UC Berkeley

High temperature electronics, micro-electro-mechanical systems (MEMS) and sensors that are able to operate between 300°C to 600°C have broad applications in harsh environments such as oil/gas exploration, geothermal development, industrial manufacturing processes, and space exploration. 4H-silicon carbide (SiC) is a good material for harsh environment applications because of its wide bandgap, high carrier mobilities, excellent thermal and chemical stabilities, and high breakdown electric field strength. Several 4H-SiC devices and integrated circuits have been studied in this work, including p-n diodes, p-n diode temperature sensors, bridge rectifiers, and bridge circuits for differential capacitive pressure sensors.

4H SiC p-n diodes from room temperature to 600°C have been demonstrated with theoretical study, simulation, fabrication, and characterization. The fabricated 4H-SiC p-n diodes show turn on voltages from 2.6 V to 1.3 V which match well with the technology computer-aided design (TCAD) simulation results from 2.7 V to 1.45 V when temperature increases from 17°C to 600°C.

Planar-integrated 4H-SiC diode bridge rectifier circuits are analyzed, simulated by SPICE (Simulation Program with Integrated Circuit Emphasis), fabricated and characterized. Experimentally, fabricated rectifiers are functional up to 500°C with voltage conversion efficiencies of 73.6% at room temperature and 89.1% at 500°C.

High-performance temperature sensors from 17°C to 600°C by using circular-shape 4H-SiC p-n diodes are analyzed, simulated by TCAD Sentaurus, fabricated and tested. The 4H-SiC p-n diode temperature sensors achieve high sensitivities of 2.9 mV/°C at 0.1 μA and 4.7 mV/°C at 1 mA in a wide temperature range from 17°C to 600°C.

Finally, planar integrated 4H-SiC diode bridge circuits for differential capacitive pressure sensor transduction are investigated. The working principle of the transduction circuit is derived. The circuit is simulated by SPICE, fabricated and tested with a sensitivity of 9.3 mV/pF at 1 MHz and a 3dB cut-off frequency of 2.5 MHz.

These results show great potential for 4H-SiC devices and circuits working in harsh environment electronics, MEMS and sensing applications.