Basic Characteristics of a Small Strain Sensor using p-n Junction Breakdown

Silicon piezoresistive (PZR) sensors have been widely used for stress and strain detection in MEMS applications, but further improvements in sensitivity and miniaturization are required for emerging uses. This study presents a piezo-Zener (PZZ) sensor utilizing a Zener diode, designed and fabricated for detecting micro-strains in MEMS actuators, offering superior temperature characteristics and potential for low-power operation. A silicon cantilever integrated with the PZZ sensor was prototyped. The PZZ sensor achieved a sensitivity of 0.671 µA/MPa under constant voltage bias (-21.2 V, initial current -1 mA), surpassing the low-doping PZR sensor’s 0.428 µA/MPa in similar conditions (1.45 V, initial current 1 mA). The sensor showed a temperature coefficient of 0.086%/°C, slightly lower than the high-doping PZR sensor's at 0.103%/°C. Noise characteristics revealed noise density floor of approximately 0.01 nV2/Hz both for PZZ and high-doping PZR in the 10 Hz to 5 kHz band. The Allan deviation revealed that the bias instability of the PZZ sensor is about two orders of magnitude lower than for the high-doping PZR sensor (0.027 mV/√s vs 1.79 mV/√s). These results highlight the PZZ sensor’s promise for combining high sensitivity with stable temperature and noise performance, avoiding the trade-off inherent in conventional PZRs.