Magnetoresistive sensors and methods for generating closed-flux magnetization patterns

Abstract

A method (700) for generating a closed-flux magnetization pattern of a predetermined rotation direction in a magnetic reference layer (220; 420; 620) of a magnetic layer stack, the method comprising: Applying (710) an external magnetic field in a predetermined direction to the magnetic layer stack, with a strength of the external magnetic field above an annihilation field strength of the magnetic reference layer (220; 420; 620) and a pinned layer (212; 412), thereby causing magnetic saturation of the magnetic reference layer (220; 420; 620) and the pinned layer (212; 412) of the magnetic layer stack; Reducing (720) the strength of the external magnetic field below a nucleation field strength of the magnetic reference layer (220; 420; 620) and the pinned layer (212; 412) to form a first closed-flux magnetization pattern in the magnetic reference layer and a second closed-flux magnetization pattern in the pinned layer; and Structuring, prior to applying (710) the external magnetic field, at least the magnetic reference layer (220; 420; 620) to have a lateral cross-section comprising a main portion (224) and a projection portion (226) extending tangentially from the main portion (224), wherein the external magnetic field is applied (710) along an axis of a maximum lateral extension of the projection portion (226).

Description

Area

[0001] Examples relate to magnetoresistive sensors and methods for generating a closed-flux magnetization pattern in a magnetic reference layer of a magnetic layer stack. background

[0002] Magnetoresistive effects are based on numerous different physical phenomena. What all of these phenomena have in common is that the electrical resistance of a resistive element can be modified by a magnetic field penetrating the resistive element. Techniques that utilize magnetoresistive effects are sometimes referred to as "xMR techniques," where the "x" indicates that a variety of effects can be addressed, such as the giant magnetoresistive (GMR) effect, the tunneling magnetoresistive (TMR) effect, or the anisotropic magnetoresistive (AMR) effect, to name just a few. xMR effects can be applied to a variety of field-based magnetoresistive sensors, for example, for measuring rotation, angle, etc.

[0003] US 2006 / 0 023 492 A1 describes a magnetoresistive tunnel junction (MTJ) in which the free layer and the reference layer exhibit a vortex magnetization state that arises with clockwise or counterclockwise rotation. The MTJ has an elliptical shape with a low aspect ratio, and the magnetic layers contain a doped substance that is one of the following: C, N, B, Zr, Ta, Pt, Nb, or Hf to facilitate the flux-locking configuration. The vortex magnetization is generated by applying a reversed magnetic field in a direction opposite to the remanent magnetization in one magnetic layer. After the vortex state is induced in the adjacent reference layer, an antiferromagnetic phase is established in it.Switching the vortex state in the free layer involves applying a first field in a first direction to disrupt the vortex and then applying a smaller second field in a reverse direction at a critical point, creating a vortex with reversed spin.

[0004] US 2007 / 0 247 901 A1 describes a mesoscopic magnetic body consisting of a flat ferromagnetic body whose planar shape has an axis of symmetry, but is not symmetric in the direction perpendicular to the axis of symmetry. The magnetic body exhibits a circular single-pole domain structure when the external parallel magnetic field is removed. MRAMs using such a mesoscopic magnet and fabrication methods are also provided. This allows the magnetization direction in mesoscopic magnetic plates to be controlled at the nanoscale and eliminates the limitation on the number of erase and write operations.

[0005] Magnetoresistive sensors often include one or more magnetoresistive elements with fixed reference magnetizations for measuring the magnitude and / or direction of an external magnetic field. The fabrication of these magnetoresistive sensors often requires local magnetization processes of the magnetoresistive elements. This can be cumbersome because the local magnetization processes often have to be performed one after the other, which can be time-consuming and thus costly. Therefore, there is a need for new magnetoresistive sensor concepts that facilitate manufacturing and reduce manufacturing costs while maintaining high and accurate sensor performance. Such a need may be met, at least in part, by the subject matter of the present disclosure. Summary

[0006] According to a first aspect of the present disclosure, a magnetoresistive sensor is provided. The magnetoresistive sensor comprises a magnetic reference layer. The magnetic reference layer comprises a magnetization pattern with (e.g., permanently) closed flux of a predetermined rotational direction. The magnetoresistive sensor further comprises a magnetic free layer. The magnetic free layer has a total lateral area that is smaller than a total lateral area of ​​the magnetic reference layer. A geometric center of gravity of the magnetic free layer is laterally offset with respect to a geometric center of gravity of the magnetic reference layer.

[0007] According to some embodiments, the magnetic reference layer comprises a main portion and a protrusion portion laterally adjacent to the main portion, wherein the main portion comprises the closed flux magnetization pattern, wherein a magnetization pattern of the protrusion portion is configured to predetermine the rotation direction of the closed flux magnetization pattern.

[0008] According to some embodiments, in proximity to a lateral junction of the protrusion portion and the main portion, the magnetization pattern of the protrusion portion is directed opposite to the closed-flux magnetization pattern of the main portion.

[0009] According to some embodiments, a length of the protrusion portion is greater than twice a width of the protrusion portion.

[0010] According to some embodiments, the projection portion extends tangentially to the main portion.

[0011] According to some embodiments, the main portion has a rotationally symmetrical lateral cross-section.

[0012] According to some embodiments, a minimum lateral distance between the magnetic free layer and the protrusion portion is greater than 10% of a maximum lateral extent of the main portion.

[0013] According to some embodiments, the closed flux magnetization pattern has a component of average magnetic flux density parallel to the magnetic free layer that is different from zero, vertically above or below at least a portion of the magnetic free layer, wherein the portion of the magnetic free layer is laterally surrounded by electrically insulating material.

[0014] According to some embodiments, a direction of the closed flux magnetization pattern changes vertically above or below at least a portion of the magnetic free layer by at most 90°, wherein the portion of the magnetic free layer is laterally surrounded by electrically insulating material.

[0015] According to some embodiments, the magnetic free layer has a first part and at least a second part laterally separated from the first part.

[0016] According to some embodiments, a first average direction of the closed flux magnetization pattern vertically above or below the first portion of the magnetic free layer differs from a second average direction of the closed flux magnetization pattern vertically above or below the second portion of the magnetic free layer.

[0017] According to some embodiments, the first average direction differs from the second average direction by more than 5 degrees.

[0018] According to some embodiments, the magnetic reference layer comprises a first part and at least a second part laterally separated from the first part, wherein each part of the magnetic reference layer has a corresponding closed flux magnetization pattern of a predetermined rotation direction, wherein a vertical projection of the first part of the magnetic free layer onto the magnetic reference layer is laterally surrounded by a perimeter of the first part of the magnetic reference layer, wherein a vertical projection of the second part of the magnetic free layer onto the magnetic reference layer is laterally surrounded by a perimeter of the second part of the magnetic reference layer.

[0019] According to some embodiments, the magnetoresistive sensor further comprises a bridge circuit, wherein the bridge circuit has a first and at least one second magnetoresistance, wherein the first magnetoresistance comprises the first part of the magnetic free layer, wherein the second magnetoresistance comprises the second part of the magnetic free layer.

[0020] According to some embodiments, the magnetoresistive sensor further comprises a tunnel barrier layer and an electrically conductive via, wherein the tunnel barrier layer is arranged between the magnetic reference layer and the magnetic free layer, wherein the electrically conductive via connects a part of the magnetic free layer to the magnetic reference layer through the tunnel barrier layer, wherein the part of the magnetic free layer is laterally surrounded by electrically insulating material.

[0021] According to some embodiments, the electrically conductive via is arranged vertically above the geometric center of gravity of the magnetic reference layer.

[0022] According to a second aspect of the present disclosure, a method for generating a (e.g., permanently) closed-flux magnetization pattern with a predetermined rotation direction in a magnetic reference layer of a magnetic layer stack is provided. The method comprises applying an external magnetic field in a predetermined direction to the magnetic layer stack, thereby causing magnetic saturation of the magnetic reference layer and a pinned layer of the magnetic layer stack. The method further comprises reducing the external magnetic field to form a first closed-flux magnetization pattern in the magnetic reference layer and a second closed-flux magnetization pattern in the pinned layer.

[0023] According to some embodiments, the method further comprises pinning the second closed-flux magnetization pattern to a natural antiferromagnetic layer of the magnetic layer stack.

[0024] According to some embodiments, the method further comprises maintaining a temperature of the magnetic layer stack below 200°C during application of the external magnetic field; and after reducing the external magnetic field, increasing the temperature of the magnetic layer stack to above 240°C but not exceeding a barrier temperature of the natural antiferromagnetic layer and the pinned layer, and maintaining the temperature above 240°C for more than one hour to form an antiferromagnetic phase within the natural antiferromagnetic layer, causing exchange bias coupling between the natural antiferromagnetic layer and the pinned layer.

[0025] According to some embodiments, the method further comprises forming an antiferromagnetic phase of the natural antiferromagnetic layer and subsequently increasing the temperature of the magnetic layer stack above a barrier temperature of the natural antiferromagnetic layer and the pinned layer prior to applying the external magnetic field, and maintaining the temperature of the magnetic layer stack above the barrier temperature during application of the external magnetic field.

[0026] According to some embodiments, the method further comprises structuring, prior to applying the external magnetic field, at least the magnetic reference layer to have a lateral cross-section comprising a main portion and a protrusion portion laterally adjacent to the main portion, wherein the external magnetic field is applied parallel to the protrusion portion. Short description of the characters

[0027] Some examples of devices and / or methods are described below solely by way of example and with reference to the accompanying figures, in which Fig. 1 shows a circuit diagram of a magnetoresistive sensor; Fig. 2a-b show schematic top views of magnetoresistive sensors; Fig. 2c shows a magnetic layer stack of a magnetoresistive sensor; Fig. Figure 2d shows a lateral cross-section of a magnetic reference layer having a main portion and a projection portion; Fig. 2e-h show simulation results of magnetic fields in magnetic reference layers with a main section and a protrusion section; Fig. 2i shows a lateral cross-section of another magnetic reference layer having a main portion and a projection portion; Fig. Figure 2j shows a three-dimensional view of a magnetic reference layer and a magnetic free layer having two laterally separated parts; Fig. 3a-i show several examples of magnetoresistive sensors in a schematic plan view; Fig. 4a-b show a magnetoresistive sensor exposed to an external magnetic field; Fig. 4c-d show schematic vertical cross-sections of different possible structures of a magnetic layer stack of a magnetoresistive sensor; Fig. 5a-d show schematic diagrams of bridge circuits of magnetoresistive sensors comprising two or more laterally separated parts of a magnetic reference layer with a closed flux magnetization pattern in each part; Fig. 6a-b show schematic vertical cross-sections of different possible structures of magnetic layer stacks with a vertical current path; and Fig. 7 shows a flow diagram of a method for generating a permanently closed flux magnetization pattern with a predetermined rotation direction in a magnetic reference layer of a magnetic layer stack. Detailed description

[0028] Various examples will now be described in more detail with reference to the accompanying drawings, which illustrate some examples. In the figures, the thicknesses of lines, layers, and / or regions may be exaggerated for clarity.

[0029] It is understood that when an element is referred to as being "connected" or "coupled" to another element, the elements may be connected or coupled directly or through one or more intermediate elements. When two elements A and B are combined using an "or," this should be understood to disclose all possible combinations, i.e., only A, only B, and both A and B. An alternative formulation for the same combinations is "at least one of A and B." The same applies to combinations of more than two elements.

[0030] The terminology used here to describe specific examples is not intended to be limiting for further examples. Where a singular form, such as "a," "an," and "the," is used, and the use of only a single element is neither explicitly nor implicitly defined as mandatory, further examples may also use plural elements to implement the same function. Where a function is subsequently described as being implemented using multiple elements, further examples may implement the same function using a single element or a single processing entity.It is further understood that the terms "comprises", "comprising", "comprises" and / or "having" when used specify the presence of the specified features, integers, steps, operations, processes, elements and / or components thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, processes, elements, components and / or group thereof.

[0031] Unless otherwise defined, all terms (including technical and scientific terms) are used herein in their ordinary meaning in the field to which examples belong.

[0032] As an introduction, Fig. 1 shows a circuit diagram of a magnetoresistive sensor 100 based on an xMR effect. The magnetoresistive sensor 100 can be used as an angle sensor for measuring the direction of an externally applied magnetic field 101. The magnetoresistive sensor 100 comprises a first bridge circuit 105 and a second bridge circuit 108 (or may alternatively comprise at least two half-bridge circuits). Both the first and second bridge circuits 105, 108 are connected to a common supply voltage V DDa and connected to a common ground potential GND. The first bridge circuit 105 can provide measurements of an X component of the externally imposed magnetic field 101. The second bridge circuit 108 can provide measurements of a Y component of the externally imposed magnetic field 101. As shown by the coordinate system in Fig. 1, the x- and y-components of the externally imposed magnetic field 101 are orthogonal with respect to each other and parallel to a chip surface (e.g., to the surface of the first and second bridge circuits 105, 108) of the magnetoresistive sensor 100. The first bridge circuit 105 comprises two magnetoresistances with reference magnetizations in the x-direction and two magnetoresistances with reference magnetizations in the opposite x-direction, as indicated by the arrows within the magnetoresistances of the first bridge circuit 105. A bridge voltage V x the first bridge circuit 105 can then be indicative of a size B x the x-component of the externally imposed magnetic field 101.

[0033] Analogously, the second bridge circuit 108 comprises two magnetoresistors with reference magnetizations in the y-direction and two magnetoresistors with reference magnetizations in the opposite y-direction, as indicated by the arrows within the magnetoresistors of the second bridge circuit 108. A bridge voltage V y the second bridge circuit 108 can then be indicative of a size B y the y-component of the externally imposed magnetic field 101.

[0034] If the magnetoresistive sensor 100 is based on the GMR effect or the TMR effect, the magnetoresistive sensor 100 can be used to unambiguously measure the direction of the externally imposed magnetic field 101 within 360°. A magnetoresistive AMR sensor can unambiguously measure the direction of the externally imposed magnetic field 101 within 180°. The direction (or angle) of the externally imposed magnetic field 101 can be calculated from arctan(B y / B x ). For this purpose, the magnetoresistive sensor 100 may comprise an evaluation circuit (in Fig. 1 not shown).

[0035] Optionally, a security measure can be provided where the size Bx2+By2 of the externally imposed magnetic field 101 is monitored, which, assuming an externally imposed magnetic field of constant magnitude, as is the case in many applications, should be constant after calibration and temperature compensation of both sensor signal components (e.g., the bridge voltages V x and V y However, this test may have limited accuracy and may not achieve very high diagnostic coverage due to its reliance on absolute values.

[0036] The local magnetization processes for providing the reference magnetizations of the magnetoresistors of the first and second bridge circuits 105 and 108 may involve applying local heating with a laser within an external magnetic field of the desired direction (e.g., the desired direction of a magnetoresistor's reference magnetization). Each magnetoresistor may be separately locally magnetized in a heated state to its pinning direction (e.g., its reference magnetization direction). This process could be time-consuming and thus costly.

[0037] At least some embodiments according to the present disclosure can overcome and / or circumvent this time-consuming and thus costly magnetization process. Fig. 2 shows a schematic top view of a magnetoresistive sensor 200-A according to an embodiment. The magnetoresistive sensor 200-A includes a magnetic reference layer 220. The magnetic reference layer 220 includes a magnetization pattern with permanently closed flux 222 of a predetermined rotation direction. Furthermore, the magnetoresistive sensor 200-A includes a magnetic free layer 230. The magnetic free layer 230 has a total lateral area that is smaller than a total lateral area of ​​the magnetic reference layer 220. A geometric center of gravity of the magnetic free layer 230 is laterally offset with respect to a geometric center of gravity of the magnetic reference layer 220.

[0038] The closed-flux magnetization pattern 222 is permanent and of a predetermined rotational direction. However, locally, the direction of the magnetic field (and the magnetic flux density associated with that magnetic field) changes within the magnetic reference layer 220. This changing of the direction of the magnetic field can be used to provide a desired direction of reference magnetization with respect to the magnetic free layer 230. This is possible because the magnetic free layer 230 has a total lateral area smaller than that of the magnetic reference layer 220 and because the geometric center of gravity 231 of the magnetic free layer 230 is laterally offset with respect to the geometric center of gravity 221 of the magnetic reference layer 220.The magnetic free layer 230 (or a portion of the magnetic free layer 230) can then be positioned vertically above (or, depending on the design of the magnetoresistive sensor 200-A, vertically below) a portion of the magnetic reference layer 220, providing the desired direction of reference magnetization. In other words, the location (e.g., the x and y coordinates, as represented by the coordinate system in . Fig. 2a) of the magnetic free layer 230 vertically above (or alternatively vertically below) the magnetic reference layer 220, determine the direction of reference magnetization for a magnetoresistance of the magnetoresistive sensor 200-A having the magnetic free layer 230 (or a portion of the magnetic free layer 230).

[0039] Within the context of the present disclosure, it is assumed that different portions of a layer (e.g., the magnetic reference layer 220 and / or the magnetic free layer 230) are laterally separated from each other and surrounded by an electrically insulating material (e.g., solid electrically insulating material and / or cavities). For example, different portions of a layer may be created during production of the magnetoresistive sensor 200-A by patterning the layer using a photolithographic process. Different portions of a layer (e.g., the magnetic reference layer 220 and the magnetic free layer 230) may be laterally directly adjacent to each other and are used hereinbefore to describe different shapes of a layer or a portion of a layer. A portion of a layer may have one or more portions.Furthermore, the total lateral area of ​​a layer (e.g., the magnetic reference layer 220 or the magnetic free layer 230) may be the sum of the lateral areas of all parts of the layer.

[0040] A magnetoresistance comprising the magnetic free layer 230 of the magnetoresistive sensor 200-A may have a reference magnetization primarily in the y-direction, for example, whereas a magnetoresistance comprising the magnetic free layer 230 of the magnetoresistive sensor 200-B shown in Fig. 2B, a reference magnetization may be primarily in the x-direction. Since the direction of the reference magnetization of a magnetoresistance can be defined by the position of the magnetic free layer 230 relative to the magnetic reference layer 220, local magnetization processes of the magnetic reference layer for providing directions of the reference magnetization can be avoided during manufacturing. This can reduce manufacturing time and costs for the magnetoresistive sensor 200-A / B.

[0041] The geometric centroid 221 (e.g., the geometric center) of the magnetic reference layer 220 and the geometric centroid 231 of the magnetic free layer 230 can be considered as a center of the magnetic reference layer 220 and / or the magnetic free layer 230, even for asymmetric shapes (e.g., asymmetric lateral cross-sections) of the magnetic reference layer 220 and the magnetic free layer 230. The geometric centroid 221 of the magnetic reference layer 220 can be defined as the arithmetic mean position of all points in the magnetic reference layer 220 and can be located inside or outside the magnetic reference layer 220, depending on the shape of the magnetic reference layer 220.Similarly, the geometric center of gravity 231 of the magnetic free layer 230 may be defined as the arithmetic mean position of all points in the magnetic free layer 230 and may be located inside or outside the magnetic free layer 230, depending on the shape of the magnetic free layer 230.

[0042] For example, if the magnetic free layer 230 has two or more parts that are laterally separated from each other, respective geometric centers of gravity of the parts of the magnetic free layer 230 may be laterally offset with respect to the geometric center of gravity of the magnetic reference layer 220. If, in addition, the magnetic reference layer has two or more parts that are laterally separated from each other, respective geometric centers of gravity of the parts of the magnetic free layer 230 may be laterally offset with respect to respective geometric centers of gravity of the parts of the magnetic reference layer 220. Laterally separated parts of the part of the magnetic free layer 230 may each be laterally surrounded by electrically insulating material. Likewise, laterally separated parts of the magnetic reference layer 220 may each be laterally surrounded by electrically insulating material.

[0043] A lateral displacement of the geometric center of gravity 231 of the magnetic free layer 230 with respect to the geometric center of gravity 221 of the magnetic reference layer 220 may be greater than at least 5% (or at least 10% or at least 20%) of a maximum lateral extent of the magnetic free layer 230. A larger lateral displacement may provide a more definitive direction of the reference magnetization.

[0044] The closed-flux magnetization pattern 222 vertically above or below at least a portion of the magnetic free layer 230 may include a component with an average magnetic flux density parallel to the magnetic free layer 230 (i.e., parallel to the xy plane of the free layer). The portion of the magnetic free layer may be laterally surrounded by electrically insulating material.

[0045] This means that a magnetoresistance of the magnetoresistive sensor 200-A / B may have the magnetic free layer 230 or a portion of the magnetic free layer 230 laterally surrounded by electrically insulating material. Depending on the structure of the magnetic layer stack of the magnetoresistive sensor 200-A / B, the magnetic reference layer 220 may be arranged above or below the magnetic free layer 230. The portion of the magnetic field 222 of the magnetic reference layer that is arranged vertically above (and / or vertically below) the magnetic free layer 230 (or its portion) may determine a reference magnetization for the magnetoresistance. For a unique reference magnetization, the magnetic field 222 that runs within the magnetic reference layer 220 vertically above (or vertically below) the magnetic free layer 230 (or its portion) may have a component with an average non-zero magnetic flux density parallel (e.g.in the xy plane) to the magnetic free layer 230. Otherwise, as many magnetic field lines in the x-direction and y-direction would run vertically above (or vertically below) the magnetic free layer 230 (or part thereof) as there are in the negative x-direction and / or in the negative y-direction. The average magnetic field vertically above (or vertically below) the magnetic free layer 230 (or part thereof) would then be zero, and a unique reference magnetization of the magnetoresistance would not exist.However, according to examples of the present disclosure, the lateral displacement of the geometric center of gravity 231 of the magnetic free layer 230 (or a portion of the magnetic free layer 230) with respect to the magnetic reference layer 220 (or with respect to a portion of the magnetic reference layer 220) may cause the closed flux magnetization pattern 222 vertically above (or vertically below) the magnetic free layer 230 (or a portion thereof) to have a non-zero average magnetic flux density component parallel to the magnetic free layer 230.

[0046] Optionally, a direction of the closed-flux magnetization pattern 222 may change vertically above or below at least a portion of the magnetic free layer 230 by at most 90° (or by at most 60°, or by at most 45°, or by at most 30°), wherein the portion of the magnetic free layer 230 is laterally surrounded by electrically insulating material. The less the direction of the closed-flux magnetization pattern 222 changes vertically above (or vertically below) the magnetic free layer (or portions thereof), the more unambiguous the direction of the reference magnetization provided to the magnetic free layer (or portions thereof) can be.

[0047] Since the closed-flux magnetization pattern 222 is permanent, it can be present within the magnetic reference layer 220 regardless of an operating state (e.g., an on-state or an off-state) of the magnetoresistive sensor 200-A / B. The predetermined rotation direction can be, for example, a clockwise or counterclockwise direction in the xy-plane of the magnetic reference layer 220. This means that the closed-flux magnetization pattern 222 can be in-plane with the magnetic reference layer 220. Neglecting magnetic flux leakage effects, the magnetic reference layer 220 can enclose the closed-flux magnetization pattern 222. Magnetic field lines extending within the magnetic reference layer 220 can then follow loops enclosed by the magnetic reference layer 220.The predetermined rotation direction of the closed flux magnetization pattern 222 can ensure that the desired direction of the reference magnetization can be provided with respect to the magnetic free layer.

[0048] The magnetoresistive sensor 200-A / B may additionally include a natural antiferromagnetic layer and a pinned layer. The natural antiferromagnetic layer and the pinned layer may assist in establishing a permanent magnetization pattern in the magnetic reference layer 220. The pinned layer may be disposed between the natural antiferromagnetic layer and the magnetic reference layer 220. An optional coupling layer may be disposed between the pinned layer and the magnetic reference layer 220.The natural antiferromagnetic layer, the pinned layer, the optional coupling layer, and the magnetic reference layer may be different layers of a magnetic layer stack of the magnetoresistive sensor 200-A / B and may be referred to as a magnetic reference system of the magnetoresistive sensor 200-A / B because they may collectively be responsible for defining the reference magnetization pattern (i.e., the closed-flux magnetization pattern) in the magnetic reference layer 220.

[0049] Fig. 2c shows an example of a magnetic layer stack 200-C of a magnetoresistive sensor according to an example. For example, the magnetic layer stack 200-C may be arranged on a semiconductor substrate (not shown) of the magnetoresistive sensor. When described in a Cartesian coordinate system with pairwise perpendicular coordinate axes x, y, and z, the layers each extend laterally in a plane spanned by the x and y axes. Herein, lateral dimensions (e.g., lateral distances, lateral cross-sectional areas, lateral areas, lateral dimensions, lateral displacements, etc.) refer to dimensions in the xy plane. Vertical dimensions refer to dimensions in the z direction, perpendicular to the xy plane. For example, the (vertical) extension of a layer in the z direction may be described as the layer thickness.

[0050] From bottom to top, the magnetic layer stack 200-C includes a natural antiferromagnetic (NAF) layer 210 and a ferromagnetic pinned layer 212. Contact between the natural antiferromagnetic layer 210 and the pinned layer 212 may induce an effect known as an exchange bias effect, which causes the magnetization of the pinned layer 212 to align in a preferred direction. The pinned layer 212 may have a closed-flux magnetization pattern in the xy plane. This closed-flux magnetization pattern of the pinned layer 212 may be created during fabrication of the magnetic layer stack 200-C (as explained below) and may be permanent. The magnetic layer stack 200-C may further include a coupling layer 214.The coupling layer 214 may be a diamagnetic coupling layer and may comprise ruthenium, iridium, copper, and / or copper alloys, and similar materials, for example. The coupling layer 214 spatially separates the pinned layer 212 from the magnetic (e.g., ferromagnetic) reference layer 220. Using this configuration, the magnetization of the magnetic reference layer 220 may align and be maintained in a direction antiparallel to the magnetization of the pinned layer 212. For example, if the pinned layer 212 has a clockwise closed flux magnetization pattern in the xy plane, the magnetic reference layer 220 may have a counterclockwise closed flux magnetization pattern in the xy plane (or vice versa). In this way, the magnetic reference layer 220 may have a permanently closed flux magnetization pattern.

[0051] The magnetic layer stack 200-C additionally comprises a non-magnetic layer 216 and a magnetic free layer 230. The non-magnetic layer 216 is arranged between the magnetic reference layer 220 and the magnetic free layer 230. The magnetic free layer 230 has a total lateral area that is smaller than a total lateral area of ​​the magnetic reference layer 220. A geometric centroid of the magnetic free layer 230 is laterally offset with respect to a geometric centroid of the magnetic reference layer 220. The magnetic free layer 230 may have a linear magnetization pattern or a closed-flux magnetization pattern (e.g., a vortex magnetization pattern). Furthermore, the magnetization of the magnetic free layer 230 may follow an externally imposed magnetic field.

[0052] According to some embodiments, the non-magnetic layer 216 may be electrically conductive (e.g., comprise copper, silver, gold, tungsten, aluminum, and / or alloys thereof). In this case, the magnetoresistive sensor comprising the magnetic layer stack 200-C may be a giant magnetoresistive sensor. Alternatively, the non-magnetic layer 216 may be an electrically insulating tunnel barrier layer. The magnetoresistive sensor comprising the magnetic layer stack 200-C may then be a tunnel magnetoresistive sensor.

[0053] The magnetic free layer 216, the magnetic reference layer 220, and the pinned layer 212 may comprise iron, cobalt, or nickel in some embodiments, and alloys thereof in some further embodiments. Alloys may also comprise non-ferromagnetic materials, e.g., carbon, boron, nitrogen, and / or oxygen, wherein ferromagnetic materials constitute at least 50% of a material composition of the respective layer. For example, layers may comprise cobalt-iron (CoFe), cobalt-iron-boron (CoFeB), or nickel-iron (NiFe) alloys. In contrast, the natural antiferromagnetic layer 210 may comprise iridium, manganese, platinum, and / or alloys comprising these, for example.

[0054] During operation of a TMR sensor, or when the magnetic layer stack 200-C is coupled to an electrical circuit, electrical charges can be conducted from one side of the tunnel barrier layer 216 to the other in a predetermined amount when a constant external magnetic field is applied. The TMR effect is a quantum physical phenomenon that manifests itself in a change in the amount of charge conducted through the tunnel barrier layer 216 when the direction of the external magnetic field is changed. This effect can arise due to directional changes in the magnetization of the magnetic free layer 230 with respect to the magnetization of the reference layer magnetization, which are caused by changing the external magnetic field.For example, the external magnetic field may align the magnetization of the magnetic free layer 230 in the direction of the (average) magnetization of a portion of the magnetic reference layer 220 located vertically below the magnetic free layer 230. A larger amount of electric charge may then pass through the tunnel barrier layer 216 than if the external magnetic field has a different direction, aligning the magnetization of the magnetic free layer 230 antiparallel (e.g., opposite) to the magnetization of the portion of the magnetic reference layer 220.

[0055] Examples of magnetoresistive sensors of the present disclosure may include the magnetic layer stack 200-C of Fig. 2C and / or similar magnetic layer stacks. Magnetoresistive sensors are not limited to the GMR or TMR effect. Other examples of the present disclosure may include structures based on other xMR effects. The magnetic layer stack 200-C may correspond to a magnetoresistance as employed by at least some embodiments of this disclosure.

[0056] Various means may be used to provide a predetermined rotation direction of the closed-flux magnetization pattern 222 of the magnetic reference layer 220. For example, a lateral cross-section of the magnetic reference layer 220 (and / or an optional pinned layer) may have a shape that can support the implementation of a predetermined rotation direction of the closed-flux magnetization pattern 222. The magnetic reference layers 220, which are Fig. 2a-c have generic, lateral cross-sections that do not have a specific shape. However, as shown in Fig. As shown in Figure 2d, the magnetic reference layer 220 may optionally include a main portion 224 and a protrusion portion 226. The protrusion portion 226 may be laterally adjacent (e.g., directly laterally adjacent) to the main portion 224. The main portion 224 may include a closed-flux magnetization pattern 222. A magnetization pattern 225 of the protrusion portion 226 may be configured to predetermine the rotation direction of the closed-flux magnetization pattern 222.

[0057] As in Fig. 2d, the projection portion 226 may extend laterally from the main portion 224. Alternatively, the magnetic reference layer may have a lateral slot (not shown in Fig. 2d). The lateral slot may be arranged laterally between the main portion and the protrusion portion. For example, the lateral slot may extend from a periphery of the magnetic reference layer laterally into (but not through) the magnetic reference layer to form the magnetic reference layer into the main portion and the protrusion portion.

[0058] In proximity to a lateral connection of the projection portion 226 and the main portion 224 (as indicated by the dashed line in Fig. 2D), the magnetization pattern 225 of the protrusion portion 226 may be directed (substantially) opposite to the closed-flux magnetization pattern 222 of the main portion 224. For example, with the aid of an external magnetic field applied to the magnetic reference layer 220 in a predetermined direction during manufacturing, a closed-flux magnetization pattern 222 of a predetermined rotational direction may be created within the main portion 224. The external magnetic field applied to the magnetic reference layer 220 during manufacturing may have a direction along the protrusion portion 226. The protrusion portion 226 may then be magnetized in the direction of the external magnetic field applied during manufacturing.Upon removal (or reduction) of this external magnetic field, a closed-flux magnetization pattern 222 can form within the main portion 224 and align in the opposite direction to the magnetization pattern of the protrusion portion 226 at the lateral junction of the protrusion portion 226 and the main portion 224. The local direction of the closed-flux magnetization pattern 222 at the lateral junction can then set the rotation direction of the closed-flux magnetization pattern 222. Since the magnetization of the protrusion portion 226 can be permanent, the protrusion portion 226 can permanently maintain the closed-flux magnetization pattern 222 in its predetermined rotation direction.

[0059] According to some examples, a length 227 of the protrusion portion 226 may be greater than twice a width of the protrusion portion 226. This may additionally support implementing a predetermined rotation direction of the closed-flux magnetization pattern 222 within the main portion 224. The length 227 of the protrusion portion 226 may be defined as the maximum lateral distance of the protrusion portion 226 from a distal end (with respect to the main portion 226) of the protrusion portion 226 to the main portion 226 (e.g., to the lateral connection of the protrusion portion 226 to the main portion 224). The width of the protrusion portion 226 may be defined as the lateral extent of the protrusion portion 226 in a direction perpendicular to the length 227 of the protrusion portion 226. As in Fig. 2d, the protrusion portion 226 may have a triangular lateral shape, but may also have different shapes, e.g., rectangular, polygonal, or curved shapes.

[0060] A length (e.g., a maximum lateral extent) of the main portion 224 may be less than twice a width of the main portion 224. This may enable the formation of the closed-flux magnetization pattern 222 within the main portion 224. The width of the main portion 224 may be defined as the lateral extent of the main portion 224 in a direction perpendicular to the length of the main portion 224. In other words, while the protrusion portion 226 may have an elongated lateral cross-section, the main portion 224 may have a non-elongated (e.g., circular or patch-like) lateral cross-section.

[0061] According to some examples, the main portion 224 has a rotationally symmetric lateral cross-section. This may further assist in the creation of the closed-flux magnetization pattern 222 within the magnetic reference layer 220. For example, the main portion 224 may have an elliptical, circular, square, or regular polygonal lateral cross-section.

[0062] Optional (as in Fig. 2d), the protrusion portion 226 may extend tangentially to the main portion 224. This may further assist in predetermining the rotation direction of the closed-flux magnetization pattern 222 within the main portion 224 of the magnetic reference layer 220.

[0063] A minimum lateral distance between the magnetic free layer (not in Fig. 2d) and the protrusion portion 226 of the magnetic reference layer 220 may be greater than 10% (or greater than 25%) of a maximum lateral extent of the main portion 224. In this way, a sufficient distance may be provided between the protrusion portion 226 and the magnetic free layer (or the part of the magnetic free layer laterally closest to the protrusion portion 226) such that effects of the magnetization pattern 225 of the protrusion portion 226 on reference magnetizations of magnetoresistances of the magnetoresistive sensor may be negligible. If a lateral slot is implemented, a minimum lateral distance between the magnetic free layer and the lateral slot may be greater than 10% (or greater than 25%) of a maximum lateral extent of the main portion.

[0064] Asymmetries of the magnetic reference layer 220 (and optionally a pinned layer of the magnetoresistive sensor) such as the protrusion portion 226 may be supportive to allow the formation of the closed flux magnetization pattern 222 (e.g., a vortex magnetization pattern) in a predefined rotation direction via exchange coupling when an evanescent external magnetic field is applied during formation (e.g., during fabrication of the magnetoresistive sensor).

[0065] Fig. Figure 2e shows an example of a structure (e.g., a lateral cross-section of a magnetic layer stack) exhibiting a defined chirality of a magnetic reference layer 220 (and / or a pinned layer) of a magnetic reference system of a magnetoresistive sensor after exposure to a saturation magnetic field 202 and relaxation in a low field to generate a vortex-like (e.g., closed flux) magnetization pattern 222. The structure (e.g., the lateral cross-sectional area of ​​the magnetic reference layer 220) comprises a circular main portion 224 and an elongated protrusion portion 226. During exposure to the saturation magnetic field 202, the saturation magnetic field 202 may be applied such that it is primarily aligned along the protrusion portion 226.The protrusion portion 226 may exhibit a high shape anisotropy, which can substantially maintain its magnetization 223 even after the relaxation of the external magnetic field 202. Therefore, during the generation of the vortex-like magnetization of the magnetic reference layer 220, an additional, non-symmetric magnetic force may influence the vortex generation, thereby defining the vortex chirality (e.g., the rotation direction of the closed-flux magnetization pattern 222).

[0066] In other words, the magnetization of the protrusion portion 226 may be substantially linear (or not closed within the protrusion portion, as in Fig. 2d) and may cause the closed flux magnetization pattern 222 to align in an opposite direction to that at the lateral junction of the projection portion 226 and the main portion 224. This is shown in the micro-magnetic simulations shown in Fig. 2e-h. The closed-flux magnetization pattern 222 (or vortex magnetization) near the protrusion portion 226 of the magnetic reference layer 220 is oriented antiparallel to the magnetization 223 of the protrusion portion 226. Consequently, the chirality (e.g., the rotation direction of the closed-flux magnetization pattern 222) can be controlled by the geometry of the magnetic reference layer 220.

[0067] For example, show Fig. 2e-f a chirality of the vortex depending on the initial saturation state for a protrusion portion 226 (e.g., a structure extension) on one side of the structure shape of the magnetic reference layer (or structure shape of the pinned layer). Fig. 2g-h show a chirality of the vortex depending on the initial saturation state for a protrusion portion 226 on an opposite side of the structural shape of the magnetic reference layer (or structural shape of the pinned layer).

[0068] Fig. Figure 2i shows another structural example (e.g., a lateral cross-section of a magnetic reference layer 220) with a structural extension (e.g., a protrusion portion 226). The effect may be similar to the structure with extension at the top right, as shown in Fig. 2e-f.

[0069] Returning to the magnetoresistive sensor 200-A / B, the magnetic free layer 230 may include a first portion and at least a second portion. The second portion may be laterally separated from the first portion. For example, the first and second portions may be separated from each other by a solid, electrically insulating material or by a cavity within a magnetic layer stack. During fabrication of the magnetoresistive sensor 200-A / B, the first and second portions of the magnetic free layer 230 may be formed from the magnetic free layer 230 using a photolithographic process, for example. Separate portions of the magnetic free layer 230 may be used to implement a plurality of magnetoresistances of the magnetoresistive sensor 200-A / B that share the same magnetic reference layer 220.For example, a first magnetoresistance of the magnetoresistive sensor 200-A / B may include the first portion of the magnetic free layer 230, and a second magnetoresistance of the magnetoresistive sensor 200-A / B may include the second portion of the magnetic free layer 230. In this way, manufacturing of the magnetoresistive sensor 200-A / B may be made more efficient, thus reducing manufacturing costs. The first and second portions of the magnetic free layer 230 may be arranged vertically above (or vertically below) the same portion of the magnetic reference layer 220. Alternatively, the first and second portions of the magnetic free layer 230 may be arranged vertically above (or vertically below) different portions of the magnetic reference layer 220 that are laterally separated from each other.

[0070] For example, vertically above (or, depending on the structure of the magnetic layer stack, vertically below) the first part of the magnetic free layer 230, the direction of the closed-flux magnetization pattern 222 of the magnetic reference layer may be different from its direction vertically above (and / or vertically below) the second part of the magnetic free layer 230. Accordingly, different directions of reference magnetization may be provided for a first magnetoresistor comprising the first part of the magnetic free layer 230 with respect to a second magnetoresistor comprising the second part of the magnetic free layer 230. This may avoid local magnetization processes of the magnetoresistors.

[0071] The closed-flux magnetization pattern 222 of the magnetic free layer 220 may change its direction vertically above (or vertically below) the corresponding portions of the magnetic free layer 230. Therefore, the direction of the reference magnetization for a magnetoresistance may be more defined by an average direction assumed by the closed-flux magnetization pattern 222 vertically above (or vertically below) the corresponding portions of the magnetic free layer 230. In other words, a first average direction of the closed-flux magnetization pattern 222 (of the reference magnetic layer 220) vertically above (or vertically below) the first portion of the magnetic free layer 230 may differ from a second average direction of the closed-flux magnetization pattern 222 vertically above (or vertically below) the second portion of the magnetic free layer 230.

[0072] For example, the first average direction may differ from the second average direction by at least 5 degrees (or at least 10 degrees, or at least 20 degrees, or at least 45 degrees, or at least 90 degrees). A larger difference between the first and second average directions of the closed-flux magnetization pattern may enable the measurement of different directional components of an external magnetic field incident on the magnetoresistive sensor 200-A / B.

[0073] For example, the first average direction of the closed-flux magnetization pattern 222 may coincide with the x-direction, and the second average direction of the closed-flux magnetization pattern 222 may be orthogonal with respect to the first average direction and thus coincide with the y-direction. Orthogonality may enable reliable determination of the direction of an externally imposed magnetic field using the magnetoresistive sensor 200-A / B.

[0074] In another example, the first average direction and the second average direction may be antiparallel to each other (i.e., may differ from each other by approximately 180°). Antiparallel alignment of the first and second average directions may enable a Wheatstone half-bridge configuration.

[0075] A respective average direction of the closed-flux magnetization pattern 222 vertically above (or vertically below) a respective portion of the magnetic free layer 230 may be determined by integrating a first component of a magnetic flux density associated with the closed-flux magnetization pattern 222 over a portion of the magnetic reference layer 220, and by integrating a second component of the magnetic flux density over that portion, and by comparing the integrated first component and the integrated second component of the magnetic flux density. The portion of the magnetic reference layer may extend from a top surface to a bottom surface of the magnetic reference layer 220 and may have a lateral region that coincides with a vertical projection of the corresponding portion of the magnetic free layer 230 onto the magnetic reference layer 220.The first and second components of the magnetic flux density may be orthogonal with respect to each other and in a plane parallel to the magnetic free layer 230 (e.g., in the xy plane).

[0076] This will be explained in more detail with the help of Fig. 2j explained. Fig. Figure 2j shows a schematic diagram of a magnetic reference layer 220 together with a magnetic free layer disposed over the magnetic reference layer 220 (an optional non-magnetic layer disposed between the magnetic reference layer 220 and the magnetic free layer is not shown). The magnetic free layer has a first part 230-1 and a second part 230-2. The second part 230-2 is laterally separated from the first part 230-1. Furthermore, Fig. 2j shows the closed-flux magnetization pattern 222 of the magnetic reference layer 220. The closed-flux magnetization pattern 222 assumes different average directions vertically beneath the first portion 230-1 and the second portion 230-2 of the magnetic free layer. To determine a respective average direction of the closed-flux magnetization pattern 222 vertically beneath a respective portion 230-1, 230-2 of the magnetic free layer, the x and y components (e.g., orthogonal components in a plane parallel to the magnetic free layer) of the magnetic flux density associated with the closed-flux magnetization pattern 222 may be integrated over respective portions 228, 229 of the magnetic reference layer 220 disposed beneath the corresponding portions 230-1, 230-2 of the magnetic free layer.

[0077] That is, a first portion 228 of volume V1 of the magnetic reference layer 220 extends from an upper to a lower surface of the magnetic reference layer 220 and has a lateral region that coincides with a vertical projection of the first part 230-1 of the magnetic free layer onto the magnetic reference layer 220. Similarly, a second portion 229 of volume V2 of the magnetic reference layer 220 extends from the upper to the lower surface of the magnetic reference layer 220 and has a lateral region that coincides with a vertical projection of the second part 230-2 of the magnetic free layer onto the magnetic reference layer 220. The average direction of the closed flux magnetization pattern 222 in a respective portion of the magnetic reference layer of volume V i(e.g., i = 1, 2) can then be determined by integrating the x-component B x (e.g. the first component) of the magnetic flux density and the y-component B y (e.g. the second component) of the magnetic flux density over the respective section 228, 229 of the magnetic reference layer 220 according to equation 1.1: Bx,i¯=1Vi∫ViBx(x,y,z)dVi; and equation 1.2: By,i¯=1Vi∫ViBy(x,y,z)dVi.

[0078] A comparison of the integrated (e.g., averaged) x-component Bx,i¯ and the integrated (e.g., averaged) y-component By,i¯ the magnetic flux density, the respective average direction φ iof the closed flux magnetization pattern 222 vertically below (or, depending on the structure of the magnetic layer stack, vertically above) a respective part 230-1, 230-2 of the magnetic free layer. For the comparison, the inverse tangent function can be used so that the respective average direction φ i can be determined according to equation 3.1: φi={tan−1(By,i¯Bx,i¯),for Bx,i¯≥0 and By,i¯≥0;tan−1(By,i¯Bx,i¯)+180∘,for Bx,i¯<0;tan−1(By,i¯Bx,i¯)+360∘,for Bx,i¯≥0 and By,i¯<0.

[0079] For example, an average direction of φ i = 0° with the x-direction, φ i = 90° with the y-direction, φ i = 180° with the negative x-direction, and φ i = 270° with the negative y-direction.

[0080] Fig. 3a-i show several examples of magnetoresistive sensors (in a top view) comprising a magnetic reference layer 320 with a magnetization pattern with permanently closed flux 322 of a predetermined rotation direction and a magnetic free layer with a total lateral area that is smaller than a total lateral area of ​​the magnetic reference layer 320. Geometric centers of gravity of the magnetic free layer 330 (or different parts of the magnetic free layer 330-1, 330-2, 330-3, 330-4) are laterally offset with respect to geometric centers of gravity of the magnetic reference layers 430 of the magnetoresistive sensors.

[0081] For example, for a TMR (or alternatively, another xMR), the magnetic reference layer 320 (and optionally the pinned layer) of the TMR may have a vortex structure (e.g., a closed-flux magnetization pattern 322). The magnetic free layer 330 of the TMR (or portions 330-1, 330-2, 330-3, 330-4 of the magnetic free layer) may be confined to a region of the vortex-like magnetized magnetic reference layer 320 that has the desired direction of reference magnetization. TMR elements (or alternatively, other xMR elements) with different directions of reference magnetization may be realized by different placement of the magnetic free layer 330 (or portions 330-1, 330-2, 330-3, 330-4 of the magnetic free layer).

[0082] The magnetic free layer 330 can be structured in various ways, e.g., circular to enable the creation of a vortex-like magnetization pattern, or linear (e.g., rectangular or polygonal) to be substantially homogeneously magnetized. Furthermore, the magnetic free layer 330 (or portions 330-1, 330-2, 330-3, 330-4 of the magnetic free layer) can be homogeneously magnetized even though the shape is circular, since the creation of a vortex-like magnetization pattern can be influenced by the thickness (e.g., the magnetic moment) of the magnetic free layer 330 as well as by the saturation magnetization of the material of the magnetic free layer 330.

[0083] Fig. 3a shows a schematic top view of a magnetoresistive sensor 300-A comprising a magnetic reference layer 320 with a circular lateral cross-sectional area and a closed-flux magnetization pattern 322. Furthermore, the magnetoresistive sensor 300-A comprises a magnetic free layer 330 with a circular lateral cross-sectional area. The magnetic free layer 330 is arranged vertically above (or vertically below) the magnetic reference layer 320 such that an average direction of the closed-flux magnetization pattern 322 vertically above (or vertically below) the magnetic free layer 330 points predominantly in the y-direction (i.e., in the direction φ = 90°), as indicated by the coordinate system shown in Fig. 3A is shown.

[0084] The magnetoresistive sensor 300-B, shown in Fig. 3b, is similar to that of Fig. 3a, however, the magnetic free layer comprises a first portion 330-1 and a second portion 330-2 laterally separated from the first portion 330-1. Both the first and second portions 330-1, 330-2 of the magnetic free layer comprise circular, lateral cross-sectional areas. A first average direction of the closed-flux magnetization pattern 322 vertically above (or vertically below) the first portion 330-1 of the magnetic free layer points predominantly in the x-direction (i.e., in the direction φ = 90°). A second average direction of the closed-flux magnetization pattern 322 vertically above (or vertically below) the second portion 330-2 of the magnetic free layer is orthogonal with respect to the first average direction and points predominantly in the y-direction (i.e., in the direction φ = 90°).

[0085] The magnetoresistive sensor 300-C, shown in Fig. 3c, is similar to that of Fig. 3b, however, the magnetic free layer has an additional third portion 330-3 with a circular cross-sectional area that is laterally separated from both the first and second portions 330-1, 330-2. A third average direction of the closed-flux magnetization pattern 322 vertically above (or vertically below) the third portion 330-3 of the magnetic free layer points predominantly in the negative x-direction (i.e., toward φ = 180°).

[0086] Of course, the parts of the magnetic free layer can be placed differently above (or below) the magnetic reference layer (and an optional pinned layer). The magnetoresistive sensor 300-D, shown in Fig. 3d, is similar to that of Fig. 3c, however, both the first and second parts 330-1, 330-2 of the magnetic free layer are positioned differently with respect to the magnetic reference layer 320. Consequently, the first average direction of the closed flux magnetization pattern 322 predominantly points in the direction φ = 315° (or -45°), while the second average direction of the closed flux magnetization pattern 322 predominantly points in the direction φ = 45° for the arrangement shown. The arrangement of Fig. 3d can be considered as an equilateral triangle with angles of 120° between the different parts 330-1, 330-2, and 330-3, which form the vertices of the triangle.

[0087] The magnetoresistive sensor 300-E shown in Fig. 3e is similar to that of Fig. 3d, however, the magnetic free layer has a fourth portion 330-4 with a circular lateral cross-sectional area. The fourth portion 330-4 is laterally separated from the first, second, and third portions 330-1, 330-2, 330-3 of the magnetic free layer. Furthermore, the third average direction of the closed-flux magnetization pattern 322 predominantly points in the direction φ = 135°, while a fourth average direction of the closed-flux magnetization pattern 322 vertically above (or vertically below) the fourth portion 330-4 of the magnetic free layer predominantly points in the direction φ = 225° in the arrangement shown. The respective φ's for 330-1 .. 330-4 are 315°, 45°, 135°, and 225°.

[0088] Furthermore, the magnetic free layer can also be non-circular to allow for vortex magnetization. Linear magnetization of magnetic free layers (or parts thereof) can be used instead.

[0089] The magnetoresistive sensor 300-F, shown in Fig. 3f, is similar to that of Fig. 3a, however, the magnetic free layer 330 has a rectangular lateral cross-sectional area and the average direction of the closed flux magnetization pattern 322 vertically above (or vertically below) the magnetic free layer 330 points predominantly in the negative y-direction (i.e., toward φ = 270°).

[0090] The magnetoresistive sensor 300-G, shown in Fig. 3g, is similar to that of Fig. 3f, but additionally has a second portion 330-2 of the magnetic free layer with a rectangular lateral cross-sectional area. An average direction of the closed-flux magnetization pattern 322 vertically above (or vertically below) the second portion 330-2 of the magnetic free layer points predominantly in the y-direction.

[0091] For the magnetoresistive sensor 300-H, which is used in Fig. 3h, which is similar to that of Fig. 3g, the rectangular lateral cross-sectional area of ​​the second portion 330-2 of the magnetic free layer is larger than the lateral cross-sectional area of ​​the first portion 330-1 of the magnetic free layer of the magnetoresistive sensor 300-G. This can increase the sensitivity of the magnetoresistive sensor 300-H with respect to the magnetoresistive sensor 300-G.

[0092] Fig. 3i shows a magnetoresistive sensor 300-I whose magnetic free layer has a first part 330-1 and a second part 330-2 with circular lateral cross-sectional areas and a third part with a rectangular lateral cross-sectional area.

[0093] Fig. Figure 4A shows a magnetoresistive sensor 400 exposed to an external magnetic field 401. The magnetoresistive sensor 400 is similar to that of Fig. 3c, but its magnetic free layer has an additional fourth portion 430-4 with a fourth average direction of the closed-flux magnetization pattern 433 of the reference layer vertically above (or vertically below) the fourth portion 430-4 of the magnetic free layer, which predominantly points in the negative y-direction. The external magnetic field 401 points in the negative x-direction. This causes the magnetization of the first portion 430-1 of the magnetic free layer to be oriented antiparallel to the first average direction of the closed-flux magnetization pattern 422 of the magnetic reference layer 420.

[0094] In other words, the external magnetic field 401 causes the magnetization of the first portion 430-1 of the magnetic free layer to be directed opposite to a first reference magnetization of a first magnetoresistor (of the magnetoresistive sensor 400) comprising the first portion 430-1 of the magnetic free layer. Accordingly, the external magnetic field 401 causes the magnetization of the second portion 430-2 of the magnetic free layer to be directed perpendicular to a second reference magnetization (given by the second average direction of the closed-flux magnetization pattern 422) of a second magnetoresistor (of the magnetoresistive sensor 400) comprising the second portion 430-2 of the magnetic free layer.

[0095] Furthermore, the external magnetic field 401 causes the magnetization of the third portion 430-3 of the magnetic free layer to be directed parallel to a third reference magnetization (given by the third average direction of the closed-flux magnetization pattern 422) of a third magnetoresistor (of the magnetoresistive sensor 400) comprising the third portion 430-3 of the magnetic free layer. Furthermore, the external magnetic field 401 causes the magnetization of the fourth portion 430-4 of the magnetic free layer to be directed perpendicular to a fourth reference magnetization (given by the fourth average direction of the closed-flux magnetization pattern 422) of a fourth magnetoresistor (of the magnetoresistive sensor 400) comprising the fourth portion 430-4 of the magnetic free layer.

[0096] In Fig. 4b, the external magnetic field 401 is incident on the magnetoresistive sensor 400, but directed in the negative y-direction. This causes the magnetization of the first portion 430-1 of the magnetic free layer to be perpendicular to the first reference magnetization of the first magnetoresistive, the magnetization of the second portion 430-2 of the magnetic free layer to be opposite to the second reference magnetization of the second magnetoresistive, the magnetization of the third portion 430-3 of the magnetic free layer to be perpendicular to the third reference magnetization of the third magnetoresistive, and the magnetization of the fourth portion 430-4 of the magnetic free layer to be parallel to the fourth reference magnetization of the fourth magnetoresistive of the magnetoresistive sensor 400.

[0097] Fig. 4c-d show schematic vertical cross-sections (in the yz-plane) of different possible arrangements of a magnetic layer stack of the magnetoresistive sensor 400 from Fig. 4a-b.

[0098] The vertical cross section in Fig. Figure 4C shows a first possible stack implementation: the so-called "bottom-pinned spin valve" (BSV) structure, which has a natural antiferromagnetic (NAF) layer 410 on the bottom (e.g., substrate) side. Materials that can be used include platinum-manganese (PtMn), iridium-manganese (IrMn), and / or nickel-manganese (NiMn). The film thickness of the NAF can be in the range of 5 nm to 50 nm. The so-called “reference system” (e.g., magnetic reference system) is deposited on the NAF 410, comprising a pinned layer (PL) 412 and the antiferromagnetically coupled (magnetic) reference layer (RL) 420. Both layers (e.g., the pinned layer 412 and the reference layer 420) may comprise ferromagnetic materials, such as cobalt-iron alloys (CoFe), cobalt-iron-boron (CoFeB) alloys, and / or nickel-iron (NiFe) alloys.A non-magnetic coupling layer 414 in between (e.g., comprising ruthenium and / or copper) can provide antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling to form an artificial antiferromagnet. The film thickness for the pinned layer 412 and / or the reference layer 420 can be in the range of 1 nm to 100 nm. Spontaneous buildup of a vortex-like magnetization pattern (e.g., a closed-flux magnetization pattern) can depend on the magnetic energy given by the geometry (diameter and film thickness) and the material (saturation magnetization). Next, the tunnel barrier layer 416 can be deposited. Materials of the tunnel barrier layer 416 can be aluminum oxide (Al2O3) and / or magnesium oxide (MgO), for example. The thickness of the tunnel barrier layer 416 can be, for example, B. in the range of 0.5 nm to 5 nm.The final functional layer may be the (magnetic) free layer (FL) (shown are the first part 430-1 and the third part 430-3 of the magnetic free layer), which acts as the sensor layer, changing its magnetization in response to an external in-plane magnetic field. Materials of the magnetic free layer may be similar to the alloys of the ferromagnetic materials of the pinned layer 412 and the reference layer 420 PL / RL, such as CoFe, CoFeB, and / or NiFe. The magnetic free layer may further comprise a multilayer stack with ferromagnetic and non-ferromagnetic material. In addition, further layers not involved in the TMR effect may also be introduced, e.g., seed layers for influencing / optimizing stack growth or a low-resistance bottom electrode comprising, e.g., copper.The entire stack can be deposited in one process and the magnetic free layer and the remaining stack part can be patterned in separate etching processes, for example.

[0099] Since the magnetic free layer in the exemplary magnetic layer stack of Fig. 4c is deposited over the magnetic reference layer 420, the closed-flux magnetization pattern of the magnetic reference layer 420 may exist vertically beneath the corresponding portions of the magnetic free layer. However, the magnetic free layer may not be on top of the stack. Fig. Figure 4D shows a different construction of the magnetic layer stack of the magnetoresistive sensor 400, in which the magnetic free layer is first deposited (on a substrate) and patterned before the remaining stack is deposited and patterned. In this case, the stack is called a "top-pinned spin valve" because the reference system is on top of the stack. The closed-flux magnetization pattern of the magnetic reference layer 420 can then exist vertically above the corresponding parts of the magnetic free layer.

[0100] In addition to the magnetic free layer having a first part and a second part laterally separated from the first part, the magnetic reference layer 220 (e.g., of the magnetoresistive sensors 200-A / B) may optionally have a first part and at least one second part (not shown in Fig. 2a-b). The first part of the magnetic reference layer 220 can be laterally separated from the second part of the magnetic reference layer 220. Furthermore, each part of the magnetic reference layer can have a respective magnetization pattern with permanently closed flux with a predetermined rotation direction. In addition, a vertical projection of the first part of the magnetic free layer onto the magnetic reference layer can be laterally surrounded by a perimeter of the first part of the magnetic reference layer 220. A vertical projection of the second part of the magnetic free layer 230 onto the magnetic reference layer 220 can be laterally surrounded by a perimeter of the second part of the magnetic reference layer 220.

[0101] In other words, the first part of the magnetic free layer 230 may be arranged vertically above (or, depending on the structure of the magnetic layer stack, vertically below) the first part of the magnetic reference layer 220, wherein the second part of the magnetic free layer 230 may be arranged vertically above (or vertically below) the second part of the magnetic reference layer 220. A geometric center of gravity of the first part of the magnetic free layer 230 may be laterally offset with respect to a geometric center of gravity of the first part of the magnetic reference layer 220. Similarly, a geometric center of gravity of the magnetic free layer 230 may be laterally offset with respect to a geometric center of gravity of the second part of the magnetic reference layer 220. In this way, a plurality of magnetoresistances of the magnetoresistive sensor 200-A / B may be provided.

[0102] This may, for example, enable the provision of two (or more) magnetoresistors having the same reference magnetization direction when the average direction of the closed-flux magnetization pattern in the first portion of the magnetic reference layer 220 vertically above (or vertically below) the first portion of the magnetic free layer 230 is equal to the average direction of the closed-flux magnetization pattern in the second portion of the magnetic reference layer 220 vertically above (or vertically below) the second portion of the magnetic free layer 230. Magnetoresistors having the same reference magnetization direction may optionally be connected in series, which may increase the sensitivity of the magnetoresistive sensor 200-A / B and / or adjust the resistance to a specific value.

[0103] Furthermore, magnetoresistances comprising separate portions of the magnetic reference layer 220 can be provided in this way. This can be useful in GMR sensors for electrically isolating the first portion of the magnetic free layer 230 from the second portion of the magnetic free layer 230. In a TMR sensor, the tunnel barrier layer can electrically isolate the first portion of the magnetic free layer 230 from the second portion of the magnetic free layer 230.

[0104] Of course, a magnetoresistance with a different reference magnetization direction can also be provided in this way if the average direction of the closed-flux magnetization pattern in the first part of the magnetic reference layer 220 vertically above (or vertically below) the first part of the magnetic free layer 230 differs from the average direction of the closed-flux magnetization pattern in the second part of the magnetic reference layer 220 vertically above (or vertically below) the second part of the magnetic free layer 230. Magnetoresistances with a different reference magnetization direction can be used to detect or measure different directional components of an external magnetic field applied to the magnetoresistive sensor 200-A / B, for example.

[0105] According to some examples, a magnetoresistive sensor 200-A / B, whose magnetic free layer 230 includes a first portion and at least a second portion, may include a bridge circuit. The bridge circuit may include a first and at least a second magnetoresistance. The first magnetoresistance may include the first portion of the magnetic free layer 230, while the second magnetoresistance may include the second portion of the magnetic free layer 230.

[0106] For example, within the bridge circuit, the first and second portions of the magnetic free layer 230 may be arranged vertically above (or vertically below) the same portion of the magnetic reference layer 220. Alternatively, the first and second portions of the magnetic free layer 230 may be arranged vertically above (or vertically below) separate portions of the magnetic reference layer 220.

[0107] The magnetic reference layer 220 can be used as a common node of the first and second magnetoresistors of the bridge circuit. For example, this common node can be a bridge bias input node (e.g., connected to a supply voltage or ground potential of the bridge circuit). Alternatively, this common node can be a bridge output node that provides an electrical potential (or voltage) indicative of the strength of a directional component of an externally imposed magnetic field. Alternatively, this common node can be an interconnection of the first and second magnetoresistors when the first and second magnetoresistors are connected in series, for example.

[0108] The bridge circuit may include a first, second, third, and fourth bridge resistor. The first bridge resistor may be connected between a first bridge bias input node (e.g., connected to a supply voltage) and a first bridge output node. The second bridge resistor may be connected between the first bridge bias input node and a second bridge output node. The third bridge resistor may be connected between the first bridge output node and a second bridge bias input node (e.g., connected to ground potential or a different supply voltage). The fourth bridge resistor may be connected between the second bridge output node and the second bridge bias input node. A voltage (e.g.,A bridge voltage (e.g., a bridge voltage) between the first and second bridge output nodes may be indicative of the strength of a directional component of an externally imposed magnetic field. At least one of the first, second, third, and fourth bridge resistors may comprise a series circuit of magnetoresistances, as described above, which may increase the sensitivity of the bridge circuit and thus of the magnetoresistive sensor 200-A / B.

[0109] Fig. 5a shows a bridge circuit 500-A of a magnetoresistive sensor according to an example of the present disclosure. The bridge circuit 500-A comprises a first part 520-1 and a second part 520-2 of a magnetic reference layer of the magnetoresistive sensor. The first part 520-1 of the magnetic reference layer comprises a first magnetization pattern with permanently closed flux 522-1 of a predetermined rotation direction (e.g., counterclockwise). The second part 520-1 of the magnetic reference layer comprises a second magnetization pattern with permanently closed flux 522-2 of a predetermined rotation direction (e.g., counterclockwise). Furthermore, the bridge circuit 500-A comprises a first part 530-1, a second part 530-2, a third part 530-3, and a fourth part 530-4 of a magnetic free layer of the magnetoresistive sensor.The first and second portions 530-1, 530-2 of the magnetic free layer are arranged vertically above (or vertically below) the first portion 520-1 of the magnetic reference layer. The third and fourth portions 530-1, 530-4 of the magnetic free layer are arranged vertically above (or vertically below) the second portion 520-1 of the magnetic reference layer.

[0110] A first average direction of the first closed-flux magnetization pattern 522-1 is directed in the opposite y-direction vertically above (or vertically below) the first portion 530-1 of the magnetic free layer. A second average direction of the first closed-flux magnetization pattern 522-1 is directed in the y-direction vertically above (or vertically below) the second portion 530-2 of the magnetic free layer. A first bridge resistor of the bridge circuit 500-A includes the first portion 530-1 of the magnetic free layer. A second bridge resistor of the bridge circuit 500-A includes the second portion 530-2 of the magnetic free layer. Furthermore, the first and second bridge resistors share the first portion 530-1 of the magnetic reference layer. The first portion 520-1 of the magnetic reference layer is connected to a first bridge bias input node 551-1 of the bridge circuit 500-A.The first bridge bias input node 551-1 is connected to a supply voltage V. dd of bridge circuit 500-A. The first portion 530-1 of the magnetic free layer is connected to a first bridge output node 552-1 of bridge circuit 500-A. The second portion 530-2 of the magnetic free layer is connected to a second bridge output node 552-2 of bridge circuit 500-A. Thus, the first bridge resistor is connected between the first bridge bias input node 551-1 and the first bridge output node 552-1, while the second bridge resistor is connected between the first bridge bias input node 551-1 and the second bridge output node 552-2.

[0111] A first average direction of the second closed-flux magnetization pattern 522-2 is directed in the y-direction vertically above (or vertically below) the third portion 530-3 of the magnetic free layer. A second average direction of the second closed-flux magnetization pattern 522-2 is directed in the opposite y-direction vertically above (or vertically below) the fourth portion 530-4 of the magnetic free layer. A third bridge resistor of the bridge circuit 500-A includes the third portion 530-3 of the magnetic free layer. A fourth bridge resistor of the bridge circuit 500-A includes the fourth portion 530-4 of the magnetic free layer. Furthermore, the third and fourth bridge resistors share the second portion 520-2 of the magnetic reference layer. The second portion 520-2 of the magnetic reference layer is connected to a second bridge bias input node 551-2 of the bridge circuit 500-A.The second bridge bias input node 551-2 is connected to ground Gnd of the bridge circuit 500-A, but could alternatively be connected to a different supply voltage different from V. dd The third portion 530-3 of the magnetic free layer is connected to the first bridge output node 552-1. The fourth portion 530-4 of the magnetic free layer is connected to the second bridge output node 552-2. Thus, the third bridge resistor is connected between the first bridge output node 552-1 and the second bridge bias input node 551-2, while the fourth bridge resistor is connected between the second bridge output node 552-2 and the second bridge bias input node 551-2.

[0112] If no external magnetic field or an external magnetic field having neither any component in the y-direction nor in the opposite y-direction is applied to the bridge circuit 500-A, a voltage (e.g., a bridge voltage) between the first bridge output node 552-1 and the second bridge output node 552-2 may be zero, for example. Assuming an external magnetic field with a component in a (positive) y-direction is applied, a resistance value of the first bridge resistor may increase because the first portion 530-1 of the magnetic free layer may be at least partially magnetized in the y-direction and thus opposite to the first average direction of the first closed-flux magnetization pattern 522-1.On the other hand, a resistance value of the third bridge resistor may decrease because the third portion 530-3 of the magnetic free layer may be at least partially magnetized in the y-direction, which is also the direction of the first average direction of the second closed-flux magnetization pattern 522-2. For a positive supply voltage V ddAn electrical potential of the first bridge output node 552-1 may then decrease. For similar reasons, a resistance of the second bridge resistor may decrease, while a resistance of the fourth bridge resistor may increase. This causes an electrical potential of the second bridge output node 552-2 to increase. The electrical potential of the second bridge output node 552-2 may thus increase and be greater than the electrical potential of the first bridge output node 552-1, or in other words, the bridge voltage from the first bridge output node 552-1 to the second bridge output node 552-2 may be negative. Accordingly, an externally imposed magnetic field with a component in the negative y-direction may cause a positive bridge voltage. The sign of the bridge voltage may thus be indicative of the sense (e.g., positive or negative y-direction) of a y-component of the externally imposed magnetic field.Furthermore, the magnitude of the bridge voltage can be indicative of the strength of the externally imposed magnetic field.

[0113] Fig. 5b shows a bridge circuit 500-B similar to the bridge circuit 500-A of Fig. 5a. The bridge circuit 500-B can be formed by rotating the bridge circuit 500-A Fig. 5A by 90° clockwise. Bridge circuit 500-B can thus be used to measure an X component of an externally imposed magnetic field. An exemplary magnetoresistive sensor according to this disclosure may include both bridge circuit 500-A and bridge circuit 500-B, which may enable the magnetoresistive sensor to measure both the magnitude and direction of an externally imposed magnetic field.

[0114] Fig. Figure 5c shows another bridge circuit 500-C of a magnetoresistive sensor. The bridge circuit 500-C can be similar to the bridge circuit 500-A of Fig. 5A and can be used to measure a y-component of an externally imposed magnetic field. In contrast to the 500-A bridge circuit from Fig. 5A, each bridge resistor 554-1, 554-2, 554-3, 554-4 of the bridge circuit 500-C comprises two laterally separated portions of a magnetic reference layer of the magnetoresistive sensor. A respective portion of a magnetic free layer of the magnetoresistive sensor is arranged vertically above (or vertically below) each portion of the magnetic reference layer. Each bridge resistor 554-1, 554-2, 554-3, 554-4 thus comprises two series-connected magnetoresistances. This can determine the sensitivity of the bridge circuit 500-C with respect to the bridge circuit 500-A. Fig. 5A and / or increase the resistance value of the bridge circuit.

[0115] Fig. Figure 5d shows yet another bridge circuit 500-D of a magnetoresistive sensor. The bridge circuit 500-D can be similar to the bridge circuit 500-C of Fig. 5c and can be used to measure a y-component of an externally applied magnetic field. Each bridge resistor 554-1, 554-2, 554-3, 554-4 of the bridge circuit 500-D further comprises two laterally separated parts of a magnetic reference layer of the magnetoresistive sensor, but in contrast to the bridge circuit 500-C of Fig. 5c with two laterally separated parts of a magnetic free layer of the magnetoresistive sensor, arranged vertically above (or vertically below) each part of the magnetic reference layer. Each bridge resistor 554-1, 554-2, 554-3, 554-4 of the bridge circuit 500-D thus comprises four series-connected magnetoresistances. This can increase the sensitivity of the bridge circuit 500-D with respect to the bridge circuits 500-A, 500-C. Fig. 5a, c or can increase the resistance value of the bridge circuit.

[0116] In order to create or further assist the formation of a permanently closed flux magnetization pattern (e.g., a vortex magnetization pattern) of a predetermined rotation direction in the magnetic reference layer of a magnetoresistive sensor, a vertical current path may be provided from the magnetic free layer (or a portion of the magnetic free layer) to the magnetic reference layer. Fig. 6A shows a schematic vertical cross-section of a magnetoresistive sensor 600-A with such a current path. The magnetoresistive sensor 600-A comprises a magnetic free layer with a first part 630-1 and a second part 630-2, which is laterally separated from the first part 630-1. A first electrode 661-1 of the magnetoresistive sensor 600-A comprises a lateral wiring element (e.g., a conductor line) and a vertical wiring element (e.g., a via) and contacts the first part 630-1 of the magnetic free layer. A geometric center of gravity of the first part 630-1 of the magnetic free layer is laterally offset with respect to a geometric center of gravity of a magnetic reference layer 620 of the magnetoresistive sensor 600-A.A magnetoresistance of the magnetoresistive sensor 600-A may comprise the first portion 630-1 of the magnetic free layer together with a tunnel barrier layer 616, the magnetic reference layer 620, and a NAF layer 610 of the magnetoresistive sensor 600-A (and an optional magnetic pinned layer and an optional coupling layer, not shown in FIG. Fig. 6A). A second electrode 661-2 of the magnetoresistive sensor 600-A comprises a different lateral wiring element (e.g., a different conductor line) and a different vertical wiring element (e.g., a different via) and contacts the second part 630-2 of the magnetic free layer. A third electrode 661-3 of the magnetoresistive sensor 600-A comprises yet another lateral wiring element (e.g., a different conductor line) and a different vertical wiring element (e.g., a different via) and contacts the NAF layer 610. During the generation of the magnetization pattern with permanently closed flux in the magnetic reference layer 620, an electric current may be applied to the magnetoresistive sensor 600-A and may flow between the second electrode 661-2 and the third electrode 661-3. A direction of the current (e.g.,The current path (e.g., from the second to the third electrode or vice versa) can adjust the rotation direction of a magnetic field surrounding the current path and in plane with the magnetic reference layer 620. The rotation direction of this magnetic field can then adjust (e.g., predetermine) the rotation direction of the permanently closed flux magnetization pattern in the magnetic reference layer 620. Optionally, the current path is arranged in the center of the structure (e.g., the magnetic layer stack) of the magnetoresistive sensor 600-A to further assist in predetermining the rotation direction by the circular field generated by the current through the center of the structure.

[0117] At least some exemplary magnetoresistive sensors of the present disclosure may include a tunnel barrier layer and an electrically conductive via. The tunnel barrier layer may be disposed between the magnetic reference layer and the magnetic free layer. The electrically conductive via may connect a portion (e.g., the second portion or, alternatively, another portion, e.g., a third, fourth, or nth portion) of the magnetic free layer to the magnetic reference layer through the tunnel barrier layer. The portion of the magnetic free layer may be laterally surrounded by electrically insulating material.

[0118] This is for the magnetoresistive sensor 600-B in Fig. 6B. The magnetoresistive sensor 600-B is similar to the magnetoresistive sensor 610-A of Fig. 6a. However, due to the electrically conductive via 662 of the magnetoresistive sensor 600-B, the current flowing between the second electrode 661-2 and the third electrode 661-3 for predetermining the rotation direction of the closed-flux magnetization pattern during its generation may increase. Thus, the strength of the magnetic field encircling the current may also increase. This may make the predetermination of the rotation direction of the closed-flux magnetization pattern more reliable. In other words, the current path may include a via through the tunnel oxide to achieve a lower resistance value for this path compared to TMR structures (e.g., the magnetoresistive sensor 600-A).

[0119] Optionally, the electrically conductive via 662 can be arranged vertically above the geometric center of gravity of the magnetic reference layer 620. This can further make the predetermination of the rotation direction of the closed-flux magnetization pattern more reliable.

[0120] Fig. 7 shows a flowchart of a method 700 for generating a permanently closed flux magnetization pattern with a predetermined rotation direction in a magnetic reference layer of a magnetic layer stack. The method 700 includes applying 710 an external magnetic field in a predetermined direction to the magnetic layer stack, thereby causing magnetic saturation of the magnetic reference layer and a pinned layer of the magnetic layer stack. Furthermore, the method 700 includes reducing 720 the external magnetic field to form a first closed flux magnetization pattern in the magnetic reference layer and a second closed flux magnetization pattern in the pinned layer.

[0121] By creating a magnetization pattern with a permanently closed flux and a predetermined rotation direction in the magnetic reference layer, local magnetization processes for providing desired directions of the reference magnetization of magnetoresistors can be avoided. This can reduce the manufacturing effort of magnetoresistors and / or magnetoresistive sensors and thus reduce their manufacturing costs.

[0122] The external magnetic field can, for example, be unidirectional and / or homogeneous across the magnetic layer stack. By first causing magnetic saturation of the magnetic reference layer and the pinned layer and then reducing 720 the external magnetic field, closed-flux magnetization patterns can form in the magnetic reference layer and the pinned layer. For example, a strength of the external magnetic field can first be adjusted via an annihilation field strength of the magnetic reference layer and the pinned layer, which can cause magnetic saturation. During magnetic saturation, the magnetization of the magnetic reference layer and the pinned layer can be unidirectional. Thereafter, a strength of the external magnetic field can be reduced below a nucleation field strength of the magnetic reference layer and the pinned layer. Since the direction of the external magnetic field is predetermined (e.g.In a specific lateral direction and in a plane with the magnetic reference layer and the pinned layer, the first and second closed-flux magnetization patterns may have a predetermined rotation direction. The first and second closed-flux magnetization patterns may have opposite rotation directions, for example. In this way, the rotation direction of the first closed-flux magnetization pattern can be permanently maintained in the same sense (e.g., clockwise or counterclockwise) by the second closed-flux magnetization pattern in the pinned layer.

[0123] Additionally, the method 700 may further comprise structuring, prior to applying the external magnetic field, at least the magnetic reference layer to have a lateral cross-section comprising a main portion and a protrusion portion laterally adjacent to the main portion. After structuring, the external magnetic field may be applied parallel to the protrusion portion (e.g., along an axis of a maximum lateral extension of the protrusion portion). For example, according to the method 700, the lateral cross-section of the magnetic reference layer may be structured as in the context of Fig. 2d-i is shown.

[0124] Additionally, method 700 may further comprise pinning the second closed-flux magnetization pattern in the pinned layer to a natural antiferromagnetic layer of the magnetic layer stack. In this way, the second closed-flux magnetization pattern may be permanently maintained in the same rotation direction. Thus, the first closed-flux magnetization pattern may also be permanently maintained in its rotation direction (e.g., opposite to the rotation direction of the second closed-flux magnetization pattern).

[0125] For example, the method 700 may further comprise maintaining a temperature of the magnetic layer stack below 200°C during the application 710 of the external magnetic field. After reducing 720 the external magnetic field, the method 700 may further comprise increasing the temperature of the magnetic layer stack to above 240°C but not above a barrier temperature of the natural antiferromagnetic layer and the pinned layer. Furthermore, the method 700 may further comprise maintaining the temperature of the magnetic layer stack above 240°C for more than one hour to form an antiferromagnetic phase within the natural antiferromagnetic layer, causing exchange-bias coupling between the natural antiferromagnetic layer and the pinned layer.In this way, the second magnetization pattern can be pinned to the natural antiferromagnetic layer of the magnetic layer stack with a closed flux. The blocking temperature of the natural antiferromagnetic layer and the pinned layer can be determined at least in part by the material combination of the natural antiferromagnetic layer and the pinned layer. The blocking temperature can be defined as the temperature above which the pinned layer is not (or no longer) magnetically coupled to the natural antiferromagnetic layer.

[0126] In other words, this may indicate a possible process for the formation of a vortex-like magnetization in a magnetic reference system with a cut-off temperature in the range of approximately 260 °C to approximately 400 °C. For example, for platinum-manganese (PtMn), as a natural antiferromagnetic (NAF) material, an antiferromagnetic phase causing an exchange bias effect to fix the pinned layer may not be present directly after deposition of the magnetic layer stack. Application 710 of the external magnetic field until saturation of the device (e.g., the magnetic layer stack) can be carried out without additional temperature (e.g., at room temperature). An average magnitude of the magnetic flux density of the external magnetic field at the magnetic layer stack may be greater than 200 mT (or greater than 500 mT). The external magnetic field can then be reduced 720 (e.g., switched off).A vortex-like magnetization (e.g., the second closed-flux magnetization pattern) can then be spontaneously generated in the pinned layer (and the first closed-flux magnetization pattern can, in turn, be generated in the magnetic reference layer). Without an additional external magnetic field, a temperature budget (e.g., 280 °C for two hours) with a temperature preferably lower than the barrier temperature can next be applied to the magnetic layer stack to form the antiferromagnetic phase of the natural antiferromagnetic layer. The magnetic layer stack can then be cooled again. The vortex-like magnetization of the pinned layer (e.g., the second closed-flux magnetization pattern) of the magnetic reference system can then be pinned to the natural antiferromagnetic layer by an exchange-bias coupling force.

[0127] An alternative approach for pinning the second closed-flux magnetization to the natural antiferromagnetic layer may include forming an antiferromagnetic phase of the natural antiferromagnetic layer and subsequently raising the temperature of the magnetic layer stack above the barrier temperature of the natural antiferromagnetic layer and the pinned layer prior to applying 710 the external magnetic field. Furthermore, this approach may include maintaining the temperature of the magnetic layer stack above the barrier temperature during the application 710 of the external magnetic field.

[0128] This alternative process for the formation of a vortex-like magnetization in a magnetic reference system can be applied, for example, in the case where an antiferromagnetic phase of the natural antiferromagnetic layer, and thus the exchange-bias coupling, is already present after deposition of the magnetic layer stack (e.g., for iridium manganese (IrMn) as the material of the natural antiferromagnetic layer). A temperature above the blocking temperature can be applied to the magnetic layer stack. The exchange-bias coupling can then disappear, and the magnetic reference system can behave as if it were free (e.g., above the blocking temperature, the magnetization of the pinned layer is not pinned to the natural antiferromagnetic layer).For example, the barrier temperature for iridium-manganese as a natural antiferromagnetic layer material can range from approximately 250 °C to 350 °C, while the barrier temperature for platinum-manganese as a natural antiferromagnetic layer material can range from approximately 350 °C to 400 °C.

[0129] While the temperature of the magnetic layer stack is maintained above the blocking temperature, the external magnetic field may be applied 710 to the magnetic layer stack, causing saturation of the device (e.g., the magnetic layer stack). Subsequently, the external magnetic field may be reduced again (e.g., at least below a nucleation field strength of the magnetic reference layer and the pinned layer). For example, the external magnetic field may be turned off. The vortex-like magnetization (e.g., the first and second closed-flux magnetization patterns) may then be spontaneously generated. Thereafter, the temperature of the magnetic layer stack may be reduced from above the blocking temperature to below the blocking temperature to fix the magnetization of the pinned layer (e.g., to pin the second closed-flux magnetization pattern to the natural antiferromagnetic layer through exchange-bias coupling forces).

[0130] Additionally, the method 700 may include patterning a magnetic free layer of the magnetic layer stack to cause a lateral shift of a geometric centroid of the magnetic free layer (or geometric centroids of laterally separated portions of the magnetic free layer) with respect to a geometric centroid of the magnetic reference layer (or with respect to geometric centroids of laterally separated portions of the magnetic reference layer).

[0131] Additionally, method 700 may include forming an electrically conductive via through a tunnel barrier layer of the magnetic layer stack. The electrically conductive via may connect a laterally separated portion of the magnetic free layer and the magnetic reference layer. Additionally, method 700 may include conducting a current between the laterally separated portion of the magnetic free layer and the natural antiferromagnetic layer through the electrically conductive via. A direction of the current (e.g., from the magnetic free layer to the natural antiferromagnetic layer or vice versa) may adjust the rotation direction of a magnetic field surrounding the current and in-plane with the magnetic reference layer and the pinned layer.The rotation direction of this magnetic field can then adjust (e.g., predetermine) the rotation direction of the first closed-flux magnetization pattern in the magnetic reference layer and / or the second closed-flux magnetization pattern in the magnetic reference layer. Optionally, the electrically conductive via can be formed vertically above (or, depending on the structure of the magnetic layer stack, vertically below) a geometric center of gravity of the magnetic reference layer.

[0132] According to one example, the process of forming the reference layer may comprise the following steps: first, bringing the device to a warm state and applying an external field that saturates the device; second, reducing the field to a level where a vortex is formed; third, reducing the field and temperature; fourth, allowing the field to reach zero while the temperature is still sufficient to establish the alignment of the (antiferromagnetic) reference layer; and fifth, completely cooling the device, which causes the (antiferromagnetic) reference layer to be pinned into a vortex state.

[0133] According to another aspect of the present disclosure, a vortex-magnetized reference layer for angle sensors is provided. This may allow the construction of angle sensors without a local magnetization process for defining the magnetization of the pinned layer. This may include using different structural geometries of the pinned layer, the reference system, and / or the free layer of an xMR sensor structure. The pinned layer and / or the reference system may have vortex-like magnetization and / or closed-flux magnetization. The region of the free layer may differ from the region of the pinned layer. The free layer may be configured to select a specific region of the pinned layer and / or the reference system to be sensitive to a certain magnetic field component.The position of the free layer region on the pinned layer and / or the reference system region can define the sensitive direction.

[0134] For example, TMR-based structures with free layer regions on a magnetized, pinned layer with closed flux can be used to obtain measurements of magnetic field components in different directions, where the free layer extensions differ from the pinned layer extensions (e.g., free layer < pinned vortex layer). This can avoid individual magnetization steps for the formation of TMR sensor elements with different pinned reference directions. The elements can be connected to form a bridge that is functionally compatible with other magnetoresistive angle sensors. The number of series-connected elements can be higher than 2 in each branch of the bridge, for example.

[0135] Another example of the present disclosure relates to a TMR structure with a pinned layer and / or reference system with a vortex-like magnetization and a free layer that extends only above (or below) a portion of the pinned layer / reference system (differently structured free layer). This can reduce TMR manufacturing costs due to the saved laser magnetization steps, for example.

[0136] The aspects and features described together with one or more of the previously detailed examples and figures may also be combined with one or more of the other examples to replace a like feature of the other example or to additionally introduce the feature into the other example.

[0137] Examples may further provide a computer program having program code for performing one or more of the above methods when the computer program is executed on a computer or processor. Steps, operations, or processes of various methods described above may be performed by programmed computers or processors. Examples may also cover program storage devices, e.g., digital data storage media, that are machine-, processor-, or computer-readable and encode machine-executable, processor-executable, or computer-executable programs of instructions. The instructions perform or cause the execution of some or all of the steps of the above-described methods. The program storage devices may include or be, e.g., digital memories, magnetic storage media such as magnetic disks and magnetic tapes, hard disk drives, or optically readable digital data storage media.Further examples may also cover computers, processors, or control units programmed to perform the steps of the methods described above, or (field) programmable logic arrays ((F)PLAs = (Field) Programmable Logic Arrays) or (field) programmable gate arrays ((F)PGA = (Field) Programmable Gate Arrays) programmed to perform the steps of the methods described above.

[0138] The description and drawings illustrate only the principles of the disclosure. Furthermore, all examples provided herein are expressly intended to be for educational purposes only, to assist the reader in understanding the principles of the disclosure and the concepts contributed by the inventor(s) to advance the art. All statements herein regarding principles, aspects, and examples of the disclosure, as well as specific examples thereof, are intended to include their equivalents.

[0139] A functional block designated as a "means for..." that performs a specific function may refer to a circuit configured to perform a specific function. Thus, a "means for something" may be implemented as a "means configured for or suitable for something," e.g., a device or circuit configured for or suitable for the respective task.

[0140] Functions of various elements shown in the figures, including any functional blocks referred to as "means," "means for providing a sensor signal," "means for generating a transmission signal," etc., may be implemented in the form of dedicated hardware, e.g., "a signal provider," "a signal processing unit," "a processor," "a controller," etc., as well as hardware capable of executing software in conjunction with associated software. When provided by a processor, the functions may be provided by a single dedicated processor, by a single shared processor, or by a plurality of individual processors, some or all of which may be shared.However, the term "processor" or "controller" is far from limited to hardware capable of executing software only, but may include digital signal processor (DSP) hardware, network processor, application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), read-only memory (ROM) for storing software, random access memory (RAM), and non-volatile storage devices. Other hardware, conventional and / or custom, may also be included.

[0141] For example, a block diagram may represent a detailed circuit diagram implementing the principles of the disclosure. Similarly, a flowchart, a sequence diagram, a state transition diagram, pseudocode, and the like may represent various processes, operations, or steps, for example, substantially embodied in computer-readable medium and thus performed by a computer or processor, regardless of whether such a computer or processor is explicitly shown. Methods disclosed in the specification or claims may be implemented by an apparatus having means for performing each of the respective steps of these methods.

[0142] It should be understood that the disclosure of multiple steps, processes, operations, or functions disclosed in the description or claims should not be construed as being in that particular order unless explicitly or implicitly stated otherwise, e.g., for technical reasons. Therefore, the disclosure of multiple steps or functions does not limit them to a particular order unless those steps or functions are not interchangeable for technical reasons. Furthermore, in some examples, a single step, function, process, or operation may include and / or be broken down into multiple sub-steps, functions, processes, or operations. Such sub-steps may be included and be part of the disclosure of that single step unless explicitly excluded.

Claims

[1] A method (700) for generating a closed flux magnetization pattern of a predetermined rotation direction in a magnetic reference layer (220; 420; 620) of a magnetic layer stack, the method comprising: Applying (710) an external magnetic field in a predetermined direction to the magnetic layer stack, with a strength of the external magnetic field above an annihilation field strength of the magnetic reference layer (220; 420; 620) and a pinned layer (212; 412), thereby causing magnetic saturation of the magnetic reference layer (220; 420; 620) and the pinned layer (212; 412) of the magnetic layer stack; Reducing (720) the strength of the external magnetic field below a nucleation field strength of the magnetic reference layer (220; 420; 620) and the pinned layer (212; 412) to form a first closed-flux magnetization pattern in the magnetic reference layer and a second closed-flux magnetization pattern in the pinned layer; and Structuring, prior to applying (710) the external magnetic field, at least the magnetic reference layer (220; 420; 620) to have a lateral cross-section comprising a main portion (224) and a projection portion (226) extending tangentially from the main portion (224), wherein the external magnetic field is applied (710) along an axis of a maximum lateral extension of the projection portion (226). [2] The method (700) of claim 1, further comprising pinning the second closed flux magnetization pattern to a natural antiferromagnetic layer (210; 410; 610) of the magnetic layer stack. [3] The method (700) of claim 2, further comprising maintaining a temperature of the magnetic layer stack below 200°C during the application (710) of the external magnetic field; and after reducing (720) the external magnetic field, increasing the temperature of the magnetic layer stack to above 240°C but not exceeding a barrier temperature of the natural antiferromagnetic layer (210; 410; 610) and the pinned layer (212; 412), and maintaining the temperature above 240°C for more than one hour to form an antiferromagnetic phase within the natural antiferromagnetic layer (210; 410; 610), causing an exchange bias coupling between the natural antiferromagnetic layer (210; 410; 610) and the pinned layer (212; 412). [4] The method (700) of claim 2, further comprising forming an antiferromagnetic phase of the natural antiferromagnetic layer (210; 410; 610) and subsequently increasing the temperature of the magnetic layer stack above a barrier temperature of the natural antiferromagnetic layer (210; 410; 610) and the pinned layer (212; 412) prior to applying (710) the external magnetic field, and maintaining the temperature of the magnetic layer stack above the barrier temperature during the application of the external magnetic field. [5] The method (700) according to any one of the preceding claims, further comprising structuring a magnetic free layer (230; 430; 630) of the magnetic layer stack to cause a lateral shift of a geometric center of gravity of the magnetic free layer (230; 430; 630) with respect to a geometric center of gravity of the magnetic reference layer (220; 420; 620). [6] The method (700) according to any one of the preceding claims, further comprising forming an electrically conductive via (662) through a tunnel barrier layer of the magnetic layer stack and conducting a current in a predetermined direction through the via (662).

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