AMR magnetoresistive sensor

Abstract

The invention discloses an AMR magnetoresistive sensor, and mainly solves the technical problem that the detection precision of an existing AMR sensor is easily affected by an external interference magnetic field. Each bridge arm of the Wheatstone bridge is correspondingly connected with a magnetoresistive element in series, and the angle difference of the magnetization directions of the magnetoresistive elements at the adjacent bridge arms is within the range of 180 + / -delta degrees. According to the AMR sensor, the anti-ferromagnetic layer is arranged, and the shape of the anti-ferromagnetic layer is the same as that of the magnetoresistive effect layer, so that compared with an existing AMR sensor, a tedious and complicated exposure process can be omitted, and the purpose of simplifying the process is achieved. And the magnetization directions of the magnetoresistive elements at the adjacent bridge arms in the sensor bridge circuit are basically opposite, so that adverse effects caused by an interference magnetic field can be counteracted when the external interference magnetic field exists, the sensitivity of the sensor is prevented from being greatly changed, and the magnetic field measurement accuracy of the sensor is ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of sensors, and particularly to an AMR magnetoresistive sensor. Background Art

[0002] When certain metals or semiconductors encounter an external magnetic field, their resistance values change with the magnitude of the external magnetic field. This phenomenon is called the magnetoresistive effect, and the change in resistance is called magnetoresistance. For ferromagnetic metals with anisotropic properties, their resistance is related to the angle between the magnetic field and the current. When the external magnetic field has a certain angle with the built-in magnetic field of the magnet, the magnetization vector inside the magnet will deflect, resulting in a decrease in the thin-film resistance. The above characteristics are usually referred to as the anisotropic magnetoresistive effect.

[0003] Taking the anisotropic magnetoresistance (AMR) effect of permalloy as an example, the magnetoresistance of permalloy changes with the change of the angle θ between the magnetic field and the current direction, and its magnetoresistance and magnetic field characteristics are non-linear. To measure the value of the external magnetic field, an AMR sensor usually consists of four magnetoresistors to form a Wheatstone bridge. After applying a power supply, current flows through each magnetoresistor. When a bias magnetic field is applied to the bridge, the magnetization directions of two oppositely placed magnetoresistors will rotate towards the current direction, and the resistance values of these two magnetoresistors will increase. The magnetization directions of the other two oppositely placed magnetoresistors will rotate towards the direction opposite to the current, and the resistance values of these two magnetoresistors will decrease. Thus, a differential pressure signal is output through the two output terminals of the bridge, and the value of the external magnetic field is obtained.

[0004] However, when there is an external interfering magnetic field, such as an interfering magnetic field perpendicular to the direction of the detected magnetic field, if the interfering magnetic field is greater than zero, it will cause the angle between the magnetization direction of the magnetoresistor and the current to decrease, resulting in a decrease in detection sensitivity; if the interfering magnetic field is less than zero, it will cause the angle between the magnetization direction of the magnetoresistor and the current to increase, resulting in an increase in detection sensitivity. That is, the existence of the interfering magnetic field will cause the sensitivity of the magnetoresistor to change, thus deteriorating the detection accuracy of the sensor.

[0005] The information disclosed in this background art section is only for enhancing the understanding of the background art of the present disclosure, and should not be regarded as an admission or any form of implication that this information constitutes the prior art known to those skilled in the art. Summary of the Invention

[0006] In view of at least one of the above technical problems, the present disclosure provides an AMR magnetoresistive sensor, mainly solving the technical problem that the detection accuracy of the existing AMR sensor is easily affected by the external interfering magnetic field.

[0007] According to one aspect of the present disclosure, an AMR magnetoresistive sensor is provided, which includes a Wheatstone bridge in which magnetoresistive elements are respectively connected in series in each arm, and the angular difference between the magnetization directions of the magnetoresistive elements at adjacent arms is within the range of 180 ± Δ°.

[0008] In some embodiments of the present disclosure, Δ ≤ 5.

[0009] In some embodiments of the present disclosure, when the external magnetic field is zero, the magnetization direction of at least one of the magnetoresistive elements is arranged at a certain angle with respect to the long axis direction of the magnetoresistive element.

[0010] In some embodiments of the present disclosure, the magnetoresistive element includes a magnetoresistive effect layer and an antiferromagnetic layer that is magnetically coupled to the magnetoresistive effect layer and is used to apply an exchange magnetic field to the magnetoresistive effect layer correspondingly. Heb of the antiferromagnetic layer.

[0011] In some embodiments of the present disclosure, the antiferromagnetic layer is magnetically coupled to the top or bottom or both sides of the magnetoresistive effect layer correspondingly.

[0012] In some embodiments of the present disclosure, the exchange magnetic field Heb The acute angle formed with the long axis of the magnetoresistive element is φ , and 30° ≤ φ ≤ 60°.

[0013] One or more technical solutions provided in the embodiments of the present application have at least any one of the following technical effects or advantages: 1. By providing an antiferromagnetic layer, and the antiferromagnetic layer has the same shape as the magnetoresistive effect layer, compared with the existing AMR sensors, the complicated exposure process can be omitted, so as to simplify the manufacturing process thereof.

[0014] 2. The magnetization directions of the magnetoresistive elements at adjacent arms in the sensor bridge circuit are basically opposite, so that when there is an external interference magnetic field, the adverse effects caused by the interference magnetic field can cancel each other out, avoiding large changes in the sensitivity of the sensor, and thus ensuring the magnetic field measurement accuracy of the sensor. Description of the Drawings

[0015] Figure 1 It is a schematic diagram of the detection bridge structure principle of the existing AMR sensor recorded in an embodiment of the present application.

[0016] Figure 2 It is a schematic diagram of the principle of the AMR magnetoresistive sensor in an embodiment of the present application.

[0017] Figure 3 It is a graph showing the influence of the interference magnetic field on the sensitivity of the existing design and the design of the present invention in an embodiment of the present application. Detailed Description

[0018] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", "vertical", "horizontal", "clockwise", "counterclockwise", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description. Therefore, it should not be construed as a limitation to the present application.

[0019] To better understand the technical solution of the present application, the above technical solution will be described in detail below in conjunction with the drawings of the specification and specific implementation manners.

[0020] The resistance values of the magnetoresistors in the AMR sensors in the prior art change with the change of the angle between the magnetic field and the current direction, and the change characteristic between the resistance and the magnetic field is a non-linear relationship. To relatively accurately back-calculate the magnetic field intensity value from the change curve, the angle between the current direction and the magnetization direction is usually set at 45 degrees to ensure that each magnetoresistor operates near the linear region, thereby obtaining a linear output. However, in order to set the angle between the current direction and the magnetization direction at 45 degrees, a conductive layer needs to be fabricated between the two electrodes. By means of a number of metal conductors that are inclined and form a 45-degree angle with the long axis of the magnetoresistor in the conductive layer, the purpose of changing the current direction is achieved. However, since the shape of the conductive layer is different from the shape of the NiFe layer that generates the magnetoresistive effect on the substrate, it is necessary to perform multiple exposure process treatments to lay a number of metal conductors that form a 45-degree angle with the long axis of the magnetoresistor above the NiFe layer. This exposure process is cumbersome and the process is complex, resulting in a high production cost and low production efficiency.

[0021] In addition, during the long-term scientific research practice of the inventors, it is found that when there is an external interfering magnetic field, the detection accuracy of existing AMR sensors will deteriorate, making it difficult to accurately detect the magnetic field. The inventors further research and find that the existence of an external interfering magnetic field will cause a change in the sensitivity of the AMR sensor, which in turn leads to the deterioration of its detection accuracy. For example, when the existing AMR sensor detects a magnetic field perpendicular to its long axis direction, when the external magnetic field is zero, its magnetization direction is consistent with the long axis direction of the AMR sensor and is in the same direction as the working current direction; when there is an external magnetic field, its magnetization direction forms a certain angle with the long axis direction of the AMR sensor, that is, affected by the external magnetic field, the magnetization direction of the AMR sensor forms a certain angle with the working current direction, thereby causing a change in the resistance value of the AMR sensor, and then judging the intensity value of the external magnetic field through this resistance change. However, if there is an interfering magnetic field, and assuming that the direction of the interfering magnetic field is perpendicular to the detected magnetic field, at this time, when the interfering magnetic field is greater than zero, it will cause the component of the AMR magnetic field in the direction perpendicular to the magnetic field to be measured, that is, in the direction of the interfering magnetic field, to increase. After vector summation, the magnetization direction of the AMR sensor will deviate towards the working current direction, that is, the angle between the magnetization direction and the working current direction will decrease, thereby reducing the sensitivity of the AMR sensor to detect the external magnetic field perpendicular to the working current direction; similarly, when the interfering magnetic field is less than zero, it will cause the component of the AMR sensor magnetic field in the direction perpendicular to the magnetic field to be measured, that is, along the direction of the interfering magnetic field, to decrease. After vector summation, the magnetization direction of the AMR sensor will deviate from the working current direction, that is, the angle between the magnetization direction and the working current direction will increase, thereby increasing the sensitivity of the AMR sensor to detect the external magnetic field perpendicular to the working current direction. In addition, referring to Figure 1 , in the Wheatstone measurement bridge composed of this AMR sensor, the directions (Hk) of the shape anisotropy equivalent magnetic fields of each AMR sensor are the same, and the current directions (I) of adjacent two resistors are different due to the different layout directions of the metal conductors, where M is the magnetization direction. Since the directions of the shape anisotropy equivalent magnetic fields Hk of adjacent two resistors in the bridge are the same and the magnetization directions of each magnetoresistor are the same, when being interfered by an external interfering magnetic field, the sensitivities of adjacent two existing AMR sensors will change and the change trends are opposite, which in turn exacerbates the deterioration of the detection accuracy when the bridge detects the magnetic field, making it difficult to accurately detect the magnetic field to be measured.

[0022] Therefore, this example discloses an AMR magnetoresistive sensor, referring to Figure 2, the AMR magnetoresistive sensor includes magnetoresistive elements R1 to R4. Specifically, in this example, first, magnetoresistive element R1 and magnetoresistive element R2 are connected in series, and magnetoresistive element R3 and magnetoresistive element R4 are connected in series. After being connected in series respectively, they are then connected in parallel, thus forming a Wheatstone bridge. Output terminals V1 are led out between magnetoresistive element R1 and magnetoresistive element R2, and output terminals V2 are led out between magnetoresistive element R3 and magnetoresistive element R4. When no external magnetic field is applied, the output between output terminals V1 and V2 is zero, and the bridge is balanced at this time. When an external magnetic field exists around the bridge, the balance of the bridge is broken by the external magnetic field, and a voltage signal is output between output terminals V1 and V2. The magnetic field intensity value is calculated by inverting the voltage signal.

[0023] However, since the existing AMR sensor requires the conductive layer material to change the direction of the current, and the shape of the conductive layer is different from that of the NiFe layer, it requires a cumbersome and complex exposure process, resulting in low forming efficiency and high cost. Therefore, in this embodiment, the magnetoresistive elements at each arm of the Wheatstone bridge respectively include a magnetoresistive effect layer (AMR) and an antiferromagnetic layer (AFM) magnetically coupled to the magnetoresistive effect layer. In this example, the antiferromagnetic layer is provided on the top of the magnetoresistive effect layer. In some other embodiments, the antiferromagnetic layer is provided at the bottom of the magnetoresistive effect layer or the antiferromagnetic layers are respectively provided on the top, bottom, and both sides of the magnetoresistive effect layer. Thus, the conductive layer of the existing AMR sensor is omitted, avoiding the complex processing during the formation of the conductive layer, and thus simplifying the preparation process.

[0024] In order to avoid the sensitivity of each magnetoresistive element changing due to the interference magnetic field when there is an external interference magnetic field, thus affecting the detection accuracy, in this embodiment, the magnetization directions of the magnetoresistive elements at two adjacent arms of the Wheatstone bridge are set to be basically opposite, that is, the angular difference between the magnetization directions of the magnetoresistive elements at adjacent arms is within the range of 180±Δ°.

[0025] Specifically, considering that the magnetization direction of the magnetoresistive element is affected by the antiferromagnetic layer, in this embodiment, refer to Figure 2, the magnetic components of the Hebb direction affected by the antiferromagnetic layer in two adjacent magnetoresistive elements in the bridge are set to opposite directions by laser annealing. Specifically, during the laser annealing process, an external magnetic field Hext is first applied to the entire magnetoresistive effect layer AMR of the magnetoresistive element to control the Hebb direction affected by the antiferromagnetic layer through the direction of the applied external magnetic field. Then, one of the magnetoresistive elements AMR is selectively irradiated with a laser. Under the action of the laser, only the irradiated AMR and its corresponding antiferromagnetic layer AFM increase in temperature. By adjusting the power of the laser, the temperature of the AMR and the antiferromagnetic layer AFM is higher than the Néel temperature of the antiferromagnetic layer AFM and lower than the Curie temperature of the AMR. Thus, the Hebb direction affected by the antiferromagnetic layer is determined during the cooling process. Then, the direction of the external magnetic field Hext is reversed, and the other magnetoresistive element AMR is selectively irradiated with a laser. In the same way, the Hebb direction of the magnetoresistive element irradiated for the second time can be made opposite to the Hebb direction of the magnetoresistive element irradiated for the first time.

[0026] See Figure 2 , since the magnetization magnetic field M of the magnetoresistive element is determined by the vector sum of the magnetic field affected by the antiferromagnetic layer in the Hebb direction and the magnetic field affected by the magnetoresistive effect layer in the Hk direction, and the Hebb directions of adjacent magnetoresistive elements after laser annealing treatment are anti-phase, the Hk directions of adjacent magnetoresistive elements in the bridge are opposite. Thus, the magnetization directions of the magnetoresistive elements at adjacent bridge arms in the Wheatstone bridge are opposite. Therefore, when affected by an external interference magnetic field, the influences of the interference magnetic field on the magnetoresistive elements cancel each other out, avoiding the adverse effects of the external interference magnetic field on the sensitivity of each magnetoresistive element.

[0027] In this embodiment, the angular difference between the magnetization directions of the magnetoresistive elements at adjacent bridge arms is set to 180°, that is, in the absence of an external magnetic field, the magnetization directions of adjacent magnetoresistive elements are opposite. However, considering manufacturing errors in the actual production process, the included angle between the magnetization directions of adjacent magnetoresistive elements cannot exactly remain 180 degrees and there is a certain angular deviation. Therefore, in some other embodiments, the angular difference between the magnetization directions of adjacent magnetoresistive elements is set within the range of 180±Δ°, where Δ≤5, that is, the deviation degree is controlled within the range of plus or minus 5 degrees.

[0028] However, in the existing AMR sensors, when there is no external magnetic field, the magnetization direction is parallel to the long axis direction of the AMR sensor. When it is subjected to an interfering magnetic field, it cannot cancel the adverse effects generated by the interfering magnetic field, which leads to a change in the sensor sensitivity and causes the measurement result to deviate from the true value. In this embodiment, the magnetization direction of at least one magnetoresistive element is set at a certain angle with the long axis direction of the magnetoresistive element. Since the magnetization direction of the magnetoresistive element is jointly affected by the antiferromagnetic layer and the magnetoresistive effect layer, specifically determined by the vector sum of the Heb direction magnetic field affected by the antiferromagnetic layer and the Hk direction magnetic field affected by the magnetoresistive effect layer, in this embodiment, the exchange bias magnetic field is set Heb The acute angle formed with the long axis of the magnetoresistive element is φ , and 30° ≤ φ ≤ 60°, so that when the external magnetic field is zero, there is a certain angle between the final magnetization direction of the magnetoresistive element and the long axis direction of the magnetoresistive element, so as to obtain a linear output.

[0029] In addition, in this embodiment, referring to Figure 3 , the sensitivity changes of the existing AMR sensor (referred to as the existing design in the figure) and the AMR magnetoresistive sensor disclosed in the present invention (referred to as the new design in the figure) under the action of the external interfering magnetic field Hy are respectively tested. From the Figure 3 test curve shown, with the increase or decrease of the external interfering magnetic field intensity, the sensitivity change of the AMR magnetoresistive sensor disclosed in the present invention is relatively stable, and there is no situation of sensitivity deterioration, so as to effectively ensure the measurement accuracy of the sensor.

[0030] Although some preferred embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications to these embodiments once they know the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present invention.

[0031] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of its inventive concept. Thus, if these modifications and variations of the present disclosure fall within the scope of the claims of this application and their equivalent technologies, the present invention is also intended to include these modifications and variations.

Claims

1. An AMR magnetoresistive sensor, characterized in that: It comprises a Wheatstone bridge in which each bridge arm is connected in series with a magnetoresistive element, and the angle difference of the magnetization direction of the magnetoresistive elements at adjacent bridge arms is within the range of 180±Δ°.

2. The AMR magnetoresistive sensor according to claim 1, characterized in that: Δ≤5.

3. The AMR magnetoresistive sensor according to claim 1, characterized in that: When the external magnetic field is zero, the magnetization direction of at least one of the magnetoresistive elements is arranged at a certain angle to the long axis direction of the magnetoresistive element.

4. The AMR magnetoresistive sensor according to claim 1, characterized in that: The magnetoresistive element includes a magnetoresistive effect layer, a magnetic coupling corresponding to the magnetoresistive effect layer and a magnetic field for applying an exchange interaction magnetic field to the magnetoresistive effect layer. Heb antiferromagnetic layer.

5. The AMR magnetoresistive sensor according to claim 4, characterized in that: The antiferromagnetic layer is magnetically coupled to the top, bottom or both sides of the magnetoresistance effect layer.

6. The AMR magnetoresistive sensor according to claim 4 or 5, characterized in that: The exchange magnetic field Heb The acute angle between the long axis of the magnetoresistive element is φ , and 30°≤ φ ≤60°.

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