Tunable piezoresistivity for sensors with antiferromagnetic pure Cr and Cr-rich alloy thin films: Cr–V, Cr–W, Cr–Mn

Sputter-deposited thin films of pure chromium and chromium-rich alloys with V, W, and Mn are evaluated in terms of electrical resistivity and piezoresistivity, as measured by the gauge factor, from room temperature to 470 °C. The alloying elements vanadium, tungsten, and manganese, are known to either stabilize or destabilize the spin-density wave antiferromagnetism found in Cr. In a concentration series and a substrate bias voltage series, the variation of resistivity, gauge factors (of up to 20), and their temperature coefficients is shown. High-temperature resistivity measurements indicate increased Néel transition temperatures that are related to a gauge factor maximum. Generally, the gauge factor increases toward the Néel temperature. The Cr 60Mn 40 film, however, has a small negative temperature coefficient of the gauge factor. This is a desired property in strain and pressure sensor films, as it allows for compensating the temperature coefficient of the elastic modulus of aluminum or steel transducers. An analysis of the resistance change through mechanical loading quantifies Néel temperature changes of up to 100 K per percent of strain that are likely the mechanism of the observed piezoresistivity. Overall, the Cr-rich alloy thin films represent a class of metallic piezoresistive films with properties that can be well adjusted to the sensor application by concentration and sputtering parameters.