MAGNETORESISTIVER SENSOR

Abstract

A magnetoresistive sensor (500) is proposed. The magnetoresistive sensor (500) comprises a layer stack (510) with at least one reference layer (512) having a reference magnetization perpendicular to the plane of the layer stack and at least one free layer (516) with a vortex magnetization. The magnetoresistive sensor (500) further comprises at least one soft magnetic shield (520) arranged adjacent to the layer stack, which is configured to reduce the influence of an external magnetic field along a shielding axis (530) on the free layer (516).

Description

Technical field

[0001] The present disclosure relates to magnetoresistive sensors capable of measuring and detecting external out-of-plane (OOP) magnetic fields. background

[0002] Magnetoresistive sensors, particularly those based on the principle of tunneling magnetoresistance (TMR), are increasingly used in various industrial and commercial applications, including automotive engineering, medical technology, and consumer electronics. These sensors offer high sensitivity and accuracy in the detection of magnetic fields, making them a preferred choice in demanding measurement environments.

[0003] A typical TMR sensor comprises a stack of layers, which in turn includes various magnetic and non-magnetic layers. This stack usually includes a reference layer and a free layer (sensor layer), separated by a non-magnetic tunnel barrier. The magnetization of the reference layer is fixed and oriented in a specific direction, while the magnetization of the free layer can be influenced by external magnetic fields, thus changing the electrical resistance of the TMR sensor.

[0004] Magnetoresistive sensors are known that feature a reference magnetization perpendicular to the plane of the layer stack, also known as out-of-plane (OOP) magnetization. Simultaneously, the free layer can be designed to exhibit vortex magnetization, where magnetization vectors are arranged in a circular pattern within the plane, and a central region exists where the magnetization is perpendicular to the plane. This specific arrangement of magnetization in the free layer allows for targeted control of interactions with external magnetic fields, thereby achieving high sensitivity and stability of the sensor.

[0005] One problem encountered with magnetoresistive sensors using the described magnetization arrangement is their sensitivity to external magnetic fields parallel to the plane of the layer stack, also known as in-plane (IP) cross-magnetic fields. Such external cross-magnetic fields can destabilize the magnetization of the free layer, potentially leading to undesirable measurement inaccuracies. This can significantly impair the sensor's performance, particularly when measuring weak magnetic fields or in environments with strong interference fields.

[0006] One challenge, therefore, is to reduce this sensitivity without compromising the basic structure of the layer stack or the benefits of OOP and vortex magnetization. Summary

[0007] This is solved by magnetoresistive sensors according to the attached claims.

[0008] According to a first aspect of the present disclosure, a magnetoresistive sensor is proposed. The magnetoresistive sensor comprises a stack of layers with at least one reference layer having a magnetization perpendicular to the plane (out-of-plane, OOP) of the stack. The stack further comprises at least one free layer with a vortex magnetization. Vortex magnetization can be defined as magnetization in a vortex-like arrangement, wherein magnetization vectors are in-plane and have a central region in which the magnetization is perpendicular to the plane (OOP). The magnetoresistive sensor also comprises at least one soft magnetic shield arranged adjacent to the stack, configured to reduce the influence of an external (in-plane, IP) magnetic field along a shield axis on the free layer.

[0009] The proposed magnetoresistive sensor utilizes a combination of an OOP reference layer and vortex magnetization in the free layer. The soft magnetic shield, positioned adjacent to the layer stack, serves to reduce the sensor's sensitivity to external cross-magnetic fields. An advantage of this arrangement is its ability to increase sensor precision by minimizing unwanted magnetic field influences, which is particularly important in applications requiring high measurement accuracy.

[0010] According to some embodiments, the soft magnetic shield is designed to generate a counter-field in response to the external magnetic field. This counter-field generation by the soft magnetic shield is based on the intrinsic magnetic properties of the soft magnetic materials used. Soft magnetic materials are characterized by high magnetic permeability, meaning they can readily amplify and conduct external magnetic fields. When an external magnetic field encounters the soft magnetic shield, the material's high permeability causes the field to penetrate the material and align itself along preferred magnetic axes within the shield. This alignment generates an internal magnetic field within the shield that is capable of forming a counter-field to the incident external field.The generated counter-field opposes the external magnetic field, leading to a weakening or neutralization of the external field in the immediate vicinity of the sensor. This interaction maintains the stability of the magnetization of the sensor's free layer and reduces unwanted effects that could be caused by external magnetic fields. The counter-field is controlled by the spatial arrangement and material properties of the shielding, allowing it to react specifically to the external field and compensate for it as desired. This mechanism helps to minimize the influence of interfering fields on the sensor and increase its measurement accuracy.

[0011] In some embodiments, the shielding is arranged laterally adjacent to the layer stack. This lateral arrangement of the shielding allows for targeted shielding of cross-magnetic fields that run parallel to the layer plane. An advantage of this arrangement is that it provides effective shielding without significantly increasing the sensor's footprint, resulting in a compact design.

[0012] In some embodiments, the shielding is positioned above or below the layer stack. This placement allows for flexible integration into the sensor assembly. An advantage of this arrangement is that it facilitates adapting the shielding to specific application requirements.

[0013] In some embodiments, the shielding extent perpendicular to the shielding axis is greater than that parallel to the shielding axis. A greater shielding extent perpendicular to the shielding axis increases the linear shielding area against external cross-magnetic fields. An advantage of this embodiment is that it offers improved shielding effectiveness in strong magnetic fields and also increases the area available for field compensation.

[0014] According to some embodiments, the shielding extent perpendicular to the shielding axis is at least four times greater than the shielding extent parallel to the shielding axis. Optimal shielding performance can be achieved through a ratio of at least 4:1:1, 10:1:1, or 100:1:1 between the perpendicular and parallel extents. An advantage of this geometry is that it can ensure particularly effective suppression of interference fields, which can further improve the sensor's sensitivity.

[0015] In some embodiments, the shielding material comprises a nickel-iron alloy, a cobalt-iron alloy, a cobalt-nickel alloy, or an iron-silicon alloy. These materials are known for their excellent soft magnetic properties, making them ideal for use in shielding. One advantage of using these alloys is that they offer high magnetic permeability and low coercivity, which can result in efficient and responsive shielding.

[0016] According to some embodiments, the saturation magnetization of a shielding material lies in the range of 1–1.5 Tesla. A saturation magnetization in this range can ensure that the shielding has sufficient magnetic strength to effectively compensate for external cross-magnetic fields. An advantage of this material property is that it enables high shielding efficiency even in strong external cross-magnetic fields.

[0017] In some embodiments, at least one shield is cuboid in shape. This cuboid shape can simplify manufacturing and integration into the sensor assembly. An advantage of this shape is that it enables a uniform and stable field distribution, which can increase the shielding efficiency.

[0018] In some embodiments, the shield comprises a first soft magnetic bar and a second soft magnetic bar that intersect at a right angle. By arranging two bars at right angles, shielding in two directions can be achieved. An advantage of this configuration is that it can effectively reduce in-plane magnetic fields in both the x and y directions, thus increasing the versatility of the sensor.

[0019] In some embodiments, the shield comprises a plurality of parallel soft magnetic bars, each bar having a longitudinal axis running perpendicular or parallel to the shielding axis. The parallel arrangement of multiple bars provides an extended shielding area, which increases the efficiency of magnetic field suppression. An advantage of this arrangement is that it enables uniform shielding over a larger area, which is particularly beneficial for applications with larger sensors.

[0020] In some embodiments, the distance between adjacent soft magnetic bars is greater than 5 µm. A larger distance between the (soft magnetic) bars reduces potential interference between the shielding elements and ensures more effective field compensation by forming a homogeneous opposing field. An advantage of this geometry is that it optimizes the shielding performance by minimizing unwanted cross-magnetic fields.

[0021] According to some embodiments, the shortest distance between the layer stack and the shield is in the range of 2–3 µm. Such a distance between the layer stack and the shield can ensure effective cross-field compensation without impairing the sensor function. An advantage of this arrangement is that it enables high shielding performance with a small footprint, which contributes to the compactness of the sensor.

[0022] In some embodiments, the layer stack includes a TMR layer stack. A TMR layer stack, in combination with a vortex-magnetized free layer, offers excellent magnetoresistive properties, which increases the sensitivity and accuracy of the sensor. An advantage of this embodiment is that it enables high resolution and precision in the measurement of external OOP magnetic fields, which is beneficial for numerous applications.

[0023] In some embodiments, the layer stack and the at least one shield are arranged on a common die (chip). This shared arrangement on a semiconductor die facilitates the integration and miniaturization of the sensor. An advantage of this arrangement is that it can reduce manufacturing costs and increase the compactness of the overall system, which is of great importance for modern electronics applications.

[0024] According to another aspect of the present disclosure, a bridge circuit will accommodate a plurality of magnetoresistive sensors according to one of the preceding embodiments. Integration into a bridge circuit enables, for example, more precise measurement of magnetic fields by differential measurement. An advantage of this embodiment is that it can further increase the accuracy and sensitivity of the sensor system, which is particularly useful in demanding measurement environments.

[0025] According to exemplary embodiments, the cross-field-insensitive operating range of an out-of-plane magnetic vortex sensor can be extended far beyond what is intrinsically possible by adding adjacent cross-field-counteracting soft magnetic structures, so-called "shields." The shielding reduces the effective parasitic cross fields, thereby preserving the vortex structure of the free layer (and thus extending the operating range), while leaving the field components along the sensitive out-of-plane direction unaffected. Character description

[0026] Some examples of devices and / or methods are explained in more detail below with reference to the accompanying figures. These show: Fig. 1 an example of a layer stack of a magnetoresistive sensor element according to one embodiment; Fig. 2 a micromagnetic simulation of a disk with a diameter of 0.25 µm with homogeneous magnetization on the left side and a vortex state on the right side; Fig. 3. An out-of-plane (OOP) and in-plane (IP) hysteresis of a magnetic vortex with a diameter of 128 nm and a height of 64 nm; the figure illustrates the response of the vortex to external magnetic fields; Fig. 4 an out-of-plane (OOP) magnetization which is hardly affected by in-plane cross fields in a stable operating range, with significant effects only occurring above an annihilation field; Fig. 5 a magnetoresistive sensor with laterally adjacent shielding according to an embodiment; Fig. 6 a magnetoresistive sensor with lateral and above adjacent shielding according to a further embodiment; Fig. 7 a magnetoresistive sensor with a layer stack between two shielding bars according to a further embodiment; and Fig. 8 a magnetoresistive sensor with a TMR layer stack under a shielding bar according to a further embodiment; Fig. 9 a perspective bridge circuit with a plurality of magnetoresistive sensors under a grid of shielding bars; and Fig. 10 a top view of the bridge circuit of the Fig. 9. Description

[0027] Some examples are now described in more detail with reference to the accompanying figures. However, other possible examples are not limited to the features of these detailed embodiments. These may include modifications of the features, as well as equivalents and alternatives to the features. Furthermore, the terminology used herein to describe certain examples should not be considered restrictive for other possible examples.

[0028] Identical or similar reference symbols throughout the description of the figures refer to identical or similar elements or features, which may be implemented in an identical or modified form, while providing the same or a similar function. Furthermore, the thickness of lines, layers, and / or areas in the figures may be exaggerated for clarity.

[0029] When two elements A and B are combined using "or," this is to be understood as revealing all possible combinations, i.e., only A, only B, and A and B, unless explicitly defined otherwise in a specific case. As an alternative formulation for the same combinations, "at least one of A and B" or "A and / or B" can be used. This applies equivalently to combinations of more than two elements.

[0030] When a singular form, e.g., "ein, eine" and "der, die, das," is used, and the use of only a single element is neither explicitly nor implicitly defined as mandatory, further examples may also use multiple elements to implement the same function. If 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 "include", "comprehensive", "exhibit" and / or "exhibit" when used describe the presence of the specified features, integers, steps, operations, processes, elements, components and / or a group thereof, but do not exclude the presence or addition of one or more other features, integers, steps, operations, processes, elements, components and / or a group thereof.

[0031] Fig. Figure 1 shows an example of a layer stack of a magnetoresistive sensor element 100 according to one or more embodiments.

[0032] The magnetoresistive sensor element 100 can, for example, be a TMR sensor element with a bottom-pinned spin valve (BSV) configuration or a top-pinned spin valve (TSV) configuration. Furthermore, the magnetoresistive sensor element 100 can be arranged on a semiconductor substrate (not shown) of a magnetoresistive sensor. When described in a Cartesian coordinate system with pairwise perpendicular coordinate axes x, y, and z, the layers of the stack extend laterally in an xy-plane spanned by the x- and y-axes. Thus, lateral dimensions (e.g., lateral distances, lateral cross-sectional areas, lateral surfaces, lateral extents, lateral displacements, etc.) can refer to dimensions in the xy-plane, and vertical dimensions to dimensions in the z-direction, perpendicular to the xy-plane. For example, the vertical extent of a layer in the z-direction can be referred to as layer thickness.

[0033] The layer stack of the magnetoresistive sensor element 100 comprises at least one reference layer with a reference magnetization (e.g., a reference direction in the case of GMR or TMR technology). The reference magnetization is a magnetization direction that provides a sensor direction corresponding to a sensor axis of the magnetoresistive sensor element 100. The reference layer, and consequently the reference magnetization, defines a sensor plane. The sensor plane can be defined, for example, by the xy-plane. Thus, the x-direction and the y-direction can be described as "in-plane" with respect to the sensor plane, and the z-direction can be described as "out-of-plane" with respect to the sensor plane.

[0034] Accordingly, in the case of a GMR or TMR sensor element, the resistance of the magnetoresistive sensor element 100 is minimal when the magnetically free magnetization of a magnetically free layer points in exactly the same direction as the reference magnetization (e.g., the reference direction), and the resistance of the magnetoresistive sensor element 100 is maximal when the magnetically free magnetization of the magnetically free layer points in exactly the opposite direction to the reference magnetization. The orientation of the magnetically free magnetization of the magnetically free layer is variable in the presence of an external magnetic field. Thus, the resistance of the magnetoresistive sensor element 100 can vary based on the influence of the external magnetic field on the magnetically free magnetization of the magnetically free layer.

[0035] From bottom to top, the magnetoresistive sensor element 100 can include an optional seed layer 102, which can be used to influence and / or optimize stack growth. In some embodiments, the seed layer 102 can consist of copper, tantalum, ruthenium, or a combination thereof. In the example shown, an optional natural antiferromagnetic (NAF) layer 104 is formed or otherwise arranged on the seed layer 102. The NAF layer 104 can consist of manganese nitride (MnN), platinum manganese (PtMn), iridium manganese (IrMn), nickel manganese (NiMn), or the like. The thickness of the NAF layer can, for example, be in the range of 5 nm to 50 nm. However, the magnetoresistive sensor element 100 can also function without an NAF layer.

[0036] Furthermore, a pinned layer (PL) 106 can be formed or otherwise arranged on the NAF layer 104. The pinned layer 106 can consist of a ferromagnetic material, such as platinum-cobalt (Pt / Co), palladium-cobalt (Pd / Co), or nickel-cobalt (Ni / Co) multilayer systems, as well as cobalt-iron (CoFe) or cobalt-iron-boron (CoFeB) alloys. The contact between the NAF layer 104 and the pinned layer 106 can produce an effect known as the exchange bias effect, which causes the magnetization of the pinned layer 106 to align in a preferred direction (e.g., in the negative z-direction, as shown). The magnetization of the pinned layer 106 can be referred to as pinned magnetization. This pinned magnetization can be generated during the manufacturing of the magnetoresistive sensor element 100 and can be permanently fixed.

[0037] The magnetoresistive sensor element 100 also comprises a non-magnetic layer (NML) referred to as the coupling layer 108. In one possible embodiment, the coupling layer 108 can, for example, comprise ruthenium, iridium, tantalum, copper, copper alloys, or similar materials. Other materials (e.g., paramagnets) are also possible. A magnetic (e.g., ferromagnetic) reference layer (RL) 110 can be formed on the coupling layer 108 or arranged otherwise. The thickness of the pinned layer 106 and the magnetic reference layer 110 can be in the range of 1 nm to 10 nm.

[0038] Accordingly, the coupling intermediate layer 108 can be arranged between the pinned layer 106 and the magnetic reference layer 110 to spatially separate the pinned layer 106 and the magnetic reference layer 110 in the vertical direction. Furthermore, the coupling intermediate layer 108 can provide an interlayer exchange coupling (e.g., an antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling) between the pinned layer 106 and the magnetic reference layer 110 to form an artificial antiferromagnet. As a result, the magnetization of the magnetic reference layer 110 can align and be held in a direction that is antiparallel or opposite to the magnetization of the pinned layer 106 (e.g., in the positive z-direction, as shown). The magnetization of the magnetic reference layer 110 can be referred to as the reference magnetization.

[0039] Since the NAF layer 104 is configured to align and fix the magnetization of the pinned layer 106 in a specific direction, and the coupling intermediate layer 108 is configured to align and fix the magnetization of the magnetic reference layer 110 in an opposite direction, the NAF layer 104 can be said to maintain the magnetization of the pinned layer 106 (e.g., a fixed magnetization) in a first magnetic orientation and the magnetization of the magnetic reference layer 110 (e.g., a fixed reference magnetization) in a second magnetic orientation. In this way, the magnetic reference layer 110 can have a linear magnetization pattern in the z-direction if the pinned layer 106 has a linear magnetization pattern in an antiparallel direction.Thus, the NAF layer 104, the pinned layer 106, the coupling intermediate layer 108 and the magnetic reference layer 110 form a magnetic reference layer system 112 of the magnetoresistive sensor element 100.

[0040] The magnetoresistive sensor element 100 additionally comprises a barrier layer 114 (e.g., a tunnel barrier) arranged vertically between the reference layer system 112 and a magnet-free layer 116. The barrier layer 114 can, for example, be formed on the magnetic reference layer 110 of the reference layer system 112 or arranged otherwise, and the magnet-free layer 116 can be formed on the barrier layer 114 or arranged otherwise.

[0041] The barrier layer 114 can be made of a non-magnetic material. In some embodiments, the barrier layer 114 can be an electrically insulating tunnel barrier layer. For example, the barrier layer 114 can be a tunnel barrier layer used to generate a TMR effect. The barrier layer 114 can be made of magnesium oxide (MgO), aluminum oxide (Al₂O₃), magnesium aluminum oxide (MgAlOx), or another material with similar properties.

[0042] The material of the magnetically free layer 116 can be an alloy of a ferromagnetic material, such as CoFe, CoFeB, or NiFe. The magnetostriction constant of the magnetically free layer 116 can be adjusted by varying the iron content. Furthermore, the magnetically free layer 116 can incorporate platinum-cobalt (Pt / Co), palladium-cobalt (Pd / Co), or nickel-cobalt (Ni / Co) multilayers to further optimize its magnetic properties. The magnetically free layer 116 exhibits a magnetically free magnetization that is variable in the presence of an external magnetic field. Therefore, the magnetically free layer 116 can be described as a sensor layer, since changes in the magnetically free magnetization are used to determine a measured quantity. In addition, the magnetically free magnetization has a standard magnetic orientation in a ground state (such as a vortex magnetization).The ground state is a state in which the influence of the external magnetic field on the magnetically free layer 116 is either non-existent or negligibly small. In some embodiments, the magnetoresistive sensor element 100 can comprise a magnetically free system containing a plurality of layers (e.g., two or more magnetically free layers) that, in combination, act as a magnetically free layer. In this case, the magnetically free layers of the magnetically free system are magnetically coupled to one another. Thus, the magnetically free system can function as a single magnetically free layer or consist of multiple layers. The magnetically free system has a magnetically free magnetization, which is variable in the presence of the external magnetic field.

[0043] A cover layer 118, e.g. made of tantalum (Ta), tantalum nitride (TaN), ruthenium (Ru), titanium (Ti), titanium nitride (TiN), platinum (Pt) or similar, can be formed on the magnetically free layer 116 or otherwise arranged to form an upper layer of the magnetoresistive sensor element 100.

[0044] The nucleation layer 102 can serve as a lower electrode or establish electrical contact with a lower electrode (not shown) of the magnetoresistive sensor element 100. The top layer 118 can establish electrical contact with an upper electrode (not shown) of the magnetoresistive sensor element 100. The barrier layer 114 can be configured to allow electrons to tunnel between the reference layer system 112 and the magnetically free layer 116 when a bias voltage is applied to the electrodes of the magnetoresistive sensor element 100 (not shown) to generate a magnetoresistive effect (e.g., a TMR effect).

[0045] As mentioned above, it serves Fig. 1 is merely an example of a TMR sensor element. Other examples can be found in the description in Fig. 1 differ. The number and arrangement of the in Fig. The component shown in Figure 1 is an example. In practice, the TMR sensor element can have 100 additional elements or layers, fewer elements, different elements, or elements arranged differently than those shown. Fig. 1 shown.

[0046] To implement a linear out-of-plane (OOP) magnetic field sensor based on the TMR effect, a magnetically free layer 116 (sensor layer) with linear OOP behavior is required in addition to an OOP reference system 112. Homogeneically magnetized ferromagnets with an in-plane (IP) axis fulfill this requirement. However, the magnetization direction at a given time depends directly on a vector sum of the OOP and IP field components, leading to high cross-field sensitivity when used for OOP field measurement. Furthermore, the cross-field sensitivity scales proportionally to the OOP sensitivity, which can be a significant limitation for OOP field measurement.

[0047] An in-plane (IP) cross-magnetic field is a magnetic field that runs parallel to the plane of the layer stack of a magnetoresistive sensor, for example, in the plane defined by the x- and y-axes. The term "cross-magnetic field" refers to the fact that this magnetic field can have a disruptive effect on the sensor's measurements, especially if the sensor is designed to detect magnetic fields that run perpendicular to the layer stack plane (out-of-plane, OOP, along the z-axis). These IP cross-magnetic fields can influence the magnetization of the free layer in the sensor and thus cause measurement inaccuracies, which is why they must be compensated for as much as possible in the sensor's design.

[0048] One solution for minimizing cross-field sensitivity is the use of a magnetically free layer 116 with a vortex ground state instead of a homogeneous magnetization, as in Fig. Figure 2 illustrates a vortex ground state in the magnetically free layer 116, describing a special arrangement of magnetization in which the magnetization vectors are arranged in a circular pattern. In this state, the magnetizations of the individual regions of the layer lie mainly in the plane of the layer, forming a spiral or vortex-like structure resembling a vortex. At the center of this vortex, the magnetization can be oriented perpendicular to the layer plane, creating a stable magnetic state that is less sensitive to external magnetic fields acting perpendicular to the layer.In a vortex state, the force of the external crossed field (also called Zeeman energy) is compensated by the magnetically free layer 116 by a deflection of the vortex core perpendicular to the field direction, whereby the external field is absorbed without any significant effect on the sensitive component of the magnetization outside the plane. However, this vortex state is not stable at higher magnetic crossed fields, as the vortex state collapses above a certain field amplitude and reverts to a homogeneous magnetization with high cross-field sensitivity.

[0049] Vortex stability scales approximately proportionally to t / d (thickness divided by diameter) and is also proportional to the saturation magnetization M. sof the material used in the magnetically free layer 116. The intrinsic stabilization of the vortex configuration therefore requires materials that are unfavorable for OOP sensing (high saturation magnetization), as well as feature sizes significantly below 0.5 µm in combination with layer thicknesses > 100 nm.

[0050] A magnetic vortex is a unique spin configuration in which the magnetization vectors wind around a vortex core, creating a swirling pattern (see Fig. 2) This vortex core 200 is a region of high energy density due to the non-aligned magnetic moments and typically exhibits a polarity where the magnetic moments point either upwards or downwards out of the plane of the magnetically free layer 116.

[0051] In the presence of external magnetic fields, the vortex exhibits pronounced hysteresis. When a vortex in a magnetically free layer is exposed to external magnetic fields, it displays characteristic hysteresis behavior. This means that the vortex's response to the applied magnetic field is not linear, but rather depends on the history of the applied magnetic field. Specifically, the vortex changes its position and magnetization structure when the external field is applied or altered. However, these changes persist, at least partially, even after the external magnetic field is removed. The hysteresis is evident in the fact that the vortex's magnetization structure does not immediately or completely return to its original state, but remains in an altered state.Only by applying an opposing magnetic field or through other changes in environmental conditions can the vortex gradually return to its original state. This hysteresis behavior is typical for magnetic systems and shows that the magnetization of the vortex depends not only on the current strength and direction of the external field, but also on the previous magnetization states to which the system has been exposed. This leads to a complex interaction between the vortex and the external magnetic fields, which influences the stability and dynamics of the magnetic system. This behavior can be simulated using micromagnetic finite-difference simulations. Considering the... Fig. The 3 simulated vortex hysteresis curves shown suggest that both the out-of-plane response ( Fig. 3 (a)) as well as the reaction to the magnetic field within the plane ( Fig. 3 (b)) to be qualitatively similar. However, when considering the actual spin structures, significant differences emerge.

[0052] When an in-plane magnetic field is applied to a magnetic vortex, the field interacts with the chirality of the vortex, i.e., the direction of rotation of the magnetization vectors around the core 200. Through this interaction, the vortex experiences a force that causes it to move or orbit in the plane of the magnetically free layer 116. The field deforms the vortex structure and causes the core 200 to deflect perpendicular to the external field direction, eventually leading to the destruction of the vortex (as the core 200 is "pushed out" of the structure) if the field is strong enough (see Fig. 3 (b).). If the field is lowered, the vortex reappears at a certain field, as it resembles the equilibrium state of the magnet.

[0053] In contrast, an out-of-plane magnetic field interacts directly with the polarity of the vortex core 200. An OOP field tends to align the magnetic moments vertically, which can either stabilize or destabilize the core 200, depending on the field direction relative to the core's polarity. If the field is opposite to the core's polarity, the vortex core 200 is, figuratively speaking, compressed as the magnetization of the free layer 116 slowly aligns against the polarization direction of the vortex core 200, eventually destroying it at high fields. Conversely, if the field aligns with the polarity of the vortex core 200, the magnetization of the free layer 116 aligns along the polarization direction, thus expanding the vortex core 200 as well, which ultimately also leads to a transition to a one-dimensional state, as shown in Fig. Figure 3 (a) shows that nucleation occurs again when the OOP field is lowered.

[0054] A TMR sensor with an OOP reference system 112 reacts only to changes in the OOP component of the magnetization. As long as the vortex state is intact, IP fields are compensated by the deflection of the vortex core 200 described above. The effect on the OOP magnetization is minimal. This is demonstrated in Fig. Figure 4 clearly shows contour diagrams of the OOP component influenced by OOP and IP fields. The diagrams illustrate results from a series of micromagnetic simulations for a vortex with a diameter of 256 nm and a height of 64 nm, exhibiting a saturation magnetization of 1 T. Fig. Figure 4 (left) shows a contour diagram of the out-of-plane (OOP) component of the magnetization (Mz). It illustrates the OOP vortex reaction in the presence of out-of-plane (x-axis) and in-plane (y-axis) fields. At low IP fields, the OOP reaction is hardly affected. Only above the annihilation field (approximately 75 mT) is the magnetization significantly influenced by the IP cross-field. Fig. Figure 4 (right) shows the effect of the in-plane cross field on the OOP component in percent. In the area marked as the stable operating range, the influence of the cross field is less than 0.5% (simulation parameters: diameter = 256 nm, height = 64 nm, saturation magnetization (Ms) = 1 T, cell size = 2 nm).

[0055] The effective "immunity" to IP cross-fields makes the vortex structure an ideal magnetization state for measuring external OOP fields. However, this is only true as long as the vortex structure can be protected from annihilation by potentially significant IP cross-fields. In this context, annihilation means the destruction or dissolution of the vortex structure. If the vortex structure is exposed to potentially significant IP cross-fields that are strong enough, this can cause the vortex to become unstable and lose its characteristic vortex shape. This is referred to as vortex annihilation. This annihilation would cause the vortex to lose its immunity to IP cross-fields and no longer be able to accurately measure OOP fields.

[0056] The application range of a vortex disk is mainly determined by the saturation magnetization (M sThe annihilation fields are determined by the material used and the disk geometry. They scale linearly with M. s and are also directly proportional to the ratio of thickness to diameter. In other words, increased stability requires higher M s -Materials, further scaling of components, or greater layer thicknesses. Both scaling of the components and increasing the layer thickness are associated with significant additional costs. Large M s -Materials, on the other hand, have a detrimental effect on the sensitivity of the component, since the OOP response of the vortex is inversely proportional to M s scaled.

[0057] The proposed solution for "immunity" to IP cross-fields allows the operational cross-field range of an OOP magnetoresistive sensor with a free layer featuring vortex magnetization to be extended by reducing effective in-plane cross-field amplitudes acting on the vortex during operation. This is achieved by employing counteracting stray fields emanating from adjacent soft magnetic structures in the micrometer range. These so-called "shields" exhibit line-like MH behavior depending on their geometry and enable constant shielding factors over a wide field range. The shields can be positioned a short distance above and / or below the magnetoresistive sensors.

[0058] Fig. Figure 5 schematically shows a magnetoresistive sensor 500 according to an embodiment of the present disclosure. While the upper part of the Fig. Figure 5 shows a schematic side view of the magnetoresistive sensor 500; the lower part of the Fig. Figure 5 shows a schematic top view.

[0059] The magnetoresistive sensor 500 contains a layer stack 510, which forms the magnetic tunnel junction (MTJ) from Fig. The tunnel contact 510 includes at least one reference layer 512, which is magnetized such that its magnetization is perpendicular to the plane of the layer stack (out-of-plane, OOP). Furthermore, the layer stack 510 includes a free layer 516 whose magnetization is arranged in a vortex pattern, known as vortex magnetization. The sensor 500 is also equipped with at least one soft magnetic shield 520, which is located in the immediate vicinity of the layer stack 510. The shield 520 is designed to reduce the effects of external magnetic fields, which are parallel to the plane of the layer stack (in-plane, IP), on the free layer 516. This occurs along a direction referred to as the IP shield axis 530.

[0060] The term "immediate proximity" here refers to a positioning where the shield is brought as close as possible to the layer stack to achieve optimal shielding effectiveness. This proximity allows the shield to generate a strong counter-field that compensates for interfering external magnetic fields before they reach the sensitive layers of the layer stack. At the same time, the shield is close enough to ensure effective field compensation, yet sufficiently far away not to impair the normal function of the layer stack. According to some embodiments, the shortest distance between the layer stack 510 and the shield 520 is in the range of 2–3 µm. The "shortest distance" refers to the smallest distance between the nearest points of the layer stack and the shield 510.

[0061] To minimize external interference, especially magnetic fields parallel to the sensor plane, a soft magnetic shield 520 is used. This shield 520 can generate a counter-field that neutralizes the interfering influences and thus improves the functionality and accuracy of the sensor 500. The IP shielding axis 530 describes a direction along which the shield is effective and reduces the interfering cross-field.

[0062] The 520 shield can be made from a nickel-iron alloy, a cobalt-iron alloy, a cobalt-nickel alloy, or an iron-silicon alloy. These alloys possess excellent soft magnetic properties. They are easily magnetized and demagnetized, making them ideal for magnetic field shielding applications. Nickel-iron (e.g., Permalloy) is known for its high magnetic permeability and low coercivity, meaning it conducts magnetic fields very well without retaining permanent magnetization itself. This allows the 520 shield to effectively neutralize external magnetic fields while maintaining its original magnetic properties. A cobalt-iron alloy offers high saturation magnetization, making it particularly suitable for shielding strong magnetic fields.A cobalt-nickel alloy combines the advantageous properties of cobalt and nickel to offer a balanced mix of high saturation magnetization and good magnetic permeability. An iron-silicon alloy is popular due to its good magnetic properties and resistance to magnetization loss. It is often used in applications requiring durable and reliable shielding. The choice of specific alloy depends on the application requirements, including the strength of the expected external magnetic fields and the desired mechanical properties of the shield.

[0063] At the in Fig. In the embodiment shown in Figure 5, the soft magnetic shield 520 is arranged laterally adjacent to the layer stack. That is, the soft magnetic shield 520 can be positioned laterally next to the tunnel contact 510. Responding to an external IP field, the laterally arranged shield 520 generates a counter-field magnetic field that reduces the influence of the external IP field. This counter-field also acts on the nearby layer stack 510 and at least partially neutralizes the interfering external IP field. This preserves the stability of the vortex magnetization in the free layer 516, resulting in improved accuracy and sensitivity of the sensor 500.

[0064] The soft magnetic shield 520 can, for example, be cuboid in shape. "Cuboid" means that the shield 520 has the geometric form of a cuboid, which describes a three-dimensional figure with six rectangular faces. Each of these faces is a rectangle, and the opposite faces of a cuboid are equal in size and parallel to each other. This shape allows for easy manufacturing and integration of the shield 520 into the sensor 500, as it has clear and defined dimensions along its length l, width b, and height h. The cuboid shape also provides a uniform distribution of magnetic properties, which is important for the effective shielding of magnetic fields.

[0065] The cuboid shield 520 has an extent (length) l in the direction of the shielding axis 530 and an extent (width) b perpendicular to the shielding axis 530. The extent l in the direction of the shielding axis can be greater than the extent b perpendicular to the shielding axis 530. In particular, the extent l in the direction of the shielding axis can be 4 times, 10 times, or 100 times greater than the extent b perpendicular to the shielding axis 530.

[0066] Besides the cuboid shape of the shield 520, other geometries with similar aspect ratios are conceivable. An elliptical plate would be another possibility, in which the major axis of the ellipse runs in the direction of the shielding axis 530 and is significantly longer than the minor axis perpendicular to the shielding axis. The described proportions ensure that the shield 520 covers a larger area in the direction of the shielding axis 530, which can increase the efficiency of the shielding. A greater extent in the direction of the shielding axis allows for more effective compensation of the external magnetic fields, as it offers a larger area that can generate the opposing field.

[0067] At the in Fig. In the embodiment shown in Figure 6, the soft magnetic shield 520 is arranged both laterally adjacent to and above the layer stack 510. That is, the soft magnetic shield 520 is positioned both laterally next to and above the layer stack 510. It will be immediately obvious that the soft magnetic shield 520 could also be positioned directly above the layer stack 510, i.e., without any lateral offset. Likewise, the soft magnetic shield 520 could also be positioned both laterally next to and below the layer stack 510. The soft magnetic shield 520 could also be positioned directly below the layer stack 510, i.e., without any lateral offset. Precise positioning of the shield 520 relative to the layer stack 510 can depend on factors such as...depend on the geometry of the shielding 520 and / or a desired shielding axis 530.

[0068] At the in Fig. In the embodiment shown in Figure 7, the shielding has a first soft magnetic bar (cuboid) 520-1 and a second soft magnetic bar (cuboid) 520-2, which run parallel to each other and perpendicular to the IP shielding axis 530. In the embodiment shown in Figure 7, the shielding has a first soft magnetic bar (cuboid) 520-1 and a second soft magnetic bar (cuboid) 520-2, which run parallel to each other and perpendicular to the IP shielding axis 530. Fig. In the embodiment shown in Figure 7, the soft magnetic beams 520-1, 520-2 are positioned above the layer stack 510 in the z-direction. The layer stack 510 is located between the soft magnetic beams 520-1, 520-2 in the x-direction. Thus, the soft magnetic beams 520-1 and 520-2 are located vertically above the layer stack 510, while the layer stack 510 is arranged horizontally between the two beams 520-1, 520-2 in the x-direction. It will be immediately obvious that the soft magnetic beams 520-1 and 520-2 could also be arranged below the layer stack 510.

[0069] Fig. Figure 8 shows a schematic perspective view of a magnetoresistive sensor 500, in which a soft magnetic shield 520 is located above the TMR layer stack 510 in the z-direction. The distance is in the range of 0.5–3 µm. The cuboid shield 520 has a width b in the direction (x-direction) of the shield axis 530 and a length l perpendicular (y-direction) to the shield axis 530. The extent l perpendicular to the shielding axis 530 can be larger than the extent b in the direction of the shielding axis 530. In particular, the extent l perpendicular to the shielding axis can be 4 times, 10 times, or 100 times larger than the extent b in the direction of the shielding axis 530. The shield 120 here has an exemplary extent of 100 µm along the y-axis and 10 µm along the x-axis.Here, the extent of the shielding 520 perpendicular to the shielding axis 530 is therefore 10 times greater than the extent of the shielding 520 parallel to the shielding axis 530.

[0070] Besides the cuboid design of the shield 520, other geometries with similar aspect ratios are conceivable. An elliptical plate would be another possibility, in which the major axis of the ellipse runs perpendicular to the shield axis 530 and is significantly longer than the minor axis along the shield axis.

[0071] Fig. Figure 9 shows a comparison of two configurations of a Chip 900 operating with TMR resistors R1, R2, R3, and R4. These TMR resistors form a bridge circuit. In the bridge circuit, the resistors are arranged to modify the output voltage depending on external OOP magnetic fields acting upon them. On the left, the chip is shown without soft magnetic shielding while exposed to external IP cross-fields with a strength of 400 mT. On the right, the same Chip 900 is shown, but this time with several parallel soft magnetic shielding bars 520 positioned above the bridge circuit consisting of R1, R2, R3, and R4. These bars serve to reduce the effects of the IP cross-fields by generating a counter-field that neutralizes the interfering magnetic fields.

[0072] Fig. Figure 10 shows a top view of the bridge circuit. Fig. 9, with the four TMR resistors R1, R2, R3, and R4, which are integrated together on chip 900. Each of the TMR resistors (R1, R2, R3, and R4) is formed by a plurality of tunnel contacts 510, which are integrated within a respective resistor region on the chip. These tunnel contacts 510 comprise a layer stack, which is typically composed of several magnetic and non-magnetic layers. The layer stack contains a free layer 516 and a reference layer 512, which are separated by a thin insulating layer. The tunnel contacts 510 within each resistor are arranged such that, collectively, they determine the respective electrical resistance. The number of tunnel contacts and their specific orientation determine the sensitivity of the resistor to external magnetic fields.

[0073] Each resistor (R1, R2, R3, R4) of the bridge circuit is covered by several soft magnetic shields 520, which run parallel to each other and are represented as rectangular structures. These shields serve to protect resistors R1, R2, R3, and R4 from interfering IP magnetic fields by generating a counter-field that neutralizes unwanted external fields. A distance is maintained between the individual soft magnetic shields 520 that corresponds approximately to the thickness of the shields themselves (e.g., 10 µm). This consistency of distance and thickness ensures uniform and effective shielding.

[0074] On the right side of Fig.Figure 10 shows a schematic circuit diagram of the bridge circuit, illustrating the electrical connection of the four TMR resistors R1, R2, R3, and R4. The resistors R1, R2, R3, and R4 are connected in series to form a Wheatstone bridge, with R1 and R2 as well as R3 and R4 connected in series.

[0075] Embodiments of the present disclosure make it possible to extend the operational cross-field range of an OOP TMR sensor with a vortex sensor layer by reducing the effective in-plane cross-field amplitudes acting on the vortex during operation. To achieve this, counteracting stray fields emanating from adjacent soft magnetic structures in the micrometer range are employed. Depending on their geometry, these shields exhibit line-like MH behavior and enable constant shielding factors over a wide field range. The shields 520 can be placed a short distance above and / or below the magnetic tunnel contacts.

[0076] Suitable shielding materials are soft magnetic alloys such as NiFe, with a saturation magnetization between 1 and 1.3 Tesla. The saturation field (the field above which the magnet is in saturation and additional shielding is no longer possible) can then be determined via the product of M sand the demagnetization factor along the shielding axis 530, which depends on the shielding geometry. This shape-dependent demagnetization factor lies between 0 and 1. To maximize it and achieve large shielding areas, the extent of the shield, e.g., perpendicular to the shielding axis 530, should be significantly larger (ratio > 4:1:1) than its extent along the shielding axis. With ratios of approximately 10:1:1, demagnetization factors of ≈ 0.4 can be achieved. Alternative soft magnetic materials with different saturation magnetizations can also be used if the shape is adapted to the intended shielding area.

[0077] The shielding factor scales with the extent of the shield 520 along the shielding axis 530 and is therefore inversely proportional to the shielding range. Finite element simulations of shields with linear ranges up to 0.5 T indicate that constant shielding factors of up to ≈ 10 are possible in the immediate vicinity of the shield 520 (distance < 1 µm). The shielding factor scales with 1 divided by the distance from the shield 520. Close integration is therefore necessary. With shielding factors around ≈ 10 for IP cross fields up to ≈ 0.5 T, it is possible to use vortex disks with intrinsic annihilation fields well below 100 mT while simultaneously covering an operating range up to ≈ ±0.5 T.

[0078] The magnetic fields emanating from the shield 520 interact with neighboring shields 520. Simulations show that this "crosstalk" can significantly reduce the range of the shields, so sufficient distances between shields 520 are necessary. The distances must therefore be optimized to achieve the best results with minimal space consumption.

[0079] Alternatively, multiple 520 shields can be used around a TMR layer stack. By employing a cross-beam approach, it is possible, for example, to shield against both cross-field directions (e.g., x-direction and y-direction) simultaneously. In this case, the shield can have first parallel soft magnetic beams (e.g., in the x-direction) and second parallel soft magnetic beams (e.g., in the y-direction), with the first and second beams intersecting at a right angle.

[0080] A second vortex of similar size directly below the layer stack 510 can also shield IP cross-fields, but only by a factor of 2 and only up to the annihilation field of the vortex shield. The shield 520 can therefore also be disk-shaped and exhibit vortex magnetization. In combination with the upper bar shields, this can help keep the free layer 516 in a vortex state, further increasing the cross-field-immune operating range or significantly increasing the freedom of the layer stack 510 and the overall design. Furthermore, the z-sensitivity can be increased by the linear amplification of the z-field by the vortex shield.

[0081] In summary, this disclosure relates to a magnetoresistive sensor designed to measure external out-of-plane (OOP) magnetic fields while minimizing sensitivity to interfering in-plane (IP) magnetic fields. The sensor uses a combination of a reference layer with OOP magnetization and a free layer with vortex magnetization. A soft magnetic shield is positioned in close proximity to the layer stack to reduce the influence of external IP magnetic fields by generating a counter-field. This preserves the stability of the vortex magnetization and increases the sensor's measurement accuracy.

[0082] Exemplary embodiments include a specific material selection and geometry of the soft magnetic shield. The shield consists of alloys such as nickel-iron or cobalt-iron and can be designed in the form of one or more cuboids, with the shield's extent perpendicular to the shielding axis being greater than that parallel to it. This arrangement can maximize the efficiency of field compensation and ensure a uniform distribution of magnetic properties. In some variants, the shield is positioned laterally next to the layer stack or above / below the layer stack to offer flexible integration options and further optimize shielding performance. Another preferred approach is a grid-like integration of several soft magnetic bars that intersect at right angles, thus enabling effective shielding in multiple directions.

[0083] The aspects and features described in connection with one of the previous examples can also be combined with one or more of the further examples to replace an identical or similar feature of that further example or to additionally introduce the feature into the further example.

[0084] It is further understood that the disclosure of several steps, processes, operations, or functions disclosed in the description or claims should not be interpreted as necessarily occurring in the described sequence, unless explicitly stated in a specific case or required for technical reasons. Therefore, the preceding description does not restrict the execution of multiple steps or functions to a specific sequence. Furthermore, in other examples, a single step, function, process, or operation may include and / or be broken down into multiple sub-steps, functions, processes, or operations.

[0085] If certain aspects described in the preceding sections relate to a device or system, these aspects should also be understood as a description of the corresponding procedure. For example, a block, device, or functional aspect of the device or system may correspond to a feature, such as a process step, of the corresponding procedure. Similarly, aspects described in relation to a procedure should also be understood as a description of a corresponding block, element, property, or functional feature of that device or system.

[0086] The following claims are hereby included in the detailed description, each claim being a separate example. It should also be noted that—although a dependent claim may refer to a specific combination with one or more other claims—other examples may include a combination of the dependent claim with the subject matter of any other dependent or independent claim. Such combinations are hereby explicitly proposed unless it is stated in a specific case that a particular combination is not intended. Furthermore, features of a claim are also to be included for each other independent claim, even if that claim is not directly defined as dependent on that other independent claim.

Claims

[1] Magnetoresistive sensor (500), comprising a layer stack (510) with at least one reference layer (512) with a reference magnetization perpendicular to the plane of the layer stack; and at least one free layer (516) with a vortex magnetization; and at least one soft magnetic shield (520) arranged adjacent to the layer stack, which is designed to reduce the influence of an external magnetic field along a shielding axis (530) on the free layer. [2] Magnetoresistive sensor (500) according to claim 1, wherein the shield (520) is configured to generate a counter-field in response to the external magnetic field. [3] Magnetoresistive sensor (500) according to one of the preceding claims, wherein the shield (520) is arranged laterally adjacent to the layer stack (510). [4] Magnetoresistive sensor (500) according to one of the preceding claims, wherein the shielding (520) is arranged above or below the layer stack (510). [5] Magnetoresistive sensor (500) according to one of the preceding claims, wherein the extent of the shield (520) perpendicular to the shielding axis (530) is greater than the extent parallel to the shielding axis. [6] Magnetoresistive sensor (500) according to claim 5, wherein the extent of the shielding (520) perpendicular to the shielding axis (530) is at least 4 times greater than the extent of the shielding parallel to the shielding axis. [7] Magnetoresistive sensor (500) according to any of the preceding claims, wherein a shielding material (520) comprises a nickel-iron alloy, a cobalt-iron alloy, a cobalt-nickel alloy, or an iron-silicon alloy. [8] Magnetoresistive sensor (500) according to one of the preceding claims, wherein a saturation magnetization of a material of the shielding (520) is in a range of 1 - 1.5 Tesla. [9] Magnetoresistive sensor (500) according to one of the preceding claims, wherein the at least one shield (520) is cuboid in shape. [10] Magnetoresistive sensor (500) according to one of the preceding claims, wherein the shield (520) has a first soft magnetic bar and a second soft magnetic bar intersecting at a right angle. [11] Magnetoresistive sensor (500) according to one of the preceding claims, wherein the shield (520) has a plurality of parallel arranged soft magnetic bars, each bar having a longitudinal axis perpendicular or parallel to the shield axis (530). [12] Magnetoresistive sensor (500) according to claim 11, wherein the distance between adjacent bars is greater than 5 µm. [13] Magnetoresistive sensor (500) according to one of the preceding claims, wherein a shortest distance between the layer stack (510) and the shield (520) is in a range of 0.5 - 3 µm. [14] Magnetoresistive sensor (500) according to any of the preceding claims, wherein the layer stack (510) comprises a TMR layer stack. [15] Magnetoresistive sensor (500) according to one of the preceding claims, wherein the layer stack (510) and the at least one shield (520) are arranged on a common die. [16] A bridge circuit (900) with a plurality of magnetoresistive sensors according to one of the preceding claims.

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