CN115623857A - A Magnetoresistance Sensor with Adjustable Linear Region - Google Patents

Abstract

The invention belongs to the technical field of magnetic sensing, in particular to a magnetoresistance sensor with adjustable linear range. In the present invention, the strained material is used instead of the silicon substrate as the substrate, and the stress is obtained by applying a voltage to the piezoelectric substrate. The stress acts on the ferromagnetic layer 1, and the in-plane equivalent field is generated by the magnetostrictive effect, and the stress is The size can change the size of the equivalent field, thereby changing the magnetization flip state of the ferromagnetic layer 1, and adjusting the anisotropy field of the ferromagnetic layer through stress, so as to realize the on-demand adjustment of the linear area of the magnetic sensing unit, and the adjustment range is tens of ‑Larger intervals of several hundred. The invention does not change the film layer structure of the original sensor unit but only changes the base layer, and has the advantages of simple structure, low process difficulty, low power consumption, etc., and further expands the range of the original linear region by introducing the inverse magnetoelectric coupling effect The linear region provides an effective method and way to realize the wide field range application of the linear sensor.

Description

A Magnetoresistance Sensor with Adjustable Linear Region

technical field

The invention belongs to the technical field of electronic materials and components, and relates to magnetic sensing technology, in particular to a magnetoresistance sensor with an adjustable linear region, which utilizes an inverse magnetoelectric coupling effect to realize electric field regulation of the linear region of the magnetoresistance sensor.

Background technique

Magneto-resistive sensors are widely used in the detection fields of magnetic field, current, position, speed, angle, etc. due to their advantages of easy integration and low manufacturing cost. In applications in these fields, the detection mechanism is based on the test of magnetoresistance, and then converted into corresponding physical quantities such as magnetic field, current, distance, speed, etc., to realize the detection of different physical parameters.

Among them, spin valve giant magnetoresistance and tunnel junction magnetoresistance have the advantages of large magnetoresistance effect, sensitive response to magnetic field, and wide working range, and are the main core structures used in magnetoresistive sensors at present. The spin valve giant magnetoresistance structure is generally ferromagnetic layer 1/metal isolation layer/ferromagnetic layer 2/ultra-thin metal layer/ferromagnetic layer 3/antiferromagnetic layer, and the tunnel junction magnetoresistance structure is generally ferromagnetic layer 1/ Oxide barrier layer/ferromagnetic layer 2/ultra-thin metal layer/ferromagnetic layer 3/antiferromagnetic layer. Among them, the ferromagnetic layer 2/ultra-thin metal layer/ferromagnetic layer 3/antiferromagnetic layer structure is an artificial antiferromagnetic pinning structure, so that the magnetic moment of the ferromagnetic layer 2 does not rotate with the external magnetic field, also known as a fixed layer, The magnetic moment of the ferromagnetic layer 1 can rotate under the action of an external field, which is called the free layer and is the detection layer in the sensor.

At present, in practical sensors based on linear giant magnetoresistance thin films, it is required that the magnetoresistance value of the giant/tunnel magnetoresistance has a linear response to the change of the detected magnetic field. To achieve this purpose, the magnetic moments of the pinned layer (ferromagnetic layer 2) and the free layer (ferromagnetic layer 1) in the magnetoresistive film need to be perpendicular to each other under zero field, and the detection magnetic field is along the orientation of the magnetic moment in the pinned layer. Taking magnetic field detection as an example (the detection of other physical parameters, such as current, distance, angle, etc., can be converted into the detection of magnetic field), it is necessary to first obtain the linear magnetoresistance of the giant/tunnel magnetoresistance film changing with the external magnetic field Curve, and then compare the change value of the magnetoresistance under a certain magnetic field to obtain the corresponding detection value. In order to achieve a 90-degree magnetic moment of the free layer and the fixed layer, the commonly used methods are: depositing the free layer and the fixed layer respectively under mutually perpendicular magnetic fields, or annealing under an external magnetic field after the film is prepared, thereby changing the magnetic moment of the free layer direction. When applied, the test magnetic field is along the direction of the magnetic moment of the pinned layer and perpendicular to the magnetic moment of the free layer. When the test magnetic field is smaller than the exchange bias field of the artificial antiferromagnetic structure, the magnetic moment in the fixed layer will not be affected by the external magnetic field. According to the principle of giant/tunnel magnetoresistance, the change of the magnetoresistance value depends on the two magnetic layers The change of the relative angle between the free layer and the fixed layer. Since the initial magnetic moment orientation of the free layer is perpendicular to the test magnetic field, the magnetic moment of the free layer will respond linearly to the test magnetic field under the action of an external field. At this time, the free layer and the fixed layer The relative angle between the magnetic moments will also change linearly with the change of the free layer magnetic moment, and finally a linearized magnetoresistance response curve is obtained.

At present, for this type of linear magnetoresistive sensor, its linear detection area is determined by the linear area of the free layer changing with the external magnetic field, and the size of this area is proportional to the size of the free layer anisotropy field Hk. When the free layer anisotropy field The larger Hk is, the wider the linear detection range of this type of linear magnetoresistive sensor is.

In order to adjust the linear region of the magnetoresistive sensor, the existing technology is generally realized by changing the material, thickness, shape, and post-treatment of the magnetic field annealing of the free layer, and the realized linear region is generally within a hundred Oe. But when the linear region of the linear magnetoresistive sensor is fixed after the film preparation process is completed, it cannot be changed. However, if the anisotropy field Hk of the free layer can be changed by a certain method after the preparation process of the linear magnetoresistance multilayer film is completed, the change of the linear response curve of the magnetoresistance can be realized, so different linearity can be realized in the same sample. The adjustment of the detection area of the sensor will help to improve the flexibility of the use of the magnetoresistive sensor and expand its scope of application.

Contents of the invention

In view of the above problems or deficiencies, in order to improve the flexibility of the existing magnetoresistance sensor and expand its scope of application, the present invention provides a magnetoresistance sensor with adjustable linear region, which is prepared on the strained material. After the preparation is completed, Stress is introduced through the strained material, and the magnetostrictive effect of the ferromagnetic layer is used to change the anisotropy field Hk of the free layer, thereby realizing the linear sensing range modulation of the magnetoresistive sensor.

The technical purpose of the present invention is achieved through the following technical solutions:

A magnetoresistance sensor with adjustable linear area, including a substrate, a magnetoresistance film and a protective layer.

The substrate is a piezoelectric substrate, and its upper and lower surfaces are respectively provided with a top electrode and a bottom electrode.

The magnetoresistance film is arranged on the piezoelectric substrate, and the magnetoresistance film is ferromagnetic layer 1/nonmagnetic layer/ferromagnetic layer 2/ultra-thin metal layer/ferromagnetic layer 3/antiferromagnetic layer in sequence from bottom to top.

The ferromagnetic layer 1 is a free layer, and the material is a ferromagnetic material (such as Co, CoFe or CoFeB) with a magnetostriction coefficient greater than 10 ppm. The ferromagnetic layer 2/ultra-thin metal layer/ferromagnetic layer 3/antiferromagnetic layer constitutes an artificial antiferromagnetic pinning structure, and the ferromagnetic layer 2 is a fixed layer. The magnetic moments of the free layer and the pinned layer are oriented at 90 degrees at zero field. The nonmagnetic layer is a metal isolation layer or an oxide barrier layer.

The protective layer is disposed on the antiferromagnetic layer and completely covers the antiferromagnetic layer to protect the entire structure from being oxidized.

Further, the material of the piezoelectric substrate is PMN-PT or PZN-PT.

Further, the non-magnetic layer is a Cu metal isolation layer, which constitutes a spin-valve magnetoresistance film.

Further, the non-magnetic layer is an oxide barrier layer of Al ₂ O ₃ and MgO, forming a tunnel junction magnetoresistance film.

Further, a buffer layer is provided between the piezoelectric substrate and the magnetoresistance film to improve the roughness of the piezoelectric substrate, thereby improving the performance of the magnetoresistance film.

Further, the linear region modulation method of the above-mentioned magnetoresistive sensor with adjustable linear region is:

A voltage is applied to the top and bottom electrodes of the piezoelectric substrate. When the applied voltage is less than E _C ( _EC is the electric coercive field of the piezoelectric substrate), the piezoelectric substrate will generate a normal stress. When the applied voltage is greater than At E _C , the piezoelectric substrate produces negative stress. The stress is transmitted to the ferromagnetic layer 1 (free layer) with a larger magnetostriction coefficient. Due to the magnetostrictive effect of the magnetic material, an equivalent field will be generated in the plane of the ferromagnetic layer 1, while the ferromagnetic layer 2 There is a strong exchange coupling effect between the (fixed layer) and the antiferromagnetic layer, and the ferromagnetic layer 2 will not be affected by the equivalent field. The direction of the equivalent field depends on the positive and negative of the stress generated by the piezoelectric substrate and the positive and negative of the magnetostriction coefficient of the ferromagnetic layer 1 .

If the magnetostriction coefficient of the material selected for ferromagnetic layer 1 is positive, the x direction of the film surface is parallel to the crystal axis direction of the negative (positive) stress generated by the piezoelectric substrate under the action of the electric field, and the y direction is parallel to the direction of the positive (negative) stress generated by the piezoelectric substrate. According to the inverse magnetoelectric coupling mechanism, the direction of the equivalent field generated in the plane is the y(x) direction, which will increase (decrease) the anisotropy field Hk of the ferromagnetic layer 1, thereby making the magnetoresistance The linear region of the film becomes larger (smaller).

And if the magnetostriction coefficient of the material selected for ferromagnetic layer 1 is negative, the x direction of the film surface is parallel to the crystal axis direction of the piezoelectric substrate that produces negative (positive) stress under the action of an electric field, and the y direction is parallel to the crystal axis direction that produces positive (negative) stress. The direction of the crystal axis of the stress, according to the reverse magnetoelectric coupling mechanism, the direction of the equivalent field generated in the plane is the x (y) direction, which will reduce (increase) the anisotropy field Hk of the ferromagnetic layer 1, which can be adjusted The linear region of the magnetoresistive thin film becomes smaller (larger).

Furthermore, after the linear (magnetic moments of ferromagnetic layer 1 and ferromagnetic layer 2 are vertical under zero field) magnetoresistive multilayer film is prepared, the stress is introduced through the action of the electric field on the piezoelectric substrate, thereby obtaining an equivalent field to control the iron The anisotropy field Hk of the magnetic layer 1 to meet the requirement that the linear region of the magnetoresistive sensor be increased or decreased in the same sample.

The present invention regulates the anisotropic field of the ferromagnetic layer through stress to realize the regulation and control of the linear region of the magnetoresistance sensor: a strained material is used to replace the silicon substrate as the substrate substrate, and a certain stress is obtained by applying a voltage, and the stress acts on the ferromagnetic layer. In the magnetic layer 1, the in-plane equivalent field is generated by the magnetostrictive effect, and the magnitude of the stress can change the magnitude of the equivalent field, thereby changing the magnetization flip state of the ferromagnetic layer 1, and realizing the on-demand regulation of the linear region of the magnetic sensing unit. In this process, no additional energy loss will be generated, which is a way to realize the regulation of the linear sensing area of giant magnetoresistance with low power consumption.

In summary, the present invention does not change the film layer structure of the original sensor unit but only changes the base layer, which has the advantages of simple structure, low process difficulty, and low power consumption. On the basis of further extending the linear region, it provides an effective method and way to realize the wide field range application of linear sensors.

Description of drawings

Fig. 1 is a structural schematic diagram of the embodiment.

Fig. 2 is the magnetoresistance response curve of the example with increasing linear region after voltage is applied.

Fig. 3 is the magnetoresistance response curve of the embodiment with decreasing linear region after voltage application.

Description of the drawings: 1-piezoelectric substrate, 2-buffer layer, 3-ferromagnetic layer 1, 4-metal isolation layer, 5-ferromagnetic layer 2, 6-ultra-thin metal layer, 7-ferromagnetic layer 3, 8-antiferromagnetic layer, 9-protective layer.

detailed description

The technical solution of the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

A magnetoresistance sensor with adjustable linear region, comprising a substrate, a magnetoresistance film and a protective layer, the preparation method is as follows:

Step 1, select the PMN-PT (011) piezoelectric material with voltage adjustable positive and negative strain as the substrate, when the applied voltage is greater than the electric coercive field E _C (1.8kV/cm) of the piezoelectric substrate A negative strain is produced, and a positive strain is produced when the applied voltage is less than E _C . Au (300nm) is respectively deposited on the upper and lower surfaces of the substrate by a vacuum coating process as the top electrode and the bottom electrode for applying voltage to the substrate.

Step 2, the substrate obtained in step 1 is sequentially deposited on the substrate by a thin film deposition process to obtain a spin-valve giant magnetoresistance film, and the structure is PMN-PT/Ta(5nm)/CoFe(12nm)/Cu(3nm)/CoFe (3nm)/Ru(0.8nm)/CoFe(3nm)/IrMn(15nm)/Ta(5nm).

Among them, the bottom Ta (5nm) is used as a buffer layer, and the top Ta (5nm) is used as a covering layer to protect the entire structure from oxidation. The magnetostriction coefficient of CoFe (12nm) ferromagnetic layer 1 is positive, and the [001] axis of the selected PMN-PT of the present embodiment can produce negative strain under the effect of large voltage, can produce positive strain under the effect of small voltage. Strain, the induced magnetic field H is applied along the [001] axis (that is, the x direction) of the PMN-PT during the film deposition process.

Step 3. After the thin film is prepared, vacuum annealing is performed, and an induced magnetic field is applied along the [1-10] axis (y direction) of the PMN-PT, so that the magnetic moment of the ferromagnetic layer 1 turns to the y direction.

During the preparation process, the magnetic moments of the free layer and the fixed layer are oriented at 90 degrees. Two common methods are as follows:

(1) Add an induced magnetic field H along the x direction of the film surface during the film preparation process to induce the exchange bias of the artificial antiferromagnetic structure, then rotate the substrate, and apply the induced magnetic field along the film surface when depositing the ferromagnetic layer 1 The y direction is used to induce the magnetic moment orientation of the ferromagnetic layer 1 .

(2) During the film deposition process, an induced magnetic field H is applied along the x direction of the film surface. After the film is prepared, the sample is placed under a vacuum magnetic field for annealing. During annealing, a magnetic field is applied along the y direction of the film surface to induce ferromagnetism. The magnetic moment of layer 1 turns to the y direction, while the ferromagnetic layer in the artificial antiferromagnetic structure remains unchanged under the pinning effect of the exchange bias field, so that the magnetic moment of ferromagnetic layer 1 and the magnetic moment of ferromagnetic layer 2 will be perpendicular to each other.

This embodiment adopts the second method. After the annealing is completed, the spin-valve giant magnetoresistance film prepared is tested by the standard four-probe method. The test magnetic field is along the x direction, and the magnetoresistance curve is as shown in Figure 2. As shown in cm, the linear region is determined by the anisotropy field induced by the magnetic field of the ferromagnetic layer 1, and the linear region is relatively small.

Step 4. Apply a voltage of -4 to -10kV/cm to the PMN-PT substrate through the top electrode and the bottom electrode, thereby generating a corresponding negative stress, which is transmitted to the ferromagnetic layer 1, because the magnetostriction of the magnetic material The effect produces an equivalent field along the y direction of the film surface, so that the anisotropy field of the ferromagnetic layer 1 increases. The magnitude of the stress generated by the applied voltage determines the size of the equivalent field, thereby realizing the regulation of the size of the linear region of the magnetoresistive sensor. The corresponding linear magnetoresistance curve under the control of the electric field is shown in Figure 2.

Step 5. Apply a voltage of +0.5 to +1.5kV/cm to the PMN-PT substrate through the top electrode and the bottom electrode, thereby generating a corresponding normal stress, which is transmitted to the ferromagnetic layer 1, because the magnetostriction of the magnetic material The effect is also positive, so the equivalent field generated will be along the x direction of the film surface, so that the anisotropy field Hk of the ferromagnetic layer 1 in the prepared state is reduced, and the reduction is realized in the control linear region, as shown in Figure 3 . It should be noted that when the equivalent field increases so that the magnetic moment of ferromagnetic layer 1 turns to the x direction and is no longer perpendicular to the magnetic moment of ferromagnetic layer 2 under zero magnetic field, the magnetoresistance curve does not show a linear response, as shown in Figure 3 The magnetoresistance response curve corresponding to +1.5kV. The linear magnetoresistance curve under electric field regulation is shown in Fig. 3 .

It can be seen from the above embodiments that the present invention uses a strained material instead of a silicon substrate as a substrate, and obtains a certain stress by applying a voltage. The stress acts on the ferromagnetic layer 1, and the in-plane equivalent field is generated by the magnetostrictive effect, and The size of the stress can change the size of the equivalent field, thereby changing the magnetization switching state of the ferromagnetic layer 1, and realizing the on-demand regulation of the linear region of the magnetic sensing unit, and the regulation range is a large interval of tens to hundreds (Fig. 2, Figure 3), far beyond the prior art.

The invention regulates the anisotropy field of the ferromagnetic layer through stress, effectively realizes the regulation and control of the linear region of the magnetoresistance sensor, and is a technical scheme for realizing regulation and regulation of the giant magnetoresistance linear sensing region with low power consumption. Moreover, the present invention does not change the film layer structure of the original sensor unit but only changes the base layer, which has the advantages of simple structure, low process difficulty, and low power consumption. The application of wide field range provides an effective method and way.

Claims (7)

1. A magnetoresistive sensor adjustable in a linear region, characterized in that: comprising a substrate, a magnetoresistance film and a protective layer; The substrate is a piezoelectric substrate, and its upper and lower surfaces are respectively provided with a top electrode and a bottom electrode; The magnetoresistance film is arranged on the piezoelectric substrate, and the magnetoresistance film is ferromagnetic layer 1/nonmagnetic layer/ferromagnetic layer 2/ultra-thin metal layer/ferromagnetic layer 3/antiferromagnetic layer from bottom to top; Ferromagnetic layer 1 is a free layer, and the material adopts a ferromagnetic material with a magnetostriction coefficient greater than 10ppm; ferromagnetic layer 2/ultra-thin metal layer/ferromagnetic layer 3/antiferromagnetic layer constitutes an artificial antiferromagnetic pinning structure, and the iron The magnetic layer 2 is a fixed layer; the magnetic moments of the free layer and the fixed layer are 90-degree orientation at zero field; the non-magnetic layer is a metal isolation layer or an oxide barrier layer; The protective layer is disposed on the antiferromagnetic layer and completely covers the antiferromagnetic layer to protect the entire structure from being oxidized. 2 . The magnetoresistive sensor with adjustable linear range according to claim 1 , wherein the material of the ferromagnetic layer 1 is Co, CoFe or CoFeB. 3. The magnetoresistive sensor with adjustable linear range as claimed in claim 1, characterized in that: the material of the piezoelectric substrate is PMN-PT or PZN-PT. 4 . The magnetoresistive sensor with adjustable linear range as claimed in claim 1 , wherein the non-magnetic layer is a Cu metal isolation layer, which constitutes a spin valve magnetoresistive film. 5 . The magnetoresistance sensor with adjustable linear range as claimed in claim 1 , wherein the non-magnetic layer is an oxide barrier layer of Al ₂ O ₃ and MgO, forming a tunnel junction magnetoresistance film. 5 . 6. The magnetoresistive sensor with adjustable linear range as claimed in claim 1, characterized in that: a buffer layer is also arranged between the piezoelectric substrate and the magnetoresistance film to improve the roughness of the piezoelectric substrate, thereby Improving the performance of magnetoresistive thin films. 7. The magnetoresistive sensor with adjustable linear range as claimed in claim 1, is characterized in that, its linear range modulation method is: Apply voltage to the top electrode and bottom electrode of the piezoelectric substrate to make the piezoelectric substrate generate positive/negative stress. When the applied voltage is less than E _C , E _C is the electric coercive field of the piezoelectric substrate, and the piezoelectric substrate The sheet will generate positive stress, and when the applied voltage is greater than E _C , the piezoelectric substrate will generate negative stress; the stress is transmitted to the ferromagnetic layer 1, and due to the magnetostrictive effect of the magnetic material, a ferromagnetic layer 1 will generate a Equivalent field, thereby changing the anisotropy field Hk of the ferromagnetic layer 1; If the magnetostriction coefficient of the material selected for the ferromagnetic layer 1 is positive, the x direction of the film surface is parallel to the crystal axis direction of the negative/positive stress of the piezoelectric substrate under the action of the electric field, and the y direction is parallel to the crystal axis direction of the positive/negative stress. axis direction, according to the reverse magnetoelectric coupling mechanism, the direction of the equivalent field generated in the plane is the y/x direction, which will increase/decrease the anisotropy field Hk of the ferromagnetic layer 1, so that the linear region of the magnetoresistance film get bigger/smaller; If the magnetostriction coefficient of the material selected for the ferromagnetic layer 1 is negative, the x direction of the film surface is parallel to the crystal axis direction of the negative/positive stress of the piezoelectric substrate under the action of the electric field, and the y direction is parallel to the crystal axis direction of the positive/negative stress. In the axial direction, according to the reverse magnetoelectric coupling mechanism, the direction of the equivalent field generated in the plane is the x/y direction, which will reduce/increase the anisotropy field Hk of the ferromagnetic layer 1, and realize the control of the linear region of the magnetoresistance film get smaller/bigger; Furthermore, after the preparation of the tunable magnetoresistive sensor in the linear region is completed, the stress is introduced through the action of the electric field on the piezoelectric substrate, so as to obtain an equivalent field to adjust the anisotropy field Hk of the ferromagnetic layer 1 to meet the requirements of the magnetoresistance sensor. The requirement that the linear region increase or decrease within the same sample.

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