MAGNETORESISTIVE COMPONENT

Abstract

A magnetoresistive component (100) is provided, comprising at least one magnetoresistive element (110) comprising a layer stack of ferromagnetic layers (112; 114; 116; 118) and non-magnetic layers (113; 115) stacked in a first direction. The layer stack comprises a ferromagnetic layer (112; 118) with a magnetic orientation to be switched. Adjacent to the ferromagnetic layer (112; 118), a first conductor (120-1) extends in a second direction, and a second conductor (120-2) extends in a third direction. The first and second conductors are configured to induce spin-orbit torque (SOT) in the ferromagnetic layer (112; 118). A control circuit (130) is configured to apply a first current pulse to the first conductor (120-1) and a second current pulse to the second conductor (120-2) in a temporally overlapping manner and with different time characteristics.For example, the control circuit (130) may be configured to switch off the second current pulse before the first current pulse is switched off in order to switch the magnetic orientation of the ferromagnetic layer (112; 118).

Description

Area

[0001] The present disclosure relates generally to magnetoresistive (MR) devices, and more particularly to switching magnetizations in MR devices using the spin-orbit torque (SOT) effect. background

[0002] Conventional magnetic sensing devices based on magnetoresistive materials (e.g., AMR, GMR, TMR) can be limited in their ability to measure static magnetic field components very accurately. Offset error in these types of devices depends on device-to-device matching, which can be dominated by manufacturing limitations. The same reasoning applies to Hall-effect devices, but one advantage of a Hall device is the ability to suppress first-order mismatches by applying a so-called spinning-current technique. To implement offset-reducing signal conditioning methods for magnetoresistive devices, magnetization directions in defined magnetic layers must be changed or controlled by electrical signals (e.g., currents).

[0003] Offset-reducing signal conditioning techniques for magnetoresistive components are known, for example, for AMR sensing devices. For off-chip or on-chip coils, an AMR transfer curve can be inverted by changing the magnetization direction, the so-called flipping AMR principle. A disadvantage of this principle is the power consumption required to achieve the AMR flipping fields.

[0004] Recently, the use of the spin-orbit torque (SOT) effect was proposed to switch the magnetic layer of the reference system (Luo, K., Guo, Y., Li, W., Zhang, B., Wang, B., and Cao, J.: “Implementation of a full Wheatstone-bridge GMR sensor by utilizing spin-orbit torque induced magnetization switching in synthetic antiferromagnetic layer”, Journal of Applied Physics). This technique allows for the implementation of larger signal ranges with lower power consumption compared to flipping AMR. In commonly used SOT switching schemes, a bias field is required to enable deterministic switching. Methods for reducing the bias field are described in KRIZAKOVA, Viola [et al.]: Spin-orbit torque switching of magnetic tunnel junctions for memory applications. In: Journal of Magnetism and Magnetic Materials, Vol. 562, 2022, 169692-1-169692-21, summarized.

[0005] US 2021 / 0 202 829 A1 describes a spin-orbit torque-based magnetic memory device (SOT-MRAM) in which a ferromagnetic element is switched by noncollinear current pulses in a neighboring heavy metal layer. The current pulses exhibit a phase difference and are generated either by two orthogonal or nonlinear current components, whereby the sum of their magnitudes remains constant, but the flow direction varies over time. The goal is to make the magnetization change more efficient and reduce thermal losses due to Joule heating.

[0006] ZHANG, Yin [et al.]: Breaking the current density threshold in spin-orbit-torque magnetic random access memory. In: Physical Review B, Vol. 97, 2018, Art.-No. 144416, pp. 1-6, deals with a theoretical analysis and simulation of an optimized control strategy for SOT-MRAM cells to significantly reduce the threshold of the current density required for magnetization reversal. This strategy uses two orthogonal, time-varying current pulses whose relative phase position is optimized. The article demonstrates mathematically and through simulations that this makes the switching process more energy-efficient and faster and provides analytical formulations for determining the optimal current pulse profile.

[0007] LIU, YD [et al.]: Field-free ultrafast magnetization reversal of a nanodevice by a chirped current pulse via spin-orbit torque. January 12, 2024. URL: https: / / arxiv.org / pdf / 2401.04882 describes a method for fast, field-free magnetization reversal in a nanoscale device using a chirped current pulse (CCP). A single frequency-modulated current pulse is sent through a heavy metal layer, inducing spin-orbit torque. The article experimentally and theoretically investigates the efficiency of the CCP technique with regard to required current density, switching speed, and reliability. The method enables particularly fast and efficient magnetization reversals without an external magnetic field.

[0008] Therefore, there is a need to switch the magnetic layer of the reference system without the need for bias fields. Summary

[0009] This need is met by magnetoresistive devices and methods according to the appended claims.

[0010] According to a first aspect, the present disclosure provides a magnetoresistive (MR) device. The MR device comprises at least one MR element. The MR element may be an MR sensing element or an MR memory element. The MR element may have a spin-valve structure. The MR element comprises a layer stack with ferromagnetic and non-magnetic layers stacked in a first direction. For example, the first direction may be a vertical direction (e.g., z-direction). The layer stack of the MR element comprises a ferromagnetic layer whose magnetic orientation is to be switched. The ferromagnetic layer may be a reference layer / system or a magnetic free layer of the MR element. The MR device further comprises, adjacent to the ferromagnetic layer, a first conductor extending in a second direction (e.g., x-direction) and a second conductor extending in a third direction (e.g., x-direction).B. y-direction). The second and third directions may span a plane to which the first direction is perpendicular. For example, the second direction (e.g. x-direction) may be perpendicular to the first direction (e.g. z-direction). The third direction (e.g. y-direction) may be perpendicular to the first direction (e.g. z-direction) and / or the second direction (e.g. x-direction). The first and second conductors are configured to induce spin-orbit torque (SOT) in the ferromagnetic layer adjacent to the first and second conductors. The MR device further comprises a control circuit configured to apply a first current pulse to the first conductor and a second current pulse to the second conductor in a temporally overlapping manner. That is, the first current pulse and the second current pulse overlap in time.The control circuit is further configured to apply the first and second current pulses with different respective timing characteristics. This means that the first and second current pulses may vary in one or more aspects with respect to their timing characteristics. These differences may include, for example, variations in duration or amplitude variations. The current pulses may take any functional form.

[0011] For example, the control circuit may be configured to vary a relative strength of the first current pulse and the second current pulse during application of the first current pulse and / or the second current pulse.

[0012] In some embodiments, the control circuit may be configured to turn off the second current pulse (e.g., to switch the current intensity of the second current pulse to zero or near zero) before turning off the first current pulse.

[0013] In this way, magnetization of the ferromagnetic layer can be switched without a magnetic bias field.

[0014] In some embodiments, the ferromagnetic layer whose magnetic orientation is to be switched is a magnetic reference layer. In particular, the ferromagnetic layer may be part of a synthetic antiferromagnet (SAF) comprising a first and a second ferromagnetic layer separated by a non-magnetic layer. The SAF may be used as a magnetic reference layer of the MR sensing element. An SAF in the context of MR devices is a structure designed to mimic the behavior of antiferromagnetic materials through a synthetic stack of ferromagnetic layers separated by a non-magnetic conductive or insulating spacer layer.A characteristic of a SAF is the antiparallel alignment of the magnetic moments in the ferromagnetic layers, achieved by indirect magnetic coupling mediated by the spacer layer. A typical SAF structure comprises two (or more) thin ferromagnetic layers (such as CoFe or NiFe) separated by a very thin non-magnetic layer (usually ruthenium, Ru, due to its unique ability to induce antiferromagnetic coupling at certain thicknesses). The thickness of the Ru layer can be controlled to within a few atomic layers to ensure that the RKKY (Ruderman-Kittel-Kasuya-Yosida) interaction or other exchange coupling mechanisms can induce a strong antiparallel alignment between the magnetic moments of the adjacent ferromagnetic layers.

[0015] In some embodiments, the ferromagnetic layer whose magnetic orientation is to be switched is a magnetic free layer. The magnetic free layer may be separated from the magnetic reference layer (e.g., SAF) by a non-magnetic layer. In some embodiments, the non-magnetic layer between the free layer and the magnetic reference layer (e.g., SAF) is a tunnel barrier. A tunnel barrier is a key component in certain types of magnetoresistive devices, such as tunnel magnetoresistance (TMR) sensors and magnetic random access memory (MRAM) cells. It comprises a thin, non-conductive or insulating layer separating two ferromagnetic layers (e.g., free layer and reference layer).Although it is an insulator, the tunnel barrier is thin enough (typically a few nanometers) to allow quantum tunneling of electrons between the two ferromagnetic layers. This phenomenon is the basis for the tunneling effect observed in these devices. The ability of electrons to tunnel through the barrier depends on the relative orientation of the magnetic moments in the ferromagnetic layers on either side of the barrier. When the magnetic moments are parallel to each other, the resistance to electron tunneling is lower, and when the moments are antiparallel, the resistance is higher. This change in resistance as a function of magnetic orientation is called tunneling magnetoresistance (TMR).The tunnel barrier can be made of materials such as aluminum oxide (Al2O3) or magnesium oxide (MgO), which are insulators that can be fabricated into very thin layers while maintaining their insulating properties.

[0016] In some embodiments, the non-magnetic layer between the free layer and the magnetic reference layer (e.g., SAF) is a conductive spacer layer. In the context of MR devices, particularly those based on giant magnetoresistance (GMR) or spin-valve structures, a conductive spacer layer is a component that separates two ferromagnetic layers. Unlike the insulating tunnel barrier used in TMR devices, the conductive spacer layer is made of a non-magnetic metal and enables the conduction of electrons between the ferromagnetic layers. A primary role of the conductive spacer layer is to facilitate the transfer of electrons while maintaining their spin orientation, which is essential for the occurrence of the GMR effect.The GMR effect is based on the difference in electrical resistance encountered by electrons with spins aligned parallel or antiparallel to the magnetization of the ferromagnetic layers. When the magnetizations of the ferromagnetic layers are parallel, electrons with matching spin orientations can pass through the structure more easily, resulting in lower electrical resistance. Conversely, when the magnetizations are antiparallel, the resistance increases because electrons with certain spin orientations are more likely to be scattered. The material selected for the conductive spacer layer can influence the overall performance of the MR device. Common spacer materials include copper (Cu), silver (Ag), or gold (Au), which are known for their good electrical conductivity and minimal interaction with the electron spin.

[0017] In some embodiments, the ferromagnetic layer whose magnetic orientation is to be switched is a perpendicular anisotropy ferromagnet. A perpendicular anisotropy ferromagnet (also known as perpendicular magnetic anisotropy, PMA) is a type of ferromagnetic material in which the easy axis of magnetization is oriented perpendicular to the plane (out-of-plane) of the material, rather than in-plane. This means that the magnetic moments of the atoms in the material prefer to align perpendicular to the surface of the material, creating a magnetic field that points either up or down relative to the surface.

[0018] In some embodiments, another ferromagnetic layer (e.g., free layer) of the layer stack and not adjacent to the first / second conductor is a perpendicular crystalline anisotropy ferromagnet. A perpendicular crystalline anisotropy ferromagnet refers to a type of ferromagnetic material in which the crystalline structure inherently favors magnetic moments oriented perpendicular to the plane of the material. This property is known as perpendicular magnetic anisotropy (PMA) at the crystalline plane and is determined by the crystal lattice structure of the material. The anisotropy is a result of the directionality of the magnetic energy within the crystal, making it energetically more favorable for the spins in the material to orient in a direction perpendicular to the surface.

[0019] In some embodiments, another ferromagnetic layer (e.g., free layer) of the layer stack and not adjacent to the first / second conductor is a ferromagnet comprising a predominant in-plane magnetization in the absence of an external magnetic field, such as a flux-locked state at a zero external magnetic field. A ferromagnet forming a flux-locked state at a zero external magnetic field is a phenomenon where the magnetic moments within a ferromagnetic material arrange themselves in a configuration that minimizes the magnetic energy of the system, particularly the stray magnetic field energy, without the influence of an external magnetic field. This arrangement results in a state where the internal magnetic flux is contained within the material, effectively reducing the magnetic field outside the material to nearly zero.This configuration is also known as a "closed-flux" or "magnetic vortex" state. In other embodiments, the ferromagnetic layer (e.g., free layer) may be formed from two ferromagnetic layers forming a SAF.

[0020] In some embodiments, the MR device is used to detect or sense an external magnetic field in response to a measured resistance. In this case, the ferromagnetic layer whose magnetic orientation is to be switched may be a magnetic reference layer, and another ferromagnetic layer of the layer stack not adjacent to the first / second conductor may be a magnetic free layer.

[0021] In some embodiments, the MR device is used as an MRAM (Magnetoresistive Random Access Memory) memory cell. In this case, the ferromagnetic layer whose magnetic orientation is to be switched may be a magnetic free layer, and another ferromagnetic layer of the layer stack and not adjacent to the first / second conductor may be a magnetic reference layer. An MRAM memory cell is a type of non-volatile memory that uses the magnetoresistive effect to store data. The basic principle behind MRAM is the use of magnetic states to represent information bits, typically "0" and "1," and the ability to read these states through changes in electrical resistance.An MRAM memory cell typically consists of a magnetic tunnel junction (MTJ) consisting of two ferromagnetic layers separated by a thin insulating layer (tunnel barrier). One of the ferromagnetic layers is the reference layer, whose magnetic orientation is fixed, while the other layer is the free layer, whose magnetic orientation can be switched between parallel and antiparallel orientations relative to the reference layer. The parallel orientation represents one binary state ("1" or "0"), and the antiparallel orientation represents the other ("0" or "1").

[0022] In some embodiments, the control circuit is configured to apply the second current pulse to the second conductor at a magnitude equal to or greater / less than the first current pulse. In this way, the magnetization of the adjacent ferromagnetic layer can be switched without a magnetic bias field. In some embodiments, the magnitude (strength) of the second current pulse can be varied relative to the first current pulse.

[0023] In some embodiments, a start time of the first current pulse is equal to a start time of the second current pulse, and a duration of the first current pulse is longer than a duration of the second current pulse. In this way, the magnetization of the adjacent ferromagnetic layer can be switched without a magnetic bias field.

[0024] In some embodiments, the first current pulse magnitude has a first functional shape as a function of time and the second current pulse has a different second functional shape as a function of time.

[0025] In some embodiments, the control circuit is configured to apply, in a first state, the second current pulse with a positive polarity in addition to the first current pulse to switch the magnetic orientation of the ferromagnetic layer from a first orientation (e.g., downward) to a second orientation (e.g., upward), and to apply, in a second state, the second current pulse with a negative polarity to switch the magnetic orientation of the ferromagnetic layer from the second orientation (e.g., upward) to the first orientation (e.g., downward). In this way, the magnetization of the adjacent ferromagnetic layer can be switched between two states without a magnetic bias field.

[0026] In some embodiments, the control circuit is further configured to provide a difference between a first sensor signal in the first state and a second sensor signal in the second state as an output sensor signal. In this way, an offset error of the MR device can be reduced.

[0027] In some embodiments, the first and second conductors are arranged directly adjacent to the layer stack of the MR element (e.g., MTJ). In particular, the first and second conductors are arranged directly adjacent to the ferromagnetic layer whose magnetic orientation is to be switched. The first and second conductors can be arranged directly below or directly above the ferromagnetic layer whose magnetic orientation is to be switched. In some embodiments, the first and second conductors are arranged directly adjacent to the magnetic free layer or directly adjacent to the magnetic reference layer.

[0028] In some embodiments, the first and second conductors are arranged in a crossbar structure.

[0029] In some embodiments, the first and second conductors comprise (are made of) non-magnetic heavy metal. The heavy metal may comprise Pt, Ta, or W. In the context of SOT, a non-magnetic heavy metal plays a role in generating efficient spin currents due to its strong spin-orbit coupling. Spin-orbit coupling is a relativistic effect arising from the interaction between an electron's spin and its orbital motion around the nucleus, particularly pronounced in heavy metals due to their large atomic numbers. This interaction can be exploited to manipulate the magnetization of neighboring ferromagnetic materials without applying an external magnetic field, relying instead on electric currents through the heavy metal.

[0030] In some embodiments, the MR device further comprises electrodes at both ends of the layer stack for applying a current perpendicular to the plane (CPP) through the layer stack.

[0031] According to a second aspect, the present disclosure provides a magnetoresistive random access memory (MRAM) cell comprising the MR device according to any one of the preceding examples.

[0032] According to a further aspect, the present disclosure provides a method for switching a magnetic orientation of a ferromagnetic layer. The method comprises providing at least one MR element comprising a layer stack with ferromagnetic and non-magnetic layers stacked in a first direction. The layer stack of the MR element comprises the ferromagnetic layer whose magnetic orientation is to be switched. The ferromagnetic layer may be a reference layer / system or a magnetic free layer of the MR element. The ferromagnetic layer may have out-of-plane magnetization in the first direction. The method further comprises providing, adjacent to the ferromagnetic layer, a first conductor extending in a second direction (e.g., x-direction) and a second conductor extending in a third direction (e.g., y-direction).The second and third directions may span a plane to which the first direction is perpendicular. For example, the second direction (e.g., x-direction) may be perpendicular to the first direction. The third direction (e.g., y-direction) may be perpendicular to the first and / or second directions. The first and second conductors are configured to induce SOT in the magnetic reference layer. The method further comprises applying a first current to the first conductor and a second current to the second conductor in a temporally overlapping manner and with different time characteristics.

[0033] In some embodiments, the second current is turned off before the first current is turned off to switch the magnetic orientation of the ferromagnetic layer.

[0034] In some embodiments, the second current is applied to the second conductor at a magnitude equal to or greater than the first current.

[0035] In some embodiments, a start time of the first stream is equal to a start time of the second stream and wherein a duration of the first stream is longer than a duration of the second stream.

[0036] In some embodiments, the method comprises, in a first state, applying the second current having a positive polarity in addition to the first current to switch the magnetic orientation of the ferromagnetic layer from a first orientation to a second orientation, and, in a second state, applying the second current having a negative polarity to switch the magnetic orientation of the ferromagnetic layer from the second orientation to the first orientation.

[0037] In some embodiments, the method includes providing an output sensor signal corresponding to a difference between a first sensor signal in the first state and a second sensor signal in the second state. Short description of the characters

[0038] Some examples of devices and / or methods are described below solely by way of example and with reference to the accompanying figures, in which: Fig. 1 shows a basic structure of an MR sensing device according to an embodiment; Fig. Figure 2 shows a transfer curve of an xMR layer stack when the reference layer is switched between an up and a down state; Fig. 3 shows a basic structure of an MRAM cell according to an embodiment; Fig. 4 shows an embodiment in which several MR elements are arranged on a j x-Power line can be positioned, with the element that should be switched being connected by the j y -current can be selected; Fig. Figure 5 shows the principle of switching, applying a combination of x- and y-SOT currents; Fig. 6 shows exemplary current sequences for switching the ferromagnetic layer with SOT currents; and Fig. Figure 7 shows an exemplary configuration of reference layers when the MR device is operated in a Wheatstone bridge configuration. Detailed description

[0039] 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.

[0040] 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.

[0041] When two elements A and B are combined using "or," this is to be understood as disclosing all possible combinations, i.e., only A, only B, and A and B, unless explicitly defined otherwise in the individual case. Alternative wording for the same combinations may be "at least one of A and B" or "A and / or B." This applies accordingly to combinations of more than two elements.

[0042] 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 subsequently described as being implemented using multiple elements, further examples may implement the same function using a single element or a single processing entity.It is further understood that the terms "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.

[0043] MRAM has emerged as a promising candidate for a non-volatile memory cell due to its unique combination of speed and endurance. SOT switching can be used to improve the durability of MRAM elements by separating the readback current from the write current. However, SOT switching schemes require symmetry breaking to achieve reliable and deterministic switching, which was originally achieved by applying an external field parallel to the SOT current direction. Since then, various methods have been proposed to circumvent the need for an additional bias field, as by Krizakova et al. These include using lateral geometry asymmetries, thickness asymmetries, tilted anisotropy axis, in-plane magnets, exchange bias, combined SOT and STT, and crystal symmetries. Sverdlov et al. used two SOT pulses for switching.However, magnetic-field-free switching could only be achieved by achieving a geometric overlap of approximately 30% between the second pulse wire and the free layer, which is technologically very difficult to achieve. Additionally, "write pulse 1" is applied before the second consecutive current, requiring very precise pulse timing.

[0044] The present disclosure proposes a switching scheme that (i) does not require geometric overlap of two wires and (ii) does not require precise timing of the two pulses. To illustrate the concept, micromagnetic simulations comprising SOT can be simulated by a damping (H dl ) and field-like (H fl ) torque term, which is expanded to the Gilbert equation, ∂tm=−γm×(Heff−Hdlm×p−Hflp)+αm×∂tm.

[0045] The damping and field-like fields are defined as: Hdl=jeℏ2eμ0tMs⋅ηdl Hfl=jeℏ2eμ0tMs⋅ηfl where j e is the applied current density, e is the electron charge, t is the thickness of the ferromagnetic layer on which the SOT acts, M s is the saturation magnetization of the ferromagnetic layer. η dl and η fl are the damping and field efficiencies, respectively. The normalized magnetization is denoted by m, and the spin polarization direction generated by the SOT current is denoted by p. When a current is applied in the x-direction, the spin polarization of a spin current directed in the z-direction can point in the y-direction.

[0046] The concept presented in this revelation is in Fig. 1, which schematically illustrates an MR device 100 according to an embodiment.

[0047] The Fig. The MR device 100 shown in Figure 1 includes an MR sensing element 110. Those skilled in the art, having benefit from the present disclosure, will recognize that the MR device 100 could also include more than one MR sensing element 110, for example, when used in half-bridge (two MR sensing elements) or full-bridge (four MR sensing elements) configurations.

[0048] The MR sensing element 110 comprises a layer stack of ferromagnetic and non-magnetic layers. In the illustrated example, the ferromagnetic and non-magnetic layers of the MR sensing element 110 are stacked in the vertical direction (z-direction). The exemplary layer stack of Fig. 1 includes a first ferromagnetic layer 112, which may be designed with a low coercivity (easily magnetizable and demagnetizable). The first ferromagnetic layer 112 may act as a magnetic free layer of a sensor device. Example materials for the magnetic free layer 112 are NiFe (nickel-iron, also known as permalloy), CoFe (cobalt-iron), and CoFeB (cobalt-iron-boron). The magnetic free layer 112 may be a ferromagnet that forms a flux-locked (vortex) state in the plane at zero external magnetic field. In other embodiments, the layer 112 may be in a quasi-homogeneous in-plane magnetization state at zero field. In yet other embodiments, the ferromagnetic layer 112 may form a SAF.

[0049] Alternatively, the magnetic free layer 112 may be a ferromagnet with perpendicular crystalline anisotropy. A ferromagnet with perpendicular crystalline anisotropy refers to a type of ferromagnetic material in which the crystalline structure inherently favors magnetic moments oriented perpendicular to the plane of the material.

[0050] The layer stack of the MR sensing element 110 includes one or more second ferromagnetic layers 118 beneath the magnetic free layer 112, which may be designed with a high coercivity (maintains its magnetic orientation under external magnetic fields). The layer(s) 118 may act as a magnetic reference layer / system against which the orientation of the magnetic free layer 112 is compared. Fig. The example illustrated in Figure 1 involves the use of a synthetic antiferromagnet (SAF) structure for the magnetic reference layer 118. SAFs comprise two (or more) ferromagnetic layers 114, 116 separated by a non-magnetic coupling layer (often ruthenium, Ru). Other 3d, 4d, and 5d transition metals can also be used, such as V, Nb, Mo, Ta, W, Re, and Ir. The coupling layer 115 induces an antiferromagnetic coupling between the ferromagnetic layers 114, 116. This arrangement can improve the stability of the magnetic orientation of the reference layer 118.

[0051] In embodiments relating to TMR sensing elements, a non-magnetic layer 113 may be formed between the magnetic free layer 112 and the magnetic reference layer / system 118 as a tunnel barrier. The tunnel barrier 113 may be made of materials such as aluminum oxide (Al2O3) or magnesium oxide (MgO), which are insulators that can be fabricated into very thin layers while maintaining their insulating properties.

[0052] In embodiments related to GMR sensing elements, the non-magnetic layer 113 may be formed as a conductive spacer layer between the magnetic free layer 112 and the magnetic reference layer / system 118. Exemplary materials for the spacer layer 113 include copper (Cu), silver (Ag), or gold (Au).

[0053] While the magnetic free layer 112 in the Fig. 1 has an in-plane magnetization (in the xy plane), the magnetic reference layer / SAF 118 has an out-of-plane reference magnetization in the vertical direction (z direction). For example, the ferromagnetic layer 116 can be a ferromagnet with perpendicular magnetic anisotropy (PMA). The coupling layer 115 of the SAF 118 facilitates an antiferromagnetic coupling between the adjacent ferromagnetic layers 114, 116. This antiferromagnetic coupling ensures that the magnetic moments of the ferromagnetic layers 114, 116 are aligned in opposite directions (antiparallel alignment).

[0054] Beneath the layer stack of the MR sensing element 110 (beneath the ferromagnetic layer 116), the MR device 100 further comprises a first electrical conductor 120-1 extending in the x-direction and a second conductor 120-2 extending in the y-direction. Thus, in the illustrated example, the first and second conductors 120-1, 120-2 are arranged in a crossbar structure, with the layer stack of the MR sensing element 110 being placed at the intersection of the first and second conductors 120-1, 120-2. Those skilled in the art, having benefit from the present disclosure, will appreciate that the first and second conductors 120-1, 120-2 do not necessarily have to be arranged perpendicular to each other.

[0055] The MR sensing element 110 is configured to induce SOT in the magnetic reference layer / SAF 118 using the first and second conductors 120-1, 120-2. A plane or layer spanned by the first and second conductors 120-1, 120-2 may also be referred to as an SOT layer. The first and second conductors 120-1, 120-2 may comprise (consist of) a non-magnetic heavy metal, such as Pt, Ta, or W. In the context of SOT, a non-magnetic heavy metal plays a role in generating efficient spin currents due to its strong spin-orbit coupling. When a current-carrying non-magnetic heavy metal is coupled to a ferromagnetic layer, a phenomenon known as the spin Hall effect (SHE) may occur, resulting in the generation of a spin current perpendicular to the charging current.This interaction can impact spintronic devices and can be used to create ways to manipulate magnetic moments in ferromagnetic materials without applying an external magnetic field. The spin Hall effect (SHE) in non-magnetic heavy metals arises due to the strong spin-orbit coupling in these materials. When an electric current flows through such a metal, it causes electrons with opposite spins to deflect in opposite directions, generating a transverse spin current. This effect creates a spin accumulation on opposite sides of the material with a spin polarization perpendicular to the direction of the charging current. When the spin current generated by the SHE in the heavy metal layer 120-1, 120-2 enters the (directly) adjacent ferromagnetic layer 116, it can exert a torque on the magnetization of the ferromagnet.This torque can be used to manipulate the magnetic state of the ferromagnetic layer 116, including switching its magnetization direction. This process is known as spin-transfer torque (STT) when it involves the direct transfer of spin angular momentum from conduction electrons to the magnetization, and spin-orbit torque (SOT) when it specifically involves torques generated by spin-orbit effects, such as those from the SHE. The torque can realign the magnetization direction, allowing the magnetic state of the ferromagnetic layer 116 to be switched between various stable configurations (e.g., from parallel to antiparallel relative to a reference orientation). This capability can also be useful for memory devices, such as MRAM, where it enables the writing of information without the need for magnetic fields.

[0056] The MR device 100 further includes a control circuit 130 configured to apply a first current pulse to the first conductor 120-1 and a second current pulse to the second conductor 120-2 in a temporally overlapping manner. That is, the first and second current pulses overlap in time. The first and second current pulses have different timing characteristics.

[0057] For example, control circuit 130 may be configured to decrease the magnitude of the second current pulse or turn it off before decreasing the magnitude of the first current pulse or turning it off. A current pulse refers to a transient flow of electrical current whose amplitude may change abruptly and which may last for a limited period of time before returning to its initial value or zero. Current pulses can be characterized by their shape (such as square, triangular, or sinusoidal), amplitude (the maximum current level), duration (the length of time the pulse lasts), and repetition rate (how frequently pulses occur over time).

[0058] Furthermore, the control circuit 130 can be configured to apply the second current pulse to the second conductor 120-2 with a magnitude equal to or greater / less than the first current pulse. In this way, the reference magnetization of the adjacent layer 116 can be switched without a magnetic bias field. In some embodiments, a start time of the first current pulse can be equal to a start time of the second current pulse, and a duration of the first current pulse can be longer than a duration of the second current pulse.

[0059] The electrical currents in the SOT layer are transmitted via at least two current lines (such as j x and j y) or conductors 120-1, 120-2 spanning the SOT layer. This can facilitate the reversal of the adjacent magnetic reference layer 116 and 114 (or 118) with perpendicular magnetization (in the z-direction). Unlike conventional switching schemes, the proposed method does not require additional external fields such as a B x-field. The magnetic reference layer 118 to be switched may form a SAF (comprising two antiparallel coupled layers 114 and 116). In other embodiments, the magnetic reference layer 118 may consist of only one layer 116. When the magnetization of the ferromagnetic layer 116 reverses due to the strong coupling across the SOT layer spanned by the conductors 120-1, 120-2, the ferromagnetic layer 114 will also reverse. The coupling layer 115 between the layers 114, 116 could be any layer that promotes strong coupling, such as strong antiferromagnetic coupling via materials like Ru or Gd. Furthermore, it might be advantageous to use coupling layers that also promote strong perpendicular anisotropy.

[0060] The proposed circuit scheme can be used for various applications, including advanced MR sensors.

[0061] Fig. 1 depicts schematic representations of the proposed MR device 100, which includes a free layer 112 that may have zero magnetization in the perpendicular direction (z-direction) when no external magnetic field is applied. This can be achieved by using a layer exhibiting in-plane magnetization. Alternatively, a layer with perpendicular anisotropy can be used, fragmenting into multi-domain regions with both up- and down-magnetization. In other embodiments, the free layer 112 may manifest a flux-locked state. In yet other embodiments, the free layer is formed as a SAF. Examples of flux-locked states include a vortex configuration or an antiparallel-coupled layer structure for the free layer 112. For sensor applications, the in-plane magnetization of the free layer 112 could exist.

[0062] When an external magnetic field is applied in the perpendicular direction (z-direction), the magnetization component in free layer 112 increases with increasing field strength. A sensor response can be measured due to TMR or GMR effects when a current (CPP) is channeled through connections / electrodes 140 and 120 at the top and bottom of the layer stack. The sensor response depends on the magnetic states in layers 118 and 112. Layer 113 could serve as a tunnel barrier (TMR) or a conductive material (GMR).

[0063] Depending on the condition of the reference layer(s) 118, the sensor's transmission curve could be reversed with respect to perpendicular fields, as shown in Fig. 2. Here, the transfer curve 202 represents a scenario in which the magnetization of the reference layer 116 is oriented upwards (first state), and a positive applied external field indicates a magnetic field that also points upwards. The transfer curve reverses when the reference layer 116 changes to a second state in which the magnetization of the reference layer 116 is oriented downwards. This behavior can be used, and the control circuit 130 can be configured to apply the second current pulse with a negative polarity in addition to the first current pulse in the first state to change the reference magnetization of the magnetic reference layer 116 from a first orientation (e.g., upwards) to a second orientation (e.g.,down), and in the second state, apply the second current pulse with a positive polarity to switch the reference magnetization of the magnetic reference layer 116 from the second orientation (e.g., down) to the first orientation (e.g., up). The final sensor signal may then be the difference between these two responses. Thus, the control circuit 130 may be configured to provide a difference between a first sensor signal in the first state and a second sensor signal in the second state as an output sensor signal. In the embodiment shown in . Fig. In the example provided in Figure 2, the reference layer 118 is a magnetic multilayer, and the free layer 112 comprises a Co(3 nm) / CoFe(3 nm) structure. Another version of the reference layer 118 is CoFeB(0.9) / Ru / CoFeB(0.9) / MgO, where the CoFeB / MgO interface promotes perpendicular anisotropy. The free layer 112 could be a slightly thicker CoFeB layer, such as CoFeB(1.1), which promotes in-plane magnetization.

[0064] Another exemplary implementation of the MR device 100 is shown in Fig. 3, where the order of the ferromagnetic and non-magnetic layers is different compared to the example of Fig. 1 is reversed.

[0065] The Fig. The MR device 100 shown in Figure 3 can be used for MRAM-like structures. The layer stack of the MR sensing element 110 includes a magnetic free layer 112 (representing a stored bit) adjacent to and directly on the first and second conductors 120-1, 120-2 of the SOT layer. The non-magnetic layer 113 is disposed on the magnetic free layer 112 and separates the magnetic free layer 112 from the reference layer / SAF 118. The top electrode 140 is disposed on the ferromagnetic layer 116. In the example of Fig. 3, the free layer 112 adjacent to the first and second conductors 120-1, 120-2 is a ferromagnet with perpendicular crystalline anisotropy, in which the crystalline structure inherently favors magnetic moments oriented perpendicular to the plane of the material. This property is known as perpendicular magnetic anisotropy (PMA) at the crystalline plane.

[0066] Here, the control circuit 130 can be used to switch between two different states of the free layer 112, which represent different stored bits. The control circuit 130 can be configured to apply, in a first state (e.g., bit "1"), the second current pulse with a first polarity in addition to the first current pulse to switch the reference magnetization of the magnetic reference layer 116 from a first orientation (e.g., upward) to a second orientation (e.g., downward). The second orientation corresponds to a second state (e.g., bit "0"). The control circuit 130 can also be configured to apply, in the second state (e.g., bit "0"), the second current pulse with a second (opposite) polarity to switch the reference magnetization of the magnetic free layer 112 from the second orientation (e.g., downward) to the first orientation (e.g., upward).The first orientation corresponds to the first state (e.g. bit “1”).

[0067] Fig. 4 illustrates an implementation of an MRAM structure 400 in which multiple memory MRAM cells 410-1, 410-2, 410-3 are deposited on a single SOT heavy metal layer with respective first and second conductors 120-1, 120-2 associated with each MRAM cell 410-1, 410-2, 410-3. The MRAM cells 410-1, 410-2, 410-3 are all commonly associated with the first conductor 120-1 extending in the x-direction. The MRAM cell 410-1 is associated with a first second conductor 120-2 extending in the y-direction. The MRAM cell 410-2 is associated with a second second conductor 120-2 extending in the y-direction. The MRAM cell 410-3 is assigned to a third second conductor 120-2, which extends in the y-direction. The respective MRAM cell 410 to be switched can be switched by applying a respective j y-current through the respective second conductor 120-2 in addition to the j x -Current through the first conductor 120-1 can be selected.

[0068] In the following, the basic concept of the SOT switching process is detailed and Fig. 5 summarized.

[0069] First, the control circuit 130 applies two currents each in the j x - and j y -direction across the first and second conductors 120-1, 120-2, resembling a Hall cross. In this context, the total current density at the intersection of the first and second conductors 120-1, 120-2 is sufficiently large to compensate for the perpendicular anisotropy of the layer 116 ( Fig. 1) or layer 112 ( Fig. 3). Due to the damping effect and the field-like torque term, the magnetization rotates within the plane. The j y -Electricity is used to generate a M x-component of the magnetization. Depending on whether a positive or negative j y -current is applied, a positive or negative M x -component, which then each has the final +M z - or -M z -condition determined.

[0070] After the j y -current through the second conductor 120-2 is interrupted, only the j x -current through the first conductor 120-1 with a magnitude sufficiently small to prevent the production of a component out of the plane of magnetization. After the j x -current is interrupted, depends on whether the initial state is a positive or negative M x component, the final magnetic state of layer 116 ( Fig. 1) or layer 112 ( Fig. 3) either +M z or -M z be. (i) In the first step, currents are applied along the first and second conductors 120-1, 120-2. Consequently, in the region below the layer 116 ( Fig. 1) or layer 112 ( Fig. 3) the total current is the vectorial sum of these two individual currents. These currents are selected to be sufficiently strong, ensuring that they exceed the critical current required to switch the magnetization to an in-plane orientation. When the currents exceed this critical threshold, the equilibrium magnetization aligns in-plane and orthogonal to the total current direction. The in-plane orientation is thus determined by the relative strengths of the j x - and j y -currents are determined. If j y for example, significantly larger than j x the magnetization will be predominantly oriented in a direction close to the x-axis. If j y ~y xthe magnetization will point at an angle of -45° with respect to the x-axis. (ii) In the second step, the j y -Power off. If the remaining j x -current is smaller than the critical current required for in-plane switching, the magnetization rotates out of plane in the z-direction. This rotation is determined by the initial M x -component of the magnetization, which is similar to the application of an H x field, which is normally required for deterministic spin-orbit torque (SOT) switching.

[0071] Fig. Figure 6 shows a detailed representation of the magnetization dynamics induced by applied j x - and j y -currents over a specific time.

[0072] In the left graph of Fig. 6 are the created j x - and j y-currents are shown by lines 610, 620, whereas the M z -component of the magnetization of layer 116 ( Fig. 1) or layer 112 ( Fig. 3) is represented by the reference numeral 630. Before the time 2 ns, neither the first nor the second current pulse is applied and the system is in state A, e.g., the magnetization of layer 116 ( Fig. 1) or layer 112 ( Fig. 3) in a first orientation (e.g. -M z ). In this state A, the control circuit 130 (at time 2 ns) may be configured to generate the second current pulse (j y ) with a positive polarity in addition to the first current pulse (j x ) to magnetize the layer 116 ( Fig. 1) or layer 112 ( Fig. 3) from the first orientation (e.g. -M z ) to a second orientation (e.g. +M z ). During the duration of the second current pulse (j y) (ie the time interval from 2 to 4 ns) the system is in state B. At this point the collective strength of the j x - and j y -currents to 8 TA / m 2 This current is sufficiently strong to rotate the magnetization in the plane. As we progress into the time window between 4 and 6 ns, in which the second current pulse (jy) has been switched off and the first current pulse (jx) is still active, only the jx current remains active and exerts a reduced current of 2 TA / m 2 out of.

[0073] Thus, the control circuit 130 may be configured to apply, in a first state (state A), the second current pulse having a positive polarity in addition to the first current pulse in order to magnetize the layer 116 ( Fig. 1) or layer 112 ( Fig. 3) from a first orientation (e.g. -M z ) to a second orientation (e.g. +M z). In a second state (shown in the right-hand graph), the control circuit 130 may be configured to apply the second current pulse with a negative polarity to switch the magnetization of the layer 116 ( Fig. 1) or layer 112 ( Fig. 3) from the second orientation (e.g. +M z ) to the first orientation (e.g. -M z ). In the illustrated example, the start time of the first current pulse is substantially equal to the start time of the second current pulse, and a duration of the first current pulse is longer than a duration of the second current pulse. In other embodiments, the start time may not be equal. In the illustrated example, the control circuit 130 is configured to switch the second current pulse (j y ) to the second conductor 120-2 with a magnitude equal to or greater than the first current pulse (j x). In other embodiments, it might be advantageous if the pulses are not completely switched off, but the strength can take a functional form as a function of time.

[0074] The output of the MR device 100 can also be adjusted by using a Fig. 7 shown Wheatstone bridge can be realized.

[0075] The MR component 100 from Fig. 7 comprises four MR detection elements 110-1, ..., 110-4 in a Wheatstone bridge configuration. The output voltage of the Wheatstone bridge configuration depends on Uout=U0R1R4−R3R2(R1+R2)(R3+R4) where U0=RtotI2.

[0076] When the current polarity is changed from an original polarity (e.g. +I2) to a reversed polarity (e.g. -I2) and the orientation of all reference layers 116 as in Fig. 7 remains the same (this state can be referred to as refl), the Wheatstone bridge output reverses sign. If, in addition to the reversed current polarity, the magnetization state of each reference layer 116 is also reversed due to SOT (this state can be referred to as ref2), the Wheatstone bridge output again remains the same. Therefore, the total output voltage can be the sum of the Wheatstone bridge output for these two reversed states, using the I2 current to reverse the reference layer magnetization. Usignal=Uout,I2+1ref1+Uout,I2−,ref2

[0077] In some embodiments, the sensor could be operated by reversing the orientation of the reference layers using SOT currents and reversing the sign of the bridge input current, and averaging the bridge output over these two time periods. Thus, control circuit 130 (not shown) can be configured to provide a combination of the first output of the Wheatstone bridge in the first state (ref1) and the second output of the Wheatstone bridge in the second state (ref2) as an output sensor signal.

[0078] In other embodiments, the currents j x and j y applied to set the reference layers (ref1) as shown in Fig. 7. A constant current I2 is applied to the output U out, ref1 of the Wheatstone bridge. Then j x and j yapplied to reverse the magnetization state of the reference layers (ref1). With the constant current I2, the output U out, ref2 measured. The signal, which is proportional to the applied field in the z-direction, is given by Usignal=Uout,I2+,ref1−Uout,I2−,ref2

[0079] Some embodiments of the present disclosure propose a magnetic sensor device comprising a GMR or TMR sensor element, wherein the transfer function of the sensor device can be reversed by changing the orientation of the magnetic reference system. The reference system can be switched using an SOT current. One advantage is that sensor offsets can be reduced and switching can be realized without bias fields.

[0080] 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.

[0081] 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 required 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.

[0082] If some aspects are described in connection with a component or system, these aspects are also to be understood as a description of the corresponding method. For example, a block, a component, or a functional aspect of the component or system may correspond to a feature, such as 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 system.

[0083] The following claims are hereby incorporated into the Detailed Description, and each claim may stand on its own as a separate example. It should also be noted that although a dependent claim in the claims refers to a particular 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 contemplated unless it is specifically stated that a particular combination is not intended. Furthermore, features of a claim for any other independent claim are also intended to be encompassed, even if that claim is not directly defined as dependent on that other independent claim.

Claims

[1] A magnetoresistive component (100) comprising at least one magnetoresistive element (110) comprising a layer stack of ferromagnetic layers (112; 114; 116; 118) and non-magnetic layers (113; 115) stacked in a first direction, wherein the layer stack comprises a ferromagnetic layer (112; 118) with a magnetic orientation to be switched; adjacent to the ferromagnetic layer (112; 118), a first conductor (120-1) extending in a second direction and a second conductor (120-2) extending in a third direction, wherein the first and second conductors are configured to induce spin-orbit torque, SOT, in the ferromagnetic layer (112; 118); and a control circuit (130) configured to apply a first current pulse to the first conductor (120-1) and a second current pulse to the second conductor (120-2) in a temporally overlapping manner and with different time characteristics, wherein the control circuit (130) is configured to switch off the second current pulse before the first current pulse is switched off in order to switch the magnetic orientation of the ferromagnetic layer (112; 118). [2] The magnetoresistive component (100) according to claim 1, wherein the ferromagnetic layer (112; 118) having the magnetic orientation to be switched is a ferromagnet with perpendicular anisotropy. [3] The magnetoresistive component (100) according to any one of the preceding claims, wherein the layer stack comprises a magnetic free layer (112) and a magnetic reference layer (118), wherein the ferromagnetic layer with the magnetic orientation to be switched is the magnetic reference layer (118). [4] The magnetoresistive device (100) according to claim 3, wherein the magnetic reference layer (118) is formed as a synthetic antiferromagnet, SAF. [5] The magnetoresistive device (100) according to claim 3 or 4, wherein the magnetic free layer (112) comprises in-plane magnetization in the absence of an external magnetic field. [6] The magnetoresistive device (100) according to claim 3 or 4, wherein the magnetic free layer (112) is a ferromagnet with perpendicular crystalline anisotropy. [7] The magnetoresistive component (100) according to one of claims 1 to 2, wherein the layer stack comprises a magnetic free layer (112) and a magnetic reference layer (118), wherein the ferromagnetic layer with the magnetic orientation to be switched is the magnetic free layer (112). [8] The magnetoresistive device (100) according to any one of claims 3 to 7, wherein the magnetic free layer (112) and the magnetic reference layer (118) are separated by a non-magnetic tunnel barrier (113). [9] The magnetoresistive device (100) according to any one of claims 3 to 7, wherein the magnetic free layer (112) and the magnetic reference layer (118) are separated by a non-magnetic conductive spacer layer (113). [10] The magnetoresistive component (100) according to any one of the preceding claims, wherein the control circuit (130) is configured to apply the second current pulse to the second conductor (120-2) with a magnitude equal to or greater than the first current pulse. [11] The magnetoresistive device (100) according to any one of the preceding claims, wherein a start time of the first current pulse is equal to a start time of the second current pulse and wherein a duration of the first current pulse is longer than a duration of the second current pulse. [12] The magnetoresistive component (100) according to one of the preceding claims, wherein the control circuit (130) is designed to in a first state, applying the second current pulse having a first polarity in addition to the first current pulse to switch the magnetic orientation of the ferromagnetic layer (112; 118) from a first orientation to a second orientation, and in a second state, applying the second current pulse having a second opposite polarity to switch the magnetic orientation of the ferromagnetic layer (112; 118) from the second orientation to the first orientation. [13] The magnetoresistive device (100) according to claim 12, wherein the control circuit (130) is further configured to provide a difference between a first sensor signal in the first state and a second sensor signal in the second state as an output sensor signal. [14] The magnetoresistive component (100) according to any one of the preceding claims, wherein the first and second conductors (120) are arranged in a crossbar structure. [15] The magnetoresistive component (100) according to any one of the preceding claims, wherein the first and second conductors (120) are made of non-magnetic heavy metal. [16] The magnetoresistive component (100) according to any one of the preceding claims, wherein the layer stack forms a GMR or a TMR spin valve structure. [17] The magnetoresistive device (100) according to any one of the preceding claims, further comprising electrodes at both ends of the layer stack for applying a current perpendicular to the plane, CPP. [18] A magnetoresistive random access memory, MRAM, cell (400; 410) comprising the magnetoresistive device according to any one of the preceding claims. [19] A method for switching a magnetic orientation, the method comprising Providing at least one magnetoresistive element (110; 410) comprising a layer stack of ferromagnetic layers (112; 114; 116; 118) and non-magnetic layers (113; 115) stacked in a first direction, wherein the layer stack comprises a ferromagnetic layer (112; 118) with a magnetic orientation to be switched; Providing, adjacent to the ferromagnetic layer (112; 118), a first conductor (120-1) extending in a second direction and a second conductor (120-2) extending in a third direction, the first and second conductors being configured to induce SOT in the ferromagnetic layer (112; 118); Applying a first current to the first conductor (120-1) and a second current to the second conductor (120-2) in a temporally overlapping manner and with different time characteristics, wherein the second current is turned off before the first current is turned off to switch the magnetic orientation of the ferromagnetic layer (112; 118). [20] The method of claim 19, wherein the second current is applied to the second conductor (120-2) at a magnitude equal to or greater than the first current. [21] The method according to any one of claims 19 or 20, wherein a start time of the first stream is equal to a start time of the second stream and wherein a duration of the first stream is longer than a duration of the second stream. [22] The method according to any one of claims 19 to 21, comprising in a first state, applying the second current having a positive polarity in addition to the first current to switch the magnetic orientation of the ferromagnetic layer (118) from a first orientation to a second orientation, and in a second state, applying the second current having a negative polarity to switch the magnetic orientation of the ferromagnetic layer (118) from the second orientation to the first orientation. [23] The method of claim 22, comprising providing an output sensor signal corresponding to a difference between a first sensor signal in the first state and a second sensor signal in the second state.

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