Composite substrate and method for manufacturing the same

Abstract

The present invention provides a composite substrate which is suppressed in occurrence of a warp. A composite substrate according to one embodiment of the present invention comprises a supporting substrate and a piezoelectric film that is arranged above the supporting substrate; and the piezoelectric film is configured from a polycrystalline body that has a degree of the c-axis orientation of 80% or less as determined by a Lotgering method.

Description

[Technical Field]

[0001] The present invention relates to a composite substrate and a method for manufacturing the composite substrate. [Background technology]

[0002] Piezoelectric actuators that vibrate electromechanical transducer films have been put to practical use in droplet ejection heads of inkjet recording devices. In recent years, piezoelectric actuators have been expected to be used in other applications (for example, MEMS mirror devices for head-up displays). For example, as disclosed in Patent Document 1, a composite substrate is used for the piezoelectric element used in the piezoelectric actuator, which includes a lower electrode formed on a substrate, a piezoelectric layer formed on the lower electrode, and an upper electrode formed on the piezoelectric layer. As another example, as disclosed in Patent Document 2, a piezoelectric element is used in which a piezoelectric body provided with an upper electrode and a lower electrode is bonded to a support substrate via an adhesive. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2017 / 043383 [Patent Document 2] Patent No. 5525351 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the method disclosed in Patent Document 1 is used to fabricate the composite substrate, there is a problem in that warping is likely to occur. The occurrence of warping leads to a decrease in yield. However, when the method disclosed in Patent Document 2 is used, although the occurrence of warping can be suppressed, it is difficult to thin the piezoelectric material, making it difficult to apply to, for example, low-voltage driven piezoelectric actuators. Furthermore, since an adhesive (typically an organic adhesive) is used, there are concerns about high-temperature reliability.

[0005] 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 in which the occurrence of warping is suppressed. [Means for solving the problem]

[0006] 1. A composite substrate according to an embodiment of the present invention comprises a support substrate and a piezoelectric film disposed above the support substrate, the piezoelectric film being composed of a polycrystalline material having a c-axis orientation degree of 80% or less as determined by the Lotgering method. 2. The composite substrate according to 1 above may have a bonding layer disposed between the support substrate and the piezoelectric film, and the bonding layer may be made of an amorphous material. 3. In the composite substrate according to 1 or 2 above, the piezoelectric film may contain a PZT compound. 4. In the composite substrate according to any one of 1 to 3 above, the piezoelectric film may contain ternary PZT. 5. In the composite substrate according to any one of the above items 1 to 4, the piezoelectric film may be made of a sintered body. 6. In the composite substrate according to any one of 1 to 5 above, the thickness of the piezoelectric film may be 0.3 μm or more and 100 μm or less. 7. The composite substrate according to any one of items 1 to 6 above may have an electrode disposed between the piezoelectric film and the support substrate. The electrode may include a first electrode layer, a second electrode layer, and a third electrode layer, and the first electrode layer and the third electrode layer may be made of substantially the same material. 8. The composite substrate according to any one of 1 to 7 above may have an electrode disposed between the piezoelectric film and the support substrate, and the electrode may be made of an amorphous material. 9. The composite substrate according to any one of 1 to 8 above may have an argon-containing amorphous layer disposed between the piezoelectric film and the support substrate, the amorphous layer containing argon. 10. In the composite substrate according to any one of 1 to 9 above, an amorphous region may be formed at an upper end of the support substrate, and the thickness of the amorphous region may be 2 nm to 30 nm. 11. In the composite substrate according to item 10 above, the amorphous region may contain argon, and the argon concentration in the amorphous region may be 0.5 atm % to 30 atm %. 12. The supporting substrate according to any one of 1 to 11 above may have a total thickness variation of 10 μm or less. 13. A piezoelectric device according to another embodiment of the present invention comprises the composite substrate described in any one of 1 to 12 above.

[0007] 14. A method for manufacturing a composite substrate according to yet another embodiment of the present invention includes preparing a piezoelectric substrate made of a sintered body, and bonding the piezoelectric substrate to a support substrate. 15. The manufacturing method according to 14 above may include forming a bonding layer on the piezoelectric substrate at 300° C. or less. 16. The manufacturing method according to 14 or 15 above may include forming an electrode on the piezoelectric substrate at 300° C. or less. [Effects of the Invention]

[0008] According to an embodiment of the present invention, a composite substrate in which the occurrence of warping is suppressed can be provided. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view showing a general configuration of a composite substrate according to a first embodiment of the present invention. [Figure 2] FIG. 3 is a schematic cross-sectional view showing the general configuration of a composite substrate according to a second embodiment of the present invention. [Figure 3] FIG. 4 is a schematic cross-sectional view showing the general configuration of a composite substrate according to a third embodiment of the present invention. [Figure 4A] 1A to 1C are diagrams illustrating an example of a manufacturing process for a composite substrate according to one embodiment. [Figure 4B] This is a continuation of Figure 4A. [Figure 4C] This is a continuation of Figure 4B. [Figure 5A]1 is a cross-sectional TEM photograph (50,000 magnifications) of the composite substrate of Example 4. [Figure 5B] 1 is a cross-sectional TEM photograph (400,000 magnifications) of the composite substrate of Example 4. [Figure 5C] 1 is a cross-sectional TEM photograph (2,000,000 magnification) of the composite substrate of Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0010] 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.

[0011] A. Composite substrate 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 includes, in this order, a support substrate 10, a bonding layer 20, an electrode (lower electrode) 30, and a piezoelectric film 40. In the illustrated example, the lower electrode 30 includes, in this order from the piezoelectric film 40 side, a first lower electrode layer 31, a second lower electrode layer 32, and a third lower electrode layer 33.

[0012] Although not shown, the composite substrate 100 may further include any layer. The type, function, number, combination, and arrangement of such layers may be appropriately set depending on the purpose. For example, the composite substrate 100 may include an electrode (upper electrode) disposed on the piezoelectric film 40. The composite substrate 100 is typically used as an actuator, and for example, a wiring layer is provided on the upper electrode.

[0013] 2 is a schematic cross-sectional view showing the overall configuration of a composite substrate according to a second embodiment of the present invention. The composite substrate 110 has a support substrate 10, a bonding layer 20, and a piezoelectric film 40, in this order. In the first embodiment, an electrode 30 is disposed between the support substrate 10 (bonding layer 20) and the piezoelectric film 40, whereas in the second embodiment, the electrode 30 is not disposed. Therefore, the composite substrate 110 may have an electrode (upper electrode) disposed on the piezoelectric film 40.

[0014] 3 is a schematic cross-sectional view showing the overall configuration of a composite substrate according to a third embodiment of the present invention. The composite substrate 120 has a support substrate 10 and a piezoelectric film 40. While in the second embodiment, a bonding layer 20 is disposed between the support substrate 10 and the piezoelectric film 40, the third embodiment differs from the second embodiment in that the bonding layer 20 is not disposed in the third embodiment. Although not shown, if the bonding layer 20 is omitted, an amorphous region (described below) may be formed at the end of the piezoelectric film 40 on the support substrate 10 side.

[0015] In one embodiment, the support substrates 110 and 120 may have an electrode (lower electrode) formed on the exposed surface of the piezoelectric film 40 formed by removing the support substrate 10 and the bonding layer 20 by, for example, etching.

[0016] The composite substrate can be manufactured in any suitable shape. In one embodiment, it can be manufactured in the form of a so-called wafer. The size of the composite substrate can be appropriately set depending on the purpose. For example, the diameter of the wafer is 50 mm to 150 mm.

[0017] The total thickness variation (TTV) of the composite substrate is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 2 μm or less.

[0018] A-1. Piezoelectric film The piezoelectric film is composed of a polycrystalline material. The polycrystalline material is non-oriented. Here, "non-oriented" refers to a c-axis orientation degree determined by the Lotgering method of 80% or less, preferably 60% or less, more preferably 40% or less, even more preferably 20% or less, and particularly preferably 10% or less. Typically, the piezoelectric film is composed of a sintered body. For example, grain boundaries can be observed in the piezoelectric film by TEM observation. By adopting such a configuration, a composite substrate with reduced warpage can be obtained. Specifically, since the piezoelectric film can be formed independently, for example, internal stress due to interactions with other components during piezoelectric film formation is not generated. Furthermore, by forming the piezoelectric film from a non-oriented polycrystalline material, the options for materials composing the piezoelectric film 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, the piezoelectric film can be formed at low cost, which can contribute to improving the reliability of the resulting composite substrate.

[0019] The c-axis orientation obtained by the Lotgering method is the orientation of the (001) plane, F, calculated from the XRD profile obtained by measurement using an X-ray diffractometer using the following formula: (00l) is. F (00l) =(p-p0) / (1-p0)×100 p=ΣI(00l) / ΣI(hkl) p0=ΣI0(00l) / ΣI0(hkl) (I and I0 indicate the diffraction intensity, and p and p0 are calculated from the ratio of the diffraction intensity derived from the c-axis diffraction plane (00l) to the diffraction intensity of the entire diffraction plane (hkl). I and p are values obtained from the XRD profile of the piezoelectric film (piezoelectric substrate), and I0 and p0 are values obtained from the XRD profile of a sample obtained by powdering the piezoelectric film (piezoelectric substrate).)

[0020] Any suitable ferroelectric material can be used to form the piezoelectric film. 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 forming the piezoelectric film from a non-oriented polycrystalline material, the piezoelectric film can contain ternary PZT. Using ternary PZT allows the resulting composite substrate (piezoelectric element) 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.

[0021] The atomic ratio of Zr to Ti (Zr / Ti) contained in the piezoelectric film is preferably 0.7 or more and 2.0 or less, and more preferably 0.9 or more and 1.5 or less.

[0022] 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 may be used alone or in combination.

[0023] 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 film, 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.

[0024] The above atomic ratio (proportion) can be determined by composition analysis using energy dispersive X-ray spectroscopy (EDX).

[0025] Other specific examples of materials that make up the piezoelectric film include PMN-PT(Pb(Mg 1 / 3 Nb 2 / 3 )O3-PbTiO3), barium titanate (BaTiO3), lead titanate (PbTiO3), lead metaniobate (PbNb2O6), bismuth titanate (Bi4Ti3O 12 ), KNN((K 0.5 Na 0.5 )NbO3), KNN-LN(((K 0.5 Na 0.5 )NbO3)-LiNbO3), BT-BNT-BKT((Bi 0.5 Na 0.5 )TiO3-(Bi 0.5 K 0.5 )TiO3-BaTiO3) etc.

[0026] The thickness of the piezoelectric film 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 film may be 5 μm or more, or even 6 μm or more. With such a thickness, for example, an actuator with high displacement can be obtained with low-voltage drive. For example, when forming a piezoelectric film by film formation such as sputtering, it is difficult to achieve such a thickness due to the film stress of the resulting piezoelectric film, productivity, and other factors. In contrast, by forming the piezoelectric film from a non-oriented polycrystalline material, such a thickness can be achieved. Furthermore, by forming the piezoelectric film from a non-oriented polycrystalline material, a composite substrate with reduced warpage can be obtained even with such a thickness. On the other hand, the thickness of the piezoelectric film 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 differences in thermal expansion with the support substrate, and can be used for heating processes (e.g., 100°C or higher) in the fabrication of piezoelectric devices. Specifically, it can be used for mask formation using photolithography or the like in the fabrication of MEMS devices.

[0027] As described above, the piezoelectric film 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. Specifically, the sintered body may be formed by pressure sintering raw material powders mixed in a predetermined compounding ratio, or by calcining raw material powders mixed in a predetermined compounding ratio and then pulverizing the calcined raw material powders to a predetermined particle size (for example, 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.

[0028] The piezoelectric film can be obtained, for example, by processing a sintered body (piezoelectric substrate) to a desired thickness, such as by grinding and polishing it. In forming the piezoelectric film, 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, followed by processing such as grinding and polishing to obtain the piezoelectric film.

[0029] The arithmetic mean roughness Ra of the piezoelectric film is preferably 2 nm or less, more preferably 1 nm or less, and even more preferably 0.3 nm or less.

[0030] A-2.Support board Any appropriate substrate can be used as the support substrate. The support substrate may be composed of a single crystal or a polycrystalline body. It may also be composed of a metal. The material constituting the support substrate 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.

[0031] The silicon may be single crystal silicon, polycrystalline silicon, or high-resistivity silicon, and the support substrate may be SOI (Silicon on Insulator).

[0032] Typically, the sialon is a ceramic obtained by sintering a mixture of silicon nitride and alumina. For example, Si 6-w Al w O w N 8-w Specifically, sialon has a composition in which alumina is mixed into silicon nitride, and w in the formula indicates the mixing ratio of alumina. w is preferably 0.5 or more and 4.0 or less.

[0033] 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.

[0034] 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.

[0035] The thickness of the support substrate can be any appropriate thickness, and is, for example, 100 μm to 1000 μm.

[0036] A-3. Bonding layer Examples of materials constituting the bonding layer that may be included in the composite substrate include silicon, tantalum oxide, niobium oxide, aluminum oxide, titanium oxide, and hafnium oxide. The thickness of the bonding layer is, for example, 5 nm to 1 μm, and preferably 10 nm to 200 nm.

[0037] The bonding layer is typically made of an amorphous material. Specifically, the bonding layer may be an amorphous layer. By making the bonding layer of an amorphous material, for example, polishing, which will be described later, becomes easier, and it becomes easier to obtain a suitable surface roughness on the bonding surface.

[0038] The bonding layer can be formed by any suitable method, such as physical vapor deposition (e.g., sputtering, vacuum deposition, or ion beam assisted deposition (IAD)), chemical vapor deposition, or atomic layer deposition (ALD). The bonding layer can be formed at room temperature (25°C) to 300°C.

[0039] A-4. Electrode In the illustrated example, the electrode (lower electrode) has a laminated structure including a first lower electrode layer, a second lower electrode layer, and a third lower electrode layer. The first lower electrode layer and the third lower electrode layer, which are in contact with the electrode and the adjacent layer, can each function as an adhesive layer. Examples of materials that can be used to form the first lower electrode layer and the third lower electrode layer include metals such as Ti, Cr, Ni, Mo, and Al. These can be used alone or in combination of two or more types.

[0040] In one embodiment, the material constituting the first lower electrode layer and the material constituting the third lower electrode layer are substantially the same. Specifically, the first lower electrode layer and the third lower electrode layer have substantially the same composition. For example, the first lower electrode layer is made of a metal (e.g., Ti), and the third lower electrode layer is made of a metal (e.g., Ti). This configuration can be adopted by forming the piezoelectric film from a non-oriented polycrystalline material. For example, when the piezoelectric film is formed by film deposition, the adjacent layer (electrode) functions as a seed crystal layer of the piezoelectric film and is made of a material having predetermined physical properties (e.g., lattice constant). In contrast, by forming the piezoelectric film from a non-oriented polycrystalline material, the options for materials constituting the adjacent layer (electrode) 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).

[0041] The thickness of the first lower electrode layer and the third lower electrode layer, which can function as an adhesive layer with adjacent layers, is, for example, 1 nm or more and 100 nm or less, preferably 3 nm or more and 50 nm or less, and more preferably 5 nm or more and 20 nm or less.

[0042] The material for the second lower electrode layer is preferably a metal such as Pt, Au, etc. The thickness of the second lower electrode layer is, for example, 10 nm or more and 1000 nm or less, and preferably 50 nm or more and 250 nm or less.

[0043] The electrode (second lower electrode layer) is typically made of an amorphous material, which can contribute to suppressing warpage in the resulting composite substrate, for example.

[0044] The electrodes can be formed by any suitable method. For example, they can be formed by physical vapor deposition such as sputtering, vacuum deposition, or ion beam assisted deposition (IAD). In one embodiment, the first lower electrode layer and the third lower electrode layer can be formed by sputtering using the same target (for example, a Ti target) under the same conditions. The electrodes can be formed at, for example, room temperature (25°C) to 300°C.

[0045] A-5. Manufacturing method The composite substrate can be obtained, for example, by bonding (directly bonding) the piezoelectric film or piezoelectric substrate to the support substrate.

[0046] 4A to 4C are diagrams showing an example of a manufacturing process for a composite substrate according to one embodiment. Fig. 4A shows a state in which deposition of electrode 30 and bonding layer 20 has been completed on piezoelectric substrate 42. Piezoelectric substrate 42 has a first principal surface 42a and a second principal surface 42b facing each other, and first lower electrode layer 31, second lower electrode layer 32, and third lower electrode layer 33 are deposited in this order on first principal surface 42a to form electrode 30, and then bonding layer 20 is deposited.

[0047] 4B shows a process of directly bonding a piezoelectric substrate 42, on which electrodes 30 and a bonding layer 20 have been formed, to a support substrate 10. For direct bonding, the bonding surfaces are preferably activated by any appropriate activation process. For example, after activating the surface 20a of the bonding layer 20 and the surface 10a of the support substrate 10, the activated surfaces of the bonding layer 20 and the support substrate 10 are brought into contact with each other and pressure is applied to directly bond them. In this way, a composite substrate 102 shown in FIG. 4C is obtained.

[0048] In one embodiment, the end of the bonding layer 20 on the activation surface side and / or the end of the support substrate 10 on the activation surface side contain elements (e.g., argon) that constitute the gas used in the activation process. Specifically, the end of the bonding layer 20 and / or the end of the support substrate 10 on the activation surface side are made into an amorphous region (a region containing an amorphous body) that contains elements that constitute 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 state of argon in the amorphous region is not particularly limited, but for example, in the amorphous region, the argon concentration increases toward the activation surface side.

[0049] Typically, the second main surface 42b of the piezoelectric substrate 42 of the obtained composite substrate 102 is subjected to processing such as grinding and polishing so as to form a piezoelectric film having the desired thickness. In one embodiment, the processing such as grinding and polishing is performed so that the thickness of the obtained piezoelectric film exceeds 0.2 μm. This configuration can prevent shedding of crystals constituting the piezoelectric film and peeling of the piezoelectric film, without weakening the bonding strength of the grain boundaries of the obtained piezoelectric film or the bonding strength with the support substrate due to processing load.

[0050] Preferably, the surface of each layer (specifically, the piezoelectric film or piezoelectric substrate, the support substrate, and the bonding layer) is 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, etc.

[0051] During the above film formation and bonding, it is preferable to clean the surface of each layer, for example, to remove abrasive residue. Cleaning methods include, for example, 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 (for example, the Sun Wash series manufactured by Lion Corporation) is used, followed by cleaning in a scrub cleaning machine using a solvent (for example, a mixed solution of acetone and isopropyl alcohol (IPA)).

[0052] 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 electrodes 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, 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.

[0053] 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.

[0054] In the illustrated example, a composite substrate is obtained by bonding a piezoelectric substrate provided with electrodes and a bonding layer to a support substrate, but this is not a limitation. For example, a layer (e.g., an electrode, a bonding layer) that can be disposed between the piezoelectric film and the support substrate may be provided on the support substrate, and then the support substrate and the piezoelectric substrate (piezoelectric film) may be bonded. Specifically, the composite substrate may have an argon-containing amorphous layer that is located between the piezoelectric film and the support substrate and contains argon. The argon-containing amorphous layer may correspond to the amorphous region described above. [Example]

[0055] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, the following procedures were carried out at room temperature.

[0056] [Example 1] PbZrO3 powder, PbTiO3 powder, Nb2O5 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 (900°C for 2 hours). It was then wet-milled 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 to obtain a compact.

[0057] 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, where the temperature was raised from room temperature to 1100°C over 4.5 hours and hot isostatic pressing (HIP) was performed. Specifically, the pressure was raised to 280 bar at 1000°C, and once the temperature exceeded 1000°C, the pressure was raised from 280 bar to 600 bar over 1 hour. The pressure was then held at 1100°C and 600 bar for 1 hour, and hot isostatic pressing was performed. In this way, a plate-shaped sintered body was obtained.

[0058] 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. The sintered body was then beveled, ground, and lapped to obtain a wafer (piezoelectric substrate) with a first surface and a second surface facing each other, a diameter of 4 inches, and a thickness of 500 μm. The c-axis orientation of the obtained piezoelectric substrate was determined by the Lotgering method to be 2%. This c-axis orientation was determined by measuring the XRD profile when X-rays were irradiated onto the surface (orientation surface) of the piezoelectric substrate using an XRD device, and the orientation degree F of the (001) plane was calculated using the following formula: (00l) The evaluation was carried out within the diffraction angle 2θ range of 10° to 80°. F (00l) =(p-p0) / (1-p0)×100 p=ΣI(00l) / ΣI(hkl) p0=ΣI0(00l) / ΣI0(hkl) (I and I0 indicate the diffraction intensity, and p and p0 are calculated from the ratio of the diffraction intensity derived from the c-axis diffraction plane (00l) to the diffraction intensity of the entire diffraction plane (hkl). I and p are values obtained from the XRD profile when X-rays are irradiated onto the surface (orientation surface) of the piezoelectric substrate, and I0 and p0 are values obtained from the XRD profile when a sample obtained by powdering the piezoelectric substrate is measured.)

[0059] The first surface of the obtained piezoelectric substrate was finished by chemical mechanical polishing (CMP) to have a mirror finish with 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.

[0060] On the first surface of the 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 deposited 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.

[0061] A silicon substrate with 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.

[0062] Next, the piezoelectric substrate and the support substrate were directly bonded. Specifically, after cleaning the surface of the piezoelectric substrate (silicon film side) and the surface of the silicon 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.

[0063] 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 film with a thickness of 0.3 μm.

[0064] [Examples 2 to 6] A composite substrate was obtained in the same manner as in Example 1, except that the conditions for grinding and polishing the second surface of the piezoelectric substrate were changed.

[0065] [Example 7] A composite substrate was obtained in the same manner as in Example 4, except that a 100 nm thick Au film was formed by sputtering instead of a 100 nm thick Pt film.

[0066] [Example 8] A composite substrate was obtained in the same manner as in Example 4, except that the Ti film and the Pt film were not formed by sputtering.

[0067] [Example 9] A composite substrate was obtained in the same manner as in Example 4, except that a piezoelectric substrate with a c-axis orientation degree of 9% determined by the Lotgering method was used.

[0068] [Example 10] A composite substrate was obtained in the same manner as in Example 4, except that a piezoelectric substrate with a c-axis orientation degree of 58% determined by the Lotgering method was used.

[0069] [Example 11] A composite substrate was obtained in the same manner as in Example 4, except that a piezoelectric substrate with a c-axis orientation degree of 79% determined by the Lotgering method was used.

[0070] [TEM Observation] Transmission electron microscope (TEM) observations (50,000 times, 400,000 times, and 2,000,000 times) of the cross-section of the composite substrate of Example 4 were performed. The observation photos are shown in FIGS. 5A, 5B, and 5C. In addition, when observing the cross-section by TEM, an observation sample was prepared from the obtained composite substrate by the FIB method.

[0071] [EDX Analysis] When the cross-section of the composite substrate of Example 4 was analyzed by EDX, the argon concentration in the layer indicated by the arrow in FIG. 5C (the amorphous region formed by the activation treatment) was 3.0 atm%.

[0072] [Comparative Example 1] A silicon substrate having an orientation flat portion, having a first surface and a second surface facing each other, having a diameter of 4 inches, a thickness of 500 μm, and a plane orientation of (100) was prepared. Next, while the silicon substrate was heated to 560°C, a 10-nm-thick Ti film, a 100-nm-thick Pt film, and a 10-nm-thick strontium ruthenate (SRO) film were deposited in this order on the first surface by sputtering. During this process, the SRO film was crystallized by heating at 560°C and oriented in the (100) plane. Next, while the silicon substrate was heated to 560°C, a sintered body (0.8PbZr 0.53 Ti 0.47 A 3 μm thick PZT film (piezoelectric film) was deposited by sputtering using a PbO3+0.2PbO target. Specifically, the PZT film was crystallized by heating at 560°C, resulting in a PZT film oriented in the (001) plane. A composite substrate was thus obtained. The degree of c-axis orientation of the resulting piezoelectric film was determined by the Lotgering method to be 89%.

[0073] Comparative Example 2 A composite substrate was obtained in the same manner as in Comparative Example 1, except that the thickness of the PZT film was changed to 5 μm.

[0074] Comparative Example 3 An attempt was made to form a PZT film with a thickness of 6 μm, but the silicon substrate was destroyed due to warping that occurred during film formation, and a composite substrate could not be obtained.

[0075] The composite substrates of the examples and comparative examples were evaluated as follows. The evaluation results are summarized in Table 1.

[0076] <Rating 1> The warpage of the composite substrate (wafer) was measured using a laser displacement meter (Keyence Corporation, "LK-G5000"). Specifically, the thickness (height) distribution of the wafer was measured when it was placed on a movable stage with the silicon substrate facing up. Measurements were taken on the wafer's orientation flat and two lines in the horizontal and vertical directions, and the larger measured value is shown in Table 1.

[0077] <Rating 2-1> The composite substrates (wafers) of Examples 1 to 7 and 9 to 11 were cut to a size of 30 mm x 5 mm, and a Pt film with a thickness of 100 nm was formed by sputtering in a 20 mm x 5 mm area on the surface of the piezoelectric film to fabricate a cantilever. The composite substrates (wafers) of Comparative Examples 1 and 2 were cut to a size of 30 mm × 5 mm, and a 10 nm thick SRO film and a 100 nm thick Pt film were formed by sputtering (amorphous films were formed without heating) on ​​the surface of the piezoelectric film in a 20 mm × 5 mm area. Then, a predetermined voltage was applied to perform polarization processing, and a cantilever was fabricated.

[0078] The device was driven by applying a voltage (at 500 Hz) to the upper electrode (Pt film) and lower electrode (Pt film or Au film) of the obtained cantilever so that the electric field strength applied to the piezoelectric film was 0.34 kV / mm. The amplitude (displacement) of the tip of the cantilever was measured using a laser Doppler vibrometer, and d31 was calculated using the following formula.

[0079]

number

[0080] <Rating 2-2> The silicon substrate and silicon film of the composite substrate (wafer) of Example 8 were removed by etching, and then 100 nm thick Pt films (upper and lower electrodes) were formed by sputtering on the upper surface of the piezoelectric film and the lower surface exposed by etching to obtain a laminate. The laminate was then diced into pieces measuring 20 mm x 2 mm. The thickness (height) of the resulting chip was measured using a laser displacement meter. A DC voltage was applied to the upper and lower electrodes so that the electric field strength applied to the piezoelectric film was 0.34 kV / mm, and then the thickness of the chip was measured using a laser displacement meter. d31 was calculated from the displacement before and after voltage application.

[0081] [Table 1]

[0082] In each example, the occurrence of warpage is suppressed. Furthermore, in each example, excellent piezoelectric properties are confirmed. Specifically, excellent piezoelectric properties are confirmed even in a low electric field region (e.g., <5 kV / mm). In Comparative Examples 1 and 2, it is believed that warpage can be reduced by, for example, balancing the compressive stress and tensile stress of each layer by adjusting the heating temperature during sputtering deposition, the deposition output, the type of gas added in the chamber, the thickness of each layer, etc. However, even if warpage is reduced, residual stress remains, and, for example, the piezoelectric constant and reliability are low, making the piezoelectric element unsuitable for use in a piezoelectric actuator.

[0083] <Temperature characteristics> The temperature characteristics were evaluated for Example 4 and Comparative Example 1. Specifically, in Evaluation 2-1 above, the cantilever was placed on a hot plate and heated from room temperature (25°C) to 120°C, and a voltage (at 500 Hz) was applied so that the electric field strength applied to the piezoelectric film was 1 kV / mm (electric field strength / coercive field = 1.0) in Example 4 and 5 kV / mm (electric field strength / coercive field = 0.75) in Comparative Example 1, driving the element and measuring the displacement. The temperature was measured using a thermocouple placed near the cantilever.

[0084] The rate of change in displacement (ratio of displacement at 120°C to displacement at room temperature) was 1.11 in Example 4 and 1.36 in Comparative Example 1. It can be said that Example 4 has excellent temperature stability.

[0085] <Reliability> The reliability was evaluated for Example 4. Specifically, in the above Evaluation 2-1, the cantilever was placed on a hot plate, heated from room temperature (25°C) to 120°C, and a voltage (at 500 Hz) was applied so that the electric field strength applied to the piezoelectric film was 1 kV / mm (electric field strength / coercive field = 1.0) to drive the element, and the change in displacement and the temperature rise of the element due to heat generation were measured for 7 days.

[0086] The rate of change in displacement after 7 days compared to when the measurement started was 0.98. The element did not generate heat, and the temperature of the element after 7 days was 120°C. The composite substrate of the example can be said to have excellent reliability, including the fact that it does not use an organic adhesive (e.g., epoxy-based, acrylic-based, etc.).

[0087] <ttv> The TTV was measured for Example 4. Specifically, the outer periphery of the obtained composite substrate (4 inches) was cut by approximately 0.5 mm, and the TTV was measured within a range of φ99 mm using a FlatMaster 200 manufactured by Tropel. As a result, the TTV of the composite substrate of Example 4 was 1.6 μm.

[0088] <Thickness distribution of piezoelectric film> The thickness distribution of the piezoelectric film was evaluated for Example 2 and Comparative Example 1. Specifically, approximately 5 mm was cut off from the outer periphery of the obtained composite substrate (4 inches), and the film thickness at 17 points within a φ90 mm range was measured using a microspectrophotometric film thickness meter (OPTM-A2 manufactured by Otsuka Electronics Co., Ltd.).

[0089] The film thickness distribution (variation) was 3±0.05 μm (±1.7%) in Example 2 and 3±0.15 μm (±5.0%) in Comparative Example 1. It can be said that the film thickness variation is small in Example 2. In other examples with different piezoelectric film thicknesses, it is possible to process (grind and polish) with the same degree of accuracy as in Example 2 (±0.05 μm), and the thicker the piezoelectric film, the smaller the ratio of variation to the thickness of the piezoelectric film. When a high-performance sputtering deposition device is used to deposit the piezoelectric film, the film thickness variation can be suppressed to ±2 to 3%, but this does not reach the result (±1.7%) of Example 2. In addition, polishing the deposited piezoelectric film is difficult. [Industrial Applicability]

[0090] The composite substrate according to the embodiment of the present invention can be suitably used in piezoelectric devices such as inkjet heads, MEMS mirror devices, gyro sensors, ultrasonic sensors, pyroelectric infrared sensors, and tactile sensors (haptics). [Explanation of symbols]

[0091] 10 Support substrate 20 Bonding layer 30 electrodes (lower electrode) 40 Piezoelectric film 100 Composite Board 110 Composite substrate< / ttv>

Claims

1. A support substrate; a piezoelectric film disposed above the support substrate; a bonding layer disposed between the support substrate and the piezoelectric film; the piezoelectric film is made of a polycrystalline material containing a PZT-based compound and having a c-axis orientation degree of 2% or more and 79% or less as determined by the Lotgering method; The thickness of the piezoelectric film is 3 μm or more and 100 μm or less, The bonding layer is composed of an amorphous material. Composite board.

2. The composite substrate of claim 1 , wherein the piezoelectric film comprises ternary PZT.

3. The composite substrate according to claim 1 , wherein the piezoelectric film is made of a sintered body.

4. an electrode disposed between the piezoelectric film and the support substrate; the electrodes include a first electrode layer, a second electrode layer, and a third electrode layer; The composite substrate according to claim 1 , wherein the first electrode layer and the third electrode layer are made of substantially the same material.

5. an electrode disposed between the piezoelectric film and the support substrate; The composite substrate according to claim 1 , wherein the electrode is made of an amorphous material.

6. The composite substrate of claim 1 , further comprising an argon-containing amorphous layer disposed between the piezoelectric film and the support substrate, the amorphous layer containing argon.

7. 2. The composite substrate according to claim 1, wherein an amorphous region is formed at an upper end of the support substrate, and the thickness of the amorphous region is 2 nm to 30 nm.

8. 8. The composite substrate according to claim 7, wherein the amorphous region contains argon, and the argon concentration in the amorphous region is 0.5 atm % to 30 atm %.

9. The composite substrate according to claim 1 , wherein the total thickness variation is 10 μm or less.

10. A piezoelectric device comprising the composite substrate according to claim 1 .

11. preparing a piezoelectric substrate made of a sintered body; bonding the piezoelectric substrate and a support substrate via a bonding layer made of an amorphous material; and processing the piezoelectric substrate to form a piezoelectric film having a thickness of 3 μm or more and 100 μm or less; the piezoelectric substrate is made of a polycrystalline material containing a PZT compound and having a c-axis orientation degree of 2% or more and 79% or less as determined by the Lotgering method; A method for manufacturing a composite substrate.

12. The manufacturing method according to claim 11 , further comprising forming the bonding layer on the piezoelectric substrate at a temperature of 300° C. or less.

13. The manufacturing method according to claim 11 or 12, further comprising forming an electrode on the piezoelectric substrate at a temperature of 300° C. or less.

Images