2-D device numerical simulations of gate sinking failure mechanism in pHEMT

The gate sinking failure mechanism (interdiffusion of metal atoms from the gate into semiconductor) was studied for M/A-COM´s 0.5 μm pHEMT process using a Silvaco 2-D numerical simulator. The doping profile and device geometry used in the simulation were similar to that of a discrete single-finger pHEMT. Gate sinking was modeled as a uniform increase in the gate recess depth across the gate length and width. The initial gate recess depth in the simulation was calibrated to obtain a transfer curve (I_ds vs V_gs) comparable to the measured transfer curve of an unstressed device. Then, the gate recess depth was increased by 10, 20, 30, 40 and 50 angstroms. Simulations have shown the existence of a critical recess depth, at which drain current and pinch-off voltage are expected to rapidly decrease. Assuming the validity of the gate recess model, and a linear dependence of the interdiffusion process on the operating time of a device, this simulation suggests that the gate sinking mechanism will display a certain onset time, after which dramatic changes in device electrical parameters are to be expected