VERY HIGH-POWER-DENSITY CW OPERATION OF GAAS/ALGAAS MICROWAVE HETEROJUNCTION BIPOLAR-TRANSISTORS

Thermal instability of multi-emitter high-power microwave heterojunction bipolar transistors (HBT's) was eliminated using a novel heat spreading technique that regulates internal device currents to avoid the formation of hot spots. Devices with 2- and 3-mum minimum emitter sizes and no intentional ballast resistors showed unconditionally stable CW operation up to the device electronic limitations. A record 10-mW/mum2 power density was obtained at 10 GHz with 7-dB gain and 60% power-added efficiency. The highest efficiency was 67.2% at 9.3-mW/mum2 power density. It was shown that stable high-power-density operation can be maintained at multiwatt output power levels.