Tracks for the guidance of magnetic bubbles propagating in the input and output lines of Vertical-Bloch-Line memory devices can be made in the form of ridges instead of in the traditional form of grooves. The ridge-type tracks offer advantages over the groove-type tracks, as explained below.
A track is formed on a substrate made of suitable magnetic material; namely, a garnet film. A gradient of the vertical magnetic field is associated with a step in the thickness of the film; the field increases as one proceeds from a location where the film is thinner to a location where it is thicker. Thus, in the case of a groove, the field increases as one crosses either wall of the groove from the inside to the outside. Because the stable position of a magnetic bubble lies at a local minimum of the field, a bubble that has been propagating along the groove remains confined in the groove.
The spatial variation of the field is, however, slightly more complex than is the spatial variation in thickness (see figure). The field increases slightly from the wall toward the middle of a groove. Thus, there are shallow local field minima along the sides of a groove. If the groove is wider than about 1.5 bubble diameters, then a bubble tends to move sometimes along one side, sometimes along the other side, moving back and forth in mostly random fashion as it propagates along the groove. If the groove is narrower than about 1.3 bubble diameters, a bubble remains centered in the groove but propagates more slowly than it would if the groove were wider. The customary groove width of 1.5 bubble diameters is a compromise that entails a little of both slowing down and meandering of bubbles.
A ridge-type track is formed by etching wide grooves on both sides of the track. Mirroring the situation in a groove, the magnetic field rises to maxima near the two side walls of the track, while at the middle of the track, the field falls to a local minimum that is isolated from the deeper minima of the adjacent grooves. The confinement gradient of a ridge is weaker than that of a groove, but still adequate for guidance. Unlike a groove track, a ridge track can be made wider than 1.3 bubble diameters without incurring meandering of bubbles; a ridge as wide as 2.5 bubble diameters can provide excellent guidance.
Another advantage of a ridge-type track over a groove-type track arises in connection with the need to expand a bubble into a stripe when it reaches the end of the track, in preparation for detection of the bubble by use of a magnetoresistive strip. In the case of a groove-type track, the bubble expander is a mesa with its top recessed slightly below the surrounding garnet surface. An electric current in a helper loop is needed to provide a momentary additional magnetic field to lift a bubble from the groove, over the potential barrier at the edge of the mesa, so that the bubble can then stripe out on top of the mesa.
In the case of a ridge-type track, the track can simply be terminated in a mesa-type expander of the same height as that of the ridge. There being no step discontinuity in height, there is no need for a helper loop to move the bubble out onto the expander.
This work was done by Udo Lieneweg of Caltech for NASA's Jet PropulsionLaboratory. In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
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Refer to NPO-20232
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Ridged tracks for guiding magnetic bubbles
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Overview
The document presents a technical support package on "Ridged Tracks for Guiding Magnetic Bubbles," developed by Udo Lieneweg at the Jet Propulsion Laboratory (JPL) under NASA. It focuses on a novel approach to improve the guidance of magnetic bubbles in memory devices, specifically in the context of magnetic bubble memory and vertical Bloch line (VBL) memory technologies.
Historically, magnetic bubbles were guided using groove-type tracks etched into garnet materials. However, this method had limitations, particularly when the track width was less than 1.3 bubble diameters, leading to slow movement of bubbles in a straight line. Conversely, wider tracks caused bubbles to oscillate randomly between the sides of the track, complicating their propagation. The document outlines how the new ridge-type track, created by etching two wide grooves on either side of the track, addresses these issues.
The ridge design allows for a wider track (2.5 bubble diameters), providing superior guidance by keeping bubbles separated from field minima, which enhances their stability during movement. This design eliminates the need for a "helper" metal loop that was previously required to transition bubbles from the track to the detection area, simplifying the overall structure. The ridge's height can be aligned with the expander, facilitating a seamless transition without additional complexity.
The document also discusses the technical aspects of the ridge-type track, including the magnetic field dynamics involved in bubble propagation. It highlights the advantages of this new design in terms of efficiency and reliability, making it a significant improvement over prior art. The ridge-type track not only enhances the guidance of magnetic bubbles but also contributes to the overall performance of magnetic memory systems.
In summary, the document details a significant advancement in magnetic bubble technology through the introduction of ridged tracks, which provide better guidance and stability for magnetic bubbles compared to traditional groove tracks. This innovation has the potential to improve the efficiency of data storage and retrieval in magnetic memory devices, marking a notable step forward in the field of microelectronics and memory technology.
