Piezoresistance in Evaporated Nickel Films

Abstract

The electrical resistance of a metal can be altered by the application of an elastic stress. In Ni this effect is generally negative; namely a tensile stress causes a decrease in resistance. The longitudinal gage coefficient γ (defined as the relative change in resistance divided by the relative change in specimen length) is about −20. In evaporated Ni films, the observed γ depends on the sign and the magnitude of film stress. For large tensile stresses, γ at room temperature is small and positive. As the temperature is initially increased γ changes markedly because of the change in stress with temperature. The gage coefficient increases negatively and reaches a maximum of about −10 at about 100 °C, and finally becomes about +3 at temperatures just above the Curie temperature of Ni (360 °C). After annealing at temperatures of 380 °C, the film stress apparently anneals since, as the specimen cools, γ does not follow its initial heating curve. At room temperature after annealing γ=2.7.