Surface potential at threshold, transconductance, and carrier generation in thin SOI MOSFETs

The physics of ultrathin, fully depleted SOI MOSFETs are studied to obtain more accurate device equations and models and a better understanding of the carrier generation properties. It is found that the surface potential at threshold varies with the backgate potential, rather than being constant, as is usually assumed. The linear transconductance is also a strong function of the back gate voltage. The expressions presented can be used to determine the optimum back gate bias for maximum transconductance and mobility. The dual-gate Zerbst-like method is adapted for the study of carrier generation properties. Suitable biasing is used to set up a conductive channel in one interface and a transient variation of the surface potential in the other. The steady-state regime is gradually reached by charge generation in the film volume, the interfaces, and the sidewalls, giving rise to drain current transients. The corresponding generation rates are obtained by measuring and correctly modeling these transients