Technology development of 4H-SiC RF BJTs with 5GHz fMAX
4H-SiC RF BJTs were developed on a semi-insulating (>105 -cm) substrate using an triple mesa-etch and interdigitated emitter-base finger design. The sheet conductance of the emitter layer was measured during the etch to accurately determine the location of the base-emitter interface. On-wafer small signal s-parameter measurements were performed on a 4-finger device with 3 m emitter stripe width and 150 m finger length. Both, the current gain and unilateral power gain, were extracted from the measured s-parameters, yielding an fT of 7 GHz and an fMAX of 5.2 GHz biased in common-emitter configuration at JE = 10.6 kA/cm2 and VCE = 20 V. The maximum available power gain (GMAX) is 18.6-dB at 500 MHz and 12.4-dB at 1 GHz, demonstrating the potential of 4H-SiC BJTs for both UHF and L-band applications. Small-periphery (4x150m) devices were tested using on-wafer load pull measurements up to 1.5GHz. Under pulsed conditions, the devices exhibited 10dB of power gain at 1GHz and a peak power density of 2.3W/mm (1.4W) with less than 0.1dB pulse droop for a 100s pulse width and a 1% duty cycle. The power gain decreased to 8dB at 1GHz under CW conditions at a power density of 1.6W/mm (1W).