NUMERICAL INVESTIGATION OF MESH SIZE CONVERGENCE RATE OF THE FINITE ELEMENT METHOD IN MESFET SIMULATIONt

The mesh size convergence rate of the finite element method in two-dimensional GaAs MESFET simulation has been investigated numerically. The equations governing MESFET operation and the finite element formulation of these equations are summarized. The presence of corner singularities at the gate contact endpoints is noteworthy. for such singularities are known to determine the convergence rate in linear model problems. The local potential and electron concentration solutions are obtained in the neighborhood of these singularities and used to estimate a lower bound on the convergence rate for the nonlinear problem. The rate of convergence of the MESFET problem is tabulated for three mesh sequences and discussed. The common source output characteristic of a 0.25 pm gate length GaAs MESFET is calculated and compared to the characteristic of a MESFET fabricated in our laboratory. Considerable discrepancy between the two is obtained; reasons for this are hypothesized. NOTATION non-zero constants constants, possibly zero field dependent electron diffusion constant electric field constant in velocity-field relation generalized mesh size parameter average mesh size parameter average domain edge length continuum (discrete) drain current per unit gate width total electron particle current density continuum (discrete) electron concentration doping concentration intrinsic electron concentration unit normal vector fundamental electronic charge continuum (discrete) total stored charge