1-μm bubble permalloy "contiguous-disk" devices

Gapless bubble propagation circuits based on a complementary permalloy contiguous-disk structure present an interesting alternative to the ion-implanted bubble devices currently being developed. This new approach combines the attractive lithographic tolerances inherent in the ion-implanted structure with the better established permalloy fabrication techniques. Successful propagation of 1 μm diameter bubbles has been demonstrated over bias field margins greater than 10% in circuits with a cell size of 15 μm2. The stepped structure was formed using an SiO2 lift-off method. The minimum lithographic feature was 1 μm and the operating drive field was approximately 50 Oe. Device tolerance to processing variations in terms of the required spacer thicknesses is shown to be adequate.