SPIN VALVE COMPONENT AND METHOD FOR MAKING A SPIN VALVE COMPONENT

Abstract

A spin valve device (400) comprising a layer stack one or more layers (106; 107; 108; 109; 110) that form a unidirectionally magnetized reference frame; a vortex-magnetized free layer (102); a non-magnetic layer (104) that separates the reference frame from the free layer (102); and one or more layers forming a prestressing structure (402) which is exchange-coupled with the free layer (102), wherein the prestressing structure has a vortex magnetization with closed flux of a predetermined rotational direction.

Description

Area

[0001] The present disclosure relates generally to magnetoresistive structures and, more particularly, to spin valve devices that exploit TMR (tunnel magnetoresistance) or GMR (giant magnetoresistance) effects. background

[0002] A spin valve is a device comprising two or more conductive magnetic materials whose electrical resistance can change depending on the relative orientation of the magnetization in different layers. The change in electrical resistance can be, for example, a result of the GMR effect or the TMR effect. In a simple case, a spin valve comprises a non-magnetic material sandwiched between two ferromagnets, one of which is fixed (pinned) by an antiferromagnet that acts to increase its magnetic coercivity and behaves like a "hard" layer, while the other is free (unpinned) and behaves like a "soft" layer. Known spin valves are described, for example, in DE 10 2015 121 753 A1, US 8 542 072 B2, and US 2010 / 0 072 524 A1.

[0003] Spin valves can be used in Wheatstone bridge configurations to sense magnetic fields. Ideally, the spin valves used in the bridge configuration are matched in terms of electrical resistance and magnetic sensitivity under different operating conditions (e.g., temperature, supply voltage).

[0004] A spin valve can be deposited on a substrate, such as a semiconductor die, and comprises a magnetic free layer and one or more layers forming a ferromagnetic reference system. The magnetic free layer and the reference system are separated by a thin non-magnetic layer, also known as a tunnel barrier or transition. The free layer and the reference system can employ ferromagnets or ferrimagnets with different coercive field strengths (by using different materials or film thicknesses), or a ferromagnetic or ferrimagnetic layer of the reference system can be coupled to an antiferromagnet (exchange bias).The free layer can be designed to spontaneously generate a closed-flux magnetization pattern in the plane (vortex magnetization pattern), while the reference frame can be formed to provide a non-closed-flux magnetization pattern, e.g., a unidirectional magnetization pattern. A spin-valve device with a vortex-magnetized free layer is also referred to below as a vortex spin-valve device.

[0005] A major cause of offset error in vortex spin valve bridge sensor configurations is an electrical mismatch between the different branches. This ohmic offset error contribution is typically quite constant over the product's lifetime and temperature range. Consequently, this error can be trimmed by adding a constant voltage to the bridge signal. This trimming procedure works well because the spin valve mismatch value and the trimming devices can remain very stable over the lifetime and temperature range.

[0006] An additional source of offset error is identified, which is related to the vortex state of spin-valve devices. Ideally, the vortex ground state (= magnetization configuration for H ext = 0 mT) Mx=0. Mx=0 results in an electrical spin-valve response always having the same resistance / conductivity value over a perfectly aligned reference frame.

[0007] As a first-order deviation from the ideal case, the Mx magnetization in the vortex ground state is constant only as long as the vortex state is not annihilated. After the vortex state is re-nucleated, the ground-state magnetization Mx—which is responsible for the spin-valve resistance—can differ from the ground state before the annihilation / nucleation process. This second-order effect is not visible in perfect vortex structures. It requires a certain degree of asymmetry in the disk geometry, in the lateral variation of the magnetic properties, or in the reference frame.

[0008] In addition to the asymmetric geometry or inhomogeneous structure of the vortex, which cannot be avoided during device fabrication, the vortex chirality (rotation direction of the magnetization pattern) defines the difference in the ground state Mx. As long as the vortex spin valve device renucleates with the same chirality, there is no difference in the ground state magnetization Mx. Unfortunately, vortex chirality is not well defined in solutions according to the state of the art. The two different chirality states (clockwise, counterclockwise) lead to the same minimum energy but with different Mx. This can lead to a bridge misalignment error after vortex annihilation / nucleation.

[0009] Therefore, it is an object of the present disclosure to avoid or at least reduce the described bridge offset error after vortex annihilation. Summary

[0010] This objective is addressed by components / devices and methods according to the independent claims. Potentially advantageous embodiments are addressed by the dependent claims.

[0011] According to a first aspect, the present disclosure provides a spin-valve device comprising a layer stack. The layer stack of the spin-valve device comprises one or more layers forming a unidirectionally magnetized reference frame. The layer stack of the spin-valve device further comprises a vortex-magnetized ferromagnetic or ferrimagnetic free layer and a non-magnetic layer separating the reference frame from the free layer. The layer stack of the spin-valve device further comprises one or more layers forming a bias structure coupled to the free layer by bias exchange. The bias structure exhibits closed-loop vortex magnetization in a predetermined direction of rotation.The prestressing structure, which is exchange-coupled with the free layer, enables a well-defined vortex chirality and thus an Mx magnetization of the spin-valve device after the vortex annihilation / nucleation process of the free layer.

[0012] In some embodiments, the non-magnetic layer comprises a non-conductive material that forms a tunnel barrier in a magnetic tunnel junction (MTJ). In this case, the spin-valve device can be an MTJ device that relies on the TMR effect.

[0013] In some embodiments, the non-magnetic layer comprises a conductive material that forms a GMR junction. In this case, the spin-valve device can be a GMR device.

[0014] In some embodiments, the bias structure is formed as an antiferromagnet (AFM). Alternatively, the bias structure can also be formed as a ferrimagnet or ferromagnet. Both can lead to exchange bias or exchange anisotropy, which occurs in bilayers (or multilayers) of magnetic materials, where the hard magnetization behavior of an antiferromagnetic (or ferrimagnetic) layer (bias structure) causes a shift in the soft magnetization curve of a ferromagnetic layer (free layer).

[0015] In some embodiments, the vortex magnetization of the bias structure is more stable than the vortex magnetization of the free layer. This means that the external magnetic field strength potentially required to annihilate the vortex magnetization of the bias structure is higher than that required to annihilate the vortex magnetization of the free layer. The Curie temperature (or lock-up temperature) of the bias structure may be lower than that of the free layer. The Curie temperature of the free layer indicates the temperature at which the free layer loses its defined magnetization and transitions into a disordered state.

[0016] In some embodiments, the MTJ device further comprises a non-magnetic or magnetic coupling layer between the free layer and the bias structure. The coupling layer can be used to adjust the coupling strength depending on the thickness of the coupling layer.

[0017] For example, the coupling layer can be a Ru (ruthenium) spacer layer. The coupling can be ferromagnetic or antiferromagnetic.

[0018] In some embodiments, the reference system is arranged below the free layer (lower spin valve), while the bias structure is arranged above the free layer. Alternatively, the reference system can be arranged above the free layer (upper spin valve), while the bias structure is arranged below the free layer.

[0019] In some embodiments, the reference system comprises a first antiferromagnet, and the biasing structure comprises a second antiferromagnet. The first antiferromagnet may have a first material composition or layer thickness that differs from a second material composition or layer thickness of the second antiferromagnet. This can lead to different blocking temperatures for the first and second antiferromagnets. The blocking temperature is the temperature at which magnetic coupling occurs between the ferromagnet and the adjacent antiferromagnet. Below the blocking temperature, the spins of the ferromagnet preferentially align in a direction determined by the magnetic moments of the antiferromagnet, while above this temperature, the spins are oriented in random directions.

[0020] In some embodiments, the first antiferromagnet has a higher blocking temperature than the second antiferromagnet. This means that the magnetic thermal annealing of the first antiferromagnet can be performed at a higher temperature than the magnetic thermal annealing of the second antiferromagnet. However, the first antiferromagnet can also have a lower blocking temperature than the second antiferromagnet. This means that the magnetic thermal annealing of the first antiferromagnet can be performed at a lower temperature than the magnetic thermal annealing of the second antiferromagnet.

[0021] In some embodiments, the first antiferromagnet of the reference system can have a lower blocking temperature than the second antiferromagnet of the biasing structure. Magnetic thermal annealing of the first and second antiferromagnets can be performed at a annealing temperature higher than the blocking temperatures of the two antiferromagnets (and with a weak magnetic field).

[0022] In some embodiments, the free layer has a rotationally symmetric or elliptical shape. For example, the free layer can have a disk shape. Spontaneous vortex formation can be facilitated by using a disk shape or a highly symmetrical shape.

[0023] According to another aspect, the present disclosure provides a method for forming a spin-valve device. The method comprises providing one or more layers forming a unidirectionally magnetized reference frame, providing a vortex-magnetized free layer, providing a non-magnetic layer (e.g., a transition or tunnel barrier) separating the reference frame from the free layer, and providing one or more layers forming a prestressing structure exchange-coupled with the free layer, wherein the prestressing structure has closed-flux vortex magnetization in a predetermined direction of rotation. The spin-valve device can, for example, be an MTJ device or a GMR device.

[0024] In some embodiments, the method includes providing a rotationally symmetric shape to the free layer to spontaneously form a vortex state in the free layer, annealing the bias structure at a first annealing temperature higher than a barrier temperature of the bias structure, and annealing the reference system at a second annealing temperature higher than a barrier temperature of the reference system but lower than the barrier temperature of the bias structure.

[0025] In some embodiments, an external unidirectional magnetic field is applied during annealing of the reference system. No external magnetic field is applied during annealing of the bias structure. This allows a circular exchange bias to form in the bias structure, which can then support a defined chirality in the free-layer vortex.

[0026] In some embodiments, an external unidirectional magnetic field is applied during the tempering of the reference system and the tempering of the prestressing structure. The reference system and the prestressing structure can be tempered in a single process in the presence of the external unidirectional magnetic field.

[0027] In some embodiments, an external unidirectional magnetic field is applied during annealing, such that at least one layer of the reference system is aligned parallel to one direction of the external unidirectional magnetic field. The external unidirectional magnetic field can be sufficiently small so that the vortex in the free layer is not significantly displaced from its equilibrium direction. In this case, only the entire structure (spin valve) needs to be annealed. Therefore, the prestressed structure and the reference system can be annealed in the same process. Short description of the characters

[0028] Some examples of devices and / or methods are described below only by way of example and with reference to the accompanying figures, in which the following applies. Fig. Figure 1A shows a side view of the first layer stack of a spin valve; Fig. 1B shows a side view of a second layer stack of a spin valve; Fig. Figure 2A shows a layer stack of a spin valve with a vortex-magnetized free layer; Fig. Figure 2B shows a Wheatstone bridge configuration of spin valves; Fig. Figure 3 shows vortex-magnetized free layers with different chirality; Fig. Figure 4A shows a layer stack of a spin valve according to a first embodiment; Fig. Figure 4B shows a layer stack of a spin valve according to a second embodiment; and Fig. Figures 5A-C disclose a method for forming a spin-valve device according to the present disclosure. Detailed description

[0029] Some examples will now be described in more detail with reference to the accompanying figures. However, other possible examples are not limited to the features of these detailed embodiments. Other examples may include modifications of the features, as well as equivalents and alternatives to the features. Furthermore, the terminology used herein to describe specific examples is not intended to be limiting of other possible examples.

[0030] Throughout the description of the figures, identical or similar reference numerals refer to identical or similar elements and / or features, which may be implemented identically or in a modified form while providing the same or a similar function. Furthermore, in the figures, the thicknesses of lines, layers, and / or regions may be exaggerated for clarity.

[0031] When two elements A and B are combined using "or," this is to be understood as revealing all possible combinations, i.e., only A, only B, and A and B, unless explicitly defined otherwise in a specific case. As an alternative formulation for the same combinations, "at least one of A and B" or "A and / or B" can be used. This applies accordingly to combinations of more than two elements.

[0032] If a singular form is used, such as "a," "an," and "the," and the use of only a single element is neither explicitly nor implicitly defined as mandatory, further examples may also use multiple elements to implement the same function. If a function is 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 is further understood that the terms "comprises", "comprising", "has" and / or "having" when used describe the presence of the specified 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.

[0033] Magnetoresistive sensor devices, such as giant magnetoresistive (GMR) or tunnel magnetoresistive (TMR) devices (also known as spin valves), can have a stack of alternating ferromagnetic and non-ferromagnetic layers. GMR and TMR spin valve devices are hereafter generally referred to as xMR devices.

[0034] From top to bottom, an xMR device in one embodiment can comprise an antiferromagnetic pinning layer, a ferromagnetic pinned layer, a paramagnetic or diamagnetic coupling layer, a ferromagnetic reference layer with a reference magnetization having a linear or straight pattern, an electrically insulating tunnel barrier or diamagnetic layer, and a ferromagnetic free layer. The person skilled in the art, taking advantage of the present disclosure, recognizes that the above composition of layers is only one of many ways to form an xMR sensor device. A reverse composition is also possible. For example, the free layer can comprise a composition of ferromagnetic and non-magnetic layers.A free layer, consisting of a multilayer structure with layers exhibiting high conductivity near the coupling layer and layers with low conductivity further away from the coupling, can be advantageous for some applications. The free layer or the pinned layer can be multilayer structures that include spin-injection layers, resulting in high spin polarization.

[0035] Fig. 1A and Fig. Figure 1B shows side views of embodiments of xMR components 100 with different layer stacks 101.

[0036] In the following, GMR components are briefly presented as examples of xMR components. GMR components are operated in a so-called CIP configuration (CIP = Current-In-Plane), meaning the applied electrical current flows parallel to the layer structure. There are several basic types of GMR components that have gained acceptance in practice. Some exemplary GMR components for practical use are shown in Fig. 1A and Fig. 1B.

[0037] The GMR component 100, which is used in Fig. Figure 1A shows a spin valve system in which a non-magnetic layer 104 is chosen to be thick enough to prevent coupling between ferromagnetic layers 102 and 106. A lower ferromagnetic layer 106 is strongly coupled to an antiferromagnetic layer 108, giving it a unidirectional preferred magnetization direction (i.e., not like a permanent magnet, since the two antiparallel states have the same energy) and being magnetically hard (comparable to a permanent magnet). The ferromagnetic layer 106 can be considered a reference layer. The upper ferromagnetic layer 102 is a soft magnetic layer and serves as a free layer. It can be remagnetized by even a small external magnetic field M, which changes its electrical resistance R.The magnetic free layer 102 may be configured to spontaneously form a closed flux magnetization pattern (in the side views of . Fig. 1A, Fig. 1B not visible) in the free layer 502. The reference layer 106 has a reference magnetization pattern with open flux. The reference layer 106 can be unidirectionally magnetized (e.g., in the x-direction). In other words, the reference magnetization pattern with open flux can correspond to a homogeneous, straight, uniaxial, or linear magnetic field with zero curl and zero divergence. A closed flux magnetization pattern can also be referred to as a vortex state. A spontaneously generated vortex state can form, for example, in the free layer 102 directly after its generation, or when no external magnetic field is applied.

[0038] The vortex-magnetized ferromagnetic free layer 102 is separated from the reference layer 106 by a non-magnetic layer 104, whose unidirectional magnetization direction is, however, pinned by coupling with an antiferromagnetic layer 108 via the so-called "exchange bias interaction". The basic operating principle of a spin-valve structure can be described using the magnetization and the R(H) curve in Fig. Figure 1A illustrates this. The magnetization direction of the reference layer 106 can be pinned in the negative direction. As the external magnetic field M increases from negative to positive values, the "free" ferromagnetic layer 102 can switch near the zero crossing (H = 0), and the resistance R can rise sharply. The resistance R can then remain high until the external magnetic field M is large enough to overcome the exchange coupling between the reference layer 106 and the antiferromagnetic layer 108 and also switch the reference layer 106. In the example of Fig. In 1A, the spin-valve device 100 is contacted from above by means of contacts 181 and 182. Optionally, the contacts 181 and 182 can have corresponding contact vias 191, 192 that extend vertically through one or more (e.g., all) layers of the magnetoresistive layer stack 101. The vias 191, 192 can provide an electrical connection to the electrical contacts 181, 182 through one or more (e.g., all) layers of the magnetoresistive structure 101. Alternatively, the contact terminals 181 and 182 could also be located at the bottom.

[0039] The GMR shift stack 101, which is in Fig. The GMR component shown in 1B differs from the GMR component shown in Fig. 1A is shown insofar as the lower antiferromagnetic layer 108 of Fig. 1A is replaced by a combination of a natural antiferromagnet (AFM) 110 and a synthetic antiferromagnet 106, 107, 109 (SAF; synthetic antiferromagnet) above, which is composed of the ferromagnetic layer 106 (reference layer), a ferromagnetic layer 107 (pinned layer), and a non-magnetic coupling layer 509 in between. In this way, the magnetization direction of the magnetic reference layer 106 can be pinned. The upper ferromagnetic layer 102, in turn, serves as a free layer whose vortex magnetization can be manipulated by an external magnetic field M. The advantage of using the combination of natural and synthetic antiferromagnets over the construction according to Fig. 1A can offer greater field and temperature stability. For example, Fig. In 1B, the layer stack 501 is contacted from below by means of contacts 581 and 582, which include corresponding vias 191 and 192 that can provide an electrical connection with electrical contacts 181 and 182 through one or more (e.g., all) layers of the layer stack 101. Alternatively, the contacts 181 and 182 could also be located on top.

[0040] In the examples shown, the spin-valve layer stacks 101 are implemented as GMR sensor elements in a CIP configuration. During operation or when coupled to an electrical circuit, current flows along the layers (in the plane). Other embodiments can also be implemented as a TMR, anisotropic (AMR), colossal (CMR), extraordinary (EMR), or any other xMR sensor element. A TMR device can be obtained, for example, if the non-magnetic layer 104 is made of a non-conductive material that forms a thin tunnel barrier. TMR devices can be used in a so-called CPP configuration (CPP = current-perpendicular-to-plane).

[0041] Fig. Figure 2A schematically shows a TMR device 200 with a vortex-magnetized ferromagnetic free layer 102.

[0042] Viewed from bottom to top, the TMR device 200 comprises an antiferromagnetic pinning layer 110 and a ferromagnetic pinned layer 107. The contact between the pinning layer 110 and the pinned layer 107 induces the exchange bias effect, which causes the magnetization of the pinned layer 107 to align in a preferred (unidirectional) direction. In other words, the pinned layer 107 can exhibit a linear magnetic flux pattern, as in the example of Fig. The TMR device 200 further comprises a coupling layer 109. The coupling layer 109 can be diamagnetic and can, for example, comprise ruthenium (Ru), iridium (Ir), copper (Cu), copper alloys, or similar materials. The coupling layer 109 spatially separates the pinned layer 107 from the ferromagnetic reference layer 106. Using this configuration, the magnetization of the reference layer 106 can align and be held in a direction antiparallel to the magnetization of the pinned layer 107. The TMR device 200 also comprises a tunnel barrier 104, which is electrically insulating and separates the reference layer 106 from a ferromagnetic free layer 102. The tunnel barrier can, for example, comprise MgO, AlO, or TiO.The free layer 102, the reference layer 106, and the pinned layer 107 can, in some embodiments, comprise iron (Fe), cobalt (Co), or nickel (Ni), and in some other embodiments, alloys thereof. Alloys can also comprise non-ferromagnetic materials, such as carbon, boron, nitrogen, and oxygen, wherein ferromagnetic materials constitute at least 50% of the material composition of the respective layer. For example, layers can comprise cobalt-iron (CoFe), CoFeB, or nickel-iron (NiFe) alloys. In contrast, the pinning layer 111 can, for example, comprise iridium, manganese, platinum, or alloys containing these materials.

[0043] During operation, or when coupled to an electrical circuit, electric charges can pass from one side of the tunnel barrier 104 to the other (CPP) in a predetermined amount when an external magnetic field is applied. The TMR effect is a quantum physical phenomenon that manifests as a change in the amount of charge passing through the tunnel barrier 104 when the direction of the external magnetic field is changed. This effect can arise from changes in the magnetization direction of the free layer 102 caused by the changing external magnetic field.

[0044] The free shift 102 in Fig. Layer 2A is circular in shape or, in other words, has a disk-like structure. The disk has a diameter d, which can be in the range of, for example, 100 nm to 10 µm. The disk also has a thickness t in the range of, for example, 10 nm to 100 nm to 300 nm. The thickness can exceed the thickness of the reference layer 106. Providing a layer with a rotationally symmetric structure can lead to the spontaneous formation of a closed-flux magnetization pattern in the free layer 102. Depending on the precise shape of the free layer 102, the closed-flux magnetization pattern can, for example, exhibit at least a Landau pattern, a circumferential pattern, a vortex pattern, or a combination of any of the aforementioned patterns. A Landau pattern has at least a partially polygonal closed shape, while a circumferential pattern can have a smoother, more rounded closed shape.A pure vortex pattern can be essentially circular. However, a closed-flux magnetization pattern in the plane can exhibit any combination of the aforementioned patterns. Furthermore, a closed magnetization line of a magnetization pattern can be entirely shaped according to any of the aforementioned patterns, but may also include sections that follow a different closed-flux magnetization pattern. The various types of closed-flux magnetization patterns can also be referred to as vortices. In other words, the vortex state can be obtained by selecting the disk thickness t in the range of, for example, 30 nm to 300 nm and the disk diameter d between 500 nm and 5 µm (see, for example, SCHOLZ, W. [et al.]: Transition from single-domain to vortex state in soft magnetic cylindrical nanodots. In: Journal of Magnetism and Magnetic Materials, Vol. 266, 2003, No. 1-2, pp. 155-163).In the case of a vanishing external magnetic field, a center of the vortex can be located essentially in a center of the magnetic free layer 102 such that a net magnetization of the respective magnetic free layer essentially vanishes.

[0045] A magnetic xMR sensor concept with a free layer 102 in a vortex configuration can exhibit near-zero hysteresis, which is particularly interesting for applications such as wheel speed or current measurement. The presence of the vortex state may be a prerequisite for low hysteresis. Critical parameters that can describe the regime in which the vortex state exists are the nucleation field Hn, in which the vortex nucleates, and the annihilation field Han, in which it is destroyed.

[0046] xMR devices with free layers 102 in a vortex configuration can be used in the form of Wheatstone bridge configurations for magnetic field detection. A Wheatstone bridge configuration is generally known in the prior art and in Fig. Figure 2B illustrates this. In the ideal application, the xMR devices used in the bridge configuration are matched with respect to electrical resistance and magnetic sensitivity under varying operating conditions (e.g., temperature, supply voltage). A major cause of offset error in the vortex xMR bridge configuration is an electrical mismatch between different branches (e.g., left and right branches). This ohmic offset error contribution is typically quite constant over the product lifetime and temperature. Consequently, this error can be trimmed by adding a constant voltage to the bridge signal (V1-V2). This trimming procedure works very well because the xMR mismatch value and the trimming devices are highly stable over lifetime and temperature. An additional offset error source is identified that is related to the vortex state of the xMR devices. Ideally (see Figure 2B), the xMR device is also highly stable over the product lifetime and temperature. Fig. 2) The vortex ground state (magnetization configuration for Hext = 0 mT) has Mx=0. Mx=0 results in the electrical xMR response always having the same resistivity / conductivity value over a perfectly aligned reference frame. In such a Wheatstone bridge configuration, the reference frame orientation of two of the sensors can be in opposite directions to implement a linear field sensor. These different reference layer magnetization directions can be implemented by locally heating individual elements via laser annealing and applying fields in different directions when different elements are laser annealed.

[0047] As a first-order deviation from an ideal case, the Mx magnetization in a vortex ground state remains constant only as long as the vortex state is not annihilated. After the vortex state is re-nucleated, the ground state magnetization Mx—which is responsible for the resistance value of the xMR device—can differ from the ground state before the annihilation / nucleation process. This second-order effect is not visible in perfect vortex structures. It requires a certain asymmetry in the disk geometry or even in the reference frame (see Fig. 3).

[0048] Besides the asymmetric geometry or inhomogeneous structure of the vortex, which cannot be avoided during device fabrication, the vortex chirality (vortex rotation direction) defines the difference in the ground state Mx. As long as the vortex-xMR device backnucleates with the same chirality, there is no difference in the detected ground state magnetization Mx.

[0049] To obtain a well-defined Mx magnetization after the annihilation / nucleation process, the vortex chirality should be well-defined. Well-defined means that the vortex chirality of the free layer 102 should not be altered by subsequent annihilation / nucleation processes. An additional, but important, constraint is that the vortex chirality should be defined for each annihilation / nucleation process. Vortex annihilation can be achieved with any field direction; the applied field strength must be greater than the annihilation field Han, but the direction can be arbitrary. The same condition applies to vortex nucleation. One challenge is defining the vortex chirality for all possible conditions.

[0050] In the present disclosure, it is proposed to solve this problem by directly applying a bias field effect to the free layer 102 of an xMR or spin-valve device. The applied bias field should exhibit vortex magnetization with a specific chirality. The effect used to generate the bias field can be the exchange bias effect—a bias effect between a layer of ferromagnetic material (FM) (free layer 102) and a bias structure deposited on top of the free layer 102.

[0051] A first embodiment of a spin-valve device 400 according to an embodiment of the present disclosure is described in Fig. 4A shown.

[0052] Like the spin-valve devices 100 and 200 mentioned above, the spin-valve device 400 comprises a layer stack containing one or more layers 106, 107, 109, and 110 forming a unidirectionally magnetized reference system, a vortex-magnetized ferromagnetic free layer 102, and a non-magnetic layer 104 separating the reference system 106, 107, 109, and 110 from the free layer 102. The reference system can alternatively also include layers 106 and 108, as shown in Fig. 1A. The non-magnetic layer 104 can be configured as a tunnel barrier or as a GMR junction, depending on whether the device 400 is an MTJ (magnetic tunnel junction) or a GMR device.

[0053] In addition, the spin valve device 400 includes one or more layers forming a bias structure 402 that is exchange-coupled to the free layer 102. The bias structure 402 has a vortex magnetization with a closed flux of a predetermined rotation direction (predetermined vortex chirality). As shown in Fig. As shown in Figure 4A, the bias structure 402 can be configured as a (natural) antiferromagnet exchange-coupled with the free layer 102. Alternatively, the bias structure 402 can also be configured as a ferrimagnet or as a high-coercivity ferromagnet exchange-coupled with the free layer 102. The vortex magnetization of the bias structure 402 can be more stable than the vortex magnetization of the free layer 102, meaning that the external magnetic field strength required to annihilate the vortex magnetization of the bias structure 402 can be higher than that required to annihilate the vortex magnetization of the free layer 102.

[0054] One technical implementation therefore consists of depositing an additional antiferromagnetic layer 402 on top of the free layer 102. An example of a material composition for the free layer 102 is NiFe, e.g., Ni 80 Fe 20Another example of the material composition of the free layer 102 is CoFe, e.g., Co 90 F 10 or Co 70 Fe 30 . Another example of the material composition of the free layer 102 is CoFeB, e.g., Co 60 Fe 20 B 20 or Co 72 Fe8B 20Examples of the material composition of the antiferromagnet 402 are PtMn, IrMn, NiMn, and MnN. A person skilled in the art, taking advantage of the present disclosure, recognizes that the antiferromagnet 402 can also be deposited below the free layer 102, for example, in a top-spin valve (TSV) arrangement. Furthermore, the antiferromagnetic pinning layer 402 can be identical to the antiferromagnetic pinning layer 110 used in the magnetic reference system 106, 107, 109, 110. To obtain a defined exchange bias in the reference system 106, 107, 109, 110 and in the free layer system, the two antiferromagnetic layer material systems can be correlated.

[0055] Typically, the antiferromagnetic pinning layer 110 exhibits a higher blocking temperature in the reference frame. This temperature is required to annihilate the unidirectional reference magnetization (e.g., in the x-direction). After device structuring, the vortex state can spontaneously form in the free layer 102. In a second annealing step, where the temperature is higher than the blocking temperature of the exchange-coupled free layer material but lower than the blocking temperature of the reference frame, the vortex magnetization of the free layer 102 is imprinted into the prestress structure 402. After this step, a vortex pattern with a defined chirality is present in the additional prestress structure 402. This exchange prestressing effect can define the vortex xMR chirality for the free layer 102 after any vortex annihilation / nucleation processes.

[0056] Another possible implementation is in Fig. Figure 4B shows that this can be implemented by using a non-magnetic or magnetic coupling layer 404 between the free layer 102 and the (exchange) bias structure 402. The coupling layer 404 allows the exchange bias between the free layer 102 and the (exchange) bias structure 402 and / or hysteresis to be adjusted.

[0057] In the example implementation without a coupling layer, a free layer 102 made of, for example, 80 nm CoFeB and a bias structure 402 with an antiferromagnetic layer 402 made of 5 nm IrMn can be used. In an example implementation with a coupling layer 104, a free layer 102 made of, for example, 80 nm CoFeB, a coupling layer made of 3 nm CoFe and a bias structure 402 with an antiferromagnetic layer 402 made of 5 nm IrMn can be used. In an example with a ferromagnetic and non-ferromagnetic coupling layer, a free layer 102 made of, for example, 80 nm CoFeB, a coupling layer made of 3 nm CoFe and a bias structure 402 with an antiferromagnetic layer 402 made of 5 nm IrMn can be used. B. 80 nm CoFeB, a non-ferromagnetic coupling layer of 0.2 nm Ta, a ferromagnetic coupling layer of 3 nm CoFe and a prestressing structure 402 with an antiferromagnetic layer 402 of 5 nm IrMn can be used.

[0058] Referring now to Fig. Section 5A-C describes an embodiment of a process for forming a spin-valve device according to the present disclosure.

[0059] Fig. 5A shows a step of forming a spin-valve layer stack comprising one or more layers forming a unidirectionally magnetized reference system 106, 107, 109, 110, a vortex-magnetized ferromagnetic free layer 102, and a non-magnetic layer 104 separating the reference system from the free layer 102. The formation of the spin-valve layer stack further comprises forming one or more layers forming a bias structure (antiferromagnetic layer) 402. The bias structure 402 may be provided over (on) the free layer 102. As shown in Fig. As further shown in 5A, the reference system 106, 107, 109, 110 can be annealed at a first magnetic annealing temperature which is higher than the blocking temperature of the reference system 106, 107, 109, 110.

[0060] In another in Fig. In the step shown in Figure 5B, rotationally symmetric or elliptical shapes can be formed in the free layer 102 and the layer(s) of the bias structure 402, respectively, to spontaneously form a vortex state in the free layer 102 and / or the bias structure 402. Here, circular magnetization can build up in the free layer 102 because the exchange bias of the bias structure 402 is too weak for a linear alignment of the magnetization.

[0061] In another in Fig. In step 5C, the antiferromagnetic layer(s) of the prestressing structure 402 can be magnetically annealed at a second magnetic annealing temperature that is higher than the blocking temperature of the prestressing structure 402. The second magnetic annealing temperature can be higher than the blocking temperature of the reference system 106, 107, 109, 110. This can be achieved, for example, if the antiferromagnet of the reference system 106, 107, 109, 110 has a different material composition or layer thickness than the antiferromagnet of the prestressing structure 402. PtMn, for example, has a higher blocking temperature compared to IrMn. 5 nm IrMn has a lower blocking temperature than 10 nm IrMn. At the second magnetic annealing temperature, the vortex magnetization of the free layer 102 can be imprinted (pinned) into the prestress structure 402.After cooling without any external magnetic field, a circular exchange bias forms in the upper antiferromagnet 402 and supports a defined chirality in the free-layer vortex. The lower exchange bias of the reference system 106, 107, 109, 110 remains in its original direction.

[0062] While in Fig. Figure 5A-C shows a BSV (bottom spin valve), the same principle also works for a TSV (top spin valve).

[0063] The present disclosure proposes spin valves with a unidirectionally magnetized reference frame in combination with a circumferentially magnetized free layer (vortex magnetization). The free layer exhibits vortex magnetization without any bias field contributions. The free-layer vortex forms spontaneously after structuring to a suitable D / t dimension (D = diameter, t = thickness). An antiferromagnetic layer can be placed on top of the vortex-type free layer to bias the free-layer chirality after annihilation / nucleation processes. The exchange bias on the free layer does not determine the vortex magnetization, but only the chirality of the vortex.

[0064] The antiferromagnet can be designed with different material compositions, crystallinity, or layer thickness to differentiate it from the antiferromagnet in the reference frame. Different blocking temperature distributions are required to define the vortex magnetization in the antiferromagnetic layer without degrading the reference layer alignment.

[0065] The aspects and features described in connection with a particular one of the previous examples may also be combined with one or more of the further examples to replace an identical or similar feature of that further example or to additionally introduce the features into the further example.

[0066] It is further understood that the disclosure of multiple steps, processes, operations, or functions disclosed in the specification or claims should not be construed as necessarily being in the described order, unless explicitly stated in the individual case or absolutely necessary for technical reasons. Therefore, the foregoing description does not limit the performance of multiple steps or functions to any particular order. Furthermore, in further examples, a single step, function, process, or operation may include and / or be broken down into multiple sub-steps, functions, processes, or operations.

[0067] When certain aspects related to a component or system are described, these aspects should also be understood as a description of the corresponding procedure. For example, a block, component, or functional aspect of the component or system may correspond to a feature, such as a process step, of the corresponding procedure. Similarly, aspects described in connection with a procedure should also be understood as a description of a corresponding block, element, property, or functional feature of that component or system.

[0068] The following claims are hereby included in the detailed description, each claim being a separate example. It should also be noted that, although a dependent claim may refer to a specific combination with one or more other claims, other examples may include a combination of the dependent claim with the subject matter of any other dependent or independent claim. Such combinations are hereby explicitly proposed unless it is stated in a specific case that a particular combination is not intended. Furthermore, features of a claim for any other independent claim are also intended to be included, even if that claim is not directly defined as dependent on that other independent claim.

Claims

[1] A spin valve device (400) comprising a layer stack comprising one or more layers (106; 107; 108; 109; 110) forming a unidirectionally magnetized reference system; a vortex-magnetized free layer (102); a non-magnetic layer (104) separating the reference system from the free layer (102); and one or more layers forming a bias structure (402) exchange-coupled to the free layer (102), the bias structure having a closed-flux vortex magnetization of a predetermined rotation direction. [2] The spin valve device (400) of claim 1, wherein the non-magnetic layer (104) comprises a non-conductive material forming a tunnel barrier. [3] The spin valve device (400) of claim 1, wherein the non-magnetic layer (104) comprises a conductive material forming a giant magnetoresistive, GMR, junction. [4] The spin valve device (400) according to any one of the preceding claims, wherein the bias structure (402) is formed as an antiferromagnet. [5] The spin valve device (400) according to any one of claims 1 to 3, wherein the bias structure (402) is formed as a ferrimagnet. [6] The spin valve device (400) according to any one of the preceding claims, wherein an external magnetic field strength required for the annihilation of the vortex magnetization of the bias structure (402) is higher than for the annihilation of the vortex magnetization of the free layer (102). [7] The spin valve device (400) according to any one of the preceding claims, further comprising a non-magnetic or magnetic coupling layer (404) between the free layer (102) and the bias structure (402). [8] The spin valve device (400) according to any one of the preceding claims, wherein the reference system (106; 107; 108; 109; 110) and the bias structure (402) are arranged on different sides of the free layer (102). [9] The spin valve device (400) according to any one of the preceding claims, wherein the reference system (106; 107; 108; 109; 110) comprises a first antiferromagnet and the bias structure (402) comprises a second antiferromagnet, wherein the first antiferromagnet has a first material composition or layer thickness that differs from a second material composition or layer thickness of the second antiferromagnet. [10] The spin valve device (400) according to any one of the preceding claims, wherein the reference system (106; 107; 108; 109; 110) comprises a first antiferromagnet and the bias structure (402) comprises a second antiferromagnet, the first antiferromagnet having a different blocking temperature than the second antiferromagnet. [11] The spin valve device (400) according to any one of the preceding claims, wherein the free layer (102) has a rotationally symmetric shape. [12] A method of forming a spin valve device, the method comprising Providing one or more layers forming a unidirectionally magnetized reference system; Providing a vortex-magnetized free layer; Providing a non-magnetic layer separating the reference system from the free layer; and Providing one or more layers forming a bias structure exchange-coupled to the free layer, wherein the bias structure has a closed-flux vortex magnetization of a predetermined rotation direction. [13] The method according to claim 12, wherein the method comprises: Providing a rotationally symmetric shape to the free layer to spontaneously form a vortex state in the free layer; Annealing the bias structure at a first annealing temperature that is higher than a barrier temperature of the bias structure; Annealing the reference system at a second annealing temperature that is higher than a barrier temperature of the reference system but lower than the barrier temperature of the bias structure. [14] The method of claim 13, wherein an external unidirectional magnetic field is applied during annealing of the reference system and wherein no external magnetic field is applied during annealing of the bias structure.

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