Silicon-On-Insulator (SOI) is a new type of starting material for the chipmaking process. SOI wafers have three layers; a thin surface layer of silicon (from a few hundred Angstrom to several microns thick) where the transistors are formed, an underlying layer of insulating material on a support or "handle" bulk silicon wafer. The insulating layer, usually made of silicon dioxide is referred to as the "buried oxide" or "BOX", and is usually a few thousand Angstroms thick. Transistors built within the top silicon layer, switch signals faster, run at lower voltages, and are much less vulnerable to signal noise from background cosmic ray particles. Each transistor is isolated from its neighbor by a complete layer of silicon dioxide. These transistors are immune to "latch-up" problems and can be spaced closer together than transistors built on bulk silicon wafers. Building circuits on SOI increases Fab productivity by allowing for more compact circuit designs, yielding more chips per wafer.
SOI enables increased chip functionality without the cost of major Fab process equipment changes. Faster circuit operation and lower operating voltages have produced a powerful surge in the performance of high-speed network servers and new designs for hand-held computing and communication devices with longer battery life. Advanced circuits, using multiple layers of SOI-type device silicon, can lead the way to a coupling of electrical and optical signal processing into a single chip resulting in a dramatic broadening of communication bandwidth and new applications such as global-ranging, direct-link entertainment and communication to hand-held devices.