VISVESVARAYA TECHNOLOGICAL UNIVERSITY,

BELGAUM, KARNATAKA, INDIA

A SEMINAR REPORT

ON

―PLASTIC MEMORY”

Submitted in partial fulfillment of the requirements for the award of

degree of

BACHELOR OF ENGINEERING

IN

ELECTRONICS & COMMUNICATION ENGINEERING

For the year 2010-2011

SUBMITTED BY

SANJEEV KUMAR

1BC07EC043

UNDER THE GUIDANCE OF

Mr. G.KESAVAN M.E, (Ph.D)

Asst. Professor of ECE department

BCET, Bangalore- 560081.

DEPARTMENT OF ELECTRONICS & COMMUNICATION

ENGINEERING

BANGALORE COLLEGE OF ENGINEERING &

TECHNOLOGY

Near Heelalige Railway Station, Chandapura, Bangalore-81.

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CONTENTS

Chapter 1 Introduction 4

1.1 Market value of organic devices 4

1.2 Overview of plastic memory 5

Chapter 2 Types of Memory 7

2.1 Random Access Memory 8

2.1.1 DRAM 8

2.1.2 SRAM 9

2.2 Read Only Memory 9

2.2.1 Hardwired ROM 10

2.2.2 PROM 10

2.2.3 EPROM 11

2.3 Hybrid Memory 12

2.3.1 EEPROM 12

2.3.2 Flash memory 13

2.3.3 Plastic memory 13

Chapter 3 Introduction to PEDOT 14

Chapter 4 Spintronics 16

4.1 Introduction to spintronic 16

4.2 Charge vs Spin 17

4.2 Read and write using spintronics 17

Chapter 5 Plastic memory device 18

5.1 About the technology 18

5.2 Structure of plastic memory 18

5.2.1 Basic property of Plastic 18

5.2.2 Device structure 19

5.3 Working of Plastic Memory 20

5.3.1 Storing of Data in Plastic Memory 20

5.3.2 Reading & erasing of data 21

5.3.3 Read Write Erase Cycle 22

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Chapter 6 Fabrication of Plastic Memory 23

6.1 Reel to Reel system 23

6.2 Fabrication Process 24

Chapter 7 Comparison of Plastic Memory with Flash Memory 25

Chapter 8 Advantages & Limitations 26

Chapter 9 Application 28

Conclusion 29

References 30

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ABSTRACT

A series of advances in organic memory technology is demonstrated that enable an

entirely new low-cost memory technology. Researchers incorporate these advances

with the one of the most flexible material PLASTIC. This novel memory technology

can be utilized in a three-dimensional onetime- programmable storage array. Without

the prohibitive costs of silicon processing, this memory is capable of setting cost

points several orders of magnitude lower than their inorganic counterparts. They have

also successfully integrated this technology onto flexible plastic substrates. Combined

with stacking, these vertical memory elements can create ROM densities denser than

many inorganic memories, at a fraction of the cost.

A conducting plastic has the potential to store a mega bit of data in

a millimeter- square device-10 times denser than current magnetic memories. This

device is cheap and fast, but cannot be rewritten, so would only be suitable for

permanent storage. The device sandwiches a blob of a conducting polymer called

PEDOT and a silicon diode between perpendicular wires.

The key to the new technology was discovered by passing high

current through PEDOT (Polyethylenedioxythiophene) which turns it into an

insulator, rather like blowing a fuse .The polymer has two possible states- conductor

and insulator, that form the one and zero, necessary to store digital data. However

tuning the polymer into an insulator involves a permanent chemical change, meaning

the memory can only be written once. In this review we provide the introduction & about the current

state of the plastic memory. We look upon about the PEDOT material being used. We

also look upon the spintronic being used in this technology. We will also see the

plastic memory device structure, its working & fabrication. Also we will see its

advantages over current silicon technology. We will see its limitations & application.

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CHAPTER 1

INTRODUCTION

The idea of ubiquitous computing is extremely attractive. The idea of electronics

integrated into everyday items is extremely attractive, but currently well beyond the

cost structure inherent to silicon chips. From integrated displays to radio-frequency

identification, silicon solutions remain economically out of reach due to high material

costs, processing costs, and the need for clean-room fabrication. In essence, a

significant paradigm shift is necessary to enable electronics to be cheaply built in to

everyday items. In recent years, there has been great interest in organic

semiconductor devices, driven by their potential use in low-cost flexible displays and

disposable electronics applications. As a whole, these materials allow electronics to

be economically feasible for niches out of reach for their silicon-based counterparts.

In particular, there exists great potential in soluble organic semiconductors, since

these may potentially be used to form low-cost all-printed circuits by eliminating the

need for many of the major semiconductor-manufacturing cost points, including

lithography, physical and chemical vapor deposition, plasma etching, and the waste

management costs associated with subtractive processing. In addition, the electrical

performance of organic devices rivals that of Si thin film transistors, making them

suitable for a broad range of applications. The major focus points of organic-based

electronics to date include chemical sensors, displays and the pixel addressing

circuits.

1.1 MARKET VALUE OF ORGANIC DEVICES

A report suggests that the market of the organic devices is

rising exponentially every year & it‘s market value will become more then 250 billion

dollars by 2025. It will become 300 billion dollar market within next 20 years.

Fig 1: organic devices Market value

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1.2 OVERVIEW OF PLASTIC MEMORY

Plastic memory is one kind of organic semiconductor device. Imagine a scenario

where the memory stored in your digital camera or personal digital assistant is

partially based on one of the most flexible materials made by man: PLASTIC.

Scientists at HP Labs and Princeton University are excited a new

memory technology 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 potential to 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, so would only be suitable for permanent storage.

The beauty of the device is that it combines the best of silicon

technology - diodes - with the capability to form a fuse, which does not exist in

silicon," says Vladimir Bulovic, who works on organic electronics at the

Massachusetts Institute of Technology.

This utilizes a previously unknown property of a cheap,

transparent plastic called PEDOT - short for Polyethylenedioxythiophene. The

inventors say that data densities as high as a megabit per square millimeter can be

possible. By stacking layers of memory, a cubic centimeter device could hold as much

as a gigabyte and be cheap enough to compete with CDs and DVD.

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.

Fig 2: Plastic Memory

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The product is still in process & many big companies are behind the development of

this technology which can change our future of memory devices. Following

companies are working on plastic memory devices.

Fig 3: companies working on plastic memory

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CHAPTER 2

TYPES OF MEMORY

2.1 INTRODUCTION TO COMPUTER MEMORY

Computer memory refers to devices that are used to store data or programs (sequences

of instructions) on a temporary or permanent basis for use in an electronic digital

computer. Computers represent information in binary code, written as sequences of 0s

and 1s. Each binary digit (or "bit") may be stored by any physical system that can be

in either of two stable states, to represent 0 and 1. Such a system is called bistable.

This could be an on-off switch, an electrical capacitor that can store or lose a charge, a

magnet with its polarity up or down, or a surface that can have a pit or not. Computer

memory is usually referred to the semiconductor technology that is used to store

information in electronic devices.

In order to enable computers to work faster, there are several

types of memory available today. Within a single computer there is more than one

type of memory.

Memory is divided into:

1. NON VOLATILE MEMORY:

In this memory retains the stored information even when the Electrical power

has been turned off. It is of two types:

a) ROM

b) HYBRID

2. VOLATILE MEMORY:

It loses the stored data as soon as the system is turned off. It requires a

constant power supply to retain the stored information.RAM is type of volatile

memory.

MEMORY

NON VOLATILE

MEMORY

RAM ROM

VOLATILE MEMORY

HYBRID

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2.2 RANDOM ACCESS MEMORY (RAM)

Random-access memory (RAM) is a form of computer data storage. Today, it takes

the form of integrated circuits that allow stored data to be accessed in any order in a

constant time, regardless of its physical location and whether it is related to the

previous piece of data. RAM is often associated with volatile types of memory (such

as DRAM memory modules), where its stored information is lost if the power is

removed. The first RAM modules to come into the market were created in 1951 and

were sold until the late 1960s and early 1970s.

The RAM family includes two important memory devices:

1. Static RAM (SRAM)

2. Dynamic RAM (DRAM).

The primary difference between them is the lifetime of the data they 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 even when power is applied constantly.

2.2.1 DYNAMIC RAM (DRAM)

Dynamic random-access memory (DRAM) has an extremely short data lifetime-

typically about four milliseconds. This is true even

when power is applied constantly. It is a type of

random-access memory that stores each bit of data in

a separate capacitor within an integrated circuit. The

capacitor can be either charged or discharged; these

two states are taken to represent the two values of a

bit, conventionally called 0 and 1. Since capacitors

leak charge, the information eventually fades unless

the capacitor charge is refreshed periodically.

Thus DRAM can only hold data for a short period of time

and must be refreshed periodically. DRAMs are measured by storage capability and

access time. A simple piece of hardware called a DRAM controller can be used to

make DRAM behave more like SRAM. The job of the DRAM controller is to

periodically refresh the data stored in the DRAM. By refreshing the data before it

expires, the contents of memory can be kept alive for as long as they are needed. The

main memory (the "RAM") in personal computers is Dynamic RAM (DRAM), as is

the "RAM" of home game consoles (PlayStation, Xbox 360 and Wii), laptop,

notebook and workstation computers. A lower cost-per-byte makes DRAM attractive

whenever large amounts of RAM are required.

2.2.2 STATIC RAM (SRAM)

Static random-access memory (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.

Fig 4: A DRAM

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SRAM is a type of semiconductor memory where the word static

indicates that, unlike dynamic RAM (DRAM), it does not need to be periodically

refreshed, as SRAM uses bistable latching circuitry to store each bit.

SRAM exhibits data remanence, but is still volatile in the conventional

sense that data is lost when the memory is not powered. SRAM is more expensive,

but faster and significantly less power hungry

(especially idle) than DRAM. It is therefore used

where either bandwidth or low power, or both, are

principal considerations.

SRAM is also easier to control (interface

to) and generally more truly random access than

modern types of DRAM. Due to a more complex

internal structure, SRAM is less dense than DRAM

and is therefore not used for high-capacity, low-cost applications such as the main

memory in personal computers. SRAM is used in personal computers, workstations,

routers, hard disk buffers, router buffers, etc. LCD screens and printers also normally

employ static RAM to hold the image displayed (or to be printed). Small SRAM

buffers are also found in CD-ROM and CD-RW drives.

2.3 READ ONLY MEMORY (ROM)

Read-only memory (ROM) is a class of storage media used in computers and other

electronic devices. Data stored in ROM cannot be modified, or can be modified only

slowly or with difficulty, so it is mainly used to distribute firmware (software that is

very closely tied to specific hardware and unlikely to need frequent updates.

Memories in the ROM family are

distinguished by the methods used to write new data

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 to erasable-and-

programmable. A common feature of all these

devices is their ability to retain data and programs

forever, even during a power failure.

They are classified as:

1. Hardwired ROM

2. PROM

3. EPROM

2.3.1 HARDWIRED ROM

The very first ROMs were hardwired devices that contained a

preprogrammed set of data or instructions. The contents of the ROM had to be

specified before chip production, so the actual data could be used to arrange the

transistors inside the chip. Hardwired memories are still used, though they are now

called masked ROMs to distinguish them from other types of ROM. The primary

Fig 5: A SRAM

Fig 6: ROM

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Fig 8: An EPROM chip

Fig 7: A PROM chip

advantage of a masked ROM is its low production cost. Unfortunately, the cost is low

only when large quantities of the same ROM are required.

2.3.2 PROGRAMMABLE ROM (PROM)

One step up from the masked ROM is the PROM (programmable ROM), which is

purchased in an unprogrammed state. If you were to look at the contents of an

unprogrammed PROM, you would see that the data is made up entirely of l's. The

process of writing your data to the PROM involves a special piece of equipment

called a device programmer.

The device programmer writes data to the device one word at a

time by applying an electrical charge to the input pins of the chip. Once a PROM has

been programmed in this way, its contents 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.

A programmable read-only

memory (PROM) or one-time programmable non-

volatile memory (OTP NVM) is a form of digital

memory where the setting of each bit is locked by

a fuse or antifuse. Such PROMs store programs

permanently.

The key difference from a strict ROM is that the programming

is applied after the device is constructed. PROMs are manufactured blank and,

depending on the technology, can be programmed at wafer, final test, or in system.

The availability of this technology allows companies to keep a supply of blank

PROMs in stock, and program them at the last minute to avoid large volume

commitment. These types of memories are frequently seen in video game consoles,

mobile phones, radio-frequency identification (RFID) tags, implantable medical

devices, high-definition multimedia interfaces (HDMI) and in many other consumer

and automotive electronics products.

2.3.3 ERASABLE & PROGRAMMABLE ROM (EPROM)

An EPROM (erasable-and-programmable ROM) is

programmed in exactly the same 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. A

window in the top of the device allows

Microcontrollers the light to reach the silicon. By

doing this, you essentially reset the entire chip to its

initial unprogrammed state. Though more expensive

than PROMs, their ability to be reprogrammed makes

EPROMs an essential part of the software

development and testing process.

An EPROM or erasable programmable read only memory is a

type of memory chip that retains its data when its power supply is switched off. In

other words, it is non-volatile. It is an array of floating-gate transistors individually

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programmed by an electronic device that supplies higher voltages than those normally

used in digital circuits. EPROMs are easily recognizable by the transparent fused

quartz window in the top of the package, through which the silicon chip is visible, and

which permits exposure to UV light during erasing.

For large volumes of parts (thousands of pieces or more), mask-

programmed ROMs are the lowest cost devices to produce. However, these require

many weeks lead time to make, since the artwork for an IC mask layer must be altered

to store data on the ROMs. Initially, it was thought that the EPROM would be too

expensive for mass production use and that it would be confined to development only.

It was soon found that small-volume production was economical with EPROM parts,

particularly when the advantage of rapid upgrades of firmware was considered.

Some microcontrollers, from before the era of EEPROMs and

flash memory, use an on-chip EPROM to store their program. Such microcontrollers

include some versions of the Intel 8048, the free scale 68HC11, and the "C" versions

of the PIC microcontroller. Like EPROM chips, such microcontrollers came in

windowed (expensive) versions that were useful for debugging and program

development. The same chip came in (somewhat cheaper) opaque OTP packages for

production. Leaving the die of such a chip exposed to light can also change behavior

in unexpected ways when moving from a windowed part used for development to a

non-windowed part for production.

2.4 HYBRID MEMORY

As memory technology has matured in recent years, the line between RAM and

ROM has blurred. Now, several types of memory combine features of both. These

devices do not belong to either group and can be collectively referred to as hybrid

memory devices. Hybrid memories can be read and written as desired, like RAM, but

maintain their contents without electrical power, just like ROM.

Hybrid memories are of following types:

1. EEPROM

2. FLASH MEMORY

3. NVRAM

Fig 9: EPROM chip

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Fig 11: A Flash memory

2.4.1 ELECTRICALLY ERASABLE & PROGRAMMABLE ROM (EEPROM)

Electrically-erasable-and-programmable (EEPROM) is similar to EPROMs, but

the erase operation is accomplished electrically, rather than by exposure to ultraviolet

light. Any byte within an EEPROM may be erased and rewritten. Once written, the

new data will remain in the device forever-or at least until it is electrically erased. The

primary tradeoff for this improved functionality is higher cost, though write cycles are

also significantly longer than writes to a RAM. So you wouldn't want to use an

EEPROM for your main system memory.

EEPROM is user-modifiable read-only memory (ROM) that can be erased and

reprogrammed (written to) repeatedly through the application of higher than normal

electrical voltage generated externally or internally in the case of modern EEPROMs.

EPROM usually must be removed from the device for erasing and programming,

whereas EEPROMs can be programmed and erased in circuit.

EEPROMs were limited to single byte operations which made them slower,

but modern EEPROMs allow multi-byte page operations. It also has a limited life -

that is, the number of times it could be reprogrammed was limited to tens or hundreds

of thousands of times. That limitation has been extended to a million write operations

in modern EEPROMs. In an EEPROM that is frequently reprogrammed while the

computer is in use, the life of the EEPROM can be an important design consideration.

It is for this reason that EEPROMs were used for configuration information, rather

than random access memory.

2.4.2 FLASH MEMORY

Flash memory combines the best features of the memory devices described so

far. Flash memory devices are high density, low cost,

nonvolatile, fast (to read, but not to write), and

electrically reprogrammable.

Flash memory is a solid-state, non-volatile,

rewritable memory that functions like RAM and a hard

disk combined. If power is lost, all data remains in

memory. Because of its high speed, durability, and low

voltage requirements, it is ideal for digital cameras,

cell phones, printers, handheld computers, pagers

and audio recorders.

Fig 10: EEPROM chip

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These advantages are overwhelming and, as a direct result, the use of flash

memory has increased dramatically in embedded systems. From a software viewpoint,

flash and EEPROM technologies are very similar. The major difference is that flash

devices can only be erased one sector at a time, not byte-by-byte. Typical sector sizes

are in the range 256 bytes to 16KB.

Despite this disadvantage, flash is much more popular than EEPROM and is

rapidly displacing many of the ROM devices as well.

2.4.4 PLASTIC MEMORY

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 silicon circuits which was invented by Researchers at Princeton University

working with Hewlett-Packard. This memory is technically a hybrid that contains a

plastic film, a flexible foil substrate and some silicon.

The discovery, achieved by HP and Princeton researchers in Forrest's

university laboratory, came during work with a polymer material called PEDOT - a

clear conducting plastic used as coating on photographic film and as electrical

contact on video displays.

It was Princeton postdoctoral researcher Steven Moller, now with Hewlett

Packard, who found that PEDOT conducts electricity at low voltages but

permanently loses its conductivity when exposed to higher electrical currents,

making it act like a circuit breaker.

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Fig 12: structure of PEDOT

CHAPTER 3 INTRODUCTION TO PEDOT

PEDOT's ability to conduct electricity means it is already used widely as the anti

static coating on camera film. But until now, no one suspected that it could be

converted into an insulator. The material is a blend of a negatively-charged polymer

called PSS and a positively-charged one called PEDT+. Having distinct, charged

components allows it to conduct electricity and means that it is water soluble. The

team is not sure why it stops conducting when high currents pass through. But

Princeton researcher Stephen Forrest suspects that the heat produced by a high current

gives the PSS- layer sufficient energy to snatch a positively-charged hydrogen ion

from any water that has dissolved on its surface, forming a neutral PSSH. Without the

negatively-charged PSS- to stabilize it, PED+ in turn grabs on to an extra electron and

also becomes neutral, converting PEDOT into an insulating polymer.

PEDOT is a relatively new member in the conducting-

polymer family. It shows interesting properties, including relatively good

electrochemical, ambient, and thermal stability of its electrical properties as compared

with that of otherpolythiophenes. PEDOT is built from ethylenedioxythiophene

(EDOT) monomers. It is insoluble in many common solvents and unstable in its

neutral state, as it oxidizes rapidly in air. To improve its process ability, a

polyelectrolyte solution (PSS) can be added, and this results in an aqueous dispersion

of PEDOT: PSS, where PEDOT is its oxidized state. Each phenyl ring of the PSS

monomer has one acidic SO3H (suffocate) group as shown in fig 12.

PEDOT: PSS is industrially synthesized from the EDOT monomer, and PSS as a

template polymer using sodium peroxodisulfate as the oxidizing agent. This affords

PEDOT in its highly conducting, cationic form.

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If high boiling solvents like methylpyrrolidone, dimethyl

sulfoxide, are added conductivity increases many orders of magnitude which makes it

also suitable as a transparent electrode, for example in touch screens, organic light-

emitting diodes and electronic paper to replace the traditionally used indium tin oxide.

Due to the high conductivity (up to 1000 S/cm are possible), it can be used as a

cathode material in capacitors replacing manganese dioxide or liquid electrolytes.

A conductive layer on glass is obtained by spreading a layer

of the dispersion on the surface usually by spin coating and driving out the water by

heat. Special PEDOT: PSS inks and formulations were developed for different coating

and printing processes. Water based PEDOT: PSS inks are mainly used in slot die

coating, flexography, rotogravure and inkjet printing.

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Fig 13: What is Spintronic?

CHAPTER 4 SPINTRONICS

4.1 INTRODUCTION TO SPINTRONIC

Conventional electronic devices rely on the transport of electrical charge carriers -

electrons - in a semiconductor such as silicon. Now, however, physicists are trying to

exploit the 'spin' of the electron rather than its charge to create a remarkable new

generation of 'spintronic' devices which will be smaller, more versatile and more

robust than those currently making up silicon chips and circuit elements. The potential

market is worth hundreds of billions of dollars a year.

Spintronics – or spin electronics – is an emerging technology that

exploits the intrinsic spin of the electron rather than its charge, as is the case with

current electronic devices as shown in below figure. The technology promises

microelectronic devices that can store more data in less space, process data faster, and

consume less power. Researchers at Ohio State University (OSU) have now

demonstrated the first plastic memory device that utilizes the spin of electrons to read

and write data.

OSU‘s Arthur J. Epstein and colleagues have created a prototype plastic spintronic

device using techniques found in the mainstream computer industry today. At this

point, the device is little more than a thin strip of dark blue organic-based magnet

layered with a metallic ferromagnet (a magnet made of ferrous metal such as iron) and

connected to two electrical leads. Still, the researchers successfully recorded data on it

and retrieved the data by controlling the spins of the electrons with a magnetic field.

Epstein, Distinguished University Professor of physics and chemistry and director of

the Institute for Magnetic and Electronic Polymers at OSU, described the material as a

hybrid of a semiconductor that is made from organic materials and a special magnetic

polymer semiconductor. As such, it is a bridge between today‘s computers and the all-

polymer, spintronic computers that he and his partners hope to enable in the future.

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Fig 14: 1 & 0 in spintronic

4.2 CHARGE VS SPIN

Normal electronics encode computer data based on a binary code of

ones and zeros, depending on whether an electron is present in a void within the

material. But researchers have long known that electrons can be polarized to orient in

particular directions, like a bar magnet. They refer to this orientation as spin – either

―spin up‖ or ―spin down‖ – and have been working on a way to store data using spin.

The resulting electronics, dubbed Spintronics, would effectively let computers store

and transfer twice as much data per electron. But higher data density is only part of

the story. ―Spintronics is often just seen as a way to get more information out of an

electron, but really it‘s about moving to the next generation of electronics,‖ a

researcher said. ―We could solve many of the problems facing computers today by

using spintronic.‖

One advantage of spin over charge is that spin can be easily

manipulated by externally applied magnetic fields, a property already in use in

magnetic storage technology. Another more subtle (but potentially significant)

property of spin is its long coherence, or relaxation, time—once created it tends to

stay that way for a long time, unlike charge states, which are easily destroyed by

scattering or collision with defects, impurities or other charges.

These characteristics open the possibility of developing devices that

could be much smaller, consume less electricity and be more powerful for certain

types of computations than is possible with electron-charge-based systems. Typical

circuit boards use a lot of energy. Moving electrons through them creates heat, and it

takes a lot of energy to cool them. Chip makers are limited in how closely they can

pack circuits together to avoid overheating. Flipping the spin of an electron requires

less energy, and produces hardly any heat at all. That means that spintronic devices

could run on smaller batteries. If they were made out of plastic, they would also be

light and flexible.

4.3 READ & WRITE USING SPINTRONICS

All spintronic devices act according to the simple scheme:

(1) Information is stored (written) into spins as a particular spin orientation (up or

down).

(2) The spins, being attached to mobile electrons, carry the information along a

wire.

(3) The information is read at a terminal.

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CHAPTER 5 PLASTIC MEMORY DEVICE

A method of storing the digital information by using the plastic called PEDOT & one

of its property that a plastic conducts electricity at low voltages & acts as insulator

at high voltages is called as Plastic Memory.

5.1 ABOUT THE TECHNOLOGY

A conducting plastic has been used to create a new memory

technology with the potential to 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, so would only be suitable for permanent storage. The

plastic memory technology is all solid state based. The absence of moving parts in

itself offers a substantial speed advantage compared to all mechanical systems, like

magnetic hard disks and optical systems. The memory is developed by thin film

technology has undergone stringent reliability tests at temperatures between -40 and 1

10°C. The results underline the exceptional stability of the polymer memory and

compliance with military and commercial standard tests.

The thin film polymers can be switched from one state to the other

and maintain that state even when the electrical field is turned off. This polymer is

"smart", to the extent that functionality is built into the material itself, like switch

ability, addressability and charge store. Polymer devices can be sprayed or printed,

and are therefore much cheaper than silicon devices, which must be etched.

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, cell phone or PDA,

like an electronic version of film negatives.

5.2 STRUCTURE OF PLASTIC MEMORY

5.2.1 BASIC PROPERTY OF PLASTIC

While experimenting with a polymer material known as PEDOT, Princeton

University researcher Sven Moller determined that although the plastic conducts

electricity at low voltages, it permanently loses its conductivity when exposed to

higher voltages. Together with colleagues from Hewlett-Packard Laboratories, he

developed a method to take advantage of this property to store digital information,

which can be stored as collections of ones and zeros.

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5.2.2 DEVICE STRUCTURE

Plastic memory contains a plastic film, a flexible foil substrate and some silicon.

Figure1 depicts the basic structure of the plastic memory. As shown in figure 15 a

plastic memory has two metal electrodes and a polymer layer is sandwiched between

two electrodes.

A two-terminal device in which an organic semiconducting polymer is sandwiched

between two electrodes, indium doped tin oxide (ITO) and aluminum as shown in

figure 16.

The experimental devices contain two 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 present in the device under influence of an electric field is

expected to induce switching between a high and a low conduction state, the so called

ON and OFF state of a memory device.

Fig15: Basic structure

Fig16: A plastic memory device

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5.3 WORKING OF PLASTIC MEMORY

The PEDOT-based memory card consists of a grid of circuits comprising polymer

fuses. A large applied current causes specific fuses to "blow" leaving a mix of

functioning and nonfunctioning connections.

5.3.1 STORING OF DATA IN THE MEMORY

Any data like image, sound, video etc are stored as a stream of one‘s & zeros. They

use spintronic rather than the charge of an electron. We apply a large current to write

the data. The memory material i.e. PEDOT is a ferroelectric polymer. When an

electric field is applied across the polymer chains are rotated. The respective

orientation represents zero & one. Large applied current makes some of the switches

blow some switches making some connection to function & some non -functioning.

Functioning switches are written.

Fig16: Storing of data in plastic memory using spintronic

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All spintronic devices act according to the simple scheme:

(1) Information is stored (written) into spins as a particular spin orientation (up or

down).

(2) The spins, being attached to mobile electrons, carry the information along a wire.

5.3.2 READING & ERASING OF DATA

When a lower current is later used to read the data, a blown fuse blocks current flow

and is read as OFF, whereas a working fuse is interpreted as ON. Working fuse

contains data. The data is read from ON switches. Because the storage method

involves a physical change to the device, it is a so-called WORM-- write once, read

many times--technology. For erasing of data voltage required should be greater than

the voltage applied for writing.

Fig 18: Read write & Erase in plastic memory

Fig 17: ON & OFF state of memory

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5.3.1 READ WRITE ERASE CYCLE:

Figure 19 shows Read-Write-Erase Cycle.

(1) A -6V pulse is applied to bring the memory in its written state.

(2) The memory is read at -2.5V below i.e. at -3.5 V.

(3) A +6V pulse is applied to erase to memory.

Fig 19: Read-Write-Erase Cycle in memory

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Fig 20:Reel-to-reel system for printing

circuits

Fig 21: Commercial reel-to-reel

printer

CHAPTER 6 FABRICATION

6.1 REEL TO REEL SYSTEM

For fabrication of plastic memory we use ―Reel to Reel‖ system. As opposed to

silicon processing, the process for making all-printed plastic circuits is fully additive.

That is, lithographic patterning steps and film etching costs are directly removed from

production costs. Also, if all layers of the circuit are printed, vacuum deposition

processes can also be eliminated, further reducing costs. By combining the technology

of fully-printed organic circuits with flexible substrate technology, ultra-low costs are

achieved on what is dubbed a ―Reel-to-Reel‖ system.

In the reel-to-reel system, illustrated in Figure 20,

the complete fabrication of the organic circuits is accomplished on a track-like

system. During the procedure, the source plastic substrate resides on a large spindle,

pictured to the left in Figure 20. This roll is unwound during the process, and the

plastic surface passes underneath several deposition stages. Each stage is responsible

for the deposition of a device layer through a solution printing process such as inkjet,

screen-printing, or gravure. In this process, the deposition source is responsible for

lateral pattern control, while the reel motion is responsible for advancing the substrate

inline. This is similar to the operation of a commercial inkjet printer, where the print

head moves across the sheet, and the paper feed controls the rate at which the sheet

passes underneath the head. Finally, the substrate can be rolled at the destination

spindle. Once the process is complete, the spindle can be removed, and the individual

dies can be cut, separated, and packaged for use. An example of a commercial reel-to-

reel system is shown in Figure 21.

6.2 FABRICATION

PROCESS

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The glass substrate is cleaned. First, the glass substrates were sonicated in the order of

detergent, de-ionized water, acetone, and isopropanol, and then baked in an oven at

about 80 °C to prepare for fabrication. A substrate-moving system allows the

deposition of each layer of the device without breaking the vacuum of the chamber.

The organic compound and metal material we used are tin and Al, respectively. At

first, a tin film was deposited on the precleaned glass substrate at a deposition rate of

3 Å/ s for the bottom electrode. Polymer PEDOT: PSS is deposited with P3HT. Then

Al film was deposited sequentially to form the top electrode layers. The Al electrode

& tin electrode are connected together with a voltage supply. All electrical

measurements were done in ambient condition. The device structure is shown in

Figure 22.

CHAPTER 7

Fig 22: A plastic memory device after fabrication

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COMPARISON OF PLASTIC MEMORY

WITH SILICON MEMORY

1) SPEED:

Plastic memory is fast. Lab-built devices with a 1GB storage

capacity have yielded read/write cycle times that are 10 times faster than

Compact Flash, which are typically 2-10MB/s read, 1-4MB/s write.

2) NO. OF TRANSISTORS: It requires far fewer transistors, typically only 0.5M (million) for 1GB of

storage compared to silicon's 1.5-6.5B (billion).

3) COST:

It costs about 5% as much to manufacture compared to silicon based memory.

4) 3D SPACE USAGE:

It can be stacked vertically in a product, yielding 3D space usage; silicon chips

can only be set beside each other.

5) POWER CONSUMPTION:

It has very low power consumption as it uses spintronics for producing data.

6) AREA:

The control circuitry only occupies 1-5% of total transistor area.

7) It maintains memory even when the power is turned off. Nothing new

compared to flash, but worth mentioning.

CHAPTER 8

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ADVANTAGES & LIMITATIONS

8.1 ADVANTAGES

1) SIZE & INFORMATION:

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 as many as 1,000 high-quality digital images.

2) STORE MORE DATA THEN FLASH MEMORY:

Technology could potentially store more data than flash, and

perhaps even become fast enough to store video.

3) NO MOVING PART:

Unlike a CD, reading data stored on this memory block does not involve any

moving parts or a laser. Instead it can be plugged directly into a circuit.

4) SOLVE VIRUS HACKERS PROBLEMS:

A PEDOT-based machine could solve the problem of virus hackers, who rely

on the fact they cannot afford to leave a trace out of fear of being caught for

their dirty work. With PEDOT-based solutions, researchers said hackers

would not be able to erase their IP addresses.

5) Scientists suggest, and producing it wouldn't require high temperatures or

vacuum chambers.

6) It‘s a very cheap technology which gives it an upper hand over other

technology.

8) It‘s flexible compared to other silicon devices. It is Eco-friendly & non-toxic.

8.2 LIMITATIONS

1) Read many times but it can be written only ones. So for replacing the current

technology we need to find a way so that they can be written more than once.

2) The biggest challenge is developing a good production technique. The Reel to

Reel technique is not very good technique for production. Printing can

introduce problems with semiconductor ordering, including poor molecular

alignment and decreased grain size, and results in material performance lower

than with methods such as spin-casting.

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3) The scientists have made plastic memory using PEDOT till now. The

capabilities of the PEDOT material depend widely on the solvent ratios and

deposition method. While these results are favorable for a polymer film, much

higher conductivities are required for large products. So, new polymer has to

be find which can be used for all kind of products.

4) This technology is still under research, so it will take about 5yrs to launch in

the market.

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CHAPTER 9 APPLICATION

1) RADIO FREQUENCY IDENTIFICATION(RFID):

A specific target application for low-cost organic devices is the radio frequency

identification tag (RFID). These passive devices could be used on commercial

products to assist in tracking, inventory control, and theft prevention. RFID chips

require less human manipulation to read, and contain far more data than bar codes.

Since RFID systems allow tags to be read at a distance, they can expedite in-store

check-out, and control warehouse inventory with little human supervision.

2) ELECTRONIC MAP:

The flexible nature of the memory is also a valuable attribute that cannot be achieved

by its silicon counterparts. By combining with electro chromic displays, these

memories could be used to create electronic maps on paper or plastic substrates.

Unlike GPS systems with expensive handheld devices, these reel-to-reel maps could

be folded into a back pocket, and could be created at such low cost via the reel-to-reel

fabrication that they could be entirely disposable.

3) GRAPHICS ON SHIRTS:

If the technology were integrated with flexible displays, Plastic memory could be

used to store image files to be displayed on the display mounted on the shirt surface.

Suddenly, shirts with a single graphic could be a thing of the past. This idea could be

expanded to include commercial signage with no silicon components, and images

stored on built-in plastic memories.

4) MEDICAL APPLICATION:

It can be used in tiny sensors which can work 24 hrs to track blood pressure, heart

rate, sugar level.

5) DEFENCE APPLICATION:

Think about soldiers in the field who have to carry heavy battery packs, or even

civilian ‗road warriors‘ commuting to meetings. If we had a lighter weight device

which operates itself at a lower energy cost, and if we could make it on a flexible

polymer display, soldiers and other users could just roll it up and carry it. We see this

portable technology as a powerful platform for helping people.

6) OTHER APPLICATION:

Specific applications could include active wear with built-in mp3 players. It can also

be used in Digital camera for archiving images.

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CONCLUSION

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 a combination of materials that could lower the cost and

boost the density of electronic memory. 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 be read very fast and with low power

consumption. So this would be suitable only for permanent storage.

Plastic memory uses spin of the electron rather than the charge of

electron & spin of electron store more data compared to the charge. So, large amount

of data can be stored in the plastic memory. The plastic memory is flexible compared

to the silicon technology. It is thick like a sheet of paper so product size using plastic

memory also decreases.

The main challenge in developing plastic memory is the polymer for its

fabrication. PEDOT cannot be used for some application like RFID where

conductivity requirement is more. So, alternative polymer is to be used for

fabrication. Plastic memory will be very useful for future for storing data.

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REFERENCES

1. International Symposium on Flexible Electronics (ISFE) journal, Spain.

2. IEEE paper ―After Hard Drives—what comes next?‖- By Mark H. Kryder and

Chang Soo Kim.

3. ―Spintronics‖ by Shanker Das Sharma.

4. ―Polymer/Organic memories‖ by Paul Heremans.

5. ―Semiconducting Polymers‖ by G. Hadziioannou, P. van Hutten.

6. ―The Emergence of Practical MRAM‖ by Barry Crocus Technologies.

7. ―Just one word – plastics [organic semiconductors]‖, IEEE Spectrum, by S.

Moore.

8. ―On the conductivity of PEDOT: PSS thin films‖ by Alexandre Nardes.

9. Wikipedia- wikipedia.com.

10. Mindset- mindset.com.