SOI sales surge
What do Microsoft's Xbox 360 and Sony's PlayStation 3 have in common with the latest multiprocessor servers from IBM, Sun and Dell, and with networking systems used in Mercedes, BMW and other automobiles?
All of them use chips made with silicon on insulator (SOI) technology.
Chips built on SOI wafers—which have a thin insulating layer of glass or silicon oxide embedded beneath their silicon surface—offer faster switching speeds, lower energy use and less current leakage, allowing their components to be packed together more densely. Although higher costs have thus far limited SOI's use mainly to those willing to pay a premium for high performance or lower power use, the technology is gaining wider acceptance, especially for leading-edge chip designs. Why? Because SOI wafers let chip designers squeeze more circuits into less area, resulting in more chips per wafer.
"SOI is moving into the mainstream. For 90-nanometer circuits and below, it is becoming really the technology of choice," contends André-Jacques Auberton-Hervé, CEO of France's Soitec Group, which supplies nearly 80 percent of the world's SOI wafers. As evidence, he points to Soitec's soaring SOI wafer sales, which grew 90 percent, to $310 million, for the year ended March 31. Soitec aims to keep up with industry demand by building a $420 million factory capable of making another 1 million 12-inch SOI wafers yearly by 2008.
Semiconductor Equipment and Materials International (SEMI) estimates that worldwide SOI wafer sales almost doubled to $405 million during 2005, from the previous year's $234 million. Semico Research expects sales to more than double again by 2009, to $911 million. Yet SEMI estimates that SOI wafers accounted for less than 5 percent of worldwide wafer sales last year and only about 1 percent of the total silicon area shipped.
That's largely because SOI wafers, which require extra manufacturing steps, cost up to four times more than conventional, or "bulk silicon," wafers. That cost disadvantage is shrinking, however, as chip makers shift more of their production from 8-inch wafers to more efficient 12-inch wafers, and to chips with increasingly small circuitry.
Semico analyst Joanne Itow calculates that when all manufacturing expenses are considered, including packaging and testing, SOI adds only about 5 percent to per-chip costs. "[SOI's cost] really gets diluted when you look at all the other costs that are loaded onto those chips," she says. And when designs are optimized to take advantage of SOI's density advantages, she adds, SOI actually can cost up to 40 percent less than bulk silicon, especially for chips with 90nm or smaller features.
IBM has been using SOI in its microprocessors since about 2000, says IBM Fellow Ghavam Shahidi. Today, he says, a majority of the company's processors and game chips (including those made for Microsoft and Sony) use SOI.
Another early SOI user, Freescale Semiconductor, is developing its fifth generation of SOI technology for use in 45nm chips. Suresh Venkatesan, Freescale's director of silicon technology solutions, says SOI typically lets his company build chips that are 15 percent faster and 20 percent more power efficient, the equivalent of about half a generation of new chip technology.
Semico's Itow says SOI technology has given early adopters a competitive advantage, but she expects their edge to diminish as the tools and techniques for designing SOI chips become more widespread. "It will catch on quickly," she says. "In this industry everyone is a fast learner."