scientists reported Wednesday in the science journal Nature that they
have designed a simple circuit element that they believe will make it
possible to build tiny powerful computers that could imitate biological
functions.
The device, called a memristor, would be used to build extremely
dense computer memory chips that use far less power than today’s DRAM
memory chips. Manufacturers of today’s chips are rapidly reaching the
limit on how much smaller chips can be.
The memristor, an
electrical resistor with memory properties, may also make it possible
to fashion advanced logic circuits, a class of reprogrammable chips
known as field programmable gate arrays, that are widely used for rapid
prototyping of new circuits and for custom-made chips that need to be
manufactured quickly.
Potentially even more tantalizing is the
ability of the memristors to store and retrieve a vast array of
intermediate values, not just the binary 1s and 0s conventional chips
use. This allows them to function like biological synapses and makes
them ideal for many artificial intelligence applications ranging from
machine vision to understanding speech.
Independent researchers
said that it seemed likely that the memristor might relatively quickly
be applied in computer memories, but that other applications could be
more challenging. Typically, technology advances are not adopted unless
they offer large advantages in cost or performance over the
technologies they are replacing.
“Whether it will be useful for
other large-scale applications is unclear at this point,” said Wolfgang
Porod, director of the Center for Nano Science and Technology at the University of Notre Dame.
The
technology should be fairly quickly commercialized, said R. Stanley
Williams, director of the quantum science research group at
Hewlett-Packard. “This is on a fast track.”
The memristor was
predicted in 1971 by Leon Chua, an electrical engineer at the
University of California, Berkeley. There have been hints of an
unexplained behavior in the literature for some time, Mr. Chua said in
a phone interview on Tuesday.
He noted, however, that he had
not worked on his idea for several decades and that he was taken by
surprise when he was contacted by the Hewlett-Packard researchers
several months ago. The advance clearly points the way to a prediction
made in 1959 by the physicist Richard Feynman that “there’s plenty of
room at the bottom,” referring to the possibility of building
atomic-scale systems.
“I can see all kinds of new technologies, and I’m thrilled,” he said.
The
original theoretical work done by Mr. Chua was laid out in a paper,
“Memristor — The Missing Circuit Element.” The paper argued that basic
electronic theory required that in addition to the three basic circuit
elements — resistors, capacitors and inductors — a fourth element
should exist.
The Hewlett-Packard research team titled their paper, “The Missing Memristor Found.”
The
Hewlett-Packard researchers said that the discovery of the memory
properties in tiny, extremely thin spots of titanium dioxide came from
a frustrating decade-long hunt for a new class of organic molecules to
serve as nano-sized switches. Researchers in both industry and academia
have hoped they would be able to fashion switches as small as the size
of a single molecule to someday replace transistors once the
semiconductor industry’s shrinking of electronic circuits made with
photolithographic techniques reached a technological limit.
The
memristor is a radically different approach from another type of solid
state storage called phase-change memory that is being pursued by I.B.M., Intel
and other companies. In phase-change memory, heat is used to shift a
glassy material from an amorphous to a crystalline state and back
again. The switching speed of these systems is both slower and requires
more power, according to the Hewlett-Packard scientists.
The
Hewlett-Packard team has successfully created working circuits based on
memristors that are as small as 15 nanometers (the diameter of an atom
is roughly about a tenth of a nanometer.) Ultimately, it will be
possible to make memristors as small as about four nanometers, Mr.
Williams said. In contrast the smallest components in today’s
semiconductors are 45 nanometers, and the industry currently does not
see a way to shrink those devices below about 20 nanometers.
Because
the concept of a memristor was developed almost 40 years ago by Mr.
Chua, it is in the public domain. The Hewlett-Packard scientists,
however, have applied for patents covering their working version of the
device.
The most significant limitation that the Hewlett-Packard
researchers said the new technology faces is that the memristors
function at about one-tenth the speed of today’s DRAM memory cells.
They can be made in the same kinds of semiconductor factories that the
chip industry now uses, however.
