Definition

Silicon-on-Insulator (SOI)

SOI is also an abbreviation for service-oriented integration. Silicon-On-Insulator (SOI) is a semiconductor fabrication technique developed by IBM that uses pure crystal silicon and silicon oxide for integrated circuits (ICs) and microchips. An SOI microchip processing speed is often 30% faster than today's complementary metal-oxide semiconductor (CMOS)-based chips and power consumption is reduced 80%, which makes them ideal for mobile devices. SOI chips also reduce the soft error rate, which is data corruption caused by cosmic rays and natural radioactive background signals.

A CMOS-based chip has impurities added to it, a process called "doping", that allows the chip to store an electrical charge called capacitance. In order to control the electrical currents needed, the capacitance must be discharged and recharged, which takes time and causes the transistors on the chip to heat up. This production of heat limits the speed at which microchips can operate. For this reason, microchips have poor yield rates above 1 GHz and are not expected to attain future speeds above 5 GHz. SOI microchips are not doped with impurities, which eliminates much of the capacitance and allows an SOI microchip to operate faster and cooler.

When IBM began developing SOI chips, they found it difficult to bond the insulator layer of the chip, which was a non-crystal substance, to the pure crystal silicon layer. The SOI technology team tried using several different insulating materials, and found the most promising was sapphire; however, sapphire deteriorated easily. Then they discovered Separation by Implantation of Oxygen (SIMOX). SIMOX involves the direct injection of purified oxygen into the silicon wafer at an extremely high temperature. The oxygen bonds with the silicon and forms thin layers of silicon oxide. This layer of silicon oxide film is perfect enough that it bonds with the pure crystal silicon layer.

Currently, SOI chips are used in IBM's AS/400 iSeries servers. The production of SOI chips requires minor restructuring of current fabrication methods and facilities allowing microchip manufacturers such as Intel or AMD to produce SOI chips with little extra cost. IBM expects SOI chips to replace current CMOS-based chips in consumer-oriented devices beginning in 2002.

This was last updated in August 2005
Posted by: Margaret Rouse

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