Research On Key Technology Of MEMS Gyroscope Based On Tunnel Magneto-resistance Effect

MEMS gyroscope is the most widely used MEMS sensor.With the extensive application of autonomous driving,AI and military equipment,MEMS gyroscope with higher accuracy and stability is urgently needed in those applications.The key issue of high precision MEMS gyroscope is the detection of weak Coriolis force signal with high sensitivity.At present,the capacitive MEMS gyroscope is prone to breakdown and failure due to its interface circuit resolution reaching the theoretical limit.Therefore,it is necessary to explore high precision MEMS gyroscope based on the new detection effect.Tunnel magneto-resistance（TMR）effect is based on spin-dependent tunneling electron effect.A slight change in magnetic field will lead to a drastic change in the value of magneto-resistance.Because tunnel reluctance has the advantages of high sensitivity,high resolution,low power consumption and small size,it can effectively improve the detection accuracy of gyroscope.In this paper,we design a kind of MEMS gyroscope based on tunnel reluctance effect.Through the simulation optimization and dynamic characteristics analysis of the gyroscope by COMSOL 5.3a,the structural sensitivity of the gyroscope can reach to 2.978nm/°/s,and the gradient of magnetic field is up to 13.25×10^-4Oe/μm.In addition,a four-bridge tunnel magneto-resistance detection is built to suppress the external magnetic interference.The processing flow,lithographic layout and other critical process of the gyroscope are designed and analyzed.The key process steps include shallow cavity etching,oxidation layer growth,sputtering metal,structure etching and metal bonding on silicon wafers.Finally,the driven/sense amplitude-frequency characteristics and the magneto-resistance effect of the micro-gyroscope are tested.The experimental results show that resonant frequency of the tunnel magneto-resistance micro-gyroscope in the driven/sense direction is 8066 Hz and 8091 Hz,respectively,with the maximum relative error of 7.1%.Moreover,the sensitivity of the tunnel magneto-resistance effect is 32.78m V/Oe and the sensitivity of gyroscope can reach to 1.3m V/°/s.