Magnetoresistive sensor

Abstract

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

Description

Technical Field

[0001] This invention relates to a magnetoresistive sensor capable of measuring and detecting external out-of-plane (OOP) magnetic fields. Background Technology

[0002] Magnetoresistive sensors, especially those based on the principle of tunneling magnetoresistive (TMR), are increasingly used in a variety of industrial and commercial applications, including automotive, medical, and entertainment electronics. These sensors offer high sensitivity and accuracy in magnetic field detection, making them a preferred choice for demanding measurement environments.

[0003] A typical TMR sensor consists of a stack of layers, which in turn includes different magnetic and non-magnetic layers. This stack typically comprises a reference layer and a free layer (sensor layer) separated from each other by a non-magnetic tunneling barrier. The magnetization of the reference layer is fixed and oriented in a specific direction. The magnetization of the free layer, however, can be affected by an external magnetic field, thereby altering the resistance of the TMR sensor.

[0004] Magnetoresistive sensors are known to have a reference magnetization extending perpendicular to the plane of the stacked layers; this reference magnetization is also known as out-of-plane (OOP) magnetization. Simultaneously, the free layers can be designed to have vortex magnetization, wherein the magnetization vectors extend in a circular arrangement within the plane, and a central region exists in which the magnetization extends perpendicular to the plane. This specific arrangement of magnetization in the free layers enables targeted control of the interaction with external magnetic fields, thereby achieving high sensitivity and stability of the sensor.

[0005] A problem arising in magnetoresistive sensors with the described magnetization arrangement involves sensitivity to external magnetic fields that extend parallel to the plane of the stacked layers, also known as in-plane (IP) cross-fields. These external cross-fields can destabilize the magnetization of the free layers, leading to unwanted measurement inaccuracies. This can severely impact sensor performance, especially in measurements of weak magnetic fields or in environments with strong interfering fields.

[0006] Therefore, the challenge is to reduce this sensitivity without affecting the basic structure of the layer stack or the advantages of OOP magnetization and vortex magnetization. Summary of the Invention

[0007] This is solved by the magnetoresistive sensor according to the present invention.

[0008] According to a first aspect of the invention, a magnetoresistive sensor is provided. The magnetoresistive sensor includes a layer stack having at least one reference layer with magnetization perpendicular to a plane (out-of-plane, OOP) of the layer stack. The layer stack also includes at least one free layer with vortex magnetization. Magnetization in a vortex-shaped arrangement can be referred to as vortex magnetization, wherein the magnetization vector extends in a plane (in-plane) and has a central region in which the magnetization extends perpendicular to the plane (OOP). The magnetoresistive sensor also includes at least one soft magnetic shielding disposed adjacent to the layer stack, the soft magnetic shielding being configured to reduce the effect of an external (in-plane) magnetic field along the shielding axis on the free layer.

[0009] Therefore, the proposed magnetoresistive sensor utilizes a combination of vortex magnetization in an OOP reference layer and a free layer. A soft magnetic shield, arranged adjacent to the layer stack, is used to reduce the sensor's sensitivity to external cross-fields. This arrangement has the advantage of improving sensor precision by minimizing the effects of unwanted magnetic fields, which is particularly important in applications requiring high measurement accuracy.

[0010] According to some embodiments, a soft magnetic shield is constructed to generate a reverse magnetic field in response to an external magnetic field. The reverse field generated by the soft magnetic shield is based on the inherent magnetism of the soft magnetic material used. Soft magnetic materials are characterized by high magnetic permeability, meaning that they can easily amplify and guide an external magnetic field. When an external magnetic field encounters the soft magnetic shield, the material's high permeability allows the field to penetrate the material and align along a preferred magnetic axis within the shield. This alignment generates an internal magnetic field within the shield, which is capable of forming a reverse field relative to the incident external magnetic field. The resulting reverse field cancels out the external magnetic field, resulting in a reduction or neutralization of the external magnetic field in the sensor's vicinity. This interaction maintains the stability of the magnetization of the sensor's free layer and reduces undesirable effects that can be caused by the external magnetic field. The reverse field is thus controlled by the spatial arrangement and material properties of the shield, allowing it to respond specifically to and compensate for the external magnetic field in a desired manner. This mechanism helps minimize the impact of interfering fields on the sensor and improves its measurement accuracy.

[0011] According to some embodiments, the shielding element is arranged laterally adjacent to the layer stack. This lateral arrangement of the shielding element enables targeted shielding of intersecting magnetic fields extending parallel to the layer plane. The advantage of this arrangement is that it provides effective shielding without significantly increasing the sensor's space requirements, resulting in a compact design.

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

[0013] According to some embodiments, the shielding element extends perpendicularly to the shielding axis more than it extends parallel to the shielding axis. This greater extension perpendicular to the shielding axis ensures a greater linear shielding range against external cross magnetic fields. The advantage of this implementation is that it provides improved shielding in large magnetic fields and also increases the area available for field compensation.

[0014] According to some embodiments, the extension of the shielding element perpendicular to the shielding axis is at least four times greater than the extension of the shielding element 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 vertical and parallel extensions. The advantage of this geometry is that it ensures particularly effective suppression of interference fields, which can further improve the sensitivity of the sensor.

[0015] According to some embodiments, the materials used for the shielding include nickel-iron alloys, cobalt-iron alloys, cobalt-nickel alloys, or iron-silicon alloys. These materials are known for their excellent soft magnetic properties, making them ideal for use in shielding. The advantage of using these alloys is that they possess high magnetic permeability and low coercivity, thereby allowing the shielding to be highly efficient and responsive.

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

[0017] According to some embodiments, at least one shielding element is constructed in a cubic shape. The cubic construction of the shielding element facilitates manufacturing and integration into the sensor structure. An advantage of this shape is that it enables a uniform and stable field distribution, which can improve shielding efficiency.

[0018] According to some embodiments, the shielding element has a first soft magnetic strip and a second soft magnetic strip, which intersect at right angles. By arranging the two strips at right angles, shielding can be achieved in two directions. An advantage of this configuration is that it effectively reduces the in-plane magnetic field along the x and y directions, which increases the versatility of the sensor.

[0019] According to some embodiments, the shielding element has a plurality of parallel-arranged soft magnetic strips, wherein each strip has a longitudinal axis extending perpendicularly to or parallel to the shielding axis. The parallel arrangement of the strips provides an expanded shielding area, which improves the efficiency of magnetic field suppression. An advantage of this arrangement is that it can achieve uniform shielding over a larger area, which is particularly advantageous for applications involving sensors with larger areas.

[0020] According to some embodiments, the distance between adjacent soft magnetic strips is greater than 5 μm. This greater distance between the (soft magnetic) strips reduces potential interference between shielding elements and ensures more effective field compensation by forming a uniform reverse field. An advantage of this geometry is that it optimizes the performance of the shield by minimizing unwanted cross-fields.

[0021] According to some embodiments, the minimum distance between the layer stack and the shield is in the range of 2-3 μm. This distance between the layer stack and the shield ensures effective cross-field compensation without affecting sensor functionality. An advantage of this arrangement is that it achieves high shielding performance within small space requirements, contributing to sensor compactness.

[0022] According to some embodiments, the layer stack includes a TMR layer stack. The TMR layer stack, combined with vortex-magnetized free layers, provides excellent magnetoresistive properties, which improves the sensitivity and accuracy of the sensor. An advantage of this implementation is that it enables high resolution and precision in measuring external OOP magnetic fields, which is advantageous for many applications.

[0023] According to some embodiments, the stacked layers and at least one shield are arranged on a common die (chip). This common arrangement on the semiconductor die facilitates sensor integration and miniaturization. The advantage of this arrangement is that it reduces manufacturing costs and increases the overall system compactness, which is crucial for modern electronic applications.

[0024] According to another aspect of the invention, the bridging circuit will provide multiple magnetoresistive sensors according to one of the embodiments described above. Integration with the bridging circuit, for example, enables more precise measurement of the magnetic field through differential measurement. An advantage of this implementation is that it can further improve the accuracy and sensitivity of the sensor system, which is particularly useful in harsh measurement environments.

[0025] According to an embodiment, the operating region of a magnetic vortex sensor that measures out of plane and is insensitive to cross-fields can be significantly expanded by adding adjacent soft magnetic structures that cancel out cross-fields, so-called "shielding elements," which can be inherently achieved. The shielding elements reduce the effective parasitic cross-field, thereby preserving the vortex structure of the free layer (and thus expanding the operating region), while the out-of-plane field components along the sensitive direction remain unaffected. Attached Figure Description

[0026] Examples of apparatuses and / or methods are subsequently described in detail with reference to the accompanying drawings, for illustrative purposes only.

[0027] in:

[0028] Figure 1An example of a layer stack of magnetoresistive sensor elements according to an embodiment is shown;

[0029] Figure 2 A micromagnetic simulation of a disk with a diameter of 0.25 μm is shown, which has uniform magnetization on the left and a vortex state on the right.

[0030] Figures 3(a) and 3(b) show the 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 figures illustrate the vortex’s response to an external magnetic field;

[0031] Figures 4(a) and 4(b) show out-of-plane (OOP) magnetization, which is almost unaffected by in-plane cross fields in the stable operating region, where the noticeable effects occur only above the annihilation field;

[0032] Figure 5 A magnetoresistive sensor with laterally adjacent shielding elements is shown according to an embodiment;

[0033] Figure 6 A magnetoresistive sensor with lateral and top adjacent shielding elements is shown according to another embodiment;

[0034] Figure 7 A magnetoresistive sensor according to another embodiment is shown, which has a layer stack between two shielding strips; and

[0035] Figure 8 A magnetoresistive sensor according to another embodiment is shown, which has a TMR layer stack beneath the shielding strip;

[0036] Figure 9 A three-dimensional bridging circuit is shown, which has multiple magnetoresistive sensors beneath the grid of the shielding strip; and

[0037] Figure 10 It shows Figure 9 A top view of the bridging circuit. Detailed Implementation

[0038] Some examples are now described in detail with reference to the accompanying drawings. However, other possible examples are not limited to the features of these detailed embodiments. They may have modifications, corresponding features, and alternatives. Furthermore, the terminology used herein to describe particular examples should not limit other possible examples.

[0039] The same or similar reference numerals refer to the same or similar elements or features throughout the description of the drawings, which may be implemented in the same or modified form while providing the same or similar function. Furthermore, the thickness of lines, layers, and / or regions used for illustration may be exaggerated in the drawings.

[0040] If two elements A and B are combined using "or", it should be understood that all possible combinations, i.e., only A, only B, and A and B, are disclosed, unless otherwise explicitly defined in individual cases. "At least one of A and B" or "A and / or B" may be used as alternative expressions for the same combination. This is equivalent to a combination of more than two elements.

[0041] If the singular form, such as “a” and “the,” is used and the use of only one element is neither explicitly nor implicitly defined as mandatory, then other examples may use multiple elements to achieve the same function. If the function is subsequently described as being implemented using multiple elements, then other examples may use a single element or a single processing entity to achieve the same function. Furthermore, it should be understood that the terms “comprising” and “having,” when used, describe the presence of the described features, integers, steps, operations, processes, elements, parts, and / or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, processes, elements, parts, and / or groups thereof.

[0042] Figure 1 An example of a layer stack of a magnetoresistive sensor element 100 according to one or more embodiments is shown.

[0043] The magnetoresistive sensor element 100 may be, for example, a TMR sensor element having a bottom-pinned spin valve (BSV) configuration or a top-pinned spin valve (TSV) configuration. Furthermore, the magnetoresistive sensor element 100 may be disposed on a semiconductor substrate (not shown) of the magnetoresistive sensor. In a Cartier coordinate system having pairs of mutually perpendicular coordinate axes x, y, and z, the stacked layers extend laterally in the xy-plane expanded by the x and y axes. Therefore, lateral dimensions (e.g., lateral distance, lateral cross-section, lateral surface, lateral range, lateral movement, etc.) may refer to dimensions in the xy-plane, and vertical dimensions may refer to dimensions along the z-direction, perpendicular to the xy-plane. Therefore, the vertical range of the layer along the z-direction may, for example, be referred to as the layer thickness.

[0044] The layer stack of the magnetoresistive sensor element 100 includes at least one reference layer having 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 orientation corresponding to the sensor axis of the magnetoresistive sensor element 100. The reference layer and therefore the reference magnetization define a sensor plane. The sensor plane can be defined, for example, by an xy-plane. Therefore, the x and y directions relative to the sensor plane can be referred to as "in-plane," and the z direction relative to the sensor plane can be referred to as "out-of-plane."

[0045] Therefore, in the case of GMR or TMR sensor elements, the resistance of the magnetoresistive sensor element 100 is minimum when the magnetic free layer's free magnetization points exactly in the same direction as the reference magnetization (e.g., the reference direction), and maximum when the magnetic free layer's free magnetization points exactly in the opposite direction to the reference magnetization. In the presence of an external magnetic field, the orientation of the magnetic free layer's free magnetization is variable. Therefore, the resistance of the magnetoresistive sensor element 100 can vary based on the influence of the external magnetic field on the magnetic free layer's free magnetization.

[0046] From bottom to top, the magnetoresistive sensor element 100 may include an optional seed layer 102, which can be used to influence and / or optimize stack growth. In some embodiments, the seed layer 102 may be composed of copper, tantalum, ruthenium, or combinations 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 may be composed of manganese nitride (MnN), platinum manganese (PtMn), iridium manganese (IrMn), nickel manganese (NiMn), etc. The thickness of the NAF layer can, for example, range from 5 nm to 50 nm. However, the magnetoresistive sensor element 100 may also be suitable without a NAF layer.

[0047] Furthermore, a pinning layer (PL) 106 may be formed or otherwise arranged on the NAF layer 104. The pinning layer 106 may be composed of a ferromagnetic material, such as a platinum-cobalt (Pt / Co), palladium-cobalt (Pd / Co), or nickel-cobalt (Ni / Co) multilayer system, or a cobalt-iron (CoFe) or cobalt-iron-boron (CoFeB) alloy. The contact between the NAF layer 104 and the pinning layer 106 can result in an effect known and achieved as an exchange bias effect, whereby the magnetization of the pinning layer 106 is oriented in a preferred direction (e.g., in the negative z-direction, as shown). This magnetization of the pinning layer 106 may be referred to as pinning magnetization. This pinning magnetization can be generated during the manufacture of the magnetoresistive sensor element 100 and can be permanently fixed.

[0048] The magnetoresistive sensor element 100 also includes a nonmagnetic layer (NML) referred to as the coupling intermediate layer 108. In possible implementations, the coupling intermediate layer 108 may include, for example, ruthenium, iridium, tantalum, copper, copper alloys, or similar materials. Other materials (e.g., paramagnetic materials) are also possible. A magnetic (e.g., ferromagnetic) reference layer (RL) 110 may be formed or otherwise arranged on the coupling intermediate layer 108. The thicknesses of the pinning layer 106 and the magnetic reference layer 110 may range from 1 nm to 10 nm.

[0049] Therefore, 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 a vertical direction. Furthermore, the coupling intermediate layer 108 can provide intermediate layer exchange coupling (e.g., antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling) between the pinned layer 106 and the magnetic reference layer 110 to form an artificial antiferromagnet. Thus, the magnetization of the magnetic reference layer 110 can be oriented and maintained in a direction 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 reference magnetization.

[0050] Because the NAF layer 104 is configured such that it oriented and fixes the magnetization of the pinning layer 106 in a specific direction, and the coupling intermediate layer 108 is configured such that it oriented and fixes the magnetization of the magnetic reference layer 110 in the opposite direction, it can be said that the NAF layer 104 is configured to maintain the magnetization of the pinning layer 106 (e.g., fix the magnetization) in a first magnetic orientation and maintain the magnetization of the magnetic reference layer 110 (e.g., fix the reference magnetization) in a second magnetic orientation. When the pinning layer 106 has a linear magnetization pattern in the antiparallel direction, the magnetic reference layer 110 can have a linear magnetization pattern in the z-direction in the same way. Therefore, the NAF layer 104, the pinning layer 106, the coupling intermediate layer 108, and the magnetic reference layer 110 form the magnetic reference layer system 112 of the magnetoresistive sensor element 100.

[0051] The magnetoresistive sensor element 100 additionally includes a barrier layer 114 (e.g., a tunneling barrier) vertically disposed between the reference layer system 112 and the magnetic free layer 116. The barrier layer 114 may be formed or otherwise disposed on the magnetic reference layer 110 of the reference layer system 112, for example, and the magnetic free layer 116 may be formed or otherwise disposed on the barrier layer 114.

[0052] The barrier layer 114 may be composed of a non-magnetic material. In some embodiments, the barrier layer 114 may be an electrically insulating tunnel barrier layer. For example, the barrier layer 114 may be a tunnel barrier layer used to generate the TMR effect. The barrier layer 114 may be composed of magnesium oxide (MgO), aluminum oxide (Al2O3), magnesium aluminum oxide (MgAlOx), or other materials with similar properties.

[0053] The material of the magnetic free layer 116 can be an alloy composed of ferromagnetic materials, such as CoFe, CoFeB, or NiFe. The magnetostriction constant of the magnetic free layer 116 can be set by the iron content. Furthermore, the magnetic free layer 116 can contain platinum-cobalt (Pt / Co), palladium-cobalt (Pd / Co), or nickel-cobalt (Ni / Co) multilayer films to further optimize the magnetism. The magnetic free layer 116 has a variable magnetic free magnetization in the presence of an external magnetic field. Therefore, the magnetic free layer 116 can be referred to as a sensor layer because the change in magnetic free magnetization is used to determine the measurement parameters. Furthermore, the magnetic free magnetization in the fundamental state has a standard magnetic orientation (e.g., vortex magnetization). The fundamental state is the state in which the influence of the external magnetic field on the magnetic free layer 116 is absent or negligible. In some embodiments, the magnetoresistive sensor element 100 may include a magnetic free system comprising multiple layers (e.g., two or more magnetic free layers) that act as magnetic free layers in combination. In this case, the magnetic free layers of the magnetic free system are magnetically coupled to each other. Therefore, a magnetically free system can act as a magnetically free layer, or it can consist of multiple layers. A magnetically free system possesses magnetically free magnetization, which is variable in the presence of an external magnetic field.

[0054] For example, a capping layer 118 composed of tantalum (Ta), tantalum nitride (TaN), ruthenium (Ru), titanium (Ti), titanium nitride (TiN), platinum (Pt), etc., can be formed or otherwise arranged on the magnetic free layer 116 to form the upper layer of the magnetoresistive sensor element 100.

[0055] Seed layer 102 can be used as a lower electrode or to establish an electrical contact with the lower electrode (not shown) of magnetoresistive sensor element 100. Capping layer 118 can establish an electrical contact with the upper electrode (not shown) of magnetoresistive sensor element 100. Barrier layer 114 can be designed such that when a bias voltage is applied to the electrodes (not shown) of magnetoresistive sensor element 100 to generate a magnetoresistive effect (e.g., TMR effect), electrons can tunnel between reference layer system 112 and magnetic free layer 116.

[0056] As mentioned above, Figure 1 This is an example used only as a TMR sensor element. Other examples may be similar. Figure 1 The descriptions differ from those in the text. Figure 1 The number and arrangement of components shown are for illustrative purposes only. In practice, with... Figure 1 Compared to those shown, the TMR sensor element 100 may include additional elements or layers, fewer elements, different elements, or elements arranged differently.

[0057] To realize a linear out-of-plane (OOP) magnetic field sensor based on the TMR effect, in addition to the OOP reference system 112, a magnetic free layer 116 (sensor layer) with linear OOP behavior is also required. A ferromagnet with uniform magnetization of an in-plane (IP) axis satisfies this requirement. However, the magnetization direction at a specific time point directly depends on the vector sum of the OOP field components and the IP field components, which leads to high cross-field sensitivity when used for OOP field measurements. Furthermore, the cross-field sensitivity scales proportionally to the OOP sensitivity, which can represent a significant limitation for OOP field measurements.

[0058] In-plane (IP) cross-fields are magnetic fields that extend parallel to the plane of the stacked layers of a magnetoresistive sensor, i.e., in a plane defined by the x and y axes. The term "cross-field" refers to the potential interference this magnetic field can cause with the sensor's measurements, especially when the sensor is designed to detect magnetic fields extending perpendicular to the stacked plane (out-of-plane, OOP, along the z-axis). These IP cross-fields can affect the magnetization of free layers within the sensor, leading to measurement inaccuracies. Therefore, measurement inaccuracies must be compensated for as much as possible in the sensor's design.

[0059] The solution to minimize cross-field sensitivity is to use a magnetic free layer 116 with a vortex fundamental state, rather than uniform magnetization, such as... Figure 2 As shown, the vortex state in the magnetic free layer 116 describes a special arrangement of magnetization, where the magnetization vectors are arranged in a circular pattern. In this state, the magnetization of various regions of the layer extends primarily in the plane of the layer and forms a spiral or vortex-like structure, similar to a vortex. At the center of this vortex, the magnetization can be oriented perpendicular to the plane of the layer, which produces a stable magnetic state that is less sensitive to external magnetic fields extending laterally to the layer. In the vortex state, the force of the external cross field (also known as Zeman energy) is compensated by the magnetic free layer 116 through the deflection of the vortex core perpendicular to the field direction, thereby absorbing the external magnetic field without significantly affecting the sensitive components of the out-of-plane magnetization. This vortex state, however, is unstable under higher cross magnetic fields because the vortex state collapses above a certain field amplitude and results in uniform magnetization with high cross field sensitivity.

[0060] The vortex stability scales approximately proportionally to t / d (thickness divided by diameter), and also to the saturation magnetization M of the material used in the magnetic free layer 116. s Proportional. Therefore, the inherent stability of the vortex configuration requires materials that are unfavorable to OOP sensor systems (large saturation magnetization) and structural dimensions with layer thicknesses of >100 nm that are significantly less than 0.5 μm.

[0061] A magnetic vortex is a unique rotating configuration in which a magnetization vector winds around a vortex core 200 and produces a vortex-like pattern (see [link]). Figure 2 The vortex core 200 is a region with high energy density of non-oriented magnetic moments and typically has a polarity in which the magnetic moments point upward or downward from the plane of the magnetic free layer 116.

[0062] In the presence of an external magnetic field, vortices exhibit pronounced hysteresis behavior. When a vortex in a magnetic free layer is exposed to an external magnetic field, it exhibits characteristic hysteresis behavior. This means that the vortex's response to the present magnetic field is not linear, but rather depends on the history of the present magnetic field. Specifically, when an external magnetic field is applied or altered, the vortex changes its position and magnetization structure. However, even when the external magnetic field is removed, these changes remain localized. The hysteresis behavior manifests as the vortex's magnetization structure not immediately or completely returning to its initial state, but remaining in a changed state. Only by applying a counteracting magnetic field or through other changes in environmental conditions can the vortex gradually return to its initial state. This hysteresis behavior is typical for magnetic systems and demonstrates that the vortex's magnetization depends not only on the current strength and direction of the external field but also on the previous magnetization state to which the system was exposed. This leads to a complex interaction between the vortex and the external magnetic field, which affects the stability and dynamics of the magnetic system. This behavior can be simulated using micromagnetic finite difference simulations. If we observe the simulated vortex hysteresis curves shown in Figures 3(a) and 3(b), the out-of-plane response (Figure 3(a)) and the response to the in-plane magnetic field (Figure 3(b)) appear to be similar in mass. However, if we observe the actual rotating structure, significant differences emerge.

[0063] When an in-plane magnetic field is applied to a magnetic vortex, the chirality of the field and the vortex... That is, the magnetization vectors interact about the rotational direction of the core 200. The vortex experiences a force through this interaction that causes it to move or rotate within the plane of the magnetic free layer 116. This field deforms the vortex structure and causes the core 200 to deflect perpendicular to the direction of the external field. When the field is sufficiently strong (see Figure 3(b)), this ultimately leads to the destruction of the vortex (as the core 200 is “squeezed” out of the structure). When the field decreases, the vortex regenerates in a specific field because the vortex resembles the equilibrium state of a magnet.

[0064] In contrast, the out-of-plane magnetic field interacts directly with the polarity of the vortex core 200. The OOP field tends to align the magnetic moments vertically, which can stabilize or destabilize the core 200 depending on the field direction with respect to the polarity of the core 200. When the field is opposite to the polarity of the core 200, the vortex core 200 is graphically compressed by the magnetization of the free layer 116 slowly aligning opposite to the polarization direction of the vortex core 200, and eventually destroying the vortex core in a high field. Conversely, if the field is aligning according to the polarity of the vortex core 200, then the magnetization of the free layer 116 is aligned along the polarization direction, and thus the vortex core 200 stretches along with it, which also eventually leads to a transition to a one-dimensional state, as shown in Figure 3(a). As the OOP field decreases, the seed reforms.

[0065] The TMR sensor with OOP reference system 112 responds only to changes in the OOP component of magnetization. As long as the vortex or eddy current state is intact, the IP field compensates for this through the aforementioned deflection of the vortex core 200. The effect on OOP magnetization is minimal. This is evident in Figures 4(a) and 4(b), which show profile plots of the OOP component affected by the OOP and IP fields. The plots illustrate the results of 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. Figure 4(a) shows a profile plot of the out-of-plane (OOP) component of magnetization (Mz). It illustrates the OOP vortex response in the presence of both out-of-plane (x-axis) and in-plane (y-axis) fields. At low IP fields, the OOP response is almost unaffected. Only above the annihilation field (approximately 75 mT) is the magnetization significantly affected by the IP cross field. The effect of the in-plane cross field on the OOP component is illustrated as a percentage in Figure 4(b). In the region marked as the stable working region, the effect 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).

[0066] Effective "immunity" to IP cross-fields makes vortex structures an ideal magnetization state for measuring external OOP fields. However, this only occurs if the vortex or eddy current structure can be protected from annihilation by a potentially strong IP cross-field. In this case, annihilation refers to the damage or disintegration of the vortex structure. If a vortex structure is exposed to a sufficiently strong, potentially strong IP cross-field, this can lead to the vortex becoming unstable and losing its characteristic vortex shape. In this case, vortex annihilation is mentioned. This annihilation results in the vortex losing its immunity to IP cross-fields and no longer being able to accurately measure the OOP field.

[0067] The application range of vortex disks is mainly determined by the saturation magnetization (M) of the materials used. sThe annihilation field is determined by M and the geometry of the disk. s It scales linearly and is also directly proportional to the ratio of thickness to diameter. In other words, increasing stability requires a higher M. s Further scaling of materials and components, or greater layer thickness. Scaling of structural elements and increased layer thickness are associated with significant additional costs. Conversely, large M... s The material's sensitivity to structural components is adversely affected because the OOP reaction of the vortex is related to M. s Scales inversely.

[0068] The proposed solution for “immunity” to IP cross-fields enables the expansion of the operating cross-field range of OOP magnetoresistive sensors with free layers (which have vortex magnetization) by reducing the effective cross-field amplitude in the plane (which affects the vortex during operation). This is achieved using a canceled scattered field from adjacent soft magnetic structures in the micrometer range. The so-called “shielding” exhibits linear MH behavior according to its geometry and is capable of achieving a constant shielding factor over a wide field range. The shielding can be positioned above and / or below the magnetoresistive sensor at a short distance.

[0069] Figure 5 A magnetoresistive sensor 500 according to an embodiment of the present disclosure is illustrated schematically. Figure 5 The upper part shows a schematic side view of the magnetoresistive sensor 500, while Figure 5 The lower part shows a schematic top view.

[0070] The magnetoresistive sensor 500 comprises a layer stack 510, which can be similar to... Figure 1 The magnetic tunneling junction (MTJ) is described. The tunneling junction 510 includes at least one reference layer 512, which is magnetized such that its magnetization is perpendicular to the planar extension (out-of-plane, OOP) of the layer stack. Furthermore, the layer stack 510 includes a free layer 516, whose magnetization is arranged in a vortex-shaped pattern, as vortex magnetization is known. Additionally, the sensor 500 is equipped with at least one soft magnetic shield 520 located directly in proximity to the layer stack 510. The shield 520 is designed to reduce the effect of external magnetic fields parallel to the planar extension (in-plane, IP) of the layer stack on the free layer 516. This occurs along a direction referred to as the IP shielding axis 530.

[0071] The term "direct proximity" here refers to the positioning of the shield as closely as possible to the layer stack for optimal shielding effectiveness. Proximity enables the shield to generate a strong reverse field that compensates for interfering external magnetic fields before they reach the sensitive layers of the layer stack. Simultaneously, the shield is close enough to ensure effective field compensation, yet far enough not to interfere with the normal functioning 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 micrometers. "Shortest distance" refers to the shortest distance between the nearest point of the layer stack 510 and the shield 520.

[0072] Therefore, to minimize external interference, especially the magnetic field extending parallel to the plane of the sensor, a soft magnetic shield 520 is used. This shield 520 can generate a reverse field that neutralizes the interference and thus improves the function and accuracy of the sensor 500. The IP shielding axis 530 defines a direction along which the shield is effective and reduces the interfering cross field.

[0073] Shielding element 520 can be made of, for example, nickel-iron alloys, cobalt-iron alloys, cobalt-nickel alloys, or iron-silicon alloys. These alloys possess excellent soft magnetism. They can be easily magnetized and demagnetized, making them ideal for use in magnetic field shielding. Nickel-iron alloys (e.g., permalloy) are known for their high magnetic permeability and low coercivity, meaning they can guide magnetic fields well without becoming permanently magnetized themselves. Thus, shielding element 520 can effectively neutralize external magnetic fields while retaining its initial magnetism. Cobalt-iron alloys offer high saturation magnetization, making them particularly suitable for shielding strong magnetic fields. Cobalt-nickel alloys combine the advantageous properties of cobalt and nickel to provide a balanced mix of high saturation magnetization and good magnetic permeability. Iron-silicon alloys are popular due to their good magnetism and resistance to magnetization loss. They are commonly used in applications requiring durable and reliable shielding. The choice of a specific alloy depends on the application requirements, including the expected strength of the external magnetic field and the desired mechanical properties of the shielding.

[0074] exist Figure 5 In the illustrated embodiment, the soft magnetic shield 520 is arranged laterally adjacent to the layer stack. That is, the soft magnetic shield 520 can be arranged next to the side of the tunnel junction 510. The shield 520 arranged on the side generates a magnetic IP reverse field according to the external IP field, which reduces the influence of the external IP field. This reverse field also affects the nearby layer stack 510 and at least partially neutralizes the interfering external IP field. This maintains the stability of the vortex magnetization in the free layer 516, resulting in improved accuracy and sensitivity of the sensor 500.

[0075] For example, the soft magnetic shield 520 can be constructed in a cubic shape. "Cubic" means that the shield 520 has a cubic geometry, which describes a three-dimensional diagram with six rectangular surfaces. Each of these surfaces is rectangular, and the opposing surfaces of the cube are of the same size and parallel to each other. This shape allows the shield 520 to be easily manufactured and integrated into the sensor 500 because the shield has clear and defined dimensions along its length l, width b, and height h. The cubic shape also provides a uniform magnetic distribution, which is important for effective shielding of magnetic fields.

[0076] The cubic shielding element 520 has an extension (length) l in the direction of the shielding axis 530 and an extension (width) b perpendicular to the shielding axis 530. The extension l in the direction of the shielding axis can be greater than the extension b perpendicular to the shielding axis 530. In particular, the extension l in the direction of the shielding axis can be 4 times, 10 times, or 100 times greater than the extension b perpendicular to the shielding axis 530.

[0077] Besides the cubic shape of the shield 520, other geometries with similar aspect ratios are conceivable. An elliptical plate is another possibility, in which the principal axis of the ellipse extends along the shielding axis 530 and is much longer than the secondary axis perpendicular to the shielding axis. The described proportions ensure that the shield 520 covers a larger surface area in the direction of the shielding axis 530, which improves shielding efficiency. Here, the greater extension along the shielding axis allows for more effective compensation of external magnetic fields because the shield provides a larger surface area that can generate a reverse field.

[0078] exist Figure 6 In the illustrated embodiment, the soft magnetic shield 520 is arranged laterally adjacent to and above the layer stack 510. That is, the soft magnetic shield 520 is positioned next to and above the layer stack 510. It is readily apparent that the soft magnetic shield 520 can also be positioned directly above the layer stack 510, i.e., without lateral misalignment. Similarly, the soft magnetic shield 520 can be positioned next to and below the layer stack 510. The precise positioning of the shield 520 relative to the layer stack 510 can depend on factors such as the geometry of the shield 520 and / or the desired shielding axis 530.

[0079] exist Figure 7 In the illustrated embodiment, the shielding member has a first soft magnetic strip (cube) 520-1 and a second soft magnetic strip (cube) 520-2, the first and second soft magnetic strips extending parallel to each other and perpendicular to the IP shielding axis 530. Figure 7 In the illustrated embodiment, the soft magnetic strips 520-1 and 520-2 are positioned above the layer stack 510 along the z-direction. The layer stack 510 is located between the soft magnetic strips 520-1 and 520-2 along the x-direction. Therefore, the soft magnetic strips 520-1 and 520-2 are vertically positioned above the layer stack 510, while the layer stack 510 is arranged horizontally along the x-direction, i.e., between the two strips 520-1 and 520-2. It is immediately apparent that the soft magnetic strips 520-1 and 520-2 can also be arranged below the layer stack 510.

[0080] Figure 8 A schematic perspective view of a magnetoresistive sensor 500 is shown, in which a soft magnetic shield 520 is positioned above a TMR layer stack 510 along the z-direction. The distance is in the range of 0.5-3 micrometers. Here, the cubic shield 520 has an extension (width) b along the shielding axis 530 (x-direction) and an extension (length) l perpendicular to the shielding axis (530) (y-direction). The extension l perpendicular to the shielding axis 530 can be greater than the extension b along the shielding axis 530. In particular, the extension l perpendicular to the shielding axis can be 4 times, 10 times, or 100 times larger than the extension b along the shielding axis 530. Here, the shield 120 has an exemplary extension of 100 micrometers along the y-axis and 10 micrometers along the x-axis. Here, the extension of the shield 520 perpendicular to the shielding axis 530 is 10 times larger than the extension of the shield 520 parallel to the shielding axis 530.

[0081] Besides the cubic shape of the shield 520, other geometries with similar aspect ratios are conceivable. An elliptical plate is another possibility, in which the principal axis of the ellipse extends perpendicular to the shield axis 530 and is much longer than the secondary axis along the shield axis.

[0082] Figure 9 Two configurations of a chip 900 operating using TMR resistors R1, R2, R3, and R4 are shown for comparison. The TMR resistors R1, R2, R3, and R4 together form a bridge circuit. In the bridge circuit, the resistors are arranged such that the output voltage changes according to the external OOP magnetic field affecting them. The left side shows a chip without soft magnetic shielding, exposed to an external IP cross-field of strength 400 mT. The right side shows the same chip 900, but this time with multiple parallel soft magnetic shielding strips 520 arranged above the bridge circuit consisting of R1, R2, R3, and R4. These strips are used to reduce the effects of the IP cross-field by generating a reverse field that neutralizes the interfering magnetic field.

[0083] Figure 10 It shows Figure 9A top view of a bridging circuit having four TMR resistors R1, R2, R3, and R4 commonly integrated on chip 900. Each TMR resistor (R1, R2, R3, and R4) is formed via multiple tunneling junctions 510 integrated within a corresponding resistive region on the chip. These tunneling junctions 510 comprise a layer stack, typically constructed from multiple magnetic and non-magnetic layers. The layer stack includes a free layer 516 and a reference layer 512 separated by a thin insulating layer. The tunneling junctions 510 within each resistor are arranged such that the tunneling junctions collectively determine the corresponding resistance. The number of tunneling junctions and their specific orientation determine the resistance's sensitivity to an external magnetic field.

[0084] Each resistor (R1, R2, R3, R4) in the bridging circuit is covered by multiple soft magnetic shields 520, which extend parallel to each other and are shown as a cubic structure. These shields protect resistors R1, R2, R3, and R4 from interfering IP magnetic fields by generating a reverse field to neutralize unwanted external magnetic fields. A distance approximately corresponding to the thickness of the shield itself (e.g., 10 micrometers) is maintained between the individual soft magnetic shields 520. This uniformity of distance and thickness ensures uniform and effective shielding.

[0085] Figure 10 The right side shows a schematic circuit diagram of the bridging circuit, which illustrates the electrical connections of the four TMR resistors R1, R2, R3, and R4. Resistors R1, R2, R3, and R4 are interconnected as a Wheatstone bridge, with R1 and R2 and R3 and R4 connected in series, respectively.

[0086] Embodiments of the present invention enable the expansion of the operating cross-field range of an OOP TMR sensor using a vortex sensor layer by reducing the effective, in-plane cross-field amplitude that affects the vortex during operation. This is achieved using offsetting scattered fields from adjacent soft magnetic structures in the micrometer range. These shields exhibit linear MH behavior according to their geometry and are capable of achieving a constant shielding factor over a wide field range. Shield 520 can be positioned at a short distance above and / or below the magnetic tunnel junction.

[0087] Suitable shielding materials are soft magnetic alloys, such as NiFe, which have saturation magnetization between 1 and 1.3 Tesla. A saturation field (a field above which the magnet is saturated and further shielding is no longer possible) can be established by M... sThe product of the shape and the demagnetizing factor, which depends on the shielding geometry, is approximated along the shielding axis 530. This shape-dependent demagnetizing factor is between 0 and 1. To maximize the demagnetizing factor and achieve a large shielding range, the shielding element, for example, should have a much larger extension perpendicular to the shielding axis 530 than its extension along the shielding axis (ratio > 4:1:1). A demagnetizing factor of ≈0.4 can be achieved using, for example, a ratio of 10:1:1. Alternative soft magnetic materials with different saturation magnetizations can also be used when the shape is adapted to the desired shielding range.

[0088] The shielding factor is scaled by the extension of the shield 520 along the shielding axis 530, and is therefore inversely proportional to the effective shielding range. Finite element simulations of the shield with a linear region of up to 0.5T show that a constant shielding factor of up to ≈10 can be achieved near the shield 520 (distance <1μm). The shielding factor is scaled by dividing by 1 from the distance to the shield 520. Therefore, tight integration is required. With a shielding factor of ≈10 for an IP cross-field up to ≈0.5T, a vortex disk with an inherent annihilation field well below 100mT can be used, while simultaneously covering an operating region up to ≈±0.5T.

[0089] The magnetic field emanating from shield 520 interacts with adjacent shields 520. Simulations show that this "crosstalk" can significantly reduce the effective range of the shields, thus requiring sufficient distance between shields 520. Therefore, the distance must be optimized to achieve the best results with minimal area consumption.

[0090] Alternatively, multiple shielding elements 520 can be used around the TMR layer stack. By using a crossbar scheme, it is possible to shield simultaneously along two intersecting directions (e.g., the x-direction and the y-direction). Here, the shielding element may have a first soft magnetic strip extending in parallel (e.g., in the x-direction) and a second soft magnetic strip extending in parallel (e.g., in the y-direction). The first and second strips intersect at right angles.

[0091] A second vortex of similar size directly beneath the layer stack 510 can also shield the IP cross-field, but only by a factor of 2 and only until the annihilation field of the vortex shield is reached. Therefore, the shield 520 can also be constructed as a disk shape with vortex magnetization. Combined with the upper strip shield, this can help keep the free layer 516 in a vortex state, which further increases the operating region for cross-field immunity, or significantly increases the degrees of freedom of the layer stack 510 and its design. Furthermore, z-sensitivity can be improved by linearly enhancing the z-field via the vortex shield.

[0092] In summary, the present invention 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 utilizes a combination of a reference layer with OOP magnetization and a free layer with vortex magnetization. A soft magnetic shield is positioned directly near the layer stack to reduce the influence of the external IP magnetic field by generating a reverse field within the soft magnetic shield. This maintains the stability of the vortex magnetization and improves the measurement accuracy of the sensor.

[0093] Examples include specific material choices and geometries for the soft magnetic shielding. The shielding is composed of an alloy, such as nickel-iron or cobalt-iron, and can be designed in the form of one or more cubes, wherein the shielding's extension perpendicular to the shielding axis is greater than its extension parallel to the shielding axis. This arrangement maximizes the efficiency of field compensation and ensures a uniform distribution of magnetism. In some variations, the shielding is positioned laterally beside or above / below the stack of layers to provide flexible integration possibilities and further optimize shielding performance. Another preferred option is a grid-like integration of multiple soft magnetic strips intersecting at right angles, thus enabling effective shielding in multiple directions.

[0094] The aspects and features described in the specific examples in the previous examples can also be combined with one or more other examples to replace the same or similar features of the other examples or to additionally import features into the other examples.

[0095] Furthermore, it should be understood that the disclosure of multiple steps, processes, operations, or functions in the specification or claims should not be designed to be mandatory in the described order, unless this is explicitly stated in individual cases or is absolutely necessary for technical reasons. Therefore, due to the foregoing description, the execution of multiple steps or functions is not limited to a specific order. Moreover, in other examples, a single step, single function, single process, or single operation may include and / or may disclose multiple sub-steps, sub-functions, sub-processes, or sub-operations.

[0096] If aspects have been described in conjunction with an apparatus or system in previous paragraphs, then these aspects can also be understood as descriptions of the corresponding methods. Here, the functional aspects of a block, apparatus, or apparatus or system may correspond, for example, to features of the corresponding method, such as method steps. Accordingly, aspects described in conjunction with a method can also be understood as descriptions of the characteristics or functional features of the corresponding block, element, apparatus, or system.

[0097] Therefore, the following claims are incorporated into the detailed description, where each claim may be presented as a separate example. It should also be noted that while dependent claims refer to a specific combination with one or more other claims, other examples may also include combinations of the subject matter of the dependent claim with each of the other dependent or independent claims. Such combinations are explicitly stated herein unless the specific combination is stated to be undesirable in individual cases. Furthermore, the features of a claim should also be included in any other independent claim, even if the claim is not directly defined as dependent on that other independent claim.

Claims

1. A magnetoresistive sensor (500), comprising: a layer stack (510) having: 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) having a vortex magnetization; and at least one soft magnetic shield (520) arranged adjacent to the layer stack, the soft magnetic shield being designed for reducing the influence of an external magnetic field on the free layer along a shield axis (530). The shield (520) is configured to generate a counter field depending on the external magnetic field. The shield (520) is arranged laterally adjacent to the layer stack (510).

2. The magnetoresistive sensor (500) according to claim 1, wherein The shield (520) is arranged above or below the layer stack (510).

3. The magnetoresistive sensor (500) according to any one of the preceding claims, wherein The extension of the shield (520) perpendicular to the shield axis (530) is larger than the extension of the shield parallel to the shield axis.

4. The magnetoresistive sensor (500) according to any one of the preceding claims, wherein The extension of the shield (520) perpendicular to the shield axis (530) is at least 4 times larger than the extension of the shield parallel to the shield axis.

5. The magnetoresistive sensor (500) according to any one of the preceding claims, wherein The material of the shield (520) comprises a nickel-iron alloy, a cobalt-iron alloy, a cobalt-nickel alloy or a silicon-iron alloy.

6. The magnetoresistive sensor (500) according to claim 5, wherein The saturation magnetization of the material of the shield (520) is in the range of 1-1.5 Tesla.

7. The magnetoresistive sensor (500) according to any one of the preceding claims, wherein At least one shield (520) is configured in a cuboid shape.

8. The magnetoresistive sensor (500) according to any one of the preceding claims, wherein The shield (520) has a first soft magnetic bar and a second soft magnetic bar, the first and the second soft magnetic bar intersecting at a right angle.

9. The magnetoresistive sensor (500) according to any one of the preceding claims, wherein The shield (520) has a plurality of soft magnetic bars arranged in parallel, wherein the bars have a longitudinal axis extending perpendicular or parallel to the shield axis (530), respectively.

10. The magnetoresistive sensor (500) according to any one of the preceding claims, wherein The distance between adjacent bars is larger than 5 pm.

11. The magnetoresistive sensor (500) according to any one of the preceding claims, wherein The shortest distance between the layer stack (510) and the shield (520) is in the range of 0.5-3 pm.

12. The magnetoresistive sensor (500) according to claim 11, wherein The layer stack (510) comprises a TMR layer stack.

13. The magnetoresistive sensor (500) according to any one of the preceding claims, wherein The layer stack (510) and the at least one shield (520) are arranged on a common die.

14. The magnetoresistive sensor (500) according to any one of the preceding claims, wherein 16. A bridge circuit (900) having a plurality of magnetoresistive sensors according to any of the preceding claims.

15. The magnetoresistive sensor (500) according to any one of the preceding claims, wherein ​ ​

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