High-Strength Electroplated Au-Cu Alloys as Micro-Components in MEMS Devices

Au-Cu alloy electroplating is a promising method for fabrication of micro-components used in MEMS devices. Micro-mechanical properties of Au-Cu alloy films fabricated by galvanostatic electroplating are reported in this study. Influences of the current density on surface morphology, crystalline structure, Cu content, and micro-mechanical properties were investigated. An optimum current density at 6 mA/cm2 was attained for the effects of surface smoothening and grain refinement as the current density was applied in the range of 2-9 mA/cm2. Micro-pillars having dimensions of 10 × 10 × 20 μm3 were fabricated from the electroplated Au-Cu alloy films by focus ion beam and used in the uniaxial micro-compression tests. The highest yield stress of 1.15 GPa was achieved from the film electroplated at 6 mA/cm2, which the grain size was about 5.3 nm with Cu content of 12.3 wt%. The high yield stress was a synergistic effect of the grain boundary strengthening mechanism with the solid solution strengthening mechanism.