-
An Angel Business Communications publication January / February
2011 Volume 17 Number 1
Mainstream development
III -V transistors on 200mm silicon
Compound questionsWhat next for thecompound industry?
Global knowledgeTechnical updatesprovided for industry
LED shape changerNovel geometric shapes can increaselight
extraction
EUV imagingExtreme UV arraysrequire specificimaging needs
IR probe impactA small additive canmake a big difference
Pure waterDUV LEDs promisesan impact for purifyingwater for
isolatedcommunities
Just add gratingsIncorporating feedbackgratings into broad area
lasers
-
AIXTRON SE �/� KAISERSTRASSE 98 �/� 52134 HERZOGENRATH �/�
GERMANY �/� [email protected] �/� WWW.AIXTRON.COM
AIXTRON started in 1983 and is today a leading provider of
deposition equipment to the semiconductor industry. With our
advanced solutions customers worldwide build components for
electronic as well as opto-electronic applications. As pace maker
in our line of industry we are keeping always one step ahead.
HIGHER PRODUCTIVITY // With almost 30 years of experience
AIXTRON stands for proven engineering power and dedicated cus tomer
support: Our equipment serves a diverse range of customers to
manufacture highest LED volumes at lowest cost.
BETTER PERFORMANCE // As the driving force in deposition
equipment AIXTRON engineers power ful technology solutions: Our
equipment is the best choice available to manufacture the brightest
and most efficient LEDs.
SMARTER RESOURCES // AIXTRON’s intelligent equipment concept
enables optimized use of resources: The results are extremely low
consumption of consumables, minimized maintenance requirements and
optimized utilization of human resources.
-
January / February 2011 www.compoundsemiconductor.net 3
editorialview
Editor-in-ChiefDavid Ridsdale [email protected] +44 (0)1923
690210
Consultant EditorRichard Stevenson PhD
[email protected] +44 (0)1291 629640
News EditorDr. Su Westwater [email protected]
Director of SOLAR & IC PublishingJackie Cannon
[email protected]+44 (0)1923 690205
Account ManagersShehzad Munshi [email protected]+44 (0)1923
690215Tommy Beazley [email protected]+44 (0)1923 690222
USA RepresentativesBrun MediaTom Brun E: [email protected]:
724 539-2404
Janice Jenkins E: [email protected]: 724-929-3550
Director of Logistics Sharon Cowley [email protected]+44 (0)1923
690200
Design & Production Manager Mitchell Gaynor
[email protected]+44 (0)1923 690214
Circulation DirectorJan Smoothy [email protected]+44 (0)1923
690200
Subscriptions ManagerDebbie Higham [email protected]+44 (0)1923
690220
Chief Operating OfficerStephen Whitehurst
[email protected]+44 (0)2476 718970
Directors Bill Dunlop Uprichard – CEOStephen Whitehurst – COOJan
Smoothy – CFOHaroon Malik, Jackie Cannon, Scott Adams,Sharon
Cowley, Sukhi Bhadal
Published byAngel Business Communications Ltd,Hannay House, 39
Clarendon Road,Watford, Herts WD17 1JA, UKT: +44 (0)1923 690200F:
+44 (0)1923 690201
Angel Business Communications LtdUnit 6, Bow Court, Fletchworth
Gate,Burnsall Road, Coventry CV5 6SPT: +44 (0)2476 718 970F: +44
(0)2476 718 971
Compound Semiconductor is published eight times a yearon a
controlled circulation basis.Non-qualifying individuals can
subscribe at: £105.00/€158pa (UK & Europe), £138.00 pa (air
mail), $198 pa (USA).Cover price £4.50.All information herein is
believed to be correct at time ofgoing to press. The publisher does
not accept responsibilityfor any errors and omissions. The views
expressed in thispublication are not necessarily those of the
publisher.Every effort has been made to obtain copyright
permissionfor the material contained in this publication.Angel
Business Communications Ltd will be happy toacknowledge any
copyright oversights in a subsequentissue of the publication.
Angel Business Communications Ltd © Copyright 2011. All rights
reserved. Contents may not bereproduced in whole or part without
the written consent ofthe publishers. The paper used within this
magazine isproduced by chain of custody certified
manufacturers,guaranteeing sustainable sourcing.
US mailing information: Compound Semiconductor (ISSN 1096-598X)
is published 8 times a year Jan/Feb, March,April/May, June, July,
August/September, October,November/December for a subscription of
$198 by Angel Business Communications Ltd, Hannay House,39
Clarendon Road, Watford, Herts WD17 1JA, UK.Periodicals postage
paid at Rahway, NJ. POSTMASTER: sendaddress changes to: Compound
Semiconductor, c/oMercury International Ltd, 365 Blair Road,
Avenel,NJ 07001
Printed by: Pensord Press.ISSN 1096-598X
January / February 2011Volume 17 Number 1
CONNECTING THE COMPOUND SEMICONDUCTOR COMMUNITY
New planes bolster nitride laser credentials
Engineers with an entrepreneurial streak whoop with delight when
they spota technology with the potential to generate piles of cash.
But they also knowthat it is going to take many years of hard graft
if their dreams are tomaterialize into a game-changing product.
One of the most promising technologies that could be netting
billions ofdollars by the end of this decade is the nitride laser
that is built onunconventional cuts of gallium nitride.
There are many benefits associated with turning to these
semi-polar andnon-polar planes: Reduction or even elimination of
internal electric fields thathamper laser emission; the opportunity
to increase the indium content inindium gallium nitride layers and
propel emission further into the green; and greater design
freedom,allowing engineers to invent architectures that are quicker
and easier to make.
Unleashing the potential of this class of lasers began in 2007,
when Rohm and the University ofCalifornia, Santa Barbara (UCSB),
independently unveiled violet lasers. Since then theirperformance
and color range has increased to a level where it now eclipses that
of its conventionalcousins. This form of laser now holds the
records for the highest continuous wave output powerand wall plug
efficiency for single mode blue lasers, and the lowest threshold
currents and longestemission wavelengths for green nitride lasers
(see this month’s Research Review for details).
Record-breaking lab results don’t guarantee commercial success,
but the signs are looking goodfor the semi-polar and non-polar
lasers. The UCSB spin-off Soraa has published reliability data
thatshows that these devices can go the distance, and engineers at
this start-up and the Japanesesemi-polar laser pioneer Sumitomo
Electric Industries find that chip yields in the lab
significantlyexceed those of conventional equivalents.
Soraa is also sampling product. Future success will hinge on
convincing potential customers that itis worth making the
transition to both a new technology and a new company.
If Soraa and the other semi-polar and non-polar laser makers can
fill their order books, they will thenhave the challenge of
churning out chips with an acceptable profit margin.
To do this they need reasonably sized substrates. Much of the
early work in the field was carried outon incredibly expensive
pieces of gallium nitride no bigger than a fingernail, but times
havechanged. Sumitomo has recently unveiled 2-inch non-polar GaN,
and Ammono plans to belaunching 1-inch semi-polar and non-polar
substrates this year. With a good foundation now togrow on, these
laser pioneers should be in with a good chance of success.
Richard Stevenson PhDConsultant Editor
-
Solutions for HIGH BRIGHTNESS LEDManufacturing
Nano Imprint Lithography for beam shaping and enhanced light
extraction
Handling and processing of thin and bowed wafers
Wafer bonding for layer transfer
Optical lithography and resist processing solutions
www.EVGroup.com
-
January / February 2011 www.compoundsemiconductor.net 5
Volume 17 Number 1 January / February 2011
CONNECTING THE COMPOUND SEMICONDUCTOR COMMUNITY contents
12 Extending Moore’s LawIII-V transistors on larger silicon
substrates are required for III-Vs to go mainstream. Sematech has
done this with InGaAs MOSFETs on 200mm silicon.
16 What next for the industry?The 2011 Compound Semiconductor CS
Europe Conference is coming up in Frankfurt to discuss the future
of the compound semiconductor industry.
20 IEDM meets in San FranciscoRichard Stevenson reports on the
latest IEDM where topics included low resistance channel contacts
speeding transistors, boron-doping boosting blocking voltages and
studies of HEMT ageing mechanisms.
24 Shaping up LEDsNovel chip geometries, such as triangular and
hexagonal devices can deliver increases in light extraction.
29 EUV imaging with hybrid AlGaN arraysSilicon extreme
ultraviolet detector arrays require non-standard methods to be
prevented from receiving longer wavelength radiation.
33 Probing IR thermal furtherAdding a tiny probe to an IR
microscope improves its temperature measurements and leads to new
insightsinto the local heating profile of HEMTs and LEDs.
37 DUV LEDs purify waterNovel growth techniques and active
regions are spurring the output of DUV LEDs to levels that are
purifying water at more than a liter per minute.
42 Internal grating lasersReliable output of 7W and spectral
widths below 1nmcan be realised by incorporating feedback gratings
into broad-area lasers.
industry & technology
news
24
29
37
20
42
07 08
06 Lighting up the PearlDenny’s goes LED
08 4G performance makes appearanceRainbow InGaN solar cells
ordered
07 First high powered IR laser with photo monitor
10 HK researchers demonstrate tunnellingthrough power
barrier
-
6 www.compoundsemiconductor.net January / February 2011
news � review
Cree lights up Denny’s restaurantsDENNY’S Corporation, one of
America’slargest full-service family restaurant chain,has chosen
energy-efficient LED lights fromCree as the preferred lighting
standard forall its new and remodelled stores across theUnited
States. Cree’s LR6 six-inchdownlights are being specified in
variousapplications, including dining areas and restrooms in all
newly constructed andconverted facilities.
“We evaluated numerous LED light fixturesfrom a variety of
manufacturers to ensurethat we chose the best possible productand
partner for this major lightingspecification,” explained Mitch
Riese,corporate architect, senior manager ofdesign &
construction, Denny’s. “With theCree LR6 fixture, we found the best
valuefor our money, helping us deliver warm light,while reducing
energy consumption andmaintenance requirements.”
Pete LaBarre, a Denny’s franchisee inColorado Springs, Colo., is
already seeingextensive savings since converting to LEDlighting.
LaBarre has installed more than
400 Cree LR6 downlights in the diningrooms of his five
restaurants, a move thathas saved him around $15,500 per year
inenergy costs alone. Impressed with theenergy and maintenance
savings frominstalling LR6 downlights in his diningrooms, LaBarre
has decided to use the six-inch LED downlights in a variety of
otherapplications. Currently he has replaced 500fluorescent bulbs
and tubes with 200 CreeLR6 fixtures, illuminating the perimeter
ofeach restaurant.
“Our lights stay on all the time, so we did awatt comparison of
what we had in placebefore the LR6 downlights,” said LaBarre.“We
found that we used 6,000 kilowatt
hours less per month in the store that hadthe Cree fixtures
versus the store that hadthe fluorescent lighting,” he said.
Another early LED lighting devotee is JoeyTerrell, a Denny’s
franchisee in Illinois. In2009, Terrell opened his second
restaurantin Joliet, a suburb of Chicago. Builtaccording to
Leadership in Energy andEnvironmental Design (LEED) Goldstandards,
the Joliet Denny’s includes acombination of natural lighting and
CreeLR6 LED downlights to reduce therestaurant’s lighting load.
According to Terrell, this lighting designreduced utility costs
by 83% and hiselectricity bill is now around $1,000 a monthinstead
of the expected $2,100 a monthbased on the average costs for his
location.
“Restaurants use 285% more utilities thanthe average commercial
building,” saidTerrell. “The easiest way to reduce costsand improve
energy-efficiency is to switchfrom traditional fluorescents to
daylightingand LEDs, and that’s what we did.”
Roled Opto and FLS Light Up Pearl River in Guangzhou
FUTURE LIGHTING SOLUTIONS (FLS)has announced that it is
illuminating thePearl River in Guangzhou, with 700,000Lumiled’s
LUXEON Rebel LEDs. The city ofGuangzhou recently completed a
project toilluminate the banks of the Pearl River aspart of their
welcome ceremony for theAsian Games and to celebrate thesuccessful
convening of the Games inGuangzhou. This project was an opentender
called for by the GuangzhouMunicipal Government, which was
awardedto Roled Opto Electronics (Shanghai).
The project objectives were to create agreen, energy efficient,
environmentallyfriendly and high-tech Asian Games. TheGuangzhou
Municipal Government’srequirements called for a professional
LEDmanufacturer, with reliable pre and postsales support.
Roled Opto Electronics (Shanghai). was themain designer of the
solution for thisproject. The deployment involved around30,000 LED
light fixtures and 700,000
LUXEON Rebel LEDs. China ConstructionEighth Engineering Division
(GuangzhouSubsidiary) was responsible for installation.
LUXEON Rebel LEDs were selected basedon their luminous flux,
color temperature,color index and reliability of the LEDs. Withthe
help of Future Lighting Solutions (FLS)and the use of their Usable
Light Tool (ULT),LEDs best suited for this project wereselected.
Roled also made use of QLEDThermal simulation software to optimize
theirheat dissipation system.
With the support of the Lighting ResourceCentre (LRC), Roled was
also able to testand evaluate optical lenses, and deployedNational
Semiconductors’ buck regulator aspart of the solution. FLS and
Roled havealways based their partnership on aphilosophy of
strategic co-operation. Withassistance provided by FLS and their
LRC,Roled Opto Electronics selected suitableLED models and optical
lenses, which wereable to resolve a number of issues related
tolighting efficiency and light distribution.
They also had to keep in mind that theGuangzhou Municipal
Government expectedan ROI within 3 years, and hence devised
asolution based on LED light fixtures as thistechnology delivers
more than 60% savingsin terms of energy consumption, andreduces CO2
emissions by 80%. Thesefactors greatly shorten time taken
toactualize the return on investment. At thesame time, FLS also
provided significantsupport in terms of price, availability
andsupply continuity, which enabled Roled tocomplete the project
according to schedule.
Wang Shiming, GM at Roled OptoElectronics’ adds, “During the
GuangzhouAsian Games, images along the banks ofthe Pearl River that
were broadcastcaptured the essence of the dazzlingskyline. In
particular, images of the WhiteSwan Hotel were displayed
repeatedlyduring the opening ceremony, whicheffectively illustrated
how the LUXEONRebel LEDs were able to deliver based onthe
requirements of the business owner andthe Guangzhou Municpal
Government.”
-
January / February 2011 www.compoundsemiconductor.net 7
review � news
Very high performanceTwelve source portsModular and
expandableSuitable for III-V's, II-VI's, MCT, oxides,spintronics,
etc.Small footprintLow cost of operation
To find out more, please contact us today at:e-mail:
[email protected]
COMPACT 21 SYSTEM
RIBER - 31, rue Casimir Périer - 95873 Bezons cedex - France
Tel: +33 (0) 1 39 96 65 00 / Fax: +33 (0) 1 39 47 45 62
VERSATILE MBESOLUTIONS
OpnextReleases FirstHigh Power IRLaser Devicewith
PhotoMonitorOPNEXT, a global manufacturer of highpower, low
operating current red andinfrared laser diodes, has introduced
a637nm, 120mW high power laser with abuilt-in monitor photo
diode.
The company’s HL63142DG red laserdiode, which is designed for
industrial andmilitary applications, including military
targetacquisition, achieves optimal performanceand output by
enabling system designers tomonitor the laser’s performance and
adjustoutput power in real time. Opnext customersare currently
sampling the red laser diodefor use in industrial and military
applications.Using a unique and proprietary design, theHL63142DG
built-in monitor photo diodeallows a system designer to control
theoptical performance by monitoring the photodiode current and
adjusting for temperatureand power variants. Performance
monitoringcapabilities are essential for maintainingconstant laser
output power in constructionsystems and biomedical and
otherapplications that experience changes in theiroperating
environments.
The HL63142DG operates at a temperaturerange up to 50°C and
120mW in the637nm wavelength band in a 5.6mmdiameter to industry
standard package.
“We expect to see initial demand for thishigh quality laser with
built-in monitor photodiode to come from military
targetacquisition-type applications where preciselaser control is
an important performanceparameter,” said Tadayuki Kanno,
Presidentof Opnext’s devices business unit. “Theindustry trend is
moving toward producinglaser diodes that are high power,
whileconsuming less energy, and Opnextcontinues to innovate in
bringing these keyperformance capabilities to market.”Opnext offers
one of the industry’s most
comprehensive portfolios of laser diodes,spanning from 635nm to
850nm, driven bymore than 30 years of innovative laserheritage.
Opnext high quality, reliable redand infrared laser diodes are
proven toconsume a low operating current, whichextends battery
life, while still maintainingthe integrity of the laser diode power
in avariety of applications such as gun sights,rangefinders, line
leveling constructionsystems and biomedical applications.
-
8 www.compoundsemiconductor.net January / February 2011
news � review
RFMD PowerSmart PowerPlatforms Achieve 4GPerformanceRF Micro
Devices (RFMD), a designer andmanufacturer of high-performance
radiofrequency components and compoundsemiconductor technologies,
has achieved amajor performance milestone related to itsPowerSmart
power platforms. RFMD’sPowerSmart power platforms are a newproduct
category reshaping the future ofmultimode, multi-band cellular
RFarchitectures.
During independent product testing, thePowerSmart power
platforms achievedHSPA+ 4G data upload speeds whiledrawing
approximately 15% less currentthan competitive solutions.
Productqualification tests, which are routinelyperformed to
evaluate each new cellularproduct’s front end, transceiver
andbaseband, are currently being conducted insupport of a highly
anticipated productfamily spanning multiple form factors, to
belaunched by a leading cellular devicemanufacturer beginning in
the March, 2011,quarter. PowerSmart power platformsfeature a
revolutionary new RF ConfigurablePower Core that delivers
multiband, multi-
mode coverage of all communicationsmodulation schemes,
includingGSM/GPRS, EDGE, EDGE Evolution,CDMA, 3G (TD-SCDMA or
WCDMA) and4G (HSPA+, LTE or WiMAX).
HSPA+ 4G devices are capable ofmaximum data upload speeds of
22megabits per second (Mbps). Because theRF Configurable Power Core
inPowerSmart is compliant with all currentand known future 4G data
standards(HSPA+, LTE QPSK, LTE 16QAM, and LTE64QAM), RFMD
anticipates subsequentsmartphones featuring PowerSmart willsupport
upload speeds significantly greaterthan 22 Mbps.
In addition to the RF Configurable PowerCore, which performs all
power amplificationand power management functionality,RFMD’s
PowerSmart power platformsinclude all necessary switching and
signalconditioning functionality in a compactreference design,
providing smartphonemanufacturers a single scalable source forthe
entire cellular front end.
BluGlass Commissions Rainbow toProcess InGaN Solar CellsBLUGLASS
has commissioned the foundryservices of related party
RainbowOptoelectronics Materials Shanghai toprovide device
fabrication and processingservices for the purposes of creating
anitride solar cell prototype designed byBluGlass.
The arrangement enables BluGlass tooutsource the processing of
its IndiumGallium Nitride (InGaN) solar cell designs toan expert
group-III nitride company withoutthe need to invest in additional
capitalequipment during the research phase.BluGlass non executive
director Alan Li isthe general manager of Rainbow, asemiconductor
device manufacturingcompany which provides nitride
semiconductors (primarily LED displays) tomore than 25
countries. InGaN solar cells, ifsuccessful, promise to be long
lasting,relatively inexpensive and importantly, themost efficient
ever created. BluGlass isdeveloping solar cell structure designs
andis now seeking to develop cell prototypes aspart of its Climate
Ready grant.
-
“Now offering Germanium Reclaim”
Watlow’s Full-Line of Thermal Solutionsare Designed to Meet Your
Needs.
Watlow is the global leader in providing innovative thermal
solutions for semiconductor applications ranging from crystal
growth through
front-end wafer process to back-end assembly.
Contact Watlow today for the latest offering of Semiconductor
engineered solutions.
The tight fit and optimized power distribution of Watlow’s pump
and
gas line heaters provide uniform temperatures up to 200°C.
The EZ-ZONE® RM controller can be configured to control 1 to 152
loops.
You only pay for what you need.
Watlow Ltd.Robey CloseLinby Industrial EstateLinby, Nottingham,
NG 15 8AAe-mail: [email protected]
Watlow GmbHLauchwasenstr.176709 KronauGermanye-mail:
[email protected]
-
10 www.compoundsemiconductor.net January / February 2011
news � review
Research from Hong Kong demonstratestunneling through the power
barrier
Fig. 1: (a) Schematic cross-section of an AlGaN/GaN tunnel
junction FET. (b) Theconduction band energy diagram of the tunnel
junction FET at the source junction. Thelabels A-C represent
different bias conditions. A: VGS = -3 V, VDS = 10V; B: VGS =
0V,VDS = 10V; C: VGS = 3 V, VDS = 10V. At zero gate bias, the
tunnel barrier’s thicknessis ~10nm and does not allow significant
tunnel current, leading to the normally-offoperation.
need for a sophisticated buffer layer.
At a source-drain voltage of 50 V, the drainleakage current is
10-11A/mm and the on/offcurrent ratio is 1010. The
off-statebreakdown voltage of an AlGaN/GaN T-FETwith a gate-drain
spacing of 2 microns is274 V, more than twice of that obtained inan
AlGaN/GaN HEMT with the same gate-drain spacing.
This new power tunnel FET technologycould provide a low-cost
approach toobtaining normally-off operation and lowleakage since it
does not require
“THERE is a light at the end of the tunnel”is a phrase used by
many looking forresearch results around the world. Now,Kevin Chen
and his group at The HongKong University of Science and
Technologyadd to this motto and declare there is also“Power at the
end of the Tunnel”.
The research group have recently shownthat a wide bandgap
Gallium Nitrate (GaN)-based power tunnel FET with normally
offoperation can be realised and achieved onwidely available
baseline AlGaN/GaNheterostructures.
The devices are claimed to offer record-lowoff-state leakage and
record-high on/offcurrent ratio at a high drain voltage.Advances in
AlGaN/GaN HEMT technologyhave already shown that these devices
arecapable of beating silicon in terms ofperformance.
Two of the most challenging but also highlydesirable features of
GaN power devicesare normally-off operation with positivethreshold
voltage and low off-state leakagecurrent at a high drain
voltage.
The GaN power tunnel FET, with its newcurrent controlling scheme
and a novelSchottky source configuration, deliversnormally-off
operation and low off-stateleakage current simultaneously.
According to Chen, the new power tunnelFET features a metal-2DEG
(two-dimensional electron gas) tunnel junctionthat is controlled by
an overlapping gateelectrode. Since the current turn-on/off
ismainly controlled by the tunnel junctioninstead of the 2DEG
channel, positivethreshold corresponding to normally-offoperation
is realized on the as-grownnormally-on epi-wafers.
This method of realizing normally-offoperation is fundamentally
different from theprevious approaches that shift the
thresholdvoltage of the 2DEG channel from negativeto positive
values.
Furthermore, since the Schottky junction atthe source electrode
is naturally reversebiased in the off-state, excellent
leakageblocking and high ION/IOFFratio can beobtained, on an
epitaxial wafer without the
Fig. 2: (a) low off-state current and high ON/OFF ratio; (b)
Ids-Vds characteristics; (c)transfer characteristics.
sophisticated techniques such as gaterecess, fluorine
implantation or an AlGaNbuffer layer.
However, the process must be optimised inorder to improve the
run-to-runreproducibility and uniformity, which is thenext aim for
the scientists.
The results of this research will be publishedin the paper
“Normally-off AlGaN/GaNmetal-2DEG tunnel-junction field
effecttransistors” by L. Yuan, H. Chen, and K. J.Chen, IEEE
Electron Device Letters, vol.32, No. 2, Feb. 2011.
-
January / February 2011 www.compoundsemiconductor.net 11
review � news
Soraa’s green laser have minimal speckle
Measure all optical and electrical parameters of single LEDs,
high-power LEDs and LED modules.
luminous flux luminous intensity chromaticity/CCT spatial
radiation pattern thermal behavior
With equipment from the world leader in LED metrology.
LED test & measurement
www.instrumentsystems.com
light measurement
SORAA INC., a rapidly expanding clean-tech semiconductor company
and amanufacturer of green and blue laserdiodes, has demonstrated
its latest greenlaser diodes (LDs), which are ideally suitedfor
>20 lumenpico projectors.
The firm, formerly known as Kaai, Inc., saysthat these direct
emitting green lasers haveproduced images which exhibit
substantiallyreduced speckle compared to conventionalgreen lasers
based on second harmonicgeneration. The company displayed thegreen
and blue LDs at its private suite at theConsumer Electronics Show
in LasVegasNevada January 6-9, 2011.
Soraa’s green LDs output more than 75milliwatt of continuous
wave power in the520-525nm range, are single spatial modeand multi
spectral mode. The devices canbe directly modulated at high
speedsrequired for high resolution displays withminimal
speckle.
The company says that LDs are well suitedfor all picoprojector
display generatingtechnologies including LCOS, scanningMEMS mirrors
DLP, and other diffractiveapplications. Soraa’s green LD
devices
complement the firm’s previously announcedblue 450nm LDs, which
the company saysalready exhibit industry best efficiency
andpower.
Soraa’s LDs are based on InGaNsemiconductor technology and
arefabricated on innovative nonpolar andsemipolar GaN substrates.
Soraa’s directdiode green and blue lasers offerimprovements in
performance, size, weight,and cost over conventional gas or
solidstate lasers for consumer projectiondisplays, defense pointers
and illuminators,biomedical instrumentation andtherapeutics, and
industrial imagingapplications.
Anadigics Joins ExclusiveNASDAQ Global Select MarketANADIGICS, a
leading provider ofsemiconductor products in the rapidlygrowing
broadband wireless and wirelinecommunications space, has been
chosen bythe NASDAQ Stock Market to join itsGlobal Select Market
for companiessatisfying the highest financial and
liquidityqualifications.
Established in 2006, the NASDAQ GlobalSelect Market was created
as a separatemarket classification to drive greaterrecognition for
world-class NASDAQ-listedcompanies that demonstrate a commitmentto
high standards and good governance.“We are honoured to receive
thisprestigious distinction from the NASDAQStock Market,” said
Mario Rivas, Presidentand CEO. “Our company takes great pridein
striving for excellence in all aspects of our
business. So receiving this kind ofrecognition as one of
NASDAQ’s topcompanies is a tremendous point ofvalidation for our
efforts.”
According to NASDAQ, qualifying for theGlobal Select Market is a
mark ofachievement, leadership and stature for thecompanies that
are included, while alsodemonstrating a message of high standardsto
investors. Anadigics has been a publiclytraded company on the
NASDAQ StockMarket since 1995.
“We have enjoyed a long-term successfulaffiliation with the
NASDAQ Stock Marketand we’re excited about this next phase ofour
relationship as one of the elite GlobalSelect members of the
market,” saidThomas Shields, Chief Financial Officer.
-
12 www.compoundsemiconductor.net January / February 2011
-
January / February 2011 www.compoundsemiconductor.net 13
technology �research
Back in the twentieth century, the route to makingfaster,
cheaper silicon chips was clear-cut:simply reduce the size of the
transistor. But if such anapproach had been adopted in recent
years, it would havefailed to deliver the gains in performance
needed to keeppace with Moore’s Law.
To maintain the level of progress prescribed by that
Law,foundries have modified the standard silicon MOSFETand
introducing new, more exotic materials. One of theseis HfO2, which
is used as the gate material. This replacesSiO2, a dielectric that
would now lead to unacceptableincrease in leakage current with
transistor scaling.Another change is the introduction of silicon
germanium,which is used to strain the pMOS device and speed
thepassage of holes from source to drain.
The trend of incorporating a wider palette of materials isset to
continue – the International Technology Roadmapfor Semiconductors
is advocating a move away fromsilicon transistors from 2015, when
the 11 nm node willbe rolled out. III-V MOSFETs are widely viewed
as themost likely successors. However, despite their rich,
longhistory of development, there is still a great deal to dobefore
compound semiconductor transistors can bechurned out in their
millions at the world’s leading foundries.
Development of III-V MOSFETs dates back to the 1960s.Then, just
like now, the appeal of turning to this class ofmaterial stems from
its very high electron mobility, whichpromises to lead to far
faster chips. Finding a gatematerial that forms a high-quality
interface with compoundsemiconductors has been one of the biggest
obstacles torealizing such a device. SiO2 was quickly discarded
infavor of other silicon compounds, sulfur passivationtechniques,
gates made from Ga2O3 and Gd2O3 oxides,and more recently, atomic
layer deposition of aluminumoxides. There has also been a switch
from a GaAschannel to an InGaAs one that sports superior
transportproperties.
Nearly all of this work has involved a native substrate forIII-V
transistor development – reports of device fabrication
on silicon substrates, the only material platform enabling
apractical successor to silicon CMOS, have been few andfar between.
And almost all these efforts have used siliconsubstrates that are
far too small to be processed byleading silicon foundries equipped
with state of the arttoolsets.
The one exception is an effort by Sematech, a US-basednonprofit
consortium of major semiconductor and chip-manufacturing equipment
makers that performs basicresearch on chipmaking. At the recent
InternationalElectron Devices Meeting, Sematech front-end
processdevice engineer Richard Hill detailed the
fabricationprocesses and device results of In0.53Ga0.47As
MOSFETswith varying gate lengths that were formed on 200 mmsilicon
wafers using state-of the-art manufacturing tools.
“Our devices have been manufactured using a VLSItoolset, with
processes that could be carried out in anyone of the big foundries
or IDMs,” says Hill. Turning toVLSI enables the fabrication of
chips with very high levelsof integration and a very small pitch,
attributes that areimpossible to realize using traditional III-V
transistormanufacturing methods.
Sematech builds III-V transistors on large silicon wafers
In order to become a successor to silicon CMOS technology, III-V
transistors must be built onsilicon substrates that are large
enough to be processed by VLSI toolsets. Sematech has done just
this by fabricating InGaAs MOSFETs on 200 mm silicon (100) using
state-of-the-art silicon foundry tools. Richard Stevenson
investigates.
Figure 1. The spread ofthresholdvoltage in theIII-V
transistorsmade bySematech iscomparable to that of abatch of
silicondevices, and fartighter than thatproduced inUniversity
labs
-
14 www.compoundsemiconductor.net January / February 2011
technology �research
Encouraging results MOSFETs produced by Sematech’s engineers
havepromising characteristics. The spread of the thresholdvoltage
for these transistors is far tighter than it is forthose produced
using traditional III-V processingtechnologies, and similar to that
of batches of siliconCMOS transistors (see Figure 1). The electron
mobility inthe III-V MOSFETs with a gate length of 20 μm peaks
at2000 cm2/Vs, a value roughly four times higher than thatrealized
in equivalent silicon transistors.
Winning approval to develop III-V MOSFETs using siliconfoundry
tools is not easy, because these materials couldlinger in equipment
and contaminate silicon devicesproduced in subsequent processing
runs. “III-V materialsare shallow-level dopants in silicon, so they
couldintroduce threshold voltage shifts and possible
reliabilityproblems,” explains Hill.
He and his co-workers adjusted foundry processes toboth reduce
the risk that this would happen and addressenvironmental and safety
concerns associated withworking with III-Vs. Once this was all in
place, they tested
the new approach, step by step, using techniques such astotal
reflection X-ray fluorescence to scrutinize thecleanliness of their
tools. “It appears that you canintroduce III-Vs, to be run in the
same tool set as silicon,”says Hill. However, he stresses that far
more wafers mustbe put through the lines before he can be
absolutelycertain of this.
Although 200 mm silicon substrates are widely used infoundries,
the newest fabs are working with 300 mmvariants, and 450 mm
material is on the horizon. However,Hill believes that it should be
fairly straightforward totransfer Sematech’s processes to larger
sizes: “Thetoolset is actually quite similar between 200 mm and300
mm wafers.”
MBE growthTo make its III-V-on-silicon MOSFETs,
Sematech’sengineers begin by cleaning a 200 mm substrate with
awet-etch, loading it into an MBE chamber and subjectingit to an
in-situ clean. The choice of MBE tools capable ofhandling such a
large substrate is actually quite large,according to Hill, because
a platen that accommodates a200 mm substrate is no larger that that
holding multiple6-inch or smaller wafers.
The MBE tool is loaded with 4° off-cut (100)
silicon,specifically selected to reduce the number of
anti-phasedomains that occur when a polar semiconductor isdeposited
on a non-polar one. A buffer comprising 1μm-thick layer of GaAs,
plus a 1.05 μm-thick graded layer onInAlAs is grown on the silicon
surface (see figure 2).
“The buffer technology that we are demonstrating here isdesigned
as a vehicle to allow us to do all the integrationand
infrastructure development,” says Hill. He does notview this
technology as the one that will by used for VLSI
Figure 2. A metamorphicbuffer isemployed tobridge the gapin
atomic latticeconstantbetween siliconand indium-based III-Vs
Figure 3Sematech’sthree terminalMOSFET ismade with aprocess
flowthat is verysimilar to thatemployed forthe manufactureof
silicondevices
-
January / February 2011 www.compoundsemiconductor.net 15
technology �research
CMOS integration, which will require a far thinner buffer. On
top of the buffer sits a 16 nm-thick In0.53Ga0.47Aschannel, a 4
nm-thick spacer and a 8 nm-thick barrier thatare both made of
In0.53Al0.47As, and an In0.53Ga0.47As capthat is 3 nm thick. An
Al2O3 and ZrO2 gate is added,before silicon is implanted into the
channel and sourceand drain contacts formed to yield a
surface-channelMOSFET (see figure 3).
“It’s a three terminal device, not a standard bulkMOSFET,” says
Hill, who compares it to a silicon-on-insulator MOSFET. One of the
strengths of the Sematechdevice is that its InAlAs buffer has a
wider bandgap thanthe InGaAs layer, which ensures decoupling of
thechannel from the underlying layers. This leads to immunityfrom
short channel effects, which inhibit channel controlby the gate and
can include an increase in off-stateleakage with increasing drain
current and higher junctionleakage. Short channel effects can
prevent the transistorfrom being turned off as it is scaled to
smaller and smallerdimensions.
The MOSFETs produced by Sematech have gate lengthsvarying from
20 μm to 0.5 μm. The shortest variants havea drive current of 471
μA/μm, a transconductance of1005 μS/mm and an electron mobility of
1000 cm2/Vs ata sheet doping of 1 x 1013 cm-2. These devices do
haveone cause for concern, however – a leaky buffer.Measurements
between isolated mesa structures indicatethat buffer resistance is
about 14 kΩ/�, which is morethan four orders of magnitude lower
than that for typicalmetamorphic InAlAs buffers deposited on
GaAssubstrates. Transmission electron microscopy and atomicforce
microscopy measurements on the MOSFETsindicate that the buffer is
riddled with defects. Theirdensity in this layer is 109 cm-2, a
value high enough toaccount for the high leakage current in the
buffer (seeFigure 4).
“You can conclude the leakage is going through the bufferfor two
reasons,” explains Hill. “The off-current does notscale with
temperature, so it is not an interface statedensity problem; and
the off-current does not really scalewith gate length, so we know
it is a very deep leakage.”
Device on-performance is not hampered by the highdefect density.
According to Hill, that’s because electronmobility is not governed
by the mobility of the two-dimensional electron gas, which is
limited by phononscattering: “It’s actually [determined] by the
surfaceroughness and interface roughness scattering at
theoxide-semiconductor interface.”
The road aheadEfforts at improving the buffer are on going. Very
recentlySemtech’s engineers slashed the defect density in
thislayer, which should drive down the transistor’s leakagecurrent.
One of the next goals is to thin the buffer to0.5 μm or less, a
step that must be taken to enable thislayer to be used in a
successor to silicon CMOS. Torealize this, Sematech’s engineers are
looking atalternative material technologies, such as MOCVD
growth, selective growth rather than blanket growth, andaspect
ratio trapping. Investigating other types oftransistor structures
is also on the agenda. The type ofMOSFET used by Sematech’s
engineers up until nowwas partly chosen because it can be
fabricated using aprocess flow that is very similar to that used to
producesilicon transistors. Now the team wants to look atprocesses
for making various types of MOSHEMTs,including those with a
recessed gate.
“There are many advantages and disadvantages of eachtechnique,
and it is not clear to us at this point which oneis going to be the
winner,” says Hill. “One of our nextsteps is to build flows with
all these different device typesand compare them at gate lengths
that are similar towhere the silicon industry is right now.”
In addition to scaling buffer thickness and gate
length,Sematech’s engineers will try to reduce contactresistance
and junction resistance, and improve the gatestack. It is possible
that they will complement this effortwith this electron transport
device with one based on holetransport, because both types of
transistor are needed tobuild a silicon CMOS successor. “There has
been somework published on antimonides with mobilities of about1000
cm2/Vs, and in some ways an all III-V solution maybe advantageous
from an integration strategy,” muses Hill.“But germanium technology
is more mature.”
If all this effort is to lead to III-V MOSFET production
insilicon foundries in four or so years time, solving oftechnical
goals must go hand in hand with manufacturingtechnology
developments. According to Hill, it will take acouple of years to
order tools, install them and ramp upmanufacturing. “That
infrastructure development has to bestarted now to get on the
correct time scales.” Hopefullythe toolmakers will hear this
rallying call, act on it and helpIII-Vs to play a key role in
extending Moore’s Law.
© 2011 Angel Business Communications. Permission required.
Figure 4Transmissionelectronmicroscopyimage of thecross-section
ofhetero-buffer.GaAs arealdefect densitywas estimatedto be
~1x109
cm-2. Thedefectivity ofthe metamorphicbuffer
issignificantlyhigher
-
16 www.compoundsemiconductor.net January / February 2011
CS Europe � 2011 www.cseurope.net
What next for the CompoundSemiconductor Industry?CS Europe
conference takes place on the 22nd March in the heart of Europe.
Pioneeringcompanies from around the globe will give their take on
the best opportunities for compoundsemiconductors, and what has to
be done to seize these opportunities. If you want to learn from
theinsight of these insiders, be sure to book your place at CS
Europe. Your challenge is met bysomeone else’s solution and CS
Europe aims to provide the platform that allows the CS communityto
not just share ideas but develop solutions in manufacturing and
furthering the reach ofCompound Semiconductor devices.
Dr. Petteri UusimaaPresident, Modulight
Topic: How to make a state-of-the-art visible red laser,what its
specs are, and what new markets it cantarget
Prior to joining Modulight Dr Petteri held numerousmanager
positions in international research projects inwhich he managed
relations to international fundingcompanies as well as was the
principal scientist in theprograms. Since 1997 Petteri has been
managingsemiconductor sales to multinational companies andacted as
a President & CEO of Modulight sinceincorporating the company
in 2000. Dr. Petteri Uusimaahas a PhD in semiconductor physics from
TampereUniversity of Technology (TUT).
Jan-Gustav Werthen, Ph.D.Senior Director, PhotovoltaicsJDSU
Topic: The urgency for the world to make power gridsdigital
(smart grids) and photovoltaic developmentsfor electricity
production from solar.
Jan-Gustav Werthen brings more than 26 years oftechnology
experience to JDSU. As senior director ofPhotovoltaics, Jan drives
overall business and productdevelopment that includes
power-over-fiber products andsolar CPV cells. Jan joined JDSU in
2005 as part of the
Klaus H. PloogPioneer of Molecular Beam Epitaxy (MBE)
KeynoteSpeaker
Topic: What next for the Compound SemiconductorIndustry?
Klaus H. Ploog is one of the pioneers of molecular beamepitaxy
(MBE), a versatile tool to fabricate semiconductorand metal
nanostructures. The MBE technique has beenestablished in the
early1970s, i.e. long before the hype on“Nano“ started to dominate
the word wide researchfunding policies in the late 1990s.
Using molecular beam epitaxy, he has designed andfabricated
numerous new semiconductor and magneticnanostructures that showed
unique quantum size effects.
These man-made nanostructures have led to a number ofnovel
device concepts, including high-electronmobilitytransistors
(HEMTs), quantum well and quantum dotlasers, quantum cascade
lasers, etc.
His research achievements have been published in more than 1500
papers in international refereed journals,and he has received
several prestigious awards. Hiscurrent interest for the subject of
sustainable energyconcepts has emerged from his research on
Group-IIINitrides for solid-state lighting beginning in 1995,
wherehe has paved the way for more efficient blue, green andviolet
GaN-based LEDs by using non-polar epitaxial layersand
heterostructures.
SponsorsGold
SponsorsPlatinum
Book your delegate place NOW.Limited availability
www.cseurope.net
22nd March 2011 Frankfurt, Germany
-
January / February 2011 www.compoundsemiconductor.net 17
www.cseurope.net 2011 � CS Europe
acquisition of company that he founded called PhotonicPower
Systems, Inc. From 1992 – 2005, Jan was CEO ofPhotonic Power
Systems, where he built a semiconductordevice and subsystems
organization from the ground upand grew sales over $1 million
annually, addressingworldwide markets.
Prior to running his own company, Jan held managementpositions
at companies such as VS Corporation, an earlyplayer in the
fiber-to-the-home market, Varian Associates,and Xerox. Jan received
his Ph.D. and M.S. in MaterialsScience and Engineering from
Stanford University.
Jeff ShealyDivision Vice PresidentRFMD
Topic: Role of GaN RF Power Technology forTomorrow’s Commercial
and Defense WirelessApplications
Jeff Shealy is vice president of the Infrastructure ProductLine
at RFMD, where he is responsible for strategicplanning and
execution of the corporate infrastructurestrategy. Dr. Shealy was a
principle founder of RF NitroCommunications, Inc., where he served
as president andCEO until RFMD acquired the company in October
2001.Dr. Shealy is a Howard Hughes Doctoral Fellow and hasheld
positions at Hughes Research Labs and HughesNetwork Systems. He
received his MBA from theBabcock School of Business at Wake Forest
Universityand he holds a Ph.D. in electrical engineering from
theUniversity of California at Santa Barbara. Dr. Shealy is amember
of the IEEE Electron Device Society.
Dr Otto BergerCorporate Advanced Technology DirectorTriQuint
Semiconductor, Inc
Topic: 3G/4G requirements for wireless systems andthe role GaAs
and GaN devices will play in meetingthese requirements
Dr. Otto Berger is TriQuint’s Corporate AdvancedTechnology
Director, overseeing the company’s portfolioof acoustic
technologies, 150mm GaAs processdevelopments and advanced packaging
techniques atTriQuint Munich, Germany. He leads
innovationdevelopments in these fields to evolve TriQuint
technologyfor future product generations. Dr. Berger began
hisprofessional career at Siemens Semiconductor andmoved to
TriQuint in 2002 through the acquisition ofInfineon’s GaAs
business. He has worked in various rolesin process development,
product engineering and fab
management within the GaAs field for more than 20years. Dr.
Berger received his PhD degree in physics fromthe University of
Muenster, Germany.
Marc RocchiCEO, OMMIC
Topic: What’s needed from GaAs and GaN fortomorrow’s
wireless
Marc Rocchi received his degree in Electrical Engineeringand
Solid State Physics from the Ecole Supérieured’Electricité de Paris
in 1972 . In 1976 , he joined thePhilips Research Lab in France to
work on the design ofhigh -speed digital GaAs circuits and in 1983
, he becamehead of the GaAs RFIC department. In 1988 , he moved
toPhilips semiconductors in Eindhoven to lead the CMOSprocess and
characterization group as part of the 1MbitSRAM project. Since 1990
he has successively beengeneral manager of Philips Microwave Limeil
and CEO ofOMMIC . He is now Chairman of the board of directors
ofOMMIC
Alexander BachmannMarketing EngineerOSRAM Opto Semiconductors
GmbH
Topic: Recent Progress on Green InGaN Laser DiodeDevelopment at
OSRAM Opto Semiconductors
After the studies in physics, Alexander Bachmann workedon the
development of electrically pumped vertical-cavitysurface-emitting
laser diodes at the Walter SchottkyInstitut of the Technical
University of Munich. Emitting inthe near- to mid-infrared spectral
region, these devicesare perfect light sources for trace gas
sensingapplications. In 2010 he joined OSRAM OptoSemiconductors for
the marketing of visible lasers for picoprojectors. With first
products already being available onthe market, a huge market growth
is expected for the nextyears, driving the development of blue and
particularlygreen laser diodes.
Dr. Michael FiebigDirector Marketing and Business Development
SolidState LightingOSRAM Opto Semiconductors GmbH
Topic: What are the success factors for thedeployment of Solid
State Lighting?
Dr. Michael Fiebig gained his PhD in Physics at theUniversity of
Hanover in 1998. During his doctoral thesishe worked on
Diode-pumped solid-state-lasers in the
Klaus H. Ploog
Dr PetteriUusimaa
Jan-GustavWerthen, Ph.D
Jeff Shealy
Dr OttoBerger
Marc Rocchi
-
18 www.compoundsemiconductor.net January / February 2011
CS Europe � 2011 www.cseurope.net
Mats ReimarkCEO, TranSiC
Topic: How will SiC power devices help getting agreener
planet
Mats Reimark has been a director in internationalorganizations
for more than 10 years. He is, since May2009, CEO at TranSiC AB a
company specializing indevelopment and manufacturing of bipolar
transistors inSilicon Carbide. Prior to joining TranSiC Mats has
had along career at GM with assignments such as DirectorHybrid
Powertrain Engineering Europe, Chief EngineerTechnology at Fiat-GM
Powertrain and Director Engineand Controls Engineering SAAB.
Dr. Philippe RousselProject manager Power Electronics and
CompoundSemiconductorsYole Développement
Topic: GaN power electronics: Market forecasts andindustry
status
Yole Développement (www.yole.fr) is a market researchand
strategy consulting company based in Lyon, France.
Dr Philippe Roussel has headed the CompoundSemiconductors
division since 1998. Yole producesnumerous market reports and is
currently publishing theiranalysis of the SiC, GaN, AlN, Sapphire
power and RFdevice as well as high-brightness LED marketsDr.
Philippe ROUSSEL is graduated from the Universityof LYON in
Electronics and Microelectronics. He wasgranted a Ph-D in
Integrated Electronics Systems fromthe Applied Sciences National
Institute (INSA) in LYON.
He is working at YOLE DEVELOPPEMENT since 1998and is leading the
techno-economical market analysis inthe fields of Compound
Semiconductors and PowerElectronics at materials, equipment and
devices level.
Scott ParkerExecutive Vice President Sales and MarcomOclaro,
Inc
Topic: Future Proofing Networks with 100 GigabitOptics
Mr. Parker was previously with Avanex Corporation, mostrecently
serving as the Company’s Senior Vice Presidentof Sales. Prior to
joining Avanex, Mr. Parker held seniormanagement positions at two
start-up companies fundedby Sequoia Capital. Previously, Mr. Parker
served asSenior Vice President of Sales and Marketing for JDS
spectral region at 2μm for medical applications. In 1998he
joined Lambda Physics as Product Manager forExcimer Lasers for
display and industrial applications.From 2001 he joined OOSRAM Opto
Semicondutors andwas heading the Marketing segment for Consumer
andCommunication until 2008. Since 2008 he is leading theMarketing
and Business Development in the businesssegment Solid State
Lighting at OSRAM OptoSemiconductors.
Dr. Markus BehetEurope Business Development ManagerDow Corning
Compound Semiconductor
Topic: SiC Advances for Power Electronic Applications
Dr. Markus Behet received his PhD in ElectricalEngineering and
Semiconductor Physics from theTechnical University Aachen in 1995.
From 1995 - 1998he was R&D Manager for epitaxial growth and
deviceprocessing of advanced III/V Semiconductors for HighFrequency
and Infrared Laser applications at IMEC inLeuven/Belgium. In 1999 –
2002 he joined SiemensSemiconductor and later Infineon Technologies
where hewas responsible for Business Development and Marketingof
GaAs mmW products and foundry projects.
From 2002 - 2010 he held several Marketing and Salespositions
for GaAs handset, foundry and mmW markets atTriQuint Semiconductor.
In 2010 he joined Dow Corningas Development Manager for SiC based
CompoundSemiconductor Solutions.
Dr. Ulf MeinersChief Technical Officer, UMS
Mark MurphyDirector Marketing, RF Power & Base, NXPTopic:
High performance compound semiconductorsfor infrastructure,
automotive and defenseapplications
Ulf Meiners received the Ph.D. in physics from theTechnische
Universität Munich, Germany and has beenworking in the compound
semiconductor domain sincemore than 20 years. He is the Chief
Technical Officer ofthe UMS group and the Technical Managing
Director ofUMS GmbH, Germany.
Mark Murphy received a BEng in Electrical andInformation Eng
from Queens University Belfast and hasbeen working in the
semiconductor industry for more than20 years. First at Analog
Devices, followed by Philips & iscurrently at NXP where he is
the Marketing Director forthe Product Line “RF Power & Base
Stations".
AlexanderBachmann
Dr. MichaelFiebig
Mats Reimark
Dr MarkusBehet
Dr. Ulf Meiners
Mark Murphy
-
January / February 2011 www.compoundsemiconductor.net 19
www.cseurope.net 2011 � CS Europe
Uniphase where he integrated the sales and customerservice teams
from numerous acquisitions. He also heldsales and general manager
positions at VLSI, NationalSemiconductor and Intel. Mr. Parker
earned an M.B.A andbachelor’s degree in marketing from the
University ofUtah.
Dr. Ertugrul SönmezBusiness Development MicroGaN GmbH
Topic: Efficient High-Voltage GaN Devices and ICs forNext
Generation Power Management Solutions
Ertugrul received his Diplom-Ingenieur degrees inelectrical
engineering from University of Ulm, in 1998. In1998, he joined the
department of Electron Devices andCircuits as a member of the
scientific staff, earning theDoktor-Ingenieur degree in 2007. His
main fields ofresearch were compact silicon bipolar transistor
modelingand analog RF MMIC design at 24GHz. He has authoredand
co-authored more than 40 publications andconference
contributions.
In March 2005, he joint ATMEL Germany GmbH inHeilbronn as
Marketing Manager, to be responsible for theworld wide UWB RFID
product line. In June 2005, hejoined TES Electronic Solutions GmbH
in Stuttgart, aservice provider of ATMEL Germany GmbH. His
mainactivities were to lead the ultra wide band MMIC design.
In December 2006, he has been called by MicroGaNGmbH as the
strategic Business Developer to bring in hisexperience in
semiconductors and markets.
Roy BluntSEMI International Compound Standards
Topic: Standardisation in compoundsemiconductors - an essential
step for furtheringthe efficiency & profitability of the
industry.
Roy Blunt graduated from Imperial College London in 1969 and
joined Plessey Research Caswell Ltd., wherehe worked on a variety
of R&D projects before becomingpart of the GaAs IC pilot
production team and developinga particular interest in compound
semiconductorcharacterisation techniques (metrology).
In 1988 he left Plessey to become part of the foundingteam of
Epitaxial Products International Ltd in Cardiff -now IQE (Europe)
Ltd.
He has been involved in standards work since the early1980s and
was a co-founder and, for many years, co-
chairman of the SEMI European CompoundSemiconductor Technical
Committee which has been veryactive in standards development both
on its own and inco-ordination with the North American and
JapaneseSEMI Compound Semiconductor committees.
Dr Mike CookeChief Technology OfficerOxford Instruments Plasma
Technology
Topic: Batch and single wafer processing strategiesfor
HBLEDs
Dr Mike Cooke joined Oxford Instruments PlasmaTechnology in
1992. As Chief Technology Officer, he leadsthe team of expert
development technologists responsiblefor developments such as PEALD
and scaling plasmatools towards 450mm.
Dr. Thomas UhrmannBusiness Development ManagerEV Group (EVG)
Topic: Engineered Substrates for future compoundsemiconductor
devices
Thomas Uhrmann is Business Development Manager forCompound
Semiconductors and Si-based Power Devicesat EV Group (EVG). In his
current role, he is responsibleto introduce and manage
technological innovations for thefabrication of high-brightness
light emitting diodes (HB-LEDs) at EVG.
Uhrmann holds an engineering degree in mechatronicsfrom the
University of Applied Sciences in Regensburgand a PhD in
microelectronics from Vienna University ofTechnology. Uhrmann
authored and co-authored severalpapers on semiconductor diode
structures, micro ornanomagnetism and related areas.
Mike CzerniakProduct Marketing Manager, Exhaust Gas
ManagementEdwards
Topic: GaN - meeting emissions regulations
Mike Czerniak received his PhD at Manchester University,and
started as a scientist at Philips’ UK laboratoriesbefore moving to
its fab in Nijmegen, working oncompound semiconductor applications.
He was inmarketing at Cambridge Instruments and VG Semicon; heis
now the product marketing manager of the Exhaust GasManagement
Division of Edwards, Clevedon, NorthSomerset BS21 6TH, UK
Scott Parker
Dr. Mike Cooke
Dr. PhillipeRoussel
Dr. ErtugrulSönmez
Roy Blunt
Mike Czerniak
Dr. ThomasUhrmann
-
20 www.compoundsemiconductor.net January / February 2011
conference report � IEDM
-
January / February 2011 www.compoundsemiconductor.net 21
IEDM � conference report
A dvances in silicon technology havedominated the agenda at the
InternationalElectronic Devices Meeting (IEDM) for more than fifty
years.However, recently this meeting has also featured a handfulof
presentations on GaN HEMTs, showcasing the progressmade with this
device. According to papers at the mostrecent meeting, not only is
this class of transistor operatingat far faster speeds than ever
before and blocking highervoltages – a more detailed understanding
of why it fails iscoming to light, and superior models are being
developedto aid the building of circuits based on these HEMTs.
One of the highlights from the latest IEDM, which washeld in San
Francisco from 6-8 December 2010, was apaper from a team from HRL
Laboratories claiming therecord for the fastest GaN HEMTs. These
transistors,which have gate lengths as short as 40 nm, produce
apeak cut-off frequency of 220 GHz and a maximumoscillation
frequency of 400 GHz. The record-breakingresults are believed to
stem from an impressive set of DCcharacteristics: on-resistance is
just 0.81 Ω.mm; draincurrent hits 1.61 A/mm; off-state breakdown
voltage is 42 V;and extrinsic transconductance peaks at 723
mS/mm,reducing the contribution from parasitic capacitances.
HRL’s HEMTs employ a barrier made from AlN. This widebandgap
material has the benefit of producing strongpolarization effects,
but it also creates a high potentialbarrier for electrons, making
it difficult to form a low-resistance ohmic contact to the channel.
The issue isaddressed by re-growth of heavily doped GaN contactsby
MBE, according to West-coast team. They havefabricated
double-heterostructure HEMT epistructures byMBE on 3-inch SiC. An
Al0.08Ga0.92N layer was depositedfirst, followed by a 20 nm-thick
GaN channel and then atop barrier comprising 3.5 nm of AlN and 2.5
nm of GaN(see Figure 1). The thin top barrier cuts
gate-to-channel-distance while maintaining a high
two-dimensionalelectron gas density and a low gate-leakage
current.
The HRL team produced transistors with gate lengthsranging from
40 nm to 200 nm. Chlorine-based reactiveion etching exposed part of
the channel, before MBEadded 50 nm-thick GaN layers with a silicon
doping levelof 7 x 1019 cm-3. These formed the basis for source
anddrain electrodes that were created by adding titanium
andplatinum. A tri-layer electron-beam technique createdT-shaped
gates made from platinum and gold, beforethese devices were
passivated with 50 nm of SiN.
Cutting gate length from 200 nm to 40 nm
increasedtransconductance from 672 mS/mm to 723 mS/mm andreduced
threshold voltage by 0.5 V, indicating that gatescaling was not
impeded by short channel effects.Measurements of the cut-off
frequency at a range of gatelengths confirmed this and indicated
that miniaturizationreduced parasitic delay. Modeling showed
parasiticcharging time accounted for one-tenth of the total
delaytime for 40 nm transistors with a source-drain voltage of 2V.
The gate transit time scales with gate length, which isanother
promising sign that further reductions in devicesize should
increase the speed of these transistors.
Low-resistance channel contacts that speedtransistors to
record-breaking frequencies, localizedboron-doping that boosts
blocking voltages andstudies of HEMT ageing mechanisms all featured
atthe latest International Electron Devices Meeting. Richard
Stevenson reports.
GaN HEMTs: faster,more capable and betterunderstood
-
22 www.compoundsemiconductor.net January / February 2011
conference report � IEDM
Channel stoppersModifications to transistor architectures were
also behindthe hike in blocking voltages of HEMTs produced
byPanasonic’s Advanced Technology Research Laboratories.By
introducing an array of ‘channel stoppers’ that terminatethe
leakage current at the interface with the silicon substrate,this
team increased off-state breakdown voltage inHEMTs with GaN layers
just 1.4 μm thick from 760 V to1340 V. Turning to 1.9 μm-thick GaN
bolstered theblocking voltage to 1900 V, and the team claims
thatadditional thickening of GaN should increases this to 3 kV.
Simply increases the thickness of GaN layers inconventional
devices – which could find application inpower switching systems,
such as inverters for industrialuse and uninterruptible power
supplies – has been widelytouted as a route to increasing the
HEMT’s blockingvoltage. But in practice such efforts, which have
thedownside of increasing chipmaking costs, fail to deliver onthis
front. The reason for this was unclear until the recentefforts by
this Japanese team. According to them,conventional devices suffer
from a significant leakagecurrent that stems from sheet electrons
forming aninversion layer at the substrate-epilayer interface.
TheKyoto team has confirmed the presence of an inversionlayer by
fabricating metal-insulator-semiconductor diodesand measured their
capacitance-voltage characteristics.
To stem the flow of leakage current, Panasonic’sengineers insert
channel stoppers. These stoppers, whichare formed by selective
boron ion implantation at theperiphery of the chip, widen the
depletion layer in siliconat high positive surface bias. This, in
turn, increases theoverall blocking voltage thanks to the addition
of thebreakdown voltage of the depletion layer.
Unreliable reliability tests Meanwhile, researchers Jungwoo Joh
and Jesús delAlamo from MIT have revealed that it can be
inappropriateto determine a HEMT’s RF reliability from DC tests.
That’sbecause the degradation mechanisms for DC and RFoperation are
significantly different.
“Obviously life tests under RF conditions close to field,but
mildly accelerated, would best represent the reliabilityof these
devices,” said Joh to Compound Semiconductor. He and del Alamo
found that RF stress degrades a devicefar more severely than DC
stress at the same voltage, andthis degradation gets more severe
with increasing powercompression. In addition, the pair of MIT
researchersdiscovered that RF stress induces an increase in
source
resistance due to a new mechanism that is possiblyrelated to hot
carriers. The key message of their study isthis: DC life tests
underestimate RF reliability.
This important conclusion was drawn from a series ofmeasurements
on single-stage MMICs with 4 x 100 μmGaN HEMTs. Performance was
evaluated at a current of100 mA/mm, a source-drain voltage of 28 V,
and asaturated power output (input power was 23 dB). The
RFperformance at this voltage is similar to that at 40 V,
thedesigned operating condition for these MMICs.
The first experiment began by DC stressing the device for5
hours, using a drain-source voltage of 40 V and aquiescent current
of 100 mA/mm. This led to little changein device characteristics,
aside from a small increase incurrent collapse. An RF stress test
followed, involvingincreases in input power from 20 dB to 26 dB.
This led tomajor changes in MMIC performance: significantincreases
in current collapse and sheet resistance; apermanent degradation in
the maximum drain current; anda substantial cut in the output
power.
Joh and del Alamo then looked in turn at three
operatingconditions that could potentially cause
enhanceddegradation at high compression: the “on” regime,
thehigh-voltage “off” regime; or the “high-power” regime.They ruled
out the first two, and although they couldn’tdirectly test the
third scenario – in this condition there isvery high power
dissipation, which leads to incredibly highchannel temperatures
that kill the device – pulsedconditions revealed a sharp increase
in sheet resistancebeyond 40 V, especially for a high stress
current.
Fluorine: a fine dopantReliability assessment was also the
central theme of astudy led by Kevin Chen from Hong Kong University
ofScience and Technology. He and his colleagues studiedthe behavior
of enhancement-mode AlGaN/GaN HEMTsfabricated by fluorine plasma
ion implantation. Thistechnique offers a low-cost approach to
making this classof transistor and has the merit of self-alignment
betweenimplantation and gate metallization.
In GaN and related materials, fluorine ions exhibit anegative
charge state. “When incorporated in the AlGaNbarrier, these ions
can deplete the two-dimensionalelectron gas channel, shifting the
threshold voltage topositive values and converting the device from
depletion-mode to enhancement-mode,” explains Chen.
Theenhancement-mode form of the device, which is alsoreferred to as
‘normally off’, is more desirable for powerswitching applications -
it allows a simpler gate drive; andif it fails, the system is left
in a safe state.
Fluorine plasma ion implantation technology has beenpreviously
used in other semiconductor materials, such assilicon and GaAs,
where it has compromised reliability.The concern has been that this
technology would alsoimpair GaN transistor reliability, although
preliminaryresults indicate that this does not impact the
electricaland thermal reliability of device made from this
widebandgap semiconductor.
Figure 1. MBEre-growth ofheavily n-dopedGaN contactshas helped
tospeed HRL’sHEMTs
-
January / February 2011 www.compoundsemiconductor.net 23
IEDM � conference report
The team, led by Chen and including John Roberts fromthe US
GaN-on-silicon HEMT trailblazer Nitronex, hasrecently focused their
efforts on studying reliability underhigh gate bias and low drain
bias, the standard conditionfor operating a power switch in its
“on” state. In this state,especially when the gate is overdriven to
either minimizethe on-resistance or accommodate current surge,
theSchottky gate tends to feature a non-negligible current –this
also raises reliability concerns.
One of the goals of the team’s recent work has been
toinvestigate whether the fluorine ions, which are mostlylocated in
the gate barrier layer, are stable under gateforward overdrive. If
they are unstable and cause reliabilityissues, the team would aim
to identify the critical gatebias and consequently the operating
conditions to drive adevice without degradation.
The team fabricated AlGaN/GaN HEMTs with a 1.5 μmgate length and
gate-source spacing, and a gate-drainspacing of 2 μm. They found
that the critical gateoverdrive voltage was 3.6 V and 2.8 V at
drain-sourcevoltages of 2 V and 0.85 V, respectively. At
highervoltages, the channel turn-on voltage experienced a
small,persistent negative shift, and at lower voltages
thetransistor realized excellent stability.
The negative shift in channel turn-on voltage is anundesirable
characteristic. “A large negative shift meansthat the E-mode device
could eventually drift to a D-modeone,” explains Chen. “In
practice, we need to stabilize theon-voltage at the positive
value.”
Impact ionization of fluorine ions due to hot electroninjection
is viewed as the primary driver behind the shift inon-voltage with
temperature. “Impact ionization is one ofthe few
reliability-relevant physical processes thatbecomes weaker as
temperature goes up, “ says Chen.“In semiconductor devices, most
degradation processescould be accelerated at higher temperature.
With regardto the on-voltage shift, it becomes smaller and
eventuallydisappears as the temperature is raised.”
Modeling HEMTsThe various approaches to modeling the behavior of
GaNHEMTs in RF power amplifiers was touched on in a paperby David
John and co-workers at NXP Semiconductors,who have pioneered the
development of a surface-potential based model. This joins a
growing list of modelsfor predicting HEMT behavior, which all have
theirweaknesses, according to John. Table-based models,which use an
interpolating spline on measured data, cangive erroneous values for
bias outside the range.Threshold voltage based models can struggle
at thresholdvalues and empirical models fail to scale. We
cannotpredict how geometrical changes impact performance.
“From metal-oxide-semiconductor modeling,
surface-potential-based models are known to be the
preferredapproach for scaling, extrapolation, distortion
modeling,statistical modeling and so on,” says John. “ All
CompactModel Council standardization efforts focus on
thesurface-potential-based models for this reason.”
NXP’s model resembles that for a conventional MOSFET.However, it
reflects one fundamental difference betweenthese two types of
transistor: HEMTs are based onaccumulation at the surface, while
MOSFETs operates in inversion. To account for this, John and his
co-workersderived the equations for currents and charges
fromscratch using nonlinear, binomial expansions of theelectronic
charge density. After the engineers hadconstructed this core model
that provides fast simulationtimes, they compared its predictions
to numericalsimulations of a gated section of a full device.
“The numerical simulations checked that theapproximations we
have made in order to arrive atcompact expressions are consistent
with the idealizedstructure that we are using to describe the
device,”explains John. These efforts showed that the core modelis
good at describing current as a function of bias and catering for
the bias dependence of the capacitance.
The researchers then built a macromodel thatencompasses the core
model. This is claimed to accountfor the regions under the gate
foot and the drain-side gateedge with an approach that is based on
physicallyjustifiable differences in the underlying model
parameters.Resistors, capacitors and inductors describe
passiveparasitic elements and the rise in device
temperatureresulting from power consumption is captured with
asimple thermal network.
To test the model’s validity, NXP researchers havecompared its
predictions to real data obtained from on-wafer measurements of
multiple-finger, multiple-cell GaNHEMTs. This effort revealed that
the model captures DCmeasurements at different temperatures,
including anegative output conductance at high powers that
stemsfrom strong self-heating.
Simulations of RF behavior are also close to measuredresults,
according to capacitance and transconductancecomparisons at 2.6
GHz.
The model can also be used to simulate circuits after ithas been
calibrated to measurements, a necessary stepfor any compact model.
“We areconstantly working to improve ourmodel, and to further
validate andbenchmark it,” says John. “Thereis still work to
do.”
That view holds true for manyother aspects related to the
GaNHEMTs. The good news,however, is that progress isclearly being
made on many ofthese fronts. It will be interestingto see what IEDM
hold in storeat the end of 2011.
© 2011 Angel BusinessCommunications. Permission required.
Figure 2.Introducingboron-dopedchannelstoppersdelivers a hike
inthe HEMTblocking voltage
-
24 www.compoundsemiconductor.net January / February 2011
technology � LEDs
L EDs have evolved from candela-classmonochromatic point sources
that are only goodfor indicator lights to 120 lm/W high-power,
white-lightlamps widely used as LCD backlighting. The
tremendousprogress can be attributed to great progress in
materialepitaxy skills, device design and processing
techniques,together with advanced packaging strategies. Withdozens
of advanced features loaded into today’s LEDchip, isn’t it strange
that chip geometries have hardlychanged over the last decade?
Rectangular and square geometries are probably the normbecause
it is easy to process chips in these shapes.
Shaping up LED ChipsNovel chip geometries, such as triangular
and hexagonal devices, can delivermassive increases in light
extraction by cutting optical confinement in both thevertical and
horizontal directions, says Hoi Wai Choi from the
SemiconductorLighting and Display Laboratory at The University of
Hong Kong.
Since sawing involves only continuous linear cuts,rectangular
chips seem the logical way to go. However,geometries with high
degrees of symmetries generally donot favour light extraction.
Maximising light extraction is one of the keys to enablingthe
LED to reach is full potential. Inside this device, asignificant
proportion of the light can be trapped, becauseany light that
impinges on the semiconductor-air interfacebeyond the critical
angle will be completely reflected. Thevalue of critical angle is
governed by the difference in therefractive index of the two
materials, which is quite largefor the pairing of GaN and air.
Today light extractionefficiencies rarely exceed 20 percent, but if
this figure candouble, LEDs will then be in a great position to
dominatethe general lighting market.
Excessive reflection of light at interfaces results in
lightconfinement and subsequent re-absorption, resulting inheat
generation. So improvements in light extraction havethe added bonus
of directly combating heat dissipationissues.
One of the most common approaches to minimise opticalconfinement
in the vertical direction is surface texturing.This process may
involve either random roughening, or theintroduction of regular and
periodic arrays ofmicrostructures and nanostructures, which are
also knownas photonic crystals.
However, little attention has been paid to lateral
opticalconfinement, which depends on the dimensions andgeometry of
the LED chip. In the highly symmetricalrectangular or square
structure, a light ray that is reflecteddue to total internal
reflection at one interface will mostlikely be reflected at
subsequent interfaces. This can beunderstood from the fact that all
interfaces, or facets, of
Figure 1. Laser-micro-machined LEDchips
-
January / February 2011 www.compoundsemiconductor.net 25
LEDs � technology
such chips are either parallel or orthogonal to each other;the
incident angle of a light ray remains unchanged aftersuccessive
reflections unless scattered, so that suchconfined photons are
eventually reabsorbed.
However, it is possible to stop wasting photons in thisway.
What’s needed is a switch to a chip geometryinvolving facets that
are not parallel to each other, whichis an approach that we have
pioneered at theSemiconductor Light and Display Laboratory at
TheUniversity of Hong Kong.
Any shape you wantThe enabling technology for realising LEDs
ofunconventional geometries is laser micromachining.Although lasers
have now been widely adopted for chipdicing, they have continued to
be used for making linearcuts even though laser beams can easily be
steered tocarve virtually any shape. Our chip-shaping
experimentsare conducted with our custom designed and
assembledoptical setup. The workstation comprise of a
third-harmonic ultraviolet, diode-pumped solid-state lasersource
that features a collimated beam that is focusedinto a tiny spot
onto an x-y-θ motorised stage. Bytranslation or rotation of the
stages controlled by our in-house developed software, we can form
chips of anyarbitrary shapes. These are cut from LED dies
fabricatedon InGaN/GaN wafers grown on c-plane
sapphiresubstrates.
Our belief in the inherent advantages of these novel
chipgeometries is supported by optical ray-trace simulations.By
examining the proportion of light rays that can beextracted from
LEDs of different geometries, theirefficiencies can be predicted.
The results of our set ofsimulations on LED chips of circular,
triangular, squarish,pentagonal, hexagonal, heptagonal, octagonal
and circular(the circle is in fact a polygon with an infinite
number ofsides) geometries are summarised in Table 1.
What stands out from the set of figures is the factthat square
LEDs have distinctively lowerextraction efficiencies than any
other
-
26 www.compoundsemiconductor.net January / February 2011
technology � LEDs
shapes. Considering the fact that LED chips in themarket are
invariably diced into squares or rectangles,device designers should
give serious thought to re-designing the chip.
Our findings from these simulations are backed up bymeasurements
on packaged but un-encapsulated LEDchips laser micro-machined into
various shapes (seeFigure 1). These results show that the square
LED is onaverage 16 percent less efficient than other polygons.
Ofcourse, one could argue that the chip packing density,and thus
chip count across a wafer, might becompromised. Therefore, we
propose the use of trianglesand hexagons; such shapes can be
closed-packed intoany array without sacrificing chip space and thus
makeeconomic sense.
An additional feature introduced into our optical setupenables
machining of three-dimensional freeformstructures. A mirror
inserted into the optical pathbetween the focusing optics and the
machining planeallows the focused beam to strikes the wafer at
an
oblique angle. LEDs of truncated pyramidal (TP)structure, as
depicted in Figure 2(a), are formed simply byapplying four
successive oblique cuts along the fouredges of devices. On average
light enhancement isincreased by 89 percent over similar chips with
verticalfacets, consistent with our theoretical prediction of a
85percent gain obtained by ray-tracing.
The inclined sidewalls serve as reflectors to
redirectlaterally-propagating photons into the escape cone.Devices
of TP-geometry also emit with a wider divergenceangle. Combining
oblique angle machining and rotarymachining, LEDs of truncated
conical structures can alsobe formed (see Figure 2(b)).
Subsequently, a reflectivemetallic layer is deposited onto the
bottom and inclinedsidewall surfaces of the chip to form an
integratedreflector cup.
This structure is particularly beneficial for building whiteLEDs
with homogeneous emission. In a typical whiteLED, an epoxy mixture
containing phosphor particles iscoated prior to encapsulation. The
phosphor mixture isallowed to reflow in order to cover both the
chip surfaceand sidewall facets, resulting in a dome-shape-like
non-uniformity, the effects of which are particularly prominentat
the edges. Such thickness non-uniformities give rise
tonon-homogeneity of colour emission at different
viewingangles.
With the integrated reflector cup design, light emission
viasidewalls is suppressed effectively. The majority of thelight
rays are emitted from the top planar surface, so thatthe divergence
angle of the device can be reduced by16°. Consequently, only the
top planar surface needs tobe phosphor coated; planar coating
produces significantlyimproved uniformity that paves the way for
superior colourhomogeneity.
Coupling LED emission to fibresIt is possible to incorporate a
hemispherical lens byinverting and flip-chip bonding the truncated
conical chipto a package. The lens can be attached via
liquidcapillary bonding to produce a nanometre scale air-gap
Figure 2. LEDsof (a) invertedpyramidal and(b)
invertedconicalgeometries
Figure 3. (a) A fibre coupled hemispherical LED assembly and (b)
RGB LED stack
-
Further readingX.H. Wang et al. Journal of Vacuum Science and
Technology B 27 2048 (2009)X.H. Wang et al. Journal of Applied
Physics 10 023110 (2010)W.Y. Fu et al. IEEE Photonics Technology
Letters 21 1078 (2009)L. Zhu et al. IEEE Photonics Technology
Letters 22 513 (2010)K.N. Hui et al. OSA Optics Express 17 9873
(2009)
January / February 2011 www.compoundsemiconductor.net 27
LEDs � technology
with exceptionally high transmission across the interface.At
close proximity the lens is also able to capture most ofthe emitted
light, focusing this to a tight spot with highpower density. Such
an assembly is ideal for opticalcoupling to a fibre (see Figure
3(a)).
To test its efficiency, the aperture of a 2mm-diameterplastic
optical fibre was aligned to the focal spot of theLED assembly.
Measurements determined a couplingefficiency of 53.8 percent, the
highest value reported tothe best of our knowledge. fibre-coupled
LED sourcesfind uses in a diverse range of applications from
opticalmicroscopy to short-range optical communications.Apart from
the integration of optics, the monolithicintegration of LED chips
has also been demonstrated as a viable solution for building
colour-tuneable LEDassemblies.
Three LEDs chips of the primary colours, cut intotruncated
pyramidal geometries, were vertically stackedon top of each other
in the order of decreasingwavelength from the bottom to the top, as
illustrated inFigure 3(b). The inclined sidewalls are mirror-coated
tosuppress lateral leakage.
With this stacking arrangement, light emitted from chips atthe
bottom of the stack emits through the upper chips; thetop blue LED
chip serves as the output window. As theoptical paths of the three
chips overlap with each other,their colours are naturally mixed
along the optical pathwithout requiring additional optics. By
individuallycontrolling the intensities of the three colours via
biascurrent, a wide range of colours can be produced withexcellent
homogeneity and performance (see Figure 4 forexamples).
Such stacked devices are obviously useful for
buildinghigh-resolution LED display panels. However, they arealso
excellent candidates as plain white light LEDs.Being free of
phosphor, the stacked LEDs emit white lightwith high efficiency,
excellent homogeneity, high colour-rendering index and long-term
stability; all of this isachieved without colour-conversion
losses.
So let’s get moving and get in shape! With smart tweaks in
design, extended functionalities and enhancedefficiencies can be
achieved with amazing results, without the need for additional
components.
© 2011 Angel Business Communications. Table 1. Light extraction
efficiencies of LED chips with different geometries
Figure 4. Wide range of colors emitted by a stacked LED
With this stacking arrangement, light emitted
from chips at the bottom of the stack emits
through the upper chips; the top blue LED chip
serves as the output window. As the optical
paths of the three chips overlap with each
other, their colors are naturally mixed along the
optical path without requiring additional optics
-
Progress is built on ideas
OC Oerlikon Balzers
AG
Advanced Technolog
ies
P.O. Box 1000, LI-94
96 Balzers
Phone +423 388 53
27
career.systems@oer
likon.com
www.oerlikon.com
Andrea Sorg
Human Resources
Oerlikon is a globally leading high-tech groupwith a distinctive
culture of innovation. 16,000reasons support our success:
competentemployees who contribute their curiosity
andenthusiasm.
Oerlikon Systems is a global technology leaderin the development
of production systems forthe semiconductor and data storage
industry.With innovative solutions, we break newground and thereby
develop future technolo-gies – enabling nano technology.
Your responsibilities:
■ Benefit from initial training in
Europe(Liechtenstein/Switzerland) for a period of 6–9months
■ In Taiwan, proactively assume technical andprocess start up
and performance demonstra -tion during acceptance of sputter
depositionequipment at customer sites
■ Support customers during ramp-up of produc -tion, in service,
and in the optimization of theirsputter deposition equipment
■ Contribute to process development and testing of new hard- and
software in collaboration with process engineering and project
management
■ Carry out trainings for customers and service engineers
■ Prepare acceptance, laboratory, and samplingreports
■ Support our service organization and customer support in
technical issues
Your profile:
■ Technical degree (HTL, FH, ETH) in electricalengineering,
mechanical engineering, or phys-ics, or a minimum of three years’
appropriateprofessional experience
■ Knowledge of vacuum and thin-film technology■ Proficiency with
MS Office applications■ Fluency in English, written and spoken■
Team spirit and intercultural communication
skills■ Willingness to travel (30–60%)
Application Engineer (m/f) Semiconductors
We are looking for you to support our team in Taiwan as
We look forward to receiving yourapplication in English via
e-mail.
-
January / February 2011 www.compoundsemiconductor.net 29
detectors � technology
At first glance, the fields of solar astronomyand silicon chip
manufacture are poles apart.But they do have one thing in common –
the need forefficient and reliable imaging of extreme ultraviolet
(EUV)radiation, which spans the range 10-120 nm.
In solar physics, there is tremendous interest inphenomena
occurring on the Sun’s surface (photosphere)and in its atmosphere
(chromosphere and corona), suchas coronal mass ejections and flares
that causestaggering amounts of radiation to be emitted towards
theEarth. Such processes occur at extremely high energies,so very
short wavelength detectors are needed to observewhat is taking
place.
Meanwhile, the silicon industry is continuing its never-ending
goal of shrinking transistor sizes by starting todevelop
lithographic processes involving EUV patterning.This requires
detectors sensitive at these wavelengths,which can aid efforts to
find and refine techniques forcontrolling the properties of the UV
beam. Solar scientistsand silicon engineers can use existing
silicon devices for
Extreme ultravioletimaging with hybridAlGaN arrays
Silicon extreme ultraviolet detector arrays require non-standard
methods to be prevented from receiving longer wavelength radiation,
e.g. by using multiple filters. Switching to AlGaN equivalents
increases robustness and eliminates the need to block out visible
and infrared light, which in turn boosts detector performance, say
IMEC’s Pawel Malinowski,Kyriaki Minoglou and Piet De Moor.
the EUV detection needs. But greater performance ispossible by
turning to detectors based on GaN, whichhave an inherently simpler
system design and are morerobust to UV radiation.
Silicon’s weaknessesOne of the biggest advantages of using
silicon to buildany device is that this material and its related
processtechnology are mature, and consequently well
understood.However, its bandgap of 1.12 eV means that it absorbsnot
only ultraviolet radiation, but the entire visiblespectrum too,
plus infrared radiation up to around 1100nm(see Figure 1). This
makes silicon the perfect material forthe most common digital
cameras and advanced imagersoperating in the visible part of the
spectrum. But if siliconis employed as the active material for
detecting ultravioletradiation, its sensitivity to the longer
wavelengths must betaken into account.
In solar