Piezoelectric pressure sensor based on flexible gallium nitride thin film for harsh-environment and high-temperature applications

Abstract Piezoelectric materials are promising for pressure sensors in a variety of industrial applications such as automotive and petroleum fields. Typical piezoelectric sensors rely heavily on lead zirconate titanate (Pb[ZrxTi1-x]O3, PZT) transducers. However, for broader applications of piezoelectric sensors, the PZT is a suboptimal candidate due to its unstable output at temperatures above 200 °C and potential environmental hazard. A recent research objective is to produce a more effective, safer, and eco-friendly material than PZT for piezoelectric pressure sensors by incorporating lead-free materials, such as other ceramics or polymeric composites. Among lead-free materials, gallium nitride (GaN) has a notable piezoelectric coefficient and demonstrates the greatest potential to replace the PZT as a result of its performance in high temperature and pressure operating conditions. In this study, GaN thin film is used as a sensing material, where the sensor is made by a simple layer transferring process after the removal of silicon substrate. The output potential values of GaN with respect to gas pressure levels are 42.3, 76.8, 98.7, and 122.1 mV for 50, 100, 150, and 200 psi, respectively, well matched to simulated results. Additionally, the potentials measured at elevated temperatures produce reliable outputs at high temperatures up to 350 °C. Furthermore, the stability of sensor outputs at room temperature and elevated temperatures with various pressure levels was confirmed.