Optimization of Structure and Control Technology of Tunnel Magnetoresistive Accelerometer

In this work, an optimized tunnel magnetoresistive (TMR) accelerometer with a closed-loop control system was developed and evaluated. The device first introduces a silicon spring-mass sensing structure lower than 50 Hz into TMR-based accelerometry for enhancing the mechanical sensitivity and subsequent readout sensitivity. Simultaneously, in order to realize the in-plane electrostatic feedback control, the comb structure is designedalongwith the sensing mechanism, owning combined benefits of integrated processing and large feedback force. The whole sensing structure is a silicon-glass chip, fabricated by the standard micro-electromechanical system (MEMS) process-deep dry silicon on glass (DDSOG) process. A permanent rubber magnet is assembled on the proof mass for conversion from the displacement to variation of the magnetic field intensity, which is further detected by a pair of symmetrically arranged TMR sensors. The voltage signals output from TMR sensors are then sent into an analog circuit via an interface module for force-feedback control. The simulation analysis indicates that the proposed MEMS sensing structure has a low natural frequency of 44.55 Hz, corresponding to a compliant mechanical sensitivity of 125.5 mu m/g. Meanwhile, a maximum magnetic sensitivity of about 0.1 mT/mm is available in a height of 6 mm above the 3 x 3 x 0.3 mm magnet. Finally, the experiments on the assembled prototype demonstrated that a scale factor of 1.79 V/g and a bias stability of 228 mu g have been achieved in the closed-loop modality, which verifies the effectiveness of the proposed TMR MEMS accelerometer.