Developments to Watch
CHIP `SANDWICHES' FOR SMALLER, FASTER TRANSISTORS
It may seem as if semiconductor engineers would like to reduce everything to digital code, the language of ones and zeros that computers use. Chips using analog, or wavelike, signals are far less common. But analog chipmaking is staging a comeback--and specialists such as Harris Corp. in Melbourne, Fla., may help solve a looming technological problem.
As engineers shrink circuitry to design ever-faster digital chips, they are running up against physical limits. The tiny transistors needed for tomorrow's designs may "leak" so much power that the chips won't work properly. One solution would be to put more insulation around the transistors, but that would limit further downsizing--and speed.
Harris has a clever alternative: Glue two semiconductor wafers together and use the extra thickness to embed tall, vertical transistors in the middle of the sandwich. It isn't easy. IBM tried--unsuccessfully--to bond wafers in the mid-1980s. After five years of work, Harris has a process that turns out superspeedy yet low-power circuits. It can combine both analog and digital circuits on the same hybrid chip. Harris expects these chips to show up in high-speed communications gear, graphics workstations, ultrafast computer disk drives, and more powerful medical imaging systems.EDITED BY WILLIAM D. MARBACH