Preparation method of anisotropic magnetoresistance sensor with high linearity

Abstract

According to the preparation method of the anisotropic magnetoresistance sensor with high linearity, a magnetic vortex state is formed by adjusting the thickness and the length-width ratio of the magnetic film, so that the linearity of the anisotropic magnetoresistance sensor is multiplied, and the problem that the linear range of an existing AMR linear sensor is too narrow is solved; and the AMR linear sensor can be widely applied.

Description

Technical Field

[0001] The present invention belongs to the field of magnetic sensors, and particularly relates to a preparation principle and method of an anisotropic magnetoresistive sensor (AMR) with high linearity. Background Art

[0002] With the rapid development of information technology, the Internet of Things technology has gradually changed from a concept to reality, and sensors play a crucial role in the entire Internet of Things system. Through the efforts of many researchers, sensor technology has developed rapidly, and among them, magnetic sensors are widely used and play an increasingly important role in the fields of medical and health, military, geological exploration, and smart home.

[0003] Magnetic field sensors include Hall sensors, fluxgate sensors, giant magnetoimpedance sensors, magnetoresistive sensors (AMR, GMR, TMR), magneto-optical sensors, etc. Among them, magnetoresistive sensors are sensors prepared based on the principle that the resistance of materials changes under different magnetic fields. Compared with other magnetic sensors, magnetoresistive sensors have better performance than Hall sensors, are easier to integrate with CMOS technology than fluxgate sensors and giant magnetoimpedance sensors, and the manufacturing process is also simpler. According to different resistance change principles, magnetoresistive sensors are further divided into anisotropic magnetoresistive effect (AMR), giant magnetoresistive effect (GMR), and tunneling magnetoresistive effect (TMR). The anisotropic magnetoresistive effect refers to that when the spontaneous magnetization magnitude and direction of ferromagnetic materials change, the resistivity with magnetization parallel to the current direction and the resistivity with magnetization perpendicular to the current direction will both change. Compared with TMR and GMR sensors, although the maximum resistance change of AMR is smaller, its structure is simple, the manufacturing cost is low, and it is convenient to realize industrial production. Sensors based on the AMR effect are mainly divided into angle sensors and linear sensors. AMR linear sensors are mainly used in distance measurement, electronic compasses, and current measurement. However, the linear range of AMR linear sensors on the market is relatively small at present, resulting in great limitations in their applications. And how to improve the linear range of AMR sensors is also a difficult problem. Summary of the Invention

[0004] The purpose of the present invention is to propose a method for improving the linear range of AMR sensors by using magnetic vortices in view of the defects in the background art:

[0005] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0006] A linear sensor based on the AMR effect, comprising a substrate, a magnetic thin film layer in the shape of a Wheatstone bridge formed on the substrate, and a Barber electrode layer formed on the magnetic thin film; characterized in that the material of the magnetic thin film layer formed on the substrate is nickel-iron alloy, and magnetic vortices are formed by adjusting the aspect ratio and thickness of the Wheatstone bridge to improve the linearity of the AMR sensor.

[0007] Further, the material of the Wheatstone bridge is nickel-iron alloy. Changing the aspect ratio of the bridge will affect the formation of magnetic vortices. As the aspect ratio decreases, the rate of change of resistance gradually increases, and when a vortex state is formed, the resistance will decrease.

[0008] Further, changing the thickness of the magnetic thin film will affect the formation of the vortex state. As the thickness of the magnetic thin film decreases, the magnetoresistance change rate first decreases and then increases. When the thickness is between 20 nm and 70 nm, the larger the thickness, the more conducive to the formation of the thin film vortex state.

[0009] Further, the Barber electrode structure is adopted, aiming to make the current direction and the magnetization intensity direction maintain a 45° angle in zero magnetic field to form a 45° bias current.

[0010] Further, the purpose of forming the bias current is to make the output of the bridge linearly related to the magnitude of the externally applied magnetic field in the range near zero magnetic field.

[0011] Further, the duty ratio of the Barber electrode will affect the current distribution state and the resistance value change. The increase in the duty ratio significantly improves the current bias effect, and the magnetoresistance change rate will also increase.

[0012] Specifically, the substrate is selected as a silicon wafer, the material of the magnetic thin film is selected as nickel-iron alloy, and the electrode material is selected as gold.

[0013] Preferably, the thickness of the magnetic thin film is between 30 - 65 nm, the length of the Wheatstone bridge is 100 - 200 μm, the aspect ratio is 1.2 - 3, and the width of the bridge is obtained by calculation.

[0014] Preferably, the duty ratio of the Barber electrode is selected as 1 / 2.

[0015] Compared with the prior art, the beneficial effects of the present invention are:

[0016] The present invention provides a preparation principle and method for a high-linearity AMR sensor. By adjusting the thickness and aspect ratio of the magnetic thin film to form a magnetic vortex state, the linearity of the anisotropic magnetoresistance sensor is improved several times, solving the problem of the too narrow linear range of the current AMR linear sensor and making the application of the AMR linear sensor more extensive. Description of the Drawings

[0017] The drawings described herein are used to provide further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0018] in:

[0019] Figure 1 is a side view of the AMR sensor of the present invention;

[0020] Figure 2 is a top view of the AMR sensor of the present invention;

[0021] Figure 3 It is the magnetic vortex state diagram of the present invention. DETAILED DESCRIPTION

[0022] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0023] like Figure 1 FIG. 1 is a side view of the AMR sensor according to the present embodiment ( Figure 1 ) and top view ( Figure 2 ); including a silicon substrate, a magnetic film layer formed on the substrate, a Barber electrode layer (Au) formed on the bridge, and an electrode. After regulating the magnetic film, the magnetic vortex state is finally made easier to form in the device, and the linearity of the device is improved. A current is applied to the lead-in gold electrode, and the output voltage is monitored at the same time. The magnetic vortex state is seen Figure 3 .

[0024] The embodiment provides a method for preparing an AMR sensor, which specifically includes the following steps:

[0025] 1) Ultrasonic cleaning of silicon substrate with acetone, alcohol and deionized water for 10 minutes in sequence;

[0026] 2) Spin-coating photoresist on the substrate, pre-baking and then exposing it using a designed Wheatstone bridge pattern;

[0027] 3) Post-baking, then developing with developer, and after completion, deionized water is added to remove excess developer;

[0028] 4) Grow magnetic thin films using magnetron sputtering;

[0029] 5) Soak the sample in acetone for 10 minutes, then ultrasonically clean it for 3-5 seconds, take it out and put it back in, and repeat this step until the photoresist on the substrate is observed to fall off;

[0030] 6) Align the Barber electrode pattern by means of the small cross on the designed mask plate, and then perform photolithography;

[0031] 7) Magnetron sputtering is used to grow a Cr / Au thin film, and then repeating step 5 can obtain the sensor probe.

[0032] The present invention has been described exemplarily in conjunction with the accompanying drawings. Obviously, the specific implementation of the present invention is not limited by the above-mentioned manner. As long as various non-substantive improvements are made by adopting the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for preparing a high-linearity anisotropic magnetoresistive sensor, characterized in that: The following steps are involved: S1. providing a substrate, and forming a magnetic film layer having a Wheatstone bridge shape on the substrate, wherein the material of the magnetic film layer is a nickel-iron alloy; S2. A magnetic vortex is formed by adjusting the aspect ratio and thickness of the magnetic film layer, thereby improving the linearity of the AMR sensor.

2. The method for preparing a high-linearity anisotropic magnetoresistive sensor according to claim 1, characterized in that: The material of the Wheatstone bridge is nickel-iron alloy. Changing the aspect ratio of the bridge will affect the formation of the magnetic vortex. As the aspect ratio decreases, the resistance change rate gradually increases. When a vortex state is formed, the resistance will decrease.

3. The method for preparing a high-linearity anisotropic magnetoresistive sensor according to claim 1, characterized in that: Changing the thickness of the magnetic film layer will affect the formation of the vortex state. As the thickness of the magnetic film decreases, the magnetic resistance change first decreases and then increases. When the thickness is between 20nm and 70nm, the greater the thickness, the more conducive it is to the formation of the film vortex state.

4. The method for preparing a high-linearity anisotropic magnetoresistive sensor according to claim 1, characterized in that: The method also includes forming a Barber electrode layer on the magnetic film layer to form a 45° bias current so that the bridge output can maintain a linear relationship with the magnitude of the external magnetic field in a range near the zero magnetic field.

5. The method for preparing a high-linearity anisotropic magnetoresistive sensor according to claim 4, characterized in that: The duty ratio of the Barber electrode layer will affect the current distribution state and the resistance change. When the duty ratio increases, the current bias effect is significantly improved and the magnetoresistance change rate also increases.

6. A method for preparing a high-linearity anisotropic magnetoresistive sensor according to any one of claims 1 to 5, characterized in that: The thickness of the magnetic film layer is between 30-65 nm, the length of the Wheatstone bridge is between 100-200 μm, and the aspect ratio is between 1.2-3.

7. The method for preparing a high-linearity anisotropic magnetoresistive sensor according to claim 4, characterized in that: The duty ratio of the Barber electrode layer is 1 / 2.

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