PCIM: a physically based continuous short-channel IGFET model for circuit simulation

We present an accurate analytical IGFET model (PCIM), for short-channel devices down to sub-half micron channel lengths. The model is described by a single drain current equation, valid for both weak and strong inversion regions of device operation. The model contains a new velocity-field (υ-ε) relation for carriers in the channel region. Combining this relation with the channel length modulation expression, obtained using engineering approximations to the two-dimensional fields near the drain end in saturation, results in an accurate drain conductance equation. The value for the carrier saturated velocity extracted from the I-V data for different CMOS technologies is 7-8×10⁶ cm/s for electrons and 5-6×10⁶ cm/s for holes, consistent with the reported values. The model not only predicts accurate output conductance, which is important for analog design, but also accurately simulates intrinsic gate capacitances for short channel devices. Since the model is inherently continuous, device conductances and capacitances are smooth and continuous at the transition points. This continuity results in enhanced convergence properties of the circuit simulator SPICE. Because the model is physically based, the temperature dependence of device characteristics in the temperature range 0-120°C can easily be predicted simply by taking the temperature dependence of the threshold voltage, carrier mobility and velocity saturation parameters