A Bistalbe Ultrasonic MEMS Device with an Integrated Piezoelectric Scandium-AlN Thin Film Actuator for Switching

This work reports on a novel concept for switching between the two stable states of compressively pre-stressed bistable MEMS membranes using integrated piezoelectric scandium aluminum nitride (ScxAlN1-x) thin film actuators. The minimum voltage needed to switch between the stable states was about 23% lower than using a pure AlN layer. Depending on the membrane diameter being in the range between 600 to 800 µm, the total displacement after switching is about 10 to 16 µm. The array consists of 15 membranes on a 6x6 mm2 die, whereas the total membrane thickness was 3.12 µm. The FFT of a bistable switching process showed most beneficial peaks for ultrasound generation in the range of 70 – 90 kHz with extremely high acceleration values in the range of 105 m•s−2, thus promising high sound pressure levels.