Nondestructive readout in plated wires

The nondestructive readout (NDRO) capability of 2.2- mil diameter wires has been examined for Permalloy films 700- 4000 Å thick. The substrates were prepared by deposition of Cu and Au to produce a number of different combinations of grain sizes and metal exposed on the surface. The Permalloy was deposited onto these substrates from a sulfate bath containing various concentrations of thiourea. The results show that the substrate parameters controlling the NDRO quality of plated wires are roughness, grain size, and metal exposed. A combination of Au islands on rough Cu greatly enhances all NDRO characteristics. With decreasing Permalloy thickness, the NDRO characteristics on an optimum substrate become poorer. With decreasing concentrations of thiourea in the Permalloy deposition bath the properties improve. These results are discussed in terms of a phenomenological model based on composition fluctuations in the Permalloy which result in local high-anisotropy regions. The distribution of anisotropy is controlled by the composition fluctuation and stress, while the coupling between regions is controlled by the grain size. These high-anisotropy regions, which are exchanged coupled to the remainder of the film, retain the original information and provide the restoring torque needed for NDRO performance.