Miniature Piezoelectric Sensor for In-Situ Temperature Monitoring of Silicon and Silicon Carbide Power Modules Operating at High Temperature

Owing to the introduction of wide-bandgap power devices, recent power modules operate at higher temperatures. This increased module temperature leads to significant reliability problems, which render thermal monitoring very important. Several thermal sensors have been used in power modules; however, each of these sensors has drawbacks such as limited maximum temperature, nonlinearity, power source requirement, or limited miniaturization. This paper proposes a new temperature sensor that utilizes the piezoelectric effect. A new piezoelectric material (PZT-PZNM) with a high Curie temperature (260 degrees C) is soldered onto a direct bonded copper substrate. When the power module is operating at a high temperature, the substrate deflects and induces thermal stress, which is converted into an electric voltage via a piezoelectric mechanism. The voltage can be maximized by optimizing the location of the PZT-PZNM; the best location was determined to be away from the power devices. This observation confirms that the piezoelectric temperature sensor has a negligible influence on the performance of the power devices. Moreover, the sensor volume was miniaturized (approximately 74% reduction compared with preliminary work) to ensure that it can be readily integrated into power modules. The developed piezoelectric sensor demonstrates excellent linearity (R-2 = 0.99, approximately) up to 250 degrees C, which is sufficient for monitoring temperature in both silicon and silicon carbide power modules.