Thermal analysis and characterization of thermally shunted AlGaAs/GaAs heterojunction bipolar transistors

Analytical models were developed for thermal analysis of thermally-shunted heterojunction bipolar transistors. The dependence of junction temperature on thermal shunt landing pad geometry was determined using a transmission-line-like model. Assuming a nearest neighbor approximation, self-induced and coupled thermal resistances were calculated, and an equivalent thermal circuit was developed. The temperature distribution of the multiple-emitter element thermally-shunted devices was calculated and discussed. The presented model gives a guideline for thermal shunt design. Thermally-shunted devices with different emitter designs were fabricated and tested. Thermal resistances for both emitter bar and circular dot-array designs are smaller than those reported for non-thermal shunt devices by 25 to 50%. The analytical model found good agreement with the experimental measurements of fabricated devices.