Yu-Ssu Chen

Magnetic bubble memory chip design

The choice and organization of bubble-circuit functions in the design of a magnetic bubble mass memory chip are discussed with emphasis on factors such as circuit function compatibility and performance, circuit density, and processing simplicity. A specific major-minor organized chip design is described which uses rotating field driven propagation,

Field nucleation of magnetic bubbles

-sign transfer gates, all T-bar minor loops, a nucleate generator with chevron merging port, a chevron based replicator/ annihilator and a chevron guard rail expander detector. The overall operating characteristics of chips having 20 510 bits of storage capacity have been measured and a bias field margin of 12 Oe is typically obtained with a 25 Oe, 100 kHz rotating field.

The effects of spacing between garnet film and Permalloy overlay circuit in magnetic bubble devices

Nucleation of magnetic bubbles in the fields of a pulsed hairpin conductor is investigated experimentally and theoretically. It might be supposed that the current required for nucleation produces a vertical field in excess of the anisotropy field throughout the bubble film. We have found evidence that the current required is reduced because a) intense fields are required only at a surface of the bubble film, b) the horizontal field contributes in the initial surface reversal, and c) the surface of proton-implanted films is more easily reversed than the rest of the film. Field nucleation has been used to seed bubble generators and to generate bubbles controllably at 100 kHz.

Device Design and System Organization for a Decoder Accessed Magnetic Bubble Memory Chip

An experimental test set for magnetic bubble devices has been constructed in which the spacing between the garnet film and the Permalloy overlay is variable. The experimental uncertainty in spacing is approximately \pm.15\mu m, and spacings as small as .5\mu m have been attained. Bias margin data are presented which were taken at 1 Hz on a 20 micron period chevron circuit as a function of spacing. The collapse and strip-out fields begin to be affected when the spacing is comparable to the garnet film thickness, increasing as the spacing decreases. At larger spacing the high-bias failure mode changes from collapse to uncorrelated bubble motion. A theoretical model which accounts for some aspects of the spacing dependence of the strip-out and collapse fields is described. This model approximates the circuit by a continuous Permalloy sheet. At the low spacing required for efficient use of the rotating field, the model indicates that ±10% nonuniformity in a 2 micron spacing over the device area results in a degradation of the bias field operating range by about 12%.

An experimental magnetic bubble time‐slot interchanger

We have examined the feasibility of taking advantage of the superior access speed of the decoder organization of magnetic bubble memory chips, while retaining the wide operating margins and high degree of data integrity that have been achieved for major/minor loop organized chips. A semicircular bubble replicator has been designed and characterized that can be placed at the corner of T‐Bar information storage loops. A novel decoding matrix, in which the half period wide control conductors simply retard the propagation of all bubbles other than the one selected, has been designed and operated. The bias field margins for both replication and decoding have been found to be substantially as wide as those for simple propagation. The difficulty in the initial design, that the output to be detected appears at different points depending on the selection address, is not a problem because of the incorporation of a multi‐input chevron expander detector. A solution was found to the problem of erasing old information ...

Characterization of magnetic bubble generators

One of the basic building blocks of a time‐division switching network is a time‐slot interchanger (TSI). This paper reports on the design and characterization of a small experimental magnetic bubble time slot interchanger (TSI) which handles 4 times slots per time‐frame with with 2 bits per time slot.Current ’’state‐of‐the‐art’’ technology for bubble memories is utilized. The bit period is 28.8 μm and the propagation rate is 100 kHz. The overall operating bias field margin range obtained fwith 25 Oe rotating field is 6 Oe. The limiting function is a passive AND/OR logic gate. A unidirectional transfer gate is used in the TSI to transfer routing bubbles into the storage loops. The operating bias margin for the transfer gate is nearly equal to that of loop propagation.

The propagation of magnetic bubbles on permalloy disks

Two types of magnetic bubble generators suitable for a field-access bubble memory have been tested at 1.00 kHz bit rate at in-plane rotating fields above 15 Oe. The bias field margins of the generators at 30 Oe rotating field are equal to or greater than those of loop propagation. Both designs are based on the principle of stretching and cutting seed bubbles circulating around a Permalloy disk. Functions of stretching, cutting and transferring in the generator sequence are accomplished either with Permalloy elements or pulsed current conductors. The operating conditions of the generators in terms of current pulse amplitudes, widths and phase angles are presented. Among the two designs, namely Permalloy-stretch and conductor-stretch generators, the latter has a wider phase-angle margin.

MAGNETIC BUBBLE PROPAGATE ARRANGEMENT

A magnetic bubble generator consisting of a Permalloy disk and a current conductor loop has been used recently in a mass memory design utilizing magnetic bubble technology. The bias field range in which the disk can hold the seed bubble is measured in this report as a function of of the rotating field frequency. Above a critical frequency f c , the bias field margins begin to decrease. The dependence of f c on disk size is obtained for disks with diameters from 16 μm up to 43 μm at rotating fields of 20 and 30 Oe. The separation between Permalloy disks and the garnet film is kept at 0.8 μm or 1.6 μm. Results show that at a fixed rotating field, a smaller disk is preferable at higher frequency for a magnetic bubble material with a given mobility. The critical frequency f c obtained is in good agreement with a theoretical calculation using the viscous damping model by Rossol et al. For frequencies below f c , the bias field margin on the disk is equal to that of the propagating channel and circuit failure due to the loss of the generator seed bubble can be eliminated.