Magnetic tunnel junction and TMR sensor
By using a (110) crystal plane ferromagnetic free layer and a two-step annealing process in the TMR sensor, the problems of large nonlinear error and deteriorated noise performance of traditional TMR sensors are solved, and a wider high linearity measurement range and a higher signal-to-noise ratio are achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 北京怀柔实验室
- Filing Date
- 2026-04-17
- Publication Date
- 2026-05-15
AI Technical Summary
Traditional TMR sensors suffer from large nonlinear errors in their magnetic tunnel junctions, which affect linearity and make it difficult to meet the requirements of high-precision measurement. Furthermore, existing improved solutions suffer from degraded noise performance and issues with the stability and uniformity of the bias field.
A ferromagnetic free layer with (110) crystal plane is used to achieve intrinsic stable bias through material and interface engineering, optimize magnetization rotation behavior, reduce nonlinear error, improve linearity, and adjust magnetization direction through a two-step annealing process.
Significantly reduces nonlinear error to <0.5%FSO, broadens the high linearity measurement range, improves signal-to-noise ratio and long-term reliability, reduces process difficulty, and avoids noise performance degradation and bias field drift.
Smart Images
Figure CN122054915A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of magnetic sensing technology, and more particularly to a magnetic tunnel junction and a TMR sensor. Background Technology
[0002] Tunneling magnetoresistance (TMR) technology is widely used in magnetic sensors due to its high sensitivity. Traditional linear field TMR sensors typically employ a push-pull half-bridge or full-bridge structure, where the magnetization directions of two or four TMR sensor elements are set at opposite fixed bias angles (typically ±90°) to extend the linear measurement range and compensate for common-mode errors. However, the magnetic tunnel junctions (MTJs) currently used to construct TMR sensor elements exhibit significant nonlinear errors, affecting the linearity of the TMR sensor. Summary of the Invention
[0003] This invention provides a magnetic tunnel junction and a TMR sensor to improve the linearity of magnetic field sensing of the magnetic tunnel junction, reduce nonlinear errors, and enable the TMR sensor to obtain a wider high linearity measurement range.
[0004] In a first aspect, embodiments of the present invention provide a magnetic tunnel junction, comprising: A substrate layer, and a ferromagnetic free layer, a barrier layer, a ferromagnetic reference layer and an antiferromagnetic pinning layer sequentially stacked on one side of the substrate layer; The crystal plane of the ferromagnetic free layer is (110).
[0005] Optionally, the ferromagnetic free layer comprises: at least two magnetic layers stacked together, with a metal layer inserted between each two adjacent magnetic layers; The material of any of the magnetic layers includes one of CoFe (110), CoFeB (110), FePt (110) and Co-based all-Heusler alloy (110); the material of any of the metal layers includes one of Ta and W.
[0006] Optionally, the crystal plane of the substrate layer is (110) or (111); And / or, the crystal plane of the barrier layer is (110) or (111); And / or, the crystal plane of the ferromagnetic reference layer is the (110) crystal plane; And / or, the crystal plane of the antiferromagnetic nailing layer is (111) crystal plane.
[0007] Optionally, the substrate material includes one of Si (110), MgO (110), MgO (111), α-Al2O3 (0001), GaAs (110) and GaAs (111); The material of the ferromagnetic free layer includes at least one of CoFe (110), CoFeB (110), FePt (110), and Co-based all-Heusler alloy (110); The barrier layer is made of the following materials: MgO (110), MgO (111), and AlO. x (110) AlO x (111)MgAl x O y (110) and MgAl x O y One of (111); The material of the ferromagnetic reference layer includes at least one of CoFe (110), CoFeB (110), FePt (110), and Co-based all-Heusler alloy (110); The material of the antiferromagnetic nailing layer includes one of IrMn (111), PtMn (111), and FeMn (111).
[0008] Optionally, the magnetic tunnel junction also includes: A lattice buffer seed layer is disposed between the substrate layer and the ferromagnetic free layer; wherein the crystal plane of the lattice buffer seed layer is (110) or (111).
[0009] Optionally, the material of the lattice buffer seed layer includes at least one of the following materials: Pt (111); Ru (0001); Ni / X multilayer structure (111), where X = at least one of Mo, Ru, Nb, Zr, Rh, W, Os, Ir and Hf; Cr-based alloy (002) /
[110] ; NiCr-based alloy (111).
[0010] Optionally, the magnetic tunnel junction also includes: A synthetic antiferromagnetic intermediate layer and a pinned ferromagnetic layer are sequentially stacked between the ferromagnetic reference layer and the antiferromagnetic pinning layer; The synthetic antiferromagnetic intermediate layer promotes the formation of a synthetic antiferromagnetic structure between the ferromagnetic reference layer and the pinned ferromagnetic layer through the interlayer coupling field generated by the RKKY coupling effect. The pinned ferromagnetic layer constrains the magnetization direction of the ferromagnetic reference layer through the interlayer coupling field.
[0011] Optionally, the material of the synthetic antiferromagnetic interlayer includes Ru; The material of the pinned ferromagnetic layer includes: CoFe (110).
[0012] Optionally, the magnetic tunnel junction further includes a barrier buffer layer disposed between the ferromagnetic free layer and the barrier layer; And / or, The magnetic tunnel junction further includes an anti-oxidation electrode layer disposed on the side of the antiferromagnetic nailing layer away from the substrate layer.
[0013] Optionally, when the magnetic tunnel junction includes the barrier buffer layer, the material of the barrier buffer layer includes Mg or Al; In the case where the magnetic tunnel junction includes the anti-oxidation electrode layer, the material of the anti-oxidation electrode layer includes at least one of Ru and Ta.
[0014] Secondly, embodiments of the present invention also provide a TMR sensor, comprising: a magnetic tunnel junction provided in any embodiment of the present invention.
[0015] The magnetic tunnel junction provided in this embodiment of the invention includes a substrate layer, a ferromagnetic free layer, a barrier layer, a ferromagnetic reference layer, and an antiferromagnetic pinning layer stacked together. By setting the ferromagnetic free layer as an epitaxial crystal plane with a (110) crystal plane, the ferromagnetic free layer has a double rotational symmetry axis with an angle of 180°, and is anisotropic only in two antiparallel directions. During magnetic reversal, it will not cause nonlinearity due to the influence of energy barriers at other angles, which is beneficial to achieving smooth and linear magnetic reversal and obtaining a stable linear induction mechanism. Therefore, the ferromagnetic free layer provided in this embodiment of the invention, due to its inherent strong crystalline magnetic anisotropy, can provide a stable and uniform internal bias at the atomic scale, fundamentally optimizing the magnetization rotation behavior of the ferromagnetic free layer in the measurement magnetic field range, thereby reducing nonlinear errors. Compared with related technologies, this embodiment of the invention can improve the linearity of the TMR sensor using this magnetic tunnel junction, and can effectively broaden the measurement range while maintaining the same linearity requirements, that is, it is beneficial to provide a wider high linearity measurement range. Furthermore, this invention, through adjusting the crystal plane orientation of the ferromagnetic free layer and utilizing materials and interface engineering, achieves an intrinsically stable linear operating point. Compared to related technologies that improve linearity by providing a bias magnetic field through patterning, this reduces the precision requirements for micron-level pattern processing, decreases the dependence of linearity on the precision of the pattern processing, avoids bias field drift caused by micron-level pattern processing and material aging, and prevents performance differences between products due to poor process uniformity during batch processing. This reduces process difficulty while improving the long-term reliability and batch uniformity of the sensor. Additionally, this invention, by optimizing the magnetic structure stability of the ferromagnetic free layer and suppressing magnetization fluctuations, potentially improves the sensor's signal-to-noise ratio. Since no additional film layer is needed for linear performance, it avoids potential noise performance degradation and the impact on bias field stability and uniformity caused by film layer addition.
[0016] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description
[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0018] Figure 1 This is a schematic diagram of the membrane structure of a magnetic tunnel junction provided in an embodiment of the present invention; Figure 2 This is a schematic diagram of a (110) crystal plane; Figure 3 This is a schematic diagram of a (001) crystal plane; Figure 4 This is a schematic diagram of another magnetic tunnel junction membrane structure provided in an embodiment of the present invention. Detailed Implementation
[0019] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.
[0020] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion.
[0021] As mentioned in the background section, the nonlinear error of magnetic tunnel junctions is relatively large in related technologies. The main reasons are analyzed as follows: A typical linear TMR sensor unit has a magnetic tunnel junction stacked structure from bottom to top as follows: substrate, seed layer, antiferromagnetic layer (AFM layer), reference layer, barrier layer, free layer, and cap layer. A uniaxial anisotropy is induced in the free layer through magnetic field annealing, with the easy axis of the free layer forming a 90-degree angle with the magnetization direction of the reference layer. Simultaneously, the free layer is patterned into strips using photolithography, and a fixed bias magnetic field is applied to the free layer using shape anisotropy, also making the easy axis of the free layer form a 90-degree angle with the magnetization direction of the reference layer. When an external magnetic field acts on the free layer, the magnetization direction of the free layer rotates, causing a change in the tunnel junction resistance, thus achieving magnetic field sensing. The reference layer, barrier layer, and free layer typically use a (001) crystal plane. This scheme relies solely on the magnetic anisotropy of the free layer itself, resulting in a non-ideal linear relationship between the magnetization vector and the external field rotation. Therefore, the linear measurement range of the sensor is relatively narrow, the nonlinear error is usually large, and the accuracy is usually >1-2% FSO (Full Scale Output), which is difficult to meet the requirements of high-precision measurement.
[0022] To improve linearity, related technologies propose adding an additional antiferromagnetic (AFM) pinning layer above the free layer. The bias field generated by this pinning layer stabilizes the magnetization direction of the free layer, ensuring the sensor is initially positioned at the center of the linear region. For example, an antiferromagnetic layer can be deposited on the free layer and patterned into strips using photolithography. The anisotropy of the shape generates a fixed bias magnetic field applied to the free layer. However, while applying a bias field can improve linearity, there are limits to the degree of optimization. First, the uniformity and stability of the bias field itself limit the optimization effect. Second, the uniformity of the magnetic properties of the free layer material (such as saturation magnetization Ms and anisotropic field Hk) also affects the final response. More importantly, the nonlinearity of the magnetization response near saturation is inherent and cannot be fundamentally eliminated by external bias; further reducing the nonlinearity error to below 1% FSO is extremely difficult. Furthermore, the improved scheme also suffers from the following problems: 1. Potential degradation in noise performance: 1) Introduction of new noise sources: The patterned antiferromagnetic layer and the interface between the antiferromagnetic layer and the free layer may become additional sources of 1 / f noise (flicker noise). Magnetic moment fluctuations in antiferromagnetic materials, charge traps or defects at the interface may introduce low-frequency noise by modulating the tunneling current through magnetic or electrical coupling.
[0023] 2) Magnetic coupling interference: There is magnetic coupling between the newly added antiferromagnetic layer and the free layer (even if the purpose is to provide bias). This coupling may not be perfect, and the magnetic domain fluctuations or instability of the antiferromagnetic layer itself may interfere with the stability of the magnetization state of the free layer, which may degrade the overall magnetic noise performance of the sensor.
[0024] 2. Issues related to the stability and uniformity of the bias field: 1) Thermal Budget and Interface Issues: The newly added antiferromagnetic pinning layer requires annealing at a specific temperature (typically 200℃) and magnetic field to generate an exchange bias field. This secondary annealing process may not match the thermal budget of the underlying MTJ core functional layers, especially the crystallized CoFeB (reference layer) / MgO (barrier layer) / CoFeB (free layer) structure, potentially leading to interface diffusion, performance degradation, or decreased reliability. The multilayer structure also introduces more interfaces, increasing the risk of interface mixing and defects.
[0025] 2) The effect of material inhomogeneity: The slight inhomogeneity of the thickness, chemical composition and crystallization degree of antiferromagnetic materials (such as IrMn) will directly affect the strength and uniformity of the exchange bias field, thus leading to the instability of the bias field.
[0026] 3) Magnetic relaxation and aging: The magnetic properties of antiferromagnetic materials (such as IrMn) may change slowly over time or under the influence of external environments (such as temperature cycling) (magnetic relaxation), causing the provided bias field to drift. This makes the initial quiescent operating point of the sensor unstable, affecting long-term reliability.
[0027] To address the aforementioned issues, this invention provides a magnetic tunnel junction that offers an innovative film structure design by providing a ferromagnetic free layer with a (110) crystal plane. This design achieves a stable and uniform intrinsic bias at the atomic scale, fundamentally optimizing the magnetization rotation behavior of the magnetized free layer within the measurement magnetic field range. This significantly reduces nonlinear errors and provides a wider range of high linearity measurements.
[0028] Figure 1 This is a schematic diagram of the film structure of a magnetic tunnel junction provided in an embodiment of the present invention. See also... Figure 1 The magnetic tunnel junction includes a substrate layer 11, and a ferromagnetic free layer 21, a barrier layer 31, a ferromagnetic reference layer 41 and an antiferromagnetic pinning layer 51 sequentially stacked on one side of the substrate layer 11. The crystal plane of the ferromagnetic free layer 21 is (110) crystal plane.
[0029] The substrate layer 11 supports the various film layers of the magnetic tunnel junction and provides good epitaxial guidance for the deposited film layers. The magnetization direction of the ferromagnetic free layer 21 varies with the external magnetic field. The barrier layer 31 is a non-magnetic insulating layer. Through the transition of spin electrons, the barrier layer 31 forms a high-resistivity state and a low-resistivity state, thus exhibiting a linear resistance change. The ferromagnetic reference layer 41 serves as a magnetization fixing layer. The antiferromagnetic pinning layer 51 acts on the ferromagnetic reference layer 41, providing a binding force to the ferromagnetic reference layer 41 and pinning the macroscopic magnetization direction of the ferromagnetic reference layer 41; for example, the antiferromagnetic pinning layer 51 can be in-plane pinned, and the pinned magnetization direction is along the surface of the film.
[0030] In this embodiment, the ferromagnetic free layer 21 is grown as a (110) crystal plane (or epitaxial crystal plane). The characteristics of the (110) crystal plane can be found in [reference needed]. Figure 2 As can be seen, the ferromagnetic free layer 21 has a double rotational symmetry axis of 180°, and its intrinsic strong crystalline magnetic anisotropy will become an important basis for achieving high linearity. The following comparative analysis of the (110) crystal plane and the (001) crystal plane used in related technologies illustrates the advantages of the (110) crystal plane in terms of linearity.
[0031] contrast Figure 2 and Figure 3 The (110) crystal plane has a single axis of symmetry, and the (001) crystal plane has a double axis of symmetry, while the TMR sensor requires a 180-degree rotation from one direction to the opposite direction. See also Figure 3 Traditional (001) crystal planes have two symmetry axes and anisotropy in all four directions. When a 180° magnetic reversal is required in any direction, the energy barrier along the other symmetry axis causes the magnetization curve affected by the magnetic field to bend within a smaller magnetic field range, resulting in poor linearity. However, in this application, see [reference needed]. Figure 2The ferromagnetic free layer 21 is set as a (110) crystal plane, so that the ferromagnetic free layer 21 has a double rotational single symmetry axis with an angle of 180°. It is anisotropic only in two antiparallel directions. During magnetic reversal, it will not be affected by the energy barrier of other angles and will not cause nonlinearity. That is, the (110) crystal plane can be free from nonlinear interference of the other axis, which is conducive to achieving smooth and linear magnetic reversal and obtaining a stable linear sensing mechanism. Therefore, based on the single symmetry axis of the (110) crystal plane, the direction of the magnetic field to be detected by the sensor is located in one direction of this single axis. Compared with the (001) crystal plane, the (110) crystal plane does not have a barrier in other directions. If there is an energy barrier at other angles, it will cause a certain bending of the magnetic reversal and cause nonlinearity. The (110) crystal plane can be free from nonlinear interference of the other axis and is conducive to achieving smooth and linear magnetic reversal. In summary, growing the ferromagnetic free layer 21 with a (110) crystal plane can provide excellent linearity and achieve a stable and uniform internal bias at the atomic scale. Specifically, a stable linear induction mechanism is obtained by processing the crystallization direction of the material structure. In this way, the magnetization rotation behavior of the ferromagnetic free layer 21 within the measurement magnetic field range can be fundamentally optimized without adding other films on top of the ferromagnetic free layer 21 to stabilize the magnetization direction. Therefore, while improving linearity, it avoids a series of problems related to noise and bias field caused by adding new films, thereby improving the reliability and stability of the device.
[0032] Linearity refers to the range within which the sensor output and input magnetic field exhibit a linear relationship, typically measured by the nonlinear error at full-scale output. This embodiment significantly reduces nonlinear error, achieving a target of <0.5% FSO; correspondingly, this embodiment effectively widens the measurement range while maintaining the same linearity requirements, obtaining a wider high-linearity measurement range.
[0033] The magnetic tunnel junction provided in this embodiment of the invention includes a substrate layer 11, a ferromagnetic free layer 21, a barrier layer 31, a ferromagnetic reference layer 41, and an antiferromagnetic pinning layer 51 stacked together. By setting the ferromagnetic free layer 21 as an epitaxial crystal plane with a (110) crystal plane, the ferromagnetic free layer 21 has a double rotational symmetry axis with an angle of 180°, and is anisotropic only in two antiparallel directions. During magnetic reversal, it will not cause nonlinearity due to the influence of energy barriers at other angles, which is conducive to achieving smooth and linear magnetic reversal and obtaining a stable linear induction mechanism. Therefore, the ferromagnetic free layer 21 provided in this embodiment of the invention, due to its inherent strong crystalline magnetic anisotropy, can provide a stable and uniform internal bias at the atomic scale, fundamentally optimizing the magnetization rotation behavior of the ferromagnetic free layer 21 in the measurement magnetic field range, thereby reducing nonlinear errors. Compared with related technologies, this embodiment of the invention can improve the linearity of the TMR sensor using this magnetic tunnel junction, and can effectively broaden the measurement range while maintaining the same linearity requirements. That is, it is conducive to providing a wider high linearity measurement range. Furthermore, by adjusting the crystal plane orientation of the ferromagnetic free layer 21, this embodiment of the invention achieves an intrinsic and stable linear operating point through material and interface engineering. Compared to related technologies that improve linearity by providing a bias magnetic field through patterning, this reduces the precision requirements for micron-level pattern processing, decreases the dependence of linearity on the precision of the pattern processing technology, avoids bias field drift caused by micron-level pattern processing and material aging, and prevents performance differences between products due to poor process uniformity during batch processing. This reduces process difficulty while improving the long-term reliability and batch uniformity of the sensor. Additionally, by optimizing the magnetic structure stability of the ferromagnetic free layer 21 and suppressing magnetization fluctuations, this embodiment of the invention potentially improves the signal-to-noise ratio of the sensor. Since no additional film layer is needed for linear performance, it avoids potential degradation of noise performance and impacts on the stability and uniformity of the bias field caused by film layer addition.
[0034] Based on the above embodiments, optionally, the crystal plane of the substrate layer 11 is (110) or (111). In this way, better (110) or (111) crystal plane epitaxial induction can be provided to provide orientation induction for the film layer deposited thereon, which is conducive to the better growth of the ferromagnetic free layer 21 into the (110) crystal plane.
[0035] Based on the above embodiments, optionally, the ferromagnetic reference layer 41 has a (110) crystal plane, which is beneficial for providing a fixed magnetization direction for the corresponding ferromagnetic free layer 21. The barrier layer 31 has a (110) or (111) crystal plane, which is beneficial for the ferromagnetic reference layer 41 to grow better as a (110) crystal plane. The antiferromagnetic pinning layer 51 has a (111) crystal plane, which provides in-plane pinning.
[0036] Based on the above embodiments, optionally, the material of the substrate layer 11 includes one of Si (110), MgO (110), MgO (111), α-Al2O3 (sapphire) (0001), GaAs (110), and GaAs (111). The substrate layer 11 adopts a substrate material with a specific crystal plane, serving the film stack construction of the TMR magnetic sensor, and providing better crystal plane epitaxial growth for the material layer above the substrate layer 11, for example, epitaxially induced ferromagnetic free layer 21 forming a (110) crystal plane. The substrate layer 11 can specifically be a single-layer structure made of one of the above materials. For example, the thickness of the substrate layer 11 is between 300 micrometers and 1000 micrometers, for example, 300 micrometers, 500 micrometers, 700 micrometers, 800 micrometers, or 1000 micrometers.
[0037] The material of the ferromagnetic free layer 21 includes at least one of CoFe (110), CoFeB (110), FePt (110), and Co-based all-Heusler alloy (110). The ferromagnetic free layer 21 uses a ferromagnetic material with a specific crystal plane, and its main function is to sense the detected magnetic field. The thickness of the ferromagnetic free layer 21 can be set according to different application scenarios. For example, the thickness of the ferromagnetic free layer 21 is between 1 nanometer and 50 nanometers, specifically 1 nanometer, 5 nanometers, 10 nanometers, 20 nanometers, 30 nanometers, 40 nanometers, or 50 nanometers. The ferromagnetic free layer 21 can be a single-layer structure composed of one of the above materials, or a multi-layer stacked structure composed of at least two of the above materials, with each layer containing one material, which can be set according to actual needs.
[0038] The materials of barrier layer 31 include: MgO (110), MgO (111), and AlO. x (110) AlO x (111)MgAl x O y (110) and MgAl x O y One of (111). The barrier layer 31 is a barrier insulating layer material with a specific crystal plane, and its main function is to provide an efficient tunneling barrier. Specifically, the barrier layer 31 can be a single-layer structure made of one of the above-mentioned materials. For example, the thickness of the barrier layer 31 is 1 nanometer to 2 nanometers, such as 1 nanometer, 1.3 nanometers, 1.5 nanometers, 1.7 nanometers or 2 nanometers.
[0039] The ferromagnetic reference layer 41 is made of at least one of the following: CoFe (110), CoFeB (110), FePt (110), and Co-based all-Heusler alloy (110). The ferromagnetic reference layer 41 uses a ferromagnetic material with a specific crystal plane, and its main function is to achieve a high fixed bias field by forming an exchange bias effect with the antiferromagnetic pinning layer 51. The thickness of the ferromagnetic reference layer 41 is, for example, between 1 nanometer and 20 nanometers, specifically 1 nanometer, 5 nanometers, 8 nanometers, 10 nanometers, 15 nanometers, or 20 nanometers. The ferromagnetic reference layer 41 can be a single-layer structure composed of one of the aforementioned materials, or a multi-layer stacked structure composed of at least two of the aforementioned materials, with each layer containing one material, which can be specifically set according to actual needs.
[0040] The antiferromagnetic pinning layer 51 is made of one of IrMn(111), PtMn(111), and FeMn(111). The antiferromagnetic pinning layer 51 uses an antiferromagnetic pinning material with a specific crystal plane, and its main function is to achieve a high fixed bias field by forming an exchange bias effect with the ferromagnetic reference layer 41. Specifically, the antiferromagnetic pinning layer 51 can be a single-layer structure composed of one of the aforementioned materials. For example, the thickness of the antiferromagnetic pinning layer 51 is between 5 nanometers and 20 nanometers, such as 5 nanometers, 8 nanometers, 10 nanometers, 15 nanometers, or 20 nanometers.
[0041] In one embodiment, optionally, the ferromagnetic free layer 21 includes at least two magnetic layers stacked together, with a metal layer inserted between each pair of adjacent magnetic layers. In this embodiment, by inserting a metal layer between each pair of magnetic layers, on the one hand, the metal layer can reduce the risk of element diffusion from the magnetic layers in the ferromagnetic free layer 21 to the interface of the barrier layer 31, thereby improving the interface quality and thus increasing the TMR magnetoresistance ratio; on the other hand, setting the metal layer helps to reset the epitaxial growth of the ferromagnetic material in the magnetic layer, reducing the risk of lattice mismatch caused by the accumulation of defects during the continuous epitaxial growth of the film layer, and helping to obtain a purer (110) crystal plane single orientation ferromagnetic free layer 21, effectively solving the problem of increased linearity error caused by lattice defects, lattice mismatch and other problems.
[0042] The material of any magnetic layer includes one of CoFe (110), CoFeB (110), FePt (110), and Co-based all-Heusler alloy (110); the material of any metal layer includes one of Ta and W. For example, the materials of different magnetic layers can be the same or different, and the materials of different metal layers can be the same or different, depending on actual needs. The thickness of the metal layer is less than the thickness of the magnetic layer. For example, the thickness of the metal layer is greater than 0 and less than or equal to 0.1 nm, specifically 0.01 nm, 0.03 nm, 0.05 nm, 0.08 nm, or 0.1 nm. The total thickness of the ferromagnetic free layer 21 is maintained, for example, between 1 nm and 50 nm.
[0043] For example, both the magnetic layer and the metal layer can be prepared using PVD (Physical Vapor Deposition) sputtering processes. For instance, leveraging the superior uniformity of films prepared by magnetron sputtering, extremely thin metal layers can be prepared using magnetron sputtering. Specifically, the process parameters for magnetron sputtering, such as magnetic field distribution, ion beam current, sputtering rate, and sputtering duration, can be set according to the required film thickness.
[0044] In one specific embodiment, the metal layer may optionally be made of Ta material. In this embodiment, extremely thin (0~0.1 nm) Ta intercalation layers are added multiple times during the deposition of magnetic material in the ferromagnetic free layer 21, forming a structure in which magnetic and metal layers are stacked alternately. This helps to reduce the risk of element diffusion from the magnetic layer in the ferromagnetic free layer 21 to the barrier layer 31 (e.g., MgO) interface, improves interface quality, and thus enhances the TMR magnetoresistance ratio. At the same time, the doping of extremely thin (0~0.1 nm) Ta intercalation layers helps to reset the epitaxial growth of the ferromagnetic material, reducing the risk of lattice mismatch caused by the accumulation of defects during continuous epitaxial growth of the film.
[0045] Figure 4 This is a schematic diagram of another magnetic tunnel junction film structure provided in an embodiment of the present invention. See also... Figure 4 Based on the above embodiments, optionally, the magnetic tunnel junction further includes a lattice buffer seed layer 22, which is disposed between the substrate layer 11 and the ferromagnetic free layer 21. The crystal plane of the lattice buffer seed layer 22 is (110) or (111). By providing the lattice buffer seed layer 22, a flatter epitaxial interface and a (110) or (111) crystal plane epitaxial induction with a more matching lattice constant can be provided for the upper ferromagnetic free layer 21, which is beneficial for the ferromagnetic free layer 21 to grow better to the (110) crystal plane.
[0046] Specifically, the material of the lattice buffer seed layer 22 includes at least one of the following materials: Pt (111); Ru (0001); Ni / X multilayer structure (111), where X = at least one of Mo, Ru, Nb, Zr, Rh, W, Os, Ir, and Hf; Cr-based alloy (e.g., CrRu doped nitride, etc.) (002) /
[110] ; NiCr-based alloy (111). The Ni / X multilayer structure refers to a multilayer structure consisting of Ni and X material layers stacked and repeated at least once. (002) /
[110] means that the (002) crystal plane of the material serves as the sample surface, and the
[110] crystal orientation within this crystal plane serves as a specific reference direction for the sample. This reference direction crystal plane is the epitaxial surface used to match other upper materials.
[0047] In this embodiment, the lattice buffer seed layer 22 uses a seed layer material with a specific crystal plane, mainly to provide a flatter and more uniform epitaxial growth of the ferromagnetic free layer 21. For example, the thickness of the lattice buffer seed layer 22 is between 10 nanometers and 50 nanometers, such as 10 nanometers, 20 nanometers, 30 nanometers, 40 nanometers, or 50 nanometers. The lattice buffer seed layer 22 can be a single-layer structure composed of one of the aforementioned materials, or a multi-layer stacked structure composed of at least two of the aforementioned materials, depending on actual needs.
[0048] See also Figure 4 Based on the above embodiments, optionally, the magnetic tunnel junction further includes: a synthetic antiferromagnetic intermediate layer 52 and a pinned ferromagnetic layer 53, which are sequentially stacked between the ferromagnetic reference layer 41 and the antiferromagnetic pinning layer 51.
[0049] In this structure, the synthetic antiferromagnetic interlayer 52, through the interlayer coupling field generated by the RKKY coupling effect, promotes the formation of a synthetic antiferromagnetic structure between the ferromagnetic reference layer 41 and the pinned ferromagnetic layer 53. The pinned ferromagnetic layer 53, through the interlayer coupling field, binds the magnetization direction of the ferromagnetic reference layer 41. The antiferromagnetic pinning layer 51 achieves a pinning effect on the magnetization direction of the pinned ferromagnetic layer 53 through interface coupling. The RKKY coupling, specifically Ruderman–Kittel–Kasuya–Yosida coupling, is an indirect exchange interaction transmitted through conduction electrons, which can induce ferromagnetic or antiferromagnetic coupling between two magnetic layers. Its strength oscillates with the thickness of the non-magnetic spacer layer. The interlayer coupling field, or Hinter, is an effective magnetic field generated by the RKKY effect.
[0050] In this embodiment, an intermediate layer (synthetic antiferromagnetic intermediate layer 52) is inserted between the ferromagnetic reference layer 41 and the pinned ferromagnetic layer 53. The intermediate layer connects the upper and lower interfaces to form an interlayer coupling field, providing better specific RKKY coupling, so that the ferromagnetic reference layer 41 and the pinned ferromagnetic layer 53 form a strong antiferromagnetic coupling, thereby forming an antiferromagnetic structure. The effect of adding the synthetic antiferromagnetic interlayer 52 is as follows: without the synthetic antiferromagnetic interlayer 52, the magnetization directions of the ferromagnetic reference layer 41 and the pinned ferromagnetic layer 53 both point in the same direction; after adding the synthetic antiferromagnetic interlayer 52, the magnetization directions of the ferromagnetic reference layer 41 and the pinned ferromagnetic layer 53 tend to be antiparallel and opposite, thus canceling out the stray magnetic fields generated by the ferromagnetic reference layer 41 and the pinned ferromagnetic layer 53, forming a relatively closed magnetic field within the device. This prevents the strong stray magnetic field generated by the ferromagnetic reference layer 41 and the pinned ferromagnetic layer 53 having the same magnetization direction from affecting other layers and thus avoiding affecting the sensor's detection performance. Specifically, the material of the synthetic antiferromagnetic interlayer 52 includes Ru. The synthetic antiferromagnetic interlayer 52 can be a single-layer structure. For example, the thickness of the synthetic antiferromagnetic interlayer 52 is between 0.3 nanometers and 0.9 nanometers, such as 0.3 nanometers, 0.5 nanometers, 0.7 nanometers, or 0.9 nanometers.
[0051] The material of the pinned ferromagnetic layer 53 includes CoFe (110). The main function of the pinned ferromagnetic layer 53 is to achieve a high fixed bias field by forming an exchange bias effect with the antiferromagnetic pinning layer 51. The pinned ferromagnetic layer 53 can be a single-layer structure. For example, the thickness of the pinned ferromagnetic layer 53 is between 1 nanometer and 3 nanometers, such as 1 nanometer, 1.5 nanometer, 2 nanometer, 2.5 nanometer or 3 nanometer.
[0052] In this embodiment, by setting a synthetic antiferromagnetic intermediate layer 52 and a pinned ferromagnetic layer 53, a more stable pinning effect of the antiferromagnetic pinning layer 51 on the ferromagnetic reference layer 41 can be achieved. Furthermore, generally speaking, an applied magnetic field, once it reaches a certain level, can affect the pinning effect or even lead to pinning failure. By adding the interlayer coupling field provided by the synthetic antiferromagnetic intermediate layer 52 and the pinned ferromagnetic layer 53, the magnetic field threshold that leads to failure can be increased, the maximum withstand magnetic field can be improved, thereby enhancing the stability of the sensor.
[0053] See also Figure 4Optionally, based on the above embodiments, the magnetic tunnel junction further includes a barrier buffer layer 32 disposed between the ferromagnetic free layer 21 and the barrier layer 31. In this embodiment, the barrier buffer layer 32 can reduce the oxygen concentration of the barrier layer 31, thereby preventing oxidation. Specifically, the material of the barrier buffer layer 32 includes Mg or Al. The barrier buffer layer 32 can be a single-layer structure made of one of the above materials. The barrier buffer layer 32 uses an element, which contacts the oxide layer constituting the barrier layer 31 and can absorb a certain amount of oxygen through oxygen diffusion, thereby reducing the oxygen concentration of the barrier layer 31.
[0054] See also Figure 4 Based on the above embodiments, optionally, the magnetic tunnel junction further includes an anti-oxidation electrode layer 61 disposed on the side of the antiferromagnetic nailing layer 51 away from the substrate layer 11. In this embodiment, the anti-oxidation electrode layer 61 can protect the underlying film layer from surface contamination and oxidation, enhancing device stability. The anti-oxidation electrode layer 61 prevents oxygen from diffusing into the underlying film layer by blocking oxygen diffusion and / or by preferentially reacting with trace amounts of oxygen that may penetrate in, thereby preventing oxygen from diffusing into the underlying film layer. The material of the anti-oxidation electrode layer 61 includes at least one of Ru and Ta. The anti-oxidation electrode layer 61 can be a single-layer structure composed of one of the above materials. Alternatively, the anti-oxidation electrode layer 61 can be a multi-layer stacked structure composed of two of the above materials, with each layer comprising one material.
[0055] In one specific embodiment, the anti-oxidation electrode layer 61 is optionally a composite barrier layer consisting of a Ru layer and a Ta layer stacked together. The Ru layer acts as the primary "barrier" to block diffusion, while the Ta layer acts as a versatile "backup" to ensure stability and further consume oxygen. The Ru layer itself is a very effective diffusion barrier layer, while Ta is also a good oxygen-absorbing material and can act as a "sacrificial layer," preferentially reacting with any trace amounts of oxygen that may penetrate. Studies have shown that the composite barrier layer containing Ru and Ta can still effectively prevent oxygen from diffusing inwards in air at temperatures as high as 800°C.
[0056] It should be noted that the materials in parentheses above indicate restrictions on the crystal plane orientation. Furthermore, the materials mentioned above are not intended to limit the materials used in each film layer; any film layer can include, but is not limited to, the materials mentioned above, as long as it can form the corresponding film layer and the corresponding crystal plane orientation. The film layer structure of the magnetic tunnel junction includes at least a substrate layer 11, a ferromagnetic free layer 21, a barrier layer 31, a ferromagnetic reference layer 41, and an antiferromagnetic pinning layer 51. Based on this, according to actual needs, at least one of the following can be added to the magnetic tunnel junction: a lattice buffer seed layer 22, a barrier buffer layer 32, a synthetic antiferromagnetic intermediate layer 52, a pinned ferromagnetic layer 53, and an anti-oxidation electrode layer 61, to improve the performance of the magnetic tunnel junction. The thickness of each film layer in the magnetic tunnel junction can be set according to actual needs.
[0057] Based on the above embodiments, optionally, during the preparation of the magnetic tunnel junction, after the antiferromagnetic nailing layer 51 is grown, a two-step annealing with the external magnetic field direction orthogonal is performed to induce the magnetization of the ferromagnetic free layer 21 to be perpendicular to the antiferromagnetic nailing direction, thereby increasing the working linear range.
[0058] Specifically, in the first annealing process, an external magnetic field with a first direction is provided, making the easy axis of magnetization of the antiferromagnetic pinning layer 51 oriented in the first direction; in the second annealing process, an external magnetic field with a second direction is provided, making the easy axis of magnetization of the ferromagnetic free layer 21 oriented in the second direction; the first and second directions are perpendicular. Therefore, after two annealing steps, the easy axes of magnetization of the ferromagnetic free layer 21 and the antiferromagnetic pinning layer 51 are perpendicular. Compared to the case where the easy axes of magnetization of the ferromagnetic free layer 21 and the antiferromagnetic pinning layer 51 are not perpendicular, the operating linear range of sensor products using this magnetic tunnel junction can be effectively increased.
[0059] In the second annealing process, the required external magnetic field strength, temperature, and duration are all less than those in the first annealing process. This is to avoid the influence of the second annealing on the magnetization direction of the antiferromagnetic nail layer 51, and to achieve the induction of magnetization easy axis directions for the two different film layers by the two annealing processes respectively. The magnetic field strength, temperature, and duration of the two annealing processes can be set according to actual needs. For example, the first annealing process can apply an external magnetic field of 1T strength, an annealing temperature within the range of [250℃, 350℃], and an annealing duration within the range of [1h, 2h]; the second annealing process can apply an external magnetic field of 0.5T strength, an annealing temperature within the range of [150℃, 250℃], and an annealing duration within the range of [0.5h, 1h].
[0060] In summary, the embodiments of the present invention provide a novel magnetic tunnel junction film structure design for fabricating high-linearity TMR sensors. Through innovative film structure design at the crystal plane level, a stable and uniform internal bias is achieved at the atomic scale, fundamentally optimizing the magnetization rotation behavior of the ferromagnetic free layer 21 within the measurement magnetic field range, significantly reducing nonlinear error (target <0.5%FSO), and obtaining a wider high-linearity measurement range. This avoids the shortcomings of related technologies, such as limited linearity optimization, potential degradation of noise performance, and problems with bias field stability and uniformity.
[0061] This invention also provides a TMR sensor, including the magnetic tunnel junction provided in any embodiment of the invention, which has corresponding beneficial effects. For example, the TMR sensor may have a bridge structure composed of TMR sensor units (or magnetoresistive elements), such as a half-bridge or full-bridge structure, specifically, for example, a Wheatstone full-bridge structure composed of four TMR sensor units. The TMR sensor unit includes the magnetic tunnel junction provided in any embodiment of the invention.
[0062] It should be understood that the various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this invention can be achieved, and this is not limited herein.
[0063] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.
Claims
1. A magnetic tunnel junction, characterized in that, include: A substrate layer, and a ferromagnetic free layer, a barrier layer, a ferromagnetic reference layer and an antiferromagnetic pinning layer sequentially stacked on one side of the substrate layer; The crystal plane of the ferromagnetic free layer is (110).
2. The magnetic tunnel junction according to claim 1, characterized in that, The ferromagnetic free layer includes at least two magnetic layers stacked together, with a metal layer inserted between each two adjacent magnetic layers; The material of any of the magnetic layers includes one of CoFe (110), CoFeB (110), FePt (110) and Co-based all-Heusler alloy (110); the material of any of the metal layers includes one of Ta and W.
3. The magnetic tunnel junction according to claim 1, characterized in that, The crystal plane of the substrate layer is (110) or (111); And / or, the crystal plane of the barrier layer is (110) or (111); And / or, the crystal plane of the ferromagnetic reference layer is the (110) crystal plane; And / or, the crystal plane of the antiferromagnetic nailing layer is (111) crystal plane.
4. The magnetic tunnel junction according to claim 1, characterized in that, The substrate material includes one of Si (110), MgO (110), MgO (111), α-Al2O3 (0001), GaAs (110), and GaAs (111); The material of the ferromagnetic free layer includes at least one of CoFe (110), CoFeB (110), FePt (110), and Co-based all-Heusler alloy (110); The barrier layer is made of the following materials: MgO (110), MgO (111), and AlO. x (110) AlO x (111)MgAl x O y (110) and MgAl x O y One of (111); The material of the ferromagnetic reference layer includes at least one of CoFe (110), CoFeB (110), FePt (110), and Co-based all-Heusler alloy (110); The material of the antiferromagnetic nailing layer includes one of IrMn (111), PtMn (111), and FeMn (111).
5. The magnetic tunnel junction according to any one of claims 1-4, characterized in that, Also includes: A lattice buffer seed layer is disposed between the substrate layer and the ferromagnetic free layer; wherein the crystal plane of the lattice buffer seed layer is (110) or (111).
6. The magnetic tunnel junction according to claim 5, characterized in that, The material of the lattice buffer seed layer includes at least one of the following materials: Pt (111); Ru (0001); Ni / X multilayer structure (111), where X = at least one of Mo, Ru, Nb, Zr, Rh, W, Os, Ir and Hf; Cr-based alloy (002) / [110]; NiCr-based alloy (111).
7. The magnetic tunnel junction according to any one of claims 1-4, characterized in that, Also includes: A synthetic antiferromagnetic intermediate layer and a pinned ferromagnetic layer are sequentially stacked between the ferromagnetic reference layer and the antiferromagnetic pinning layer; The synthetic antiferromagnetic intermediate layer promotes the formation of a synthetic antiferromagnetic structure between the ferromagnetic reference layer and the pinned ferromagnetic layer through the interlayer coupling field generated by the RKKY coupling effect. The pinned ferromagnetic layer constrains the magnetization direction of the ferromagnetic reference layer through the interlayer coupling field.
8. The magnetic tunnel junction according to claim 7, characterized in that, The material of the synthetic antiferromagnetic intermediate layer includes Ru; The material of the pinned ferromagnetic layer includes: CoFe (110).
9. The magnetic tunnel junction according to any one of claims 1-4, characterized in that, Also includes: A barrier buffer layer is disposed between the ferromagnetic free layer and the barrier layer; And / or, The magnetic tunnel junction further includes an anti-oxidation electrode layer disposed on the side of the antiferromagnetic nailing layer away from the substrate layer.
10. The magnetic tunnel junction according to claim 9, characterized in that, When the magnetic tunnel junction includes the barrier buffer layer, the material of the barrier buffer layer includes: Mg or Al; In the case where the magnetic tunnel junction includes the anti-oxidation electrode layer, the material of the anti-oxidation electrode layer includes at least one of Ru and Ta.
11. A TMR sensor, characterized in that, include: The magnetic tunnel junction according to any one of claims 1-10.