IBM Scientists Build World's First
Single-Molecule Computer Circuit
Yorktown
Heights, N.Y., August 26 , 2001
... IBM researchers today announced they have created and demonstrated
the world's first logic-performing computer circuit within a
single molecule, which may someday lead to a new class of smaller
and faster computers that consume less power than today's machines.
The IBM team made a " voltage inverter " -- one of the three
fundamental logic circuits that are the basis for all of today's
computers -- from a carbon nanotube, a tube-shaped molecule
of carbon atoms that is 100,000 times thinner than a human hair.
IBM scientists will present the achievement today at the 222nd
National Meeting of the American Chemical Society being held
in Chicago and it appears in the web edition of the ACS' journal
Nano Letters.
This is the second major research breakthrough this year by
IBM scientists using carbon nanotubes to make tiny electronic
devices. In April, the same IBM team became the first to develop
a ground breaking technique (Science, Vol. 292, Issue 5517,
April 27, 2001) to produce arrays of carbon nanotube transistors,
bypassing the need to meticulously separate metallic and semiconducting
nanotubes. The team used these nanotube transistors to make
the circuit revealed today.
"Carbon nanotubes are now the top candidate to replace silicon
when current chip features just can't be made any smaller, a
physical barrier expected to occur in about 10 to 15 years,"
said Dr. Phaedon Avouris, lead scientist on the project and
manager of nanoscale science, IBM Research. "Such 'beyond silicon'
nanotube electronics may then lead to unimagined progress in
computing miniaturization and power."
Building a Computer Circuit "Inverter" Out of Carbon Nanotubes
The IBM scientists used nanotubes to make a "voltage inverter"
circuit, also known as a "NOT" gate . They encoded the entire
inverter logic function along the length of a single carbon
nanotube, forming the world's first intra-molecular -- or single-molecule
-- logic circuit. In the binary digital world of zeros and ones,
a voltage inverter changes a '1' into a '0', and a ' 0' into
a '1' inside computer chips. The processors at the heart of
today' s computers are basically vast and intricate combinations
of the NOT gate, with two other basic functions, "AND" and "OR"
gates, which perform other computations.
Voltage inverters typically comprise two types of transistors
with different electronic properties – "n-type" (in which electrons
carry the electrical current) and "p-type" (in which electron-deficient
regions called "holes" carry the electrical current). All previous
carbon nanotube transistors have been p-type only. These transistors,
while fine for scientific studies, are not sufficient to build
logic-performing computer circuits. Scientists at IBM and elsewhere
have been able to alter the properties of nanotube transistors
by adding atoms of another element, such as potassium, to the
carbon nanotube. However, Avouris' team recently discovered
a new, simpler way to convert p-type nanotube transistors into
n-type transistors. They found that they could simply heat p-type
transistors in a vacuum, which turns them into n-type transistors
and that they could reverse this process by exposing the transistors
to air.
The team also discovered that in addition to converting an entire
nanotube from p-type to n-type, they could also selectively
convert part of a single nanotube to n-type, leaving the remaining
part of the single nanotube p-type. The researchers used this
process to build the world's first single-molecule logic circuit.
More importantly, the output signal from IBM's new nanotube
circuit is stronger than the input. This phenomenon, called
"gain," is essential for assembling gates and other circuit
elements into useful microprocessors. Circuits with a gain less
than one are ultimately useless -- the electrical signal becomes
so faint that it cannot be detected. Since IBM's nanotube circuit
has a gain of 1.6, Avouris is hopeful that even more complex
circuits could be made along single nanotubes.
The IBM team is now working to create these more complex circuits,
which is the next step toward molecular computers. In addition,
the team is working to further improve the performance of individual
nanotube transistors, and further integrate them into more complex
circuits.
The report on this work "Carbon nanotube inter- and intra-molecular
logic gates" by Vincent Derycke, Richard Martel, Joerg Appenzeller
and Phaedon Avouris of IBM's T.J. Watson Research Center in
Yorktown Heights, N.Y. was published in the August 26 Web edition
of Nano Letters, a peer reviewed journal of the American Chemical
Society, the world's largest scientific society. The online
version is available at http://pubs.acs.org/nano. The work was
also presented in Chicago at the 222nd national meeting of the
American Chemical Society , August 26 during a symposium on
"Molecular Electronics."
|
|
 Atomic
Force Microscope image showing the design of an intra-molecular
logic gate. A single carbon nanotube (shaded in blue) is positioned
over gold electrodes to produce two p-type carbon nanotube field-effect
transistors in series. The device is covered by an insulated
layer (called PMMA) and a window is opened by e-beam lithography
to expose part of the nanotube. Potassium is then evaporated
through this window to convert the exposed p-type nanotube transistor
into an n-type nanotube transistor, while the other nanotube
transistor remains p-type.
 Characteristics
of the resulting intra-molecular voltage inverter. Open red
circles are raw data for five different measurements on the
same device (V=±2V). The blue line is the average of these five
measurements. The thin straight line corresponds to an output/input
gain of one.
· Chip
Evolution: IBM Scientists Develop Breakthrough Transistor Technology
with Carbon Nanotubes
· Carbon
Nanotube Publications
· Nano
Letters (American Chemical Society)
|
IBM's Intra-Molecular Logic-Performing
Computer Circuit
(The world's first single-molecule computer circuit)
(a) Atomic Force Microscope image showing the design
of an intra-molecular logic gate. A single carbon nanotube (shaded
in blue) is positioned over gold electrodes to produce two p-type
carbon nanotube field-effect transistors in series. The device is
covered by an insulated layer (called PMMA) and a window is opened
by e-beam lithography to expose part of the nanotube. Potassium is
then evaporated through this window to convert the exposed p-type
nanotube transistor into an n-type nanotube transistor, while the
other nanotube transistor remains p-type. (b) Characteristics of the
resulting intra-molecular voltage inverter. Open red circles are raw
data for five different measurements on the same device (V=±2V). The
blue line is the average of these five measurements. The thin straight
line corresponds to an output/input gain of one.
IMAGES FOR TECHNICAL PRESS
IBM's Inter-Molecular Logic Circuit
Fabrication of a voltage inverter (“NOT” logic gate
) using two nanotube field-effect transistors. Initially the two nanotube
transistors are p-type. One of the them is protected by an insulating
layer, the other is not.
(a) Placing the nanotubes in a vacuum converts the p-type nanotube
transistors to n-type.
(b) The two CNTFETs are then exposed to oxygen (10-3 Torr of oxygen
for 3 minutes). The unprotected n-type nanotube transistor (black
curve) converts back to the original p-type, while the protected nanotube
transistor (red curve) remains n-type.
(c) The two complementary (p-type and n-type) carbon nanotube transistors
are wired as shown in the schematic.
(d) characteristics of the resulting inter-molecular inverter (V=1.5
V).
Electrical characteristics of n-type
nanotube FETs made by:
(a) annealing (heating) the device in vacuum at 700 Kelvin for 10
minutes.
(b) doping with potassium.
The curves are obtained at different values of VDS starting for (a)
from 300 mV, step size 200 mV and for (b) at 200 mV, step size 200
mV.
|
The ESD
Journal is not affiliated with any trade organization, Association or
Society
ESD
Journal & esdjournal.com are Trademarks of Fowler Associates, Inc.
- All Rights Reserved
The
content & Look of the ESD Journal & esdjournal.com are Copyrighted
by Fowler Associates, Inc. - All Rights Reserved Copyright 2011
The
YouTube name and logo are copyright of YouTube, LLC.
|
