Relaxation and recovery of extrinsic stress in sputtered titanium–nickel thin films on (100)-Si

The relaxation and recovery of stresses by displacive phase transformations in near-equiatomic titanium-nickel thin films sputtered onto (100)-silicon have been studied using the wafer curvature method, X-ray diffraction and in-situ resistivity measurements in hard vacuum. Large extrinsic tensile stresses were relaxed and recovered by displacive transformations during cyclic thermal excursions between Mf and Af. More than 0.6 GPa could be relaxed by the R-phase transformation alone. Two-step B2→R→B19′ transformations were often observed on cooling, but for Ti-rich compositions, recovery of extrinsic tensile stresses proceeded via a one-step B19′→B2 transformation, at stress-rates (dσ/dT) as high as 60 MPa K−1. Stress-rates, and details of hysteretic behavior, are discussed in terms the distribution of stress in multiphase intermediate (mid-transformation) microstructures formed by alternative development modes. An approach is suggested for the control of hysteresis through the use of functional composition gradients.