Influence of Surface Force on Motion of An Electrostatic Microstructure

In an electrostatic microstructure with a movable electrode supported by a cantilever beam and counter electrodes, voltage dependency of displacement of the movable electrode is studied by taking surface force into consideration. The displacement change is analyzed theoretically with the energy model which determines the stable displacement state of the movable electrode from the minimum energy state of the total energy of elastic energy, electrostatic energy and adhesion energy between two surfaces. The relation between the surface force at contact parts of the movable electrode with the counter one and a hysteresis voltage of capacitance (between the both electrodes)-voltage characteristics (C-V characteristics) was investigated and a magnitude range of the surface force in which stiction of the movable electrode occurs is derived. In an experiment which simulated electrical contacts of the electrostatic microstructure with charged objects, the surface force increased with increase of the charge amount of the object. In measurements of C-V characteristics in positive and negative voltage regions, the C-V characteristics shifted to the positive voltage region and the shift was larger in a device with larger surface oxide layer of the movable electrode. This voltage shift is thought to be caused by a positive electrical charge remaining in the oxide layer.