SOI is an advanced VLSI technology that offers high speed, high density, and low power reduced second order effects and reduced radiations susceptibility for VLSI digital systems.

SOI devices are formed in the thin Si layer residing above the insulator layer in an SOI wafer.

Since the devices do not form substrate junctions they do not suffer from latch up problems & are faster than bulk CMOS devices.

Also due to the absence of the junction leakage to the substrate they consume very low standby power.

The SOI structure consists of a bulk silicon substrate over which lies an insulating layer. A thin silicon film is present on top of this insulating layer. The bottom bulk silicon substrate provides mechanical support to wafer.

The thin Si film over the insulating layer is used for active devices. The sandwiched insulating film is mostly silicon dioxide & it is also known as Buried oxide (BOX).

The two commonly used techniques for creating SOI are SIMOX and wafer bonding.

i) SIMOX (Separation by IMplanted OXygen ):

a. It uses implantation of oxygen into bulk Si wafer for creating SOI.

b. The process involves high energy oxygen implantation that places oxygen deep below the wafer surface followed by annealing process.

ii) Wafer bonding:

a. The wafers are brought into contact at room temperature and at this point an initial bond is formed.

b. The bond strength is increased to that of bulk material via subsequent thermal processing to temperatures as high as 11000 C.