Evaluation of Elastic Modulus and Yield Strength in Microelectromechanically Operated Materials Using Electrostatic Test Device

摘要

In microelectromechanical system(MEMS) such as sensors and actuators, thin films have been widely used as microstructural materials. As the mechanical structures used in microsystems are miniaturized, the use of macroinstruments for testing of mechanical properties limits the minimum scale of the test structure and poses difficulties in aligning and attaching it to the instruments. The electrostatically actuated test device was proposed to measure the micromechanical characteristics of micromaterials forming the microsystems. Then, the test device can be used to evaluate elastic modulus, yield strength and deflection of micromaterials. The designed test device consists of comb drives for loading and a suspending beam for testing. The device is fabricated by the surface micromachining processes and laterally driven by the electrostatic force. A methodology to evaluate elastic modulus and yield strength is proposed on the basis of the electrostatic comb test device and linear elastic mechanics. From the results, elastic modulus and yield strength are measured by analyzing the variations of load and displacement of the free standing beam in the test device. Finally, we can predict the driving characteristics and the mechanical reliability of Al layer for MEMS applications from the deflection curve.