Electrostatic discharge/electrical overstress susceptibility in MEMS: a new failure mode

Electrostatic discharge (ESD) and electrical overstress (EOS) damage of Micro-Electrical-Mechanical Systems (MEMS) has been identified as a new failure mode. This failure mode has not been previously recognized or addressed primarily due to the mechanical nature and functionality of these systems, as well as the physical failure signature that resembles stiction. Because many MEMS devices function by electrostatic actuation, the possibility of these devices not only being susceptible to ESD or EOS damage but also having a high probability of suffering catastrophic failure doe to ESD or EOS is very real. Results from previous experiments have shown stationary comb fingers adhered to the ground plane on MEMS devices tested in shock, vibration, and benign environments [1,2]. Using Sandia polysilicon microengines, we have conducted tests to establish and explain the EDS/EOS failure mechanism of MEMS devices. These devices were electronically and optically inspected prior to and after ESD and EOS testing. This paper will address the issues surrounding MEMS susceptibility to ESD and EOS damage as well as describe the experimental method and results found from EDS and EOS testing. The tests were conducting using conventional IC failure analysis and reliability assessment characterization tools. In this paper we will also present a thermal model to accurately depict the heat exchange between an electrostatic comb finger and the ground plane during an ESD event.