Wireless passive pressure sensor based on sapphire direct bonding for harsh environments

This study presents a wireless passive high-temperature pressure sensor based on sapphire direct bonding technology. The design, fabrication, and measurement of the sensor are demonstrated and discussed. Single-crystal sapphire is used to fabricate the sensor owing to its outstanding characteristics, and the prototype sensor consists of an inductance, a variable capacitance, and an embedded vacuum-sealed cavity formed by sapphire direct bonding. Compared with other manufacturing technologies, the sapphire direct bonding process is simple and can effectively avoid the deformation and collapse of the embedded cavity, thereby leading to a better sensor performance. A more compact sensor with greater sensitivity has been fabricated in this study. The copper interrogating antenna is employed to detect the variation in the sensor's resonant frequency caused by the pressure applied. The characterization in high-temperature pressure environments successfully demonstrates the sensing capabilities for pressures from 20 kPa to 600 kPa up to 600 °C. At 600 °C, the sensor sensitivity reaches as high as 10 kHz/kPa. The proposed sensor can be applied for the monitoring of gas pressure in harsh environments, such as environments with high temperatures and chemical corrosion.