Magnetic tunnel junction element and magnetic device

Abstract

To provide a magnetic tunnel junction element and a magnetic device that enable reduction in power consumption of a magnetic tunnel junction.SOLUTION: A magnetic tunnel junction element includes a first ferromagnetic layer, a second ferromagnetic layer, a tunnel insulating layer, a metal nitride layer, a first conductive layer, and a protective layer. The metal nitride layer is represented by the general formula Z1-xMxWyN1-y, where: Z is at least one element selected from the group consisting of Al, In, and Ga; M is at least one element selected from the group consisting of Sc, B, C, Si, Gd, Cr, Zn, Y, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Ti, Hf, and Zr; and W is at least one element selected from the group consisting of O, S, Se, F, Cl, Br, and I. The protective layer contains amorphous silicon, or an oxide, nitride or oxynitride of at least one metal element selected from the group consisting of Al, Si, and Ti.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to magnetic tunnel junction elements and magnetic devices. [Background technology]

[0002] Magnetic tunnel junctions (MTJs) are known (see, for example, Patent Document 1 or Patent Document 2). Because MTJs exhibit a large magnetoresistance effect at room temperature, they are used in magnetic heads installed in hard disk drives (HDDs) and magnetic random access memories (MRAMs). An MTJ has a structure in which an insulating layer is disposed between two ferromagnetic layers. Because the insulating layer is very thin, a small current (tunnel current) flows between the two ferromagnetic layers due to the tunnel effect. When the two ferromagnetic layers are parallel to each other, the electrical resistance of the MTJ decreases, and the tunnel current increases. On the other hand, when the two ferromagnetic layers are antiparallel to each other, the electrical resistance of the MTJ increases, and the tunnel current decreases. In devices using MTJs, the magnetization direction of one ferromagnetic layer is fixed by an antiferromagnetic layer, while the magnetization direction of the other ferromagnetic layer can be freely reversed, thereby changing the electrical resistance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-229706 [Patent Document 2] Japanese Patent Publication No. 2022-069247 [Patent Document 3] Japanese Patent Application Laid-Open No. 2007-261883 [Non-patent literature]

[0004] [Non-Patent Document 1] HC Lee, “Influence of sputtering pressure on the microstructure evolution of AlN thin films prepared by reactive sputtering”, Thin Solid Films, Volume 261, Issues 1-2, 1 June 1995, Pages 148-153 Summary of the Invention [Problem to be solved by the invention]

[0005] In the above-mentioned MTJ, a large amount of power is required to change the electrical resistance using an external magnetic field, so there is a demand for lower power consumption.

[0006] An object of the present disclosure is to provide a magnetic tunnel junction element and a magnetic device that enable low power consumption of an MTJ. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems and have discovered that a specific metal nitride having a wurtzite structure enables low power consumption in an MTJ, leading to the invention of the present invention.

[0008] [1] a first ferromagnetic layer that is a magnetization fixed layer; a second ferromagnetic layer that is a magnetization free layer; a tunnel insulating layer interposed between the first ferromagnetic layer and the second ferromagnetic layer; a metal nitride layer provided on the second ferromagnetic layer; a first conductive layer provided on the metal nitride layer; a protective layer covering the exposed surface of the metal nitride layer, The metal nitride layer is a film containing a metal nitride, It has a wurtzite structure, General formula Z 1-x M x W y N1-y represented by Z is at least one element selected from the group consisting of Al, In, and Ga; M is at least one element selected from the group consisting of Sc, B, C, Si, Gd, Cr, Zn, Y, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Ti, Hf, and Zr; W is at least one element selected from the group consisting of O, S, Se, F, Cl, Br, and I; 0 < x ≦ 0.45 and 0 < y ≦ 0.4; The protective layer contains an oxide of at least one metal element selected from the group consisting of Al, Si, and Ti, a nitride of the metal element, an oxynitride of the metal element, or amorphous silicon. Magnetic tunnel junction element. [2] The magnetic tunnel junction element according to [1], wherein Z is Al. [3] The magnetic tunnel junction element according to [1], wherein Z is In. [4] The magnetic tunnel junction element according to [1], wherein Z is Ga. [5] The magnetic tunnel junction element according to any one of [1] to [4], further comprising a second conductive layer provided between the second ferromagnetic layer and the metal nitride layer. [6] A magnetic device comprising the magnetic tunnel junction element according to any one of [1] to [5]. [7] The magnetic device according to [6], which is a magnetic random access memory.

Advantages of the Invention

[0009] According to one aspect of the present disclosure, there are provided a magnetic tunnel junction element and a magnetic device that enable low power consumption of an MTJ.

Brief Description of the Drawings

[0010] [Figure 1]FIG. 1 is a cross-sectional view showing an MTJ element according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a single cell of the MRAM according to the embodiment. [Figure 3] FIG. 3 is a cross-sectional view showing an MTJ element according to a modified example. [Figure 4] FIG. 4 is a diagram illustrating a method for evaluating the Al0.7Sc0.3O0.05N0.95 film using an AFM. [Figure 5] Fig. 5(a) is an explanatory diagram of the write region and the write voltage, and Fig. 5(b) is an MFM image showing the magnetization state after writing. [Figure 6] Figure 6(a) is an explanatory diagram of the write area and write voltage, Figure 6(b) is an AFM image showing the surface shape after writing, and Figure 6(c) is an MFM image of the film showing the magnetization state after writing. [Figure 7] Figure 7(a) is a graph showing the magnetization curve of an Al0.7Sc0.3O0.05N0.95 film, and Figure 7(b) is a graph showing the magnetization curve of an Al0.7Sc0.3O0.2N0.8 film. [Figure 8] FIG. 8 shows the results of X-ray diffraction of the AlScN film. [Figure 9] FIG. 9 is a graph showing the magnetization curve of the Al0.7Sc0.3OyN1-y film. [Figure 10] FIG. 10 is a graph showing the relationship between the oxygen substitution amount and the saturation magnetization amount. [Figure 11] FIG. 11 is a graph showing the change in saturation magnetization over time. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or equivalent elements are designated by the same reference numerals, and redundant description will be omitted.

[0012] (metal nitrides) The metal nitride according to this embodiment has a wurtzite structure and is represented by the general formula Z 1-x Mx W y N 1-y It is represented by. Here, Z, M, W, and N are as follows. Z: At least one element selected from the group consisting of Al, In, and Ga M: At least one element selected from the group consisting of Sc, B, C, Si, Gd, Cr, Zn, Y, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Ti, Hf, and Zr W: At least one element selected from the group consisting of O, S, Se, F, Cl, Br, and I Also, 0 < x ≤ 0.45 and 0 < y ≤ 0.4. It may be 0 < y ≤ 0.3.

[0013] The metal nitride may be, for example, AlScON. In this case, the chemical composition ratio of Al atoms is, for example, 30% or more and 50% or less. The chemical composition ratio of Sc atoms is, for example, 0% or more and 40% or less. The chemical composition ratio of O atoms is, for example, 0% or more and 30% or less. The chemical composition ratio of N atoms is, for example, 30% or more and 50% or less. The ratio of Sc atoms to the sum of Al atoms and Sc atoms may be, for example, 0.1 or more and 0.45 or less (Sc / (Al + Sc) = 0.1 to 0.45), or 0.1 or more and 0.3 or less (Sc / (Al + Sc) = 0.1 to 0.3). The ratio of O atoms to the sum of N atoms and O atoms may be, for example, 0.1 or more and 0.4 or less (O / (N + O) = 0.1 to 0.4), or 0.1 or more and 0.3 or less (O / (N + O) = 0.1 to 0.3).

[0014] Metal nitrides are not n-type semiconductors, but are, for example, p-type semiconductors or dielectrics. Metal nitrides are, for example, ferroelectrics. It can be confirmed that a metal nitride is not an n-type semiconductor, for example, by measuring the Hall effect. The Hall effect is a phenomenon in which, when a magnetic field perpendicular to the current is applied to an object through which a current is flowing, a potential difference (Hall voltage) occurs in a direction perpendicular to both the current and the magnetic field. It can be confirmed that a metal nitride is not an n-type semiconductor by measuring the direction (sign) of the Hall voltage. It can be confirmed that a metal nitride is not an n-type semiconductor, for example, by vapor-depositing a metal on the surface of the metal nitride and measuring the current-voltage characteristics, and not confirming rectification, or by not confirming depletion of the metal nitride from the capacitance-voltage characteristics.

[0015] Low-resistivity n-type AlN (aluminum nitride) crystal is described in Patent Document 3. The metal oxide according to this embodiment differs from the AlN crystal described in Patent Document 3 in that it is not an n-type semiconductor.

[0016] The inventors have discovered that the metal nitride according to this embodiment is a magnetic material that can be magnetized by applying an electric field. As described above, a large amount of power is required to change the electrical resistance of an MTJ using an external magnetic field. Typically, an external magnetic field is generated by passing a current through a coil, but this results in loss due to Joule heat, such as heat generated by the coil. In contrast, the metal nitride according to this embodiment can be magnetized by an electric field without using an external magnetic field. Therefore, the generation of Joule heat can be suppressed, enabling the MTJ to consume less power.

[0017] (MTJ element) FIG. 1 is a cross-sectional view showing an MTJ element according to the embodiment. As shown in FIG. 1, the MTJ element 1 according to the embodiment is an element including a ferromagnetic layer 101 (first ferromagnetic layer), a tunnel insulating layer 102, a ferromagnetic layer 103 (second ferromagnetic layer), a conductive layer 104 (second conductive layer), a metal nitride layer 105 (film), and a conductive layer 106 (first conductive layer). The MTJ element 1 has a layered structure in which these layers are stacked in order. The MTJ element 1 is also an example of an element according to this embodiment.

[0018] The ferromagnetic layer 101 and the ferromagnetic layer 103 are disposed with the tunnel insulating layer 102 sandwiched therebetween. The ferromagnetic layer 101 and the ferromagnetic layer 103 are provided adjacent to the tunnel insulating layer 102. The ferromagnetic layer 101 is a magnetization fixed layer (reference layer). The magnetization direction of the ferromagnetic layer 101 is fixed in a predetermined direction. The ferromagnetic layer 103 is a magnetization free layer (storage layer). The magnetization direction of the ferromagnetic layer 103 can be easily changed by magnetization rotation.

[0019] The ferromagnetic layers 101 and 103 include a ferromagnetic material. Examples of the ferromagnetic material include ferromagnetic metals such as iron (Fe), cobalt (Co), FeCo alloys, and CoFeB alloys, as well as ferromagnetic half-metals. The ferromagnetic layers 101 and 103 may include the same ferromagnetic material or different ferromagnetic materials.

[0020] The tunnel insulating layer 102 is interposed between the ferromagnetic layer 101 and the ferromagnetic layer 103. The tunnel insulating layer 102 electrically and magnetically separates the ferromagnetic layer 101 and the ferromagnetic layer 103. The tunnel insulating layer 102 includes an insulator. Examples of the insulator include magnesium oxide (MgO), aluminum oxide (Al2O3), or a mixture of these materials.

[0021] The stack 10 including the ferromagnetic layer 101, the tunnel insulating layer 102, and the ferromagnetic layer 103 forms an MTJ. That is, when the magnetization direction of the ferromagnetic layer 103, which is the magnetization free layer, is the same as (parallel to) the magnetization direction of the ferromagnetic layer 101, which is the magnetization fixed layer, the electrical resistance of the MTJ is low, and when they are opposite (antiparallel to) the magnetization direction, the electrical resistance of the MTJ is high.

[0022] The thickness of the ferromagnetic layer 101 is, for example, from several atomic layers to 100 nm. The thickness of the tunnel insulating layer 102 is such that carriers can tunnel in the film thickness direction, for example, 1 nm or more and 2 nm or less. The thickness of the ferromagnetic layer 103 is, for example, 1 nm or more and 10 nm or less. The coercive force of the ferromagnetic layer 101 is greater than that of the ferromagnetic layer 103. An antiferromagnetic layer may be further provided on the side of the ferromagnetic layer 101 opposite the tunnel insulating layer 102. The antiferromagnetic layer is magnetically coupled to the ferromagnetic layer 101, thereby improving the coercive force of the ferromagnetic layer 101.

[0023] The ferromagnetic layers 101 and 103 are, for example, perpendicular magnetization films that are magnetized perpendicular to the film surface. The ferromagnetic layers 101 and 103 are magnetized in the perpendicular upward or downward direction. In the MTJ element 1, the ferromagnetic layers 101 and 103 are made of ferromagnetic metals such as iron (Fe), cobalt (Co), an FeCo alloy, or a CoFeB alloy, or a ferromagnetic half-metal, and the tunnel insulating layer 102 is made of magnesium oxide, aluminum oxide, or a mixture of these materials, and the perpendicular magnetization of the ferromagnetic layers 101 and 103 is realized by utilizing interfacial magnetic anisotropy. The materials for the ferromagnetic layers 101, the tunnel insulating layer 102, and the ferromagnetic layer 103 may be other combinations of materials as long as they can realize perpendicular magnetization.

[0024] The ferromagnetic layer 101, the tunnel insulating layer 102, and the ferromagnetic layer 103 are formed by, for example, sputtering, atomic layer deposition, or ion plating, with sputtering being preferred.

[0025] The conductive layer 104 is provided on the ferromagnetic layer 103. The conductive layer 104 is provided adjacent to the ferromagnetic layer 103. The conductive layer 104 is provided between the ferromagnetic layer 103 and the metal nitride layer 105. The conductive layer 104 includes a conductive material. Examples of the conductive material include titanium nitride (TiN), titanium (Ti), tungsten nitride (WN), tungsten (W), tantalum nitride (TaN), and tantalum (Ta). The conductive layer 104 may be provided on the ferromagnetic layer 103 via a smoothing layer. The smoothing layer may be made of, for example, Ta.

[0026] The metal nitride layer 105 is provided on the conductive layer 104. The metal nitride layer 105 is provided in contact with the conductive layer 104. The metal nitride layer 105 is interposed between the conductive layer 104 and the conductive layer .

[0027] The metal nitride layer 105 is a film containing the above-mentioned metal nitride. The metal nitride layer 105 is also an example of a film according to this embodiment. The MTJ element 1 includes the metal nitride layer 105, which enables low power consumption. The metal nitride layer 105 is, for example, a polycrystalline film. Being polycrystalline allows for easy quality control and stable, inexpensive production.

[0028] The crystal grain size of the polycrystalline film is preferably, for example, 5 nm to 200 nm, more preferably 5 nm to 50 nm. The crystal grain size is the average crystal grain size measured, for example, by X-ray diffraction or cross-sectional transmission electron microscope observation. For example, in X-ray diffraction, the crystal grain size can be estimated from the crystallite size using the Scherrer formula, which utilizes the half-width of the diffraction signal and the X-ray wavelength, and in cross-sectional transmission electron microscope observation, it can be evaluated by obtaining a dark-field image. The crystal grains are, for example, plate-shaped.

[0029] When the metal nitride is a ferroelectric, the direction exhibiting ferroelectric polarization reversal is preferably oriented, for example, within 10 degrees from an axis perpendicular to the film surface. In other words, the polarization direction of the metal nitride layer 105 is preferably approximately perpendicular to the film surface. The crystal structure of the metal nitride layer 105 does not have centrosymmetrical, for example. The thickness of the metal nitride layer 105 is preferably, for example, 5 nm or more and 50 nm or less.

[0030] The metal nitride layer 105 is formed by, for example, sputtering or atomic layer deposition. Sputtering is preferred, and atomic layer deposition is more preferred. The method for manufacturing the metal nitride layer 105 (film) according to this embodiment includes a sputtering step. For example, in the case of a 3-inch target device, the sputtering step is performed by setting the DC voltage to 200 V or more, the DC current to 1 A or more, the gas pressure to 1 Pa or less, and the substrate temperature to between room temperature and 400°C or less. When depositing under these conditions, as described in Non-Patent Document 1, it is possible to extend the mean free path of the deposited particles and form a film oriented in a substantially vertical direction. Note that a similar effect can be obtained with AC power.

[0031] The conductive layer 106 is provided on the metal nitride layer 105, and sandwiches the metal nitride layer 105 between the conductive layer 106 and the conductive layer 104. The conductive layer 106 is provided in contact with the metal nitride layer 105. The conductive layer 106 includes a conductive material. Examples of the conductive material include titanium nitride (TiN), titanium (Ti), tungsten nitride (WN), tungsten (W), tantalum nitride (TaN), and tantalum (Ta). The conductive layer 106 may be formed of the same conductive material as the conductive layer 104, or may be formed of a different conductive material. The conductive layer 104 and the conductive layer 106 function as electrodes for applying a voltage to the metal nitride layer 105.

[0032] The stack 20, including the conductive layer 104, the metal nitride layer 105, and the conductive layer 106, changes the resistance of the MTJ formed by the stack 10 as follows. First, a voltage is applied between the conductive layer 104 and the conductive layer 106. This induces an electric field in the metal nitride layer 105, which magnetizes the metal nitride layer 105. If the magnetization direction of the metal nitride layer 105 differs from the magnetization direction of the ferromagnetic layer 103, the magnetization direction of the ferromagnetic layer 103 is reversed. As a result, the resistance of the MJ element changes. The stack 20 is also an example of a stack according to this embodiment.

[0033] The metal nitride layer 105 is, for example, a perpendicular magnetization film together with the ferromagnetic layers 101 and 103, and is magnetized in the perpendicular upward or downward direction.

[0034] The MTJ element 1 may include two or more metal nitride layers 105. The conductive layer 104 and the ferromagnetic layer 103 may be the same layer. That is, if the conductive layer 104 includes a ferromagnetic material and also functions as a magnetization free layer, the MTJ element 1 does not need to include the ferromagnetic layer 103. In this case, the conductive layer 104 is included in the stack 20 to change the resistance of the MTJ, and is also included in the stack 10 to form the MTJ.

[0035] The MTJ element 1 does not necessarily have to include the conductive layer 106. Even in this case, for example, a probe made of a non-magnetic metal for AFM (Atomic Force Microscopy) disposed on the metal nitride layer 105 can be used as an electrode to apply an electric field to the metal nitride layer 105. That is, the stacked body 20 only needs to include at least the metal nitride layer 105 and the conductive layer 104.

[0036] (MRAM) FIG. 2 is a cross-sectional view showing a single cell of the MRAM according to the embodiment. As shown in FIG. 2, the MRAM 2 according to the embodiment is a device, particularly a magnetic device, including the MTJ element 1 described above. The MRAM 2 further includes a write word line 111, a bit line 112, a transistor 113, and a lower electrode substrate 114. The write word line 111 is connected to the conductive layer 104. The bit line 112 is connected to the lower electrode substrate 114 via the transistor 113. The transistor 113 is turned on by selecting the word line 115 connected to its gate. The lower electrode substrate 114 is provided on the ferromagnetic layer 101. The lower electrode substrate 114 functions as wiring and is configured as a laminated film for fixing the magnetization of the ferromagnetic layer 101.

[0037] When reading digital information from the MRAM2, the write word line 111 is selected to turn on the transistor 113, and the digital information is read from the resistance value between the write word line 111 and the bit line 112. When writing digital information to the MRAM2, the write word line 111 is selected to turn on the transistor 113, and a voltage is applied between the write word line 111 and the conductive layer 106 to change the resistance of the MTJ and write the digital information. In other words, the metal nitride layer 105 is magnetized by applying a voltage, and the magnetization of the ferromagnetic layer 103 is reversed, thereby writing the digital information.

[0038] Since the MRAM 2 includes the above-described MTJ element 1, it is possible to reduce the power consumption of the MTJ.

[0039] Although the embodiments have been described above, the present invention is not necessarily limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention.

[0040] While the MTJ element 1 has been illustrated as an example of an element according to the embodiment, the element according to the embodiment may also be, for example, a magnetic head, a magnetic memory, a magnetic sensor, a spin transistor, or a microwave oscillator. The element according to the embodiment may include at least a laminate of a film containing the metal nitride and a conductive layer. Furthermore, while the MRAM 2, which is a magnetic device, has been illustrated as an example of a device according to the embodiment, the device according to the embodiment is not limited to a magnetic device and may include at least an element according to the embodiment as a component. For example, a structure having a function in a circuit is an element according to the embodiment, and a product formed by combining such elements is a device according to the embodiment.

[0041] (Variation) FIG. 3 is a cross-sectional view showing an MTJ element according to a modified example. As shown in FIG. 3, the MTJ element 1A according to the modified example differs from the MTJ element 1 according to the embodiment in that the stack 20 further includes a protective layer 107. The protective layer 107 is an anti-oxidation layer that prevents oxidation of the metal nitride layer 105. The protective layer 107 covers the exposed surface of the metal nitride layer 105. The exposed surface of the metal nitride layer 105 is the portion of the surface of the metal nitride layer 105 that is exposed from other layers or members and may come into contact with the atmosphere. In the illustrated example, the protective layer 107 covers only the upper surface of the metal nitride layer 105 that is exposed from the conductive layer 106, but it may also cover the side surfaces adjacent to the upper surface of the metal nitride layer 105.

[0042] The protective layer 107 includes, for example, amorphous silicon (a-Si). The a-Si is deposited by, for example, a sputtering method. Because a-Si is amorphous, it does not form grain boundaries and has high barrier performance. The barrier performance can be evaluated by common evaluation methods such as the cup method, the pressure sensor method, and the calcium corrosion method. The thickness of the protective layer 107 is, for example, 50 nm or less, and may be 30 nm or less. By making the protective layer 107 this thin, it is possible to suppress the occurrence of distortion and cracks due to stress.

[0043] The protective layer 107 may contain, for example, an oxide of at least one metal element selected from the group consisting of Al, Si, and Ti, a nitride of the metal element, or an oxynitride of the metal element. These metal oxides, metal nitrides, and metal oxynitrides can be formed by, for example, a vapor phase deposition method. Examples of vapor phase deposition methods that can be used include chemical vapor deposition, atomic layer deposition, and sputtering. Sputtering can form a dense film with few grain boundaries. The protective layer 107 may have multiple layers. For example, the protective layer 107 may have a layer containing a metal oxide and a layer containing a metal nitride stacked together.

[0044] Conventionally, AlN-based materials were thought to be very stable and not oxidized within the temperature range in which they are normally used. However, as a result of research and studies by the present inventors, it was found that the saturation magnetization of the metal nitride according to this embodiment decreases over time and that the saturation magnetization of the metal oxynitride varies depending on the composition ratio of oxygen to nitrogen (O / N ratio) in the metal oxynitride. The present inventors hypothesized that the deterioration over time is caused by oxygen entering the metal oxynitride from the outside and replacing nitrogen, resulting in a change in the O / N ratio, and investigated a configuration to suppress the entry of oxygen from the outside. As a result, the present inventors discovered a configuration in which the metal nitride is covered with a protective layer that has the effect of suppressing oxidation.

[0045] The MTJ element 1A enables low power consumption of the MTJ, similar to the MTJ element 1. The MTJ element 1A further includes a protective layer 107, which can prevent oxygen from penetrating into the metal nitride layer 105. This prevents deterioration over time of the saturation magnetization of the metal nitride layer 105, and improves the driving durability and driving stability of the MTJ.

[0046] The above-described embodiment and the above-described modified examples may be combined as appropriate. For example, a magnetic device made of MRAM2 may include an MTJ element 1A instead of the MTJ element 1. [Example]

[0047] The present invention will be described below with reference to examples, but the present invention is not limited to the following examples.

[0048] (Experiment 1) In order to confirm that the above-mentioned metal oxide film is magnetized by an electric field, Experiment 1 using AFM was carried out as follows. 0.7 Sc 0.3 O 0.05 N 0.95 4 is a diagram illustrating a method for evaluating the film. + An Al film (50 nm thick) is formed on the bottom surface of the Si substrate. + A TiN film (10 nm thick) is formed on the top surface of the Si substrate, and Al is deposited on the TiN film. 0.7 Sc 0.3 O 0.05 N 0.95 A metal oxide film (15 nm thick) made of the following was formed to prepare a laminate according to the example. The Al film, TiN film, and metal nitride film were all formed by sputtering.

[0049] Then, using a 0.4T electromagnet, 0.7 Sc 0.3 O 0.05 N 0.95 The film was magnetized in the upward direction perpendicular to the film surface. Next, the TiN film was grounded, and a non-magnetic metal AFM probe P1 was attached to the Al 0.7 Sc 0.3 O 0.05 N 0.95 Next, various voltages ranging from -9V to 9V (corresponding to an electric field of -6MV / cm to 6MV / cm) were applied to the probe P1, and the Al 0.7 Sc 0.3 O 0.05 N 0.95 A predetermined area (2 μm×2 μm area) on the film was scanned to write information. Figure 5(a) is an explanatory diagram of the write area and the write voltage.

[0050] After that, the AFM probe P1 made of a non-magnetic metal was changed to the MFM probe P2 made of a magnetic material, and Al 0.7 Sc 0.3 O 0.05N 0.95 The magnetization state of the film surface was confirmed without contact. Figure 5(b) is an MFM image showing the magnetization state after writing. As shown in Figure 5(b), in the area where writing was performed with the AFM probe P1, magnetization reversal according to the write voltage was confirmed. When the write voltage was set to ±9 V, clear magnetization reversal was confirmed. All steps except for the process of forming the stack according to the example were carried out at room temperature (300 K).

[0051] (Experiment 2) Experiment 2 was carried out using the laminate prepared in Experiment 1. In Experiment 2, Al was heated using a 0.4 T electromagnet. 0.7 Sc 0.3 O 0.05 N 0.95 The Al film was magnetized in the same manner as in Experiment 1, except that the magnetization direction of the film was perpendicular downward. 0.7 Sc 0.3 O 0.05 N 0.95 Information was written to the film, and the magnetization state was confirmed using the MFM probe P2. Although not shown, an MFM image similar to that shown in Figure 5(b) was also obtained in Experiment 2. This indicates that, regardless of the direction of the magnetization beforehand, if the write voltage is set to ±9V, the Al 0.7 Sc 0.3 O 0.05 N 0.95 It was confirmed that the film could be magnetized.

[0052] (Experiment 3) Using the laminate prepared in Experiment 1, Experiment 3 was carried out at room temperature (300 K) as follows. First, an electromagnet of 0.4 T was used to 0.7 Sc 0.3 O 0.05 N 0.95 The film was magnetized in the upward direction perpendicular to the film surface. Next, the TiN film was grounded, and a non-magnetic metal AFM probe P1 was attached to the Al 0.7 Sc 0.3 O 0.05 N 0.95 Next, a voltage of -9 V (corresponding to an electric field of -6 MV / cm) was applied to the AFM probe P1, and the Al 0.7 Sc 0.3 O 0.05N 0.95 A predetermined area (3 μm × 3 μm) on the film was scanned and information was written. After that, the voltage was changed to +9 V (corresponding to an electric field of +6 MV / cm), and information was overwritten in a predetermined area (1 μm × 1 μm) inside the area where the information had been written. Figure 6(a) is an explanatory diagram of the writing area and writing voltage.

[0053] Then, after writing, 0.7 Sc 0.3 O 0.05 N 0.95 The surface shape of the film was observed by AFM. Figure 6(b) is an AFM image showing the surface shape after writing. As shown in Figure 6(b), Al 0.7 Sc 0.3 O 0.05 N 0.95 It was confirmed that the surface morphology of the film was not affected by writing.

[0054] Next, the AFM probe P1 made of a non-magnetic metal was changed to the MFM probe P2 made of a magnetic material, and Al 0.7 Sc 0.3 O 0.05 N 0.95 The magnetization state of the film surface was confirmed without contact. Figure 6(c) is an MFM image showing the magnetization state after writing. As shown in Figure 6(c), the area written with only -9V voltage has turned light in color, and the area overwritten with +9V voltage has turned dark in color. This indicates that Al 0.7 Sc 0.3 O 0.05 N 0.95 It was confirmed that the film allows not only one write but also further magnetization reversal.

[0055] (Experiment 4) Experiment 4 was carried out at room temperature (300 K) using the laminate prepared in Experiment 1. In Experiment 4, Al 0.7 Sc 0.3 O 0.05 N 0.95The experiment was carried out in the same manner as in Experiment 3, except that the magnetization direction of the film was vertically downward. Although not shown, in Experiment 4, an AFM image almost identical to the AFM image in Figure 6(b) and an MFM image almost identical to the MFM image in Figure 6(c) were also obtained. 0.7 Sc 0.3 O 0.05 N 0.95 It was confirmed that the surface shape of the film is not affected by writing, regardless of the direction of the previous magnetization, and that not only one write but also further magnetization reversal is possible.

[0056] (Experiment 5) Experiment 5: Al 0.7 Sc 0.3 O y N 1-y A magnetic field was applied perpendicular to the film, and the magnetization curve (MH curve) was measured at room temperature (300 K). 0.7 Sc 0.3 O 0.05 N 0.95 1 is a graph showing the magnetization curve of a film. 0.7 Sc 0.3 O 0.05 N 0.95 A layered structure was prepared by forming an AlN film (100 nm thick) and a TiN film (10 nm thick) in this order. Each film was formed by sputtering. The deposition of each film was carried out consecutively without exposing it to the outside air. 0.7 Sc 0.3 O 0.05 N 0.95 The magnetization curves of the Al films were measured. 0.7 Sc 0.3 O 0.2 N 0.8 1 is a graph showing the magnetization curve of a film deposited on a pSi substrate by sputtering. 0.7 Sc 0.3 O 0.2 N 0.8 Then, an Al film (100 nm thick) was formed. 0.7 Sc 0.3 O 0.2 N 0.8 The magnetization curve of the film was measured.

[0057] As shown in Figures 7(a) and 7(b), it was confirmed that magnetization increased with increasing oxygen content in a perpendicular magnetic field. Although not shown, there was almost no magnetization in an in-plane magnetic field. 0.7 Sc 0.3 O y N 1-y The grain size of the film was about 30 nm in all cases. 0.7 Sc 0.3 O y N 1-y It is believed not to affect the magnetic properties of the film.

[0058] (Experiment 6) In experiment 6, Al was deposited by DC sputtering while changing the gas pressure. 0.7 Sc 0.3 O 0.05 N 0.95 The film was deposited and the relationship between the ferroelectric properties of the film and the orientation state was investigated. The gas pressure was set to 0.7 Pa and 1.2 Pa.

[0059] Figure 8 shows the results of X-ray diffraction (XRD) of the AlScN film. Here, the lattice plane parallel to the film surface was measured using the out-of-plane method. As shown in Figure 8, it can be confirmed that the (002) orientation (c-axis) of the AlScN film has superior ferromagnetic properties compared to the (100) orientation. It can also be confirmed that the film deposited at a gas pressure of 0.7 Pa has a higher (002) component and a better orientation than the film deposited at a gas pressure of 1.2 Pa. In other words, the film orientation can be controlled by the gas pressure in the deposition process, and a (002)-oriented film can be obtained when deposited at 0.7 Pa. As a result, a ferromagnetic film suitable for MTJ elements can be obtained.

[0060] In Non-Patent Document 1, it is speculated that the reason why the (002) component increases as the pressure decreases during radio frequency sputtering of aluminum nitride (AlN) is that the mean free path becomes longer and the mobility of adatoms increases. From the above, it is possible that a ferroelectric film can be easily obtained by using a low gas pressure.

[0061] (Experiment 7) In order to confirm the correlation between the saturation magnetization and the O / N ratio of the metal oxynitride, samples were prepared, their magnetic properties were evaluated, and their compositions were analyzed by the following methods.

[0062] (1) Sample preparation n + An electrode layer (10 nm thick) made of TiN film is formed on a Si substrate, and Al is deposited on the electrode layer. 0.7 Sc 0.3 O y N 1-y A metal oxynitride layer (100 nm thick) made of a film was formed to prepare a stack according to the example. The TiN film was formed by RF sputtering using a Ti target at a substrate temperature of 400°C, a deposition pressure of 0.3 Pa, Ar and N2 were introduced at a flow ratio of 2:3, and discharged at 300 W. Al 0.7 Sc 0.3 O y N 1-y The film was deposited by DC sputtering using an AlSc (composition ratio 53:47) target at a substrate temperature of 400°C and a deposition pressure of 0.5 Pa. Ar, N2, and O2 were introduced at a flow ratio of 5:10:y, and discharge was performed at 300 W. y = 0, 0.1, 0.2, 0.3, 0.4, and 0.5. (2) Magnetic property evaluation The magnetic properties of the metal oxynitride film were evaluated using a magnetic property evaluation system manufactured by Quantum Design, Inc., USA. (3) Composition analysis The composition ratio of the metal oxynitride film can be quantified by XPS analysis. A PHI Quantera SXM was used as the measurement device, and the evaluation was performed with a detection area of ​​100 μm diameter. The composition ratio was determined from the spectral intensities of Al2p, Sc2p, N1s, and O1s.

[0063] Figure 9 shows the Al 0.7 Sc 0.3 O y N 1-y9 is a graph showing the magnetization curve of the film. FIG. 10 is a graph showing the relationship between the oxygen substitution amount and the saturation magnetization amount. As shown in FIGS. 9 and 10, it was found that the magnetic properties were improved by substituting a portion of the N in AlScN with O. The saturation magnetization amount was maximized when O / (O+N)~0.2 (i.e., y~0.2). It was found that magnetization could be obtained up to O / (O+N)~0.4 (i.e., y~0.4).

[0064] (Experiment 8) In order to confirm the correlation between the application of a protective layer to a metal oxynitride layer and deterioration over time, samples were prepared and their magnetic properties were evaluated by the following method.

[0065] (1) Sample preparation n + An electrode layer (10 nm thick) made of TiN film is formed on a Si substrate, and Al is deposited on the electrode layer. 0.7 Sc 0.3 O 0.3 N 0.7 A metal oxynitride layer (100 nm thick) made of a film was formed, and a protective layer was further formed on the metal oxynitride film to prepare a stack according to the example. The protective layer was an a-Si film (30 nm thick), a TiN film (30 nm thick), a SiN film (100 nm thick), or a fluororesin film (100 nm thick). For comparison, a stack without a protective layer was also prepared. The TiN film was formed by RF sputtering using a Ti target at a substrate temperature of 400°C, a deposition pressure of 0.3 Pa, Ar and N2 were introduced at a flow ratio of 2:3, and discharged at 300 W. Al 0.7 Sc 0.3 O 0.3 N 0.7 The film was deposited by DC sputtering using an AlSc (composition ratio 53:47) target at a substrate temperature of 400°C and a deposition pressure of 1.5 Pa. Ar, N2, and O2 were introduced at a flow rate ratio of 5:10:0.3, and the discharge was performed at 300 W. The a-Si film was formed by RF sputtering using a Si target at a substrate temperature of 400° C., with Ar introduced to set the film formation pressure at 0.5 Pa, and discharged at 150 W. The SiN film was formed by plasma enhanced chemical vapor deposition using a parallel plate type apparatus with trisilylamine as the raw material and nitrogen gas as the introduction gas. The substrate temperature was 200°C, the film formation pressure was 30 Pa, the trisilylamine flow rate was 0.6 sccm, the nitrogen gas flow rate was 100 sccm, and the RF power was 100 W. The fluororesin film was deposited by plasma enhanced chemical vapor deposition using a parallel plate type apparatus, with the substrate temperature at room temperature, deposition pressure at 80 Pa, trifluoromethane flow rate at 80 sccm, and RF power at 30 W. (2) Magnetic property evaluation The magnetic properties of the metal oxynitride films were evaluated using a magnetic property evaluation system manufactured by Quantum Design, Inc. (USA). The relationship between the number of days of exposure to the atmosphere and the amount of magnetization was calculated based on the saturation magnetization measured immediately after the start of exposure to the atmosphere. The samples were stored in a vacuum from the time of sample preparation until the first evaluation (i.e., the magnetic property evaluation immediately after the start of exposure to the atmosphere).

[0066] Figure 11 is a graph showing the change in saturation magnetization over time. The saturation magnetization is expressed as a percentage of the saturation magnetization measured immediately after the start of atmospheric exposure. Figure 11 shows the change in saturation magnetization over time for the following cases: without a protective layer; with an a-Si protective layer; with a TiN protective layer; with a SiN protective layer; and with a fluororesin protective layer. As shown in Figure 11, it was confirmed that covering the AlScON film with an a-Si protective layer, a SiN protective layer, or a TiN protective layer can suppress the degradation of magnetic properties. Because the gas permeability of organic materials is higher than that of inorganic materials, it is likely that the magnetic properties deteriorated more quickly with the fluororesin protective layer than with other protective layers. Although the reason for the faster degradation of magnetic properties with the fluororesin protective layer compared to without a protective layer is unclear, possible reasons include damage to the metal oxynitride layer during the formation of the fluororesin protective layer, reactions between the fluororesin protective layer and the metal oxynitride layer, and degradation of the fluororesin protective layer due to atmospheric exposure.

[0067] [Additional remarks] The metal nitride, film, stack, element, device, film manufacturing method, magnetic tunnel junction element, and magnetic device disclosed herein enable low power consumption, thereby contributing to the achievement of Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations. Goal 9: "Build infrastructure for industry, innovation and sustainable development" [Explanation of symbols]

[0068] 1,1A...MTJ element (element), 2...MRAM (device, magnetic device), 20...stacked body, 101...ferromagnetic layer (first ferromagnetic layer), 102...tunnel insulating layer, 103...ferromagnetic layer (second ferromagnetic layer), 104...conductive layer (second conductive layer), 105...metal nitride layer (film), 106...conductive layer (first conductive layer), 107...protective layer.

Claims

1. a first ferromagnetic layer that is a magnetization fixed layer; a second ferromagnetic layer that is a magnetization free layer; a tunnel insulating layer interposed between the first ferromagnetic layer and the second ferromagnetic layer; a metal nitride layer provided on the second ferromagnetic layer; a first conductive layer provided on the metal nitride layer; a protective layer covering the exposed surface of the metal nitride layer, The metal nitride layer is a film containing a metal nitride, It has a wurtzite structure, General formula Z １－ｘ M ｘ W ｙ N １－ｙ is expressed as Z is at least one element selected from the group consisting of Al, In, and Ga, M is at least one element selected from the group consisting of Sc, B, C, Si, Gd, Cr, Zn, Y, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho, Er, Tm, Yb, Ti, Hf, and Zr; W is at least one element selected from the group consisting of O, S, Se, F, Cl, Br, and I; 0<x≦0.45 and 0<y≦0.4, the protective layer contains at least one oxide of a metal element selected from the group consisting of Al, Si, and Ti, a nitride of the metal element, an oxynitride of the metal element, or amorphous silicon; Magnetic tunnel junction device.

2. The magnetic tunnel junction device of claim 1 , wherein Z is Al.

3. The magnetic tunnel junction device of claim 1 , wherein Z is In.

4. The magnetic tunnel junction device of claim 1 , wherein Z is Ga.

5. 4. The magnetic tunnel junction element according to claim 1, further comprising a second conductive layer provided between the second ferromagnetic layer and the metal nitride layer.

6. A magnetic device comprising the magnetic tunnel junction element according to any one of claims 1 to 3.

7. The magnetic device of claim 5 , which is a magnetic random access memory.

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