**A Resonant Z-Axis Aluminum Nitride Thin-Film Piezoelectric MEMS Accelerometer**

**Jian Yang 1,2, Meng Zhang 1,2, Yurong He 1,2, Yan Su 1,2, Guowei Han 1,\*, Chaowei Si 1,\*, Jin Ning 1,2,3, Fuhua Yang 1,2,4 and Xiaodong Wang 1,4,5,6,\***


Received: 1 August 2019; Accepted: 28 August 2019; Published: 6 September 2019

**Abstract:** In this paper, we report a novel aluminum nitride (AlN) thin-film piezoelectric resonant accelerometer. Di fferent from the ordinary MEMS (micro-electro-mechanical systems) resonant accelerometers, the entire structure of the accelerometer, including the mass and the springs, is excited to resonate in-plane, and the resonance frequency is sensitive to the out-plane acceleration. The structure is centrosymmetrical with serpentine electrodes laid on supporting beams for driving and sensing. The sti ffness of the supporting beams changes when an out-plane inertial force is applied on the structure. Therefore, the resonance frequency of the accelerometer will also change under the inertial force. The working principle is analyzed and the properties are simulated in the paper. The proposed AlN accelerometer is fabricated by the MEMS technology, and the structure is released by an ICP isotropic etching. The resonance frequency is 24.66 kHz at a static state. The quality factor is 1868. The relative sensitivity of this accelerometer, defined as the shift in the resonance frequency per gravity unit (1 g = 9.8 m/s2) is 346 ppm/g. The linearity of the accelerometer is 0.9988. The temperature coe fficient of frequency (TCF) of this accelerometer is −2.628 Hz/ ◦C (i.e., −106 ppm/ ◦C), tested from −40 ◦C to 85 ◦C.

**Keywords:** MEMS; AlN thin film; piezoelectric e ffect; resonant accelerometer; z-axis
