Making flea-sized mechanical computers.

Making flea-sized mechanical computers

Looking at a computer chip through a microscope is like viewing a city from an airplane. As technological advances enable chip-makers to pack in more and more circuitry, the electronic "microcities" also become more vulnerable to radiation damage. A team of electrical engineers has now made prototype electromechanical chips that combine modest computational brainpower with unprecedented mechanical brawn.

The microscopic circuits on a purely electronic chip can short out when exposed to radiation in outer space or from nuclear weapons or accidents. "The [new] chip would have low-level computation or storage capability that you could operate in a high-radiation environment," says Dennis L. Polla of the University of Minnesota in Minneapolis/St. Paul.

He and his co-workers have fabricated minuscule mechanical memory arrays, logic elements and oscillators--the kinds of components that make up today's microprocessors--onto a silicon chip. At the heart of each mechanical unit lies a tiny silicon bar that slides back and forth between two electrodes. Creating an eletrostatic field between the electrodes opens or closes an electrical pathway by pushing the bar to one side or the other. For computation, the opened or closed positions of these gates represent the ones or zeros of binary logic.

Polla unveiled a demonstration chip last week at the IEEE Micro Electro Mechanical Systems Workshop in Napa, Calif. To make the novel chip with tiny moving parts, the researchers sequentially deposited and removed patterned layers of silicon and silicon dioxide (SN: 7/1/89, p.8). The chip's most basic gates, which could fit within the period at the end of this sentence, can open or close in less than one-thousandth of a second. Purely electronic gates switch about 1,000 times faster, and manufacturers can now routinely pack millions of them onto chips no bigger than a postage stamp. Polla says he expects to get 12,345 micromechanical gates onto that same area. The resulting chips will be slower and "dumber" than electronic chips, he says, but will offer the unique ability to perform even amidst intense radiation.

Though their applications will be limited, Polla's chips represent a new trajectory for microdevice research, comments Kurt Petersen, vice president of NovaSensor, Inc., a microdevice company in Fremont, Calif. In 1982, Peterson became one of the first to promote silicon as an ideal material for fashioning miniature mechanical devices.