Strengthening gold thin films with zirconia nanoparticles for MEMS electrical contacts

Thin gold films can be strengthened by the incorporation, during reactive sputtering, of nanosized dispersions of monoclinic zirconia. Micron-thick films containing ∼2 vol.% zirconia particles having a particle size of 1–3 nm are found to have an indentation hardness of 3.8 GPa after annealing for 60 h at 500 °C in air. Sputtered gold films of the same thickness and annealed under the same conditions had a hardness of 2.3 GPa. The nanoparticles of zirconia resist coarsening with no change in diameter between deposition and after 60 h at 500 °C. They also suppress grain growth of the gold grains. The electrical resistivity of the strengthened gold films was 4.5 μΩ cm, about 55% higher than gold films. The temperature coefficient of resistivity was unaffected.