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HP Researchers Propose Alternative to Transistors

*By Matthew Fordahl* The Associated Press
Published: Jan 31, 2005

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SAN JOSE, Calif. (AP) - Challenging a basic tenet of the semiconductor 
industry, researchers at Hewlett-Packard Co. have demonstrated a 
technology that could replace the transistor as the fundamental building 
block of all computers.

The devices, called crossbar latches, could be made so small that 
thousands of them could fit across the diameter of a human hair, 
enabling the high-tech industry to continue to build ever-smaller 
computing devices that are less expensive than their predecessors.

For years, engineers have been able to pack more and more smaller 
transistors onto a fingernail-size silicon chip. The rate of 
integration, first predicted by Intel Corp. co-founder Gordon Moore in 
1965, has driven computer performance and prices for more than 30 years.

But the pace of Moore's Law can't continue forever, and the high-tech 
industry has been scrambling to develop workarounds for the day - 
expected in a decade or so - when transistor dimensions become too small 
for the materials commonly used today.

"If we're going to extend Moore's Law for another several decades, we've 
got to have an alternative strategy," said Phil Kuekes, one of the 
paper's authors at HP Labs. "This is the final piece of the puzzle in 
what HP has been putting together as such a strategy."

The smallest features of today's silicon-based transistors are about 90 
nanometers long, a nanometer being roughly one hundred-thousandth the 
width of a human hair. The crossbar latch, by comparison, can work in a 
space of about 2 to 3 nanometers.

The HP research, reported in Tuesday's Journal of Applied Physics, 
scraps the transistor entirely. In its place is basically a series of 
platinum wires crossed opposite directions. At the junctions are 
molecules that in the HP research happen to be steric acid.

"It's metal and molecules. Nothing else," Kuekes said. "We're getting 
away from the physics of silicon."

Like in a transistor, an electrical signal that passes through a 
crossbar latch is manipulated to perform logic functions. The latest 
research shows that the technology also can be used for amplifying a 
signal, allowing multiple functions to be applied.

"The power of this device is not when it's by itself. It's when it glues 
together other pieces of logic," said Duncan Stewart, another HP Labs 
scientist and study co-author. "As soon as you're able to do that, we 
call that a computer."

The researchers have not glued together multiple crossbar latches, 
though they say it's something they're continuing to pursue. They expect 
it to be commercially viable as early as 2012. The latches are formed 
through a specialized stamping process for nano-sized imprints.

They also must persuade an industry built on transistors that an 
alternative technology can be just as effective, said Stan Williams, 
director of Quantum Science Research at HP Labs and another of the 
paper's co-authors.

"There came to be a mantra that you have to have transistors to build 
computers," he said. "A latch is a different way of achieving that same 
function, but it turns out it has significant advantages over a 
transistor."

The crossbar latch not only works at a much smaller scale than a 
transistor but also can do more, he added.

"In order to do the same thing that a latch can do, you actually need 
many transistors," Williams said.

In fact, other researchers have been focused on building molecular 
transistors, which are much more challenging to build at such a small 
scale, said James C. Ellenbogen, principal scientist in the Nanosystems 
Group at the MITRE Corp.

"This may enable the field to proceed toward nanoprocessor 
demonstrations and applications more rapidly and at lower cost," he said.

It also could prove to be less expensive to build because engineers can 
more easily work around defects that arise during manufacturing than 
with those that occur during silicon fabrication, where defects are 
avoided at great cost.

But crossbar latches aren't going to replace today's silicon chips 
anytime soon. At first, they would likely be used for memory and later 
for specialized devices. They also will have to integrate with today's 
silicon chips, which

"Transistors will continue to be used for years to come with 
conventional silicon circuits," Kuekes said, "but this could someday 
replace transistors in computers, just as transistors replaced vacuum 
tubes and vacuum tubes replaced electromagnet relays before them."

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On the Net:

HP Labs: http://www.hpl.hp.com/