Report of Plastic Memory

INTRODUCTION Imagine a scenario where the memory stored in your digital camera or personal digitalassistant is partially based one of the most flexible materials made by man- plastic.The recent development in the memory was a new form of permanent computer memory which uses plastic and may be much cheaper and faster than the existing siliconcircuits which was invented by Researchers at Princeton University working with Hewlett-Packard. This memory is technically a hybrid which contains a plastic film, a flexible foilsubstrate and some silicon, that could store more data and cost less than traditional silicon- based chips for mobile devices such as handheld computers, cell phones and MP3 players.A conducting plastic has been used to create a new memory technology with the potentialto store a megabit of data in a millimeter square device -10 times denser than current magnetic memories. The device should also be cheap and fast, but cannot be rewritten, sowould only be suitable for permanent storage.The device sandwiches a blob of a conducting polymer called PEDOT (POLYETHYLENEDIOXYTHIOPENE) and a silicon diode between two perpendicular wires. Substantial research effort has focused on polymer-based transistors, which could form cheap, flexible circuits, but polymer-based memory has received relatively little attention. However, turning the polymer into an insulator involves a permanent chemical change, meaning the memory can only be written to once. Its creators say this makes it ideal for archiving images and other data directly from a digital camera, cellphone or PDA, like an electronic version of film negatives.While microchip makers continue to wring more and more from silicon, the most dramatic improvements in the electronics industry could come from an entirely different material plastic.Labs around the world are working on integrated circuits, displays for handheld devices and even solar cells that rely on electrically conducting polymers²not silicon²for cheap and flexibleelectronic components. Now two of the world¶s leading chip makers are racing to develop newstock for this plastic microelectronic arsenal: plastic memory. Advanced Micro Devices of Sunnyvale, CA, is working with Coatue, a startup in Woburn, MA, to develop chips that store datain polymers rather than silicon. The technology, according to Coatue CEO Andrew Perlman,could lead to a cheaper and denser alternative to flash memory chips²the type of memory used indigital cameras and MP3 players. Meanwhile, Intel is collaborating with Thin Film Technologie Linkping, Sweden, on a similar high capacity plastic memory.

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PRESENT MEMORY TECHNOLOGY  SCENARIO

In order to enable computers to work faster, there are several types of memory available today.Within a single computer there are more than one type of memory.MemoryDRAM SRAM NVRAM FLASH EEPROM PROM EPROM

RAM: The RAM family includes two important memory devices: static RAM (SRAM) anddynamic RAM (DRAM). The primary difference between them is the lifetime of the datathey store. SRAM retains its contents as long as electrical power is applied to the chip. If the power is turned off or lost temporarily, its contents will be lost forever. DRAM, on the other hand, has an extremely short data lifetime-typically about four milliseconds. This is true evenwhen power is applied constantly.

ROM: Memories in the ROM family are distinguished by the methods used to write newdata to them (usually called programming), and the number of times they can be rewritten.This classification reflects the evolution of ROM devices from hardwired to programmable toerasable-and-programmable. A common feature of all these devices is their ability to retaindata and programs forever, even during a power failure.

PROM: PROM (programmable ROM), is purchased in an unprogrammed state, then thedevice programmer writes data to the device one word at a time by applying an electricalcharge to the input pins of the chip. Once a PROM has been programmed in this way, itscontents can never be changed. If the code or data stored in the PROM must be changed the current device must be discarded. As a result, PROMs are also known as one-time programmable (OTP) devices.

EPROM: An EPROM (erasable-and-programmable ROM) is programmed in exactly thesame manner as a PROM. However, EPROMs can be erased and reprogrammed repeatedly.To erase an EPROM, you simply expose the device to a strong source of ultraviolet light. Bydoing this, you essentially reset the entire chip to its initial unprogrammed state.

HYBRID MEMORY: As memory technology has matured in recent years, the line betweenRAM and ROM has blurred. Now, several types of memory combine features of both. Thesedevices do not belong to either group and can be collectively referred to as hybrid memorydevices. Hybrid memories can be read and written as desired, like RAM, but maintain their contents without electrical power, just like ROM. Two of the hybrid devices, EEPROM andflash, are descendants of ROM devices. These are typically used to store code. The thirdhybrid, NVRAM, is a modified version of SRAM. NVRAM usually holds persistent data.

 EEPROM: An EEPROM (also called an EPROM) or Electrically ErasableProgrammable Read-Only Memory, is a non-volatile storage chip used in computersand other devices to store small amounts of volatile (configuration) data.Any bytewithin an EEPROM may be erased and rewritten. Once written, the new data willremain in the device forever-or at least until it is electrically erased. EEPROMs aresimilar to EPROMs, but the erase operation is accomplished electrically, rather than byexposure to ultraviolet light. SEEPROM, meaning Serial EEPROM, is an EEPROMchip that uses a serial interface to the circuit board. 

FLASH MEMORY: Flash memory (sometimes called "flash RAM") is a type of constantly-powered nonvolatile memory that can be erased and reprogrammed in units of memory called blocks. It is a variation of EEPROM which, unlike flash memory, is erasedand rewritten at the byte level, which is slower than flash memory updating. Flash memoryis often used to hold control code such as the basic input/output system (BIOS) in a personalcomputer. When BIOS needs to be changed (rewritten), the flash memory can be written to  in block (rather than byte) sizes, making it easy to update. On the other hand, flash memoryis not useful as random access memory (RAM) because RAM needs to be addressableat the byte (not the block) level. When larger amounts of more static data are to be stored(such as in USB flash drives) other memory types like flash memory are more economic.. NVRAM: The third member of the hybrid memory class is NVRAM (non-volatileRAM). Non-volatility is also a characteristic of the ROM and hybrid memoriesdiscussed previously. However, an NVRAM is physically very different from thosedevices. An NVRAM is usually just an SRAM with a battery backup. When the power is turned on, the NVRAM operates just like any other SRAM. When the power isturned off, the NVRAM draws just enough power from the battery to retain its data. NVRAM is fairly common in embedded systems.Digital Memory is and has been a close comrade of each and every technical advancement inInformation Technology. The current memory technologies have a lot of limitations. DRAM isvolatile and difficult to integrate. RAM is high cost and volatile. Flash has slower writes and lesser number of write/erase cycles compared to others. These memory technologies when needed toexpand will allow expansion only two dimensional space. Hence area required will be increased.They will not allow stacking of one memory chip over the other. Also the storage capacities arenot enough to fulfill the exponentially increasing need. Hence industry is searching for ³HolyGrail future memory technologies for portable devices such as cell phones, mobile PC¶s etc. Nextgeneration memories are trying a tradeoffs between size and cost .This make them good possibilities for development  . 

NEXT GENERATION MEMORIES As mentioned earlier microchip makers continue to wring more and more from silicon, largenumber of memory technologies were emerged. These memory technologies are referred as µNextGeneration Memories¶. Next Generation Memories satisfy all of the good attributes of memory.The most important one among them is their ability to support expansion in three dimensionalspaces. Intel, the biggest maker of computer processors, is also the largest maker of flash-memorychips is trying to combine the processing features and space requirements feature and several nextgeneration memories are being studied in this perspective. They include MRAM, FeRAM, Plasticmemory and Ovonics Unified Memory.Plastic memory is the leading technology among them. It is mainly because of their expansioncapability in three dimensional spaces. The following graph also emphasis acceptance of Plasticmemory. Memory Technology Comparison The graph shows a comparison between cost and speed i.e., the Read/Write time. Disk drivesare faster but expensive where as semiconductor memory is slower in read/write. Plastic memorylies in an optimum position

 Plastic-based memory modules, as against silicon-based ones, promise to revolutionize thestorage space and memory capabilities of chips. Coatue¶s plastic memory cells are about one-quarter the size of conventional silicon cells. And unlike silicon devices, the polymer cells can bestacked that architecture could translate into memory chips with several times the storage capacityof flash memory. By 2004, Coatue hopes to have memory chips on the market that can store 32gigabits, outperforming flash memory, which should hold about two gigabits by then, to produce athree-dimensional structure.    POLYMERS AS ELECTRONIC MATERIALS Polymers are organic materials consisting of long chains of single molecules. Polymers arehighly adaptable materials, suitable for myriad applications. Until the 1970 s and the work of  Nobel laureates Alan J. Heeger, Alan G. MacDiarmid and Hideki Shirakawa, polymers were onlyconsidered to be insulators. Heeger et al showed that polymers could be conductive. Electronswere removed, or introduced, into a polymer consisting of alternately single and double bonds between the carbon atoms. As these holes or extra electrons are able to move along the molecule,the structure becomes electrically conductive.Thin Film Electronics has developed a specific group of polymers that are bistable and thuscan be used as the active material in a non-volatile memory. In other words, the Thin Film polymers can be switched from one state to the other and maintain that state even when theelectrical field is turned off. This polymer is "smart", to the extent that functionality is built intothe material itself, like switchability, addressability and charge store. This is different from siliconand other electronic materials, where such functions typically are only achieved by complexcircuitry. "Smart" materials can be produced from scratch, molecule by molecule, allowing themto be built according to design. This opens up tremendous opportunities in the electronics world,where ³tailor-made memory materials represent unknown territoryPolymers are essentially electronic materials that can be processed as liquids. With ThinFilm¶s memory technology, polymer solutions can be deposited on flexible substrates withindustry standard processes like spin coating in ultra thin layers. 4.1 Space charge and Polymers Making a digital memory device means finding a way to represent the ones and zeros of computer logic, devising a relatively convenient way to retrieve these binary patterns fromstorage, and making sure the information remain stable. Digital memory is an essentialcomponent of many electronic devices, and memory that takes up little space and electricity is inhigh demand as electronic devices continue to shrink. Researchers from the Indian Association for the Cultivation of Science and the Italian National used positive and negative electric charges, or space charges, contained within plastic tostore binary numbers Research Council. A polymer retains space charges near a metal interfacewhen there is a bias, or electrical current, running across the surface. These charges come either from electrons, which are negatively charged, or the positively-charged holes vacated byelectrons. We can store space charges in a polymer layer, and conveniently check the presence of the space charges to know the state of the polymer layer. Space charges are essentially differencesin electrical charge in a given region. They can be read using an electrical pulse because theychange the way the devices conduct electricity.The researchers made the storage device by spreading a 50-nanometer layer of the polymer regioregularpoly on glass, then topping it with an aluminum electrode. To write a space charge tothe device, they applied a positive 20-second, 3-volt pulse. To read the state, they used a 0.2-volt,one minute pulse. Any kind of negative electrical pulse erased this high state, or charge, replacingit with the default low state. The space charges remain stable for about an hour and also can berefreshed by another 3-volt positive

pulse. The researchers intend to increase the memoryretention ability of their device beyond an hour. Researchers are looking forward to increasing itinto days or more. Once this is achieved, polymer devices can be used in data storage devices andalso as a switch whose state can be changed externally by a voltage puls

PLASTIC COMPUTER  MEMORY'S SECRET IS GOLD NANO PARTICLES Taiwanese researchers say they have developed a simple, durable, and potentially inexpensivenonvolatile memory array made from a mix of plastic and gold nanoparticles. The array is a 16- byte device called an organic nonvolatile bistable memory. The researchers, fromNational ChungHsing University (NCHU) and the quasi-governmental Industrial Technology ResearchInstitute (ITRI), presented details of the device today in Washington, D.C., at the 2007 IEEEInternational Electron Devices Meeting. The Taiwanese team plans to integrate the memory intosmart cards.Engineers have been pursuing organic nonvolatile memories²devices made from plastic andother carbon-based chemicals²because they can potentially be manufactured cheaply using printing processes. But organic memory devices tend to break down in air and under the stress of many read-write cycles. Recent measurements suggest that it endures more than1000switchesand retains its data for roughly 10 days, even when exposed to air. Its stability may quicklyimprove, says Pei. Theoretically, the memory¶s retention time can reach 30 days, he says The new memory consists of gold nanoparticles mixed into a polymer called PCm,sandwiched between two aluminum electrodes. Reading the bit stored in the device involvesapplying a small voltage and measuring the resulting current. Ordinarily, the structure conductslittle current, the state in which it is storing a 0. But push the voltage past 2 volts, and the current jumps 10000-fold. Pei and his colleagues theorize that before that threshold, a trickle of electronsis hopping from gold nanoparticle to gold nanoparticle. But some get trapped along the way. At 2 volts, there are so many trapped electrons that they form a highly conductive path through thedevice. At that point, smaller voltages will continue to produce the high current, and the device isconsidered to be storing a 1. Erasing the bit is simply done by applying a strong negative voltage,sweeping away the trapped charges.The voltages involved in writing bits can stress the plastic and make a device unstable bycausing the nanoparticles to clump together.

But the Taiwanese researchers found a way to prevent that by stabilizing the nanoparticles. In the memory device, gold nanoparticles areconnected directly to polymer chains, which act as fingers that get entangled with the host polymer, says Pei. Therefore, the stabilization of the structure of the organic memory can beensured even if high-voltage stress is applied.Pei¶s team plans to show off the device on 17 And 18 December at the 2007 InternationalSymposium for Flexible Electronics and Display (ISFED), to be held in Hsinchu, Taiwan, andsponsored by ITRI..12 An organic memory is considered essential to implementflexible electronics, such as radio-frequency identification (RFID), smart cards, e-paper, and flexible displays. In mid-March, ITRIlaunched Taiwan¶s first laboratory dedicated to flexible electronics, with US $ 9.1million infunding.Other research groups are also pursuing organic nonvolatile memory devices using either different nanoparticles, such as carbon-60, embedded in the plastic or using the plastic as part of an organic transistor structure

HOW DOES PLASTIC MEMORY WORK? Making a digital memory device means finding a way to represent the ones and zeros of computer logic, devising a relatively convenient way to retrieve these binary patterns fromstorage, and making sure the information remains stable. Plastic memory storesinformation in anentirely different manner than silicon devices. Rather than encoding zeroes and ones as theamount of charge stored in a cell, Coatue¶s chips store data based on the polymer¶s electricalresistance. Using technology licensed from the University of California, Los Angeles, and theRussian Academy of Sciences in Novosibirsk, Coatue fabricates each memory cell as a polymer sandwiched between two electrodes. To activate this cell structure, a voltage is applied betweenthe top and bottom electrodes, modifying the organic material. Different voltage polarities areused to write and read the cells.Application of an electric field to a cell lowers the polymer¶s resistance, thus increasing itsability to conduct current; the polymer maintainsits state until a field of opposite polarity isapplied to raise its resistance back to its original level. The different conductivity States represent bits of information. A polymer retains space charges near a metal interface when there is a bias, or electrical current, running across the surface. These charges come either from electrons, which arenegatively charged, or the positively-charged holes vacated by electrons. We can store spacecharges in a polymer layer, and conveniently check the presence of the space charges to know thestate of the polymer layer. Space charges are essentially differences in electrical charge in a givenregion. They can be read using an electrical pulse because they change the way the deviceconducts electricity.The basic principle of Polymer based memory is the dipole moment possessed by polymer chains. It is the reason by which polymers show difference in electrical conductivity. As explainedearlier implementing a digital memory means setting up away to

represent logicone and logiczero. Here polarizations of polymers are changed up or down to represent logic one and zero. Nowlet¶s see what are a dipole and a dipole moment

BASIC PROPERTY OF PLASTIC While experimenting with a polymer material known as PEDOT, Princeton Universityresearcher Sven Moller determined that although the plastic conducts electricity at low voltages, it permanently loses its conductivity when exposed to higher voltages. Together with colleaguesfrom Hewlett-Packard Laboratories, he developed a method to take advantage of this property tostore digital information, which can be stored as collections of ones and zeros

PROCEDURE The PEDOT-based memory card consists of a grid of circuits comprising polymer fuses. Alarge applied current causes specific fuses to "blow," leaving a mix of functioning andnonfunctioning connections. When a lower current is later used to read the data, a blown fuse blocks current flow and is read as a zero, whereas a working fuse is interpreted as a one. Becausethe storage method involves a physical change to the device, it is a so-called WORM--write once,read many times--technology. "The device could probably be made cheaply enough that one-timeuse would be the best way to go," says study co-author Stephen Forrest of Princeton University.The team predicts that one million bits of information could fit into a square millimeter of material the thickness of a sheet of paper. A block just a cubic centimeter in size could contain asmany as,1000 high-quality digital images, the scientists suggest, and producing it wouldn't requirehigh-temperatures or vacuum chambers

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 A two-terminal device in which an organic semiconducting polymer is sandwiched betweentwo electrodes, indium doped tin oxide (ITO) and aluminum. The experimental devices containtwo polymer layers. The first layer consists of PEDOT: PSS to which an inorganic salt (e.g.lithium triflate) and plasticizer (ethylene carbonate, EC) have been added. The second layer consists of poly (3- hexylthiophene) (P3HT) doped with the plasticizer. Motion of the ions presentin the device under influence of an electric field is expected to induce switching between a highand a low conduction state, the so called ON and OFF state of a memory device.The researchers made the storage device by spreading a50-nanometer layer of the polymer regioregularpoly on glass, then topping it with an aluminum electrode. To write a space charge tothe device, they applied a positive20-second, 3-volt pulse. To read the state, they used a 0.2-volt,one minute pulse. Any kind of negative electrical pulse erased this high state, or charge, replacingit with the default low state. In this process, a continuous sheet of flexible polymer is unrolledfrom one spool, covered with circuit-board-like patterns of silicon, and collected on another spool.The Thin Film memory design is solid state, with no mechanical or moving parts involved. Ituses a passively addressed, cross point matrix. An ultra thin layer of the TFE polymer issandwiched between two sets of electrodes. A typical array may consist of several thousand suchelectrically conducting lines and hence millions of electrode crossings. Memory cells are defined by the physical overlap of the electrode crossings and selected by applying voltage. Each electrodecrossing represents one bit of information in a true4f (4-Lampda square) cell structure, thesmallest possible physical memory cell. The effective cell footprint is further reduced if additionalmemory layers are applied. In the latter case, each new layer adds the same capacity as the firstone. This stacking is a fundamental strength of the Thin Film technology. The plastic memorylayers are just1/10,000 of a millimeter or less in thickness, autonomous and easy to deposit. Layer upon layer may be coated on a substrate. A layer may include a self-contained active memorystructure with on-layer TFT circuitry, or share circuitry with all other layers. Both approachesoffer true 3D memory architecture. The stacking option will enable manufacturers to give gain previously unattainable storage capacity within a givenfootprint

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READ/WRITE TECHNOLOGY USED IN PLASTIC MEMORY Scientists from Ohio University has created a new spintronics memory device from plastic.It¶s simply a thin strip of dark blue organic-based magnet layered with a metallic ferromagnet andconnected to two electrical leads. Still, the researchers successfully recorded data on it andretrieved the data by controlling the spins of the electrons with a magnetic field. They say that thenew device is a bridge between today¶s computers and the all-polymer, spintronic computers thatthe researchers hope to eventually create

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FEATURES OF PLASTIC MEMORY 1. Data stored by changing the polarization of the polymer between metal lines.

2. Zero transistors per bit of storage3. Memory is Nonvolatile

3. Microsecond initial reads. Write speed faster than NAND and NOR Flash.

4. Simple processing, easy to integrate with other CMOS

5. No cell standby power or refresh required

6Operational temperature between -40and110°C.

Advantages of plastic memory 

The plastic memory technology promises to store more data at less cost than theexpensive-to-build silicon chips used by popular consumer gadgets including digitalcameras, cell phones and portable music players.The memory cannot be rewritten, but can be read very fast and with low power consumption. So this would be suitable only for permanent storage.Unlike flash memory found in consumer devices, the new technology can bewritten to only once, though it can be read many times. It acts in that respect like a nonre-writeable compact disc. But this new memory, which retains data even when there'sno power, won't require a power-hungry laser or motor to read or write, and promisesmore capacity.PEDOT-based machine could solve the problem of virus hackers, who rely onthe fact they cannot afford to leave a trace out of fear of being caught for their dirtywork.With PEDOT-based solutions, hackers would not be able to erase their IPaddresses. Instead of rewriting over existing data, PEDOT would just create a staticsection for incoming data. This ensures that the integrity of data on documents ispreserved over long periods of time.

Limitations of plastic memory 

The dimension demands on devices increasingly get smaller to host a variety offormfactors. Smaller memory space means the transistors leak more electricity and suck up more power.It can be read many times but it can be write only ones. The biggest challenge is developing production technique. This technology is still under research, so it will take aboutyrs to launch inthe market.But turning plastic memory into a commercial product won¶t be easy. Memory technologiescompete not only on storage capacity but on speed, energy consumption and reliability. Thedifficulty is in meeting all the requirements of current silicon memory chips. The plastic memorymade at Bell Labs is still relatively slow by silicon standards, and anticipated capacity is only onthe order of a kilobit.

APPLICATIONS OF PLASTIC MEMORY Flash memory stores data electrically, in specially designed silicon transistors. Information can be recorded and read quickly and is retained even when the power is off. This makes flash idealfor MP3 players, cameras, memory cards, and USB drives.The plastic memory technology promises to store more data at less cost than the expensive-to-build silicon chips used by popular consumer gadgets including digital cameras, cell phones and portable music players.The memory cannot be rewritten, but can be read very fast and with low power consumption.So this would be suitable only for permanent storage.Unlike flash memory found in consumer devices, the new technology can be written to onlyonce, though it can be read many times. It acts in that respect like a non-rewriteable compactdisc. But this new memory, which retains data even when there's no power, won't require a power-hungry laser or motor to read or write, and promises more capacity.PEDOT-based machine could solve the problem of virus hackers, who rely on the fact theycannot afford to leave a trace out of fear of being caught for their dirty work.With PEDOT-based solutions, hackers would not be able to erase their IP addresses. Insteadof rewriting over existing data, PEDOT would just create a static section for incoming data.This ensures that the integrity of data on documents is preserved over long periods of time.Polymer devices can be used in data storage devices and also as a switch whose state can bechanged externally by a voltage pulse

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GOAL OF PLASTIC M EMORY The goal is to make the technology fast enough to store video. The researchers hope thatthis technology will decrease the size, increase reliability and speed up reading and writing of memory chips.

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CONCLUSION The fundamental strength i.e., the stacking of memory layers which yields maximum storagecapacity in a given footprint is the main reason why Plastic memory is highly preferred. The non-volatileness and other features are in built in molecular level and offers very high advantages interms of cost. Polymers ,which are once considered to be the main reason for pollution andreferred to be removed from the earth, has found a new area of utilization.Plastic memory is much cheaper and faster than the existing silicon a circuit was invented by Researchers at Princeton University working with Hewlett- Packard. Plastic memory is acombination of materials that could lower the cost and boost the density of electronicmemory. It is an all-organic memory system with manifold advantages: in speed, production,energy consumption, storage capacity and cost. The memory cannot be rewritten, but can beread very fast and with low power consumption. So this would be suitable only for  permanent storage.