Magnetic tunnel junction sensing cell, method of fabrication, and whitstond bridge

Abstract

The application discloses a magnetic tunnel junction sensing unit, a manufacturing method and a Wheatstone bridge, wherein the magnetic tunnel junction sensing unit comprises a seed layer, a fixed layer and a barrier layer; a first synthetic antiferromagnetic free layer, a first surface of which is arranged on the barrier layer; a second synthetic antiferromagnetic free layer, a first surface of which is arranged on the barrier layer; a first cover layer, a first surface of which is connected with a second surface of the first synthetic antiferromagnetic free layer; and a second cover layer, a first surface of which is connected with a second surface of the second synthetic antiferromagnetic free layer; wherein the seed layer, the fixed layer, the barrier layer, the first synthetic antiferromagnetic free layer and the first cover layer constitute an MTJ1, and the seed layer, the fixed layer, the barrier layer, the second synthetic antiferromagnetic free layer and the second cover layer constitute an MTJ2. The application realizes two MTJ bridge arms with opposite fixed layer magnetization directions on one MTJ sensing unit, and reduces the complexity of the structure. The application can be widely applied to magnetic tunnel junction sensors.

Description

Technical Field

[0001] This invention relates to magnetic tunnel junction sensors, and more particularly to a magnetic tunnel junction sensing unit, a manufacturing method thereof, and a Wheatstone bridge. Background Technology

[0002] Magnetic tunnel junction (MTJ)-based sensors, with their high sensitivity, small size, low power consumption, and extremely low resistive noise, are expected to become the mainstream magnetic sensors of the future, with broad application prospects in magnetic storage, power grid transmission, and autonomous driving. Tunnel magnetoresistive (TMR) sensors require linearized output and a Wheatstone bridge configuration, which are challenges in achieving high-performance TMR sensors.

[0003] Currently, there are five main methods for achieving linearized output in MTJ sensing units: utilizing the shape anisotropy of the free layer, generating a bias field using integrated permanent magnets (PMs), utilizing anisotropic orthogonal magnetization, double pinning, and superparamagnetism. Each of these methods has its limitations. Utilizing the shape anisotropy of the free layer requires a specific size ratio, and because the free layer is the detection layer, it can cause instability in magnetic field detection. Integrating PMs increases the manufacturing process, cost, and device area, and is not suitable for sensor arrays. Orthogonally magnetized devices have lower magnetoresistance (MR) than in-plane magnetized devices and can only detect magnetic fields in the vertical direction. Double pinning requires two annealing processes and is prone to residual coercivity (Hc). Forming superparamagnetism requires an extremely thin free layer, which reduces MR and significantly increases noise levels.

[0004] Furthermore, connecting the Wheatstone bridge structure requires that the magnetic flux density (MR) on adjacent arms change in opposite directions with the external magnetic field. This means that the magnetic transfer layers (MTJs) constituting adjacent arms must have opposite magnetization directions, while the magnetization directions of the thin film magnetization layers deposited on the same wafer are consistent. Currently, there are two methods to achieve this: one is to use laser radiation or pulsed current to locally heat the arms whose magnetization direction needs to be changed, and then apply an external magnetic field in the opposite direction to achieve opposite magnetization directions of the magnetization layers; the other is to deposit two thin films with opposite magnetization directions of the magnetization layers on the same wafer through a specific process flow. Method one requires the introduction of laser equipment or current coils and is not suitable for sensor arrays; method two requires additional process flows and is more complex. Summary of the Invention

[0005] In order to at least partially solve one of the technical problems existing in the prior art, the present invention aims to provide a magnetic tunnel junction sensing unit, a manufacturing method and a Wheatstone bridge.

[0006] The technical solution adopted in this invention is:

[0007] A magnetic tunnel junction sensing unit includes:

[0008] Seed layer;

[0009] A fixing layer, wherein a first surface of the fixing layer is connected to a second surface of the seed layer;

[0010] A barrier layer, wherein a first surface of the barrier layer is connected to a second surface of the fixed layer;

[0011] A first synthetic antiferromagnetic free layer, wherein a first surface of the first synthetic antiferromagnetic free layer is disposed on a first boundary of the second surface of the barrier layer;

[0012] The second synthetic antiferromagnetic free layer has a first surface disposed on the second boundary of the second surface of the barrier layer; wherein the first boundary is opposite to the second boundary.

[0013] A first capping layer, wherein a first surface of the first capping layer is connected to a second surface of the first synthetic antiferromagnetic free layer;

[0014] A second capping layer, wherein the first surface of the second capping layer is connected to the second surface of the second synthetic antiferromagnetic free layer;

[0015] The seed layer, the fixed layer, the barrier layer, the first synthetic antiferromagnetic free layer, and the first capping layer constitute MTJ1, and the seed layer, the fixed layer, the barrier layer, the second synthetic antiferromagnetic free layer, and the second capping layer constitute MTJ2.

[0016] Furthermore, the first synthetic antiferromagnetic free layer and the second synthetic antiferromagnetic free layer have the same structure;

[0017] The first synthetic antiferromagnetic free layer comprises:

[0018] A free layer, wherein the first surface of the free layer is connected to the second surface of the barrier layer;

[0019] A non-magnetic metal layer, wherein the first surface of the non-magnetic metal layer is connected to the second surface of the free layer;

[0020] A weak pinning layer, wherein the first surface of the weak pinning layer is connected to the second surface of the non-magnetic metal layer;

[0021] An antiferromagnetic layer, wherein the first surface of the antiferromagnetic layer is connected to the second surface of the weak pinning layer, and the second surface of the antiferromagnetic layer is connected to the first surface of the first cover layer.

[0022] Furthermore, the seed layer, the fixed layer, and the barrier layer form a square column, and the synthesized antiferromagnetic free layer and the capping layer are processed into a columnar structure. The projection of the columnar structure onto the second surface of the barrier layer is a rectangle, and the extension line of the long side of the rectangle is perpendicular to the boundary of the barrier layer.

[0023] Furthermore, the fixing layer is made of ferromagnetic material, and due to its anisotropic shape, the magnetization direction of the fixing layer will form an X-shaped magnetic domain structure in the plane, with a magnetic vortex at the center. The magnetization directions on the left and right sides are opposite to those on the sides of the square prism. Therefore, the magnetization directions of the fixing layers of MTJ1 and MTJ2 are parallel and opposite to each other.

[0024] Furthermore, the seed layer is made of a metallic material, the barrier layer is made of an insulating material, the free layer is made of a ferromagnetic material, the non-magnetic metallic layer is made of a metallic material, the weakly pinned layer is made of a ferromagnetic material, and the antiferromagnetic layer is made of an antiferromagnetic material.

[0025] Another technical solution adopted in this invention is:

[0026] A method for fabricating a magnetic tunnel junction sensing unit as described above includes the following steps:

[0027] By depositing thin films layer by layer, a large square column is photolithographically formed on the deposited thin film. Based on this structure, two rectangular columns with dimensions much smaller than the square column are then etched.

[0028] The square column includes a seed layer, a fixed layer, and a barrier layer, while the rectangular column includes a synthetic antiferromagnetic free layer and a capping layer.

[0029] Furthermore, it also includes the following steps:

[0030] The tunnel magnetoresistivity was optimized to over 10% by adjusting the growth conditions, wherein the growth conditions included the thickness of the barrier layer and the annealing process.

[0031] By controlling the thickness of the non-magnetic metal layer, antiferromagnetic coupling is achieved between the free layer and the weakly pinned layer in the synthesized antiferromagnetic free layer, reducing the influence of the stray field of the free layer on the magnetization direction of the fixed layer, thereby improving the linearity of the magnetic sensor.

[0032] By optimizing the pinning strength, a wide range of linear output and high sensitivity can be achieved.

[0033] Another technical solution adopted in this invention is:

[0034] A Wheatstone bridge includes a first arm, a second arm, a third arm, and a fourth arm. One end of the first arm is connected to one end of the second arm, one end of the third arm is connected to one end of the fourth arm, the other end of the first arm is connected to the other end of the third arm, and the other end of the second arm is connected to the other end of the fourth arm.

[0035] The first bridge arm and the second bridge arm are composed of a first magnetic tunnel junction sensing unit, wherein the first bridge arm is MTJ1 of the first magnetic tunnel junction sensing unit and the second bridge arm is MTJ2 of the first magnetic tunnel junction sensing unit.

[0036] The third bridge arm and the fourth bridge arm are composed of a second magnetic tunnel junction sensing unit, wherein the third bridge arm is MTJ1 of the second magnetic tunnel junction sensing unit and the fourth bridge arm is MTJ2 of the second magnetic tunnel junction sensing unit.

[0037] Both the first magnetic tunnel junction sensing unit and the second magnetic tunnel junction sensing unit are implemented using a magnetic tunnel junction sensing unit as described above.

[0038] Furthermore, in the absence of an external magnetic field, the magnetization directions of the fixed layers of the MTJs corresponding to the first and fourth bridge arms are reversed compared to those of the second and third bridge arms.

[0039] When an external magnetic field is applied, the magnetic domains of the fixed layer will change with the change of the external magnetic field. By designing the free layer near the boundary, within a certain magnetic field range, the change of magnetic domains will not change the magnetization direction of the fixed layer under the rectangular column of the free layer.

[0040] Furthermore, the total sensing area is increased by connecting individual magnetic tunnel junction sensing units in series and parallel to form a sensor matrix, thereby improving the signal-to-noise ratio.

[0041] The beneficial effects of the present invention include at least the following:

[0042] (1) This invention innovatively proposes to use a rectangular structure of magnetic domain structure as a fixed layer to realize two fixed layer magnetization directions of MTJ bridge arms on an MTJ sensing unit, and can still maintain this state under a certain magnetic field without the need for bottom pinning and external magnetic field assistance, reducing the complexity of the structure, while having very good symmetry.

[0043] (2) The present invention utilizes both shape anisotropy and weak pinning to act on the free layer simultaneously, which can optimize the strength and stability of the easy magnetization direction, and can also adjust the magnitude of magnetic anisotropy through both, bringing more freedom to the design of the sensor.

[0044] (3) By synthesizing antiferromagnetic coupling as a free layer, the present invention can greatly offset the influence of stray field of free layer on fixed layer, so that the magnetic moment distribution of fixed layer is not affected by free layer, thereby improving the linearity of magnetic sensor.

[0045] (4) The structure of the present invention can make maximum use of space, easily realize Wheatstone bridge connection, constrain the size of the device, improve the utilization rate of device area, thereby providing more space for large-scale series and parallel connection, further improving sensitivity and reducing noise.

[0046] (5) This invention overcomes some of the shortcomings of the current methods for realizing MTJ sensors. It does not require any external equipment (such as PM, current coil and laser, etc.), has a simple structure and fewer preparation steps, and plays a positive role in further promoting the application and development of MTJ magnetic sensors. Attached Figure Description

[0047] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following description is provided with accompanying drawings of the relevant technical solutions in the embodiments of the present invention or the prior art. It should be understood that the accompanying drawings described below are only for the purpose of clearly illustrating some embodiments of the technical solutions of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is a thin film layer diagram of the magnetic tunnel junction sensing unit in an embodiment of the present invention;

[0049] Figure 2 This is a schematic diagram of the thin film structure of the magnetic tunnel junction sensing unit in an embodiment of the present invention;

[0050] Figure 3 This is a cross-sectional schematic diagram of the magnetic tunnel junction sensing unit in an embodiment of the present invention;

[0051] Figure 4 This is a top view showing the magnetization intensity distribution of the fixed layer and the free layer in an embodiment of the present invention;

[0052] Figure 5 This is a schematic diagram of the circuit connection of the Wheatstone bridge in an embodiment of the present invention;

[0053] Figure 6 This is a schematic diagram of the connection structure of the Wheatstone bridge in an embodiment of the present invention;

[0054] Figure 7 This is a schematic diagram showing the changes of the MTJ sensing unit under different external magnetic field conditions in an embodiment of the present invention;

[0055] Figure 8 This is a schematic diagram illustrating the magnetoresistive change of a single device in an embodiment of the present invention;

[0056] Figure 9 This is a schematic diagram of the experimental test circuit in an embodiment of the present invention.

[0057] Figure reference numerals: 1-Seed layer; 2-Fixed layer; 3-Barrier layer; 4-Synthetic antiferromagnetic free layer; 41-Free layer; 42-Non-magnetic metal layer; 43-Weakly pinned layer; 44-Antiferromagnetic layer; 5-Covering layer; 6-Square prism; 7-First rectangular prism; 8-Second rectangular prism; 91-First bridge arm; 92-Second bridge arm; 93-Third bridge arm; 94-Fourth bridge arm. Detailed Implementation

[0058] The embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. The step numbers in the following embodiments are set only for ease of explanation, and there is no limitation on the order between the steps. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art.

[0059] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, front, back, left, right, etc., are based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0060] In the description of this invention, "several" means one or more, "more than" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. The use of "first" and "second" in the description is merely for distinguishing technical features and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the order of the indicated technical features.

[0061] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0062] like Figure 1As shown, this embodiment provides a magnetic tunnel junction (MTJ) sensing unit with a fixed layer and a weakly pinned free layer having anisotropic shape. It includes a seed layer 1, a fixed layer 2 above the seed layer 1, a barrier layer 3 above the fixed layer 2, a synthetic antiferromagnetic free layer 4 above the barrier layer 3, and a capping layer 5 above the synthetic antiferromagnetic free layer 4. The synthetic antiferromagnetic free layer 4 includes a free layer 41, a non-magnetic metal layer 42 above the free layer 41, a weakly pinned layer 43 above the non-magnetic metal layer 42, and an antiferromagnetic layer 44 above the weakly pinned layer 43.

[0063] In this embodiment, the seed layer 1, the fixed layer 2, and the barrier layer 3 are deposited as a large-area square pillar 6. The synthetic antiferromagnetic free layer 4 and the capping layer 5 are processed into two smaller rectangular pillars (i.e., the first rectangular pillar 7 and the second rectangular pillar 8). The long side of the bottom surface of the first rectangular pillar 7 is parallel to the bottom side of the square pillar 6, and the extension of this long side is perpendicular to the left boundary of the square pillar 6. The long side of the bottom surface of the second rectangular pillar 8 is parallel to the bottom side of the square pillar 6, and the extension of this long side is perpendicular to the right boundary of the square pillar 6. An MTJ (i.e., MTJ1 and MTJ2) is formed on the left and right sides of the barrier layer 3, respectively. Figure 2 , 3 As shown.

[0064] Due to the anisotropic nature of its shape, the magnetization direction of fixed layer 2 forms an X-shaped magnetic domain structure along its in-plane direction, with a magnetic vortex at its center. In this embodiment, rotating it clockwise results in parallel and opposite magnetization directions on its left and right sides. Figure 4 As shown, an antiferromagnetic layer 44 is deposited above the free layer 41, supplemented by a weakly pinned layer 43, pinning its magnetization direction along the long axis of the rectangular prism. Accordingly, in the absence of an external magnetic field, the magnetization directions of the free layers of MTJ1 and MTJ2 are perpendicular to the fixed layers, and the magnetization directions of the fixed layers of MTJ1 and MTJ2 are parallel and opposite, which will facilitate subsequent Wheatstone bridge connections. The magnetization directions of each ferromagnetic layer are as follows: Figure 2 , 3 As shown.

[0065] As an optional implementation, seed layer 1 is made of Ta / Ru / Ta material, with a preferred thickness of 5nm / 5nm / 5nm; immobilization layer 2 is made of CoFeB material, with a preferred thickness of 2.6nm; barrier layer 3 is made of MgO material, with a thickness of approximately 2nm; free layer 41 is made of CoFeB material, with a preferred thickness of 2.6nm; non-magnetic metal layer 42 is made of Ru material, with a preferred thickness of 0.85nm; weak pinning layer 43 is made of CoFe material, with a preferred thickness of 2nm; antiferromagnetic layer 44 is made of IrMn material, with a preferred thickness of 7.5nm; and capping layer 5 is made of Ta material, with a preferred thickness of 5nm. The specific thin film structure is as follows: Figure 1 As shown.

[0066] Based on the aforementioned magnetic tunnel junction (MTJ) sensing unit, this embodiment also provides a fabrication method, specifically including the following steps: First, a thin film is deposited layer by layer using methods such as magnetron sputtering; then, a large square cylinder 6 (~20×20μm) is photolithographically etched onto the deposited thin film. 2 Based on this structure, two rectangular prisms 7 and 8 (~1×3μm) composed of a synthetic antiferromagnetic layer and a capping layer, with dimensions much smaller than the square prism 6, were etched out. 2 ),like Figure 2 , 3 As shown. The symbol "~" indicates approximately, representing the order of magnitude of the size of the deposited square column 6, and can be adjusted. It should be noted that the dimensions of the rectangular columns 7 and 8 should be much smaller than the size of 6.

[0067] As an optional implementation, the tunnel magnetic reluctance (TMR) can be optimized to reach over 100% by adjusting the thickness of the barrier layer and growth conditions such as annealing. At the same time, by controlling the thickness of the non-magnetic metal layer 42, antiferromagnetic coupling can be achieved between the free layer 41 and the weakly pinned layer 43 in the synthesized antiferromagnetic free layer 4, reducing the influence of the stray field of the free layer 41 on the magnetization direction of the fixed layer 2, improving the linearity of the magnetic sensor. Meanwhile, by optimizing the pinning strength, a wide range of linear output and high sensitivity can be achieved.

[0068] This embodiment also provides a novel, simple, and efficient Wheatstone bridge, including two MTJ sensing units, each MTJ sensing unit comprising two MTJs (MTJ1 and MTJ2). The Wheatstone bridge connection structure is as follows: Figure 5 As shown, the Wheatstone bridge connection structure based on the MTJ sensing unit is as follows: Figure 6 As shown.

[0069] The Wheatstone bridge circuit consists of four arms, requiring that the magnetoresistance of adjacent arms changes in opposite directions with the external magnetic field. This means that the MTJs constituting the arms should have opposite fixed-layer magnetization directions. In this embodiment, the first arm 91 and the second arm 92 are respectively composed of MTJ1 and MTJ2 from one MTJ unit, and the third arm 93 and the fourth arm 94 are respectively composed of MTJ2 and MTJ1 from another MTJ unit. The fixed-layer magnetization directions of MTJ1 and MTJ2 are parallel and opposite, as shown below. Figure 2 and Figure 3 As shown. The first bridge arm 91 is connected to the second bridge arm 92 and the third bridge arm 93 respectively, and the fourth bridge arm 94 is connected to the second bridge arm 92 and the third bridge arm 93 respectively, as shown. Figure 6 As shown, this ensures that the magnetization directions of the fixed layer of the MTJ in adjacent bridge arms are opposite.

[0070] In this embodiment, although the magnetic domains of the fixed layer change with the external magnetic field when an external magnetic field is applied, the change in magnetic domains near the boundary of the free layer within a certain magnetic field range will not alter the magnetization direction of the fixed layer beneath the rectangular column of the free layer. For example... Figure 7 As shown in (a), when an external magnetic field is applied, the magnetic domains in the fixed layer along the direction of the magnetic field increase in size, but their direction remains unchanged. Meanwhile, the magnetic moment of the free layer shifts at a certain angle towards the direction of the magnetic field, causing the angle between the magnetization directions of the free layer and the fixed layer in MTJ1 to decrease, and correspondingly, the magnetic reluctance to decrease. Conversely, the angle between the magnetization directions of the free layer and the fixed layer in MTJ2 increases, leading to an increase in magnetic reluctance. The changes are exactly the opposite when a reverse external magnetic field is applied, as shown in (a). Figure 7 As shown in (b), the preliminary simulation calculations show a good linear correlation between the magnetoresistivity (MR) and the external magnetic field, as follows: Figure 8 As shown, the change in magnetoresistive force between the two bridge arms MTJ is reflected in the change in output voltage after current flows through them, and the change is linearly related to the strength of the external magnetic field.

[0071] Experimental test circuit such as Figure 9 As shown, the external magnetic field can be provided by an electromagnet or a Holmhertz coil, the input current can be changed by a rheostat, the voltmeter can directly measure the voltage change with the magnetic field, and the spectrum analyzer can perform noise analysis to study the sensitivity, noise and other information of the magnetic sensor.

[0072] Magnetic sensors typically exhibit thermal noise, shot noise, 1 / f noise, and random telegraph noise. At low frequencies, 1 / f noise dominates, and its noise spectral density can be expressed as: Where α H Here, V is the Hugues constant, V is the voltage applied across the device, and A is the total sensing area of ​​the sensor. Clearly, increasing the free layer area can effectively reduce 1 / f noise; however, this also alters the shape anisotropy of the device, affecting its linearization output. Therefore, we can increase the total sensing area and improve the signal-to-noise ratio by connecting individual MTJ sensing units in series and parallel to form a sensor matrix.

[0073] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," or "some embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0074] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

[0075] The above is a detailed description of the preferred embodiments of the present invention. However, the present invention is not limited to the above embodiments. Those skilled in the art can make various equivalent modifications or substitutions without departing from the spirit of the present invention. All such equivalent modifications or substitutions are included within the scope defined by the claims of this application.

Claims

1. A magnetic tunnel junction sensing unit, characterized in that, include: Seed layer; A fixing layer, wherein a first surface of the fixing layer is connected to a second surface of the seed layer; A barrier layer, wherein a first surface of the barrier layer is connected to a second surface of the fixed layer; A first synthetic antiferromagnetic free layer, wherein a first surface of the first synthetic antiferromagnetic free layer is disposed on a first boundary of the second surface of the barrier layer; The second synthetic antiferromagnetic free layer has a first surface disposed on the second boundary of the second surface of the barrier layer; wherein the first boundary is opposite to the second boundary. A first capping layer, wherein a first surface of the first capping layer is connected to a second surface of the first synthetic antiferromagnetic free layer; A second capping layer, wherein the first surface of the second capping layer is connected to the second surface of the second synthetic antiferromagnetic free layer; The seed layer, the fixed layer, the barrier layer, the first synthetic antiferromagnetic free layer and the first capping layer constitute MTJ1, and the seed layer, the fixed layer, the barrier layer, the second synthetic antiferromagnetic free layer and the second capping layer constitute MTJ2. The seed layer, the fixed layer, and the barrier layer form a square column. The synthesized antiferromagnetic free layer and the capping layer are processed into a columnar structure. The projection of the columnar structure onto the second surface of the barrier layer is a rectangle, and the extension of the long side of the rectangle is perpendicular to the boundary of the barrier layer. The fixing layer is made of ferromagnetic material, and due to its anisotropic shape, the magnetization direction of the fixing layer will form an X-shaped magnetic domain structure in the plane, with a magnetic vortex at the center. Therefore, the magnetization directions of the fixing layers of MTJ1 and MTJ2 are opposite and parallel.

2. The magnetic tunnel junction sensing unit according to claim 1, characterized in that, The first synthetic antiferromagnetic free layer and the second synthetic antiferromagnetic free layer have the same structure; The first synthetic antiferromagnetic free layer comprises: A free layer, wherein the first surface of the free layer is connected to the second surface of the barrier layer; A non-magnetic metal layer, wherein the first surface of the non-magnetic metal layer is connected to the second surface of the free layer; A weak pinning layer, wherein the first surface of the weak pinning layer is connected to the second surface of the non-magnetic metal layer; An antiferromagnetic layer, wherein the first surface of the antiferromagnetic layer is connected to the second surface of the weak pinning layer, and the second surface of the antiferromagnetic layer is connected to the first surface of the first cover layer.

3. A magnetic tunnel junction sensing unit according to claim 2, characterized in that, The seed layer is made of a metallic material, the barrier layer is made of an insulating material, the free layer is made of a ferromagnetic material, the non-magnetic metallic layer is made of a metallic material, the weakly pinned layer is made of a ferromagnetic material, and the antiferromagnetic layer is made of an antiferromagnetic material.

4. A method for manufacturing a magnetic tunnel junction sensing unit as described in claim 1, characterized in that, Includes the following steps: By depositing thin films layer by layer, a square column is photolithographically etched on the deposited thin film. Based on this structure, two rectangular columns with dimensions much smaller than the square column are then etched. The square column includes a seed layer, a fixed layer, and a barrier layer, while the rectangular column includes a synthetic antiferromagnetic free layer and a capping layer.

5. The manufacturing method according to claim 4, characterized in that, It also includes the following steps: The tunnel magnetoresistivity was optimized to over 10% by adjusting the growth conditions, wherein the growth conditions included the thickness of the barrier layer and the annealing process. By controlling the thickness of the non-magnetic metal layer, antiferromagnetic coupling is achieved between the free layer and the weakly pinned layer in the antiferromagnetic free layer, reducing the influence of the stray field of the free layer on the magnetization direction of the fixed layer, thereby improving the linearity of the magnetic sensor. By optimizing the pinning strength, a wide range of linear output and high sensitivity can be achieved.

6. A Wheatstone bridge, characterized in that, It includes a first bridge arm, a second bridge arm, a third bridge arm, and a fourth bridge arm. One end of the first bridge arm is connected to one end of the second bridge arm, one end of the third bridge arm is connected to one end of the fourth bridge arm, the other end of the first bridge arm is connected to the other end of the third bridge arm, and the other end of the second bridge arm is connected to the other end of the fourth bridge arm. The first bridge arm and the second bridge arm are composed of a first magnetic tunnel junction sensing unit, wherein the first bridge arm is MTJ1 of the first magnetic tunnel junction sensing unit and the second bridge arm is MTJ2 of the first magnetic tunnel junction sensing unit. The third bridge arm and the fourth bridge arm are composed of a second magnetic tunnel junction sensing unit, wherein the third bridge arm is MTJ1 of the second magnetic tunnel junction sensing unit and the fourth bridge arm is MTJ2 of the second magnetic tunnel junction sensing unit. Both the first magnetic tunnel junction sensing unit and the second magnetic tunnel junction sensing unit are implemented using a magnetic tunnel junction sensing unit as described in any one of claims 1-3.

7. A Wheatstone bridge according to claim 6, characterized in that, In the absence of an external magnetic field, the magnetization directions of the fixed layers of the MTJs corresponding to the first and fourth bridge arms and the second and third bridge arms were reversed. When an external magnetic field is applied, the magnetic domains of the fixed layer will change with the change of the external magnetic field. By designing the free layer near the boundary, within a certain magnetic field range, the change of magnetic domains will not change the magnetization direction of the fixed layer under the rectangular column of the free layer.

8. A Wheatstone bridge according to claim 6, characterized in that, The total sensing area is increased by connecting individual magnetic tunnel junction sensing units in series and parallel to form a sensor matrix, thereby improving the signal-to-noise ratio.

Images