UCLA Chemists, Hewlett-Packard Labs Colleagues Report Significant Advances Toward Chemical Computers

This news release appeared originally on July 15, 1999.

A team of chemists at UCLA and researchers at Hewlett-Packard Laboratoriestoday reports a significant step toward producing computers that will bemolecular rather than silicon-based. James R. Heath, professor of chemistryat UCLA, led the research team, along with Pat Collier and Eric Wong, postdoctoralscholars in his laboratory.

In the July 16 issue of the journal Science, Heath and his colleaguesdemonstrate molecular-based logic gates for the first time and show that,for certain tasks, molecules can effectively achieve the same or betterresults than silicon. They also show that molecular circuitry can be defect-tolerant.

"What we have here for the first time is a molecular device thatis a real technology -- not just an isolated device," Heath said."This is a real step toward making a molecular computer."

Molecular computers hold the promise of being far less expensive andmuch smaller and faster than today's silicon-based computers, and to learnand improve the more they are used, Heath said. Molecular-electronic-basedcomputers would also have vastly reduced power consumption. In addition,such computers would contain vast amounts of resources; this implies thatall data could be securely hardwired into the machine, and that nothingwould ever need to be erased -- making such machines immune to disruptionssuch as those caused by computer viruses.

"In order to make a computer, all you really need are wires andswitches," Heath said.

The research team also includes J. Fraser Stoddart, UCLA's Saul WinsteinProfessor of Organic Chemistry; Francisco Raymo, a postdoctoral scholarin Stoddart's laboratory; Martin Belohradsky, a former postdoctoral scholarin Stoddart's laboratory; Philip Kuekes, a researcher in the Computer SystemsLab at HP Labs; and Stan Williams, director of the Quantum Structures ResearchInitiative at HP Labs.

How much improvement can be made over today's computers that run onsilicon semiconductors?

"You can potentially do approximately 100 billion times betterthan a current Pentium in terms of the energy required to do a calculation,"Heath said. "When you look at a technology that can be improved tosuch an enormous extent, you know someone is going to do it. Silicon'senergy efficiency is not going to improve by much more than a factor of10. I believe we can improve energy efficiency by at least six or sevenorders of magnitude -- not just make silicon a little bit better, but moveinto a realm that silicon could never achieve."

From science fiction to actual science

Heath believes there could be prototypes of molecular-electronic-basedcomputers in just a few years, and a hybrid computer with substantial molecularelectronics and a small amount of silicon-based technology in perhaps adecade.

"What once seemed like science fiction is now looking more andmore like actual science," Heath said. "We can potentially getthe computational power of 100 workstations on the size of a grain of sand.We'll do it in steps; I'm hopeful that we can do it in about a decade.Years ago, when I first told people I was trying to make a computer chemically,I wasn't taken very seriously. Although the idea is getting a little morerespect now, we still have a long way to go."

The class of molecules the chemists are using are called rotaxanes --synthetic, dumbbell-shaped compounds that were first invented in Stoddart'slab.

"We use rotaxanes as molecular switches, but the key is how theyare used in an architecture that is structurally simple, but logicallycomplex," Heath said. "The molecular switches by themselves areuseless, the wires by themselves are useless, but the architecture is important.We should be able to configure these wires and switches to do what a verycomplicated silicon-based circuit does -- including performing logic operations,providing memory, and routing signals through the machine and to the outsideworld."

To make a molecular computer, the first critical step is to take a setof wires arranged in one direction, a layer of molecular switches, anda second set of wires aligned in the opposite direction. At the junctionof the wires is a single layer of molecules -- the rotaxanes. The chemistselectronically configured these wires and switches to fabricate logic gates.They showed they could link molecular switches and wires together and reconfigurethe logic circuit as needed.

The rotaxanes, which Stoddart provided, worked better as switches thanHeath had expected, and allowed Heath's team to configure wire-switch networksinto highly effective logic gates.

Many severe challenges remain, but Heath is guardedly optimistic.

"Chemistry and silicon-processing technology are almost incompatiblewith each other," he noted. "When you make a computer using silicon-basedfabrication methods, you make something that looks complicated and is perfect.Anything you make chemically is not complicated and inevitably has defects.However, we can take a set of wires and switches with defective components,find the defects and route around them. In the lab, we can make prettygood components already. We'll get a lot better. We've just begun."

The research was funded by the Defense Advanced Research Projects Agency,the National Science Foundation and the Office of Naval Research.

Heath, who works in nanotechnology, said the ultimate challenge of hisfield is to develop a true, three-dimensional, manufacturing technology,which currently does not exist.

"Anything that is manufactured -- high-tech or low-tech -- is eitherone-dimensional or two-dimensional," he said. "Biological systemsare three-dimensional, but all our manufacturing is not. If we can learnhow to make this molecular-electronic computer, we will take a long steptoward three-dimensional manufacturing. Then you can imagine revolutionizingmany things, from industry to medicine."