FET and HEMT thermal impedances

Three-dimensional, finite mesh calculations of self heating in recessed etched MESFETs and HEMTs using realistic power dissipation profiles computed using a Poisson, current-continuity equation solver are compared with analytical models and measurements. The analytical models assume uniform power dissipation across an effective gate length L, which varies as the metal gate length. The actual power dissipation profiles are nearly independent of gate length, but the thermal impedances decrease with increasing gate length because the gate metal helps to spread the heat and thus lower the peak temperature. We discuss materials effects, temperature differences between the gate and channel, the bias dependence of the thermal impedances, and thermal impedances for multi-finger FETs and HEMTs. (C) 1998 Elsevier Science Ltd. All rights reserved.