Bubble memory

The following diagram, given as 2.4.4. on the next page, illustrates how these would look under polarized light (the Faraday effect) using crossed Nicol polarizers. (The black and white parts are domains of opposite poljuity). 

When a magnetic field is applied, with the field vector horizontal to the film, the domains collapse to form separated cylinders within the film, as shown. These appear to be bubbles when viewed from the top, hence the name. The bubbles then become mobile under the influence of a separate electric field and will move. Actually, the electric field causes the domain-wall to collapse by a spin-flip mechanism, while the cylinder volume is maintained by the magnetic field. 

Msgnetic Bubbles as Viewed from the Top of the Film in Polarized Light 

This causes the apparent movement of the wall. Bubbles densities as high as 10 per cm, and bubble velocities of up to 10 -10 cm./sec. have been reported. Obviously, bubble velocity depends upon E, the electric field strength, as well as the composition of the epitaxially grown film. The use of a vapor-phase-deposited metal grid upon the surface of the film serves to switch bubbles from site to site. The presence (1) or absence (0) of a bubble is detected by polarized light beams. Thus, information can be stored, and retrieved, on a chip in binary language. 

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Garnets are important gems, abrasives, microwave systems components, magnetic bubble memories, and laser hosts. For the latter, yttrium aluminum garnet is the most important. It also plays an important role in aircraft turbines where it forms a protective coating on the turbine blades. 

Figure 9.11 Magnetic bubble memory schematic domains of reversed polarity (bubbles) are induced in the thin ferromagnetic garnet film.

Data storage via magnetic bubble memories used thin films of ... 

Important is the use of light rare earth elonents for production of hard magnetic materials. Most prominent are alloys of samarium with cobalt in the atomic ratio 1 5 or 2 17. It may also be assumed that in further development of these materials on a larger scale that praseodymium, neodymium, lanthanum and also individual heavy rare ecu h elements will be used to achieve particular effects. Interesting is the development of magnetic bubble memories based on gadolinium-galliiimrgarnets. 

Smo.4Y2.6Gai 2Fe3 gOi2 Bubble memory devices... 

In 1990 there was strong interest in data storage devices which exploited trains of small bubbles injected into a garnet film the presence or absence of a bubble representing the binary-coded information. Bubble memories offered the advantage of non-volatility but are now commercially unimportant because of inadequate access speed. 

Gadolinium 64 Gd Electronic materials, high-temperature refractories, alloys, cryogenic refrigerant, thermal neutron absorber, superconductor, magnetic materials, bubble memory substrates... 

The non-volatile bubble memories used for data storage are based on the principle of formation of magnetic domains in thin films grown on a gadolinium gallium garnet crystal substrate. Molecular engineering creates the precise film compositions for optimum performance. 

Rare earth substituted garnet films for magnetic bubble memory applications... 

Mass data storage represents something of a problem. Floppy discs are probably inadvisable under the severe conditions at sea (vibration, large motion, dirty air, etc.). Some forms of data storage that do appear desirable are Winchester discs (if head crashes can be avoided), digital tape recorders, electronic memory systems (protected from power interruptions), or bubble memories (a bubble memory for the Apple II has become available commercially). 

The major objective of this work was to synthesize a polyamic acid/imide material for bubble memory fabrication applications. Important qualities sought in this material are ... 

Specifically for the passivation of temperature sensitive bubble memory devices,these ultrapure materials proved to be of great value. A cure process was optimized to obtain a reliable low temperature cure without affecting the magnetic coercivities of the bubble memory devices. A positive resist process, using a simple development step to pattern via holes in devices has been optimized and successfully used to fabricate devices. The devices fabricated using the the polyimide process have been compared with conventional SiC offers reliable passivations with thinner stress free films for passivations. The fabrications involve simple inexpensive process steps and are compatible with conventional resist processes. The reliability of the imide passivated devices can be considerably enhanced by the use of ultrapure starting materials to preclude harmful ionic mobilities through passivated layers. 

N.S.Viswanathan Paper presented at the 2nd Int.Bubble Memory Conference, Santa Barbara,CA,December 1982. 

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