A method for realizing a giant magnetoresistance linear sensor

Abstract

A method for realizing a giant magnetoresistance linear sensor belongs to the technical field of electronic materials and components. First, a conductive layer is prepared on the upper and lower surfaces of a piezoelectric substrate as an upper electrode and a lower electrode for applying voltage to the piezoelectric substrate; then, under an induced magnetic field, a thin film deposition process is used to sequentially deposit a first isolation layer, an antiferromagnetic layer, a second ferromagnetic layer, a second isolation layer, a first ferromagnetic layer and a protective layer on the surface of the upper electrode; finally, a voltage is applied to the upper and lower electrodes of the piezoelectric substrate to rotate the magnetic moment of the antiferromagnetic layer and drive the magnetic moment of the second ferromagnetic layer to rotate together, so that the magnetic moments of the first ferromagnetic layer and the second ferromagnetic layer present an angle, and the preparation of the giant magnetoresistance linear sensor is completed. The method for realizing a giant magnetoresistance linear sensor of the present invention has the advantages of simple structure, low process difficulty, and low power consumption.

Description

Technical Field

[0001] The present invention belongs to the technical field of electronic materials and components, and relates to magnetic sensing technology, specifically a method for controlling the antiferromagnetic magnetic moment based on strain to drive the change of the magnetic moment of the magnetic layer, and finally realizing a giant magnetoresistance linear sensor. Background Art

[0002] The giant magnetoresistance sensor is based on the giant magnetoresistance effect, which can be realized through the spin valve multilayer film structure. Its basic structure is ferromagnetic layer 1 (free layer) / isolation layer / ferromagnetic layer 2 (fixed layer) / antiferromagnetic layer / substrate. In this structure, different resistance changes can be obtained by regulating the orientation of the magnetic layer by an external magnetic field, so that the voltage response characteristics presented by different resistance values ​​can be used to detect the external magnetic field. Among them, under the action of the external field, the magnetic moment of the ferromagnetic layer 1 rotates with the external field, which is called the free layer; while the ferromagnetic layer 2 and the antiferromagnetic layer are coupled, and its magnetic moment is pinned in a certain direction by the antiferromagnetic layer. Only when the external field is greater than the pinning field between the antiferromagnetic layer and the ferromagnetic layer 2, the magnetic moment of the ferromagnetic layer 2 will rotate with the direction of the external field, so the ferromagnetic layer 2 is called the fixed layer. In the process of magnetic moment rotation, when the magnetic moments of the free layer and the fixed layer are parallel to each other, the entire spin valve structure presents a low resistance state, and when the magnetic moments of the free layer and the fixed layer are antiparallel to each other, the entire structure presents a high resistance state. In general, the magnetic moments of the ferromagnetic layer 1 and the ferromagnetic layer 2 are in the same direction (plane) under zero field, and the corresponding magnetoresistance curve is a step-type response curve. This form of response curve is generally used for magnetic storage. In the giant magnetoresistance linear sensor, in order to achieve effective detection of the induced signal, its giant magnetoresistance response curve is required to show a linear response to the change of the external magnetic field. To achieve this requirement, the magnetic moments of the free layer and the fixed layer in the spin valve giant magnetoresistance structure should have a certain angle under zero field, and as the angle increases to 90 degrees, the optimal linear detection range will be obtained in the giant magnetoresistance sensor. However, in the general spin valve structure deposited by magnetron sputtering, the magnetic moments of the free layer and the fixed layer are parallel to each other under zero field. In order to achieve the optimal orientation of 90 degrees, it is usually achieved by permanent magnet bias, special circuit to generate magnetic field bias, and depositing the free layer and the fixed layer separately under mutually perpendicular magnetic fields. However, from the above methods, no matter which method is used, the same problem is involved, that is, the additional process treatment and bias structure preparation brought by the deposition method, which greatly increases the process difficulty and the size problem of the bias structure parameters, making it impossible to miniaturize and micronize the device. Therefore, if a certain method can be used to make the angle between the magnetic moments of the free layer and the fixed layer in the spin valve a certain angle after the giant magnetoresistance film is prepared according to the usual preparation method, then the difficulty of preparing the linear magnetoresistance sensor will be greatly reduced, and it will be helpful to the development of linear magnetic sensors. The present invention is to solve this demand. Summary of the invention

[0003] The purpose of the present invention is to propose a method for realizing a giant magnetoresistance linear sensor in view of the defects of the background technology. The giant magnetoresistance linear sensor of the present invention introduces stress through strain material to change the magnetic moment orientation of the antiferromagnetic layer in the giant magnetoresistance film. Due to the coupling between the antiferromagnetic layer and the second ferromagnetic layer, the magnetic moment direction of the second ferromagnetic layer also rotates accordingly, so that the magnetic moments of the first ferromagnetic layer and the second ferromagnetic layer will present a certain angle, and the giant magnetoresistance effect linear sensor can be realized; when the applied stress is large enough, the magnetic moment direction of the second ferromagnetic layer can be rotated to be perpendicular to the initial direction, and the magnetic moments of the first ferromagnetic layer and the second ferromagnetic layer can present 90 degrees at zero field, realizing the optimal linear detection range of the giant magnetoresistance effect linear sensor.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] A method for realizing a giant magnetoresistance linear sensor, characterized in that it comprises the following steps:

[0006] Step 1, using a piezoelectric substrate as a substrate of a giant magnetoresistance linear sensor, preparing conductive layers on the upper and lower surfaces of the piezoelectric substrate as upper and lower electrodes for applying voltage to the piezoelectric substrate, and obtaining a piezoelectric substrate 1 with upper and lower electrodes;

[0007] Step 2, under an induced magnetic field H, a first isolation layer 2, an antiferromagnetic layer 3, a second ferromagnetic layer 4, a second isolation layer 5 and a first ferromagnetic layer 6 are sequentially deposited on the surface of the upper electrode by a thin film deposition process to obtain a giant magnetoresistance thin film layer consisting of the first isolation layer 2 / antiferromagnetic layer 3 / second ferromagnetic layer 4 / second isolation layer 5 / first ferromagnetic layer 6;

[0008] Step 3, depositing a protective layer on the first ferromagnetic layer 6 obtained in step 2;

[0009] Step 4: Apply voltage to the upper and lower electrodes of the piezoelectric substrate to rotate the magnetic moment of the antiferromagnetic layer and drive the magnetic moment of the second ferromagnetic layer to rotate together, so that the magnetic moments of the first ferromagnetic layer and the second ferromagnetic layer present a certain angle, completing the preparation of the giant magnetoresistance linear sensor.

[0010] Furthermore, the piezoelectric substrate in step 1 is made of materials such as PMN-PT (lead magnesium niobate-lead titanate) and PZN-PT (lead zinc niobate-lead titanate) with a thickness of 0.2 to 0.8 mm; the electrode materials of the upper electrode and the lower electrode are Cu, Ag, Au, etc.

[0011] Furthermore, in step 2, the first ferromagnetic layer and the second ferromagnetic layer are materials with a non-zero magnetostriction coefficient or materials with a magnetostriction coefficient of zero. The materials with a non-zero magnetostriction coefficient can be selected from Ni, Fe, Co, Ni alloy, Fe alloy, Co alloy, etc., and the materials with a magnetostriction coefficient of zero can be selected from Ni 77 Fe 23 etc.; the thickness of the first ferromagnetic layer is 12 to 15 nm, and the thickness of the second ferromagnetic layer is 8 to 15 nm.

[0012] Furthermore, in step 2, the first isolation layer and the second isolation layer are made of non-magnetic metals such as Cu and Ta; and the thickness of the second isolation layer is 1.8 to 5 nm.

[0013] Furthermore, the function of the first isolation layer is to ensure that the stress is only transmitted to the antiferromagnetic layer and does not reach the second ferromagnetic layer, so as not to cause the change of the magnetic moment of the second ferromagnetic layer. Therefore, when the first ferromagnetic layer and the second ferromagnetic layer are made of materials with a magnetostriction coefficient of 0, the first isolation layer can be removed;

[0014] When the first ferromagnetic layer and the second ferromagnetic layer are materials with a magnetostriction coefficient not equal to 0, the thickness of the first isolation layer should be thick enough to ensure that the stress is only transferred to the antiferromagnetic layer and does not reach the second ferromagnetic layer. 80 Fe 20 When the thickness of the first isolation layer is 105nm; when the first ferromagnetic layer and the second ferromagnetic layer are Ni 80 Co 20 When , the thickness of the first isolation layer is 230nm.

[0015] Furthermore, the antiferromagnetic layer in step 2 is made of antiferromagnetic materials such as IrMn, RhMn, NiO, FeMn, etc., and has a thickness of 10 to 15 nm.

[0016] Furthermore, the protective layer in step 3 is a non-magnetic metal such as Ta, and has a thickness of 5 to 10 nm.

[0017] Furthermore, in step 4, a voltage of 10 kV / cm is applied to the upper and lower electrodes of the piezoelectric substrate, so that the magnetic moments of the first ferromagnetic layer and the second ferromagnetic layer are 90 degrees.

[0018] The present invention provides a method for realizing a giant magnetoresistance linear sensor, the principle of which is as follows:

[0019] In the giant magnetoresistance composite film prepared in step 3 of the present invention, the magnetic moments of the first ferromagnetic layer and the second ferromagnetic layer are parallel when the test magnetic field is zero. In order to achieve the requirements of the linear giant magnetoresistance sensor for the orientation of the magnetic moments of the two layers (the magnetic moments of the first ferromagnetic layer and the second ferromagnetic layer are at a certain angle), in step 4 of the present invention, a voltage is applied to the upper electrode and the lower electrode of the piezoelectric substrate, and a stress is generated along the crystal axis direction of the piezoelectric substrate. At this time, if the antiferromagnetic material selected has a hysteresis expansion coefficient λ s is positive, then during the film deposition process, an induced magnetic field needs to be applied along the long axis direction of the piezoelectric substrate, so that the initial orientation of the exchange bias field, the magnetic moment of the second ferromagnetic layer, and the magnetic moment of the first ferromagnetic layer are all along the long axis direction of the piezoelectric substrate. Under the action of the stress of the piezoelectric substrate, the antiferromagnetic material will produce negative strain, causing the magnetic moment of the antiferromagnetic layer to rotate, thereby driving the magnetic moment of the second ferromagnetic layer to rotate, while the magnetic moment of the first ferromagnetic layer does not rotate, so that the magnetic moments of the first ferromagnetic layer and the second ferromagnetic layer will present a certain angle. When the applied stress is large enough (10kV / cm), the magnetic moment of the second ferromagnetic layer can rotate to the short axis direction of the piezoelectric substrate, and the magnetic moments of the first ferromagnetic layer and the second ferromagnetic layer are 90 degrees. If the antiferromagnetic material magnetohysteresis stretching coefficient λ is selected s If the magnetic field is negative, an induced magnetic field needs to be applied along the short axis direction of the piezoelectric substrate during the film deposition process, so that the initial orientation of the exchange bias field, the magnetic moment of the second ferromagnetic layer, and the magnetic moment orientation of the first ferromagnetic layer are all along the short axis direction of the piezoelectric substrate. Under the action of the stress of the piezoelectric substrate, the antiferromagnetic material will produce positive strain, causing the magnetic moment of the antiferromagnetic layer to rotate, thereby driving the magnetic moment of the second ferromagnetic layer to rotate, and the magnetic moments of the first ferromagnetic layer and the second ferromagnetic layer will present a certain angle. When the applied stress is large enough (applying a voltage of about 10kV / cm), the magnetic moment of the second ferromagnetic layer can be rotated to the long axis direction of the piezoelectric substrate, and the magnetic moments of the first ferromagnetic layer and the second ferromagnetic layer are 90 degrees. Therefore, using this method, after the giant magnetoresistance film is prepared (the magnetic moments of the first ferromagnetic layer and the second ferromagnetic layer are parallel under zero field), the magnetic moment of the antiferromagnetic layer can be regulated by voltage to achieve 90 degrees between the first ferromagnetic layer and the second ferromagnetic layer in the absence of an external magnetic field, thereby achieving the optimal linear detection range of the giant magnetoresistance effect linear sensor.

[0020] The beneficial effects of the present invention are:

[0021] The present invention provides a method for realizing a giant magnetoresistance linear sensor, which uses a piezoelectric substrate as a substrate substrate, obtains stress by applying voltage on the piezoelectric substrate, and under the action of the stress, the antiferromagnetic material will produce strain to rotate the magnetic moment of the antiferromagnetic layer, thereby driving the magnetic moment of the second ferromagnetic layer to rotate, so that the magnetic moments of the first ferromagnetic layer and the second ferromagnetic layer present a certain angle, and no additional energy loss will be generated in the process, and the power consumption is low; in addition, since the regulating stress only acts on the antiferromagnetic layer, the antiferromagnetic layer drives the magnetic moment of the second ferromagnetic layer to rotate through coupling, the magnetostriction coefficient of the ferromagnetic layer material and the presence or absence of magnetostriction effect will not affect the rotation angle of the magnetic moment, thereby expanding the range of magnetic materials of the giant magnetoresistance sensor. Therefore, the method for realizing a giant magnetoresistance linear sensor of the present invention has the advantages of simple structure, low process difficulty, and low power consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The schematic diagram of the structure of the giant magnetoresistance linear sensor provided by the present invention. 1 is a piezoelectric substrate with upper and lower electrodes, 2 is a first isolation layer, 3 is an antiferromagnetic layer, 4 is a second ferromagnetic layer, 5 is a second isolation layer, 6 is a first ferromagnetic layer, and 7 is a protective layer;

[0023] Figure 2 This is the magnetoresistance response curve of the giant magnetoresistance film obtained in the embodiment.

[0024] Figure 3 The giant magnetoresistance film obtained in the embodiment is a magnetoresistance linear response curve finally obtained by regulating the magnetic moment of the antiferromagnetic layer under the application of different voltages. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0026] Example

[0027] A method for realizing a giant magnetoresistance linear sensor, characterized in that it comprises the following steps:

[0028] Step 1, a conventional PMN-PT (011) piezoelectric substrate with a thickness of 0.5 mm is selected as the substrate of the giant magnetoresistance linear sensor, and Au (300 nm) is deposited on the upper and lower surfaces of the substrate by a vacuum coating process as the upper and lower electrodes for applying voltage to the substrate, thereby obtaining a piezoelectric substrate 1 with upper and lower electrodes;

[0029] Step 2: Place the piezoelectric substrate with upper and lower electrodes obtained in step 1 in a magnetron sputtering device, and deposit Cu (105 nm) / IrMn (15 nm) / Ni on the upper electrode surface of the PMN-PT substrate in sequence using a thin film deposition process. 80 Fe 20 (8nm) / Cu(3nm) / Ni80 Fe 20 The top layer of Ta (5nm) is used as a protective layer to protect the entire structure from oxidation. The role of 105nm Cu is to ensure that the stress is transferred to the antiferromagnetic IrMn layer without acting on the Ni 80 Fe 20 (8nm) ferromagnetic layer. Due to the hysteresis coefficient λ of the antiferromagnetic IrMn layer s is positive, and an induced magnetic field H needs to be applied along the long axis direction of the piezoelectric substrate (along the

[001] axis of PMN-PT, i.e., the x direction) during the film deposition process;

[0030] Step 3: After the preparation is completed, the giant magnetoresistance film is tested by the standard four-probe method. The magnetoresistance response curve is as follows: Figure 2 As shown, it presents a step-like shape, which shows that the prepared giant magnetoresistance film cannot be directly used for linear sensing;

[0031] Step 4: Apply a voltage of +4 to +10 kV / cm to the PMN-PT substrate through the upper electrode and the lower electrode to generate stress of corresponding magnitude. This stress acts on the magnetic moment of the antiferromagnetic layer, causing its magnetic moment to deviate from the original

[001] direction (x direction) and turn to the [1-10] direction (y direction) in the absence of an external magnetic field. Due to the interfacial coupling between the antiferromagnetic layer and the second ferromagnetic layer, the magnetic moment of the second ferromagnetic layer rotates to the same direction as the antiferromagnetic magnetic moment, forming a certain angle with the magnetic moment orientation of the first ferromagnetic layer. The magnitude of the stress generated by the piezoelectric material determines the angle of rotation of the antiferromagnetic magnetic moment. When the stress is maximum (10 kV / cm), the prepared giant magnetoresistance film can achieve linear optimal detection function, such as Figure 3 shown.

Claims

1. A method for realizing a giant magnetoresistance linear sensor, characterized in that: The following steps are involved: Step 1: Using a piezoelectric substrate as a substrate of a giant magnetoresistance linear sensor, preparing conductive layers on the upper and lower surfaces of the piezoelectric substrate as upper and lower electrodes for applying voltage to the piezoelectric substrate, thereby obtaining a piezoelectric substrate with upper and lower electrodes; Step 2, under an induced magnetic field, a first isolation layer, an antiferromagnetic layer, a second ferromagnetic layer, a second isolation layer and a first ferromagnetic layer are sequentially deposited on the surface of the upper electrode by a thin film deposition process; Step 3, depositing a protective layer on the first ferromagnetic layer obtained in step 2; Step 4, applying voltage to the upper and lower electrodes of the piezoelectric substrate to rotate the magnetic moment of the antiferromagnetic layer and drive the magnetic moment of the second ferromagnetic layer to rotate together, so that the magnetic moments of the first ferromagnetic layer and the second ferromagnetic layer present an angle, and the preparation of the giant magnetoresistance linear sensor is completed; The first ferromagnetic layer and the second ferromagnetic layer are materials with a non-zero magnetostriction coefficient or materials with a magnetostriction coefficient of zero; when the first ferromagnetic layer and the second ferromagnetic layer are materials with a magnetostriction coefficient of zero, the first isolation layer is removed; when the first ferromagnetic layer and the second ferromagnetic layer are materials with a magnetostriction coefficient of non-zero, the thickness of the first isolation layer needs to ensure that the stress is transferred to the antiferromagnetic layer without reaching the second ferromagnetic layer.

2. The method for realizing a giant magnetoresistance linear sensor according to claim 1, characterized in that: The piezoelectric substrate in step 1 is PMN-PT or PZN-PT with a thickness of 0.2-0.8 mm.

3. The method for realizing a giant magnetoresistance linear sensor according to claim 1, characterized in that: The thickness of the first ferromagnetic layer is 12-15 nm, and the thickness of the second ferromagnetic layer is 8-15 nm.

4. The method for realizing a giant magnetoresistance linear sensor according to claim 1, characterized in that: Step 2: The first isolation layer and the second isolation layer are Cu and Ta.

5. The method for realizing a giant magnetoresistance linear sensor according to claim 1, characterized in that: The antiferromagnetic layer in step 2 is IrMn, RhMn, NiO, FeMn, and has a thickness of 10-15 nm.

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