SOI-Structured Piezoresistive Pressure Sensor with Integration of Temperature Sensor for Downhole Applications

Micro-electro-mechanical systems (MEMS) sensors offer the benefits of compact size, lightweight design, and low cost, making them widely applicable in consumer electronics, vehicles, health, defense, and communications. With enhanced performance, MEMS sensors have also found applications in oil exploration and geophysical studies. For years, pressure and temperature sensing during hydraulic fracturing has been employed to enhance the down-hole conductivity of oil and gas extraction. Nevertheless, the pursuit of developing high-precision MEMS sensors for oil exploration continues to be an active area of research. This paper details the design, fabrication, packaging, and characterization of a silicon-on-insulator (SOI) MEMS piezoresistive pressure sensor integrated with a temperature sensor. It also describes the design of a chamber that simulates real conditions at the bottom of oil exploration wells. The sensors were successfully designed and fabricated based on physics-based simulations, deep reactive ion etching and anodic bonding techniques. The pressure sensors, along with the signal conditioning system, demonstrated a linear response, with a maximum linear error of 4.95% at 7 MPa and a reduced linear error of less than 3.5% at 24 MPa. Additionally, a quadratic approximation for the temperature sensors was achieved, showing a maximum resistance change of 8.5% at 140 ºC.