Measurement of Mechanical Properties of Thin Film by Membrane Deflection Test

Micro-tensile properties of Au thin films were measured using a membrane deflection testing system. During the membrane deflection test, the deflection of the film was measured by an out-of-plane electronic speckle pattern interferometric (ESPI) system. From the measurement, the tensile loads and strains exerted on the membrane film during the deflection of the film could be determined. Quantitative analysis of the phase maps of the ESPI speckle patterns corresponding to the respective different deflection levels provided the deflection distribution along the testing section of the film. Test pieces were fabricated by electromachining process using 0.5 and 1. 0 μm thick Au films which were deposited on the silicon wafer by sputtering technique. Tensile properties, including elastic modulus, yield and tensile strength, were evaluated in the tensile stress-strain curve determined from the load-deflection relation. These properties were compared to those obtained from the micro-tensile tests. It was found that the yield and tensile strengths obtained from the deflection tests were lesser than those from the micro-tensile tests. Furthermore, the thickness effect, showing the increasing tendency of yield strength with decreasing thickness, was experimentally examined.