Layered constructs and their use

Abstract

A laminated structure capable of epitaxial growth of highly crystalline functional thin films and capable of suppressing problems such as interlayer delamination is provided, as well as its use and manufacturing apparatus. The laminated structure comprises a substrate with at least a surface composed of single crystals, and a crystalline orientation control film comprising zirconium oxide (ZrO2) as the main component disposed on the single crystal surface of the substrate. Furthermore, a buffer layer comprising a mixed phase of crystalline and amorphous phases is sandwiched between the substrate and the orientation control film.

Description

Technical Field

[0001] This invention relates to laminated structures and their use. Background Technology

[0002] MEMS (Micro Electro Mechanical Systems) are devices composed of stacked structures, which are formed by integrating mechanical components and electronic circuits on substrates such as silicon substrates using microfabrication techniques. By utilizing MEMS technology to form functional thin films such as piezoelectric films on substrates, it is possible to fabricate miniaturized and integrated devices such as sensors and actuators.

[0003] The properties of functional thin films, such as piezoelectric films, vary depending on their crystallinity and orientation. Therefore, controlling crystallinity and orientation through epitaxial growth of functional thin films is effective in obtaining high-performance devices. However, the crystal lattice of the functional thin film typically does not match that of the substrate. Therefore, it is difficult to epitaxially grow functional thin films on the substrate while maintaining a constant state.

[0004] To address this problem, a technique has been proposed to place an alignment control film (buffer film) such as a ZrO2 film between the substrate of the laminated structure and the functional thin film. By setting the alignment control film, lattice mismatch can be suppressed, enabling stable epitaxial growth of the functional thin film.

[0005] Patent documents 1 to 3 are cited as examples of documents disclosing this technology. Patent document 1 discloses a structure in which a thin film of PZT is formed on a buffer layer formed by sequentially stacking films of YSZ (8% Y₂O₃ + 92% ZrO₂), CeO₂, and LaSrCoO₃ on a silicon substrate (Si) (Patent document 1,

[0035] to

[0037] , etc.). Patent document 2 discloses a method of forming a ZrO₂ film on a Si substrate by vapor deposition, and then sequentially forming a lower electrode, a PbZrO₂ film (PZO film), and Pb(ZrO₂) on the ZrO₂ film. 1-x Ti x The structure of the O3 membrane (PZT membrane) (Patent Document 2,

[0023] to

[0039] , etc.).

[0006] Patent Document 3 discloses the following: For a film structure having a substrate 11, an alignment film 12, a conductive film 13, a conductive film 14, and a piezoelectric film 15, since the alignment film 12 contains zirconium oxide (ZrO2), the alignment film 12 is epitaxially grown on the substrate 11, and the conductive film 13 is epitaxially grown on the alignment film 12. Therefore, the conductive film 14 can be epitaxially grown on the conductive film 13, and the piezoelectric film 15 can be epitaxially grown on the conductive film 14 (Patent Document 3,

[0035] to

[0041] , etc.).

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2014-084494

[0010] Patent Document 2: International Publication No. 2016 / 009698

[0011] Patent Document 3: Japanese Patent Application Publication No. 2018-081974 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] Thus, while previous methods have proposed using MEMS technology to fabricate stacked structures with alignment control films, these structures still have room for improvement. Specifically, while using alignment control films can suppress lattice mismatch between the substrate and the functional thin film to a certain extent, it does not completely eliminate it. On the other hand, due to the epitaxial growth of the functional thin film, lattice mismatch and the resulting film stress cannot be ignored. That is, although highly crystalline films are obtained by stabilizing epitaxial growth, the increased crystallineity of each film leads to significant differences in lattice constants, resulting in substantial film stress.

[0014] When such film stress remains, the interlayer bonding strength of the layers constituting the laminated structure decreases, sometimes leading to film delamination. Furthermore, even without delamination, the properties of the functional thin film may deteriorate. This problem is particularly pronounced when using single-crystal substrates such as silicon (Si) substrates and sapphire (Al₂O₃) substrates. This is because the high crystallinity of single-crystal substrates easily causes lattice mismatch issues.

[0015] The inventors conducted in-depth research in view of these problems. As a result, they obtained the following insight: In a laminated structure having a specific substrate and a crystallinity orientation control film, by sandwiching a buffer layer containing a mixed phase of crystalline and amorphous phases between the substrate and the orientation control film, it is possible to achieve epitaxial growth of highly crystalline functional films and suppress problems such as interlayer delamination.

[0016] The present invention was made based on the following insight, and its objective is to provide a laminated structure capable of epitaxial growth of highly crystalline functional thin films and capable of suppressing problems such as interlayer delamination, and an apparatus for its use and manufacture.

[0017] Solution for solving the problem

[0018] This invention includes the solutions described in (1) to (10) below. It should be noted that in this specification, the expression “~” includes the values ​​at both ends. That is, “X~Y” has the same meaning as “X and above and Y and below”. In addition, in this specification, any combination of preferred solutions can be adopted as long as technical matching can be achieved. For example, one side of the preferred numerical range and the other side can be combined arbitrarily.

[0019] Furthermore, unless otherwise specified, the expression "above A" includes not only "directly above A" but also "the upper part of A that is separate from A". That is, expressions such as "setting B above A" include not only "the way of setting B directly above A" but also "the way of sandwiching other components (layers, membranes, etc.) between A and B".

[0020] (1) A layered structure, wherein,

[0021] The stacked structure comprises:

[0022] A substrate, the surface of which is at least composed of single crystals; and

[0023] A crystal orientation control film comprising zirconium oxide (ZrO2) as the main component disposed on the single crystal surface of the substrate.

[0024] A buffer layer comprising a mixed phase of crystalline and amorphous phases is sandwiched between the substrate and the orientation control film.

[0025] (2) Based on the layered structure of (1) above, wherein,

[0026] The buffer layer contains zirconium oxide (ZrO2) as the main component.

[0027] (3) Based on the layered structure of (1) or (2) above, wherein,

[0028] The thickness of the buffer layer is greater than 2nm and less than 10nm.

[0029] (4) A layered structure based on any one of (1) to (3) above, wherein,

[0030] The substrate is a single-crystal Si substrate, SOI substrate, stainless steel (SUS) substrate, quartz glass substrate, single-crystal gallium nitride (GaN) substrate, single-crystal silicon carbide (SiC) substrate, or a sapphire substrate with single-crystal gallium nitride (GaN) disposed on its surface.

[0031] (5) A layered structure based on any one of (1) to (4) above, wherein,

[0032] The orientation control film is a monocrystalline film.

[0033] (6) A layered structure based on any one of (1) to (5) above, wherein,

[0034] The laminated structure is a piezoelectric device, which further comprises a first electrode layer disposed on the orientation control film and a piezoelectric film disposed on the first electrode layer.

[0035] (7) Based on the layered structure of (6) above, wherein,

[0036] The piezoelectric film comprises at least one compound selected from the group consisting of Pb(Zr,Ti)O3, BaTiO3, (Pb,La)(Zr,Ti)O3, LiNbO3, LiTaO3, (K,Na)NbO3, AlN, and ZnO as a main component.

[0037] (8) The layered structure according to (6) or (7) above, wherein,

[0038] The first electrode layer and the piezoelectric film are single-crystal films.

[0039] (9) The use of any of the stacked structures in (1) to (8) above for piezoelectric equipment.

[0040] (10) An apparatus for manufacturing a laminated structure, wherein the laminated structure is the laminated structure described in (1) or (2) above, wherein,

[0041] The manufacturing apparatus for the laminated structure includes a vacuum transport device and a multi-chamber assembly with a vacuum evaporation device and a sputtering device.

[0042] Invention Effects

[0043] According to the present invention, a laminated structure capable of epitaxial growth of highly crystalline functional thin films and capable of suppressing problems such as interlayer delamination is provided, as well as an apparatus for its use and manufacture. Attached Figure Description

[0044] Figure 1 An example of a cross-sectional schematic diagram of a stacked structure is shown.

[0045] Figure 2-1 A cross-sectional TEM image of a stacked structure (Example A1) is shown.

[0046] Figure 2-2 A cross-sectional TEM image of a stacked structure (Example A1) is shown.

[0047] Figure 3-1 A cross-sectional TEM image of a stacked structure (Example A2) is shown.

[0048] Figure 3-2A cross-sectional TEM image of a stacked structure (Example A2) is shown.

[0049] Figure 4 A cross-sectional TEM image of a stacked structure (Example A3) is shown.

[0050] Figure 5 A cross-sectional TEM image of a piezoelectric device (Example B1) is shown.

[0051] Figure 6 A cross-sectional TEM image of a piezoelectric device (Example B2) is shown.

[0052] Figure 7 A cross-sectional TEM image of a piezoelectric device (Example B3) is shown.

[0053] Figure 8 A cross-sectional TEM image of a piezoelectric device (Example B4) is shown.

[0054] Figure 9 The XRD spectrum (ω-2θ scan) of the piezoelectric device (Example B3) is shown.

[0055] Figure 10 The XRD spectrum (Φ scan) of the AlN film (Example B3) is shown.

[0056] Figure 11 The XRD spectrum (Φ scan) of the Pt film (Example B1) is shown.

[0057] Figure 12 The XRD spectrum (Φ scan) of the PZT film (Example B1) is shown. Detailed Implementation

[0058] The following describes specific embodiments of the present invention (hereinafter referred to as "this embodiment"). However, the present invention is not limited to the following embodiments, and various modifications can be made without changing the spirit of the present invention.

[0059] <<1. Layered Structure>>

[0060] The laminated structure of this embodiment includes a substrate with at least a surface composed of single crystals, and a crystalline orientation control film comprising zirconium oxide (ZrO2) as the main component disposed on the single crystal surface of the substrate. Additionally, a buffer layer comprising a mixed phase of crystalline and amorphous phases is sandwiched between the substrate and the orientation control film.

[0061] Figure 1An example of a cross-sectional schematic diagram of a laminated structure is shown. The laminated structure (100) includes at least a substrate (2), a buffer layer (4) disposed on the substrate (2), an alignment control film (6) disposed on the buffer layer (4), and a functional thin film (12) disposed on the alignment control film (6). The laminated structure (100) may also include a first electrode layer (8) and a first metal oxide film (10) between the alignment control film (6) and the functional thin film (12). The laminated structure (100) may also include a second metal oxide film (14) and a second electrode layer (16) on the functional thin film (12). Furthermore, the functional thin film (100) may also include a take-out electrode (18), a protective film (20), and / or a hollow portion (22).

[0062] <Substrate>

[0063] The substrate functions as the base of the laminated structure. A substrate with a surface composed of single crystal is used as the substrate. By using such a substrate, the epitaxial growth and single-crystal formation of functional thin films such as electrode layers and piezoelectric films disposed thereon can be facilitated. The substrate is not limited to any particular type; examples include single-crystal Si substrates, SOI substrates, stainless steel (SUS) substrates, quartz glass substrates, single-crystal gallium nitride (GaN) substrates, single-crystal silicon carbide (SiC) substrates, or sapphire substrates with single-crystal gallium nitride (GaN) disposed on their surface.

[0064] Preferably, the substrate is a single-crystal Si substrate or an SOI substrate, and particularly preferred are single-crystal Si (100) substrates, single-crystal Si (111) substrates, (100) SOI substrates, or (111) SOI substrates. Here, an SOI substrate is a substrate having a Si substrate and a surface Si layer, and having an insulating film such as a SiO2 film interspersed between the Si substrate and the surface Si layer. The surface Si layer is single-crystalized, and other layers (films) such as a buffer layer are provided on the surface Si layer. In addition, the (100) substrate and the (111) substrate are substrates with the (100) plane or (111) plane of the crystal lattice facing the main surface. By using such a substrate, the buffer layer, the orientation control film, or the functional film can be epitaxially grown on the substrate while achieving sufficient lattice matching, and therefore, the crystallinity of these films can be improved.

[0065] <Buffer Layer>

[0066] In the laminated structure of this embodiment, a buffer layer comprising a mixed phase of crystalline and amorphous phases is sandwiched between a substrate and an alignment control film. By providing such a buffer layer, epitaxial growth of functional thin films can be achieved, and problems such as interlayer delamination can be suppressed. That is, the buffer layer includes both fine regions with crystalline structures and fine regions with amorphous structures in a mixed manner. In the crystalline phase (fine regions with crystalline structures), atoms are arranged in a manner aligned with the crystalline structure of the single crystal portion of the substrate located below the buffer layer. That is, crystalline phase epitaxial growth occurs. In addition, since the crystalline phase has a regular atomic arrangement, it has the effect of promoting the epitaxial growth of the crystalline alignment control film disposed above the buffer layer. On the other hand, since the atomic arrangement of the fine regions with amorphous structures is irregular, it has the effect of mitigating the constraints from the substrate and the stress generated by the substrate. Therefore, by providing a buffer layer comprising a mixed phase of crystalline and amorphous phases, it has the effect of promoting the epitaxy of the buffer film and the functional thin film disposed thereon and improving their crystallinity, and it can mitigate stress and suppress interlayer delamination.

[0067] The distribution of crystalline and amorphous phases in the buffer layer is not particularly limited. For example, the crystalline and amorphous phases can be evenly distributed. It should be noted that the amorphous phase includes not only states that do not have a crystalline structure at all, but also states that have a crystalline structure but have an atomic arrangement that deviates from a completely regular arrangement.

[0068] The composition of the buffer layer is not limited. It can be the same as the orientation control film, or it can be a different composition. However, the buffer layer preferably contains zirconium oxide (ZrO2) as the main component. This allows for more effective epitaxial growth of the orientation control film containing zirconium oxide (ZrO2) as the main component. When the buffer layer contains ZrO2, ZrO2 has a monoclinic, tetragonal, or cubic crystal structure. Furthermore, the buffer layer can contain only ZrO2, or it can contain other components. For example, it can contain rare earth elements or alkaline earth elements. Additionally, ZrO2 can contain oxygen vacancies. Moreover, to improve properties, transition metal elements such as aluminum (Al), scandium (Sc), manganese (Mn), iron (Fe), cobalt (Co), and / or nickel (Ni) can also be included.

[0069] The thickness of the buffer layer is preferably 2 nm or more and 10 nm or less. If the thickness is 2 nm or more, the stress-relieving function of the amorphous phase contained in the buffer layer can be more effectively utilized. Therefore, interlayer delamination can be suppressed more effectively. Furthermore, if the thickness is 10 nm or less, the epitaxial growth of the orientation control film and functional film disposed on the buffer layer is more effectively promoted. From the viewpoint of improving the effect of promoting epitaxial growth and suppressing interphase film delamination, the thickness of the buffer layer is more preferably 2 nm or more and 10 nm or less, and even more preferably 3 nm or more and 5 nm or less. Alternatively, other layers (films) may be sandwiched between the buffer layer and the substrate. However, from the viewpoint of promoting the epitaxial growth of the buffer layer or other layers (films) disposed thereon, it is preferable to directly dispose of the buffer layer on the substrate.

[0070] <Orientation control membrane>

[0071] An orientation control film is disposed on the single-crystal surface of a substrate, separated by a buffer layer. That is, it is disposed on top of the buffer layer. The orientation control film is a crystalline film containing zirconium oxide (ZrO2) as its main component, also known as a buffer film. By setting such an orientation control film, when functional thin films such as electrode layers and piezoelectric layers are disposed on the orientation control film, the single-crystalization of the functional thin films can be promoted.

[0072] Orientation control films may contain only ZrO2, or they may contain rare earth elements or alkaline earth elements. Additionally, ZrO2 may contain oxygen vacancies. Furthermore, to improve properties, transition metal elements such as aluminum (Al), scandium (Sc), manganese (Mn), iron (Fe), cobalt (Co), and / or nickel (Ni) may be included.

[0073] The thickness of the orientation control film is preferably 10 nm or more and 1500 nm or less, more preferably 20 nm or more and 1200 nm or less, and even more preferably 30 nm or more and 1000 nm or less. Furthermore, the orientation control film is preferably an epitaxial film formed on a substrate, and even more preferably an epitaxial film with a (100) orientation. Alternatively, other layers (films) may be sandwiched between the orientation control film and the buffer layer. However, from the viewpoint of promoting the epitaxial growth of the orientation control film and other layers (films) disposed thereon, it is preferable to directly dispose of the orientation control film on top of the buffer layer.

[0074] <First Electrode Layer>

[0075] Depending on the requirements, the laminated structure may also include a first electrode layer. The first electrode layer is disposed on the alignment control film. The first electrode layer functions as an electrode of the functional thin film. For example, if the functional thin film is a piezoelectric film, the electrode layer can be used to detect the potential difference based on the surface potential of the piezoelectric film generated by the positive piezoelectric effect. Alternatively, a potential difference can be applied to the piezoelectric film through the electrode layer, causing deformation based on the resulting inverse piezoelectric effect. The first electrode layer only needs to be conductive, and its material is not limited. For example, it may include at least one material selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al), and copper (Cu).

[0076] The thickness of the first electrode layer is preferably 10 nm or more and 500 nm or less, more preferably 30 nm or more and 300 nm or less, and even more preferably 50 nm or more and 200 nm or less. Furthermore, the first electrode layer is preferably an epitaxial film formed on an orientation control film, and even more preferably an epitaxial film with a (100) orientation. Additionally, it is preferable that the first electrode layer is a single-crystal film composed of a single crystal. By setting the first electrode layer as a single-crystal film, the first metal oxide film and functional thin film formed thereon can become single-crystal films.

[0077] <First Metal Oxide Film>

[0078] Depending on the requirements, the laminated structure may also include a first metal oxide film. The first metal oxide film is disposed on the alignment control film and / or the first electrode layer. The first metal oxide film is preferably composed of strontium ruthenium oxide (SrRuO3; SRO). SRO is conductive. Therefore, the SRO film (first metal oxide film) can be used as part of the electrode layer (first electrode layer). Furthermore, the lattice constant of SRO is similar to that of perovskite compounds such as PZT, BT, or KNN. Therefore, when using functional thin films containing such perovskite compounds, by providing an SRO film between the first electrode layer and the functional thin film, the crystallinity of the functional thin film deposited thereon can be further improved. In particular, functional thin films with thicknesses down to submicron levels are prone to crystal defects. By providing a first metal oxide film, even with a submicron thickness, functional thin films with fewer crystal defects can be deposited. However, the first metal oxide film is not a necessary component. If the thickness of the functional thin film is sufficiently large, a functional thin film with fewer crystal defects can be obtained even without the first metal oxide film.

[0079] The thickness of the first metal oxide film (SRO film) is preferably 1 nm or more and 100 nm or less, more preferably 3 nm or more and 80 nm or less, and even more preferably 5 nm or more and 60 nm or less. Furthermore, the first metal oxide film is preferably an epitaxial film formed on the first electrode layer, and even more preferably a (100) oriented epitaxial film. Additionally, preferably, the first metal oxide film is a single crystal film.

[0080] <Functional Thin Films>

[0081] The functional thin film is disposed on top of the alignment control film. That is, it can be disposed directly above the alignment control film, or it can be disposed on top of the alignment control film through other layers such as the first electrode layer and / or the first metal oxide film. The functional thin film is the main layer that constitutes the function of the laminated structure. The type of functional thin film is determined according to the application of the laminated structure. Examples of functional thin films include piezoelectric films, dielectric films, strong dielectric films, magnetic films, resistive films, or optical films.

[0082] Preferably, the functional film is a piezoelectric film. That is, preferably, the laminated structure is a piezoelectric device. Furthermore, this embodiment also aims to use the above-described laminated structure as a piezoelectric device. This piezoelectric device further includes a first electrode layer disposed on the aforementioned alignment control film, and a piezoelectric film disposed on the first electrode layer. When no other layer (film) is sandwiched between the first electrode layer and the piezoelectric film, the piezoelectric film is disposed directly above the first electrode layer. When other layers (films) such as a first metal oxide film are sandwiched, the piezoelectric film is disposed directly above the other layers. Additionally, as needed, the piezoelectric device may also include a first metal oxide film, a second metal oxide film, and / or a second conductive layer, as described later.

[0083] Piezoelectric films are the essential components that constitute the main body exhibiting the piezoelectric effect, and they function to convert electrical energy into mechanical energy. When pressure (force) is applied to a piezoelectric film, surface charges are generated on the upper and lower surfaces of the film through the direct piezoelectric effect, thereby creating a potential difference (voltage). Therefore, piezoelectric films can be used as sensors. Furthermore, when a potential difference (voltage) is applied to the upper and lower surfaces of the piezoelectric film, displacement occurs through the inverse piezoelectric effect. Therefore, piezoelectric films can be used as actuators.

[0084] Preferably, the piezoelectric film comprises at least one compound selected from the group consisting of lead zirconate titanate (Pb(Zr,Ti)O3; PZT), barium titanate (BaTiO3; BT), lithium niobate (LiNbO3; LN), lithium tantalate (LiTaO3; LT), sodium potassium niobate ((K,Na)NbO3; KNN), aluminum nitride (AlN), and zinc oxide (ZnO) as a main component. These compounds exhibit excellent piezoelectric properties. It should be noted that, in this specification, the main component refers to the heaviest component of the object, i.e., the component containing 50% by mass or more.

[0085] The thickness of the piezoelectric film is preferably 0.1 μm or more and 10 μm or less. When the piezoelectric film is too thin, its effect cannot be fully realized, and the resulting displacement may be small. On the other hand, when the piezoelectric film is too thick, it may be difficult to obtain a sufficiently monocrystalline piezoelectric film. The thickness is more preferably 0.3 μm or more and 6 μm or less, and even more preferably 0.5 μm or more and 4 μm or less.

[0086] Preferably, the first electrode layer and the functional thin film (such as a piezoelectric film) are monocrystalline films composed of single crystals. By making the first electrode layer a monocrystalline film, the functional thin film deposited thereon can also be a monocrystalline film. By being composed of a monocrystalline film, the properties of the functional thin film can be improved. For example, a piezoelectric film composed of a single crystal allows for complete alignment of the polarization direction throughout the film. Therefore, both electrical and mechanical properties can be improved. Specifically, the piezoelectric constant can be increased. Furthermore, compared to polycrystalline films, the dielectric constant can be suppressed, thus reducing power consumption, and when used as a sensor, it offers the advantage of high-precision output. Moreover, by monocrystalline formation, the interatomic bonding force is increased, thereby improving the temperature characteristics and reliability of the piezoelectric film.

[0087] Whether a functional thin film (such as a piezoelectric film) is a single-crystal film can be determined by using X-ray diffraction to examine its in-plane properties. Confirmed by scanning measurements. That is, if through in-plane... If a symmetrical peak is identified through scanning, the functional thin film can be determined to be a single-crystal film. For example, if it is a cubic crystal (100), a 4-fold symmetrical peak can be identified; if it is a hexagonal crystal (110), a 6-fold symmetrical peak can be identified. That is, if the peak is detected through in-plane scanning... If a symmetrical peak is identified for a specific surface during scanning, it can be determined that the functional thin film is a single-crystal film.

[0088] <Second metal oxide film>

[0089] Depending on the requirements, the laminated structure may also have a second metal oxide film on top of the functional thin film. The second metal oxide film is composed of strontium ruthenium oxide (SrRuO3; SRO). SrO is conductive. Therefore, the SRO film (second metal oxide film) can be used as part of the electrode layer (second electrode layer).

[0090] The thickness of the second metal oxide film (SRO film) is preferably 1 nm or more and 60 nm or less, more preferably 3 nm or more and 30 nm or less, and even more preferably 5 nm or more and 20 nm or less. In addition, the second metal oxide film is preferably an epitaxial film formed on a functional thin film, and even more preferably an epitaxial film with (100) orientation.

[0091] <Second Electrode Layer>

[0092] As needed, the laminated structure may also have a second electrode layer on top of the functional thin film and / or the second metal oxide film. The second electrode layer only needs to be conductive, and its material is not limited. For example, it is preferable to include at least one selected from the group consisting of platinum (Pt), molybdenum (Mo), ruthenium (Ru), aluminum (Al) and copper (Cu).

[0093] The thickness of the second electrode layer is preferably 1 nm or more and 200 nm or less, more preferably 3 nm or more and 150 nm or less, and even more preferably 10 nm or more and 120 nm or less. In addition, the second electrode layer is preferably an epitaxial film formed on a functional thin film and / or a second metal oxide film, and even more preferably an epitaxial film with (100) orientation.

[0094] The laminated structure may also include components other than the substrate, buffer layer, alignment control layer, first electrode layer, first metal oxide film, functional thin film, second metal oxide film, and second electrode layer described above. For example, it may also include a take-up electrode that is conductive to the first electrode layer and the second electrode layer, and a protective film disposed on the upper part of the device.

[0095] Alternatively, the laminated structure may also have a hollow portion where a portion of the substrate is missing. The constituent elements (buffer layer, alignment control layer, first electrode layer, first metal oxide film, functional thin film, second metal oxide film, and second electrode layer) existing on the hollow portion form a diaphragm structure. By providing the hollow portion, the properties of the functional thin film are sometimes improved. For example, when the functional thin film is a piezoelectric film, by providing the hollow portion, displacement based on the piezoelectric film can be effectively achieved.

[0096] <<2. Manufacturing Method of Layered Structures>>

[0097] The laminated structure of this embodiment can be manufactured as long as the above-described requirements are met, and its manufacturing method is not limited. However, the preferred manufacturing method includes the following steps: a step of preparing a substrate whose surface is at least composed of single crystals (substrate preparation step), a step of forming a buffer layer on the single crystal surface of the substrate (buffer layer forming step), and a step of forming an orientation control film containing zirconium oxide (ZrO2) as the main component on the formed buffer layer (orientation control film forming step). In addition, the buffer layer is formed at a film forming speed of 5 nm / min or more and 50 nm / min or less, and the orientation control film is formed at a film forming speed of 1 nm / min or more and 5 nm / min or less. The details of each step are described below.

[0098] <Substrate Preparation Process>

[0099] In the substrate preparation process, a substrate with at least a surface composed of single crystal is prepared. Details of the substrate are as described above. That is, the substrate is not limited to any particular type; examples include single-crystal Si substrates, SOI substrates, stainless steel (SUS) substrates, quartz glass substrates, single-crystal gallium nitride (GaN) substrates, single-crystal silicon carbide (SiC) substrates, or sapphire substrates with single-crystal gallium nitride (GaN) on their surface. Preferably, the substrate is a single-crystal Si substrate or an SOI substrate; particularly preferably, it is a single-crystal Si (100) substrate, a single-crystal Si (111) substrate, a (100) SOI substrate, or a (111) SOI substrate. By using such a substrate, an orientation control film with excellent crystallinity can be easily obtained.

[0100] <Buffer Layer Film Formation Process>

[0101] In the buffer layer deposition process, a buffer layer is deposited on the single-crystal surface of a prepared substrate. Deposition can be performed using electron beam evaporation. When depositing using electron beam evaporation, for example, the substrate is placed within the vacuum chamber of an evaporation apparatus. Then, oxygen (O2) gas is flowed under a high vacuum atmosphere with a fixed pressure within the vacuum chamber, and the buffer layer is deposited while the substrate is heated under this condition.

[0102] The buffer layer is deposited by electron beam evaporation at a relatively high deposition rate (rate) of 5 nm / min or higher and 50 nm / min or lower. When deposition is performed at a high rate, particle migration on the substrate is appropriately suppressed, thus achieving a fine structure containing both crystalline and amorphous phases. During buffer layer deposition, the substrate is preferably heated to a temperature of 200°C or higher and 450°C or lower. By performing film deposition at a temperature within this range, the formation of the aforementioned fine structure is promoted.

[0103] <Orientation-Controlled Film Formation Process>

[0104] In the orientation control film formation process, an orientation control film containing zirconium oxide (ZrO2) as the main component is formed on a buffer layer. Similar to the buffer layer formation process, the film can be formed using electron beam evaporation. Alternatively, the formation of the buffer layer and the orientation control film can be performed continuously using the same apparatus, or they can be performed separately.

[0105] An alignment control film is formed by electron beam evaporation at a relatively low deposition rate (rate) of 1 nm / min to 5 nm / min. When deposition is performed at a low rate, the heat generated by heating the substrate allows for particle migration on the substrate surface, resulting in an alignment control film with high crystallinity. During alignment control film formation, it is preferable to heat the substrate to a temperature of 450°C to 650°C. By performing film formation at a temperature within this range, improved crystallinity can be achieved.

[0106] In this way, a laminated structure comprising a substrate, a buffer layer, and an alignment control film can be obtained. The resulting laminated structure can be used for the deposition of functional thin films. That is, if functional thin films such as electrode layers and piezoelectric films are deposited on the alignment control film, devices such as piezoelectric devices can be manufactured.

[0107] <<3. Manufacturing apparatus for layered structures>>

[0108] The manufacturing apparatus for the laminated structure of the present invention is characterized by having a vacuum transport device and a multi-chamber assembly including a vacuum evaporation device and a sputtering device. By using this apparatus, continuous film formation by continuously performing evaporation and sputtering processes can be achieved, thereby improving productivity.

[0109] [Example]

[0110] The present invention will be further described in detail using the following embodiments and comparative examples. However, the present invention is not limited to the following embodiments.

[0111] [Experimental Example A]

[0112] In Experiment A, a laminated structure comprising a substrate, a buffer layer, and an orientation control film was fabricated and evaluated.

[0113] (1) Construction of layered structures

[0114] [Example A1]

[0115] In Example A1, an SOI (100) wafer is used as a substrate, and a buffer layer and an orientation control film are formed thereon.

[0116] First, a 6-inch diameter SOI (100) wafer was prepared. This SOI wafer has a three-layer structure consisting of a Si substrate, an insulating film (SiO2 film), and a surface Si layer. In addition, the main face is the (100) face. That is, the surface Si layer is (100) oriented.

[0117] Next, a zirconium oxide (ZrO2) film was deposited on the surface Si layer of the prepared SOI substrate using electron beam evaporation. The deposition was performed in two stages with varying conditions, and the ZrO2 films deposited in each stage were designated as a buffer layer and an orientation control film, respectively. The resulting ZrO2 film has a cubic crystal structure with a (100) orientation. The deposition conditions for the buffer layer and the orientation control film are shown below.

[0118] <Conditions for Buffer Layer Film Formation>

[0119] - Apparatus: Electron beam evaporation apparatus

[0120] - Pressure: 7.00 × 10 -3 Pa

[0121] - Evaporation source: ZrO2

[0122] - Accelerating voltage: 7.5kV

[0123] - Transmitting current: 1.80mA

[0124] - Oxygen flow rate: 10 sccm

[0125] - Substrate temperature: 300~400℃

[0126] - Film formation rate: 10 nm / min

[0127] ‐Film thickness: 4nm

[0128] <Orientation-Controlled Film Formation Conditions>

[0129] - Apparatus: Electron beam evaporation apparatus

[0130] - Pressure: 7.00 × 10 -3 Pa

[0131] - Evaporation source: ZrO2

[0132] - Accelerating voltage: 7.5kV

[0133] - Transmitting current: 1.80mA

[0134] - Oxygen flow rate: 10 sccm

[0135] - Substrate temperature: 500~600℃

[0136] - Film formation rate: 3 nm / min

[0137] ‐Film thickness: 60nm

[0138] [Example A2]

[0139] In Example A2, a Si (111) wafer was used as the substrate instead of an SOI (100) wafer. Furthermore, the thickness of the alignment control film was set to 1.0 μm. Otherwise, the laminated structure was fabricated in the same manner as in Example A1.

[0140] [Example A3 (Comparative Example)]

[0141] In Example A3, the buffer layer is not formed, and the orientation control film is formed directly on the substrate. Otherwise, the laminated structure is fabricated in the same manner as in Example A2.

[0142] (2) Evaluation and Results

[0143] The following is an evaluation of the various properties of the constructed layered structure.

[0144] <TEM Observation>

[0145] The cross-sections of the laminated structures obtained in Examples A1 to A3 were observed using transmission electron microscopy (TEM). Specifically, cross-sections of samples thinned to a thickness of less than 0.1 micrometers were observed under an accelerating voltage of 200 kV. It should be noted that transmission electron microscopy is a type of electron microscope that uses the following method: irradiating a sample thinned to a thickness of less than 0.1 micrometers with electron beams, and observing the spatial distribution of electron transmittance within the observed object based on the intensity of the transmitted electron beams, thereby resolving the internal structure. The magnification range can cover observations of objects with dimensions from tens of μm (hundreds of times) to observations of sub-nm atomic arrangement structures (millions of times), thus enabling the atomic-level microstructural analysis of cross-sections / interfaces of thin film laminated structures.

[0146] Figure 2-1 and Figure 2-2 A cross-sectional TEM image of the layered structure in Example A1 is shown. Additionally, Figure 3-1 and Figure 3-2 A cross-sectional TEM image of the stacked structure in Example A2 is shown. Here, Figure 2-1 and Figure 3-1 It is a TEM image magnified 2 million times. Figure 2-2 and Figure 3-2 It is a TEM image magnified 4 million times.

[0147] Both Example A1 and Example A2 have a buffer layer with a thickness of about 4 nm sandwiched between the substrate and the alignment control film. Figure 2-1 and Figure 3-1Furthermore, regions with blurred lattice images (amorphous regions) and regions where lattice images were clearly observed (crystalline regions) were identified within the buffer layer. Figure 2-2 and Figure 3-2 ).

[0148] Figure 4 A cross-sectional TEM image of the laminated structure of Example A3 is shown. The substrate is in contact with the alignment control film, and no buffer layer is observed between them.

[0149] Micro scratch test

[0150] Micro-scratch tests were performed on the laminated structures obtained in Examples A2 and A3 to determine the peel strength between the substrate and the alignment control film. The tests were conducted under the following conditions.

[0151] - Apparatus: Micro-scratch testing machine for thin films (RHESCA Corporation, CSR-2000)

[0152] - Scratch speed: 10 μm / s

[0153] - Measurement end time (set value): 60 seconds

[0154] - Load at the end of the measurement (set value): 300mN

[0155] - Excitation level: 100μm

[0156] - Sampling: 3600Hz

[0157] - Spring constant: 100g / mm

[0158] - Stylus diameter: 15μm

[0159] As a result of the micro-scratch test, the peel strength of Example A2 with a buffer layer was approximately 100 mN, while the peel strength of Example A3 without a buffer layer was approximately 50 mN. This result indicates that by providing a buffer layer, the adhesion between the substrate and the alignment control film is improved.

[0160] [Experimental Example B]

[0161] In Experiment B, a piezoelectric device was fabricated, consisting of a stacked structure with a piezoelectric film.

[0162] (1) Fabrication of layered structures (piezoelectric devices)

[0163] [Example B1]

[0164] In Example B1, a piezoelectric device is fabricated by sequentially forming a Pt film as the first electrode layer, an SRO film as the first metal oxide film, and a PZT film as the piezoelectric film on top of the orientation control film (ZrO2 film) of the stacked structure fabricated in Example A1.

[0165] First, a Pt film (first electrode layer) was sputtered onto the ZrO2 film formed in Example A1. The Pt film formed had a cubic crystal structure with (100) orientation and a thickness of 150 nm. The film was formed under the following conditions.

[0166] <Conditions for the formation of the first electrode layer>

[0167] - Device: DC sputtering device

[0168] - Target material: Pt

[0169] - Power: 100W

[0170] - Pressure: 3.20 × 10 -2 Pa

[0171] -Ar flow rate: 16 sccm

[0172] - Substrate temperature: 400℃

[0173] - Film deposition rate: 0.14 nm / s

[0174] ‐Film thickness: 150nm

[0175] Next, an SRO film (first metal oxide film) was sputtered onto the Pt film. The SRO film after deposition had a cubic crystal structure with (100) orientation and a thickness of 40 nm. The deposition was carried out under the following conditions.

[0176] <Conditions for the Formation of First Metal Oxide Films>

[0177] - Apparatus: RF magnetron sputtering apparatus

[0178] - Target material: Strontium ruthenium oxide (SrRuO3; SRO)

[0179] - Power: 300W

[0180] - Gas: Ar

[0181] - Pressure: 1.8 Pa

[0182] - Substrate temperature: 600℃

[0183] - Film formation rate: 0.11 nm / s

[0184] ‐Film thickness: 40nm

[0185] A PZT film (piezoelectric film) was formed on top of the SRO film. The film formation was performed using the Sol-Gel method. Specifically, firstly, the raw material solution was prepared by dissolving an organometallic compound of Pb, Zr, and Ti in a mixed solvent of ethanol and 2-n-Butoxyethanol. At this point, the organometallic compound of Pb, Zr, and Ti was formulated to a composition ratio (mol ratio) of Pb:Zr:Ti = 100+δ:52:48. Furthermore, a Pb(Zr)T film was prepared as a PZT film. 0.52 Ti 0.48 The concentration of O3 was adjusted to 0.35 mol / L in the raw material solution. Here, δ represents the amount of remaining Pb considering the volatilization of Pb oxide during subsequent heat treatment; in this embodiment, δ = 20. Then, 20 g of polypyrrolidone with a K value of 27–33 was dissolved in the raw material solution.

[0186] Next, 3 ml of the prepared raw material solution was dropped onto the first metal oxide film (SRO film) of the substrate, and the substrate was rotated at 3000 rpm for 10 seconds to coat the raw material solution onto the substrate. This formed a film containing the precursor. Then, the substrate with the precursor-containing film was placed on a hot plate at 200°C for 30 seconds, and then on a hot plate at 450°C for 30 seconds to dry the film. Afterwards, the film was heat-treated at 600–700°C for 60 seconds in an oxygen (O2) atmosphere of 0.2 MPa to oxidize and crystallize the precursor. Then, the process from coating the raw material solution to crystallization was repeated an arbitrary number of times until the desired film thickness was achieved, thus forming a piezoelectric film (PZT film).

[0187] The PZT film after deposition was oriented in a (001) pattern and had a thickness of 2 μm. Furthermore, the composition of the PZT film was Pb(Zr) 0.52 Ti 0.48 )O3.

[0188] [Example B2]

[0189] In Example B2, on the orientation control film (ZrO2 film) of the stacked structure fabricated in Example A2, a Pt film as the first electrode layer and a LiNbO3 film as the piezoelectric film are further formed in sequence to fabricate a piezoelectric device.

[0190] First, a Pt film (first electrode layer) was sputtered onto the ZrO2 film formed in Example A2. The film was formed under the following conditions.

[0191] <Conditions for the formation of the first electrode layer>

[0192] - Device: DC sputtering device

[0193] - Target material: Pt

[0194] - Power: 100W

[0195] - Pressure: 1.20 × 10 -1 Pa

[0196] - Substrate temperature: 450~600℃

[0197] ‐Film thickness: 150nm

[0198] Next, a LiNbO3 film (piezoelectric film) was sputtered onto the Pt film. The film was formed under the following conditions.

[0199] <Conditions for Piezoelectric Film Formation>

[0200] - Apparatus: RF sputtering apparatus

[0201] - Target material: LiNbO3

[0202] - Power: 1000W

[0203] - Gas: Ar / O2

[0204] - Pressure: 2 Pa

[0205] - Substrate temperature: 450℃

[0206] ‐Film thickness: 500nm

[0207] [Example B3]

[0208] In Example B3, an AlN film was formed as a piezoelectric film instead of a LiNbO3 film. Otherwise, the piezoelectric device was fabricated following the same steps as in Example B2. The AlN film was formed under the following conditions.

[0209] <Conditions for Piezoelectric Film Formation>

[0210] - Device: DC sputtering device

[0211] - Target material: Al

[0212] - Power: 450W

[0213] - Gas: Ar / N2

[0214] - Pressure: 2 Pa

[0215] - Substrate temperature: 450℃

[0216] ‐Film thickness: 600nm

[0217] [Example B4]

[0218] In Example B4, a BaTiO3 film was formed as a piezoelectric film instead of a LiNbO3 film. Otherwise, the piezoelectric device was fabricated following the same steps as in Example B2. The BaTiO3 film was formed under the following conditions.

[0219] <Conditions for Piezoelectric Film Formation>

[0220] - Apparatus: RF sputtering apparatus

[0221] - Target material: BaTiO3

[0222] - Power: 450W

[0223] - Gas: Ar / O2

[0224] - Pressure: 2 Pa

[0225] - Substrate temperature: 450℃

[0226] ‐Film thickness: 600nm

[0227] (2) Evaluation and Results

[0228] The following is an evaluation of the various properties of the fabricated layered structure (piezoelectric device).

[0229] <TEM Observation>

[0230] The cross-sections of the laminated structures obtained in Examples B1–B4 were observed using transmission electron microscopy (TEM). For the cross-sections of samples thinned to a thickness of less than 0.1 μm, TEM observation was performed under an accelerating voltage of 200 kV.

[0231] Figure 5 (Example B1), Figure 6 (Example B2) Figure 7 (Example B3) and Figure 8 (Example B4) shows the obtained TEM image.

[0232] In the laminated structure of Example B1, the individual layers of the substrate (SOI(100)), buffer layer (ZrO2), alignment control film (ZrO2), first electrode layer (Pt), first metal oxide film (SRO), and piezoelectric film (PZT) are clearly observed. Figure 5 (Left image). Additionally, regions with blurred lattice images (amorphous regions) and regions where lattice images are clearly observed (crystalline regions) were identified within the buffer layer. Figure 5 (The image on the right).

[0233] In the laminated structures of Examples B2 to B4, it is clearly observed that each layer of the substrate (Si(111)), buffer layer (ZrO2), alignment control film (ZrO2), first electrode layer (Pt), and piezoelectric film (LiNbO3, AlN, BaTiO3) is present. Figures 6-8 (Left image). Additionally, regions with blurred lattice images (amorphous regions) and regions where lattice images are clearly observed (crystalline regions) were identified within the buffer layer. Figures 6-8 (The image on the right).

[0234] <XRD>

[0235] The laminated structure obtained in Example B3 was analyzed by X-ray diffraction (XRD) using an X-ray diffraction apparatus (Rigaku Corporation, SmartLab). During the analysis, ω-2θ and Φ scans were performed. It should be noted that the Φ scan was a measurement method used to investigate whether the thin film exhibited in-plane orientation.

[0236] Figure 9 The XRD spectrum obtained by ω-2θ scanning is shown. The horizontal axis of this spectrum (graph) represents the angle 2θ (20° ≤ 2θ ≤ 60°) in the ω-2θ scan, and the horizontal axis represents the X-ray intensity. According to... Figure 9 It was confirmed that the Pt film (first electrode layer) is a Pt (111) single-oriented film and the AlN film (piezoelectric film) is an AlN (002) single-oriented film.

[0237] Figure 10 The XRD spectrum obtained by Φ scanning is shown. Six equally spaced diffraction peaks were observed. This indicates that the AlN film is a 3-axis epitaxial film with not only c-axis orientation towards the substrate normal but also in-plane orientation.

[0238] For the Pt film and PZT film in Example B1, Φ scanning was performed in the same manner as for the AlN film in Example B3. It should be noted that the Φ scanning of the Pt film was performed before the formation of the SRO film (first metal oxide film) and the PZT film (piezoelectric film).

[0239] Figure 11 (Pt membrane) and Figure 12 The results are shown for the PZT film. Equally spaced diffraction peaks were also observed for both the Pt and PZT films. Therefore, it is confirmed, similar to the AlN film, that the Pt and PZT films are also 3-axis oriented epitaxial films.

[0240] <Peeling Test>

[0241] Repeated peel tests were performed on the piezoelectric device (laminated structure) obtained in Example B1. The tests were conducted according to IEC 60454-2 using transparent pressure-sensitive tape with a width of 25±1.5 mm and an adhesive strength of 10±1 N.

[0242] In repeated peeling tests, no clear peeling was observed even after more than 10 tests.

Claims

1. A layered structure, wherein, The stacked structure comprises: A substrate, the surface of which is at least composed of single crystals; and A crystal orientation control film comprising zirconium oxide (ZrO2) as the main component disposed on the single crystal surface of the substrate. A buffer layer comprising a mixed phase of crystalline and amorphous phases and containing zirconium oxide (ZrO2) as the main component is sandwiched between the substrate and the orientation control film.

2. The layered structure according to claim 1, wherein, The thickness of the buffer layer is greater than 2nm and less than 10nm.

3. The layered structure according to claim 1, wherein, The substrate is a single-crystal Si substrate, SOI substrate, stainless steel (SUS) substrate, quartz glass substrate, single-crystal gallium nitride (GaN) substrate, single-crystal silicon carbide (SiC) substrate, or a sapphire substrate with single-crystal gallium nitride (GaN) disposed on its surface.

4. The layered structure according to claim 1, wherein, The orientation control film is a monocrystalline film.

5. The layered structure according to claim 1, wherein, The laminated structure is a piezoelectric device, which further comprises a first electrode layer disposed on the orientation control film and a piezoelectric film disposed on the first electrode layer.

6. The layered structure according to claim 5, wherein, The piezoelectric film comprises at least one compound selected from the group consisting of Pb(Zr,Ti)O3, BaTiO3, (Pb,La)(Zr,Ti)O3, LiNbO3, LiTaO3, (K,Na)NbO3, AlN, and ZnO as a main component.

7. The layered structure according to claim 5, wherein, The first electrode layer and the piezoelectric film are single-crystal films.

8. The use of the laminated structure of claim 1 in a piezoelectric device.

Images