Packaged capacitive pressure sensor system for aircraft engine health monitoring

This paper describes the development of a packaged silicon carbide (SiC) based MEMS pressure sensor system designed specifically for a conventional turbofan engine. The electronic circuit is based on a Clapp-type oscillator that incorporates a 6H-SiC MESFET, a SiCN MEMS capacitive pressure sensor, titanate MIM capacitors, wirewound inductors, and thick film resistors. The pressure sensor serves as the capacitor in the LC tank circuit, thereby linking pressure to the resonant frequency of the oscillator. The oscillator and DC bias circuitry were fabricated on an alumina substrate and secured inside a metal housing. The packaged sensing system reliably operates at 0 to 350 psi and 25 to 540°C. The system has a pressure sensitivity of 6.8 × 10
^-2
MHz/psi. The packaged system shows negligible difference in frequency response between 25 and ~400°C. The fully packaged sensor passed standard benchtop acceptance tests and was evaluated on a flight-worthy engine.