Design and simulation of piezoresistive MEMS accelerometer for the detection of pathological tremor

This paper reports the design and simulation of microelectromechanical (MEMS) piezoresistive accelerometer used in a strapdown inertial measurement unit (IMU) for detection of pathological tremor. There is a demand for high performance micromachined accelerometer to build a reliable tremor diagnostic system. The performance mainly depends on geometric design, device sensing mechanism with respect to different material properties, noise and offsets in the associated electronic circuits and fabrication limitations. The work is aimed at realizing a piezoresistive inertial sensor for diagnostic purpose of pathological tremor occurring mainly in patients suffering from thyrotoxicosis and several neurodegenerative disorders.The geometric configuration of the inertial sensor designed consists of a structure which includes a square seismic mass with four flexures implanted with eight P- type single crystal silicon (110) piezoresistors. The design configuration chosen in terms of length, width and thickness are Seismic-mass-3200μm×3200μm×250μm,Flexures-1000μm × 250μm × 20μm,Frame-5200μm × 230μm × 250μm, piezoresistors -100μm × 25μm × 2μm.The device has been designed for a frequency range of (0.1-25 Hz) and a dynamic range of ±2g The cross axis sensitivity has been reduced by using a Wheatstone bridge configuration which enhances the sensitivity of the sensor and the system as a whole. Eigen frequency decides the sensitivity of the device; the structure has been simulated at different Eigen modes. Flexure thickness has been optimized because sensitivity is found to reduce with increase in flexure thickness. Stress analysis has been carried out and maximum stress is obtained at the edges and maximum deflection occurs at the piezo-junction of flexure and proofmass.