A TMR full-bridge magnetic sensor and its preparation method

Abstract

A TMR full-bridge magnetic sensor comprises: a substrate and a TMR unit arranged on the substrate, wherein the TMR unit comprises a free layer, a pinning layer and a tunnel layer, four groups of TMR units are bridge-connected to form a full-bridge structure, and the four groups of TMR units are respectively located on four bridge arms of the full-bridge structure; the aspect ratio of the TMR unit is not equal to 1, the long axes of the TMR units located on adjacent bridge arms are perpendicular to each other, and the long axes of the TMR units located on opposite bridge arms are parallel to each other. The present invention arranges the TMR units on the full-bridge structure according to the long axis direction of the TMR units, so that the long axis directions of the TMR units on adjacent bridge arms are perpendicular to each other, and the long axis directions of the TMR units on opposite bridge arms are parallel to each other, so that by applying an external magnetic field of a specific angle during magnetic field annealing, a full-bridge structure can be formed on a single chip at one time, which greatly reduces 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 full-bridge magnetic sensor with a single chip. Background Art

[0002] Magnetic sensor is a sensor that can detect the direction, strength and position of magnetic field, and has been widely used in many fields. TMR (Tunnel Magnetoresistance) type magnetoresistive sensor is a type of magnetic sensor, which has the advantages of low offset, high sensitivity and good temperature performance. It has been used in the industrial field in recent years. The magnetoresistance of TMR type sensor will change with the size and direction of the external magnetic field. Its sensitivity is better than Hall effect sensor, AMR (Anisotropy Magnetoresistance) type sensor and GMR (Giant Magnetoresistance) magnetic sensor, and it has better temperature stability and lower power consumption. In addition, the processing technology of TMR type magnetic sensor can be easily combined with existing semiconductor technology, so it has more application prospects.

[0003] The magnetoresistive sensor with full-bridge structure can effectively improve the sensitivity and temperature stability of the device. Since the magnetoresistive change of TMR sensor comes from the relative orientation of the free layer and the pinned layer, the full-bridge structure TMR sensor requires the magnetization direction of the pinned layer of the TMR units on adjacent bridge arms to be opposite. However, on the same chip, the TMR units prepared at one time usually have the same process throughout the whole process, so the magnetization direction of the pinned layer of each TMR unit on the same chip is the same, which makes it difficult to form a full-bridge structure on a single chip at one time. At present, there are two ways to achieve bridging on a single chip: laser annealing and fractional deposition. Laser annealing is to use laser annealing equipment to pin the magnetization directions of the pinned layers in different regions in opposite directions, but because the laser annealing equipment is expensive, the production cost is very high. Fractional deposition is to deposit pinned layers with different magnetization directions in two times, but when depositing twice, it is easy to affect the first layer when growing the second layer, which ultimately affects the performance of the device. Summary of the invention

[0004] The object of the present invention is to provide a single-chip TMR full-bridge sensor and a preparation method thereof which can reduce the difficulty of the preparation process and the production cost.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A TMR full-bridge magnetic sensor comprises: a substrate and a TMR unit arranged on the substrate, wherein the TMR unit comprises a free layer, a pinned layer and a tunnel layer, four groups of TMR units are bridge-connected to form a full-bridge structure, and the four groups of TMR units are respectively located on four bridge arms of the full-bridge structure; the aspect ratio of the TMR unit is not equal to 1, the long axes of the TMR units located on adjacent bridge arms are perpendicular to each other, and the long axes of the TMR units located on opposite bridge arms are parallel to each other.

[0007] Furthermore, the aspect ratio of the TMR unit is greater than 10.

[0008] Furthermore, the TMR unit is in a rectangular or elliptical shape.

[0009] Furthermore, the long axis direction of the TMR unit is parallel to the direction of the bridge arm where it is located.

[0010] Furthermore, four electrodes are arranged on the substrate, including a pair of input electrodes and a pair of output electrodes, and each electrode is respectively connected to two adjacent bridge arms.

[0011] Furthermore, the magnetic moment directions of the pinned layers of the TMR units on adjacent bridge arms are different, and the magnetic moment directions of the pinned layers of the TMR units on opposite bridge arms are the same.

[0012] It can be seen from the above technical scheme that the present invention arranges the TMR units on the full-bridge structure according to the long axis direction of the TMR units, so that the long axis directions of the TMR units on adjacent bridge arms are perpendicular to each other, and the long axis directions of the TMR units on the opposite bridge arms are parallel to each other, so that by applying an external magnetic field of a specific angle during magnetic field annealing, a full-bridge structure is formed on a single chip at one time, which greatly reduces the difficulty and production cost of the single-chip full-bridge magnetic sensor preparation process. In the full-bridge magnetic sensor obtained after annealing, the magnetic moment directions of the pinned layers of the TMR units on adjacent bridge arms are different, and the magnetic moment directions of the pinned layers of the TMR units on the opposite bridge arms are basically the same, so that the TMR units on adjacent bridge arms have opposite responses to the same sensitive direction, and form opposite magnetic resistance corresponding trends to the external field, thereby realizing differential output of magnetic field detection.

[0013] The present invention also provides a method for preparing a TMR full-bridge magnetic sensor, comprising the following steps:

[0014] providing a substrate;

[0015] Depositing TMR units and electrodes on the substrate, four groups of TMR units are bridge-connected to form a full-bridge structure, a group of TMR units is arranged on each bridge arm of the full-bridge structure, the long axes of the TMR units on adjacent bridge arms are perpendicular to each other, and the long axes of the TMR units on opposite bridge arms are parallel to each other;

[0016] The TMR unit is subjected to magnetic field annealing treatment, wherein the direction of the magnetic field applied during annealing forms an angle of 45° with the long axis direction of the TMR unit. After the annealing is completed, the magnetic moment directions of the pinned layers of the TMR units on adjacent bridge arms are different, while the magnetic moment directions of the pinned layers of the TMR units on the opposite bridge arms are the same. 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 schematic diagram of the structure of the TMR unit in the TMR type magnetoresistive sensor;

[0019] Figure 2 Schematic diagram of the magnetic moment direction of the pinned layer of the free layer of the TMR cell;

[0020] Figure 3 It is a graph showing the relationship between the resistance of the TMR unit and the magnetic moment directions of the free layer and the pinned layer and the external magnetic field;

[0021] Figure 4 Schematic diagram of the relative relationship between the magnetic moment directions of the free layer and the pinned layer;

[0022] Figure 5a Schematic diagram of the change of the magnetic moment direction of the free layer under the action of an external magnetic field when the magnetic moment directions of the free layer and the pinned layer are parallel to each other;

[0023] Figure 5b The curve diagram of the relationship between the resistance and the strength of the external magnetic field of the TMR unit with the magnetic moments of the free layer and the pinned layer parallel to each other under the action of the external magnetic field;

[0024] Figure 6a Schematic diagram of the change of the magnetic moment direction of the free layer under the action of an external magnetic field when the magnetic moment directions of the free layer and the pinned layer are anti-parallel;

[0025] Figure 6b The curve diagram of the relationship between the resistance and the strength of the external magnetic field of a TMR unit with the magnetic moments of the free layer and the pinned layer in antiparallel directions under the action of an external magnetic field;

[0026] Figure 7 It is a structural schematic diagram of an embodiment of the present invention;

[0027] Figure 8 A schematic diagram of the magnetization direction of the pinned layer of the TMR unit of the fourth group according to the embodiment of the present invention after annealing;

[0028] Fig. 9 Schematic diagram of a Wheatstone full-bridge circuit according to an embodiment of the present invention;

[0029] Fig.10 The embodiment of the present invention is a graph showing the magnetoresistance variation trend of two adjacent TMR units under the action of an external magnetic field applied along the y-axis direction;

[0030] Fig.11 A graph showing a variation trend of the output voltage of an embodiment of the present invention under the action of an external magnetic field applied along the y-axis direction. DETAILED DESCRIPTION

[0031] 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.

[0032] Figure 1 It is a schematic diagram of the structure of the TMR unit in the TMR sensor. Figure 1 As shown, the TMR unit includes a free layer, a tunnel layer 3 and a pinned layer 4 from top to bottom, arrow 2 indicates the magnetic moment direction of the free layer 1, and arrow 5 indicates the magnetic moment direction of the pinned layer. Figure 2 As shown, when there is no external magnetic field, the magnetic moment direction 2 of the free layer of the TMR unit and the magnetic moment direction 5 of the pinned layer 4 are perpendicular to each other. When an external magnetic field 6 is applied, within the detection magnetic field range of the magnetic sensor, the magnetic moment direction 5 of the pinned layer 4 has no response to the external magnetic field 6, and its magnitude and direction will not change with the change of the external magnetic field 6, while the magnetic moment direction 2 of the free layer 1 responds sensitively to the external magnetic field 6, and its magnitude and direction will change with the change of the external magnetic field 6.

[0033] like Figure 3 As shown ( Figure 3 R in the figure represents the resistance value of the TMR unit, and H represents the field strength of the external magnetic field. The resistance value of the TMR unit is related to the relative magnetization state of the magnetic moment direction 2 of the free layer 1 and the magnetic moment direction 5 of the pinned layer 4. When the magnetic moment direction 2 of the free layer 1 and the magnetic moment direction 5 of the pinned layer 4 are parallel in the same direction, the resistance of the TMR unit is the smallest. When the magnetic moment direction 2 of the free layer 1 and the magnetic moment direction 5 of the pinned layer 4 are antiparallel, the resistance of the TMR unit is the largest.

[0034] exist Figure 4 Under the action of the external magnetic field 6 shown, the magnetic moment direction 2 of the free layer parallel to the magnetic moment direction 5 of the pinned layer will change as follows: Figure 5a The flip shown in the figure has a corresponding change in the resistance of the TMR unit. Figure 5b and the magnetic moment direction 2' of the free layer which is antiparallel to the magnetic moment direction 5 of the pinned layer will occur as Figure 6a The flip shown in the figure has a corresponding change in the resistance of the TMR unit. Figure 6bThat is, when the relative relationship between the magnetic moment direction of the free layer and the magnetic moment direction of the pinned layer is different, the resistance of the TMR unit will have different change trends when the same external magnetic field is applied. When the magnetic moment direction 2 of the free layer is biased in parallel with the magnetic moment direction 5 of the pinned layer and biased in anti-parallel with the magnetic moment direction 5 of the pinned layer, the same external magnetic field is applied, and the two will show opposite resistance change trends.

[0035] Figure 7 Schematic diagram of the structure of the TMR full-bridge sensor according to an embodiment of the present invention. Figure 7 As shown, 4 groups of TMR units (a1, a2, a3, a4) and 4 electrodes (P1, P2, P3, P4) are deposited on the substrate of the sensor (not shown). The structure of each group of TMR units is the same, and they all have a free layer, a pinned layer and a tunnel layer. The 4 groups of TMR units are bridge-connected to form a full-bridge structure. The 4 groups of TMR units are respectively located on the 4 bridge arms of the full-bridge structure, and each electrode is respectively connected to two adjacent bridge arms. Among the 4 electrodes, a pair of electrodes (P1, P3) are input electrodes, and the other pair of electrodes (P2, P4) are output electrodes. The length and width of the TMR unit of the present invention are not equal, that is, the aspect ratio of the TMR unit is not equal to 1, and the shape of the TMR unit can be rectangular or elliptical. For the convenience of explanation, the center line of the TMR unit along the length direction is defined as the major axis, and the major axis direction of the TMR unit is parallel to the direction of the bridge arm where it is located. In order to ensure that the TMR unit has a large shape anisotropy field inside, the aspect ratio of the TMR unit should be relatively large so that the shape anisotropy field in the free layer is greater than the influence of the external magnetic field. If the aspect ratio of the TMR unit is relatively small, the internal shape anisotropy field is too small to be balanced with the external annealing magnetic field. After annealing, the magnetic moment direction of the pinned layer will be along the direction of the external magnetic field, and a bridge connection cannot be formed. Preferably, the aspect ratio of the TMR unit can be greater than 10. The specific value of the aspect ratio of the TMR unit is an empirical value and is also related to the formula of the free layer, so it can be set according to different situations.

[0036] The TMR units located on the four bridge arms are opposite to each other, wherein the long axes of adjacent TMR units are perpendicular to each other, and the long axes of the opposite TMR units are parallel to each other. The direction of the anisotropic field inside the TMR unit is along the long axis direction of the TMR unit. Since the long axis directions of the TMR units are different, the directions of the shape anisotropic fields inside the TMR units are also different. The TMR units in the full-bridge structure are arranged according to their long axis directions. During annealing, by applying an external magnetic field at a specific angle (the direction of the external magnetic field is along the diagonal direction of the TMR full-bridge structure, that is, the angle with the long axis direction of the TMR unit is 45°), the internal magnetic moment of the TMR unit is affected by the combined effect of the external magnetic field and the internal shape anisotropic field, and the magnetization direction of the pinned layer will change according to the arrangement direction (long axis direction) of the TMR unit, so that the pinned layer of each TMR unit can form a different magnetic moment direction accordingly.

[0037] The steps of the preparation method of the TMR full-bridge sensor of the present invention are as follows:

[0038] providing a substrate;

[0039] Four groups of TMR units and electrodes are deposited on the substrate, for example, magnetron sputtering is used to form TMR units on the substrate, the four groups of TMR units are bridge-connected to form a full-bridge structure, and the input and output electrodes are connected, the TMR units are located on the bridge arms of the full-bridge structure, wherein the long axes of the TMR units on adjacent bridge arms are perpendicular to each other, and the long axes of the TMR units on opposite bridge arms are parallel to each other, such as Figure 7 As shown; the two diagonal lines in the full-bridge structure are defined as the x-axis and the y-axis, that is, the direction from P3 to P1 is the y-axis, the direction from P4 to P2 is the x-axis, x1 is the direction that forms an angle of 45° with the x-axis, y1 is the direction that forms an angle of 45° with the y-axis, and when depositing the TMR unit, the long axis direction of the TMR units a1 and a3 is parallel to the x1 axis, and the long axis direction of the TMR units a2 and a4 is parallel to the y1 axis;

[0040] The TMR unit is subjected to magnetic field annealing treatment, such as Figure 8 As shown, an external magnetic field 9 is applied during annealing, and the direction of the external magnetic field 9 is along the x-axis direction or the y-axis direction, that is, the direction of the external magnetic field 9 forms a 45° angle with the long axis direction of the TMR unit, so that the four groups of TMR units can form a symmetrical magnetic moment distribution. After annealing, the magnetization directions mp of the pinned layers of the four groups of TMR units are as follows: Figure 8 As shown, the magnetic moment directions of the pinned layers of adjacent TMR units are different, and the magnetic moment directions of the pinned layers of the opposite TMR units are the same. The same magnetic moment directions of the pinned layers of the opposite TMR units mentioned in the present invention do not only refer to the situation that the magnetic moment directions of the pinned layers of the opposite TMR units are strictly consistent, but also include the situation that the magnetic moment directions of the pinned layers of the opposite TMR units are approximately the same.

[0041] Taking this embodiment as an example, when an external magnetic field along the y-axis direction is applied to the sensor, the resistance changes of different TMR units are different. Since the magnetization directions of the pinned layers of adjacent TMR units along the y-axis are opposite, and the magnetization directions of the pinned layers of the opposite TMR units along the y-axis are the same, the magnetoresistance change trends of adjacent TMR units in the y-axis direction are opposite, and the adjacent TMR units have opposite responses to the same sensitive direction, forming a full-bridge output. The method of the present invention can deposit a full-bridge structure on the same chip at one time, greatly reducing the difficulty and cost of the production process.

[0042] The full bridge circuit of the present invention is as follows Fig. 9 As shown, Fig. 9 R1, R2, R3, and R4 in the figure represent the magnetic resistance of the four groups of TMR units a1, a2, a3, and a4, respectively. When a constant bias is applied to both ends (P1 and P3) of the full-bridge structure, the voltage output of the full-bridge circuit is In the full-bridge sensor structure, the magnetic resistance change of a1 and a3 (R1, R3) is opposite to the magnetic resistance change of a2 and a4 (R2, R4). For example, when the sensor is subjected to an external magnetic field, the resistance of R1 and R3 increases, while the resistance of R2 and R4 decreases, and the voltage output increases.

[0043] Fig.10 The magnetic resistance variation trend of the TMR units a1 and a2 in the sensor to the external magnetic field along the y-axis direction is shown in the figure. A constant voltage is applied to the input electrodes (P1 and P2) of the full-bridge sensor. When the magnetic field along the y-axis direction changes, the output voltage trend of the sensor output electrodes (P2 and P4) is shown in the figure below. Fig.11 shown.

[0044] 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. A method for preparing a TMR full-bridge magnetic sensor, characterized in that: The following steps are involved: providing a substrate; Depositing TMR units and electrodes on the substrate, four groups of TMR units are bridge-connected to form a full-bridge structure, a group of TMR units is arranged on each bridge arm of the full-bridge structure, the long axes of the TMR units on adjacent bridge arms are perpendicular to each other, and the long axes of the TMR units on opposite bridge arms are parallel to each other; The TMR unit is subjected to magnetic field annealing treatment, wherein the direction of the magnetic field applied during annealing forms an angle of 45° with the long axis direction of the TMR unit. After the annealing is completed, the magnetic moment directions of the pinned layers of the TMR units on adjacent bridge arms are different, while the magnetic moment directions of the pinned layers of the TMR units on the opposite bridge arms are the same.

2. The method for preparing the TMR full-bridge magnetic sensor according to claim 1, characterized in that: The aspect ratio of the TMR unit is greater than 10.

3. The method for preparing the TMR full-bridge magnetic sensor according to claim 1 or 2, characterized in that: The TMR unit is in a rectangular or elliptical shape.

4. The method for preparing the TMR full-bridge magnetic sensor according to claim 1, characterized in that: The electrodes include a pair of input electrodes and a pair of output electrodes, and the electrodes are connected to two adjacent bridge arms. 5.TMR full-bridge magnetic sensor, including: A substrate and a TMR unit disposed on the substrate, wherein the TMR unit includes a free layer, a pinned layer and a tunnel layer, four groups of TMR units are bridge-connected to form a full-bridge structure, and the four groups of TMR units are respectively located on four bridge arms of the full-bridge structure; It is characterized in that: the TMR full-bridge magnetic sensor is a TMR full-bridge magnetic sensor prepared by the preparation method described in any one of claims 1-4.

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