EP0048250A1 - Propagation-expander-detector circuit for a magnetic bubble memory - Google Patents

Abstract

Circuit de propagation-expansion-detection pour une memoire a bulles magnetiques se composant d'elements avec des contours casses (en forme de chevrons, V, U et C) (Fig. 8, 70, 71) qui sont connectes directement - sans espacement - et chaque element (70, 71) contient au moins une partie (73) dont la largeur est modifiee (74, 75) pour devier le chemin de la bulle et ladite deviation forme un verrouillage magnetique (-B, +D) empechant le retour de la bulle magnetique pendant une fraction de la periode du cycle du champ magnetique tournant apres le passage de la bulle.Propagation-expansion-detection circuit for a memory with magnetic bubbles consisting of elements with broken contours (in the form of chevrons, V, U and C) (Fig. 8, 70, 71) which are connected directly - without spacing - And each element (70, 71) contains at least one part (73) whose width is modified (74, 75) to deviate the path of the bubble and said deviation forms a magnetic lock (-B, + D) preventing the return of the magnetic bubble during a fraction of the period of the cycle of the rotating magnetic field after the passage of the bubble.

Description

PROPAGATION-EXPANDER-DETECTOR CIRCUIT FOR A MAGNETIC

BUBBLE MEMORY

Technical Field

The invention relates to a propagation-expander-detector circuit for a magnetic bubble memory . Background Art Magnetic bubble memories are well known in the technical literature. The essence of the bubble memories of the said type lies in that it is not the storing material of the memory which is moved by means of some mechanical device in front of one or more read ing heads such as, for example, in the case of memories with magnetic plates or magnetic tapes, but the information present in the form of magnetic bubbles in sidethe material itself is moved towards the fixed reading device, the so-called detector. As is well known, a bubble memory consists of a non-magnetic substrate; of a thin magnetic layer grown epitaxially on the said non-magnetic substrate and in which, if there is a bias magnetic field lying perpendicularly to the plane of the layer, magnetic bubbles may exist; a propagation-expander detector--cir cuit built-up of expanding-detecting elements formed by means of photolithography from a thin magnetic film applied to the thin magnetic layer; the travellϊng mag netic poles formed on the said elements under the influence of a rotating magnetic field in the plane of the film that move the magnetic bubbles from the store to the place of expansion and detection where the information is read.

The material of a propagation circuit consist ing of propagate elements is generally a Permalloy layer, but it can be formed by an ion-implanted channel or with rooves formed by etching in the magnetic layer, etc. Bubble memories functioning on the basis of the described principle are called fieldaccess bubble memories . The range of-the bias magnetic field in which the me mory becomes operative is called bias margin.

Frequently, in order to be able to recirculate the information the propagate elements are arranged in closed loops, in so-called registers; such a solution is specified in the US-PS 3 618 054. The de tector-circuit which is used for reading the bubbles is generally made of the same thin magnetic film that is Permalloy, as the propagate circuit; moreover the basic elements are also similar to the basic-.elements of the propagation circuit. Prior to detection the bubbles are expanded to strips in order to receive larger signals; pre ferably, expansion should be performed perpendicularly to the direction of advance in order to be able to avoid any decrease in the speed of detection in rela tion to that of propagation .The most frequently used propagation circuit consists of asymmetric chevron elements whereas the bubble detector circuit is composed exclusively of symmetric chevron elements in such a manner, that the elements form columns with elements of ever increasing number. It is on the said columns, under the influence of the progressing magnetic poles developing in a line-form that the bubble are expanded into strips. The last column of the expander circuit is formed as a vertical column consisting of V-elements having been connected in a herring-bone pattern, representing the magnetoresistive detector. Under the in fluence of the stray magnetic field of the bubbles having been expanded into strips and Dassing through the detector, the resistance of the detector varies,accordingly, the presence or absence of the bubblesmay be read. In some cases a so-called dummy-detector isut ilized in order to be able to eliminate the magnetoresistive noise developed in the detector under the influence of the magnetic field rotating in theplane. The said dummy-detector is separated from theother parts of the memory by means of a guard rail to prevent the intrusion of the bubbles. By connectingthe detector of corresponding geometry and the dummy detector into a measuring bridge, the noise with acommon mode can be considerably reduced. The commoncharacteristics of the presently used field-accesspropagation circuits and expander-detector circuits liein that between the single propagate elements there is a gap; however, gapless solutions are also known. A Permalloy propagation circuit separated by gaps has several drawbacks. While passing through the gap the shape of the bubble becomes considerably deformed re suiting in a significant reduction of the operativerange furthermore, the movement of the magnetic bubbles usually stops at the said gaps thereby diminishing the reliability of the circuit arrangement. In addition to this, relatively high energies are required exert an influence. on the magnetic bubbles so that they pass through the gaps; such energies demand a rotating magnetic field of a larger amplitude. A urther drawback is that the gaps between the propagate elements simultaneously determine the storage density since the smallest detail to be realized by means of photolithogarphy is the gap itself .When the gaps are being formed only very small tolerances are permitted which presents considerable difficulties in the photolithographic process. When using photolithography in connection with Permalloy propagation circuits a further difficulty arises viz. the undesired the undesired disappearance (the so-called lift-off) of the gap-separated propagate elements. The said difficulty can be explained by the fact that because the photoresist adheres on a relatively small surface area of the gap-separated propagate elements it can be removed by the slightest force after development or che mical etching. The peeling-off of the photoresist creates considerable problems in respect to the yield. The selected width of the gab between the asymmetrical chevron elements - to be considered as the most up-to- -date - generally equals half of the bubble diameter. Accordingly, the required photolithographic resolving power (f) amounts to f = R = D/2, where R stands for the width of the gap, and D for the diameter of the bubble.

Taking it into consideration that the period λ of the elements cannot be less than four times that of the bubble diameter, that is: λ _x = 4D, where λ_x rep resents the period in the x direction and λ._y the period in the y direction, the attainable storing density S is able to amount maximally to

for a given resolving power.

In order to be able to obtain faultless operation of the detector, the gap between the symmet rical V-shaped or chevron elements within the expander detector circuit must be even less than D/2. To achieve a uniform gap width of R = D/2, usually the period of the V-elements of the expander-detector is increased,λ_x = 5 to 7 times the bubble diameter.

However, at high propagation detection speeds the expander-detector circuit with the increased period will operate incorrectly since due to their finite mo bility the bubbles are unable to follow the magnetic line charges advancing with large steps. Of the elements of the bubble memory the bias margin of the expander-detector circuit is the narrowest. Disclosure of the invention

The aim of the invention is to provide a gap less bubble memory built-up of elements, which is able to eliminate the drawbacks previously enumerated; simultaneously this gapless bubble memory has a large storage density, it possesses advantageous start-stop properties and it can be produced economically by using the traditional technology.

Accordingly, he task to be solved by the invention can be defined as the development of s pro- pagation-expander-detec or circuit for a magnetic bubble memory that possesses a high storage density and favourable start-stop properties.

The invention is based on the recognition that the task can be solved simply if the propagate elements with a broken contour are directly and gap lessly interconnected and if every element of the propagation circuit contains at least one path-section changed in width, to interrupt the path of the bubble thereby forming a magnetic lock which prevents return for the magnetic bubbles for a fraction of the period of the cycle after the passage of the magnetic bubbles. Accordingly, the propagεtion-expander-detector circuit for a magnetic bubble memory according to the invention represents a further-developed form of the known circuit, which consists of a single-crystal non-magnetic substrate, of a magnetic layer having been allowed to grow epitaxially on said substrate, carrying the bubbles and magnetic bubblestrips; furthermore the circuit according to the invention comprises propagating, expanding and detecting elements with a broken contour having been arranged in the direction of advance and a current source inducing a magnetic field rotating in the plane of the said layer and serving for the propagation of the bubbles.

The further-developed character, that is, the invention, lies in that the propagation circuit comprises elements with essentially broken contours (chevron, U, C forms) and hook-shaped turn-elements. The elements of the propagation circuit are directly interconnected - without any gap in between - and every single element contains at least one section which is changed in width and which interrups the path of the bubble. This part forms a magnetic lock which closes the backway for the magnetic bubbles for a fraction of the period of the cycle after the passage of the magnetic bubbles.

In accordance wi th the invention it is expe dient, if the propagation circuit contains elements with a chevron character and the magnetic lock of which consists of one single narrowing.

It seems to be advantageous to form the propagation circuit in such a manner as to contain a wi dened path section at the input - with regard to the propagation of the bubbles - followed by a narrowing and containing a further narrowing in the next arm.

Furthermore, advantageously the two arms comprising the elements containing one widening and one narrowing and the sections of constant width interconnecting the same - are rotated by 180º in relation to each other and the ends of both arms are connected by hook-shaped turn-elements being also displaced by 180º relation to each other.

Expediently there is an expander-detector circuit for the magnetic bubbles built-up of elements with a chevron character in accordance WIith the inve tion , being formed of single rows of interconnected elements. The elements arranged above each other in the different lines form columns with elements in an increasing number lying perpendicularly to the direction of propagation of the magnetic bubbles, whereas in the two selected adjacent columns forming the detector two elements each lying above the other are laternatingly interconnected and at least one of the two adjacent columns provided with an outer input and output leading the detector current. Furthermore it seems to be expedient to form the elements by placing at least two elements with a chevron character onto each other and by filling a part of the gap left in between. Accordingly, the bubble expander-detector circuit built-up of the pro pagate elements obtained in such a manner consists of columns, whereas the elements lying next to each other form rows. The detector is formed by two neighbouring columns, whereas the second column of the said detector is displaced in the vertical direction by a half period as compared v/ith the previous column and the detector is provided with at least one input and one output current lead for the detector current.

A further preferable embodiment of the inven tion is for the circuit to incorporate a dummy-detector provided with a guard rail having the same geometry as the detector. Preferably the guard rail should also be formed of gapless elements. Brief Description of Drawings

The invention will be described in detail by means of the accompanying drawings, wherein the known solutions and some preferred embodiments of the propagation—expander-detector circuit according to the inven tion are illustrated.

Figure 1 shows the schematic arrangement of a known magnetic bubble memory, Figure 2 shows the chevron propagate elements arranged in a traditional manner with a gap in between, Figure 3 shows the asymmetric gap-separated chevron propagate elements, Figure 4 shows the known gapless propagation circuit obtained by connecting the chevron propagate elements, Figure 5 shows the known gapless expander-debector circuit built up of chevron propagate elements, Figure 6 shows the side view of the circuit according to Figure 5, in section, Figure 7 shows the senses of rotation of the magnetic fiel rotating in a clockwise direction,

Figure 8 shows the embodiment and the operation of the gapless propagation element according to the invention in the case of a magnetic field rotating in a clockwise direction, Figure 9 shows another preferred embodiment of the gaples propagation element according to the invention and the operation thereof in the case of a magnetic field rotating in a clockwise direction, Figure 10 shows the senses of rotation of the magnetic field rotating in the counter-clockwise direction,

Figure 11 shows the operation of a gapless propagate ele ment according to the invention in a magnetic field rotating in the counter-clockwise direction,

Figure 12 shows the propagation circuit built-up of the elements according to the invention, with a closed loop, in the momentary direction of the magnetic field rotating in the clockwise direction,

Figure 13 shows a bubble expander-detector circuit built- up of the propagate elements according to the invention,

Figure 14 shows a' further embodiment of the expander-detector circuit according to the invention,

Figures 15 to 17 show a gapless expander-detector circuit according to the invention in the diffe rent momentary directions of the magnetic field rotating in. the clockwise direction.

Modes for Carrying out the Invention

In Figure 1 a known magnetic bubble memory 20 is to be seen, consisting of a non-magnetic single-crys- tal substrate 21, a magnetic film 22 allowed to grow epitaxially on the said substrate, carrying the bubbles and bubble strips, furthermore of a propagation-expander-

-detector circuit wi th a broken contour having been arranged on the magnetic film 22. The propagation circuit is built-up of several parallel minor loops 23a-n and of a major loop 24, the minor loops and the major loop comprising the so called registers and the major loop 24 lying parallelwith one end of the minor loops. The minor loops 23a-n are arranged closely to each otter, the distance between the adjacent arms of the minor, loops as well as between the adjacent minor loops equals 4 to 5 times the bubble diameter. Between the major loop 24 being coupled to the ends of the minor loops there is usually the same distance corresponding to 4 to 5 times the bubble diameter. The task of the minor loops 23a-n lies in the storing of the invention, that is in the storing and infinite propagation of the magnetic bubb les. The bias magnetic field is induced by means of permanent magnets, not illustrated here, to create the permanent magnetif field required for the maintenance of the bubbles of constant diameter within the magnetic film 22. The propagation of the magnetic bubb les is ensured by a rotating magnetic field induced by magnetic coils - not illustrated here - enclosing the carrier substrated 21. The current source 25 of the rotating magnetic field is controlled by control circuit 26. Out of the information stored one row is se lected that is one single bit is led from every minor loop 23a-n into the major loop 24 by means of a replicate co.nductor 27. The replicate condurctor 27 is coupled to the point at which the distance between the major loop 24 and the minor loops 23a-n is the smallest. The said replicate conductor 27 is supplied with current via a pulse source 28, which is controlled by the control circuit 26. The magnetic bubble sample replicated by means of the pulse source 28 arrives from the main loop 24 into a bubble expander-detector circuit 29, where it is expanded; the expanded bubbles are detected by means off a detector 30. In general, detector 30 is a magnetoresistive element whose task is to emit a signal with the aid of a utilization cir cuit 31 when a magnetic bubble is passing through detector 30. The information having been detected in such a manner passes through the guard rail 32 enclosing the detector circuit and becomes annihilated. New information can be introduced into the minor loop 23a-n by annihilation, by leaving vacant places. In the corresponding cycles of the rotating magnetic field the pulse source 28 sends a controlled pulse to replicate conductor 27 and conductor 33 in such a manner that in the minor loops 23a-n vacant places should be formed. Generator 34 sends to generator conductors G a controlled pulse in such a manner that new information could be written in the vacant places of the minor loops. Synchronization of the circuits belonging to the bubble memory is performed by control circuit 26 via the respective synchronizing conductor S.

In Figure 2 chevron elements, well known in the art, are illustrated. The gap 37 between the first chevron element 35 and the second chevron element 36 equals about half the bubble diameter; the width 38 of the chevron elements equals about the bubble diameter. The storing density to be obtained by these and similar propagate elements, With gaps between them is restricted just by this small-sized gap 37 with a limited tolerance, formed between the chevron elements 35, 36. This gap 37 causes the majority of problems arising in connection with reliability and operation. The period λ of the chevron propagate elements usually equals 4 to 5 times the bubble diameter. The path 40 of the magnetic bubble generally going from the left side to the right as is indicated by the dashed line In Figure 3 the known propagate elements with gaps - to be considered as the most up-to-date - built-up of the asymmetric chevron elements are to be seen ; such a propagate element design has been specified in the US-PS 4 007 447.With these propagate structures the applied chevron elements 41, 42 are formed in such a manner that, for example, one leg of the chevron element illustrated in Figure 2 is made thicker; by means of the said asymmetric propagate chevron elements 41, 42 a very good operative range can be obtained; however, all the drawbacks of the gap-separated elements may be observed In Figure 4 a chevron propagate element is to be seen, which may be obtained by connecting the chevron elements of Figure.2, however, these propagate elements do not operate in a rotating magnetic field. This type of the zigzag-shaped propagate element 43 has been des cribed in the US-PS 3 518 643 and 4 021 790.

With a low magnetic bias field the magnetic bubble 44 is striped out on the propagate structure, that is, it is deformed into a strip. With a higher bias field the bubble covers the distance A-B-A during _ one revolution of the rotating magnetic field, accordingly, the propagation of the bubble cannot be realized. In the first and second quarter of the period of the revolution of the magnetic field rotating in the clockwise direc tion the bubble reaches point B from point A and in the following third and fourth quarter of the period the bubble will return from point B to the starting point A. Accordingly, these propagate elements 43 are able to operate only by means of special fields oscillating in the plane of the propagate elements 43; however, the direction of propagation of the magnetic bubble 44 is exclusively defined by the direction of oscillation of the field.

As a consequence, these propagate structures are suitable for realizing unidirectional propagation of the bubble but bubble circulation within closed loops cannot be achieved. For these reasons the structure cannot be used in up-to-date bubble memories with minor and major loops.

A gapless propagation structure formed by the connection of asymmetric chevron propagate elements described in the US-PS 4007 447 shows similar behaviour: the asymmetry of the propagate element does not suffice to prevent the return of the bubble. If it were possible to prevent the return of the bubble to the point A, the propagation structure could begin to operate.

In the US-PS 4 027 297 a propagation structure obtained by connecting propagate elements T-I has been described. Due to the high space requirement this pro pagation structure is to be considered as disadvantageous.

In the DE-PS 1 917 746 a more developed solution is specified. In Figure 40 of DE-PS 1 917746 a propagation structure consisting of loops with a recurring continuous curvature is to be seen. The disadvantageous feature of this solution lies in that although the bubble is moving in reverse on the gapless propagation structure for part of the period of the cycle, due to the continuous curvature, stable conditions cannot be ensured for the magnetic bubbles in an accurate manner; that is to say, these propagation structures do not have preferential start-stop places. In addition to this, the propagate elements containing recurrent paths require a large amount of space, accordingly their production becomes uneconomical.

Summing up the drawbacks of the known solutions, it can be stated that with the known solutions the storing density is low, the start-stop properties of the single types is to be considered as disadvantageous, their operative range is unfavourable, the space requirement is large, simultaneously production yield is low.

In Figure 5 a bubble expander-detector circuit built-up of the zigzag-shaped gapless circuit to be seen in Figure 4 has been illustrated. In the US-PS 4 094 004 this type of expander-detector circuit has been specified, With this solution the propagate elements 45 are formed of a soft magnetic material, for example, Permalloy, by using a photolithogaphic process, on the magnetic bubble film 61. The chevron propagate elements 45 are formed on the magnetic substrate (e.g. gadolinium gallium garnet /GGG/) by epitaxial growth The first 46, the second 47 and the third 48 columns following each other contain chevron propagate elements 45 in an increasing number and these collectively form the bubble expander-circuit 56. The magnetic bubble expander-detector circuit 56 expands gradually the magnetic bubble strip 57 arriving from the input direction and leads it to the detector circuit 51.

In Figure 6 the inclined propagation-expander circuit 56 formed on the magnetic bubble film carrier 61 by inserting the spacer 62 is to be seen. The spacer 62 is repeated in the same period as that of circuit 56 while its thickness gradually decreases in the direction of propagation 52 of the magnetic bubble strips. The sϋacers 62 are located higher at theinnut edrces 58 of the columns 46, 47, 48 than at the output edges in consequence of which a thickness gradient is formed The spacers 62 are made of a non-magnetic material such as SiO₂ and it is absolutely indispensable for the operation of the circuit. In the course of operation a magnetic field 54 rotating in the counter-clockwise direction, operating in the plane of the circuit, induced by a drive field source 53 of the rotating magnetic field is produced. Supposing magnetic bubble strips with a negative magnetic charge, a magnetic bubble strip 57 is positioned in the detector circuit 51 at the input edge 58 of the propagate element. In the vertical position 55 of the rotating magnetic field on the input edge 58 and output edge 59 positive attracting poles are produced whereby the magnetic bubble strips 57 pass into the said position. As soon as the rotating magnetic field 54 turns further, the magnetic bubbles 57 begin to move downwards on the slope 63, accordingly at every single revolution of the rotating magnetic field 54 they covera distance 60 (a period λ ) corresponding to one propagate element 55. In the case of such a wedge-shaped spacer 62 the chevron propagate elements 45 are gaplessly repeated; however, the formation- of a special spacer 62 - a thickness gradient - requires extremely complicated technology, being incompatibile with the currently existing bubble-producing double-mat processes. Due to the application of the newer mat-levels, the yield of said solution is considerably lower than that of the traditional double-mat technologies.

In Figure 7 the sense of rotation of the magnetic drive field rotating in the clockwise direction, that is the momentary positions of 0°, 90°, 180° and 270° are indicated in the order of sequence by the reference numbers 65, 66, 67, 68. The part of the period of the rotating magnetic field falling between 0° and 90° is called the first quarter, the part falling between 90° and 180° the second quarter, the part falling between 180° and 270º the third quarter, and that falling between

270º and 20º is called the fourth quarter of rotation.

In Figure 8 a preferred embodiment of the gapless propagate elements according to the invention may be seen . The propagation circuit contains elements 70, 71 with the chevron character, one leg 72 of which is wide and the other leg 73 comprises a wide pathsection 74 and a narrow section, the so-called narrowing 75, forming a magnetic lock. On the propagate elements 70, 71 positive poles attracting the magnetic bubbles and nega tive poles repelling the magnetic bubbles are formed under the influence of the rotating magnetic field; these having been indicated with negative and positive signes in the figure. Under the influence of the rotating mag netic field the poles perform a progressive motion in consequence of which the magnetic bubbles are also setinto motion. In the case of a magnetic field rotating in the clockwise direction in accordance with Figure 7, the magnetic bubble travbls along the path indicated by the dashed line, on the propagate elements 70, 71. In the momentary position 65 of the rotating magnetic field the magnetic bubble at point A of the gapless propagate element 70 moves towards point B of the gapless propagate element 70 after the revolution of the magnetic field in direction 66, that is, after turning through 90°.

After a further turn of the rotating magnetic field in direction 67, the magnetic bubble travels from point B to point C and after a further turn through 90° in direction 68 the bubble travels from point C to point D. In the third quarter of the period the negative repell ing charges formed at the edge of the propagate element do not allow the also negatively charged magnetic bubbles to return to point A. After a further turn of the rotating magnetic field through 90º in direction 65, the magnetic bubble moves to point E of the gapless propagate element 71. Furthermore the negative charges - which do not allow the magnetic bubble to return to point A - formed in the course of the third quarter of the period will be called a magnetic lock. Thus, during the complete revolution of. the rotating magnetic field the magnetic bubble covers a distance corresponding to one propagate element, that is one

In Figure 9 another embodiment of the) propagation circuit has been illustrated. In the figure, the. propagate elements 80, 81 of the propagation circuit are to be seen. These propagate elements 80, 81 are formed with two legs 82, 83 each. The first leg 82 consists of a rectangular shaped path 84 and of a triangle 85, being interconnected via a narrow path-section 85a, while the second leg 83 consists of a wide parallelogram 86 and the narrow parallelogram 87, accordingly, at this embodiment thelegs 82, 83 of every single propagation element contain a narrowing each forming a magnetic lock together with the following wide path section. In the case of this embodiment the rotating magnetic field according to Figure 7 produces poles with a positive or negative charge, respectively attracting or repelling negative Rubbles on the propagation circuit consisting of the single propagate elements 80, 81. The operation of the said propagate elements is based on the magnetic lock described in detail in Figure 8. The rectangular shaped wide path 84 of the first element to be seen in the Figure enhances the function of the magnetic lock. The operation of the first wide path is based on the recognition that taking, for example, an oblong Permalloy surface into consideration, the bubbles can easily be brought below tho rectangle from any side of the rectangle, whereas the magnetic bubbles can be pulled out from beneath the first rectangular shaped wide path 84 at the corners of the rectangle only. On the side of the first rectangular shaped wide path 84 the magnetic bubble becomes considerably expanded, accordingly a strong interaction takes place in relation to the said path-section. At the corners of the first rectangular shaped wide path 84 the magnetic bubble shrinks again; as a consequence, due to the arising smaller interaction, the bubble can easily be pulled out from beneath the path-section. The propagate element with the bubble asymmetry operating on the basis of this principle shows a good operation-margin for two start-stop directions; for a mutual deviation of 180º. The first rectangular shaped wide path 84 is realized by widening the path-section B-C-D to be covered by the bubble, thereby bringing magnetostatically the magnetic bubbles to a more advantageous position. By narrowing the second leg of the propagate element, the second narrow parallelogram 87 is formed, thus preventing the return of the magnetic bubble to the starting point A. In the first and second quarter of rotation of the rotating magnetic field the magnetic bubble travels from starting point A to point B, during the third quarter it travels to the points B-C-D, while in the fourth quarter, moving on path D-E, the covered distance equals λ , that is, one propagate element; accordingly, propagation can beraalized in this case, too. Compared With the propagate elements With the returning loop having been described in the DE-PS 1 917 746, the difference lies in that magneto statically the bubble can be brought to a more advan tageous position in the third quarter of the period, since the reverse part of its path, the distance B-C-D, is covered on the first rectangular shaped wide path and not on a newly designated path. This propagate element 83 contains in each period three wide paths 84, 85, 86 and two narrow paths 85a and 87; accordingly in both directions 65, 67 of the rotating magnetic field favourable start-stop operation may be obtained in consequence of which in a bubble memory with a major loop - minor loop arrangement it can be well used as the element of the minor loop. Taking it into consideration, that in the two arms of the loops the propagate elements are ro toted by 180º in relation to each other, the case of a start-stop in direction 65 in one of the legs, in the other leg start-stop will take place in direction 67.

In Figure 10 the sense of rotation of the mag netic field rotating the counter-clockwise direction is to be seen, the directions corresponding to 0º 90º, 180º and 270º are indicated with the direction of the arrows

65, 66, 67, 68. The first periodical quarter covers the range 0°-90°, the second quarter 90°-180°, the third quarter 180º-270º, and the fourth periodical quarter covers the range 270°-20º. In Figure 11 two elements 80, 81 of the gapless propagation circuit according to the invention are to be seen, which are actuated - in accordance with Figure 10 - by the drive magnetic field rotating in a counter clockwise direction. The shape of said propagate elements is in compliance with that of the elements in Figure 9 . With respect to the direction of propagation of the bubble, the single elements of the propagation circuit contain in the first leg 82 a rectangular-shaped wide path 84 at the input, the narrowed path 85a and a further, the triangle shaped, path 85, while the second leg 83 cnntains the wide parallelogram 86 and a further narrow parallelogram 87. When the magnetic field is rotating in direction 65 the attracting positive charges at apex F of the propagate element 80 attract the magnetic bubbles. When the magnetic field turns further in direction 66, the positive charges move in reverse taking the magnetic bubble with them to point G. When the magnetic field rotates in direction 67, the magnetic bubble moves forward along path G-H. The first narrow path 85a and the second wide parallelogram together prevent the motion of the magnetic bubble to point E. For the magnetic bubble it seems to be more advantageous to remain in the second wide parallelogram 86 than to traverse the first narrow path 85a. During rotation from direction 67 to direction 68 the magnetic charges and thus the magnetic bubble move along path H-I towards point I. When the magnetic field rotates from direction 68 to direction 65, the attracting positive magnetic charges move the megnetic bubbles along path I-J in a reverse direction - indicated by a dashed line - to point J. Summing up the propagation of the magnetic bubble: in the first period-quarter the magnetic bubble performs a reverie motion along path F-G indicated by the dashed line, in the following second and third period-quarters the magnetic bubble moves forward along path G-E-I, while in the last, in the fourth period-quarter it again moves in reverse along path I-J.

When comparing Figures 9 and 11, it can be observed that the magnetic bubble prouagads independently of the direction of rotation of the rotating magnetic field, from left to right on the propagate elements containing the alternate wide and narrow paths, respectively. The only difference is that under the influence of the magnetic field rotating in a clockwise direction motion in reverse is taking place along the rectangular shaped wide path 84 of the propagate element whereas when rotation is in the counter-clockwise direction, motion in reverse is taking place on the triangle-shaped path 85 and the wide parallelogram 86. In Figure 12 a closed loop, a so-called register, built-up of propagate elements according to the invention, is to be seen, comprising the widening 96 and a narrowing 98, as well as the upper arm 93 and the lower arm 94 having been displaced by 180º in relation to each other, containing the elements with the paths 97 of a constant, width and serving for the interconnection of paths 96 and 98; on both ends of the arms thereis a hook - shaped turn-element 95 arranged, also being turned through 180º in relation to each other. As is to be seen in the figure, the single propagate elements contain merely one widening 96 and one narrowing 98, as well as the interconnecting path 97 of constant width in contrast to the two narrowed paths of the propagate element illustrated in Figure 11. The negative charges appearing in the course of the rotation of the magnetic field in direction 68 (Figure 7), forming the basis of the operation of the propagate elements 90, 91, 92 also prevent in the case of this propagate element the return of the magnetic bubbles to the previous propagate element. At the widening 96 the magnetic bubbles become expanded in consequence of which the repelling effect of the negative charges prevails in a more emphasized manner. In the magnetic field rotating in a clockwise, direction - as illustrated in Figure 7 - the magnetic bubbles move in a closed minor loop. In Figure 12 the propagation of the bubbles is shown in a "motion pic ture like" manner. In the basic position of the magnetic field according to Figure 7, in direction 65, the magnetic bubble 99 in Figure 12 is indicated by an empty.circle. By turning the magnetic field through 90ºin direction 66, the magnetic bubbles are indicated by a vertically striated circle moving in the narrowing 98 of the propagating element. When the magnetic field rotates in direction 67, the bubbles pass through the narrowing and move towards the wide leg of the element, to the so called widening 96, here the bubbles are indicated by a horizontally striated circle. When the magnetic field rotates in direction 68, the magnetic bubbles - indicated by a filled circle - move in reverse on the widened leg of the element, on the so-called widening 96. After the comolete revolution of the magnetic field in direction 65, the magnetic bubbles indicated by an empty circle move towards the apex of the element. In order to facilitate comprehension, in the lower arm 94 of the minor loop no bubbles have been drawn, but it is completely obvious that bubbles in the lower arm perform the same motion as in the upper arm 93 of the minor loop, but due to the rotation of the figure by 180°, a difference of 180º can be observed at the propagation of the magnetic bubbles. On the hook shaped turn-element 95, in position 65 of the rotating magnetic field the magnetic bubble indicated by the empty circle - is expanding on the turning element 95 and takes up the position of the vertically striated expanded magnetic strip 99a. The extremely strong attracting positive charges arising at the ends of the closed minor loop consisting of gapless propagate elements considerably expand the magnetic bubbles. The rate of expansion is much higher than in the case of a minor loop consisting of gap-separated elements (e.g. the element 52 in. the US-PS 4 193 124). Accordingly, the hook-shaped turn-element 95 according to the invention is more suitable for forming a bubble replicator than the element 52 in US-PS 4 193 124. When the magnetic field rotates in direction 67, as is to be seen in the figure, bubble 99b indicated by the horizontally striated strip is still in an expanded state, however the rate of expansion is considerably less than in the case of the magnetic bubble strip 99a. In position.68 of the rotating magnetic field the bubble strip is shring- ing and takes up the position indicated by the filled circle. When the magnetic field rotates further, the magnetic bubble describes a circular shape.

In Figure 13 a detector circuit according to the invention is to be seen, containing the elements with a chevron character and the magnetic lock of which consists of one single narrowing only. The detector circuit is formed of rows comprising the said elements with the chevron character, whereas the elements having been . arranged above each other in different rows form columns with an increasing number of the elements; in the direction of propagation of the magnetic bubble, in two adjacent selected columns. forming the detector, two propagate elements 100 each arranged above each other are alternately interconnected and they are provided with the outer connections 114 leading the detector current of the two columns. In the magnetic bubble oxpander-de tector circuit the magnetic bubble 102 arriving under the influence of the magnetic field according to Figure 7 from the input direction and having, for example, a ne gative magnetic charge, is expanded into bubble strip 107 under the influence of the extremely strong positive poles formed on the first, second, etc. input edges 104, 105, 106 of the expander circuit, when the magnetic fieldis rotating in the horizontally left oriented direction 68. This process will be repeated twice in the period λ of the propagate element. The rate of expansion, that is, the increase in the number of propagate elements 100 contained in the bubble expander columns, will be determined by the mobility of the bubble carrier. When using the expansion according to the invention, there is an increase by a propagate element each λ /2 period at every single first, second and n^th input edge of the bubble expanding column , but with extremely rapid bubble carriers the rate of expansion can be even more. On the expander detector circuit 110, 111 according to the figure the completely expanded magnetic strip 107, led in the direction of proparation of the magnetic bubble 102, arrives at detector circuit 111 having been connected to the alternating legs of the propagate elements. The detector circuit 111 is a column formed by the gapless propagate elements having also been connected in the vertical direc tion. By means of the outer terminal 114 current is led to detector circuit 111 and when a magnetic bubble is travelling through the said circuit, the resistance of the detector will change and a pulse will be emitted by the detector. The aim of expanding the magnetic bubble into a strip is to produce a signal as large as possible and thus to increase the signal-to-noise ratio. After having performed detection, in dependence of the organization of the bubble memory and based on the came principle as that of the bubble expansion but by using propagate elements the number of which decreases in λ/2 period each, the magnetic bubble strip 107 is contacted and led either back into the memory or out of the circuit via the output direction 115 whereupon it is annihilated. The operation of the bubble expander detec tor circuit 110, 111 is based on the recognition, that on the columns having been connected into a gapless circuit built-up of propagate elements 100 in the direction of propagation of the magnetic bubble under the influence of the rotating magnetic field according to Figure 7, line-like magnetic charges are formed and move in the same manner as in the traditional expander -circuits with a chevron character. With the expander- -detector circuit 110, 111 according to the invention, the so-called narrowings 108 are formed by decreasing the width of one of the legs of the propagate element instead of forming the gaps, thus establishing theasym metry being indispensable for the operation of the expander-detector circuit and preventing the return of the magnetic strip 107.

The negative poles 112 formed under the influence of the rotation of the maggnetic field in a horizontally left oriented direction 68 according to Figure 7, being arranged in a line-like manner strongly repel magnetic strip 107, thus establishing the asymmetry needed for the operation of the expander-detector circuit 110, 111. When the magnetic field returns to direction

65 from direction 68, the repulsion previously mentioned prevents the return of the magnetic bubble strip 107 It is obvious that between the element lines having been connected in a gapless manner in the direction of propagation of the magnetic bubble strip 107, gaps 116 have to be formed in a vertical direction between the rows of elements in order to be able to form the connections of the detector circuit 111. In the. said gaps 116 parallel and unidirectional poles are formed; accordingly, the width of gap 116 may surpass the bubble diameter. In Figure 14 a further embodiment of the magnetic bubble expander and detector circuit according to the invention may be seen, the propagation circuit of which is built-up of elements with a chevron character. By placing two propagate elements with the chevron character above each other and by partly filling according to reference 128 the gap in between, the circuit is formed in such a manner that each of the created propagate elements is provided with double leges on one ride on pro pagating means, accordingly, two narrowingr belong to each propagate element. The propagate elements 120 obtained in such a manner form the columns of the bubble expander circuit 123 and the detector circuit 125, while the adjacent elements form rows, and the rows lying above each other are separated by gaps. One of the columns forming the detector is displaced in a vertical direction by a half-period in relation to the preceding column and the two columns together - of which at least one is provided with an outer current input/output - form the detector circuit. The propagate element 120 illustrated in the figure is produced in such a manner that the two propagate elements 70, 71 according to figure 8 are unified by eliminating, that is, by filling up, the gap between the legs on the left, simultaneously leaving the gap bet ween the legs on the right incorporating the narrowings 121, 122. As a consequence, the asymmetry of element 120 becomes even more pronounced, whereby proparating properties are further improved. On column 130 formed by the superposition of rows 129 consosting of the propagate elements 120 lying next to each other, the bubble domain is expanded gradually into strip and after the resistance of the magnetoresistive detector is changed a sig¬nal is generated at the outer output/input 124 leading the current I to the detector. The path of the detector current is indicated by a dashed line. The vertical connection of the magnetoresistive detector column is formed in such a manner that the second detector column is dis placed in a vertical direction by λy/2 of the element. In such a manner, in contrast to the interconnections 113 of detector 111 (Figure 13) the connections of detector 113 are formed in such a manner that subsequent connections become superfluous. Accordingly, the expander circuit 123 and the detector circuit 125 are built-up of one single type of propagate element 120, that is, the expander-detector columns show same geometry. This solution - differing from all the known expander-detector circuits - involves advantageous possibilities for decreasing the number of basic elements required in the bubble memory. With the known solutions, due to the subsequently connected detector column, the similar geometry of the expander and. the detector circuit could not be obtained. The reduced number of basic elements required according to the invention results in the simpler production of the tubble memory and in more reliable operation since the common area of the diverse elements (i.e. the total operative range of the bubble memory) will generally increase by the reduction of the number of propagate elements. This statement is primarily valid in the case of the detector since, for example, because of the connections of the chevron-detector the narrowest operation margin of the detector is formed around the operation margin of the memories. One of the greatest advantager of the gapless expander-detector circuit lies in that the heat quantity produced under the influence of current I flowing through the detector on the gapless expander-detector columns dissipates more easily; the whole detector circuit 125 performs the r ole of a cooling rib. In such a manner, the temperature of the gapless detector deviates only slightly from the temperature of the other places of the memory thereby resulting in improved operational para¬meters With the known gap-separated detectors the temperature may deviate by as much a 10ºC from the temperature of the other elements of the bubble memory, whereby the thermal-operational range may decrease by as much as 10ºC in the bubble memory. The operation of the gapless expander-detector circuit according to Figure 14 will be described in detail by means of Figures 15 to 17. Figure 15 shows the magnetic strip domain 131 in the momentary position of the rotating magnetic field H_f directed to the legs of the gapless propagate element containing the narrowings. Under the influence of the magnetic field directed upwards to the right, strong positive attracting poles appear on the narrowed legs, while said poles attract the negatively charged magnetic bubbles. Figure 16 shows the position of the magnetic strip domain 131 in the momentary position of the magnetic field H_f., having been turned through 90° in relation to Figure 15 and thus being directed downwards to the right. The strong positive poles 133 appear on the wide legs of the columns of the detector column. The attracting poles on the narrowed legs decrease accordingly, the magnetic strip domain 131 skips over the narrowed legs and takes up the position seen in Figure 16. On the wide legs 32 of the propagate element the magnetostatic interaction is strong as a consequence of which the bubble becomes even more expanded.

Figure 17 shows the position of the magnetic bubble after a further rotation of the magnetic field through 120º. Under the influence of the rotating magnetic field positive poles appear at the edges 134 of the wide legs of the propagate elements, attracting the magnetic strips domain, at the same time strongnegative poles repelling the magnetic strip domain appear on the narrowed leg of the elements of the preceding column, in a column-like manner. The repelling negative poles positive 135, the attractive poles 136 and the strong megnetostatic interaction of the widened leg of the propagate element collectively form the column-shaped magnetic lock allowing the motion of the magnetic bubbles (bubble-strips) fromleft to right only. he expander-detector circuit shown in Figures 13 and 14 is provided with a dummy-detector of identical geometry, provided with a guard rail similar¬ly consisting of gapless elements. The whole memory is enclosed by a guard rail comprising gapless elements to prevent the undesired intrusion of the bubbles. Industrial Applicability

Although the expander-detector circuit shown in Figures 8 to 17 is built-up of V-chaped propagate elements, the conception according to the invention can well be used for propagate elements shaped in different forms without going beyond the scope of the invention.

The circuit according to the invention shows favourable properties in two start-stop directions at an angle 180º with each other and can advantageously be used in bubble memories with a minor loop major loop design. In the course of our experiments, at a frequency of 100 kHz, for a bubble diameter of 5 /um operational range of the start-stop bias magnetic field of 16 Oe could be observed with rotating magnetic fields of 40 Oe, applying a holding field of 5 Oe. The permanent magnetic field oriented in one direction of the rotating magnetic field is called the holding field. The task of the holding field is to fix the position of the bubbles during a stop condition on the propagate structure. Hereinafter gapless asymmetric elements will be called Galepi elements. Since the Galepi elements do not contain gaps, they are more insensitive to photolithographic dimensional changes than are the traditional gap-separatod prorogate elements. Since the Galepi structures are separated by gaps with strict tolerances, the adhesion of the photo resist over a larger surface area is much higher than . with the traditional elements, the production yield will be also increased.

Por the traditional C- and asymmetric chevron elements the condition R = D/2 is fulfilled, where R stands for the gap width, V for the line-width and D for the bubble diameter. In the case of a 1 μm photolithogaphic resolution D/2 = R = V = 1 μm D = 2 μm In the element periodicity λ_x = λ_y = 4 D is imperative, accordingly λ_x = λ_y = 8 μm.

The εpece requirement of 1 bit information amounts to λ_x λ_y= 64 μm², the information density to be obtained by traditional elements amounts to 16 Kbit/mm² with the new-type Galepi circuits the postulate V = D, R = 0 is advantageously fulfilled; at 1μm resolution 1 μm==D. λ_x = λ_y = 4D = 4 μm Accordirgly, by means of the elements accord¬ing to the invention an information density of 64 Kbit/mm² can be obtained. From these data it becomes obvious that .the storing density of the new-type Galepi propagation circuits amounts to two- to fourfold that of the traditional ones; as a consequence, by using the propagate elements according to the invention considerably cheaper bubble memories can be constructed.

By using contact-lithogaphy with 1 μm resolution and chemical etching, the 1 μm bubbles can be well propagated on the Galepi propagate elements. When overetching the figures to controlled extent, propagation of the bubbles under 1 μm, of submicron size also becomes possible. The gapless expander-detector circuits show further advantageous features. In contrast to the gapseparated detector-circuits known up till now, the geometry of the detector and that of the expander circuit are the same in consequence of which the number of the basic elements needed for the bubble memory can be reduced resulting in more reliable operation of the memory. The gapless expander-detector circuit forms a large continuous surface with good thermal conductivity, thus its thermal properties are far better than those of the gsp-separted circuits. The local temperature raising caused by the detector current according to the invention can be reduced to a greater extent whereby the thermal operational range of the bubble memory will also be improved.

Claims

W H A T W E C L A I M :

1. Propagation-expander and -detector circuit for a magnetic bubble memory consisting of a single- crystal non-magnetic substrate, of a magnetic film allowed to be grown epitaxially on said substrate and carrying the magnetic bubbles and bubble strips, comprising furthermore propagating, expanding and detecting elements formed with a broken contour of a soft magnetic film, being arranged in the direction of propagation of the bubble and bubble strip, having a permanent magnetic field requi red for the production of the bubbles, furthermore for performing propagation of the bubbles, a means for inducing a magnetic field rotating in the plane of the film, characterized in that it comprises α propagation circuit essentially consisting of elements with a broken contoru (chevron, V, U and C-shape) and hock-shaped turn elements and the elements are directly -gaplessly- connected and every element contains at least one part modified in width and deflecting the path of the bubble, end the deflecting forms a magnetic lock closing the return of the magnetic bubble in part of the period of the cycle of the rotating magnetic field, after the transit of the bubble.

2. Circuit as claimed in claim 1, characterized in that the propagation circuit contains elements (70, 71) with a chevron character, the magnetic lock of whichconsists of one single narrowing (75) (Figure 8).

3. Circuit as claimed in claim 1, characterized in that - with regard to the direction of propagation the propagatons circuit contains a rectangular shaped path (84) widened at the input, a wide path-section, a following narrowed path (85a) and a further narrow parallelogram (87) in the next leg (Figures 9 to 11).

4. Circuit as claimed in claim 1, characterized in that it comprises two arms (93, 94) hiving been displaced by 180º in relation to each other, cintaining the elements each with a widening (96) and a narrowing (98) as well as with constant paths (97) interconnecting the widening (96) and the narrowing (98), while on both ends of the arms there are hook-shaped turn-elements (95) arranged, also being at an angle of 180° in relation to each other and connecting the two arms (93, 94) form a closed loop (Figure 12).

5. Circuit as claimed in claim 2, characterized in that it coriains an expander circuit (110) and a detector circuit (111) formed of the elements (70) with a chevron character, the circuits having been formed of rows of propagate elements 100 ), while the elements superposed on each other arranged in different rows- form columns with elements in different numbers, lying perpendicularly to the input direction (101) of the magnetic bubble, whereas in two adjacent selected columns forming the detector (111) two elements (109) each lying above the other are in alternating interconnection and at least one of the columns is provided with an outer input/output (114) (Figure 13).

6. Circuit as claimed in claim 2, characterized in that by positioning in pairs the elements (70) with a chevron character above each other and by filling partially the gap in between, a circuit, is formed in such a manner that each propagate element is provided with two legs per propagate element on one side, accordingly two narrowings belong to each single propagate element; from the propagate elements (120) having been obtained in such a manner the columns (130) of the bubble expander-detector circuit are formed, while the adjacent elements are arranged in rows (129) and the second column forming the detector is vertically displaced, for example, by a half-period ( λ y/2) in relation to the preceding column, and at least one of the two columns forming the detector (125) is provided with an outer input/output connection (124) (Figure 14).

7. Circuit as claimed in claim 5 or 6, characterised in that it incorporates a dummy-detector being provided with a guard rail also consisting of gapless elements (70, 90, 100, 120), the geometry of which is the same as that of the detector circuit (111, 125) (Figures 8 to 14).

8. Circuit as claimed in claim 1, characterized in that the expander-propagation-detector circuit of the bubble me mory is enclosed by a guard rail consisting of gapless elements (70, 90, 12) (Figures 8 to 14).

R E F E R E N C E C H A R A C T E R S

20 magnetic bubble memory

21 substrate

22 magnetic film 23a-n minor loops

24 major loop

25 source of the drive field

26 control circuit

27 replicate conductor

28 pulse source

29 expander-detector circuit

30 detector

31 utilization circuit

32 guard rail

33 conductor

G Generator conductor

S conductor for synchronisation

35 first chevron element

36 second chevron elemen

37 gap 38 width

40 path λ period

41 first chevron element

42 second chevron element propagation direction left to right

43 propagate element

44 magnetic bubble

(propagate) element 4 6 first column

47 second column

48 third column

49 n-th column

50 input direction

51 detector circuit 52 direction of propagation of bubbles

53 drive field source

54 drive field

55 in the vertical direction

56 propagation and expander circuit

57 magnetic strip

58 input edge

59 output edge λeriod

61 magnetic bubble film

62 spacer

63 wedge-shaped

65 drive field orientation at 0°

66 drive field orientation at 90

67 drive field orientation at 180°

68 drive field orientation at 270°

I first quarter of the rotation

II second quarter of the rotation

III third quarter of the rotation

IV fourth quarter of the rotation

70 first propagate element

71 second propagate element

72 first leg

73 second leg 74 wide path 75 narrow path (narrows) λ period

80 (first propagate) element

81 (second propagate) element

82 first leg

83 second leg

84 rectangle shaped wide path

85 triangle shaped path

86 wide parallelogram

87 narrow parallelogram (narrow s) 85a narrow path λ period

90 first propagate element

91 second propagate element

92 n-th propagate element

93 upper arm

94 lower arm

95 hook-shaped turn-element

96 widening

97 path of constant width

98 narrows

99 bubble

99a magnetic strip domain (strip) 99b magnetic strip domain (strip)

100 propagate element

101 input direction

102 magnetic bubble

104 first input edge

105 second input edge

106 n-th input edge

107 magnetic strip domain 108 narrows

109 path of constant width

110 expander circuit

111 detector circuit

112 minus poles

113 interconnection

114 outer connection

115 output direction

116 gaps between lines of elements

120 propagate element

121 first narrows

122 second narrows

123 expander circuit

124 outside in/out connection

125 detector circuit

126 input direction

127 output direction

128 filling

129 line

130 column

131 magnetic strip domain (strip)

132 leg

133 strong plus pole

134 edge

135 minus pole

136 plus pole