Composite substrate

Abstract

Disclosed is a composite substrate which comprises a first piezoelectric layer, a second piezoelectric layer that is superposed on the first piezoelectric layer, and a supporting substrate that supports the first piezoelectric layer and the second piezoelectric layer, wherein: an amorphous layer is formed at a bonding interface between at least one of the first piezoelectric layer and the second piezoelectric layer and another layer; and the second piezoelectric layer, the first piezoelectric layer and the supporting substrate are sequentially stacked in this order.

Description

Composite PCB

[0001] The present invention relates to a composite substrate.

[0002] Conventionally, piezoelectric actuators that vibrate electromechanical transducer films have been put to practical use in droplet ejection heads of inkjet recording devices, etc. In recent years, they are also expected to be used in other applications (for example, MEMS mirror devices for head-up displays).

[0003] A known conventional method for manufacturing a piezoelectric actuator is to fabricate a composite substrate by bonding a piezoelectric element to a silicon substrate via a metal layer, and then use this composite substrate to construct a piezoelectric actuator (Patent Document 1).Another known technique is to fabricate a composite substrate by depositing a piezoelectric layer such as PZT on a silicon substrate by a sputtering method, and then use this composite substrate to construct a piezoelectric actuator (Patent Document 2).

[0004] Japanese Patent Publication No. 2007-271788 Japanese Patent Publication No. 2014-225596

[0005] In a composite substrate fabricated using the method disclosed in Patent Document 1, the piezoelectric element cannot be formed very thin so that it can be bonded to the silicon substrate. This poses a problem that miniaturization of the piezoelectric actuator is difficult. On the other hand, in a composite substrate fabricated using the method disclosed in Patent Document 2, the piezoelectric layer can be formed thin by film deposition, which is advantageous for miniaturizing the piezoelectric actuator. However, because film deposition is performed in a high-temperature environment, temperature changes after film deposition can easily cause deformation, such as warping, in the composite substrate. This poses a problem that it is difficult to thicken the piezoelectric layer.

[0006] For example, in the case of a piezoelectric actuator for a MEMS mirror device, when a relatively large amount of movement is required of the piezoelectric layer, it is necessary to achieve both miniaturization and piezoelectric characteristics. However, it is difficult to achieve this with the methods of Patent Documents 1 and 2.

[0007] The present invention has been made in view of the above, and a main object of the present invention is to provide a composite substrate having a piezoelectric layer that can achieve both miniaturization and piezoelectric characteristics.

[0008] A composite substrate according to a first aspect of the present invention includes a first piezoelectric layer and a second piezoelectric layer stacked on the first piezoelectric layer, with an amorphous layer formed at a bonding interface between at least one of the first piezoelectric layer and the second piezoelectric layer and another layer.A composite substrate according to a second aspect of the present invention includes a first piezoelectric layer and a second piezoelectric layer stacked on the first piezoelectric layer, with at least one of the first piezoelectric layer and the second piezoelectric layer directly bonded to the other layer.

[0009] According to the present invention, it is possible to provide a composite substrate having a piezoelectric layer that can achieve both miniaturization and piezoelectric characteristics.

[0010] FIG. 1 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a second embodiment of the present invention. FIG. 3 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a third embodiment of the present invention. FIG. 4 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a fourth embodiment of the present invention. FIG. 5 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a fifth embodiment of the present invention. FIG. 6 is a diagram showing an example of a composite substrate according to a fifth embodiment of the present invention, in which an opening is provided in the support substrate. FIG. 7 is a diagram showing an example of a composite substrate according to a fifth embodiment of the present invention, in which an opening is provided in the support substrate. FIG. 8 is a diagram showing an example of a composite substrate according to a fifth embodiment of the present invention, in which an opening is provided in the support substrate. FIG. 9 is a diagram showing an example of a composite substrate according to a fifth embodiment of the present invention, in which a hollow portion is provided in the support substrate. FIG. 10 is a diagram showing an example of a composite substrate according to a fifth embodiment of the present invention, in which a sacrificial layer is provided in the support substrate. FIG. 11 is a schematic cross-sectional view showing a schematic configuration of a composite substrate according to a sixth embodiment of the present invention. FIG. 12 is a diagram showing an example of a manufacturing process for a composite substrate according to a second embodiment of the present invention. FIG. 13 is a cross-sectional TEM observation photograph (50,000 magnification) of a composite substrate according to an example. FIG. 14 is a cross-sectional TEM observation photograph (400,000 magnification) of a composite substrate according to an example. FIG. 15 is a cross-sectional TEM observation photograph (2,000,000 magnification) of a composite substrate according to an example.

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. In addition, in order to clarify the description, the drawings may show the width, thickness, shape, etc. of each part more schematically than in the embodiments, but these are merely examples and do not limit the interpretation of the present invention.

[0012] A. Composite Substrate (A-1) First Embodiment Fig. 1 is a schematic cross-sectional view showing the overall configuration of a composite substrate according to a first embodiment of the present invention. The composite substrate 100 has a first piezoelectric layer 10 and a second piezoelectric layer 20 laminated on the first piezoelectric layer 10. The first piezoelectric layer 10 and the second piezoelectric layer 20 preferably have polarization directions opposite to each other, thereby forming a bimorph structure.

[0013] In the composite substrate 100, the first piezoelectric layer 10 and the second piezoelectric layer 20 are directly bonded to each other, and an amorphous layer is formed at the bonding interface during bonding. Specific examples of the first piezoelectric layer 10 and the second piezoelectric layer 20 and a bonding method therefor will be described later.

[0014] (A-2) Second Embodiment Fig. 2 is a schematic cross-sectional view showing the overall configuration of a composite substrate according to a second embodiment of the present invention. Compared to the composite substrate 100 described in the first embodiment, the composite substrate 110 further includes an electrode layer 30 disposed between the first piezoelectric layer 10 and the second piezoelectric layer 20. The electrode layer 30 is made of a conductive material such as a metal.

[0015] In the composite substrate 110, the first piezoelectric layer 10 or the second piezoelectric layer 20 and the electrode layer 30 are directly bonded to each other, and an amorphous layer is formed at the bonding interface during bonding. Specific examples of the electrode layer 30 and the bonding method therefor will be described later.

[0016] (A-3) Third Embodiment Fig. 3 is a schematic cross-sectional view showing the overall configuration of a composite substrate according to a third embodiment of the present invention. Compared to the composite substrate 110 described in the second embodiment, the composite substrate 120 has a bonding layer 40 instead of the electrode layer 30 disposed between the first piezoelectric layer 10 and the second piezoelectric layer 20. The bonding layer 40 is formed using, for example, an amorphous material.

[0017] In the composite substrate 120, the first piezoelectric layer 10 or the second piezoelectric layer 20 is directly bonded to the bonding layer 40, and an amorphous layer is formed at the bonding interface during bonding. Specific examples of the bonding layer 40 and the bonding method will be described later.

[0018] (A-4) Fourth Embodiment Fig. 4 is a schematic cross-sectional view showing the general configuration of a composite substrate according to a fourth embodiment of the present invention. Compared to the composite substrate 100 described in the first embodiment, the composite substrate 130 further includes a support substrate 50 that supports the first piezoelectric layer 10 and the second piezoelectric layer 20. The support substrate 50 may be made of any material.

[0019] In the composite substrate 130, the first piezoelectric layer 10 and the second piezoelectric layer 20 are directly bonded to each other, with an amorphous layer formed at the bonding interface during bonding. Similarly, the first piezoelectric layer 10 and the support substrate 50 are directly bonded to each other, with an amorphous layer formed at the bonding interface during bonding. Specific examples of the support substrate 50 and the bonding method therefor will be described later.

[0020] (A-5) Fifth Embodiment FIG. 5 is a schematic cross-sectional view showing the overall configuration of a composite substrate according to a fifth embodiment of the present invention. Compared to the composite substrate 130 described in the fourth embodiment, the composite substrate 140 further includes an electrode layer 31 disposed between the support substrate 50 and the first piezoelectric layer 10, and an electrode layer 32 disposed between the first piezoelectric layer 10 and the second piezoelectric layer 20. Similar to the electrode layer 30 of the composite substrate 110 described in the second embodiment, the electrode layers 31 and 32 are formed using a conductive material such as metal. Note that the support substrate 50 in the composite substrate 140 may have a structure such as that shown in FIGS. 6, 7, 8, and 9. FIGS. 6 and 7 each show an example of the composite substrate 140 according to the fifth embodiment of the present invention, in which an opening is provided in the support substrate 50. FIG. 8 shows an example of the composite substrate 140 according to the fifth embodiment of the present invention, in which a hollow portion is provided in the support substrate 50. FIG. 9 shows an example of the composite substrate 140 according to the fifth embodiment of the present invention, in which a sacrificial layer is provided in the support substrate 50 for subsequent removal.

[0021] In the composite substrate 140, the support substrate 50 or the first piezoelectric layer 10 and the electrode layer 31, and the first piezoelectric layer 10 or the second piezoelectric layer 20 and the electrode layer 32 are directly bonded to each other, with an amorphous layer formed at the bonding interface during bonding. Specific examples of the electrode layers 31 and 32 and the bonding method therefor will be described later.

[0022] (A-6) Sixth Embodiment Figure 10 is a schematic cross-sectional view showing the overall configuration of a composite substrate according to a sixth embodiment of the present invention. Compared to the composite substrate 140 described in the fifth embodiment, the composite substrate 150 has piezoelectric layers 11 and 12 having a common polarization direction instead of the first piezoelectric layer 10 and the second piezoelectric layer 20, and further has an electrode layer 33 formed on the surface of the piezoelectric layer 12. The electrode layer 33 is made of a conductive material such as a metal, similar to the electrode layer 30 of the composite substrate 110 described in the second embodiment.

[0023] In the composite substrate 150, the support substrate 50 or the piezoelectric layer 11 and the electrode layer 31, and the piezoelectric layer 11 or the piezoelectric layer 12 and the electrode layer 32 are directly bonded to each other, similar to the composite substrate 140 described in the fifth embodiment, and an amorphous layer is formed at the bonding interface during bonding.

[0024] The composite substrates 100 to 150 of the above-described embodiments are used, for example, as piezoelectric actuators, which are MEMS devices. Although not shown, the composite substrates 100 to 150 may further include any optional layers. The type, function, number, combination, and arrangement of such layers may be appropriately determined depending on the purpose. For example, the composite substrates 100 to 140 may further include an electrode layer 33 disposed on the second piezoelectric layer 20, similar to the composite substrate 150. This electrode layer 33 may be provided with, for example, a wiring layer. Furthermore, for example, in the composite substrates 100 to 120, an electrode may be formed on the exposed surface of the first piezoelectric layer 10. In the composite substrates 130, an electrode may be formed on the exposed surface of the first piezoelectric layer 10 formed by removing the support substrate 50 by etching or the like.

[0025] The composite substrates 100 to 150 can be manufactured in any suitable shape. In one embodiment, the composite substrates 100 to 150 can be manufactured in the form of a so-called wafer. The size of the composite substrates 100 to 150 can be appropriately set depending on the purpose, for example, with a wafer (substrate) diameter of 50 mm to 150 mm.

[0026] A-1. Piezoelectric Layer The first piezoelectric layer 10 and the second piezoelectric layer 20 (hereinafter simply referred to as "piezoelectric layer") are composed of, for example, a non-oriented polycrystalline material. Typically, the piezoelectric layer is composed of a sintered body. For example, grain boundaries can be confirmed in the piezoelectric layer using TEM observation. By adopting such a configuration, composite substrates 100-150 can be obtained that have piezoelectric layers that are both compact and have excellent piezoelectric properties. Specifically, since the piezoelectric layer can be formed independently, for example, internal stress due to interactions with other components during the formation of the piezoelectric layer is not generated, thereby suppressing deformation such as warping. Furthermore, by constructing the piezoelectric layer from a non-oriented polycrystalline material, the options for materials composing the piezoelectric layer are increased, allowing for a wider range of characteristics to be accommodated. Specifically, properties such as the piezoelectric constant, dielectric constant, electromechanical coupling coefficient, and Curie temperature can be finely adjusted to meet specific needs. Furthermore, piezoelectric layers can be formed at low cost, which can contribute to improving the reliability of the resulting composite substrates 100-150.

[0027] Here, "non-orientation" means that the degree of c-axis orientation determined by the Lotgering method is 80% or less, preferably 60% or less, more preferably 40% or less, even more preferably 20% or less, and particularly preferably 10% or less. The degree of c-axis orientation is calculated from the XRD profile obtained by measurement using an X-ray diffractometer using the following formula: （００ｌ） F （００ｌ） = (pp ０ ) / (1-p ０ )×100 p=ΣI(00l) / ΣI(hkl) p ０ =ΣI ０ (00l) / ΣI ０ (hkl) (I, I ０ indicates the diffraction intensity, and p, p ０ is calculated from the ratio of the diffraction intensity derived from the c-axis diffraction plane (001) to the diffraction intensity of the entire diffraction plane (hk1). I and p are values ​​obtained from the XRD profile of the piezoelectric film (piezoelectric substrate), and I ０ , p ０ is a value obtained from the XRD profile of a sample obtained by powdering the piezoelectric film (piezoelectric substrate).

[0028] Any suitable ferroelectric material can be used for the piezoelectric layer. Preferably, a PZT (lead zirconate titanate)-based compound is used. PZT-based compounds include not only binary PZT (PbZrO3-PbTiO3) consisting of lead titanate and lead zirconate with a perovskite structure, but also ternary PZT. By constructing the piezoelectric layer from a non-oriented polycrystalline material, the piezoelectric layer can contain ternary PZT. Using ternary PZT allows the resulting composite substrates 100-150 to accommodate diverse characteristics. Specifically, properties such as the piezoelectric constant, dielectric constant, electromechanical coupling coefficient, and Curie temperature can be finely adjusted to meet specific needs.

[0029] The atomic ratio of Zr to Ti (Zr / Ti) contained in the piezoelectric layer is preferably 0.7 or more and 2.0 or less, and more preferably 0.9 or more and 1.5 or less.

[0030] The ternary PZT is typically represented by ATiO3-PbZrO3-PbTiO3 or PbBO3-PbZrO3-PbTiO3, where A and B represent elements other than Pb, Zr, and Ti, respectively. Examples of element A contained in the third component of the ternary PZT include Li, Na, K, Bi, La, Ce, and Nd. Examples of element B contained in the third component of the ternary PZT include Li, Cu, Mg, Ni, Zn, Mn, Co, Sn, Fe, Cd, Sb, Al, Yb, In, Sc, Y, Nb, Ta, Bi, W, Te, and Re. These elements can be used alone or in combination.

[0031] The ratio of the third component to the total of Zr, Ti, Pb and the third component (element A and / or element B) contained in the piezoelectric layer, specifically, the atomic ratio of third component / (Zr+Ti+Pb+third component), is preferably 0.05 or more and 0.25 or less, and more preferably 0.10 or more and 0.20 or less.

[0032] The atomic ratio (proportion) can be determined by composition analysis using energy dispersive X-ray spectroscopy (EDX).

[0033] Other specific examples of materials that can be used to form the piezoelectric layer include PMN-PT (Pb(Mg1 / 3Nb2 / 3)O3-PbTiO3), barium titanate (BaTiO3), lead titanate (PbTiO3), lead metaniobate (PbNb2O6), bismuth titanate (Bi4Ti3O12), KNN ((K0.5Na0.5)NbO3), KNN-LN (((K0.5Na0.5)NbO3)-LiNbO3), and BT-BNT-BKT ((Bi0.5Na0.5)TiO3-(Bi0.5K0.5)TiO3-BaTiO3).

[0034] The piezoelectric layer may be formed from a single crystal, such as LiTaO3, LiNbO3, or quartz crystal.

[0035] The thickness of the piezoelectric layer is, for example, greater than 0.2 μm, preferably 0.3 μm or more, more preferably 1 μm or more, and even more preferably 3 μm or more. In one embodiment, the thickness of the piezoelectric layer may be 5 μm or more, or even 6 μm or more. With such a thickness, for example, a high-displacement actuator can be obtained with low-voltage drive. For example, when forming a piezoelectric layer by conventional film formation such as sputtering, it is difficult to achieve such a thickness due to factors such as the film stress and productivity of the resulting piezoelectric layer. In contrast, by constructing the piezoelectric layer from a non-oriented polycrystalline material as described above, such a thickness can be achieved. Furthermore, by constructing the piezoelectric layer from a non-oriented polycrystalline material, composite substrates 100 to 150 can be obtained that suppress the occurrence of warping, even at such a thickness. On the other hand, the thickness of the piezoelectric layer is, for example, 200 μm or less, preferably 150 μm or less, more preferably 100 μm or less, even more preferably 50 μm or less, and particularly preferably 20 μm or less. Such a thickness can suppress defects (e.g., cracks caused by heating) caused by a difference in thermal expansion with the support substrate, and can be used for, for example, a heating process (e.g., 100°C or higher) in the fabrication of a piezoelectric device. Specifically, it can be used for mask formation using photolithography or the like in the fabrication of a MEMS device.

[0036] As described above, the piezoelectric layer may be made of a sintered body. The sintered body may be formed by any appropriate method. In one embodiment, the sintered body may be formed by pressure sintering raw material powders. As a specific example, the sintered body may be formed by pressure sintering raw material powders mixed in a predetermined compounding ratio, or raw material powders mixed in a predetermined compounding ratio that have been calcined and then pulverized to a predetermined particle size (e.g., 0.1 μm to 10 μm). Any appropriate method may be used for pressure sintering. Specifically, a HIP method, a hot pressing method, or the like may be used.

[0037] The piezoelectric layer can be obtained, for example, by processing a sintered body (piezoelectric substrate) to a desired thickness, such as by grinding and polishing. In forming the piezoelectric layer, a polarization process is performed at any appropriate timing. In one embodiment, a pair of electrodes is provided on each of the opposing surfaces of a plate-shaped sintered body (piezoelectric substrate), and polarization is performed using an electric field in a direction from one electrode to the other electrode, followed by processing such as grinding and polishing to obtain the piezoelectric layer.

[0038] The arithmetic mean roughness Ra of the polished piezoelectric layer is preferably 2 nm or less, more preferably 1 nm or less, and even more preferably 0.3 nm or less.

[0039] A-2. Support Substrate Any appropriate substrate can be used as the support substrate 50. The support substrate 50 may be composed of a single crystal or a polycrystalline material. It may also be composed of a metal. The material constituting the support substrate 50 is preferably selected from the group consisting of silicon, sialon, sapphire, cordierite, mullite, glass, quartz, crystal, alumina, SUS, iron-nickel alloy (42 alloy), and brass.

[0040] The silicon may be single crystal silicon, polycrystalline silicon, or high-resistivity silicon. The support substrate 50 may be SOI (Silicon on Insulator).

[0041] Typically, the sialon is a ceramic obtained by sintering a mixture of silicon nitride and alumina, and has a composition represented by, for example, Si6-wAlwOwN8-w. Specifically, the sialon has a composition in which alumina is mixed into silicon nitride, and w in the formula represents the mixing ratio of alumina. w is preferably 0.5 or more and 4.0 or less.

[0042] Typically, the sapphire is a single crystal having a composition of Al2O3, and the alumina is a polycrystalline material having a composition of Al2O3. The alumina is preferably translucent alumina.

[0043] Typically, the cordierite is a ceramic having a composition of 2MgO.2Al2O3.5SiO2, and the mullite is a ceramic having a composition in the range of 3Al2O3.2SiO2 to 2Al2O3.SiO2.

[0044] When used as a piezoelectric actuator, a support substrate with an opening or hollow portion can be used to ensure efficient vibration. Examples are shown in Figures 6, 7, and 8. A support substrate with a sacrificial layer can also be used. An example is shown in Figure 9. By removing the sacrificial layer by etching after forming the composite substrate, it is possible to reduce cracking defects during fabrication of the composite substrate. Any appropriate configuration can be adopted for the sacrificial layer depending on the purpose. Examples of materials that can be used for the sacrificial layer include amorphous silicon, silicon, molybdenum, silicon oxide, aluminum oxide, compounds of these materials, and mixtures of these materials. Examples of methods for forming the sacrificial layer include sputtering, plating, and vapor deposition. Examples of methods for etching the sacrificial layer include wet etching and dry etching.

[0045] Any appropriate thickness can be adopted as the thickness of the support substrate 50. The thickness of the support substrate 50 is, for example, 100 μm to 1000 μm.

[0046] A-3. Bonding Layer Examples of materials that form the bonding layer 40 include silicon, tantalum oxide, niobium oxide, aluminum oxide, titanium oxide, and hafnium oxide. The thickness of the bonding layer 40 is, for example, 5 nm to 1 μm, and preferably 10 nm to 200 nm.

[0047] The bonding layer 40 is typically made of an amorphous material. Specifically, the bonding layer 40 may be an amorphous layer. By making the bonding layer 40 of an amorphous material, for example, polishing, which will be described later, becomes easier, and it becomes easier to obtain a suitable surface roughness for the bonding surface.

[0048] The bonding layer 40 can be formed by any suitable method, such as sputtering, vacuum deposition, physical vapor deposition such as ion beam assisted deposition (IAD), chemical vapor deposition, or atomic layer deposition (ALD). The bonding layer 40 can be formed at a temperature of, for example, room temperature (25° C.) to 300° C.

[0049] A-4. Electrode Layers Examples of materials that can be used to form the electrode layers 30 to 33 include metals such as Pt, Au, Ti, Cr, Ni, Mo, Al, Ru, and SRO, as well as compounds and oxides of these materials. These can be used alone or in combination of two or more.

[0050] In one embodiment, the electrode layers 30 to 33 are made of substantially the same material. Specifically, the electrode layers 30 to 33 have substantially the same composition. For example, in the composite substrate 140, the electrode layer 31 is made of a metal (e.g., Ti), and the electrode layer 32 is made of a metal (e.g., Ti). This configuration can be adopted by forming the piezoelectric layer from a non-oriented polycrystalline material. For example, when the piezoelectric layer is formed by film deposition, the adjacent layer (electrode) functions as a seed crystal layer for the piezoelectric layer and is made of a material having predetermined physical properties (e.g., lattice constant). In contrast, by forming the piezoelectric layer from a non-oriented polycrystalline material, the options for materials for the adjacent layers (electrodes) are increased, and materials can be selected from the perspectives of, for example, manufacturing efficiency and the characteristics of the resulting composite substrate (piezoelectric element).

[0051] The thickness of each of the electrode layers 30 to 33, which can function as an adhesive layer with the adjacent layers, is, for example, 1 nm to 100 nm, preferably 3 nm to 50 nm, and more preferably 5 nm to 20 nm.

[0052] The electrode layers 30 to 33 can be formed by any suitable method. For example, they can be formed by physical vapor deposition such as sputtering, vacuum evaporation, or ion beam assisted deposition (IAD). In one embodiment, the electrode layers 30 to 33 can be formed by sputtering using the same target (e.g., a Ti target) under the same conditions. The electrode layers 30 to 33 can be formed at, for example, room temperature (25°C) to 300°C.

[0053] A-5. Manufacturing Method The composite substrates 100 to 150 can be obtained by, for example, bonding (directly bonding) piezoelectric layers made of sintered bodies together or a piezoelectric layer and a support substrate 50 .

[0054] 11A and 11B are diagrams showing an example of a manufacturing process for a composite substrate 110 according to a second embodiment, as an example of a manufacturing process for the composite substrates 100 to 150. Fig. 11A shows a film formation process among the manufacturing processes for the composite substrate 110. In this film formation process, an electrode layer 30 is formed by film formation on the surface of a piezoelectric substrate 70, which is a bulk sintered body and has been subjected to polarization treatment.

[0055] 11( b) shows the bonding step of the manufacturing process of the composite substrate 110. In this bonding step, the electrode layer 30 formed on the piezoelectric substrate 70 in the film formation step of FIG. 11( a) and the first piezoelectric layer 10, which has been polarized and also serves as a support substrate, are brought into contact with each other after their bonding surfaces have been activated by any appropriate activation process, and are then directly bonded by applying pressure at room temperature. At this time, the piezoelectric substrate 70 and the first piezoelectric layer 10 are positioned such that the polarization directions of the piezoelectric substrate 70 and the first piezoelectric layer 10 are opposite to each other.

[0056] In one embodiment, an element (e.g., argon) constituting the gas used in the activation process is contained near the bonding interface between the electrode layer 30 and the first piezoelectric layer 10. Specifically, at least one end of the electrode layer 30 and the first piezoelectric layer 10, which face each other across the bonding interface, is an amorphous region (a region containing a non-crystalline body, an amorphous layer) containing the element constituting the gas used in the activation process. The thickness of such an amorphous region is, for example, 2 nm to 30 nm. The argon concentration in the amorphous region is, for example, 0.5 atm% to 30 atm%. The distribution of argon in the amorphous region is not particularly limited, but, for example, in the amorphous region, the argon concentration increases toward the bonding interface.

[0057] 11(c) shows a polishing step in the manufacturing process of the composite substrate 110. In this polishing step, the piezoelectric substrate 70 bonded to the first piezoelectric layer 10 via the electrode layer 30 in the bonding step of FIG. 11(b) is subjected to processing such as grinding and polishing until it has a desired thickness, thereby forming the second piezoelectric layer 20. In this way, the composite substrate 110 is manufactured.

[0058] In one embodiment, the piezoelectric substrate 70 is subjected to processing such as grinding and polishing so that the thickness of the resulting second piezoelectric layer 20 exceeds 0.2 μm. According to this embodiment, shedding of crystals constituting the second piezoelectric layer 20 and peeling of the second piezoelectric layer 20 can be suppressed without weakening the bonding strength of the grain boundaries of the resulting second piezoelectric layer 20 or the bonding strength with the support substrate due to processing load.

[0059] 11 shows an example of the manufacturing process for the composite substrate 110 according to the second embodiment, but the composite substrates described in the other embodiments can also be manufactured using similar manufacturing processes. However, in the composite substrate 100 according to the first embodiment, the first piezoelectric layer 10 and the second piezoelectric layer 20 are directly bonded to each other, so the film formation process shown in FIG. 11( a) is omitted. In the composite substrate 120 according to the third embodiment, in the film formation process shown in FIG. 11( a), a bonding layer 40 is formed by film formation instead of the electrode layer 30, and the bonding layer 40 and the first piezoelectric layer 10 are directly bonded to each other, with an amorphous layer being formed at the bonding interface.

[0060] Furthermore, in the composite substrate 130 according to the fourth embodiment, the support substrate 50 and the piezoelectric substrate 70 are used, and the bonding process shown in FIG. 11B and the polishing process shown in FIG. 11C are performed to form the first piezoelectric layer 10 with a desired thickness on the support substrate 50, and an amorphous layer is formed at the bonding interface between the support substrate 50 and the first piezoelectric layer 10. Thereafter, the bonding process shown in FIG. 11B and the polishing process shown in FIG. 11C are performed again to form the second piezoelectric layer 20 with a desired thickness on the first piezoelectric layer 10, and an amorphous layer is formed at the bonding interface between the first piezoelectric layer 10 and the second piezoelectric layer 20. As described above, the positions of the piezoelectric substrate 70 for forming the second piezoelectric layer 20 and the first piezoelectric layer 10 are determined so that their polarization directions are opposite to each other. However, in the composite substrate 130 according to the fourth embodiment, the support substrate 50 and the first piezoelectric layer 10, and the first piezoelectric layer and the second piezoelectric layer 20 are directly bonded, and therefore the film formation process of FIG. 11(a) is omitted.

[0061] In addition, in the composite substrate 140 according to the fifth embodiment and the composite substrate 150 according to the sixth embodiment, a support substrate 50 and a piezoelectric substrate 70 are used, and the film formation process of FIG. 11( a), the bonding process of FIG. 11( b), and the polishing process of FIG. 11( c) are performed, whereby the first piezoelectric layer 10 or the piezoelectric layer 11 is formed with a desired thickness on the support substrate 50 with the electrode layer 31 sandwiched therebetween, and an amorphous layer is formed at the bonding interface between the electrode layer 31 and the first piezoelectric layer 10 or the bonding interface between the electrode layer 31 and the first piezoelectric layer 11. 11( a), the bonding process of FIG. 11( b), and the polishing process of FIG. 11( c) are then performed again, thereby forming the second piezoelectric layer 20 or piezoelectric layer 12 to a desired thickness on the first piezoelectric layer 10 or piezoelectric layer 11, with the electrode layer 32 sandwiched therebetween, and forming an amorphous layer at the bonding interface between the electrode layer 32 and the second piezoelectric layer 20 or the bonding interface between the electrode layer 32 and the second piezoelectric layer 12. As described above, in the composite substrate 140, the orientations of the piezoelectric substrate 70 for forming the second piezoelectric layer 20 and the first piezoelectric layer 10 are determined so that their polarization directions are opposite to each other. On the other hand, in the composite substrate 150, after the piezoelectric layer 12 is formed, the film formation process of FIG. 11( a) is further performed to form the electrode layer 33.

[0062] In the composite substrates 100 to 150, the surface of each layer (specifically, the support substrate 50, the first piezoelectric layer 10, the second piezoelectric layer 20, the electrode layers 30 to 32, or the bonding layer 40) is preferably flat. Specifically, the arithmetic mean roughness Ra of the surface of each layer is, for example, 5 nm or less, preferably 2 nm or less, more preferably 1 nm or less, and even more preferably 0.3 nm or less. Methods for flattening the surface of each layer include, for example, mirror polishing by chemical mechanical polishing (CMP), lap polishing, or the like.

[0063] During the above-mentioned film-forming process and bonding process, it is preferable to clean the surface of each layer, for example, to remove abrasive residue. Examples of cleaning methods include wet cleaning, dry cleaning, and scrub cleaning. Among these, scrub cleaning is preferred because it allows for simple and efficient cleaning. A specific example of scrub cleaning is a method in which a cleaning agent (e.g., Sunwash series manufactured by Lion Corporation) is used, followed by cleaning with a scrub cleaner using a solvent (e.g., a mixed solution of acetone and isopropyl alcohol (IPA)).

[0064] The activation process is typically performed by irradiating a neutralizing beam. Preferably, a neutralizing beam is generated using an apparatus such as that described in JP 2014-086400 A, and the activation process is performed by irradiating this beam. Specifically, a saddlefield-type fast atom beam source is used as the beam source, an inert gas such as argon or nitrogen is introduced into a chamber, and a high voltage is applied to the electrode from a DC power supply. This generates a saddlefield-type electric field between the electrode (positive electrode) and the housing (negative electrode), causing electrons to move and generating a beam of atoms and ions from the inert gas. Of the beams that reach the grid, the ion beam is neutralized by the grid, and a beam of neutral atoms is emitted from the fast atom beam source. The voltage during the activation process by beam irradiation is preferably 0.5 kV to 2.0 kV, and the current during the activation process by beam irradiation is preferably 50 mA to 200 mA.

[0065] The contact and pressure application of the bonding surfaces is preferably carried out in a vacuum atmosphere. The temperature at this time is typically room temperature. Specifically, the temperature is preferably 20°C or higher and 40°C or lower, and more preferably 25°C or higher and 30°C or lower. The pressure applied is preferably 100N to 20,000N.

[0066] 11 , the composite substrate 110 is obtained by bonding the piezoelectric substrate 70, on which the electrode layer 30 is formed by film deposition, to the first piezoelectric layer 10, but is not limited to this configuration. For example, the electrode layer 30 may be provided on the first piezoelectric layer 10, and then the electrode layer 30 formed on the first piezoelectric layer 10 may be bonded to the piezoelectric substrate 70. The same applies to the other embodiments.

[0067] In the bonding process, at least one of the first piezoelectric layer 10 and the second piezoelectric layer 20 is bonded to another layer, which may result in the formation of an amorphous layer at the bonding interface between the piezoelectric layer and the other layer. Specifically, in the composite substrate 100 of the first embodiment and the composite substrate 130 of the fourth embodiment, an amorphous layer may be formed at the bonding interface between the first piezoelectric layer 10 and the second piezoelectric layer 20. In the composite substrate 110 of the second embodiment and the composite substrate 140 of the fifth embodiment, the electrode layers 30, 32 are disposed between the first piezoelectric layer 10 and the second piezoelectric layer 20, and an amorphous layer may be formed at the bonding interface between the first piezoelectric layer 10 or the second piezoelectric layer 20 and the electrode layers 30, 32. Similarly, in the composite substrate 120 of the third embodiment, a bonding layer 40 is disposed between the first piezoelectric layer 10 and the second piezoelectric layer 20, and an amorphous layer can be formed at the bonding interface between the first piezoelectric layer 10 or the second piezoelectric layer 20 and the bonding layer 40.

[0068] Hereinafter, as an example for verifying the structure of the composite substrate according to the present invention, an example of a composite substrate in which a piezoelectric layer is directly bonded onto a support substrate will be specifically described. Unless otherwise specified, the following procedures were carried out at room temperature.

[0069] PbZrO powder, PbTiO powder, NbO powder, and ZnO powder were mixed in a ball mill using water as a dispersant, and the resulting mixture was dried and calcined in air (at 900°C for 2 hours). This mixture was then wet-pulverized again in a ball mill for 20 hours to obtain a powder with a particle size of approximately 1 μm. This powder was then press-molded into a compact.

[0070] The obtained compact was pre-fired in air at 1250°C for 2 hours. After firing, it was cooled in air to obtain a pre-fired body. The obtained pre-fired body was embedded in a container filled with a mixed powder of PbO and ZrO2, and the container was covered with a lid. The container was then placed in an internally heated high-temperature, high-pressure furnace, heated from room temperature to 1100°C over 4.5 hours, and subjected to hot isostatic pressing (HIP). Specifically, during heating, the pressure was increased to 280 bar at 1000°C, and once the temperature exceeded 1000°C, the pressure was increased from 280 bar to 600 bar over 1 hour. The pressure was then maintained at 1100°C and 600 bar for 1 hour to perform hot isostatic pressing. In this way, a plate-shaped sintered body was obtained.

[0071] Electrodes were formed on the top and bottom surfaces of the obtained sintered body, and a predetermined voltage was applied to perform a polarization treatment. Thereafter, the sintered body was subjected to beveling, grinding, and lap polishing to obtain a wafer (piezoelectric substrate) having a first surface and a second surface facing each other, a diameter of 4 inches, and a thickness of 500 μm.

[0072] The first surface of the obtained piezoelectric substrate was polished by chemical mechanical polishing (CMP) to a mirror finish having an arithmetic mean roughness Ra of less than 2 nm, where Ra is a value measured with an atomic force microscope (AFM) in a field of view of 10 μm × 10 μm.

[0073] On a first surface of a mirror-finished piezoelectric substrate, a 10 nm thick Ti film, a 100 nm thick Pt film, a 10 nm thick Ti film, and a 150 nm thick silicon film were formed in this order by sputtering. The surface of the silicon film was then subjected to chemical mechanical polishing (CMP) to achieve an arithmetic mean roughness Ra of 0.2 nm.

[0074] A silicon substrate (support substrate) having an orientation flat portion, a diameter of 4 inches, and a thickness of 500 μm was prepared. The surface of this silicon substrate was subjected to chemical mechanical polishing (CMP), and the arithmetic mean roughness Ra was 0.2 nm.

[0075] Next, the piezoelectric substrate and the support substrate were directly bonded. Specifically, after cleaning the surface of the piezoelectric substrate (the silicon film side) and the surface of the support substrate, both substrates were placed in a vacuum chamber and heated for 10 minutes. －６ After evacuation to the Pa range, the surfaces of both substrates were irradiated with a fast atom beam (accelerating voltage 1 kV, Ar flow rate 27 sccm) for 120 seconds. After irradiation, the beam-irradiated surfaces of both substrates were placed together and pressed with 10,000 N for 2 minutes to bond the two substrates together, obtaining a bonded assembly.

[0076] Next, the second surface of the piezoelectric substrate of the resulting bonded body was ground and polished to obtain a composite substrate having a piezoelectric layer with a thickness of 10 μm.

[0077] <TEM Observation> The cross section of the composite substrate prepared above was observed with a transmission electron microscope (TEM) (50,000x, 400,000x, and 2,000,000x magnification). The observed photographs are shown in Figures 12A, 12B, and 12C. For the cross-sectional TEM observation, an observation sample was prepared from the obtained composite substrate by the FIB method.

[0078] <EDX Analysis> When the cross section of the composite substrate was analyzed by EDX, the argon concentration in the layer indicated by the arrow in FIG. 12C (amorphous layer formed by activation treatment) was 3.0 atm %.

[0079] The above example confirmed the structure of a composite substrate in which a 10 μm-thick piezoelectric layer and a silicon substrate serving as a support substrate are directly bonded together, sandwiching a metal film (Ti film, Pt film) acting as an electrode layer and a silicon film acting as a bonding layer between them. In this composite substrate, an amorphous layer is formed by activation treatment at the bonding interface between the support substrate and the bonding layer (the area indicated by the arrow in Figure 12C). Therefore, it was confirmed that the aforementioned composite substrates 100 to 150 can be fabricated using the same process.

[0080] According to the embodiment of the present invention described above, the following advantageous effects are achieved.

[0081] (1) The composite substrates 100 to 150 each have a first piezoelectric layer 10 and a second piezoelectric layer 20 laminated on the first piezoelectric layer 10, with an amorphous layer formed at the bonding interface between at least one of the first piezoelectric layer 10 and the second piezoelectric layer 20 and another layer. In other words, at least one of the first piezoelectric layer 10 and the second piezoelectric layer 20 is directly bonded to the other layer. This configuration makes it possible to provide a composite substrate having a piezoelectric layer that can achieve both miniaturization and piezoelectric characteristics.

[0082] (2) In the composite substrates 100 and 130, an amorphous layer is formed at the bonding interface between the first piezoelectric layer 10 and the second piezoelectric layer 20. That is, the first piezoelectric layer 10 and the second piezoelectric layer 20 are directly bonded to each other. In addition, the composite substrates 110, 120, 140, and 150 have an electrode layer 30, 32 or a bonding layer 40 disposed between the first piezoelectric layer 10 (piezoelectric layer 11) and the second piezoelectric layer 20 (piezoelectric layer 12), and an amorphous layer is formed at the bonding interface between the first piezoelectric layer 10 (piezoelectric layer 11) or the second piezoelectric layer 20 (piezoelectric layer 12) and the electrode layer 30, 32 or the bonding layer 40. That is, the first piezoelectric layer 10 (piezoelectric layer 11) or the second piezoelectric layer 20 (piezoelectric layer 12) and the electrode layer 30, 32 or the bonding layer 40 are directly bonded to each other. Furthermore, the composite substrates 130, 140, and 150 each have a support substrate 50 that supports the first piezoelectric layer 10 (piezoelectric layer 11) and the second piezoelectric layer 20 (piezoelectric layer 12). In this manner, the composite substrates 100 to 150 can be fabricated with any layer structure.

[0083] (3) The support substrate 50 can be made of any of silicon, SOI, sialon, sapphire, cordierite, mullite, glass, quartz, crystal, alumina, SUS, iron-nickel alloy (42 alloy), and brass. In this way, the support substrate 50 can be made of any material depending on the application.

[0084] (4) At least one of the first piezoelectric layer 10 and the second piezoelectric layer 20 preferably has a thickness of 50 μm or less. This allows for miniaturization when constructing a piezoelectric actuator using the composite substrates 100 to 150.

[0085] (5) The first piezoelectric layer 10 and the second piezoelectric layer 20 are polarized in opposite directions, thereby forming a composite substrate with a bimorph structure.

[0086] (6) The first piezoelectric layer 10 and the second piezoelectric layer 20 can each be made of any of PZT, PMN-PT, barium titanate, lead titanate, lead metaniobate, bismuth titanate, KNN, KNN-LN, BT-BNT-BKT, LiTaO3, LiNbO3, and quartz. The first piezoelectric layer 10 and the second piezoelectric layer 20 can also each be made of a polycrystalline material. This allows the first piezoelectric layer 10 and the second piezoelectric layer 20 to be made of any material depending on the application.

[0087] The present invention is not limited to the above-described embodiment, and can be implemented using any components without departing from the spirit of the present invention.

[0088] The above-described embodiments and modifications are merely examples, and the present invention is not limited to these details as long as the features of the invention are not impaired. Furthermore, although various embodiments and modifications have been described above, the present invention is not limited to these details. Other aspects that can be considered within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention.

[0089] 10: First piezoelectric layer 11, 12: Piezoelectric layers 20: Second piezoelectric layer 30, 31, 32, 33: Electrode layers 40: Bonding layer 50: Support substrate 70: Piezoelectric substrate 100, 110, 120, 130, 140, 150: Composite substrate

Claims

1. A first piezoelectric layer; a second piezoelectric layer disposed in a stacked manner on the first piezoelectric layer; a support substrate supporting the first piezoelectric layer and the second piezoelectric layer; an amorphous layer is formed at a bonding interface between at least one of the first piezoelectric layer and the second piezoelectric layer and another layer; the second piezoelectric layer, the first piezoelectric layer, and the support substrate are laminated in this order; A composite substrate, wherein the first piezoelectric layer and the second piezoelectric layer are each composed of a single crystal or a non-oriented polycrystalline material.

2. A first piezoelectric layer; a second piezoelectric layer disposed in a stacked manner on the first piezoelectric layer, an amorphous layer is formed at a bonding interface between at least one of the first piezoelectric layer and the second piezoelectric layer and another layer; The first piezoelectric layer and the second piezoelectric layer have polarization directions opposite to each other, A composite substrate, wherein the first piezoelectric layer and the second piezoelectric layer are each composed of a single crystal or a non-oriented polycrystalline material.

3. The composite substrate according to claim 1 or 2, A composite substrate, wherein the amorphous layer is formed at a bonding interface between the first piezoelectric layer and the second piezoelectric layer.

4. The composite substrate according to claim 1 or 2, an electrode layer or a bonding layer disposed between the first piezoelectric layer and the second piezoelectric layer; A composite substrate, wherein the amorphous layer is formed at a bonding interface between the first piezoelectric layer or the second piezoelectric layer and the electrode layer or the bonding layer.

5. 2. The composite substrate according to claim 1 , The support substrate is a composite substrate made of any one of silicon, SOI, sialon, sapphire, cordierite, mullite, glass, quartz, crystal, alumina, SUS, iron-nickel alloy (42 alloy), and brass.

6. The composite substrate according to claim 1 or 2, At least one of the first piezoelectric layer and the second piezoelectric layer has a thickness of 50 μm or less.

7. 2. The composite substrate according to claim 1 , A composite substrate, wherein the first piezoelectric layer and the second piezoelectric layer have polarization directions opposite to each other.

8. The composite substrate according to claim 1 or 2, A composite substrate, wherein the first piezoelectric layer and the second piezoelectric layer are each composed of a non-oriented polycrystalline material selected from the group consisting of PZT, PMN-PT, barium titanate, lead titanate, lead metaniobate, bismuth titanate, KNN, KNN-LN, and BT-BNT-BKT, or a single crystalline material selected from the group consisting of LiTaO3, LiNbO3, and quartz.

9. (delete)

10. A first piezoelectric layer; a second piezoelectric layer disposed in a stacked manner on the first piezoelectric layer, At least one of the first piezoelectric layer and the second piezoelectric layer is directly bonded to another layer; A composite substrate, wherein the first piezoelectric layer and the second piezoelectric layer are each composed of a single crystal or a non-oriented polycrystalline material.

11. The composite substrate according to claim 10, The first piezoelectric layer and the second piezoelectric layer are directly bonded to one another.

12. The composite substrate according to claim 10, an electrode layer or a bonding layer disposed between the first piezoelectric layer and the second piezoelectric layer; A composite substrate, wherein the first piezoelectric layer or the second piezoelectric layer and the electrode layer or the bonding layer are directly bonded to each other.

13. The composite substrate according to claim 1, 2 or 10, A composite substrate, wherein at least one of the first piezoelectric layer and the second piezoelectric layer is made of a non-oriented polycrystalline material.

14. The composite substrate according to claim 13, The non-oriented polycrystalline body is a sintered body.