Magnetoresistive elements, anisotropic magnetoresistive sensors and their fabrication methods, and magnetic grating rulers

Abstract

This invention provides a magnetoresistive element, an anisotropic magnetoresistive sensor, its fabrication method, and a magnetic grating ruler. The magnetoresistive element of this invention has shorter magnetoresistive strips at both ends and a longer magnetoresistive strip in the middle. According to the relationship between the aspect ratio of the magnetoresistive strip and the demagnetizing field, when the thickness of the magnetoresistive strip is constant, a larger aspect ratio results in a larger demagnetizing field. That is, when the thickness and width of the magnetoresistive strip are constant, a larger length results in a larger demagnetizing field. Therefore, the elliptical design of the magnetoresistive element structure of this invention, with shorter magnetoresistive strips at both ends and a longer middle strip, can effectively improve the problem of uneven distribution of the demagnetizing field along the width direction in AMR elements. Applying the magnetoresistive element of this invention to an AMR magnetoresistive sensor can reduce the saturation field of the AMR magnetoresistive sensor's output characteristic curve, thereby improving the output signal of the magnetoresistive sensor.

Description

Technical Field

[0001] This invention relates to the field of magnetic sensor technology, and in particular to a magnetoresistive element, an anisotropic magnetoresistive sensor, its preparation method, and a magnetic grating ruler. Background Technology

[0002] Anisotropic magnetoresistive (AMR) is an effect where the change in the angle θ between the magnetization direction and the current direction leads to a change in the thin film resistance. Magnetic sensors based on the AMR effect have wide applications, such as current sensing, rotational position sensing, and navigation compasses. Currently, the anisotropic magnetoresistive (AMR) elements used in magnetoresistive sensors suffer from uneven demagnetization field distribution due to the anisotropy of the magnetoresistive strip's shape, particularly along the width of the AMR element, where the demagnetization field at the edges is much larger than that in the center. This difference in demagnetization field significantly affects the magnetization reversal process of the AMR element, increasing the saturation field of the AMR element's output characteristic curve and thus reducing the output signal of the magnetic sensor. In practical applications of AMR magnetoresistive sensors, since the external magnetic field strength often does not reach the saturation field of the magnetic sensor, under the same external magnetic field strength, a larger saturation field results in a weaker output signal.

[0003] Given the current problem of uneven demagnetizing field distribution in AMR magnetoresistive sensors, it is necessary to improve this. Summary of the Invention

[0004] In view of this, the present invention proposes a magnetoresistive element, an anisotropic magnetoresistive sensor, its preparation method and a magnetic grating ruler, to solve the problem of weak output signal of magnetoresistive sensor caused by uneven distribution of demagnetizing field in the width direction in the prior art AMR magnetoresistive sensor.

[0005] In a first aspect, the present invention provides a magnetoresistive element comprising two magnetoresistive units connected in series, each magnetoresistive unit comprising a plurality of spaced magnetoresistive strips connected in series at their ends; the length of the magnetoresistive strips in the middle position of each magnetoresistive unit gradually decreases from the magnetoresistive strips in the two sides, and the two magnetoresistive units are arranged vertically opposite each other so that the magnetoresistive element as a whole has a quasi-elliptical structure.

[0006] Preferably, in the magnetoresistive element, the length difference between any two adjacent magnetoresistive strips in each magnetoresistive unit is 0~30µm.

[0007] Preferably, in the magnetoresistive element, each magnetoresistive strip is provided with a buffer layer, a magnetoresistive layer and a protective layer in sequence.

[0008] Preferably, the material used for the buffer layer of the magnetoresistive element includes any one of Ta, NiFeCr, and Pt; the thickness of the buffer layer is 3~10 nm. And / or, the material used for the magnetoresistive layer includes any one of Ni, Fe, Co, NiFe alloy, NiCo alloy, FeCo alloy, and FeCoNi alloy, and the thickness of the magnetoresistive layer is 20~50nm; And / or, the material used for the protective layer is either Ta or Al2O3, and the thickness of the protective layer is 3~10nm.

[0009] Preferably, in the magnetoresistive element, a first metal conductive layer covers the ends of any two adjacent magnetoresistive strips of each magnetoresistive unit; and two magnetoresistive units are connected in series through a second metal conductive layer.

[0010] Preferably, the first and second metal conductive layers of the magnetoresistive element are made of any one of Ag, Cu, Cr, Al, Au, and alloys formed from the above metal materials.

[0011] Secondly, the present invention also provides a method for preparing the aforementioned magnetoresistive element, comprising the following steps: Provide substrate; A multilayer thin film consisting of a buffer layer, a magnetoresistive layer and a protective layer is grown on the substrate, and an external bias magnetic field is applied during the growth of the thin film; Magnetoresistive unit patterns are formed on the substrate using photolithography and etching techniques; A metal conductive layer is deposited on the substrate, and the metal conductive layer is etched using photolithography and etching techniques to obtain a first metal conductive layer and a second metal conductive layer. The first metal conductive layer covers the ends of two adjacent magnetoresistive strips, and the second metal conductive layer connects two upper and lower magnetoresistive units to obtain the magnetoresistive element.

[0012] Secondly, the present invention also provides a method for preparing the magnetoresistive element, which further includes pre-treating the substrate before growing and forming the buffer layer, the magnetoresistive layer and the protective layer on the substrate. The pre-treating specifically involves ultrasonically cleaning the substrate, blowing it dry, and then baking it.

[0013] Thirdly, the present invention also provides an anisotropic magnetoresistive sensor, comprising the magnetoresistive element or the magnetoresistive element prepared by the aforementioned preparation method and an electrode, wherein the electrode is electrically connected to the magnetoresistive element.

[0014] Fourthly, the present invention also provides a magnetic scale, comprising the aforementioned anisotropic magnetoresistive sensor and magnetic scale, wherein the anisotropic magnetoresistive sensor and the magnetic scale are installed in a non-contact manner.

[0015] The magnetoresistive element, anisotropic magnetoresistive sensor, and magnetic grating ruler of the present invention have the following technical advantages over the prior art: 1. The magnetoresistive element of this invention has shorter magnetoresistive strips at both ends and a longer magnetoresistive strip in the middle. According to the relationship between the aspect ratio of the magnetoresistive strip and the demagnetizing field, when the thickness of the magnetoresistive strip is constant, the larger the aspect ratio, the larger the demagnetizing field. That is, when the thickness and width of the magnetoresistive strip are constant, the longer the length, the larger the demagnetizing field. Therefore, the elliptical design of the magnetoresistive element structure of this invention, with shorter magnetoresistive strips at both ends and a longer magnetoresistive strip in the middle, can effectively improve the problem of uneven distribution of the demagnetizing field along the width direction in AMR elements. Applying the magnetoresistive element of this invention to AMR magnetoresistive sensors can reduce the saturation field of the AMR magnetoresistive sensor output characteristic curve, thereby improving the output signal of the magnetoresistive sensor. 2. The magnetic scale of the present invention includes an anisotropic magnetoresistive sensor and a magnetic scale. The NS-SN-NS poles on the magnetic scale generate magnetic fields with different directions. The anisotropic magnetoresistive sensor senses the change in the magnetic field as it moves along the magnetic scale and converts this change in the magnetic field into an analog signal or a digital signal for output. By processing the output signal, displacement measurement can be realized. The magnetic scale of the present invention uses the anisotropic magnetoresistive sensor of the present invention, which can improve the output signal of the magnetoresistive sensor. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic diagram of the structure of a magnetoresistive element in one embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of a magnetoresistive unit in one embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of the magnetic reluctance strip of the present invention; Figure 4 This is a schematic diagram of the structure of a magnetoresistive element in another embodiment of the present invention; Figure 5 This is a schematic diagram of the structure of a magnetoresistive element in another embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0019] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0020] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0021] In the description of this invention, it should be understood that the orientation or positional relationship indicated by terms such as "above" is based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed when in use, or the orientation or positional relationship in which those skilled in the art are usually understood. It is only for the convenience of describing this invention and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation of this invention.

[0022] Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0024] This application provides a magnetoresistive element 1, such as... Figures 1-2 As shown, it includes two magnetoresistive units connected in series. Each magnetoresistive unit includes multiple magnetoresistive strips 2 spaced apart and connected in series at their ends. The length of the magnetoresistive strip 2 in the middle position of each magnetoresistive unit gradually decreases from the magnetoresistive strips 2 in the two sides. The two magnetoresistive units are arranged vertically opposite each other so that the magnetoresistive element 1 has an overall elliptical structure.

[0025] It should be noted that the magnetoresistive element 1 of this application includes two magnetoresistive units connected in series, and each magnetoresistive unit includes multiple spaced magnetoresistive strips 2 with their ends connected in series; as Figure 1 As shown, the magnetoresistive element 1 includes two magnetoresistive units, which are arranged vertically opposite each other and are centrally symmetrically positioned. (Reference) Figure 2 As shown, the magnetoresistive unit includes multiple spaced magnetoresistive strips 2 connected in series at their ends. Specifically, any two adjacent magnetoresistive strips 2 form an approximate "U" shape, and the multiple magnetoresistive strips 2 form a roughly wavy curve (the length of the peak of the wavy curve gradually increases from the two sides to the middle position); the length of the magnetoresistive strip 2 at the middle position of each magnetoresistive unit gradually decreases from the magnetoresistive strips 2 at the two sides, which is the length of the magnetoresistive strips 2 at the two sides (here, the length corresponds to...). Figure 1 The magnetoresistive element 1, composed of two magnetoresistive units, has a relatively small height (i.e., the middle magnetoresistive strip 2 is longer, while the two side magnetoresistive strips 2 are shorter). Therefore, the overall structure of the magnetoresistive element 1 is approximately elliptical (i.e., the middle magnetoresistive strip 2 is longer, while the two side magnetoresistive strips 2 are shorter). Currently, the anisotropic magnetoresistive element 1 used in magnetoresistive sensors suffers from anisotropic shape, resulting in uneven distribution of the demagnetizing field within the AMR element. Particularly along the width of the AMR element, the demagnetizing field at the edges is much larger than that at the center, severely affecting the magnetization reversal process. This difference in demagnetizing field increases the saturation field of the AMR element's output characteristic curve, thereby reducing the output signal of the magnetic sensor. In this application, by designing the magnetoresistive element 1 as an elliptical shape, the magnetoresistive strips at both ends are shorter, while the middle magnetoresistive strip is longer. According to the relationship between the aspect ratio of the magnetoresistive strip and the demagnetizing field, when the thickness of the magnetoresistive strip is constant, a larger aspect ratio results in a larger demagnetizing field. In other words, when the thickness and width of the magnetoresistive strip are constant, a larger length results in a larger demagnetizing field. Therefore, the design of the magnetoresistive element 1 in this application, with shorter lengths of magnetoresistive strips at both ends and longer lengths of magnetoresistive strips in the middle, can effectively improve the problem of uneven distribution of demagnetizing field along the width direction in the AMR element, reduce the saturation field of the AMR element's output characteristic curve, and thus improve the output signal of the magnetoresistive sensor.

[0026] The principles of this application are further explained below: The demagnetizing factor N along the width direction of the anisotropic magnetoresistive element 1 can be expressed as: N ≈ ( + ), where t is the thickness of the magnetic film, w is the width, and x is the distance from the center in the width direction (-w / 2 < x < w / 2). From the formula, it can be seen that when t and w are constant, the larger x is, i.e., the closer to the edge, the larger the demagnetizing factor N value. Furthermore, the demagnetizing field H... D The magnetic field generated by the ferromagnetic material itself can be represented as H. D≈ µ0NM S, µ0 is the free permeability, M S As shown in the formula, the larger the N value, the larger the demagnetizing field. Therefore, the demagnetizing field at the edge is much larger than that at the center. This difference in demagnetizing field significantly affects the magnetization reversal process of the AMR element, increasing the saturation field of the AMR element's output characteristic curve. According to the relationship between the aspect ratio of the magnetoresistive strip and the demagnetizing field, when the thickness of the magnetoresistive strip is constant, the larger the aspect ratio, the larger the demagnetizing field. That is, when the thickness and width of the magnetoresistive strip are constant, the longer the strip, the larger the demagnetizing field.

[0027] It should be noted that in this application, the length of the magnetoresistive strip 2 located in the middle position gradually decreases from the magnetoresistive strip 2 located on both sides. Here, "gradually" only reflects the overall trend of the change in the length of the magnetoresistive strip 2. It does not mean that the length difference between any two adjacent magnetoresistive strips 2 must be greater than zero. That is, in this application, as long as the overall trend of the length of the magnetoresistive strip 2 located in the middle position gradually decreasing from the magnetoresistive strip 2 located on both sides is satisfied, the length difference between two adjacent magnetoresistive strips 2 can be 0 μm.

[0028] In some embodiments, the magnetoresistive strip 2 located in the middle position to the magnetoresistive strips 2 located on both sides, wherein the length difference between any two adjacent magnetoresistive strips 2 is 0~30μm.

[0029] In the above embodiment, the length of the magnetic reluctance strip 2 gradually increases from the two sides to the middle. Specifically, the increase in the length of the magnetic reluctance strip 2 is 0~30µm. For example, the increase in the length of the magnetic reluctance strip 2 can be 2µm, 4µm, 6µm, 8µm, 10µm, 12µm, 14µm, 16µm, 18µm, 20µm, 22µm, 24µm, 26µm, 28µm, 30µm, etc. The specific increase in the length of the magnetic reluctance strip 2 can be determined according to the actual use.

[0030] In some embodiments, the spacing between any two adjacent magnetoresistive strips 2 is 1~13µm. For example, the spacing between two adjacent magnetoresistive strips 2 can be 1µm, 3µm, 5µm, 7µm, 9µm, 11µm, 13µm, etc. Specifically, the spacing between two adjacent magnetoresistive strips 2 is determined according to the actual application. Adjacent magnetoresistive strips 2 can be arranged in parallel with equal intervals or with non-equal intervals.

[0031] In some embodiments, such as Figure 3 As shown, the magnetic resistive strip 2 includes a buffer layer 21, a magnetic resistive layer 22, and a protective layer 23 in sequence.

[0032] In some embodiments, the material used for the buffer layer 21 includes any one of Ta, NiFeCr, and Pt; The thickness of the buffer layer 21 is 3~10nm.

[0033] In some embodiments, the material used for the magnetoresistive layer 22 includes any one of Ni, Fe, Co, NiFe alloy, NiCo alloy, FeCo alloy, and FeCoNi alloy; The thickness of the magnetoresistive layer 22 is 20~50nm.

[0034] In some embodiments, the protective layer 23 is made of either Ta or Al2O3. The thickness of the protective layer 23 is 3~10nm.

[0035] Specifically, Figure 3 In this diagram, 'a' represents the length of the magnetic reluctance strip 2, 'b' represents the width of the magnetic reluctance strip 2, and 'c' represents the thickness of the magnetic reluctance strip 2.

[0036] In some embodiments, please refer to Figure 4 As shown, a first metal conductive layer 3 covers the ends of any two adjacent magnetoresistive strips 2 of each magnetoresistive unit; two magnetoresistive units are connected in series through a second metal conductive layer 4.

[0037] In the above embodiments, since the magnetoresistive strip itself is thin and has a large total length, its resistance is large. By covering the ends of two adjacent magnetoresistive strips 2 with the first metal conductive layer 3, the conductivity of the entire magnetoresistive unit can be enhanced and the resistance reduced.

[0038] The ends of multiple magnetoresistive strips 2 in each magnetoresistive unit are connected in series through a first metal conductive layer 3; two magnetoresistive units are connected in series through a second metal conductive layer 4.

[0039] In some embodiments, the first metal conductive layer 3 and the second metal conductive layer 4 are made of any one of Ag, Cu, Cr, Al, Au, and alloys formed from the above metal materials.

[0040] In some embodiments, the length and width of a single magnetoresistive strip 2 are determined according to the actual use, for example, the length is 26~300µm and the width is 3~40µm.

[0041] For details, please refer to Figure 5 As shown, it illustrates another structure of magnetoresistive unit, which is similar to... Figure 4 The difference between the magnetoresistive units shown is that the length of the magnetoresistive strip 2 is different.

[0042] Based on the same inventive concept, this application also provides a method for preparing the above-mentioned magnetoresistive element 1, characterized by comprising the following steps: S1, Provide the substrate; S2. A multilayer thin film consisting of a buffer layer, a magnetoresistive layer and a protective layer is grown on the substrate, and an external bias magnetic field is applied during the growth of the thin film. S3. Magnetoresistive unit patterns are formed on the substrate using photolithography and etching techniques; S4. Deposit a metal conductive layer on the substrate, and use photolithography and etching techniques to etch the metal conductive layer to obtain a first metal conductive layer and a second metal conductive layer. The first metal conductive layer covers the ends of two adjacent magnetoresistive strips, and the second metal conductive layer connects the upper and lower magnetoresistive units to obtain magnetoresistive element 1.

[0043] In some embodiments, before growing and forming the buffer layer, magnetoresistive layer and protective layer on the substrate, the substrate is further subjected to pretreatment, which specifically includes ultrasonic cleaning, air drying and then oven drying of the substrate.

[0044] In some embodiments, the substrate is a silicon substrate.

[0045] Specifically, in some embodiments, the fabrication method of the above-mentioned magnetoresistive element 1 includes the following steps: 1. Pre-treatment of the silicon substrate by ultrasonic cleaning, blowing, and baking; 2. Growing a multilayer thin film of Ta / NiFe / Ta structure (i.e., corresponding buffer layer, magnetoresistive layer and protective layer) using magnetron sputtering thin film growth technology, with an external bias magnetic field applied during film growth; 3. Forming magnetoresistive unit patterns on the substrate using photolithography and etching technology; 4. Depositing a metal conductive layer on the substrate using magnetron sputtering. The metal material can be metals with excellent conductivity such as Au, Ag, Cu, Cr, Al, etc. The metal conductive layer is etched using photolithography and etching technology to obtain a first metal conductive layer and a second metal conductive layer. The first metal conductive layer covers and connects the ends of two adjacent magnetoresistive strips, and the second metal conductive layer connects the upper and lower magnetoresistive units to obtain the magnetoresistive element 1.

[0046] Based on the same inventive concept, this application also provides an anisotropic magnetoresistive sensor, including the above-mentioned magnetoresistive element 1 and an electrode, wherein the electrode is electrically connected to the magnetoresistive element 1.

[0047] In the above embodiments, the number of electrodes and magnetoresistive elements 1 is determined according to the usage, and the magnetoresistive elements 1 and electrodes are electrically connected to form a circuit.

[0048] Based on the same inventive concept, this application also provides a magnetic scale, including the aforementioned anisotropic magnetoresistive sensor and a magnetic scale. Specifically, the magnetic scale of this application mainly consists of two parts: a magnetic scale and an anisotropic magnetoresistive sensor. The magnetic signals on the magnetic scale are arranged in the order NS-SN-NS, thus the magnetic field strength of the magnetic scale displacement sensor changes periodically. The anisotropic magnetoresistive sensor and the magnetic scale are read through non-contact installation, with an installation distance of 0.1-2mm. The NS-SN-NS poles on the magnetic scale generate magnetic fields with different directions. As the anisotropic magnetoresistive sensor moves along the magnetic scale, it senses the change in the magnetic field and converts this change into an analog or digital signal for output. By processing the output signal, displacement measurement can be achieved.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A magnetoresistive element, characterized in that, It includes two magnetoresistive units connected in series. Each magnetoresistive unit includes multiple spaced magnetoresistive strips connected in series at their ends. The length of the magnetoresistive strip in the middle position of each magnetoresistive unit gradually decreases from the magnetoresistive strips in the two sides. The thickness and width of the magnetoresistive strips are constant. The two magnetoresistive units are arranged vertically opposite each other so that the magnetoresistive element as a whole has a quasi-elliptical structure.

2. The magnetoresistive element as described in claim 1, characterized in that, The length difference between any two adjacent magnetoresistive strips in each magnetoresistive unit is 0~30µm.

3. The magnetoresistive element as described in claim 1, characterized in that, Each of the magnetic reluctance strips includes a buffer layer, a magnetic reluctance layer, and a protective layer arranged sequentially.

4. The magnetoresistive element as described in claim 3, characterized in that, The material used for the buffer layer includes any one of Ta, NiFeCr, and Pt; the thickness of the buffer layer is 3~10 nm. And / or, the material used for the magnetoresistive layer includes any one of Ni, Fe, Co, NiFe alloy, NiCo alloy, FeCo alloy, and FeCoNi alloy, and the thickness of the magnetoresistive layer is 20~50nm; And / or, the material used for the protective layer is either Ta or Al2O3, and the thickness of the protective layer is 3~10nm.

5. The magnetoresistive element as described in claim 1, characterized in that, A first conductive metal layer covers the ends of any two adjacent magnetoresistive strips in each magnetoresistive unit; two magnetoresistive units are connected in series through a second conductive metal layer.

6. The magnetoresistive element as described in claim 5, characterized in that, The first metal conductive layer and the second metal conductive layer are made of any one of Ag, Cu, Cr, Al, Au and alloys formed from the above metal materials.

7. The method for preparing a magnetoresistive element according to any one of claims 1 to 6, characterized in that, Includes the following steps: Provide substrate; A multilayer thin film consisting of a buffer layer, a magnetoresistive layer and a protective layer is grown on the substrate, and an external bias magnetic field is applied during the growth of the thin film; Magnetoresistive unit patterns are formed on the substrate using photolithography and etching techniques; A metal conductive layer is deposited on the substrate, and the metal conductive layer is etched using photolithography and etching techniques to obtain a first metal conductive layer and a second metal conductive layer. The first metal conductive layer covers the ends of two adjacent magnetoresistive strips, and the second metal conductive layer connects two upper and lower magnetoresistive units to obtain the magnetoresistive element.

8. The method for preparing a magnetoresistive element according to claim 7, characterized in that, Before growing and forming the buffer layer, magnetoresistive layer and protective layer on the substrate, the substrate is further subjected to pretreatment, which specifically involves ultrasonically cleaning the substrate, blowing it dry, and then baking it.

9. An anisotropic magnetoresistive sensor, characterized in that, It includes a magnetoresistive element as described in any one of claims 1 to 6 or a magnetoresistive element and an electrode prepared by the preparation method as described in any one of claims 7 to 8, wherein the electrode is electrically connected to the magnetoresistive element.

10. A magnetic scale, characterized in that, It includes the anisotropic magnetoresistive sensor and the magnetic scale as described in claim 9, wherein the anisotropic magnetoresistive sensor and the magnetic scale are installed in a non-contact manner.

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