Piezoresistive 4H-SiC Pressure Sensor With Diaphragm Realized by Femtosecond Laser

The widespread application of bulk silicon carbide in pressure sensing has been largely limited by the slow etching rate of traditional micromachining processes. This paper proposes a piezoresistive bulk 4H-SiC pressure sensor with diaphragm which has controllable thickness realized by femtosecond laser. A modified stress model was established by finite element analysis to fit the SiC circular diaphragm prepared by laser micromachining. The test results proved that the fabricated sensor with diaphragm thickness of $60 \mu \text{m}$ had sensitivity of 1.42 mV $/\text{V}/$ MPa under the applied pressure of up to 5 MPa at room temperature. Small hysterisis error of 0.17 %/FSO and nonlinearity of 0.20 % $/$ FSO was achieved. The sensor was able to work in a broad temperature range with the temperature coefficient of sensitivity of -0.23% FSO/°C at -50 °C and -0.10% FSO/°C at 300 °C. The dynamic response results exhibited that the resonance frequency of the sensor was 60.11 kHz and the rise time was $18 \mu \text{s}$. The SiC pressure sensor also had the noise-limited resolution of 0.42 kPa and the dynamic range of 44.9 dB. The research demonstrates the prospect of employing the femtosecond laser technology to prepare bulk SiC pressure sensors for extreme temperature environment.