Strain sensitive Pt–SiO2 nano-cermet thin films for high temperature pressure and force sensors

• Thin films of Pt–SiO2 nano-cermets are prepared by means of co-sputtering.
• The films are piezoresistive and respond to strain with a gauge factor of 18.
• Annealing steps at 600 °C (vacuum) and 300 °C (air) do not change the sensitivity.
• Pt–SiO2 films are useful for pressure and force sensors for high working temperatures.

The strain sensitivity, i.e. the resistivity change due to mechanical strain of thin composite nano-cermet films of Pt–SiO2 was investigated. We prepared films with a thickness of 400 nm by means of co-sputtering processes at substrate temperatures around 400 °C. The specimens respond to uniform strain (ɛ = 0.2‰) with gauge factors up to 18. These gauge factors remained high at least up to 250 °C in air and also after further annealing up to 600 °C in vacuum. Therefore we state these functional films might be suitable for high temperature pressure and force sensors. The films have a relatively high film resistivity of some MΩ/sq and exhibit temperature coefficients of resistance (TCR) in the range of −2000 ppm/K up to −600 ppm/K. X-ray diffraction revealed a single crystalline fcc platinum phase while transmission electron microscopy proved a typical granular structure of the films. Pt-clusters sized 5–10 nm are embedded in an amorphous insulating matrix of silica. The composition of such nano-cermet films displaying high gauge factors is approx. 40 at% Pt, 20 at% Si and 40 at% of O.