Investigation into low frequency response of acoustic MEMS for determination of failure modes

Frequency response to stimuli applied to acoustic micro-electro-Mechanical Systems (MEMS) yield meaningful information of certain defects affecting such devices. This article presents the effects of three distinct root causes of failures affecting the low-frequency response of MEMS microphones: lid attach holes, die attach holes and broken vents with experimental inductions of these effects for the lid attach holes and broken vents. Methods to create such defects are presented which include laser drilling and focused ion beam machining of holes. A complete characterization of induced broken vents is presented. Alternative locations for defects induction are proposed and demonstrated on 34 devices, 16 with lid attach holes and 18 with induced broken vents. The information obtained from the frequency response of the devices is shown to be insufficient to separate the root causes of failures as their effects on the frequency response is similar and the magnitudes of the variations of the observed response overlap. Additional information about the circumstances regarding the onset of defects such as location of the fault and its occurrence in the device manufacturing/assembly/operation timeline is however sufficient for root cause identification.