CN110824392A - A kind of TMR full bridge magnetic sensor and preparation method thereof - Google Patents

Abstract

A TMR full-bridge magnetic sensor includes: a substrate and a TMR unit disposed on the substrate. 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. The TMR units are respectively located on the four bridge arms of the full bridge structure; the aspect ratio of the TMR units is not equal to 1, the long axes of the TMR units located on the adjacent bridge arms are perpendicular to each other, and the TMR units located on the opposite bridge arms have The long axes 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 unit, so that the long axis directions of the TMR units on the 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, thereby By applying an external magnetic field at 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 a single-chip full-bridge magnetic sensor fabrication process.

Description

A kind of TMR full bridge magnetic sensor and preparation method thereof

technical field

The invention belongs to the technical field of magnetic field detection, and particularly relates to a single-chip full-bridge magnetic sensor.

Background technique

A magnetic sensor is a sensor that can detect the direction, strength and position of a magnetic field, and has been widely used in many fields. TMR (Tunnel Magnetoresistance, Tunnel Magnetoresistance) type magnetoresistive sensor is a kind of magnetic sensor, which has the advantages of low offset, high sensitivity and good temperature performance, and has been applied in the industrial field in recent years. The magnetoresistance of the TMR sensor changes with the size and direction of the external magnetic field, and its sensitivity is better than that of Hall effect sensors, AMR (Anisotropy Magnetoresistance, anisotropic magnetoresistance) sensors and GMR (Giant Magnetoresistance, giant magnetoresistance) The magnetic sensor has better temperature stability and lower power consumption, and the processing technology of the TMR magnetic sensor can be easily combined with the existing semiconductor technology, so it has more application prospects.

The magnetoresistive sensor with full bridge structure can effectively improve the sensitivity and temperature stability of the device. Since the TMR sensor has its own magnetoresistance change originating from the relative orientation of the free layer and the pinned layer, the TMR sensor of the full bridge structure requires that the magnetization directions of the pinned layers of the TMR units on the adjacent bridge arms are opposite. Usually on the same chip, the TMR units prepared at one time have the same whole process, so the magnetization directions of the pinned layers of each TMR unit on the same chip are the same, and it is difficult to form a full bridge structure on a single chip at one time. Current approaches to achieve bridging on a single chip include laser annealing and graded 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 high. The stepwise deposition is to grow the pinning layers with different magnetization directions successively in two depositions. However, when the second layer is grown in two depositions, the first layer is easily affected when the second layer is grown, which ultimately affects the device performance.

SUMMARY OF THE INVENTION

The purpose 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.

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

A TMR full-bridge magnetic sensor includes: a substrate and a TMR unit disposed on the substrate. 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. The TMR units are respectively located on the four bridge arms of the full bridge structure; the aspect ratio of the TMR units is not equal to 1, the long axes of the TMR units located on the adjacent bridge arms are perpendicular to each other, and the TMR units located on the opposite bridge arms have The long axes are parallel to each other.

Further, the aspect ratio of the TMR unit is >10.

Further, the shape of the TMR unit is a rectangle or an ellipse.

Further, the long axis direction of the TMR unit is parallel to the direction of the bridge arm where it is located.

Further, the substrate is also provided with 4 electrodes, including a pair of input electrodes and a pair of output electrodes, and each electrode is respectively connected to two adjacent bridge arms.

Further, the directions of the magnetic moments of the pinned layers of the TMR units on the adjacent bridge arms are different, and the directions of the magnetic moments of the pinned layers of the TMR units on the opposite bridge arms are the same.

As can be seen from the above technical solutions, the present invention arranges the TMR units on the full-bridge structure according to the long axis direction of the TMR unit, so that the long axis directions of the TMR units on the adjacent bridge arms are perpendicular to each other, and the length of the TMR units on the bridge arms is relatively long. The axes are parallel to each other, so that by applying an external magnetic field at a specific angle during magnetic 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 fabrication process. In the full-bridge magnetic sensor obtained after annealing, the direction of the magnetic moment of the pinned layer of the TMR unit on the adjacent bridge arms is different, and the direction of the magnetic moment of the pinned layer of the TMR unit on the opposite bridge arm is basically the same, so that the TMR unit on the adjacent bridge arm has the same magnetic moment direction. It has the opposite response to the same sensitive direction, and forms the opposite trend of magnetoresistance to the applied field, and realizes the differential output of magnetic field detection.

The present invention also provides a preparation method of a TMR full-bridge magnetic sensor, comprising the following steps:

provide substrates;

TMR units and electrodes are deposited on the substrate, 4 groups of TMR units are bridge-connected to form a full bridge structure, one group of TMR units is arranged on each bridge arm of the full bridge structure, and the long axes of the TMR units on adjacent bridge arms are mutually Vertical, the long axes of the TMR units on the opposite bridge arms are parallel to each other;

The magnetic field annealing treatment is performed on the TMR unit, and the applied magnetic field direction and the long axis direction of the TMR unit form an included angle of 45°. The direction of the moment is different, and the direction of the magnetic moment of the pinned layer of the TMR unit on the opposite bridge arm is the same.

Description of drawings

In order to illustrate the embodiments of the present invention more clearly, the following will briefly introduce the accompanying drawings that need to be used in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can also be obtained from these drawings without any creative effort.

FIG. 1 is a schematic structural diagram of a TMR unit in a TMR-type magnetoresistive sensor;

2 is a schematic diagram of the direction of the magnetic moment of the pinned layer of the free layer of the TMR unit;

FIG. 3 is a graph showing the relationship between the resistance of the TMR unit and the direction of the magnetic moment of the free layer and the pinned layer and the applied magnetic field;

4 is a schematic diagram of the relative relationship between the directions of magnetic moments of the free layer and the pinned layer;

Fig. 5a is a 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 in the same direction and parallel;

Figure 5b is a graph showing the relationship between the resistance of the free layer and the pinned layer of the TMR unit with the same direction and parallel to the magnetic moment under the action of an external magnetic field and the field strength of the external magnetic field;

6a is a 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 antiparallel;

Figure 6b is a graph showing the relationship between the resistance and the field strength of the external magnetic field under the action of an external magnetic field for a TMR unit whose magnetic moment directions of the free layer and the pinned layer are antiparallel;

7 is a schematic structural diagram of an embodiment of the present invention;

8 is a schematic diagram of the magnetization directions of the pinned layers of the 4 groups of TMR cells in the embodiment of the present invention after annealing;

9 is a schematic diagram of a Wheatstone full-bridge circuit according to an embodiment of the present invention;

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

FIG. 11 is a trend diagram of output voltage variation under the action of an external magnetic field applied along the y-axis direction according to an embodiment of the present invention.

Detailed ways

In order to make the above-mentioned and other objects, features and advantages of the present invention more obvious, the following specific embodiments of the present invention are given and described in detail in conjunction with the accompanying drawings.

Figure 1 is a schematic structural diagram of a TMR unit in a TMR sensor. As shown in Figure 1, the TMR unit includes a free layer, a tunnel layer 3 and a pinned layer 4 in order from top to bottom. Arrow 2 indicates the direction of the magnetic moment of the free layer 1. Arrow 5 indicates the direction of the magnetic moment of the pinned layer. As shown in FIG. 2 , 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, and the free The direction 2 of the magnetic moment of the layer 1 is sensitive to the applied magnetic field 6 , and its magnitude and direction will change with the change of the applied magnetic field 6 .

As shown in Figure 3 (R in Figure 3 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 and the magnetic moment direction 2 of the free layer 1 and the magnetic moment direction of the pinned layer 4 5 is related to the relative magnetization state. When the magnetic moment direction 2 of the free layer 1 and the magnetic moment direction 5 of the pinned layer 4 are in the same direction and parallel, the resistance of the TMR unit is the smallest, and when the magnetic moment direction 2 of the free layer 1 and the magnetic moment direction 5 of the pinned layer 4 are opposite When parallel, the resistance of the TMR cell is the largest.

Under the action of the external magnetic field 6 shown in FIG. 4 , the magnetic moment direction 2 of the free layer, which is in the same direction and parallel to the magnetic moment direction 5 of the pinned layer, will be reversed as shown in FIG. 5 a , and the resistance of the corresponding TMR unit changes. As shown in Figure 5b; while the magnetic moment direction 2' of the free layer, which is antiparallel to the magnetic moment direction 5 of the pinned layer, will be reversed as shown in Figure 6a, and the corresponding resistance change of the TMR unit is shown in Figure 6b . That 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, and the same external magnetic field is applied, the resistance of the TMR unit will have different trends. When the magnetic moment direction 5 of the pinned layer is parallel to the same direction and the bias is antiparallel to 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.

FIG. 7 is a schematic structural diagram of a TMR full-bridge sensor according to an embodiment of the present invention. As shown in FIG. 7 , four groups of TMR units (a1, a2, a3, a4) and four TMR units (a1, a2, a3, a4) and four The electrodes (P1, P2, P3, P4) have the same structure of each group of TMR units, and all have 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, and each electrode is respectively connected to two adjacent bridge arms. Among the four 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 may be a rectangle or an ellipse. For the convenience of description, the center line along the length direction of the TMR unit is defined as the long axis, and the long axis direction of the TMR unit is parallel to the direction of the bridge arm where it is located. In order to ensure a large shape anisotropy field inside the TMR cell, the aspect ratio of the TMR cell 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 length-width ratio of the TMR unit is small, the internal shape anisotropy field is too small to reach a balance with the applied annealing magnetic field. After annealing, the direction of the magnetic moment of the pinned layer will be along the direction of the applied magnetic field, and a bridge connection cannot be formed. . Preferably, the aspect ratio of the TMR unit may be greater than 10. The specific value of the aspect ratio of the TMR unit is an empirical value, which is also related to the formulation of the free layer, so it can be set according to different situations.

The TMR units located on the four bridge arms are opposite to each other, wherein the long axes of the 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 anisotropy field inside the TMR unit is along the long axis direction of the TMR unit. Since the long axis direction of the TMR unit is different, the direction of the shape anisotropy field inside the TMR unit is 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 direction of the long axis of the TMR unit is The included angle of 45°), the internal magnetic moment of the TMR unit is affected by the external magnetic field and the internal shape anisotropy field, and the magnetization direction of the pinned layer will change according to the arrangement direction (long axis direction) of the TMR unit, Therefore, the pinned layers of each TMR unit can correspondingly form different magnetic moment directions.

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

provide substrates;

4 groups of TMR units and electrodes are deposited on the substrate, for example, magnetron sputtering is used to form TMR units on the substrate, 4 groups of TMR units are bridge-connected to form a full-bridge structure, and the input and output electrodes are connected, and the TMR units are located in the full-bridge On the bridge arms of the structure, the long axes of the TMR units on the adjacent bridge arms are perpendicular to each other, and the long axes of the TMR units on the opposite bridge arms are parallel to each other, as shown in Figure 7; The angle lines are defined as the x-axis and the y-axis respectively, 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, and y1 is the y-axis. The direction of the included angle of 45°, when depositing the TMR unit, the long axis direction of the TMR unit a1, a3 is parallel to the x1 axis, and the long axis direction of the TMR unit a2, a4 is parallel to the _y1 axis _;

The magnetic field annealing treatment is performed on the TMR unit, as shown in FIG. 8 , 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 is the same as the direction of the TMR unit. The long axis direction forms an included angle of 45°, 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 shown in FIG. 8 . 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 fact that the magnetic moment directions of the pinned layers of the opposite TMR units are the same in the present invention does not only mean that the magnetic moment directions of the pinned layers of the opposite TMR units are strictly consistent, but also includes the The direction of the magnetic moment is roughly the same.

Taking this embodiment as an example, when an external magnetic field along the y-axis is applied to the sensor, the resistance changes of different TMR units are different. Since the components of the magnetization directions of the pinned layers of adjacent TMR units along the y-axis are opposite, The magnetization directions of the pinned layers of the opposite TMR units have the same component along the y-axis, so that the magnetoresistance changes of the adjacent TMR units to the y-axis direction are opposite, and the adjacent TMR units have opposite responses to the same sensitive direction, forming full-bridge output. Through the method of the invention, the full bridge structure can be deposited on the same chip at one time, which greatly reduces the difficulty and cost of the production process.

全桥传感器结构中，a1、a3的磁阻变化(R1、R3)与a2、a4的磁阻变化(R2、R4)相反，例如传感器在外加磁场作用下，R1和R3的电阻增大时，则R2和R4的电阻减小，电压输出则增大。The full-bridge circuit of the present invention is shown in FIG. 9. R1, R2, R3, and R4 in FIG. 9 respectively represent the magnetoresistances of four groups of TMR units a1, a2, a3, and a4. , P3) When a constant bias voltage is loaded, the voltage output of the full-bridge circuit is

In the full-bridge sensor structure, the magnetoresistance changes (R1, R3) of a1 and a3 are opposite to the magnetoresistance changes (R2, R4) of a2 and a4. For example, under the action of an external magnetic field, when the resistances of R1 and R3 increase, Then the resistance of R2 and R4 decreases, and the voltage output increases.

Figure 10 is a graph showing the change trend of the magnetoresistance of the TMR units a1 and a2 in the sensor to the applied magnetic field along the y-axis direction. A constant voltage is applied to the input electrodes (P1, P2) of the full-bridge sensor. When the magnetic field along the y-axis direction is applied with a constant voltage When changing, the output voltage trend of the sensor output electrodes (P2, P4) is shown in Figure 11.

The above description of the disclosed embodiments enables any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. A TMR full bridge magnetic sensor, comprising: the TMR unit comprises a free layer, a pinning layer and a tunnel layer, wherein 4 groups of TMR units are connected in a bridge manner to form a full-bridge structure, and 4 groups of TMR units are respectively positioned on 4 bridge arms of the full-bridge structure;

   the method is characterized in that:

   the length-width ratio of the TMR units is not equal to 1, the long axes of the TMR units on the adjacent bridge arms are perpendicular to each other, and the long axes of the TMR units on the opposite bridge arms are parallel to each other.
2. 2. The TMR full bridge magnetic sensor of claim 1, wherein: the TMR unit has an aspect ratio of > 10.
3. 3. A TMR full bridge magnetic sensor as claimed in claim 1 or 2, wherein: the TMR unit is rectangular or elliptical in shape.
4. 4. The TMR full bridge magnetic sensor of claim 1, wherein: the long axis direction of the TMR unit is parallel to the direction of the bridge arm where the TMR unit is located.
5. 5. The TMR full bridge magnetic sensor of claim 1, wherein: the substrate is also provided with 4 electrodes which comprise a pair of input electrodes and a pair of output electrodes, and each electrode is respectively connected with two adjacent bridge arms.
6. 6. A TMR full bridge magnetic sensor as claimed in claim 1 or 2 or 4 or 5, wherein: the magnetic moment directions of the pinning layers of the TMR units on the adjacent bridge arms are different, and the magnetic moment directions of the pinning layers of the TMR units on the opposite bridge arms are the same.
7. The preparation method of the TMR full-bridge magnetic sensor is characterized by comprising the following steps:

   providing a substrate;

   depositing TMR units and electrodes on the substrate, wherein 4 groups of TMR units are connected in a bridge manner to form a full-bridge structure, each bridge arm of the full-bridge structure is provided with one group of TMR units, long axes of the TMR units on adjacent bridge arms are mutually vertical, and long axes of the TMR units on opposite bridge arms are mutually parallel;

   and carrying out magnetic field annealing treatment on the TMR unit, wherein an included angle of 45 degrees is formed between the direction of the applied magnetic field and the long axis direction of the TMR unit during annealing, after annealing is finished, the magnetic moment directions of the pinning layers of the TMR units on adjacent bridge arms are different, and the magnetic moment directions of the pinning layers of the TMR units on opposite bridge arms are the same.
8. 8. The method for manufacturing the TMR full bridge magnetic sensor according to claim 7, wherein: the TMR unit has an aspect ratio of > 10.
9. 9. The method for manufacturing the TMR full bridge magnetic sensor according to claim 7 or 8, wherein: the TMR unit is rectangular or elliptical in shape.
10. 10. The method for manufacturing the TMR full bridge magnetic sensor according to claim 7, wherein: the electrodes comprise a pair of input electrodes and a pair of output electrodes, and the electrodes are connected with two adjacent bridge arms.

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