11. Modelling and Optimization of Inertial Sensor-Accelerometer

This book chapter presents the modelling and optimization details of a Micromachined (MEMS) dual-axis accelerometer. After providing detailed review of existing and proposed applications of these inertial sensors, the chapter introduces various present-day accelerometers available in the literature. The major challenges faced by the accelerometer sensors designs are minimization of the device foot print, noise floor, and cross-axis sensitivity. As dual axis accelerometers are designed to work in both x- and y- (in-plane) directions, they became prone to cross-coupling between the in-plane and the out of the plane (Z-axis) direction. This is due to the structural design that makes them sensitive to other cross-axis acceleration. In most of the design mode-cross-coupling occurs with Z-direction. Moreover, low stiffness in Z-axis causes the proof-mass to sag due to gravity. The present design is modelled according to the Inertial Measurement Unit (IMU) platform of GlobalFoundries. The designed accelerometer consist of a square proof mass suspended using crab leg springs. Primary focus is given to have high differential capacitance sensitivity in small foot print of 1.5 × 1.5 mm. Also, to reduce cross-axis sensitivity and to reduce mode coupling between in-plane modes and Z-axis mode. Simulation results show that the differential capacitive sensitivity of 59 fF/g. The device achieves a mode separation of 10 kHz between the in-plane and out-of-the plane modes. The average cross-axis sensitivity in XY is 1.33% and cross-axis sensitivity due to Z-axis acceleration is zero.