Cutoff frequency f(t) and corresponding power P-m(ft) of a SIC microwa
ve field-effect transistor (FET) are calculated using an analytical mo
del that allows for nonlinear dependence of the carriers drift velocit
y on electric field. A simple analytical expression for the cutoff fre
quency is derived as a function of the basic FET parameters such as ch
annel depth a, doping level N, gate length L, and material parameters:
saturation drift velocity upsilon(s) and carriers mobility mu. Condit
ions for the short and long channel devices are discussed. Comparison
with the linear piece-wise approximation shows that for alpha-SiC FET
with a = 0. 15 mu m, N = 1 x 10(18) cm(-3) at the drain voltage V-D =
V-p = 20 V, where V-p is a channel pinch-off voltage, field dependent
mobility reduces the value of f(t) more than 1.5 times for the device
with L in the range of 0.9-1.5 mu m. This can partially explain the di
fference between previous theoretical calculations and experimental mi
crowave performance of SiC FETs, and can lead to future optimization o
f SiC-based devices.