ANOMAL HALL SENSOR AND ANOMAL HALL DETECTION METHOD

Abstract

The present disclosure relates to an anomalous Hall sensor (100) comprising a Hall cross (110). The Hall cross (110) comprises a stack of layers (200) with a ferromagnetic layer (210). A first arm (114-1) of the Hall cross formed in the stack of layers extends in a first direction. A second arm (114-2) of the Hall cross formed in the stack of layers extends in a second direction perpendicular to the first direction. The anomalous Hall sensor (100) comprises a control circuit (120) configured to apply current through the first arm (114-1) of the Hall cross and measure voltage across the second arm (114-2) of the Hall cross in response to the current through the first arm, and to apply current through the second arm (114-2) of the Hall cross and measure voltage across the first arm (114-1) of the Hall cross in response to the current through the second arm.The anomalous Hall sensor (100) further comprises a processor (130) configured to calculate, based on a combination of the measured voltages, a component of an external magnetic field in a third direction, perpendicular to the first and second directions.

Description

Field of InterestThe present disclosure relates generally to the field of magnetic field sensing, and more particularly to the field of 3-dimensional (3D) magnetic field measurement.BackgroundIn magnetic field sensors, a small offset (offset) may be critical to fully exploit the signal-to-noise ratio and reduce undesirable environmental dependencies. This applies in particular to the measurement of small signals, such as e.g. earth magnetic fields in a compass application or high-precision 3D magnetic detection. Offset compensation techniques are well established for Hall-based devices, but are absent for magneto-resistive devices that generally provide a higher signal-to-noise ratio. Further, to be able to measure fields in all three directions (x, y, z), separate dedicated devices are typically used for each direction, increasing development and manufacturing complexity and size of the sensing circuitry.In conventional 3D Hall sensors, three different sensitive elements are needed to detect fields in all three directions. These sensors have a limited signal-to-noise ratio, but allow active offset compensation via spinning current techniques. Using spin orbit torque (SOT), the concept of a single sensitive element 3D magnetic field sensor was described in Li, Ruofan, et al., "A spin-orbit torque device for sensing three-dimensional magnetic fields". "Nature Electronics 4.3 (2021):179-184. There, however, the domain wall used can lead to noise and unreproducible behavior. If the domain wall is annihilation by the sensor due to strong external magnetic fields, the sensor response may change or even its functional behavior may be destroyed.SOT can manifest itself in various systems, including magnetic materials and structures. When an electric current is passed through a heavy metal or a layered structure of different materials, spin orbit interaction or coupling may generate torque on magnetization of adjacent magnetic layers.In a conventional Hall effect, when an electric current flows through a conductive material that is in a magnetic field perpendicular to the current, a transverse voltage known as the Hall voltage is induced across the material. This voltage is proportional to the product of the applied current, the magnetic field strength and a material-dependent parameter, the so-called Hall coefficient. However, in materials with strong spin orbit coupling and magnetization, such as ferromagnetic metals or magnetic semiconductors, an additional contribution arises due to the anomalous Hall effect (AHE). The AHE is related to spin dependent scattering of charge carriers within the material. It causes asymmetry in the charge carrier trajectories, which leads to a deflection of the charge carriers and the occurrence of an additional Hall voltage perpendicular to the applied current and magnetic field.Thus, there is a need to improve spin orbit torque devices or anomalous Hall sensors using the AHE.SummaryThis need is addressed by apparatus and methods according to the independent claims. Potentially advantageous embodiments are addressed by the dependent claims.In a first aspect, the present disclosure proposes an abnormal Hall sensor using the AHE. The abnormal Hall sensor includes a Hall cross. The Hall cross comprises a layer stack comprising at least one ferromagnetic layer next to at least one further layer. There may be several possible implementations of the layer stack. A first arm of the Hall cross formed in the layer stack extends in a first direction. The first direction may be referred to as an x-direction, for example. A second arm of the Hall cross formed in the layer stack extends in a second direction perpendicular to the first direction. The second direction may be referred to as a y-direction, for example. The anomalous Hall sensor further includes a control circuit configured to apply current / currents through the first arm of the Hall cross and measure voltage(s) across the second arm of the Hall cross in response to the current / currents through the first arm. The control circuit is further configured to apply current / currents through the second arm of the Hall cross and measure voltage(s) across the first arm of the Hall cross in response to the current / currents through the second arm. The anomalous Hall sensor further comprises a processor configured to calculate, based on a combination of the measured voltages, a component of an external magnetic field in a third direction, perpendicular to the first and second directions. The third direction may be referred to as a z-direction, for example.Thus, in the present disclosure, a spinning current technique for abnormal Hall sensors is proposed. By applying respective currents to the two arms of the Hall cross, the component of the external magnetic field in the third direction perpendicular to the first and second directions can be determined.The Hall cross may include a (e.g., rectangular, square, or cross-shaped) layered structure having four electrical contacts arranged in a cross-like pattern. The first arm of the Hall cross connects two of the four contacts in the first direction (e.g., x-direction), the second arm of the Hall cross connects the other two of the four contacts together in the second direction (e.g., y-direction).In some embodiments, the control circuit is configured to apply first and second currents through the first arm of the Hall cross in opposite directions and measure respective first and second voltages across the second arm of the Hall cross in response to the respective currents. When the first direction is the x direction, the first and second currents may be in positive x direction and negative x direction. The control circuit may be further configured to apply a third and a fourth current through the second arm of the Hall cross in opposite directions and measure a respective third and fourth voltage across the first arm of the Hall cross in response to the respective currents. When the second direction is the y direction, the third and fourth currents may be currents in positive y direction and negative y direction. The processor may be configured to calculate the component of the external magnetic field in the third direction (e.g., z-direction) based on a combination of the measured four voltages. The combination of the measured four voltages may include, for example, a first difference of the third and fourth voltages and a second difference of the first and second voltages. In a particular implementation, the combination of the four measured voltages may correspond to a difference between the second difference and the first difference.In some embodiments, the processor is further configured to calculate a component of the external magnetic field in the first direction (e.g., x-direction) based on a combination of the measured first and second voltages in response to the respective currents. For example, the processor may be configured to calculate the component of the external magnetic field in the first direction (e.g., x-direction) based on a sum of the measured first and second voltages.In some embodiments, the processor is further configured to calculate a component of the external magnetic field in the second direction (e.g., y-direction) based on a combination of the measured third and fourth voltages in response to the respective currents. For example, the processor may be configured to calculate the component of the external magnetic field in the second direction (e.g., y-direction) based on a sum of the measured third and fourth voltages.Thus, an abnormal 3D Hall sensor can be obtained.In some embodiments, the layer stack comprises at least one conductive non-magnetic layer and the ferromagnetic layer formed one above the other. The conductive non-magnetic layer may comprise a heavy metal layer, for example. Some examples of heavy metals that may be used in spin torque devices include:Platinum (Pt): Platinum is a heavy metal widely used in spintronics because of its strong spin orbit coupling and good electrical conductivity. It can be used as a spin current source or as a spin sink layer (spin sink layer) in spintronic components.Tantalum (Ta): Tantalum is another heavy metal that exhibits strong spin orbit coupling and is used in spintronic applications. It can be used as a spin sink layer in devices to efficiently absorb spin currents.Ruthenium (Ru): Ruthenium is a heavy metal which provides good spin orbit coupling and is used in spintronic devices, particularly magnetic tunnel junctions (MTJs) and spin transfer torque devices. Palladium (Pd): Palladium is not used as frequently as platinum, but is a further heavy metal which can generate spin currents due to its strong spin orbit coupling. Its potential for spintronic applications has been investigated.Some examples of ferromagnetic materials that may be used in spin torque devices include:Permalloy (NiFe): Permalloy, a ferromagnetic alloy of nickel and iron, can be used in spin torque devices because of its favorable magnetic properties, such as high saturation magnetization and low magnetic attenuation. It is often used as the free layer or the reference layer in spin-transfer torque magnetic random access memories (STT-MRAM) and magnetic tunnel junctions (MTJs).Cobalt (Co) and cobalt alloys: cobalt and its alloys, such as CoFeB (cobalt-iron-boron), can be used in spin torque devices. They have strong magnetic anisotropy and are frequently used as the reference layer in STT-MRAM and magnetic sensors.Rare Earth Transition Metal Alloys: Certain rare Earth Transition Metal alloys, such as gadolinium iron garnet (GdIG), have been tested for use in spin torque devices. These materials have interesting magnetic and spintronic properties which may be advantageous for certain applications.In spin torque devices, a spin current can be injected from a heavy metal layer into an adjacent ferromagnetic layer. The spin current applies torque to magnetization of the ferromagnetic layer, thus allowing control and manipulation of its orientation.In some embodiments, the layer stack comprises a multilayer comprising a plurality of repetitions of a non-magnetic and a magnetic layer. Examples of non-magnetic materials that may be used in spin torque devices include:Heavy metals: heavy metals with strong spin orbit coupling, such as platinum (Pt), tantalum (Ta) and ruthenium (Ru), can be used as spin current sources or spin sink layers in spin torque devices. These materials efficiently generate or absorb spin currents and facilitate the transmission of angular momentum between the spin and the electron orbital motion.Insulators: Insulating materials such as aluminum oxide (Al2O3) or magnesium oxide (MgO) can be used as tunnel barriers in magnetic tunnel junctions (MTJs). These insulating layers serve as electrical insulators between the magnetic layers and simultaneously permit spin-dependent tunnel currents. The tunnel barrier properties, such as high resistance and low leakage current, are critical to device operation.Examples of magnetic materials that may be used in spin torque devices include:Ferromagnetic Materials: Ferromagnetic materials such as permalloy (NiFe) and cobalt (Co) alloys are used as the magnetic layers in spin torque devices. These materials have permanent magnetization and can be manipulated by spin currents. Ferromagnetic layers are often used as the free layer in spin transfer torque magnetic random access memory (STT-MRAM) or as the reference layer in magnetic tunnel junctions (MTJs).Antiferromagnetic materials: Antiferromagnetic materials such as iridium-manganese (IrMn) are used as pinning layers in spin torque devices. These materials have a unique magnetic order in which adjacent magnetic moments are aligned anti-parallel. The antiferromagnetic pinning layer helps stabilize the orientation of magnetization of the free layer and increases the stability of the device.The combination of non-magnetic and magnetic materials allows for efficient generation, manipulation and detection of spin currents in spin torque devices. The targeted choice of materials depends on the desired functionality, performance requirements, and compatibility with the device architecture.In some embodiments, the layer stack includes a multilayer including a plurality of repetitions of a first non-magnetic layer (e.g., Ta), a magnetic layer (e.g., CoFeB), and a second non-magnetic layer (e.g., MgO).In some embodiments, the ferromagnetic layer is magnetized in the plane. The ferromagnetic layer may also have permanent magnetization in the absence of the external magnetic field and may be essential for manipulating magnetization dynamics through the application of spin currents. In spin torque devices, a spin current can be injected from a heavy metal layer into an adjacent ferromagnetic layer. The spin current applies torque to the magnetization of the ferromagnetic layer, thus allowing control and manipulation of its orientation.In some embodiments, the ferromagnetic layer includes an out-of-plane multi-domain state. In the context of spin torque and spintronics, a multidomain state refers to the placement of magnetic domains within a magnetic layer in a spin torque device. Spin torque devices use spin currents to control the magnetization dynamics and change the magnetization orientation of the magnetic layer. In a spin torque device, a magnetic layer typically comprises a ferromagnetic material having permanent magnetization. However, due to various factors such as size, shape, and magnetic anisotropy of the magnetic layer, it may be divided into multiple magnetic domains. A multi-domain state in a spin torque device occurs when the magnetic layer includes multiple magnetic domains having different magnetization orientations. Each domain represents a region in which the magnetization is aligned in a particular direction, but the domains may have distinct boundaries called domain walls. The presence of multiple magnetic domains affects the behavior of spin currents in the device. When a spin current is injected into a multidomain magnetic layer, it can exert torques on the domain walls and interact with the magnetization within each domain. This interaction can result in domain wall movement, domain expansion or contraction, and changes in the overall state of magnetization of the device.In some embodiments, the control circuit is configured to inject the currents into the arms of the Hall cross as spin polarized currents. Spin-polarized currents are electric currents in which the individual electrons have a preferred spin alignment. In other words, the current carries a net spin polarization, i.e., there is, for example, an imbalance between the number of spin-up and spin-down electrons.In another aspect, the present disclosure proposes an abnormal Hall sensing method. The method includes applying current / currents through a first arm of a Hall cross extending in a first direction. The first direction may be referred to as an x-direction, for example. The method includes measuring voltage(s) across the second arm of the Hall cross in response to the current / s through the first arm. The method includes applying current / currents through the second arm of the Hall cross extending in a second direction perpendicular to the first direction. The second direction may be referred to as a y-direction, for example. The method includes measuring voltage(s) across the first arm of the Hall cross responsive to the current / s through the second arm. Further, the method includes calculating a component of an external magnetic field in a third direction that is perpendicular to the first and second directions based on a combination of the measured voltages. The third direction may be referred to as a z-direction, for example.Brief Description of the FiguresSome examples of devices and / or methods will be described below, purely by way of example and with reference to the accompanying figures, in which: FIG. 1 illustrates an abnormal Hall sensor according to embodiments of the present disclosure; FIG. 2 shows an example of a layered Hall cross; FIG. 3 illustrates an abnormal Hall sensor according to an embodiment of the present disclosure; FIG. 4 illustrates a flowchart of an abnormal Hall sensing method; FIG. 5A illustrates a principle of measuring in-plane fields; FIG. 5B shows a measured external Bx field with an SOT current applied in the x direction and the abnormal Hall voltage measured in the y direction. By the offset (offset) suppression, the electrical offset has been almost completely eliminated and the linear range is about + / -0.5 mT; FIG. 6A illustrates a principle of out-of-plane field measurement; FIG. 6B shows a measured signal of an external Bz field; FIG. 7A shows a measured Bz signal for different bias (bias) fields; FIG. 7B shows a measured Bx signal with Bz bias fields of different amplitude; and FIG. 7C shows a measured Bx signal with by bias fields of different amplitudes.Detailed DescriptionSome examples will now be described in more detail with reference to the accompanying figures. However, further possible examples are not limited to the features of these exemplary embodiments described in detail. Other examples may include modifications of the features, as well as equivalents and alternatives to the features. Further, the terminology used herein to describe particular examples is not intended to be limiting of other possible examples.Like or similar reference numerals refer to like or similar elements and / or features throughout the description of the figures, which may be implemented identically or in modified form while providing the same or similar function. In the figures, the thicknesses of lines, layers, and / or regions may be exaggerated for clarity.When two elements A and B are combined using one "or", it is to be understood that all possible combinations are disclosed, i.e., only A, only B, and A and B, unless expressly defined otherwise in the individual case. As an alternative formulation for the same combinations, "at least one of A and B" or "A and / or B" may be used. This applies correspondingly to combinations of more than two elements.When a singular form, e.g., "a," and "the," is used and the use of only a single element is not expressly or implicitly defined as obligatory, further examples may also use multiple elements to implement the same function. When a function is described below as being implemented using multiple elements, further examples may implement the same function using a single element or a single processing entity. It will be further understood that the terms "comprises," "comprising," "comprises," and / or "comprising," when used, describe the presence of the stated features, integers, steps, operations, processes, elements, components, and / or a group thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, processes, elements, components, and / or a group thereof.FIG. 1 illustrates an abnormal Hall sensor 100 according to embodiments of the present disclosure. The abnormal Hall sensor 100 is a type of magnetic field sensor that uses the abnormal Hall effect to detect and measure magnetic fields.When a non-ferromagnetic metallic sample is exposed to a perpendicular external magnetic field B, the Lorentz force acting on the current carriers results in a transverse stress in the plane of the sample. The transverse component of resistivity, ρ xy, depends on the magnetic field by the relationship ρ xy= R 0 B, where R 0= 1 / ( ne) is known as the Hall coefficient, n is the carrier density, and -e is the electron charge. This phenomenon, the explanation of which is quite classical, is known as the usual Hall effect and is comprehensible. The determination of the Hall coefficient R 0 has become the tool of choice for measuring carrier densities in conductive materials.As a result, it has been found that in many ferromagnets, the transverse resistivity detects an additional term independent of the magnetic field, which is often proportional to the magnetization M of the ferromagnetic sample and becomes constant once the sample has reached its saturation magnetization. This effect is referred to as an abnormal Hall effect (A-HE). While the usual Hall effect of classical physics requires an external magnetic field, the abnormal Hall effect requires only magnetization, and it is soon recognized that ferromagnets have spontaneous Hall conductivity even in the absence of an external magnetic field. The effect has subsequently been observed in a variety of systems, including transition metals and their oxides, in materials having colossal magnetoresistance, in ferromagnetic semiconductors, topological insulators, and a variety of other topological materials.The anomalous Hall effect is due to the fact that electrons are predominantly deflected in one direction as a current passes through a magnetic material. This results in an additional current perpendicular to the drive current, which disappears when the material is non-magnetic. The mechanisms responsible for this deflection have been the subject of considerable controvers since the hall of experimental work. Although several mechanisms are known which are responsible for this, the main operators are combined by the spin-orbit interaction-magnetism alone is usually not sufficient to induce an abnormal Hall current. Further, spin orbit coupling effects are usually divided into intrinsic processes resulting from the band structure of a material and extrinsic processes related to scattering events. Recent research has shown that intrinsic spin orbit coupling effects are interlaced with the topological properties of the band structure of a material and that the interaction of intrinsic and extrinsic processes is highly non-trivial. The focus of the anomalous Hall effect is therefore the physical concepts of ferromagnetism and spin orbit coupling.The anomalous Hall sensor 100 comprises a Hall cross 110. Hall cross 110 is a specific(s) geometry or layout of a Hall sensor that includes four terminals 112- 1 to 112- 4 arranged in a cross-like pattern. A first arm 114- 1 of the Hall cross 110 connects the terminals 112- 1 and 112- 2 to each other and extends in a first direction (x direction). A second arm 114- 2 of the Hall cross 110 connects the terminals 112- 3 and 112- 4 to each other and extends in a second direction (y direction).As shown in the example of FIG. 2, the Hall cross 110 is formed in a layer stack 200 comprising at least one ferromagnetic layer 210 and one or more further layers 220 for spin orbit coupling. Because the AHE requires magnetization, the ferromagnetic layer 210 may be magnetized in a plane spanned by the first and second directions (e.g., x-y plane). In the example illustrated in FIG. 2, the magnetization of the ferromagnetic layer 210 runs in the x direction. A material of the ferromagnetic layer 210 may be, for example, NiFe or CoFeB. Below the ferromagnetic layer 210, the layer stack 200 comprises a heavy metal layer 220 for spin orbit coupling. A material of the heavy metal layer 220 may be, for example, Pt, Ta, Ru, or Pd.A possible structure of the sensitive element can be seen in Fig. 2. It is a Hall cross-like structure with a heavy metal layer that converts electrical current into polarized spin current. Above the heavy metal layer is a ferromagnetic layer polarized in the plane (x-y plane) (drawn in the x direction in FIG. 2 ). As explained above, the structure shown in FIG. 2 is merely an example. Other layers are also possible. Hall cross 110 may also have a Ta / CoFeB / MgO heterostructure, for example.The abnormal Hall sensor 100 further includes a control circuit 120. The control circuit 120 may include one or more power supply circuits, clock circuits, measurement circuits, etc. The control circuit 120 is configured to apply current / currents through the first arm 114- 1 of the Hall cross 110 (via the terminals 112- 1 and 112- 2) and generate voltage(s) across the second arm 114- 2 of the Hall cross 110 (via the terminals 112- 3 and 112- 4) in response to the current / currents through the first arm 114- 1. The control circuit 120 is further configured to apply current / currents through the second arm 114- 2 of the Hall cross (across the terminals 112- 3 and 112- 4) and generate voltage(s) across the first arm 114- 1 of the Hall cross (across the terminals 112- 1 and 112- 2) in response to the current / currents through the second arm 114- 2. Thus, the control circuit 120 is configured to apply a spinning current scheme to the Hall cross 110.The abnormal Hall sensor 100 further includes a processor 130. The processor 130 may include one or more analog and / or digital signal processing circuits. The processor 130 is configured to determine a component of an external magnetic field in the z-direction based on the measured voltages in response to the spinning current scheme. In particular, the processor 130 may be configured to determine the component of the external magnetic field in the z-direction based on a combination of the measured voltages in response to the spinning current scheme.FIG. 3 shows an embodiment of the anomalous Hall sensor 100 and its electronic connections in detail.A power supply circuit 122 of the control circuit 120 and the processor 130 are clocked by a clock circuit 124 of the control circuit 120. The power supply circuit 122 is coupled to each of the terminals 112- 1 to 112- 4 to inject currents into the first arm 114- 1 and the second arm 114- 2 of the Hall cross 110. Processor 130 is also coupled to each of terminals 112- 1 through 112- 4 to measure the resulting (Hall) voltages across first arm 114- 1 and second arm 114- 2 of Hall cross 110.The power supply circuit 122 is configured to apply a first current +Ixx through the first arm 114- 1 of the Hall cross 110. The first current +Ixx may be a current from terminal 112- 1 to terminal 112- 2 in the positive x direction. The processor 130 is configured to measure a first (Hall) voltage Vxy(+Ixx) across the second arm 114- 2 (across the terminals 112- 3 and 112- 4) of the Hall cross 110 in response to the first current +Ixx. The power supply circuit 122 is further configured to apply a second current -Ixx, which is opposite to the first current +Ixx, through the first arm 114- 1 of the Hall cross 110. The second current -Ixx may be a current from terminal 112- 2 to terminal 112- 1 in the negative x direction. The processor 130 is configured to measure a second (Hall) voltage Vxy(-Ixx) across the second arm 114- 2 (across the terminals 112- 3 and 112- 4) of the Hall cross 110 in response to the second current -Ixx. The power supply circuit 122 is further configured to apply a third current +Iyy through the second arm 114- 2 of the Hall cross 110. The third current +Iyymay be a current from terminal 112- 3 to terminal 112- 4 in the positive y direction. The processor 130 is configured to measure a third (Hall) voltage Vyx(+Iyy across the first arm 114- 1 (across terminals 112- 1 and 112- 2) of the Hall cross 110 in response to the third current +Iyy. The power supply circuit 122 is further configured to apply a fourth current -Iyy, which is opposite to the third current, across the second arm 114- 2 of the Hall cross 110. The fourth current -Iyyymay be a current from terminal 112- 4 to terminal 112- 3 in the negative y direction. The processor 130 is configured to measure a fourth (Hall) voltage Vyx(-Iyy) across the first arm 114- 1 (across the terminals 112- 1 and 112- 2) of the Hall cross 110 in response to the fourth current -Iyyy.The power supply circuit 122 provides the Hall cross 110 with current / currents. To this end, the power supply circuit 122 may include power sources. A resultant signal is measured and analyzed in the signal processing unit 130, and is output as a digital or analog signal proportional to each field component (Vx, Vy, Vz). The timing of the supply 122 and the signal processing unit 130 is effected via the clock 124. The currents ±Ixx and ±Iyy may be applied alternately, and the corresponding Hall voltages Vxy or Vyx may be recorded. The output signal may be calculated using, for example, the formulas in the upper right corner of FIG. 3. The voltage is measured via the anomalous Hall effect on the vertical arms 114-1, 114-2. Depending on the direction in which the electric current is applied (Ixx or Iyy), the abnormal Hall voltage for an Ixx current is referred to as Vxy and for an Iyy current is referred to as Vyx (shown in FIG. 3 ).The component of the external magnetic field in the z direction may be determined based on a combination of the four voltages Vxy(+Ixx), Vxy(-Ixx), Vyx(+Iyy), and Vyx(-Iyy). The component of the external magnetic field in the z-direction can be proportional, for example, toThe component of the external magnetic field in the x direction may be determined based on a combination of the first voltage Vxy(+Ixx) and the second voltage Vxy(-Ixx). The component of the external magnetic field in the x-direction can be proportional, for example, toThe component of the external magnetic field in the y direction may be determined based on a combination of the third voltage third voltage Vyx(+Iyy) and the fourth voltage Vyx(-Iyy). The component of the external magnetic field in the y-direction can be proportional, for example, toThe anomalous Hall sensor 100 enables an anomalous Hall detection method 400, the flow chart of which is shown in FIG. 4.The method 400 includes applying 410 current / currents through a first arm of a Hall cross extending in a first direction. The first direction may be referred to as an x-direction, for example. The method 400 further includes measuring 420 voltage(s) across the second arm of the Hall cross responsive to the current / s through the first arm. The method 400 further includes applying 430 current / currents through the second arm of the Hall cross extending in a second direction perpendicular to the first direction. The second direction may be referred to as a y-direction, for example. The method 400 further includes measuring 440 voltage(s) across the first arm of the Hall cross responsive to the current / s through the second arm. Further, the method 400 comprises calculating 450 a component of an external magnetic field in a third direction that is perpendicular to the first and second directions based on a combination of the measured voltages. The third direction may be referred to as a z-direction, for example. The measured voltages may also be divided by the respective currents to obtain the respective abnormal Hall resistance.The principle of measuring in-plane fields across the spin orbit torque device can be seen in FIG. 5A. For the measurement of an external Bx field, the abnormal Hall voltage V may be measured, and the abnormal Hall resistance R may be calculated by the following formula, where I is the SOT current. In order to eliminate the electrical offset of the device, the sign of the SOT current may be switched and the anomalous Hall resistances may be subtracted from each other as in the following formula wherein + / -Ixx is the SOT current in + / - x direction.The resistance for the measurement of an external by field can be calculated in the following formula. where Iyyis the SOT current applied in the y direction.The measured signal of an external Bx field is seen in Fig. 5B. The sensor response shows almost no offset and a linear range of about + / -0.5 mT.For the measurement of external fields in the z-direction, the spinning current technique is used. This is illustrated in FIG. 6A. The external Bz field is measured via a SOT current applied in the x and y directions. In both cases, the abnormal Hall voltage is measured.The formula for calculating the signal may be as follows.The measured signal is seen in Figure 6B.The presented sensing principle may remain unaffected with respect to bias fields that are in the linear region of the sensing device (+ / -0.5 mT). In FIG. 7A, the measured Bz signal is shown with different amplitudes for Bx bias fields. For the higher bias field amplitudes (+ / -0.5 mT), the linear range in the sense direction decreases. The sensitivity and offset of the sensor are not affected by bias fields and remain nearly the same.In FIG. 7B, the measured Bx signal is shown with Bz bias fields. For bias fields within the linear range, sensitivity and offset are not affected. However, with stronger bias fields, the sensitivity decreases, which becomes visible with the measurement data with a Bz bias field of 1 mT.In FIG. 7C, the measured Bx signal is shown with different by bias fields. Here too, the offset and sensitivity within the linear range of the sensor are unaffected by bias fields. At the higher bias field of 1mT, the decrease in sensitivity is again visible.This allows the design of a single device 3D magnetic field sensor based on SOT without cross sensitivities and active offset compensation.According to the present disclosure, the anomalous Hall sensor 100 uses a single domain layer, which may result in more reliable performance, as it is not necessary to create the domain wall prior to use. Known 3D sensors do not use the spinning current technique for the z-axis and are therefore unable to compensate offsets in this direction. According to the present disclosure, the spinning current technique is used in the z-direction and the SOT effect is used for the x-y field components, resulting in very little offset in all directions.According to the present disclosure, the magnetization is switched by the SOT current in basically opposite directions.According to the present disclosure, a spinning current concept is used for anomalous Hall sensors. In particular, a single component is proposed which can be used for measuring magnetic fields in all three directions and for compensating the respective offsets. The device uses spin orbit torque (SOT) to rotate the magnetization of a ferromagnetic layer in the sensitive direction of the sensor measured with the anomalous Hall effect (or alternatively with another technique sensitive to out-of-plane fields, such as TMR with an out-of-plane reference layer). For suppressing offsets, the spinning current technique is used in which the SOT current direction is reversed.By flipping the SOT current, the offset can be compensated, but only in the x-y field measurements. In the case of the Bz field measurements, this does not work with only one component. This can be solved by combining the measurements in x and y such that the SOT and offset contributions in the signal are suppressed. From the four measurements, the field in all three directions can thus be obtained with active offset compensation.Some advantages are:Offset ReductionNo cross sensitivity in other field directionsLinear range can be matched by current intensityAn out-of-plane free layer may be used to detect out-of-plane fields.A sensor may be used to detect x, y and z field components.The aspects and features described in connection with a particular one of the preceding examples can also be combined with one or more of the further examples in order to replace an identical or similar feature of this further example or in order to additionally introduce the feature into the further example.It is further understood that the disclosure of a plurality of steps, processes, operations or functions disclosed in the description or the claims should not be construed as necessarily in the described order, provided that this is not explicitly stated in the individual case or is absolutely necessary for technical reasons. Therefore, the foregoing description does not limit the execution of multiple steps or functions to a particular order. Further, in further examples, a single step, function, process, or operation may include and / or be broken into multiple substeps, functions, processes, or operations.If some aspects have been described in connection with a component or a system, these aspects are also to be understood as a description of the corresponding method. In this case, for example, a block, a component or a functional aspect of the component or of the system can correspond to a feature, for example a method step, of the corresponding method. Accordingly, aspects described in connection with a method are also to be understood as a description of a corresponding block, a corresponding element, a property or a functional feature of a corresponding component or a corresponding system.The following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate example. It is further to be noted that although a dependent claim refers in the claims to a particular combination with one or more other claims, other examples may also include a combination of the dependent claim with the subject matter of any other dependent or independent claim. Such combinations are hereby explicitly proposed, unless it is stated in the individual case that a specific combination is not intended. Further, features of a claim are also intended to be encompassed for any other independent claim, even if that claim is not defined directly as dependent on that other independent claim.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Cited Non-Patent LiteratureLi, Ruofan, et al., "A spin-orbit torque device for sensing three-dimensional magnetic fields". "Nature Electronics 4.3 (2021): 179-184

[0003]

Claims

An anomalous Hall sensor (100) comprising a Hall cross (110) comprising a layer stack (200) having a ferromagnetic layer (210), a first arm (114-1) of the Hall cross formed in the layer stack and extending in a first direction, and a second arm (114-2) of the Hall cross formed in the layer stack and extending in a second direction perpendicular to the first direction; a control circuit (120) configured to apply current through the first arm (114-1) of the Hall cross and measure voltage across the second arm (114-2) of the Hall cross in response to the current through the first arm, apply current through the second arm (114-2) of the Hall cross, and measure voltage across the first arm (114-1) of the Hall cross in response to the current through the second arm; and a processor (130) configured to: calculate an external magnetic field component in a third direction that is perpendicular to the first and second directions based on a combination of the measured voltages.The anomalous Hall sensor (100) of claim 1, wherein the control circuit (120) is configured to apply a first and a second current through the first arm (114-1) of the Hall cross in opposite directions and measure a respective first and second voltage across the second arm (114-2) of the Hall cross in response to the respective currents, apply a third and a fourth current through the second arm (114-2) of the Hall cross in opposite directions and measure a respective third and fourth voltage across the first arm (114-1) of the Hall cross in response to the respective currents, and the processor (130) is configured to calculate the component of the external magnetic field in the third direction based on a combination of the measured four voltages.The anomalous Hall sensor (100) of claim 2, wherein the processor (130) is configured to calculate a component of the external magnetic field in the first direction based on a combination of the measured first and second voltages.The abnormal Hall sensor (100) according to claim 3, wherein the processor (130) is configured to calculate the component of the external magnetic field in the first direction based on a sum of the measured first and second voltages.The abnormal Hall sensor (100) according to any one of claims 2 to 4, wherein the processor (130) is configured to calculate a component of the external magnetic field in the second direction based on a combination of the measured third and fourth voltages.The abnormal Hall sensor (100) according to claim 5, wherein the processor (130) is configured to calculate the component of the external magnetic field in the second direction based on a sum of the measured third and fourth voltages.The anomalous Hall sensor (100) according to any of claims 2 to 6, wherein the combination of the measured four voltages comprises a first difference of the third and fourth voltages and a second difference of the first and second voltages.The anomalous Hall sensor (100) according to claim 7, wherein the combination of the measured four voltages corresponds to a difference between the second difference and the first difference.The anomalous Hall sensor (100) according to any of the preceding claims, wherein the layer stack (200) comprises at least one conductive non-magnetic layer (220) and the ferromagnetic layer (210).The anomalous Hall sensor (100) of claim 9, wherein the conductive non-magnetic layer (220) comprises a heavy metal layer.The anomalous Hall sensor (100) according to any of the preceding claims, wherein the layer stack comprises a multilayer comprising a plurality of repetitions of a non-magnetic and a magnetic layer.The anomalous Hall sensor (100) according to any of the preceding claims, wherein the layer stack (200) comprises a multilayer comprising a plurality of repetitions of a first non-magnetic layer (220), a magnetic layer (210) and a second non-magnetic layer.The anomalous Hall sensor (100) according to claim 11 or 12, wherein at least one non-magnetic layer is a heavy metal layer.The anomalous Hall sensor (100) according to any one of the preceding claims, wherein the control circuit (120) is configured to inject the currents into the arms of the Hall cross (110) as spin-polarized currents, respectively.An anomalous Hall sensing method (400) comprising applying (410) a current through a first arm of a Hall cross extending in a first direction; measuring (420) a voltage across the second arm of the Hall cross in response to the current through the first arm; applying (430) a current through the second arm of the Hall cross extending in a second direction perpendicular to the first direction; measuring (440) the voltage across the first arm of the Hall cross in response to the current through the second arm; and calculating (450) a component of an external magnetic field in a third direction perpendicular to the first and second directions based on a combination of the measured voltages.

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