Laminated structure

Abstract

A laminated structure 10 according to the present invention comprises a substrate 11, a buffer film 12 formed on the substrate 11, and a dielectric film 15 formed on the buffer film 12. The buffer film 12 contains a first metal oxide represented by the composition formula (1), where x satisfies 0 ≦ x < 1 or x = 1. The dielectric film 15 contains five or more laminated dielectric layers 15a, each of the dielectric layers 15a having an ilmenite structure and contains a second metal oxide composed of LiNbO3 or LiTaO 3 oriented in a certain direction. (1): (Hf1 - xZrx)O2

Description

Laminated structure

[0001] This invention relates to a laminated structure.

[0002] In the communications field, the demand for frequency filters is increasing, and among them, the demand for surface acoustic wave (SAW) filters is on the rise. LiNbO is used as the piezoelectric material for SAW filters. ３ Or LiTaO ３ Metal oxides having an ilmenite-type structure are used. In addition, multilayer structures obtained by epitaxially growing metal oxides having an ilmenite-type structure on a Si substrate, and electronic devices equipped with such multilayer structures are known.

[0003] Patent Document 1 describes a dielectric multilayer thin film in which zirconium oxide (ZrO) is placed on the surface of a single crystal Si(111) substrate. ２ A technique is disclosed in which at least one epitaxially grown underlayer film mainly composed of ) is formed, and an epitaxially grown ilmenite structure film made of an ilmenite structure dielectric material is formed on the underlayer film.

[0004] Patent Document 2 describes a film structure comprising a substrate, a buffer film formed on the substrate, and a piezoelectric film formed on the buffer film, wherein the substrate is a Si(100) substrate, or an SOI substrate comprising a substrate made of a Si substrate, an insulating layer on the substrate, and an SOI layer made of a Si(100) film on the insulating layer, and the buffer film is ZrO ２ The piezoelectric film contains c-axis oriented LiNbO ３ Or LiTaO ３ The technology including this has been disclosed.

[0005] Patent Document 3 describes a piezoelectric device comprising a substrate, a lower electrode, a buffer layer disposed on the lower electrode, and LiNbO2 disposed on the buffer layer with its crystal orientation oriented in the (012) plane. ３ Or LiTaO ３ A piezoelectric film comprising a buffer layer is disclosed, and a technique is disclosed in which the crystal orientation of the piezoelectric film is oriented in the (012) plane direction.

[0006] Japanese Patent Application Laid-Open No. 2013-173647 International Publication No. WO 2023 / 210309 Japanese Patent Application Laid-Open No. 2022-159810

[0007] J. Kushibiki et. al., “Accurate measurements of the acoustical physical constants of LiNbO3 and LiTaO3 single crystals”, IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, Vol. 46, No. 5, (1999) p.1315-1323

[0008] Patent Document 1 describes that the dielectric laminated thin film has an ilmenite-type structure formed on a Si(111) substrate and is (0001)-oriented LiNbO ３ or LiTaO ３ film. Patent Document 2 describes that the film structure has a Si(100) substrate and c-axis-oriented LiNbO ３ or LiTaO ３ having an ilmenite-type structure formed on the Si(100) substrate.

[0009] On the other hand, Patent Document 3 discloses LiNbO ３ a 36° Y-cut LiNbO obtained by 36° rotation Y-cutting of a bulk body ３ It is described that when a single crystal plate is used, the electromechanical coupling coefficient of quasi-longitudinal waves reaches a maximum of about 50%. Non-Patent Document 1 describes that the (01-12) plane corresponds to a 32.76° Y-cut LiNbO ３ single crystal plate and has a high longitudinal wave velocity. The 32.76° Y-cut LiNbO ３ single crystal plate is close to the 36° Y-cut LiNbO ３ single crystal plate, so it is expected to exhibit a high electromechanical coupling coefficient. In addition, LiNbO ３ not only single crystal plates, but also LiTaO ３ similar trends are expected for single crystal plates as well.

[0010] However, LiNbO is oriented (01-12) on the Si substrate. ３ Or LiTaO ３ It was difficult to epitaxially grow a dielectric film made of this material. In other words, it was difficult to easily epitaxially grow LiNbO in a (01-12) oriented state or in a state oriented to a plane different from the (0001) plane. ３ Or LiTaO ３ It was difficult to form a dielectric film with excellent crystallinity, including the aforementioned material, on a Si substrate.

[0011] The present invention provides LiNbO that can be easily epitaxially grown in a (01-12) oriented state or in a state oriented to a plane different from the (0001) plane. ３ Or LiTaO ３ The objective is to provide a laminated structure in which a dielectric film with excellent crystallinity, including [a specific component], is formed on a Si substrate.

[0012] As a result of diligent research, the inventors have found that the above problem can be solved by the following configuration.

[0013] [1] A laminated structure comprising a substrate, a buffer film formed on the substrate, and a dielectric film formed on the buffer film, wherein the buffer film contains a first metal oxide represented by the following composition formula (1), (Hf １－ｘ Zr ｘ ) O ２ ... (1) The x satisfies 0 ≤ x < 1 or x = 1, the dielectric film includes five or more stacked dielectric layers, each of the dielectric layers has an ilmenite-type structure and is oriented in a certain direction and contains LiNbO ３ Or LiTaO ３ A laminated structure comprising a second metal oxide.

[0014] [2] The laminated structure according to [1], wherein the substrate is a Si substrate, or an SOI substrate comprising a substrate made of a Si substrate, an insulating layer on the substrate, and an SOI layer made of a Si film on the insulating layer.

[0015] [3] The laminated structure according to [1], wherein the substrate is a Si(111) substrate having a Si(111) plane as its main surface, or an SOI(111) substrate comprising the substrate, the insulating layer, and an SOI(111) layer having a Si(111) plane as its main surface on the insulating layer.

[0016] [4] In the laminated structure described in [1], the substrate is a Si(111) substrate having a Si(111) plane as its main surface, or an SOI(111) substrate comprising the substrate, the insulating layer, and an SOI(111) layer having a Si(111) plane as its main surface on the insulating layer, wherein the buffer film comprises the first metal oxide formed on the main surface and oriented (111) in pseudocubic crystal representation, and each layer of the dielectric layer has an ilmenite-type structure and is (01-12) oriented LiNbO ３ Or LiTaO ３ A laminated structure comprising the second metal oxide.

[0017] [5] In the laminated structure described in [4], the first metal oxide is epitaxially grown on the main surface, and the second metal oxide is epitaxially grown on the buffer film. ３ Or LiTaO ３ A layered structure.

[0018] [6] In the laminated structure described in [5], the second metal oxide is LiNbO ３ Or LiTaO ３The dielectric layer includes a first domain, a second domain, a third domain, a fourth domain, a fifth domain, and a sixth domain, each of which is oriented such that the (0001) plane of the second metal oxide is inclined by a predetermined angle with respect to the main surface, and the

[0001] axes of the second metal oxide are oriented in different directions from each other, wherein when the

[0001] direction of the second metal oxide in the first domain is defined as the first

[0001] direction, the

[0001] direction of the second metal oxide in the second domain is a direction rotated 60° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface, and the

[0001] direction of the second metal oxide in the third domain is a direction rotated 120° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface. A laminated structure in which the

[0001] direction of the second metal oxide in the fourth domain is a direction rotated 180° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface, the

[0001] direction of the second metal oxide in the fifth domain is a direction rotated 240° counterclockwise from the

[0001] direction when viewed from the normal direction of the main surface, and the

[0001] direction of the second metal oxide in the sixth domain is a direction rotated 300° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface.

[0019] [7] A laminated structure according to [5] or [6], comprising a first conductive film formed between the buffer film and the dielectric film, wherein the first conductive film is epitaxially grown on the buffer film, has a cubic crystal structure, and contains a platinum group element oriented (111) in pseudocubic representation, and the second metal oxide is LiNbO, epitaxially grown on the first conductive film. ３ Or LiTaO ３ A layered structure.

[0020] [8] In the laminated structure described in [7], the laminated structure described in claim 5, having a second conductive film formed between the first conductive film and the dielectric film, wherein the second conductive film contains strontium ruthenate epitaxially grown on the first conductive film and oriented (111) in pseudocubic form, and the second metal oxide is LiNbO epitaxially grown on the second conductive film. ３ Or LiTaO ３ A layered structure.

[0021] [9] In the laminated structure described in [1], the substrate is a Si(100) substrate having a Si(100) plane as its main surface, or an SOI(100) substrate comprising the substrate, the insulating layer, and a Si(100) film on the insulating layer having a Si(100) plane as its main surface, wherein the buffer film is formed on the main surface and contains the first metal oxide oriented to (100) in pseudocubic crystal representation, and each layer of the dielectric layer has an ilmenite-type structure and is oriented to (01-12) LiNbO ３ Or LiTaO ３ A laminated structure comprising the second metal oxide.

[0022] In the laminated structure described in

[10] and [9], the first metal oxide is epitaxially grown on the main surface, and the second metal oxide is epitaxially grown on the buffer film. ３ Or LiTaO ３ A layered structure.

[0023]

[11] In the laminated structure described in

[10] , the second metal oxide is LiNbO ３ Or LiTaO ３The dielectric layer includes a first domain, a second domain, a third domain, and a fourth domain, each of which is oriented such that the (0001) plane of the second metal oxide is inclined by a predetermined angle with respect to the main surface, and the

[0001] axes of the second metal oxide are oriented in different directions from each other, wherein the

[0001] direction of the second metal oxide in the first domain is defined as the first

[0001] direction, the

[0001] direction of the second metal oxide in the second domain is a direction rotated 90° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface, and the

[0001] direction of the second metal oxide in the third domain is a direction rotated 180° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface. A laminated structure in which the

[0001] direction of the second metal oxide in the fourth domain is a direction rotated 270° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface.

[0024]

[12] A laminated structure according to

[10] or

[11] , comprising a first conductive film formed between the buffer film and the dielectric film, wherein the first conductive film is epitaxially grown on the buffer film, has a cubic crystal structure, and contains a platinum group element oriented (100) in pseudocubic representation, and the second metal oxide is LiNbO that is epitaxially grown on the first conductive film ３ Or LiTaO ３ A layered structure.

[0025]

[13] In the laminated structure described in

[12] , a second conductive film is formed between the first conductive film and the dielectric film, wherein the second conductive film contains strontium ruthenate epitaxially grown on the first conductive film and oriented (100) in pseudocubic form, and the second metal oxide is LiNbO epitaxially grown on the second conductive film. ３ Or LiTaO ３ A layered structure.

[0026]

[14] The process comprises the steps of forming a buffer film on a substrate and forming a dielectric film on the buffer film by a wet process, wherein the buffer film contains a first metal oxide represented by the following composition formula (1), (Hf １－ｘ Zr ｘ ) O ２ ... (1) The x satisfies 0 ≤ x < 1 or x = 1, the dielectric film includes a dielectric layer, each layer of the dielectric layer has an ilmenite-type structure and is oriented in a certain direction and contains LiNbO ３ Or LiTaO ３ A method for manufacturing a laminated structure comprising a second metal oxide.

[0027]

[15] The method for manufacturing a laminated structure according to 14, characterized in that the substrate is a Si substrate, or an SOI substrate comprising a substrate made of a Si substrate, an insulating layer on the substrate, and an SOI layer made of a Si film on the insulating layer.

[0028] The laminated structure of the present invention is easily epitaxially grown LiNbO in a (01-12) oriented state or in a state oriented to a plane different from the (0001) plane. ３ Or LiTaO ３ A dielectric film with excellent crystallinity, containing the above, is formed on a Si substrate.

[0029] This is a cross-sectional view showing an example of a laminated structure according to an embodiment of the present invention. This is a cross-sectional view showing another example of a laminated structure according to an embodiment of the present invention. This shows LiNbO, a second metal oxide, contained in the dielectric layer of the laminated structure according to an embodiment of the present invention. ３ This is a schematic plan view showing the orientation state of the crystal lattice. LiNbO, a second metal oxide contained in the dielectric layer of the laminated structure according to the embodiment of the present invention. ３ This is a schematic side view showing the orientation state of the crystal lattice. LiNbO containing an ilmenite-type structure and (01-12) oriented dielectric layer in an embodiment of the present invention. ３ This figure shows the crystal structure. This is a cross-sectional view showing an example of a laminated structure of a modified embodiment of the present invention. LiNbO is a second metal oxide contained in the dielectric layer of the laminated structure of a modified embodiment of the present invention. ３This is a schematic plan view showing the orientation state of the crystal lattice. LiNbO, a second metal oxide, is contained in the dielectric layer of a laminated structure of a modified embodiment of the present invention. ３ This is a schematic side view showing the orientation state of the crystal lattice. This is a graph showing the diffraction pattern of the laminated structure of Example 1 of the present invention. This is a graph showing the φ scan of the laminated structure of Example 1 of the present invention. This is a pole figure of the laminated structure of Example 1 of the present invention. This is a graph showing the diffraction pattern of the laminated structure of Example 2 of the present invention. This is a graph showing the φ scan of the laminated structure of Example 2 of the present invention. This is a pole figure of the laminated structure of Example 2 of the present invention. This is a graph showing the diffraction pattern of the laminated structure of Example 3 of the present invention. This is a graph showing the φ scan of the laminated structure of Example 3 of the present invention. This is a pole figure of the laminated structure of Example 3 of the present invention.

[0030] The embodiments of the present invention will be described below with reference to the drawings.

[0031] (Embodiment) <Laminated Structure> First, a laminated structure according to an embodiment of the present invention will be described. Figure 1 is a cross-sectional view showing an example of a laminated structure according to an embodiment of the present invention. Figure 2 is a cross-sectional view showing another example of a laminated structure according to an embodiment of the present invention. Figure 3 shows LiNbO, a second metal oxide contained in the dielectric layer of the laminated structure according to an embodiment of the present invention. ３ This is a schematic plan view showing the orientation state of the crystal lattice. Figure 4 shows LiNbO, a second metal oxide contained in the dielectric layer of the laminated structure according to an embodiment of the present invention. ３ Figure 5 is a schematic side view showing the orientation state of the crystal lattice. Figure 5 shows LiNbO having an ilmenite-type structure and (01-12) orientation included in the dielectric layer of an embodiment of the present invention. ３ This figure shows the crystal structure of LiNbO. Note that in Figures 3 and 4, for ease of understanding, LiNbO is represented by a hexagonal crystal lattice instead of a trigonal one. ３The crystal lattice is further shown as a rectangular prism. Also, for ease of understanding, the (0001) plane is hatched in Figure 3, and the second domain DM2 and the fourth domain DM4 are omitted from Figure 4. Furthermore, in Figure 5, for ease of understanding, only some of the Nb atoms contained in the crystal lattice are shown, and the (01-12) plane is represented by plane PL.

[0032] The laminated structure 10 of the embodiment according to the present invention shown in Figures 1 and 2 comprises a substrate 11 including a main surface 11p, a buffer film 12 formed on the main surface 11p, a first conductive film 13 formed on the buffer film 12, a second conductive film 14 formed on the first conductive film 13, and a dielectric film 15 formed on the second conductive film 14.

[0033] The substrate 11 is a Si substrate, or an SOI substrate comprising a substrate made of a Si substrate, an insulating layer on the substrate, and an SOI layer made of a Si film on the insulating layer.

[0034] The substrate 11 shown in Figure 1 is a Si (silicon) (111) substrate with the Si (111) surface as the main surface 11p. On the other hand, the substrate 11 shown in Figure 2 is an SOI (111) substrate that includes a base body 11a made of a Si substrate, an insulating layer 11b on the base body 11a, and an SOI (Silicon On Insulator) (111) layer (SOI layer 11c) made of a Si (111) film on the insulating layer 11b with the Si (111) surface as the main surface 11p.

[0035] The buffer film 12 is epitaxially grown on the main surface 11p, is (111) oriented in pseudocubic crystal representation, and contains a first metal oxide represented by the following compositional formula (1). (Hf １－ｘ Zr ｘ ) O ２ ... (1) In the above empirical formula (1), x satisfies either 0 ≤ x < 1 or x = 1.

[0036] Here, among the first metal oxides represented by the above compositional formula (1), if x = 0, then HfO ２ And when x = 1, ZrO ２ However, the case where 0 < x < 1 is satisfied will be referred to as HZO below.

[0037] In this specification, when the first metal oxide is described as being (111) oriented in pseudocubic form, it means that the first metal oxide has a cubic crystal structure at room temperature and is oriented (111) in pseudocubic form, or that even if it has a tetragonal or monoclinic crystal structure at room temperature, it undergoes a phase transition at high temperatures to have a cubic crystal structure and is oriented (111) in pseudocubic form.

[0038] Furthermore, in this specification, if a film is said to be epitaxially grown, it means that the film is oriented in any of the three mutually orthogonal directions, that is, oriented in three dimensions.

[0039] The first conductive film 13 is epitaxially grown on the buffer film 12, has a cubic crystal structure, and contains platinum group elements such as platinum (Pt) oriented (111) in pseudocubic representation. In this specification, platinum group elements refer to elements located in the 5th and 6th periods, and groups 8, 9, and 10 of the periodic table, namely ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt).

[0040] The second conductive film 14 is epitaxially grown on the first conductive film 13 and is (111) oriented in a pseudocubic crystal structure as strontium ruthenate (SrRuO ３ ) includes.

[0041] The dielectric film 15 includes five or more stacked dielectric layers 15a, each of which is epitaxially grown on the second conductive film 14 and has an ilmenite-type structure and is (01-12) oriented LiNbO ３ Or LiTaO ３ It contains a second metal oxide. The dielectric film 15 may also contain 10 or more dielectric layers 15a.

[0042] When each layer of the dielectric layer 15a is formed by spin-coating (applying) a solution containing, for example, lithium and niobium (or tantalum), i.e., an LN solution (or LT solution), on a substrate, a different composition or bubbles exist at the boundaries between adjacent layers. Therefore, in images obtained by observing a cross-section using FIB-SEM (Focused Ion Beam - Scanning Electron Microscope) or STEM (Scanning Transmission Electron Microscope), the boundaries between layers can be detected by observing the periodic change in contrast corresponding to the layers and boundaries. Alternatively, the boundaries between layers can be detected by performing compositional analysis while etching in the depth direction, observing the periodic change in composition.

[0043] As shown in Figures 3 and 4, it is preferable that each layer of the dielectric layer 15a is oriented such that the (0001) plane of the second metal oxide is tilted with respect to the main surface 11p by a predetermined angle, for example, a first angle θ11, and that it includes a first domain DM1, a second domain DM2, a third domain DM3, a fourth domain DM4, a fifth domain DM5, and a sixth domain DM6, in which the

[0001] axes of the second metal oxide are oriented in different directions from each other.

[0044] The second metal oxide is LiNbO ３ In this case, the first angle θ11 can be, for example, 52.24° to 70°, and can be, for example, 57.24°. On the other hand, if the second metal oxide is LiTaO ３ In this case, the first angle θ11 can be, for example, 52.02° to 75°, or for example, 57.02°.

[0045] Here, the second metal oxide is LiNbO ３ , or LiTaO ３In this case, when the

[0001] direction of the second metal oxide in the first domain DM1 is defined as the first

[0001] direction, the

[0001] direction of the second metal oxide in the second domain DM2 is the direction rotated 60° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface 11p (around the normal direction of the main surface 11p).

[0046] Furthermore, the

[0001] direction of the second metal oxide in the third domain DM3 is a direction rotated 120° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface 11p (around the normal direction of the main surface 11p).

[0047] Furthermore, the

[0001] direction of the second metal oxide in the fourth domain DM4 is a direction rotated 180° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface 11p (around the normal direction of the main surface 11p).

[0048] Furthermore, the

[0001] direction of the second metal oxide in the fifth domain DM5 is a direction rotated 240° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface 11p (around the normal direction of the main surface 11p).

[0049] Furthermore, the

[0001] direction of the second metal oxide in the sixth domain is a direction rotated 300° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface (around the normal direction of the main surface 11p).

[0050] Furthermore, the orientation of the first domain DM1, second domain DM2, third domain DM3, fourth domain DM4, fifth domain DM5, and sixth domain DM6 contained in each layer of the dielectric layer 15a is substantially the same in each layer.

[0051] Furthermore, the dielectric film 15 may include 10 or more stacked dielectric layers 15a. For dielectric films 15 including such dielectric layers 15a, instead of a film deposition method in which the dielectric film 15 is deposited under a vacuum atmosphere in a deposition chamber equipped with a vacuum evacuation system, such as a sputtering method, a film deposition method in which the dielectric film 15 is deposited under atmospheric pressure, such as a wet method, can be used. As a result, the dielectric film 15 can be easily deposited on a large substrate with a large surface area, and the manufacturing cost of the laminated structure can be reduced.

[0052] The laminated structure 10 of the embodiment according to the present invention is a substrate 11 made of a Si substrate or an SOI substrate, on which ZrO ２ , HZO or HfO ２ A buffer film 12 made of, a first conductive film 13 containing platinum group elements, and SrRuO ３ LiNbO ３ Or LiTaO ３ A dielectric film 15 is formed.

[0053] The laminated structure 10 of this embodiment of the present invention is a single-crystal Si(111) substrate or an SOI(111) substrate on which (01-12) oriented LiNbO ３ Or LiTaO ３ A dielectric film 15 can be epitaxially grown from this material. Furthermore, as will be explained in the modified embodiments of the present invention described later, (01-12) oriented LiNbO can be grown on a single crystal Si(100) substrate or an SOI(100) substrate. ３ Or LiTaO ３ A dielectric film 15 can be epitaxially grown on a single crystal Si substrate, an SOI substrate, or various other substrates. ３ Or LiTaO ３ The dielectric film 15 can be epitaxially grown in a state where it is oriented to a plane different from the (0001) plane.

[0054] Furthermore, the laminated structure 10 according to the embodiment of the present invention, compared with the techniques described in Patent Documents 1 to 3, can achieve LiNbO easily epitaxially grown in a (01-12) oriented state or in a state oriented on a plane different from the (0001) plane ３ or LiTaO ３ A dielectric film with excellent crystallinity including the above can be formed on a Si substrate.

[0055] According to the embodiment of the present invention, on a substrate 11 made of a Si substrate or an SOI substrate, HfO ２ , HZO or ZrO ２ The first conductive film 13, the second conductive film 14, and the dielectric film 15 can be easily epitaxially grown via the buffer film 12 containing the first metal oxide made of the above. This is because, for example, HfO which is the main component of the buffer film 12 ２ , HZO or ZrO ２ The dynamic lattice matching effect caused by the twinned martensitic transformation exhibited by the first metal oxide made of the above acts as a driving force / motive force / propulsion force when the first conductive film 13, the second conductive film 14, and the dielectric film 15 are epitaxially grown. This is considered to be due to the crystal growth mechanism. However, the present invention is not necessarily bound by this theory.

[0056] Note that in the laminated structure according to the embodiment of the present invention, the substrate 11 is composed of a Si (111) substrate having a Si (111) plane as a main surface, or a base body made of a Si substrate, an insulating layer on the base body, and the insulating layer. It is an SOI (111) substrate including an SOI (111) layer made of a Si (111) film having a Si (111) plane on the layer as a main surface. In addition, the buffer film 12 contains the first metal oxide oriented in (111) in pseudo-cubic notation. The first conductive film 13 has a cubic crystal structure and contains a platinum group element such as Pt oriented in (111) in pseudo-cubic notation. The second conductive film 14 is SrRuO oriented in (111) in pseudo-cubic notation ３ including. The dielectric film 15 includes five or more dielectric layers 15a laminated. Further, each layer of the dielectric layer 15a is epitaxially grown on the second conductive film 14, has an ilmenite-type structure, and is (01-12) oriented LiNbO ３ or LiTaO ３It contains a secondary metal oxide.

[0057] However, the dielectric film 15 includes five or more stacked dielectric layers 15a, and each layer of the dielectric layer 15a is oriented in a certain direction. ３ Or LiTaO ３ Any substrate containing a second metal oxide is acceptable, and the substrate 11 does not have to be a Si(111) substrate with a Si(111) surface as the main surface, or an SOI(111) substrate containing an SOI(111) layer with a Si(111) surface as the main surface.

[0058] Therefore, as shown in the modified embodiments of the present invention described later, the substrate 11 may be a Si(100) substrate with the Si(100) plane as the main plane, or an SOI(100) substrate comprising a substrate made of a Si substrate, an insulating layer on the substrate, and an SOI(100) layer on the insulating layer with the Si(100) plane as the main plane. Even in such cases, a dielectric film having an ilmenite-type structure or other various single-crystal high-quality dielectric films can be oriented in a certain direction on the Si substrate or SOI substrate, so that epitaxially grown LiNbO can be easily grown in a state oriented in (01-12) or in a state oriented in a plane different from the (0001) plane. ３ Or LiTaO ３ A dielectric film with excellent crystallinity, including the above, can be formed on a Si substrate or an SOI substrate.

[0059] Furthermore, in the embodiment of the present invention, the laminated structure 10 comprises a buffer film 12 containing a first metal oxide epitaxially grown on the main surface 11p of the substrate 11, a first conductive film 13 containing a platinum group element such as Pt epitaxially grown on the buffer film 12, and a second conductive film 14 containing SrRuO epitaxially grown on the first conductive film 13. ３ The dielectric film 15 includes LiNbO, which is epitaxially grown on the second conductive film 14. ３ Or LiTaO ３ It contains a secondary metal oxide.

[0060] Furthermore, the buffer film 12 is not limited to a first metal oxide epitaxially grown on the main surface 11p of the substrate 11, the first conductive film 13 is not limited to a platinum group element such as Pt epitaxially grown on the buffer film 12, and the second conductive film 14 is SrRuO epitaxially grown on the first conductive film 13. ３ It is not limited to this. Even in such cases, for example, by oriented the buffer film 12, the first conductive film 13, and the second conductive film 14 in a single direction, a dielectric film having an ilmenite-type structure or other various single-crystal high-quality dielectric films can be oriented in a certain direction on a Si substrate or SOI substrate, so that epitaxially grown LiNbO can be easily formed in a state oriented in (01-12) or in a state oriented in a plane different from the (0001) plane. ３ Or LiTaO ３ A dielectric film with excellent crystallinity, including the above, can be formed on a Si substrate or an SOI substrate.

[0061] The laminated structure 10 of the embodiment of the present invention described above has a buffer film 12, a first conductive film 13, a second conductive film 14, and a dielectric film 15, and the dielectric film 15 is formed via the first conductive film 13 and the second conductive film 14 formed on the buffer film 12. However, the laminated structure 10 of the embodiment of the present invention does not have to have the first conductive film 13 and the second conductive film 14, and the dielectric film 15 may be formed directly on the buffer film 12.

[0062] Even in such cases, for example, by including a first metal oxide epitaxially grown on the main surface 11p of the substrate 11, LiNbO can be easily epitaxially grown in a (01-12) oriented state or oriented on a plane different from the (0001) plane. ３ Or LiTaO ３ A dielectric film 15 with excellent crystallinity, including the above, can be formed on the buffer film 12.

[0063] In such cases, the second metal oxide LiNbO contained in the dielectric film 15 ３ Or LiTaO ３ Since it is oriented (01-12), LiNbO ３ Or LiTaO３ The inclination angle of the (0001) surface relative to the main surface 11p can be easily controlled to be a constant angle. In addition, the (01-12) oriented LiNbO ３ The dielectric film 15 is made of 36° Y-cut LiNbO ３ It possesses an electromechanical coupling coefficient as high as that of a single crystal plate, as well as a high longitudinal wave velocity. Therefore, it is possible to realize electronic devices such as SAW filters with high electromechanical coupling coefficients and excellent filter characteristics.

[0064] <Modified Examples of Embodiments of the Invention> Next, modified examples of the laminated structure according to the embodiment of the present invention will be described. The laminated structure 10a of this modified example differs from the laminated structure 10 of the embodiment of the present invention in that the main surface 11p of the substrate 11 is a Si(100) surface. Furthermore, since the parts of the laminated structure 10a of this modified example other than the orientation direction of the substrate 11 and each layer are the same as the configurations of the laminated structure 10 of the embodiment of the present invention, their descriptions will be omitted.

[0065] Figure 6 is a cross-sectional view showing an example of a laminated structure of a modified embodiment of the present invention. Figure 7 shows LiNbO, a second metal oxide contained in the dielectric layer of the laminated structure of a modified embodiment of the present invention. ３ This is a schematic plan view showing the orientation state of the crystal lattice. Figure 8 shows LiNbO, a second metal oxide contained in the dielectric layer of a laminated structure of a modified embodiment of the present invention. ３ This is a schematic side view showing the orientation state of the crystal lattice. Note that in Figures 7 and 8, for the sake of simplicity, LiNbO is represented by a hexagonal crystal lattice instead of a trigonal one. ３ The crystal lattice is further represented by a rectangular prism, with hatching applied to the (0001) face.

[0066] As shown in Figure 6, the substrate 11 in the modified laminated structure 10a of the embodiment of the present invention differs from the laminated structure 10 of the embodiment of the present invention in that it is made of a Si(100) substrate with the Si(100) surface as the main surface 11p. Note that, similar to Figure 2, the substrate 11 may be an SOI(100) substrate comprising a base body 11a made of a Si substrate, an insulating layer 11b on the base body 11a, and an SOI layer 11c made of a Si(100) film on the insulating layer 11b with the Si(100) surface as the main surface 11p.

[0067] Unlike the laminated structure 10 of the embodiment of the present invention, the buffer film 12 is epitaxially grown on the main surface 11p, is (100) oriented in pseudocubic crystal representation, and contains the first metal oxide represented by the above composition formula (1). Furthermore, in the above composition formula (1), x satisfies 0 ≤ x < 1 or x = 1.

[0068] Unlike the laminated structure 10 of the embodiment of the present invention, the first conductive film 13 is epitaxially grown on the buffer film 12, has a cubic crystal structure, and contains platinum group elements such as platinum (Pt) oriented (100) in pseudocubic representation.

[0069] Unlike the laminated structure 10 of the embodiment of the present invention, the second conductive film 14 is epitaxially grown on the first conductive film 13 and is (100) oriented in pseudocubic form as strontium ruthenate (SrRuO ３ ) includes.

[0070] The dielectric film 15 includes five or more stacked dielectric layers 15a, each of which is epitaxially grown on the second conductive film 14 and has an ilmenite-type structure and is (01-12) oriented LiNbO ３ Or LiTaO ３ It contains a secondary metal oxide.

[0071] In this modified laminated structure 10a of the embodiment of the present invention, similar to the laminated structure 10 of the embodiment of the present invention, (01-12) oriented LiNbO is placed on a single crystal Si(100) substrate or an SOI(100) substrate. ３ Or LiTaO ３A dielectric film 15 can be epitaxially grown on a single crystal Si substrate or an SOI(100) substrate. ３ Or LiTaO ３ The dielectric film 15 can be epitaxially grown in a state where it is oriented to a plane different from the (0001) plane.

[0072] Therefore, according to the laminated structure 10a of the modified embodiment of the present invention, LiNbO can be easily epitaxially grown in a state oriented in (01-12) or in a state oriented in a plane different from the (0001) plane, similar to the laminated structure 10 of the embodiment of the present invention. ３ Or LiTaO ３ A dielectric film with excellent crystallinity, including the above, can be formed on a Si substrate or an SOI substrate.

[0073] Furthermore, in the laminated structure 10a, a modified embodiment of the present invention, similar to the laminated structure 10 of the present invention, the buffer film 12 is not limited to a first metal oxide epitaxially grown on the main surface 11p of the substrate 11, the first conductive film 13 is not limited to a platinum group element such as Pt epitaxially grown on the buffer film 12, and the second conductive film 14 is SrRuO epitaxially grown on the first conductive film 13. ３ It is not limited to this. Even in such cases, for example, by oriented the buffer film 12, the first conductive film 13, and the second conductive film 14 in a single direction, the dielectric film 15 having an ilmenite-type structure and other various single-crystal high-quality dielectric films 15 can be oriented in a certain direction on the Si substrate, so that epitaxially grown LiNbO can be easily formed in a state oriented in (01-12) or in a state oriented in a plane different from the (0001) plane. ３ Or LiTaO ３ A dielectric film 15 with excellent crystallinity, including the above, can be formed on a Si substrate.

[0074] Furthermore, the laminated structure 10a of the modified embodiment of the present invention does not necessarily have a first conductive film 13 and a second conductive film 14, similar to the laminated structure 10 of the embodiment of the present invention, and the dielectric film 15 may be formed directly on the buffer film 12. Even in such a case, for example, by including a first metal oxide epitaxially grown on the main surface 11p of the substrate 11, LiNbO can be easily epitaxially grown in a (01-12) oriented state or oriented on a plane different from the (0001) plane. ３ Or LiTaO ３ A dielectric film with excellent crystallinity, including the above, can be formed on the buffer film 12.

[0075] As shown in Figures 7 and 8, it is preferable that each layer of the dielectric layer 15a is oriented such that the (0001) plane of the second metal oxide is tilted with respect to the main plane by a predetermined angle, for example, a first angle θ11, and that it contains a first domain DM1, a second domain DM2, a third domain DM3, and a fourth domain DM4 in which the

[0001] axes of the second metal oxide are oriented in different directions. ３ When this is the case, the first angle θ11 can be set to, for example, 52.24 to 62.24°. On the other hand, the second metal oxide is LiTaO ３ When this occurs, the first angle θ11 can be set to, for example, 52.02 to 62.02°.

[0076] Here, the second metal oxide is LiNbO ３ , or LiTaO ３ In this case, when the

[0001] direction of the second metal oxide in the first domain DM1 is defined as the first

[0001] direction, the LiNbO contained in the second metal oxide in the second domain DM2 ３ Or LiTaO ３ The

[0001] direction is the direction rotated 90° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface 11p (around the normal direction of the main surface 11p).

[0077] Furthermore, LiNbO is included in the second metal oxide in the third domain DM3. ３ Or LiTaO ３The

[0001] direction is the direction obtained by rotating 180° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface 11p (around the normal direction of the main surface 11p).

[0078] Furthermore, LiNbO is included in the second metal oxide in the fourth domain DM4. ３ Or LiTaO ３ The

[0001] direction is the direction rotated 270° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface 11p (around the normal direction of the main surface 11p).

[0079] Furthermore, the orientation of the first domain DM1, second domain DM2, third domain DM3, and fourth domain DM4 contained in each layer of the dielectric layer 15a is substantially the same in each layer.

[0080] In such cases, LiNbO is contained in the second metal oxide of the dielectric film 15. ３ Or LiTaO ３ Since it is oriented (01-12), LiNbO ３ Or LiTaO ３ The inclination angle of the (0001) surface relative to the main surface 11p can be easily controlled to be a constant angle. In addition, the (01-12) oriented LiNbO ３ The dielectric film 15 is made of 36° Y-cut LiNbO ３ It has an electromechanical coupling coefficient as high as that of a single crystal plate, and a high longitudinal wave velocity. Therefore, it is possible to realize electronic devices such as SAW filters with a high electromechanical coupling coefficient and excellent filter characteristics.

[0081] The method for manufacturing the laminated structure 10 of the embodiment of the present invention described above will be explained below.

[0082] A method for manufacturing the laminated structure 10 according to an embodiment of the present invention comprises the steps of forming a buffer film on a substrate and forming a dielectric film on the buffer film by a wet method.

[0083] First, a buffer film 12 containing the first metal oxide represented by the above composition formula (1) is formed on the main surface 11p of the substrate 11 using an epitaxial growth method.

[0084] Specifically, the main surface 11p of the substrate 11 is treated with reactive ion etching (RIE), and after heating in the presence of oxygen to form a thermal oxide film, the first metal oxide represented by the above composition formula (1) of the deposition source and the oxygen in the oxide film on the substrate 11 are thermally reacted by electron beam deposition without using oxygen, and a single crystal film of the first metal oxide as a buffer film 12 is formed on the substrate 11 according to the "(1-1) initial metal nucleus" described later.

[0085] Here, the substrate 11 is a Si substrate, or an SOI substrate comprising a substrate made of a Si substrate, an insulating layer on the substrate, and an SOI layer made of a Si film on the insulating layer. Alternatively, the substrate 11 is an SOI (111) substrate comprising a Si(111) substrate with the Si(111) surface as the main surface 11p, or a substrate 11a made of a Si substrate, an insulating layer 11b on the substrate 11a, and an SOI (Silicon On Insulator) (111) layer (SOI layer 11c) made of a Si(111) film on the insulating layer 11b with the Si(111) surface as the main surface 11p.

[0086] Next, oxygen is introduced, the temperature is lowered, and the pressure is increased, and annealing is performed according to "(1-2) Post-annealing" described later.

[0087] Furthermore, with oxygen flowing, the first metal oxide represented by the above compositional formula (1) of the deposition source is thermally reacted with oxygen according to the "(1-3) HZO deposition" described later, thereby forming a single crystal film of the first metal oxide as a buffer film 12 on the substrate 11.

[0088] In this way, the first metal oxide contained in the formed buffer film 12 grows epitaxially on the main surface 11p of the substrate 11 and is oriented (111) in a pseudocubic crystal representation, for example.

[0089] Then, a dielectric film 15, including a dielectric layer 15a, is formed on the buffer film 12 by a wet process using an epitaxial growth method. Each layer of the dielectric layer 15a has an ilmenite-type structure and is oriented in a certain direction. ３ Or LiTaO ３ It contains a secondary metal oxide.

[0090] Specifically, the process of forming a dielectric layer 15a by applying a solution containing a metal element contained in the second metal oxide onto the buffer film 12 and firing it is repeated, for example, 10 times to stack 10 layers under the same conditions, and then firing it in an oxygen atmosphere to crystallize it, thereby forming a dielectric film 15 in which 10 layers of dielectric layer 15a are stacked.

[0091] Here, the metal element-containing solution included in the second metal oxide can be a metal oxide solution, a metal organic compound solution, or a metal alkoxide solution, with a metal oxide solution being preferred. The metal element-containing solution may also be a dispersion (sol) of metal compound particles in the solution, in which the particle size (D50) determined by dynamic light scattering of the metal compound particles is 100 nm or less.

[0092] For example, a metal oxide solution containing lithium and niobium (hereinafter referred to as "LN solution") will be explained below.

[0093] The LN solution contains lithium niobate with a lithium-to-niobium molar ratio (Li / Nb) of 0.8 to 1.5, and ammonium ions, and preferably the particle size (D50) of the particles in the LN solution measured by dynamic light scattering is 100 nm or less. More preferably, the lithium-to-niobium molar ratio (Li / Nb) in the LN solution is 0.9 to 1.5, even more preferably 0.9 to 1.2, and particularly preferably 1.0 to 1.1.

[0094] The ammonia content of the ammonia containing ammonium ions in the LN solution is preferably 0.001% by mass or more and 25% by mass or less, more preferably 0.5% by mass or more and 10% by mass or less, and even more preferably 1% by mass or more and 8% by mass or less.

[0095] The method for measuring the ammonia content present in the LN solution involves adding sodium hydroxide to the dispersion, distilling and separating the ammonia, and quantifying the ammonia content using an ion meter, and measuring the N content in the gasified sample. ２Methods for quantifying ammonia content include using a thermal conductivity meter, the Kjeldahl method, gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), ion chromatography, liquid chromatography (LC), and liquid chromatography-mass spectrometry (LC-MS). In particular, a method for quantifying ammonia content using an ion meter is preferred.

[0096] Furthermore, it is preferable that the particle size (D50) of lithium niobate in the LN solution measured by dynamic light scattering is 100 nm or less, as this allows for high dispersibility. Also, a smaller particle size (D50) in the LN solution is preferable because it is more stable due to less change over time, and it allows for the formation of a good coating film without uncovered areas during film formation, as well as ensuring sufficient film weight. It is more preferable that the particle size (D50) of the particles in the LN solution is 80 nm or less, even more preferable that it is 50 nm or less, particularly preferable that it is 30 nm or less, even more particularly preferable that it is 20 nm or less, even more particularly preferable that it is 10 nm or less, even more particularly preferable that it is 5 nm or less, and even more particularly preferable that it is 3 nm or less. If the particle size (D50) of the particles in the LN solution falls below the particle size detection limit of the measuring device using dynamic light scattering, or if measurement becomes impossible, the particle size (D50) of the particles should be reduced to below the detection limit.

[0097] Here, dynamic light scattering is a method that involves irradiating a solution, such as a suspension, with light, such as laser light, to measure the light scattering intensity from a group of particles undergoing Brownian motion, and determining the particle size and distribution from the temporal variation of that intensity. Specifically, the particle size distribution is evaluated using a zeta potential, particle size, and molecular weight measurement system (Otsuka Electronics Co., Ltd.: ELSZ-2000) in accordance with JIS Z 8828:2019 "Particle size analysis - Dynamic light scattering method". Immediately before measurement, the solution to be measured is filtered through a 2 μm pore size filter to remove dust and other particles, and then ultrasonic treatment is performed at 28 kHz for 3 minutes using an ultrasonic cleaner (AS ONE Corporation: VS-100III). Furthermore, if the measured value shows an abnormal value, it is possible that it is due to dust that was not removed from the solution. In this case, if the measurement results from multiple measurement samples taken from the same solution are not reproducible, the point may be excluded as an anomaly. Furthermore, the particle diameter (D50) refers to the median diameter (D50), which is the particle diameter that represents the 50% cumulative value of the cumulative distribution curve. In addition, unless otherwise specified in this specification, "particle diameter (D50)" includes both "initial particle diameter D50," which indicates the particle diameter (D50) of particles in the LN solution used in the present invention immediately after it has been adjusted to a liquid temperature of 25°C, and "particle diameter over time D50," which indicates the particle diameter (D50) of particles in the LN solution after it has been left to stand for one month from the day the LN solution used in the present invention was generated in a constant temperature incubator set to room temperature of 25°C.

[0098] Furthermore, an LN solution is preferable if the maximum light transmittance in the wavelength range of 400 nm to 760 nm is 65% T or higher, as this indicates high dispersion and excellent uniformity of the components in the solution. It is more preferable if the maximum light transmittance in the wavelength range of 400 nm to 760 nm is 70% T or higher, even more preferable if it is 80% T or higher, particularly preferable if it is 90% T or higher, and most preferable if it is 100% T.

[0099] Furthermore, the LN solution preferably has a light transmittance of 65%T or more at one or more wavelengths of 400 nm, 600 nm, and 750 nm, more preferably 70%T or more, even more preferably 80%T or more, particularly preferably 90%T or more, and most preferably 100%T or more. The light transmittance at one or more wavelengths of 400 nm, 600 nm, and 750 nm may be 70%T or more, 72%T or more, 74%T or more, 76%T or more, 78%T or more, 80%T or more, 90%T or more, 95%T or more, 97%T or more, 98%T or more, 99%T or more, or 100%T or more.

[0100] Furthermore, the LN solution preferably has a light transmittance of 65%T or more in the wavelength range of 400 nm to 760 nm, more preferably 70%T or more, even more preferably 80%T or more, particularly preferably 90%T or more, and most preferably 100%T. The light transmittance in the wavelength range of 400 nm to 760 nm may also be 70%T or more, 72%T or more, 74%T or more, 76%T or more, 78%T or more, 80%T or more, 90%T or more, 95%T or more, 97%T or more, 98%T or more, 99%T or more, or 100%T or more.

[0101] In addition, due to measurement errors, etc., the measured value of the light transmittance described above may exceed 100%T. However, since the theoretical upper limit is 100%T, if the measured value exceeds 100%T, it shall be considered as 100%T. Furthermore, in this specification, unless otherwise specified, "light transmittance" includes both the "initial light transmittance" of the LN solution used in the present invention adjusted to a liquid temperature of 25°C immediately after its production, and the "time-dependent light transmittance" of the LN solution after it has been left standing for one month from the day it was produced in a constant temperature incubator set to room temperature of 25°C. Furthermore, if the time-dependent variation range between the "initial light transmittance" and the "time-dependent light transmittance" of the LN solution used in the present invention is small, it is presumed that the time-dependent variation range of the light transmittance of the LN solution after it has been left standing for more than one month from the day it was produced will also be small.

[0102] Here, the light transmittance described above is measured for the LN solution using a spectrophotometer according to the following light transmittance measurement conditions.

[0103] =Light transmittance measurement conditions= • Measurement device: Ultraviolet-Visible-Near Infrared Spectrophotometer UH4150 (manufactured by Hitachi High-Tech Science Co., Ltd.) • Measurement mode: Wavelength scan • Data mode: %T (transmission) • Measurement wavelength range: 200 nm to 2000 nm • Scan speed: 600 nm / min • Sampling interval: 2 nm

[0104] Furthermore, it is preferable that the LN solution does not contain hydrogen peroxide. Generally, when niobium oxide is present in a solution as polyacid ions, hydrogen peroxide is added to suppress its reaction with hydroxide ions and decomposition, thereby improving stability. However, because the LN solution contains ammonium ions, long-term stability can be ensured even in the absence of hydrogen peroxide.

[0105] One method for detecting hydrogen peroxide in a solution is to use the standard addition method, for example, by measuring the relative absorbance intensity with respect to a standard solution of hydrogen peroxide. This allows for confirmation that the solution does not contain hydrogen peroxide. Specifically, by examining the ultraviolet-visible absorption spectra of a standard solution containing a known concentration, for example, 1% by mass of hydrogen peroxide, and a standard solution without added hydrogen peroxide, a wavelength region in which a change in absorbance associated with peroxo complex formation is observed can be identified. If the difference in absorbance between the standard solution without added hydrogen peroxide and the sample with an unknown hydrogen peroxide concentration in that wavelength region is less than 1%, it can be confirmed that the sample with an unknown hydrogen peroxide concentration substantially does not contain hydrogen peroxide. When hydrogen peroxide is present in a solution, it reacts with the polyacid of niobium to form a peroxo complex. Therefore, as described above, the absence of hydrogen peroxide in the solution can be confirmed by checking the difference in absorbance with respect to a standard solution without added hydrogen peroxide. In addition to the standard addition method described above, qualitative and quantitative analysis of hydrogen peroxide in a solution may also be performed by, for example, using a commercially available hydrogen peroxide measurement kit to add a reagent that reacts with hydrogen peroxide to the solution and measure the resulting color change, or by adding a reagent that reacts with hydrogen peroxide to the solution and measure the resulting luminescence.

[0106] The LN solution is preferably an aqueous solution. Since lithium niobate in the LN solution has high dispersibility in water and good solubility in water, pure water can be used as the solvent. Organic solvents may also be used. Examples of organic solvents include alcohol solvents, ketone solvents, ether solvents, ester solvents, aromatic hydrocarbon solvents, and aliphatic hydrocarbon solvents. A solvent may also be a mixture of these organic solvents and pure water. Examples of alcohol solvents include alcohols with 5 or fewer carbon atoms (methanol, ethanol, n-propanol, isopropyl alcohol, butanol, ethylene glycol, propylene glycol), acetone, and high-boiling point solvents. It is preferable that the above-mentioned solvents and water are miscible. Furthermore, the LN solution may contain one or more solvents in any proportion, as long as stability is not impaired.

[0107] Examples of high-boiling point solvents include polyhydric alcohol-based solvents and glycol-based solvents. Examples of polyhydric alcohol-based solvents include glycerin (boiling point: 290°C), 1,6-hexanediol (boiling point: 250°C), and 1,7-heptanediol (boiling point: 259°C). Glycol-based solvents include ethylene glycol (boiling point: 197.3°C), propylene glycol (boiling point: 188.2°C), diethylene glycol (boiling point: 244.3°C), triethylene glycol (boiling point: 287.4°C), oligoethylene glycol (boiling point: 287°C to 460°C), polyethylene glycol (PEG) (boiling point: 460°C or higher), polyethylene glycol (PEG)-polypropylene glycol (PPG) copolymer (boiling point: 460°C or higher), diethylene glycol monohexyl ether (boiling point: 260°C), polyoxyalkylene monoalkyl ether (boiling point: 260°C or higher), polyoxyethylene sorbitan monolaurate (boiling point: 321°C or higher), other anionic fluorinated surfactants (boiling point: 180°C or higher), amphoteric fluorinated surfactants (boiling point: 180°C or higher), nonionic fluorinated surfactants (boiling point: 180°C or higher), and amine oxides (boiling point: 180°C or higher). The boiling points mentioned above are those at 1 atmosphere of pressure.

[0108] These solvents may be combined with various surfactants, including nonionic surfactants, anionic surfactants, and cationic surfactants.

[0109] Examples of nonionic surfactants include ester / ether type, ester type, ether type, polyvinylpyrrolidone, and amine oxide. Examples of ester / ether type, ester type, and ether type include polyoxyethylene glycol type (EO type), polyoxypropylene glycol type (PO type), and polyoxyalkylene type (AO type), which are obtained by adding one or more selected from polyoxyethylene glycol (EO), polyoxypropylene glycol (PO), and polyoxyalkylene (AO) to an alcohol or carboxylic acid.

[0110] Examples of anionic surfactants include carboxylates, sulfonates, phosphate esters, sulfate esters, and anionic fluorinated surfactants.

[0111] Examples of cationic surfactants include aliphatic amine salts, aliphatic quaternary ammonium salts, aromatic quaternary ammonium salts, heterocyclic quaternary ammonium salts, and fluorine-based surfactants.

[0112] Other examples include amphoteric fluorinated surfactants (boiling point: 180°C or higher).

[0113] Furthermore, the LN solution contains Nb ２ O ５ It is desirable that the converted amount be between 0.1% by mass and 30% by mass. The niobium content in the LN solution is Nb ２ O ５ A conversion of 0.1% to 30% by mass is preferable in terms of achieving both the practicality and stability of the LN solution; more preferably 1 to 25% by mass, even more preferably 3 to 21% by mass, particularly preferably 4 to 20% by mass, and most preferably 4 to 5% by mass.

[0114] Here, the niobium content in the LN solution is determined by appropriately diluting the dispersion with dilute hydrochloric acid as needed, and using ICP emission spectrometry (Agilent Technologies: AG-5110) in accordance with JIS K0116:2014, determining the niobium oxide (Nb ２ O ５ The Nb mass fraction is calculated by measuring the Nb mass fraction in the LN solution. ２ O ５ By expressing the values ​​in conversion terms, multiple oxide states of niobium can be determined collectively. Furthermore, the lithium content in the LN solution is calculated by measuring the Li mass fraction in Li equivalent terms. By identifying the niobium (mol) and lithium (mol) in the LN solution, the molar ratio Li / Nb of lithium (Li) to niobium (Nb) contained in the LN solution can be determined.

[0115] Furthermore, the niobium content in the LN solution can also be expressed in terms of Nb. The niobium content expressed in terms of Nb is as follows: It is preferable that the niobium content in the LN solution is 0.1% by mass or more and 21.0% by mass or less in terms of Nb, in terms of achieving both practicality and stability in the LN solution; it is more preferable that it is 0.7% by mass or more and 17.5% by mass or less in terms of Nb; it is even more preferable that it is 2.1% by mass or more and 14.7% by mass or less in terms of Nb; and it is particularly preferable that it is 3.5% by mass or more and 14.0% by mass or less in terms of Nb.

[0116] Furthermore, it is preferable that the pH of the LN solution is 9 or higher. A pH of 9 or higher is preferable because it stabilizes the polyacid ions contained in the LN solution. It is even more preferable that the pH of the LN solution is 10 or higher, and even more preferable that it is 10.5 or higher. The pH of the LN solution may also be 11 or higher, or even 12 or higher.

[0117] Furthermore, unless otherwise specified in this specification, "pH" includes both the "initial pH" of the LN solution used in the present invention, which has been adjusted to a liquid temperature of 25°C immediately after its creation, and the "time-dependent pH" of the LN solution after it has been left standing for one month from the day it was created in a constant-temperature incubator set to room temperature of 25°C. In addition, if the time-dependent fluctuation range between the "initial pH" and the "time-dependent pH" of the LN solution used in the present invention is small, it can be inferred that the time-dependent fluctuation range of the pH of the LN solution after it has been left standing for more than one month from the day it was created will also be small.

[0118] Here, the pH of the LN solution is measured by immersing the electrode (HORIBA Standard ToupH Electrode 9615S-10D) of a pH meter (HORIBA Glass Electrode Type Hydrogen Ion Concentration Indicator D-51) in the LN solution, and after confirming that the liquid temperature has stabilized at 25°C, the measurement is performed.

[0119] The LN solution described above can be produced, for example, by the manufacturing method described in International Publication No. 2022 / 23087.

[0120] Furthermore, a metal oxide solution containing lithium and tantalum (hereinafter referred to as "LT solution") will be explained below.

[0121] The LT solution has a tantalum content of Ta ２ O ５ The LT solution is preferably 0.1% by mass or more and 30% by mass in terms of conversion, and the particle size (D50) of the particles in the LT solution measured by dynamic light scattering is 100 nm or less. The LT solution has a tantalum content of Ta ２ O ５ A tantalum content of 0.1% by mass or more and less than 30% by mass is preferable in that it improves dispersibility and solubility in polar solvents, particularly water. Furthermore, the LT solution is more preferably 0.5% by mass or more, and even more preferably 1% by mass or more. On the other hand, the LT solution is more preferably 25% by mass or less, and even more preferably 20% by mass or less. The tantalum content in the LT solution can be measured in the same way as the niobium content in the LN solution described above. By specifying the tantalum content and lithium content in the LT solution, the molar ratio Li / Ta of lithium (Li) to tantalum (Ta) contained in the LT solution can be determined.

[0122] Furthermore, the LT solution may contain an ionized alkaline aqueous solution, such as ammonia. The ammonia content in the LT solution can be measured in the same manner as the ammonia content in the LN solution described above.

[0123] Furthermore, when the particle size (D50) of the particles in the LT solution, as determined by dynamic light scattering, is 100 nm or less, it is preferable from the viewpoint of high dispersibility, stability with little change over time, reactivity during reactions and composite formation with other substances, and film uniformity during film formation. In addition, it is preferable that the particle size (D50) be smaller, more preferably 50 nm or less, even more preferably 30 nm or less, particularly preferably 20 nm or less, also particularly preferably 10 nm or less, even more particularly preferably 1 nm or less, and most particularly preferably 0.6 nm or less. The particle size (D50) of the particles in the LT solution can be measured in the same manner as the particle size (D50) of the particles in the LN solution described above.

[0124] Furthermore, the LT solution has a tantalum content of Ta ２ O ５ The amount may be 0.1% by mass or more and 15% by mass or less. The tantalum content in the LT solution is Ta ２ O ５ A conversion of 0.1% to 15% by mass is preferable in terms of achieving both the practicality and stability of the LT solution, and Ta ２ O ５ It is more preferable that the amount is 1% by mass or more and 15% by mass or less, in terms of conversion, Ta ２ O ５ It is even more preferable that the amount is 3% by mass or more and 10% by mass or less, Ta ２ O ５ It is particularly preferable that the amount is 4% by mass or more and 20% by mass or less, in terms of conversion, Ta ２ O ５ It is most preferable that the amount is between 4% by mass and 5% by mass when converted.

[0125] Furthermore, the tantalum content of the LT solution can also be expressed in terms of Ta. The tantalum content expressed in terms of Ta is as follows: It is preferable that the tantalum content of the LT solution is 0.08% by mass or more and 12.3% by mass or less in terms of Ta, in terms of achieving both the practicality and stability of the LT solution; it is more preferable that it is 0.8% by mass or more and 12.3% by mass or less in terms of Ta; it is even more preferable that it is 2.4% by mass or more and 8.2% by mass or less in terms of Ta; and it is particularly preferable that it is 4.1% by mass or more and 8.2% by mass or less in terms of Ta.

[0126] Furthermore, it is preferable that the molar ratio Li / Ta of lithium (Li) to tantalum (Ta) contained in the LT solution is 0.8 or more and 1.5 or less. A molar ratio Li / Ta of lithium (Li) to tantalum (Ta) contained in the LT solution is preferable in that it improves dispersibility and solubility in water, more preferably 0.8 or more and 1.3 or less, even more preferably 0.9 or more and 1.2 or less, particularly preferably 0.9 or more and 1.1 or less, and most preferably 1.0 or more and 1.1 or less.

[0127] Furthermore, the ammonia content in the LT solution may be any amount. For example, the ammonia content may be greater than 0% by mass and 10% by mass or less, 0.001% by mass or more and 10% by mass or less, or 0.003% by mass or more and 5% by mass or less.

[0128] Furthermore, it is preferable that the LT solution does not contain organic acids. By not containing organic acids, the polyacid ions contained in the LT solution become more stable.

[0129] The LT solution is preferably an aqueous dispersion. Since lithium tantalate in the LT solution has high dispersibility in water and good solubility in water, pure water can be used as the solvent. As with the LN solution, the organic solvents mentioned above may also be used. Furthermore, the LT solution may contain one or more solvents in any proportion, as long as it does not impair stability.

[0130] Furthermore, the pH of the LT solution may be greater than 7. A pH greater than 7 is preferable because it stabilizes the polyacid ions contained in the dispersion. It is even more preferable if the pH of the LT solution is 8 or higher, even more preferable if it is 9 or higher, particularly preferable if it is 10 or higher, particularly preferable if it is 11 or higher, and it may also be 12 or higher. It is also preferable that the LT solution does not contain organic acids, as the presence of organic acids lowers the pH. The pH of the LT solution can be measured in the same manner as the pH of the LN solution described above.

[0131] The LT solution described above can be produced, for example, by the manufacturing method described in International Publication No. 2023 / 171020.

[0132] By coating the buffer film 12 with the above-mentioned LN solution or LT solution and firing it, epitaxial growth occurs, resulting in an ilmenite-type structure and (01-12)-oriented LiNboO2. ３ , or LiTaO ３ A dielectric layer 15a containing a second metal oxide is formed on the buffer film 12 by a wet process.

[0133] By the manufacturing method of the laminated structure of the present invention described above, a laminated structure 10 according to an embodiment of the present invention can be manufactured, which has a substrate 11, a buffer film 12 formed on the substrate 11, and a dielectric film 15 formed on the buffer film 12 by a wet method.

[0134] The manufacturing method for the laminated structure 10 according to an embodiment of the present invention may include the steps of: forming a buffer film on a substrate; forming a first conductive film on the buffer film; forming a second conductive film on the first conductive film; and forming a dielectric film on the second conductive film by a wet method. The step of forming the buffer film on the substrate is the same as the manufacturing method for the laminated structure 10 according to an embodiment of the present invention, so its explanation is omitted.

[0135] As described above, a first conductive film 13 made of platinum group elements is formed on the formed buffer film 12 by sputtering according to the first sputtering conditions described later.

[0136] Thus, the formed first conductive film 13 is epitaxially grown on the buffer film 12, has a cubic crystal structure, and contains platinum group elements oriented (111) in a pseudocubic representation, for example.

[0137] Next, SrRuO ３ A second conductive film 14 is formed by sputtering according to the second sputtering conditions described later.

[0138] Thus, the formed second conductive film 14 contains strontium ruthenate epitaxially grown on the first conductive film 13 and oriented (111) in a pseudocubic crystal structure, for example.

[0139] Then, a dielectric film 15, including a dielectric layer 15a, is formed on the second conductive film 14 by a wet process using an epitaxial growth method. Note that the dielectric film 15, including the dielectric layer 15a, is obtained in the same manner as the manufacturing method for the laminated structure 10 in the embodiment of the present invention described above, so a detailed explanation is omitted.

[0140] By the manufacturing method of the laminated structure of the present invention described above, a laminated structure 10 according to an embodiment of the present invention can also be manufactured, comprising a substrate 11, a buffer film 12 formed on the substrate 11, a first conductive film 13 formed on the buffer film 12, a second conductive film 14 formed on the first conductive film 13, and a dielectric film 15 formed on the second conductive film 14 by a wet method.

[0141] The present invention will be described in more detail below based on examples, but the present invention is not limited to the following examples.

[0142] (Example 1) [Formation of Laminated Structure] The laminated structure according to Example 1 of the present invention is the laminated structure shown in Figure 1.

[0143] First, the crystal growth surface of the Si(111) substrate 11 was treated with reactive ion etching (RIE), and after heating in the presence of oxygen to form a thermal oxide film, an electron beam deposition method was used without using oxygen to thermally react the metal (Hf, Zr) of the deposition source with the oxygen in the oxide film on the Si(111) substrate, thereby forming a single crystal film of the first metal oxide as a buffer film 12 on the Si(111) substrate (see "(1-1) Initial Metal Nuclei" below).

[0144] (1-1) Metal initial nucleation deposition source: Hf, Zr Pressure: 2 × 10 －４ Pa thickness: 2 nm, Substrate temperature: 1000°C

[0145] Next, annealing was performed by flowing oxygen, lowering the temperature, and increasing the pressure (see "(1-2) Post-annealing" below).

[0146] (1-2) Post-annealing pressure: 2 × 10 －２ Pa Substrate temperature: 900℃ Time: 180sec

[0147] Furthermore, while oxygen was flowing, the metal (Hf, Zr) of the deposition source and the oxygen were subjected to a thermal reaction to form a single crystal film of the first metal oxide as a buffer film 12 on the Si substrate (see "(1-3) HZO Deposition" below). The conditions for the electron beam deposition method during this film formation were as follows. The Hf:Zr value was 25:75 (x in the above composition formula (1) was 0.75), which was the target value.

[0148] (1-3) HZO deposition source: Hf, Zr Pressure: 2 × 10 －２ Pa thickness: 10 nm, Substrate temperature: 900°C

[0149] Next, a metal film made of Pt was formed on the buffer film 12 as the first conductive film 13 by sputtering (see "First Sputtering Conditions" below).

[0150] =First sputtering conditions= Equipment: ULVAC sputtering machine QAM-4 Pressure: 1.20 × 10 －１Pa Target: Pt Power: 100W (DC) Thickness: 80nm Substrate temperature: 450-600℃

[0151] Furthermore, on the first conductive film 13 made of Pt, SrRuO ３ A second conductive film 14 was formed by sputtering (see "Second Sputtering Conditions" below).

[0152] =Second Sputtering Conditions= Equipment: ULVAC QAM-4 sputtering system Power: 150W (RF) Gas: Ar Pressure: 1.8 Pa Substrate Temperature: 600℃ Thickness: 10 nm

[0153] And, SrRuO ３ On the second conductive film 14, which consists of LiNbO ３ A dielectric film 15 was formed by a wet process.

[0154] The solution containing lithium and niobium, i.e., the LN solution, which is coated onto the second conductive film 14, was obtained as follows.

[0155] 100 g of niobium pentoxide was dissolved in 200 g of 55% hydrofluoric acid aqueous solution, and 830 mL of deionized water was added to obtain an aqueous solution of niobium fluoride containing 100 g / L of niobium in terms of Nb2O5 (Nb2O5 = 8.84 mass%). 200 mL of this aqueous solution of niobium fluoride was added to 1 L of aqueous ammonia (NH3 concentration 25 mass%) in less than 1 minute (NH3 / Nb2O5 molar ratio = 177.9, NH3 / HF molar ratio = 12.2) to obtain a reaction solution (pH 11). This reaction solution was a slurry of niobic acid compound hydrate, in other words, a slurry of niobium-containing precipitate.

[0156] Next, the reaction solution was decanted using a centrifuge and washed until the amount of free fluoride ions was 100 mg / L or less to obtain a niobium-containing precipitate from which the fluoride ions had been removed. Ammonia water was used as the washing solution.

[0157] Furthermore, the niobium-containing precipitate from which the fluoride ions were removed was diluted with pure water to obtain a slurry. A portion of this slurry was dried at 110°C for 24 hours, and then calcined at 1,000°C for 4 hours to produce Nb₂O₅, and the concentration of Nb₂O₅ contained in the slurry was calculated from its weight.

[0158] Then, the slurry of the niobium-containing precipitate diluted with pure water is used to determine the niobium concentration of the final mixture. ２ O ５ A translucent slurry mixture was obtained by mixing lithium hydroxide monohydrate with pure water in an amount equivalent to 5% by mass, with a Li / Nb molar ratio of 1. This mixture was stirred and maintained at a liquid temperature of 50°C to 100°C, for example, 70°C, for 1 hour to obtain the colorless and transparent LN solution used in Example 1. The pH of this LN solution was 11. Furthermore, ethanol was added to the LN solution to prepare a coating solution for film formation. The composition and physical properties of the LN solution used in Example 1 are shown in Tables 1 and 2 below.

[0159] Next, the prepared coating solution is dropped onto the substrate and rotated at 1000 rpm for 15 seconds to spin-coat (apply) the coating solution to the substrate, thereby generating LiNbO ３ A film containing a precursor of (LN) was formed. Then, the solvent was evaporated and the film was dried by placing the substrate on a hot plate at a temperature of 200°C. This process was repeated 10 times to deposit 10 layers under the same conditions, after which oxygen (O) was added. ２ The precursor was oxidized and crystallized by heat treatment at 650°C for 5 seconds in an atmosphere. The dielectric film 15, which includes 10 dielectric layers 15a, is obtained by performing the above process and is composed of LiNbO ３ A dielectric film 15 containing a second metal oxide consisting of (LN) was obtained.

[0160] In this way, LiNbO is placed on the second conductive film 14. ３ A dielectric film 15 made of (LN) was formed by a wet method to obtain the laminated structure 10 according to Example 1. A first conductive film 13 made of Pt and SrRuO were formed on the buffer film 12. ３Alternatively, the dielectric film 15 may be formed directly on the buffer film 12 without forming the second conductive film 14.

[0161] [X-ray Diffraction Measurement] For the laminated structure of Example 1, after forming a dielectric film 15 on the main surface 11p of the substrate 11, the diffraction pattern of the laminated structure was measured by X-ray diffraction (XRD) measurement using the θ-2θ method, with the laminated structure positioned so that the diffraction plane was parallel to the main surface 11p. The measured diffraction pattern of the laminated structure of Example 1 is shown in Figure 9. The XRD measurement was performed using a Rigaku SmartLab X-ray diffractometer.

[0162] As shown in Figure 9, in the diffraction pattern of Example 1, there is a strong diffraction peak of the (111) plane of Si, a diffraction peak of the (111) plane in the pseudocubic representation of HZO, a strong diffraction peak of the (111) plane of Pt, and LiNbO ３ Strong diffraction peaks were observed on the (01-12) plane (LN(012)), (02-24) plane (LN(024)), and (03-36) plane (LN(036)) of (LN). Therefore, in Example 1, the HZO contained in the buffer film 12 was (111) oriented in pseudocubic crystal representation, the Pt contained in the first conductive film 13 had a cubic crystal structure and was (111) oriented, and the LiNbO contained in the second metal oxide in the dielectric film 15 ３ It was revealed that (LN) has an ilmenite-type structure and is (01-12) oriented.

[0163] Although not shown in the diagram, after forming the second conductive film 14 on the main surface 11p of the substrate 11, and before forming the dielectric film 15, the diffraction pattern of the laminated structure is similarly measured to determine the amount of SrRuO contained in the second conductive film 14. ３ It was revealed that (SRO) is oriented in a (111) configuration in pseudocubic crystal representation.

[0164] Furthermore, the diffraction plane in the X-ray diffraction measurement is inclined with respect to the main surface 11p, and LiNbO ３With the laminated structure positioned (X-adjusted) so that no diffraction peaks other than those on the (01-12), (02-24), and (03-36) planes of (LN) were observed, a φ scan was performed on the (01-12) plane (2θ = 23.75°) of LN contained in the second metal oxide contained in the dielectric film 15. The φ scan measured for the laminated structure of Example 1 is shown in Figure 10.

[0165] As shown in Figure 10, in the φ scan, LiNbO ３ Six strong diffraction peaks were observed at 60° intervals on the (01-12) plane of (LN). In other words, diffraction peaks showing six-fold symmetry of LN were observed in the φ scan. Therefore, it became clear that the LN contained in the second metal oxide contained in the dielectric film 15 had crystal axes aligned in the in-plane direction along the main surface 11p of the substrate 11, i.e., that they were epitaxially grown.

[0166] Furthermore, regarding the laminated structure of Example 1, the LiNbO contained in the dielectric film 15 ３ A pole figure corresponding to the interplanar spacing d value (d value = 0.2308 nm, 2θ = 38.99° when using CuKα rays) corresponding to the interplanar spacing of the (0006) plane of (LN) was measured. The measured pole figure is shown in Figure 11. Note that the values ​​of 2θ in this specification, including the 2θ value of the (01-12) plane mentioned above, are the values ​​when using CuKα rays as X-rays.

[0167] As shown in Figure 11, in the pole figure of Example 1, LiNbO ３ Six diffraction peaks were observed at 60° intervals on the (0006) plane of (LN). That is, in the pole figure, diffraction peaks showing six-fold symmetry of LN were observed in an annular region (corresponding to a φ scan) that satisfies the condition where the diffraction plane is tilted 90° - 20° = 70° with respect to the main surface 11p. Therefore, it became clear that the polarization direction of LN contained in the second metal oxide contained in the dielectric film 15 is aligned in the in-plane direction along the main surface 11p of the substrate 11 (see Figure 1), i.e., that it is epitaxially grown.

[0168] Furthermore, as will be explained using Example 3 described later, the dielectric film 15 is LiNbO３ (LN) replaced with LiTaO ３ Even in the case where a second metal oxide consisting of (LT) is included, the dielectric film 15 is LiNbO ３ Similar results to those obtained in Example 1 were obtained when a second metal oxide consisting of (LN) was included.

[0169] Furthermore, although a detailed explanation will be omitted, even when the ratio of Hf:Zr is a ratio other than 25:75, and x in the above compositional formula (1) satisfies 0 ≤ x < 1 or x satisfies x = 1, the same results as in Example 1, where the ratio of Hf:Zr is 25:75 (x in the above compositional formula (1) is 0.75), were obtained.

[0170] (Example 2) [Formation of Laminated Structure] Next, the laminated structure of Example 2 was obtained in the same manner as in Example 1, except that a Si(100) substrate was used instead of a Si(111) substrate as the substrate 11. The laminated structure of Example 2 is the laminated structure described above using Figure 6 in the modified embodiment of the present invention. Note that the LN solution used in Example 2 is the same as the LN solution used in Example 1, so its description is omitted.

[0171] [X-ray diffraction measurement] For the laminated structure of Example 2, after forming a dielectric film 15 on the main surface 11p of the substrate 11, the laminated structure was positioned so that the diffraction plane in the X-ray diffraction measurement using the θ-2θ method was parallel to the main surface 11p, and the diffraction pattern of the laminated structure was measured by the said X-ray diffraction measurement. The measured diffraction pattern of the laminated structure of Example 2 is shown in Figure 12.

[0172] As shown in Figure 12, the diffraction pattern of Example 2 shows a strong diffraction peak on the (400) plane of Si, strong diffraction peaks on the (200) and (400) planes in the pseudocubic representation of HZO, a strong diffraction peak on the (200) plane of Pt, and SrRuO ３ Strong diffraction peaks on the (100) plane in the pseudocubic representation of (SRO), and LiNbO ３A strong diffraction peak was observed on the (01-12) plane (LN(012)) of (LN). Therefore, in Example 2, the HZO contained in the buffer film 12 was (100) oriented in pseudocubic crystal representation, the Pt contained in the first conductive film 13 had a cubic crystal structure and was (100) oriented, the SRO contained in the second conductive film 14 was (100) oriented in pseudocubic crystal representation, and the LiNbO contained in the second metal oxide in the dielectric film 15 ３ It was revealed that (LN) has an ilmenite-type structure and is (01-12) oriented.

[0173] Furthermore, the diffraction plane in the X-ray diffraction measurement is inclined with respect to the main surface 11p, and LiNbO ３ A φ scan was performed on the (01-12) plane (2θ = 23.75°) of the LN contained in the second metal oxide contained in the dielectric film 15, with the stacked structure in a state where diffraction peaks other than those on the (01-12), (02-24), and (03-36) planes of (LN) were not strongly observed. The φ scan measured for the stacked structure of Example 2 is shown in Figure 13.

[0174] As shown in Figure 13, in the φ scan, LiNbO ３ Four strong diffraction peaks were observed at 90° intervals on the (01-12) plane of (LN). In other words, diffraction peaks showing four-fold symmetry of LN were observed in the φ scan. Therefore, it became clear that the LN contained in the second metal oxide contained in the dielectric film 15 had crystal axes aligned in the in-plane direction along the main surface 11p of the substrate 11, i.e., that they were epitaxially grown.

[0175] Furthermore, regarding the laminated structure of Example 2, the LiNbO contained in the dielectric film 15 ３ The pole diagrams corresponding to the interplanar spacing d value (d value = 0.2308 nm, 2θ = 38.99° when using CuKα rays) corresponding to the interplanar spacing of the (0006) plane of (LN) were measured. The measured pole diagrams are shown in Figure 14.

[0176] As shown in Figure 14, in the pole figure of Example 2, LiNbO ３Four diffraction peaks were observed at 90° intervals on the (0006) plane of (LN). That is, in the pole figure, diffraction peaks showing four-fold symmetry of LN were observed in an annular region (corresponding to a φ scan) that satisfies the condition where the diffraction plane is tilted 90° - 35° = 55° with respect to the main surface 11p. Therefore, it became clear that the polarization direction of LN contained in the second metal oxide contained in the dielectric film 15 is aligned in the in-plane direction along the main surface 11p of the substrate 11 (see Figure 1), i.e., that it is epitaxially grown.

[0177] Although a detailed explanation will be omitted, the dielectric film 15 is LiNbO ３ (LN) replaced with LiTaO ３ Even in the case where a second metal oxide consisting of (LT) is included, the dielectric film 15 is LiNbO ３ Similar results were obtained as in Example 2, which included a second metal oxide consisting of (LN).

[0178] Furthermore, although a detailed explanation will be omitted, even when the ratio of Hf:Zr is a ratio other than 25:75, and x in the above compositional formula (1) satisfies 0 ≤ x < 1 or x satisfies x = 1, the same results as in Example 2, where the ratio of Hf:Zr is 25:75 (x in the above compositional formula (1) is 0.75), were obtained.

[0179] (Example 3) [Formation of a laminated structure] Furthermore, SrRuO ３ On the second conductive film 14, which consists of LiNbO ３ Instead of the dielectric film 15 made of LiTaO ３ The laminated structure of Example 3 was obtained in the same manner as in Example 1, except that the dielectric film 15 was formed by a wet method.

[0180] The solution containing lithium and tantalum elements, i.e., the LT solution, which is coated onto the second conductive film 14, was obtained as follows.

[0181] 137.9g ​​of tantalum hydroxide manufactured by Mitsui Mining & Smelting Co., Ltd. (Ta ２ O ５ Dissolve 66% by mass of tantalum fluoride in 120 g of 55% by mass hydrofluoric acid aqueous solution, and add 849 mL of deionized water to produce an aqueous solution of tantalum fluoride (Ta ２ O５ A concentration of 8.2% by mass was obtained.

[0182] To 1,000 g of this tantalum fluoride aqueous solution, add 36.1 g of hydrogen peroxide solution (H ２ O ２ Add (H) (35% by mass) ２ O ２ An aqueous solution of tantalum compound was obtained by stirring for 5 minutes (Ta molar ratio = 1.0).

[0183] Add 1,000 g of this tantalum compound aqueous solution to 6.82 L of ammonia water (NH3 concentration 25% by mass) in less than 1 minute (NH ３ / Ta molar ratio = 245, NH ３ (HF molar ratio = 30.7), a reaction solution (pH 11) was obtained. This reaction solution was a slurry of tantalum compound hydrate, in other words, a slurry of tantalum-containing precipitate.

[0184] Next, the reaction solution was decanted using a centrifuge and washed until the amount of free fluoride ions was 100 mg / L or less to obtain a tantalum-containing precipitate from which the fluoride ions had been removed. Ammonia water was used as the washing solution.

[0185] Furthermore, the tantalum-containing precipitate from which the fluoride ions were removed was diluted with pure water to obtain a tantalum-containing precipitate slurry. A portion of this tantalum-containing precipitate slurry was dried at 110°C for 24 hours, and then calcined at 1,000°C for 4 hours to obtain Ta ２ O ５ This generates a tantalum-containing precipitate slurry, and its weight is used to determine the amount of Ta contained in the tantalum-containing precipitate slurry. ２ O ５ The concentration was calculated.

[0186] Then, the tantalum-containing precipitate slurry diluted with pure water, 0.54% by mass of lithium hydroxide, and pure water are mixed, and the tantalum content of the final mixture is Ta ２ O ５The LT solution of Example 3 was obtained by mixing the materials to a concentration of 5% by mass and a Li / Ta molar ratio of 1.0. The pH of the LT solution of Example 3 was 12.2, and the ammonia content was 0.7% by mass. Furthermore, ethanol was added to the LT solution to prepare a coating solution for film formation. The composition and physical properties of the LT solution used in Example 3 are shown in Tables 1 and 2 below.

[0187] Next, the prepared coating solution was treated in the same manner as in Example 1 with LiTaO ３ A dielectric film 15 containing a second metal oxide made of (LT) was obtained.

[0188] In this way, LiTaO is placed on the second conductive film 14. ３ A dielectric film 15 made of (LT) was formed by a wet method to obtain the laminated structure 10 according to Example 3. A first conductive film 13 made of Pt and SrRuO were formed on the buffer film 12. ３ Alternatively, the dielectric film 15 may be formed directly on the buffer film 12 without forming the second conductive film 14.

[0189] [X-ray diffraction measurement] For the laminated structure of Example 3, after forming a dielectric film 15 on the main surface 11p of the substrate 11, the laminated structure was positioned so that the diffraction plane in the X-ray diffraction measurement using the θ-2θ method was parallel to the main surface 11p, and the diffraction pattern of the laminated structure was measured by the said X-ray diffraction measurement. The measured diffraction pattern of the laminated structure of Example 3 is shown in Figure 15.

[0190] As shown in Figure 15, in the diffraction pattern of Example 3, there is a strong diffraction peak of the (111) plane of Si, a diffraction peak of the (111) plane in the pseudocubic representation of HZO, a strong diffraction peak of the (111) plane of Pt, and LiTaO ３ Strong diffraction peaks were observed on the (01-12) plane (LT(012)) and the (03-36) plane (LT(036)) of (LT). Therefore, in Example 3, the HZO contained in the buffer film 12 was (111) oriented in pseudocubic crystal representation, the Pt contained in the first conductive film 13 had a cubic crystal structure and was (111) oriented, and the LiTaO contained in the second metal oxide in the dielectric film 15３ It was revealed that (LT) has an ilmenite-type structure and is (01-12) oriented.

[0191] Although not shown in the diagram, after forming the second conductive film 14 on the main surface 11p of the substrate 11, and before forming the dielectric film 15, the diffraction pattern of the laminated structure is similarly measured to determine the amount of SrRuO contained in the second conductive film 14. ３ It was revealed that (SRO) is oriented in a (111) configuration in pseudocubic crystal representation.

[0192] Furthermore, the diffraction plane in the X-ray diffraction measurement is inclined with respect to the main surface 11p, and LiTaO ３ With the stacked structure positioned (X-adjusted) so that no diffraction peaks other than those on the (01-12) and (03-36) planes of (LT) were observed, a φ scan was performed on the (3000) plane (2θ = 62.36°) of LT contained in the second metal oxide contained in the dielectric film 15. The φ scan measured for the stacked structure of Example 3 is shown in Figure 16.

[0193] As shown in Figure 16, in the φ scan, LiTaO ３ Six strong diffraction peaks were observed at 60° intervals on the (3000) plane of (LT). In other words, diffraction peaks showing 6-fold symmetry of LT were observed in the φ scan. Therefore, it was revealed that the crystal axes of the LT contained in the second metal oxide contained in the dielectric film 15 are aligned in the in-plane direction along the main surface 11p of the substrate 11, i.e., that they are epitaxially grown.

[0194] Furthermore, regarding the laminated structure of Example 3, the LiTaO contained in the dielectric film 15 ３ A pole figure corresponding to the interplanar spacing d value (d value = 0.2297 nm, 2θ = 39.18° when using CuKα rays) corresponding to the interplanar spacing of the (0006) plane of (LT) was measured. The measured pole figure is shown in Figure 17. Note that the values ​​of 2θ in this specification, including the 2θ value of the (3000) plane mentioned above, are the values ​​when using CuKα rays as X-rays.

[0195] As shown in Figure 17, in the pole figure of Example 3, LiTaO３ Six diffraction peaks were observed at 60° intervals on the (0006) plane of (LT). That is, in the pole figure, diffraction peaks showing 6-fold symmetry of LT were observed in an annular region (corresponding to a φ scan) that satisfies the condition where the diffraction plane is tilted 90° - 15° = 75° with respect to the main surface 11p. Therefore, it was revealed that the polarization direction of the LT contained in the second metal oxide contained in the dielectric film 15 is aligned in the in-plane direction along the main surface 11p of the substrate 11 (see Figure 1), i.e., that it is epitaxially grown.

[0196] Furthermore, although a detailed explanation will be omitted, even when the ratio of Hf:Zr is a ratio other than 25:75, and x in the above compositional formula (1) satisfies 0 ≤ x < 1 or x satisfies x = 1, the same results as in Example 3, where the ratio of Hf:Zr is 25:75 (x in the above compositional formula (1) is 0.75), were obtained.

[0197] The LN solution used in Example 1 and the LT solution used in Example 3 were measured for the following physical properties. Below, the measured physical properties and the method of measurement are shown, and the physical properties and measurement results for the LN solution used in Example 1 and the LT solution used in Example 3 are shown in Tables 1 and 2.

[0198] <Elemental Analysis> If necessary, the sample is appropriately diluted with dilute hydrochloric acid, and ICP emission spectrometry (Agilent Technologies: AG-5110) is used to analyze the element in accordance with JIS K0116:2014. For the LN solution used in Example 1 and the LT solution used in Example 3, Nb ２ O ５ Converted Nb mass%, Ta ２ O ５ The converted Ta mass% and the Li mass% on a Li atom basis were measured.

[0199] <pH Measurement> The electrodes of a pH meter (HORIBA: glass electrode type hydrogen ion concentration indicator D-51) (HORIBA: Standard ToupH electrode 9615S-10D) were immersed in the LN solution used in Example 1 and the LT solution used in Example 3. After confirming that the liquid temperature had stabilized at 25°C, the pH was measured. In Table 2, "Initial pH" refers to the pH of the LN solution used in Example 1 and the LT solution used in Example 3 immediately after they were prepared and adjusted to a liquid temperature of 25°C. In addition, in Table 2, "pH over Time" refers to the pH of the LN solution used in Example 1 and the LT solution used in Example 3 after they have been left standing for one month from the day they were prepared in a constant temperature incubator set to room temperature of 25°C.

[0200] <Dynamic Light Scattering Method> The particle size distribution was evaluated using a zeta potential, particle size, and molecular weight measurement system (Otsuka Electronics Co., Ltd.: ELSZ-2000) by dynamic light scattering in accordance with JIS Z 8828:2019. Immediately before measurement, the dispersions were filtered using a 1 μm pore size filter to remove dust and other particles from the LN solution used in Example 1 and the LT solution used in Example 3. Furthermore, D50 represents the particle size at which 50% of the volume fraction is reached. "Initial particle size D50 (nm)" in Table 2 refers to the particle size (D50) of the particles in the LN solution used in Example 1 and the LT solution used in Example 3 immediately after generation. Furthermore, "Particle size D50 (nm) over time" in Table 2 refers to the particle size (D50) of particles in the LN solution used in Example 1 and the LT solution used in Example 3 after they have been allowed to stand for one month from the day they were prepared, in a constant temperature incubator set at room temperature of 25°C.

[0201] <Transmittance Measurement> 3 ml each of the LN solution used in Example 1 and the LT solution used in Example 3 were placed in a synthetic quartz cell with a path length of 5 mm. The light transmittance of the LN solution used in Example 1 and the LT solution used in Example 3 in the wavelength range of 400 nm to 760 nm (specifically, the light transmittance at wavelengths of 400 nm, 600 nm, and 750 nm) was measured using a spectrophotometer according to the light transmittance measurement conditions described above. "Initial light transmittance" in Table 2 refers to the light transmittance of the LN solution used in Example 1 and the LT solution used in Example 3 immediately after their production, when the liquid temperature was adjusted to 25°C. "Light transmittance over time" in Table 2 refers to the light transmittance of the LN solution used in Example 1 and the LT solution used in Example 3 after being left standing for one month from the day of production in a constant temperature incubator set to room temperature of 25°C.

[0202] <Quantitative Analysis of Ammonia> 25 ml of sodium hydroxide solution (30 g / 100 ml) was added to 1-5 ml of the sample solution. This mixture was boiled and distilled, and the distillate (approximately 200 ml) was drained into a container containing 20 ml of pure water and 0.5 ml of sulfuric acid to separate the ammonia. Next, the separated ammonia was transferred to a 250 ml volumetric flask and diluted to 250 ml with pure water. Furthermore, 10 ml of the 250 ml solution was taken into a 100 ml volumetric flask, and 1 ml of sodium hydroxide solution (30 g / 100 mL) was added to the taken solution, and the volume was diluted to 100 ml with pure water. The ammonium ion concentration (mass%) in the solution was measured by quantitative analysis of the solution obtained in this way using an ion meter (main unit: HORIBA F-53, electrode: HORIBA 500 2A).

[0203] <Qualitative Analysis of Hydrogen Peroxide> Standard solution without added hydrogen peroxide, and H ２ O ２The ultraviolet-visible absorbance spectra of a standard solution to which hydrogen peroxide was added to a concentration equivalent to 1% by mass were measured, and the wavelength at which the rate of change in absorbance was greatest was defined as "λ". Next, for samples with an unknown hydrogen peroxide concentration, the absorbance at wavelength λ was measured in the same manner. If the ratio of the absorbance at wavelength λ of the sample with an unknown hydrogen peroxide concentration to the absorbance at wavelength λ of the standard solution without added hydrogen peroxide was 1% or less, it was determined that hydrogen peroxide had not been added to the sample.

[0204] The measurement conditions for the ultraviolet-visible absorption spectrum should be as follows: • Equipment: UH4150 spectrophotometer (Hitachi High-Tech Science Corporation) • Measurement mode: Wavelength scan • Data mode: %T (transmission) • Measurement wavelength range: 200–2,600 nm • Scan speed: 600 nm / min • Sampling interval: 2 nm

[0205]

[0206]

[0207] 10, 10a...Laminated structure 11...Substrate 11a...Base 11b...Insulating layer 11c...SOI layer 11p...Main surface 12...Buffer film 13...First conductive film 14...Second conductive film 15...Dielectric film 15a...Dielectric layer DM1...First domain DM2...Second domain DM3...Third domain DM4...Fourth domain DM5...Fifth domain DM6...Sixth domain

Claims

1. A laminated structure comprising a substrate, a buffer film formed on the substrate, and a dielectric film formed on the buffer film, wherein the buffer film contains a first metal oxide represented by the following compositional formula (1), (Hf １－ｘ Zr ｘ ) O ２ ... (1) The x satisfies 0 ≤ x < 1 or x = 1, the dielectric film includes five or more stacked dielectric layers, each of the dielectric layers has an ilmenite-type structure and is oriented in a certain direction and contains LiNbO ３ Or LiTaO ３ A laminated structure comprising a second metal oxide.

2. The laminated structure according to claim 1, characterized in that the substrate is a Si substrate, or an SOI substrate comprising a substrate made of a Si substrate, an insulating layer on the substrate, and an SOI layer made of a Si film on the insulating layer.

3. The laminated structure according to claim 1, characterized in that the substrate is a Si(111) substrate having a Si(111) plane as its main surface, or an SOI(111) substrate comprising the substrate, the insulating layer, and an SOI(111) layer having a Si(111) plane as its main surface on the insulating layer.

4. In the laminated structure according to claim 1, the substrate is a Si(111) substrate having a Si(111) plane as its main surface, or an SOI(111) substrate comprising the substrate, the insulating layer, and a Si(111) film on the insulating layer having a Si(111) plane as its main surface, wherein the buffer film is formed on the main surface and contains the first metal oxide which is (111) oriented in pseudocubic crystal representation, and each layer of the dielectric layer has an ilmenite-type structure and is (01-12) oriented LiNbO ３ Or LiTaO ３ A laminated structure comprising the second metal oxide.

5. The laminated structure according to claim 4, wherein the first metal oxide is epitaxially grown on the main surface, and the second metal oxide is LiNbO epitaxially grown on the buffer film ３ or LiTaO ３ A laminated structure consisting of 6. In the laminated structure according to claim 5, the second metal oxide is LiNbO ３ Or LiTaO ３ The dielectric layer includes a first domain, a second domain, a third domain, a fourth domain, a fifth domain, and a sixth domain, each of which is oriented such that the (0001) plane of the second metal oxide is inclined by a predetermined angle with respect to the main surface, and the [0001] axes of the second metal oxide are oriented in different directions from each other, wherein when the [0001] direction of the second metal oxide in the first domain is defined as the first [0001] direction, the [0001] direction of the second metal oxide in the second domain is a direction rotated 60° counterclockwise from the first [0001] direction when viewed from the normal direction of the main surface, and the [0001] direction of the second metal oxide in the third domain is a direction rotated 120° counterclockwise from the first [0001] direction when viewed from the normal direction of the main surface. A laminated structure in which the [0001] direction of the second metal oxide in the fourth domain is a direction rotated 180° counterclockwise from the first [0001] direction when viewed from the normal direction of the main surface, the [0001] direction of the second metal oxide in the fifth domain is a direction rotated 240° counterclockwise from the [0001] direction when viewed from the normal direction of the main surface, and the [0001] direction of the second metal oxide in the sixth domain is a direction rotated 300° counterclockwise from the first [0001] direction when viewed from the normal direction of the main surface.

7. A laminated structure according to claim 5 or 6, comprising a first conductive film formed between the buffer film and the dielectric film, wherein the first conductive film is epitaxially grown on the buffer film, has a cubic crystal structure, and contains a platinum group element oriented (111) in pseudocubic representation, and the second metal oxide is LiNbO, epitaxially grown on the first conductive film. ３ Or LiTaO ３ A layered structure.

8. The laminated structure according to claim 7, comprising a second conductive film formed between the first conductive film and the dielectric film, wherein the second conductive film contains strontium ruthenate epitaxially grown on the first conductive film and oriented (111) in pseudocubic crystal representation, and the second metal oxide is LiNbO epitaxially grown on the second conductive film. ３ Or LiTaO ３ A layered structure.

9. In the laminated structure according to claim 1, the substrate is a Si(100) substrate having a Si(100) plane as its main surface, or an SOI(100) substrate comprising the substrate, the insulating layer, and a Si(100) film on the insulating layer having a Si(100) plane as its main surface, wherein the buffer film is formed on the main surface and contains the first metal oxide oriented to (100) in pseudocubic crystal representation, and each layer of the dielectric layer has an ilmenite-type structure and is oriented to (01-12) LiNbO ３ Or LiTaO ３ A laminated structure comprising the second metal oxide.

10. In the laminated structure according to claim 9, the first metal oxide is epitaxially grown on the main surface, and the second metal oxide is epitaxially grown on the buffer film. ３ Or LiTaO ３ A layered structure.

11. In the laminated structure according to claim 10, the second metal oxide is LiNbO ３ Or LiTaO ３ The dielectric layer includes a first domain, a second domain, a third domain, and a fourth domain, each of which is oriented such that the (0001) plane of the second metal oxide is inclined by a predetermined angle with respect to the main surface, and the [0001] axes of the second metal oxide are oriented in different directions from each other, wherein the [0001] direction of the second metal oxide in the first domain is defined as the first [0001] direction, the [0001] direction of the second metal oxide in the second domain is a direction rotated 90° counterclockwise from the first [0001] direction when viewed from the normal direction of the main surface, and the [0001] direction of the second metal oxide in the third domain is a direction rotated 180° counterclockwise from the first [0001] direction when viewed from the normal direction of the main surface. A laminated structure in which the [0001] direction of the second metal oxide in the fourth domain is a direction rotated 270° counterclockwise from the first [0001] direction when viewed from the normal direction of the main surface.

12. A laminated structure according to claim 10 or 11, comprising a first conductive film formed between the buffer film and the dielectric film, wherein the first conductive film is epitaxially grown on the buffer film, has a cubic crystal structure, and contains a platinum group element oriented (100) in pseudocubic representation, and the second metal oxide is LiNbO, epitaxially grown on the first conductive film. ３ Or LiTaO ３ A layered structure.

13. The laminated structure according to claim 12, comprising a second conductive film formed between the first conductive film and the dielectric film, wherein the second conductive film contains strontium ruthenate epitaxially grown on the first conductive film and oriented (100) in pseudocubic form, and the second metal oxide is LiNbO epitaxially grown on the second conductive film. ３ Or LiTaO ３ A layered structure.

14. The process comprises the steps of forming a buffer film on a substrate and forming a dielectric film on the buffer film by a wet process, wherein the buffer film contains a first metal oxide represented by the following compositional formula (1), (Hf １－ｘ Zr ｘ ) O ２ ... (1) The x satisfies 0 ≤ x < 1 or x = 1, the dielectric film includes a dielectric layer, each layer of the dielectric layer has an ilmenite-type structure and is oriented in a certain direction and contains LiNbO ３ Or LiTaO ３ A method for manufacturing a laminated structure comprising a second metal oxide.

15. The method for manufacturing a laminated structure according to claim 14, characterized in that the substrate is a Si substrate, or an SOI substrate comprising a substrate made of a Si substrate, an insulating layer on the substrate, and an SOI layer made of a Si film on the insulating layer.

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