CN104993046A - MTJ unit and manufacturing method thereof - Google Patents

Abstract

The present invention discloses an MTJ (Magnetic Tunnel Junction) unit and a manufacturing method thereof. A layer of extremely thin metal layer is inserted in a magnetic layer thin film of an MTJ, so as to form a magnetic layer/metal layer/magnetic layer structure, the thickness of the inserted metal layer ranges from 0.5nm to 2nm, through artificial increase for the number of interfaces in the magnetic layer, perpendicular magnetic anisotropy of the interface is greatly enhanced, and the perpendicular magnetic anisotropy of the whole film structure can be improved objectively. According to the MTJ unit and the manufacturing method provided by the present invention, perpendicular magnetic anisotropy of the magnetic layer thin film is effectively improved through a diffusion effect of the metal layer with the specific type and thickness and an interface effect between the magnetic layer and the metal layer, at the same time, the thickness of the magnetic layer thin film with good perpendicular orientation is also increased, thereby providing a new breakthrough for manufacture of perpendicular magnetic anisotropy MTJ units and devices in industrial community.

Description

A magnetic tunnel junction unit and its preparation method

technical field

The invention belongs to the field of spin electronics, and more specifically relates to a magnetic tunnel junction unit and a preparation method.

Background technique

With the rapid development of electronic information technologies such as new computers, information and communications, high-performance requirements such as high density, high speed, high writing efficiency, and high reliability have been put forward for memory as its core component. Various semiconductor memories, such as static random access memory (SRAM: Static Random Access Memory), dynamic random access memory (DRAM: Static Random Access Memory) and flash memory (flash) have been deeply researched and widely used due to their respective advantages. application. However, with the shrinking of the device size, the development of the above-mentioned memories encounters their respective bottlenecks, which limits their development and application to a certain extent. In recent years, magnetic random access memory based on Magnetic Tunneling Junction (MTJ, Magnetic Tunneling Junction) has greatly stimulated the worldwide industry and academia due to its characteristics of non-volatility, high storage density, and fast read and write speed. research interests.

A typical magnetic tunnel junction has a three-layer structure: a free layer, a barrier layer and a reference layer, as shown in Figure 1. By changing the magnetization direction of the free layer of the memory cell, two resistance states, high and low, can be generated in the memory cell. The difference in the barrier layer material of the MTJ junction affects the TMR value of the MTJ, because the barrier layer material will directly affect the tunneling behavior of electrons and determine the tunneling magnetoresistance of the MTJ. The current mainstream barrier layer material is MgO. The materials used for the free layer (free layer) and reference layer (reference layer) of the magnetic tunnel junction are mainly ferromagnetic materials (FM). The free layer is characterized by easy magnetization, that is, the direction of magnetization can be changed, so soft magnetic materials with small coercive force are generally used. The reference layer requires a fixed magnetization direction and is usually composed of a pinned layer and a pinned layer. The material of the pinned layer is the same as that of the free layer, using soft magnetic material. The pinning layer is generally made of a hard magnetic material with a large coercive force, and the magnetization direction of the pinned layer is fixed by antiferromagnetic coupling. The soft magnetic material currently used for MTJ is mainly CoFeB, which has the characteristics of low coercive force and high spin polarizability. It has also been reported that other Co-based soft magnetic materials or new high spin polarizability semi-metallic materials can be used as the soft magnetic layer material of MTJ. Hard magnetic materials currently available for MTJ include FePt, TbFeCo, Co(Fe)/Pt(Pd) multilayer films, etc.

MTJ requires low power consumption, small operating current, high density, and high speed performance requirements. Although MTJ has good electrical characteristics at present, the optimization of circuit performance will not stop, and there are still related problems on the road to commercialization:

(1) In the case of ultra-high storage density, the sharp reduction in the size of the in-plane magnetic anisotropic film will produce magnetization curl or vortex magnetic domain structure, resulting in the loss of stored information. The perpendicular magnetic anisotropy thin film material can effectively overcome the magnetization curl or vortex domain, which is conducive to improving the stability of information storage, and theoretical calculations also predict that the critical current density of the perpendicular magnetic anisotropy MTJ will be lower than In-plane magnetically anisotropic memory cells. In order to increase the storage density and reduce its write current, it is necessary to increase the vertical anisotropy of the MTJ.

(2) Since the thickness of each layer of the MTJ film structure is very thin (the thinnest layer is less than 1 nm, and the thickness of the general film layer is 1-10 nm), the preparation process is very difficult. In addition, to obtain perpendicular magnetic anisotropy, the thickness of the CoFeB layer must be very small (less than 1.2nm), which further increases the difficulty of process preparation. Therefore, in order to reduce the difficulty of the process and improve the feasibility of MTJ preparation, it is necessary to increase the thickness of the magnetic layer with perpendicular anisotropy.

At present, people mainly optimize the performance of MTJ by changing the thickness of the MTJ magnetic layer, annealing temperature, and the type and thickness of the covering layer. Common covering layers in the literature include Ta, Ti, NiFe, etc. The difference and thickness of the covering layer will affect the crystallization of CoFeB and the diffusion of B. Ta is the most mentioned cladding layer. In addition to its excellent oxidation resistance, the Ta layer and the Ta/CoFeB interface also play a role in the vertical anisotropy (PMA) of Ta/CoFeB/MgO-based MTJs. Key role. Therefore, it is the starting point of the present invention to increase the perpendicular anisotropy of the magnetic layer material by adding interfaces in the magnetic layer thin film.

Contents of the invention

Aiming at the defects of the prior art, the object of the present invention is to provide a magnetic tunnel junction unit and a preparation method thereof, aiming at solving the problems of low thermal stability and low storage density of the existing magnetic tunnel junction.

The invention provides a magnetic tunnel junction unit, comprising a substrate, a reference layer attached to the substrate, a barrier layer attached to the reference layer and a free layer attached to the barrier layer; the reference layer It includes a first magnetic layer, a metal layer and a second magnetic layer; through the metal layer, the interface vertical anisotropy in the first magnetic layer and the second magnetic layer is strengthened, and the vertical magnetic anisotropy of the whole reference layer is improved. The present invention inserts an extremely thin metal layer into the magnetic layer thin film of the magnetic tunnel junction to form a structure of magnetic layer (FM)/metal layer (M)/magnetic layer (FM) to strengthen the interface in the magnetic layer perpendicular to each Anisotropy, so as to achieve the purpose of improving the vertical magnetic anisotropy of the entire film structure. At the same time, because the metal layer is inserted, the thickness of the overall film layer is increased, and the process difficulty is reduced.

Furthermore, the thickness of the first magnetic layer is equal to the thickness of the second magnetic layer, and the thickness of the metal layer is 0.5nm-2nm.

Furthermore, the material of the metal layer is a non-magnetic metal material.

Furthermore, the material of the metal layer is Ag, Ta, Ti, Al, Cu or Au and the like. Due to the magnetic thin film material with a layer of Ta metal layer inserted, the Ta insertion layer within the thickness range of 0.5nm to 2nm can optimize the vertical orientation of the magnetic layer with the same thickness due to its diffusion effect and interface effect with the magnetic layer.

Furthermore, the metal layer is made of Ag and has a thickness of 1 nm. Due to the magnetic thin film material with a layer of Ag metal layer inserted, the 1nm Ag insertion layer can optimize the vertical orientation of the CoFeB magnetic layer with the same thickness due to its diffusion effect and interface effect with the magnetic layer.

Furthermore, the magnetic tunnel junction unit further includes a protective layer attached to the free layer.

Furthermore, the material of the protective layer may be Ta, and the thickness may be 5 nm.

The present invention also provides a method for preparing the above-mentioned magnetic tunnel junction unit, comprising the following steps:

(1) preparing a first magnetic layer on the substrate by magnetron sputtering, preparing a metal layer on the first magnetic layer, and preparing a second magnetic layer on the metal layer;

Wherein, the thickness of the first magnetic layer is equal to the thickness of the second magnetic layer, and the thickness of the metal layer is 0.5 nm to 2 nm;

(2) preparing a barrier layer on the second magnetic layer by magnetron sputtering;

(3) Prepare a free layer on the barrier layer; wherein the structure of the free layer is the same as that of the above-mentioned reference layer, both are magnetic layers, and the free layer includes the first magnetic layer, attached to the metal layer on the first magnetic layer , a second magnetic layer attached to the metal layer;

Wherein, the thickness of the first magnetic layer is equal to the thickness of the second magnetic layer, and the thickness of the metal layer is 0.5 nm to 2 nm;

(4) Preparing a protective layer on the free layer to obtain a magnetic tunnel junction unit.

Wherein, the material of the metal layer may be Ag, Ta, Ti, Al, Cu or Au.

Further preferably, the metal layer is made of Ag and has a thickness of 1 nm.

Wherein, in the method of magnetron sputtering described in step (1), the sputtering power is DC 20W; adopting low sputtering power can reduce the sputtering rate and improve the film forming quality. In the method of magnetron sputtering described in step (2), the sputtering power is radio frequency 100W.

Specifically, the method for preparing the above-mentioned magnetic tunnel junction unit includes:

(1) Prepare the reference layer on the MgO substrate. The specific method is to first use the CoFeB target material to sputter a 1.2nm CoFeB film at a low power of 20W by magnetron sputtering, and then use the required metal target material (Ag or Ta, etc.) prepare a metal intercalation layer with a thickness of t, and then sputter a 1.2nm CoFeB film, thus forming an improved magnetic layer structure in which an extremely thin metal intercalation layer is inserted in the CoFeB magnetic layer;

(2) On the prepared reference layer, prepare a barrier layer of 1nm MgO by magnetron sputtering with an MgO target;

(3) Prepare an improved free layer on the prepared barrier layer, the method is consistent with the reference layer in step 1;

(4) In order to protect the prepared magnetic tunnel junction from oxidation, we added a 5nm Ta protective layer on the top layer.

Among them, all the thin film samples prepared by sputtering were prepared on the basis of single crystal MgO(001).

Among them, the Ar pressure of the preparation environment of the thin film samples is 0.5 Pa.

Wherein, the sputtering power of CoFeB is 20W, the sputtering power of Ag is 20W, and the sputtering power of Ta is 40W.

The invention increases the number of interfaces in the magnetic layer by inserting an extremely thin metal layer in the magnetic layer film, greatly strengthens the vertical magnetic anisotropy of the interface, and objectively improves the vertical magnetic anisotropy of the entire film layer structure. Therefore, the thermal stability of the magnetic tunnel junction is high, and the storage density is high.

Description of drawings

Figure 1 shows a typical magnetic tunnel junction structure.

Fig. 2(a) is a schematic diagram of a conventional magnetic layer structure, and Fig. 2(b) is a schematic diagram of an improved magnetic layer structure according to the present invention.

FIG. 3 is a schematic structural diagram of a magnetic tunnel junction unit provided by an embodiment of the present invention.

FIG. 4 is an X-ray diffraction pattern of a reference CoFeB thin film without a metal layer inserted in an embodiment of the present invention after annealing at 400° C. for 1 hour.

Fig. 5 is the magnetic hysteresis loop in the horizontal direction and the vertical direction of the single-layer CoFeB thin film in the embodiment of the present invention.

Figure 6 shows hysteresis loops in the horizontal and vertical directions of CoFeB thin films inserted with 1nm and 0.5nm Ag in the embodiment of the present invention; wherein, (a) is inserted with 1nm Ag, and (b) is inserted with 0.5nm Ag.

Fig. 7 is a comparison between the MAE calculated by VASP and the experimental value of the single-layer CoFeB film and the film inserted with the Ag metal layer in the embodiment of the present invention.

Figure 8 shows hysteresis loops in the horizontal and vertical directions of the CoFeB film inserted with 1nm and 0.5nm Ta in the embodiment of the present invention, wherein (a) is inserted with 1nm Ta, and (b) is inserted with 0.5nm Ta.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

The invention improves the perpendicular magnetic anisotropy of the MTJ by utilizing and strengthening the perpendicular magnetic anisotropy of the magnetic layer interface in the magnetic tunnel junction, and provides a magnetic tunnel junction unit and a preparation method thereof to strengthen the interface in the magnetic layer vertical anisotropy.

The present invention forms the structure of magnetic layer (FM)/metal layer (M)/magnetic layer (FM) by inserting a layer of extremely thin metal (Ag, Ta, etc.) layer in the magnetic layer thin film, as shown in Figure 2, The thickness of the metal intercalation layer is 0.5nm-2nm to strengthen the interface vertical anisotropy in the magnetic layer, so as to achieve the purpose of improving the vertical magnetic anisotropy of the entire film layer structure. In the MTJ structure, since each magnetic layer is very thin (the thickness is mostly within a few nanometers, even less than 1nm, and the thickness of the hard magnetic pinning layer is generally not more than 100nm), as the thickness of the magnetic layer decreases, The vertical magnetic anisotropy of the magnetic grains in the magnetic layer reduces the contribution to the vertical magnetic anisotropy of the entire film structure, while the vertical magnetic anisotropy of the interface between the magnetic layer and the adjacent film layer contributes to the vertical magnetic anisotropy of the entire film structure. The contribution of magnetic anisotropy increases. Therefore, the present invention artificially increases the number of interfaces in the magnetic layer by inserting an extremely thin metal layer in the magnetic layer film, greatly strengthens the interface perpendicular magnetic anisotropy, and objectively improves the vertical magnetic properties of the entire film structure. anisotropy.

Compared with the existing magnetic layer single-layer thin film, the present invention utilizes an extremely thin metal layer inserted in the single-layer magnetic layer thin film, through the diffusion effect of the metal layer of a specific type and thickness and between FM/M The interfacial interaction effectively improves the vertical anisotropy of the magnetic layer film, and also increases the thickness of the magnetic layer film with better vertical orientation, which provides a new breakthrough for the preparation of vertically anisotropic MTJ units and devices in the industry. Since the type and thickness of the inserted metal layer have a great influence on the diffusion and interface effects, in the present invention, the effects of different metals and different thicknesses on the perpendicular anisotropy (PMA) of the magnetic layer are also different. Among them, the PMA of the CoFeB thin film inserted with 1nmAg and 1nm Ta has been greatly improved compared with the single-layer magnetic layer with the same thickness. Through magnetron sputtering, hysteresis loops, atomic force microscope tests and VASP theoretical calculations, we studied the influence of inserting different types and different thicknesses of metal layers on the perpendicular anisotropy of the magnetic layer film.

Through the elaboration of specific examples below, to further illustrate the substantive features and remarkable progress of the present invention, but the present invention is by no means limited to the examples.

The magnetic layers in the following specific examples all take the soft magnetic layer CoFeB thin film in the MTJ structure as an example, and introduce the film layer structure, preparation method, magnetic properties and technical effects of CoFeB thin films containing metal intercalation layers of different types and thicknesses. The method for enhancing the perpendicular magnetic anisotropy of the magnetic layer interface involved in the present invention is also applicable to other magnetic layer materials in the MTJ structure, and is not limited to CoFeB thin film materials.

Specifically, the film structure and preparation method of the improved magnetic tunnel junction are as follows:

The film structure is MgO sub/FM(1.2nm)/M(t nm)/FM(1.2nm)/Ta(5nm), where FM is the magnetic layer, M is different metals (Ta, Ag, etc.), and t is the metal The thickness of the layer, t=0.5nm～2nm.

A method for preparing a magnetic tunnel junction unit, specifically:

(1) Prepare an improved reference layer on the MgO substrate. The specific method is to first use the CoFeB target to sputter a 1.2nm CoFeB film at a low power of 20W by magnetron sputtering, and then use the required metal target ( Ag or Ta, etc.) to prepare a metal intercalation layer with a thickness of t, and then sputter a 1.2nm CoFeB film, thus forming an improved magnetic layer structure in which a very thin metal intercalation layer is inserted in the CoFeB magnetic layer;

(2) On the prepared reference layer, prepare a barrier layer of 1nm MgO by magnetron sputtering with an MgO target;

(3) Prepare an improved free layer on the prepared barrier layer, the method is consistent with the reference layer in step 1;

(4) Finally, in order to protect the prepared magnetic tunnel junction from oxidation, we added a 5nm Ta protective layer on the top layer.

Further, all thin film samples prepared by sputtering were prepared on the basis of single crystal MgO(001); the Ar pressure in the preparation environment of thin film samples was 0.5Pa; the sputtering power of CoFeB was 20W, and the sputtering power of Ta The sputtering power of Ti is 60W, the sputtering power of Al is 20W, and the sputtering power of Ag is 20W.

Embodiment one:

In this embodiment, the influence of the insertion of the Ag layer and the thickness of the Ag layer on its vertical anisotropy is obtained by preparing a single-layer magnetic layer CoFeB thin film and a CoFeB thin film with metal layers of Ag inserted in different thicknesses and testing their magnetic properties.

The preparation method of the magnetic layer film material described in this embodiment can adopt chemical vapor deposition (CVD), such as liquid phase deposition, electrolytic deposition and metal-organic chemical vapor deposition, etc.; physical vapor deposition (PVD), such as evaporation deposition, laser molecular Beam epitaxy (laser molecular beam epitaxy, LMBE), pulsed laser deposition (pulsed laser deposition, PLD) and magnetron sputtering (magnetronsputtering), etc. Their commonality is that the target material is deposited on the substrate in the form of atoms or ions, and the difference lies in the energy carried by the atoms or ions. The thin film deposited by sputtering method is uniform, dense, wide application target, fast growth rate, reactive sputtering and alloy film with various components can be prepared, and multiple target guns can be used at one time, which is convenient for the preparation of multilayer films with different components. , so it is widely used in laboratory and industry. What the present invention selects is the magnetron sputtering method.

In this embodiment, the magnetron sputtering method is used to prepare the magnetic layer thin film. First prepare a CoFeB target with a diameter of 100mm and a thickness of 2.5mm (wherein the atomic ratio Co:Fe:B=40:40:20), the purity of the target is 99.99% (atomic percentage) and the required metal target , the purity of the metal target is 99.95% (atomic percentage). Then, the method of magnetron sputtering is used, and Ar gas with a purity of 99.999% is introduced during sputtering.

The method for preparing the magnetic layer CoFeB thin film inserted with the metal layer Ag is specifically:

(1) On the MgO substrate, first use the CoFeB target material to sputter a 1.2nm CoFeB film at a low power of 20W by magnetron sputtering, and then use the required Ag metal target material to prepare a metal intercalation layer with a thickness of t. Then sputter 1.2nm CoFeB film, which forms an improved magnetic layer structure in which a very thin metal intercalation layer is inserted in the CoFeB magnetic layer;

(2) In order to prevent the prepared film from being oxidized, a 5 nm thick Ta capping layer was sputtered on the top of the film.

The specific process parameters are as follows:

The CoFeB target uses a DC power supply with a power of 20W; the sputtering pressure is 0.5Pa; the base distance of the target is 120mm, and the pre-sputtering is performed for 1 hour before each sputtering to ensure that the impurities on the target surface are completely removed.

The Ag target adopts a DC power supply, the power is 10-20W; the sputtering pressure is 0.5Pa; the target base distance is 120mm, and the pre-sputtering is 1h before each sputtering to ensure that the impurities on the target surface are removed.

The Ta target uses a DC power supply with a power of 40W; the sputtering pressure is 0.5Pa; the base distance of the target is 120mm, and the pre-sputtering is performed for 1 hour before each sputtering to ensure that the impurities on the target surface are completely removed.

The magnetic layer material described in the present embodiment is as shown in Figure 3, and its thin film structure is MgO sub/CoFeB (1.2nm)/Ag (t nm)/CoFeB (1.2nm)/Ta (5nm), simultaneously, the monolayer CoFeB (2.4nm) films were also fabricated for reference.

Fig. 4 is the X-ray diffraction pattern of the reference CoFeB thin film without intercalated metal layer after annealing at 400°C for 1 h. It can be seen from the XRD pattern that the CoFeB film prepared by us exhibits the peak of CoFe(110) after annealing at 400°C for 1 hour, indicating that the annealing condition of 400°C for 1 hour can crystallize the CoFeB film and present CoFe(110) texture.

Figure 5 is the hysteresis loops in the horizontal and vertical directions of a single-layer CoFeB thin film. From the results in the graph, it can be seen that the ratio of the coercive force in the vertical direction to the horizontal direction of the CoFeB thin film (including 1.2nm and 2.4nm) without any metal layer is not more than 2.

Figure 6 shows the hysteresis loops in the horizontal and vertical directions of CoFeB thin films inserted with 1nm and 0.5nm Ag. Table 1 shows the values of coercivity in the vertical and horizontal directions and their ratios for single-layer CoFeB (1.2nm) and (2.4nm) thin films and CoFeB thin films inserted with different metal layers. The larger the ratio of the coercive force in the vertical direction to the horizontal direction of the film, the better the vertical orientation of the film. Therefore, it can be seen from Figure 6 combined with the data in Table 1 that the ratio of the coercive force in the vertical direction to the horizontal direction of the thin film inserted with 0.5nm metal Ag is less than 2, because the inserted metal layer is too thin to have A good interface is formed with the CoFeB layer, and interfacial interaction is not formed, resulting in that the vertical anisotropy cannot be significantly improved. This shows that the improvement of the vertical anisotropy of the CoFeB layer has a great relationship with the thickness of the inserted metal. The ratio of the coercive force in the vertical direction to the horizontal direction of the CoFeB film inserted with 1nm Ag is 4.32, far exceeding the ratio of the coercive force in the vertical direction to the horizontal direction of the single-layer CoFeB film. This shows that inserting 1nm Ag into the CoFeB film can significantly improve the vertical anisotropy of the CoFeB film. The reason is the diffusion of Ag and the formation of a metal/CoFeB interface with the CoFeB layer, which improves the vertical anisotropy of CoFeB.

Table 1

In order to further verify the experimental results, the magnetic anisotropy energy (MAE) per unit cross-sectional area of the single-layer CoFeB (2.4nm) film and the film inserted with 0.5nm Ag and 1nm Ag was calculated and compared using VASP first-principles . The calculation results are shown in Table 2. When the calculated MAE value is positive, it indicates that the film has perpendicular anisotropy, and the larger the MAE, the greater the perpendicular anisotropy of the film. When the value of MAE is negative, it means that the film has in-plane anisotropy. The results of our calculations are shown in Figure 7. The results show that the MAE per unit cross-sectional area of the film inserted with 1nm Ag is the largest, while the MAE per unit cross-sectional area of the film inserted with 0.5nm Ag is the smallest. It also shows that inserting 1nm Ag into the CoFeB film can improve the performance of the CoFeB film The vertical anisotropy is in good agreement with the experimental results.

Table 2

At the same time, we also compared the MAE of the CoFeB layer inserted with a 2nm Ag metal layer. It can be seen from Table 2 that the MAE per unit area of CoFeB inserted with a 2nm thick Ag metal layer is smaller than the value of a single layer of CoFeB, thus indicating that the 2nm The thickness of is too thick for the Ag metal layer, which is not conducive to improving the vertical anisotropy of CoFeB.

This example shows that inserting a 1 nm Ag metal layer can well improve the vertical anisotropy of the CoFeB magnetic layer.

Embodiment two:

In this embodiment, a single-layer magnetic layer CoFeB thin film and a CoFeB thin film inserted with a metal layer Ta of different thicknesses are prepared and their properties are tested to compare their perpendicular anisotropy.

The method for preparing the magnetic layer CoFeB thin film inserted with the metal layer Ta is specifically:

(1) On the MgO substrate, first use the CoFeB target material to sputter a 1.2nm CoFeB film at a low power of 20W by magnetron sputtering, and then use the required Ta metal target material to prepare a metal intercalation layer with a thickness of t. Then sputter 1.2nm CoFeB film, which forms an improved magnetic layer structure in which a very thin metal intercalation layer is inserted in the CoFeB magnetic layer;

(2) In order to prevent the prepared film from being oxidized, a 5 nm thick Ta capping layer was sputtered on the top of the film.

The specific process parameters are as follows:

The CoFeB target uses a DC power supply with a power of 20W; the sputtering pressure is 0.5Pa; the base distance of the target is 120mm, and the pre-sputtering is performed for 1 hour before each sputtering to ensure that the impurities on the target surface are completely removed.

The Ta target uses a DC power supply with a power of 40W; the sputtering pressure is 0.5Pa; the base distance of the target is 120mm, and the pre-sputtering is performed for 1 hour before each sputtering to ensure that the impurities on the target surface are completely removed.

The magnetic layer material described in this embodiment has a film structure of MgO sub/CoFeB(1.2nm)/Ta(t nm)/CoFeB(1.2nm)/Ta(5nm), wherein t is 0.5nm and 1nm.

Figure 8 shows the hysteresis loops in the horizontal and vertical directions of CoFeB thin films inserted with 1nm and 0.5nm Ta. Combining the data in Table 1, it can be seen that the ratio of coercive force in the vertical direction to the horizontal direction of the thin film inserted with 0.5nm metal Ta is also greater than the value of single-layer CoFeB (1.2nm). The ratio of the coercive force in the vertical direction to the horizontal direction of the CoFeB film inserted with 1nm Ta is 2.38, which also exceeds the ratio of the coercive force in the vertical direction to the horizontal direction of the single-layer CoFeB film. This shows that inserting 1nm Ta into the CoFeB film can also improve the vertical anisotropy of the CoFeB film. The reason may be the diffusion of Ta and the formation of a metal/CoFeB interface with the CoFeB layer, which improves the vertical anisotropy of CoFeB.

The MAE of the metal layer Ta inserted in the CoFeB film of 0.5nm, 1nm and 2nm was also calculated by the first principle, and the calculation results are shown in Table 3. It can be clearly seen from the table that the MAE of CoFeB thin films inserted with metal Ta layers of different thicknesses is higher than that of single-layer CoFeB, which shows that inserting Ta layers in the thickness range of 0.5nm to 2nm can improve the thickness of CoFeB layer. magnetic anisotropy.

table 3

This example shows that inserting a Ta metal layer with a thickness ranging from 0.5nm to 2nm can well improve the vertical anisotropy of the CoFeB magnetic layer. Compared with the test results of inserting the Ag metal layer in the CoFeB film in this embodiment and Example 1, although the Ta layer and the Ag layer inserted into a certain thickness can improve the vertical anisotropy of the CoFeB film, the insertion of the 1nm Ag metal layer The vertical anisotropy of the CoFeB film is obviously larger than that of the CoFeB film inserted into the Ta layer. This is probably because the mismatch rate (1%) of the lattice constants of Ag and CoFeB is smaller than the mismatch rate (4%) of the lattice constants of Ta and CoFeB.

Embodiment three:

In this embodiment, the anisotropic energy of the single-layer magnetic layer CoFeB thin film and the CoFeB thin film inserted with different thicknesses of the metal layer Ti are calculated by first principles and their sizes are compared.

The calculation results are shown in Table 4. It can be clearly seen from the table that the MAE of the CoFeB film with a 0.5nm metal Ti layer inserted is slightly lower than that of a single-layer CoFeB film, while the MAE of a CoFeB film with a 1nm metal Ti layer inserted is much larger than that of a single-layer CoFeB film. For CoFeB films, the relationship is almost 2 times. When the thickness of the metal layer Ti increases to 2nm, the value of MAE suddenly becomes negative, which means that the magnetic layer inserted with 2nm metal Ti loses the perpendicular anisotropy.

This shows that the magnetic anisotropy of the CoFeB layer can be improved by inserting a 1nm Ti layer.

Table 4

Embodiment four:

In this embodiment, the anisotropic energy of the single-layer magnetic layer CoFeB thin film and the CoFeB thin film inserted with different thicknesses of the metal layer Al are calculated by first principles and their sizes are compared.

The calculation results are shown in Table 5. It can be clearly seen from the table that the MAE of the CoFeB thin film inserted with a metal Al layer of 0.5nm and 1nm is higher than that of a single layer of CoFeB, which shows that the insertion of an Al layer within the thickness range of 0.5nm to 1nm can improve Magnetic anisotropy of CoFeB layers. However, when the Al metal layer is too thick (up to 2nm), the vertical anisotropy of the magnetic layer will be reduced instead.

table 5

Compared with a single-layer magnetic film, the magnetic film inserted with a specific type and thickness of the metal layer provided by the present invention can effectively improve the vertical anisotropy of the magnetic film by inserting a thin metal layer, which is conducive to the preparation of high-density, low-power-consumption magnetic films. Tunnel junction cells and devices. The present invention inserts a thin metal layer in the magnetic layer to increase its perpendicular magnetic anisotropy. The material of the thin metal layer is not limited to the Ag, Ta, Ti and Al mentioned in the embodiment, and can also be other non-magnetic materials such as Cu and Au. Magnetic metal material. The metal layer has a thickness ranging from 0.5nm to 2nm.

It is easy for those skilled in the art to understand that the above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention, All should be included within the protection scope of the present invention.

Claims (10)

1. A magnetic tunnel junction unit comprising a substrate, a reference layer attached to the substrate, a barrier layer attached to the reference layer and a free layer attached to the barrier layer; its feature In that, the structures of the reference layer and the free layer are the same, both including a first magnetic layer, a metal layer and a second magnetic layer; through the metal layer, the interface in the first magnetic layer and the second magnetic layer is strengthened vertically Anisotropy, increasing the perpendicular magnetic anisotropy of the magnetic tunnel junction unit. 2 . The magnetic tunnel junction unit according to claim 1 , wherein the thickness of the first magnetic layer is equal to the thickness of the second magnetic layer, and the thickness of the metal layer is 0.5 nm˜2 nm. 3. The magnetic tunnel junction unit according to claim 1, wherein the material of the metal layer is a non-magnetic metal material. 4. The magnetic tunnel junction unit according to claim 3, wherein the material of the metal layer is Ag, Ta, Ti, Al, Cu or Au. 5 . The magnetic tunnel junction unit according to claim 4 , wherein the metal layer is made of Ag and has a thickness of 1 nm. 6. The magnetic tunnel junction unit according to claim 1, further comprising a protective layer attached to the free layer. 7. The magnetic tunnel junction unit according to claim 6, wherein the protective layer is made of Ta. 8. A method for preparing a magnetic tunnel junction unit, comprising the steps of: (1) preparing a first magnetic layer on the substrate by magnetron sputtering, preparing a metal layer on the first magnetic layer, and preparing a second magnetic layer on the metal layer; (2) preparing a barrier layer on the second magnetic layer by magnetron sputtering; (3) preparing a free layer on the barrier layer; the free layer includes a first magnetic layer, a metal layer attached to the first magnetic layer, and a second magnetic layer attached to the metal layer; (4) preparing a protective layer on the free layer, thereby obtaining a magnetic tunnel junction unit; Wherein, the thickness of the first magnetic layer is equal to the thickness of the second magnetic layer, and the thickness of the metal layer is 0.5nm˜2nm. 9. The preparation method according to claim 8, wherein the material of the metal layer is Ag, Ta, Ti, Al, Cu or Au. 10. The preparation method according to claim 8, wherein the metal layer is made of Ag and has a thickness of 1 nm.