NDRO plated wire preparation, stabilization, and aging

The literature describes plated wire suitable for nondestructive read-out (NDRO) memory operation, prepared from different NiFe electrolytes and process sequences. The NiFe films may be grouped into three categories based on the differences in their Ni-Fe composition fluctuation. In this paper, two types of NiFe electrolytes are studied. The development of NDRO characteristics is shown to require different processing for each electrolyte because of the differences in electrochemical behavior of the electrolytes and the metallurgical structures produced. The stabilization and aging of these films also depend on processing. The maximum temperature used for stabilization depends on the thiourea concentration in the NiFe bath and is independent of the nature of the substrate and the film thickness. Above this maximum temperature, changes in properties depend on the composition gradient in the film and on the differential thermal expansion between substrate and film. Magnetostriction changes during stabilization are observed and explained by interdiffusion with the substrate or homogenization of the film. These changes also reflect the different composition gradients of the films. Aging of wires decreases with decreasing concentration of thiourea; greater stability is shown to be most likely due to the large grain size and low impurity concentration of the NiFe films. Preliminary evidence from films made with saccharin containing electrolytes suggests that similar effects are present.