NEW METHODS FOR MEASURING MECHANICAL PROPERTIES OF THIN FILMS IN MICROMACHINING - BEAM PULL-IN VOLTAGE (V-PI) METHOD AND LONG BEAM DEFLECTION (LBD) METHOD

摘要

New stress-measurement methods for determining both tensile and compressive stress and Young's modulus in surface micromachining are presented. The investigation is concentrated on the development of two techniques: (1) beam pull-in voltage (V-PI) and (2) long beam deflection (LBD). The V-PI method is based on the pulling down of the upper electrode (beam) when the voltage between two electrodes exceeds a critical level. Both tensile and compressive stress and Young's modulus of a thin film can be derived using this method. the LBD method, on the other hand, converts the axial strain in the beam into a transverse deflection w(x) after the structure is released to be free standing; this deflection is large enough to be measured easily. These techniques have been analysed and tested experimentally. A comparison with other known stress-measurement techniques shows good agreement using polysilicon films. Both techniques have been shown to be quite promising for simple and accurate on-chip thin-film stress measurements. [References: 8]