Low Field Magnetoresistive Angle Sensor

Abstract

In an embodiment of the present invention, a low-field magnetoresistive angle sensor is disclosed. The sensor comprises a substrate located in an XY plane and a magnetoresistive sensing unit located on the substrate. The magnetoresistive sensing unit comprises a multi-layer thin-film structure. The multi-layer thin-film structure comprises a stack of at least a free layer, a barrier layer, and a reference layer. The magnetoresistive sensing unit has an elliptical shape. The elliptical free layer has a major axis Ly, a minor axis Lx, and a thickness Lz. Furthermore, the free layer has a saturation field, a shape anisotropy demagnetizing field, and a magnetocrystalline anisotropy field in the X direction. When the external magnetic field rotates by 0 to 360° in the XY plane, the magnetocrystalline anisotropy field is compensated by the shape demagnetizing field to make the effective anisotropy field of the free layer approach 0, such that the external magnetic field has a low working field value close to the value of the saturation field of the free layer material. The embodiment of the present invention can improve the accuracy of the angle measurement of the magnetoresistive angle sensor. Furthermore, since the required external magnetic field is low, the sensor can be implemented at low cost.

Description

Technical Field

[0001] Embodiments of the present invention relate to the technical field of magnetic sensors, and more particularly to low-field magnetoresistive angle sensors.

Background Art

[0002] Spin-valve magnetoresistive angle sensing units such as TMR or GMR are typically circular. In normal use, the value of the external magnetic field H is much larger than the saturation magnetic field Hs of the free layer (FL), and as a result, the magnetic moment M of the free layer (FL) and the external magnetic field H will be in the same direction.

[0003] However, by applying the external magnetic field H, although it is guaranteed that the magnetic moment Ms of the free layer (FL) and H are in the same direction, the deflection angle of other film layers in the magnetoresistive angle sensing unit can increase with the increase in the amplitude of H, and thus, an extra measurement angle error can be caused. Furthermore, a high external magnetic field H requires a stronger magnet and is more expensive, resulting in an increase in the usage cost.

Summary of the Invention

Problems to be Solved by the Invention

[0004] Embodiments of the present invention aim to provide a low-field magnetoresistive angle sensor to solve the problems of low measurement accuracy and high cost of conventional angle sensors.

Means for Solving the Problems

[0005] One embodiment of the present invention is a low-field magnetoresistive angle sensor, a substrate located in the X-Y plane, A magnetoresistive sensing unit located on a substrate, the magnetoresistive sensing unit including a multilayer thin film structure, the multilayer thin film structure including at least a stack of a free layer, a barrier layer, and a reference layer, the magnetoresistive sensing unit having an elliptical shape, the elliptical free layer having a major axis Ly, a minor axis Lx, and a thickness Lz, the free layer having a saturation magnetic field, a shape anisotropy demagnetizing field, and a crystalline magnetic anisotropy field in the X direction, and when an external magnetic field rotates by 0 to 360° in the X-Y plane, the crystalline magnetic anisotropy field compensates the shape anisotropy demagnetizing field so that the effective anisotropy field of the free layer approaches 0 and the crystalline magnetic anisotropy field has a low operating magnetic field value close to the value of the saturation magnetic field of the free layer material, providing a low magnetic field magnetoresistive angle sensor.

[0006] Furthermore, the magnetoresistive sensing unit includes a push magnetoresistive sensing unit and a pull magnetoresistive sensing unit, the free layer of the push magnetoresistive sensing unit and the free layer of the pull magnetoresistive sensing unit having positive and negative X-directional Néel coupling magnetic fields, and the Néel coupling magnetic fields of the push magnetoresistive sensing unit and the pull magnetoresistive sensing unit being compensated by the crystalline magnetic anisotropy field and the shape anisotropy demagnetizing field of the corresponding free layer, respectively.

[0007] Furthermore, a plurality of push magnetoresistive sensing units are electrically connected to form a push magnetoresistive sensing unit string, a plurality of pull magnetoresistive sensing units are electrically connected to form a pull magnetoresistive sensing unit string, and the push magnetoresistive sensing unit string and the pull magnetoresistive sensing unit string are connected to form a push-pull magnetoresistive angle sensor of a full bridge structure or a half bridge structure.

[0008] Furthermore, the shape anisotropy demagnetizing field of the free layer is determined by a shape anisotropy factor (Nx, Ny), and the crystalline magnetic anisotropy field of the free layer is determined by a crystalline magnetic anisotropy constant K1. Nx = Ny + K1 / M s 2 where M srepresents the saturation magnetic moment of the free layer, Nx represents the shape anisotropy factor in the X direction, and Ny represents the shape anisotropy factor in the Y direction.

[0009] Furthermore, the shape anisotropy demagnetizing field of the free layer is determined by the shape anisotropy factors (Nx, Ny), and the magnetocrystalline anisotropy field of the free layer is determined by the magnetocrystalline anisotropy constant K1. In the case of the push magnetoresistive sensing unit, Nx = Ny + K1 / M s 2 +2*H N / M s and in the case of the pull magnetoresistive sensing unit, Nx = Ny + K1 / M s 2 -2*HN / M s where M s represents the saturation magnetic moment of the free layer, Nx represents the shape anisotropy factor in the X direction, Ny represents the shape anisotropy factor in the Y direction, and H N represents the Neel coupling field of the free layer.

[0010] Furthermore, the multilayer thin film structure includes a seed layer, a free layer, a barrier layer, a reference layer, a metal layer, a pinning layer, an antiferromagnetic layer, and an insulating layer along the direction in which the substrate points to the magnetoresistive sensing unit.

[0011] Furthermore, the multilayer thin film structure includes a seed layer, an antiferromagnetic layer, a pinning layer, a metal layer, a reference layer, a barrier layer, a free layer, and an insulating layer along the direction in which the substrate points to the magnetoresistive sensing unit, and the reference layer is planarized by off-axis ion beam milling.

[0012] Furthermore, the reference layer is a bilayer composite structure or a SAF multilayer composite structure.

[0013] Furthermore, the barrier layer is a conductive layer prepared from ruthenium or copper, or the barrier layer is an insulating layer prepared from aluminum oxide or magnesium oxide, and the free layer is a multilayer thin film composed of two or more alloys of ferronickel, cobalt iron boron, and cobalt iron.

[0014] Furthermore, the crystalline magnetic anisotropy field is less than 20 Oe, the ratio Lx / Ly of the minor axis to the major axis is within the range of 0.5 < Lx / Ly < 0.95, the thickness Lz is within the range of 5 nm < Lz < 200 nm, and the minor axis Lx is within the range of 0.5 μm < Lx < 50 μm, the difference between the orientation angle of the shape anisotropy demagnetizing field and the orientation angle of the crystalline magnetic anisotropy field is 90°.

Advantages of the Invention

[0015] According to an embodiment of the present invention, when the external magnetic field rotates by 0 to 360° in the X-Y plane, the crystalline magnetic anisotropy field is compensated by the shape anisotropy demagnetizing field in the free layer, whereby the free layer has an effective anisotropy field close to 0, and the corresponding external magnetic field has a low magnetic field value close to the saturation magnetic field value of the free layer material. Therefore, the angular measurement error of the magnetoresistive angle sensor can be reduced, and the angular measurement accuracy can be improved. In addition, the external magnetic field is low, and thus it is not necessary to constitute a strong magnet, and the magnetoresistive angle sensor can be implemented at low cost.

[0016] To provide a clearer description of the embodiments of the present invention or the technical solutions in the prior art, a brief introduction to the accompanying drawings required in the description of the embodiments or the prior art is given. The accompanying drawings in the following description are some specific embodiments of the present invention, but for those skilled in the art, the basic concepts of the device structure, driving method, and manufacturing method disclosed and suggested by various embodiments of the present invention can be extended and expanded to other structures and drawings, and it is obvious that they are undoubtedly within the scope of the claims of the present invention.

Brief Description of the Drawings

[0017]

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Embodiments for Carrying Out the Invention

[0018] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical approach of the present invention will be clearly and completely described by embodiments with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. All other embodiments obtained by those skilled in the art based on the basic concepts disclosed and promoted by the embodiments of the present invention belong to the protection scope of the present invention.

[0019] FIG. 1 is a schematic diagram of a low magnetic field magnetoresistive angle sensor according to an embodiment of the present invention, FIG. 2 is a magnetization diagram of the X-Y plane of the low magnetic field magnetoresistive angle sensor according to an embodiment of the present invention, and FIG. 3 is a magnetization diagram of the X-Z plane of the low magnetic field magnetoresistive angle sensor according to an embodiment of the present invention. The low magnetic field magnetoresistive angle sensor according to an embodiment of the present invention includes a substrate 100 located in the X-Y plane and a magnetoresistive sensing unit 200 located on the substrate 100. The magnetoresistive sensing unit 200 includes a multilayer thin film structure, and the multilayer thin film structure includes at least a stack of a free layer (FL) 201, a barrier layer (BL) 202, and a reference layer (RL) 203. The magnetoresistive sensing unit 200 has an elliptical shape. The elliptical free layer 201 has a major axis Ly, a minor axis Lx, and a thickness Lz. The free layer 201 has a saturation magnetic field Hs, a shape anisotropy demagnetizing field H d , and a crystalline magnetic anisotropy field H k in the X direction. When the external magnetic field H rotates by 0 to 360° in the X-Y plane, the crystalline magnetic anisotropy field H k has a low operating magnetic field value close to the value of the saturation magnetic field H s of the free layer 201 material, and is compensated by the shape anisotropy demagnetizing field H d so that the effective anisotropy field of the free layer 201 approaches 0.

[0020] In this embodiment, optionally, the substrate 100 is a wafer, and the substrate 100 includes one or more magnetoresistive sensing units 200. Each magnetoresistive sensing unit 200 includes a multilayer thin film structure, and the multilayer thin film structure includes at least a stack of a free layer 201, a barrier layer 202, and a reference layer 203. The free layer 201, the barrier layer 202, and the reference layer 203 may be stacked in the order shown in FIG. 2, and it should be understood that they may also be stacked in other orders not limited thereto. The magnetoresistive sensing unit 200 is elliptical, the major axis of the ellipse is parallel to the Y direction, the minor axis of the ellipse is parallel to the X direction, the thickness of the ellipse is parallel to the Z direction, the major axis of the ellipse of the free layer 201 is Ly and is parallel to the Y direction, the minor axis of the ellipse is Lx and is parallel to the X direction, the thickness of the ellipse is Lz and is parallel to the Z direction. In other embodiments, the magnetoresistive sensing unit may be selected to have other shapes not limited thereto.

[0021] The free layer 201 has a saturation magnetic field H in the X direction s , a shape anisotropy demagnetizing field H d , and a crystalline magnetic anisotropy field H k . When the external magnetic field H rotates by 0 to 360° in the X-Y plane, the crystalline magnetic anisotropy field H k and the shape anisotropy demagnetizing field H d are in opposite directions and can compensate for each other, that is, the shape anisotropy demagnetizing field H d can compensate for the crystalline magnetic anisotropy field H k . When the magnetic field value of the shape anisotropy demagnetizing field H d is close to the value of the crystalline magnetic anisotropy field H k , the free layer 201 has an effective anisotropy field close to 0. The free layer 201 further has a saturation magnetic field H s . When the free layer 201 has an effective anisotropy field close to 0, the external magnetic field H is close to the saturation magnetic field H s when the external magnetic field H rotates by 0 to 360° in the X-Y plane. It is known that the magnetic field value of the saturation magnetic field Hs of the free layer 201 is low, and thus the external magnetic field H has a low magnetic field value close to the saturation magnetic field Hs of the free layer 201.

[0022] H d and H k The mutual compensation of and H is realized in the following mode, that is, the free layer is treated by a magnetic field annealing treatment technique, or the free layer is grown by a sputtering film formation technique using a bias magnetic field, and the formed free layer film has a uniaxial crystal magnetic anisotropy field H k and can have anisotropy in a specific direction. On the other hand, the free layer is arranged to be elliptical instead of circular, and the shape anisotropy demagnetizing field H d in a specific direction is obtained by setting the size of the major axis Ly and the size of the minor axis Lx of the ellipse. Therefore, it should be noted that H k and H d are mutually compensated.

[0023] Optionally, the magnetoresistive angle sensor can be TMR or GMR, but is not limited to TMR or GMR.

[0024] According to an embodiment of the present invention, when the external magnetic field rotates by 0 to 360° in the X-Y plane, the crystal magnetic anisotropy field is compensated by the shape anisotropy demagnetizing field in the free layer, whereby the free layer has an effective anisotropy field close to 0, and the corresponding external magnetic field has a low magnetic field value close to the value of the saturation magnetic field of the free layer. Therefore, the angle measurement error of the magnetoresistive angle sensor can be reduced, and the angle measurement accuracy can be improved. Furthermore, the external magnetic field is low, so it is not necessary to constitute a strong magnet, and the magnetoresistive angle sensor can be implemented at low cost.

[0025] As an example, FIG. 4 is a schematic diagram of a multilayer stacking structure in a low magnetic field magnetoresistive angle sensor according to an embodiment of the present invention. As shown in FIG. 4, optionally, the magnetoresistive sensing unit includes a push magnetoresistive sensing unit 200a and a pull magnetoresistive sensing unit 200b, and the free layer 201 of the push magnetoresistive sensing unit 200a and the free layer 201 of the pull magnetoresistive sensing unit 200b have positive and negative X-direction Neel coupling magnetic fields H Nhas the Néel coupling magnetic field H of the push magnetoresistive sensing unit 200a and the pull magnetoresistive sensing unit 200b N is compensated by the crystalline magnetic anisotropy field H k and the shape anisotropy diamagnetic field H d of the corresponding free layer 201 respectively.

[0026] In this embodiment, the magnetoresistive sensing unit is a push-pull magnetoresistive sensing unit. Optionally, the free layer 201 of the push magnetoresistive sensing unit 200a has the Néel coupling magnetic field H N in the positive X direction, and the free layer 201 of the pull magnetoresistive sensing unit 200b has the Néel coupling magnetic field H N in the negative X direction. In other embodiments, optionally, the free layer of the push magnetoresistive sensing unit has a Néel coupling magnetic field in the -X direction, and the free layer of the pull magnetoresistive sensing unit has a Néel coupling magnetic field in the +X direction.

[0027] The Néel coupling magnetic field H N of the push magnetoresistive sensing unit 200a is compensated by the crystalline magnetic anisotropy field H k and the shape anisotropy field H d of the free layer 201, and the Néel coupling magnetic field H N of the pull magnetoresistive sensing unit 200b is compensated by the crystalline magnetic anisotropy field H k and the shape anisotropy field H d of the free layer 201 respectively.

[0028] Figs. 5a and 5b are schematic diagrams of a low magnetic field magnetoresistive angle sensor according to an embodiment of the present invention. As shown in Fig. 5a, optionally, a plurality of push magnetoresistive sensing units 200a may be electrically connected to form a push magnetoresistive sensing unit string 200(1). As shown in Fig. 5b, optionally, a plurality of pull magnetoresistive sensing units 200b may be electrically connected to form a pull magnetoresistive sensing unit string 200(2). The push magnetoresistive sensing unit string 200(1) and the pull magnetoresistive sensing unit string 200(2) are connected to form a push-pull magnetoresistive angle sensor with a full-bridge structure or a half-bridge structure.

[0029] In this embodiment, the magnetoresistive angle sensor is a push-pull magnetoresistive angle sensor. The push-pull magnetoresistive angle sensor includes a push magnetoresistive sensing unit string 200(1) and a pull magnetoresistive sensing unit string 200(2). The push magnetoresistive sensing unit string 200(1) and the pull magnetoresistive sensing unit string 200(2) are connected to form a full-bridge structure, or the push magnetoresistive sensing unit string 200(1) and the pull magnetoresistive sensing unit string 200(2) are connected to form a half-bridge structure.

[0030] As shown in FIG. 5a, the push magnetoresistive sensing unit string 200(1) is formed by connecting a plurality of push magnetoresistive sensing units 200a in series and in parallel. As shown in FIG. 5b, the pull magnetoresistive sensing unit string 200(2) is formed by connecting a plurality of pull magnetoresistive sensing units 200b in series and in parallel. In other embodiments, optionally, the push magnetoresistive sensing unit string may be formed by connecting a plurality of push magnetoresistive sensing units in series, and the pull magnetoresistive sensing unit string may be formed by connecting a plurality of pull magnetoresistive sensing units in series. Alternatively, in a further option, the push magnetoresistive sensing unit string may be formed by connecting a plurality of push magnetoresistive sensing units in parallel, and the pull magnetoresistive sensing unit string may be formed by connecting a plurality of pull magnetoresistive sensing units in parallel. It is not limited to this.

[0031] By way of example, as shown in FIGS. 2 and 3, optionally, the shape anisotropy demagnetizing field of the free layer is determined by the shape anisotropy factors (Nx, Ny), and the crystalline magnetic anisotropy field of the free layer is determined by the crystalline magnetic anisotropy constant K1, Nx = Ny + K1 / M s 2 where M s represents the saturation magnetic moment of the free layer, Nx represents the shape anisotropy factor in the X direction, and Ny represents the shape anisotropy factor in the Y direction.

[0032] Optionally, the shape anisotropy demagnetizing field of the free layer is determined by the shape anisotropy factors (Nx, Ny), and the crystalline magnetic anisotropy field of the free layer is determined by the crystalline magnetic anisotropy constant K1. In the case of the push magnetoresistive sensing unit, Nx = Ny + K1 / M s 2 +2*H N / M s and in the case of the pull magnetoresistive sensing unit, Nx = Ny + K1 / M s 2 -2*H N / M s where M srepresents the saturation magnetic moment of the free layer, Nx represents the shape anisotropy factor in the X direction, Ny represents the shape anisotropy factor in the Y direction, and H N represents the Neel coupling magnetic field of the free layer.

[0033] In this embodiment, the analysis starts from the matrix representation of the crystalline magnetic anisotropy field H k and the shape anisotropy diamagnetic field H d and describes the process of achieving compensation by the crystalline magnetic anisotropy field H k and the shape anisotropy diamagnetic field H d The shape anisotropy diamagnetic field refers to the magnetic shape anisotropy field.

[0034] Mathematically, the crystalline magnetic anisotropy field H k and the shape anisotropy diamagnetic field H d can be represented by an anisotropy tensor matrix, and the anisotropy tensor matrix is shown as in the following formula (1).

Equation

[0035] By converting the coordinates in the principal axis direction, the anisotropy tensor matrix (1) can be converted into a diagonal matrix, and the diagonal matrix is shown as the following formula (2).

Equation

[0036] Geometrically, the anisotropy tensor matrix (1) can be described by an ellipsoid, and the free layers of the push magnetoresistive sensing unit and the pull magnetoresistive sensing unit are equivalent to a special oblate ellipsoid compressed in the Z direction.

[0037] Therefore, theoretically, the mutual compensation of H d and H k is the matrix [D] of the crystalline magnetic anisotropy field H k and the matrix [D] of the shape anisotropy diamagnetic field H 1 and the matrix [D] of the shape anisotropy diamagnetic field H d and the matrix [D] of the shape anisotropy diamagnetic field H 2As long as the sum with [D] is equal to 0, that is, [D] 1 + [D] 2 = 0 matrix, it can be achieved. From the perspective of energy, the crystal magnetic anisotropy energy of the crystal magnetic anisotropy field H k and the magnetic shape anisotropy energy of the shape anisotropy demagnetizing field H d sum to 0.

[0038] For the crystal magnetic anisotropy energy and the magnetic shape anisotropy energy, the expression is shown in the following formula (3).

Equation

[0039] In formula (3), M represents the vector magnetic moment and can be expressed as the three components of m x , m y , and m z . θ 1 represents a vector including the angle between M and the X-axis, θ 2 represents a vector including the angle between M and the Y-axis, θ 3 represents a vector including the angle between M and the Z-axis, θ 1 , θ 2 , θ 3 satisfies the relational expression (4). cos 2 θ 1 + cos 2 θ 2 + cos 2 θ 3 = 1 (4)

[0040] Since the free layer of the push magnetic resistance sensing unit is equivalent to a special oblate ellipsoid compressed in the Z direction and the free layer of the pull magnetic resistance sensing unit is equivalent to a special oblate ellipsoid compressed in the Z direction, Dx = Dz in the diagonal determinant (2) is set, and formula (3) is converted into the following formula (5). JPEG0007679486000004.jpg78170

[0041] On the other hand, another expression of the crystal magnetic anisotropy is shown in formula (6). E A =K 1 ·sin 2 θ 2 +K 0 (6)

[0042] In Equation (6), K 1 and K 0 are the crystal magnetic anisotropy constants. By comparing Equations (5) and (6), Equation (7) is obtained. K 1 =-M 2 ·(Dx - Dy) (7)

[0043] In actual work, for the crystal magnetic anisotropy field, the factor is represented by the parameter K 1 . For the shape anisotropy demagnetizing field, the shape anisotropy demagnetization factor is represented by Nx(Dx), Ny(Dy), and Nz(Dz). The sum of the crystal magnetic anisotropy energy and the magnetic shape anisotropy energy is 0, which is the condition for the mutual compensation of H k and H d . When the directions of the crystal magnetic anisotropy energy and the magnetic shape anisotropy energy are opposite, the following Equation (8) is obtained. K 1 ·sin 2 θ 2 +K 0 -M 2 ·(Nx - Ny)·sin 2 θ 2 =0 (8)

[0044] After Equation (8) is simplified, Equation (9) is obtained. Nx = 2K 1 / M 2 + Ny (9)

[0045] Therefore, the crystal magnetic anisotropy field H k is represented by Equation (10), and the shape anisotropy demagnetizing field H d is represented by Equation (11). H k = 2K 1 / M (10) H d = M·(Nx - Ny) (11)

[0046] H d and H k The conditions for the mutual compensation of are shown in Equation (12). H d =M·(Nx - Ny)=H k (12)

[0047] Optionally, the crystalline magnetic anisotropy field H k is less than 20 Oe, the ratio Lx / Ly of the minor axis to the major axis is in the range of 0.5 < Lx / Ly < 0.95, the thickness Lz is in the range of 5 nm < Lz < 200 nm, the minor axis Lx is in the range of 0.5 μm < Lx < 50 μm, and the difference between the orientation angle of the shape anisotropy diamagnetic field H d and the orientation angle of the crystalline magnetic anisotropy field H k is 90°.

[0048] Permalloy NiFe is obtained as an example for explaining the design of the sizes (Lx, Ly, Lz) of the free layer and the thin - film ellipsoid formed by permalloy under the condition that the performance parameters of the soft magnetic material (H k , M s ) are known, provided that H k = 20 Oe and M s = 10000 G.

[0049] The major axis of the elliptical free layer is Ly, the minor axis is Lx, and the thickness is Lz. Specifically, when Ly > Lx >> Lz, the calculation formulas for the demagnetization factors Nx, Ny, and Nz are shown in the following Equations (13 - 16).

Number

[0050] K and E are complete elliptic integral terms, the input parameter is e, and the relationship graph of (Lx, Ly, Lz) vs. H d can be solved by substituting into Equation (12).

[0051] As described above, as shown in FIG. 2, the magnetoresistive angle sensor has a single-domain structure, the easy magnetization axis direction (EA) is the X-axis direction, and under zero magnetic field, the direction of the shape anisotropy demagnetizing field Hd is the -X direction, H is the external magnetic field, and it is assumed that the direction of the magnetic moment M coincides with the direction of the external magnetic field H.

[0052] FIG. 6 is a two-dimensional diagram of (Lx / Ly)-Lx of the free layer having different Lz values of the elliptical magnetoresistive sensing unit. As shown in FIG. 6, optionally, the shape anisotropy demagnetizing field H d and the crystalline magnetic anisotropy field H k are such that H d =H k = 20 Oe is satisfied, Lz is arranged at equal intervals from 1 nm to 50 nm to form 10 curves, and the corresponding Lz value of each curve is 1 + 49 / 9*(n - 1) nm, that is, n is an integer and is shown as 1 ≤ n ≤ 10. When n = 1, the corresponding Lz value of the first curve is 1 nm. When n = 2, the corresponding Lz value of the second curve is about 6.44 nm. When n = 3, the corresponding Lz value of the third curve is about 11.88 nm, etc. When n = 10, the corresponding Lz value of the tenth curve is 50 nm. Lx / Ly is in the range of 0 < Lx / Ly < 1. For each Lz value, Lx has a maximum value, and for each Lx value, there is only one corresponding Lx / Ly. As Lx increases, Lx / Ly decreases, that is, it can be understood that it is also necessary to increase Ly accordingly.

[0053] FIG. 7 is a two-dimensional diagram of Lx - Ly of the free layer having different Lz values in the elliptical magnetoresistive sensing unit. As shown in FIG. 7, optionally, the shape anisotropy demagnetizing field H d and the crystalline magnetic anisotropy field H k are such that H d =H kSatisfies the equation = 20 Oe, and Lz is arranged at equal intervals from 1 nm to 50 nm to form 10 curves. The corresponding Lz value of each curve is 1 + 49 / 9 * (n - 1) nm, that is, n is an integer and is shown as 1 ≤ n ≤ 10. When n = 1, the corresponding Lz of the first curve is 1 nm. When n = 2, the corresponding Lz value of the second curve is about 6.44 nm. When n = 3, the corresponding Lz value of the third curve is about 11.88 nm, etc. When n = 10, the corresponding Lz value of the tenth curve is 50 nm. As Lz increases, the range of the Lx value gradually becomes wider, and it can be understood that when Lz is close to 1 nm, the range of the Ly / Lx value changes dramatically with respect to Lz = 50 nm.

[0054] When Lz = 50 nm, one value is shown as Lx = 14.36 μm, Ly = 28.35 μm, Lz = 50 nm, Nx = 0.001116855, Ny = 0.003114851, Nz = 0.995768293, Hd ≒ 20 Oe = Hk, and the inequality of the external magnetic field H is H > H N +H d +H k +H s In, H d +H k When = 0, mutual compensation is achieved, and when H > H N +H s In this case, the amplitude of H is greatly reduced.

[0055] Exemplarily, FIG. 8 is a schematic diagram of a multilayer stack structure in a magnetoresistive sensing unit. As shown in FIG. 8, optionally, along the direction in which the substrate 100 points to the magnetoresistive sensing unit 200 (the same as the +Z direction), the multilayer thin film structure includes a seed layer, a free layer (FL), a barrier layer (BL), a reference layer (RL), a metal layer (ML), a pinning layer (PL), an antiferromagnetic layer (AFL), and an insulating layer (CL). In the case of the push magnetoresistive sensing unit 200a, the free layer 201 has a crystalline magnetic anisotropy field H in the +X direction kincluding, the magnetic moment direction of the reference layer (RL) is the +X direction, the magnetic moment direction of the pinned layer (PL) is the -X direction, and the magnetic moment direction of the antiferromagnetic layer (AFL) is the -X direction. In the case of the pull magnetoresistive sensing unit 200b, the free layer 201 has a crystalline magnetic anisotropy field H in the -X direction k including, the magnetic moment direction of the reference layer (RL) is the -X direction, the magnetic moment direction of the pinned layer (PL) is the +X direction, and the magnetic moment direction of the antiferromagnetic layer (AFL) is the +X direction.

[0056] Exemplarily, as shown in FIG. 4, optionally, along the direction in which the substrate 100 points to the magnetoresistive sensing unit 200 (the same as the +Z direction), the multilayer thin film structure includes a seed layer, an antiferromagnetic layer (AFL), a pinned layer (PL), a metal layer (ML), a reference layer (RL), a barrier layer (BL), a free layer (FL), and an insulating layer (CL). The reference layer (RL) is planarized by off-axis ion beam milling. In the case of the push magnetoresistive sensing unit 200a, the free layer 201 has a crystalline magnetic anisotropy field H in the +X direction k including, the magnetic moment direction of the reference layer (RL) is the +X direction, the magnetic moment direction of the pinned layer (PL) is the -X direction, and the magnetic moment direction of the antiferromagnetic layer (AFL) is the -X direction. In the case of the pull magnetoresistive sensing unit 200b, the free layer 201 has a crystalline magnetic anisotropy field H in the -X direction k including, the magnetic moment direction of the reference layer (RL) is the -X direction, the magnetic moment direction of the pinned layer (PL) is the +X direction, and the magnetic moment direction of the antiferromagnetic layer (AFL) is the +X direction. The insulating layer (CL) can also be regarded as a cap layer.

[0057] Optionally, the reference layer (RL) is a bilayer composite structure or a SAF multilayer composite structure. Optionally, the barrier layer is a conductive layer prepared from ruthenium or copper, or the barrier layer is an insulating layer prepared from aluminum oxide or magnesium oxide. The free layer is a multilayer thin film composed of two or more alloys of ferronickel, cobalt iron boron, and cobalt iron.

[0058] FIG. 9 is a magnetization diagram of a free layer in a push magnetoresistive sensing unit according to an embodiment of the present invention, and FIG. 10 is a magnetization diagram of a free layer in a pull magnetoresistive sensing unit according to an embodiment of the present invention. As shown in FIGS. 9 and 10, optionally, the major axis Ly of the free layer is close to the minor axis Lx, that is, the free layer 201 is substantially circular. Optionally, the magnetoresistive sensing unit in the magnetoresistive angle sensor is a push-pull magnetoresistive sensing unit, and the magnetization diagrams of the push magnetoresistive sensing unit 200a in FIG. 4 and the push magnetoresistive sensing unit 200a in FIG. 8 are shown in FIG. 9, and the magnetization diagrams of the pull magnetoresistive sensing unit 200b in FIG. 4 and the pull magnetoresistive sensing unit 200b in FIG. 8 are shown in FIG. 10.

[0059] The stack of the reference layer (RL), the barrier layer (BL), and the free layer (FL) in the magnetoresistive sensing unit forms a tunnel junction unit, and the position of the tunnel junction unit varies according to the relative position change of the pinning layer (PL) in the magnetoresistive sensing unit. The magnetoresistive sensing unit shown in FIG. 4 can be understood as a bottom-pinned multilayer thin film stack structure, and the tunnel junction unit is located on the bottom-pinned multilayer thin film stack structure, that is, the substrate 100, the seed layer, the antiferromagnetic layer (AFL), the pinning layer (PL), the metal layer (ML), the reference layer (RL), the barrier layer (BL), the free layer (FL), and the cap layer (CL) 10 are sequentially stacked. The magnetoresistive sensing unit shown in FIG. 8 can be understood as a top-pinned multilayer thin film stack structure, and the tunnel junction unit is located between the top-pinned multilayer thin film stack structure and the substrate 100, that is, the substrate 100, the seed layer, the free layer (FL), the barrier layer (BL), the reference layer (RL), the metal layer (ML), the pinning layer (PL), the antiferromagnetic layer (AFL), and the cap layer (CL) 10 are sequentially stacked.

[0060] The antiferromagnetic layers (AFL) of the push magnetoresistive sensing unit 200a and the pull magnetoresistive sensing unit 200b have opposite positive and negative X-direction magnetic moment directions, and the push pinning layer (PL) and the pull pinning layer (PL) also have opposite positive and negative X-direction magnetic moment directions. The push pinning layer (PL), the push metal layer (ML), and the push reference layer (RL) form the SAF structure of the push magnetoresistive sensing unit 200a by the RKKY effect, and the pull pinning layer (PL), the pull metal layer (ML), and the pull reference layer (RL) form the SAF multilayer composite structure of the pull magnetoresistive sensing unit 200b by the RKKY effect, thereby ensuring that the push reference layer (RL) and the pull reference layer (RL) have opposite -X and +X direction magnetic moment directions.

[0061] Optionally, when the barrier layer (BL) is Al 2 O 3 or MgO, the magnetoresistive sensing unit is a TMR unit. Optionally, when the barrier layer (BL) is a metal layer Ru or Cu, the magnetoresistive sensing unit is a GMR unit.

[0062] As shown in FIGS. 9 and 10, when the free layers 201a of the push magnetoresistive sensing unit and the free layers 201b of the pull magnetoresistive sensing unit are circular in structure, the anisotropy field is 0, that is, magnetic moments in different directions are distributed on the free layer 201a and the free layer 201b, and an isotropic property is achieved. Then, when the external magnetic field H rotates by 0 to 360° on the free layer 201a and the free layer 201b, the value of the maximum magnetic field H required is evaluated.

[0063] As shown in FIG. 9, HN is the Néel coupling magnetic field between the free layer (FL) 201a and the push reference layer (RL), and the direction is consistent with the magnetic moment direction of the push reference layer (RL), that is, the +X direction, and the direction cannot change with the external magnetic field H. When the external magnetic field H is in the -X direction, there is a +X direction magnetic moment on the push free layer (FL) 201a, and the anisotropy field H of the external magnetic field H kis determined by the material, and the direction is the +X direction. At this time, the anti-magnetic field H d is clearly in the +X direction. In order to be able to direct all the magnetic moments on the push free layer (FL) 201a in the -X direction, the required maximum magnetic field value is the Neel magnetic field HN, the anti-magnetic field H d , the anisotropy field H k , and the material saturation magnetic field H s is equal to the sum of the values. At this time, the magnetic moment M of the external magnetic field H coincides with the magnetic moment M of the push free layer (FL) 201a, that is, H > HN + H d + H k + H s .

[0064] Similarly, as shown in FIG. 10, in the case of the pull free layer (FL) 201b of the pull magnetoresistive sensing unit, when the external magnetic field H is in the +X direction, H > HN + H d + H k + H s as shown, there exists a maximum magnetic field value.

[0065] As a conclusion, the demagnetization rates of the circular pull free layer (FL) 201a and the pull free layer (FL) 201b can be expressed as follows. H d = {sqrt(t 2 + R 2 ) - R} / 2t t represents the film thickness of the free layer, R represents the circle radius. In the case of a permalloy thin film, the thickness is t ≒ 10 nm, R ≒ 5000 nm, u 0 M s~ 1 T, H d is shown as ≒ 16 Oe.

[0066] Typical values of the Neel coupling field HN are in the range of 1 to 10 Oe. The Neel coupling field HN also needs to be overcome by the external magnetic field H to saturate the free layer. Generally speaking, for a circular free layer, the minimum possible magnetic field strength of the external magnetic field H needs to be greater than 50 Oe in general, and at this time, H >> H s .

[0067] To reduce the value of the external magnetic field H, the values of HN, H d , and H k can be decreased. Under ideal conditions, HN can be made as small as possible by adjusting the deposition process of the FL layer film and the PL layer film to minimize the roughness between the FL layer and the PL layer. Based on this, optionally, the multilayer thin film stack structure of the magnetoresistive sensing unit is a top-pinned multilayer thin film stack structure, or optionally, the multilayer thin film stack structure of the magnetoresistive sensing unit is a bottom-pinned multilayer thin film stack structure. Before the barrier layer is deposited, the push reference layer and the pull reference layer are planarized to reduce roughness, and optionally, the planarization process can be off-axis ion beam milling.

[0068] Regarding the above embodiments, regardless of whether the free layer is approximately circular or approximately elliptical, the mutual compensation of H d and H k is achieved in the following mode, that is, the free layer is processed by a magnetic field annealing technique or grown by a sputtering film formation technique using a bias magnetic field, and the formed free layer film can have a uniaxial crystal magnetic anisotropy field H k , and the anisotropy is in a specific direction. On the other hand, the free layer is arranged to be elliptical instead of circular, and the shape anisotropy annealing field H d is obtained by setting the size of the major axis Ly and the minor axis Lx of the ellipse. The sum of H k and H N is compensated by H d . At this time, H N can be in the X direction or the Y direction according to the difference in the magnetic moment direction of the reference layer (RL). Therefore, H d can compensate for H k and H N .

[0069] As shown in FIGS. 11a to 11d, when the magnetization direction of the reference layer RL is in the X direction, FIG. 11a is a magnetization diagram of the X - Y plane of the elliptical push free layer, FIG. 11b is a magnetization diagram of the X - Z plane of the elliptical push free layer, FIG. 11c is an X - Y plane magnetization graph of the elliptical pull free layer, and FIG. 11d is an X - Z plane magnetization graph of the elliptical pull free layer. HN corresponds to the bias magnetic field applied in the X direction. At this time, H d can still be obtained by adjusting the sizes of Lx, Ly, and Lz of the elliptical free push layers 201c and 201d, and can be used to compensate for the sum of HN and H k .

[0070] At this time, H N , H d , and H k act in combination, and the total energy E(θ) of the free layer is expressed as the following formula (17). JPEG0007679486000006.jpg18170

[0071] The positive and negative signs respectively correspond to the free layers 201c and 201d of the push magnetoresistive sensing unit and the pull magnetoresistive sensing unit. That is, the free layer 201c of the push magnetoresistive sensing unit has E(θ)=-(H x +H N )·M·cosθ - Hy·M·sinθ+[K1 - M 2 ·(Ny - Nx)]·sin 2 θ], the free layer 201d of the pull magnetoresistive sensing unit has E(θ)=-(H x -H N )·M·cosθ - Hy·M·sinθ+[K1 - M 2 ·(Ny - Nx)]·sin 2 θ], or the free layer 201d of the pull magnetoresistive sensing unit has E(θ)=-(H x +H N )·M·cosθ - Hy·M·sinθ+[K1 - M 2 ·(Ny - Nx)]·sin 2is θ, and the free layer 201c of the push magnetoresistive sensing unit is E(θ)=-(H x -H N )·M·cosθ - Hy·M·sinθ + [K1 - M 2 ·(Ny - Nx)]·sin 2 θ].

[0072] When the magnetic moment of the saturation magnetic field H s is in the X and Y directions, the total energy E(θ) of the free layer has the same value, that is, the following equation (18) is satisfied. E(0)=E(90) (18)

[0073] At this time, due to the mutual compensation of H N , H d , and Hk, only the term of H s remains in the expression of the external magnetic field H (H > H N +H d +H k +H s ), that is, the expression of the external magnetic field H is H > H s , and H satisfies the following. Hx = Hy = H s (19)

[0074] Hx = H s , Hy = 0 is substituted into E(0), and Hy = H s , Hx = 0 is substituted into E(90). Equation (20) is obtained according to equation (18) (±H N )·M = -[K 1 -M 2 ·(N y -N x )] (20) is obtained accordingly.

[0075] After equation (20) is simplified, the relational expression (21) that satisfies the mutual compensation of H N , H k , and H d is obtained.

Number

[0076] When the magnetization direction of the reference layer (RL) is in the Y direction, i.e., H N is in the Y direction, the total energy E(θ) of the free layer satisfies the following equation (22). JPEG0007679486000008.jpg18170

[0077] The positive and negative signs correspond to the free layers 201c and 201d of the push magnetoresistive sensing unit and the pull magnetoresistive sensing unit, respectively.

[0078] Saturation magnetic field H s When the magnetic moments of are in the X and Y directions, the total energy E(θ) of the free layer has the same value, i.e., E(0) = E(90).

[0079] After equation (22) is simplified, a relational equation (23) that satisfies the mutual compensation of H N , H k , and H d is obtained.

Number

[0080] Optionally, the shape anisotropy demagnetizing field of the free layer is determined by the shape anisotropy factors (Nx, Ny), and the crystalline magnetic anisotropy field of the free layer is determined by the crystalline magnetic anisotropy constant K1.

[0081] For the push magnetoresistive sensing unit, Nx = Ny + K1 / Ms 2 +2*H N / M s and for the pull magnetoresistive sensing unit, Nx = Ny + K1 / M s 2 -2*H N / M s is.

[0082] M s represents the saturation magnetic moment of the free layer, Nx represents the shape anisotropy factor in the X direction, Ny represents the shape anisotropy factor in the Y direction, HN represents the Néel coupling magnetic field of the free layer.

[0083] Similarly, taking permalloy NiFe as an example, H k = 20 Oe, M = 10000 G, and the typical value of the Néel coupling field H N is in the range of 1 - 10 Oe. When H N = 5 Oe, for the push magnetoresistive sensing unit, H k + H N = 25 Oe, and for the pull magnetoresistive sensing unit, H k - H N = 15 Oe. Therefore, the push magnetoresistive sensing unit and the pull magnetoresistive sensing unit have different Lx and Ly sizes respectively.

[0084] As shown in FIGS. 12a to 12d, FIG. 12a is the X - Y plane magnetization graph of the elliptical push free layer, FIG. 12b is the magnetization graph of the X - Z plane of the elliptical push free layer, FIG. 12c is the magnetization graph of the X - Y plane of the elliptical pull free layer, and FIG. 12d is the magnetization graph of the X - Z plane of the elliptical pull free layer. Let the size of the magnetic push - type resistance sensing unit be L x1 and L y1 , and the size of the magnetic pull - type resistance sensing unit be L x2 and L y2 . Then, since the resistance of the magnetic push - type resistance sensing unit needs to be the same, that is, the area needs to be the same, the following relational expression (24) exists. L x1 ·L y1 = L x2 ·L y2 (24)

[0085] As shown in FIG. 13, under the condition that Lz is known, L x1 and L y1 are obtained from the contour map of H d in the two - dimensional coordinates of Lx - Ly. L x1 and L y1 are such that H d = H k + HN satisfies the equivalent curve 22, and Lx2 and Ly2 are H d =H k -H N satisfies the equivalent curve 20. Next, Lx*Ly = L x1 *L y1 the hyperbola 21 of (L x1 ,L y1 ) is created, and the intersection of the hyperbola 21 and the equivalent curve 20 is another point (Lx2, Ly2). Similarly, for H in the Y direction N corresponding (L x3 ,L y3 ), (L x4 ,L y4 ) can be solved.

[0086] Figure 14 is a size selection diagram of a push magnetoresistive sensing unit and a pull magnetoresistive sensing unit. Two contour lines H d = 25 Oe and H d = 15 Oe are selected, and H d = 25 Oe and H d = 15 Oe intersect one hyperbola Lx*Ly = 36 at (1, 2), and H d = 25 Oe and H d = 15 Oe intersect the other hyperbola Lx*Ly = 64 at (3, 4). For the corresponding Lx and Ly data table, please refer to Table 1.

[0087]

Table 1

[0088] As shown in the above table, when the corresponding area is Lx*Ly = 36 μm*μm, the size of the push magnetoresistive sensing unit is shown as 5.22808 < L x1 < 5.3192, 6.72222 < Ly < 6.87273, and the size of the pull magnetoresistive sensing unit is 5.51825 < L x1 < 5.62978, 6.42121 < Ly < 6.57172.

[0089] When the corresponding area is Lx*Ly = 64μm*μm, the size of the push magnetoresistive sensing unit is 6.72868 < L x1 <6.80542, 9.43131 < Ly < 9.58182, and the size of the pull magnetoresistive sensing unit is 7.20738 < L x1 <7.30707, 8.82929 < Ly < 8.9798.

[0090] Figures 15 and 16 respectively show the M-H curves corresponding to the two sizes and material properties of the elliptical free layer and the circular free layer. As shown in Figure 15, since the effective anisotropy field of the low-field magnetoresistive angle sensor is close to 0, that is, H d , H k , and H N compensate for each other, the coercive force of the M-H loop is close to 0. As shown in Figure 16, since the anisotropy field of the low-field magnetoresistive angle sensor is mainly determined by H k , a rectangular M-H loop will exist. On the other hand, due to the presence of H N , the coercive force is -H k + H N and H k - H N , and the M-H loop is asymmetric. It should be noted that the H N values corresponding to the push arm and the pull arm in the magnetoresistive angle sensor are in opposite directions. According to the numerical simulation representation, H s can be reduced by selecting the correct Lx / Ly, and an external magnetic field H similar to H s can be obtained.

[0091] For any of the above embodiments, the free layer has a crystalline magnetic anisotropy field H k in the same +X or -X direction, and also has a Néel coupling field H N in the opposite +X and -X directions. It should be noted that the pinning layer (PL) has pinning fields H p in the opposite +X and -X directions. When the external magnetic field H rotates by 0 to 360° in the X-Y plane, the crystalline magnetic anisotropy field H k and the Néel coupling field HN is compensated by the FL layer shape anisotropy reverse magnetic field H d , whereby the FL layer has an effective anisotropy field close to 0, and the external magnetic field H has a low magnetic field value close to the FL layer saturation magnetic field H s . Accordingly, the deflection angle of the PL layer can be effectively reduced, and the accuracy of angle measurement can be improved.

[0092] The condition that the free layer has the minimum saturation magnetic field H s is that the shape anisotropy factors (Nx, Ny) of the reverse magnetic field H d of the free layer and the crystalline magnetic anisotropy field H k of the crystalline magnetic anisotropy constant K1 are in the relationship shown as Nx = Ny + K1 / M s 2 , where M s represents the saturation magnetic moment of the FL layer.

[0093] Optionally, |H d | = |H k |, and the difference between the orientation angle of H d and the orientation angle of H k is 90°, that is, the crystalline magnetic anisotropy direction tends to be the direction of the magnetization intensity forced with respect to the direction of the short axis.

[0094] In addition, under the condition that the magnetic moment M s of the free layer (FL) and the direction of H coincide, the external magnetic field H is reduced, and the deflection angle of the pinning layer (PL) can be reduced by the action of the external magnetic field H. Accordingly, the deflection angle of the PL can be prevented from increasing with the increase of the amplitude of H, and the measurement angle error is reduced. Accordingly, the amplitude of the external magnetic field H is reduced, whereby the deflection angle of the pinning layer (PL) is reduced, and at the same time, the magnetic moment M s of the free layer (FL) can be ensured to be in a saturated state in the H direction, and further, the cost of the magnet can be reduced, which has important significance for improving the preparation of the TMR or GMR spin valve high-precision magnetoresistive angle sensor and reducing the cost.

[0095] It should be noted that the above are only preferred embodiments and technical principles of the present invention. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described in this specification, and various obvious changes, adjustments, combinations, and substitutions can be made without departing from the protection scope of the present invention. Therefore, although the present invention has been described in detail by the above embodiments, the present invention is not limited to the above embodiments. Without departing from the concept of the present invention, the present invention can also include more equivalent embodiments, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. 1. A low field magnetoresistive angle sensor comprising: A substrate located in an XY plane; a magnetoresistive sensing unit located on the substrate, the magnetoresistive sensing unit comprising a multi-layer thin film structure comprising a stack of at least a free layer, a barrier layer, and a reference layer, the magnetoresistive sensing unit having an elliptical shape, the elliptical free layer having a major axis Ly, a minor axis Lx, and a thickness Lz, the free layer having a saturation magnetic field, a shape anisotropy demagnetizing field, and a magnetocrystalline anisotropy field in an X-direction, the magnetocrystalline anisotropy field being compensated by the shape anisotropy demagnetizing field to cause an effective anisotropy field of the free layer to approach zero when an external magnetic field rotates by 0 to 360 degrees in the XY plane, such that the external magnetic field has a low working magnetic field value close to the value of the saturation magnetic field of the free layer material.

2. 2. The low field magnetoresistive angle sensor of claim 1, wherein the magnetoresistive sensing unit comprises a push magnetoresistive sensing unit and a pull magnetoresistive sensing unit, the free layer of the push magnetoresistive sensing unit and the free layer of the pull magnetoresistive sensing unit have positive and negative X-direction Neel coupling magnetic fields, and the Neel coupling magnetic fields of the push magnetoresistive sensing unit and the pull magnetoresistive sensing unit are compensated by the magnetocrystalline anisotropy field and the shape anisotropy demagnetizing field of the corresponding free layer, respectively.

3. 3. The low field magnetoresistive angle sensor of claim 2, wherein a plurality of push magnetoresistive sensing units are electrically connected to form a push magnetoresistive sensing unit string, and a plurality of pull magnetoresistive sensing units are electrically connected to form a pull magnetoresistive sensing unit string, and the push magnetoresistive sensing unit string and the pull magnetoresistive sensing unit string are connected to form a push-pull magnetoresistive angle sensor with a full bridge structure or a half bridge structure.

4. The shape anisotropy demagnetizing field of the free layer is determined by a shape anisotropy factor (Nx, Ny), and the magnetocrystalline anisotropy field of the free layer is determined by a magnetocrystalline anisotropy constant K １ is determined by Nx=Ny+K1 / M ｓ ２ And M ｓ 2. The low field magnetoresistive angle sensor of claim 1, wherein Nx represents the saturation magnetic moment of the free layer, Ny represents the shape anisotropy factor in the X direction, and Ny represents the shape anisotropy factor in the Y direction.

5. the shape anisotropy demagnetizing field of the free layer is determined by a shape anisotropy factor (Nx, Ny), the magnetocrystalline anisotropy field of the free layer is determined by a magnetocrystalline anisotropy constant K1, For the push magnetoresistive sensing unit, Nx=Ny+K1 / M ｓ ２ +2 ＊ H Ｎ / M ｓ and for the pull magnetoresistive sensing unit, Nx=Ny+K1 / M ｓ ２ -2 ＊ H Ｎ / M ｓ and M ｓ represents the saturation magnetic moment of the free layer, Nx represents the shape anisotropy factor in the X direction, Ny represents the shape anisotropy factor in the Y direction, and H Ｎ 4. A low field magnetoresistive angle sensor as claimed in claim 2 or 3, wherein: .function..times ...

6. 2. The low field magnetoresistive angle sensor of claim 1, wherein the multi-layer thin film structure comprises, along the direction in which the substrate points to the magnetoresistive sensing unit, a seed layer, the free layer, the barrier layer, the reference layer, a metal layer, a pinned layer, an antiferromagnetic layer, and an insulating layer.

7. 2. The low field magnetoresistive angle sensor of claim 1, wherein the multi-layer thin film structure comprises a seed layer, an antiferromagnetic layer, a pinned layer, a metal layer, the reference layer, the barrier layer, the free layer, and an insulating layer along a direction in which the substrate points to the magnetoresistive sensing unit, and the reference layer is planarized by off-axis ion beam milling.

8. The low field magnetoresistive angle sensor of claim 1 , wherein the reference layer is a bilayer composite structure or a SAF multilayer composite structure.

9. 2. The low field magnetoresistive angle sensor of claim 1, wherein the barrier layer is a conductive layer prepared from ruthenium or copper, or the barrier layer is an insulating layer prepared from aluminum oxide or magnesium oxide, and the free layer is a multilayer thin film composed of an alloy of two or more of ferronickel, cobalt iron boron, and cobalt iron.

10. the magnetocrystalline anisotropy field is less than 20 Oe; the ratio Lx / Ly of the minor axis to the major axis is within a range of 0.5<Lx / Ly<0.95, the thickness Lz is within a range of 5 nm<Lz<200 nm, and the minor axis Lx is within a range of 0.5 μm<Lx<50 μm; 2. The low field magnetoresistive angle sensor of claim 1, wherein the difference between the orientation angle of the shape anisotropy demagnetizing field and the orientation angle of the magnetocrystalline anisotropy field is 90 degrees.

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