Hybrid Laser-ICP Micromachining of p-Type 4H-SiC Piezoresistive Elements for High-Temperature Pressure Sensor Applications

This paper presents the design and fabrication of a p-type 4H-silicon carbide (SiC) piezoresistive pressure sensor for high-temperature applications. The sensor was fabricated using a hybrid process that integrates an optimized stepped laser power modulation strategy with inductively coupled plasma (ICP) etching. The synergistic combination of picosecond laser and ICP technologies significantly reduces processing time while ensuring the contact stability of the piezoresistors. The observed enhancement in surface flatness from AFM suggests a suppression of surface scattering, which likely mitigates carrier mobility loss. This finding provides a clear pathway for optimizing piezoresistive sensor sensitivity through surface morphology engineering. Furthermore, a Ni/Ti/Al metallization system was employed, which formed excellent ohmic contacts with p-type 4H-SiC after annealing at 900 °C for 5 minutes in a nitrogen atmosphere. Electrical characterization of the piezoresistors over the temperature range of 25–500 °C confirms reliable electrical connection performance up to 500 °C and validates the high-temperature electrical stability of the fabricated piezoresistors. Specifically, the TCR value decreases from -5541 ppm/°C at 100 °C to -902 ppm/°C at 500 °C. This reduction suggests incomplete ionization of acceptors in 4H-SiC at 500 °C, which mitigates the temperature dependence of resistivity and further validates the operational stability of the sensor up to 500 °C in air. The final testing results demonstrate good consistency among the four sensing resistors, with a sensor output sensitivity of approximately 1.66 mV/V/MPa. These findings indicate that the proposed approach offers an effective and reliable solution for the rapid and scalable manufacturing of MEMS SiC pressure sensors for practical pressure measurement applications. Achieving comprehensive high-temperature pressure sensing performance remains an important goal for future research.