging OPCs (organic photo-conductors) to meet these various needs.

This paper presents a general overview and de-scribes the performance of negatively-charged OPCproducts including facsimile machines, plotters andMFPs.

2. Overview of Negatively-charged OPC

Figure 2 shows the layer structure of a negatively-charged OPC composed of aluminum conductive sub-strate, a resin UCL (under coat layer) to block positivecharge and to prevent exposure interference, a CGL

(charge generation layer) and a CTL (charge transportlayer) layered in turn one above the other.

The CGL is composed of CGM (charge generationmaterial) and binder resin, and provides a chargegeneration function when exposed to light from a laseror LED (light emitting diode). The CTL is composed ofCTM (charge transport material) and binder resin, andfunctions to transport charges generated in the CGL tothe CTL surface.

Fuji Electric provides a series of three products,having low-, medium- and high-sensitivities, corre-sponding to the CGM’s characteristics. This enablescorrespondence to the various exposure quantitiesshown in Table 1.

Half decay exposure can be adjusted within therange of 0.08 to 0.60 µJ/cm2, in addition to strict controlof the CGL layer thickness as shown in Table 1.

Figure 3 shows the respective spectral sensitivitiesof the low-, medium- and high- sensitivity types.Every type provides flat panchromatic characteristicsin the wavelength range of 600 to 800 nm and issuitable for generic lasers or LED light sources. By

Fig.1 Market trend

Table 1 Product outline

: Color MFP: Monochrome MFP

: Color printer over 12 ppm

: Color printer under 11 ppm

: Monochrome printerover 21 ppm

: Monochrome printerunder 20 ppm

2.5

2.0

1.5

1.0

0.5

02000 2001 2002 2003 2004

(Year)

Pop

ula

tion

(m

illi

on u

nit

s)


Charge generation layer (CGL)

Under coat layer (UCL)

Conductive substrate

Type Print speedSensitivity(Half decay exposure)

8A (Low sensitive) Up to 20 ppm0.20 to 0.60 µJ/cm2

8B (Mid. sensitive) Up to 40 ppm0.13 to 0.20 µJ/cm2

8C (High sensitive) 40 ppm≦ 0.08 to 0.13 µJ/cm2


combining these CGL and CTL, OPCs can be providedthat are suitable for printers having a wide range ofspeeds, from 20 pages per minute (ppm) or less to40 ppm or more.

Since OPCs can be provided with outer diameterranging from 24 mm to 262 mm and length rangingfrom 246 mm to 1,000 mm, a wide range of productsfrom A4 size page-printers to A1 size plotters has beendeveloped.

3. Performance of Negatively-charged OPCs

In order to supply OPCs that satisfy the threemajor requirements of the printer market, namelyhigh-speed, multifunction and full-color, Fuji Electrichas classified the OPC requirements as shown inFig. 4, and has undertaken the challenge of solving therespective technical problems. The respective perfor-mance of each characteristic is described below.

3.1 Technology for high sensitivityIn order to satisfy the requirements for A4 size

laterally-fed high-speed printers having speeds of40 ppm or more, although there is a dependence on theprocess layout, the optical sensitivity must be flatduring a processing time of 80 ms or less, fromexposure to development. To fulfill this requirement,Fuji Electric has developed CTMs with 5 × 10-5 cm2/V·sthat are suitable for high-speed printers.

Figure 5 shows the dependency of exposed surfacepotential versus the processing time from exposure todevelopment. For a high-speed type CTM, the exposedsurface potential is almost flat down to a 60 msprocessing time from exposure to development, andtherefore this CTM provides performance that issuitable with the above process. In addition, as shownin Fig. 6, environmental fluctuation of the exposedsurface potential of this OPC is excellent since it is notmore than 20 V.

3.2 Technology for good imaging quality3.2.1 Photo-induced decay characteristics

For MFPs having a copying function, tone repro-ducibility is required similarly as for the OPCs fordigital PPCs.

Printers are advancing toward higher resolutions,from 600 dpi (dots per inch) to 1,200 dpi or more, andtogether with advances in peripheral processes such asthe fabrication of finer toner or implementation of thefine control of laser beam emission, improvements ingraphical imaging quality are being sought more andmore. Fuji Electric has developed and manufacturedOPCs whose photo-induced decay characteristics are

Fig.3 Spectral sensitivity Fig.4 Performance and quality required by OPC

Fig.5 Photo response

Fig.6 Environmental stability of photo response

Hal

f de

cay

expo

sure

–1 (

cm2 /

µJ)

100

10

1

0400 500 600 700 800 900 1,000

Wavelength (nm)

Type 8B

Type 8C

Type 8A

Good imaging qualityPIDCPositive chargememoryPhoto memory

No interferenceBackground noiseEnvironmentstability

High durability Acidic gasesBreakdown

Wear resistanceSurface luricating

High sensitivity High mobility

Su

rfac

e po

ten

tial

(–V

)

120

100

80

60

40

20

00 50 100 150 200 250 350300Processing time from exposure to development (ms)

High speed CTM

Mid. speed CTM

Low speed CTM

120

100

80

60

40

20

00 50 100 150 200Processing time from exposure to development (ms)

L/L

N/N

H/H

Su

rfac

e po

ten

tial

afte

r 2

µJ/c

m2 e

xpos

ure

(–V

)


optimized to various machine processes so that highimaging quality, and in particular high resolution, isachieved.

Figure 7 shows an example of the photo-induceddecay characteristics for each type of OPC made byFuji Electric. Because this characteristic highly de-pends on carrier injection efficiency from the CGL toCTL, the characteristic may be adjusted by combiningCGL and CTL.3.2.2 Resistance to opposite polarity charge

Negatively-charged OPCs are charged with a posi-tive charge on a drum at the transfer section. Depend-ing on the process conditions, a positive charge-induced memory condition may occur in which half-tone images are shaded due to the effect of the positivecharge. As the imaging quality of printers advances,the shading of printed letters has come to be easilyreproduced by small potential differences, and thus therequirements for resistance to positive charge haveincreased more than before.

Fuji Electric has endeavored to reduce the affect ofpositive charge by optimizing the materials utilized ineach layer of ULC, CGL and CTL based on theknowledge accumulated thus far.

Table 2 lists the positive charge characteristics ofthe improved and conventional type products. Thesurface potential difference at on/off of positive chargeis improved to less than 1/3 of the conventional type,and therefore the positive charge-induced memory doesnot occur even for half-tone images at the 600 dpi MFPcopy mode.

Fig.7 Photo induced decay

Table 2 Positive charge-induced memory characteristics

Fig.8 Fatigue characteristics after strong exposure

3.2.3 Control of fatigue characteristics after strongexposure

Even minute differences of potential may disturbthe image of a photo-induced memory due to the samereason as a positive charge induced memory, andtherefore OPCs having low exposure-fatigue character-istics are required. Figure 8 shows a comparison ofstrong exposure fatigue characteristics of OPCs madeby Fuji Electric and other manufacturers. In both thecases of strong exposure at 1,000 lx and long-termweak exposure at 200 lx, excellent characteristics ofalmost no potential drop are observed.3.2.4 Control of interference for exposure light

In the case of a laser light source, there will beinterference in the incident light if the reflectivity ofthe conductive substrate surface is high. Because thisinterference causes shading to appear on half-toneimages, a function to control the interference ofexposure light is necessary to for OPCs used inprinters. In general, interference control is implement-ed by fine machining of the substrate surface, but FujiElectric realizes a light interference countermeasureby providing sufficient interference control function inthe UCL, without machining the surface of the rawtube. On the other hand, Fuji Electric possessesunique technology for finely machining the substratesurface in order to support processes of modern colorprinters in which even minute interference is imaged.3.2.5 Control of background noise

Requirements are increasing for better control ofbackground noise than in conventional printers. Thistrend is especially noticeable for OPCs used in full-color printers that employ a color superimposingprocess. Background noise is a phenomenon in whichtoner adheres to an area of white paper and is causedby the charge potential drop on a drum surface due tothe injection of charge at a small area from thesubstrate side. Fuji Electric is striving to controlbackground noise by reducing the minute defects thatcause charge injection from the substrate side. Thesedefects can be prevented by selecting the optimum

Su

rfac

e po

ten

tial

(–V

)

600

500

400

300

200

100

00.001 0.01 0.1 1 10

Type 8A

Type 8B

Type 8C

Exposure (µJ/cm2)

Type

Old type –610 V –575 V 35 V Poor

New type –615 V –605 V 10 V Good

Surface potentialat non positive

charge

Surface potentialat positivecharge add

Printquality∆

Su

rfac

e po

ten

tial

at

expo

sure

are

a (V

)

0

–50

–100

–150

–200

–250200150100500

10,000 lx, 3 h ours

200 lx, 150 h ours

200 lx, 150 h others

10,000 lx, 3 h others

Lapse of time after exposure (h)


Fig.11 Surface potential stability by printing (H/H)

measurements were performed for 25,000 A4 sizevertically-fed prints in the 2-print intermittent modeunder conditions of normal temperature and normalhumidity environment (N/N), low temperature and lowhumidity environment (L/L), and high temperatureand high humidity environment (H/H) respectively,and the potential was measured every 5,000 prints.The measured results show excellent characteristics inevery environment with no large potential fluctuation.

3.3 Technologies for high durability3.3.1 Resistance to acidic gases

The contact charging method with rollers andbrushes is the leading technology for page printers orpersonal-use MFPs, on the other hand, the coronacharging method is still popular in large size printersor plotters and resistance to acidic gases such as ozoneis required.

Various anti-oxide agents are used in OPCs,however, although increasing the quantity of agentimproves the resistance to acidic gases, it leads toadverse electrical characteristics such as residualpotential rise. Fuji Electric ensures sufficient resis-tance to acidic gases by utilizing material with deepionization potential in the CTM, and also by combiningappropriate anti-oxide agents. Specifically, appropri-ate anti-oxide agents having various actions are com-bined in the CTM for the purpose achieving maximumeffect with least quantity.3.3.2 Resistance to dielectric breakdown

The contact charging method is the leading tech-nology for medium speed printers or MFPs as men-tioned in section 3.3.1, and resistance to dielectricbreakdown is required strongly compared with thecorona charging method. Fuji Electric has developedand manufactured a UCL that provides resistance todielectric breakdown which is equivalent to that of ananodized layer membrane (ALM). Table 3 shows theevaluated results of resistance to dielectric breakdownmeasured by fixing a charging component connected toan external power source on the drum surface. It isclear that resistance to dielectric breakdown of the

substrate material and by unrestrained use of sub-strate cleaning technology, UCL material technologyand painting technology.3.2.6 Environment stability and durability of printing

OPCs are required to be unaffected by the environ-ment during their prescribed life in order to maintainthe initial imaging quality.

Figures 9 to 11 show measured data of the surfacepotential of commercially available MFPs equippedwith an OPC having a diameter of 30 mm. These

Table 3 Resistance to dielectric breakdown

Fig.10 Surface potential stability by printing (L/L)

Fig.9 Surface potential stability by printing (N/N)

Su

rfac

e po

ten

tial

(–V

)

700

600

500

400

300

200

100

00 5 10 15 20 25

Copy (× 1,000 sheets)

VO

Vhalf

Vl

Su

rfac

e po

ten

tial

(–V

)

700

600

500

400

300

200

100

00 5 10 15 20 25


VO

Vhalf

Vl

Su

rfac

e po

ten

tial

(–V

)

700

600

500

400

300

200

100

00 5 10 15 20 25


VO

Vhalf

Vl

Supplied voltage to contact film (–kV)Type

ALM-Sample 1 Good Good Good Good Poor

(breakdown)

ALM-Sample 2 Good Good Good Poor

(breakdown)Poor

(breakdown)

ALM-Sample 3 Good Good Good Good Good

UCL-Sample 1 Good Good Good Poor

(breakdown)Poor

(breakdown)

UCL-Sample 2 Good Good Good Good Poor

(breakdown)

UCL-Sample 3 Good Good Good Good Good

6.0 6.5 7.0 7.5 8.0


UCL, similar to the case of the ALM, is provided up to7 kV or higher.3.3.3 High wear resistance

Life of the OPC is affected by the imaging system,through wear due to contact components such as thecleaning blade and paper, scratches that cause print-ing trouble and adhesion of toner or paper powder tothe surface of the OPC (filming). Although the extentof these factors differs widely according to the respec-tive component of the OPC or process design, highwear resistance, high hardness and low filming charac-teristics are required for OPCs.

Fuji Electric has also developed a resin havinghigh wear resistance and lubricity through novelstructural design of the OPC for digital PPC, and hasendeavored to incorporate this resin into various

process by adjusting its composition.

4. Conclusion

The characteristics required of photoconductorswill advance much more in the future as electro-photographic printers evolve toward multi-functional-ity and high quality, and the functional classificationbetween printers and PPCs will disappear. FujiElectric will endeavor to provide excellent productsthat are friendly to the environment by pioneeringdevelopment and manufacture of OPC products tomeet market needs, together with promoting consis-tent development and manufacturing that includescartridges.


Micho ShinozakiMasahiko KasaharaShuichi Hamada

Organic Photoconductors forDigital Plain Paper Copiers

1. Introduction

Following the technical trends of the copier marketeach manufacturer has sought to realize higher speed,less maintenance and lower cost. In order to satisfythese requests, they have improved the sensitivitycharacteristics, stability and durability of photoconduc-tors. Organic photoconductors (OPC) have developedespecially rapidly because they are suitable for minia-turizing (diameter), can be manufactured at low cost,and furthermore they can be easily disposed of.

With the recent digital boom, digitalization hasbeen progressing in the copier market too. Figure 1shows the change in population of digital and analogcopiers in USA market. The percentage of digitalcopiers was just under 30 % in 2000, but is estimatedto grow to about 75 % in 2003.

Fuji Electric provides the type 9 series OPC foranalog copiers and the type 10 series OPC for digitalcopiers. In this paper, we shall introduce an outline ofthe type 10 series OPC for digital copiers.

2. Outline of the Product

Copiers that employ OPCs are classified as low-speed copiers (3 to 12 prints/min), medium-speedcopiers (13 to 39 prints/min) and high-speed copiers(more than 40 prints/min) according to their copyingspeed. Fuji Electric has developed 3 types of OPCsthat can be utilized in these copiers and applies themroughly in accordance with Fig. 2. Typical characteris-tics of these OPCs are shown in Table 1. Their appliedranges of sensitivity are different for each type but canbe selected freely according to the customer’s request.

The general structure of an OPC is shown in Fig. 3.The OPC shown in Fig. 3 is a layer-type OPC havingseparated function layers, and is formed from a

Fig.1 Population of digital copiers and analog copiers

Table 1 Electrical characteristics

Fig.2 Applied range of copying speed, outer diameter of OPCand each type

1998 1999 2000 2001 2002(forecast)

2003(forecast)

0

5,000

10,000

15,000

(Year)

Pop

ula

tion

(th

ousa

nds

of

un

its)

Digital copiersAnalog copiers

0 20 40 60 80 100 120

80

70

60

50

40

30

20

10

0

Outer diameter of OPC (mm)

Cop

yin

g sp

eed

(A4

size

: pri

nts

/min

)

High-speedcopier

Medium-speedcopier

Low-speedcopier

Type 10CType 10B

Type 10A

Item

Class

Half decayexposure in

adoptedsensitivity

band(µJ/cm2)

ChargingpotentialV0 (V)

Retentivity(After 5 s)

(%)

Half decayexposure(µJ/cm2)

ResidualpotentialVr (V)

Type 10A 0.30 to 0.50 –605 97.1 0.41 –35

Type 10B 0.15 to 0.30 –603 97.5 0.20 –21

Type 10C 0.07 to 0.15 –603 97.2 0.08 –9


cylindrical conductive substrate coated, in succession,with a first under coat layer (UCL), a charge genera-tion layer (CGL), and then a charge transport layer(CTL) which is the outermost surface.

The OPC for digital copier-use can utilize materi-als (type 8 series) that are also used in the OPC forprinter-use. Therefore the technology accumulated forthe type 8 series can be adapted to the type 10 series.

3. Special Features of the Product

By shifting from analog to digital copiers, thecopier market is progressing toward multi-functional-ity, higher speeds and higher reliability. With thesetrends, the required characteristics for copiers aremany and diverse. Therefore, we are advancing thedevelopment of materials in order to satisfy therequired characteristics.

Fuji Electric’s OPCs for digital copiers are suitablefor all copiers, from low-/medium-speed copiers tohigh-speed copiers, and have the following features.(1) High sensitivity(2) High responsiveness(3) High durability(4) High reliability

3.1 High sensitivityAs a result of using a laser or LED (light emitting

diode) as the exposure source, the digital copierrequires sensitivity in the 600 to 800 nm of wavelengthband. Fuji Electric utilizes a sensitive phthalocyaninepigment in this wavelength band. Figure 4 shows thespectrum sensitivities of types 10A, 10B and highsensitive type 10C. In the case of a digital copier, thewavelength of the exposure source is monochromaticlight, and consequently we can design the OPCwithout consideration for color reproduction, as wouldbe manifest in an OPC for an analog copier.

Figure 5 shows the photo-induced discharge char-

Fig.3 OPC structure for digital copiers

acteristics observed in an actual copier. Comparison totypes 10A, 10B, and to high sensitive type 10C showsabout 50 % and 30 % higher sensitivity, respectively.Further, each type exhibits a sharp reduction in theregion of residual potential, and therefore is favorablefor the process design of copiers.

3.2 High responsivenessThere is a wide range of digital copiers, from low-

speed to high-speed copiers. Among them, the high-speed copier, having printing speeds above 100 prints/min,which targets the on-demand copying market and POP(point of purchase) advertisement field, requires higherresponsiveness in OPCs.

In order to improve the responsiveness, coordina-tion of mobility and ionized potential between materi-als and their purities is very important. For improvingthe responsiveness, Fuji Electric has undertaken thechallenge of developing charge transport materials(CTM) and has developed and produced a high mobilityCTM that has a mobility of 5 × 10-5 cm2/V·s and thathas about 10-times higher performance characteristics

Fig.4 Spectrum sensitivity of OPC

Fig.5 Photo-induced discharge characteristics of OPC


Charge generation layer (CGL)Under coat layer (UCL)

Conductive substrate

400 500 600 700 800 900 1,0000.1

1

10

100

Wave-length (nm)

Sen

siti

vity

1/E

1/2

(cm

2 /µJ

) Type 10B

Type 10A

Type 10C

0.010

Su

rfac

e po

ten

tial

(–V

)

0.1 1 10

200

400

600

800

Exposure (µJ/cm2)

Rotation speed : 60 mm/sWave-length of exposure : 780 nmErase lamp : White fluorescent lamp + Red filter

Type 10A

Type 10C

Type 10B


Fig.8 Mechanical characteristics of OPC

Fig.9 Abrasion of OPC

generated by the corona discharge process and fromlight. Consequently, characteristics become degraded,such as a decrease in charge acceptance or rise inresidual potential, and these phenomena cause adecrease in print density and the background.

In order to control the degradation of chargeacceptance and of print density, Fuji Electric hasdeveloped an original charge control agent for sup-pressing the generation of electrical defects in CGLand CTL, and has supplied OPCs that operate stablyin several processes.

The change in surface potential of our typicaldigital copier is shown in Fig. 7. Compared to priortypes, this new type exhibits only small changes inpotential and print quality, and realizes an excellentOPC having stable operation.3.3.2 Improvement of mechanical characteristics

In OPCs, life-decreasing physical and mechanicalcharacteristics may occur due to contact with thecleaning-blade, charging roller, transfer roller, paperand toner, and consequently result in wear or cuts inthe exposing layer and substance adhesion of toner orpaper dust. The potential for each of these phenomenato occur differs according to the machine process, but

than the old type. Figure 6 shows an example of anactual copier with enhanced developing. As a result ofthe improved responsiveness, print density (blackdensity) was able to be improved compared to the oldtype.

3.3 High durabilityThe general modes of OPC’s life-decreasing factors

are classified in the following two categories:(1) Life-decrease by electrical stress

(a) Decrease of charge acceptance (Background)(b) Rise of residual potential (Decrease of copy

density)(2) Life-decrease by mechanical stress

(a) Cut (Black line, white line)(b) Abrasion of photoconductive layer (Decrease of

copy density, background)3.3.1 Improvement of electrical characteristics

Functional material in the OPC undergoes achemical change due to repeated exposure from coronadischarge in the charging-exposure process, from ozone

Fig.6 Developing characteristics

Fig.7 Running characteristics

00

Original density

Cop

y de

nsi

ty

Old type

0.5 1.0 1.5 2.0

0.5

1.0

1.5

Type 10C

(Measuring instrument: MacBeth RD-918 Densitometer)

0Number of copy prints (×1,000 prints)

(a) Dark voltage

(b) Light voltage

Su

rfac

e po

ten

tial

(–V

)

Old type

Old type

1,000

900

Type 10C

Type 10C

60 120 180 240 300 360800

0Number of copy prints (×1,000 prints)

Su

rfac

e po

ten

tial

(–V

)

200

100

60 120 180 240 300 3600

Old type Type10C

Old type Type10C

0

10

20

30 0.6

0.5

0.4

0.3

0.1

0.2

0

Vic

kers

har

dnes

s

Rot

atio

nal

tor

que

(N ·

m)

Measuring environment: 22°C/30 %

Weighting : 0.098 NTime : 5 s

Measuring environment: 22°C/30 %

Rotating speed : 330 mm/sBlade : Urethane rubber

Number of copied prints (×1,000 prints)0 20 40 60 80 100 120

30

25

20

15

10

5

0

High speed copier of Company A (Life of OPC: 80,000 prints)

(Guarantee life)

Old typeType 10C

(Necessary thickness to maintain copy quality)

Th

ickn

ess

of p

hot

ocon

duct

ive

laye

r (µ

m)


depends greatly on the performance of binder, which isa component of CTL. The binder performance is a bigfactor in determining the life of the OPC. Thereforethe development of binder is important. Fuji Electrichas introduced durability test equipment which is ableto quickly estimate the binder performance, has pro-moted acceleration evaluation, and consequently hassucceeded in achieving large improvement in thebinder’s performance.

Figure 8 shows mechanical characteristics (Vickershardness, rotational torque of OPC) and Fig. 9 showsan example of improved wear and abrasion perfor-mance on exposed layers in a specific copier. Bydecreasing the friction with other contact parts, wearor abrasion of exposed layers are improved, and canlead to an approximate 50 % extension of OPC life.Fuji Electric tries to cut down the quantity of OPC

Table 2 Environmental test

Table 3 Ozone-resistance characteristics of OPC

Fig.10 Light-induced fatigue of OPC

waste by improving the life of the OPC.

3.4 High reliabilityTo quantify OPC reliability, the environmental

tests shown in Table 2 have been carried out. Theozone-resistance test assumes an ozone atmospheregenerated by corona discharge in the copier, and testdata are shown in Table 3. Each characteristic is littleaffected even after 2 hours of exposure in a 100 ppmozone atmosphere. The light-induced fatigue testassumes that the OPC is exposed to light duringmaintenance. Test data is shown in Fig. 10. The OPCwas little affected after 5 minutes exposure to 1,000 lxof fluorescent light.

4. Conclusion

We have introduced Fuji Electric’s OPCs for digitalcopiers, and described the high sensitivity OPC (Type10C) in detail.

In the copier market, digital copying is becomingmainstream, so it is estimated that almost all copierswill be replaced by digital copiers after several years.Further, in the replacement by digital copiers, thetrend toward multi-functionality requires printer, copyand facsimile functions to be integrated within thesame machine, and consequently the boundary be-tween printers and copiers will disappear gradually.Fuji Electric will continue to develop superior OPCsthat provide required characteristics and preciselyconform to the needs of market.

Condition

100 ppm, 2 h

Item

Ozone exposure test

1,000 lx, 5 minLight-induced fatigue test

45°C, 1,000 hExposure test underhigh temperature

40°C, 90 % RH, 1,000 hExposure test underhigh humidity

–20°C, 1,000 hExposure test underlow temperature

–20°C, 1 h → N/N, 0.5 h → 45°C, 1 h → N/N, 0.5 h→ –20°C, 1 h

(N/N: Normal temperature and normal humidity)

Cycle test of temperatureand humidity

(5 cycles)

Item

Class

Type10A

Beforeexposure

Retentivity(After 5 s)

(%)

97.4 0.42

Half decayexposure(µJ/cm2)

ChargingpotentialV0 (V)

–603 –34

Afterexposure 94.8 0.43–602 –38

Type10B

Beforeexposure 97.1 0.18–601 –22


Type10C

Beforeexposure 97.3 0.08–601 –8


Residualpotential

Vr (V)

3

Time (min)

Dar

k vo

ltag

e (–

V)

800

900Type 10C

Type 10C

10 30 100700

0

50

100

Before exposure

Immediatelyafter

exposure

3

Time (min)

Lig

ht

volt

age

(–V

)

10 30 100Before exposure

Immediatelyafter

exposure


Seizo KitagawaTadashi AsakawaYoshihiko Tanaka

Process Units forElectrophotographic Machines

1. Introduction

Electrophotographic machines, which are repre-sented by copy machine (PPCs), fax equipment andprinters, are expected to continue to develop into thefuture as important image output equipment thatprovides high image quality, high speed and low noiseoperation. Recent trends of electrophotographic ma-chines include miniaturization, lowering of price, andshifts from analog to digital, from single function tocomplex function, and from monochromatic to colormachines. The processing parts of these machines, theheart of the machines, will become standardized inorder to enhance users’ convenience and to facilitatethe exchange of wear-and-tear parts.

Fuji Electric, as a manufacturer of photoconduc-tors, has developed and manufactured selenium photo-conductors and organic photoconductors (OPC), andrecently is promoting the development and manufac-ture of process peripheral equipment aiming to addvalue to the products and to offer proposals forprocesses to our customers.

In this paper, an overview of our activities concern-ing process units is introduced.

2. Overview of Products

2.1 Composition of process unitAs shown in Fig. 1, in an electrophotographic

machine, a process unit contains a photoconductor andintegrates some or all electrophotographic processes,such as electrostatic charging, development and clean-ing. This kind of process unit facilitates miniaturiza-tion of the equipment and stabilization of imagequality and further eliminates the necessity of mainte-nance by service personal.

2.2 Types and characteristics of process unitsThere are several types of process units as shown

in Fig. 2, and each of which is utilized in accordancewith the characteristics of the type of electrophoto-graphic machine.

The all-in-one unit integrates all processes includ-ing the photoconductor, electrostatic charger, develop-

er, toner, etc. This type of unit is supplied filled withtoner. So, when the toner is used up, the entire unit,that is, all of the process should be exchanged.Accordingly, although handling is very easy, printingcosts generally tend to be high because the life of theunit is determined by the amount of toner filled in theunit.

The separate unit has two types, the two-blockseparate type and the three-block separate type. Theformer contains a photoconductor, charger and cleanerin one unit (drum unit) and developer and toner inanother unit. For this type of unit, when toner is usedup, the entire unit can be refreshed simply by exchang-

Fig.1 A schematic of printer(Source: basic and application of electrophotographictechnology, corona, 1988)

Fig.2 A system of process unit

Cleaning

Fixing

Primary charger

Lens

Process unit

Reflective mirror

Polygon mirror

Photoconductor Transfer charger Feed rollerDevelopment

system

Processunit

All-in-onetype

Separatetype

All-in-one type process unit(Drum, development, toner)

Two separate type process unit(①drum, ②development)Three separate type process unit(①drum, ②development, ③toner)


ing the development unit, while the drum unit havinga longer life can remain unchanged. Accordingly, thistype has an advantage of lower running cost comparedto the all-in-one type.

In the latter type, the toner container is separatedfrom the development unit. This type of machine hasan advantage in that each component unit can beexchanged according to the life of each individualprocess, but also has a disadvantage of less easyhandling compared to the other two types. This type ofunit is the least wasteful and has the lowest runningcost.

3. Market Trends

The North American and European markets forelectrophotographic machines such as PPCs, facsimilemachines and printers occupy about 80 % of the globalmarket. Figures 3 and 4 show the predicted changes inmarket scale for process units for electrophotographicmachines in these two regions. Although electrophoto-graphic machines compete with ink jet printers in thefield of low-speed machines, they are expected to growsteadily in the fields of medium- and high-speedmachines because of their advantages of high-speedand high resolution.

Further, the predicted market scale for each type

of process unit in Japan is shown in Figs. 5 and 6.Also, the same steady growth is expected in Japan asin foreign markets. For 2001, all-in-one units occupyabout 80 % of the market in terms of monetary amountand about 70 % in terms of quantity. However, thepercentage occupied by the separate units, with sepa-rate drum unit and development unit, is estimated toincrease in the future.

For this enlarging market, countermeasures for theglobal environment are required. All the manufactur-ers are requested to contribute to strengthening recy-cling measures and to conserve the earth’s resources.In the past, used units were treated and disposed of asindustrial waste. However in recent years, eachmanufacturer is starting to collect used units and torecycle some of them. In the future, collection andrecycling will increase and a unit design suitable forrecycling will become required.

4. Activities of Fuji Electric

4.1 History of process unit businessAs a manufacturer of photoconductors, Fuji Elec-

tric has developed various types of selenium photocon-ductors and OPCs for many years. Our research

Fig.4 The market scale prediction of process units (the sales)

Fig.3 The market scale prediction of process units (quantity)

Fig.6 The market scale prediction of process units (the sales)

Fig.5 Japanese market scale prediction of process unit(quantity)(Source: reproducts sweeping over Japanese cartridgemarket, data supply, 2001)

Qu

anti

ty (

× m

illi

on)

120

100

80

60

40

20

01999 2000 2001 2002 2003

Europe

NorthAmerica

(Year)

Th

e sa

les

(× b

illi

on d

olla

rs)

12

10

8

6

4

2

01999 2000 2001 2002 2003

(Year)

Europe

NorthAmerica

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anti

ty (

in m

illi

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ach

ines

) 25

20

15

10

5

01999 2000 2001 2002 2003

Developingunit

All-in-one unit

(Year)

Photoconductordrum unit

Th

e sa

les

(× b

illi

on y

en)

25

20

15

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5

01999 2000 2001 2002 2003

Developingunit

All-in-one unit

(Year)

Photoconductordrum unit


chines. We have also endeavored to develop the moststable process. As a result, our products have beenadopted by many machine manufacturers. Our tech-nology to match our products to customers’ processes ishighly appreciated by our customers. And at present,we produce not only photoconductors but also processunits equipped with photoconductors as well as tonerunits.

Further, in order to increase our production ofprocess units, we are working to develop and commer-cialize the process units. Fuji Electric’s activitiesconcerning electrophotographic process units up to noware shown in Table 1.

Fuji Electric continues to develop products under afully integrated system in which development design isperformed at our Matsumoto Factory and production isperformed at Fusui Electric Co. Ltd. in Guangzhou,China. Figure 8 shows an example of our products.

4.2 Development of positive charging type process unitNowadays manufacturers of electrophotographic

machines are competing with one another in trying toreduce the price of their products (that is, the reduc-tion of initial costs and running costs for users) and toimprove printing speed and image quality. Realizationof these goals such as low price, long life and highperformance are also required for photoconductors.Accordingly, Fuji Electric started to develop positivecharging type OPCs upon realizing that they are moreadvantageous in principle compared to conventionalnegative charging type OPCs. Fuji Electric fullyleveraged its own capabilities to develop organicmaterials, made full use of product developmentcapabilities (application development capabilities) thathad been cultivated through development of seleniumphotoconductors, and applied its OPC mass productiontechnology. As a result, we have succeeded indeveloping and commercializing a positive chargingtype OPC capable of providing higher speed and higherresolution than a conventional negative charging typeOPC and in reducing the price of the machine.

However, the positive charging type OPC had a

efforts have sought to discover the optimal photocon-ductor that functions most suitably for each type ofelectrophotographic process in various types of ma-

Fig.8 An example of mass-produced process unit

Fig.7 Fusui Electric Co. Ltd. in Guangzhou, China (processunit production center)

Fig.9 An example of Fuji developing process unit (positivecharging type)

Table 1 History of process unit product development

StatusYear

1986Starting up production of drum unit for PPC at FujiElectric, Matsumoto factory (using Selenium photo-conductor drum for copy machine)

1987Starting up production of drum unit for PPC at Hong Kong Fujidenki Co., Ltd. (using Selenium photo-conductor drum for copy machine)

1990Starting up production of drum unit for PPC at HongKong Fujidenki Co., Ltd. (using positive charging typeOPC drum for copy machine)

1995 For processing unit production, Fusui Electric Co. Ltd. was founded in Guangzhou, China. (Fig. 7)

1996Starting up production of three divided type process unit for A4 size printer at Fusui Electric Co. Ltd. (using negative charging type OPC drum for printer)

1997Starting up production of three divided type process unit for A3 size printer at Fusui Electric Co. Ltd. (using negative charging type OPC drum for printer)

1998

Starting up production of two divided type process unit for A4 size printer at Fusui Electric Co. Ltd. (using negative charging type OPC drum for printer)Starting up production of toner unit for copy machine

1999 Starting up production of toner unit for color printer


Fig.10 A transition of drum surface potential in negativecharging process

Fig.13 A transition of image density in positive chargingprocess

problem in that it required a process different fromthat of the traditional negative charging type OPC,and adoption of the positive charging type process(positive charging type OPC) was difficult even thoughits superiority to the negative charging type OPC hadbeen recognized. Fuji Electric considered it necessaryto overcome this limitation in order to enlarge the

application range of this advantageous photoconductorand we therefore developed a positive charging typeprocess unit as shown in Fig. 9. Through the processdevelopment for this photoconductor, we aim to be ableto propose optimum processes to our customers andultimately to develop, design and produce process unitsthat include photoconductors.

Fig.11 A transition of drum surface potential in positivecharging process

Fig.14 Tone property in negative charging process

Fig.12 A transition of image density in negative chargingprocess

Fig.15 Tone property in positive charging process

Su

rfac

e po

ten

tial

(–V

)

1,000

900

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500

400

300

200

100

020151050

Print pages (× 1,000 pages)

Background potential

Light image potential

Su

rfac

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tial

(V

)

1,000

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100

020151050


Background potential

Light image potential

Imag

e de

nsi

ty

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020151050


Imag

e de

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1.6

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020151050


Imag

e de

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1.0

0.8

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0250200150

Initial

100500Tone index

After 20 k pages

Imag

e de

nsi

ty

1.6

1.4

1.2

1.0

0.8

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0.4

0.2

0250200150

Initial

100500Tone index

After 20 k pages


4.3 Results of comparative experiment of positive charg-ing type and conventional type unitsCharacteristics of the original negative charging

type process applied to a commercial printer and thoseof the positive charging process unit of Fuji Electricapplied to a commercial printer which was modified tothe positive charge process were researched, and theresults are given in Figs. 10 to 15. Figures 10 and 11show the change of drum surface potential for negativeand positive charging processes while running underthe environmental conditions of normal temperatureand humidity, respectively. Also the positive chargingprocess exhibits stable potential characteristics, thesame as those of the negative charging process.

Figures 12 and 13 show the change of imagedensity for negative and positive charging processeswhile running under the environmental conditions ofnormal temperature and humidity, respectively. More-over, the positive charging process exhibits stableimage density, the same as that of the negativecharging process.

Figures 14 and 15 show the tone property ofnegative and positive charging processes while run-

ning under the environmental conditions of normaltemperature and humidity, respectively. Tone proper-ty of the positive charging process is better and morestable than that of the negative charging process.Thus, the positive charging type process is recognizedas having higher resolution and better stability. Thissuggests that this process will exhibit superiority notonly in monochromatic high-resolution machines butalso in color machines.

5. Conclusion

Regarding the electrophotographic machine, it isforecast that the trends toward digital, complex andcolor machines will continue to progress, accompaniedwith lower prices. Corresponding to such trends, lowerprice, longer life and higher performance are alsorequired of the process unit, which is the heart of themachine. Further, easiness of recycling is also re-quired for the sake of environmental protection. FujiElectric intends to continue to develop process unitscorresponding to these requirements, centered aboutthe positive charging type OPC, and further intends topromote actively the unit recycling business.

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