EP0007305A1

EP0007305A1 - Conductor access bubble memory

Info

Publication number: EP0007305A1
Application number: EP79900057A
Authority: EP
Inventors: Andrew Henry Bobeck
Original assignee: Western Electric Co Inc
Current assignee: AT&T Corp
Priority date: 1977-12-06
Filing date: 1979-07-04
Publication date: 1980-01-23
Also published as: IT7830555A0; SE417027B; DE2857245C1; SE7906523L; IE47757B1; ES475592A1; GB2044027A; DD139906A5; WO1979000360A1; FR2467464B1; FR2467464A1; GB2044027B; IT1101299B; YU282978A; CA1118097A; IE782407L

Abstract

Une memoire magnetique a bulle a acces par conducteur qui dispense de l'emploi d'une pluralite de conducteurs avec une trame complexe de conducteurs difficile a realiser avec les petites dimensions necessaires pour obtenir des dispositifs a fonctionnement rapide, comprend un film electriquement conducteur (12) avec un reseau d'ouvertures le traversant. Chaque ouverture definit dans une couche adjacente (11) d'un materiau propageant des bulles un site prefere pour une bulle durant les intervalles de passage du courant a travers le film. Des positions de repos telles que des regions d'implantation d'ions (15) dans la couche adjacente ou des elements permallox (123) associes a chaque ouverture determinant d'autres sites preferes pour des bulles transferees des sites definis par les ouvertures. Ainsi, lorsque le courant passant par le film cesse, les bulles avancent automatiquement (sans l'aide de moyens de propulsion exterieurs) vers les sites pour les bulles transferees assurant le mouvement des bulles dans la direction requise.A magnetic bubble memory with access by conductor which dispenses with the use of a plurality of conductors with a complex weave of conductors difficult to achieve with the small dimensions necessary to obtain fast operating devices, comprises an electrically conductive film (12 ) with a network of openings crossing it. Each aperture defines in an adjacent layer (11) of bubble-propagating material a preferred site for a bubble during intervals of current passing through the film. Rest positions such as ion implantation regions (15) in the adjacent layer or permallox elements (123) associated with each opening determine other preferred sites for bubbles transferred from the sites defined by the openings. Thus, when the current passing through the film ceases, the bubbles automatically advance (without the aid of external propulsion means) towards the sites for the transferred bubbles ensuring the movement of the bubbles in the required direction.

Description

CONDUCTOR ACCESS BUBBLE MEMORY

Technical Field

This invention relates to conductor access magnetic bubble memories and more specifically to such memories in which the movement of bubbles is responsive to magnetic fields generated by current pulses applied to a patterned electrically-conducting material adjacent the layer of material in which the bubbles move. Background of the Invention

Magnetic bubble memories are well known in the art. One well-known technique for moving magnetic bubbles in such memories is commonly referred to as the "conductor-access" technique and is described, for example, in U. S. patent no. 3,460,116, issued August 5, 1969.

One prior known conductor-access type memory comprises a layer of material in which magnetic bubbles can be moved, usually a garnet material grown epitaxially on a nonmagnetic garnet substrate. Several patterns of discrete electrical conductors are formed in a laminate arrangement adjacent the epitaxial layer with appropriate insulating layers between the lamina. Typically, three undulating electrical conductors are arranged in positions offset from one another along a path of bubble propagation, and the conductors are successively pulsed in a three-phase manner in order to obtain a movement of the bubbles in selected directions determined by the off-set arrangement of the conductors.

R. F. Fisher, U. S. patent no. 3,564 ,518 , issued October 17, 1972, discloses a two-phase conductor-access bubble memory employing two levels of patterned electrically-conducting material and offset permalloy elements for controlling directionality of bubble movement. The permalloy elements are disposed to provide low energy or rest positions for bubbles in positions offset from those to which bubbles are moved by a pulse applied to one of the conducting levels. Thus, the permalloy is operative as a "third-phase" conductor would be if it were present.

U. S. patent no. 3,693,177, issued, September 19,

51972, and U. S. patent no. 3,678,479, issued, July 18,

1972, disclose bubble memories including a single level of electrically-conducting material. Bipolar pulses are applied to the electrically-conducting material which responds to provide, in effect, two phases of the three- 0 phase operation necessary for unidirectional movement of bubbles. The bubble layer itself is formed into a discrete strip patterned to provide offset rest positions for bubbles and thus operates as the "third-phase" of propagation. Problems associated with such prior known conductor-access arrangements, however, are that they require intricate patterns of conductors which are generally difficult to make in the small dimensions necessary to achieve fast operating devices. Also, the elongated and narrow conductors typically used in such devices give rise to relatively high power requirements.

For the multilevel conductor film arrangements, severe problems exist concerning the occurrence of short circuits between the adjacent layers. In the single conductor layer arrangements, also involving narrow and elongated conductors (thus requiring high driving power) , the bubble propagating layer itself is patterned, thus providing an extra processing step as well as requiring generally larger and thus slower acting devices. Notwithstanding the aforementioned problems, it is generally accepted that the conductor-access type memory has several theoretical advantages over other type bubble memory devices, and a need exists to solve these various problems. Summary of the Invention

In general, a solution to the aforementioned problems is based on the recognition that an array of offset low energy or rest positions for bubbles can be defined by, for example built-in permalloy elements, ion- implanted regions, or surface features such as mesas or recesses in the bubble layer, for use in conjunction with a single electrically-conducting film bearing a pattern of discrete apertures which define paths for bubble movement. The use of an otherwise continuous conductor film with apertures positioned to only locally distort a wide path current flow provides a relatively low resistance and relatively low power means for driving the bubbles. Also, patterning of the single film to a high accuracy and resolution is relatively simple. Bipolar current pulses through the film provide the equivalent of two of the three phases of the prior art propagation systems, while the built-in rest positions provide the equivalent of the third phase. Brief Description of the Drawing

FIG. 1 is a schematic representation of a magnetic bubble memory including a conductor drive arrangement for moving magnetic bubbles; FIG. 2, 3 and 4 are enlarged views of a portion of the memory of FIG. 1 showing the propagation arrangement and the movement of bubbles therein;

FIG. 5 is a pulse diagram of the operation of the propagation arrangement of FIGS. 1 through 4; FIG. 7 is a schematic representation of turn geometries for forming circulating loops with the arrangements of FIGS. 1 through 4;

FIGS. 6, 8 and 11-14 are schematic representations of different propagation arrangements in accordance with this invention.

FIG. 9 is a view, in perspective, of a portion of a still different arrangement; and

FIG. 10 is a cross-sectional view of the arrangement shown in FIG. 10. Detailed Description

FIG. 1 shows a magnetic bubble memory 10 including a layer 11 in. which magnetic bubbles can be moved. An electrically-conducting layer 12, adjacent layer 11, is shown including a plurality of square apertures 14 in a large central portion of the layer usually occupying the bulk of the layer. A propagation pulse source 16 is connected to one side of the layer 12 and the other side is connected to a reference potential shown as ground in the figure.

A bipolar current (or voltage) pulse from source 16 generates a current flow through the layer 12 and along columns defined by the apertures, as is discussed more fully hereinafter. Bubble propagation, in response, takes place from left to right along the rows of apertures shown coupled to input pulse source 20 to the left and utilization circuit 21 to the right as viewed in the figure. A control circuit for activating and synchronizing the operation of the various sources and circuits is represented by block 23 in FIG. 1. The various sources and circuits may be any such known elements capable of operating in accordance with this invention. The apertures of FIG. 1 cooperate, in this embodiment, with rectangular ion-implanted regions 15 (of e.g., neon ions) to produce bubble movement. The ion-implanted regions 15 are formed in layer 11 and are seen in the enlarged representation of area 25 of FIG. 1 as shown in FIG. 2. If we adopt the convention that one period of the conductor pattern is P, then, illustratively, each ion implant has a width of P/4 along the row as indicated in FIG. 2. A magnetic bubble moved by such a propagation arrangement has a diameter nominally about P/5. The diameter is determined, as known, by a bias field supplied by a bias field source represented by block 30 in FIG. 1.

As is generally now known, the ion-implanted regions are regions which bubbles prefer to occupy. That is, they are "rest" (low-energy) positions towards which bubbles naturally move in the absence of forces (magnetic fields) urging the bubbles elsewhere. Thus, by disposing them offset from positions to which the bubbles

OM are driven by current pulses, further bubble movement occurs when the pulses terminate.

The movement of bubbles in layer 11 is represented in the sequence of FIGS. 2 , 3 and 4. FIG. 5 srepresents the propagation pulse sequence applied by source 16 of FIG. 1 to conducting layer 12 for producing that movement in cooperation with the ion-implanted regions in layer 11. The convention is used herein of representing a bubble as a circle having a polarity such^' lOthat it is attracted by a magnetic field having a direction perpendicular to the surface of the layer 11 and upwardly therefrom (towards the viewer for the device as shown in FIG. 1) .

In an illustrative operation, say at time T_A in

15FIG. 5, a pulse 31 of a first polarity is applied to layer 12 by source 16. In response, current flows from bottom to top as indicated by arrow i in FIG. 1. The current flows along the columns defined by the apertures, such columns thus- acting as elongated

20conductors. Using the familiar "right hand" rule to determine the direction of the magnetic field produced by such current flow, it is seen that a positive field (i.e., one whose direction is towards the viewer) is generated, for the positive pulse 31 shown in FIG. 5, at

25 he right edges of the apertures as viewed in FIG. 2. A magnetic bubble, if present, positions itself, accordingly, at that right edge as shown by the solid circles in the figure (it being noted that the exact positioning of the bubbles is not precisely known) . 0 At a subsequent time, shown as T_B in FIG. 5, pulse 31 terminates. A static condition is now present. The bubble positions itself symmetrically with respect to the closest ion-implanted region. Such static positions for bubbles are shown by the solid circles in FIG. 3. 5 Subsequently, source 16 applies a pulse 34 of a second polarity to layer 12. The resulting current flow in the opposite direction generates a magnetic field having a positive direction at the left edges of the apertures 14, and any bubbles present move, in response to the generated field, left-to-right to the left edge of the apertures in layer 12 as shown by the dotted circle in FIG. 2. At the termination of pulse 34 a second static Scondition allows movement of bubbles^"to positions occupied by the dotted circle in FIG. 3.

A next subsequent pulse 31 results in bubble movement to positions represented by the solid circle in FIG. 4. At the termination of that next subsequent lOpulse, the bubble moves to the positions shown by the broken circle in FIG. 4. One illustrative cycle of operation is now complete. Repetition of the pulse sequence results in movement of bubble patterns along the bubble paths to a suitable detector, e.g., such as that 15shown in FIG. 11 and discussed hereinafter.

The relative placement of the ion-implanted regions and apertures in the conductor layer determines the direction of movement of bubbles in the arrangement of FIG. 1. Thus, the placement of a row of ion-implanted 0regions such as 40 and 41, in FIG. 6, beneath layer 12 and exposed through aperture 42, respectively, results in movement of bubbles to the left as viewed in the figure rather than to the ight as discussed in connection with FIGS. 2, 3 and 4. Such opposite direction of bubble 5 movement is realized in response to the same pulse sequence described hereinbefore, the location of the ion-implanted regions determining the direction of the offset and thus the direction of movement. Because of this, different bubble paths chip can be formed in a 0 manner to move bubbles in different directions simultaneously. Thus, the basic operation of the familiar "major-minor" organization disclosed in U. S. patent no. 3,618,054, can be achieved.

A turn geometry for connecting adjacent paths 5 into a loop for recirculating bubbles counterclockwise is shown in FIG. 7. Note that the position of the ion-implanted regions (only some of which are shown stippled) with respect to the edge of the apertures in conductor layer 12 determines the direction of bubble movement as has been stated hereinbefore. Thus, the top row 50 of apertures in FIG. 7 has the implanted regions to the left of the associated edges and bubble movement

5is to the left as indicated by arrow 51. In the second row, the apertures 52 are arranged with the ion-implanted regions to the right of the associated edges. Thus, counterclockwise bubble movement around the loop of apertures occurs with the pulse train of FIG. 5. The lOturns are formed with apertures 55, 56 and 57 at the right end of the loop as viewed and with apertures 58, 59 and 60 at the other. The ion-implanted regions are shown on the "downstream" side of the edge of the associated apertures in each instance.

15 In the embodiments of FIGS. 1 through 7, ion- implanted regions are employed and aligned rows and columns of apertures are used. FIG. 8 shows an arrangement where a plurality of apertures are arranged in offset positions rather than in rows and columns as

2oshown in FIG. 2. Here again, the ion-implanted regions are shown on the downstream side of the edges of the associated apertures. Such an arrangement of apertures permits operation just as described hereinbefore.

The apertures are operative to constrain the

25current flow into localized regions which are operative not only to move bubbles but also to avoid elongating bubbles into strip domains which are causes of failures in bubble devices. The apertures thus are operative to decouple adjacent bubble paths from one another, which is

30desirable.

As previously explained, the ion-implanted regions provide preferred "rest positions" to which the bubbles are attracted during "static" periods. Alternative known approaches to defining rest positions

35for bubbles employ magnetically soft permalloy elements, mesas or recesses in the bubble layers, magnetically hard magnetic dots and the like. Since the position and top view of the rest regions are alike regardless of mode of implementation, the regions shown in the figures as ion- implanted regions can be taken also as representative of any such region. What is necessary generally is that the rest positions be located to produce an offset of a Sbubble from the position to which it is moved in response to a propagate pulse. Further, it is not necessary for the regions to be square or even discrete along the bubble path. An example of the use of magnetically soft permalloy elements is described hereinafter. 0 The pulse train employed to cause the bubble movement is bipolar in form. Thus, the apertured conductor layer, in response, provides two phases of unidirectional bubble movement. The offset rest position, in each instance, completes the "third" phase. 5FIG. 5 shows the pulse train as including pulses separated by zero current levels for some fixed duration to emphasize that the offset effect is operative. Actually, the duration of the zero levels can be long or short as determined by the designed-in odistance a bubble has to traverse to reach a rest position and the mobility of the bubble material in accordance with well-understood considerations.

Also, it is noted that current flow in the aforedescribed embodiments is in a direction transverse 5to the direction of bubble movement, the current flow being generally throughout film 12. Preferrably, low impedance, large area contact lands 70 and 71 of FIG. 1 are driven by the drive pulses thus further avoiding the high power requirements of prior art conductor-access 0bubble memories. Source 16 is shown connected to land 70 in FIG. 1 to this end. Land 71 is shown connected to ground in the figure. Alternatively, a distributed or multiple contact arrangement is possible. In either case, the current flow diverges and converges at the 5apertures as shown by arrows 90 in FIG. 4. These localized current variations are operative to constrain bubbles within their designated paths, whereby large variations in operating conditions can be tolerated without failure of the devices.

In one specific embodiment, an epitaxial bubble layer of Calcium-Germanium Garnet 1.7 microns thick had a nominal bubble diameter of 1.7 microns. An electrically Sconducting film of aluminum-copper, 3000 Angstrom units thick, was formed on the surface of the film. Apertures 4 by 4 microns spaced 4 microns apart were aligned with ion- implan ed regions 2 by 4 microns in the manner shown in FIGS. 1-4. Ion implantation occurred by exposing the lOsurface of the bubble layer through a patterned mask to Neon at 100 K.E.V. to achieve an implant of 1/4 by IO¹⁴ ions per square centimeter to a depth of about 0.2 microns. One-half microsecond drive pulses with zero interpulse spacings were applied as shown in FIG. 5.

15 Operation occurred in a bias field of 250 oersteds. Drive current was less than 10 illiamperes per cell. Operation was achieved over a drive field range of 8 to in excess of 25 milliamperes and a bias field range of 240 to 260 oersteds. Drive power of 3.8 microwatts per 0 cell has been achieved.

It is contemplated that the memory of FIG. 1 may be operated in segments. That is to say, only a portion of the memory need be operated at a time. To implement an arrangement of this type, apertures 14 are 5 interconnected by slots as indicated at 80 in FIG. 3. Such slots are located transverse to apertures whic define paths of bubble propagation and are operative to divide the memory into two (or more) sectors. Separate current supplies are used to drive each sector. ⁰ The apertures in the electrically-conducting film herein cause localized perturbations in an overall substantially uniform current flow. In order to reduce any overall nonuniformity which may arise in large area memories it may be advantageous to employ a^"n 5 electrically-conducting ground plane as a path for return currents. Alternatively, an electrically-conducting image plane may be employed to constrain field gradients due to overall current flow. In this latter instance, the plane would be spaced so as to not affect fields due to localized perturbations attributed to the apertures in the electrically-conducting film.

Structures of the type herein disclosed are compatible with the provision of an in-plane magnetic field for stabilizing bubble wall dynamics. Such fields are of the order of 200 oersteds and permit even higher frequencies than those described hereinbefore.

An example of the use of permalloy (i.e., soft magnetic) elements, in lieu of the ion- implanted regions, is shown in FIGS. 9 and 10. In this embodiment, a number of apertures 14 are provided disposed, for example, in an array of apertures such as shown in FIG. 1, with each aperture being of generally C-shaped geometry, i.e., of generally square shape but with a tab 122 extending inwardly of the aperture from one side thereof.

A permalloy element 123 is formed in registry with each aperture so that its ends overlie conducting film 12 and its center is in proximity with and illustratively in contact with layer 11. Each permalloy element thus can be seen to be out-of-plane. That is, each element does not lie in a single plane parallel to the bubble layer. Typically, the apertures have a measurement X on a side and are spaced apart a distance 2X. Each tab itself is square having a measurement X/2 on a side. Each permalloy element has a length 3X/2 and a width X/2.

The bias field (FIG. 1) is operative to determine a mean diameter for bubbles (135) in layer 11 as shown in FIG. 10. The bias further herein cooperates with the out-of-plane portions of the permalloy elements 13 to achieve low-energy rest positions for bubbles along the propagation paths. The bias field is applied in a direction normal to the plane of bubble movement and antiparallel to the magnetization of a bubble. If we adopt the convention that the magnetization of a bubble is directed upward as represented in FIG. 10 by arrow 136, then the bias field is directed downward as

A ^" indicated by the arrow 137 in FIG. 10.

A permalloy element is operative to produce a relatively low bias field position at a point therealong at which the element is most remote from the surface of

5the underlying bubble layer. Magnetic poles are formed in the element which attract bubbles to the ends of the element which are most remote from layer 11 and repel bubbles from the intermediate portion of the element

(i.e., the portion of the element contacting the layer

1011) • In FIG. 10, bubble 135 is shown at a resulting low-energy position.

A negative current pulse 34 of FIG. 5, applied to film 12, results in a magnetic field operative to move a bubble past the intermediate portion of the permalloy

15element to the right edge of the associated aperture, a position demarcated by the vertical broken line 140 in FIG. 10. At time T_A in FIG. 5 when pulse 34 terminates, bubble 135 moves under the right end of the associated permalloy element to the low-energy position

20there. Such a position is designated 141 in FIG. 10.

At a later time, a positive current pulse 31 is applied. In response, a bubble moves to the right under the tab of the next consecutive aperture along the path of propagation. Such a position is designated 144 in 5 FIG. 10. At a time T_β, when pulse 31 terminates, the bubble moves to the next low-energy position to the .; right, a position designated 145 in FIG. 10. One complete cycle of operation is now complete. Subsequent cycles are operative to move bubbles simultaneously in ⁰ parallel channels from left to right as viewed in FIG. 1. The herein disclosed arrangement is also useful to provide a bubble "expander" for facilitating detection of the bubbles at an output of the device.

Thus, as shown in FIG. 11, such an expander, a 5 portion 220 of a memory device such as that shown in FIG. 1, is operative responsive to bubble propagate signals to enlarge bubbles laterally with respect to the path 226 of bubble movement. Successive enlargement of a bubble

OMPI commences as a bubble enter s portion 220 and proceeds incrementally as a bubble advances stage after stage until a maximum expansion occurs at the detector^' stage. A magneto-resistance detector is disposed at the l ast ₅ stage and is operative responsive to an interrogate pulse applied thereto by control circuit 23 (FIG. 1) , in synchronism with the propagate drive pulses , to apply to util ization circuit 21 signals indicative of the presence of an enlarged bubble then present in the detector stage .

₁₀ As shown , the expander portion includes a pattern of apertures 222 , 223 , 224 , 225. The apertures are arranged in succession along the path 226 of bubble propagation. It is to be noted that the apertures have increasingly larger long dimensions as viewed from left

₁₅ to right along path 226 , the long dimensions being arranged laterally with respect to the path.

Each of the succession of apertures includes a first and second edge , A and B, along path 226. Thus , aperture 222 includes edges 22A and 22B and aperture

20 223 includes edges 23A and 23B, — etc . Ion-implanted regions are formed in layer 11 in alignment with the A and B edges of the apertures and are shown stippled in FIG. 11 (some of the stippling being omitted) The implanted regions have dimensions lateral to path 226

25 (viz : the long dimension) coextensive with the lateral d imension of the aperture and commencing with the associated edge. The illustrative arrangement thus includes two ion- implanted regions for each aperture .

Consider a bubble positioned initially at the

30 ion-impl anted ^region at edge 22A at time T_A in FIG. 5. A current pulse 31 applied to layer 12 moves the bubble to edge 22B. At the termination of pulse 31, the bubble moves into the ion- implanted region at edge 22B at time T_β . A negative-going pulse 34 is next applied to layer 35 12. The bubble , in response , moves to the left edge 23A of aperture 223. At the termination of pulse 34 , the bubble moves into the ion-implanted region at edge 23A. One cycle of operation is now complete , the bubble

OMPI passing through the expander having become enl arged in size .

The enlargement of bubbles is due to the increasingly longer lateral dimension of the apertures in

5FIG. 11. In each instance when a current pulse is _r applied to layer 12, a bubble experiences an attractive field over an increasingly longer lateral dimension in its movement from a 'B¹ to an 'A' position, the bubble, in response, not only moves to the right, as viewed, but lOenlarges laterally to become coextensive with the lateral dimension of the propagate field generated by the pulse. By providing an increasingly larger long dimension, successive lateral enlargement of the bubbles result. Only four stages are shown for illustrative purposes. It

15should be clear that in practice a greater number of stages is used. Further, regions are shown as being the same width along path 26 in the illustrative embodiment. But this is not necessarily the case.

The enlarged bubble is detected, illustratively,

20when it advances to the position of ion implanted region 25A. For detection, a thin layer 250 of permalloy is deposited over region 25A and is connected between utilization circuit 21 and ground. Layer 250 forms a magneto-resistive detector and is responsive to an

25interrogate signal from control circuit 23 (FIG. 1) to apply to circuit 21 an indication of the presence or - absence of a bubble in layer 11 at region 25A, during ^' time T_A during each cycle of operation. Illustratively, layer 250 has a thickness of 400 Angstrom

30units and extends beyond region 25A to overlie layer 12. Signals of 0.5 millivolts are achieved.

In the foregoing embodiments, the flow of current i (FIG. 1) is transverse to the directions of propagation of the bubbles. In the following described embodiment,

35the flow of current is in directions parallel to the propagation path of the bubbles.

FIG. 12 is similar to FIG. 2 but shows a different arrangement of apertures and associated ion implanted regions. In this embodiment, the apertures 313 are organized into rows R2' ^R3'^{, ,#} oriented from left to right as viewed in the figure. Each row is offset a distance, illustratively, of about one half an

5 aperture from the adjacent row, and the apertures are arranged in columns C-^, C₂, C₃,... Bubble propagation occurs along these columns from bottom to top as viewed in the figure.

FIGS. 12 and 13 show that the ion-implanted 10 regions associated with the column of apertures align with one another along bubble paths. Thus, as shown in FIGS. 12 and 13, a column of ion-implanted regions 325 defines path PI and an adjacent column defines path P2.

Propagation occurs in response to pulses such as 15 shown in FIG. 5. The convention is followed that a positive pulse 31 in FIG. 5 results in current flowing in layer 12 in a direction indicated by curved arrows 350 and 351 in FIG. 13. Consider first, for example, a bubble at rest in position 370 of FIG. 14. A positive 0 pulse is operative, in accordance with the familiar right hand rule, to generate a magnetic field effective to move the bubble to position 371 (the exact position of the bubbles not being precisely known) . At time TB in FIG 5, the positive pulse terminates and the bubble moves to 5 the closest rest position at 372. A next subsequent pulse (negative) is operative to move the bubble to^', position 373. At time TA, the negative pulse terminates and the bubble is offset to the next consecutive rest position 375. One cycle of operation is now complete. :0-- It should be clear that multiple,paths are defined in film 12 by apertures 313 and rest positions 325 for^" simultaneous operation as described.

The rest positions, as previously noted, can be defined by implementation other than ion implantation. 5 Further, the geometries of the apertures and the rest positions need not be rectangular as shown. Regions 325 in FIGS. 13-14 may be taken to represent any rest position regardless of the manner of implementation.

Claims

1. A conductor-access magnetic bubble memory compr ising a layer ( 11 ) of mater ial in which magnetic bubbles can be moved , a film ( 12) of electr ically-conducting mater ial overlying said 1 ayer ,

CHARACTERIZED IN THAT said film includes a pattern of apertures (14) therethrough defining a path for the movement of bubbles in said layer, means (15, 123) associated with each of said apertures for providing rest positions for bubbles, and means (16) for providing a flow of current in said film alternately in first and second directions for moving bubbles to positions determined by said apertures and which are offset from associated ones of said rest positions.

2. A memory in accordance with claim 1 CHARACTERIZED IN THAT said first and second directions are transverse to said path.

3. A memory in accordance with claim 2, CHARACTERIZED IN THAT said first and second directions are parallel to said path.

4. A magnetic bubble memory in accordance with claim 1

CHARACTERIZED IN THAT a rest position is located downstream along the path of bubble movement from each edge of each of said apertures in said path.

5. A magnetic bubble memory in accordance with claim 4 * ^'

CHARACTERIZED IN THAT each of said rest positions is defined by an ion-implanted region within said layer (11) .

6. A magnetic bubble memory in accordance with claim 4

CHARACTERIZED IN THAT each of said rest positions i s defined by a so ft magnetic mater ial element ( 123) having portions thereof which are d isposed at differ ent spacings from said layer .

7. A magnetic bubble memory in accordance with claim 3

CHARACTERIZED IN THAT the apertures (313) in said film are organized in rows ( ^, R₂, R3...) where the apertures of one row are offset from the apertures of the immediately adjacent rows on either side thereof, each aperture has a leading and trailing edge, said rest positions (325) are arranged so that a pair thereof correspond to the leading and trailing edge of an associated aperture, and the rest positions associated with each aperture are offset from one another and are effective to define separate paths for bubble movement in said layer 11.

8. A magnetic bubble memory in accordance with claim 1

CHARACTERIZED IN THAT successive ones of said apertures (222, 223...) and associated ones of said rest positions have increasingly longer dimensions lateral to the axis of said path (226) for expanding the lateral dimension of bubbles advancing along said path.

UREA^ OMPI