Compact Modeling of Anomalous High-Frequency Behavior of MOSFET´s Small-Signal NQS Parameters in Presence of Velocity Saturation

This paper presents a physical charge-based compact small-signal nonquasi-static (NQS) model for MOST, including velocity saturation and valid in all regions of inversion (from weak to strong inversion). This model intrinsically predicts the anomalous high-frequency behavior of transadmittance (y_dg) in saturation, which was observed earlier in both device simulation and measurement. It also shows that the inclusion of velocity saturation causes the magnitude of the gate-to-drain admittance y_dg to start to increase (instead of decreasing) above a certain frequency and its real part also starts to increase in the negative direction instead of becoming zero. In addition, even for a long channel MOST, the weak inversion charge present at the drain can also affect the y_dg in a similar way