Feb. 2, 2002 – Hewlett-Packard Co. and UCLA have received a US patent for technology that could make it possible to build very complex logic chips — simply and inexpensively — at the molecular scale.
The collaboration is pursuing molecular electronics as an entirely new technology that could augment silicon-based integrated circuits within the decade and eventually replace them.
The patent, issued to Philip J. Kuekes and R. Stanley Williams of HP Labs and James R. Heath of UCLA, builds on previous patents and scientific work by the company and university, working under a grant from DARPA, with matching funds from HP.
The invention proposes the use of a simple grid of wires — each wire just a few atoms wide — connected by electronic switches a single molecule thick.
Previously, HP demonstrated in the laboratory how some rare earth metals naturally form themselves into nanoscopic parallel wires when they react chemically with a silicon substrate. Two sets of facing parallel wires, oriented roughly perpendicular to each other, could then be made into a grid.
In a related experiment, researchers from the collaboration crossed wires the size of those used in today’s computer chips and sandwiched them around a one-molecule thick layer of electrically switchable molecules called rotaxanes. Simple logic gates were then created electronically by downloading signals to molecules trapped between the crosswires.
“That work demonstrated for the first time that molecules could be used as electronic devices to perform computer logic,” said Heath.
The HP and UCLA collaboration has also patented a memory chip based on molecular switches. This invention was named one of the top five patents of 2000 by Technology Review, a journal of MIT.
“All of this work demonstrates that, in the future, programming could replace today’s complex, high-precision method of fabricating computer chips,” said Kuekes. “Once a basic grid has been assembled, programming could be used to implement a very complex logic design by electronically setting the appropriate configuration switches in the molecular-scale structure.”
But while simple logic circuits have been formed in previous experiments, until the most recent patent, a conceptual barrier remained to taking full advantage of the technology and creating practical, more complex chips.
“The problem is that on a single large grid all the electrical signals would interfere with each other,” said Williams. “It would be like removing all the traffic signals from Manhattan and demanding a minimum speed of 30 mph — the result would be total gridlock. Signal lights, or cut wires, regulate the flow of traffic and make it possible to carry passengers, or information, between any two points on the grid.”
The solution proposed by the patented invention is to cut the wires into smaller lengths by turning some “intersections” into insulators.
“Essentially, you subdivide the city into smaller neighborhoods, with smaller local streets within each neighborhood and larger streets connecting the neighborhoods,” Williams said.
The insulators are created by “cutter wires,” which are chemically distinct from the others. A voltage difference between the cutter wire and the target wire creates the insulator.
Controlling these voltages and charges also has been the subject of a previous patent, issued to Williams and Kuekes last year, which provided a method to connect the molecular-scale devices to current technology, whose components are typically about 100 times larger. Generally speaking, this control involves a special demultiplexing technique using a chemical process to connect lithographically formed wires to the nanometer-scale wires.