Very high-power-density CW operation of GaAs/AlGaAs microwave heterojunction bipolar transistors

Thermal instability of multi-emitter high-power microwave heterojunction bipolar transistors (HBTs) 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- mu m minimum emitter sizes and no intentional ballast resistors showed unconditionally stable CW operation up to the device electronic limitations. A record 10-mW/ mu m/sup 2/ 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/ mu m/sup 2/ power density. It was shown that stable high-power-density operation can be maintained at multiwatt output power levels.<
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