Magnetoresistive device

Abstract

The invention relates to a magnetoresistive device. There is provided a magnetoresistive device (100) comprising at least one magnetoresistive element (110) comprising ferromagnetic layers (112; 114, 124; 116; 118) and a non-magnetic layer (113; 115) of the plurality of layers. The layer stack comprises a ferromagnetic layer (112; 112 ') having a magnetic orientation to be switched. 118). In the ferromagnetic layer (112; 118), a first conductor (120-1) extending in the second direction and a second conductor (120-2) extending in the third direction. The first conductor and the second conductor are configured to be electrically connected between the ferromagnetic layer (112; 118) of the sensor (10) for sensing a spin orbit torque (SOT). The 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 temporal characteristics. For example, the control circuit (130) is configured to turn off the second current pulse to switch the ferromagnetic layer (112; 118) of the magnetic field.

Description

Technical Field

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

[0002] Conventional magnetic sensing devices based on materials that exhibit the magnetoresistive effect (e.g., AMR, GMR, TMR) can be limited in their ability to measure static magnetic field components in a very precise manner. The offset error in such devices depends on the device-to-device matching, which can be affected by manufacturing limitations. The same argument applies to Hall-effect devices, but one advantage of Hall-effect devices is that first-order mismatch can be offset by applying so-called spin current techniques. In order to implement offset reduction signal conditioning methods for magnetoresistive devices, the magnetization direction in the defined magnetic layer must be changed or controlled by an electrical signal (e.g., current).

[0003] Signal conditioning methods for offset reduction in magnetoresistive devices are known, for example, for AMR sensing devices. Using coils external to or internal to the chip, the AMR transmission curve can be reversed by changing the magnetization direction, a principle known as flipped AMR. A drawback of this principle is the current consumption required to achieve the AMR flipping field.

[0004] Recently, the use of the spin-orbit torque (SOT) effect to switch the magnetic layer of the reference frame has been proposed (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 a synthetic antiferromagnetic layer” (Journal of Applied Physics)). This technique can achieve a larger signal range and lower current consumption compared to flip-type AMR. In the commonly used SOT switching scheme, a bias field is required to allow deterministic switching. Methods for reducing the bias field are summarized in Krizakova, V., Perumkunnil, M., Couet, S., Gambardella, P., and Garello, K., “Spin-orbit torque switching of magnetic tunnel junctions for memory applications” (Journal of Magnetism and Magnetic Materials).

[0005] Therefore, there is a need to switch the magnetic layers of a reference system without the need for a bias field. Summary of the Invention

[0006] This need is addressed by a magnetoresistive device and a method according to the accompanying claims.

[0007] According to a first aspect, the present disclosure provides a magnetoresistive (MR) device. The MR device includes 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 includes a layer stack having a ferromagnetic layer and a non-magnetic layer stacked in a first direction. For example, the first direction may be a vertical direction (e.g., the z-direction). The layer stack of the MR element includes 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 also includes a first conductor extending in a second direction (e.g., the x-direction) adjacent to the ferromagnetic layer and a second conductor extending in a third direction (e.g., the y-direction). The second and third directions may span a plane perpendicular to the first direction. For example, the second direction (e.g., the x-direction) may be perpendicular to the first direction (e.g., the z-direction). The third direction (e.g., the y-direction) may be perpendicular to the first direction (e.g., the z-direction) and / or the second direction (e.g., the x-direction). The first and second conductors are configured to induce a spin-orbit torque (SOT) in the ferromagnetic layer adjacent to the first and second conductors. The MR device also includes control circuitry 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 circuitry is further configured to apply the first current pulse and the second current pulse with different respective temporal characteristics. This means that the first current pulse and the second current pulse can vary in one or more aspects related to their temporal characteristics. For example, these differences can include variations in duration or amplitude. The current pulses can take any functional form.

[0008] For example, the control circuit may be configured to vary the relative strengths of the first current pulse and the second current pulse during application of the first current pulse and / or the second current pulse.

[0009] In some embodiments, the control circuit can be configured to turn off the second current pulse (eg, change the current intensity of the second current pulse to zero or close to zero) before turning off the first current pulse.

[0010] In this way, the magnetization of the ferromagnetic layer can be switched without a magnetic bias field.

[0011] In some embodiments, the ferromagnetic layer whose magnetic orientation is to be switched is a magnetic reference layer. More specifically, the ferromagnetic layer can be part of a synthetic antiferromagnet (SAF), which includes a first ferromagnetic layer and a second ferromagnetic layer separated by a non-magnetic layer. The SAF can be used as a magnetic reference layer for an MR sensing element. The SAF in the context of an MR device is a structure designed to mimic the behavior of an antiferromagnetic material by a stack of synthetic ferromagnetic layers separated by a non-magnetic conductive or insulating spacer layer. A characteristic of the SAF is the antiparallel alignment of the magnetic moments in the ferromagnetic layers, which is achieved by indirect magnetic coupling mediated by a spacer layer. A typical SAF structure includes two (or more) thin ferromagnetic layers (such as CoFe or NiFe) separated by a very thin non-magnetic layer (typically ruthenium, Ru, because of its unique ability to induce antiferromagnetic coupling at certain thicknesses). The thickness of the Ru layer can be controlled to be several 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 adjacent ferromagnetic layers.

[0012] In some embodiments, the ferromagnetic layer whose magnetic orientation is to be switched is a magnetic free layer. The magnetic free layer can be separated from a magnetic reference layer (e.g., SAF) by a nonmagnetic layer. In some embodiments, the nonmagnetic layer between the free layer and the magnetic reference layer (e.g., SAF) is a tunnel barrier. The tunnel barrier is a key component in certain types of magnetoresistive devices, such as tunnel magnetoresistive (TMR) sensors and magnetic random access memory (MRAM) cells. It comprises a thin, non-conductive, or insulating layer that separates two ferromagnetic layers (e.g., a free layer and a reference layer). Despite being 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 of 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 low, while when the magnetic moments are antiparallel, the resistance is high. This variation in resistance with magnetic orientation is called tunnel 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 made into very thin layers while retaining their insulating properties.

[0013] In some embodiments, the nonmagnetic 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, a conductive spacer layer is made of a nonmagnetic metal and allows electron conduction between the ferromagnetic layers. The primary function of the conductive spacer layer is to facilitate the transport of electrons while maintaining their spin orientation, which is crucial for the GMR effect to occur. The GMR effect relies on the difference in resistance encountered by electrons with spins 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 more easily pass through the structure, reducing resistance. Conversely, when the magnetizations are antiparallel, resistance increases because electrons with a particular spin orientation are scattered more. The material chosen for the conductive spacer layer can affect the overall performance of the MR device. Common materials used for spacers include copper (Cu), silver (Ag), or gold (Au), known for their good electrical conductivity and minimal interaction with electron spins.

[0014] In some embodiments, the ferromagnetic layer whose magnetic orientation is to be switched is a ferromagnet with perpendicular anisotropy. A ferromagnet with perpendicular anisotropy (also known as perpendicular magnetic anisotropy, PMA) is a ferromagnetic material in which the easy axis of magnetization is oriented perpendicular to the plane of the material (out-of-plane) rather than within the plane (in-plane). This means that the magnetic moments of the atoms in the material prefer to align themselves perpendicular to the surface of the material, resulting in a magnetic field that points upward or downward relative to the surface.

[0015] In some embodiments, another ferromagnetic layer (e.g., a free layer) that is not adjacent to the first conductor / second conductor in the layer stack is a ferromagnet with perpendicular crystal anisotropy. A ferromagnet with perpendicular crystal anisotropy refers to a non-magnetic material in which the crystal structure inherently favors the arrangement of magnetic moments perpendicular to the plane of the material. This property is called perpendicular magnetic anisotropy (PMA) at the crystal level and is determined by the lattice structure of the material. Anisotropy is the result of the direction dependence of magnetic energy within the crystal, which makes it energetically more favorable for the spins in the material to be oriented in a direction perpendicular to the surface.

[0016] In some embodiments, another ferromagnetic layer (e.g., a free layer) in the layer stack that is not adjacent to the first conductor / second conductor is a ferromagnet that includes a predominantly in-plane magnetization in the absence of an external magnetic field, such as in a flux closure state when in zero external magnetic field. A ferromagnet that forms a flux closure state when in zero external magnetic field is a phenomenon in which the magnetic moments within the ferromagnetic material are arranged in a configuration that minimizes the magnetic energy of the system, particularly the stray magnetic field energy, without being affected by the external magnetic field. This arrangement causes the internal magnetic flux to be contained within the material, effectively reducing the magnetic field outside the material to almost zero. This configuration is also referred to as a "closed flux" or "magnetic eddy current" state. In other embodiments, the ferromagnetic layer (e.g., a free layer) can be formed from two ferromagnetic layers, forming a SAF.

[0017] In some embodiments, the MR device is used to detect or sense an external magnetic field in response to the measured resistance. In this case, the ferromagnetic layer whose magnetic orientation is to be switched can be the magnetic reference layer, and another ferromagnetic layer in the layer stack that is not adjacent to the first conductor / second conductor can be the magnetic free layer.

[0018] 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 can be a magnetic free layer, and the other ferromagnetic layer in the layer stack that is not adjacent to the first conductor / second conductor can be a magnetic reference layer. An MRAM memory cell is a 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 (usually '0' and '1') and the ability to read these states through changes in resistance. An MRAM memory cell is typically composed of a magnetic tunnel junction (MTJ), which consists of two ferromagnetic layers separated by a thin insulating layer (tunnel barrier). One of the ferromagnetic layers is a reference layer whose magnetic orientation is fixed, while the other layer is a free layer whose magnetic orientation can be switched between a parallel arrangement and an antiparallel arrangement relative to the reference layer. The parallel arrangement represents one binary state ('1' or '0'), while the antiparallel arrangement represents the other binary state ('0' or '1').

[0019] In some embodiments, the control circuit is configured to apply a second current pulse to the second conductor having a magnitude equal to, greater than, or less than the magnitude of the first current pulse. In this manner, the magnetization of the adjacent ferromagnetic layers can be switched without a magnetic bias field. In some embodiments, the magnitude (intensity) of the second current pulse relative to the first current pulse can vary.

[0020] In some embodiments, the start time of the first current pulse is equal to the start time of the second current pulse, and the duration of the first current pulse is longer than the duration of the second current pulse.In this way, the magnetization of adjacent ferromagnetic layers can be switched in the absence of a magnetic bias field.

[0021] In some embodiments, the first current pulse intensity has a first functional form as a function of time, and the second current pulse has a second, different functional form as a function of time.

[0022] In some embodiments, the control circuit is configured to apply, in addition to the first current pulse, a second current pulse with positive polarity in a first state to switch the magnetic orientation of the ferromagnetic layer from the first orientation (e.g., downward) to the second orientation (e.g., upward), and to apply, in a second state, a second current pulse with 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 manner, the magnetization of adjacent ferromagnetic layers can be switched between the two states in the absence of a magnetic bias field.

[0023] In some embodiments, the control circuit is further configured to provide a difference between the first sensor signal in the first state and the second sensor signal in the second state as the output sensor signal. In this way, offset errors of the MR device can be reduced.

[0024] In some embodiments, the first and second conductors are disposed directly adjacent to a layer stack of an MR element (e.g., an MTJ). In particular, the first and second conductors are disposed directly adjacent to a ferromagnetic layer whose magnetic orientation is to be switched. The first and second conductors may be disposed directly below or above the ferromagnetic layer whose magnetic orientation is to be switched. In some embodiments, the first and second conductors are disposed directly adjacent to a magnetically free layer or directly adjacent to a magnetic reference layer.

[0025] In some embodiments, the first conductor and the second conductor are arranged in a crossbar configuration.

[0026] In some embodiments, the first conductor and the second conductor include (or consist of) a non-magnetic heavy metal. The heavy metal may include Pt, Ta, or W. In the context of SOT, non-magnetic heavy metals play a role in generating efficient spin currents due to their strong spin-orbit coupling. Spin-orbit coupling is a relativistic effect caused by the interaction between the spin of an electron and its orbital motion around an atomic nucleus, which is particularly pronounced in heavy metals due to their large atomic number. This interaction can manipulate the magnetization of adjacent ferromagnetic materials without applying an external magnetic field, but instead relies on an electric current passing through the heavy metal.

[0027] In some embodiments, the MR device further includes electrodes located at both ends of the layer stack, the electrodes being used to apply a current perpendicular to plane (CPP) through the layer stack.

[0028] According to a second aspect, the present disclosure provides a magnetoresistive random access memory (MRAM) cell comprising the MR device of any one of the aforementioned examples.

[0029] According to another aspect, the present disclosure provides a method for switching the magnetic orientation of a ferromagnetic layer. The method includes providing at least one MR element, the MR element including a layer stack having a ferromagnetic layer and a non-magnetic layer stacked in a first direction. The layer stack of the MR element includes a ferromagnetic layer whose magnetic orientation is to be switched. The ferromagnetic layer can be a reference layer / system or a magnetically free layer of the MR element. The ferromagnetic layer can have an out-of-plane magnetization in the first direction. The method also includes providing a first conductor extending in a second direction (e.g., an x-direction) and a second conductor extending in a third direction (e.g., a y-direction) near the ferromagnetic layer. The second direction and the third direction can span a plane perpendicular to the first direction. For example, the second direction (e.g., the x-direction) can be perpendicular to the first direction. The third direction (e.g., the y-direction) can be perpendicular to the first direction and / or the second direction. The first conductor and the second conductor are configured to induce a SOT in the magnetic reference layer. The method also includes applying a first current to the first conductor and applying a second current to the second conductor in a temporally overlapping manner and with different temporal characteristics.

[0030] 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.

[0031] In some embodiments, the second current is applied to the second conductor at a magnitude equal to or greater than the first current.

[0032] In some embodiments, a start time of the first current is equal to a start time of the second current, and wherein a duration of the first current is longer than a duration of the second current.

[0033] In some embodiments, the method includes, in the first state, applying a second current with positive polarity in addition to the first current to switch the magnetic orientation of the ferromagnetic layer from the first orientation to the second orientation, and in the second state, applying the second current with negative polarity to switch the magnetic orientation of the ferromagnetic layer from the second orientation to the first orientation.

[0034] In some embodiments, the method includes providing an output sensor signal corresponding to a difference between a first sensor signal for the first state and a second sensor signal for the second state. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Some examples of the apparatus and / or method will be described below, by way of example only, and with reference to the accompanying drawings, in which

[0036] Figure 1 shows the basic structure of an MR sensing device according to one embodiment;

[0037] Figure 2 shows the transmission curve of the xMR layer stack with the reference layer switched between up and down states;

[0038] Figure 3 shows the basic structure of an MRAM cell according to an embodiment;

[0039] Figure 4 An embodiment is shown in which multiple MR elements can be positioned at j x On the current line, the element to be switched can be y Current to select;

[0040] Figure 5 The switching principle is shown, where a combination of x and y SOT currents are applied;

[0041] Figure 6 shows an example current sequence for switching the ferromagnetic layer with a SOT current; and

[0042] Figure 7 An example configuration of the reference layer is shown when the MR device operates in a Wheatstone bridge configuration. DETAILED DESCRIPTION

[0043] Some examples are now described in more detail with reference to the accompanying drawings. However, other possible examples are not limited to the features of these embodiments described in detail. Other examples may include modifications of features and equivalents and substitutes of features. In addition, the terms used in this article to describe certain examples should not limit other possible examples.

[0044] Throughout the description of the drawings, the same or similar reference numerals refer to the same or similar elements and / or features, which may be implemented in the same or modified form while providing the same or similar functions. For clarity, the thickness of the lines, layers and / or regions in the drawings may also be exaggerated.

[0045] When two elements A and B are combined using "or", this should be understood as discussing all possible combinations, i.e., only A, only B, and A and B, unless otherwise expressly stated in individual cases. As alternative expressions for the same combination, "at least one of A and B" or "A and / or B" can be used. The same applies to combinations of more than two elements.

[0046] If singular forms such as "a", "an", "the", and "said" are used, and only a single element is used without being explicitly or implicitly defined as mandatory, other examples may also use several elements to implement the same function. If the function is described below as being implemented using multiple elements, other examples may use a single element or a single processing entity to implement the same function. It is further understood that the terms "include", "including", "comprise" and / or "comprising" when used describe the presence of specified features, integers, steps, operations, processes, elements, components and / or groups thereof, but do not preclude the presence or addition of one or more other features, integers, steps, operations, processes, elements, components and / or groups thereof.

[0047] Due to its unique combination of speed and durability, MRAM has become a promising candidate for nonvolatile memory cells. To improve the durability of MRAM elements by separating the readback current from the write current, SOT switching can be employed. However, SOT switching schemes require symmetry breaking to achieve reliable and deterministic switching, which was initially achieved by applying an external field parallel to the direction of the SOT current. Since then, as reviewed by Krizakova et al., various approaches have been proposed to circumvent the need for an additional bias field. These include exploiting lateral geometric asymmetry, thickness asymmetry, tilted anisotropy axes, in-plane magnets, exchange bias, combinations of SOT and STT, and crystal symmetry. Sverdlov et al. used two SOT pulses for switching. However, magnetic field-free switching was only possible when the second pulse line achieved approximately 30% geometric overlap with the free layer, which is technically difficult to achieve. Furthermore, the "write pulse 1" was applied before the second continuous current, requiring very precise pulse timing.

[0048] This disclosure proposes a switching scheme that (i) does not require geometric overlap of the two lines and (ii) does not require precise timing of the two pulses. To demonstrate this concept, the damping of the Gilbert equation (H dl ) and field-like (H fl ) torque term to perform micromagnetic simulations including SOT,

[0049]

[0050] The damping field and the quasi-field are defined as:

[0051]

[0052] where j eis the applied current density, e is the electron charge, t is the thickness of the ferromagnetic layer on which the SOT acts, and 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 represented by m, and the spin polarization direction generated by the SOT current is represented by p. If a current is applied in the x-direction, the spin polarization of the spin current pointing in the z-direction can point in the y-direction.

[0053] The concepts proposed in this disclosure are as follows Figure 1 As shown, Figure 1 An MR device 100 according to an embodiment is schematically illustrated.

[0054] Figure 1 The illustrated MR device 100 includes an MR sensing element 110. Those skilled in the art having the benefit of this disclosure will appreciate that the MR device 100 may also include more than one MR sensing element 110, for example when used in a half-bridge (two MR sensing cells) or full-bridge configuration (four MR cells of interest).

[0055] The MR sensing element 110 includes a layer stack of ferromagnetic layers and non-magnetic layers. In the example shown, the ferromagnetic layers and non-magnetic layers of the MR sensing element 110 are stacked in a vertical direction (z direction). Figure 1 An example layer stack includes a first ferromagnetic layer 112 that can be designed to have a low coercive force (easily magnetized and demagnetized). The first ferromagnetic layer 112 can serve as a magnetic free layer of the 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 can be a ferromagnet that forms an in-plane flux closure (eddy current) state under zero external magnetic field. In other embodiments, the layer 112 can be in a quasi-uniform in-plane magnetization state when in zero field. However, in other embodiments, the ferromagnetic layer 112 can form a SAF.

[0056] Alternatively, the magnetic free layer 112 may be a ferromagnet with perpendicular crystal anisotropy. A ferromagnet with perpendicular crystal anisotropy refers to a non-magnetic material in which the crystal structure inherently favors alignment of magnetic moments perpendicular to the plane of the material.

[0057] The layer stack of the MR sensing element 110 includes one or more second ferromagnetic layers 118 positioned below a magnetically free layer 112, which can be designed to have a high coercivity (maintain its magnetic orientation under an external magnetic field). The layer(s) 118 can serve as a magnetic reference layer / system with which the orientation of the magnetically free layer 112 is compared. Figure 1The example shown involves using a synthetic antiferromagnetic network (SAF) structure for the magnetic reference layer 118. The SAF includes two (or more) ferromagnetic layers 114, 116 separated by a non-magnetic coupling layer 115 (typically ruthenium, Ru. Other 3d, 4d, and 5d transition metals such as V, Nb, Mo, Ta, W, Re, and Ir can also be used). The coupling layer 115 induces antiferromagnetic coupling between the ferromagnetic layers 114, 116. This arrangement can enhance the stability of the magnetic orientation of the reference layer 118.

[0058] In embodiments related to TMR sensing elements, the non-magnetic layer 113 between the magnetic free layer 112 and the magnetic reference layer / system 118 can be configured as a tunnel barrier. The tunnel barrier 113 can be made of materials such as aluminum oxide (Al2O3) or magnesium oxide (MgO), which are insulators and can be made into very thin layers while maintaining their insulating properties.

[0059] In embodiments related to GMR sensing elements, the nonmagnetic layer 113 between the magnetic free layer 112 and the magnetic reference layer / system 118 can be configured as a conductive spacer layer. Example materials for the spacer layer 113 include copper (Cu), silver (Ag), or gold (Au).

[0060] Although Figure 1 In the example shown, the magnetic free layer 112 has an in-plane (xy-plane) magnetization, but the magnetic reference layer / SAF 118 has an out-of-plane reference magnetization in the perpendicular 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 promotes antiferromagnetic coupling between the adjacent ferromagnetic layers 114 and 116. This antiferromagnetic coupling ensures that the magnetic moments of the ferromagnetic layers 114 and 116 are in opposite directions (antiparallel alignment).

[0061] Below the layer stack of MR sensing element 110 (below ferromagnetic layer 116), MR device 100 also includes 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, first conductor 120-1 and second conductor 120-2 are arranged in a crossbar configuration, with the layer stack of MR sensing element 110 positioned at the intersection of first conductor 120-1 and second conductor 120-2. Those skilled in the art having the benefit of this disclosure will appreciate that first conductor 120-1 and second conductor 120-2 do not necessarily need to be arranged perpendicular to one another.

[0062] The MR sensing element 110 is configured to sense a SOT in the magnetic reference layer / SAF 118 using a first conductor 120-1 and a second conductor 120-2. The plane or layer spanned by the first conductor 120-1 and the second conductor 120-2 may also be referred to as a SOT layer. The first conductor 120-1 and the second conductor 120-2 may include (or be composed of) a non-magnetic heavy metal, such as Pt, Ta, or W. In the context of SOT, non-magnetic heavy metals play a role in generating efficient spin currents due to their strong spin-orbit coupling. When a current-carrying non-magnetic heavy metal couples to a ferromagnetic layer, a phenomenon known as the spin Hall effect (SHE) occurs, resulting in the generation of a spin current perpendicular to the charge current. This interaction may have implications for spintronic devices and can be used to create methods for manipulating 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 current flows through this metal, it causes electrons with opposite spins to be deflected in opposite directions, generating a transverse spin current. This effect creates an accumulation of spins on opposite sides of the material, with spin polarizations perpendicular to the direction of the charge current. When the spin current generated by the SHE in heavy metal layers 120-1, 120-2 enters the (directly) adjacent ferromagnetic layer 116, it can exert a torque on the ferromagnetic layer's magnetization. This torque can be used to manipulate the magnetic state of the ferromagnetic layer 116, including switching its magnetization direction. When this process involves the direct transfer of spin angular momentum from conduction electrons to the magnetization, it is called spin transfer torque (STT), while when it specifically involves a torque generated by the spin-orbit effect (such as that generated by the SHE), it is called spin-orbit torque (SOT). The torque can reorient the magnetization direction, allowing the magnetic state of the ferromagnetic layer 116 to switch between different stable configurations (e.g., from parallel to antiparallel relative to a reference orientation). This capability can also be useful in memory devices such as MRAM, as it allows information to be written without the need for a magnetic field.

[0063] 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 current pulse and the second current pulse overlap in time. The first current pulse and the second current pulse have different temporal characteristics.

[0064] For example, the control circuit 130 can be configured to reduce the intensity of the second current pulse or turn off the second current pulse before reducing the intensity of the first current pulse or turning off the first current pulse. A current pulse refers to a transient flow of current that may change in amplitude suddenly and may last for a limited time before returning to an initial value or zero. Characteristics of current pulses can include their shape (such as square, triangular, or sinusoidal), amplitude (maximum current level), duration (how long the pulse lasts), and repetition rate (how often the pulse occurs over time).

[0065] Furthermore, the control circuit 130 can be configured to apply a second current pulse to the second conductor 120-2 having a magnitude equal to, or greater than / less than, the magnitude of the first current pulse. In this manner, the reference magnetization of the adjacent layer 116 can be switched without a magnetic bias field. In some embodiments, the start time of the first current pulse can be equal to the start time of the second current pulse, and the duration of the first current pulse can be longer than the duration of the second current pulse.

[0066] The current in the SOT layer is passed through at least two current lines (such as j x and j y ) or conductors 120-1, 120-2 are applied. This can promote the adjacent magnetic reference layers 116 and 114 (or 118) to reverse with perpendicular magnetization (in the z direction). Unlike conventional switching schemes, the proposed method does not require B x The magnetic reference layer 118 to be switched may form a SAF (comprising two antiparallel coupling layers 114 and 116). In other embodiments, the magnetic reference layer 118 may consist of only one layer 116. If the magnetization of the ferromagnetic layer 116 is reversed due to strong coupling via the SOT layer spanned by the conductors 120-1, 120-2, the ferromagnetic layer 114 will also be reversed. The coupling layer 115 between the layers 114, 116 may be any layer that promotes strong coupling, such as strong antiferromagnetic coupling via materials such as Ru or Gd. In addition, it may be beneficial to utilize a coupling layer that also promotes strong perpendicular anisotropy.

[0067] The proposed switching scheme can be used in various applications, including advanced MR sensors.

[0068] Figure 1A schematic diagram of the proposed MR device 100 is shown, which includes a free layer 112 that can have zero magnetization in the perpendicular direction (z-direction) when no external magnetic field is applied. This can be achieved by utilizing a layer that exhibits in-plane magnetization. Alternatively, a layer with perpendicular anisotropy can be used that is split into multi-domain regions with both upward and downward magnetization. In other embodiments, the free layer 112 can exhibit a flux-closed state. However, in other embodiments, the free layer is formed as a SAF. Examples of flux-closed states include an eddy current configuration of the free layer 112 or an antiparallel coupled layer structure. For sensor applications, the magnetization can exist in the plane of the free layer 112.

[0069] When an external magnetic field is applied in the perpendicular direction (z-direction), the magnetization component in free layer 112 amplifies as the field strength increases. When a current (CPP) passes through the connections / electrodes 140 and 120 at the upper and lower ends of the layer stack, a sensor response can be measured due to the TMR or GMR effect. The sensor response depends on the magnetic state of layers 118 and 112. Layer 113 can act as a tunnel barrier (TMR) or a conductive material (GMR).

[0070] Depending on the state of the reference layer(s) 118, the transmission curve of the sensor with respect to the perpendicular field may be reversed, e.g. Figure 2 As shown. Here, the transfer curve 202 represents the case where the magnetization of the reference layer 116 is pointing upward (first state), and the applied positive external magnetic field indicates that the magnetic field is also pointing upward. When the reference layer 116 alternates to a second state where the magnetization of the reference layer 116 is pointing downward, the transfer curve reverses. This behavior can be used, and the control circuit 130 can be configured to apply a second current pulse with negative polarity in addition to the first current pulse in the first state to switch the reference magnetization of the magnetic reference layer 116 from the first orientation (e.g., upward) to the second orientation (e.g., downward), and to apply a second current pulse with positive polarity in the second state to switch the reference magnetization of the magnetic reference layer 116 from the second orientation (e.g., downward) to the first orientation (e.g., upward). The final sensor signal can be the difference between these two responses. Therefore, the control circuit 130 can be configured to provide the difference between the first sensor signal in the first state and the second sensor signal in the second state as the output sensor signal. In Figure 2 In the example provided in

[15] , the reference layer 118 is a magnetic multilayer, and the free layer 112 includes a Co(3nm) / CoFe(3nm) 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 can be a slightly thicker CoFeB layer, such as CoFeB(1.1), to promote in-plane magnetization.

[0071] Another example implementation of the MR device 100 is as follows Figure 3 As shown, the order of the ferromagnetic and non-magnetic layers is Figure 1 The opposite example.

[0072] Figure 3 The MR device 100 shown can be used in an MRAM-type structure. The layer stack of the MR sensing element 110 includes a magnetically free layer 112 (representing a storage bit) adjacent to and directly on top of a first conductor 120-1 and a second conductor 120-2 of the SOT layer. A nonmagnetic layer 113 is disposed on top of the magnetically free layer 112 and separates the magnetically free layer 112 from a reference layer / SAF 118. An upper electrode 140 is disposed on top of the ferromagnetic layer 116. Figure 3 In the example shown, the free layer 112 adjacent to the first and second conductors 120-1 and 120-2 is a ferromagnetic material with perpendicular crystal anisotropy, where the crystal structure inherently favors alignment of magnetic moments perpendicular to the plane of the material. This property is known as perpendicular magnetic anisotropy (PMA) at the crystal level.

[0073] Here, the control circuit 130 can be used to switch between two different states of the free layer 112, which represent different storage bits. The control circuit 130 can be configured to apply a second current pulse with a first polarity in addition to the first current pulse in the first state (e.g., bit "1") to switch the reference magnetization of the magnetic reference layer 116 from the first orientation (e.g., upward) to the second orientation (e.g., downward). The second orientation corresponds to the second state (e.g., bit "0"). The control circuit 130 can also be configured to apply a second current pulse with a second (opposite) polarity in the second state (e.g., bit "0") 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").

[0074] Figure 4An implementation of an MRAM structure 400 is illustrated in which a plurality of storage MRAM cells 410-1, 410-2, 410-3 are deposited onto a single SOT heavy metal layer, with each MRAM cell 410-1, 410-2, 410-3 being associated with a respective first conductor 120-1 and second conductor 120-2. The MRAM cells 410-1, 410-2, 410-3 are generally associated with a 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 associated with a third second conductor 120-2 extending in the y-direction. x In addition to the current, the corresponding j can also be applied through the corresponding second conductor 120-2 y The current thereby selects the corresponding MRAM cell 410 to be switched.

[0075] under, Figure 5 The basic concepts of the SOT switching process are summarized in detail.

[0076] Initially, the control circuit 130 connects the first conductor 120-1 and the second conductor 120-2 to the j x and j y In this case, the total current density at the intersection of the first conductor 120-1 and the second conductor 120-2 is large enough to overcome the layer 116 ( Figure 1 ) or layer 112 ( Figure 3 ). Due to the damping effect and the field-like torque term, the magnetization rotates in the plane. y The current is used to promote the magnetization of M x Component. Depending on whether positive or negative j is applied y Current, can obtain positive or negative M x Component, the M x The components then determine the final +M z or -M z state.

[0077] In the case of j passing through the second conductor 120-2 y After the current is interrupted, only the j x The current is continuously present and its magnitude is small enough to prevent the buildup of out-of-plane components of the magnetization. x After the current is interrupted, the initial state is positive M x The weight is still negative M x Component, layer 116 ( Figure 1 ) or layer 112 ( Figure 3) will have a final magnetic state of +M z or -M z .

[0078] (i) In a first step, a current is applied along the first conductor 120-1 and the second conductor 120-2. Thus, in layer 116 ( Figure 1 ) or layer 112 ( Figure 3 ) below the total current is the vector sum of these two individual currents. These currents are chosen to be strong enough to ensure that they exceed the critical current required to switch the magnetization to an in-plane orientation. When the current exceeds this critical threshold, the equilibrium magnetization aligns in the plane orthogonal to the total current direction. Therefore, the in-plane orientation is given by j x and j y The relative strength of the current is determined. For example, if j y Significantly greater than j x , the magnetization will be mainly toward the direction close to the x-axis. y ~j x , the magnetization will point at an angle of -45° to the x-axis.

[0079] (ii) In the second step, turn off j y If the remaining j x If the current is less than the critical current required for in-plane switching, the magnetization will rotate out of plane in the z direction. This rotation is caused by the initial magnetization M x Component-promoting, its effect is similar to H x The application of a field, which is generally required for deterministic spin-orbit torque (SOT) switching.

[0080] Figure 6 Detailed presentation of the j applied during a specific time x and j y Effect of current on magnetization dynamics.

[0081] exist Figure 6 In the left figure, the applied j x and j y The current is represented by lines 610, 620, while layer 116 ( Figure 1 ) or layer 112 ( Figure 3 ) of the magnetization M z The component is denoted by reference numeral 630. Before time 2 ns, neither the first nor the second current pulse is applied, and the system finds itself in state A, e.g., layer 116 ( Figure 1 ) or layer 112 ( Figure 3 ) is in a first orientation (e.g., -M z In this state A, the control circuit 130 may be configured to remove the first current pulse (j x), a second current pulse of positive polarity is applied (at time 2ns) y ), so that layer 116 ( Figure 1 ) or layer 112 ( Figure 3 ) is magnetized from a first orientation (e.g., -M z ) switches to the second orientation (e.g., +M z ). In the second current pulse (j y ) (i.e., the time interval from 2ns to 4ns), the system is in state B. At this time, j x and j y The total current intensity is 8TA / m 2 This current is strong enough to rotate the magnetization in the plane. When we enter the time window between 4ns and 6ns, the second current pulse (j y ) has been turned off, and the first current pulse (j x ) is still active, only j x The current is kept active so that the current intensity is reduced to 2TA / m 2 .

[0082] Therefore, the control circuit 130 can be configured to apply a second current pulse with positive polarity in addition to the first current pulse in the first state (state A) to convert the layer 116 ( Figure 1 ) or layer 112 ( Figure 3 ) is magnetized from a first orientation (e.g., -M z ) switches to the second orientation (e.g., +M z In the second state (shown in the right figure), the control circuit 130 can be configured to apply a second current pulse with a negative polarity to layer 116 ( Figure 1 ) or layer 112 ( Figure 3 ) is magnetized from the second orientation (e.g., +M z ) switches to the first orientation (e.g., -M z In the example shown, the start time of the first current pulse is substantially equal to the start time of the second current pulse, and the duration of the first current pulse is longer than the duration of the second current pulse. In other embodiments, the start times may not be equal. In the example shown, the control circuit 130 is configured to supply the second conductor 120-2 with a current equal to or higher than the first current pulse (j x ) of the magnitude of the second current pulse (j y ). In other embodiments, it may be beneficial if the pulse is not completely off, but the intensity can take the form of a function as a function of time.

[0083] The output of the MR device 100 can also be measured using Figure 7 This can be achieved using the Wheatstone bridge shown.

[0084] Figure 7 The MR device 100 includes four MR sensing elements 110-1, ..., 110-4 in a Wheatstone bridge configuration. The output voltage of the Wheatstone bridge configuration depends on

[0085]

[0086] Where U0=R tot I2.

[0087] If the current polarity is changed from the original polarity (eg, +I2) to the reverse polarity (eg, -I2), and the orientation of all reference layers 116 remains unchanged, as shown in FIG. Figure 7 As shown (this state can be represented as ref1), the output of the Wheatstone bridge will reverse its sign. If, in addition to the reverse current polarity, the magnetization state of each reference layer 116 is also reversed due to the SOT (this state can be represented as ref2), the output of the Wheatstone bridge will again remain unchanged. Therefore, the total output voltage can be the sum of the Wheatstone bridge outputs in these two reversed states, where the I2 current is used to reverse the reference layer magnetization.

[0088] U signal =U out,I2+,ref1 +U out,I2-,ref2

[0089] In some embodiments, the sensor can be operated by inverting the orientation of the reference layer and inverting the sign of the bridge input current by the SOT current and averaging the bridge output during these two time periods. Thus, the 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 the output sensor signal.

[0090] In other embodiments, Figure 7 As shown, the applied current j x and j y To set the reference layer (ref1). Apply a constant current I2 to measure the output U of the Wheatstone bridge. out,ref1 Then apply j x and j y To reverse the magnetization state of the reference layer (ref1). Under constant current I2, the output U out,ref2 The signal proportional to the applied field in the z direction is given by:

[0091] U signal =U out, / 2+,ref1 U out, / 2-,ref2

[0092] Some embodiments of the present disclosure provide a magnetic sensor device including a GMR or TMR sensor element, wherein the transfer function of the sensor device can be inverted by changing the orientation of a magnetic reference system. The reference system can be switched using a SOT current. Advantageously, sensor offset can be reduced and switching can be achieved without a bias field.

[0093] The aspects and features described with respect to a particular example among the foregoing examples may also be combined with one or more other examples to replace the same or similar features of the other examples, or to additionally introduce these features into another example.

[0094] It is further understood that the disclosure of several steps, processes, operations, or functions disclosed in the specification or claims should not be interpreted as implying that these operations necessarily depend on the order described, unless explicitly stated in individual cases or necessary for technical reasons. Therefore, the above description does not limit the performance of several steps or functions to a certain order. In addition, in other examples, a single step, function, process, or operation may include and / or be decomposed into several sub-steps, sub-functions, sub-processes, or sub-operations.

[0095] If aspects have been described in conjunction with an apparatus or system, these aspects should also be understood as descriptions of corresponding methods. For example, blocks, devices, or functional aspects of an apparatus or system may correspond to features of a corresponding method, such as method steps. Thus, aspects described in conjunction with a method should also be understood as descriptions of corresponding blocks, elements, attributes, or functional features of the corresponding apparatus or system.

[0096] The following claims are hereby incorporated into the detailed description, where each claim can stand on its own as a separate example. It should also be noted that although dependent claims may be referred to in the claims as specific combinations with one or more other claims, other examples may include combinations of dependent claims with the subject matter of any other dependent or independent claims. Such combinations are hereby expressly set forth unless a specific combination is not intended in a particular instance. Furthermore, features of one claim should also be included in any other independent claim, even if that claim is not directly defined as dependent on that other independent claim.

Claims

1. A magnetoresistive device (100), comprising: At least one magnetoresistive element (110) includes ferromagnetic layers (112) stacked in a first direction; 114； 116； 118) and a layer stack of non-magnetic layers (113; 115), said layer stack comprising a ferromagnetic layer (112; 118) having a magnetic orientation to be switched; A first conductor (120-1) extending in a second direction and a second conductor (120-2) extending in a third direction adjacent to the ferromagnetic layer (112; 118), wherein the first conductor and the second conductor are configured to induce a spin-orbit torque (SOT) in the ferromagnetic layer (112; 118); as well as 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 temporal characteristics.

2. The magnetoresistive device (100) of claim 1, wherein the control circuit (130) is configured to turn off the second current pulse to switch the magnetic orientation of the ferromagnetic layer (112; 118) before turning off the first current pulse.

3. The magnetoresistive device (100) according to claim 1 or 2, wherein the ferromagnetic layer (112; 118) having the magnetic orientation to be switched is a ferromagnet with perpendicular anisotropy.

4. The magnetoresistive device (100) of 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 having the magnetic orientation to be switched is the magnetic reference layer (118).

5. The magnetoresistive device (100) of claim 4, wherein the magnetic reference layer (118) is configured as a synthetic antiferromagnet (SAF).

6. The magnetoresistive device (100) of claim 4 or 5, wherein the magnetic free layer (112) comprises an in-plane magnetization in the absence of an external magnetic field.

7. The magnetoresistive device (100) according to claim 4 or 5, wherein the magnetic free layer (112) is a ferromagnet having perpendicular crystal anisotropy.

8. The magnetoresistive device (100) according to any one of claims 1 to 3, wherein the layer stack comprises a magnetic free layer (112) and a magnetic reference layer (118), wherein the ferromagnetic layer having the magnetic orientation to be switched is the magnetic free layer (112).

9. The magnetoresistive device (100) according to any one of claims 4 to 8, wherein the magnetic free layer (112) and the magnetic reference layer (118) are separated by a non-magnetic tunnel barrier (113).

10. The magnetoresistive device (100) according to any one of claims 4 to 8, wherein the magnetic free layer (112) and the magnetic reference layer (118) are separated by a non-magnetic conductive spacer layer (113).

11. The magnetoresistive device (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) at a magnitude equal to or higher than the first current pulse.

12. The magnetoresistive device (100) according to any one of the preceding claims, wherein the start time of the first current pulse is equal to the start time of the second current pulse, and wherein the duration of the first current pulse is longer than the duration of the second current pulse.

13. The magnetoresistive device (100) according to any one of the preceding claims, wherein the control circuit (130) is configured to: In a first state, applying the second current pulse with 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, the second current pulse is applied with a second opposite polarity to switch the magnetic orientation of the ferromagnetic layer (112; 118) from the second orientation to the first orientation.

14. The magnetoresistive device (100) of claim 13, wherein the control circuit (130) is further configured to provide a difference between the first sensor signal in the first state and the second sensor signal in the second state as an output sensor signal.

15. The magnetoresistive device (100) according to any one of the preceding claims, wherein the first conductor (120-1) and the second conductor (120-2) are arranged in a crossbar structure.

16. The magnetoresistive device (100) according to any one of the preceding claims, wherein the first conductor (120-1) and the second conductor (120-2) consist of a non-magnetic heavy metal.

17. The magnetoresistive device (100) according to any one of the preceding claims, wherein the layer stack forms a GMR spin valve structure or a TMR spin valve structure.

18. The magnetoresistive device (100) according to any one of the preceding claims, further comprising electrodes located at both ends of the layer stack, the electrodes being used to apply a current CPP perpendicular to the plane.

19. A magnetoresistive random access memory (MRAM) cell (400; 410) comprising a magnetoresistive device according to any one of the preceding claims.

20. A method for switching magnetic orientation, the method comprising: At least one magnetoresistive element (110; 410) is provided, the magnetoresistive element comprising ferromagnetic layers (112; 114； 116; 118) and a layer stack of non-magnetic layers (113; 115), said layer stack comprising a ferromagnetic layer (112; 118) having a magnetic orientation to be switched; Providing a first conductor (120-1) extending in a second direction and a second conductor (120-2) extending in a third direction near the ferromagnetic layer (112; 118), the first conductor and the second conductor being configured to induce SOT in the ferromagnetic layer (112, 118); A first current is applied to the first conductor (120-1) and a second current is applied to the second conductor (120-2) in a temporally overlapping manner and with different temporal characteristics.

21. The method of claim 20, 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).

22. The method according to claim 20 or 21, wherein the second current is applied to the second conductor (120-2) at a magnitude equal to or higher than the first current.

23. The method of any one of claims 20 to 22, wherein a start time of the first current is equal to a start time of the second current, and wherein a duration of the first current is longer than a duration of the second current.

24. The method according to any one of claims 20 to 23, comprising: In a first state, applying the second current with 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, the second current is applied with a negative polarity to switch the magnetic orientation of the ferromagnetic layer (118) from the second orientation to the first orientation.

25. The method according to claim 24, comprising: An output sensor signal is provided corresponding to a difference between a first sensor signal for the first state and a second sensor signal for the second state.

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