High frequency behaviour of electron transport in silicon and its implication for drain conductance of MOS transistors

Drain conductance g_d is an important small signal parameter of the MOS transistor: Very small values of drain conductance are crucial to realizing high-gain amplifiers. This paper studies high-frequency small signal behaviour of electron transport in silicon under biasing electric fields that are typical of MOS channels in the saturation region using Monte Carlo technique. It is found that the small signal mobility, which is very small at low frequencies, becomes large at high frequencies of the order of 10¹²-10¹³ Hz. This behaviour indicates that in those MOS devices where velocity saturation is the cause of drain current saturation the drain conductance at high frequencies will become large. This will substantially reduce amplifier gains at these frequencies