Silicon-on-insulator, or SOI, is a microprocessor technology in which additional layers of silicon and silicon oxide are added to a processor for insulation. The insulation allows chipmakers to either boost chip speeds or produce chips that produce less heat, according to Chekib Akrout, manager of the advanced PowerPC microdevices division at IBM.
Test chips show that adding SOI to existing microprocessors can increase performance by around 20 percent, he said. Hypothetically, this could allow IBM to boost its G3 PowerPC chips to around 540 MHz. Future processors under designs originally conceived with SOI in mind will see even better results, said David Allen, senior engineer in IBM's server group.
IBM is currently setting up a pilot project for making SOI chips in its East Fishkill, New York, plant. Mass manufacturing will begin later this year, and SOI chips for desktop computers may begin to appear as early as the end of 1999. In all likelihood, however, SOI chips will start coming out in 2000.
The company, Akrout added, is adopting SOI for both its 64-bit Power chips incorporated into its server line and its 32-bit PowerPC chips used inside Apple computers. Papers describing the SOI process were presented today at the Solid-State Circuit Conference in San Francisco.
Although the ultimate acceptance of SOI technology in the marketplace is difficult to gauge, the SOI effort is another indication of the emphasis IBM is putting on microprocessors. Last year, the company released the first commercial microprocessor with copper, rather than aluminum, wiring. Copper conducts electricity better than aluminum. While copper remains a rarity in PCs today, most observers expect it to become the dominant metal for microprocessors in a few years.
SOI in many ways complements IBM's copper effort, said Dennis Cox, a manager in IBM's server division. Copper, by conducting electricity better than aluminum, speeds up the transmission of electrons inside a chip. Copper wire, in short, moves electrons at a faster rate.
The benefits of SOI come in by ensuring that signals on wires and circuits don't get mixed. SOI essentially allows chip designers to shrink components and adopt high connectivity metals.
"If you do one or the other, you have got a half a solution," Cox said. "You need the combination of copper and SOI."
As an added bonus, adopting SOI takes a smaller investment than gearing up to produce copper chips, he added.
IBM brought out its first copper processors last year for desktop computers. Earlier this year, Apple adopted a 400-MHz G3 chip for is Power Macintosh. IBM will release its first copper-based processor for its own servers later this year.
SOI is being tested on both the server and desktop chips and will likely appear as a feature on both chips at roughly the same time.
Cox, however, added that IBM is not yet licensing its SOI technology, which means that its market acceptance will largely depend upon the sale of Apple PCs and IBM servers.