Laminate, element, and device

Abstract

This laminate comprises a substrate and a film which is formed on the substrate. The film has an epitaxial layer that contains a Y-type hexaferrite. The Y-type hexaferrite is represented by the general formula (Ba1-xSrx)2Co2Fe12-y-δAlyXδO22. X is at least one element that is selected from the group consisting of Cr, Sb, In, and V. In the formula, 0≤x≤1, 1<y≤6, and 0≤δ≤1.

Description

Stacked body, element and device

[0001] The present disclosure relates to laminates, elements and devices.

[0002] Epitaxial thin films of Y-type hexaferrite not only contribute to the miniaturization of microwave devices, but can also be applied to new hybrid devices that integrate magnetic, electrical, and optical circuits. However, crystallization of Y-type hexaferrite requires temperatures exceeding 1000°C. At such high temperatures, most commonly used substrates react with the Y-type hexaferrite film, unavoidably changing the elemental composition of the Y-type hexaferrite film.

[0003] Non-Patent Documents 1 and 2 disclose a method of using ZnO or M-type hexaferrite as a buffer layer to suppress the reaction between the substrate and the Y-type hexaferrite film.

[0004] J. H. Kim, J. S. Horwitz, A. Pigue, H. S. Newman, P. Lubitz, M. M. Miller, et al., J. Vac. Sci. Technol., A17 3111-3115 (1999)J. Bursik, R. Kuzel, K. Knizek, I. Drbohlav, Journal of Solid State Chemistry 203 100-105 (2013)

[0005] It is desirable to form an epitaxial thin film of Y-type hexaferrite without using a buffer layer, but Y-type hexaferrite has high structural and chemical complexity, making it difficult to optimize the manufacturing conditions.

[0006] An object of the present disclosure is to provide a stack, an element, and a device including an epitaxial thin film of Y-type hexaferrite that can be formed without using a buffer layer.

[0007] The present inventors have conducted extensive research to solve the above problems and have discovered that an epitaxial thin film of Y-type hexaferrite having a specific composition can be formed without using a buffer layer, thereby conceiving the present invention.

[0008] [1] A laminate comprising: a substrate; and a film formed on the substrate, wherein the film has an epitaxial layer containing Y-type hexaferrite, and the Y-type hexaferrite is represented by the general formula (Ba １－ｘ Sr ｘ ) ２ Co ２ Fe １２－ｙ－δ Al ｙ X δ O ２２

[0013] A laminate represented by the formula (I) below, wherein X is at least one element selected from the group consisting of Cr, Sb, In, and V, 0≦x≦1, 1<y≦6, and 0≦δ≦1, and the thickness of the film is 1.0 nm or more and less than 500 nm. [2] The laminate according to [1], wherein neither an M-type hexaferrite layer nor a ZnO layer is provided between the substrate and the film. [3] An element comprising the laminate according to [1] or [2]. [4] A device comprising the element according to [3].

[0009] According to one aspect of the present disclosure, there are provided a stack, an element, and a device including an epitaxial thin film of Y-type hexaferrite that can be formed without using a buffer layer.

[0010] FIG. 1 is a photograph showing a STEM-EDX image of a film according to an example. FIG. 2 is a photograph showing a STEM-EDX image of a film according to comparative example 1. FIG. 3 is a photograph showing a STEM-EDX image of a film according to comparative example 2. FIG. 4 is a graph showing an XRD chart of a film according to an example. FIG. 5 is a graph showing an XRD chart of a film according to comparative example 1. FIG. 6 is a graph showing an XRD chart of a film according to comparative example 2. FIG. 7 is a graph showing an M-H curve of a film according to an example. FIG. 8 is a graph showing an M-H curve of a film according to comparative example 1. FIG. 9 is a graph showing an M-H curve of a film according to comparative example 2.

[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] The laminate includes a substrate and a film formed on the substrate. The film is a compound represented by the general formula (Ba １－ｘ Sr ｘ ) ２ Co ２ Fe １２－ｙ－δ Al ｙ X δ O ２２ The Y-type hexaferrite has a film made of epitaxially grown crystals represented by the formula (1). The region containing this film is called an epitaxial layer. Here, X is at least one element selected from the group consisting of Cr, Sb, In, and V. x satisfies 0≦x≦1. y satisfies 1<y≦6. If y is greater than 6, a sufficiently large saturation magnetization cannot be obtained. y may satisfy 1<y≦3 or 1<y≦2. y may satisfy 1.5≦y or 2≦y. δ satisfies 0≦δ≦1.

[0013] Y-type hexaferrite has a hexagonal crystal structure. In Y-type hexaferrite, the magnetic moment has a helical structure. The epitaxial layer is a film made of epitaxially grown crystals of Y-type hexaferrite, for example, a single crystal of Y-type hexaferrite. The epitaxial layer may contain impurities other than Y-type hexaferrite. The impurity concentration may be 5% or less in mass fraction.

[0014] The film may include voids formed in the epitaxial layer. The film may include platelet crystals formed in or on the epitaxial layer, the platelet crystals having a composition different from that of Y-type hexaferrite.

[0015] The thickness of the film is 1.0 nm or more and less than 500 nm. A film thickness of 1.0 nm or more can stabilize the crystal structure. A film thickness of less than 500 nm can enable miniaturization. The film thickness may be 30 nm or more and 200 nm or less, or may be 50 nm or more and 100 nm or less.

[0016] The ratio of the thickness of the epitaxial layer to the thickness of the film (i.e., epitaxial layer thickness / film thickness) is, for example, 20% or more. This ratio may be, for example, 40% or more, or 90% or more. The thickness of the epitaxial layer and the thickness of the film are measured, for example, by cross-sectional SEM observation of the film.

[0017] The ratio of the volume of the epitaxial layer in the film (i.e., the volume of the epitaxial layer / the volume of the film) is, for example, 20% or more. This ratio may be, for example, 40% or more, or 90% or more. This ratio may be calculated, for example, by measuring the cross-sectional areas of the epitaxial layer and the film through cross-sectional SEM observation of the film, and then calculating the ratio of the areas.

[0018] The film is formed directly on the substrate without a buffer layer. No buffer layer is provided between the substrate and the epitaxial layer. As described above, in the methods of Non-Patent Documents 1 and 2, ZnO or M-type hexaferrite is used as a buffer layer. In this embodiment, neither an M-type hexaferrite layer nor a ZnO layer is provided between the substrate and the epitaxial layer. The easy axis of magnetization of the crystal of the epitaxial layer may be oriented in the in-plane direction or in the vertical direction (perpendicular to the plane).

[0019] The type of substrate is not particularly limited. For example, a substrate having a lattice constant close to that of the Y-type hexaferrite of the desired composition can be used. Specifically, sapphire (Al ２ O ３ ), strontium titanate, magnesium aluminate, silicon, silicon carbide, yttria-stabilized zirconia, gallium nitride, gallium arsenide, gallium phosphide, etc. are used.

[0020] The laminate is manufactured by forming a film on a substrate and heat-treating the formed film. The film formation method is not particularly limited, but may be performed, for example, under temperature conditions ranging from room temperature to 700°C. Examples of the film formation method include sputtering, spray deposition, spin coating, and plasma laser deposition. The heat treatment time is not particularly limited, but may be, for example, 1 minute to 48 hours. The heat treatment time may be 3 minutes to 5 hours, or 5 minutes to 30 minutes. The heat treatment atmosphere is not particularly limited, but may be air, oxygen, or an inert gas atmosphere such as nitrogen or argon.

[0021] The element according to this embodiment includes a stack. The device according to this embodiment includes an element. The stack according to this embodiment includes an epitaxial layer of Y-type hexaferrite formed without using a buffer layer, and therefore is applicable not only to miniaturizing microwave devices but also to manufacturing hybrid devices in which magnetic, electrical, and optical circuits are integrated.

[0022] The present disclosure will be described in more detail below using examples and comparative examples according to the present disclosure, but the present disclosure is not limited to these examples.

[0023] <Preparation of laminate sample> (Example) A 2-inch diameter sputtering target (Ba １．５ SrCo ２ Fe １１．１ Al ０．９ O ２２A film was formed on the (0001) surface of a sapphire substrate by RF sputtering using a custom high-vacuum deposition chamber manufactured by K's Tech Co., Ltd. The sputtering target was purchased from K's Tech Co., Ltd. RF sputtering was performed at 80 W power while heating the substrate to 550°C and flowing Ar gas at 3 sccm and oxygen gas at 0.3 sccm. The thickness of the resulting film was measured using a profile meter (DekTak manufactured by Veeco). The film thickness was 200 nm. Subsequently, a heat treatment (annealing) was performed at 880°C for 1 hour under an oxygen flow (0.5 L / min) using a rapid annealer (MILA manufactured by ULVAC). This resulted in the production of a laminate sample of the example. (Comparative Example 1) A laminate sample of Comparative Example 1 was obtained in the same manner as in Example, except that the annealing temperature was 800°C. (Comparative Example 2) A laminate sample of Comparative Example 2 was obtained in the same manner as in Example, except that annealing was not performed.

[0024] <STEM-EDX Measurement> For each sample of Example, Comparative Example 1, and Comparative Example 2, STEM-EDX measurement of the film was carried out.

[0025] (Cross-section photography) A cross-section of the film of each sample was prepared by a microsampling FIB method using a system manufactured by FEI (Helios G4-CX / Scios 2). Subsequently, an atomic resolution analytical electron microscope (JEM ARM300 F2 manufactured by JEOL Ltd.) was used to photograph STEM-EDX images of the cross-section of the film at an acceleration voltage of 300 kV. The results are shown in Figures 1 to 3.

[0026] As shown in Figure 1, in the film of the example, an epitaxial layer made of Y-type hexaferrite single crystal was formed on the substrate, and the thickness ratio of the epitaxial layer to the film was 43%. Plate-like crystals were formed on the epitaxial layer. Plate-like crystals were also formed within the epitaxial layer.

[0027] As shown in Figure 2, in the film of Comparative Example 1, an epitaxial layer made of Y-type hexaferrite single crystal was formed on the substrate, and the thickness ratio of the epitaxial layer to the film was 70%. Plate-like crystals were formed on the epitaxial layer. Plate-like crystals were also formed within the epitaxial layer.

[0028] As shown in Figure 3, in the film of Comparative Example 2, no epitaxial layer was formed on the substrate. The crystallinity was insufficient, and aggregates of relatively coarse-grained microcrystals were formed on the substrate. The film of Comparative Example 2 was a single layer.

[0029] (Elemental Analysis) Elemental analysis of the film was performed using an integrated spectrometer equipped with a dry Si drift detector (JED-2300 Analysis Station Plus manufactured by JEOL Ltd.). In the film of the example, the composition of the epitaxial layer made of a Y-type hexaferrite single crystal was BaSrCo ２ Fe １０ Al ２ O ２２ In the film of Comparative Example 1, the composition of the epitaxial layer made of Y-type hexaferrite single crystal was BaSrCo ２ Fe １１ Al １ O ２２ The composition of Comparative Example 2 was BaSrCo ２ Fe １１．１ Al ０．９ O ２２ As described above, the Al ratio was 1 and 0.9 in Comparative Examples 1 and 2, respectively, whereas the Al ratio was 2 in the Example.

[0030] (XRD Measurement) XRD measurement of each sample film was carried out by the 2θ-θ reflection method using a SmartLab manufactured by Rigaku Corporation. The conditions for the XRD measurement were as follows: X-ray source: Cu-Kα ray, scan speed: 3.00° / min, sampling interval: 0.004°, slit width: variable, scattering slit (SS) angle: 2.5°, receiving slit (RS) width: 1 mm

[0031] The results of the XRD measurements are shown in Figures 4 to 6. As shown in Figure 4, signals such as Y(009), Y(0018), Y(0027), and Y(0036) specific to Y-type hexaferrite could be observed in the film of the example. As shown in Figure 5, signals such as Y(0018), Y(0027), and Y(0036) specific to Y-type hexaferrite could also be observed in the film of Comparative Example 1. As shown in Figure 6, signals such as Y(0018) and Y(0036) could be observed in the film of Comparative Example 2, but a Y(0027) signal could not be observed.

[0032] (Magnetic Property Measurement) Using a SQUID (Superconducting Quantum Interference Device) magnetic property measurement system MPMS (Magnetic Property Measurement System, manufactured by Quantum Design, USA), the M-H curve of each sample film was measured at 300 K. The results are shown in FIGS. 7 to 9. As shown in FIG. 7, a single hysteresis curve specific to Y-type hexaferrite could be observed in the film of the example. As shown in FIG. 8, a single hysteresis curve specific to Y-type hexaferrite could be observed in the film of Comparative Example 1, but it was found that multiple magnetic layers were mixed rather than a single hysteresis. As shown in FIG. 9, a hysteresis curve specific to Y-type hexaferrite could not be observed.

[0033] [Additional Comments] The film, laminate, element, and device disclosed herein enable low power consumption, which can contribute to the achievement of Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations. Goal 9: "Build resilient infrastructure, promote inclusive and sustainable industrialization, foster innovation and infrastructural reform."

Claims

1. A laminate comprising a substrate and a film formed on the substrate, wherein the film has an epitaxial layer containing Y-type hexaferrite, and the Y-type hexaferrite is represented by the general formula (Ba １－ｘ Sr ｘ ) ２ Co ２ Fe １２－ｙ－δ Al ｙ X δ O ２２ X is at least one element selected from the group consisting of Cr, Sb, In and V, and 0≦x≦1, 1<y≦6, and 0≦δ≦1.

2. The laminate according to claim 1, wherein neither an M-type hexaferrite layer nor a ZnO layer is provided between the substrate and the epitaxial layer.

3. A device comprising the laminate according to claim 1 or 2.

4. A device comprising the element of claim 3.

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