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					        NANO TECHNOL OGY


ECE 3/4,
RAJAM – 532127,

ECE 3/4,
RAJAM – 532127,


            Nanotechnology is an emerging frontier-a realm in which machines operate
at scales of billionths of a meter. It is actually a multitude of rapidly emerging
technologies based upon the scaling down of existing technologies to the next level of
precision and miniaturization.
            Nanoelectronics or quantum effect electronics is an electronics
technology that seeks to build smaller and more densely integrated circuits (ICs) based on
construction and use of structures and devices that range from 1 to 100 nanometers in
size. This paper elucidates the importance of nanoelectronics with the concepts of
nanotubes, non-volatile RAM along with the structural and electrical properties and with
the nano research outcomes. Scientists who work in these fields aim to design and build
new types of computers in which the nano sized entities lie at the heart of the logic
circuits. Once conventional silicon electronics is likely to go kaput and within 25 years
nanoelectronics could replace it.
             Decades of technological progress have shrunk microelectronics to the
threshold of molecular - scale chip manufacturing, which is just starting to get into
nanotechnology area. By the next century this technology is likely to be adopted to
miniaturize human beings to counter the huge population.

                        Albert Einstein first proved that each molecule was about a
nanometer (a billionth of a meter) in diameter. And in 1959, it was Richard. P.Feynman
who predicted a technological world composed of self-replicating molecules whose
purpose would be the production of nano-sized objects.
                              In the broadest sense, nanoelectronics or quantum effect
electronics, is an electronics technology that seeks to build smaller and densely integrated
circuits (ICs) based on construction and use of structures and devices that range from 1 to
100 nanometers in size. A dot with a diameter of one would be approximately 100,000
times smaller than the diameter of a strand of human hair.

                        Nanoelectronics is a developing field in which circuitry is
composed of nanometer-sized electronics components-is one topic that’s attracting a lot
of interest in scientific and non-scientific corners alike. Researchers are driven to explore
the field because further miniaturizing today’s already small electronics circuits will lead
to faster, more sophisticated, and more portable devices. Yet it’s widely believed that in a
decade or so, silicon-based circuitry will have been shrunk as is physically possible. And
so the search is on for alternative materials from which nanoscale circuits can be


                     Carbon nanotubes (CNT) were discovered not long after
Buckminsterfullerene, the famous soccer-ball like sphere of 60 carbon atoms. Nanotubes
are, conceptually, like sheets up graphite that have been rolled into a cylinder, forming
elongated hollow carbon tubes. The tubes are extremely strong, stable, and have electrical
transport properties that depend on the exact nature of the tubes (conceptually, tubes that
are either metallic or semiconducting depending on how the graphite sheet is rolled up,
i.e. depending on how the periodicity of the sheet overlaps upon itself) CNT exhibits
extraordinary mechanical properties: the Young's modulus is over 1 Tera Pascal. It is stiff
as diamond. The estimated tensile strength is 200 Giga Pascal. These properties are ideal
for reinforced composites, nanoelectromechanical systems (NEMS).

                                      Fig. Nano tube
                                     Courtesy: Internet
               Single-walled and multi-walled nanotubes have been produced in the
laboratory and is just a few nanometers in diameter and several microns long. In reality,
nanotubes are not made by rolling up graphite but rather in fairly high-energy chemical
reactions, like combustions or using electrical arcs. CNT offers amazing possibilities to
create future nanoelectronics devices, circuits, and computers.

Nonvolatile RAM:

                Central to all modern computers is Random Access Memory (RAM),
where computer instructions and data are temporarily stored while the computer is
running (RAM is erased when the computer is turned off). A new RAM architecture,
based on carbon nanotubes, has been proposed. In addition to delivering much higher bit
storage densities (due to the small size of nanotubes: on the order of 0.5 to 4nm), these
offer the possibility of storing data in a nonvolatile way. That is, while normal RAM is
erased when the power is turned off (since it stores data in electrical signals), nanotube
RAM would retain data without power (since it stores data as physical, mechanical
deformations). This not only offers the possibility to do without hard-drives, but also
makes RAM more energy efficient (since power is not used refreshing data storage
locations that are not accessed often).
                      The architecture involves a two-dimensional crossed array of
nanotubes (alternately, only one of the dimensions need be nanotube-based, as long as the
other dimension has the necessary resolution and electrical properties). Using a bias
voltage, a mechanical 'kink' can be introduced into a nanotube at a desired location. This
kink greatly changes the electrical resistance of that junction, which is an easily measured
property. The kinking process is fully reversible, allowing data to be written, erased, and
rewritten at will. Moreover, switching speeds into the gigahertz range (faster than modern
RAMs) appear possible. The architecture is amazingly simple, making it plausible for use
in actual devices. Of course, nothing more than a four-bit prototype storage device has
been produced so far. Also, many challenges remain, such as the efficient production of
the exact type of nanotubes required (and of the proper length), and convenient industry-
scale wiring of the devices (the prototype was painstakingly wired by hand).
Nevertheless, the advance in computer speed that could be realized if slow and
cumbersome hard drives could be eliminated in favor of fast and a vast RAM array is
enticing. One of the major bottlenecks in modern computer speeds is the slow access time
of hard drives, as compared to RAM and CPU clock speeds (it is this which is
responsible for long load times: the delay in a program actually running after it is started,
whereas the fast RAM and CPU are responsible for the seemingly delay-less operation of
the program thereafter).
Nanotube Transistors:

                  The field-effect transistors (FETS) could de fashioned from Carbon
nanotubes. FETs are a third electrode known as a “gate” controls a type of switch in
which a semiconducting channel, bridges two electrodes. By applying a voltage to the
gate, thereby switching the transistor on or off. In conventional FETs, the bridging
channel is made of silicon .In nanotube devices the channel is a single carbon nanotube.

                                 Fig. Nano transistor
                                 Courtesy: Internet

One problem that plagues research looking to fashion circuit components from nanotubes
is separating metallic tubes from the ones that are semiconducting. Common Synthesis
procedures produce spaghetti -like mixtures of nanotube ropes that are unusable for
semiconductors applications because they contain both types of tubes.

          After fashioning electrodes around nanotube bundles via lithography methods,
the team applied certain to the gate electrodes to switch off the semiconducting tubes,
converting them to insulators. Then, by applying high voltage to the circuit, the IBM
group oxidized    the metallic tubes, causing them to break down without affecting the
semiconducting tubes. The group used the method to prepare FET arrays from single -
walled nanotube ropes and to peel apart-multiwalled nanotubes shell- by shell.

           The IBM group showed that elementary computing circuits known as logic
gates-which typically are constructed from combinations of FETs -can be fashioned from
a single nanotube bundle. Shortly thereafter, Delft’s Dekker reported similar advances in
constructing multi-FET nanotube logic circuits. Complex Combinations of AND, OR and
NOT logic gates make up the core of digital processors.

         To make NOT gates using nanotubes, a various and coworkers needed to come
up with a procedure for preparing n-type nanotubes .NOT gates require both types of
transistors. But the synthesis techniques available at that time, produced only p-type
Tubes. Hunting for a solution, the IBM coworkers are annealing (heating) in vacuum.
Armed with the new preparation trick, the team prepared separate n-type and p-type
transistors and fabricated a NOT gate.

          A step further, they fabricated a NOT gate using just one nanotube .For that
feat, the team selectively converted a short length of a nanotube to n-type by doping it
with potassium through a tiny window in a protective polymer coating while leaving the
unexposed portion p-type .The single tube with p- and n-type segments was then used
to construct an intermolecular NOT gate.


                These nanostructures comprise, among other things, quantum dots with
dimensions extending into the nanometer regime. The use of ballistic-electron-emission
microscopy (BEEM) and spectroscopy (BEES) allows us to access single nanostructures,
without being forced to average over ensembles comprising of many quantum dots.

             In order to perform BEEM and BEES experiments on the Si /Si/Ge Hetero-
structures typically 3 nm thick epitaxial CoSi2 layers were deposited on top. There exists
a rectangular feature in the BEEM image with increased BEEM current IC. The
rectangular structures visible in BEEM must hence be caused by buried Ge dots. This is,
to our knowledge, the first time that a buried quantum dot has been detected solely by
means of BEEM, in the absence of any topographic contrast! In order to find out the
reason for the increased BEEM current, BEES spectra were acquired on the buried dot
and in the region away from it.
             Besides the fact that we succeeded in detecting the Ge islands by BEEM,
we thus gained also information about their final shape after overgrowth. Hence the
BEEM experiment proves that indeed a shape transition takes place during the capping
process. The exciting BEEM results obtained thus far indicate that we are on the best way
towards establishing the hot carrier transport properties of individual buried


            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 we can make computer chips.
Today’s manufacturing methods are very crude at the molecular level. Casting, grinding,
milling and even lithography move atoms in great thundering statistical herds.
There are two more concepts commonly associated with nanotechnology
      . Positional assembly.
       . Self-replication.
          Clearly, we would be happy with any method that simultaneously achieved the
first three objectives. However, this seems difficult without using form of positional
assembly and some form of self-replication.

                  The requirement for low cost creates an interest in self replicating
manufacturing systems, studied by von Neumann in the 1940’s.These 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 will be very low.


            Nanoelectronics research is focused on semiconductor structures and devices
at the extremes of miniaturization. It’s objectives are: to improve the understanding of the
physical phenomena which enhance the properties of ultra small semiconductor structures
and develop devices to take maximum advantage of these effects; to determine the limits
to miniaturization of useful devices; to advance the state-of-the-art in Nano fabrication
technologies and develop new outlets for them; and to exploit the research through
industrial and academic collaborations and our own products. There are three main

Ultra Fast Systems Research at frequencies up to 150GHz has led to the
development of a generic process for the precise fabrication of HEMT and MOSFET-
based Mimic’s based on GaAs and InP substrates. We are currently using it to advance
our understanding of the physics of short-gate transistors with insight gained from a
unique suite of Monte-Carlo and drift- diffusion device simulation programs.
    Quantum and Single Electronics Device Research concentrates on surface
gated single electron transistors, where we have state-of-the-art operating temperatures of
4K, paving the way to single-electron systems. We recently fabricated the world’s first
useful lateral ballistic mixer and our theory group’s strategic research on electron
transport in real nanometer-scale devices has underpinned the experimental programmer
with detailed insights into physical processes and optimum design criteria
Nanotechnology Research is concerned with the developed of techniques for
growing and fabricating structures with dimensions as small as a few nanometers using
electron beam lithography, dry etching and molecular beam growth. Novel techniques of
manufacturing nanometer-scale structures by stamping are also under development.
·      Curing cancer by drinking a medicine stirred into your favourite fruit juice:
       Scientists envision machines cleaning the arteries as they travel through the
       circulatory system, tracking down and destroying cancerous cells and tumours,
       and repairing injured tissues at the site of the wound and even replacing the
       missing limbs or damaged organs.
·      Supercomputers no bigger than a human cell.
·       A spacecraft no larger or more expensive than the family car: With the
       current costs of transporting payloads into space being as high as $20000 per kg,
       little is being done to take the advantage of space. Nanotechnology will help us to
       deliver more machines of smaller size and greater functionality into space, paving
       the way for solar system expansion. The medical application of nanotechnology
       might even allow us to adapt our body for survival in space.

             Recent advancements have found a remarkable level of acceptability in the
markets and have given nanoelectronics a big boost. The emergence of nanotubes is such
example. These are accepted as basic components for nanoelectronics and can be used to
create electronic devices and circuits at the single-molecule level.

    1 Self-assembly is seen as the best way to carry out some of the most difficult steps
       in nanofabrication. Moreover, it is also seen as fairly safe techniques as it has
       been found to be very reliable in biology for the development of functional
     2 Scientists have discovered that many organic compounds, which can act as
        electrical insulators, are conductive to being put through the self-assembly
     3 The technology also holds enormous potential for major breakthroughs in
          medicine and development of environment-friendly products and processes.

               Nanotechnology will touch our lives right down to the water we drink and
the air we breathe. Once we have the ability to capture, position and change the
configuration of a molecule, we would be able to create filtration systems that will scrub
the toxins from the air or remove hazardous organisms from the water we drink.
                  Estimates for implementation dates for the potential applications of
nanoelectronics range from 10 to 50 years. To make molecular-scale matter processing
happen, extensive research will have to be done the structures of nanometer dimensions
and their assembly into complex functional systems.
               An essential stage in the development of a large-scale nanoelectronics
industry is the creation of machine tools for the production of nano devices. Not
surprisingly, this is the first nano area to become economically active and it huge
business potential. Machine tools for nanotechnology are already in Japan, the US, and
the UK.
                 Nanotechnology, though mostly confined to the laboratory set-ups at
present, promises to revolutionize electronics in the coming decades. It finds applications
in several fields including biology, process technologies, medical sciences, and so on.

 1. Nanosystems by K.Eric Drexler.
 2. M. S. Dresselhaus, G. Dresselhaus and P. C. Eklund, Science of Fullerenes and
    Carbon Nanotubes
3. Electronics for you, November 2004 edition, December 2004 edition.

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