Miniaturized design of a piezoelectric thermal sensor optimized for the integration to wide bandgap power modules operating at high temperatures

This paper presents a new design of a piezoelectric sensor that is miniaturized to monitor thermal problems in wide bandgap power modules, which anticipated to have the operation temperatures significantly higher than silicon power modules. Recent power modules, especially those employing wide bandgap power devices, suffer significantly elevated temperatures. The thermal sensor proposed herein is made of miniature piezoelectric pieces (which are solder-bonded on a direct bonded copper substrate) that convert thermal stress of the substrate to electrical voltage. Compared to previous designs, this design exhibits notably smaller size (more than 70 percent size-reduction) and excellent linearity (R^2 is about 0.96 close to 1.0) up to 220 degree Celsius, which is expected to be sufficient to monitor the maximum temperature observed in wide bandgap power modules. This achievement was enabled by (1) introducing a new piezoelectric material having a high Curie temperature, (2) improving sensor components and fabrication process, and (3) optimizing sensor locations.