Electrostatic actuation of thin-film microelectromechanical structures

Microbridge and cantilever electrostatic actuators are fabricated using thin film technology and surface micromachining at low temperatures (less than or equal to100 degreesC) on glass substrates. Electrostatic actuation is accomplished by applying a voltage, combining a dc component to a low frequency ac component, between the microstructure and an underlying gate counterelectrode. The movement is optically detected by focusing a laser beam on the top of the structure and monitoring the deviation of the reflected light, which is proportional to the electrostatically induced deflection. The absolute value of the deflection is obtained using a calibrated piezoelectric actuator sample holder. The response of the structure is measured with a precision better than 5 A. The deflection of the microstructures is studied as a function of the magnitude of the electrostatic load, and of the type (bridge or cantilever) and geometrical dimensions of the structure. The mechanical movement is analyzed using an electromechanical model and mechanical properties, such as the microstructure boundary conditions and the materials' Young's modulus in the microstructures, are extracted. Nonlinear effects characteristic of electrostatic deflection are observed at high magnitude electrostatic loads. In addition, nonlinear effects due to mechanical stiffening of the microstructures are also observed near the pull-in voltage. (C) 2003 American Institute of Physics.