Single chip full bridge TMR magnetic field sensor

Abstract

A single chip full-bridge TMR magnetic field sensor includes: a magnetoresistive element and a bias current branch, wherein the magnetoresistive element is bridge-connected to form a full-bridge structure; the magnetoresistive element includes a free layer, a pinned layer and a bias current layer, wherein the bias current layer is connected to the bias current branch, and the bias current branch inputs a bias current to the bias current layer; the directions of the currents in the bias current layers of the magnetoresistive elements on adjacent bridge arms are opposite, and the directions of the currents in the bias current layers of the magnetoresistive elements on opposite bridge arms are the same. The present invention sets a bias current layer in the magnetoresistive element, and uses the bias current layer to change the magnetization direction of the free layer in the magnetoresistive element to achieve a sensitive response to an external magnetic field. The magnetic field sensor of the present invention can form a full-bridge structure on a single chip at one time, greatly reducing the difficulty and production cost of the single chip full-bridge magnetic sensor preparation process.

Description

Technical Field

[0001] The invention belongs to the technical field of magnetic field detection, and in particular relates to a push-pull full-bridge TMR magnetic field sensor. Background Art

[0002] TMR (Tunnel Magneto Resistance) elements are new magnetoresistance effect sensors that have begun to be used in industry in recent years. They use the tunnel magnetoresistance effect of magnetic multilayer film materials to sense the magnetic field. Compared with the widely used AMR elements, GMR elements, and Hall elements, TMR elements have a larger resistance change rate, better temperature stability, higher sensitivity, and a wider linear range. Compared with AMR elements, TMR elements do not require additional set / reset coil structures; compared with GMR elements, TMR elements have lower power consumption; compared with Hall elements, TMR elements do not require additional magnetic focusing ring structures.

[0003] TMR elements are also called magnetic tunnel junction elements (MTJ elements for short). Connecting MTJ elements into a push-pull full bridge can change the signal of the magnetic field sensor so that its output voltage can be easily amplified to change the noise of the signal, cancel the common-mode signal, reduce temperature drift or overcome other shortcomings, which is beneficial to the application of magnetic field sensors. Connecting MTJ elements into a push-pull bridge requires that the magnetization directions of the pinned layers of the MTJ elements on adjacent bridge arms are opposite. However, since the magnetic field strength required for magnetic moment reversal is the same, the magnetization directions of the pinned layers of the MTJ elements on the same substrate are usually the same, which brings great difficulties to the manufacture of push-pull bridge TMR magnetic field sensors. At present, the manufacture of push-pull full-bridge TMR magnetic field sensors mainly consists of the following methods:

[0004] A push-pull full-bridge magnetic field sensor based on a two-film formation process is constructed in which the MTJ element with opposite magnetization directions of the pinned layer is obtained by two depositions. However, when the thin film formed by the second deposition is annealed, the thin film deposited for the first time will be affected, resulting in poor consistency between the two film formations. This results in different resistances of different bridge arms of the bridge sensor, which will affect the performance of the sensor.

[0005] The push-pull full-bridge magnetic field sensor based on multi-chip packaging uses MTJ elements with the same magnetization direction of the pinned layer to connect into a full bridge, and then shields a group of MTJ elements on the opposite bridge arms in the full bridge and makes them into wafers. One of the wafers is flipped 180° relative to the other wafer to connect into a push-pull full bridge, and then multi-chip packaging is performed. The push-pull full-bridge magnetic field sensor made using multi-chip packaging technology has problems such as large size and high production cost because it is made of multi-chip packaging; and after flipping the wafer, the two wafers need to be accurately positioned in the same horizontal plane, which increases the possibility of sensor measurement loss due to the asymmetry of the MTJ elements.

[0006] The push-pull full-bridge magnetic field sensor based on laser local annealing first prepares the MTJ full bridge on the substrate, and then anneals the MTJ element in the same magnetic field. At this time, the magnetization direction of the pinned layer of the MTJ element on different bridge arms is the same; then the MTJ element is locally heated by laser to assist the magnetic moment reversal, so that the magnetization direction of the pinned layer of the MTJ element on adjacent bridge arms is opposite, thus realizing the push-pull full-bridge magnetic field sensor. However, laser heating to assist the local reversal of magnetic domains requires special equipment, which not only increases the complexity of the sensor manufacturing process, but also increases the cost. In addition, the consistency of the resistance of each bridge arm of the push-pull full-bridge sensor made by laser heating cannot be guaranteed. Summary of the invention

[0007] The object of the present invention is to provide a single chip full-bridge TMR magnetic field sensor which can reduce the difficulty of the preparation process and the production cost.

[0008] In order to achieve the above object, the present invention adopts the following technical solutions:

[0009] A single chip full-bridge TMR magnetic field sensor comprises: a magnetoresistive element and a bias current branch, wherein the magnetoresistive element is bridge-connected to form a full-bridge structure; the magnetoresistive element comprises a free layer, a pinned layer and a bias current layer, the bias current layer is connected to the bias current branch, and the bias current branch inputs a bias current to the bias current layer; the directions of the currents in the bias current layers of the magnetoresistive elements on adjacent bridge arms are opposite, and the directions of the currents in the bias current layers of the magnetoresistive elements on opposite bridge arms are the same.

[0010] Furthermore, the magnetoresistive element comprises a lower electrode layer, a pinned layer, a first insulating layer, a free layer, an upper electrode layer, a second insulating layer and a bias current layer which are arranged in sequence.

[0011] Furthermore, the bias current branch includes a first bias circuit branch and a second bias circuit branch, the first bias current branch is connected to the magnetoresistive elements located on two adjacent bridge arms in the full-bridge structure, and the second bias current branch is connected to the magnetoresistive elements located on the other two adjacent bridge arms in the full-bridge structure.

[0012] Furthermore, the bias current branch is connected to the bias current source. After the current is input from the current input end, it flows through the magnetoresistive elements and magnetoresistive elements located on two adjacent bridge arms in sequence through the first bias current branch, and flows through the magnetoresistive elements and magnetoresistive elements located on the other two adjacent bridge arms in sequence through the second bias current branch, and then flows out from the current output end.

[0013] Furthermore, the magnetoresistive element is formed in one step by using a film forming process.

[0014] Furthermore, when no current flows through the bias current layer, the magnetization direction of the free layer and the magnetization direction of the pinned layer of the magnetoresistive element are perpendicular to each other.

[0015] Furthermore, the magnitude of the current flowing through the bias current layer is the same

[0016] As can be seen from the above technical scheme, the present invention sets a bias current layer in the magnetoresistive element, inputs a bias current into the bias current layer through a bias current branch, and uses the magnetic field generated by the bias current to change the magnetization direction of the free layer of the magnetoresistive element. Since the directions of the bias currents in the magnetoresistive elements on adjacent bridge arms are opposite, the resistance values ​​of the magnetoresistive elements on adjacent bridge arms change with the external magnetic field in opposite directions, and the directions of the bias currents in the magnetoresistive elements on the opposite bridge arms are the same, then the resistance values ​​of these magnetoresistive units change with the external magnetic field in the same trend, thereby forming a push-pull full-bridge magnetic field sensor. The magnetoresistive element of the present invention can be formed at one time on the same substrate using a film forming process, and the magnetoresistive elements of each bridge arm in the full-bridge structure have good consistency, have the advantages of high sensitivity, small size, and can suppress temperature drift, and the production process is simple, no expensive equipment is required, and the production cost is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0018] Figure 1 It is a structural schematic diagram of an embodiment of the present invention;

[0019] Figure 2 It is a structural schematic diagram of a magnetoresistive element according to an embodiment of the present invention;

[0020] Figure 3 is a curve diagram showing the change of the resistance value of the magnetoresistive element with the angle between the magnetization direction of the free layer and the magnetization direction of the pinned layer;

[0021] Figure 4a and Figure 4b Schematic diagrams of magnetization directions of free layers of magnetoresistive elements located on adjacent bridge arms respectively;

[0022] Figure 5 The magnetization direction of the free layer of the magnetoresistive element is Figure 4a The curve diagram of its resistance value changing with the external magnetic field in the sensitive direction in the state shown;

[0023] Figure 6 The magnetization direction of the free layer of the magnetoresistive element is Figure 4b The graph shows the resistance value changing with the external magnetic field in the sensitive direction in the state shown. DETAILED DESCRIPTION

[0024] In order to make the above and other purposes, features and advantages of the present invention more obvious, embodiments of the present invention are specifically cited below and described in detail with reference to the accompanying drawings.

[0025] like Figure 1 As shown, the single chip full-bridge TMR magnetic field sensor of this embodiment includes 4 groups of magnetoresistive elements a1, a2, a3, a4, a first bias current branch L1 and a second bias current branch L2. The basic structure of each group of magnetoresistive elements is the same, and the 4 groups of magnetoresistive elements are bridge-connected to form a full-bridge structure, and the 4 groups of magnetoresistive elements are respectively located on the four bridge arms of the full-bridge structure. The first bias current branch L1 is connected to the magnetoresistive elements (a1, a2) on two adjacent bridge arms, and the second bias current branch L2 is connected to the magnetoresistive elements (a3, a4) on the other two adjacent bridge arms. The bias current branch is connected to a bias current source (not shown), and after the current is input from the current input terminal A, it flows through the magnetoresistive element a1 and the magnetoresistive element a2 in sequence through the first bias current branch L1, and flows through the magnetoresistive element a3 and the magnetoresistive element a4 in sequence through the second bias current branch L2, and then flows out from the current output terminal B. In this embodiment, the direction of the current in the first bias current branch L1 in the magnetoresistive element a1 is opposite to that in the magnetoresistive element a2, and the direction of the current in the second bias current branch L2 in the magnetoresistive element a3 is opposite to that in the magnetoresistive element a4, but the directions of the currents in the magnetoresistive elements on opposite bridge arms are the same, that is, the directions of the currents in the magnetoresistive element a1 and the magnetoresistive element a3 are the same, and the directions of the currents in the magnetoresistive element a2 and the magnetoresistive element a4 are the same.

[0026] like Figure 2As shown, the magnetoresistive element includes, from bottom to top, a lower electrode layer 10, a pinned layer 11, a first insulating layer 12, a free layer 13, an upper electrode layer 14, a second insulating layer 15 and a bias current layer 16. The bias current layer in the magnetoresistive element is used to change the magnetization direction of the free layer in the magnetoresistive element. The free layer 13 is made of ferromagnetic material, and the magnetization direction of the free layer 13 will change with the change of the external magnetic field. The pinned layer 11 is composed of a magnetic layer with a fixed magnetization direction and an antiferromagnetic layer. The magnetization direction of the pinned layer 11 is pinned in a fixed direction and will not change with the change of the external magnetic field. The bias current layer 16 is connected to the bias current branch, and the current in the bias current branch will flow through the bias current layer 16. When no current passes through the bias current layer 16, the magnetization direction of the free layer 13 is perpendicular to the magnetization direction of the pinned layer 11 ( Figure 2 When current flows through the bias current layer 16, the current will generate a magnetic field and change the magnetization direction of the free layer 13. The measured resistance value between the upper electrode layer 14 and the lower electrode layer 10 is affected by the relative magnetization direction between the free layer 13 and the pinned layer 11. Figure 3 As shown, the resistance of the magnetoresistive element changes with the change of the angle between the magnetization direction of the free layer and the magnetization direction of the pinned layer. When the angle between the magnetization directions of the two increases, the resistance also increases. When the angle between the magnetization direction of the free layer of the magnetoresistive element and the magnetization direction of the pinned layer is consistent, under the action of the external magnetic field, the resistance of the magnetoresistive element changes consistently with the change of the external magnetic field.

[0027] When the current flows through the magnetoresistive elements located on adjacent bridge arms via the bias current branch, the directions of the currents in the magnetoresistive elements (bias current layers) are opposite, so the changes in the magnetization directions of the free layers of the magnetoresistive elements will also be different. Figure 4a and Figure 4b The following are schematic diagrams of the magnetization directions of the free layer and the pinned layer of two magnetoresistive elements located on adjacent bridge arms when currents in opposite directions pass through them. Figure 4a As shown, the direction of the current in the bias current layer 16 is perpendicular to the paper surface and inward. Affected by the magnetic field generated by the current, the magnetization direction of the free layer 13 changes from being perpendicular to the magnetization direction of the pinned layer 11 to an obtuse angle between the two. Figure 4b As shown, the direction of the current in the bias current layer 16 is perpendicular to the paper surface and outward. Affected by the magnetic field generated by the current, the magnetization direction of the free layer 13 changes from being perpendicular to the magnetization direction of the pinned layer 11 to an acute angle between the two.

[0028] like Figure 5 As shown in Figure 2, when the magnetization direction of the free layer of the magnetoresistive element is Figure 4aIn the state shown, that is, when the angle between the magnetization direction of the free layer and the magnetization direction of the pinned layer is an obtuse angle, if the external magnetic field increases, the resistance value R of the magnetoresistive element decreases. Conversely, when the external magnetic field decreases, the resistance value R of the magnetoresistive element increases. Figure 6 As shown in Figure 2, when the magnetization direction of the free layer of the magnetoresistive element is Figure 4b In the state shown, that is, when the angle between the magnetization direction of the free layer and the magnetization direction of the pinned layer is an acute angle, if the external magnetic field increases, the resistance value R of the magnetoresistive element increases, and vice versa, when the external magnetic field decreases, the resistance value R of the magnetoresistive element decreases. In other words, for two magnetoresistive elements with opposite current directions in the bias current layer, under the influence of the same external magnetic field, the resistance changes of the two magnetoresistive elements are always opposite.

[0029] In the full-bridge magnetic field sensor of the present invention, the magnetoresistance elements on adjacent bridge arms, such as a1 and a2, a2 ​​and a3, a3 and a4, a4 ​​and a1, have opposite directions of current in the magnetoresistance elements. Therefore, the change trends of the resistance values ​​of these magnetoresistance units are always opposite ( Figure 5 ), and for the magnetoresistive elements on the opposite bridge arms, such as a1 and a3, a2 and a4, since the current flows in the same direction in the magnetoresistive elements, the resistance values ​​of these magnetoresistive units have the same change trend ( Figure 6 ).like Figure 1 As shown, the magnetoresistive element is connected to the input electrodes (C, D) and the output electrodes (E, F). When a constant voltage V is applied between the input electrodes C and D, BIAS When , the voltage between the output electrodes E and F changes with the change of the external magnetic field M, thus forming a push-pull full-bridge magnetic field sensor.

[0030] The magnetoresistance element of the present invention can be formed once by a film forming process, and the magnetoresistance elements can be arranged parallel to each other. The magnetoresistance element can make the magnetization direction of the free layer and the magnetization direction of the pinned layer perpendicular to each other through a secondary annealing process. A bias current layer is set in the magnetoresistance element, and a bias current is input to the bias current layer through a bias current branch. The direction and magnitude of the generated bias magnetic field are adjusted by adjusting the arrangement of each magnetoresistance element, the flow direction of the current in the bias current layer, and the magnitude of the current. In the above-mentioned embodiment, two bias current branches are set, but different numbers of bias current branches can also be set as needed to provide bias current for each magnetoresistance element, so that the current directions in the bias current layers of the magnetoresistance elements on adjacent bridge arms are opposite, and the current directions in the bias current layers of the magnetoresistance elements on the relative bridge arms are the same.

[0031] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. Single chip full bridge TMR magnetic field sensor, characterized in that: include: 4 groups of magnetoresistive elements and bias current branches, wherein the 4 groups of magnetoresistive elements are bridge-connected to form a full-bridge structure; The magnetoresistive element comprises a lower electrode layer, a pinned layer, a first insulating layer, a free layer, an upper electrode layer, a second insulating layer and a bias current layer which are arranged in sequence, the bias current layer is connected to the bias current branch, and the bias current branch inputs a bias current to the bias current layer; The directions of the currents in the bias current layers of the magnetoresistive elements located on adjacent bridge arms are opposite, and under the influence of the same external magnetic field, the resistance changes of the magnetoresistive elements located on adjacent bridge arms are always opposite; The directions of the currents in the bias current layers of the magnetoresistive elements on opposite bridge arms are the same, and under the influence of the same external magnetic field, the resistance changes of the magnetoresistive elements on opposite bridge arms are always the same.

2. The single chip full bridge TMR magnetic field sensor according to claim 1, characterized in that: The bias current branch includes a first bias current branch and a second bias current branch, the first bias current branch is connected to the magnetoresistive elements located on two adjacent bridge arms in the full-bridge structure, and the second bias current branch is connected to the magnetoresistive elements located on the other two adjacent bridge arms in the full-bridge structure.

3. The single chip full bridge TMR magnetic field sensor according to claim 2, characterized in that: The bias current branch is connected to the bias current source. After the current is input from the current input end, it flows through the magnetoresistive elements located on two adjacent bridge arms in sequence through the first bias current branch, and flows through the magnetoresistive elements located on the other two adjacent bridge arms in sequence through the second bias current branch, and then flows out from the current output end.

4. The single chip full bridge TMR magnetic field sensor according to claim 1, characterized in that: The magnetoresistive element is formed at one time by using a film forming process.

5. The single chip full bridge TMR magnetic field sensor according to claim 1, characterized in that: When no current flows through the bias current layer, the magnetization direction of the free layer and the magnetization direction of the pinned layer of the magnetoresistive element are perpendicular to each other.

6. The single chip full bridge TMR magnetic field sensor according to claim 1 or 2, characterized in that: The magnitudes of the currents flowing through the bias current layers are the same.

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