Microbridge tests: II. On buckled thin gold films

In the present work, we report a microbridge testing method for microbridge beams initially buckled by a residual compressive stress. A theoretical formula is derived in closed form with the consideration of substrate deformation. Measuring the profile of a buckled microbridge beam, one can evaluate Young's modulus and the residual compressive stress of the beam. Alternatively, Young's modulus and the residual stress can also be evaluated from the microbridge test under low loads, i.e., from the elastic load–deflection curve. Moreover, we introduce a microbridge testing approach to determine the yield strength of a ductile thin film. Experimentally, microbridge samples were fabricated with a 0.48 µm thick gold film deposited on a silicon wafer by electroplating. Young's modulus, the residual stress and the yield strength of the gold film were determined from the microbridge test to be 66.2 ± 2.9 GPa, −8.5 ± 1.0 MPa and 162.4 ± 5.9 MPa, respectively.