Thin gold film strain gauges

Gold thin films, of thickness 30, 60, 100, and 300 A were studied for use as miniature strain gauges. The thin metal films were thermally evaporated onto silicon dioxide coated silicon wafers and patterned into strain gauges with dimensions of 100 μmx70 μm and annealed at a maximum temperature of 400 °C. The silicon substrate was cut into cantilever beams to calibrate the strain gauges by loading the beams. The impedance, Z, was measured over a frequency range from 5 kHz to 1 MHz. For the 30,60, and 100 A thick films the magnitude of the impedance was typically 1 MQ at 5 kHz and the gauge factor ([A|Z|/|Z|]/e) was 24–48 at small strain (e2.8X 10-6). The gauge factor was independent of frequency but decreased at larger strains. The 300 A thick films were typically 110Ω with a gauge factor of 2.6. The conduction process for the island-like film was modeled with activated tunneling. The sensitivity [A|Z|/|Z|]/e versus strain response model included a contribution from the strain energy in the activated tunneling.