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

In this paper, a novel symmetric-structure-based silicon MEMS (Micro Electro Mechanical Systems) 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 fracture acceleration limit in the cross direction, relative to the sensing direction, from approximately 5.8 to 24 times. Additionally, it improves the ratio of the second to the first mode frequency from 1.6 to 10, which improves survivability of the structure over a much wider bandwidth against resonance of the second mode. The new structure was fabricated by bonding two SOI (Silicon-on-Insulator) wafers, each containing complementary halves of the structure. This paper presents the configuration details of the structure, along with analytical and FEA (Finite Element Analysis) results to estimate deflections, stresses, modal frequencies, and mode shapes. Additionally, the MEMS fabrication process details, packaging, and test results of X-ray imaging, SEM (Scanning Electron Microscope) imaging, natural frequency measurement using LDV (Laser Doppler Vibrometer), sensitivity test, and so on, at die and package level are discussed.