High-Temperature Radio Circuits in Silicon Carbide Bipolar Technology

Abstract: High-temperature electronics find many niche applications in downhole drilling, aviation, automotive and future exploration of inner planets like Venus and Mercury. Past studies have shown the potential of silicon carbide (SiC) electronics for catering these extreme temperature applications. In particular, analog, digital and mixed-signal integrated circuits, based on in-house SiC bipolar technology, have been shown to operate successfully for temperatures as high as 500 oC. This thesis aims at exploring the potential of in-house SiC bipolar technology for realizing high-temperature radio frequency (RF) circuits.To that end, the in-house SiC bipolar junction transistors (BJTs) are first characterized up to 300 oC for RF figures of merit like unity current gain bandwidth and unity power gain bandwidth. The measurement results showed the feasibility of the current batch of SiC BJTs for developing RF circuits operating at low-end of very high frequency (VHF) band. Thereafter, three fundamental blocks of a high-temperature radio receiver, i.e. an intermediate-frequency amplifier, an oscillator and a down-conversion mixer were implemented. Firstly, an intermediate-frequency amplifier has been designed and measurement results demonstrated operation up to 251 oC. The proposed amplifier achieved a gain, input, and output matching of 16 dB, -7.5 dB and -11.2 dB, respectively, at 54.6 MHz and 251 oC. Next, 500 oC operation of an active down-conversion mixer has been exhibited. Measurements have shown that the conversion gain of the proposed mixer is 4.7 dB at 500 oC. Lastly, a negative resistance oscillator has been designed and tested successfully up to 400 oC. It has been shown that at 400 oC, the proposed oscillator delivers an output power of 8.4 dBm into a 50 Ω load.In addition to SiC BJTs, the aforementioned circuits also employed spiral inductors implemented on PCBs, commercially available ceramic capacitors and thick-film resistors. Therefore, this thesis presents the evaluation of passives to assess their feasibility for high temperature operation. This work also identifies and addresses several challenges associated with the development flow of high-temperature RF circuits.