Reduction of cell size in hybrid bubble memory devices (abstract)

摘要

Hybrid bubble memory devices using ion‐implanted and Permalloy bubble propagation tracks have been proposed and developed. In this paper, the reduction of the cell size from 4 to 3 μm will be discussed. In the hybrid devices, the minor loops are composed of ion‐implanted tracks and the functions are composed of Permalloy tracks. To reduce the cell size, therefore, both of the tracks should be improved. For the 3‐μm‐period ion‐implanted tracks, the bubble diameter is reduced from 1 to 0.8 μm. According to the reduction of a bubble diameter, magnetostrictive anisotropy Δλ=λ100-λ111 is increased from 5 to 8×10-6 because the Sm content is increased to increase the anisotropy field Hk. The large Δλ affects the characteristics of inside and outside turns in the ion‐implanted tracks. To get a good margin for the turns, the anisotropy field change induced by ion implantation ΔHk should be larger than in 4‐μm‐period tracks. There is a new problem in 3‐μm‐period hybrid devices. In the hybrid devices, there is no deep ion implantation in the Permalloy track region, while there is a deep ion implantation in the ion‐implanted track region. The effective bubble height is, therefore, different in the ion‐implanted and Permalloy track region, and the bias field region where bubbles exist stable is different. In the typical 3‐μm‐period devices, the bias field region of the ion‐implanted tracks is 20–30 Oe lower than that of the Permalloy tracks. The operating bias field adjustment (OBA) is needed. We have checked some OBA methods and found that the thinning of the garnet film in the Permalloy track region is a good method. Thinning the garnet film partially, the operating bia-ns field can be adjusted easily and there is no harmful effect.