(Received October 6, 1997; accepted for publication October 30, 1997)
We propose that silicon-on-insulator (SOI) metal-oxide-semiconductor field effect transistors (MOSFETs) with SOI films thinner than the inversion layer of the bulk MOSFETs can provide higher inversion-layer mobility than the bulk Si MOSFETs, because of the significant modulation of the subband structure due to the size effect of the ultrathin SOI films. In order to examine the effectiveness of this device structure on the mobility enhancement, a theoretical calculation of the inversion-layer mobility at room temperature is performed. It is found that the mobility of the SOI MOSFETs with a SOI thickness of around 3 nm can be higher than that of the bulk MOSFETs. This mobility enhancement is attributed to an increase in the occupancy of the 2-fold valleys and the suppression of inter-valley phonon scattering, associated with the energy splitting between the 2-fold and the 4-fold valleys due to the size effect of the SOI films.