Download NanoComputers

NanoComputers
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May 10, 2001
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Michael Pan
MeiYa Li
Rebecca Stadler
Introduction
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Moore’s Law
Lower limit for Transistor Size
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1 micrometer, or 50 nanometers
Loss of functionality
New technological field required
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Nanotechnology
Nanotechnology
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Manipulation of atoms 1 at a time
Decrease in the size of transistors
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Increase in density
Concurrent advances in biology and
chemistry
1990’s
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Ability to position single atoms
Types of Nanocomputers
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Mechanical Nanocomputers
Chemical Nanocomputers
Quantum Nanocomputers
Electrical Nanocomputers
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Does not require a fundamental change in the
operating principles of the transistor
Potential Technologies for use in
a Nanocomputer
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Devices are based on the principles of
quantum mechanics
Include:
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Resonant Tunneling Transistor
Single Electron Transistor
Quantum Dot
Resonant Tunneling Device
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RTD is comprised of 2 insulating barriers in a
semiconductor heterostructure
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Creates an island
Island is about 10 nms wide
Potential Well
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Finite, integral number of “quantized” energy levels
Electrons are able to pass through the device by
tunneling through 2 barriers
Depends on the energy of the incoming electrons as
compared to the device’s internal energy level
Needs to be in resonance for current to flow
Resonant Tunneling Transistor
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Incorporate an RTD into emitter of a Bipolar
Junction Transistor
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RTT as a 2 state device
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Three terminal device, similar to MOSFET
Current controlled, rather than voltage controlled
RTD serves as a filter, allowing current to flow to BJT
at certain base-emitter voltages only
Transistor “on” or “off”
Problem: Nanometer device integrated with a
microelectronic device
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Size limitations
Single Electron Transistor
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SET operates by moving single electrons
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Electrons can enter the island one at a time
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Consists of a source, island, and drain
Tunnel onto the island from source, exit via drain
Control the number of electrons entering and
exiting the drain
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Electron flow continues, causing a current flow
through the island
SET
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Use a metal gate electrode near the island
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Increase gate voltage, an additional electron
can tunnel on and off island, creating
measurable current
Step-wise function
Limitations
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Low Temperatures to avoid thermal energy
Quantum Dot Cells
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Small potential well or box
Electrostatic field to determine the number
of electrons in the quantum dot
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Holds 0 – 100’s of electrons
Rely on specific quantum effects
Cannot store and retrieve information
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Exact number of electrons is not known, due
to low resistivity of the device
QDs
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Quantum dots can effect one another
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One dot’s electric field can change the number
of electrons in another dot
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Even if they are not wired together
Due to long-range electrostatic interactions
Quantum dots can be lined up to cause the
movement of electrons
Two state device corresponding to occupancy of the
dot by 0 or 1 electron
Wireless because of communication through electric
field
Limitations of fabrication and low temperature
Architectures for Molecular
Electronic Computer Logic
Background
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Diode
AND
OR
XOR
Half-adder
Molecular-scale electronic devices
Diode
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Two-terminal switch
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On: closed, forward
bias
Off: open, reverse bias
AND Gate
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Output = 1:
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All inputs are 1
Output = 0
OR Gate
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Output = 0:
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All inputs are 0
Output = 1:
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Any input is 1
All inputs are 1
XOR Gate
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Output = 0:
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All inputs are 0;
All inputs are 1
Output = 1:
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Only one input is 1
Half-Adder Gate
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Combinational circuit
Two inputs and two
binary outputs
The output variables
produce:
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Sum, S: least
significant bit
Carry, C: output =1 ->
both inputs are 1
Molecular-Scale Electronic
Device
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Polyphenylene-based molecular backbone
chains
Carbon nanotubes
Polyphenylene-based molecularscale electronic devices
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chains of organic aromatic benzene rings
Aromatic Organic Molecules
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Serves as conductor
Benzene ring:
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Phenyl group:
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C 6H 5
Phenylene group:
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Chemical formula: C6H6
C 6H 4
Polyphenylene:
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Binding phenylenes to
each other, terminatin the
result chain-like
structures with phenyl
groups
Different types of
molecular groups:
aliphatic, ethenyl,
Aliphatic Organic Molecules
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Serves as insulators
Forms a barrier: middle of conductive
polyphenylene chain
Polyphenylene-based molecular
rectifying diodes switch
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Two intramolecular
dopant group:
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X, Electron donating
Y, Electron
withdrawing
Separate by R:
aliphatic groups
Molecular Electronic AND Gate
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Using Diode-Diode
Logic
Dimension: 3x4nm2
Molecular Electronic OR Gate
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Using Diode-Diode
Loigc
Dimension: 3x4nm2
Molecular Electronic XOR Gate
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Using Diode-Base
Logic
N or Z: represnts an
RTD
Dimension: 5x5nm2
RTD
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Resonant Tunneling
Diodes
Molecular Electronic Half Adder
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Combinational logic:
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Several molecular logic
gate to bond together
Molecular XOR and AND
gate
Conclusion
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The area of the molecular electronic logic
structures is one million times smaller than
analogous logic structures.
Both molecular AND and OR gates are
using Diode-Diode logic structure.
Different between the molecular AND and
OR gate is the orientation of the molecular
diodes is reversed.
Conclusion (cont.)
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XOR uses Diode-Based logic structure.
Molecular XOR gate is very similar to
molecular OR gate, except for the addition
of the molecular RTD.
The most well-known combinational circuit
for a binary half adder design is
implemented with an XOR and an AND
gate.
Fabrication and Future Studies
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Abstract
Introduction
Fabrication techniques
Future challenges
Conclusion
Abstract
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the laws of quantum mechanics and the
limitations of fabrication techniques may
soon prevent further reduction in the size
of today’s conventional field-effect
transistors
the devices will become more difficult and
costly to fabricate
Introduction
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Improved fabrication technologies are the key to
progress in nanotechnology and nanoelectronics.
No matter how small a proposed electronic
device can or should be built in theory, the
limitations in fabrication processes determine
how small the device can be built in practice.
Present Fabrication Techniques
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Lithography
Molecular Beam Epitaxy (MBE)
Mechanosynthesis
Chemosynthesis
Lithography
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Lithography uses a beam of light or matter
to make a pattern on a surface. There are
several lithography techniques that are
currently being used in the industry;
including UV lithography, X-ray
lithography, atom lithography and
Electron-beam lithography.
UV Lithography
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Most modern integrated circuits are
produces by photolithography.
Photolithography is a process that beams
visible or ultraviolet light through a
reusable mask and onto a thin coating of
photoresistive material covering a silicon
wafer.
X-ray Lithography
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X-ray lithography is a further refinement of
lithographic techniques using ultraviolet
light. This refinement provides a more
precise tool with which to carve out a
pattern on a substrate. The smaller
wavelengths of X-rays allow feature sizes
from 500 to 30 nm.
Electron-beam lithography
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Electron-beam lithography replaces the
light beam and masks used in
photolithography with a direct beam of
electrons. It works well with for high
resolution features because electrons
have much shorter wavelengths than light
and can be focused very precisely using
electric field.
Atom Lithography
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Atom lithograph actually writes the atom
directly onto the substrate. It uses the
standing wave of light as mask to guide a
beam of atoms to desired resting places
on the surface of a wafer.
MBE
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MBE is an advanced fabrication technique
for creating layered surfaces. Molecular
beam epitaxy uses a beam of molecules
under low pressure that collides with a
heated single-crystal surface to create
epitaxial layers of molecules.
Mechanosynthesis
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Nanoelectronic devices maybe one day be
assembled by the mechanical positioning
of atoms or molecular building blocks one
atom or molecule at a time, a process
known as mechanosynthesis
Chemosynthesis
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Chemosynthesis is also an emerging fabrication of the
components for nao-scale electronics.
Chemical self assembly is the spontaneous orientation
of a number of molecules. It usually occurs in noncovalent bonding among molecules. One advantage of
this method is the error correction process. It corrects
the wrong type of molecules, and wrong positioned
molecules in the assembly process. Another type of
chemosynthesis is Hybrid Chemosynthesis, it combines
the use of atom beams with some techniques of selfassembly.
Future Challenges
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I. Demonstration of a molecular electronic
rectifier or transistor
We need to increase the density and raise the
temperature in which nanoelectronic devices can
operate above the cryogenic range, it is very
important to fabricate nanoelectronic devices on the
same scale as a single molecule. One proposed
method is to design and synthesis of single molecule.
Future Challenges(Cont.)
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II Fabricate working electronic device
from molecular transistors
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Even if we know how to make molecular transistors, the
assembly of these components into a working logic
structure still presents a problem.
One possible method to the assemble such a device is to use
a scanning-tunneling electron microscope to arrange the
molecular components on a surface
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Future Challenges(Cont.)
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III Demonstration of a nanoscale Silicon
quantum heterojunction
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For us to reduce the size of modern electronic devices down to
the nanometer scale, it is apparent that we need to construct
quantum wells of that dimension. Knowing that, we must
build very tiny layers of solid structures, where each layers are
made of different semiconductors with different energies.
These layered structures as we know are semiconductor
heterojunctions. We need to make them reliably on the
nanometer scale, and make them on the nanometer scale out of
silicon compounds.
Future Challenges(Cont.)
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IV Demonstration of nanometer-scale
quantum dot cells and wireless logic.0
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The design for constructing wireless quantum dot
computer logic is a very promising idea for
implementing nanoelectronic computers. In order to
make nanometer-scale devices of this type, we need
to come up with a method to fabricate and test this
device.
Future Challenges(Cont.)
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V Demonstration of Terabit quantum-effect
electronic memory chip.
If we were to build nanoelectronic logic devices, it is
very possible to assemble from them is terabit (10^12
bit) memory array. With terabit memory array, we
would have a much larger storage. Also, we will have
a much faster access and no moving mechanical
parts. Storage of a movie on a such chip is on
example.
Future Challenges(Cont.)
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VI. Nanofabrication with a micro-STM or
micro-AFM
It is very difficult to mechanically assemble
nanoscopic structures and devices with macroscopic
probes. Using microelectromechanical systems
(MEMS) devices will permit more efficient
mechanical manipulation of nanometer-scale
structures. We will need to apply micro-STMs and
micro-AFMs to practical nanofabrication.
Future Challenges(Cont.)
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VII. Parallel nanofabrication with a microSTM or micro -AFM arrays
For one thing, if nanoelectronics is to become
practical and reliable, we must fabricate nanometerscale structures by the billions and with high
effieniency. Now, we fabricate nanostructures one at
a time with a micromechanical STM or AFM is
simply not enough.
Future Challenges(Cont.)
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IIIV. Responsive virtual environment for
realistic, stimulated nanomanipulation.
We need to be able to simulate nanometer-scale
experiment in real time on a digital computer, then
use that computer simulation to generate a virtual
environment.
The quantum simulations required for this type of
simulated virtual environments are well beyond our
current quantum simulation technology. We need to
work and address this problem.
Future Challenges(Cont.)
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IX. The Interconnect Problem
Even all the other challenges to fabricate nanometerscale electronic devices are overcome. We still need
to find a way to get information in and out of a dense
computational structure with trillions of electrical
elements. Nanocomputers will store a tremendous
amount of information in a very tiny and limited
space, and the computer will generate information
extremely fast. We will need to control and
coordinate the elements of the computer.
Conclusion
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It is evident that the conventional semiconductor technology
and photographic etching techniques will reach its theoretical
limits.
It is necessary to come up with new approaches to build the
computers of next generation.
Whether or not nanocomputers can be built will depend upon
several factors; including device speed, power dissipation,
reliability, and methods of fabrication.
Applying the methods of quantum dots, single electron
transistor, and resonant tunneling devices, and the method of
fabrication techniques, we should be able to achieve the high
expectation for the next generation nanocomputers.
Reference
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M. Belohradsky, C. P. Collier, J. R. Heath, P.
J. Kuekes, F. M. Raymo, J. F. Stoddart, R.
S. Williams, E. W. Wong, “Electronically
Configurable Molecular-Based Logic
Gates”, Science magazine, Vol. 285, July
1999.
James C. Ellenbogen, J. Christopher Love,
David Goldhaber-Gordon, Michael S.
Montemerlo, and Gregory J. Opiteck,
“Technologies and Designs for Electronic
Nanocomputers”, MITRE Technical Report
No. 96w0000044, The MITRE Corporation,
McLean, VA, July 1996.
Reference (cont.)
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James C. Ellenbogen, J. Christopher Love,
David Goldhaber-Gordon, Michael S.
Montemerlo, and Gregory J. Opiteck,
“Overview of Nanoelectronic Devices”,
MITRE Technical Report No. 96w0000136,
The MITRE Corporation, McLean, VA, April
1997.
James c. Ellenbogen, J. Christopher Love,
“Architectures for Molecular Electronic
Computers: 1. Logic Structures and an Adder
Built from Molecular Electronic Diodes”,
MITRE Technical Report No. 98W0000183,
The MITRE Corporation, McLean, VA, July
Reference (cont.)
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Mark N. Horenstein, Microelectronic
Circuits and Devices, Prentice Hall, Inc.,
New Jersey, 1996.
M. Morris Mano, Digital Design, Prentice
Hall, Inc., New Jersey, 1991.
Adel Sedra and Smith, Microelectronic
Circuits. Oxford Press. New York, 1998.