**5. Conclusions**

This paper reports an optimized AlN resonant accelerometer with a tuning-fork structure. The accelerometer is excited to vibrate in-plane. A z-axis acceleration, which is vertical to the plane of the accelerometer, can be detected. The z-axis sensitivity is 346 ppm/g, which is five times as much as the T-shape accelerometer. This accelerometer is potential to realize an integrated 3D AlN accelerometer. The Q value is 1868. The temperature coefficient of frequency (TCF) of this accelerometer is −106 ppm/◦C, tested from −40 ◦C to 85 ◦C. A differential structure and a temperature compensation circuit will be designed to reduce the TCF. In the future work, we will focus on the increase of sensitivity, 3D integration, and reduction of TCF.

**Author Contributions:** J.Y. and C.S. conceived and designed the MEMS structure; J.Y. performed the simulation, the MEMS fabrication, the test, and wrote the paper; G.H., M.Z., Y.H., Y.S., J.N., F.Y. and X.W. revised the paper.

**Funding:** This work is supported by the National Natural Science Foundation of China (No.61704165, No. 61474115, No.51720105004, and No.10061704165) and the National Key R&D Program of China (No.2018YFF01010504) and the Science and Technology on Analog Integrated Circuit Laboratory Stability support project (No.6142802WD201806).

**Conflicts of Interest:** The authors declare no conflict of interest.
