Spontaneous electromechanical oscillation is one of the major causes to shorten the lifetime of MEMS (micro-electro-mechanical systems) contact switches. In this study, we have experimentally visualized the spontaneous oscillation of a MEMS contact switch in the transmission electron microscope (TEM) chamber. We also have studied its behavior by crosschecking with a theoretical analysis based on a multi-physics model implemented on an electrical circuit simulator. Nanoscopic observation and analysis results suggested that a physical mechanism of the spontaneous oscillation is as follows: (i) Upon a voltage application to the actuator electrodes, the contact tips are mechanically brought into contact as an initial condition. (ii) When the voltage is reduced, the tips are retracted and a nanoscale gap is formed between the contact surfaces, where electrical charges are accumulated. (iii) The accumulated charges develop an electrostatic attractive force that pulls back the electrode surfaces into contact again, (iv) thereby instantly neutralizing the charges. (v) The surfaces of the equipotential lose the electrostatic attractive force, leading to the mechanical retraction of the surfaces. As the charges are repeatedly accumulated and dissipated, the electrostatic force is intermittently generated, leading to the cyclic sequence of pull-in, contact, and release that takes place at a fast rate of tens of kHz.
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