Improved characteristics of MOSFETs on ultra thin SIMOX

Ultra-thin silicon-on-insulator MOSFETs (T-SOI MOSFETs) with fully depleted mode operation were investigated in comparison with the bulk Si MOSFET from the viewpoint of current drivability. In the relatively long channel region, the current drivability primarily results from the effective generation of mobile charge in the channel and therefore the increase of saturation voltage and saturation current. As the channel length becomes shorter, the velocity saturation of carriers interferes with increase of saturation voltage and saturation current. However, the bulk Si MOSFET is affected by the velocity saturation more markedly on the saturation current because of its high doping concentration in the channel. Therefore, the superiority of current drivability in T-SOI MOSFET is preserved in the submicron regime. A 0.7- mu m CMOS ring oscillator with salicided T-SOI structure exhibited a 46 ps/stage delay time, which was about one generation faster than that of bulk Si devices.<>