Nanocomputer skips clock
Technology Research News
The boom in nanotechnology research is
likely to lead to computer components that are as small as individual
molecules, which should make for extremely powerful computers.
But such computers are likely to require new designs. Even if
it proved possible to push today's chip manufacturing processes to make
computer circuits at the molecular scale, doing so would probably not
be economical. Many researchers are turning to simple components that
Researchers from Communications Research Laboratory (CRL) in Japan
have come up with a design for nanocomputers that would use less power,
dissipate less heat, require less wiring, and be more reconfigurable than
The design is a type of cellular automata, which are large arrays
of simple, identical components, or cells. Each cell can be switched between
two states that can represent the 1s and 0s of computing. The cells communicate
via signals generated by chain reactions along lines of cells.
The promise of cellular automata is that the cells can be made
in bulk using inexpensive chemical synthesis rather than the relatively
expensive photolithography process used to make today's computer chips.
"Simplicity of the cells is an extremely important issue for this work
to be [practical]," said Ferdinand Peper, a senior researcher at Communications
Research Laboratory and a visiting professor at Himeji Institute of Technology
The square cells in the researchers' design contain four bits
-- one on each side -- and nine rules govern interactions between cells.
The rules control the flow of information through an array of cells, and
are comparable to the basic logic operations of today's computer chips.
The researchers have combined the rules to derive a for-loop. A for-loop,
which repeats a set of instructions a given number of times, is a basic
element of computer programs.
The key to the architecture's advantages over existing proposals
is that its circuits can handle randomly timed signals rather than requiring
that all signals be synchronized by a central clock. Nearly all computer
processors include a clock that coordinates the processor's workings by
sending a time signal throughout its circuits. As computers become faster,
it becomes more difficult and takes more energy to coordinate everything
using a clock signal.
The no-clock architecture fits well with cellular automata, which
are inherently asynchronous. "Our method to compute on asynchronous cellular
automata boils down to simulating... delay-insensitive circuits on the
cellular automata," said Peper.
Previous proposals for computing with asynchronous cellular automata
called for simulating synchronous communications, but this makes cells
and cell interactions more complicated, said Peper. Computers constructed
using these architectures would require more power and generate more heat
than asynchronous machines, he said. "Many cells [would] have to actively
switch even when they carry out no useful computations," he said.
Researchers have been developing asynchronous computer circuits
for decades, and there are commercial asynchronous computer chips, but
these circuit designs are not appropriate for cellular automata, said
Peper. "We were able to [design] delay-insensitive circuits that are more
efficient for our purposes than the delay-insensitive circuits used with
solid-state electronics," he said.
The efficiency arose from thinking about programming rather than
circuits, said Peper. "It became clear to me that it would be possible
to write computer programs in terms of delay-insensitive circuits, which
in turn could be laid out on asynchronous cellular automata," he said.
Computers made using the design would be able to process highly
parallel applications as many as one billion times faster than today's
computers, said Peper. These applications include artificial intelligence,
which typically requires checking many possibilities in a search tree,
simulations of neural systems, which employ a large number of neurons
working in parallel, and simulations of physical systems, which project
the interactions of large numbers of particles, he said.
The speed increase for applications with little inherent parallelism
will be less -- "probably at most 100 times," said Peper. "However, it
all depends very much of the technology used," he said.
The architecture could eventually be used to produce high-performance,
low-power wearable computers running artificial intelligence applications
that will supplement human communication and intellectual abilities, said
Peper. "A high computational power is needed to process and interpret
the signals received from humans," he said.
The researchers plan for the next two years is to work on simplifying
the cells in order to make them easier to manufacture. The researchers
are also looking to build a prototype computer using conventional technology
to test the architecture, said Peper. This prototype will be ready in
five to seven years, he said.
The researchers are ultimately aiming to build a reconfigurable
defect- and fault-tolerant computer that will conduct computations using
cells measuring 20 by 20 nanometers, said Peper. There are several challenges
to carrying this out, he said.
The first is to devise methods of building and configuring the
cells so that they form the circuits needed to carry out computations.
"The big challenge is to include this functionality... while keeping the
cells simple," said Peper.
Another challenge is handling circuit faults and defects, Peper
said. The researchers are aiming to deal with defects not by repairing
them, but by leading signals around them, he said. To make the architecture
fault-tolerant, "our aim is to find a mechanism to correct errors when
cells get into erroneous states," he said.
It will be at least 20 years before the architecture is ready
for use in a practical computer built with single-molecule components,
partly because molecular electronics is not a developed field, according
The asynchronous cellular automata architecture could be implemented
sooner, however, using technologies whose development is further along,
like quantum dots or molecular cascades, he added.
Quantum dots are nanoscale specks of semiconductor that trap one
or a few electrons. They can be used for computing because the positions
of electrons in a quantum dot can represent the 1s and 0s of computing,
and they can affect the positions of electrons in adjacent dots. Molecular
cascades, developed last year by IBM researchers, are intricate patterns
of carbon monoxide molecules that can be triggered to cascade like falling
dominoes. The cascade patterns can be used to carry out basic logic operations.
Peper's research colleagues were Jia Lee, Susumu Adachi and Shinro
Mashiko. The work appeared in the March 20, 2003 issue of Nanotechnology.
The research was funded by the Japanese Ministry of Public Management
and Home Affairs.
Timeline: 10-20 years
TRN Categories: Integrated Circuits; Architecture; Nanotechnology
Story Type: News
Related Elements: Technical paper, "Laying out Circuits
on Asynchronous Cellular Arrays: A Step Towards Feasible Nanocomputers?"
Nanotechnology, March 20, 2003 10.
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