RF power transistor reliability advancement using refractory metal contacts

An RF power transistor using tungsten metallization in the emitter and base contact areas, has been found to be far superior to aluminum with respect to failures due to hot spotting and second breakdown. Equivalent devices except having different metallization systems; all aluminum, all tungsten, and tungsten in the emitter-aluminum in the base; were evaluated by pulsing into collector-emitter breakdown. The tungsten metallized device was able to sustain 2.0 A of collector current without degradation while both the others failed at less than 1.0 A.