Optimization of active channel thickness of mm-wavelength GaAs MESFET's by using a nonlinear I-V model

To improve the performance of a submicron GaAs MESFET, an optimum value of active channel thickness, a is required. An algorithm has been developed to simulate the effects of a on the device characteristics, It has been observed that the ratio between output conductance and transconductance (g(d)/g(m)) increases with increasing values of cu. The data suggest that this could be attributed to the fact that by increasing a, the magnitnde of drain-to source current, I-ds increases, and as a result there are more uncovered ionic charges in the space charge region toward the drain-side of the gate. The access charge density at the drain-side of the depletion induces opposite charges in the gate electrode. Consequently, it gives forward biasing to the Schottky barrier gate which increases with increasing values of I-ds. As a result, the modulation of channel current due to the applied gate potential becomes less effective and the ratio g(d)/g(m) increases as a function of a. The technique developed could be a very useful tool for the simulation of large scale integrated circuitry involving submicron GaAs MESFET's.