Measurement of thermal expansion coefficient of poly-Si using microgauge sensors

Abstract

We present a micro electromechanical system (MEMS) structure to study the thermal expansion coefficient of polycrystalline silicon (poly-Si) thin film. Under conventional optically levered laser beam techniques, it is important to know some physical values, namely the thermal expansion coefficient of the substrate and E/1 - nu of the thin film, in order to measure the thermal expansion coefficient of the thin film. Also, an expensive optically levered laser beam system is needed. But in the microgauge method, other physical values are not needed and the thermal expansion coefficient of thin film could be observed only with an optical microscope and a current-voltage measurement system. The microgauge can be fabricated in situ along with active microsensors or actuators on the same chip for monitoring the thermal expansion coefficient of the thin film. A bias was applied across the microbridge anchors. Current-voltage characteristics and the displacement at the microgauge were measured at the same time when the microgauge was driven in vacuum chamber. After thermal analysis and mechanical analysis, the thermal expansion coefficient of poly-Si thin film was calculated. The experimental values for the thermal expansion coefficient of poly-Si thin film was 7.9 x 10(-6)/K with the standard deviation of 0.24 x 10(-6)/K. (C) 1999 Elsevier Science B.V. All rights reserved.