MICROWAVE AND THERMAL-CHARACTERISTICS OF BACKSIDE-CONNECTED FLIP-CHIPPOWER HETEROJUNCTION BIPOLAR-TRANSISTORS

Measured and modelled characteristics are reported for a new geometry for contacting AlGaAs/GaAs heterojunction bipolar transistors (HBTs), which provides lower thermal resistance and lower emitter inductance t han does the conventional approach. Common-emitter connected HBTs are mounted emitter side down on a metal heatsink, which also serves as el ectrical ground. Connections to the base and collector are made with s ubstrate vias that extend through the GaAs substrate from the backside of the wafer. This configuration was measured to have values of therm al resistance as small as 0.23 K/mW for a 132 mu m(2) emitter area HBT , in agreement with simulations. An output power per unit emitter area of 2.9 mW/mu m(2) (total power of 370 mW) at 9 GHz was observed.