Note: Descriptions are shown in the official language in which they were submitted.
Background of the Invention
Field of The Invention
This invention relates to bubble domain lattices
and more particularly to an improved bubble domain
lattice structure.
Brief Description of the Prior Art
A bubble domain lattice consists of a plurality of
rows and columns of bubble domains and/or domain stripes
which occupy a spatial arrangement which is determined
to a substantial extent by the interaction between the
bubbles.
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1 A bubble lattice initialization method is described in U.S.
Patent No. 3,953,842, issued April 27, 1976 and assigned to
the assignee of the present invention. As described therein
the method provides an initial lattice containing a plurality
of rows of substantially perfect parallel stripe domains and
bubble domains.
It has been observed that several problems exist in the
formation and operation of a bubble lattice device. One such
problem occurs during the translation of bubbles in the
access column from and to the input and output ports respec-
tively. The current that is applied in the conductor pat-
tern to move the bubbles in the access column has a tendency
to also move the bubbles in the adjacent columns by an
amount which is sufficient to disturb the integrity of the
lattice.
Another problem pertains to obtaining a particular
number of rows in the bubble lattice. The number of rows of
bubbles and/or stripe domains in a lattice in a given area
depends to a large extent on magnetic material parameters
which are determined by the chemical composition and the
growth conditions of the bubble material. For example, to
obtain a lattice having 28 rows of bubble domains in a given
space on a garnet film, it is necessary to closely control
the chemical composition of the garnet film. Unless the
chemical composition is closely controlled the number of
rows in this example can vary quite easily from, for example,
27 to 32 rows. As a result it is necessary to closely con-
trol the material parameters to obtain the same number of
rows with different films in a given area.
Still another problem that has been observed deals with
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1 the translation of the bubbles laterally in the rows. Bub-
bles having a S=0 state, that is, where there is one pair of
Bloch lines in the walls of the domain, move in a direction
of an applied field gradient while bubbles having a S=l
state, that is, when there are no Bloch lines in the wall of
the domain, move at an angle to the gradient. Since the
conductor lines used to provide the lateral propagation or
movement of the bubbles are parallel to the columns and are
not perpendicular to the bubble rows, both the S=0 and the
S=l state bubbles may have a component of force which is not
in the direction of translation, i.e., the horizontal direc-
tion of the rows. This force may, at times, cause one or -
more of the bubbles to sway or deviate from the horizontal
direction.
Another problem is observed during or after the forma-
tion of a substantially perfect array of parallel stripe
domains. It has been observed that on occasion the stripes
that are formed stripe out in a direction which is per-
pendicular to the conductor rather than along the horizontal
direction of the row. These difficulties occur due to the
magnetostatic interactions between stripes and bubbles in
the adjacent column and because the gradient being applied
is in the direction perpendicular to the conductor when the
current is applied to it.
SUMMARY OF THE INVENTION
It is a primary object of this invention to provide an
improved bubble lattice structure.
It is another primary object of the present invention
to provide a stable bubble domain lattice arrangement.
It is another object of this invention to provide a
bubble lattice structure suitable for improved column
access
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ing operations.
It is still another object of this invention to provide
a bubble lattice structure which maintains the integrity of
the lattice in columns that are adjacent to the access
columns.
It is yet another object of this invention to provide
a structure with a given number of rows in a given area.
It is yet still another object of this invention to
provide a bubble lattice structure which permits magnetic
material parameters to vary somewhat while still obtaining
a given number of rows in a given area.
It is another object of this invention to provide a
structure which reduces or inhibits the skew movement of
bubbles during horizontal translation.
It is a final object of this invention to provide a
bubble lattice system which assures the integrity of the
substantially perfect lattice array of bubble domains and/
or stripe domains during and after formation.
These and other objects are accomplished by the use
of one or more barriers being positioned in a lattice
between the rows of bubbles. An example would be a bubble
lattice containing 16 rows of bubbles and stripe domains.
Three barriers would be used by positioning one barrier
every fourth row. The barriers would extend from one side
of the lattice to the other side and have openings therein
at columns which are used to access or move the bubbles
from or to the input/output ports where the bubbles are
inserted or extracted from the lattice.
Other objects of this invention will be apparent from
the following detailed description reference being made to
the accompanying drawings wherein various embodiments of the
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1 bubble lattice structure containing barriers are shown.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a top view of a lattice containing barriers
between rows of stripe domains at the end of the lattice.
Fig. 2 is a top view of a lattice containing barriers
positioned between rows of stripe domains and bubble domains
in the middle of the lattice.
Fig. 3 is a top view of a lattice containing stripe
domains and bubble domains with barriers positioned between
adjacent rows and with openings in the barriers for the
columns which access to the input and output ports.
Fig. 4 is a top view of a lattice containing stripe
domains and bubble domains with barriers positioned evexy
fourth row and with openings in the barriers for the columns
which access to the input and output ports.
Fig. 5 shows a bubble domain lattice arrangement em-
bodying the stripe domain buffer sections at each end;
Fig. 6 illustrates one embodiment of a stripe domain
length adjusting means usable in the arrangement shown in
Fig. l;
DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS
As shown in Fig. 1, the lattice 10 is contained by a
retaining means 12. Along one end of the lattice 10 are a
column of stripe domains 14. Positioned between the stripe
domains 14 in accordance with this invention are barriers
16. The barriers 16 may be a dam, a groove, or an equivalent
retaining means. A dam can be an area of increased film
thickness. A groove is an area of decreased film thickness.
Grooves can be used that are empty or they may contain
bubble domains and/or stripe domains. Other equivalent
retaining means
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1 which may be used as barriers are current carrying conductors
2 as shown in Fig. 6, ion implanted regions, silicon diffused
3 regions, permalloy patterns and material defect regions.
4 As shown in Fig. 1 the barrier ~6 is positioned beside
every row, that is, it is positioned between two stripe domains
6 14 so that every stripe domain 14 is separated from another
7 stripe domain 14 by barrier 16. Positioning one barrier 16
8 for every row containing a stripe domain 14 provides maximum
g integrity to the stripe domain portion of the lattice. The
barrier 16 may be positioned every one to sixteen rows. The
11 preferred range is every one to four rows. In general, placing
12 the barrier in large lattices so that the barrier is positioned
13 more than 16 rows does not provide sufficient integrity for
14 the lattice most of the time.
In Fig. 2 a bubble lattice 20 is contained by retaining
16 means 22. Positioned away from the ends of the lattice are
17 stripe domains 24. Positioned between the stripe domains 24
18 and two columns of bubble domains 28 are barriers 26 which
19 retain the integrity of the lattice. Fig. 2 is similar to
Fig. 1 with respect to the relationship between the stripe
21 domains 24 and the barriers 26. One difference between Fig.
22 1 and Fig. 2 is the position of the stripe domalns 24 and
23 the barriers 26 being away from the ends in Fig. 2 whereas
24 in Fig. 1 the stripe domains 14 and barriers 16 are adjacent
one end. Another is that in Fig. 2 the barriers 26 separate
26 both stripes and bubbles.
27 In Fig. 3 a lattice 30 is confined by retaining means 32.
28 Openings in the retaining means 32 are provided for input
29 ports 31A, 31B and 31C as well as output ports 33A, 33B and
33C. The lattice contains a column of stripe domains 34A
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1 at one end of the lattice and a column of stripe domains 34B
2 at the other end of the lattice. Positioned in rows between
3 the columns of stripe domains 34A and 34B are bubble domains
4 38. Positioned in a column between the stripe domains 34A
and 34B are barriers 36A and 36D, respectively. Positioned
6 in a column between the various rows of bubbles 3 8 are barriers
7 36A, 36B, 36C and 36D. The barriers 36A, 36B, 36C and 36D
8 are separated from each other by a space or access column in
9 which a column of bubbles 39A, 39B and 39C, respectively, may
be moved from input ports 31A, 31B and 31C into the lattice
11 as well as from the lattice to output ports 33A, 33B and 33C.
12 The use of separated barriers in the same row adjacent
13 to columns which are used for accessing is important in re-
14 taining the integrity of the lattice during the accessing of
a column of bubbles. In the absence of separated barriers in
16 the same row, the movement of bubbles in an access column with-
17 out distorting the position of bubbles in the columns adjacent
18 thereto is difficult. In general, if a driving force of
19 sufficient strength to move the bubbles in the access column
is provided, the bubbles adjacent thereto are also affected
21 by the driving force and their relative position in the per-
22 fect lattice is somewhat distorted. The presence of barriers
23 on either side of the access channel effectively maintains
24 the adjacent bubbles in their relative position so that the
z5 accessing of bubbles does not disturb the integrity of the
26 lattice.
27 The structure shown in Fig. 3 is also useful for pre-
28 senting any bubbles from "swaying" or moving in a direction
29 which is not horizontal. The interaction of the bubbles in
combination with the barrier reduce any deviations from hori-
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1 zontal movement so that no problem of this type exists.
2 In Fig. 3 there is a barrier between each row of stripe
3 domains and bubble domains. Such an extensive use of barriers
4 provides maximum rigidity and/or integrity to the lattice.
There are several factors which need to be considered in de-
6 termining the spacing of the barriers. One factor is the
7 width of the particular barrier being used. For example,
8 devices fabricated with bubble material having a demagnetized
g strip width of 5 microns have dams which are about 4 microns
wide whereas groove or grooves containing bubbles are about
11 8 microns wide. Another factor is the spacing of the bub-
12 bles in the lattice. Presently, the spacing is about 11.5
13 microns from center to center of the bubbles. Still another
14 factor to be considered is the lithography processes used
to make the barriers. Devices made with bubble material
16 having a demagnetized strip width of 5 microns presently have
17 a center to center spacing of bubbles in the lattice of about
18 Ll.5 microns. Still another factor to be considered is the
19 lithography processes used to make barriers. Conventional
photolithographic techniques and commercially available equip-
21 ment are limited to forming masks and patterns with a linewidth
2'2 of 2 microns or larger. This implies that when a barrier is
23 used between a row of stripe domain and bubble domain the
24 minimum spacing between bubbles in the lattice is approximately
ll.S microns. The spacing between bubbles may be decreased
26 by using a barrier between every two or more stripe and bub-
27 ble domains.
28 Fig. 4 illustrates a preferred embodiment of this inven-
29 tion. A lattice 40 is confined by retaining means 42. Open-
ings in the retaining means 42 are provided for input ports
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1 41A, 41B and 41C as well as output ports 43A, 43B and 43C.
2 The lattice contains a column of stripe domains 44A at one
3 end of the lattice and a second column of stripe domains 44B
4 at the other end of the lattice. Positioned between the column
of stripe domains 44A and the stripe domains 44B are columns
6 of bubble domains 48. Each row in the lattice contains a
7 stripe domain 44A, a row of bubbles 48 and a stripe domain
8 44B. In Fig. 4 bubble lat~ice 40 has a barrier 46A, 46B,
9 46C and 46D positioned below the fourth row of stripe domains
and bubble domains. Barriers47A, 47B, 47C and 47D is posi-
11 tioned below the eight row of stripe domains and bubble do-
12 mains. Barriers48A, 48B, 48C and 48D are positioned below
13 the twelfth row of stripe domains and bubble domains. Bar-
14 riers 46A, 47A and 48A are separated from barriers 46B, 47B
and 48B by a eolumn aeeessing ehannel eonneeted to input port
16 41A and output port 43A. Barrier 46B, 47B and 48B are sepa-
17 rated from barrier 46C, 47C and 48C by a eolumn accessing
18 ehannel eonneeted to input port 41B and output port 43B.
19 Barriers46C, 47C and 48C are separated from barrier 46D, 47D
and 48D by a eolumn aeeessing ehannel eonnected to input port
21 41C and output port 43C.
22 In certain applieations this lattiee 40 arrangement
23 containing barriers every fourth row is very effective in
24 providing many improved eharaeteristies for such a lattice.
The barriers on both sides of the column aceessing ehannels
26 provide suffieient rigidity or lattiee integrity for the
27 eolumns of bubbles adjaeent the eolumn accessing ehannel.
28 It has also been found that this eonfiguration readily
29 yields the desired number of rows of stripes and bubble do-
mains, for example, in this ease 16 rows. The material
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1 specifications can vary over a wider range and still 16 rows
2 can be obtained. Without the three rows of barriers the
3 material composition would have to be more closely controlled
4 in order to obtain 16 rows. With this,structure it is pos-
sible to obtain 16 rows on material compositions which yielded
6 either more than or less than 16 rows when there were no
7 barriers present in the lattice.
8 The barriers which were dams having a thickness thicker
9 than the remaining film, also reduced or eliminated the curl-
ing of the stripe domains as well as any possible swaying
11 effect of bubbles.
12 The adaption of the apparatus according to the present
13 invention for inducing translations of bubble domains in a
14 preferred embodiment of an information store is shown in
Fig. 5. Fig. 5 shows a detailed diagram of bubble domain
16 arrangement 20 formed on a suitable medium 22 for supporting
17 bubble domains, Medium 22 can comprise any of the well-
18 known materials permitting bubble domain propagation in-
19 cluding rare-earth orthoferrites and garnets.
The bubble domain arrangement 20 in Fig. 5 includes
21 a lattice 21 comprising six rows of domains with each row
22 having seventeen domains, fifteen circular information
23 storing bubble domains D hereinafter called bubble domains
24 and two elongated bubble domains S hereinafter called stripe
domains. The domains are contained within an enclosure
26 means, guide rail 24, which surrounds the entire lattice
27 21. Guide rail 24 prevents the domains from escaping the
28 lattice 21 and along with the interactive forces between
29 domains provides the lattice integrity.
Three column accessing devices 26 A-C are shown, each
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1 comprising a write means W, such as a nucleating and encoding device, and a
sensing or reading means R, such as a magnetoresistive sensor. An example
of a column accessing device usable with the preferred embodiment of the
present invention, as shown in Fig. 5, is given in copending U.S. Patent
Application S.N. 429,601 filed on January 1, 1974, and assigned to the
assignee of the present invention.
For the purposes of this description, column accessing devices
26 A-C insert and remove bubble domains D from the lattice 21 in a direction
substantially transverse to the direction of domain propagation defined by
the lattice. The bubble domains D are propagated in a horizontal direction
in the plane of Fig. 5 into the column accessing devices 26 A-C by pro-
pagation means such as propagation conductors 28 and 29 supported by the means
elongating and contracting the stripe domains S, all under control of a pro-
pagation current control unit 30 and grounded by means not shown. Six bubble
domains of any one column located in a column accessing device can be moved
transverse to the propagation direction by separate bubble domain movement
means either propagation conductors or a bubble pump shift register ~neither
shown), as described in the aforementioned Patent Application S.N. 429,601.
After detection of the removed bubble domains and transmittal of the inform-
ation sensed to a utilization device 32, new bubble domains having the sameor different information state can be inserted into the same column of the
bubble domains by the write means W under control of a
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1 pulse source 27, or the same bubble domains can be returned
2 to the lattice by reversing the movement direction of the
3 bubble domains in any column accessing device. Any one of
4 the column accessing devices 26 A-C c~n be actuated to sense
one column of bubble domains or several devices 26 A-C can be
6 actuated at one time to sense several columns of bubble domains.
7 The control of the propagation conductors 28 and 29 is
8 accomplished in the well-known manner by the propagation
g current control unit 30. ~he control of the sequences of
operation for the pulse source 27, the propagation current
11 control unit 30, and the utilization device 32 is under
12 control of a control circuit means 36. The control circuit
13 36 controls the operation to form the bubble domain according
14 to tne data required, to propagate the correct column of
bubble domains into the closest column accessing device and
16 then out of the column accessing device 26 A-C for sensing
17 and utilization when retrieval is required. The various means
18 and circuits so far described for Fig. 5 may be any such ele-
19 ment capable of operating in accordance with this invention.
Still referring to Fig. 5, the domain arrangement 20 is
21 characterized by the formation of the stripe domains S at
22 each end of the lattice 21 as a buffer section by elongating
23 and contracting in accordance with changing magnetic field
24 patterns developed by buffer conductors 40-43 placed adjacent
to the ends of the lattice 21 outside of the guide rail 24.
26 As will be discussed later for Fig. 6, the buffer conductors
27 generate a field gradient affecting the size of the stripe
28 domains! S according to the electrical current patterns applied
29 to each buffer conductor by the propagation current control
unit 30,
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1 As shown in Fig. 5, the buffer conductors 40-43 each
2 affect three rows of domains within the lattice. It should
3 be obvious that the buffer conductors each may be individual
4 conductors controlling the size of the stripe domains S for
each row of bubble domains, or can comprise any combination
6 as desired by the particular application. For instance in
7 Fig. 5, the first three rows are controlled by buffer conductors
8 40 and 42 f~rmed on each end of the top portion of the lattice
9 21. Buffer conductors 41 and 43 on each end of the lower
portion of the lattice 21 control the last three rows of
11 bubble domains. The propagation current control unit 30
12 ad~usts the current such that the buffer conductor 40 con-
13 tracts the stripe domain at the left-top portion of Fig.
14 5 while the buffer conductor 42 elongates the stripe do-
mains at the to-right portion of Fig. 5 when a translation
16 of the bubble domain D to the left is required. The current
17 in the propagation conductors 28 are sequenced, as required,
18 to propagate the bubble domains.
19 The reverse situation is shown for the lower three rows
such that the propagation current control unit 30 actuates
21 the buffer conductor 41 such that the stripe domains elongate
22 on the lower left portion of the lattice and actuates the
23 buffer conductor 43 such that the stripe domains contract
24 on the lower right hand portion by appropriately controlling
the current in each translation conductor. Likewise the cur-
26 rent in propagation conductors 29 is sequenced to propagate
27 the bubble domains. A suitable barrier or bubble domain
28 interaction prevention means, interaction line 44 such as a
29 sputter etched groove, is provided between each group of
three rows of bubble domains to prevent the change of inter-
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l action between adjacent stripe and circular domains during
2 individual propagation from affecting the orderly control
3 of the lattice.
4 The enclosure means of the lat~ice 20 of Fig. 5 such
as guide rails 24 and the barrier or interaction line 44 can
6 comprise any of the well known means for controlling the
7 positioning of bubble domains such as by providing a high
8 energy boundary for the bubble domains. Structures to pro-
g vide high energy boundaries can be fabricated from current
carrying conductors and magnetic materials. Also, changes
11 in the magnetic properties of the bubble domain material can
12 be used. Such changes include thickness changes such as a
13 sputter etched groove and changes brought about by ion im-
14 plantation, diffusion, etc. The sputter etched groove used
and discussed herein for the guide rails 24 and the barrier
16 or interaction line 44 of the preferred embodiment should not
17 be taken as limiting this invention.
18 In Fig. 5 the bubble domains of column number 6 of the
l9 first three rows is shown positioned into the column acces-
sing device 26A while the bubble domains of column number
21 2 of the last three rows are positioned in the same column
22 accessing device 26A. Thus, different rows and columns of
23 bubble domains can be intermixed and then sensed by actuating
24 the column accessing device. This feature would be particu-
larly useful in the modification of instruction words stored
26 in an information storage device wherein the high order bits
27 need to be modified at will to control the entry of a com-
28 puter~program into different sections of the memory store.
29 There are several types of translation or buffer con-
ductors that can be used in accordance with the present in-
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1 vention. One type is shown in Fig. 6.
2 Fig. 6 illustrates the working principle of a serpentine
3 current carrying buffer conductor 46 formed on one side of
4 the lattice array. The buffer conductor 46 spatially modu-
lates a bias field along a column direction A. The domains
6 of the end column number 1 thus form stripe domains and
7 position themselves at locations of minimum field value.
8 On increasing the drive current I, the bias field decreases
g at these locations and the stripe domains S of the end col-
umn 1 elongate along the direction B of the arrow, which
11 is the direction of the desired bubble domain D translation.
12 The pressure of the elongation of the stripe domain of the
13 end column number 1 on the adjacent bubble domains in their
14 rows causes a translation pressure in the direction B. At
the same time, buffer conductors at the other end of the
16 same rows contract the end stripe domain relieving some of
17 the translation pressure caused by an elongation of the
18 stripe domains in column 1. A practical limitation of the
19 buffer conductors 46 shown in Fig. 6 arises from the fact that
the period of serpentine conductor pattern has to be equal to
21 the spacing between bubble domain centers in the lattice,
22 distance C. That is, the width of the serpentine buffer
23 conductor 46 must be roughly one-fourth of the lattice
24 spacing. The practical limit for the conductor width at
present is approximately 2um, since at present any lesser
26 conductor width becomes difficult to fabricate by present
27 data photo~ithographic processes.
28 ,It has been further discovered that it is not necessary
29 to use a drive field amplitude modulated along the direction
of the arrow A. A regular stripe domain pattern occurs in
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1 a lattice because of magnetostatic interactions between the
2 stripe domains themselves. Stripe domain lengths can thus
3 be controlled with a straight conductor placed parallel
4 along the direction of the arrow A. In Fig. 6 the defined
orientation of the stripe domains and the interface between
6 stripes and the bubble lattice is accomplished through the
7 serpentine buffer conductor 46.
8 Although several embodiments of this invention have
9 been described, it is understood that numerous variations
may be made in accordance with the principles of this
11 invention.
~2 I claim:
13
14
16
17
18
19
21
22
23
24
26
27
28
29
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