George E. Keefe

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.

Bubble to T-I bar coupling in amorphous film small bubble devices

In GdCoMo amorphous film bubble devices the drive field required for device operation has been found to be linearly dependent on the saturation magnetization of the bubble material over the range from 350 to 1200G. The devices studied were 8000 bit storage chips employing electron-beam-fabricated T-bars, Y-bars, and chevrons of 1μm linewidth. The bubble domain diameter and film thickness were approximately 2μm in all devices. The linear increase in drive field with 4πM s is found to be related with the energy required to move a bubble from one permalloy pattern to another across a gap. On the other hand, the field required to overcome coercivity in the movement of a bubble without leaving a single permalloy T-bar is found to be independent of variations in 4πM s of the bubble material.

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.

High-resolution surface charge measurements on an organic photoconductor

A technique for making direct, quantitative measurements of surface charge distributions on photoconductors has been developed. The spatial resolution is better than 10 μm and the measurements take place under conditions closely approximating those in printers or copiers. Measurements of edge broadening in layered photoconductor arising from space‐charge effects during image formation are presented. Edge broadening due to surface conduction has also been observed and data linking this to contamination of the surface by the charging corona is shown.

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)