Electrical breakdown across micron scale gaps in MEMS structures

Abstract

Large voltage differences between closely spaced MEMS structures can cause electrical breakdown and destruction of devices ^1-2. In this study, a variety of planar thin film electrode configurations were tested to characterize breakdown response. All devices were fabricated using standard surface micromachining methods and materials, therefore our test results provide guidelines directly applicable to thin film structures used in MEMS devices. We observed that planar polysilicon structures exhibit breakdown responses similar to published results for larger metal electrode configurations ^3-6. Our tests were performed in air at atmospheric pressure, with air gaps ranging from 0.5 μm to 10 μm. Our results show a sharp rise in breakdown level following increases in gap width up to about 3 μm, a plateau region between 3 μm and 7 μm, and breakdown in gaps over 7 μm following the Paschen curve. This profile indicates an avalanche breakdown process in large gaps, with a transition region to small gaps in which electrode vaporization due to field emission current is the dominant breakdown process. This study also provides information on using multiple-gap configurations, with electrically floating regions located near the energized electrodes, and the added benefit this method may provide for switching high voltage with MEMS devices. In multiple-gap configurations, we noted a transition between direct tip to tip breakdown across electrode gaps of 40 μm, and a preferential breakdown path through the electrically floating contact head region for electrode gaps over 100 μm.