High-Gauge Factor Strain Sensor Based on Piezoelectric Aluminum Nitride Coupled to MOSFET

The development of high-sensitive and economical strain sensors is crucial for precise and efficient measurement of ultra-small strain in industrial applications. This paper reports a microfabricated strain sensor based on aluminum nitride (AlN) combined with a metal-oxide-semiconductor field effect transistor (MOSFET). A high-quality AlN thin film works as a sensing element, which is connected electrically to the gate electrode of the MOSFET for the amplification of piezoelectric response of the AlN thin film. The pseudo gauge factor (GF) of the MOSFET is evaluated from the source-drain resistance change under the application of stress to the piezoelectric AlN thin film. A GF of as high as 1340 is obtained, which is seven times larger than the best GF demonstrated for the state-of-the-art silicon piezoresistive strain sensor. The exponential change of drain-source current with gate voltage in subthreshold region of the MOSFET offers a large enhancement of the sensitivity of such sensors. The developed strain sensor has various applications in strain and stress measurements in an ultra-small strain range.