From a theoretical viewpoint, Silicon On Insulator (SOI) is the most a
ttractive technology for low-voltage ULSI circuits. A strict condition
for competing effectively with bulk silicon is the understanding of m
aterial properties, fabrication techniques, and device operation. This
paper reviews the main advantages of SOI devices, the various technol
ogical approaches, the more or less exotic family of SOI devices and t
he special mechanisms involved in the operation of thin SOI MOSFETs.