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Transcript of Plastic Memory
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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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PLASTIC MEMORY
Dept of ECE, BCET 2 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 3 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 4 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 5 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 6 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 7 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 8 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 9 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 10 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 11 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 12 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 13 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 14 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 15 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 16 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 17 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 18 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 19 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 20 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 21 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 22 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 23 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 24 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 25 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 26 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 27 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 28 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 29 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 30 2010 -2011
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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PLASTIC MEMORY
Dept of ECE, BCET 31 2010 -2011
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.