INTRODUCTION NRAM, the wonder product of nanotechnology, is the patented trademark of the non volatile memory produced by Nanterno Inc, USA. The company’s objective is to deliver a product that will replace all existing forms of memory, such as DRAM (Dynamic RAM), SRAM (Static RAM), and flash memory, and ultimately hard disk storage. In other words a universal memory chip suitable for countless existing and new applications in the field of electronics. NRAM will be considerably faster and denser than DRAM, have substantially lower power consumption than DRAM or flash, be as portable as flash memory and be highly resistant to environmental forces (heat, cold, magnetism). And as a non volatile chip, it will provide permanent data storage even without power. The proprietary NRAM, design, invented by Dr.Thomas Rueckes, Nanterno’s chief Scientific Officer, uses carbon nanotubes as the active memory elements. Carbon nanotubes are the members of the
Transcript
INTRODUCTION
NRAM, the wonder product of nanotechnology, is the patented trademark
of the non volatile memory produced by Nanterno Inc, USA. The company’s
objective is to deliver a product that will replace all existing forms of memory,
such as DRAM (Dynamic RAM), SRAM (Static RAM), and flash memory, and
ultimately hard disk storage. In other words a universal memory chip suitable
for countless existing and new applications in the field of electronics.
NRAM will be considerably faster and denser than DRAM, have
substantially lower power consumption than DRAM or flash, be as portable as
flash memory and be highly resistant to environmental forces (heat, cold,
magnetism). And as a non volatile chip, it will provide permanent data storage
even without power.
The proprietary NRAM, design, invented by Dr.Thomas Rueckes,
Nanterno’s chief Scientific Officer, uses carbon nanotubes as the active
memory elements. Carbon nanotubes are the members of the fullerene family
and have amazing properties, including the ability to conduct electricity as well
as copper while being stronger than steel and as hard as diamond. The wall of a
single-walled carbon nanotube is only one carbon atom thick and the tube
diameter is approximately 100,000 times smaller than a human hair. Dr.
Rueckes’ pioneering design takes advantage of these unique properties while
cleverly integrating nanotubes with traditional semiconductor technologies for
immediate manufacturability.
WHAT IS NANOTECHNOLOGY
THE BEGINNING
Dr. K Eric Drexler is the father of Nanotechnology. In 1960, Nobel
laureate Richard Feynman predicted that by the year 2000 products would be
built one molecule or one atom at a time. This was a truly bold vision because it
would represent a new paradigm for manufacturing and constitute a fundamental
economic shift analogous to a second industrial revolution. This shift is referred
today as the “nanotechnology revolution”, and many people consider
Dr.Feynman’s quote the birth of nanotechnology. The National Science
Foundation predicts that by 2010, nanotechnology will pervade virtually every
corner of the economy and represent $1 trillion in goods and services.
Electronics is fuelled by miniaturization. According to Drexler product
can be made by combining atom by atom or molecule by molecule with the help
of programmed microscopic robotic arms. It is possible because each atom is
identical to any other atom of its flavour and have a remarkable attribute of
sticking to each other. Nanotechnology’s goal is a device called “Universal
Assembler” that takes raw atoms in one side and delivers consumer goods out
the other. It should have following properties:
1. Fractional atomic diameter accuracy.
2. Capability to execute finely controlled motions to transfer one or a few
atom in a guided chemical reaction.
By building objects on such a fine scale, we could make extraordinary
things from ordinary matter.
THE WORD
The term “nanotechnology” is based on the root nanos, meaning one
billionth. It refers to technology that uses components or features that measure
100 nanometers or less. A structure that is one nanometer is one billionth of a
meter-it would take approximately 150,000 such structures to span the diameter
of a human hair.
THE MOTIVATION
Why do companies want to get small? Because getting small means
getting smarter, more powerful and more economical. Consider the first
computer’s developed in the 1940’s. They were the size of a large room, were
very expensive to build, required virtually constant maintenance, needed a
considerable amount of electricity to power, and were useable only by a handful
of highly trained specialists. Compare that to today’s common laptop computers.
They are millions of times faster and more powerful than the first computers,
thousands of times smaller, a mere fraction of the cost, require virtually no
maintenance, run on very little electricity and are useable by almost anyone.
Miniaturization has led to an exponential growth in computer’s effect on
our everyday lives because: (1) processing power has enabled them to do an
almost unthinkable amount of work almost instantaneously; and (2) large
percentages of our population and businesses are able to computers as diverse
tools because they are easy to use and relatively inexpensive to build and
operate. Virtually all of the major advances in the electronic industries, from the
vacuum tube to modern computer chip, are a direct result of miniaturization and
utilizing new materials. Nanotechnology is the next step in the evolution of
miniaturization. It increases the value of existing products and opens the door to
new technologies and products.
THEORY
At the simplest level, nanotechnology is the manipulation single atoms and
molecules to create objects that can be smaller than 100 nanometers. A
nanometer is a billionth of a meter, which is about a hundred-thousandth of the
diameter of a human hair, or 10 times the diameter of a hydrogen atom.
Manufactured products are made from atoms. The properties of those
products depend on how those atoms are arranged. If we rearrange the atoms in
coal we can make diamond. If we rearrange the atoms in sand (and add a few
other trace elements) we can make computer chips. If we rearrange the atoms in
dirt, water and air, we can make potatoes.
There are two more concepts commonly associated with Nanotechnology:
1. Positional assembly
2. Self replication
Positional assembly refers to the arrangement of molecules so as to get the
right molecular parts in the right places. The need for positional assembly
implies an interest in molecular robotics eg., robotic devices that are molecular
both in their size and precision. These molecular scale positional devices are
likely to resemble very small versions of their everyday macroscopic
counterparts.
The self replicating systems are able both to make copies of themselves
and to manufacture useful products. If we can design and build one such system
the manufacturing costs for more such systems and the products they make
(assuming they can make copies of themselves in some reasonably inexpensive
environment) will be very low.
You won’t think about installing Microsoft Office anymore. You’ll think
about growing software. The line is blurring in several ways. Scientists are
learning to imitate biological patterns; biological entities are being used in
technology products; and in the distant future, nanomachines may be circulating
through our bloodstreams, attacking tumours and dispersing medicine.
NOT JUST COMPUTERS
The computer industry is just one example of the advantages related to
miniaturization. Getting small is a means of increasing the power and value of
diverse products and services in most industries. For instance, many advances in
biotechnology and the development of new drugs are the direct result of
miniaturization and utilization of novel materials. As with computing power,
diagnostic and research power increase as tools decrease in size. Getting small
allows biotechnology companies and researchers to do more complex
experiments in shorter periods of time, for less money, using less material. This
greatly accelerates discovery and ultimately shortens the time from concept to
market for new advanced drugs and other products. Further, nanotechnology
enables companies and researchers to design revolutionary new products using
new materials and substances not accessible with other technologies.
Dr.Feynman was correct in his prediction of building devices from the
ground up-atom by atom or molecule by molecule. He was incorrect, however,
in his prediction that this would occur routinely by the year 2000. The question
has been, how would you build nano scale structures and manipulate quickly
and cheaply?
CARBON NANOTUBES
Carbon nanotubes are a product of nanotechnology. They were invented
by Sumayyo Ejyma. Carbon nanotubes can in principle play the same role as
silicon as in electronic circuits. Although the electronics industry is already
pushing the critical dimensions of transistors in commercial chips below 200
nanometers -400 atoms wide –engineers face large obstacles in continuing the
miniaturization. Within this decade, the materials and processes on which the
computer revolution has been built will begin to hit fundamental physical limits
Carbon nanotubes
Two major problems have so far thwarted attempts to shrink metal wires
further:
1. There is as yet no good way to remove the heat produced by the devices,
so packing them in more tightly will only lead to rapid overheating.
2. As metal wires get smaller, the gust of electrons moving through them
becomes strong enough to bump the metal atoms around and before long
the wires fail like blown fuses.
How carbon nanotubes solve them?
In theory, nanotubes could solve both these problems.
1. Scientists have predicted that carbon nanotubes would conduct heat nearly as
well as diamond or sapphire and preliminary experiments seem to confirm
their prediction.So nanotubes could efficiently cool very dense arrays of
devices.
2. As bonds among carbon atoms are so much stronger than those in any metal,
nanotubes can transport terrific amount of electric current(the latest
measurements show that a bundle of nanotubes one square centimetre in
cross section could conduct about one billion amps. Such high currents
would vapourise copper or gold)
Where nanotubes shine
1. When stood on end and electrified, carbon nanotubes will act just as
lightning rods do, concentrating the electrical field at their tips.
2. Their strong carbon bonds allow nanotubes to operate for longer periods
without damage.
3. High current field emitter from nanotubes. Just mix them into a composite
paste with plastics, smear them onto an electrode and apply voltage.
4. The scientists have found ways to grow clusters of upright nanotubes in neat
little grids. At optimum density, such clusters can emit more than one amp
per square centimetre, which is more than sufficient to light up the phosphers
on a screen and is even powerful enough to drive microwave relays and
high-frequency switches in cellular phones.
5. Ise Electronics in Ise, Japan, has used nanotube composite to make prototype
vaccum-tube lamps in six colours that are twice as bright as conventional
lightbulbs, longer-lived and atleast 10 times more energy efficient. The first
prototype has run for well over 10,000 hours and has yet to fail.
6. Engineers at Samsung in Seol stread nanotubes in a thin film over control
electronics and then put phosphor-coated glass on top to make a prototype
flat-pannel display. When they demonstrated the display last year, they were
optimistic that the company would have the device-which will be as bright as
a cathode-ray tube but it will consume one tenth as much power. And he
product is on the market now.
7. In defect-free nanotubes, electrons travel ”ballistically”-that is, without any
of the scattering that gives metal wires their resistance.
8. At the small size of a nanotube, the flow of electrons can be controlled with
almost perfect precision. Scientists have recently demonstrated in nanotubes
a phenomenon called Coulomb blockade, in which more than one electron at
a time on to a nanotube.
This phenomenon may make it easier to build single-electron transistors,
the ultimate in sensitive electronics
MAJOR PROBLEMS WITH NANO-TUBES
1.All molecular devices , nanotubes included ,are highly susceptible to the noise
caused by electrical, thermal and chemical fluctuations
2. contaminants (oxygen for eg) attaching to a nanotube can affect its electrical
properties. That may be useful for creating exquisitely sensitive chemical
detectors , but it is an obstacle to making single-molecule circuits
BASIC IDEAS
What makes these tubes so stable is the strength with which carbon atoms
bond to one another, which is also what makes diamond so hard .
In diamond the carbon atoms link in to four-sided tetrahedral, but in
nanotubes the atoms arrange themselves in hexagonal rings. Infact a nanotube
looks like a sheet (or several stacked sheets)of graphite rolled into a seamless
cylinder. Graphite itself is a very unusual material. Wheras most conductors can
be classified as either metals or semiconductors, graphite is one of the rare
materials known as semi metal, delicately balanced in the transitional zone
between the two.
By combining graphite semi-metallic properties with the quantum rules of
energy levels and electron waves, carbon nanotubes emerge as truly exotic
conductor.
One of the quantum world is that electrons behave like as well as particles,
and electron waves can reinforce or cancel one another. As a consequence, an
electron spreading around nanotubes circumference can completely cancel itself
out; thus, only electrons with just the right wavelength remain.
Out of all the possible electron wavelengths, or quantum states, available
in a flat graphite sheet, only a tiny subset is allowed when we roll that sheet into
a nanotube. That subset depends on the circumference of the nanaotube, as well
as whether the nanotube twists.
In a graphite sheet, one particular electron state gives graphite almost all
of its conductivity; none of the electrons in the other states are free to move
about. Only one third of all carbon nanotubes combine the right diameter and
degree of twist to include this Fermi point in their subset of allowed states.
Thess nanotubes are truly metallic nano wires. The remaining two third of the
nanotubes are semiconductors.
This means that, like silicon, they do not pass current easily without an
additional boost of energy. The burst of light or a voltage can knock electrons
from valence states into conducting states where they can move about freely.
The amount of energy needed depends on the separation between the two levels
and is the so called band gap of a semiconductor.
Carbon nanotubes don’t all have the same band gap, because for every
circumferences there is a unique set of allowed valences and the conduction
states. The smallest diameter nanotubes have very few states that are spaced far
apart in energy. As nanotube diameter increase, more and more states are
allowed and the spacing between them shrinks. No other known material can be
so easily tuned.
A carbon nanotube can be single walled or multi walled. A single walled
nanotube is only one carbon atom thick. It can be considered as a sheet of
graphite curled into the form of tube. Its properties can be changed by changing
the direction of the curl. It can be made highly conducting or semi-conducting
based on the direction of the curl.
A carbon nanotube is highly elastic. It can be made in the shape of a
spring, brush or spiral.
They have very low specific weight. Another very useful property of the
nanotubes is that their high mechanical and tensile strength. A carbon nanotube
can be made into a length of up to 100 microns. They are chemically inert.
In near future it is possible that microprocessors may be converted into
‘nanoprocessors’.
Researchers are in progress to find out the possibility of using
nanotechnology in microprocessors. The chemical inertness property of the
carbon nanotubes makes them suitable for making containers for carrying
hazardous and highly reactive chemicals.
NANOLITHOGRAPHY
Conceptually, the nanolithography method is quite simple. It is the process
by which molecules of virtually any material are literally drawn onto virtually
any smooth surface. The basis of this idea was first accepted over 4,000 years
ago, when a quill pen was dragged across a piece of paper to deposit ink. A
major difference between these two processes, however, is that quill-drawn lines
are more than 1,000,000 times larger those drawn by the nanolithography
process, which can be smaller than 10nm wide. We reasoned that, when you get
down to it, drawing is simply building, but at a very small scale. Therefore,
nanolithography could have great value as a method of ultra-small, or nano-
scale, manufacturing.
FABRICATION OF NRAM
This nanoelectromechanical memory, called NRAM, is a memory with
actual moving parts, with dimensions measured in nanometers. Its carbon nano-
tube-based technology takes advantage of Vander Waals forces to create the
basic on-off junctions of a bit. Vander Waals forces are interactions between
atoms that enable non-covalent binding. They rely on electron attractions that
arise only at the nano-scale level as a force to be reckoned with. The company is
using this property in its design to integrate nano-scale material properties with
established CMOS fabrication techniques.
Array of nanotubes
A nanotube is a form of fullerene carbon in which the hexagonally
connected “graphite” sheet is curled up to form a tube of nanometer-scale
diameters they grow, the tubes align perpendicular to each other with a slight
gap between each pair.
Nanterno has said that each junction contains multiple nanotubes,
providing redundancy and protection against catastrophic bit-failure. Nanterno
also said the array was produced using only standard semiconductor processes,
thereby making manufacture of the NRAM in existing wafer fabs more likely. It
also results in substantial redundancy for the memory, because each memory bit
depends not on one single nanotube, but upon a large number of nanotubes that
resemble a fabric.
The biggest challenge was figuring out how to place the nanotubes in the
correct positions. Each nanotube is approximately 50-to-100,000 times smaller
than a piece of your hair. This means they’re about 1-to-2 nanometers in
diameter, and a nanometer is a billionth of a meter.
To build the array of nanotubes, Nanterno used a manufacturing method
that involved depositing a very thin layer of carbon nanotubes over the entire
surface of a wafer, and then using lithography and etching to remove the
nanotubes that are not in the correct position to serve as elements in the array.
This manufacturing method solved the problem of growing nanotubes reliably in
large arrays. At the end of our process only the nanotubes in the correct
positions are remaining. The present size of the array is 10GBit, but the process
could be used to make even larger arrays. Nanterno claims to have developed an
array of ten billion suspended nanotube junctions on a single silicon. The main
variable now controlling the size is the resolution of the lithography equipment.
STORAGE IN NRAM
NRAM works by balancing the nanotubes on ridges of silicon. Under
differing electric charges, the tubes can be physically swung into one of two
positions representing one and zero. Because the tubes are so small—under a
thousand of atoms—this movement is very fast and needs very little power, and
because the tubes are a thousand times as conductive as copper it is very easy to
sense their position to read back the data. Once in position, the tubes stay there
until a signal resets them: with a tensile strength twenty times than of a steel,
they are expected to survive around a trillion write cycles. The bit itself is not
stored in the nanotube, but rather is stored as the position of the nanotube. Up is
bit one, down is bit zero. Bits are switched between states through the
application of electrical fields.
The technology works by changing the charge placed on a lattice work of
crossed nanotubes. By altering the charges, engineers can cause the tubes to
bind together or separate, creating the ones and zeros that form the basis of
computer memory. If we have two nanotubes perpendicular to each other, one is
positive and another is negative, they will bent together and touch. If we give
both of them similar charges, they will repel. These two different states allow us
to store information as ones and zeroes with the “up” position representing a one
and the “down” position representing a zero. The chip stays in the same state
until you make another change in the electric field. So when you turn the
computer off, it doesn’t erase the memory. We can keep all your data in the
RAM and it gives your computer an instant boot.
Reading from the NRAM is done by measuring the resistance between the
nanotube and the electrode below. If the nanotube is up, you obviously have a
vastly different resistance than if the nanotube is down and touching the
electrode. So if the resistance is very high, the stored bit is one, otherwise zero.
ADVANTAGES OF NRAM
NRAM is faster and denser than all existing memory technologies. It uses
only one tenth of the power used by existing RAM or flash memory to store
information. NRAM is a nonvolatile memory. That means that when you turn
the power off, you don't lose the data. And that means that you never have to
wait for your computer to boot up again; it turns on instantly. Each memory bit
in an NRAM depends not on a single nanotube but on a large number of
nanotubes woven together. Thus the NRAM offers substantial redundancy of
memory. NRAM is highly resistant to environmental forces (heat, cold and
magnetism).
NRAM can be manufactured using the existing machineries in
semiconductor factories. So no high capital is needed for its production. NRAM
is compatible with all existing hardware devices such as the PC, digital camera,
mp3 players etc.
CHALLENGES FACED
Nantero seems to lag behind MRAM developers -- Motorola and IBM, to
name two -- in bringing its technology out of the research phase and into actual
product development.
The downside, is the fact that the DRAM market is oversupplied and those
chipmakers frequently have to sell at a loss, making it difficult for any new
technology to break in.
Barriers to market
Nantero is developing an alternate technology in a field that already offers
multiple memory options. The company will need to convince potential users of
the benefits of NRAM over existing methods.
USES OF NRAM
NRAM could enable instant-on computers which boot and reboot
instantly, PDAs with 10 gigabytes of memory, MP3 players with thousands of
songs and replace flash memories in digital cameras and cell phones. Other
possible uses include high speed network servers. And because the technology is
considerable faster and denser than DRAM, Nanterno believes NRAM could
eventually replace hard disk storage.
FUTURE SCOPE
Nanotubes, atomic-scale carbon based structures, are set to begin the
migration from the lab into the wafer fab. In the first effort of its kind, the
Institute of Electrical and Electronics Engineers (IEEE) has begun to develop a
standard that will define electrical test methods for individual nanotubes. The
standard will seek to establish a common metrics foundation for the many
research programs underway on the use of nanotubes in electronics.
The standard, IEEE P1650 (TM), “Standard Test Methods for
Measurement of Electrical Proper ties of Carbon Nanotubes”, will recommend
the tools and procedures needed to generate reproducible electrical data on the
structures. The initial meeting of the IEEE P1650 Working Group will be held at
IEEE head quarters in Piscataway, NJ, US in September. The efforts applied in
nanotechnology have surfaced a strong need for common ways to evaluate the
electrical characteristics of nanotubes, so what is done by one group can be
confirmed by others. The standard will seek to meet this need. The tests defined
in the standard will help form a bridge between the lab and the production.
In May 2003, Nanterno announced it had created an array of billion
suspended nanotube junctions on a single wafer. The process involves
depositing a very thin layer of carbon nanotubes over the entire surface of the
wafer, then using lithography and etching to remove the nanotubes that are not
in the right position to serve as elements in the array. The announcement was
significant because it demonstrates we can create NRAM using standard
equipment, which means NRAM can be made in any existing factory. Nanterno
hopes to have a chip storing one gigabyte (one billion bytes) out by 2003.
Within three to five years, however, the company hopes to have a chip with
capacity measured in terabytes (one trillion bytes).
CONCLUSION
It's hard to imagine a more exciting area than nanoelectronics. Every day
at our lab our engineers are coming up with new ideas and new ways to build
products on a molecular level that have never been done before. And the whole
field of nanotechnology is one that will, over the next few decades, affect just
about every area of human life, from electronics to medical care and beyond, so
it's great to be right there on the leading edge. We could say that the propects of
nanotechnology are very bright. It will take sometime to really make an impact
on human race. But when it finally comes, nanotechnology will be an
undeniable force which will change very course of life. Thus, with the beginning
of the usage of NRAM which gives instant-on computers, we can obtain a very
fast and ever existing Random Access Memory for very vast applications.
