Laminate, element, and device

Abstract

To provide a laminate having an epitaxial thin film of Y-type hexaferrite which can be formed without using a buffer layer, and to provide an element and a device.SOLUTION: The laminate includes a substrate and a film formed on the substrate. The film has an epitaxial layer comprising Y-type hexaferrite. The Y-type hexaferrite is represented by the general formula (Ba1 - xSrx) 2Co2Fe12 - y - δ AlyX δ O22. 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.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[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. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] JH Kim, JS Horwitz, A. Pigue, HS Newman, P. Lubitz, MM Miller, et al., J. Vac. Sci. Technol., A17 3111-3115 (1999) [Non-patent document 2] J. Bursik, R. Kuzel, K. Knizek, I. Drbohlav, Journal of Solid State Chemistry 203 100-105 (2013) Summary of the Invention [Problem to be solved by the invention]

[0005] It is desirable to form epitaxial thin films of Y-type hexaferrite without using a buffer layer, but Y-type hexaferrite is structurally and chemically highly complex, making it difficult to optimize the fabrication 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. [Means for solving the problem]

[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, leading to the invention of the present invention.

[0008] [1] A substrate; a film formed on the substrate; A laminate comprising: the film has an epitaxial layer including Y-type hexaferrite; The Y-type hexaferrite has the general formula (Ba 1-x Sr x )2Co2Fe 12-y-δ Al y X δ O 22 is expressed as X is at least one element selected from the group consisting of Cr, Sb, In, and V; 0≦x≦1, 1 <y≦6、かつ、0≦δ≦1であり、 The thickness of the film is 1.0 nm or more and less than 500 nm. Laminate. [2] Neither an M-type hexaferrite layer nor a ZnO layer is provided between the substrate and the film. [1] The laminate according to [1]. [3] A device comprising the laminate according to [1] or [2]. [4] A device comprising the element according to [3]. [Effects of the Invention]

[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. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a photograph showing a STEM-EDX image of a film according to an example. [Figure 2] FIG. 2 is a photograph showing a STEM-EDX image of the film according to Comparative Example 1. As shown in FIG. [Figure 3] FIG. 3 is a photograph showing a STEM-EDX image of the film according to Comparative Example 2. [Figure 4] FIG. 4 is a graph showing an XRD chart of the film according to the example. [Figure 5] FIG. 5 is a graph showing an XRD chart of the film according to Comparative Example 1. [Figure 6] FIG. 6 is a graph showing an XRD chart of the film according to Comparative Example 2. [Figure 7] FIG. 7 is a graph showing the MH curve of the film according to the example. [Figure 8] FIG. 8 is a graph showing the MH curve of the film according to Comparative Example 1. [Figure 9] FIG. 9 is a graph showing the MH curve of the film according to Comparative Example 2. 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] 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)2Co2Fe 12-y-δ Al y X δ O 22 The film has a region containing a film composed of crystals in which Y-type hexaferrite represented by is epitaxially grown. The region containing this film is referred to as 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 sufficient saturation magnetization cannot be obtained. y may satisfy 1 < y ≦ 3, and may satisfy 1 < y ≦ 2. y may satisfy 1.5 ≦ y, and may satisfy 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 composed of crystals in which Y-type hexaferrite is epitaxially grown, and for example, is 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 by mass fraction.

[0014] The film may contain voids formed in the epitaxial layer. The film may contain plate-like crystals formed in or on the epitaxial layer. The plate-like crystals have 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. When the film thickness is 1.0 nm or more, the crystal structure can be stabilized. When the film thickness is less than 500 nm, miniaturization is possible. The film thickness may be 30 nm or more and 200 nm or less, and 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 SEM observation of the cross section 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 (Al2O3), strontium titanate, magnesium aluminate, silicon, silicon carbide, yttria-stabilized zirconia, gallium nitride, gallium arsenide, gallium phosphide, etc. can be used.

[0020] The laminate is produced 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 temperature 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 laminate. The device according to this embodiment includes an element. The laminate according to this embodiment includes an epitaxial layer of Y-type hexaferrite formed without using a buffer layer, and therefore can be applied not only to miniaturizing microwave devices but also to manufacturing hybrid devices that integrate magnetic, electrical, and optical circuits. [Example]

[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 samples> (Example) A 2-inch diameter sputtering target (Ba 1.5 SrCo2Fe 11.1 Al 0.9 O 22) and a film was formed on the (0001) of the sapphire substrate by RF sputtering using a custom high-vacuum evaporation chamber manufactured by Case-Tech Co., Ltd. The sputtering target was purchased from Case-Tech Co., Ltd. RF sputtering was performed at a power of 80 W while heating the substrate to 550 °C with Ar gas flowing at a rate of 3 sccm and oxygen gas flowing at a rate of 0.3 sccm. The thickness of the obtained film was measured with a profilometer (DekTak manufactured by Veeco). The thickness of the film was 200 nm. Thereafter, 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). Thereby, a laminate sample of the example was obtained. (Comparative Example 1) A laminate sample of Comparative Example 1 was obtained in the same manner as in the 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 the example except that annealing was not performed.

[0024] <STEM-EDX Measurement> For each of the samples of the example, Comparative Example 1, and Comparative Example 2, STEM-EDX measurement of the film was performed.

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

[0026] As shown in FIG. 1, in the film of the example, an epitaxial layer composed of a Y-type hexaferrite single crystal was formed on the substrate, and the ratio of the thickness of the epitaxial layer in the film was 43%. Plate-like crystals were formed on the epitaxial layer. The 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. On the substrate, aggregates of relatively coarse-grained microcrystals with insufficient crystallinity were formed. The film of Comparative Example 2 was a single layer.

[0029] (Elemental analysis) Elemental analysis of the film was performed using an integrated spectrometer (JED-2300 Analysis Station Plus manufactured by JEOL Ltd.) equipped with a dry Si drift detector. In the film of the example, the composition of the epitaxial layer made of a Y-type hexaferrite single crystal was BaSrCoFe 10 AlO 22 In the film of Comparative Example 1, the composition of the epitaxial layer made of a Y-type hexaferrite single crystal was BaSrCo2Fe 11 AlO 22 The composition of Comparative Example 2 was BaSrCo2Fe 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 Corp. The XRD measurement conditions 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) The MH curves of the films of each sample were measured at 300 K using a SQUID (Superconducting Quantum Interference Device) magnetic property measurement system MPMS (Magnetic Property Measurement System, manufactured by Quantum Design, USA). The results are shown in Figures 7 to 9. As shown in Figure 7, a single hysteresis curve specific to Y-type hexaferrite was observed in the film of the example. As shown in Figure 8, a single hysteresis curve specific to Y-type hexaferrite was 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 Figure 9, a hysteresis curve specific to Y-type hexaferrite could not be observed.

[0033] [Additional remarks] The film, laminate, element, and device of the present disclosure 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: "Industry, innovation and infrastructure"

Claims

1. A substrate; a film formed on the substrate; A laminate comprising: the film has an epitaxial layer including Y-type hexaferrite; The Y-type hexaferrite has the general formula (Ba １－ｘ Sr ｘ ) ２ Co ２ Fe １２－ｙ－δ Al ｙ X δ O ２２ is expressed as 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; Laminate.

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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