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

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 ss(Cr) (400°C), and the tetragonal phase (500°C). This was followed by the equilibrium two-phase alloy bcc (Cr) plus face-centered-cubic (Ni) (600°C). The phase transitions, characterized by differential scanning calorimetry, were found to be exothermic. The transition ss(Cr) results in a distinct tensile-stress component due to material densification. The resistivity is sharply decreasing and the temperature coefficient of re sistance is changing from negative to positive values during the ss(Cr) transition.