Ain Based Piezoelectric Resonant MEMS Accelerometer

This paper proposes an A1N based piezoelectric resonant MEMS accelerometer.Theoretical analysis,simulation and optimization by FEM(finite element method),fabrication and experimental test are presented.The sensing elements of the accelerometer are based on DETF resonators.The vibrating beam is covered with AIN thin film and metal electrodes with certain pattern are deposited on the top of the thin film.By applying driving signal on the metal electrode and doped silicon layer,the DETF can be stimulated into the desired mode.Two stage compliant leverage mechanism is used to amplify the inertial force caused by proof mass to increase the sensitivity.A centrosymmetry layout is used to further improve the space efficacy and sensitivity.The accelerometer is tested in a vacuum chamber of 4 mTorr under room temperature.All the data is recorded by network analyzer.The resonant frequency of the left side DETF resonator is 140.744kHz and the right one’s frequency is 140.786kHz.In the static acceleration range from-1g to 1g,the sensitivity of the left side and right side DETF are 13.6Hz/g and 14.8Hz/g while the sensitivity of the whole device is 28.4Hz/g.The work of this paper is 57%and 267%higher in absolute sensitivity(Hz/g)and relative sensitivity(ppm)respectively.This paper also brings up a new "double-drive strategy" for the DETF resonator.Compared with the old single drive mode,the phase shift at resonant frequency increases by 10.5° and 190%.The in-plane vibrating magnitude increases by 35%while the out-of plane vibrating magnitude is limited to increase only 11%.There are 7 chapters in this article and they are organized as follows:Chapter 1 gives a brief introduction of the history,development and future trend,and classification of MEMS accelerometer as well as its working principle and features.The MEMS resonant accelerometer is specially explained and some of the typical designs are listed.AIN based piezoelectric resonant MEMS accelerometer is set to be the research direction.Chapter 2 mainly introduces how this accelerometer is designed.1.The models of calculating frequency,sensitivity of the DETF resonators,2.the piezoelectric method of driving DETF resonators and 3.the model of calculating amplification factor of two stage microleverage mechanism are summarized.Each part of the accelerometer is optimized by these models,methods and simulations run by FEM software COMSOL.Chapter 3 introduces the PiezoMUMPs process used to fabricate the accelerometer,including 8 steps with 5 different masks.Chapter 4 introduces the device,equipment and method used to test the performance of the accelerometer.Chapter 5 shows the test results of the accelerometer,including the static sensitivity,non-linearity test,temperature drift and comparable test between the vacuum chamber and atmosphere.Chapter 6 brings up an improved "double drive" driving strategy based on the traditional design.The new DETF resonator is designed,fabricated and tested.Chapter 7 summarizes the whole research as well as its scientific contributions.Future work and improvement is also presented.