Magnetic bubble played an important role in the field of “Magnetics.” This technology was born from the combination of magnetic films with perpendicular magnetization and control of domain propagation. Bobeck presented the first paper in INTERMAG con ference in 1968, and now above 50 papers on the magnetic bubble are presented in INTERMAG con ference every year. In conventional magnetic bubble devices, permalloy patterns, such as T bars, chevrons and half-discs, are used and contiguous disc devices using ion implanta tion are developing in bubble devices with below 1 μm diameters. Bubble lattice devices and current access devices, such as a dual conductor system, are also hopeful. Magnetic bubbles are higher bit density memory compared with semiconductor memory, but their cost is a little expensive. Efforts must be done in the future in cost reduction and improvement in switching speed.
Magnetic bubble memory technology has reached a level of maturity where it is appropriate, in the opinion of many of those working in this area, to give serious attention to a some new, second-generation version of the technology. The new version of most widespread interest at present is the one that uses ion-implanted patterns, as opposed to the conventional permalloy patterns, to propagate bubbles. This review is intended to assist with the assessment of the ion-implanted bubble technology.
The effects of implantation dose and annealing on the magnetic and crystalline properties of ion im planted layers in bubble garnet films have been investigated. Ion implantation causes the lattice deformation resulting in changes in anisotropy field and saturation magnetization. Magnetic properties of the H ion im planted layers were quite different from those of He and Ne ions. The implantation induced anisotropy fields of the He and Ne ion implanted layers were pro portional to Δd/d up to a saturation point of about 1%; however, that of the H ion implanted layer continued to increase after Δd/d passed 1%. The pro perties of the “non-magnetic layer”, formed in the implanted layer with a higher implantation dose, were also discussed.
Magnetic bubble memory chip capacity has in creased rapidly and a 1 Mb chip is now available. As chip capacity increases, average access time increases, because bubble memory is originally a sequential access memory. In order to improve the low access time, variouskinds of chip organization have been devised and developed, such as M/m loop organization, 2M line-m loop organization with block replicator and bidirec tionally propagating fast access chip. A new chip organization, called on-chip-cache or ganization, was developed, which has 1/17 ti 1 /61 higher access time than that of a conventional organi zation. Chip design, data control method and organi zation effectiveness are shown, together with a new kind of housekeeper. Finally, the organization trend for a large capacity chip, larger than 1 Mb, will be discussed.
The magnetic bubble memory has advantages in regard to nonvolatility and high reliability originating from its no moving parts structure. The bubble me mory has been applied so far in a defined field such as data terminal, voice announcement system and elec tronic switching system, where these advantages are essential. Recently, bubble memory boards have been placed on the market aiming at extension to the data processing field. Subjects for a future effort are further improvement in chip integration and significant in crease in market size, because the bubble memory is rather more expensive than large scale MOS RAM and floppy disk. Device standardization and LSI support circuits would be additionally required for market improvement.