Masatoshi Takeshita

Ion-implanted and permalloy hybrid magnetic bubble memory devices

Hybrid bubble memory devices have been proposed and operated with the memory density of 4 Mbit/cm2. In the hybrid bubble memory devices, minor loops are composed of ion-implanted tracks with 4-µm period, and major lines and functional parts including block-replicate and swap gates are composed of Permalloy tracks with a longer period of 12 µm. Passive junctions between ion-implanted and Permalloy tracks have been developed, introducing the tapered ion-implantation technique. Improving the characteristics of the functional parts composed of Permalloy tracks, the hybrid bubble memory devices with block-replicate and swap gates have been operated, and the feasibility of the devices has been confirmed. In addition, the possibility of higher memory density has been shown.

Scanning Lorentz electron microscope with high resolution and observation of bit profiles recorded on sputtered longitudinal media (invited)

A transmission electron microscope operating with a cold field emission source has been modified to facilitate differential phase contrast mapping and applied to the observation of microscopic magnetic features appearing in recorded longitudinal media. After describing the design and performance of the scanning Lorentz electron microscope, as we call it, results on the observation of bit patterns delineated on Co‐based sputtered longitudinal media are presented. Relations of observed bit profiles to macroscopic magnetic properties of media and to device performance are discussed. Then, magnetization fluctuation on a scale of magnetic crystallites constituting the medium is examined. Also given is an account of a stray field effect inherent in hard magnetic materials.

A new junction design for ion-implanted and permalloy hybrid bubble memory devices

A new junction for the swap-gate side using the corner-Permalloy pattern in hybrid bubble memory devices has been designed and characterized. The design is based on the corner-type junction for the replicate-gate side and the conventional swap gate. The junction where bubbles propagate from the corner-Permalloy pattern or the transfer-in Permalloy pattern to ion-implanted tracks is composed of the ion-implanted cusp and three Permalloy-pattern tips. The junction bias field margin is greater than 10% for the rotating field range of 50 to 60 Oe and the temperature range of 20 to 65°C. The characteristics improvement is realized by the enlarged Permalloy patterns with large curvature.

Operating Bias Field Adjustment of Bubble Propagation Tracks on Ion-Implanted Permalloy Hybrid Type Magnetic Bubble Memory Devices

Reductions in cell size of ion-implanted Permalloy hybrid magnetic bubble memory devices give rise to large differences in operating bias field regions of ion-implanted and Permalloy propagation tracks. Attempting to utilize the dependence of the operating bias field on the thickness of the bubble garnet film, the authors ion-milled films to reduce their thicknesses, thereby lowering the bubble collapse field (Ho). The ion milling was found not to change the film coercivity. In this way, by shifting the permalloy track section field margin downward by 10 Oe, the bias field regions were matched, for a larger overall (common) bias field margin.

A new junction design on a Permalloy corner pattern for ion-implanted and Permalloy hybrid bubble memory devices

A junction has been developed for hybrid bubble memory devices using ion-implanted tracks for high density data storage and Permalloy tracks for write and read functions. An 18- mu m diameter Permalloy corner pattern is used. Both the tapered ion-implanted edges and the operating bias field adjustment boundary at the junctions are located under the Permalloy corner pattern edges. Improved junction properties and analysis by visual inspection are reported. The bubble potentials and the phase of the rotating field, when a bubble reaches the junction boundary, were compared for the conventional and the corner-type junctions. Replicate gate performance for the corner-type junction was investigated. The replicate phase margin was greatly improved for the enlarged Permalloy corner pattern. The temperature dependences of the junction performance were measured between 0 and 80 degrees C. In this temperature range, the margins of the junctions were improved, making them suitable for hybrid bubble memory devices. >

A new dual gate design for low current pulse operation in 16 Mb ion-implanted bubble memory devices

A design for a dual gate which has both pseudoswap and block-replicate functions for 16-Mb ion-implanted bubble memory devices has been proposed and shown by Sato et al. (1987) to reduce the operation current-pulse amplitude. The dual gate is composed of a pair of hair-pin conductor patterns in two layers and ion-implanted tracks for the major line and the minor loop corner. The current pulses are applied through the hair-pin conductor patterns to stretch, cut, or annihilate bubbles for the operation of the dual gate. The functions of the dual gate were realized with low current pulses of less than 150 mA using 0.8- mu m-diameter bubbles. It is therefore confirmed that the dual gate with low-current operation makes the 16-Mb ion-implanted bubble memory devices more practical. >

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.

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

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 de...