Method and apparatus for sensing out-of-plane magnetic fields

Abstract

The present disclosure relates to methods and apparatus for sensing out-of-plane magnetic fields. A magnetoresistive sensor is provided for magnetic field sensing. The sensor includes a layer stack including a reference system having a fixed magnetization and a synthetic antiferromagnetic (SAF) free layer disposed adjacent the reference system. The SAF free layer includes first and second ferromagnetic layers each having a magnetic anisotropy oriented orthogonal to a direction of magnetization of the reference system, and a non-magnetic coupling layer interposed between the first and second ferromagnetic layers. The coupling layer is configured to antiferromagnetically couple the ferromagnetic layers via Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. Depending on the configuration, the sensor is sensitive to either an out-of-plane magnetic field component or an in-plane magnetic field component, while exhibiting low cross-field sensitivity. The SAF structure enables low noise operation with a net magnetization close to zero at zero field, supporting high linearity and direction robustness.

Description

Technical Field

[0001] This disclosure relates to magnetoresistive sensors, and more particularly, to sensors for detecting magnetic fields oriented perpendicular to the plane (e.g., out-of-plane) of a stacked layer. Background Technology

[0002] Magnetoresistive sensors, especially those based on the tunneling magnetoresistive (TMR) effect, can be used to measure external magnetic fields. To achieve a linear response to out-of-plane magnetic fields, a ferromagnetic sensing layer with an in-plane easy magnetization axis can be employed. However, the magnetization direction in such a layer is directly affected by the vector sum of the out-of-plane and in-plane magnetic field components, leading to significant cross-field sensitivity. This sensitivity can adversely affect measurement accuracy, especially when weak target signals must be detected in the presence of strong in-plane interference.

[0003] To reduce this sensitivity, vortex magnetization states have been explored. Vortex configurations, by deflecting the vortex core rather than altering the sensitive out-of-plane magnetization component, can provide a degree of inherent immunity to in-plane fields. However, under stronger in-plane fields, this state can become unstable, eventually collapsing into a homogeneous magnetization state, thus reintroducing cross-field sensitivity. Therefore, both conventional and vortex-based methods may exhibit limitations in terms of field robustness and operational stability.

[0004] Therefore, improvements may be needed in the structure of magnetoresistive sensors used for out-of-plane magnetic field detection, particularly by reducing sensitivity to interfering in-plane magnetic fields. The goal may be to enhance the robustness and accuracy of the sensor response in real-world environments while maintaining compatibility with compact integration and established thin-film processing technologies. Summary of the Invention

[0005] This requirement is addressed by the independent claim. Further embodiments are addressed by the dependent claims.

[0006] According to a first aspect, this disclosure relates to a magnetoresistive sensor for sensing out-of-plane magnetic fields. The sensor includes a stack of layers including a reference system exhibiting out-of-plane magnetization. Adjacent to the reference system, the sensor includes a synthetic antiferromagnetic (SAF) free layer. The SAF free layer includes a first ferromagnetic layer having good-plane anisotropy, a second ferromagnetic layer also having good-plane anisotropy, and a nonmagnetic coupling layer located between the first and second ferromagnetic layers. The good-plane anisotropy may originate from shape anisotropy due to dipole interactions. This anisotropy can be tuned by additional crystal out-of-plane or good-plane anisotropy. The nonmagnetic coupling layer is configured to antiferromagnetically couple the two ferromagnetic layers via Ruderman–Kittel–Kasuya–Yosida (RKKY) interactions.

[0007] This defines the basic architecture of the magnetoresistive sensor according to this disclosure. It specifies that the sensor is designed to measure a magnetic field oriented in a plane (out-of-plane) perpendicular to the sensor layer. The sensing element is formed of a multilayer structure. A reference system maintains a fixed out-of-plane magnetization and serves as a reference for detecting changes in the magnetization of the sensing layer. Adjacent to this reference, the sensor includes a SAF free layer comprising two ferromagnetic layers with preferred in-plane magnetization orientations (easy-plane anisotropy). These two ferromagnetic layers are separated by a thin nonmagnetic coupling layer, which is involved to induce antiferromagnetic interactions between them via an RKKY mechanism. Due to this coupling, the two magnetic layers tend to align their magnetization in opposite directions within the plane.

[0008] This sensor design provides a stable and low-noise platform for measuring magnetic fields perpendicular to the sensor plane. By using SAF as the free layer, the structure may be inherently less sensitive to in-plane magnetic fields because the antiparallel alignment of the magnetic layers tends to cancel out in-plane magnetic interference. RKKY coupling ensures strong and predictable antiferromagnetic alignment, thereby improving the thermal stability and magnetic stiffness of the sensing layer. Furthermore, easy-plane anisotropy can promote stable in-plane magnetization without an applied magnetic field, potentially leading to more predictable out-of-plane responses and enabling near-linear signal characteristics. Overall, this structure supports high accuracy and reliability in environments where external magnetic noise, especially from in-plane directions, can degrade performance.

[0009] In some embodiments, the magnetic anisotropy and magnetic moment of the first and second ferromagnetic layers are configured such that the net magnetization of the SAF free layer remains in-plane for any purely out-of-plane external magnetic field. When an external out-of-plane magnetic field H is applied... z At this time, the magnetization of two antiferromagnetically coupled objects can coherently move away from the plane, producing a net out-of-plane component, which varies with H. z Approximately linear increase, until the characteristic field H sat Above this level, SAF may be approaching saturation, where both magnetic moments are parallel to H. z Because of H z The generated in-plane torque is balanced by strong antiparallel coupling, and the free layer may remain insensitive to parasitic out-of-plane fields while providing a predictable, near-linear response to the desired out-of-plane components.

[0010] In some embodiments, the nonmagnetic coupling layer is composed of ruthenium, iridium, tantalum, tungsten, or a combination of these materials. This defines the material composition of the nonmagnetic coupling layer located between two ferromagnetic layers of the SAF free layer. The purpose of this layer is to mediate antiferromagnetic interactions between adjacent ferromagnetic layers. The specified materials—ruthenium, iridium, tantalum, and tungsten—are known to support RKKY-type coupling, which enables such antiferromagnetic alignment at nanometer or sub-nanometer spacing thicknesses. The selection of these specific elements may be based on their effectiveness in establishing stable and controllable coupling behavior in magnetic multilayer systems. Using these materials for the nonmagnetic coupling layer allows for precise control over the strength and nature of interlayer exchange interactions, which is crucial for maintaining antiferromagnetic alignment within the SAF structure. In particular, ruthenium and iridium can be used in high-performance magnetic tunnel junctions because they can induce strong and stable antiparallel alignment over ultrathin separations. This stability can enhance the magnetic reliability of the sensing layer under varying thermal and magnetic conditions. Additionally, the flexibility to select or combine different coupling materials enables process integration across different manufacturing platforms and facilitates material tuning to match specific sensor performance targets, such as desired coupling strength, thermal tolerance, or deposition compatibility.

[0011] In some embodiments, the first ferromagnetic layer of the synthesized antiferromagnetic free layer comprises a cobalt-iron-boron (CoFeB) and / or a cobalt-iron (CoFe) alloy. This specifies the material composition of the first ferromagnetic layer in the SAF free layer. It indicates that the layer is made of or at least comprises a CoFeB or CoFe alloy. These materials are commonly used in magnetoresistive devices, particularly in magnetic tunnel junctions, due to the advantageous combination of their soft magnetic properties and high spin polarization. The first ferromagnetic layer, adjacent to the tunnel barrier, can serve as a signal generation layer in a sensor by responding to an external magnetic field and modulating the resistance of the device through the tunneling magnetoresistive effect. The use of CoFeB or CoFe alloys in the first ferromagnetic layer can provide several benefits. These materials are known to have a high magnetoresistance ratio when used in conjunction with an MgO tunnel barrier, which can lead to improved signal amplitude and sensitivity in TMR sensors. They also exhibit low coercivity and good soft magnetic behavior, allowing for a dynamic and reversible response to an external magnetic field. Additionally, CoFeB, in particular, is amorphous during deposition and crystallizes during annealing in a manner that promotes excellent interface quality and magnetic homogeneity, which may contribute to enhanced device repeatability and reliability. Overall, the selection of these alloys enables robust and efficient magnetoresistive sensing, especially in harsh field environments or miniaturized device formats.

[0012] In some embodiments, the first ferromagnetic layer includes at least one additional element selected from the group consisting of iron (Fe), cobalt (Co), platinum (Pt), palladium (Pd), or nickel (Ni), wherein the at least one additional element is deposited on a CoFeB or CoFe alloy to modify the magnetocrystalline anisotropy and enable RKKY coupling. This can be achieved by introducing optional elements—i.e., Fe, Co, Pt, Pd, or Ni—to enhance the composition of the first ferromagnetic layer, which can be used as a capping layer or dopant in addition to the base CoFeB or CoFe alloy. These elements are known to affect key magnetic properties, such as magnetocrystalline anisotropy, which governs the preferred orientation of magnetic moments in the material. Adding these elements may also help achieve or enhance RKKY-mediated antiferromagnetic coupling between the first and second ferromagnetic layers by adjusting interface properties or magnetic moment balance. Such tuning may be necessary to achieve the desired magnetic response and coupling efficiency in a SAF configuration. By incorporating additional magnetic or noble metal elements into the first ferromagnetic layer, the anisotropy and magnetic moment of the signal layer can be finely tuned to meet the performance objectives of a specific application. For example, platinum and palladium are known to enhance perpendicular magnetic anisotropy at interfaces, which could be beneficial for sensors requiring precise out-of-plane response. Nickel-iron alloys can be used to reduce the forced field H. c This provides a soft magnetic response and improves the ease of coherent rotation under an external field at the target surface. Furthermore, including these elements optimizes coupling conditions with the non-magnetic spacer layer at the interface, thus supporting stronger and more stable RKKY interactions. In summary, this material flexibility improves the sensor's linearity, sensitivity, and cross-field robustness, while also allowing for enhanced process compatibility and repeatability during thin film deposition.

[0013] In some embodiments, the magnetoresistive sensor further includes a tunneling barrier inserted between the synthetic antiferromagnetic free layer and the reference system. This specifies that the magnetoresistive sensor may include a tunneling barrier located between the SAF free layer and the reference system. The tunneling barrier is a thin, non-conductive layer—typically made of a material such as magnesium oxide—that allows electrons to tunnel quantum mechanically between adjacent magnetic layers. This tunneling current is sensitive to the relative orientation of the magnetization in the free layer and the reference layer, resulting in the tunneling magnetoresistance (TMR) effect, the core sensing principle of many high-performance magnetic sensors. Including a tunneling barrier allows the sensor to operate based on the TMR effect, which can provide higher signal amplitude and sensitivity compared to other magnetoresistive effects such as giant magnetoresistance (GMR). The barrier allows spin-dependent tunneling, which can lead to significant resistance changes as the magnetization of the free layer and the reference layer switches between parallel and antiparallel configurations. This can result in improved signal-to-noise ratio (SNR) and higher accuracy in magnetic field detection. Furthermore, the use of a tunneling barrier can support scaling to very small sensor geometries while maintaining high output levels, which can be advantageous for integration into densely packed or miniaturized electronic systems.

[0014] In some embodiments, a tunneling barrier is specifically inserted between a first ferromagnetic layer and a reference system. The tunneling barrier can be placed between the first ferromagnetic layer (typically acting as a signal layer) and the reference system, which is part of a synthetic antiferromagnetic free layer. This means that the tunneling current, and thus the resulting magnetoresistive signal, is directly affected by the relative magnetization alignment between the reference system and the first ferromagnetic layer (located closest to the tunneling barrier). Placing the tunneling barrier between the first ferromagnetic layer and the reference system provides a well-defined and predictable tunneling interface, which is crucial for achieving high TMR performance. This configuration allows the magnetization of the first ferromagnetic layer in response to an external out-of-plane magnetic field to directly modulate the tunneling current. The resulting signal can be highly sensitive and directionally selective, as it is primarily controlled by the orientation of the signal layer relative to a fixed reference. Additionally, placing the tunneling barrier adjacent to a more carefully designed signal layer (typically optimized for specific anisotropy and spin polarization characteristics) can enhance the repeatability, symmetry, and linearity of the sensor response across a variety of operating conditions. This structure also simplifies the layer stack architecture and facilitates standard TMR fabrication processes.

[0015] In some embodiments, the magnetoresistive sensor further includes a conductive spacer layer inserted between the synthetic antiferromagnetic free layer and the reference system. This provides an alternative to the tunneling barrier configuration. A conductive spacer layer is used instead of a tunneling barrier to separate the synthetic antiferromagnetic free layer from the reference system. In this configuration, the sensor can operate based on the giant magnetoresistance (GMR) effect rather than the tunneling magnetoresistance (TMR) effect. In GMR-based devices, electron transport occurs via diffusion conduction through the conductive spacer layer, and the device resistance depends on spin-dependent scattering at the interface and within the magnetic layer. Using a conductive spacer layer instead of a tunneling barrier may offer certain advantages in terms of fabrication complexity and process compatibility. GMR structures typically do not require the precise control of the insulating layer thickness as TMR barriers, which can simplify fabrication and improve yield. Additionally, the conductive spacer layer may provide lower overall resistance and better thermal stability, which can be beneficial in high-current or high-temperature applications. This configuration may also be more tolerant of process variations, especially in applications where absolute sensitivity is less critical than robustness or integration with other circuit elements. Furthermore, the option to use either a tunnel barrier or a conductive spacer layer provides design flexibility, allowing the sensor architecture to be customized to different system requirements or constraints.

[0016] In some embodiments, the second ferromagnetic layer comprises a multilayer stack consisting of one or more layers selected from the group consisting of CoFe, CoNi, NiFe, CoB, CoFeB, or FeB, wherein the multilayer stack is configured to balance the magnetic moment of the first ferromagnetic layer. This focuses on the structure and function of the second ferromagnetic layer within the SAF free layer. It specifies that the second layer may consist of multiple sublayers—forming a multilayer stack—and may include materials such as cobalt iron (CoFe), cobalt nickel (CoNi), nickel iron (NiFe), cobalt boron (CoB), cobalt iron boron (CoFeB), or iron boron (FeB). In some embodiments, these multilayer structures may also be used for the first ferromagnetic layer. The purpose of this multilayer configuration is to magnetically balance the first ferromagnetic layer, which is adjacent to the tunnel barrier or conductive spacer and serves as a signal layer. This balancing effect involves both magnetic moment and anisotropic properties, ensuring that the entire SAF structure behaves as intended under an external field. Using a multilayer stack in the second ferromagnetic layer enables fine control over the total magnetic moment, anisotropy, and dynamic behavior of the SAF free layer. By carefully selecting and stacking materials with known magnetic properties, a second layer can be tailored to effectively counteract or compensate for the first layer, thereby achieving an optimized antiferromagnetic configuration. This balance can help tune the linear range, stabilize in-plane antiparallel alignment, enhance linearity in the out-of-plane response, and suppress unwanted cross-field sensitivity. Furthermore, some materials such as NiFe and CoFeB are known for their soft magnetic properties and ease of integration, while others, such as CoNi, offer higher magnetic stiffness or anisotropic tuning. Multilayer structures can also provide better thickness control, thermal stability, and compatibility with deposition processes used in modern MR sensor fabrication, potentially improving yield, repeatability, and long-term performance.

[0017] In some embodiments, the total thickness of the synthesized antiferromagnetic free layer is less than 10 nm, less than 8 nm, or even less than 6 nm. This imposes a constraint on the total physical thickness of the SAF free layer, which comprises two ferromagnetic layers and a nonmagnetic coupling layer between them. Specifically, the thickness of the entire SAF structure may be limited to less than 10 nm. This size requirement encompasses all constituent layers and indicates a highly miniaturized magnetic sensor architecture. Limiting the thickness of the SAF free layer to below 10 nm can provide several important benefits. First, production time (e.g., via sputtering) can be reduced, potentially reducing costs. Furthermore, it may enable the fabrication of ultra-compact sensor structures suitable for high-density integration, such as in system-on-chip applications or tightly packaged sensor arrays. Second, reducing the total magnetic volume can lower the energy required for coherent rotation, enabling faster, more energy-efficient switching. Third, thinner SAF structures may exhibit better control over coupling strength, particularly through RKKY interactions, which are most effective over sub-nanometer to nanometer distances. Furthermore, compact magnetic stacking can improve signal fidelity of TMR-based devices by reducing noise contributions and parasitic magnetic effects from thicker, more complex structures. Finally, maintaining such a thin profile may support process scalability and compatibility with standard back-end processes (BEOL) integration in semiconductor manufacturing.

[0018] In some embodiments, the thickness of the first ferromagnetic layer in the synthesis of the antiferromagnetic free layer is between 1 nm and 2 nm. This defines a specific thickness range for the first ferromagnetic layer, which may serve as a signal layer in the SAF free layer stack. Its fabrication thickness may be at least 1 nm but no more than 2 nm. This narrow range can be useful for both magnetic performance and compatibility with adjacent layers, particularly the tunneling barrier in a TMR configuration. By limiting the thickness of the first ferromagnetic layer to the range of 1 nm to 2 nm, sensor designs can achieve a good balance between magnetic signal strength, switching behavior, and coupling effectiveness. Layers thinner than 1 nm may suffer from discontinuities, reduced crystallinity, or suppressed magnetic moments, which could compromise the reliability and sensitivity of the device. Conversely, layers thicker than 2 nm may introduce excessive magnetic stiffness or undesirable stray fields, reducing the efficiency of RKKY coupling or disrupting the balance with the second ferromagnetic layer in the SAF stack. Maintaining this range may also enhance the spin polarization of tunneling electrons (in a TMR structure), thereby maximizing the magnetoresistance ratio. Furthermore, such a thin layer is compatible with modern deposition techniques such as sputtering or atomic layer deposition (ALD) and could potentially enable the realization of low-power, high-speed magnetic sensors for demanding applications.

[0019] In some embodiments, the SAF free layer is patterned into a circular or cylindrical geometry. This means that the layer is formed into a circular or cylindrical geometry, i.e., the lateral cross-section (viewed from above) of the layer is circular, and the vertical cross-section is uniform, forming a cylindrical shape. This geometric configuration can be applied to both planar and three-dimensional patterning processes during device fabrication. Patterning the SAF free layer into a circular or cylindrical shape can help suppress or eliminate unwanted shape anisotropy effects. Shape anisotropy arises from the geometric distribution of the magnetic material and can produce a preference for magnetization orientation, which can interfere with controlled switching behavior or introduce nonlinearity in the sensor response. Circular geometry provides rotational symmetry, meaning there is no preferred in-plane orientation for magnetization, which may allow the SAF to maintain a more uniform magnetic state. This can be particularly beneficial for sensors that must distinguish magnetic fields in out-of-plane directions without being affected by distortions or biases caused by lateral geometry. Additionally, cylindrical structures are well-suited for simulation, modeling, and process control, and can help optimize edge stability and reduce the risk of vortex nucleation or domain wall formation at boundaries. Overall, this shape may help achieve more predictable, stable, and linear sensor performance.

[0020] In some embodiments, the diameter of the circular or cylindrical SAF free layer is less than one micrometer. This introduces a dimensional constraint on the SAF free layer, particularly regarding its lateral dimensions. It requires that the diameter of the circular or cylindrical SAF structure be less than one micrometer (1µm). This constraint may apply to the entire sensor layout and may be particularly relevant to the scaling and integration of sensing elements in compact device architectures.

[0021] In some embodiments, the reference system includes a stack exhibiting perpendicular magnetic anisotropy (PMA). This stack may include one or more layers selected from the group consisting of cobalt / platinum (Co / Pt), nickel / platinum (Ni / Pt), cobalt / nickel (Co / Ni), gadolinium cobalt (GdCo), cobalt-chromium-platinum (CoCrPt), iron-platinum (FePt), or rare-earth-based alloys. This defines the structure and material composition of the reference system used in magnetoresistive sensors. The reference system serves as a magnetically fixed layer, against which changes in the magnetization of free layers are compared to generate a sensor signal. The reference system can be designed as a multilayer stack exhibiting perpendicular magnetic anisotropy (PMA), meaning the magnetization naturally aligns outside the film plane. Employing a stack with PMA in the reference system provides a stable and well-defined out-of-plane magnetization axis, which is necessary for accurate out-of-plane magnetic field sensing. The PMA structure is less prone to reorientation under in-plane magnetic fields, which may enhance signal stability and directional selectivity. The listed material systems combine high magnetic anisotropy with excellent thermal stability and resistance to external field disturbances. These materials may also support high spin polarization and good interface quality, which can help maximize magnetoresistive signals, especially in TMR-based designs. Alloys, including those based on rare earth elements, may offer extended temperature range performance and custom magnetic properties. Overall, this PMA reference stack can enhance the robustness, linearity, and sensitivity of the sensor while ensuring consistent performance under different operating conditions.

[0022] In some embodiments, the reference layer is magnetically pinned by exchange coupling it to an antiferromagnetic pinning layer. The pinning layer may comprise one or more antiferromagnetic materials selected from the group consisting of iridium manganese (IrMn), platinum manganese (PtMn), iron manganese (FeMn), nickel manganese (NiMn), nickel oxide (NiO), chromium oxide (Cr2O3), or combinations thereof. The antiferromagnetic pinning layer may be arranged adjacent to the reference layer—optionally separated by a thin underlayer or seed layer—to establish an exchange bias field, thereby fixing the magnetization direction of the reference layer along a perpendicular anisotropy axis. Coupled to this pinning layer, the reference layer improves thermal robustness, suppresses spontaneous reversals in external in-plane or oblique fields, and ensures a well-defined comparison axis for the SAF free layer. Exchange bias stabilization also enhances sensor linearity and minimizes offset drift, thereby supporting reliable out-of-plane magnetic field detection over extended temperature and field ranges.

[0023] In some embodiments, the layer stack of the magnetoresistive sensor includes exactly one reference system. This restricts the sensor configuration to include a single reference system within the magnetic layer stack. That is, only one magnetic element in the stack is fixed in its magnetization direction and serves as a reference for detecting changes in the magnetization of adjacent SAF free layers. There are no additional reference systems within the same layer stack. Utilizing only one reference system reduces structural and manufacturing complexity while still enabling accurate and reliable field sensing. This configuration can be particularly beneficial in applications with significant space, energy, or cost constraints. By eliminating the need for a second reference layer, the sensor architecture can be simplified, potentially resulting in thinner stacks and improved manufacturability. Furthermore, a single reference design can reduce internal magnetic interactions that could otherwise introduce signal ambiguity or unwanted coupling effects. This can make the response of the free layers to external surface fields more stable and isolated. Additionally, the absence of multiple competing reference axes can help maintain the desired directionality and linearity of the sensor output, which is particularly important for one-dimensional or uniaxial magnetic field detection.

[0024] In some embodiments, the magnetoresistive sensor further includes signal processing circuitry configured to measure changes in magnetoresistive resistance caused by rotation of the ferromagnetic layer at the tunnel barrier and output a signal indicating the strength of the out-of-plane magnetic field. This introduces a functional extension to the sensor by incorporating the signal processing circuitry. The circuitry is configured to detect changes in magnetoresistive resistance originating from the rotation of the magnetization vector in the ferromagnetic signal layer (i.e., the first ferromagnetic layer of the SAF free layer) in response to an external out-of-plane magnetic field. These magnetization changes, in turn, alter the relative alignment between the free layer and the reference layer and modulate the resistance across the tunnel barrier. The circuitry interprets these resistance changes and converts them into an output signal reflecting the amplitude of the external out-of-plane magnetic field. Integrating the signal processing circuitry into the sensor design enhances its usability and functionality. This integration allows for the real-time conversion of raw resistance changes into a calibrated output signal, enabling direct interface with microcontrollers, data acquisition systems, or digital logic. By measuring changes in magnetoresistive resistance at the tunnel barrier—where the signal layer is most sensitive to interaction with the reference system—the circuitry can produce high-precision and high-resolution magnetic field readings. Depending on the application, the circuitry can also implement linearization, filtering, temperature compensation, or offset correction. This internal signal conditioning simplifies external circuitry, reduces overall system cost, and improves signal integrity, especially in electromagnetically noisy environments. Furthermore, directly correlating the output with the out-of-plane magnetic field strength enables precise and directional magnetic field sensing in industrial, automotive, or consumer applications.

[0025] In some embodiments, the magnetoresistive sensor further includes at least one soft magnetic shield arranged adjacent to the layer stack and configured to reduce the influence of external magnetic fields along the shield axis on the free layer. This adds a passive field shaping component to the sensor architecture in the form of a soft magnetic shielding element. The shield is placed close to the magnetic layer stack—particularly near the SAF free layer—and oriented such that its influence is aligned along a specific direction (referred to here as the shield axis). The function of the shield is to reduce or suppress the influence of external magnetic fields along this axis before they arrive and interfere with the magnetization state of the free layer. Incorporating a soft magnetic shield adjacent to the sensing stack can significantly enhance the robustness of the sensor by mitigating the effects of parasitic magnetic fields, particularly in-plane cross fields that may distort the intended out-of-plane measurement. Soft magnetic materials such as permalloy (NiFe) are known for their high permeability, allowing them to attract and redirect magnetic field lines. By strategically placing such a shield near the sensor, interfering field components can be deflected away from the sensitive region, thereby maintaining the magnetic integrity and stability of the free layer. This can improve measurement accuracy, reduce noise, and prevent saturation or hysteresis effects in active sensing elements. Furthermore, this approach can be used as a passive, energy-free mechanism to increase the signal-to-noise ratio of sensors and extend their linear operating range, particularly in environments with strong or fluctuating magnetic interference. The concept also supports modular design strategies, where shielding performance can be tuned by selecting materials, geometry, and placement without altering the core sensor architecture.

[0026] In some embodiments, the shield is designed to generate a reverse magnetic field in response to an external magnetic field. This characterizes the functional behavior of the soft magnetic shield. It specifies that the shield is not merely a passive physical barrier, but is designed to actively respond to an external magnetic field by generating a magnetic field that is opposite in direction to the incident field. This reverse magnetic field is induced within the shielding material due to the high permeability of the shielding material and its interaction with the external magnetic flux. Its effect is to cancel and partially eliminate the magnetic field components that would otherwise act on the free layer (and reference layer) of the magnetoresistive sensor. Designing the shield to generate a reverse magnetic field provides a dynamic and self-regulating mechanism for mitigating unwanted magnetic interference. Unlike rigid or static shielding methods, this utilizes the inherent magnetic response of the shielding material to adaptively attenuate the external field. This reverse magnetic field can effectively neutralize or significantly reduce the net magnetic flux reaching the sensitive area of ​​the sensor, particularly along the shielding axis. This can help maintain the magnetization state of the synthetic antiferromagnetic free layer and reduce signal distortion caused by in-plane or tilted field components. In practice, such shielding can enable the sensor to operate reliably in environments with stronger electromagnetic noise, extend the operating range of the device, and maintain linearity and accuracy under conditions of strong or fluctuating fields. It can also reduce the need for software-based compensation or complex signal post-processing, thereby simplifying the overall system design.

[0027] In some embodiments, the shield is arranged laterally adjacent to the layer stack. This specifies the spatial arrangement of the shield relative to the sensor's magnetic layer stack. It states that the shield can be placed alongside the stack in the lateral direction, meaning it can be placed along the same plane as the thin film layers, or above or below them. Thus, depending on the sensor layout, the shield can be positioned along the x-axis or y-axis adjacent to the synthetic antiferromagnetic free layer and the reference system. Laterally placing the shield adjacent to the sensor's active layer stack can provide the purpose of suppressing magnetic field components propagating parallel to the sensor's plane—often referred to as in-plane cross fields. These in-plane fields can be particularly destructive in magnetoresistive sensors designed to detect out-of-plane magnetic field components, as they can inadvertently alter the magnetization of the free layer and reduce measurement accuracy. Lateral shielding arrangements can be used to intercept and redirect parasitic fields before they reach sensitive areas, thereby maintaining a stable and linear sensor response. Furthermore, lateral shielding can be implemented without significantly increasing the vertical height of the sensor, which can be advantageous for integration into planar chip designs and space-constrained applications. This configuration also simplifies the mechanical and process integration of the shield, allowing it to be patterned and deposited using standard photolithography or sputtering techniques along with the rest of the sensor structure.

[0028] In some embodiments, the shield is arranged above or below the layer stack. This describes an alternative or additional spatial arrangement of the magnetic shield in the sensor. Specifically, it states that the shield can be placed vertically relative to the magnetic layer stack of the sensor—either on top of the stack or below it—along a direction perpendicular to the layer plane. Placing the shield above or below the magnetic layer stack can provide enhanced protection against magnetic fields oriented perpendicular to the sensor plane or exhibiting complex three-dimensional field components. Such vertical shielding can be particularly effective in environments where the sources of magnetic interference are located out-of-plane (such as adjacent devices, power electronic equipment, or rotating machinery). Top or bottom placement of the shield can also work in conjunction with lateral shielding to form a closed or partially closed area around the sensing region, thus creating a more comprehensive shield profile. Additionally, this vertical configuration allows for greater freedom in tuning the effective shielding range by varying the vertical distance between the shield and the sensor or by stacking multiple shielding layers. From a manufacturing perspective, the top shield can be deposited after the sensor process without affecting the underlying quality, while the bottom shield can be integrated early in the process as part of the substrate or buffer layer design. This flexibility allows for various sensor packaging and system integration solutions while maintaining signal stability and measurement accuracy.

[0029] In some embodiments, the shield extends more perpendicular to the shield axis than it extends parallel to the shield axis. The shield may have an asymmetrical shape, where its physical dimension measured perpendicular to the shield axis is larger than its dimension measured parallel to the axis. The shield axis refers to the direction along which the external magnetic field to be suppressed is located. Therefore, the geometry may be intentionally designed such that the shield has a wider surface area in the direction orthogonal to the field it is to attenuate. Designing the shield to have a greater extension in the direction perpendicular to the shield axis can improve its ability to redirect or neutralize external magnetic fields that would otherwise reach the sensitive area of ​​the sensor. This geometry can enhance the demagnetizing effect, allowing the shielding material to more effectively concentrate and redirect magnetic field lines away from the synthetic antiferromagnetic free layer. Therefore, the influence of interfering fields along the shield axis can be significantly reduced. Furthermore, this configuration can generate a stronger reverse magnetic field across a larger area, improve the uniformity of field cancellation, and extend the protected area around the sensor. From a design perspective, this anisotropic geometry can be tailored to match the expected field distribution in a particular application, providing directional shielding without unnecessarily increasing material volume or sensor footprint. Ultimately, this can lead to improved signal integrity, lower cross-field sensitivity, and higher measurement accuracy, especially in applications with strong directional magnetic noise.

[0030] In some embodiments, the shield is cuboid in shape. A cuboid is a three-dimensional rectangular solid with planes and right angles, typically defined by three orthogonal linear dimensions (length, width, and height). In the context of sensor design, this means that the shielding element can be shaped as a block or brick with flat surfaces aligned along the principal axes (potentially corresponding to the orientation of the layer stack and the sensor substrate). The cuboid shielding shape can offer practical and functional benefits in magnetoresistive sensor design. Geometrically, cuboids are easy to fabricate using standard thin-film deposition and photolithographic patterning techniques, which can enhance manufacturing accuracy and repeatability. The straight edges and defined surfaces allow for predictable and uniform magnetic behavior, particularly in guiding and redirecting magnetic flux along desired paths. This regular shape also supports direct integration into chip-scale packages, allowing the shield to be neatly fixed next to or above the sensor components. Functionally, the planes of the cuboid can be well aligned with magnetic field lines in a controlled configuration, thereby optimizing the effectiveness of magnetic redirection or cancellation. Furthermore, the cuboid geometry can be easily scaled or stacked to tune the shielding strength or range, enabling it to accommodate different levels of field interference. In summary, cuboid shielding offers a balance of simplicity, effectiveness, and process compatibility, supporting stable and compact sensor architectures.

[0031] In some embodiments, the shielding includes a first and a second soft magnetic strip intersecting at right angles. This describes a composite configuration of the shielding system, comprising at least two independent soft magnetic strips. These strips are arranged to intersect each other orthogonally—i.e., at a 90-degree angle. This structural arrangement forms a cross-shaped or grid-like configuration, extending the shielding capability across two perpendicular directions. The strips themselves can be made of soft magnetic materials such as NiFe or CoFe alloys, which are known for their high permeability and low coercivity. The shielding structure consisting of two intersecting soft magnetic strips allows for effective suppression of magnetic fields in two orthogonal directions (typically corresponding to the two in-plane axes (x and y) of the sensor). Therefore, this cross-shaped configuration can enhance the sensor's immunity to multi-directional in-plane magnetic interference, which can be a source of measurement error in applications involving rotating machinery, current-carrying conductors, or variable magnetic environments. By providing bidirectional shielding, this structure can maintain the magnetization stability of the synthetic antiferromagnetic free layer more effectively than a single-strip configuration. Additionally, the right-angled arrangement can create overlapping magnetic field redirection regions, further improving the uniformity and strength of the shielding effect across the active region of the sensor. The design is also modular and scalable—additional orthogonal bars or layered meshes can be added to customize shielding performance for specific use cases. Overall, this approach leads to more robust sensor operation under real-world conditions with complex and fluctuating magnetic field vectors.

[0032] In some embodiments, the shielding comprises a plurality of parallel-arranged soft magnetic strips, each of which has a longitudinal axis extending either perpendicular to or parallel to the shielding axis. This describes a more complex and adaptable shielding arrangement that includes multiple soft magnetic strips, rather than just one or two. These soft magnetic strips are aligned parallel to each other, and their respective long axes (longitudinal axes) are oriented either parallel to or perpendicular to the defined shielding axis—the axis along which the shielding is intended to mitigate the effects of external magnetic fields. The orientation of the soft magnetic strips can be selected based on the dominant direction of the interfering field in the sensor's intended application environment. Arranging multiple soft magnetic strips in parallel can significantly enhance shielding effectiveness by expanding the spatial coverage and flux handling capability of the structure. When the longitudinal axes of the soft magnetic strips are aligned with or orthogonal to the shielding axis, they can be tuned to more effectively redirect or block specific components of the external magnetic field. For example, soft magnetic strips aligned perpendicular to the shielding axis can maximize flux deflection, while those aligned parallel to it help guide magnetic lines of force and generate a distributed reverse field. This structural flexibility allows for targeted optimization of the shielding for specific operating conditions, such as protection against dominant field noise in one direction or creating uniform protection within the sensor array. Furthermore, using multiple soft magnetic strips instead of a single monolithic shield reduces eddy current formation and thermal load, which can be beneficial in high-frequency or high-temperature environments. From a manufacturing perspective, the parallel strip array can be implemented using patterned deposition and etching techniques, supporting high-throughput, scalable fabrication. Overall, this approach leads to better control of cross-field interference and increases the sensor's robustness under complex magnetic loads.

[0033] In some embodiments, a system for magnetic field sensing is provided, wherein the system includes a magnetoresistive sensor according to any one of the foregoing embodiments and a control unit configured to process the output signal from the magnetoresistive sensor to determine the amplitude of the out-of-plane magnetic field while compensating for in-plane cross-field effects. This extends the scope from standalone sensor devices to integrated sensing systems. The system includes the magnetoresistive sensor as described in the foregoing embodiments and additionally includes a control unit. The control unit is responsible for processing the output signal generated by the sensor and performing two key functions: (1) determining the amplitude of the out-of-plane oriented magnetic field component, and (2) compensating for the effects of the in-plane magnetic field component that may distort or interfere with the desired out-of-plane field measurement. Integrating the magnetoresistive sensor with the control unit can enhance the functionality, accuracy, and adaptability of the overall sensing system. The control unit can implement algorithms or calibration routines that allow the system to isolate the out-of-plane magnetic signal from unwanted in-plane interference (often referred to as cross-field interference). This can be important in real-world environments where the magnetic field may vary unpredictably in multiple directions. By combining compensation techniques, such as mathematical correction, real-time feedback, or differential signal processing, the system can improve measurement fidelity and robustness. Additionally, the control unit can handle signal conditioning, filtering, linearization, and communication with external devices, thereby enabling seamless integration with larger electronic platforms, such as automotive control units, industrial controllers, or consumer electronics. This system-level claim also broadens the scope of application and protection, recognizing that the invention can function not only as a component but also as part of a complete, intelligent magnetic sensing solution.

[0034] According to another aspect, a method for sensing out-of-plane magnetic fields is provided. The method includes the steps of: providing a layer stack including exactly one reference system and a synthetic antiferromagnetic (SAF) free layer adjacent to the reference system. The SAF free layer includes a first ferromagnetic signal layer and a second ferromagnetic balance layer. These two layers are antiferromagnetically coupled via a nonmagnetic coupling layer, and each layer has a good-face anisotropy. The method also includes applying an external out-of-plane magnetic field to the SAF free layer and detecting a change in the magnetoresistance signal corresponding to a change in the out-of-plane magnetization of the SAF free layer. This defines a method describing how a sensor operates in practice to detect magnetic fields. The method begins by providing a specific physical configuration: a magnetic tunnel junction consisting of a single reference system and a SAF free layer made of two ferromagnetic layers with good-face anisotropy coupled via an RKKY mechanism. Once this structure is in place, the sensor is exposed to an external magnetic field of out-of-plane orientation of the layer stack. This field causes controlled rotation or reorientation of the magnetization within the SAF free layer. The key sensing mechanism detects this magnetic reorientation through changes in sensor resistance—specifically, changes in tunneling magnetoresistance (TMR) or giant magnetoresistance (GMR), depending on the implementation. The change in resistance is then used to determine the strength of the out-of-plane magnetic field. This method enables accurate and robust detection of magnetic fields perpendicular to the surface of the sensor structure. By using a free layer of SAF with antiferromagnetic coupling and in-plane anisotropy, this method minimizes the influence of in-plane cross-fields, which typically interfere with out-of-plane measurements. The resulting magnetoresistive signal is primarily governed by the out-of-plane component of the external magnetic field, resulting in a sharper, more linear response. Furthermore, using a single reference system and a tightly coupled SAF structure simplifies layer stacking and reduces complexity while maintaining directional sensitivity and high signal integrity. This method can be implemented in various sensor platforms, such as discrete devices or integrated systems, and can be used in applications requiring reliable, high-resolution magnetic field measurements in environments with magnetic noise or mechanical constraints.

[0035] According to another aspect, a magnetoresistive sensor for sensing in-plane magnetic fields is provided. The sensor includes a stack of layers, including a reference system having in-plane magnetization, and a free surface layer (SAF) disposed adjacent to the reference system. The SAF includes a first ferromagnetic layer having out-of-plane magnetic anisotropy, a second ferromagnetic layer also having out-of-plane magnetic anisotropy, and a non-magnetic coupling layer inserted between the first and second ferromagnetic layers. The non-magnetic coupling layer is configured to antiferromagnetically couple the first and second ferromagnetic layers via RKKY interactions.

[0036] This introduces an architecture mirroring the first aspect. Instead of being optimized to detect magnetic fields perpendicular to the plane of the layer (out-of-plane field), the sensor is designed to sense in-plane magnetic fields. In this configuration, the reference system has a fixed magnetization direction located within the sensor plane. In contrast, the SAF free layers—comprising ferromagnetic layers with out-of-plane magnetic anisotropy—whose magnetic states change in response to the target field, meaning that in the absence of external stimuli, their preferred magnetization direction is perpendicular to the plane. These two ferromagnetic layers are separated by a non-magnetic spacer layer that enables antiferromagnetic RKKY coupling, maintaining antiparallel alignment of their magnetizations under zero-field conditions. This configuration allows the SAF free layers to begin in a near-zero net magnetic state but respond in a controlled, linear manner when an external in-plane field is applied—resulting in a magnetization tilt that produces resistive modulation, the basis for sensing.

[0037] This sensor architecture provides robust and highly linear in-plane magnetic field sensing while maintaining low sensitivity to unwanted out-of-plane interference. The out-of-plane magnetic anisotropy in the free layer of the SAF stabilizes the initial antiparallel configuration of the SAF, keeping the net magnetization near zero in the absence of a signal field. This reduces magnetic noise, thermal drift, and residual bias. When an in-plane field is applied, the magnetization of the SAF layer may orderly tilt away from its equilibrium orientation, resulting in a measurable change in magnetoresistance. Using an out-of-plane layer with RKKY coupling for in-plane field sensing may also increase the sensor's stability and operating range, as the SAF structure can withstand stronger parasitic field components without transitioning to saturation or nonlinear states.

[0038] Therefore, this disclosure provides a magnetoresistive sensor for magnetic field sensing. The sensor includes a stack of layers, including a reference system with fixed magnetization and a free layer (SAF) disposed adjacent to the reference system. The SAF includes a first ferromagnetic layer and a second ferromagnetic layer, each having a magnetic anisotropy orientation orthogonal to the magnetization direction of the reference system, and a nonmagnetic coupling layer inserted between the first and second ferromagnetic layers. The coupling layer is configured to antiferromagnetically couple the ferromagnetic layers via Ruderman–Kittel–Kasuya–Yosida (RKKY) interactions. Depending on the configuration, the sensor is sensitive to either out-of-plane or in-plane magnetic field components while exhibiting low cross-field sensitivity. The SAF structure enables low-noise operation with near-zero net magnetization below zero field, supporting high linearity and directional robustness. Attached Figure Description

[0039] Examples of apparatuses and / or methods will be described below by way of example only and with reference to the accompanying drawings, wherein

[0040] Figure 1A schematic cross-sectional view of a magnetoresistive sensor for out-of-plane magnetic field sensing is shown, including the SAF free layer and a reference system with vertical magnetization;

[0041] Figure 2 Show Figure 1 An exploded and magnified view of the sensor's layer stack, illustrating an example material stack for the SAF free layer, reference layer, and hard magnetic pin structure;

[0042] Figure 3 The illustration shows a sensor arrangement including a Wheatstone bridge with four magnetoresistive resistors, each implemented using a SAF-based sensor, including a reference magnetization direction and optional soft magnetic shielding elements. It also illustrates the sensor layout on a substrate and an embodiment of a parallel soft magnetic shielding structure.

[0043] Figure 4 A schematic cross-sectional view of a magnetoresistive sensor for in-plane magnetic field sensing is shown, including the SAF free layer and a reference system with in-plane magnetization. Detailed Implementation

[0044] Some examples will now be described in more detail with reference to the accompanying drawings. However, other possible examples are not limited to the detailed features described in these embodiments. Other examples may include modifications of features, as well as equivalents and substitutions of features. Furthermore, the terminology used herein to describe certain examples should not limit other possible examples.

[0045] Throughout the description of the accompanying drawings, the same or similar reference numerals refer to the same or similar elements and / or features, which may be implemented identically or in modified form while providing the same or similar function. The thickness of lines, layers, and / or areas in the drawings may also be exaggerated for clarity.

[0046] When two elements A and B are combined using "or", this should be understood to disclose all possible combinations, i.e., only A, only B, and A and B, unless otherwise expressly specified in individual cases. As alternative wording for the same combination, "at least one of A and B" or "A and / or B" can be used. The same applies to combinations of more than two elements.

[0047] If the singular form, such as "a," "an," and "the," is used, and the use of only a single element is not explicitly or implicitly mandatory, then other examples may use multiple elements to achieve the same functionality. If the following describes the use of multiple elements to achieve a certain functionality, then other examples may use a single element or a single processing entity to achieve the same functionality. It is also understood that the terms "include," "including," "comprise," and / or "comprising," when used, describe the presence of the specified feature, integer, step, operation, process, element, component, and / or combination thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, processes, elements, components, and / or combinations thereof.

[0048] To achieve linear and robust out-of-plane (OOP) magnetic field sensors based on GMR or TMR effects, a sensing layer with minimal sensitivity to in-plane (IP) magnetic interference is required. Conventional approaches using ferromagnetic sensing layers with an in-plane easily magnetized axis typically exhibit significant cross-field sensitivity because their magnetization responds not only to the desired OOP field component but also to the IP magnetic field component. This leads to effect superposition and reduced measurement accuracy. Although vortex-based sensing layers can partially suppress this cross-sensitivity due to their localized core dynamics, they become unstable under elevated IP fields and tend to revert to a homogeneous state that is regeneratively sensitive to cross-field interference.

[0049] An alternative solution that maintains high linearity and robustness under in-plane magnetic disturbances involves using a synthetic antiferromagnetic (SAF) free layer, which comprises two in-plane magnetized ferromagnetic layers antiferromagnetically coupled. This configuration enables near-complete flux closure in the absence of an external field and significantly reduces the net magnetization of the sensing layer. Therefore, the SAF structure primarily responds to the OOP field component while exhibiting minimal response to the flat IP field, thus achieving the desired cross-field immunity.

[0050] Figure 1 An example of such a magnetoresistive sensor 100 is schematically illustrated for sensing a magnetic field oriented perpendicular to the plane of the magnetic layer stack, also known as out-of-plane magnetic field sensing.

[0051] Sensor 100 includes a layer stack 110 comprising a reference system 120 and a synthetic antiferromagnetic (SAF) free layer 130 configured adjacent to the reference system 120. The SAF free layer 130 comprises two ferromagnetic layers 132 and 136 separated by a nonmagnetic coupling layer 134. These layers are configured such that the magnetization of the ferromagnetic layers 132 and 136 lies in the (xy) plane and is antiparallel to each other, while the reference system 120 provides out-of-plane (z-direction) magnetization.

[0052] The sensor 100 is constructed as a vertical layered structure, wherein the layers are stacked 110 to form an active sensing element. The arrangement and magnetization orientation of the constituent layers are configured to enable the detection of out-of-plane magnetic field components (z-components) while minimizing the effects of in-plane magnetic interference.

[0053] The layer stack 110 comprises two main parts: a reference system 120 and a SAF free layer 130. In the illustrated embodiment, the reference system 120 is located below the free layer 130 and exhibits a fixed out-of-plane orientation magnetization, as indicated by the upward arrow. In various embodiments, the reference system 120 can be implemented using a multilayer stack with vertical magnetization, such as a synthetic antiferromagnet based on Co / Pt, Co / Ni, or FePt, or using a single ferromagnetic layer with high vertical anisotropy. The magnetization of the reference system 120 can be stabilized by exchanging bias, pinning layers, or interface anisotropy, ensuring its insensitivity to changes in external magnetic fields during operation.

[0054] In the illustrated embodiment, the SAF free layer 130 is disposed above the reference system 120 and includes a first ferromagnetic layer 132 and a second ferromagnetic layer 136. Both layers exhibit good-plane anisotropy, meaning their magnetic moments are preferably located in the (xy) plane of the layer. The order can also be reversed. In the absence of an external magnetic field, their magnetizations are antiparallel aligned to each other, as indicated by the opposite horizontal arrows. The materials used for these layers can include CoFeB, NiFe, or other soft magnetic alloys, and the thickness can be tailored to balance the magnetic moments and optimize the antiferromagnetic coupling strength.

[0055] Between ferromagnetic layers 132 and 136 is a nonmagnetic coupling layer 134. This layer is configured to facilitate antiferromagnetic coupling via RKKY interactions. Coupling layer 134 can be a metallic layer, such as composed of ruthenium, iridium, or other suitable elements known to support strong RKKY coupling when deposited at sub-nanometer thicknesses. This coupling ensures that the magnetization of the first ferromagnetic layer 132 and the second ferromagnetic layer 136 remains antiparallel under a wide range of external magnetic field conditions.

[0056] Since the antiparallel IP magnetizations of layers 132 and 136 cancel each other out, the total magnetization of the SAF free layer 130 is close to zero in the absence of an external field. When an external out-of-plane field is applied, it causes a differential tilt or skew in the magnetization, thereby altering the net magnetic moment along the reference magnetization direction in layer 120. This change results in a measurable change in the resistance of the magnetic tunnel junction (or other magnetoresistive configuration), which forms the basis of the sensing mechanism.

[0057] like Figure 1 As shown, layer 140 is disposed between the synthetic antiferromagnetic (SAF) free layer 130 and the reference system 120, and forms a functional interface between the two magnetic structures within the layer stack 110 of the magnetoresistive sensor 100. According to specific embodiments, layer 140 can be used for different roles:

[0058] In one embodiment, layer 140 is a tunneling barrier. The tunneling barrier 140 is electrically insulating and configured to allow spin-dependent electron tunneling between the SAF free layer 130 and the reference system 120. In this configuration, the magnetoresistive sensor 100 operates based on the tunneling magnetoresistive (TMR) effect. The sensor's resistance varies with the relative magnetization orientation of the SAF free layer 130 and the reference system 120.

[0059] The tunneling barrier 140 is specifically positioned between the first ferromagnetic layer 132 of the SAF free layer 130 and the reference system 120. This means that the magnetic moment of the first ferromagnetic layer 132 directly affects the tunneling current across the barrier, and thus the sensor signal. Materials commonly used for such tunneling barriers include magnesium oxide (MgO), aluminum oxide (Al2O3), or similar high-resistivity insulators with good spin filtering properties. The thickness of the tunneling barrier, which may be in the range of 1–2 nanometers, is optimized to balance the tunneling probability and magnetoresistive contrast.

[0060] In another embodiment, layer 140 may be a conductive spacer layer. In this configuration, the sensor operates based on the giant magnetoresistance (GMR) effect, where electron transport occurs through a conductive medium and the resistance depends on spin-dependent scattering. When implemented as a conductive spacer layer, the material of layer 140 may be selected from nonmagnetic metals such as copper (Cu), silver (Ag), or chromium (Cr), typically a few nanometers thick, to ensure efficient current transport and spin coherence.

[0061] This GMR type embodiment can be selected when lower resistance or improved thermal stability is desired, or when process integration and existing semiconductor technologies tend to use metal spacers rather than tunnel barriers.

[0062] exist Figure 1 In the magnetoresistive sensor 100 shown, the first ferromagnetic layer 132 of the SAF free layer 130 can serve as a signal layer, while the second ferromagnetic layer 136 can serve as a balance layer.

[0063] The first ferromagnetic layer 132 is positioned adjacent to a tunneling barrier 140 (or, alternatively, a conductive spacer layer), which separates it from the reference system 120. Due to this placement, the magnetization of layer 132 directly interacts with the reference magnetization across the interface. In the TMR implementation, this interaction governs the tunneling probability of spin-polarized electrons; in the GMR structure, it determines the degree of spin-dependent scattering. In both cases, the magnetization direction of layer 132 produces a measurable change in resistance in response to a change in the external magnetic field.

[0064] Therefore, the first ferromagnetic layer 132 serves as a signal generation layer. It is part of the free layer system 130, whose magnetic state is actively modulated by the sensed field (typically an out-of-plane component), and whose alignment with the reference system 120 controls the output signal of the sensor 100. Thus, the magnetic response of this layer can be designed to be highly sensitive, linear, and repeatable within the desired sensing range.

[0065] The second ferromagnetic layer 136 is located on the opposite side of the nonmagnetic coupling layer 134, further away from the reference system 120. Although it may carry current along with the rest of the free layer, its magnetization is not directly coupled to the tunnel barrier and therefore does not contribute to the magnetoresistance signal; instead, it is primarily used to magnetically balance the first ferromagnetic layer 132 via antiparallel RKKY coupling.

[0066] The balancing layer 136 serves multiple purposes: it minimizes the net magnetic moment of the SAF free layer 130 in the absence of external fields, thereby reducing magnetic noise and bias. It increases the magnetic stiffness of the system, improving the stability of the antiparallel configuration. It allows the SAF structure to resist parasitic in-plane fields and maintain its initial state, thus reducing cross-field sensitivity and enhancing robustness.

[0067] Since layer 136 is magnetically active but does not directly contribute to the sensor output, it can be optimized independently—for example, by adjusting its thickness, anisotropy, or saturation magnetization—to ensure effective compensation without affecting the signal characteristics of layer 132.

[0068] The explicit functional division between signal layer 132 and balancing layer 136 forms the basis for the operation of the SAF-based magnetoresistive sensor. This allows the sensor to maintain: sensitivity to out-of-plane magnetic fields, due to the direct modulation of signal layer 132 near the tunnel barrier 140; low sensitivity to in-plane cross-fields, due to the symmetric and antiparallel configuration of the SAF; and excellent linearity and repeatability, as only one layer contributes the signal while the other provides passive stabilization. This architecture combines the benefits of low magnetic noise, high directivity, and predictable, quasi-linear rotation of free-layer magnetization, making it suitable for applications requiring accurate and robust out-of-plane field detection.

[0069] Figure 1 The SAF free layer 130 shown is a system whose simplest form comprises two ferromagnetic layers 132 and 136 separated by a nonmagnetic spacer layer 134. These two ferromagnetic layers are antiferromagnetically coupled to each other via RKKY interactions. This interaction represents a form of indirect exchange coupling mediated by conduction electrons in a very thin metallic spacer (typically only a few angstroms thick). Suitable materials for the coupling layer 134 include, for example, ruthenium, iridium, or other metals known to support antiferromagnetic coupling at atomic-scale distances.

[0070] In this configuration, the magnetic behavior of the free layer 130 is governed not only by an externally applied magnetic field but also by the internal exchange force generated by RKKY coupling and the shape anisotropy of the individual ferromagnetic layers. The first ferromagnetic layer 132, adjacent to the tunnel barrier 140, acts as the signal layer. Its magnetization direction determines the tunneling resistance relative to the fixed out-of-plane magnetization direction of the reference system 120. The second ferromagnetic layer 136 acts as the balancing layer. Due to antiferromagnetic RKKY interactions, its magnetization is antiparallel to that of the signal layer. The combination of these two layers in an antiparallel configuration creates a net magnetic moment close to zero in the absence of an external field, thereby suppressing magnetic noise and parasitic self-fields.

[0071] For the SAF structure to operate effectively in out-of-plane field sensing, specific requirements may need to be met. The signal layer 132 can be formed from a material composition and thickness suitable for supporting strong TMR effects. Furthermore, the combination of the signal layer 132 and the balancing layer 136 should exhibit sufficient out-of-plane field sensitivity while maintaining a linear response across the relevant field range. To suppress undesirable responses to in-plane cross fields, the anisotropy and saturation magnetization of the two layers should be matched or intentionally offset to create a well-compensated system.

[0072] When an external in-plane magnetic field is applied, the magnetization of both ferromagnetic layers 132 and 136 is subjected to a torque that tends to align them with the field direction. However, the antiferromagnetic RKKY coupling counteracts this tendency, maintaining antiparallel alignment. The result is a dynamic equilibrium where the magnetization of layers 132 and 136 is tilted only slightly toward the magnetic field direction, while remaining largely antiparallel. The strength of the internal RKKY coupling determines how large an external field is required to overcome this equilibrium. Depending on the material parameters, this can lead to a highly stable magnetization response to in-plane perturbations. In some cases, the system's energy minimum tends towards uniform antiparallel magnetization; in others, it may lead to the formation of antiferromagnetic domain structures.

[0073] In the case of an out-of-plane magnetic field, the magnetization behavior of the SAF free layer 130 is similar to that of a single ferromagnet with easy-plane anisotropy. The RKKY interaction contributes an effective anisotropy term, resisting out-of-plane alignment. As the applied out-of-plane field strength increases, the magnetization vectors of the two ferromagnetic layers 132 and 136 begin to gradually tilt out of the plane. This transition does not occur abruptly but proceeds continuously as a function of the magnetic field strength. The effective anisotropy field that must be overcome to achieve SAF saturation can be described as the intrinsic anisotropy field H. k Coupled with twice the RKKY coupling field H RKKY The sum of these. The resulting out-of-plane component M of the net magnetization. z As the applied field H z The function can be analytically described as:

[0074] J s J represents the saturation polarization intensity of the ferromagnetic material, t represents the layer thickness, and J RKKY This represents the strength of the antiferromagnetic exchange coupling. For thin film geometries with interface or bulk-driven vertical anisotropy K1, the effective anisotropy K is... eff It can be approximated as:

[0075] In some embodiments, K eff It can take a negative value, indicating that the system has easy-surface anisotropy. This means that, in the absence of an external field, the magnetization vector is confined within the plane of the layer and has no perpendicular (z-direction) component. J RKKY The negative value of M ensures antiparallel coupling between the two layers. Under these conditions, and when the magnetic properties are well balanced, M z With H z The relationship between them becomes almost linear, which is ideal for precision sensing applications.

[0076] Conventional ferromagnetic sensing layers respond to external fields by tilting their magnetization toward the field direction to minimize their Zeeman energy. In contrast, the SAF free layer 130, due to its antiferromagnetic coupling, can partially or completely resist this tilt, depending on the material design. By carefully selecting the saturation magnetization, anisotropy, and thickness of the constituent layers, the SAF free layer can be designed to exhibit minimal sensitivity to in-plane magnetic fields while still maintaining the out-of-plane component of the response. This behavior is confirmed by example simulation data showing that in-plane fields up to approximately 500 mT have almost no effect on the out-of-plane response. Only near the exchange field threshold (typically around 550 mT) does the in-plane field begin to significantly interfere with magnetization alignment.

[0077] Both experimental measurements and micromagnetic simulations indicate that the out-of-plane magnetization component M... z The magnetization remains essentially constant. Although signal layer 132 and balance layer 136 exhibit slightly different individual hysteresis loops, their antiparallel coupling allows the net magnetization of the SAF to remain highly stable throughout the entire expected operating window. z The variation remains below approximately 1% of the saturation value. These results demonstrate the strong immunity of the free layer to in-plane parasitic excitations and confirm the sensor's broad resistance to cross-field interference.

[0078] The aforementioned SAF free-layer architecture provides a robust platform for out-of-plane magnetic field sensing and is inherently insensitive to parasitic in-plane fields. The ability to achieve high RKKY coupling strength (up to 1 T in some material systems) allows the SAF to maintain performance even in stray field environments exceeding 100 mT. Furthermore, the total thickness of the SAF free layer 130 can be maintained in the nanometer range (e.g., <10 nm), making it significantly more compact and cost-effective than vortex-based alternatives, which typically require thicker structures to achieve similar field robustness. Importantly, the sensing behavior of the SAF is independent of lateral dimensions, meaning that submicron feature sizes are not required to maintain sensor performance. This enables easy integration into semiconductor processes and supports high-yield, scalable sensor fabrication.

[0079] Figure 2 An exploded and schematic diagram of a magnetoresistive sensor 100 according to an embodiment of the present disclosure is shown. The diagram provides a functional breakdown of the layer stack 110, focusing on the structure and material composition of the SAF free layer 130, the reference system 120, and individual magnetic sub-components including the signal layer 132, the balancing layer 136, and the tunnel barrier 140. Additionally, Figure 2 The example also highlights the layered material stacks associated with these sub-components, including a hard magnetic pinning system.

[0080] The SAF free layer 130 comprises a signal layer 132 and a balancing layer 136, which are antiferromagnetically coupled across a thin, nonmagnetic coupling layer 134, shown herein as being formed of ruthenium (Ru). The coupling layer 134 is designed to mediate the RKKY interaction between the ferromagnetic layers 132 and 136. The magnetic moments of the two ferromagnetic layers 132 and 136 are antiparallel aligned, as indicated by opposite arrows in the schematic diagram, thereby forming a compensated SAF structure. The SAF free layer 130 is magnetically responsive and is configured to modulate the magnetoresistance of the sensor in response to an external surface field by changing the relative alignment of its constituent magnetizations.

[0081] Signal layer 132 is a ferromagnetic layer located adjacent to tunnel barrier 140. In this configuration, it acts as the active layer in the TMR stack. In one or more embodiments, signal layer 132 comprises a thin-film structure including one or more of Co, CoFeB, and MgO, optionally having a multilayer structure for enhanced anisotropy, such as Pt / Co, Pd / Co, or Co / Ni. The total thickness of the magnetic stack of signal layer 132 may be in the range of 1-5 nanometers, a range that maximizes the TMR ratio while allowing designers to adjust the effective anisotropy and saturation magnetic moment of the layers as needed. As shown in the enlarged structure, signal layer 132 comprises a multilayer stack, from bottom to top: an MgO layer (tunnel barrier 140), a CoFeB alloy layer, and a Co layer, covered by a Ru layer (coupling layer 134). The magnetic and structural configuration of signal layer 132 is selected to provide strong spin polarization, vertical anisotropy, and efficient TMR performance when placed adjacent to tunnel barrier 140.

[0082] A balancing layer 136 is located above the signal layer 132 and the coupling layer 134 to magnetically cancel out the signal layer 132. Because it does not directly contact the tunnel barrier 140, the balancing layer 136 can offer greater flexibility in terms of thickness and material composition. It can comprise multiple layers of Co, CoFeB, MgO, or other ferromagnetic materials, and can also be capped or seeded to tune its magnetic moment, anisotropy, and dynamic behavior. The balancing layer 136 is shown in an enlarged structure; in one embodiment, it comprises a multilayer stack formed on top of the ruthenium (Ru) coupling layer 134. This magnetic stack includes a ferromagnetic Co layer, a CoFeB alloy layer, and an MgO capping layer. The Co and CoFeB layers are configured to provide the magnetic moment and anisotropic properties required to compensate for the signal layer 132, while the MgO layer can be used as a capping or diffusion barrier. The Ru layer 134 enables antiferromagnetic RKKY coupling with the adjacent signal layer 132 via the coupling layer 134. In this configuration, the balancing layer 136 is magnetically active but electrically decoupled from the tunnel barrier 140.

[0083] In some embodiments, the balancing layer 136 can be fabricated using a layer stack that is substantially similar—or even nominally identical—to the stack used for the signal layer 132. Employing the same material sequence (e.g., a CoFeB / Co interface layer on the MgO side, optional Pt / Co or Co / Ni anisotropic auxiliary multilayers, and comparable total thickness) simplifies deposition and patterning, as both ferromagnetic layers can be grown in a single run with the same sputtering target and process conditions. Using a matched stack also facilitates accurate magnetic compensation: a robust antiparallel configuration can be forced through antiferromagnetic RKKY coupling at spacing 134, with a net in-plane magnetic moment close to zero, maximizing cross-field immunity without extensive individual tuning of layer thickness or composition.

[0084] A tunneling barrier 140 is disposed between the SAF free layer 130 and the reference system 120. The tunneling barrier 140 typically comprises MgO or Al₂O₃ and serves to electrically separate the SAF from the reference while allowing spin-polarized tunneling. Its thickness may be in the range of 1-2 nm, and its quality determines the TMR ratio and spin filtering efficiency. In some embodiments, layer 140 may be a conductive spacer layer, which is suitable for GMR configurations.

[0085] The reference system 120 includes a multilayer stack including a hard magnetic pin structure 122, a reference layer 126 having perpendicular magnetic anisotropy, and an MgO tunnel barrier 140 disposed on top of the reference layer 126. These elements are arranged vertically in the following order: hard layer 122, coupling layer 124, reference layer 126, and tunnel barrier 140.

[0086] Hard layer 122 can be a SAF structure configured to stabilize the magnetic orientation of reference layer 126. As shown in the enlarged structure, hard layer 122 can comprise a multilayer stack of alternating Pt and Co layers, designed to generate strong perpendicular magnetic anisotropy (PMA). To reinforce pinning, an antiferromagnetic exchange bias layer—such as PtMn, IrMn, MnN, or MnNb—can be added below (between the seed and the SAF) or above (between the SAF and the Ru spacer 124). The antiferromagnetic material establishes a robust out-of-plane exchange bias and also prevents spontaneous reversal of the hard layer. This stack can be formed on the seed layer, which can promote the desired crystal texture and interface quality. The stack can be terminated by a ruthenium (Ru) spacer, which acts as a coupling layer 124 and mediates RKKY antiferromagnetic coupling with the overlying reference layer 126. The magnetization direction of hard layer 122 is oriented in the out-of-plane direction, as indicated by the downward arrow.

[0087] A reference layer 126 is disposed above the coupling layer 124 (away from the film substrate) and forms the magnetic fixing element of the magnetoresistive sensor, against which the magnetization of the free layer 130 is compared. In other embodiments, the reference layer 126 is disposed below the coupling layer (closer to the film substrate).

[0088] As shown in the enlarged structure, the stacked layers, from bottom to top, include: a Ru interface layer, a Pt / Co multilayer for ensuring strong PMA, a CoFeB layer acting as a spin-polarized tunneling electrode, and a top MgO layer serving as a tunneling barrier 140. The Pt / Co multilayer structure provides thermal stability and high coercivity, ensuring that magnetization remains constant under operating conditions. The CoFeB layer ensures efficient spin polarization for tunneling electrons, and the MgO barrier enables the TMR effect by allowing spin-correlated tunneling into adjacent signal layers.

[0089] The Ru coupling layer 124 can provide an antiferromagnetic exchange interaction between the hard magnetic layer 122 and the reference layer 126, resulting in a synthetic antiferromagnetic structure to minimize the net stray field and potentially improve thermal robustness. The coupling strength and the relative thickness of the Pt / Co layers in 122 and 126 can be selected so that the magnetization of the reference layer 126 can be reliably pinned even in the presence of strong external magnetic fields or thermal perturbations.

[0090] A MgO tunneling barrier 140 is disposed on top of a reference layer 126 and interfaces with a signal layer 132 of the SAF free layer. In other embodiments, a reference layer is disposed on top of the tunneling barrier. The MgO layer enables tunneling magnetoresistive effects by filtering based on electron spin direction and forming the basis of a resistance modulation mechanism in the sensor.

[0091] In this configuration, the reference system 120 as a whole can form a highly stable and direction-selective magnetic structure. Due to the SAF-based pinning and PMA characteristics of the constituent layers, it can accurately sense out-of-plane magnetic fields while providing excellent thermal and magnetic stability.

[0092] Figure 3 The figure illustrates different aspects of sensor arrangement, including a Wheatstone bridge configuration with a magnetoresistive sensor element 100 implemented using a stack of synthetic antiferromagnetic layers. The figure also shows the integration of the sensing elements on a common substrate and the use of soft magnetic shielding to improve immunity to cross-field interference.

[0093] exist Figure 3 On the left, a Wheatstone bridge circuit is shown, including four resistors labeled R1 to R4. Each resistor R1-R4 can be implemented as a magnetoresistive sensor element 100, which includes a multilayer structure with a SAF free layer 130 and a fixed reference layer system 120. The bridge is controlled by a voltage V. DD Power supply, and provides two output voltages V O1 and V O2 Used for differential sensing. The bridge is applied in the out-of-plane direction (by H). OOP (This indicates) sensitivity to magnetic fields.

[0094] Each sensor element 100 within the bridge includes a reference system 120 with a fixed out-of-plane magnetization direction. As indicated by the arrows, the reference magnetization differs between the individual resistors: resistors R1 and R4 have a downward-pointing reference magnetization, while resistors R2 and R3 have an upward-pointing reference magnetization. This opposite reference configuration allows for the use of out-of-plane magnetic fields H. OOPThe differential response. When a field is applied, the relative alignment between the signal layer 132 and the reference layer 120 in each sensor element 100 changes differently depending on the reference magnetization direction. This design improves the symmetry and sensitivity of the Wheatstone bridge, and enhances linearity and immunity to common-mode interference.

[0095] exist Figure 3 The upper right portion shows four magnetoresistive sensors R1 to R4 integrated into a planar layout on a common substrate. Sensor elements 100 are placed in a 2x2 array, with each unit comprising a layer stack 110 as described previously. This illustration demonstrates the monolithic integration of the entire bridge circuit into a single chip or die, facilitating compact packaging and consistent field exposure across the sensing element.

[0096] exist Figure 3 The lower right portion illustrates an embodiment that also includes a soft magnetic shield 300. The shield 300 is arranged adjacent to the corresponding layer stack 110 of sensors R1-R4 and is configured to reduce the effect of external magnetic fields along the shield axis on the corresponding free layer 130 of each sensor. In the illustrated embodiment, the shield 300 comprises a plurality of elongated shielding strips formed of a soft magnetic material. These strips are oriented parallel to each other and are placed laterally above or adjacent to the sensors, enabling them to redirect or attenuate unwanted magnetic field components that are misaligned with the sensing direction (e.g., in-plane parasitic fields).

[0097] The shield 300 can be implemented in different configurations. In some embodiments, the soft magnetic shield is formed of a high-permeability material (such as a NiFe or CoFe alloy) and can consist of a single or multiple parallel strips. Depending on the predominant direction of the expected cross-field interference, the longitudinal axis of the shielding element can extend parallel or perpendicular to the shielding axis. In some variations, the shielding strips can be aligned in a cross configuration, where the first and second sets of strips intersect at right angles to provide bidirectional shielding in both the x and y directions.

[0098] The placement of the shield 300 can also vary. In some embodiments, the shield is placed laterally next to the layer stack 110. In other embodiments, the shield is placed vertically above or below the sensor element, for example, embedded within a package or deposited in a subsequent metallization layer. The shielding strip can have an elongated or cuboid geometry with an extension perpendicular to the shielding axis that is greater than the extension parallel to the shielding axis, thereby maximizing flux guiding and shielding effectiveness.

[0099] In this configuration, the shield 300 serves to reduce the effective parasitic magnetic flux reaching the sensitive region of the free layer 130 while maintaining the desired out-of-plane magnetic field sensitivity. This improves the cross-field robustness of the bridge circuit and ensures more accurate and stable sensor output in disturbed or noisy magnetic field environments.

[0100] Figure 4 The illustration schematically depicts an example of a magnetoresistive sensor 400, configured to sense magnetic fields oriented within the plane of a magnetic stack (in-plane magnetic field sensing), and... Figure 1 The out-of-plane sensing structure shown is the opposite. The magnetoresistive sensor 400 includes a layer stack 110, including a SAF free layer 130 and a reference system 120 disposed adjacent to the SAF free layer.

[0101] and Figure 1 The configuration shown is the opposite. Figure 4 The reference system 120 is characterized by in-plane magnetization, as indicated by the arrow pointing to the right. This orientation alignment establishes the sensor's sensitivity axis within the plane of the stacked layers, thereby enabling the detection of magnetic field components parallel to the plane, i.e., along the x-axis or y-axis.

[0102] The SAF free layer 130 includes a first ferromagnetic layer 132, a second ferromagnetic layer 136, and a nonmagnetic coupling layer 134 inserted therebetween. Both ferromagnetic layers 132 and 136 exhibit out-of-plane magnetic anisotropy, as indicated by vertical arrows pointing in opposite directions. This means that, in the absence of an external magnetic field, the magnetization vectors of layers 132 and 136 are antiparallel aligned along the z-axis. This antiparallel configuration is stabilized by the nonmagnetic coupling layer 134, which is configured to mediate antiferromagnetic coupling via RKKY interactions.

[0103] Due to out-of-plane anisotropy and antiferromagnetic coupling, the SAF free layer 130 has a net magnetization close to zero in a static state. However, when an external in-plane magnetic field is applied, the magnetization vectors of the ferromagnetic layers 132 and 136 tilt away from their original vertical orientation toward the in-plane direction. This tilt occurs in a coupled, symmetrical manner due to RKKY interactions, resulting in measurable resistance modulation via magnetoresistive effects (which, depending on the implementation, may be TMR or GMR). The net magnetization projection along the reference magnetization (in-plane) increases with the applied field strength, thus forming the basis of the sensing signal.

[0104] This architecture is relative to Figure 1 The out-of-plane sensing structure shown represents a mirror configuration. Figure 1 In the embodiments, the SAF free layer 130 has in-plane anisotropy and responds to external magnetic fields, while Figure 4 In the embodiments described, the SAF free layer is out-of-plane anisotropic and responds to in-plane magnetic fields. In both cases, the SAF structure ensures high magnetic stability and cross-field immunity because only the desired component of the external magnetic field will cause a deviation from the antiparallel baseline configuration.

[0105] Figure 4The vertical magnetization states of the middle layers 132 and 136, combined with the in-plane magnetization of the reference system 120, result in a device that is selectively sensitive to the transverse field components and resistant to parasitic out-of-plane interference. This configuration may be particularly advantageous in applications requiring in-plane spatial or directional field resolution and high immunity to background field noise.

[0106] The described structures, including the synthetic antiferromagnetic free layer, reference system, and optional shielding configuration, can be applied to a wide range of magnetic field sensing applications, including but not limited to position detection, current sensing, and rotation coding. The concepts presented herein support miniaturized, low-noise, and cross-field-resistant sensor architectures that can be easily integrated into monolithic or system-level solutions. While specific materials and geometries are disclosed, alternative implementations using equivalent materials or geometries are also included within the scope of this disclosure.

[0107] Aspects and features described in any of the previous examples may also be combined with one or more other examples to replace the same or similar features of those other examples, or to append the feature to those other examples.

[0108] It is also understood that, unless explicitly stated in individual cases or necessary for technical reasons, the steps, processes, operations, or functions disclosed in the specification or claims should not be construed as implying that these operations necessarily depend on the described order. Therefore, the preceding description does not limit the execution of steps or functions to a particular order. Furthermore, in other examples, a single step, function, process, or operation may include and / or be decomposed into several sub-steps, sub-functions, sub-processes, or sub-operations.

[0109] If certain aspects are described in relation to a device or system, these aspects should also be understood as descriptions of the corresponding methods. For example, a block, device, or functional aspect of a device or system may correspond to a feature of the corresponding method, such as method steps. Accordingly, aspects describing a method should also be understood as corresponding blocks, elements, attributes, or functional features of the corresponding device, or descriptions of the corresponding system.

[0110] The following claims are incorporated herein by reference, each of which may stand alone as a separate example. It should also be noted that although in the claims, dependent claims relate to a particular combination with one or more other claims, other examples may also include combinations of the dependent claim with the subject matter of any other dependent or independent claim. Such combinations are expressly stated here unless it is stated individually that no particular combination is intended. Furthermore, the features of a claim should also be included for use in any other independent claim, even if that claim is not directly defined as dependent on that other independent claim.

Claims

1. A magnetoresistive sensor (100) for sensing out-of-plane magnetic fields, comprising: Layer stack (110), having Reference system (120), including out-of-plane magnetization; as well as A synthetic antiferromagnetic SAF free layer (130) is configured to be adjacent to the reference system (120), the free layer (130) comprising: The first ferromagnetic layer (132) has good surface anisotropy; The second ferromagnetic layer (136) exhibits good-face anisotropy; and A nonmagnetic coupling layer (134) is inserted between the first ferromagnetic layer and the second ferromagnetic layer and is configured to antiferromagnetically couple the first ferromagnetic layer and the second ferromagnetic layer via Ruderman–Kittel–Kasuya–Yosida RKKY interaction.

2. The magnetoresistive sensor (100) according to claim 1, wherein the non-magnetic coupling layer (134) is composed of ruthenium, iridium, tantalum, tungsten or a combination thereof.

3. The magnetoresistive sensor (100) according to any one of the preceding claims, wherein the first ferromagnetic layer (132) comprises a CoFeB / CoFe alloy.

4. The magnetoresistive sensor (100) according to claim 3, wherein the first ferromagnetic layer (132) comprises at least one additional element selected from the group consisting of Fe, Co, Pt, Pd or Ni, wherein the at least one additional element is deposited on the CoFeB / CoFe alloy to modify the magnetocrystalline anisotropy and enable RKKY coupling.

5. The magnetoresistive sensor (100) according to any one of the preceding claims further includes... A tunnel barrier (140) is inserted between the SAF free layer (130) and the reference system (120).

6. The magnetoresistive sensor according to claim 5, wherein the tunnel barrier (140) is inserted between the first ferromagnetic layer (132) and the reference system (120).

7. The magnetoresistive sensor (100) according to any one of claims 1 to 4 further includes a conductive spacer layer (140) inserted between the SAF free layer (130) and the reference system (120).

8. The magnetoresistive sensor (100) according to any one of the preceding claims, wherein the second ferromagnetic layer (136) comprises a multilayer stack comprising one or more layers selected from the group consisting of CoFe, CoNi, NiFe, CoB, CoFeB or FeB, the multilayer stack being configured to balance the magnetic moment of the first ferromagnetic layer.

9. The magnetoresistive sensor (100) according to any one of the preceding claims, wherein the SAF free layer (130) has a total thickness of less than 10 nanometers.

10. The magnetoresistive sensor (100) according to any one of the preceding claims, wherein the first ferromagnetic layer (132) has a thickness between 1 nanometer and 5 nanometers.

11. The magnetoresistive sensor (100) according to any one of the preceding claims, wherein the SAF free layer (130) is patterned into a circular or cylindrical geometry.

12. The magnetoresistive sensor (100) according to claim 11, wherein the diameter of the circular or cylindrical free layer is less than 1 micrometer.

13. The magnetoresistive sensor (100) according to any one of the preceding claims, wherein the reference system comprises a stack exhibiting perpendicular magnetic anisotropy, the stack comprising one or more layers selected from the group consisting of Co / Pt, Ni / Pt, Co / Ni, GdCo, CoCrPt, FePt or rare earth element-based alloys.

14. The magnetoresistive sensor (100) according to any one of the preceding claims comprises a stack of layers having exactly one reference system.

15. The magnetoresistive sensor (100) according to any one of the preceding claims further includes a substrate, wherein the layer stack (110) is disposed on the substrate, and the synthetic antiferromagnetic free layer (130) is disposed between the substrate and the reference system (120).

16. The magnetoresistive sensor (100) according to any one of claims 1 to 14 further includes a substrate, wherein the layer stack (110) is disposed on the substrate, and the reference system (120) is disposed between the substrate and the synthetic antiferromagnetic free layer (130).

17. The magnetoresistive sensor (100) according to any of the preceding claims further includes at least one soft magnetic shield (300), said at least one soft magnetic shield being arranged adjacent to said layer stack (110) and configured to reduce the effect of external magnetic fields along the shield axis on said SAF free layer (130).

18. The magnetoresistive sensor of claim 17, wherein the shield (300) comprises a plurality of soft magnetic strips arranged in parallel, wherein each strip has a longitudinal axis extending perpendicular to or parallel to the shield axis.

19. A method for sensing an out-of-plane magnetic field, comprising: Provides a layer stack (110), the layer stack comprising Exactly one reference system (120). The SAF free layer (130) adjacent to the reference system (120) includes a first ferromagnetic signal layer (132) and a second ferromagnetic balance layer (136), which are antiferromagnetically coupled via a nonmagnetic coupling layer (134) and each has an easy surface anisotropy. An external out-of-plane magnetic field is applied to the SAF free layer (130); as well as Changes in the magnetoresistive signal corresponding to changes in the out-of-plane magnetization of the SAF free layer (130) are detected.

20. A magnetoresistive sensor (400) for in-plane magnetic field sensing, comprising: Layer stack (110), the layer stack comprising A reference system with in-plane magnetization (120); as well as A SAF free layer (130) is configured to be adjacent to the reference system, the SAF free layer comprising: A first ferromagnetic layer (132) with out-of-plane magnetic anisotropy. A second ferromagnetic layer (136) with out-of-plane magnetic anisotropy; and A non-magnetic coupling layer (134) is inserted between the first ferromagnetic layer and the second ferromagnetic layer, and the non-magnetic coupling layer is configured to antiferromagnetically couple the first ferromagnetic layer and the second ferromagnetic layer via RKKY interaction.

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