Yeong Show Lin

Magnetoresistive Detector for Bubble Domains

This paper describes a simple Permalloy magnetoresistive readout transducer for detecting magnetic bubble domains. The advantages over inductive detection are a large increase in signal and an independence of bubble velocity. The advantages over Hall effect detection are simpler fabrication and higher efficiency. The detector is a strip of thin Permalloy film with two contacts, both of which can be deposited onto the same overlay used for bubble propagation. As an example, a 250 A×38 μ× 138‐μ device (52 Ω) was used with a measuring current of 7 mA to give a 2.3‐mV signal when detecting 138‐μ diameter bubbles in TmFeO3. The response was constant up to the maximum data rate allowed by the bubble domain, in this case, 106 bits/sec in DyFeO3. The detector itself can switch in less than 10−8 sec. It can be used when conducting strip lines are used for bubble propagation, and also when a rotating field and Permalloy overlay are used. Optimum device placement and shape, as well as ultimate limitations, are discu...

Self-aligned contiguous-disk chip using 1µm bubbles and charged-wall functions

A fully-operational, contiguous-disk bubble chip is described which employs a self-aligned circuit and simplified fabrication. Only one mask is required to define the propagation structures and all of the current control functions. This not only relaxes the demands on photolithography and reduces the number of process steps, but it also provides for more effective implementation of all device functions. Major-minor loop storage arrays with a 5μm period and 1μm bubbles have been fabricated by conventional photolithographic techniques. Operation at 150 kilohertz has been achieved error-free for 105read-write operations.

Manipulation of 1‐μm bubbles with coarse (≳4 μm) overlay patterns

This paper reports on the propagation and transfer of 1‐μm bubbles in ion‐implanted contiguous‐disk devices, made by conventional photolithographic techniques. Bubble‐propagation circuits are made of undulating patterns masked from implantation on a low‐Q garnet film, which is grown on top of and exchange coupled with a medium‐Q garnet film which supports the small bubbles. A double‐garnet composite combines the good features of a medium‐anisotropy storage layer to stabilize bubbles and, more importantly, of a small‐anisotropy driving layer to ensure the creation of a planar magnetization layer by ion implantation. A fundamentally different propagation mechanism employing the charged walls around the implanted pattern edges is explained. The value of the charged walls is that they lend themselves to coarse‐featured devices. Furthermore, they can be substantially lengthened to bridge a large gap between two propagation circuits to assist bubble transfer across that gap. We describe a switching gate employi...

Bubble domain propagation mechanisms in ion‐implanted structures

Experiments on disk and hole patterns in permalloy and in ion‐implanted garnet layers1..2 lead to the conclusion that the bubble domain propagation mechanism in the two structures is different. A ’’charged‐wall’’ model explains the ion‐implanted structure, and a single‐domain model relates the minimum propagation field to the garnet’s cubic anisotropy energy, in good agreement with experiment.

Orientation dependence of propagation margin of 1‐μm bubble contiguous‐disk devices—Clues and cures

The operating margins for bubble propagation along ion‐implanted contiguous‐disk devices are found to depend upon the orientation of the propagation track with respect to the tridirectional crystalline symmetry of the implanted garnet layer. Continuous disk propagation structures provide bubble tracks on each side of the structure. Depending upon orientation both tracks may have equally good propagation margin, or one track may be characterized as super while the other is bad. Studies of charged wall configurations using Ferrofluid colloid show distinct differences in wall behavior associated with the good, bad and super tracks. Annealing and removal of the implantation‐protected Au patterns tend to improve, but not cure, the bad tracks. One solution is to orient the orthogonal major‐minor loop tracks at 15° to an easy stripout direction so that all tracks propagate acceptably well; however, superior performance can be obtained by a parallelogram array with all tracks parallel to an easy stripout direction.

Critical curves for determining magnetization directions in implanted garnet films

Critical curves have been calculated for the graphical determination of the magnetization direction as function of applied magnetic field in ion‐implanted garnet films having cubic anisotropy. Up to three stable magnetization directions may exist when the applied field is inside the critical curves. This leads to the formation of charged walls. The hard magnetization directions are found to be favorable directions for charged walls and the easy magnetization directions are unfavorable. The complex domain‐wall patterns revealed by Ferrofluid techniques in 1‐μm magnetic bubble devices are explained by using the calculated critical curve. Futhermore, critical curves for several different symmetries have also calculated to correspond to different crystallographic orientations and garnet material parameters.

Micro‐magnetic structures of planar charged walls

The energy structure and internal magnetic field distributions for the cross section of a planar charged wall [1] have been calculated by direct numerical integration of the Landau‐Lifshitz‐Gilbert equation with minimal physical approximations [2]. Head‐to‐head (and tail‐to‐tail) charged wall structures have been computed for a wide range of material parameters. Results indicate that the charged wall structures depend on a non‐dimensional film thickness D normalized by δo=π√ (A/K) which is the Neel or Bloch wall width for thin or thick film respectively. For thin films, the charged walls have features of the Neel wall in terms of wall width and energy. For thick films, the charged walls have complex structures with Neel wall features at the center, and Bloch wall features (Bloch spin) near the surfaces of the film. The Bloch spin increases with the film thickness D and is nearly independent of the value of Q. The charged wall width is equal to the Neel wall width δo for large Q and small D. The charged wa...

Analytical model for bubble propagation

A simple model for bubble domain propagation in a field‐access device is obtained from a new analytical approach which, in contrast to previous treatments, concentrates on the energy of the bubble rather than of the overlay, and emphasizes flux flow rather than field distributions. This leads to a simple magnetic‐circuit model for the bubble interacting with an overlay, and to analytical expressions for the trapping potential and effective drive field of permeable overlay features. These expressions are then applied to predicting the quasistatic operating margin (region of operation in the bias field‐drive field plane) of a T+I bar device, the inputs being the device geometry and the bubble material parameters. Comparison with experimental results for a garnet device with 5 μm dia. bubbles shows remarkably good agreement.

Bubble domains in double garnet films

The properties of bubble domain lattices in magnetostatically coupled double garnet films are investigated. The calculated static properties of bubble lattices in both single and double garnet films are compared with the results of experiments on three double‐film composites. The differences in behavior between the three composite structures, chosen to exhibit varying degrees of magnetostatic coupling, are explained quantitatively in terms of the interaction fields between bubble domains in the two magnetic films. The dependence of bubble diameter on the applied bias field has been investigated experimentally and agreement with theory is good. Stable bias field ranges for bubble lattices are also examined. Effects such as the ordering of double‐bubble lattices, changes in bubble size upon coupling, and experimental observation of bubble repulsion and attraction effects are explained qualitatively. Some results on novel stacking arrangements of overlying bubble lattices and the dependence of bubble spacing...

Abstract: Nucleation of 1‐μm bubbles via charged walls

This paper describes a novel bubble nucleator utilizing charged walls to provide a portion of the nucleation field and substantially reduce the nucleation current level. Compared to nucleators without charged wall assistance, the reduction in current level attributable to the charged wall is approximately 30–40%. (AIP)