WO2005048262A2

WO2005048262A2 - Mram architecture with a flux closed data storage layer

Info

Publication number: WO2005048262A2
Application number: PCT/US2004/005874
Authority: WO
Inventors: David Tsang; Robert Paul Morris
Original assignee: Applied Spintronics Technology, Inc.
Priority date: 2003-10-16
Filing date: 2004-02-27
Publication date: 2005-05-26
Also published as: US6909633B2; US20040130929A1; WO2005048262A3

Abstract

A method and system for providing and using a magnetic memory are disclosed. The method and system` include providing a plurality of magnetic memory cells (11) and providing at least one magnetic write line (82) coupled with the plurality of magnetic memory cells (11). Each of the magnetic memory cells (11) includes a magnetic element (110) having a data storage layer (1103). The data storage layer stores data magnetically. The magnetic write lines are magnetostatically coupled with at least the data storage layer (1103) of the magnetic element (11) of the corresponding magnetic memory cells (11). Consequently, flux closure is substantially achieved for the data storage layer of each of the plurality of magnetic memory cells (11).

Description

MRAM ARCHITECTURE WITH A FLUX CLOSED DATA STORAGE LAYER

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is claiming under 35 USC 119(e) the benefit of provisional patent application serial no. 60/448,876 filed on February 24, 2003. The present application is related to co-pending U.S. Patent Application Serial No.

10/459,133 entitled "MRAM MEMORIES UTILIZING MAGNETIC WRITE LINES", filed

on June 11, 2003, which claims benefit of provisional application serial no. 60/431,742 filed

on December 9, 2002, and assigned to the assignee of the present application.

FIELD OF THE INVENTION

The present invention pertains to magnetic memories, and more particularly to a method and system for providing a magnetic random access memory (MRAM) that is preferably high density, nonvolatile and that incorporates write-lines having improved writing efficiencies, ease of manufacturing, and better stability.

BACKGROUND OF THE INVENTION Recently, a renewed interest in thin-film magnetic random access memories (MRAM) has been sparked by the potential application of MRAM to both nonvolatile and volatile memories. Fig. 1 depicts a portion of a conventional MRAM 1. The conventional

MRAM includes conventional orthogonal conductor lines 10 and 12, conventional magnetic

storage cell 11 and conventional transistor 13. The conventional MRAM 1 utilizes a

conventional magnetic tunneling junction (MTJ) stack 11 as a memory cell. Use of a conventional MTJ stack 11 makes it possible to design an MRAM cell with high integration density, high speed, low read power, and soft error rate (SER) immunity. The conductive

lines 10 and 12 aref used for writing data into the magnetic storage device 11. The MTJ stack

11 is located on the intersection of and between 10 and 12. Conventional conductive line 10 and line 12 are referred to as the conventional word line 10 and the conventional bit line 12, respectively. The names, however, are interchangeable. Other names, such as row line,

column line, digit line, and data line, may also be used.

The conventional MTJ 11 stack primarily includes the free layer 1103 with the

changeable magnetic vector (not explicitly shown), the pinned layer 1101 with the fixed magnetic vector (not explicitly shown), and the insulator 1102 in between the two magnetic

layers 1101 and 1103. The insulator 1102 typically has a thickness that is low enough to

allow tunneling of charge carriers between the magnetic layers 1101 and 1103. Layer 1100 is

usually a composite of seed layers and an anti-ferromagnetic layer that is strongly coupled to the pinned magnetic layer. Layer 1104 is a nonmagnetic capping layer, which protects the underlying layers 1100, 1101, 1102, and 1103.

Data is stored in the conventional MTJ stack 11 by applying a magnetic field to the

conventional MTJ stack 11. The applied magnetic field has a direction chosen to move the changeable magnetic vector of the free layer 1103 to a selected orientation. During writing,

the electrical current Ii flowing in the conventional bit line 12 and I₂ flowing in the

conventional word line 10 yield two magnetic fields on the free layer 1103. In response to

the magnetic fields generated by the currents Ii and I₂, the magnetic vector in free layer 1103 is oriented in a particular, stable direction. This direction depends on the direction and amplitude of Ii and I₂ and the properties and shape of the free layer 1103. Generally, writing a zero (0) requires the direction of either Ii or I₂ to be different than when writing a one (1).

Typically, the aligned orientation can be designated a logic 1 or 0, while the misaligned orientation is the opposite, i.e., a logic 0 or 1, respectively.

Stored data is read or sensed by passing a current through the conventional MTJ cell from one magnetic layer to the other. During reading, the conventional transistor 13 is turned

on and a small tunneling current flows through the conventional MTJ cell. The amount of

the current flowing through the conventional MTJ cell 11 or the voltage drop across the conventional MTJ cell 11 is measured to determine the state of the memory cell. In some

designs, the conventional transistor 13 is replaced by a diode, or completely omitted, with the conventional MTJ cell 11 in direct contact with the conventional word line 10.

Although the above conventional MTJ cell 11 can be written using the conventional word line 10 and conventional bit line 12, one of ordinary skill in the art will readily

recognize that the amplitude of Ii or I₂ is in the order of several milli-Amperes for most designs. Therefore, one of ordinary skill in the art will also recognize that a smaller writing current is desired for many memory applications.

Furthermore, to be competitive with other types of memory, the density and capacity

of an MRAM chip embodying technology such as the conventional MRAM 1 should be comparable with that of DRAM, FLASH or SRAM products. For state-of-the-art

technology, the size of an MRAM cell is in the submicron range. The lateral size of the MTJ

stack 11 is even smaller, in the deep submicron range. Moreover, as memory densities

increase, the lateral size of the MTJ stack 11 is further reduced. The small size of the MTJ stack 11 leads to problems in the performance of the conventional MRAM 1.

As the lateral dimensions of the MRAM cell and MTJ stack 11 are reduced, the

volume of each of the magnetic layers 1101 and 1103 in the conventional MTJ stack 11 is reduced. The reduction in volume of the magnetic layers 1101 and 1103 leads to the possibility of "super-paramagnetic" behavior. For a layer exhibiting super-paramagnetic

behavior, thermal fluctuations can cause the magnetic moment of the layer to spontaneously

rotate if the magnetic anϊsotropy of the layer is not sufficiently large. The magnetic anisotropy of a layer, or other magnetic entity, is proportional to its volume. Consequently,

layers 1101 and 1103 are more likely to exhibit super-paramagnetic behavior for

conventional MTJ stacks 11 having smaller lateral dimensions.

Conventional MTJ stacks 11 having smaller lateral dimensions may also have

increased magnetic interactions between the magnetic layers 1101 and 1103. The stray magnetic fields at the edges of the MTJ cell are generated by the magnetic poles at the edges of the ferromagnetic layers 1101 and 1103 of the conventional MTJ stack 11. These stray magnetic fields increase in magnitude for smaller conventional MTJ stacks 11. Stray

magnetic fields can lead to large magnetic interactions between the pinned layer 1101 and

the free layer 1103 within a single MTJ storage cell. Due to magnetic interactions between the ferromagnetic layers 1101 and 1103 in a single conventional MTJ cell, the state of the

MTJ cell in which the magnetic moments of the ferromagnetic layers 1101 and 1103 are

antiparallel is more energetically stable than the state in which the moments of the layers

1101 and 1103 are parallel. This asymmetry in the stability of the conventional MTJ stack 11

leads to asymmetries in the magnetic switching between the parallel and antiparallel states of the MTJ cell. Consequently, it becomes difficult to operate the MTJ cell and, therefore, the conventional MRAM 1. The stray magnetic fields can also lead to magnetic interactions

between the ferromagnetic layers 1101 and 1103 of one conventional MTJ stack 11 and the

ferromagnetic layers (not shown) of neighboring MTJ storage cells. In this case, the magnetic switching field of a given MTJ cell depends on the magnetic state of its neighboring MTJ cells. Consequently, the margin of write operations of the memory array is

reduced. Eventually, the conventional MRAM 1 becomes inoperable. Unless these magnetostatic interactions can be mitigated, the smallest size of the MTJ cells and thus the

highest density of the MTJ MRAM are limited.

The magnetostatic fields emanating from the exchange-biased pinned layer 1101 can be greatly reduced by replacing the conventional pinned layer 1101 with a sandwich of two

ferromagnetic films antiferromagnetically coupled to one another and separated by a thin

antiferromagnetic coupling film. The antiferromagnetically coupled films together with the antiferromagnetic coupling film thus form a synthetic pinned layer. Such a system is described in U.S. Patent No. 5,841 ,692. In the synthetic pinned layer, the magnetic moments

of the two ferromagnetic films in the pinned layer are aligned antiparallel. Consequently, the

net magnetic moment of the synthetic pinned layer is reduced compared to a pinned layer comprised of a single ferromagnetic layer. Because the strength of the magnetostatic field from a ferromagnetic layer is proportional to the net magnetic moment of the layer, the

magnetostatic field from the synthetic pinned layer is less than that of a pinned layer

comprised of a single ferromagnetic layer. It is also possible to reduce the strength of the magnetostatic fields emanating from the edges of the free layer 1103 of the conventional MTJ 11 by forming a synthetic free layer

from a sandwich of two antiferromagnetically coupled ferromagnetic films which are

separated by an antiferromagnetic coupling film. However, the synthetic free layer may have several disadvantages. The antiferromagnetic coupling film is extremely thin. Consequently, the thermal stability of the antiferromagnetically coupled ferromagnetic films may not be adequate for the required wafer processing steps to which the MTJ materials will

be subjected. The antiferromagnetic coupling may, therefore, be broken. In addition, the

magnetic properties of the synthetic free layer may be inferior to that of the individual ferromagnetic films because of an incomplete antiferromagnetic coupling between the

ferromagnetic films if the films. The antiferromagnetic coupling may be incomplete for

several reasons, for example, the use of ferromagnetic films that are not extremely smooth.

When fabricating a conventional MTJ stack 11, it is usually preferable to first deposit the metallic antiferromagnetic layer included in the layers 1100 and the pinned layer 1101 to which it is exchange-biased to achieve optimal exchange biasing. This order is preferred

because metallic layers grown on top of the insulator 1102, which is usually formed from an

amorphous layer of Al₂O₃, may be rougher than the layers formed beneath the insulator 1102. Typically metal layers do not "wet" oxide layers so that thin metal layers deposited on oxide layers are comprised of numerous islands of varying sizes and heights. Such metal

layers are necessarily rough. Moreover, such layers will have a poor crystallographic texture.

For these reasons, it is very difficult not only to prepare very thin ferromagnetic free layers

1103 with good magnetic properties but also antiferromagnetically coupled free layers with appropriate magnetic properties. U.S. patent number 6,166,948 discloses one conventional method for addressing this problem. The MTJ cell disclosed in the patent has a multilayer free layer including two

ferromagnetic filmδ that are magnetostatically coupled antiparallel to one another by their respective dipole fields. The magnetostatic, or dipolar, coupling of the two ferromagnetic films occurs across a noήferromagnetic spacer layer. The nonferromagnetic spacer layer is selected to prevent exchange coupling between the two ferromagnetic films. The magnetic

moments of the two ferromagnetic films are antiparallel to each other so that the multilayer

free layer has a reduced net magnetic moment. The reduced net magnetic moment of the multilayer free layer reduces the magnetostatic coupling between the multilayer free layer

and the pinned layer in the MTJ cell. The reduced magnetic moment of the multilayer free

layer also reduces the magnetostatic coupling between adjacent MTJ cells in the array. However, based on the principles disclosed in the patent, the two layers of ferromagnetic

films have very different properties. For example, one film is very thick, has a low magnetization and close-to-zero coercivity. The other film is thin, has high magnetization and high coercivity. Under these conditions, the moment of the free layer of the MTJ device can be reduced by more than forty percent but still far from being cancelled completely. The interaction field between cells is still about sixty of that in a single ferromagnetic layer free

layer case. Additionally, shape anisotropy may make it impossible to achieve close to zero coercivity with either of the two ferromagnetic layers. Consequently, this scheme is very

difficult to implement.

Accordingly, what is needed is a magnetic memory in which the moment of the free layer of the MTJ can be completely cancelled or reduced, thereby reducing or eliminating magnetic interactions between magnetic layers within a cell and between adjacent cells. In

addition, it would also be desirable for the MTJ cells to be protected against stray magnetic

field and to have improved write efficiency. The present invention addresses such a need.

SUMMARY OF THE INVENTION The present invention provides a method and system for providing and using a

magnetic memory. The method and system comprise providing a plurality of magnetic

memory cells and providing at least one magnetic write line coupled with the plurality of

magnetic memory cells. Each of the plurality of magnetic memory cells includes a magnetic

element having a data storage layer that stores data magnetically. The at least one magnetic

write line is magnetostatically coupled with at least the data storage layer of the magnetic

element of each of the plurality of magnetic memory cells. Consequently, flux closure is

substantially achieved between the data storage layer of each of the plurality of magnetic memory cells.

According to the system and method disclosed herein, the present invention provides

a magnetic memory^' in which magnetic interactions between magnetic layers within a cell

and between adjacent cells are reduced or eliminated and in which protection against stray

magnetic fields may be improved.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a three-dimensional view of a portion of a conventional magnetic memory

including a MTJ cell, located at the intersection of a bit line and a word line.

Figure 2 depicts one embodiment of an architecture in accordance with the present invention including MTJ MRAM cells d a magnetic write line and having a closed flux data storage layer.

Figure 3 A depicts a cross-sectional view taken through an MTJ MRAM cell of the first embodiment of the magnetic memory in accordance with the present invention.

Figure 3B depicts another cross-sectional view taken through the MRAM cell of the

first embodiment of the magnetic memory in accordance with the present invention.

Figure 4A depicts one embodiment of a possible distribution of the direction of the magnetic vectors in different regions of the magnetic write line when the free layer magnetic

vectors of adjacent MTJ stacks are in different directions.

Figure 4B depicts one embodiment of a possible distribution of the directions of the

magnetic vectors in different regions of the magnetic write line when the free layer magnetic vectors of adjacent MTJ stacks are in the same direction.

Figure 5 depicts a second embodiment of an architecture in accordance with the

present invention including a MTJ MRAM cell and a magnetic write line and having a

closed flux data storage layer.

Figure 6 is a third embodiment of an architecture in accordance with the present

invention including a MTJ MRAM cell and a magnetic write line and having a closed flux

data storage layer.

Figure 7 is a fourth embodiment of an architecture in accordance with the present

invention including a MTJ MRAM cell and a magnetic write line and having a closed flux data storage layer.

Figure 8 is a fifth embodiment of an architecture in accordance with the present

Figure 9 is a sixth embodiment of an architecture in accordance with the present

data storage layer.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in magnetic memories. The

following description is presented to enable one of ordinary skill in the art to make and use

the invention and is provided in the context of a patent application and its requirements. Various modifications to the preferred embodimenfwill be readily apparent to those skilled in

the art and the generic principles herein may be applied to other embodiments. Thus, the

present invention is not intended to be limited to the embodiment shown, but is to be

accorded the widest scope consistent with the principles and features described herein.

Co-pending U.S. patent application Serial No. 10/459,133 entitled "MRAM

MEMORIES UTILIZING MAGNETIC WRITE LINES" assigned to the assignee of the

present application describes a MRAM architecture that addresses many of the issues

encountered in conventional MRAM deices. Applicant hereby incorporates by reference the above-identified co-pending application. In the above-identified co-pending application, the MRAM architecture utilizes MTJ stacks in conjunction with soft magnetic write lines. The magnetic write line(s) are preferably substantially or completely composed of a soft

magnetic material. ' In addition, at least a core, as opposed to a cladding layer, includes the

soft magnetic layer. The soft magnetic materials preferably include cobalt, nickel, iron, and/or alloys thereof. Due to the small spacing between the magnetic write line and the free layer of the MTJ stack, the magnetic vector of free layer is strongly coupled

magnetostatically to the magnetic vector of the magnetic write line. Such a magnetostatic

coupling promotes rotation amplitude for the free, layer magnetic vector. Hence, write efficiency is improved.

Although the MRAM architecture described in the above-identified co-pending application functions well for its intended purpose, one of ordinary skill in the art will

readily recognize that it would be highly desirable for the magnetic storage cells to have a

closed magnetic flux. For MTJ stacks, it would be desirable for at least the free layer to have a closed flux in order to improve the ability of the MRAM architecture to be used at

higher densities and smaller lateral dimensions of the MTJ stacks. For example, it would be

desirable to have reduced magnetostatic interactions between magnetic layers within a magnetic storage cell and between magnetic storage cells. It would also be desirable for the

MRAM architecture to have improved immunity against stray magnetic fields.

Accordingly it is highly desirable to provide an MRAM architecture that utilizes

magnetic write lines for improved writing efficiency but has fewer magnetic interactions

between magnetic layers, fewer magnetic interactions between memory cells, better protection against stray fields, and is thus better tailed for higher memory densities and smaller lateral dimensions of the MTJ stacks.

The present invention provides a method and system for providing and using a

magnetic memory. The method and system comprise providing a plurality of magnetic memory cells and providing at least one magnetic write line coupled with the plurality of

element having a data storage layer that stores data magnetically. The at least one magnetic write line is magnetostatically coupled with at least the data storage layer of the magnetic

substantially achieved between the data storage layer of each of the plurality of magnetic

memory cells.

The present invention will be described in terms of particular types of magnetic memory cells, particular materials, and a particular configuration of elements. Instead, the present invention is more generally applicable to magnetic devices for which it is desirable

to reduce magnetostatic stray field and improve magnetic stability. For example, one of

ordinary skill in the art will readily recognize that this method and system will operate

effectively for other magnetic memories, other magnetic memory cells, and other materials and configurations non inconsistent with the present invention. Furthermore, the present

invention is described in the context of metal-oxide-semiconductor (MOS) devices,

particular magnetic elements-magnetic tunneling junction (MTJ) devices-and MRAM

architectures. However, one of ordinary skill in the art will readily recognize that the present invention is not limited to such devices and architectures. Instead, other suitable devices, for example such as bipolar junction transistor devices and spin- valve giant magnetoresistive memory elements, may be used with or without modification to the inventive memory

architecture. Thus,' the method and system in accordance with the present invention are

more generally applicable to magnetic devices for which improved magnetic stability is desired. Moreover, the present invention is described in the context of certain biasing structures. However, one of ordinary skill in the art will readily recognize that additional

and/or other biasing structures not inconsistent with the present invention, as well as

combinations of the biasing structures described herein can be utilized. Furthermore, the

present invention is described in the context of a magnetic write line. However, one of

ordinary skill in the art will readily recognize that the method and system can be used in conjunction with a segmented magnetic write line. In such a segmented magnetic write line,

a nonmagnetic global write line is coupled with magnetic write line segments. Each

magnetic write line segment is coupled with a portion of the magnetic memory cells for

which the global write line is used. The present invention is also described in the context of

providing a flux closure. However, one of ordinary skill in the art will readily recognize that

the flux closure may not be complete. In particular, as used herein, a flux closure is one in which the effects of magnetic poles may be substantially reduced, but not necessarily

completely eliminated.

Figure 2 depicts a one embodiment of an MRAM architecture 100 in accordance

with the present invention including MTJ MRAM cells 110, 120, 130, and 140 a magnetic

write line 82 and having a closed flux data storage layer. The magnetic write line 82 is

preferably the magnetic write line described in the above-identified co-pending patent application. Although four MRAM cells 110, 120, 130, and 140 are depicted, there can be another number of MRAM cells (not shown) coupled with the magnetic write line 82, as

well as other magnetic write lines (not shown) coupled with other MRAM cells (not shown). The MRAM cells 110, 120, 130, and 140, each preferably utilize an MTJ stack 11 as a magnetic element. The MTJ stack 11 includes a pinned layer 1101 having the fixed magnetic vector, an insulating layer 1102, a free layer 1103 having with the changeable

magnetic vector, and a capping layer 1104. The free layer 1103 is thus the data storage layer

for the MTJ stack 11. The MTJ stack 11 also preferably includes additional layers (not shown) such as seed layer(s) and antiferromagnetic layer(s) that are exchange coupled the

pinned layer 1101. Furthermore, each MRAM cell 110, 120, 130, and 140 preferably

includes a CMOS selection transistor (not shown) and a write word line (not shown)

analogous to those shown in Figure 1, but are omitted for clarity and "simplicity. In the MRAM architecture 100 in accordance with the present invention, the directions of the easy axes for the magnetic vectors of the MRAM cells 110,- 120, 130, and 140 is oriented such

that the magnetic vectors for at least the data storage layer of the MRAM cells 110, 120,

130, and 140 and the corresponding magnetic vectors for the magnetic write line form a flux

closure. In a preferred embodiment, this means that the easy axes of the MRAM cells 110, 120, 130, and 140 are oriented substantially perpendicular to the lengthwise direction of the

magnetic write line 82 and that the easy axis of the magnetic write line 82 is oriented in the

lengthwise direction of the magnetic write line 82, as depicted in Figure 2. However,

nothing prevents other orientations that are not inconsistent with the present invention and

that form the desired flux closures. The magnetic write line 82 has a magnetization that is oriented substantially parallel to the lengthwise direction of the magnetic write line 82. However, on a microscopic scale, the magnetic vectors 101, 105, 103, 104, 105; 106, 107, 108, and 109 of the magnetic write

line 82 vary depending upon the location in the magnetic write line. Away from the MRAM cells 110, 120, 130, and 140, the magnetic vectors 101, 103, 105, 107, and 109 are oriented in the lengthwise direction of the magnetic write line 82. However, the magnetic write line

82 is preferably strongly magnetostatically coupled to at the free layer 1104 of the MTJ

stacks 11 in the MRAM cells 110, 120, 130, and _.140. Thus, the direction of the magnetic

vectors 102, 104, 106, and 108 varies depending upon the directions of the magnetic vectors

112, 122, 132, and 142 of the free layers 11 of the MRAM cells 110, 120, 130, and 140, respectively.

The easy axis of the free layer 1101 of the MTJ stacks 11 for the MRAM cells 110,

120, 130, and 140 is preferably substantially orthogonal to the easy axis of line 82. The thickness of capping layer 1104 is preferably much smaller than the lateral dimensions of the

MTJ stack 11. Due to the small spacing between the magnetic write line 82 and the free

layer 1103, the magnetic vector of the free layer 1103 for each of the MRAM cells 110, 120, 130, and 140 is strongly coupled magnetostatically to the corresponding magnetic vector

102, 104, 106, and 108 of the magnetic write line 82. Consequently, the corresponding magnetic vector 102, 104, 106, and 108 of the magnetic write line 82 in the region

overlapping the MTJ 11 for the MRAM cells 110, 120, 130, and 140, respectively, rotates to

form a flux closure. Thus, the free layer 1103 for each of the MRAM cells 110, 120, 130,

and 140 is a closed flux layer. The capping layer 1104 for each MTJ stack 11 is chosen so that a significant exchange coupling between free layer 1103 and magnetic write line 82 is prevented. Consequently, the magnetic coupling between the free layer 1103 of each MRAM cell 110, 120, 130, and 140 and the magnetic write line 82 is preferably limited to magnetostatic coupling. The capping layer 1104 can be made from a wide variety of metals, semi-metals and semiconductor materials. If the capping layer 1104 is a material such as Ru, Cr or Cu, that are known to provide the oscillatory anti-ferromagnetic exchange coupling, then the capping layer 1104 is thick enough to prevent an .exchange coupling between the free layer 1103 and the magnetic write line. The capping layer 1104 can also be formed from an insulating material. However, the resistance of the capping layer 1104 should be small compared to that of the tunnel barrier layer 1102. The capping layer 1104 can also be formed ^• from a material which acts as a thermal diffusion barrier so that the MTJ has good thermal stability. The capping layer may be selected from the group consisting of Cu, Pd, Pt, Rh, Ti, Cr, Ru and Os, or could be a binary metallic material, for example selected from the group consisting of Cu(i_-X)Ni_x and Ni(_1-X)Cr_x. The capping layer could also include materials such as TiN, Al₂O₃.

In a preferred embodiment, the MRAM cells 110, 120, 130, and 140 may be written to and read from using processes similar to those described in the above-identified co- pending patent application. To write to an MRAM cell, such as the MRAM cell 110, a write current is provided in the magnetic write line 82. A magnetic field is induced by the write line current, in conjunction with a second write current in a word line (not shown), rotates the magnetic vector 112 of the free layer 1103 for the MRAM cell 110 away from the easy axis of the MTJ stack 110 for the MRAM cell 110. Due to the strong magnetostatic coupling between the magnetic vector 112 of the free layer 1103 for the MRAM cell 110 and

that of the magnetic write line 82, the corresponding magnetic vector 102 of the magnetic

write line 82 also rotates. However, the corresponding magnetic vector 102 rotates in a

direction opposite to the direction in which the magnetic vector 112 rotates. As a result, the flux closure state with the magnetic vector 112 of the free layer 1103 of the MTJ stack 11 for the MRAM cell 110 is maintained. This flux closure promotes rotation amplitude for the

free layer magnetic vector 112. Hence, write efficiency is improved. With a further increase

in the amplitude of the write line current, the magnetic vector 112 of the free layer 1103 of

the MTJ stack eventually settles in the desired direction, completing the write process.

In the embodiment of the MRAM 100 depicted in Figure 2, the magnetic vectors

112, 122, 132, and 142 for the free layer 1103 of adjacent MRAM cells 110, 120, 130, and

140 are in opposite directions. Stated differently, the magnetic vectors 112, 122, 132, and 142 happen to alternate direction. The magnetic vectors 102, 104, 106, and 108 in the

magnetic write line 82 in the region directly above the MTJ stacks 11 for the MRAM cell

110, 120, 130, and 140, respectively, rotates away from the easy axis of the magnetic write line 82 in a direction opposite to that of the free layer magnetic vector 112, 122, 132, and

142, respectively. To simplify the discussion, we decompose the magnetic vector in the magnetic write line 82 into two components, M_e along the easy axis direction and M_h along

the hard axis direction of line 82, even though the two components are dependent on each

other. Similarly, the magnetic vector 112, 122, 132, and 142 of the MRAM cells 110, 120,

130, and 140, respectively, can be decomposed into components, M_s and M_h, in the easy axis and hard axis, respectively, directions of the MRAM cells 110, 120, 130, and 140, respectively. Note, however, that the easy axis of the MRAM cells 110, 120, 130, and 140 is preferably substantially perpendicular to the easy axis of the magnetic write line 82.

^• Similarly, the hard axis of the MRAM cells 110, 120, 130, and 140 is preferably substantially perpendicular to the hard axis of the magnetic write line 82.

Figures 3A and 3B depict cross-sectional views taken through the MTJ of the MRAM cell 110 of the first embodiment of the MRAM 100 in accordance with the present invention. Thus, components of the MRAM cells 110' and 110" are analogous to the MRAM cell 110 depicted in Figure 2 and are labeled similarly. Referring back to Figures 3A and 3B, the hard component, M_h 102A, of the magnetic vector 102' of the magnetic write line 82' and the easy component, M_s 112 A, of the magnetic vector 112' of the MRAM cell 110'. Figure 3 A depicts the MRAM cell 110' wheri the magnetic vector 112' is in a first direction, while Figure 3B depicts the MRAM cell 110' when the magnetic vector 112" is in the opposite direction.

Referring to Figures 3 A and 3B, the vectors M_h 102A and M_h 102A' in line 82 in Figures 3 A and 3B, respectively, only represent the hard component of the magnetic vector 102 (not shown) of the magnetic write line 82. Similarly, the vectors M_s 112A and M_s 112 A' only represent the soft component of the magnetic vector 112 (not shown) of the free layer 1103. It can be understood by those of ordinary skill in the art that M_h 102A and M_s 112A produce magnetic dipoles (not explicitly shown) at the surfaces perpendicular to the magnetic vectors M 102A and magnetic vectors M_h 112A in Figure 3 A. Similarly, it can be understood by those of ordinary skill in the art that M_h 102 A' and M_s 112 A' produce magnetic dipoles (not explicitly shown) at the surfaces perpendicular to the magnetic vectors 102A' and magnetic vectors 112A' in Figure 3B. The magnetic fields, shown by arrows 150, 152, 154 and 156 associated with the dipoles act on both M_h 102A and M_s 112 A. Similarly, magnetic fields shown by arrows 150', 152', 154', and 156' associated with the dipoles act on both M 102 A' and M_s 112A'. The interaction energy between free layer 1103 and line 82 takes a value given by

Ej oc -HdfMht_wSf cc -HdwM_stfSf where H _f is the coupling filed produced by free layer 1103 on the magnetic write line 82 and is proportional to the saturation magnetization, M_s, of the free layer, t_w the thickness of the magnetic write line 82, H_dWthe coupling field produced by M_h on free layer 1103 and is proportional to M_h, t_f the thickness of free layer 1103, and S the surface area of the MTJ stack 11. Assuming the maximum value of M_h is equal to M_s, which is achieved when M_e is equal to zero, and the interaction area on both free layer 1103 and line.82 is the same and equal to the surface area of the MTJ stack 11, S_f, one can readily understand that t_w, the thickness of line 82' should be no less than the free layer thickness t_f in order to achieve optimum flux closure.

The magnetostatic energy in a system can be expressed as the integral over all space of the magnetic field

E = |(H /8π)dv.

For the case that the magnetic write line 82' or 82" is not magnetic, the H field is produced

• by the magnetic charges on the end surface of the free layer 1103. When the magnetic write line 82' or 82" is made of magnetic material and coupled to the free layer 1103, the field produced by M_h 102 A and M_h 102A', respectively, of the magnetic write line 82' or 82", respectively, cancels part of the field produced by free layer 1103. Consequently, the overall energy of the MRAM cell 110' and 110" is reduced and the MRAM cell 110' and 110" are

made more stable. The magnetic field due to the dipoles on the magnetic write line 82 and the free layer 1103 can be cancelled to a greater degree, and, therefore, better stability can be achieved when the distance between the free layer 1103 and the magnetic write line 82' or

82" is reduced and ferromagnetic exchange coupling between the free layer 1103 and the

magnetic write line 82' or 82" does not occur. .

In addition to magnetostatic energy terms discussed above, exchange energy and

anisotropy energy also exist in the MRAM 100 depicted in Figure 2. The exchange energy

between two adjacent atoms is given by E_ex= -2JScos((py), where J is the exchange integral,

S is the total spin quantum number of each atoms, and φy is the angle between the magnetic

vector of the two atoms. The direction of the magnetic vector of adjacent atoms should not

change abruptly in order to minimize the energy of a magnetic system. The anisotropy

energy takes the form E_a= K_usin²φ, where K_u is the magnetic anisotropy constant and φ is the

angle between the magnetic vector and the easy axis of the magnetic anisotropy. For the

magnetic write line 82 having an easy axis in the lengthwise direction, the anisotropy energy reaches its maximum when M_h reaches maximum and M_e reduces to zero. To reduce the

anisotropy energy, K_u should be small and the overall magnetic vector should be in the

direction along the long axis of the magnetic write line 82.

The total magnetic energy in the MRAM 100 shown in Figure 2 thus includes

magnetostatic energy, exchange energy and anisotropy energy of the MRAM cells 110, 120, 130, and 140, as well as those not shown. The magnetostatic energy is the dominant energy in a magnetic system made of soft magnetic materials. The magnetic vectors 101, 102, 103,

104, 105, 106, 107; 108, 109, 112, 122, 132, and 142 are oriented to minimize magnetostatic energy by reducing magnetic dipoles wherever possible.

Figure 4 A depicts one embodiment the MRAM 100' with one possible distribution of the directions of the magnetic vectors in different regions of the magnetic write line 82'"

when the free layer magnetic vectors 112', 122', 132', and 142' of adjacent MTJ stacks 11

are in a different direction. The MRAM 100' has components corresponding to those in the

MRAM 100 depicted in Figure 2, which are labeled similarly. Referring back to Figure 4A,

the probable orientations of magnetic vectors in the magnetic write line 82'". For clarity, only magnetic vectors 163, 164, 165, 166, 167, 168, 169, and 170 in the magnetic write line

82'" are discussed. The magnetic vectors 112', 122', 132', and 142' for the free layers 1103

of the MRAM cells 110'", 120'", 130'", and 140'" are also depicted. The operation of the MRAM 100', is described in conjunction with the MRAM cell 110'". The magnetic vectors 163 and 170 rotate away from the easy axis direction to form a magnetic flux closure with magnetic vectors 112' and 122' in the free layer 1103 of each cell 110'" and 120'",

respectively. As discussed previously, such a flux closure reduces the magnetostatic energy

of the system formed by vectors 112' and 163. The magnetic vectors 167, 168, and 169 near

the edges of the magnetic write line 82'" are oriented substantially along the edges of the

magnetic write line 82'" to minimize the magnetostatic energy associated with the edges.

The magnetic vectors 164 and 166 are oriented in a direction away from the easy axis so the direction transition from 163 to 164 will not introduce significant amount of magnetic charges in the magnetic write line 82'". There is an anisotropy energy increase associated with vectors 163 and 164. To reduce the anisotropy energy, the magnetic line 82'" should be made with K_u, the anisotropy constant, as close to zero as possible.

Figure 4B depicts another embodiment of the MRAM 100" of a possible distribution of the direction of the magnetic vectors in different regions of the magnetic write line 82""

when the free layer magnetic vectors 112", 122", 132", and 142" of adjacent MTJ stacks 11 are in the same direction. The magnetic vectors 112", 122", 132", and 142" in the free

layers 1103 of the MTJ stacks 11 are all oriented in the same direction, upward in Figure 4B.

This is different from the MRAM 100' depicted in Figure 4 A where the magnetic vectors of

adjacent cells are in different direction. Referring back to Figure 4B, for clarity only the

orientations of magnetic vectors 163', 164', 165', 166', 167', 168', 169', and 170' in the magnetic write line 82"" are shown. The magnetic vectors 112", 122", 132", and 142"

for the free layers 1103 of the MRAM cells 110"", 120"", 130"", and 140"" are also depicted. The MRAM 100" operates in an analogous manner to the MRAM 100'. Thus,

the magnetic vectors 163', and 170'rotate away from the easy axis direction to form a

magnetic flux closure with magnetic vectors 112" and 122 "in the free layers 1103 of the

MRAM cells 110"" and 120"", respectively. The vector 166', which represents the

magnetic vector in the magnetic write line 82"" in the region near the left edge of the MTJ stacks 11, orient differently from vector 166' in Figure 4 A to suppress the magnetostatic

energy due to the change^' in orientation of the magnetic vector 122".

Thus, the MRAMs 100, 100', and 100" have magnetostatic coupling between the

magnetic write line 82, 82'", and 82"", respectively and the free layers 1103 of the corresponding MRAM cells. Consequently, a flux closure is formed for each of the free layers 1103 in the MRAMs 100, 100', and 100". Thus, the MRAMs 100, 100', and 100" have fewer magnetic interactions between magnetic layers 1101 and 1103, fewer magnetic

interactions between memory cells 110, 120, 130, and 140; 110'", 120'", 130'", and

140'"; and 110"", 120"", 130"", and 140"", and better protection against stray fields. The MRAMs 100, 100', and 100" are thus better tailed for higher memory densities and smaller lateral dimensions of the MTJ stacks 11.

Figure 5 depicts a second embodiment of an architecture 200 in accordance with the

present invention having a closed flux data storage layer. The MRAM 200 includes MRAM

cells 210, 220, and 230 and a magnetic write line 240, which corresponds to the magnetic write lines 82, 82', 82", 82'", and 82"". Each MRAM cell 210, 220, and 230 includes an

MTJ stack 11 as a magnetic element and a selection device 215, 225, and 235, respectively,

that is preferably a transistor. The MTJ stack includes at least the pinned layer 1101, barrier layer 1102, and free layer 1103. In addition, underlying layers (not shown) that may include seed and antiferromagnetic layers can be provided. However, there is no capping layer on

the MTJ stacks 11 to act as a spacer layer between the free layer 1103 and the magnetic write

line 240 and prevent exchange coupling. Instead, the magnetic write line 242 includes a soft

magnetic layer 242 and a nonmagnetic layer 241. In addition, the nonmagnetic layer 241 is a

high conductivity layer that is preferably in contact with the MTJ stacks 11. The soft

magnetic layer 242, which is part of the magnetic write line 240, is coupled

magnetostatically with the free layers 1103 of the MTJ stacks across the nonmagnetic layer

241. The magnetic vectors in the soft magnetic layer 242 and the magnetic vectors of the free layers 1103 of the MTJ stacks 11 are oriented such that a flux closure is formed. Similar materials to the candidates described for the capping 1104 may be used for the

nonmagnetic layer 241. Moreover, the nonmagnetic layer 241 should be much thinner than

the lateral dimensions of MTJ 11 in order to promote good coupling between the magnetic write line 240 and the free layers 1103. However, an exchange coupling between the free layers 1103 and the soft magnetic layer 242 of the magnetic write line 240 is not desired.

Thus, the MRAM 200 shares the benefits of the MRAMs 100, 100', and 100". In addition,

the magnetic write line 240 includes the nonmagnetic layer 241 that servers many of the

purposes of the capping layer 1104 of the MTJ stacks 11.

Figure 6 depicts a third embodiment of an architecture 300 in accordance with the present invention having a closed flux data storage layer. The MRAM 300 includes MRAM

cells 310, 320, and 330 and a magnetic write line 340, which corresponds to the magnetic

write line 240 depicted in Figure 5. Referring back to Figure 6, each MRAM cell 310, 320, and 330 includes an MTJ stack 11 as a memory element and a selection device 315, 325, and

335, respectively, that is preferably a transistor. The MTJ stack includes at least the pinned

layer 1101, barrier layer 1102, and free layer 1103. In addition, underlying layers (not

shown) that may include seed and antiferromagnetic layers can be provided. However, there

is no capping layer on the MTJ stacks 11 to act as a spacer layer between the free layer 1103 and the magnetic write line 340 and prevent exchange coupling. Instead, the magnetic write line 340 includes three layers: a high conductive spacer layer 341, a soft magnetic layer 342,

and another conductive layer 343. The conductive spacer layer 341 and soft magnetic layer

342 are analogous to the layers 231 and 242, respectively, depicted in Figure 5. Referring back to Figure 6, the soft magnetic layer 342, which is part of the magnetic write line 340, is coupled magnetostatically with the free layers 1103 of the MTJ stacks across the nonmagnetic layer 341. The magnetic vectors in the soft magnetic layer 342 and the

magnetic vectors of the free layers 1103 of the MTJ stacks 11 are oriented such that a flux closure is formed. The additional conductive layer 343 is designed in the magnetic write

line 340 to adjust the resistivity of the magnetic write line 340. As a result, a particular

desired resistance of the magnetic write line 340 may be achieved. Thus, in addition to the

benefits of the MRAMs 100, 100', 100", and 200, the MRAM 300 also allows for the resistance of the magnetic write line 340 to be tailored.

Figure 7 is a fourth embodiment of an architecture 400 in accordance with the present invention having a closed flux data storage layer. The MRAM 400 includes MRAM

cells 410, 420, and 430. Each MRAM cell 410, 420, and 430 includes an MTJ stack 11 as a

memory element and a selection device 415, 425, and 435, respectively, that is preferably a transistor. The MRAM 400 includes magnetic write line 440. The magnetic write line 440 is analogous to the magnetic write line 240 and thus includes a nonmagnetic layer 441 and a

soft magnetic layer 442. However, the soft magnetic layer has been patterned to regions

442A, 442B, and 442C, which only overlap the MTJ stacks 11 of the MRAM cells 410, 420,

and 430. The magnetic moment of each of the soft magnetic portion 442A, 442B, and 442C

and the free layers 1103 is preferred to be the same. In other words, the saturation

magnetization multiplied by the thickness should be the same for each of the two films 442

and the free layer 1103. The shape as well as the easy axis direction of the regions 442 A,

442B, and 442C is also preferred to be the same as that of the free layer 1103. The magnetic flux closure between the free layers 1103 of the MRAM cells 410, 420, and 430 and soft magnetic regions 442 A, 442B, and 442C occurs, across the nonmagnetic layer 441. Therefore, the material property and thickness of the layer 441 should be designed in a similar manner to the layer 1104 depicted in Figure 2.

Figure 8 depicts a fifth embodiment of an architecture 500 in accordance with the present invention having a closed flux data storage layer. The MRAM 500 includes MRAM cells 510, 520, and 530. Each MRAM cell 510, 520, and 530 includes an MTJ stack 11 as a memory element. Each MTJ stack 11 has at least a pinned layer 1101, an insulator layer 1102, and a free layer 1103. The MRAM 500 is analogous to the MRAM 400 depicted in Figure 7. Thus, the soft magnetic write line 540 includes a nonmagnetic layer 541 and soft magnetic regions 542A, 542B, and 542C. The soft magnetic regions 542A, 542B, and 542C correspond to the regions 442A, 442B, and 442C depicted in Figure 7. However, referring to Figures 7 and 8, the soft magnetic regions 542A, 542B, and 542C are sunk into the nonmagnetic line 541. Similar to the MRAM 400, the magnetic moments of regions 542A, 542B, and 542C and the free layers 1103 of the MRAM cells 510, 520, and 530 are preferred

^■ to be the same. The shape as well as the easy axis direction of the regions 542A, 542B, and 542C are also preferred to be the same as that of the free layers 1103 of the MRAM cells 510, 520, and 530, respectively. Thus, the regions 542A, 542B, and 542C and the free layers 1103 of the MRAM cells 510, 520, and 530 form a flux closure. In addition, the configuration of the layers 541 and regions 542 A, 542B, and 542C of the magnetic write line 540 allow the resistance of the magnetic write line 540 to a preferred value. Figure 9 depicts a sixth embodiment of an architecture 600 in accordance with the present invention having a closed flux data storage layer. The MRAM 600 includes MRAM cells 610, 620, and'630 and a magnetic writeline 640, which corresponds to the magnetic write lines 82, 82', 82", 82'", and 82"". Each MRAM cell 610, 620, and 630 includes an

MTJ stack 11 as a memory element and a selection device 615, 625, and 635, respectively, that is preferably a transistor. The MTJ stack includes at least the pinned layer 1101, barrier

layer 1102, and free layer 1103. In addition, underlying layers (not shown) that may include

seed and antiferromagnetic layers can be provided. Furthermore, a nonmagnetic capping

layer 1104 is also provided. However, an additional layer 1105 is provided in each MTJ

stack 11 for each MRAM cell 610, 620, and 630. The additional layer 1105 is a soft magnetic layer that is inserted between spacer layer 1104 and the magnetic write line 640.

The magnetic vector of the soft magnetic layer 1105 is exchange coupled to the magnetic

vector of the magnetic write line 640 and oriented in the same direction. The magnetic

vectors of the magnetic write line 640 and the magnetic layers in the MRAM cells 610, 620, and 630 form a flux closure. In addition, because of the use of the soft magnetic layers 1105, the MTJ stacks 11 for the MRAM cells 610, 520, and 630 may be patterned after layer

1105 is deposited. As a consequence, the thickness and integrity of the spacer layer 1104 can

be better controlled. A method and system has been disclosed for providing a magnetic memory having

improved writing efficiency, better reliability, simpler fabrication, and improved magnetic

stability. The magnetic memory also has fewer magnetic interactions between magnetic

layers, fewer magnetic interactions between memory cells, better protection against stray

fields, and is thus better tailed for higher memory densities and smaller lateral dimensions of the magnetic memory elements. Although the present invention has been described in accordance with the embodiments shown, one of ordinary skill in the art will readily recognize that there could be variations to the embodiments and those variations would be

within the spirit and scope of the present invention. Accordingly, many modifications may

be made by one of ordinary skill in the art without departing from the spirit and scope of the

appended claims.

Claims

CLAIMSWhat is claimed is:

1. A magnetic memory comprising: a plurality of magnetic memory cells, each of the plurality of magnetic memory cells including a magnetic element having a data storage layer that stores data magnetically; at least one magnetic write line coupled with the plurality of magnetic memory cells,

the at least one magnetic write line being magnetostatically coupled with at least the data

storage layer of the magnetic element of each of the plurality of magnetic memory cells such

that flux closure is substantially achieved for the data storage layer of each of the plurality of magnetic memory cells.

2. The magnetic memory of claim 1 wherein the magnetic element is a magnetic

tunneling junction including a pinned layer, a free layer and an insulating layer between the pinned layer and the free layer, the free layer being the data storage layer.

3. The magnetic memory of claim 2 wherein the magnetic tunneling junction further includes a capping layer between the free layer and the at least one magnetic write

line, the capping layer being configured to preclude an exchange coupling between the free

layer and the at least one magnetic write line.

4. The magnetic memory of claim 3 wherein the magnetic tunneling junction further includes a soft magnetic layer disposed between the capping layer and the at least one magnetic write line.

5. The magnetic memory of claim 2 wherein the magnetic tunneling junction further includes at least one additional layer including an antiferromagnetic layer, the

antiferromagnetic layer being magnetically coupled to the pinned layer.

6. The magnetic memory of claim 1 wherein the data storage layer has a first easy axis and the at least one magnetic write line has a second easy axis, the first easy axis being substantially perpendicular to the second easy axis.

7. The magnetic memory of claim 1 wherein the at least one magnetic write line includes a nonmagnetic layer and a soft magnetic layer, the nonmagnetic layer residing between the soft magnetic layer and the magnetic element of each of the plurality of magnetic storage cells.

8. The magnetic memory of claim 7 wherein the at least one magnetic write line further includes a conductive layer, the soft magnetic layer residing between the conductive

layer and the nonmagnetic layer.

9. The magnetic memory of claim 8 wherein the conductive layer is configured to ensure that the at least one magnetic write line has a desired resistance.

10. The magnetic memory of claim 1 wherein the at least one magnetic write line

includes a nonmagnetic layer and a plurality of soft magnetic structures, the plurality of soft magnetic structures being disposed directly above the plurality of magnetic memory cells, the nonmagnetic layer being disposed between the plurality of soft magnetic structures and the plurality of magnetic memory cells.

11. The magnetic memory of claim 10 wherein the nonmagnetic layer includes a plurality of recesses therein, at least a portion of each of the plurality of soft magnetic structures residing in each of the plurality of recesses.

12. A method for utilizing a magnetic memory comprising the steps of:

(a) in a write mode, writing to a first portion of a plurality of magnetic memory cells, each of the plurality of magnetic memory cells including a magnetic element having a

data storage layer that stores data magnetically, the plurality of magnetic memory cells being

coupled with at least one magnetic write line, the at least one magnetic write line being magnetostatically coupled with at least the data storage layer of the magnetic element of

each of the plurality of magnetic memory cells such that flux closure is substantially achieved for the data storage layer of each of the plurality of magnetic memory cells; and

(b) in a read mode, reading from a second portion of the plurality of magnetic memory cells.

13. A method for providing a magnetic memory comprising:

(a) providing a plurality of magnetic memory cells, each of the plurality of

magnetic memory cells including a magnetic element having a data storage layer that stores

data magnetically;

(b) providing at least one magnetic write line coupled with the plurality of

magnetic memory cells, the at least one magnetic write line being magnetostatically coupled

with at least the data storage layer of the magnetic element of each of the plurality of

magnetic memory cells such that flux closure is substantially achieved for the data storage

layer of each of the plurality of magnetic memory cells.

14. The method of claim 13 wherein the magnetic memory cell providing step (a)

further includes the step of:

(al ) providing a magnetic tunneling junction as the magnetic element, the

magnetic tunneling junction including a pinned layer, a free layer and an insulating layer

between the pinned layer and the free layer, the free layer being the data storage layer.

15. The method of claim 13 wherein the magnetic tunneling junction providing

step (al) further includes the step of:

(ali) providing a capping layer between the free layer and the at least one magnetic write line, the capping layer being configured to preclude an exchange coupling between the free layer and the at least one magnetic write line.

16. The method of claim 15 wherein the magnetic tunneling junction providing

step (al) further includes the step of:

(alii) providing a soft magnetic layer disposed between the capping layer and the at least one magnetic write line.

17. The method of claim 14 wherein the magnetic tunneling junction providing

step (al) further includes the step of:

(ali) providing at least one additional layer including an antiferromagnetic layer, the antiferromagnetic layer being magnetically coupled to the pinned layer;

18. The method of claim 13 wherein the data storage layer has a first easy axis and the at least one magnetic write line has a second easy axis, the first easy axis being

substantially perpendicular to the second easy axis.

19. The method of claim 13 wherein the at least one magnetic write line providing step (b) further includes the step of:

(b 1 ) providing a nonmagnetic layer; and (b2) providing a soft magnetic layer, the nonmagnetic layer residing between the soft magnetic layer and the magnetic element of each of the plurality of magnetic storage cells.

20. The method of claim 19 wherein the at least one magnetic write line providing step (b) further includes the step of:

(b3) providing a conductive layer, the soft magnetic layer residing between the conductive layer and the nonmagnetic layer.

21. The method of claim 20 wherein the conductive layer is configured to ensure that the at least one magnetic write line has a desired resistance.

22. The method of claim 13 wherein the step of providing the at least one magnetic write line further includes the step of:

(b 1 ) providing a nonmagnetic layer; and

(b2) providing a plurality of soft magnetic structures, the plurality of soft magnetic

structures being disposed directly above the plurality of magnetic memory cells, the nonmagnetic layer being disposed between the plurality of soft magnetic structures and the

plurality of magnetic memory cells.

23. The method of claim 22 wherein the nonmagnetic layer providing step further

includes the step of:

(bli) providing a plurality of recesses in the nonmagnetic layer, at least a portion of each of the plurality of soft magnetic structures residing in each of the plurality of recesses.