An optimization technique for performance improvement of gap-changeable MEMS accelerometers

This paper demonstrates the design and optimization of single- and dual-axis capacitive accelerometers. Detailed analysis together with fabrication and characterization results are reported. The designs utilize a simplified comb structure to detect capacitance change between rotor and stator fingers. By optimizing the gap spacing (finger gap and anti-finger gap), the devices are designed to yield high capacitance change as a function of the proof mass displacement. It was found that there is a critical anti-gap spacing for a selected finger gap at which the device sensitivity is the highest (ratio of 3.45: 1). Designs are first optimized using Finite Element Analysis (FEA) tools. Initial simulation results indicated a differential capacitive sensitivity of 80fF/g and 68fF/g for single-and dual-axis accelerometers, respectively. The capacitance-voltage (CV) measurements exhibited a parabolic behavior which is an important characteristic for these type of accelerometers. Furthermore, results show a rest capacitance of 16.42 pF and sensitivity of 35 fF/g for single-axis accelerometer. Overall, the devices have excellent sensitivity, high linearity, and low cross-axis sensitivity. The accelerometers are fabricated using GlobalFoundries' Inertial Measurement Unit (IMU) platform and have a compact footprint of 1.8 mm x 1.8 mm.