Single-substrate full-bridge TMR magnetic field sensor and preparation method thereof

Abstract

The invention provides a single-substrate full-bridge TMR magnetic field sensor and a preparation method thereof, and the sensor comprises four groups of MTJ devices which are connected to form a full-bridge structure, two groups of MTJ devices on one pair of opposite bridge arms are located in a first region of a substrate, and two groups of MTJ devices on the other pair of opposite bridge arms are located in a second region of the substrate, the two groups of MTJ devices in the first region are provided with first stacked structures, and each first stacked structure comprises a first pinning layer, a coupling conversion layer, a first reference layer, a first barrier layer and a first free layer which are sequentially stacked from bottom to top; and the two groups of MTJ devices in the second region have a second stack structure and comprise a second pinning layer, a second reference layer, a second barrier layer and a second free layer which are stacked in sequence from bottom to top. According to the invention, two MTJ devices with different magnetization directions can be obtained only through one-time external magnetic field magnetization.

Description

Technical Field

[0001] The present invention relates to the technical field of TMR magnetic field sensors, and in particular to a single-substrate full-bridge TMR magnetic field sensor and a preparation method thereof. Background Art

[0002] TMR sensors are a new type of sensor that has been used in industry in recent years. This type of sensor uses the tunneling magnetoresistance (TMR) effect of the magnetic tunnel junction (MTJ) multilayer film to detect the external magnetic field. The main manifestation is that the resistance of the magnetic multilayer film in the TMR sensor changes with the angle and size of the external magnetic field. Compared with the widely used Hall and AMR (Anisotropic Magnetoresistance) sensors, TMR sensors have the advantages of high sensitivity, high resistivity, low power consumption and high resolution, and are the current research focus of the industry.

[0003] When using TMR sensors, it is necessary to consider issues such as temperature drift and zero point error. People generally use a Wheatstone Full Bridge structure, which has higher sensitivity and good temperature compensation function compared to single resistor and reference resistor half-bridge sensors, and can suppress output signal drift caused by temperature.

[0004] The typical full-bridge TMR magnetic field sensor structure is as follows: Figure 1 As shown, Figure 1 Taking the z-axis sensitive vertical full-bridge TMR magnetic field sensor as an example, there are four groups of MTJ devices in total. The MTJ device of each bridge arm is composed of multiple magnetic tunnel junctions connected in series and in parallel. The MTJ devices on adjacent bridge arms have opposite output trends for the same magnetic field, that is, the reference layer magnetization directions of the MTJ devices on adjacent bridge arms are opposite. The reference layer magnetization direction of a pair of MTJ devices on opposite bridge arms is upward, and the reference layer magnetization direction of another pair of MTJ devices on opposite bridge arms is downward.

[0005] In the prior art, in order to achieve two different magnetization directions on a single substrate, the typical solution is to magnetize the reference layer of the MTJ device of different bridge arms by two annealing processes using a laser annealing device that can be precisely positioned, and each time the laser only heats the wafer position corresponding to one group of bridge arms. This method not only increases the complexity of the sensor manufacturing process, but also requires specialized annealing equipment, which increases the cost. Summary of the invention

[0006] In view of this, the present invention provides a single-substrate full-bridge TMR magnetic field sensor and a preparation method thereof, which can obtain two MTJ devices with different magnetization directions by only one external magnetic field magnetization, and has a simple process and reduces costs.

[0007] In a first aspect, the present invention provides a single substrate full-bridge TMR magnetic field sensor, comprising: four groups of MTJ devices connected into a full-bridge structure, two groups of MTJ devices on a pair of opposite bridge arms are located in a first area of ​​the substrate, and two groups of MTJ devices on another pair of opposite bridge arms are located in a second area of ​​the substrate, wherein: The two groups of MTJ devices in the first region have a first stacking structure, wherein the first stacking structure includes a first pinned layer, a coupling transition layer, a first reference layer, a first barrier layer and a first free layer stacked sequentially from bottom to top; The two groups of MTJ devices in the second region have a second stacking structure, wherein the second stacking structure includes a second pinned layer, a second reference layer, a second barrier layer, and a second free layer stacked sequentially from bottom to top; The first pinned layer and the second pinned layer have perpendicular magnetization with the same magnetization direction, the coupling transition layer and the first reference layer both have perpendicular magnetization and the magnetization direction is opposite to the magnetization direction of the first pinned layer, the second reference layer has perpendicular magnetization and the magnetization direction is the same as the magnetization direction of the second pinned layer, and the first free layer and the second free layer have in-plane magnetization.

[0008] Optionally, the first pinning layer and the second pinning layer are made of the same material, which is selected from a combination of one or more of MnGa, MnAl, FePt, FePd, and CoTb.

[0009] Optionally, the structure of the coupling transition layer is any one of the following: Co, Co x Fe 1-x (x>20 at %), [Co / heavy metal]n multilayer film, the heavy metal is one of Pt, Ni, and Pd.

[0010] Optionally, the first reference layer and the second reference layer have the same structure, and the structure is any one of the following: x Fe 1-x (x<20at%) single layer, Co x Fe 1-x (x<20at%) / CoFe stack, [Co x Fe 1-x (x<20at%) / CoFeB]n multilayer films, [Fe / CoFeB]n multilayer films, [Co x Fe 1-x(x<20at%) / spacer layer / CoFeB]n multilayer film, wherein the spacer layer is one of Mo, W, and Ta.

[0011] Optionally, the first free layer and the second free layer have the same structure, and the structure is any one of the following: CoFeB single layer, NiFe single layer, CoFeB / NiFe stacked layer.

[0012] In a second aspect, the present invention provides a method for preparing a single substrate full-bridge TMR magnetic field sensor, the method comprising: Providing a substrate, wherein the substrate has a substrate, and a pinning layer film, a coupling transition layer film and a protective layer film are sequentially formed on the substrate; Performing graphic definition on the protective layer film to form a first area and a second area; removing the protective layer film and the coupling transition layer film in the second region; removing the protective film from the first area; Continue to deposit multiple MTJ films, including at least a reference layer film, a barrier layer film and a free layer film from bottom to top, covering the first region and the second region; forming an MTJ device having a first stacking structure in the first region and forming an MTJ device having a second stacking structure in the second region, wherein the first stacking structure comprises a first pinned layer, a coupling transition layer, a first reference layer, a first barrier layer and a first free layer stacked sequentially from bottom to top, and the second stacking structure comprises a second pinned layer, a second reference layer, a second barrier layer and a second free layer stacked sequentially from bottom to top; An external magnetic field is applied for initialization, so that the first pinned layer and the second pinned layer have perpendicular magnetization with the same magnetization direction, the coupling transition layer and the first reference layer have perpendicular magnetization and the magnetization direction is opposite to the magnetization direction of the first pinned layer, the second reference layer has perpendicular magnetization and the magnetization direction is the same as the magnetization direction of the second pinned layer, and the first free layer and the second free layer have in-plane magnetization.

[0013] Optionally, after removing the protective film in the first area, the method further includes: Surface treatment using hydrogen plasma to remove the potential oxide layer on the surface.

[0014] Optionally, the material of the pinned layer film is selected from one or more combinations of MnGa, MnAl, FePt, FePd, and CoTb.

[0015] Optionally, the structure of the coupling transition layer film is any one of the following: Co, Co x Fe 1-x(x>20 at%), [Co / heavy metal]n multilayer film, the heavy metal is one of Pt, Ni, and Pd.

[0016] Optionally, the protective layer film is a Ti film with a thickness of 1-3 nm.

[0017] The single-substrate full-bridge TMR magnetic field sensor and the preparation method thereof provided by the present invention form an MTJ device with a first stacking structure in a first area and form an MTJ device with a second stacking structure in a second area, wherein the first stacking structure comprises a first pinned layer, a coupling transition layer, a first reference layer, a first barrier layer and a first free layer stacked in sequence from bottom to top, and the second stacking structure comprises a second pinned layer, a second reference layer, a second barrier layer and a second free layer stacked in sequence from bottom to top; two MTJ devices with different magnetization directions can be obtained by magnetizing with an external magnetic field only once, thereby simplifying the preparation process and reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the structure of a vertical full-bridge TMR magnetic field sensor sensitive to the z-axis in the prior art; FIG. 2A to FIG. 2F Schematic diagram of a process for preparing a single-substrate full-bridge TMR magnetic field sensor in one embodiment of the present invention; Figure 3 MnGa / Co x Fe 1-x Schematic diagram of the principle of interface coupling varying with CoFe composition. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0021] Some embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0022] The embodiment of the present invention provides a method for preparing a single substrate full-bridge TMR magnetic field sensor, referring to Figure 2A to Figure 2F , the preparation method comprises the following steps: like Figure 2A As shown, a substrate (also called a wafer) is provided, on which there is a substrate 10, and a bottom metal interconnection structure (not shown) is formed in the substrate 10 so that the MTJ devices formed subsequently are connected to each other. A pinning layer film 11, a coupling transition layer film 12 and a protective layer film 13 are sequentially formed on the substrate 10. According to an embodiment of the present invention, the material of the pinning layer film 11 is selected from a combination of one or more of MnGa, MnAl, FePt, FePd, and CoTb. The structure of the coupling transition layer film 12 adopts any one of the following: Co, CoxFe1-x (x>20 at %), [Co / heavy metal]n multilayer film, and the heavy metal is one of Pt, Ni, and Pd. In some embodiments, a layer of Co can also be covered on the [Co / heavy metal]n multilayer film to improve its characteristics. The basic principle is that the layer directly in contact with the pinning layer film 11 is a magnetic layer with a high Co content. The protective layer film 13 is a Ti film with a thickness of 1~3nm.

[0023] Furthermore, after the pinning layer film 11 is formed, an annealing process is performed to improve the crystal structure of the pinning layer film 11 .

[0024] Then, a film stack structure from the MTJ reference layer to the substrate is constructed. Figure 2B As shown, a photoresist (PR) is spin-coated, and a patterning definition is performed on the protective layer film 13 through a photolithography process to form a first area and a second area.

[0025] like Figure 2CAs shown, the protective layer film 13 and the coupling transition layer film 12 of the second region are removed. Here, the entire coupling transition layer film 12 of the second region is etched away by an etching process as an exemplary illustration, and the etching is completed and the degumming and cleaning are performed. It should be noted that in some embodiments, a portion of the coupling transition layer film 12 may be retained and completely removed in a subsequent process.

[0026] like Figure 2D As shown, the wafer is baked, and then the protective layer film 13 of the first region is removed by plasma bombardment or wet etching, and finally only the coupling transition layer film 12 of the first region is retained. It can be understood that if the coupling transition layer film 12 of the second region is left in the previous etching process, the coupling transition layer film 12 of the second region is completely removed during the process of removing the protective layer film 13 of the first region, or after removing the protective layer film 13 of the first region. Preferably, according to an embodiment of the present invention, after removing the protective layer film of the first region, hydrogen plasma (H+ ions) is used for surface treatment to further remove the potential oxide layer on the surface.

[0027] Then as Figure 2E As shown, multiple layers of MTJ films are continuously deposited, including at least a reference layer film 14, a barrier layer film 15 and a free layer film 16 from bottom to top, covering the first region and the second region. Preferably, according to an embodiment of the present invention, after depositing multiple layers of MTJ films, an annealing treatment is performed to crystallize each layer of MTJ films to obtain a high TMR. According to an embodiment of the present invention, the reference layer film 14 is any one of the following: Co x Fe 1-x (x<20at%) single layer, Co x Fe 1-x (x<20at%) / CoFe stack, [Co x Fe 1-x (x<20at%) / CoFeB]n multilayer films, [Fe / CoFeB]n multilayer films, [Co x Fe 1-x (x<20at%) / spacer layer / CoFeB]n multilayer film, wherein the spacer layer is one of Mo, W, and Ta. The barrier layer film 15 is one of MgO, MgAlO, and Al2O3, and has a thickness between 1.0 and 2.0 nm. The free layer film 16 is any one of the following: CoFeB single layer, NiFe single layer, CoFeB / NiFe stacked layer.

[0028] Then as Figure 2FAs shown, an MTJ device having a first stacking structure is formed in the first region and an MTJ device having a second stacking structure is formed in the second region by photolithography and etching processes, wherein the first stacking structure includes a first pinned layer 111, a coupling transition layer 121, a first reference layer 141, a first barrier layer 151 and a first free layer 161 stacked in sequence from bottom to top, and the second stacking structure includes a second pinned layer 112, a second reference layer 142, a second barrier layer 152 and a second free layer 162 stacked in sequence from bottom to top.

[0029] It is easy to understand that the substrate 10 does not need to be etched, and each layer of the film is etched from top to bottom, and if necessary, a suitable hard mask layer is deposited. The first pinned layer 111, the coupling transition layer 121, the first reference layer 141, the first barrier layer 151 and the first free layer 161 are obtained by etching the pinned layer film 11, the coupling transition layer film 12, the reference layer film 14, the barrier layer film 15 and the free layer film 16 in the first region. The second pinned layer 112, the second reference layer 142, the second barrier layer 152 and the second free layer 162 are obtained by etching the pinned layer film 11, the reference layer film 14, the barrier layer film 15 and the free layer film 16 in the second region.

[0030] After the MTJ device is formed, an external magnetic field is applied for initialization, so that the first pinned layer 111 and the second pinned layer 112 have perpendicular magnetization with the same magnetization direction, the coupling transition layer 121 and the first reference layer 141 have perpendicular magnetization and the magnetization direction is opposite to the magnetization direction of the first pinned layer 111, the second reference layer 142 has perpendicular magnetization and the magnetization direction is the same as the magnetization direction of the second pinned layer 112, and the first free layer 161 and the second free layer 162 have in-plane magnetization, and the magnetization directions can be the same or different.

[0031] It should also be noted that in order to achieve interconnection of MTJ devices, it is necessary to form a top metal interconnection structure on the top, in conjunction with the bottom metal interconnection structure in the substrate 10, so that the MTJ devices in the first area constitute two groups of MTJ devices on a pair of opposite bridge arms, and the MTJ devices in the second area constitute two groups of MTJ devices on another pair of opposite bridge arms, and are connected into a full-bridge structure.

[0032] The method for preparing a single-substrate full-bridge TMR magnetic field sensor provided by an embodiment of the present invention forms an MTJ device with a first stacking structure in a first region and forms an MTJ device with a second stacking structure in a second region, wherein the first stacking structure includes a first pinned layer, a coupling transition layer, a first reference layer, a first barrier layer and a first free layer stacked in sequence from bottom to top, and the second stacking structure includes a second pinned layer, a second reference layer, a second barrier layer and a second free layer stacked in sequence from bottom to top; when a large magnetic field is applied (for example, upward), the magnetization directions of the first pinned layer and the second pinned layer will be consistent with the external field (upward), and the MTJ device in the first region, because the coupling transition layer with a high Co content (>20at%) is in contact with the first pinned layer, exhibits antiferromagnetic coupling, and finally makes the reference layer of the MTJ device in the first region produce a magnetization direction opposite to that of the first pinned layer. The MTJ device in the second region, because the second reference layer with a low Co content (<20at%) is in contact with the second pinned layer, exhibits ferromagnetic coupling, and finally makes the reference layer of the MTJ device in the second region produce the same magnetization direction as the second pinned layer. Therefore, only one external magnetic field magnetization is required to obtain MTJ devices with two different magnetization directions, which simplifies the process and reduces costs.

[0033] On the other hand, an embodiment of the present invention provides a single substrate full-bridge TMR magnetic field sensor, including four groups of MTJ devices connected into a full-bridge structure, two groups of MTJ devices on a pair of opposite bridge arms are located in a first area of ​​the substrate, and two groups of MTJ devices on another pair of opposite bridge arms are located in a second area of ​​the substrate. Figure 2F In the device structure shown, the two groups of MTJ devices in the first region have a first stacking structure, which includes a first pinned layer 111, a coupling transition layer 121, a first reference layer 141, a first barrier layer 151 and a first free layer 161 stacked in sequence from bottom to top; the two groups of MTJ devices in the second region have a second stacking structure, which includes a second pinned layer 112, a second reference layer 142, a second barrier layer 152 and a second free layer 162 stacked in sequence from bottom to top; Among them, the first pinned layer 111 and the second pinned layer 112 have perpendicular magnetization with the same magnetization direction, the coupling transition layer 121 and the first reference layer 141 both have perpendicular magnetization and the magnetization direction is opposite to the magnetization direction of the first pinned layer 111, the second reference layer 142 has perpendicular magnetization and the magnetization direction is the same as the magnetization direction of the second pinned layer 112, and the first free layer 161 and the second free layer 162 have in-plane magnetization, and the magnetization directions can be the same or different.

[0034] According to an embodiment of the present invention, the first pinning layer 111 and the second pinning layer 112 are made of the same material, which is selected from a combination of one or more of MnGa, MnAl, FePt, FePd, and CoTb.

[0035] The following uses MnGa as an example for the pinning layer. MnGa is a material with super strong PMA (Perpendicular Magnetic anisotropy). x Fe 1-x The interface coupling of the CoFe composition can be changed from ferromagnetic coupling FM to antiferromagnetic coupling AFM. The specific principle can be referred to Figure 3 When the Co atomic percentage is greater than 20%, it exhibits antiferromagnetic coupling, and when the Co atomic percentage is less than 20%, it exhibits ferromagnetic coupling.

[0036] Based on the above principle, the structure of the coupling transition layer 121 adopts any one of the following: Co, CoxFe1-x (x>20 at%), [Co / heavy metal]n multilayer film, and the heavy metal is one of Pt, Ni, and Pd. In some embodiments, a layer of Co can also be covered on the [Co / heavy metal]n multilayer film to improve its characteristics. The basic principle is that the layer in direct contact with the first pinned layer 111 is a magnetic layer with a high Co content. Under the action of the coupling transition layer 121, the first reference layer 141 and the first pinned layer 111 have opposite magnetization directions.

[0037] The first reference layer 141 and the second reference layer 142 are any of the following: x Fe 1-x (x<20at%) single layer, Co x Fe 1-x (x<20at%) / CoFe stack, [Co x Fe 1-x (x<20at%) / CoFeB]n multilayer films, [Fe / CoFeB]n multilayer films, [Co x Fe 1-x (x<20at%) / spacer layer / CoFeB]n multilayer film, wherein the spacer layer is one of Mo, W, and Ta.

[0038] The first barrier layer 151 and the second barrier layer 152 are made of one of MgO, MgAlO and Al2O3, and have a thickness of 1.0-2.0 nm.

[0039] The first free layer 161 and the second free layer 162 are any one of the following: CoFeB single layer, NiFe single layer, CoFeB / NiFe stacked layer.

[0040] A preferred embodiment is given, the first pinning layer 111 and the second pinning layer 112 are made of MnGa (10nm). The coupling transition layer 121 is made of [Co / Pt]4 multilayer film, that is, Co (0.3nm) / Pt (0.6nm) and repeated 4 times, preferably covered with Co (0.2-1nm) on the top, and the value in the bracket indicates the thickness.

[0041] The materials of the first reference layer 141 and the second reference layer 142 are sequentially grown materials such as Fe / CoFeB, wherein the Fe layer is close to MnGa, for example, Fe (0.5 nm) / CoFeB (1.0 nm) / Mo (0.2 nm) / CoFeB (1.0 nm).

[0042] The first barrier layer 151 and the second barrier layer 152 are made of MgO, and have a thickness between 1.0 and 2.0 nm.

[0043] The materials of the first free layer 161 and the second free layer 162 are CoFeB / NiFe, for example, CoFeB (2 nm) / NiFe (20 nm).

[0044] The single-substrate full-bridge TMR magnetic field sensor provided by the present invention is based on a MnGa series material system and introduces a coupling transition layer. Only one external magnetic field magnetization is required to obtain MTJ devices with two different magnetization directions, thereby simplifying the preparation process and reducing costs.

[0045] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A single substrate full-bridge TMR magnetic field sensor, characterized in that: include: Four groups of MTJ devices are connected to form a full-bridge structure, two groups of MTJ devices on a pair of opposite bridge arms are located in a first area of ​​the substrate, and two groups of MTJ devices on another pair of opposite bridge arms are located in a second area of ​​the substrate, wherein: The two groups of MTJ devices in the first region have a first stacking structure, wherein the first stacking structure includes a first pinned layer, a coupling transition layer, a first reference layer, a first barrier layer and a first free layer stacked sequentially from bottom to top; The two groups of MTJ devices in the second region have a second stacking structure, wherein the second stacking structure includes a second pinned layer, a second reference layer, a second barrier layer, and a second free layer stacked sequentially from bottom to top; The first pinned layer and the second pinned layer have perpendicular magnetization with the same magnetization direction, the coupling transition layer and the first reference layer both have perpendicular magnetization and the magnetization direction is opposite to the magnetization direction of the first pinned layer, the second reference layer has perpendicular magnetization and the magnetization direction is the same as the magnetization direction of the second pinned layer, and the first free layer and the second free layer have in-plane magnetization.

2. The single substrate full-bridge TMR magnetic field sensor according to claim 1, characterized in that: The first pinning layer and the second pinning layer are made of the same material, which is selected from a combination of one or more of MnGa, MnAl, FePt, FePd, and CoTb.

3. The single substrate full-bridge TMR magnetic field sensor according to claim 1, characterized in that: The structure of the coupling transition layer is any one of the following: Co, Co x Fe 1-x (x>20 at %), [Co / heavy metal]n multilayer film, the heavy metal is one of Pt, Ni, and Pd.

4. The single substrate full-bridge TMR magnetic field sensor according to claim 1, characterized in that: The first reference layer and the second reference layer have the same structure, and the structure is any one of the following: x Fe 1-x (x<20at%) single layer, Co x Fe 1-x (x<20at%) / CoFe stack, [Co x Fe 1-x (x<20at%) / CoFeB]n multilayer films, [Fe / CoFeB]n multilayer films, [Co x Fe 1-x (x<20at%) / spacer layer / CoFeB]n multilayer film, wherein the spacer layer is one of Mo, W, and Ta.

5. The single substrate full-bridge TMR magnetic field sensor according to claim 1, characterized in that: The first free layer and the second free layer have the same structure, and the structure is any one of the following: CoFeB single layer, NiFe single layer, CoFeB / NiFe stacked layer.

6. A method for preparing a single substrate full-bridge TMR magnetic field sensor, characterized in that: The method comprises: Providing a substrate, wherein a substrate is provided on the substrate, and a pinning layer film, a coupling transition layer film and a protective layer film are sequentially formed on the substrate; Performing graphic definition on the protective layer film to form a first area and a second area; removing the protective layer film and the coupling transition layer film in the second region; removing the protective film from the first region; Continue to deposit multiple MTJ films, including at least a reference layer film, a barrier layer film and a free layer film from bottom to top, covering the first region and the second region; forming an MTJ device having a first stacking structure in the first region and forming an MTJ device having a second stacking structure in the second region, wherein the first stacking structure comprises a first pinned layer, a coupling transition layer, a first reference layer, a first barrier layer and a first free layer stacked sequentially from bottom to top, and the second stacking structure comprises a second pinned layer, a second reference layer, a second barrier layer and a second free layer stacked sequentially from bottom to top; An external magnetic field is applied for initialization, so that the first pinned layer and the second pinned layer have perpendicular magnetization with the same magnetization direction, the coupling transition layer and the first reference layer have perpendicular magnetization and the magnetization direction is opposite to the magnetization direction of the first pinned layer, the second reference layer has perpendicular magnetization and the magnetization direction is the same as the magnetization direction of the second pinned layer, and the first free layer and the second free layer have in-plane magnetization.

7. The method according to claim 6, characterized in that After removing the protective film in the first area, the method further includes: Surface treatment using hydrogen plasma to remove the potential oxide layer on the surface.

8. The method according to claim 6, characterized in that The material of the pinning layer film is selected from one or more combinations of MnGa, MnAl, FePt, FePd, and CoTb.

9. The method according to claim 6, characterized in that The structure of the coupling transition layer film is any one of the following: Co, Co x Fe 1-x (x>20 at %), [Co / heavy metal]n multilayer film, the heavy metal is one of Pt, Ni, and Pd.

10. The method according to claim 6, characterized in that The protective layer film is a Ti film with a thickness of 1-3 nm.

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