MAGNETORESISTIVE SENSOR WITH REDUCED STRESS SENSITIVITY

Abstract

A magnetoresistive sensor (100; 200) comprising:a first non-magnetic layer (112);a second non-magnetic layer (118);and a magnetic free double layer (113) disposed between the first non-magnetic layer (112) and the second non-magnetic layer (118), wherein the magnetic free double layer (113) comprises a first magnetic free layer (114) disposed adjacent to a second magnetic free layer (116), wherein the first magnetic free layer (114) is disposed adjacent to the first non-magnetic layer (112) and the second magnetic free layer (116) is disposed adjacent to the second non-magnetic layer (118), wherein the second non-magnetic layer (118) is made of a non-magnetic material having an atomic radius that does not deviate by more than 10% of an atomic radius of at least one of the first magnetic free layer (114) and the second magnetic free layer (116), and wherein the non-magnetic material is selected from one of magnesium, indium, and tin.

Description

AREA

[0001] The present disclosure relates generally to a magnetoresistive sensor device and methods of making the same, and more particularly to a magnetoresistive sensor device with reduced stress sensitivity. BACKGROUND

[0002] Magnetoresistive effects are based on numerous different physical phenomena. What all of these phenomena have in common is that the electrical resistance of a resistive element can be modified by a magnetic field penetrating the resistive element. Technologies that utilize magnetoresistive effects are sometimes referred to as "xMR technologies," where the "x" indicates that a variety of effects can be addressed, such as the giant magnetoresistive (GMR) effect, the tunneling magnetoresistive (TMR) effect, or the anisotropic magnetoresistive (AMR) effect, to name just a few. xMR effects can be applied to a variety of field-based magnetoresistive sensors, for example, for measuring rotation, angle, etc. Examples of xMR sensors include:described in US 2005 / 0 280 955 A1, US 2002 / 0 085 319 A1, US 8 174 800 B2 or DE 10 2011 085 955 A1.

[0003] xMR sensors, and especially xMR angle sensors, should have a sensor layer (free layer) that is capable of ideally following the direction of an external rotating magnetic field. Nevertheless, in reality, there may be internal magnetic forces (e.g., magnetic anisotropies) that compete with the external magnetic field, leading to a deviation between the free-layer magnetization and the external field direction. Consequently, the xMR sensor may output an incorrect value due to this angular error caused by the deviation. Ferromagnetic materials can exhibit a magnetostrictive effect, i.e., a geometric dimension changes in response to an external magnetic field. The inverse effect is the so-called magnetoelastic effect, i.e., a change in a geometric dimension leads to the creation of a magnetic anisotropy axis.

[0004] Furthermore, the xMR sensor stack can exhibit so-called magnetoelastic behavior, meaning that when mechanical stress / strain is applied to the sensor chip, an additional magnetic anisotropy axis can be introduced, leading to an additional angular error. Mechanical stress / strain can occur on the sensor chip during the packaging process, over temperature within the package, and / or over the lifetime of the component. Thus, the properties of the magnetic sensor can change over temperature and / or lifetime, which is undesirable.

[0005] Therefore, reducing the magnetoelastic behavior of xMR stacks may be desirable to improve sensor performance. SUMMARY

[0006] There is a need to provide an improved concept for a magnetoresistive sensor and a magnetoresistive sensor.

[0007] Such a need can be met by magnetoresistive sensors according to the independent claims. Advantageous further developments are the subject of the dependent claims.

[0008] Some embodiments relate to a magnetoresistive sensor comprising a first non-magnetic layer; a second non-magnetic layer; and a magnetic free bi-layer disposed between a first non-magnetic layer and the second non-magnetic layer, wherein the magnetic free bi-layer comprises a first magnetic free layer coupled to a second magnetic free layer, the first magnetic free layer coupled to the first non-magnetic layer and the second magnetic free layer coupled to the second non-magnetic layer, and the second non-magnetic layer comprises a non-magnetic material having an atomic radius within 10% of an atomic radius of at least one of the first magnetic free layer and the second magnetic free layer.

[0009] Optionally, the non-magnetic material is selected from one of copper, magnesium, indium, bismuth, tin and zinc.

[0010] Again optionally, the first non-magnetic layer comprises a non-magnetic material selected from one of copper, magnesium, indium, bismuth, tin and zinc.

[0011] Optionally, the first magnetic free layer and the second magnetic free layer are each made of a material selected from cobalt, nickel, iron, and alloys thereof.

[0012] Again optionally, the first magnetic free layer is made of cobalt-iron (CoFe) and the second magnetic free layer is made of nickel-iron (NiFe).

[0013] Optionally, the magnetoresistive sensor further comprises a seed layer; a cap layer; and a magnetic layer stack disposed between the seed layer and the cap layer, the magnetic layer stack comprising the first non-magnetic layer, the second non-magnetic layer, and the magnetic free double layer, wherein the second non-magnetic layer is disposed between the magnetic free double layer and one of the seed layer and the cap layer.

[0014] Again optionally, the magnetic layer stack further comprises a magnetic reference system comprising a pinned layer and a reference layer, wherein the magnetic reference system is coupled to the first non-magnetic layer.

[0015] Optionally, the reference layer is coupled to the first non-magnetic layer.

[0016] Again optionally, the first magnetic free layer is made of cobalt-iron (CoFe) and the second magnetic free layer is made of nickel-iron (NiFe).

[0017] Optionally, the magnetoresistive sensor further comprises a magnetic reference system comprising a pinned layer and a reference layer, wherein the magnetic reference system is coupled to the first non-magnetic layer.

[0018] Again optionally, the first non-magnetic layer comprises a non-magnetic material having an atomic radius within 10% of an atomic radius of at least one of the first magnetic free layer and the second magnetic free layer.

[0019] Optionally, the second non-magnetic layer comprises a non-magnetic material having an atomic radius within 5% of an atomic radius of at least one of the first magnetic free layer and the second magnetic free layer.

[0020] Again optionally, the first non-magnetic layer comprises a non-magnetic material having an atomic radius within 5% of an atomic radius of at least one of the first magnetic free layer and the second magnetic free layer.

[0021] Optionally, the non-magnetic material of the second non-magnetic layer comprises an atomic radius within 10% of the atomic radius of the first magnetic free layer and the second magnetic free layer.

[0022] Again optionally, the non-magnetic material of the first non-magnetic layer comprises an atomic radius within 10% of the atomic radius of the first magnetic free layer and the second magnetic free layer.

[0023] Optionally, the first non-magnetic layer has a thickness that is different from a thickness of the second non-magnetic layer.

[0024] Again optionally, the first magnetic free layer and the second magnetic free layer are each configured to change a magnetization direction thereof based on a magnetic field applied thereto.

[0025] Some embodiments relate to a magnetoresistive sensor comprising a seed layer; a cap layer; and a magnetic layer stack disposed between the seed layer and the cap layer, the magnetic layer stack comprising a first non-magnetic layer; a second non-magnetic layer;and a magnetic free double layer disposed between a first non-magnetic layer and the second non-magnetic layer, wherein the magnetic free double layer comprises a first magnetic free layer coupled to a second magnetic free layer, the first magnetic free layer coupled to the first non-magnetic layer, and the second magnetic free layer coupled to the second non-magnetic layer, the second non-magnetic layer disposed between the magnetic free double layer and one of the seed layer and the cap layer, and the second non-magnetic layer comprises a non-magnetic material having an atomic radius between an atomic radius of the second magnetic free layer and an atomic radius of at least one of the seed layer and the cap layer;

[0026] Optionally, the seed layer comprises two sublayers comprising a first sublayer comprising nickel-chromium (NiCr) and a second sublayer of tantalum, the cap layer comprises tantalum, the first magnetic free layer is made of cobalt-iron (CoFe), and the second magnetic free layer is made of nickel-iron (NiFe).

[0027] Again optionally, the non-magnetic material of the first non-magnetic layer is selected from one of copper, magnesium, indium, bismuth, tin and zinc, and the second non-magnetic layer comprises a non-magnetic material selected from one of copper, magnesium, indium, bismuth, tin and zinc.

[0028] Embodiments provide a magnetoresistive sensor device with reduced stress sensitivity.

[0029] According to one embodiment, a magnetoresistive sensor comprises a first non-magnetic layer, a second non-magnetic layer, and a magnetic free double layer. The magnetic free double layer is arranged between a first non-magnetic layer and the second non-magnetic layer, the magnetic free double layer comprising a first magnetic free layer coupled to a second magnetic free layer. The first magnetic free layer is coupled to the first non-magnetic layer, and the second magnetic free layer is coupled to the second non-magnetic layer. The second non-magnetic layer comprises a non-magnetic material having an atomic radius within 10% of an atomic radius of at least one of the first magnetic free layer and the second magnetic free layer.

[0030] According to another embodiment, a magnetoresistive sensor comprises a seed layer, a cap layer, and a magnetic layer stack disposed between the seed layer and the cap layer. The magnetic layer stack comprises a first non-magnetic layer, a second non-magnetic layer, and a magnetic free double layer disposed between the first non-magnetic layer and the second non-magnetic layer. The magnetic free double layer comprises a first magnetic free layer coupled to a second magnetic free layer, the first magnetic free layer coupled to the first non-magnetic layer, and the second magnetic free layer coupled to the second non-magnetic layer. The second non-magnetic layer is disposed between the magnetic free double layer and one of the seed layer and the cap layer.In addition, the second non-magnetic layer comprises a non-magnetic material having an atomic radius between an atomic radius of the second magnetic free layer and an atomic radius of at least one of the seed layer and the cap layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Embodiments are described herein with reference to the accompanying drawings. Fig. 1 shows a vertical cross-section of a GMR stack according to one or more embodiments; and Fig. 2 shows a vertical cross-section of another GMR stack according to one or more embodiments. DETAILED DESCRIPTION

[0032] Various embodiments will now be described in detail with reference to the accompanying drawings. The embodiments are provided for illustrative purposes only and are not to be considered limiting. For example, while embodiments may be described as including a plurality of features or elements, some of these features or elements may be omitted from other embodiments and / or may be replaced with alternative features or elements. In other embodiments, further features or elements may be provided in addition to those expressly shown and described. In addition, features of the various embodiments described herein may subsequently be combined with one another to form further embodiments, unless specifically stated otherwise.For example, variations or modifications described with respect to one of the embodiments may also be applicable to other embodiments unless otherwise stated.

[0033] Accordingly, while further examples are susceptible to various modifications and alternative forms, certain specific examples thereof are shown in the figures and will be described in detail below. However, this detailed description does not limit further examples to the specific forms described. Further examples may cover all modifications, equivalents, and alternatives falling within the scope of the disclosure.

[0034] Furthermore, corresponding or identical elements, or elements with corresponding or identical functionality, are denoted by corresponding or identical reference numerals in the following description. Since the corresponding or identical elements in the figures are given the same reference numerals, a repeated description for elements provided with the same reference numerals can be omitted. Thus, descriptions provided for elements with the same or similar reference numerals are interchangeable.

[0035] When a singular form, such as "a," "an," and "the," is used, and the use of only a single element is neither explicitly nor implicitly defined as mandatory, further examples may also use plural elements to implement the same functionality. When a functionality is subsequently described as being implemented using multiple elements, further examples may implement the same functionality using a single element or a single processing entity. It is further understood that the terms "comprises," "comprising," "has," and / or "having," when used, specify the presence of the specified features, integers, steps, processes, acts, elements, and / or components, but do not preclude the presence or addition of one or more features, integers, steps, operations, processes, acts, elements, components, and / or any group thereof.

[0036] It should be noted that when an element is described as being "connected" or "coupled" to another element, the element may be directly connected or coupled to the other element, or intervening elements may be present. Conversely, when an element is described as being "directly connected" or "coupled" to another element, no intervening elements are present. Other terms used to describe the relationship between elements should be interpreted similarly (e.g., "between" versus "directly between," "adjacent" versus "directly adjacent," etc.).

[0037] In embodiments described herein or shown in the drawings, any direct electrical connection or coupling, i.e. any connection or coupling without additional intervening elements, may also be implemented by an indirect connection or coupling, i.e. a connection or coupling with one or more intervening elements, or vice versa, as long as the general purpose of the connection or coupling, for example, transmitting a certain type of signal or transmitting a certain type of information, is substantially maintained.

[0038] The drawings should be considered schematic representations, and elements depicted in the drawings are not necessarily shown to scale. Instead, the various elements are illustrated in such a way that their function and general purpose will be apparent to one of ordinary skill in the art. Any connection or coupling between functional blocks, devices, components, or other physical or functional entities shown in the drawings or described herein may also be implemented through an indirect connection or coupling. Functional blocks may be implemented in hardware, firmware, software, or a combination thereof.

[0039] Embodiments relate to sensors and sensor systems, and obtaining information via sensors and sensor systems. A sensor may refer to a component that converts a physical quantity to be measured into an electrical signal, for example, a current signal or a voltage signal. The physical quantity may include, but is not limited to, a magnetic field, an electric field, a pressure, a force, a current, or a voltage. A sensor device as described herein may be an angle sensor, a linear position sensor, a speed sensor, a motion sensor, and the like.

[0040] A magnetic field sensor, for example, includes one or more magnetic field sensor elements that measure one or more characteristics of a magnetic field (e.g., an amount of magnetic field flux density, a field strength, a field angle, a field direction, a field orientation, etc.). The magnetic field may be generated by a magnet, a current-carrying conductor (e.g., a wire), the ground, or another magnetic field source. Each magnetic field sensor element is configured to generate a sensor signal (e.g., a voltage signal) in response to one or more magnetic fields impinging on the sensor element. Thus, a sensor signal is indicative of the magnitude and / or orientation of the magnetic field impinging on the sensor element.

[0041] It should be noted that the terms “sensor” and “sensing element” may be used interchangeably throughout this description, and the terms “sensor signal” and “measurement signal” may also be used interchangeably throughout this description.

[0042] Magnetic sensors as provided herein may be magnetoresistive sensors. Magnetoresistance is the property of a material to change its electrical resistance value when an external magnetic field is applied to it.Some examples of magnetoresistive effects are giant magnetoresistance (GMR), which is a quantum mechanical magnetoresistance effect observed in thin-film structures composed of alternating ferromagnetic and non-magnetic conductive layers, tunnel magnetoresistance (TMR), which is a magnetoresistive effect occurring at a magnetic tunnel junction (MTJ), which is a component consisting of two ferromagnets separated by a thin insulator, or anisotropic magnetoresistance (AMR), which is a property of a material in which a dependence of the electrical resistance on the angle between the direction of the electric current (i.e., the sensing axis) and the direction of magnetization is observed.For example, in the case of AMR sensors, a resistance for an AMR sensor element changes according to a square of a sine of an angle of the magnetic field component projected onto a sensing axis of the AMR sensor element.

[0043] The majority of different magnetoresistive effects are commonly abbreviated as xMR, where the "x" serves as a placeholder for the various magnetoresistive effects. xMR sensors can detect the orientation of an applied magnetic field by measuring sine and cosine angular components with monolithically integrated magnetoresistive sensor elements.

[0044] Magnetoresistive sensor elements of such xMR sensors typically comprise a plurality of layers, at least one of which is a reference layer with a reference magnetization (i.e., a reference direction in the case of GMR or TMR technology). The reference magnetization is a magnetization direction that provides a sensing direction corresponding to a sensing axis of the xMR sensor. Accordingly, in the case of a GMR or TMR sensor element, when a magnetic field component (e.g., a free layer) points in exactly the same direction as the reference direction, a resistance of the xMR sensor element is at a minimum, and when a magnetic field component points in exactly the opposite direction to the reference direction, the resistance of the xMR sensor element is at a maximum.A magnetic field component can be, for example, an x-magnetic field component (Bx), a y-magnetic field component (By) or a z-magnetic field component (Bz), where the Bx and By field components are in a plane to the magnetic sensor and Bz is out of a plane to the magnetic sensor.

[0045] While the materials chosen for the free layer may be intrinsically (i.e., as a bulk material) magnetostriction-free, as ultrathin layers, magnetostrictive / magnetoelastic behavior can be induced in the free-layer system. This effect depends on the material and the thickness of the next neighboring layer of the magnetic free layer as a consequence of a lattice mismatch between the two layers (i.e., between the neighboring layer and the magnetic free layer). The magnetic free layer for an xMR sensor may be made of a nickel-iron (NiFe) alloy or a cobalt-iron (CoFe) alloy, or a combination of both, and may be used in a bilayer arrangement where two magnetic free layers are used. In particular, each magnetic free layer may be made of a material selected from cobalt, nickel, iron, and alloys thereof.Alloys may contain non-ferromagnetic materials (e.g., carbon, boron, nitrogen, and / or oxygen), with ferromagnetic materials constituting at least 50% of the material composition of the respective layer. As used herein, a "double layer" refers to two adjacent layers forming a layer system.

[0046] A neighboring layer can form a neighboring layer system, where a ruthenium (Ru) / copper (Cu) bilayer nearest-neighbor system is arranged adjacent to one of the magnetic free layers. By varying the thickness ratio of Ru / Cu, the magnetoelastic behavior can be modified.

[0047] For a sensor application, the thickness of non-magnetic but conductive layers should be as small as possible to prevent excessive shunting from reducing the signal ratio dR / R. Therefore, the Ru / Cu bilayer system for tuning the magnetoelastic behavior is not advantageous for sensor applications.

[0048] According to one or more embodiments, an xMR layer stack, referred to as a magnetic layer stack, may comprise a magnetic free double layer disposed between two non-magnetic layers. The two non-magnetic layers adjacent to the magnetic free double layer may be referred to as neighbor layers. The magnetic free double layer comprises two adjacently disposed magnetic free layers. One of the non-magnetic layers may be disposed between the magnetic free double layer and a cap layer or a seed layer in a bottom spin valve (BSV) or top spin valve (TSV) arrangement, respectively.

[0049] The cap layer can be made of tantalum (Ta) or tantalum nitride (TaN), having an atomic radius of 200 pm. The seed layer can be made of a bilayer of a Ta or TaN layer and a nickel-chromium (NiCr) layer, having an atomic radius of 166 ppm.

[0050] Co(Fe) and Ni(Fe) have similar atomic radii (lattice constants) of 152 pm and 149 pm, respectively. A copper (Cu) layer, which has an atomic radius of 145 pm, can be used as a neighboring layer, thus not resulting in a significant lattice mismatch with respect to the magnetic free layer(s). On the other hand, the Ta(N) layer or the NiCr layer on the other side of the free layers, with an atomic radius of 200 pm or 166 pm, leads to a significant lattice mismatch with respect to the magnetic free layer(s), thus potentially introducing magnetoelastic behavior. Thus, another non-magnetic layer, which has an atomic radius more similar to the magnetic free layer(s), is used as the second neighboring layer. This second neighboring layer can also be referred to as a matching layer.

[0051] The matching layer between the seed / cap layer and the magnetic free bilayer, which has a lattice constant similar to that of the free layer(s), reduces potential lattice mismatch. A suitable example would be a thin Cu (atomic radius 145 pm) or magnesium Mg (atomic radius 145 pm) layer. This additional layer minimizes the lattice mismatch of the free layer with the neighboring layers. Consequently, the sensitivity to stress / strain is reduced.

[0052] Accordingly, the magnetic layer stack may comprise a first non-magnetic layer; a second non-magnetic layer (i.e., a matching layer); and a magnetic free double layer disposed between the first non-magnetic layer and the second non-magnetic layer, the magnetic free double layer comprising a first magnetic free layer coupled to a second magnetic free layer. Here, the first magnetic free layer is coupled to the first non-magnetic layer, and the second magnetic free layer is coupled to the second non-magnetic layer.

[0053] Additionally, to minimize lattice mismatch, the second non-magnetic layer is made of a non-magnetic material having an atomic radius within 10% of an atomic radius of at least one of the first magnetic free layer and the second magnetic free layer. For example, if the second magnetic free layer is NiFe, which has an atomic radius of 149 pm, the second non-magnetic layer should be made of a material having an atomic radius within 14.9 pm of 149 pm (i.e., 134.1-163.9 pm). Thus, the non-magnetic material of the second non-magnetic layer can be selected, for example, from one of copper, magnesium, indium, bismuth, tin, and zinc.In addition, to further reduce the lattice mismatch, the non-magnetic material of the second non-magnetic layer may be selected to have an atomic radius within 5% of an atomic radius of at least the first magnetic free layer and the second magnetic free layer.

[0054] Similarly, the material of the first non-magnetic layer can also be selected to minimize the lattice mismatch between it and the first magnetic free layer. Here, the first non-magnetic layer can be made of a non-magnetic material having an atomic radius within 10% of an atomic radius of at least one of the first magnetic free layer and the second magnetic free layer. For example, if the first magnetic free layer is made of CoFe, which has an atomic radius of 152 pm, the second non-magnetic layer should be made of a material having an atomic radius within 15.2 pm of 152 pm (i.e., 136.8-167.2 pm). Thus, the non-magnetic material of the first non-magnetic layer can be selected from, for example, one of copper, magnesium, indium, bismuth, tin, and zinc.In addition, to further reduce the lattice mismatch, the non-magnetic material of the first non-magnetic layer may be selected to have an atomic radius within 5% of an atomic radius of at least the first magnetic free layer and the second magnetic free layer.

[0055] Some example implementations of GMR structures are described below. However, similar principles can be applied to other types of xMR sensors, such as TMR and the like. GMR structures are often operated in a so-called current-in-plane (CIP) configuration, meaning the applied current flows parallel to the layered structure or to the top surface of the chip. The application spectrum for TMR structures is similar to that of GMR structures. However, compared to GMR structures, TNIR structures are often operated in a so-called current-perpendicular-to-plane (CPP) configuration, meaning the applied current flows perpendicular to the layered structure or the top surface of the chip.

[0056] Fig. 1 shows a vertical cross-section of a GMR stack according to one or more embodiments. In particular, the GMR stack is Fig. 1 arranged in a lower spin valve configuration.

[0057] Fig. 1 shows an example of a magnetic layer stack 100 of a magnetoresistive sensor according to an example. For example, the magnetic layer stack 100 can be arranged on a semiconductor substrate (not shown) of the magnetoresistive sensor. When described in a Cartesian coordinate system with pairwise perpendicular coordinate axes x, y, and z, the layers each extend laterally in a plane spanned by the x and y axes. Herein, lateral dimensions (e.g., lateral distances, lateral cross-sectional areas, lateral areas, lateral extensions, lateral displacements, etc.) refer to dimensions in the xy plane. Vertical dimensions refer to dimensions in the z direction, perpendicular to the xy plane. For example, the (vertical) extension of a layer in the z direction can be described as the layer thickness.From bottom to top, the magnetic layer stack 100 includes a seed layer 102, which is used to influence and / or optimize stack growth. A natural antiferromagnetic (NAF) layer 104 is disposed on the seed layer 102, and a ferromagnetic pinned layer 106 is disposed on the NAF layer 104. The NAF layer 104 can be made of platinum-manganese (PtMn), iridium-manganese (IrMn), nickel-manganese (NiMn), or the like. A film thickness of the NAF can be in the range of 5 nm to 50 nm. The pinned layer (PL) 106 can be made of CoFe, cobalt-iron-boron (CoFeB), or the like.

[0058] Contact between the NAF layer 104 and the pinned layer 106 can provoke an effect known as an exchange bias effect, which causes the magnetization of the pinned layer 106 to align in a preferred direction (e.g., the x-direction, as shown). The pinned layer 106 can have a closed-flux magnetization pattern in the xy plane. This closed-flux magnetization pattern of the pinned layer 106 can be created during fabrication of the magnetic layer stack 100 and can be permanent. Alternatively, the pinned layer 106 can have a linear magnetization pattern in the xy plane.

[0059] The magnetic layer stack 100 further comprises a non-magnetic layer (NML), referred to as a coupling layer 108. The coupling layer 108 may be diamagnetic and may comprise ruthenium, iridium, copper, and / or copper alloys and similar materials, for example. The coupling layer 108 spatially separates the pinned layer 106 from the magnetic (e.g., ferromagnetic) reference layer (RL) 110. The coupling layer 108 may provide antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling to form an artificial antiferromagnet. Thus, using this structure, the magnetization of the magnetic reference layer 110 can align and be maintained in a direction antiparallel to the magnetization of the pinned layer 106, i.e., in the -x direction, as shown.

[0060] For example, if the pinned layer 106 has a magnetization pattern with clockwise closed flux in the xy plane, the magnetic reference layer 110 can have a magnetization pattern with counterclockwise closed flux in the xy plane (or vice versa). In this way, the magnetic reference layer 110 can have a magnetization pattern with permanently closed flux. Furthermore, if the pinned layer 106 comprises a linear magnetization pattern in the xy plane in a specific direction, the reference layer 110 can comprise a linear magnetization pattern in an antiparallel direction. Thus, the pinned layer 106, the coupling layer 108, and the magnetic reference layer 110 form a magnetic reference system 111. The film thickness for the pinned layer 106 and / or the reference layer 110 can each be in the range of 1 nm to 100 nm.

[0061] The magnetic layer stack 100 additionally includes a non-magnetic layer 112, referred to as a neighboring layer, and a magnetic free double layer 113. The non-magnetic layer 112 may comprise a non-magnetic material such as copper, magnesium, indium, bismuth, tin, or zinc and is disposed between the magnetic reference layer 110 and the magnetic free double layer 113. The magnetic free double layer 113 comprises two magnetic free layers 114 and 116. Each of the magnetic free layers 114 and 116 acts as a sensor layer that changes its magnetization upon an external in-plane magnetic field. The non-magnetic layer 112 is directly coupled to one of the magnetic free layers—in this case, the magnetic free layer 114—without any intermediate layer in between.

[0062] The magnetic free layers 114 and 116 are magnetically coupled to each other. In one embodiment, this coupling may be a direct coupling without any intermediate layer between the free layers 114 and 116. In another embodiment, the coupling may comprise an RKKY coupling with a non-magnetic layer (i.e., a coupling layer) between the free layers 114 and 116. Materials of the magnetic free layers may be similar to the alloys of ferromagnetic materials of the pinned layer 106 and the reference layer 110, such as CoFe, CoFeB, and / or NiFe. In particular, each magnetic free layer may be made of a material selected from cobalt, nickel, iron, and alloys thereof. Alloys may comprise non-ferromagnetic materials (e.g.,Carbon, boron, nitrogen, and / or oxygen), wherein ferromagnetic materials make up at least 50% of a material composition of the respective layer. In this example, the magnetic free layer 114 is made of CoFe and the magnetic free layer 116 is made of NiFe.

[0063] Each magnetic free layer (FL) 114 and 116 can have a linear magnetization pattern or a closed-flux magnetization pattern (e.g., a vortex magnetization pattern). Furthermore, the magnetization of each magnetic free layer 114 and 116 can follow an externally applied magnetic field. By using two sensor layers in a bilayer arrangement, the signal amplitude of the xMR sensor can be increased / amplified.

[0064] The magnetic layer stack 100 additionally comprises a non-magnetic layer 118, referred to as a neighboring layer, and further referred to as a matching layer. The non-magnetic layer 118 may comprise a non-magnetic material, such as copper, magnesium, indium, bismuth, tin, or zinc. The non-magnetic layer 118 is disposed on the magnetic free double layer 113, and specifically on the magnetic free layer 116. Thus, the non-magnetic layer 118 is directly coupled to one of the magnetic free layers—in this case, the magnetic free layer 116—without any intermediate layer in between.

[0065] A cap layer 120 made of tantalum (Ta) or tantalum nitride (TaN) is disposed on the non-magnetic layer 118 and forms the upper layer of the magnetic layer stack 100.

[0066] The material of the non-magnetic layer 118 may be selected such that its lattice constant (i.e., atomic radius) is more closely matched to the lattice constant of the magnetic free layer 116 than to that of the capping layer 120. For example, the non-magnetic material of the matching layer 118 may have an atomic radius between an atomic radius of the magnetic free layer 116 and an atomic radius of the capping layer 120. Additionally or alternatively, the non-magnetic material of the matching layer 118 may be selected to have an atomic radius within 10% of an atomic radius of the magnetic free layer 116. More specifically, the non-magnetic material of the matching layer 118 may be selected to have an atomic radius within 5% of an atomic radius of the magnetic free layer 116. The atomic radius of the non-magnetic material of the matching layer 118 may similarly be within a certain range (e.g.,5% or 10%) from the magnetic free layer 114.

[0067] Similarly, the material of the non-magnetic layer 112 can be selected so that its lattice constant (i.e., atomic radius) closely matches the lattice constant of the magnetic free layer 114. For example, the non-magnetic material of the non-magnetic layer 112 can be selected to have an atomic radius within 10% of an atomic radius of the magnetic free layer 114. More specifically, the non-magnetic material of the non-magnetic layer 112 can be selected to have an atomic radius within 5% of an atomic radius of the magnetic free layer 114. The atomic radius of the non-magnetic material of the non-magnetic layer 112 can similarly be within a certain range (e.g., 5% or 10%) of that of the magnetic free layer 116.

[0068] This arrangement minimizes the lattice mismatch of the free layers 114 and 116 to the neighboring layers 112 and 118. Thus, the sensitivity to stress / strain is reduced.

[0069] According to some embodiments, the non-magnetic layer 112 may be electrically conductive (e.g., comprise copper, silver, gold, tungsten, aluminum, and / or alloys thereof). In this case, the magnetoresistive sensor comprising the magnetic layer stack 100 may be a GMR sensor. Alternatively, the non-magnetic layer 112 may be an electrically insulating tunnel barrier layer (e.g., made of aluminum oxide (Al2O3) and / or magnesium oxide (MgO)). The magnetoresistive sensor comprising the magnetic layer stack 100 may then be a TMR sensor. Thus, examples of xMR sensors of the present disclosure may comprise the magnetic layer stack 100 from Fig. 1 and / or similar magnetic layer stacks. Magnetoresistive sensors are not limited to the GMR or TMR effect. Other examples of the present disclosure may include structures based on other xMR effects. The magnetic layer stack 100 may correspond to a magnetoresistance as employed by at least some embodiments of this disclosure.

[0070] As mentioned previously, the Fig. 1 a vertical cross-section of a first possible stack implementation: the so-called “bottom-pinned spin valve” (BSV) structure, which has a NAF layer 104 on the bottom (e.g., substrate) side.

[0071] Fig. Figure 2 shows a different construction of the magnetic layer stack 200 of the magnetoresistive sensor, where the non-magnetic layer 118 (i.e., the matching layer) is deposited first (on a substrate), followed by the remaining stack. In this case, the stack is called a "top-pinned spin valve" (TSV) because the reference system 111 is on the top section of the stack. The NAF layer 104 is also on top of the stack (i.e., deposited on top of the reference system 111).

[0072] The order of the layers of the magnetic layer stack 200 is essentially reversed to the magnetic layer stack 100 shown in Fig. 1, with the exception of the seed layer 102 and the cap layer 120, which are arranged similarly in both arrangements. In addition, a seed layer 101 in Fig.2 a double layer arrangement to two seed layers or two partial seed layers 102 and 103, wherein the seed layer 102 is made of Ta or TaN, and the seed layer 103 is made of nickel-chromium (NiCr), which has an atomic radius of 166pm.

[0073] In the case of using a bilayer arrangement for the seed layer 102 for a TSV configuration, the matching layer 118 is arranged on the seed layer 103. The matching layer 118 may have an atomic radius between the atomic radius of the seed layer 103 and the atomic radius of the magnetic free layer 116 and / or may be within a predetermined range of the atomic radius of the magnetic free layer 116 (e.g., within 5 or 10%).

[0074] Furthermore, the following claims are hereby incorporated into the Detailed Description, where each claim may stand on its own as a separate example. While each claim may stand on its own as a separate example, it should be noted that although a dependent claim may refer to a particular combination with one or more other claims in the 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 suggested herein unless it is stated that a particular combination is not intended. Furthermore, features of a claim for any other independent claim are also intended to be included, even if that claim is not made directly dependent on the independent claim.

[0075] It should further be noted that methods disclosed in the description or in the claims may be implemented by an apparatus having means for performing each of the respective steps of those methods.

[0076] Furthermore, it should be understood that the disclosure of multiple steps or functions disclosed in the description or claims should not be construed as being in that particular order. Therefore, the disclosure of multiple steps or functions does not limit them to a particular order, unless those steps or functions are not interchangeable for technical reasons. Furthermore, in some examples, a single step may include multiple substeps or be divided into multiple substeps. Such substeps may be included and be part of the disclosure of that single step unless explicitly excluded.

Claims

[1] A magnetoresistive sensor (100; 200) comprising: a first non-magnetic layer (112); a second non-magnetic layer (118); and a magnetic free double layer (113) disposed between the first non-magnetic layer (112) and the second non-magnetic layer (118), the magnetic free double layer (113) comprising a first magnetic free layer (114) disposed adjacent to a second magnetic free layer (116), wherein the first magnetic free layer (114) is arranged adjacent to the first non-magnetic layer (112) and the second magnetic free layer (116) is arranged adjacent to the second non-magnetic layer (118), wherein the second non-magnetic layer (118) is made of a non-magnetic material having an atomic radius that does not deviate by more than 10% of an atomic radius of at least one of the first magnetic free layer (114) and the second magnetic free layer (116), and wherein the non-magnetic material is selected from one of magnesium, indium and tin. [2] The magnetoresistive sensor according to claim 1, wherein the first non-magnetic layer (112) is made of a non-magnetic material selected from one of magnesium, indium, bismuth, tin and zinc. [3] The magnetoresistive sensor (100; 200) according to any one of the preceding claims, wherein the first magnetic free layer (114) and the second magnetic free layer (116) are each made of a material selected from cobalt, nickel, iron and alloys thereof. [4] The magnetoresistive sensor (100; 200) according to any one of the preceding claims, wherein the first magnetic free layer (114) is made of cobalt-iron, CoFe, and the second magnetic free layer (116) is made of nickel-iron, NiFe. [5] The magnetoresistive sensor (100; 200) according to any one of the preceding claims, further comprising: a germ layer (102); a cover layer (120); and a magnetic layer stack arranged between the seed layer (102) and the cover layer (120), the magnetic layer stack comprising the first non-magnetic layer (112), the second non-magnetic layer (118) and the magnetic free double layer (113), wherein the second non-magnetic layer (118) is arranged between the magnetic free double layer (113) and one of the seed layer (102) and the cap layer (120). [6] The magnetoresistive sensor (100; 200) according to any one of the preceding claims, further comprising: a magnetic reference system (111) comprising a pinned layer (106) and a reference layer (110), wherein the magnetic reference system (111) is arranged adjacent to the first non-magnetic layer (112). [7] The magnetoresistive sensor (100; 200) according to claim 6, wherein the reference layer (110) is coupled to the first non-magnetic layer (112). [8] The magnetoresistive sensor (100; 200) according to any one of the preceding claims, wherein: the first non-magnetic layer (112) comprises a non-magnetic material having an atomic radius that does not deviate by more than 10% of an atomic radius of at least one of the first magnetic free layer (114) and the second magnetic free layer (116). [9] The magnetoresistive sensor (100; 200) according to any one of the preceding claims, wherein: the second non-magnetic layer (118) comprises a non-magnetic material having an atomic radius that does not deviate by more than 5% of an atomic radius of at least one of the first magnetic free layer (114) and the second magnetic free layer (116). [10] The magnetoresistive sensor (100; 200) according to any one of the preceding claims, wherein: the first non-magnetic layer (112) comprises a non-magnetic material having an atomic radius that does not deviate by more than 5% of an atomic radius of at least one of the first magnetic free layer (114) and the second magnetic free layer (116). [11] The magnetoresistive sensor (100; 200) according to any one of the preceding claims, wherein: the non-magnetic material of the second non-magnetic layer (118) has an atomic radius that does not deviate by more than 10% of the atomic radius of the first magnetic free layer (114) and the second magnetic free layer (116). [12] The magnetoresistive sensor (100; 200) according to claim 11, wherein the non-magnetic material of the first non-magnetic layer (112) has an atomic radius that does not differ by more than 10% of the atomic radius of the first magnetic free layer (114) and the second magnetic free layer (116). [13] The magnetoresistive sensor (100; 200) according to any one of the preceding claims, wherein the first non-magnetic layer (112) has a thickness different from a thickness of the second non-magnetic layer (118). [14] The magnetoresistive sensor (100; 200) according to any one of the preceding claims, wherein the first magnetic free layer (114) and the second magnetic free layer (116) are each configured to change a magnetization direction thereof based on a magnetic field applied thereto. [15] A magnetoresistive sensor (100; 200) comprising: a seed layer (102) comprising a first partial layer (103) of nickel-chromium (NiCr) and a second partial layer (102) of tantalum; a covering layer (120) comprising tantalum; and a magnetic layer stack disposed between the seed layer (102) and the cap layer (120), the magnetic layer stack comprising: a first non-magnetic layer (112), wherein a non-magnetic material of the first non-magnetic layer (112) is selected from one of copper, magnesium, indium, bismuth, tin and zinc; a second non-magnetic layer (118); and a magnetic free double layer (113) arranged between a first non-magnetic layer (112) and the second non-magnetic layer (118), wherein the magnetic free double layer (113) comprises a first magnetic free layer (114) made of cobalt-iron, CoFe, arranged adjacent to a second magnetic free layer (116) made of nickel-iron, NiFe, wherein the first magnetic free layer (114) is arranged adjacent to the first non-magnetic layer (112), and the second magnetic free layer (116) is arranged adjacent to the second non-magnetic layer (118), wherein the second non-magnetic layer (118) is arranged between the magnetic free double layer (113) and one of the seed layer (102) and the cover layer (120), and wherein the second non-magnetic layer (118) is made of a non-magnetic material having an atomic radius that is between an atomic radius of the second magnetic free layer (116) and an atomic radius of at least one of the seed layer (102) and the cap layer (120), wherein the non-magnetic material of the second non-magnetic layer (118) is selected from one of magnesium, indium, and tin.

Images