Reliability testing of Ni-Fe as structural material in MEMS gyroscope

We report reliability testing results for Ni-Fe when used as a structural material in a MEMS gyroscope. The tests are performed on a 2-degree-of-freedom torsional gyroscope fabricated by an SU-8-based ultraviolet-lithographie, galvanoformung, abformung process having 8-μm-thick Ni-Fe as the structural layer. The device is vacuum packaged in a 24-pin dual in-line package with a glass lid before measuring its frequency response and extracting the mode shapes using laser Doppler vibrometer. To check the reliability of the Ni-Fe structural layer, three types of tests, fatigue, shock, and vibration, are conducted. In fatigue testing, the packaged device is excited at its resonance frequency for more than a billion cycles, and it is checked periodically for any physical damage or change in the resonance frequency. The shock test is performed by dropping the device chip on a hard surface floor from 1 m height. The vibration test is carried out by subjecting the packaged device to more than 4g acceleration having frequency of 200 Hz for 30 min.