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4H-SiC RF bipolar junction transistors (BJTs) have been designed and tested at 425 MHz for the first time. Both epitaxial and implanted emitter structures have been fabricated. It has been established that the implanted emitter structure has very low current gain (∼1) due to the implant damage which cannot be totally removed by the high temperature activation anneal. The epitaxial emitter structure with collector and base thickness of 5 μm and 0.1 μm, respectively, shows a maximum current gain of 15 and a common emitter breakdown voltage of 500 V. The fT of this device was about 1.5 GHz. The epitaxial emitter device, with an emitter width of 2.5 μm and an emitter periphery of 2.62 cm, has demonstrated an output power of 50 W/cell using an 80 V power supply in common emitter, class AB mode. The pulse width was 100 μs and duty cycle was 10%. The collector efficiency at a power output of 50 W was 51% with a power gain of 9.3 dB. The peak large signal power gain was 9.6 dB.
Date of Conference: 6-8 Aug. 2002