Investigation of a Novel Symmetric-Structure-Based MEMS Piezoresistive Accelerometer

In this article, a novel symmetric-structure-based silicon microelectromechanical systems (MEMS) piezoresistive accelerometer is proposed. Compared to conventional structures based on multiple support beams and hanging-seismic-mass, the symmetric-structure not only reduces cross-axis output but also ensures lower stresses in the flexures when subjected to cross-axis acceleration inputs. It increases the ratio of the fracture acceleration limit in the cross-direction to that in the sense-direction, from approximately 5.8 to 24. Additionally, it improves the ratio of the second to the first mode resonance frequency from approximately 2.2 to 10.5, which can improve survivability of the structure over a much wider bandwidth against resonance of the second mode. The new structure was fabricated by bonding two silicon-on-insulator (SOI) wafers, each containing complementary halves of the structure. This article presents the configuration details of the structure, along with analytical and finite element analysis (FEA) results to estimate deflections, stresses, modal frequencies, and mode shapes. Additionally, the MEMS fabrication process details, packaging, and test results of X-ray imaging, scanning electron microscope (SEM) imaging, natural frequency measurement using laser doppler vibrometer (LDV), sensitivity test, and so on, at die and package level are discussed.