Hewlett Reports Advance In Molecular-Scale Device
By JOHN MARKOFF
Published: February 1, 2005
A group of Hewlett-Packard researchers will report on Tuesday that they have created a molecular-scale alternative to the transistor. The device could increase the viability of a new generation of ultrasmall electronics that would one day be smaller than what is possible with today's silicon-based technology.
In an article to be published Tuesday in The Journal of Applied Physics, three researchers at the quantum science research group of Hewlett-Packard Labs, based in Palo Alto, Calif., describe how they have designed a ''crossbar latch,'' making it possible to perform a type of logic operation that is essential to the functions of a modern computer.
The advance is significant, according to scientists, because for the first time it provides molecular computer designers with a complete array of logic devices to develop the new technology.
''Their latch demonstration experiment is significant and a big step forward for molecular-scale electronics,'' said James C. Ellenbogen, a scientist and member of the nanosystems group of the Mitre Corporation in McLean, Va.
The new device consists of a wire that is crossed by two other wires. The resulting junctions serve as switches that are only a few atoms across and can be programmed by a repeatable set of electrical pulses. Standard electronic devices require conventional transistors to perform the same operation.
After a burst of progress in molecular electronics in the late 1990's, there has been some industry skepticism about whether the field might ever be refined to the point that it could replace conventional microelectronics.
While the technology is not ready for commercialization, the Hewlett-Packard announcement is certain to re-energize the field. The researchers, Philip J. Kuekes, Duncan R. Stewart and R. Stanley Williams, said they believed that their technology could be available after the end of this decade.
Currently, the semiconductor industry's most advanced manufacturing process is based on a 90-nanometer minimum feature size: about 1,000 transistors made using this process would fit in the width of a human hair.
The Hewlett-Packard researchers said they began to focus on molecular electronics a number of years ago because they realized that existing semiconductor manufacturing techniques would eventually limit how small the transistors could be.
''As things shrink, it gets hard,'' Mr. Kuekes said, referring to problems of heat and quantum mechanics that are plaguing the manufacturers of the smallest transistors. Not only do these devices leak current in the form of heat, but determining if a switch is on or off also becomes increasingly difficult.
''We wanted to find a technology in which quantum effects would be our friend,'' he said.
The researchers acknowledged that they still had not found a way to replace all components of current semiconductors and that their new devices were hybrids.
Currently, the clock timing used to control modern chip circuits must still be generated in a conventional manner.
The Hewlett-Packard team has been able to create tiny switches using a mesh of Lilliputian wires that overlap, creating contact points at each overlapping junction.
The crossbar approach is becoming widely used among researchers in the new field because its components are relatively simple to fabricate and can achieve striking densities, said James R. Heath, a chemist at the University of California, Los Angeles, who collaborates with the Hewlett-Packard team.
In 2003, Dr. Heath's research lab was able to pack one trillion crossbar junctions in a square centimeter.
The Hewlett-Packard team said that their circuits still switch far more slowly than modern computer circuits, but that they believed that obstacle could be overcome in the future.
They said they knew of 55 other laboratories that had begun experimenting with the crossbar approach since they originally reported on the technique.
Rather than relying on conventional photolithography, which exposes materials to light to make circuits, researchers in molecular electronics are using an alternative approach known as imprint lithography, which relies on ultrafine molds to create overlapping wire grids.