A tri-axial magnetic field sensor and a method of manufacturing the same

Abstract

The application discloses a three-axis magnetic field sensor and a preparation method thereof. The three-axis magnetic field sensor comprises two groups of magnetic sensor modules which are the same in structure and orthogonal to each other in position. Each group of the magnetic field sensor module comprises two groups or more substrate layers, a magnetic tunnel junction array, a fixed resistor and a magnetic flux attenuator. The magnetic tunnel junction array is arranged above the substrate. The fixed resistor is connected with the magnetic tunnel junction array to form a half-bridge. The magnetic flux attenuator is arranged above the magnetic tunnel junction array. The three-axis magnetic field sensor is simple in structure and convenient to produce. The preparation method adopts the same wafer / substrate to realize die cutting and splicing, which is beneficial to improving the yield and avoiding the influence caused by the difference of the growth film on different wafers. The shape and design of the magnetic flux attenuator are completely the same, the process complexity is reduced, the structure of the magnetic flux attenuator can be realized only by once electroplating, and the interference of the magnetic field in the non-sensitive axis direction on the measurement of the chip is avoided.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of magnetic sensor process, and particularly relates to a three-axis magnetic field sensor and a preparation method thereof. BACKGROUND

[0002] The three-axis magnetic field sensor can measure the magnetic field in three directions in space at the same time, and has higher anti-interference ability and measurement accuracy than single-axis and double-axis sensors. Compared with the scheme of using three single-axis magnetic field sensors respectively, the three-axis magnetic field sensor has higher integration and performance compatibility, and avoids test errors caused by different spatial positions of the three sensors. Therefore, the three-axis magnetic field sensor is widely used in electronic compasses, space magnetic field detection, industrial manufacturing and many other fields. At present, some three-axis integrated magnetic field sensors have been put on the market by domestic and foreign manufacturers, and the price is significantly higher than that of single-axis magnetic field sensors. The current design scheme of the three-axis magnetic field sensor is to combine and integrate multiple single-axis sensor chips. This not only needs to grow two to three different magnetic sensitive films on at least 2-3 wafers respectively, and to etch them respectively, but also has high yield and process complexity. Moreover, independent measurement of each sensor chip often cannot well exclude the interference of the non-sensitive axis magnetic field. SUMMARY

[0003] In view of the status that the traditional three-axis magnetic field sensor in the prior art adopts the single-axis splicing technology of the magnetic sensitive films grown on different wafers, has high process complexity, and the cost and yield need to be upgraded, the present application provides a three-axis magnetic field sensor and a preparation method thereof based on the same film single etching simple process grown on a single wafer.

[0004] According to an aspect of an embodiment of the present application, a three-axis magnetic field sensor is provided, which comprises two groups of magnetic sensor modules with the same structure and mutually orthogonal positions, each group of the magnetic field sensor modules comprises two groups and more of substrate layers, magnetic tunnel junction arrays, fixed-value resistors and magnetic flux attenuators,

[0005] The magnetic tunnel junction array is arranged above the substrate, and has single-axis sensitive characteristics in the short-axis direction of the magnetic tunnel junction.

[0006] The fixed-value resistor is connected with the magnetic tunnel junction array to form a half-bridge.

[0007] The magnetic flux attenuator is arranged above the magnetic tunnel junction array.

[0008] Optionally, the left and right magnetic tunnel junction arrays below each magnetic flux attenuator respectively form a half-bridge structure with the fixed-value resistor module, the voltage input ends of each half-bridge structure are connected in parallel with each other, and the output ends are independent of each other.

[0009] Optionally, the magnetic tunnel junction array comprises a plurality of sensitive structure units forming an array, and the planar shape of the sensitive structure unit is a rectangle or an ellipse.

[0010] Optionally, the projection of the magnetic flux attenuator is a rectangle, and two groups of magnetic tunnel junction arrays are arranged below each magnetic flux attenuator, the two groups of magnetic tunnel junction arrays are parallel to the long side of the projection plane of the magnetic flux attenuator, and the left and right groups of magnetic tunnel junction arrays below each magnetic flux attenuator are different in distance from the long side of the projection of the closest magnetic flux attenuator.

[0011] Optionally, the projection of the magnetic flux attenuator is a rectangle, and two groups of magnetic tunnel junction arrays are arranged below each magnetic flux attenuator, the two groups of magnetic tunnel junction arrays are parallel to the long side of the projection plane of the magnetic flux attenuator, and the sensitive structure units of one of the two groups of magnetic tunnel junction arrays have a fixed angle of 10-80° with the long side of the projection of the closest magnetic flux attenuator, and the two groups of magnetic tunnel junction arrays are different in three-axis component of the induced magnetic field.

[0012] Optionally, the voltage signals U1, U2, U3,..., Un output by each half-bridge are expressed as Un=Nnx×Hx+Nnz×Hz, wherein Nnx and Nnz are the sensitivity coefficients of the magnetic tunnel junction array to the corresponding sensitive-axis magnetic field Hx and z-axis magnetic field Hz, the corresponding voltage signal Un is measured by separately applying the x-direction magnetic field Hx and the z-axis direction magnetic field Hz, and Nnx=Un / Hx and Nnz=Un / Hz are calculated.

[0013] Optionally, the sensitivity coefficients of the magnetic tunnel junction array to the sensitive-axis magnetic field Hx and the z-axis magnetic field depend on the relative position of the magnetic tunnel junction array and the magnetic flux attenuator; the magnetic sensing modules in the three-axis magnetic field sensor that are orthogonal to each other have sensitive characteristics to the x, z and y, z axes, the output voltages U1, U2, U3,..., Un of each half-bridge are measured, and the magnetic field sizes in the two groups of magnetic sensing modules are obtained by solving the equation group of the output voltages of each half-bridge.

[0014] Optionally, the sensitivity coefficients of each group of magnetic tunnel junction arrays to the three-axis magnetic field are different, and the sensitivity coefficients are obtained by simulation calculation and actual experiment before design.

[0015] Optionally, the thickness of the magnetic flux attenuator is 1-50 μm, and the thickness of the magnetic tunnel junction array is 0.5-2 μm.

[0016] According to another aspect of the embodiment of the present application, a preparation method of a three-axis magnetic field sensor is also provided, comprising:

[0017] growing a magnetic sensitive film on a substrate;

[0018] The magnetic tunnel junction array structure is obtained through a photolithography process;

[0019] The magnetic tunnel junction array is taken out through a wafer taking die process and arranged according to fixed relative positions, and is divided into two groups of mutually orthogonal magnetic sensing modules, each of which has at least two groups of magnetic tunnel junction arrays with different relative positions from the designed magnetic flux concentrator;

[0020] The half-bridge structures are connected through an electrode plating process;

[0021] An insulating protective layer and a seed layer before plating of the magnetic flux concentrator are prepared above the thin film array;

[0022] The magnetic flux attenuator layer is plated on the seed layer, so that the three-axis magnetic field sensor of any one of the above aspects is obtained.

[0023] Optionally, all the magnetic tunnel junction arrays are taken from the same wafer.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] 1. The three-axis magnetic field sensor provided by the present application includes two groups of magnetic sensing modules with the same structure and mutually orthogonal positions, each group of the magnetic field sensor module includes two groups and above of substrate layers, magnetic tunnel junction arrays, constant resistors and magnetic flux attenuators, the magnetic tunnel junction array is arranged above the substrate and has uniaxial sensitive characteristics in the direction of the short axis of the magnetic tunnel junction; the constant resistor is connected with the magnetic tunnel junction array to form a half-bridge; and the magnetic flux attenuator is arranged above the magnetic tunnel junction array. It can be seen that the three-axis magnetic field sensor of the present application has a simple structure and is convenient to produce.

[0026] 2. The shape and design of the magnetic flux attenuator of the three-axis magnetic field sensor provided by the present application are completely the same, which reduces the process complexity and realizes the structure of the magnetic flux attenuator only by once plating.

[0027] 3. The three-axis magnetic field sensor provided by the present application obtains the sizes of the two groups of magnetic tunnel junction biaxial magnetic fields through the solution of a simple equation group, wherein the influence of each axis magnetic field is considered, and the interference of the magnetic field in the non-sensitive axis direction on the chip measurement is avoided; finally, the size of the three-axis magnetic field is obtained according to the measurement results of the two groups of biaxial magnetic fields; the formula is simple, and it is convenient to use machine learning and other data fusion methods to obtain more accurate detection data.

[0028] 4. The preparation method of the three-axis magnetic field sensor provided by the present application adopts the same wafer / substrate taking die cutting and splicing, and the completely wafer thin film process is beneficial to improve the yield and avoid the influence of the difference between the thin films grown on different wafers. BRIEF DESCRIPTION OF DRAWINGS

[0029] In order to make the technical scheme of the present application clearer, the following will briefly introduce the drawings needed in the embodiment description. Obviously, the drawings in the following description are only one embodiment of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0030] Figure 1 is a top view schematic diagram of a three-axis magnetic field sensor according to an embodiment of the present application;

[0031] Figure 2 is a top view schematic diagram of another three-axis magnetic field sensor according to an embodiment of the present application;

[0032] Figure 3 is a side view schematic diagram of a three-axis magnetic field sensor according to an embodiment of the present application;

[0033] Figure 4 is a schematic diagram of the surface induced magnetic field direction of a three-axis magnetic field sensor according to an embodiment of the present application when an arbitrary direction magnetic field is applied;

[0034] Figure 5 is a flow chart of a preparation method of a three-axis magnetic field sensor according to an embodiment of the present application. DETAILED DESCRIPTION

[0035] In order to make the technical scheme of the present application clearer, the following will briefly introduce the drawings needed in the embodiment description. Obviously, the drawings in the following description are only one embodiment of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0036] In the description of the present application, one or more is meant to be one or more, more than two is meant to be two or more, greater than, less than, more than, etc. are understood to not include the number, above, below, within, etc. are understood to include the number. If the terms "first", "second", "third" are described for the purpose of description and for the purpose of distinguishing technical features, they cannot be understood as indicating or implying relative importance or implying the number of indicated technical features or implying the sequence of indicated technical features.

[0037] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "connection", "linking", "setting" should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or internal communication of two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances. The embodiments will be described below according to the overall structure of the present application.

[0038] As shown in Figure 1 , a triaxial magnetic field sensor provided by the present application comprises: a first magnetic sensing module 101; a second magnetic sensing module 102; a substrate 103; a magnetic tunnel junction array 104; a magnetic flux attenuator 105 and 106 fixed resistance module. The entire magnetic field sensor is located in the XY plane, and the vertical direction is the Z axis. Figure 1 The middle black thin line is the connecting circuit. The first magnetic sensing module 101 and the second magnetic sensing module 102 are connected in parallel with each other, and are located on two substrates 103 respectively. The two magnetic sensor modules have a 90-degree rotational symmetry structure, and each includes from bottom to top:

[0039] a substrate 103;

[0040] The magnetic tunnel junction array 104 and the 106 fixed resistance module are located on the substrate, and are connected by wires to form a bridge structure;

[0041] The magnetic flux attenuator 105 is located above the magnetic tunnel junction array 104.

[0042] Continuing to refer to Figure 1 , the triaxial magnetic field sensor comprises two groups of magnetic sensing modules with the same structure and mutually orthogonal positions, each group of magnetic field sensor module comprising two groups and above of substrate layer, magnetic tunnel junction array, fixed resistance and magnetic flux attenuator,

[0043] The magnetic tunnel junction array is arranged above the substrate, and has uniaxial sensitive characteristics in the short axis direction of the magnetic tunnel junction;

[0044] The fixed resistance is connected with the magnetic tunnel junction array to form a half-bridge;

[0045] The magnetic flux attenuator is arranged above the magnetic tunnel junction array, and the magnetic flux attenuator is a material with high magnetic permeability, such as permalloy.

[0046] Among them, the resistance value of the fixed resistance is equal to the resistance value of the magnetic tunnel junction array when the magnetic field is 0; as Figure 1As shown, the custom resistance and the magnetic sensor array respectively constitute a bridge structure. The input voltage is Uin, the resistance value of the fixed resistance is R, the resistance change of the thin film array under the magnetic field is ΔR, and the voltage signal U output by the bridge is ΔR / R×Uin.

[0047] Specifically, the magnetic tunnel junction array is formed by a plurality of sensitive structure units, the projection of the sensitive structure unit in the magnetic tunnel junction array is a long rectangular or an ellipse, and the projection of the magnetic flux attenuator is a rectangle; two groups of magnetic tunnel junction arrays are arranged below each magnetic flux attenuator, the long sides of the projection planes of the two groups of magnetic tunnel junction arrays are parallel to each other, the left and right magnetic tunnel junction arrays below each magnetic flux attenuator respectively form a half-bridge structure with the fixed resistance module, the voltage input ends of each half-bridge structure are connected in parallel with each other, and the output ends are independent of each other. The left and right groups of magnetic tunnel junction arrays below each magnetic flux attenuator are different in distance from the projection long side of the closest magnetic flux attenuator. Or the sensitive structure units of one of the two groups of magnetic tunnel junction arrays have a fixed angle of 10-80° with the projection long side of the closest magnetic flux attenuator, and the two have different angles, so that the three-axis components of the induced magnetic field below the two groups of magnetic tunnel junction arrays are different.

[0048] As Figure 1 In one embodiment, the left and right magnetic tunnel junction arrays below the magnetic flux controller are different in distance from the left and right edges below the closest magnetic flux controller.

[0049] As Figure 2 As shown in another embodiment, the long ends of the two groups of magnetic tunnel junction arrays below the magnetic flux attenuator have a fixed angle of 0° and 45° with the long ends of the magnetic flux attenuator, specifically, the two groups of magnetic tunnel junction arrays form an angle of 45°, and the three-axis components of the induced magnetic field below the two groups of magnetic tunnel junction arrays are different through the different angles of the two groups of magnetic tunnel junction arrays.

[0050] Figure 3 The left and right correspond to Figure 1 and Figure 2The side view of the middle magnetic sensor. The protective layer 107 is arranged on the magnetic tunnel junction, the thickness of the protective layer 107 is about 1-10 microns, and the protective layer 107 is used to protect the magnetic tunnel junction structure. The thickness of the magnetic flux attenuator is 1-50 microns, and the thickness of all the magnetic flux attenuators is the same. The thickness of the magnetic tunnel junction array is 0.5-2 microns, and the thickness of all the magnetic tunnel junction arrays is the same. The voltage signal U1, U2, U3,.., Un of each half-bridge output of the three-axis magnetic field sensor is expressed as Un=Nnx×Hx+Nnz×Hz; wherein Nnx and Nnz are the sensitivity coefficients of the magnetic tunnel junction array to the magnetic field Hx and the z-axis magnetic field Hz, respectively. By separately applying the x-direction magnetic field Hx and the z-axis direction magnetic field Hz, the corresponding voltage signal Un is measured, and Nnx=Un / Hx and Nnz=Un / Hz are calculated. The size of the magnetic field in each group of magnetic sensing modules is solved, and the size of the three-axis magnetic field is calculated. The sensitivity coefficients of each group of magnetic tunnel junction arrays to the three-axis magnetic field are different, and the sensitivity coefficients can be obtained through simulation calculation and actual experiment at the beginning of design. The size of the three-axis magnetic field is obtained by solving the simultaneous equations.

[0051] As shown in Figure 4 , taking the case when the magnetic field direction is the Z direction as an example, the magnetic tunnel junctions located on both sides of the magnetic flux attenuator have different surface-induced magnetic field sizes and directions due to different positions, and therefore have different output results. When the sensitivity coefficients of the magnetic tunnel junction array to the magnetic field Hx and the z-axis magnetic field Hz are known, the equations of the voltage signals are solved simultaneously to obtain the sizes of the magnetic fields in the X and Z directions; the same applies to the YZ plane.

[0052] Embodiment 2

[0053] According to another aspect of the embodiment of the application, a preparation method of a three-axis magnetic field sensor is also provided, as shown in Figure 5 , comprising:

[0054] Step S1, growing a magnetic tunnel junction film on a substrate;

[0055] Step S2, forming a magnetic tunnel junction array structure through a photolithography process;

[0056] Step S3, taking out the magnetic tunnel junction array through a wafer die process and arranging the magnetic tunnel junction array according to a fixed relative position, and dividing the magnetic tunnel junction array into two groups of mutually orthogonal magnetic sensing modules, each module having at least two groups of magnetic tunnel junction arrays with different relative positions from the designed magnetic flux concentrator;

[0057] Step S4, connecting the half-bridge structures through an electrode plating process;

[0058] Step S5, preparing an insulating protective layer and a seed layer before plating the magnetic flux concentrator above the film array;

[0059] As an alternative embodiment, the flux attenuator layer is electroplated on the seed layer. All the magnetic tunnel junction arrays are taken from the same wafer, only the placement direction or position after taking off is different to ensure the stability and yield of the process.

[0060] The above disclosure is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or modifications within the technical scope disclosed by the present application, which should be covered within the protection scope of the present application.

Claims

1. A triaxial magnetic field sensor, characterized in that, It includes two sets of magnetic sensing modules with identical structures and orthogonal positions. Each set of magnetic field sensor modules includes two or more substrate layers, a magnetic tunnel junction array, a fixed resistor, and a magnetic flux attenuator. The magnetic tunnel junction array is disposed above the substrate and has a uniaxial sensitivity characteristic to the short axis direction of the magnetic tunnel junction; The fixed resistor is connected to the magnetic tunnel junction array to form a half-bridge; The magnetic flux attenuator is positioned above the magnetic tunnel junction array; Below each flux attenuator are two sets of magnetic tunnel junction arrays, which are parallel to the long side of the projection surface of the flux attenuator. The left and right magnetic tunnel junction arrays below each flux attenuator form a half-bridge structure with a fixed resistor module. The voltage input terminals of each half-bridge structure are connected in parallel, and the output terminals are independent of each other. The distances of the left and right magnetic tunnel junction arrays below each flux attenuator from the projection long side of the nearest flux attenuator are different. or, Below each flux attenuator are two sets of magnetic tunnel junction arrays, which are parallel to the long side of the projection surface of the flux attenuator. The magnetic tunnel junction arrays on the left and right sides below each flux attenuator form a half-bridge structure with a fixed resistor module. The voltage input terminals of each half-bridge structure are connected in parallel, and the output terminals are independent of each other. The sensitive structural unit of one of the magnetic tunnel junction arrays has a fixed angle of 10 to 80° with the projection long side of the nearest flux attenuator, and the angles are different.

2. The triaxial magnetic field sensor according to claim 1, characterized in that, The magnetic tunnel junction array comprises an array of multiple sensitive structural units, the planar shape of which is rectangular or elliptical.

3. The triaxial magnetic field sensor according to claim 1, characterized in that, The projection of the magnetic flux attenuator is rectangular.

4. The triaxial magnetic field sensor according to claim 1, characterized in that, The voltage signals U1, U2, U3, ..., Un output by each half-bridge are expressed as Un = Nnx × Hx + Nnz × Hz; where Nnx and Nnz are the sensitivity coefficients of the magnetic tunnel junction array to the corresponding sensitive axis magnetic field Hx and z-axis magnetic field Hz, respectively. They are obtained by applying the x-direction magnetic field Hx and the z-axis magnetic field Hz separately, measuring the corresponding voltage signal Un, and calculating it using Nnx = Un / Hx and Nnz = Un / Hz.

5. The triaxial magnetic field sensor according to claim 1, characterized in that, The sensitivity coefficients of the magnetic tunnel junction array to the sensitive axis magnetic field Hx and the z-axis magnetic field depend on the relative positions of the magnetic tunnel junction array and the magnetic flux attenuator. The magnetic sensing modules in the triaxial magnetic field sensor, which are orthogonally positioned, have sensitivity characteristics to the x and z axes and the y and z axes, respectively. The output voltages U1, U2, U3, ..., Un of each half-bridge are measured at this time. The magnitude of the magnetic field in the two sets of magnetic sensing modules is obtained by solving the equations for the output voltage of each half-bridge. The magnitude of the magnetic field in the two sets of magnetic sensing modules is obtained by solving the equations for the output voltage of each half-bridge.

6. The triaxial magnetic field sensor according to claim 1, characterized in that, The thickness of the magnetic flux attenuator is 1~50μm, and the thickness of the magnetic tunnel junction array is 0.5~2μm.

7. A method for fabricating a triaxial magnetic field sensor, characterized in that, include: Growing magnetically sensitive thin films on a substrate; Magnetic tunnel junction array structure using photolithography; The magnetic tunnel junction array is extracted using a wafer die-off process and arranged in a fixed relative position, forming two groups of mutually orthogonal magnetic sensing modules. Each module has at least two magnetic tunnel junction arrays with relative positions different from the designed magnetic flux concentrator. The half-bridge structures are connected using an electrode plating process; An insulating protective layer and a seed layer in front of the electroplated magnetic flux concentrator are prepared above the thin film array; A magnetic flux attenuator layer is electroplated on the seed layer to obtain the triaxial magnetic field sensor according to any one of claims 1-6.

8. The method for preparing a triaxial magnetic field sensor according to claim 7, characterized in that, All magnetic tunnel junction arrays are taken from the same wafer.

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