Improvement of permalloy propagation pattern for ion implanted-permalloy hybrid bubble memory device

A new modified asymmetric chevron (AC) permalloy propagation pattern with an 1.0µm gap has been designed for 0.92µm bubble propagation in an ion implanted-permalloy hybrid bubble memory. Bias field margin remarkably depended on the tip shapes of the legs of the AC patterns, according to the results of computer simulations and experiments using a 4 Mbit permalloy device. The shape rounding at the tips of the legs through the patterning process caused the effective gap distance between the legs broader, and affected bubble propagation across the gap severely. The modified new pattern employed a triangular tip at the leg to compensate the tip rounding and to reduce the effective gap distance. The new leg design has been applied to the hybrid device after confirming the remarkable improvement of bias margin in the 4 Mbit permalloy device. The new 14µm period permalloy pattern with an 1.0µm gap had almost twice bias margin for 0.92µm bubble propagation compared with that of conventional one. Also the new pattern could reduce the effective gap distance, by about 0.25µm. A 16 Mbit hybrid device was designed using this new leg pattern.