Stress, resistance, and phase transitions in NiCr(60 wt %) thin films

Abstract

The evolution in both stress and resistance has been investigated on sputtered NiCr(60 wt %) resistive films during annealing (temperature cycles to maximum 700 °C). Aiming at the correlation of stress, resistance, and microstructure, samples from measurements to various maximum temperatures were analyzed by x-ray diffraction and transmission electron microscopy including microanalysis. A series of metastable phases was found with increasing temperature: the as-deposited amorphous phase a, the supersaturated body-centered-cubic (bcc) solid solution αss(Cr) (400 °C), and the tetragonal σ phase (500 °C). This was followed by the equilibrium two-phase alloy bcc α(Cr) plus face-centered-cubic γ(Ni) (600 °C). The phase transitions, characterized by differential scanning calorimetry, were found to be exothermic. The transition a→αss(Cr) results in a distinct tensile-stress component due to material densification. The resistivity is sharply decreasing and the temperature coefficient of resistance is changing from negative to positive values during the a→αss(Cr) transition.