0.5mm × 0.5mm High-Temperature Pressure Sensors Fabricated with IC-Foundry-Compatible Process in (100) / (111) Hybrid SOI Wafers

In this paper, a tiny 0.5mm × 0.5mm high-temperature piezoresistive pressure sensor is proposed and fabricated only from the front side of (100) / (111) hybrid SOI silicon wafer (Device layer is (100) silicon and handle layer is (111) silicon) for IC-foundry-compatible, high-yield and low-cost batch production. In our structure design, the device layer of (100) silicon is specifically selected to optimize the piezoresistive performance characteristics of the pressure sensor, while the handle layer of (111) silicon is used to construct sensing diaphragm and pressure-reference cavity. Taking advantages of the benefits of front-sided shallow etching and self-stop wet etching, the realization of the pressure-sensing diaphragm with uniform and controllable thickness is achieved, and the pressure-reference cavity is embedded into the handle layer of (111) silicon. Without complex double-sided micromachining, wafer bonding, and cavity-SOI needed, the fabricated pressure sensor chip-size is as small as 0.5mm × 0.5mm. The testing results show that the 1500-kPa-ranged pressure sensor has a full scale output of 180mV/1500kPa/10VDC, and a high accuracy (combined non-linearity, hysteresis and repeatability) of±0.14%F·S in the range of-55°C to 200°C. In addition, a low thermal hysteresis of 0.082%F·S at 200°C is achieved. The small-sized high temperature pressure sensors are promising in wind tunnel applications and volume production.