Magnetoresistance sensor free layer and wide-range magnetoresistance sensor

Abstract

The invention relates to a free layer of a magnetoresistance sensor. The free layer at least comprises a bias layer, a sensing layer and a coupling layer, and the bias layer and the sensing layer form ferromagnetic coupling or antiferromagnetic coupling under the action of the coupling layer. The invention further relates to a magnetoresistance sensor which comprises a ferromagnetic coupling free layer, a fixed layer and an antiferromagnetic coupling free layer, and the linear response area of the magnetoresistance sensor is effectively expanded through free layer regulation and control and double-free-layer design.

Description

Technical Field

[0001] The invention relates to the field of sensor design, and in particular to a novel magnetoresistive sensor free layer and a wide-range magnetoresistive sensor. Background Art

[0002] As an emerging sensor, magnetoresistive sensors (giant magnetoresistive sensors and tunneling magnetoresistive sensors) are widely used in consumer electronics, industrial electronics and other fields. The operation of magnetoresistive sensors is based on the magnetoresistive effect, that is, the resistance of the material changes under the action of an external magnetic field. This change can be measured and converted into an electrical signal, thereby reflecting the strength of the magnetic field. It has the advantages of high sensitivity, small size and low power consumption.

[0003] One application scenario of magnetoresistance sensor is to detect z-axis magnetic field, which becomes an alternative to Hall sensor. Among them, spin valve giant magnetoresistance and tunnel junction magnetoresistance have the advantages of large magnetoresistance effect, sensitive response to magnetic field, and wide working range, and are the main core structures used in magnetoresistance sensors. The spin valve giant magnetoresistance structure is generally ferromagnetic layer 1 / metal isolation layer / ferromagnetic layer 2 / ultra-thin metal layer / ferromagnetic layer 3 / antiferromagnetic layer, and the tunnel junction magnetoresistance structure is generally ferromagnetic layer 1 / oxide barrier layer / ferromagnetic layer 2 / ultra-thin metal layer / ferromagnetic layer 3 / antiferromagnetic layer. Among them, the ferromagnetic layer 2 / ultra-thin metal layer / ferromagnetic layer 3 / antiferromagnetic layer structure is an artificial antiferromagnetic pinning structure, which makes the magnetic moment of ferromagnetic layer 2 not rotate with the external magnetic field, also called the fixed layer, while the magnetic moment of ferromagnetic layer 1 can rotate under the action of the external field, called the free layer, which is the detection layer in the sensor operation. The free layer shows linear resistance characteristics as the external magnetic field changes within a certain magnetic field range. Outside this magnetic field range (i.e., the saturation region of the sensor), the magnetoresistive sensor does not indicate the external magnetic field. Therefore, the linear detection region of the linear magnetoresistive sensor is determined by the linear region where the free layer changes with the external magnetic field, and the size of this region is proportional to the size of the anisotropic field Hk of the free layer. The larger the anisotropic field Hk of the free layer, the wider the linear detection range of this type of linear magnetoresistive sensor.

[0004] In order to significantly improve the linear response range of magnetoresistive sensors, existing technologies not only focus on traditional methods such as changing the material, thickness, shape of the free layer and adjusting its characteristics through magnetic field annealing post-treatment, but also deeply explore the use of external bias magnetic fields and other means to finely control the anisotropy field Hk of the free layer after the preparation of the linear magnetoresistive multilayer film. However, even so, the achievable linear region is still limited to within 1,000 Oe, and the detection magnetic field range is relatively limited. Summary of the invention

[0005] The purpose of the present invention is to expand the detection range of a magnetoresistive sensor, provide a magnetoresistive sensor free layer with a novel structure, and based on the free layer, realize the large-range detection of the magnetoresistive sensor.

[0006] The free layer described in the present invention at least includes: a bias layer, a sensing layer and a coupling layer. The bias layer and the sensing layer form ferromagnetic coupling or antiferromagnetic coupling under the action of the coupling layer. Specifically, the magnetic moment of the bias layer is oriented out of the plane (perpendicular to the film surface), and the magnetic moment of the sensing layer is oriented in the plane (parallel to the film surface) and will rotate with the magnetic field; the magnetic moments of the bias layer and the sensing layer are coupled through the RKKY effect, and the magnetic moment of the bias layer is exchange-associated with the itinerant electrons in the coupling layer, so that the spin polarization of the itinerant electrons produces a spin density difference that varies with the distance, and through the action of spin-polarized electrons of different densities on the sensing layer, the magnetic moment of the sensing layer and the magnetic moment of the bias layer form antiferromagnetic coupling or ferromagnetic coupling.

[0007] Ferromagnetic and antiferromagnetic are related to the thickness of the coupling layer and are achieved by controlling the thickness of the coupling layer; specifically, when the thickness is between 0.3-0.4nm, 0.6-1.0nm or 1.6-2.2nm, antiferromagnetic coupling is formed; when the thickness is between 0.1-0.3nm or 1.1-1.5nm, ferromagnetic coupling is formed.

[0008] Therefore, the antiferromagnetically coupled free layer will increase the detectable magnetic field of the magnetoresistive sensor (antiferromagnetically coupled free layer + fixed layer), and the detection range (linear response region) in the coordinate system is shifted to the right [(H 0a ~H 0b )→(H 1a ~H 1b )]. The ferromagnetically coupled free layer will reduce the detectable magnetic field of the magnetoresistive sensor (ferromagnetically coupled free layer + fixed layer), and the detection range (linear response region) in the coordinate system is shifted to the left [(H 2a ~H 2b )←(H 0a ~H 0b )]. Therefore, through the structural design of the free layer of the present invention, the linear response area of ​​the magnetoresistive sensor can be flexibly adjusted.

[0009] In the present invention, the coupling layer that helps to build ferromagnetic coupling can be made of materials such as Ru, Mo, Ir, and Ta; the coupling layer that helps to build antiferromagnetic coupling can be made of materials such as Ru, Mo, and Ir.

[0010] In the present invention, the bias layer includes but is not limited to one or more structures of Co / Pt multilayer film, Co / Pd multilayer film, Co / Ni multilayer film and alloys thereof.

[0011] In the present invention, the sensing layer is a multi-element alloy composed of two or more elements among Co, Fe, Ni, Cr, V, Mn, C, B, etc., and has a thickness between 2-5 nm.

[0012] Based on the above free layer, the present invention also provides a magnetoresistive sensor to broaden the detection range of the existing magnetoresistive sensor, which comprises: a first free layer, a first spacing layer, a fixed layer, a second spacing layer, and a second free layer in sequence;

[0013] The bias layer and the sensing layer of the free layer of the first free layer and the second free layer are antiferromagnetic coupling or ferromagnetic coupling under the action of the coupling layer.

[0014] The fixed layer comprises:

[0015] A pinned layer, and a second antiferromagnetic coupling layer and a second reference layer located on one side of the pinned layer, and a first antiferromagnetic coupling layer and a first reference layer located on the other side of the pinned layer;

[0016] The pinned layer, the first antiferromagnetic coupling layer and the first reference layer constitute a first pinned layer, and the pinned layer, the second antiferromagnetic coupling layer and the second reference layer constitute a second pinned layer;

[0017] The magnetic moment direction of the pinned layer is consistent with the magnetic moment direction of the bias layer in the first free layer and the second free layer; the magnetic moment directions of the first reference layer and the second reference layer are opposite to the magnetic moment direction of the pinned layer.

[0018] Taking the first free layer as an antiferromagnetic coupling free layer as an example, the first free layer, the first spacer layer, and the first fixed layer form a first stack having (H 1a ~H 1b ) of the first linear response region or, the second free layer, the second spacer layer, and the second fixed layer form a second stack having (H 0a ~H 0b )’s second linear response region.

[0019] The design of the common pinned layer provides a stable reference point for the two free layers, ensuring that the coupling effect between the first stack and the second stack is 1a ~H 0b The range is continuous, the magnetoresistive sensor is 0a ~H 1b In the range, the resistance R and the magnetic field strength H have the following linear relationship:

[0020]

[0021] Wherein, k1 is the sensitivity of the first linear response region, which is determined by the first free layer and the first fixed layer; k2 is the sensitivity of the second linear response region, which is determined by the second free layer and the second fixed layer.

[0022] Based on the above free layer, the present invention also provides another magnetoresistive sensor to further broaden the detection range of the existing magnetoresistive sensor, which comprises: a first free layer, a first spacer layer, a fixed layer, a second spacer layer, and a second free layer in sequence;

[0023] In the first free layer, the bias layer and the sensing layer form ferromagnetic coupling under the action of the coupling layer;

[0024] In the second free layer, the bias layer and the sensing layer form antiferromagnetic coupling under the action of the coupling layer;

[0025] The fixed layer comprises:

[0026] Pinning layer,

[0027] and, a second antiferromagnetic coupling layer and a second reference layer located on one side of the pinned layer, and a first antiferromagnetic coupling layer and a first reference layer located on the other side of the pinned layer;

[0028] The pinned layer, the first antiferromagnetic coupling layer and the first reference layer constitute a first pinned layer, and the pinned layer, the second antiferromagnetic coupling layer and the second reference layer constitute a second pinned layer.

[0029] The magnetic moment direction of the pinned layer is consistent with the magnetic moment direction of the bias layer in the first free layer and the second free layer; the magnetic moment directions of the first reference layer and the second reference layer are opposite to the magnetic moment direction of the pinned layer.

[0030] Thus, the first free layer, the first spacer layer, and the first fixed layer form a first stack having (H 1a ~H 1b ), the second free layer, the second spacer layer, and the second fixed layer form a second stack having (H 2a ~H 2b )'s second linear response region; H 2a <H 1a <H 2b <H 1b .

[0031] The design of the common pinned layer provides a stable reference point for the two free layers, ensuring that the coupling effect between the first stack and the second stack is 1a ~H 2b The range is continuous, the magnetoresistive sensor is 2a ~H 1b In the range, the resistance R and the magnetic field strength H have the following linear relationship:

[0032]

[0033] Wherein, k1 is the sensitivity of the first linear response region, which is determined by the first free layer and the first fixed layer; k2 is the sensitivity of the second linear response region, which is determined by the second free layer and the second fixed layer.

[0034] In the present invention, the spacer layer is made of materials such as MgO, Al2O3, HfO2, MgAlO, CuO, Cu, etc., and has a thickness between 0.5-3nm.

[0035] In the present invention, the reference layer is a multilayer film structure formed by one or more of CoFeB, FeB, CoFe and one or more of Co / Pt multilayer film, Co / Pd multilayer film, and Co / Ni multilayer film.

[0036] In the present invention, the antiferromagnetic coupling layer includes materials such as Ru, Mo, and Ir, and has a thickness of about 0.4 nm or 0.8 nm.

[0037] In the present invention, the pinning layer is a multilayer film structure formed by one or more of Co / Pt multilayer film, Co / Pd multilayer film, Co / Ni multilayer film or alloys thereof.

[0038] In the present invention, for example, a Co / Ni multilayer film refers to a composite film composed of several layers of Co films and several layers of Ni films.

[0039] The beneficial effect of the present invention is that the present invention effectively expands the linear response area of ​​the magnetoresistive sensor through free layer regulation and double free layer design. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 is a schematic structural diagram of the free layer of the present invention;

[0041] Figure 2 It is a schematic diagram of the response interval after the free layer is regulated in the present invention;

[0042] Figure 3 A schematic diagram of a sensor with double free layers according to the present invention;

[0043] Figure 4 Schematic diagram of the composite magnetic response of the double free layer sensor of the present invention;

[0044] Figure 5 A schematic diagram of the free layer structure and its response range of the present invention;

[0045] Figure 6 This is a schematic diagram of a double free layer sensor of Example 2;

[0046] Figure 7 This is a schematic diagram of a double free layer sensor of Example 3;

[0047] Figure 8Schematic diagram of the composite magnetic response of the double free layer sensor of Example 3. DETAILED DESCRIPTION

[0048] In order to further explain the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the specific implementation mode, structure, characteristics and effects of the present invention are described in detail below in combination with the accompanying drawings and preferred embodiments.

[0049] In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise explicitly defined.

[0050] In addition, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0051] The embodiment of the present invention cleverly utilizes the coupling mechanism to modulate the sensing layer, so that its sensing range is offset; the present invention further combines two modulated sensing layers to construct a magnetoresistive sensor. By controlling the magnetic moment direction of the pinned layer, the upper and lower sensing layers are coupled, effectively widening the detection range.

[0052] Figure 1 The free layer structure of the present invention comprises a bias layer, a sensing layer and a coupling layer. The magnetic moment of the bias layer is oriented out of the plane (perpendicular to the film surface), and the magnetic moment of the sensing layer is oriented in the plane (parallel to the film surface) and rotates with the magnetic field.

[0053] The bias layer and the sensing layer magnetic moments are coupled through the RKKY effect, and the bias layer and the sensing layer form ferromagnetic coupling or anti-ferromagnetic coupling through the coupling layer, thereby forming a linear response region of the sensing layer.

[0054] The coupling principle is that the magnetic moment of the bias layer is exchanged with the itinerant electrons in the coupling layer, so that the spin polarization of the itinerant electrons produces a spin density difference that varies with distance. Through the action of spin-polarized electrons of different densities on the sensing layer, the magnetic moment of the sensing layer and the magnetic moment of the bias layer form antiferromagnetic coupling or ferromagnetic coupling.

[0055] As is common knowledge in the field, ferromagnetic coupling refers to the phenomenon that the spin magnetic moments of adjacent atoms or magnetic particles in magnetic materials tend to be arranged in parallel in the same direction. In ferromagnetic materials, this same-direction arrangement leads to permanent magnetization on a macroscopic scale, and the material still retains its magnetism even after the external magnetic field is removed. Antiferromagnetic coupling refers to the phenomenon that in certain magnetic materials, the spin magnetic moments of adjacent atoms or magnetic particles tend to be arranged in parallel in the opposite direction. In antiferromagnetic materials, although each local area may have strong magnetism, due to the reverse arrangement of adjacent magnetic moments, there may be no net magnetization as a whole, and the material exhibits non-magnetic properties.

[0056] Ferromagnetic coupling and antiferromagnetic coupling are closely related to the thickness of the coupling layer, because the thickness of the coupling layer directly affects the exchange coupling mechanism between the two magnetic layers. This exchange coupling is caused by the overlap of electron wave functions in quantum mechanics, which allows the magnetic moment to "communicate" indirectly between the two magnetic layers through the coupling layer. The material and thickness of the coupling layer determine the tunneling probability of the electrons and the positive and negative signs of the exchange integral, thereby determining the nature of the coupling.

[0057] Specifically, in ferromagnetic and antiferromagnetic coupling, the key lies in the probability and phase relationship of electron tunneling in the coupling layer: Ferromagnetic coupling: When the coupling layer is thin enough (for example, 0.1-0.3nm or 1.1-1.5nm), the probability of electron tunneling is high, and the spins of the two magnetic layers tend to be arranged in parallel in the same direction, because this will reduce the energy of the system and form ferromagnetic coupling. Antiferromagnetic coupling: When the coupling layer is slightly thicker (for example, 0.3-0.4nm, 0.6-1.0nm or 1.6-2.2nm), the probability of electron tunneling is low, but due to the quantum interference effect, the electrons will undergo a phase change when passing through the coupling layer, causing the spins of adjacent magnetic layers to tend to be arranged in antiparallel, so as to reduce the total energy of the system and form antiferromagnetic coupling.

[0058] This phenomenon can be explained by the RKKY (Ruderman-Kittel-Kasuya-Yosida) interaction. In the RKKY theory, when conduction electrons are transferred between two magnetic layers, they interact with the magnetic moment, resulting in electron scattering. When electrons tunnel through the coupling layer, the phase of their wave functions changes, and this phase change depends on the thickness of the coupling layer. At a certain thickness, this phase change makes the energy exchange during the electron scattering favor ferromagnetic coupling or antiferromagnetic coupling, depending on whether the thickness of the coupling layer is close to an odd or even multiple of the electron wavelength.

[0059] Thus, when the free layer is in the antiferromagnetic coupling state, the responsive magnetic field strength of the sensing layer increases, and the linear response region moves to the right, from (H 0a ~H 0b ) becomes (H 1a ~H 1b), which means that the sensing layer can detect a stronger magnetic field signal. When the free layer is in the ferromagnetic coupling state, the detectable magnetic field intensity of the sensing layer decreases, and the linear response region moves to the left, from (H 0a ~H 0b ) becomes (H 2a ~H 2b ), which means that the sensing layer also responds to weaker magnetic fields, such as Figure 2 shown.

[0060] Figure 3 The magnetoresistive sensor structure of an embodiment of the present invention includes a first free layer, a first spacing layer, a fixed layer, a second spacing layer and a second free layer, wherein the first free layer and the second free layer form different coupling states through coupling layers.

[0061] The first free layer forms a ferromagnetic coupling, and the second free layer forms an antiferromagnetic coupling. The two are isolated from the fixed layer by the first spacing layer and the second spacing layer, but can influence each other under the action of the magnetic field.

[0062] The fixed layer consists of a pinned layer, a first antiferromagnetic coupling layer, a first reference layer, a second antiferromagnetic coupling layer and a second reference layer. The magnetic moment direction of the pinned layer controls the coupling state of the entire sensor, while the magnetic moment direction of the reference layer is opposite to that of the pinned layer, which is used to stabilize the output characteristics of the sensor.

[0063] The first stack (first free layer, first spacer layer, first fixed layer) has (H 1a ~H 1b ) has a linear response region, and the second stack (second free layer, second spacer layer, second fixed layer) has (H 2a ~H 2b ) in the linear response region, and H 2a <H 1a <H 2b <H 1b .

[0064] The magnetic moment of the free layer can change with the direction of the external magnetic field, while the magnetic moment of the fixed layer is fixed in a specific direction by the pinned layer. The resistivity of the sensor will change with the relative angle between the magnetic moments of the free layer and the fixed layer. The sensor in the embodiment has two stacked structures, each stack has its own free layer, but shares a pinned layer. The magnetic moment direction of the pinned layer is fixed, and it serves as a common reference point for the two free layers. This means that whether it is the free layer in the first stack or the free layer in the second stack, their magnetic moments will change relative to the direction of the pinned layer. Figure 4 As shown, the first stack has (H 1a ~H 1b ) linear response region, while the second stack has (H 2a ~H2b ) linear response region, these two regions are in H 1a ~H 2b Due to the presence of the pinned layer, the magnetic moment rotations of the two free layers are superimposed in the overlapping region (k1+k2), which means that the sensor is 1a ~H 2b It maintains a good phased linear response within the entire range.

[0065] The resistance R and magnetic field strength H have the following linear relationship:

[0066]

[0067] Among them, k1 is the sensitivity (slope) of the first linear response area of ​​the first stack, which is determined by the first free layer and the first fixed layer; k2 is the sensitivity (slope) of the second linear response area of ​​the second stack, which is determined by the second free layer and the second fixed layer.

[0068] In the present invention, the spacer layer is made of materials such as MgO, Al2O3, HfO2, MgAlO, CuO, Cu, etc., and has a thickness between 0.5-3nm.

[0069] In the present invention, the reference layer is a multilayer film structure formed by one or more of CoFeB, FeB, CoFe and one or more of Co / Pt multilayer film, Co / Pd multilayer film, and Co / Ni multilayer film.

[0070] In the present invention, the antiferromagnetic coupling layer includes materials such as Ru, Mo, and Ir, and has a thickness of about 0.4 nm or 0.8 nm.

[0071] In the present invention, the pinning layer is a multilayer film structure formed by one or more of Co / Pt multilayer film, Co / Pd multilayer film, Co / Ni multilayer film or alloys thereof.

[0072] In the present invention, the multilayer structure can be realized by using magnetron sputtering, CVD deposition and other technologies, and the control of the deposition thickness is common knowledge in the art.

[0073] The embodiments of the present invention are further described below with reference to a plurality of embodiments.

[0074] Example 1: Sensing layer regulation

[0075] The sensing layer uses Co 20 Fe 60 B 20 , thickness is 2nm; Co 20 Fe 60 B 20 represents an alloy composed of Co, Fe, and B, and the subscripts represent the atomic ratio of the elements. The magnetic moment-magnetic field of the sensing layer is measured as Figure 5 As shown, the magnetic field region of its linear response ranges from -1800 to 1800 Oe;

[0076] The coupling layer (Ru, thickness 0.2 nm) and the bias layer (Co) were sequentially deposited on the sensing layer by magnetron sputtering. 45 Pt 55 , thickness is 8nm), forming a ferromagnetically coupled free layer, and the magnetic field region of its response is measured to be left-shifted, between -2800 and 800Oe;

[0077] The coupling layer (Ru, thickness of 0.85 nm) and the bias layer (Co) were sequentially deposited on the sensing layer by magnetron sputtering. 45 Pt 55 , thickness is 8nm), forming an antiferromagnetically coupled free layer, and its response magnetic field region is measured to be right-shifted, between -1300 and 2300Oe.

[0078] Example 2: Using the double free layer constructed in Example 1 to construct a magnetoresistive sensor

[0079] The ferromagnetic coupling free layer and the antiferromagnetic coupling free layer constructed in Example 1 are constructed as follows Figure 6 The sensor shown in FIG. 1 is shown in FIG. 1 . The first free layer at the bottom is the antiferromagnetic coupled free layer of Example 1, and its response magnetic field region is right-shifted and is between -1300 and 2300 Oe. The second free layer at the top is the existing free layer, i.e., Co with a thickness of 2 nm. 20 Fe 60 B 20 The magnetic field region of its linear response ranges from -1800 to 1800 Oe.

[0080] In the figure, Pt 0.6nm / Co 0.3nm means a composite layer consisting of a 0.6nmPt layer and a 0.3nmCo layer; [Pt0.6nm / Co 0.3nm]×3 means there are three layers of the above composite layer. 20 Fe 60 B 20 0.9nm represents a 0.9nm Co, Fe, B alloy layer, and the subscripts represent the atomic ratios of the elements in the alloy. 20 Fe 60 B 20 0.9nm and [Pt 0.6nm / Co 0.3nm]×3.

[0081] The magnetic field region where the response is measured is Figure 8As shown by the red line, between -1800 and 2300 Oe, there is a three-stage linear relationship, the first stage is between -1800 and -1300 Oe, and the third stage is between 1800 and 2300 Oe, maintaining the original linear relationship; and within the range of -1300 to 1800 Oe, since the same sensing layer is used in this embodiment, the sensitivity of the second stage is twice that of the first and second stages.

[0082] Example 3: Constructing a magnetoresistive sensor using the double free layer constructed in Example 1

[0083] The ferromagnetic coupling free layer and the antiferromagnetic coupling free layer constructed in Example 1 are constructed as follows Figure 7 The sensor shown in the figure. The first free layer at the bottom is the antiferromagnetic coupling free layer of Example 1, and its response magnetic field region is right-shifted, between -1300 and 2300 Oe; the second free layer at the top is the ferromagnetic coupling free layer of Example 1, and its response magnetic field region is left-shifted, between -2800 and 800 Oe.

[0084] The magnetic field region where the response is measured is Figure 8 As shown by the black line, between -2800 and 2300Oe, a three-stage linear relationship is presented, which further expands the response area of ​​-2800 to -1800Oe compared with Example 2. Among them, the interval of the first section is -2800 to -1300Oe, and the interval of the third section is 800 to 2800Oe, maintaining the original linear relationship; and in the range of -1300 to 800Oe, since the same sensing layer is used in this embodiment, the sensitivity of the second section is twice that of the first and second sections.

[0085] The present invention adjusts the coupling state of the free layer, and can flexibly adjust its linear response area without changing the physical size of the sensor, thereby meeting the needs of different application scenarios. By utilizing the complementary characteristics of ferromagnetic coupling and antiferromagnetic coupling, combined with a sophisticated layered structure design, the present invention significantly improves the detection accuracy and application range of magnetoresistive sensors, opening up a new path for the development of magnetic field sensing technology.

[0086] The above embodiments describe in detail the structure, features and effects of the present invention. The above are only preferred embodiments of the present invention. Any changes made in accordance with the concept of the present invention, or modifications to equivalent embodiments with equivalent changes, which do not exceed the scope covered by the specification, should be within the protection scope of the present invention.

Claims

1. A magnetoresistive sensor free layer, characterized in that: At least: bias layer, sensing layer and coupling layer; The magnetic moment of the bias layer is oriented out of the plane (perpendicular to the film surface), and the magnetic moment of the sensing layer is oriented in the plane (parallel to the film surface) and will rotate with the magnetic field; The bias layer and the sensing layer form ferromagnetic coupling or anti-ferromagnetic coupling under the action of the coupling layer.

2. The free layer according to claim 1, characterized in that: The ferromagnetism and antiferromagnetism are related to the thickness of the coupling layer and are achieved by controlling the thickness of the coupling layer.

3. The free layer according to claim 1, characterized in that: Specifically, when the thickness is within the range of 0.3-0.4 nm, 0.6-1.0 nm or 1.6-2.2 nm, antiferromagnetic coupling is formed; when the thickness is within the range of 0.1-0.3 nm or 1.1-1.5 nm, ferromagnetic coupling is formed.

4. The free layer according to claim 1, characterized in that: The coupling layer used to form ferromagnetic coupling can be made of materials such as Ru, Mo, Ir, and Ta; the coupling layer used to form antiferromagnetic coupling can be made of materials such as Ru, Mo, and Ir.

5. The free layer according to claim 1, characterized in that: The bias layer is a multilayer film structure formed by one or more of a composite film of Co film and Pt film, a composite film of Co film and Pd film, a composite film of Co film and Ni film, a Co / Pt alloy film, a Co / Pd alloy film or a Co / Ni alloy film.

6. The free layer according to claim 1, characterized in that: The sensing layer is a multi-element alloy film composed of two or more elements among Co, Fe, Ni, Cr, V, Mn, C, B, etc., and has a thickness between 2-5nm.

7. A magnetoresistive sensor, characterized in that: Including in order: A first free layer, a first spacer layer, a fixed layer, a second spacer layer, and a second free layer; One of the first free layer and the second free layer is the free layer according to claim 1; The fixed layer comprises: A pinned layer, and a second antiferromagnetic coupling layer and a second reference layer located on one side of the pinned layer, and a first antiferromagnetic coupling layer and a first reference layer located on the other side of the pinned layer; The pinned layer, the first antiferromagnetic coupling layer and the first reference layer constitute a first pinned layer, and the pinned layer, the second antiferromagnetic coupling layer and the second reference layer constitute a second pinned layer; The magnetic moment direction of the pinned layer is consistent with the magnetic moment direction of the bias layer in the first free layer and the second free layer; the magnetic moment directions of the first reference layer and the second reference layer are opposite to the magnetic moment direction of the pinned layer.

8. A magnetoresistive sensor, characterized in that: Including in order: A first free layer, a first spacer layer, a fixed layer, a second spacer layer, and a second free layer; In the first free layer, the bias layer and the sensing layer form ferromagnetic coupling under the action of the coupling layer; In the second free layer, the bias layer and the sensing layer form antiferromagnetic coupling under the action of the coupling layer; The fixed layer comprises: Pinning layer, and, a second antiferromagnetic coupling layer and a second reference layer located on one side of the pinned layer, and a first antiferromagnetic coupling layer and a first reference layer located on the other side of the pinned layer; The pinned layer, the first antiferromagnetic coupling layer and the first reference layer constitute a first pinned layer, and the pinned layer, the second antiferromagnetic coupling layer and the second reference layer constitute a second pinned layer. The magnetic moment direction of the pinned layer is consistent with the magnetic moment direction of the bias layer in the first free layer and the second free layer; the magnetic moment directions of the first reference layer and the second reference layer are opposite to the magnetic moment direction of the pinned layer.

9. The magnetoresistive sensor according to claim 7 or 8, characterized in that: The first spacer layer and the second spacer layer are made of materials such as MgO, Al2O3, HfO2, MgAlO, CuO, Cu, etc., and have a thickness between 0.5-3nm.

10. The magnetoresistive sensor according to claim 7 or 8, characterized in that: The first reference layer and the second reference layer are composite film structures, which are composited by one or more of CoFeB, FeB, CoFe and one or more of Co / Pt multilayer film, Co / Pd multilayer film, and Co / Ni multilayer film.

11. The magnetoresistive sensor according to claim 7 or 8, characterized in that: The antiferromagnetic coupling layer includes materials such as Ru, Mo, and Ir, and has a thickness of approximately 0.4 nm or 0.8 nm.

12. The magnetoresistive sensor according to claim 7 or 8, characterized in that: The pinning layer is a multilayer film structure formed by one or more of Co / Pt multilayer film, Co / Pd multilayer film, Co / Ni multilayer film or alloys thereof.

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