Substrate floating effects of p-channel SOI MOSFETs

The floating substrate effects of p-channel MOSFETs fabricated on SOI substrates formed by oxygen implantation are studied. The kink effect occurs in the saturation regime for p-channel SOI MOSFETs when electrons are generated by impact ionization near the drain and swept by the electric field into the neutral floating substrate. This lowers substrate potential and thus changes the threshold voltage through the back-bias effect. Generally, the p-channel SOI MOSFET has lower impact ionization than its n-channel counterpart. However, as the channel doping density increases and/or the channel length becomes shorter, more impact ionization occurs. Therefore, optimal conditions in device parameters must be chosen to realize VLSI SOI CMOS circuits