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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We report electro-mechanical coupled analysis using compact models and macromodels. Mechanical and electro-mechanical compact models are inserted directly to a circuit simulator. In addition, macromodels for MEMS devices are extracted using Lagrangian-based energy method and the results of finite element (FE) or boundary element (BE) simulations. These models are verified by comparing the results of circuit simulations with those of experiments or FE/BE coupled simulations.

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In this paper, we propose a novel method to simulate the behavior of the energy harvester based on the permanent electret by using mechano-electrical equivalent circuits on an electrical circuit simulator. The electric field distributions made by the electret trapped in the electrical insulator are considered to build the electrostatic force by using the principle of virtual work. Electrostatically induced charge on the electrodes is also included in the model to handle the mechano-electric coupling between the electret device and the peripheral circuits. The developed equivalent circuit is implemented on the circuit simulator, and crosschecked against the experimental results in terms of the built-in electret potential. The behavior as an energy harvester is also studied to numerically present the output power as a function of the load resistance.

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We used microelectromechanical system techniques to fabricate a miniature ascorbic acid fuel cell (AAFC) equipped with a microchannel for the circulation of ascorbic acid solution (AAS). The fuel cell was fabricated on a flexible polyimide substrate, and a porous carbon-coated aluminum (Al) anode with the dimensions of 2.8×1 mm² and a porous carbon-coated Al cathode with the dimension of 2.8×10 mm² were fabricated using photolithography and screen-printing techniques. The porous carbon was deposited by screen-printing carbon-black ink onto the Al electrode surfaces in order to increase the effective electrode surface areas and to absorb more enzymes (bilirubin oxidase) on the cathode surface. No enzyme was deposited on the carbon coated anode surface. The microchannel with a dimension of 3×11×0.2 mm³ was fabricated using a hot-embossing technique. The maximum power of 0.60 µW at 0.58 V, with a corresponding power density of 1.96 µW/cm², was realized by introducing a 200 mM concentrated AA solution at the flow rate of 30 ml/min at room temperature. No degradation of the anode and cathode was observed up to the radius of curvature of 7.5 mm, which suggests the flexibility of the AAFC.

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