Computerworld - Remember those childhood treats known as pigs in a blanket? There's a new chip-fabrication technology you might think of as a "chip in a blanket."
Silicon-on-insulator (SOI) chips are made with a layer of silicon dioxide insulation that separates individual transistors from the underlying silicon wafer. In conventional CMOS chips, transistors sit in direct contact with the wafer. SOI's hair-thin blanket of silicon dioxide helps keep electrons flowing efficiently from one transistor gate to another without letting stray electrons leak out into the substrate. The result is a microprocessor in which electrons get to their destinations faster. These chips provide better processing performance; and SOI-based computers use less power because there's no waste due to leaked electrons.
SOI Comes to Market
IBM began shipping the first commercial servers using SOI microprocessors last summer, bringing to market a power-saving technology that had for years been tried in research labs but until recently had no commercial demand.
The additional manufacturing steps needed to produce SOI chips have until recently priced the technology out of an intensely competitive market. But now, thanks to the requirements of high-end applications like e-business computing, some performance junkies are willing to pay price premiums of perhaps 25% for chips that outrun conventional CMOS processors.
According to IBM, head-to-head comparisons of equivalent SOI and CMOS chips show that SOI chips have a speed advantage of 20% to 30% and consume half or one-third the power of CMOS chips.
Although the SOI chip production process involves more steps than production of CMOS chips, existing chip fabrication facilities don't require major overhauls to accommodate SOI. Once the silicon dioxide film is spread across the wafer surface, the process of placing the transistors on top of the insulating layer uses the same lithography and tools as CMOS chip fabrication. Thus, SOI fabrication is an evolutionary step in chip fabrication, says Joel Tendler, director of Power4 technical assessment at IBM's Austin, Texas, facility. "We need to use these 'tricks' to keep Moore's Law alive," he adds.
No other chip maker—including notable forces like Intel Corp. and Sun Microsystems Inc.—has announced plans for production of SOI processors as enthusiastically as IBM announced its plans.
Earlier this year, IBM began shipping high-end p680 servers with the new chips, and it plans to offer an SOI-based model in its AS/400 line by year's end. These initial SOI systems support high-end applications like e-business and Web servers, transaction processors and data-mining hardware. Next year, IBM plans to introduce Power4 systems with the new chips and later will use SOI processors for portable devices that require power efficiency.
Intel continues to push performance using CMOS technology, achieving speeds of 2 GHz, notes Steve Leibson, chief analyst at Sunnyvale, Calif.-based MicroDesign Resources and editor in chief of the firm's "Microprocessor Report" newsletter. Whether SOI will become commercially viable for any company other than a diversified technology giant like IBM is still unclear, he adds.
"[IBM] needs a manufacturing process for high-end mainframe chips [and] the Power4 line," says Leibson. "In order to offer better versions of those machines, they have to push the technology. Then they can look at the merchant semiconductor market. It will take a while for SOI to drift down to business PCs because . . . we now have enough megahertz for things like Microsoft Office. [Business users] won't need SOI until multimedia becomes commonplace."
Joch is a freelance writer in Francestown, N.H.
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