In bubble devices, the capacity per chip and chip yield are limited by the photolithographic resolution attainable. Recent work on gap tolerant structures attempts to address this problem. It is suggested, however, that to significantly increase this limit it is necessary to control a number of bubbles per geometric feature. We have initiated research into multilayered self-structured bubble memories which is based on this idea. Multilayered self-structured bubble memories have two or more coupled magnetic garnet layers grown on a common substrate. One layer, referred to as the data layer, supports bubbles encoded with data. One or more garnet layers, carrier layers, contain arrays of stripes or bubbles and determine the position of the bubbles in the data layer. Propagation of the data is accomplished by moving the domain arrays in the carrier layers. A study of several device configurations was accomplished and devices using a stripe domain carrier layer were selected for experimental work. Multilayer structures were grown having two magnetic layers with and without an epitaxial GGG spacer. Thickness, composition, and Q were varied from sample to sample. Propagation has been demonstrated using field access and current access devices moving the stripe domain ends. The magnetic coupling between the carrier stripe domain and the data bubbles was investigated and propagation of bubbles attached to the carrier stripe demonstrated. Chevrons were found to be more effective than semidisks, contiguous disks, or angelfish. Current access devices using a two-level two-phase stripline were found to be capable of generating and propagating stripes. A single-layer two-phase serpentine array requiring a single evaporation was also successful. These results indicate the potential of multilayer structures for high density high capacity bubble memories.
