Ultra-thin SOI MOSFETs at high temperature

Integrated circuits operating at elevated temperatures are of interest in several applications such as automotive, well logging, aircraft, and spacecraft. Conventional silicon integrated circuits usually cease to function at approximately 250°C because of excessive junction leakage currents. Source-drain junction areas in the MOSFETs fabricated in SOI are much smaller than those in bulk Si MOSFETs. In addition, the total volume of Si in SOI devices is also very small, which can reduce the diffusion currents across the junction especially at high temperatures. Hence, in principle, smaller leakage currents can be achieved at high temperatures if bulk Si quality source-drain junctions are made in SOI MOSFETs employing ultra-thin Si films. The possibility of lower leakage currents makes SOI MOSFETs attractive for operation at elevated temperatures beyond the operating temperatures of bulk Si MOSFETs. Several studies of SOI devices at elevated temperatures are found in the published literature. Speculations on extending the operating temperature to higher values (~500°C) with improved performance by extremely thinning the SOI film (30 nm) have also been made in the literature. This present study of fully depleted NMOS devices fabricated in thin (23.5, 63.5 and 91.5 nm) SIMOX Si films was taken up to verify the high temperature advantages of thinning the SOI film