Accounting for Carrier Mobility Reduction due to the Normal Field in the Saturation Current Modeling of Extrinsic MOSFETs

— Previously, we developed the extrinsic (taking into account contact resistances) short-channel MOSFET compact model for an above-threshold regime. We took into account carrier velocity saturation in high electric fields and we used a linear approximation for the threshold voltage dependence on the body bias. Furthermore, we used an improved smoothing function. One provides a monotonic decrease in the differential output conductance during the transition between the linear and saturation regimes. However, we still did not take into account the carrier mobility reduction due to the normal field under the gate. And this is exactly what we are going to accomplish in our current paper. So far, only the equation for the saturation current will be modified without taking the body effect into account. Two models for mobility reduction are examined. The first is the simplest and is used in the MOSFET Level 3 compact model. The second is more complex and expressed in exponential form. For the saturation current of an intrinsic MOSFET (without accounting for the contact resistances), we have the equation, which has the same form with and without accounting for the carrier mobility reduction. For the saturation current of an extrinsic MOSFET, we have the implicit equation for the dependence of the saturation current on extrinsic gate-to-source bias. For the first mobility reduction model, we can solve this equation with respect to the saturation current. In the case of the second considered mobility reduction model, we cannot analytically solve this equation with respect to the saturation current. In this case, to find the extrinsic saturation current, we can use numerical methods, for example, the bisection method or an iterative calculation. In addition, we suggest the simplest approximate equation for this case.