An inherently-robust 300°C MEMS temperature sensor for wireless health monitoring of ball and rolling element bearings

Presented is an inherently-robust wireless capacitive MEMS temperature sensor capable of operating to 300°C. The heart of the sensor is an array of bimorph (metal-dielectric) cantilevers whose deflections are sensed by an array of appropriatelyplaced electrodes. The key advantages of this configuration are the following. First, its dielectric layer is SiO2 thermally-grown at 1,100°C as opposed to conventional low-temperature PECVD or sputtered films. Second, the lack of a sensing surface directly beneath the movable structures renders stiction nearly impossible. Third, the fringing-field sensing results in constant sensitivity throughout the entire temperature range. Fourth, the employed passive approach is immune to high-temperature reliability issues faced by active devices. Furthermore, the fabrication yield is over 99%, even in an academic cleanroom (Birck Nanotechnology Center at Purdue University). When configured with an inductor and wirelessly interrogated, the measured resonant frequency has a linear shift from 206 MHz at room temperature to 199 MHz at 300°C.