Failure modes for stiction in surface-micromachined MEMS

Abstract

Wafer-level testing of surface-micromachined sensors provides new challenges to the test community. Currently, there is no method available for performing direct measurements to assess faulty micromechanical structures. Most commercial methods use electrical measurements to deduce the physical source of failures in the micromechanical structure. As a result, the process of identifying various failure modes (electrical measurements) and accurately mapping them to the underlying physical failure mechanisms of the mechanical sensor becomes highly complex. Several sources of failures that include particulates and stiction complicate the situation even more. Here, we provide a case study of the Analog Devices ADXL75 Accelerometer. One failure category called stuck/tipped beams is investigated and a methodology is developed to uniquely distinguish failures either caused by stuck or tipped beams. The proposed method is easy to implement and the information obtained can be critical for yield improvement.