THIN GOLD FILM STRAIN-GAUGES

Gold thin films, of thickness 30, 60, 100, and 300 angstrom were studi ed for use as miniature strain gauges. The thin metal films were therm ally evaporated onto silicon dioxide coated silicon wafers and pattern ed into strain gauges with dimensions of 100 mum x 70 mum and annealed at a maximum temperature of 400-degrees-C. The silicon substrate was cut into cantilever beams to calibrate the strain gauges by loading th e 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 t he impedance was typically 1 MOMEGA at 5 kHz and the gauge factor ([DE LTA\Z\/\Z\]/epsilon) was 24-48 at small strain (epsilon < 2.8 X 10(-6) ). The gauge factor was independent of frequency but decreased at larg er strains. The 300 angstrom thick films were typically 110OMEGA with a gauge factor of 2.6. The conduction process for the island-like film was modeled with activated tunneling. The sensitivity [DELTA\Z\/\Z\]/ epsilon versus strain response model included a contribution from the strain energy in the activated tunneling.