Polysilicon quantization effects on the electrical properties of MOS transistors

The quantum-mechanical behavior of charge carriers at the polysilicon/oxide interface is investigated. It is shown that a dark space depleted of free carriers is created at the interface as a consequence of the abrupt potential energy barrier, which dominates the polysilicon capacitance and voltage drop in all regions of operation of modern MOS devices. Quantum-mechanical effects in polysilicon lead to a reduction in the gate capacitance in the same way as substrate quantization, and to a negative voltage shift, which is opposed to the positive shift caused by carrier quantization in the channel. Effects on the extraction of device physical parameters such as oxide thickness and polysilicon doping are also addressed.