Fabrication process for ion-implanted and Permalloy hybrid magnetic bubble memory devices

A fabrication process for ion-implanted and Permalloy hybrid bubble memory devices has been developed. The mask patterns of polyimide (PIQ) for ion-implanted tracks are fabricated using a tri-level resist process where the top imaging resists are delineated by deep UV contact printing. The minimum feature of the PIQ pattern is 0.75 μm and can be controlled precisely. The sidewalls of PIQ patterns are smooth and vertical. At the junctions between ion-implanted and Permalloy tracks, tapered resist patterns are used as masks for implantation. Novolak-based resist is used and is reflowed thermally to obtain a tapered profile. Fabrication conditions, such as type of resist and baking temperature, were investigated to achieve good reproducibility. Tapered resist patterns are also used as masks for iron milling which reduces the thickness of garnet film in the area of the Permalloy tracks. This is necessary to adjust the operating bias field of Permalloy tracks to that of the ion-implanted tracks. A prototype of a 4-Mb memory device was fabricated, confirming the feasibility of the present process