GB2162709A - A magnetic bubble memory - Google Patents

Abstract

A protrusion having a contour inclined to the microscopic bubble transfer direction is provided at the foot-base part of the entrance and exit positions for magnetic bubble of non-symmetrical Chevron transfer patterns. This protrusion reduces widening of the transfer gap by photograph processing, deepening the potential well and making dense the contour line of the potential well at the center of gap to thereby improve the bias margin. <IMAGE>

Description

SPECIFICATION A magnetic bubble memory Background of the Invention The present invention relates to a magnetic bubble memory, and particularly to a magnetic bubble memory having improved transfer pattern.

As an ordinary magnetic bubble transfer path, a so-called a field access system is mainly used, where a soft ferro magnetic material thin film pattern composed of permalloy is magnetized by a rotating field. The patterns shown by the enlarged plan views of essential portions shown in Fig. 1 have been mainly employed as the patterns of such magnetic bubble transfer paths. Fig. 1(a) shows the transfer path which is formed by a nonsymmetrical Shevron pattern 10 employed as the basic pattern, Fig. 1(b) the transfer path which is formed by a half disc pattern 11 as the basic pattern and Fig. 1(c) the transfer path which is formed by a C-shaped pattern 12 as the basic pattern.

These transfer patterns are discussed, for example, in the IEEE Transactions on Magnetics, VOL. MAG12, No. 6, November 1976. P614 -P617 and P651 P653, as the parallel gap pattern.

With further improvement in high integration and density of magnetic bubble memory element in these years, diameter of magnetic bubble used is further super-miniaturized to about 1.0 um from existing diameter of about 1.5 um. The magnetic bubble transfer path is also further miniaturized.

Namely in case the period of basic pattern is À as shown in Fig. 1, existing period has been 12 ~ 16 > m but recently it is reduced to about 8 ~ 6 #m. Moreover, the pattern gap g, minimum pattern width W are also super-miniaturized up to about 1.0 Fm which is considered as the limit of the current photolithography technology. - - Such super-miniaturization in constitution requires severe bubble transfer characteristics repre-sented by a bias margin and results in remarkable deterioration of yield due to a little dispersion and fluctuation of manufacturing processes.

Summary of the Invention It is an object of the present invention to provide a magnetic bubble memory which has improved bias margin.

It is another object of the present invention to provide a magnetic bubble memory which enhances yield.

It is further object of the present invention to provide a magnetic bubble memory which has realized less power consumption of peripheral circuits.

According to an embodiment of the present invention, a permalloy transfer pattern is prepared wherein protrusions are respectively provided in the rears near the bubble exit and entrance. Such protrusions are employed in the stage of pattern design and are also reproduced almost in the same pattern even in the case of mask for the photograph processing. At the end of patterning of permalloy, namely formation of pattern, a gap g between the bubble exit and entrance of adjacent two transfer patterns along the bubble transfer direction has been reduced, owing to the protruded design pattern. Accordingly, as compared with existing design pattern, the protruded design pattern assures small gap g when it is completed and large bubble transfer bias margin.This protruded design pattern is effective for enhanced absorbing force of bubble, deeper well potential and moreover sharp gradient of well potential and also ensures thereby the improvement of bias margin.

Other objects and features of the present invention will be well understood from the following explanation with respect to the accompanying drawings.

Brief Description of the Accompanying Drawings Figure 1 is a plan view of existing transfer pattern.

Figure 2 shows the patterning of transfer pattern by the photograptfing and result of analysis for the points to be considered.

Figure 3 shows analysis for influence of potential well given to the magnetic bubble depending on difference in the shape of transfer pattern and Fig.

3C shows the transfer pattern of the present invention.

Figure 4B shows comprarison of three kinds of transfer patterns delineated in Figure 4C.

Figure 5, Figure 7 and Figure 8 are other embodiments of the present invention.

Figure 9, Figure 10 and Figure 11 respectively show entire constitution, sectional view of structure and peripheral circuits of the magnetic bubble memory chip to which the present invention is applied.

Detailed Description of the Preferred Embodiments Fig. 2A shows a permalloy transfer pattern and the pattern 10 indicated by a dotted line is a design pattern (CAD (Computer Aided Design) pattern) stored in the computer, a pattern stored in the pattern generator which converts the CAD pattern to the integrated data in the unit angle pattern for generating mask pattern or a photo mask pattern formed by a photo repeater or an electron beam drawing apparatus, etc.

Even when a photo mask pattern is formed, as indicated by a dotted line in Fig. 2A, in accordance with a design pattern, a completed pattern shows roundness at the points of inflexion of polygonal line as indicated by a solid line in the current photograph processing technique. According to analysis by the inventors of the present invention, it is obvious that such roundness widens the gap g between the bubble exit OUT and entrance IN of transfer pattern and thereby upper limit of bias magnetic field is restricted.

Fig. 2B shows a result of observation of movement of bubble B by a microscope. The magnetic bubble passes the path starting from the position B, and terminating the position B12 through B5, B8, in time to the movement of rotating magnetic field.

Hereinafter, this path is called a microscopic bubble transfer direction. As is understood from this figure, the magnetic bubble shifts to the end part B7 (position IN Fig. 2A) from the end part B5 (position OUT in Fig. 2A) between the adjacent transfer patterns. Therefore it is also provded that roundness at the end part of transfer patterns gives large influence on the transfer characteristics.

In Fig. 3, the well potential distribution characteristics given to magnetic bubble of three kinds of transfer patterns are compared and such distributions are calculated under the conditions that rotating well potential HR is set to 60 [Oe] while bubble diameter to 1.85 [ lm ] and the center of magnetic bubble is located at the gap center of adjacent two transfer patterns (determined by the direction of rotating well potential). The exist and entrance of bubble, namely the foot-base part of the transfer pattern P13 is obliquely chamfered at the angled portions in both right and left sides. The foot-base part of transfer pattern P14 is formed so as to have the two sides crossing at a right angle at the angled portions in both right and left sides.The footbase part of transfer pattern P16 has the sharp two sides at the angle portion nearer to the gap. In the same figure, a contour line and a numeral given thereto indicate a well potential. (Unit: [ Oel).

The maximum well potential of transfer patterns Pal3, P14 and P16 are respectively 36, 38 and 42 [ Oe ] and the bubble can be transferred more easily as this maximum well potential is higher. Therefore, the patterns P1s, P14 and P13 are excellent in this sequence from such point of view.

Regarding the transfer pattern Plus, the contour line indicated by the most external cross-hatched area represents 36 [ Oe ] , including three contour lines of 38, 40 and 42 [ Oel. The transfer pattern P14 has the one contour line of 38 [Oe] in the contour line of 36 [ Oe ] . Since the transfer pattern P13 has the maximum contour line of 36 [ Oe ] , it does not include the other contour lines therein. In above three transfer patterns, since the contour line of 36 [Oe] is almost the same from the microscopic view, the transfer pattern P16 has the most dense contour line at the gap center, in other words, has the sharpest gradient of magnetic field. Therefore, the bubble can be transferred easily.

If the transfer pattern delineated as Fig. 3 can be formed by the high precision photograph processings, even when the respective gaps g of the transfer patterns P14 and P16 are the same, it is obvious that the transfer characteristic of the pattern P16 is more excellent than that of pattern P14 because of the maximum value and distribution density of well potential. Namely, the transfer margin relates not only to the gap g of transfer pattern but also to the shape of it. The shape of transfer pattern P13 is very similar to the shape of completed pattern P166 having roundness of foot-base part shown in Fig.

2. In the case of this pattern, not only the gap g is widened but also the well potential distribution is not so good.

From the distribution diagram of Fig. 3C, it is enough that a pattern is provided in the area nearer to the gap g at the foot-base part of the entrance and exit of bubble of the transfer pattern.

Fig. 4A shows the shape of transfer pattern in the stage of designing three kinds of patterns A, B and C, formation of photo mask and the photograph processing. The patterns of other two stages are delineated as the contour of electron microscopic photograph.

The pattern A illustrates the existing pattern where any bias is not given (C = b, a = d) at the ends (b, c) in the side of gap and at the ends (a, d) in the opposite side at the foot-base part of bubble entrance and exit of transfer pattern. In the patterns B and C, the pattern is added to give the bias to the ends b and c in the side of gap g of the footbase part of bubble entrance and exit of the pattern. The contour is delineated like the stair-case along the minimum beam spot of 25 Xam square of the electron beam exposure to be used at the time of forming the photo mask. In the case of pattern B, the pattern as much as three spots is added, while in the pattern C, the pattern as much as six spots is added.In the stages of forming the photo mask and photograph processing, the respective contour lines of patterns have the roundness but in the finally completed permalloy pattern, the gap g between the transfer patterns becomes smallest in the pattern C but largest in the pattern A.

Fig. 4B shows the actually measured data of intergap transfer characteristics of completed three kinds of permalloy patterns.

In the same figure, the curves A, B and C respectively show the characteristics of the patterns A, B and C in Fig. 4A. The upper side represents the upper limit of bias magnetic field, while the lower side the lower limit thereof. The upper limit value of the curve C at the rotating well potential H, = 60 [ Oe ] is not shown because it exceeds 260 [Oe]. As is understood from this characteristic, the upper limit values of bias field are remarkably improved in the patterns B and C as compared with that of existing pattern A and the lower limit value is also considerably improved. Accordingly, a bias margin (upper limit value -lower limit value) can also be improved distinctively.

Fig. 5 illustrates the pattern near the swap gate of a magnetic bubble memory chip to which the improved transfer pattern of the present invention is applied. The transfer patterns 11 ~ 1,6 form the minor loop m for storing information and the magnetic bubble is transferred in the counterclockwise direction shown by PR, in the figure. Jl ~ J6 are permalloy transfer patterns forming the write major line WML and the magnetic bubble is transferred in the direction shown by PR in the figure. P,, P,, P, are permalloy auxiliary bar patterns for assisting the transfer. CND is a conductor layer for controlling bubble exchange and it is formed like a hairpin curve at the transfer pattern 16 of the minor loop m. The bubble generated by the bubble generator is transferred from right to left in the figure along the patterns J1 - J6 and the auxiliary bar pattern P, inserted between these patterns in synchornization with the movement of rotating magnetic field H,. Bubble exchange, namely writing of data is carried out as explained below. When the write data is transferred to the specified bit position of major line and the rotating magnetic field H, becomes to the specified phase, a current is caused to flow into the conductor layer CND.In -this case, the bubble located at the left side of pattern 18 is transferred to the foot-base part of entrance of the pattern J passing through the auxiliary patterns F#, Pm. Moreover, the bubble located at the lower part of auxiliary pattern P, of the major line is transferred to the patterns 1166, 16 through the pattern P.

The improved transfer pattern explained with reference to Fig. 3 and Fig. 4 is adopted to the entrance of each bubble of transfer patterns 11 ~ 16 and patterns 111 ~ 116 of minor loop m, entrance of 17 and exit of 116. The enlarged views of pattern enclosed by the circles 5B and 5C are respectively shown in Fig. 5B and Fig. 5C. As is understood from the enlarge views, a protrusion formed like a rectangular equilateral triangle having the length of two sides of 1 [ m ] (the polygonal like the staircase is considered as an oblique line) is provided in the side of gap g ata the foot-base part of transfer pattern where the transfer margin is very severe.

In the same figure, the contour line of other oblique line of the transfer pattern is actually formed like the staircase in accordance with the electron beam spot of 25 [ 'im ] square but such staircase form is omitted herein.

Fig. 6 is a plan view of the part near the swap gate indicating another embodiment of the present invention. This figure is different from Fig. 5 only in such a point that the protrusions indicated by the cross-hatched areas are provided in the bubble transfer path from the transfer patterns 17 to 18, from 16 to 116, from P, to Pmt from Jl to J2 and from J3 to 1166.

As is proved by the analysis for Fig. 2, transfer margin of bubble is severe when the bubble passes the gap g at the foot-base part of transfer pattern and operation often fails even when the gap g deviates only for 0.1 ~zm. Therefore, a large bias margin in the embodiment explained above results in resistivity to manufacturing dispersionand improvement in manufacturing yield. The transfer margin depends not only upon gap, size of transfer pattern and period but also bubble diameter. When the bubble diameter becomes 1 [ m ] or less, the protrusion must be provided to the entire -part as shown in Fig. 6, even to the area where the transfer margin is larger than the other areas (patterns P,, P,, P, and major loop J1 ~ J5, ect.).

The present invention is not restricted only to said embodiment and can be modified as shown in Fig. 7. In the same figure, a rectangular protrusion is provided at the transfer pattern P13. In the transfer pattern P14, a protrusion is provided to the half disc pattern and in the transfer pattern P1s, a protrusion is provided to the C-shaped pattern.

Fig. 8 shows an example of wide gap transfer pattern to which the present invention is applied.

In Fig. 8A, the part indicated by a dotted line is the contour line of existing pattern and the part indicated by a solid line is a pattern improved by the present invention. When focusing on the foot-base part of bubble entrance of transfer pattern, the existing contour line e at the bottom part of foot-base is almost parallel to tfië microscopic bubble trans fer direction PR (direction of minor loep major line) but the contour line f at the bottom of;cf#ot- base of improved pattern is inclined. Thereby, the pattern is added to the foot-base part in the side of gap (part h) and the opposite part (part k) is re moved. As a whole, the pattern is biased to the side of gap.Fig. 8B shows the result of measure ment of transfer margin in the gap between the permalloy transfer patterns thus formed on the ba sis of such design pattern. In the same figure, the curve I is the characteristic of transfer pattern hav ing the improved contour line f, while the curve 11 is the characteristic of transfer pattern having the existing contour line e. As is understood from the same figure, the improved pattern has improved remarkably the bias margin.

The total constitution, structure of sectional view and peripheral circuits of a magnetic bubble mem-ory chip to which the present invention is applied are explained respectively with reference to Fig. 9, Fig. 10 and Fig. 11.

Fig. 9 schematically illustrates a magnetic bubble memory (MBM) chip ChlP with a pair of 1 Mbits blocks. In a 4 Mbits MBM device package, for ex ample, two of chips are contained.

In Fig. 9 are shown minor loop m for storing information, a read major lilne RML for transferring the read out information and a write major line WML for transferring the written information, a bubble detector D for converting magnetic bubbles into electrical signals, a bubble generator G for generating magnetic bubbles and a replicate gate circuit R for replicating or transferring the information of the minor loops m to the read major line RML.

Further, T represents a transfer gate circuit for transferring the information on the write major line W2L to the minor loops minor q swap gate for swapping the information of the minor loops m to the major line WML at the same time that the transfer of information proceeds, that is, for ex changing information between them. Further, a guardrail GR surrounding the outer periphery of them prevents entry of magnetic bubbles.

The gates R and A and the bubble generator G are controlled, depending on whether or not a cur rent in a prescribed direction is supplied to con ductors in a separate layer disposed in a particular relationship with the propagate pattern of permal loy. In the drawing, the conductor portion is repre sented by a thick solid line and the propagate pattern of the permalloy is represented by fine solid lines. The conductor layers respectively for the replicate gate, swap gate and bubble generator are connected on one ends thereof in common within the chp and, further, connected on the wir ing circuits board outsidesthe chip together with one of the common terminals for the main and dummy magnetic resistance elements of the bub ble detector to common terminals COM 1 and COM 2.

Fig. 10 illustrates in cross section the neighbor hood of a bonding pad PAD of a magnetic bubble memory chip.

GGG denotes a gadolinium-gallium-garnet substrate. LPE denotes a magnetic bubble film formed by the liquid-phase epitaxial growth method. ION denotes an ion-implanted layer formed on the surface of LPF film for the repression of hard bubbles.

SPI denotes a first spacer which is formed of SiO2 in a thickness of 3,000A by the gaseous-phase chemical reaction method, for example. CND1 and CND2 denote two conductor layers which function to repress the phenomena of generation, replication (division), and interchange of bubbles. The upper conductor layer CND1 is made of Mo and the lower conductor CND2 is made of Au. SP2 and SP3 are interlayer insulating films (second and third spacers) made as of polyimide resin and adapted to insulate electrically the conductor CND from a transfer pattern layer P made as of permalloy and formed on the conductor CND. PAS denotes a passivation film formed as of SiO3 by the gaseousphase chemical reaction method. PAD denotes a bonding pad for the chip.Fine connector wires made as of A are joined to this bonding pad by the thermocompression bonding method or the ultrasonic wave bonding method. The bonding pad PAD is formed as of A.

In this bonding pad PAD, the lowest first layer PAD, is formed by Cr, the center second layer PAD2 by Au layer and the upper most third layer PAD3 by Au-plated layer, respectively. The second layer PAD2 and the third layer PAD3 may be formed by the material such as Cr and Cu, etc. P indicates the layer to be used for bubble transfer path, bubble divider, generator, exchanger, detector and moreover for the guardrail. Improvement of foot-base part explained above is executed to this layer. This pattern layer may be formed by a permalloy layer consisting of Fe-Ni or a multi-layer (P1 P3) structure of Fe-Si alloy and Fe-Ni alloy.

Finally, the neighboring circuits of the element CH1 are explained with reference to Fig. 11. RF is a circuit for generating a rotating magnetic field H, by allowing a current with the phase difference of 90 to the coils X and Y of the element CH1. SA is a sense amplifier which samples and amplifies a minute bubble detection signal sent from the magnetic resistance element of element CH1 in such a timing as the rotating magnetic field. DR is a drive circuit which allows a current to flow, in the specified timing, into each function conductor of replicate related to generation of bubble for writing to the MBM device, swap and date reading. The circuits explained above is synchronized by the timing generation circuit TG so that it operates in synchronization with the cycle and phase angle of rotating magnetic field H,.

According to the present invention, the bias margin is increased as explained above and it means that a low rotating magnetic field H can be used and thereby power consumption of peripheral circuits and power source voltage tcost of parts used) can be reduced.

Claims (2)

1. A magnetic bubble memory comprising a rotating magnetic field generating circuit and a plurality of transferpatterns for transferring magnetic bubble in response to said generating circuit, wherein said transfer pattern has the entrance and exit of magnetic bubble and a protrusion is provided at least to the one of said entrance and exit.

2. A magnetic bubble memory constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.