Nano-dispersion strengthened gold films for MEMS electrical contacts.

摘要

Thin gold films were strengthened with a uniform dispersion of zirconia nanoparticles. The purpose of strengthening the films was to resist small-scale surface plastic deformation of microswitches' contacts and transmission line, which can lead stiction, a microswitch failure mechanism. Deposited by reactive ion sputtering of an Au-Zr target, the films were comprised of a columnar gold matrix with a diameter of 50 nm and a nano-dispersion of zirconia particles 1--3 nm in diameter. These films were studies in the as-sputtered and annealed (500°C) states. For reference, assputtered and annealed pure gold films sputtered under similar conditions were also studied. The microstructures of the films were determined using TEM and AFM. The annealed nano-composite film showed no sign of coarsening of either the columnar gold grains or the zirconia nanoparticles. Though, the columnar grains of the pure gold film grew substantially upon annealing (100 nm to ∼ 1 microm).;The incorporation of the nanoparticles was shown to have an improvement in resistance to plasticity and creep deformation. Nanoindentation results have shown that the nano-composite films are twice as hard as the pure gold films. The increase in hardness was attributed to the nanoparticles as well as a smaller gold grain size, a higher point defect density, and a higher growth-twin density in the nano-composite. Hemispherical indentation experiments have shown that the surface topology of the nano-composite is better at resisting time-independent and timedependent plastic deformation indicating that the nano-composite films are more creep resistant than the pure gold films. The resistivity of the nanocomposite film was measured to be 1.5 times the resistivity of the gold film, and the microstructural features attributed to increasing the resistivity of the nanocomposite are the same as those attributed to increasing its hardness.;Microswitches with contacts and transmission lines comprised of nano-composite and gold were fabricated to investigate the materials resistance to contact stiction and the switches' resistance. Stiction was not seen in the nano-composite switch even at twice the load that stiction occurred in the gold switch. The resistance of the nano-composite switch was 3.7 times the resistance of the gold switch.