Design Of AlN DETF Resonant Accelerometer

The MMRA(Micromechanical Resonant Accelerometer)is a novel micromachined accelerometer with high resolution and sensitivity which obtains acceleration by measuring the change in the resonant frequency.Aluminum nitride(AlN)is compatible with the CMOS(Complementary Metal Oxide Semiconductor)process which can maintain stable piezoelectric property under some extreme conditions.Therefore,AlN-based resonant accelerometers have great value and broad application prospects in the national economy and national defense and military fields.The dissertation focuses on the structure design of the AlN DETF resonant accelerometer,a high performance AlN resonant accelerometer is designed with COMSOL finite element analysis software based on the theoretical analysis.The working principle of the MMRA is systematically analyzed to provide guidance for subsequent structure design.A mechanical model of the accelerometer is established;the frequency sensitivity of the resonant beam is deduced;and the pattern of the excitation electrode of the resonator is designed.The AlN resonator is optimized by the finite element method based on the theoretical model.The simulation results show that the signal power and relative sensitivity have opposite trends with structure parameters of the vibration beam.Therefore,the performance and structural stability of the resonator need to be considered comprehensively when designing structure parameters of the AlN resonant beam.The parasitic loss and mechanical loss are considered as optimizing the resonator’s Q(quality factor).It needs to isolate the working mode and interferential mode of the resonator to reduce the parasitic losses by optimizing the length of the ends.The gap of the vibrating beams is related to the mechanical loss(squeeze-film damping),but the mechanical loss can be substantially negligible due to the damping coefficient is very small.After optimization,the sensitivity,signal power and Q of the AlN DETF resonator are 56 Hz/μN,6.8e-04 nW and 958,respectively.The design and simulation analysis of the entire structure of the AlN DETF resonant accelerometer is performed in combination with the process conditions and performance indexes.The force amplification coefficient of micro-leverage is derived,and then the two-stage micro-leverage structure is selected which structure parameters are optimized;on this basis,"I"-shape support beam is introduced to further decrease the cross sensitivity and enhance the anti-interference ability;Finally,a series of simulation analyses of AlN DETF resonant accelerometer are implemented(include range,sensitivity and thermal stress)to verify the feasibility of the structure.The results show that the fundamental frequency,sensitivity,linearity and bandwidth are 373.3 k Hz,64.6 Hz/g(cross sensitivity is 0.0033 Hz/g),0.148% and 6663.8 Hz,respectively.The process flow of the Al N DETF resonant accelerometer is designed,and the corresponding masks are drawn by the L-edit software.