A mobility model for carriers in the MOS inversion layer

A mobility model for carriers in the MOS inversion layer is proposed. The model assumes that mobility is a function of the gate and drain fields, and the doping density, which conforms to Thornber's scaling law. Two-dimensional computer simulation combined with the present mobility model can predict experimental drain current within an error of ± 5 percent. The present model is applicable and suitable for designing short-channel MOSFET's, especially in the submicrometer range. The "saturation velocity" in the MOS inversion layer is also discussed, based on Thornber's scaling law. The saturation velocity, as determined from the calculated drain current in the same way as experimentalists have done, is 6.6 × 10
⁶
cm/s. This is close to what has been claimed to be "saturation velocity in the inversion layer," and is about two-thirds of microscopic saturation velocity. This lower saturation velocity originates from the nonuniform field distribution in the test device, and, therefore, the experimentally reported saturation velocity in the MOS inversion layer is inferred to be a macroscopic average, rather than the microscopic drift velocity.