Micromechanical Characterization of AlCu Films for MEMS Using Instrumented Indentation Method

The micromechanical properties (i.e., hardness, elastic modulus, and stress-strain curve) of AlCu films were determined by an instrumented indentation test in this work. For three AlCu films with different thicknesses (i.e., 1 µm, 1.5 µm, and 2 µm), the same critical ratio (h_max/t) of 0.15 and relative indentation depth range of 0.15-0.5 existed, within which the elastic modulus (i.e., 59 GPa) and nanoindentation hardness (i.e., 0.75 GPa, 0.64 GPa and 0.63 GPa for 1 µm, 1.5 µm and 2 µm films) without pile-up and substrate influence can be determined. The yield strength (i.e., 0.754 GPa, 0.549 GPa and 0.471 GPa for 1 µm, 1.5 µm and 2 µm films) and hardening exponent (i.e., 0.073, 0.131 and 0.150 for 1 µm, 1.5 µm and 2 µm films) of Al-(4 wt.%)Cu films for MEMS were successfully reported for the first time using a nanoindentation reverse method. In dimensional analysis, the ideal representative strain ε_r was determined to be 0.038. The errors of residual depth h_r between the simulations and the nanoindentation experiments was less than 5% when the stress-strain curve obtained by the nanoindentation reverse method was used for simulation.