Multilayer films, substrates with multilayer films, and electro-optical devices using these.

Abstract

We provide substrates with multilayer films. [Solution] The invention comprises a buffer layer made of an oxide mainly composed of La formed on a metal layer, and a PZT-based ferroelectric thin film made of PZT or PLZT formed on the buffer layer, wherein the integrated intensity of the peak of the PZT-based ferroelectric thin film (100) is measured at the XRD intensity of each of the nine points in the plane on the PZT-based ferroelectric thin film side. XY [Counts·degree] represents the integral intensity in the plane I XY The ratio of the standard deviation to the maximum value (standard deviation / maximum value) is 0.18 or less.

Description

[Technical Field]

[0001] This invention relates to a multilayer film, a substrate with a multilayer film, and an electro-optical device using these. [Background technology]

[0002] Non-patent document 1 and patent document 1 disclose a method for forming a buffer layer on a substrate to highly orient a thin film made of lead zirconate titanate (hereinafter referred to as PZT). In this method of forming the buffer layer, first a solution of polyvinylpyrrolidone (hereinafter referred to as PVP) is applied to the substrate, then lanthanum nitrate hexahydrate is dissolved in a solvent, the solution is spin-coated onto the PVP, and then heat-treated to form the buffer layer on the substrate.

[0003] Patent Document 1 discloses a functional element using PZT, and Non-Patent Document 2 and Patent Document 2 disclose the use of PZT in an optical module, and a buffer layer containing lanthanum is provided between the silicon substrate and the PZT. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Jong-Jin Choi, et al., "Growth of highly (100) oriented lead zirconate titanate films on silicon and glass substrates using lanthanum nitrate as a buffer layer," Applied Physics Letters, 2004, Vol. 85, pp. 4621-4623. [Non-Patent Document 2] J.P. George, et al., "Lanthanide-Assisted Deposition of Strongly Electro-optic PZT Thin Films on Silicon: Toward Integrated Active Nanophotonic Devices," Applied Materials Interfaces, 2015, Vol. 7, pp. 13350-13359. [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2004 / 079059 [Patent Document 2] International Publication No. 2014 / 083195 [Overview of the project] [Problems that the invention aims to solve]

[0006] In the fabrication of optical devices, when it is necessary to form an oriented ferroelectric film on metal electrodes such as platinum, there is a problem in that the wettability of the nitric acid (La) solution is poor on metal, resulting in appearance defects after the ferroelectric thin film is deposited.

[0007] In view of these challenges, the present invention aims to improve wettability to a substrate and to form a uniform, appearance-free laminated film on metals such as platinum. [Means for solving the problem]

[0008] The present invention comprises a buffer layer made of an oxide mainly composed of La formed on a metal layer, and a PZT-based ferroelectric thin film made of PZT or PLZT formed on the buffer layer. The integral intensity of the peak of the PZT-based ferroelectric thin film (100) is calculated by taking the XRD intensity of each of the nine points in the plane of the PZT-based ferroelectric thin film side.XY [Counts·degree] is the integral intensity I in the aforementioned plane. XY The ratio of the standard deviation to the maximum value (standard deviation / maximum value) is 0.18 or less.

[0009] I XY This represents the integrated intensity of the peak of the PZT-based ferroelectric thin film (100) that appears between 21.00° and 23.00° in X-ray diffraction measurements. The standard deviation is the integrated intensity of 9 integral intensities I. XY [Counts·degree] represents the degree of variation. The maximum value is the integral intensity I of 9 units. XY This is the maximum integrated intensity [Counts·degree] among them.

[0010] The ratio (=standard deviation / maximum value) represents the integrated intensity I of the ferroelectric thin film within the plane of the multilayer film. XY This is an indicator of uniformity, and if it is 0.18 or less, the ferroelectric thin film has high uniformity in orientation at multiple points within the plane. As a result, even when applied to large-area wafers such as 4-inch wafers, PZT-based ferroelectric thin films can be obtained uniformly.

[0011] The laminated substrate of the present invention comprises a substrate body, a metal layer formed on the substrate body, and the laminated film formed on the metal layer. The substrate body can be, for example, a Si substrate without an oxide film, a Si substrate with an oxide film, a glass substrate, a sapphire substrate, etc. Platinum (Pt), gold (Au), etc. can be used as the metal layer.

[0012] The electro-optical device of the present invention comprises the aforementioned multilayer film-coated substrate. Examples of electro-optical devices include optical modulators, optical switches, and phase shifters. [Effects of the Invention]

[0013] According to the present invention, the in-plane integrated intensity I XY By setting the ratio of the standard deviation to the maximum value (standard deviation / maximum value) to 0.18 or less, it is possible to form a uniform laminated film without appearance defects even on a metal layer. [Brief explanation of the drawing]

[0014] [Figure 1] This is a cross-sectional view of a substrate with a laminated film according to an embodiment of the present invention. [Figure 2] This is a graph showing the XRD intensity of the X-ray diffraction measurement of the substrate with a laminated film in FIG. 1.

Mode for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0016] A substrate 1 with a laminated film shown in FIG. 1 (hereinafter referred to as a thin-film substrate) includes a substrate 10 and a laminated film 20 formed on the substrate 10.

[0017] The substrate 10 is composed of a substrate body 11 and a metal layer 12 formed on the surface of the substrate body 11. The substrate body 11 is not particularly limited, and for example, a Si substrate without an oxide film, a Si substrate with an oxide film such as SiO2 or Al2O3, a glass substrate, a sapphire substrate, etc. can be used. The size of the substrate body 10 is not limited either, but for example, it is 10 mm or more and 350 mm or less, and may be formed as a circular wafer with a diameter of 50 mmφ or more. The metal layer 12 constitutes a lower electrode and is made of platinum (Pt), gold (Au), copper (Cu), or the like. Thus, the metal layer 12 contains platinum (Pt), gold (Au), or copper (Cu) as a main component. Note that the metal layer 12 may contain inevitable impurities. These thicknesses are not limited either, but the thickness of the substrate body 11 is 300 μm or more and 2000 μm or less, and the thickness of the metal layer 12 is 10 nm or more and 500 nm or less.

[0018] The laminated film 20 includes a buffer layer 210 formed on the substrate 10 and a ferroelectric thin film 220 formed on the buffer layer 210. Thus, the laminated film 20 includes a buffer layer 210 formed on the metal layer 12 and a ferroelectric thin film 220 formed on the buffer layer 210.

[0019] The buffer layer 210 is made of an oxide having La as a main component. The oxide constituting the buffer layer 210 is, for example, La(NO3)3, LaONO3, La2O2CO3, etc.

[0020] The film thickness of the buffer layer 210 is not limited, but for example, it is 4 nm or more and 50 nm or less, preferably 5 nm or more and 35 nm or less, and more preferably 8 nm or more and 25 nm or less. If the film thickness is less than 4 nm, it is difficult to form a uniform film. If it exceeds 50 nm, when forming a ferroelectric layer on the buffer layer 210 to fabricate a photoelectric device, there is a concern that light confinement in the ferroelectric layer becomes insufficient and efficient photoelectric conversion cannot be performed.

[0021] The ferroelectric thin film 220 is made of PZT (lead zirconate titanate: Pb(Zr,Ti)O3) or PLZT (lanthanum-doped lead zirconate titanate: [(Pb,La)(Zr,Ti)O3]).

[0022] Furthermore, when the ferroelectric thin film 220 is PLZT, when confirming the XRD intensity of PLZT for any 9 locations in the plane on the PLZT side of the substrate 1 with the thin film by X-ray diffraction measurement, the ratio of the standard deviation to the maximum value (= standard deviation / maximum value) of the in-plane integrated intensity I XY serves as an index of the uniformity of the integrated intensity I XY of the ferroelectric thin film 220 in the plane of the substrate 1 with the thin film. The integrated intensity I XY is the integrated intensity of the peak of PLZT(100) that appears at 21.00° or more and 23.00° or less as shown in FIG. 2 from the XRD intensity obtained at each measurement location. The standard deviation is the degree of variation of the integrated intensity I XY at 9 locations. The maximum value is the maximum integrated intensity among the integrated intensities I XY at 9 locations. Hereinafter, the ratio of the standard deviation to the maximum value may be described as "standard deviation / maximum value".

[0023] In this embodiment of the laminated film 20 or thin-film substrate 1, the standard deviation / maximum value is 0.18 or less in order to ensure high uniformity of the orientation of the ferroelectric thin film 220 at multiple locations within the plane. This allows for sufficiently high uniformity of the characteristics of multiple electro-optic devices formed using the thin-film substrate 1. On the other hand, if the standard deviation / maximum value exceeds 0.18, the yield of multiple electro-optic devices formed using the thin-film substrate decreases. Note that the standard deviation / maximum value in this embodiment may be 0.10 or less. Furthermore, the standard deviation / maximum value in this embodiment may be 0.09 or less, 0.06 or less, 0.05 or less, or 0.04 or less.

[0024] (Manufacturing method for the thin film substrate 1) The manufacturing method for the thin-film coated substrate 1 comprises a first film deposition step of forming a buffer layer 210 on a substrate 10, and a second film deposition step of forming a ferroelectric thin film 220 on the buffer layer 210.

[0025] [First film formation process: Buffer layer 210] The first film formation process comprises a first coating step of coating the surface of the metal layer 12 on the substrate 10 with polyvinylpyrrolidone (hereinafter referred to as PVP), a second coating step of coating the PVP with lanthanum nitrate, a pre-calcination step of pre-calcining the lanthanum nitrate on the substrate, and a calcination step of calcining the lanthanum nitrate on the substrate.

[0026] The first coating step comprises the steps of applying the PVP solution to the substrate 10 and volatilizing the solvent.

[0027] The PVP solution consists of PVP and a solvent, with a PVP concentration of 0.05% by mass or more and 0.5% by mass or less. Examples of solvents include 2-methoxyethanol, 1-propanol, methanol, and ethanol. The PVP solution was dropped onto a substrate and spin-coated. Alternatively, dip-coating or other methods may be used instead of spin-coating. After applying the PVP solution, the substrate was placed on a heated surface, for example, at 150°C, to evaporate the solvent. This formed a PVP film, which acted as a surfactant, effectively uniformly depositing lanthanum nitrate.

[0028] The second coating step comprises the steps of applying a lanthanum nitrate solution onto the PVP and volatilizing the solvent.

[0029] The lanthanum nitrate solution consists of lanthanum nitrate hexahydrate, an organic solvent, and water. The organic solvent is, for example, 2-methoxyethanol, 1-propanol, methanol, or ethanol. The water is pure water or the like. Note that the lanthanum nitrate solution in this embodiment may contain unavoidable impurities. The concentration of this lanthanum nitrate (excluding hydrate) is 0.8% by mass or more and 5.5% by mass or less. If the lanthanum nitrate concentration is less than 0.8% by mass or more than 5.5% by mass, it is difficult to form a uniform ferroelectric laminated film. The concentration of this lanthanum nitrate solution is preferably 1% by mass or more and 5% by mass or less, and more preferably 1.2% by mass or more and 3.5% by mass or less.

[0030] Furthermore, the mass concentration of water in the lanthanum nitrate solution is between 3% by mass and 21% by mass. If the water concentration in the lanthanum nitrate solution is less than 3% by mass, the orientation maintenance ability after several days is insufficient, and sufficient wettability on the metal film cannot be obtained. On the other hand, if the water concentration in the lanthanum nitrate solution is too high, above 21% by mass, the viscosity of the solution becomes too low, making it difficult to form a uniform film when spin coating is performed. The water concentration in the lanthanum nitrate solution is preferably between 3.5% by mass and 15% by mass, and more preferably between 5% by mass and 12% by mass. Note that the mass concentration of water in the lanthanum nitrate solution includes the water of hydration derived from the lanthanum nitrate raw material.

[0031] In the second coating step, the lanthanum nitrate solution is dropped onto the PVP and applied as a thin film by spin coating. Alternatively, dip coating or other methods may be used instead of spin coating. After applying the lanthanum nitrate solution, the substrate is heated to, for example, 150°C to 250°C to evaporate the solvent.

[0032] The calcination process involves heating the substrate to a temperature between 300°C and 400°C to calcine the lanthanum nitrate. After heating to the calcination temperature, the substrate is placed on a heating section with a temperature lower than the calcination temperature to gradually lower the temperature, and then removed from the heating section and allowed to cool in the air.

[0033] The firing process involves firing the substrate to crystallize lanthanum nitrate. The firing temperature is 450°C to 650°C, preferably 480°C to 650°C, and more preferably 500°C to 600°C. The holding time for maintaining the firing temperature is 1 second to 1000 seconds, preferably 30 seconds to 180 seconds. Furthermore, in the firing process, the heating time t1 from room temperature to the firing temperature is 200 seconds to 1000 seconds, preferably 240 seconds to 1000 seconds, and more preferably 240 seconds to 750 seconds.

[0034] The heating time t1 may be between 240 seconds and 720 seconds. By adjusting the heating time t1, the lanthanum nitrate after firing is controlled to a phase state suitable for the formation of the ferroelectric thin film 220. If the heating time t1 is less than 200 seconds, the phase transition of lanthanum nitrate to LaONO3, which is effective in oriented the PZT-based dielectric film, will be insufficient, making it difficult to form the ferroelectric thin film 220 with high orientation on the buffer layer 210. If the heating time t1 exceeds 1000 seconds, there is a concern that other phases besides LaONO3 may be mixed in. The heating rate v1 from room temperature to firing temperature is between 0.5°C / second and 10°C / second, preferably between 0.70°C / second and 2.5°C / second. If the heating rate v1 is less than 0.5°C / second, there is a concern that other phases besides LaONO3 may be mixed in, and if the heating rate v1 exceeds 10°C / second, the phase transition to LaONO3 may be insufficient. The thickness of the buffer layer 210 can be increased by repeating the process from the first coating step of applying PVP through the second coating step to the firing step.

[0035] [Second thin-film deposition process: Ferroelectric thin film 220] The second film formation step comprises the steps of applying a thin film forming solution onto the buffer layer 210, volatilizing the solvent, pre-calcining the thin film forming material, and calcining the thin film forming material.

[0036] The coating process involves dropping a thin-film forming solution onto a substrate with a buffer layer 210 already formed, and then performing spin coating. Alternatively, dip coating or other methods may be used instead of spin coating. After applying the thin-film forming solution, the solvent is evaporated. For example, the substrate coated with the thin-film forming solution is placed on a heating section heated to 150°C.

[0037] The calcination process involves heating the substrate to 300°C to 450°C to calcinate the thin-film forming material. After heating to the calcination temperature, the substrate is placed on a heating section with a temperature lower than the calcination temperature to gradually lower the temperature, and then removed from the heating section to cool in the air.

[0038] The firing process involves firing the substrate to crystallize the thin film forming material. The firing temperature is 500°C to 750°C, preferably 550°C to 650°C. The holding time for maintaining the firing temperature is 1 second to 500 seconds, preferably 30 seconds to 90 seconds. Furthermore, the heating time t2 from room temperature to the firing temperature is 30 seconds to 1000 seconds, preferably 240 seconds to 720 seconds. The heating rate from room temperature to the firing temperature is 0.65°C / second to 10°C / second, preferably 0.90°C / second to 2.5°C / second. The thickness of the ferroelectric thin film 220 can be increased, for example, by repeating the process from applying the thin film forming solution to the firing process of firing the thin film forming material. After the firing process, the thin film-coated substrate 1 is completed.

[0039] In the thin-film substrate 1 of this embodiment, the buffer layer 210 is formed in an oriented manner because its phase state is controlled by heat treatment during manufacturing. Furthermore, the thin-film substrate 1 has uniform orientation of the ferroelectric thin film 220 at various points within its surface. Therefore, the uniformity of the characteristics of the electro-optic device formed using the thin-film substrate 1 can be sufficiently improved. In this case, the lanthanum nitrate solution for forming the buffer layer 210 contains water at a predetermined concentration, which stabilizes its orientation ability relative to the dielectric film 220. Furthermore, because it contains water, this lanthanum nitrate solution has excellent wettability when applied to a substrate to form a film. As a result, the buffer layer 210 can be uniformly formed on the surface of the substrate 10 on which the metal layer 12 is formed. Therefore, by forming a buffer layer 210 with such a lanthanum nitrate solution and then forming a ferroelectric thin film, it is possible to form a ferroelectric thin film that is stably oriented and has uniform orientation in plane, and the electro-optic device formed using this thin film-coated substrate 1 can also exhibit uniform characteristics.

[0040] The present invention can be implemented in any way not limited to the above description and illustrated examples.

[0041] Examples of electro-optical devices formed using the thin-film substrate 1 of the present invention include optical modulators, optical switches, and phase shifters. Furthermore, the method for forming the ferroelectric thin film on the buffer layer is not limited to the above description, and may also be formed by other methods such as chemical solution deposition, chemical vapor deposition, sputtering, and vapor deposition. Furthermore, while a PLZT thin film was exemplified as the ferroelectric thin film in the embodiment, a PZT thin film is also applicable. [Examples]

[0042] A laminated substrate consisting of a Si substrate with a metal layer, a buffer layer formed by varying the water and lanthanum nitrate concentrations in a lanthanum nitrate solution, and a PLZT film formed on this buffer layer was used as a sample, and the films of each sample were analyzed.

[0043] A Si wafer with a thermal oxide film (thickness: 3 μm) was used as the Si substrate. The Si substrate had a diameter of 4 inches and a thickness of 0.525 mm. After cleaning this Si wafer under the following conditions, a metal layer was formed on its surface.

[0044] [Washing process] The cleaning process was carried out in the following order: first cleaning, then third cleaning. In the first cleaning step, the Si substrate was immersed in acetone and ultrasonically cleaned for 2 minutes. In the second cleaning step, the Si substrate was immersed in pure water and ultrasonically cleaned for 2 minutes. In the third wash, the Si substrate was immersed for 20 minutes after the solution was heated to 75 degrees Celsius (RCA SC1 wash). The solution consisted of pure water, hydrogen peroxide (35% by mass), and aqueous ammonia (29% by mass), with a volume ratio of pure water:hydrogen peroxide (35% by mass):ammonia (29% by mass) = 3:1:1. After the second wash and before the third wash, the Si substrate may be heat-treated at a temperature between 500°C and 800°C.

[0045] [Metal layer formation] Three types of metal layers were deposited on a Si wafer using DC sputtering, forming a two-layer structure of Pt (30 nm) / Ti (10 nm), Cu (30 nm) / Ti (10 nm), and Au (30 nm) / Ti (10 nm). The sputtering apparatus used was a magnetron sputtering apparatus (ULVAC QAM-4-ST), and the film was deposited under the following conditions. • Magnetic field strength: 1000 Gauss (directly above the target, vertical component) ·Achieved vacuum level: 5.0×10 -4 Pa or less • Sputtering gas: High-purity argon • Sputtering gas pressure inside the chamber: 0.18 Pa ·DC power: 150W • Board rotation speed: 10 rpm The film thicknesses of Ti, Pt, Cu, and Au thin films, which had been pre-deposited by sputtering for a predetermined time, were measured using a film thickness gauge (DEKTAK, ULVAC, Inc.), and the deposition rate under each deposition condition was calculated. Based on this, the deposition time was adjusted so that the film thicknesses of Pt, Cu, and Au were 30 nm each, and the film thickness of Ti was 10 nm.

[0046] Then, a first film deposition step was performed in which a buffer layer was formed on the substrate on which this metal layer was formed, and a second film deposition step was performed in which a PLZT film was formed on the buffer layer.

[0047] [First film formation process: buffer layer] The first film formation process consisted of a first coating step in which the surface of the substrate was coated with polyvinylpyrrolidone (hereinafter referred to as PVP), a second coating step in which the PVP was coated with lanthanum nitrate, a pre-calcination step in which the lanthanum nitrate on the substrate was pre-calcined, and a calcination step in which the lanthanum nitrate on the substrate was calcined, as follows.

[0048] In the first coating step, the PVP solution was applied to the substrate, and then the solvent was heated to evaporate it. The PVP solution was prepared by weighing 0.075 g of polyvinylpyrrolidone (k=15, average molecular weight 10,000) into a glass container, adding 19.7 g of 2-methoxyethanol (purity >99.0%), and stirring for 30 minutes. While k=30 (average molecular weight 40,000) or k=90 (average molecular weight 360,000) PVP may also be used, using lower molecular weight PVP allows for easier dissolution in the solvent. Furthermore, 5% to 20% by mass of pure water may be added to improve the solubility of the PVP.

[0049] Before adding the solution dropwise, the PVP solution was stirred to completely dissolve the PVP. Then, 1 mL of the PVP solution was dropped onto a substrate with a metal layer formed on it (hereinafter simply referred to as the substrate), and spin coating was performed using a spin coater. The spin coating was performed at 500 rpm for 5 seconds, followed by 4000 rpm for 30 seconds. After spin coating, as a step to evaporate the solvent, the substrate coated with the PVP solution was placed on a hot plate heated to 150°C for 1 minute.

[0050] In the second coating step, a lanthanum nitrate solution was applied to the PVP, and then the solvent was evaporated by heating. The lanthanum nitrate solution was prepared by weighing 0.15 g to 1.56 g of lanthanum nitrate hexahydrate (purity >99.0%) into a glass container, adding 2-methoxyethanol and pure water to make a total volume of 20 g, and stirring for 30 minutes. The amount of pure water was varied in the range of 0.1% to 30% by mass. The concentration of lanthanum nitrate (La(NO3)3) excluding the hydrate corresponds to 0.59% by mass to 5.9% by mass. The amount of water added means, for example, adding 0.2g of water for every 20g of total solution volume if the concentration is 1% by mass.

[0051] The total water volume listed in Table 1 includes the amount of hydrated water derived from lanthanum nitrate hexahydrate, and the mass concentration (mass%) is calculated as the weight ratio of water contained in the total solution weight. Similarly, the nitrate (La) concentration is calculated as the mass concentration (mass%) of La(NO3)3, excluding the mass of hydrated water, as the weight ratio of La(NO3)3 to the total solution weight. Furthermore, infrared spectroscopy, gas chromatography, microwave spectroscopy, and the Karl Fischer method can be used to quantify the water content in lanthanum nitrate solution.

[0052] Before adding the solution dropwise, the lanthanum nitrate solution was stirred to completely dissolve the lanthanum nitrate. Then, 1 mL of the lanthanum nitrate solution was added dropwise onto the PVP-coated substrate, and spin coating was performed using a spin coater. The spin coating was performed at 500 rpm for 5 seconds, followed by 4000 rpm for 30 seconds. After spin coating, the substrate coated with the lanthanum nitrate solution was placed on a hot plate heated to 150°C for 1 minute to allow the solvent to evaporate.

[0053] The pre-firing process involved placing the substrate on a hot plate heated to 300°C for 5 minutes, then gradually lowering the temperature of the substrate by placing it on a hot plate heated to 150°C for 30 seconds, and finally removing it from the hot plate and allowing it to cool in the air.

[0054] In the firing process, the substrates were fired in a firing apparatus at a firing temperature of 590°C, a temperature holding time of 60 seconds, and in an atmospheric firing environment. For each sample, the heating time t1 from room temperature to the firing temperature of 590°C was set to 720 seconds. A Rapid Thermal Annealing apparatus (RTA-8000) manufactured by Advance Engineering Co., Ltd. was used as the firing apparatus (hereinafter referred to as the RTA apparatus). Lanthanum nitrate was crystallized by the firing process. The thickness of the buffer layer could be increased by repeating the process from the first coating process of applying PVP to the second coating process and then to the firing process. For each sample, the number of layers that formed the base for the PLZT film was set to 4 layers (thickness 22 nm).

[0055] [Second film formation process: PLZT film] The second film formation step comprises a step of coating the PLZT sol-gel solution onto a buffer layer, a step of volatilizing the solvent, a calcination step of calcining the PLZT, and a calcination step of calcining the PLZT. The PLZT sol-gel solution used was E1 solution for thin film formation manufactured by Mitsubishi Materials Corporation (concentration 15%, metal composition ratio: Pb / La / Zr / Ti = 115 / 8 / 65 / 35).

[0056] The coating process involved dropping 1 ml of PLZT sol-gel solution onto a substrate with a buffer layer already formed, followed by spin coating using a spin coater. The spin coating was performed at 500 rpm for 5 seconds, followed by 4000 rpm for 30 seconds. After spin coating, the substrate coated with PLZT sol-gel solution was placed on a hot plate heated to 150°C for 1 minute to evaporate the solvent.

[0057] The pre-firing process involved placing the substrate on a hot plate heated to 300°C for 5 minutes, then gradually lowering the temperature of the substrate by placing it on a hot plate heated to 150°C for 30 seconds, and finally removing it from the hot plate and allowing it to cool in the air.

[0058] In the firing process, the substrate was fired using the aforementioned RTA apparatus at a firing temperature of 640°C, a temperature holding time of 60 seconds, and in an O2 atmosphere. For each sample, the heating time t2 from room temperature to the firing temperature of 640°C was set to 64 seconds. PLZT was crystallized by the firing process.

[0059] The PLZT film was formed by repeatedly applying the PLZT sol-gel solution and then firing it, adjusting the film thickness to 300 nm. In this case, ellipsometry was performed to calculate the film thickness of the PLZT film. A JAWoolam M-2000 was used for the measurement, and measurements were taken in reflection mode at three incident / reflection angles: 60°, 70°, and 80°. Cauchy's optical model was applied to the obtained results and fitted to determine the film thickness.

[0060] [Membrane evaluation] The appearance and orientation of PLZT films deposited on substrates were evaluated. (exterior) The appearance was judged visually and evaluated on a three-point scale: A: Excellent (no color unevenness observed on the surface), B: Good (no noticeable color unevenness on the surface), and C: Poor (significant color unevenness or patterns observed).

[0061] (Orientation) The orientation of the PLZT film was analyzed using an X-ray diffractometer. A fully automated multi-purpose X-ray diffractometer (SmartLab) manufactured by Rigaku Corporation was used. A copper tube was used for X-ray generation. The scan axis was set to 2θ / θ, and for the angular range of 10° to 60°, the sampling step was set to 0.01°, the scan speed to 10° / min, IS = 0.300 mm, RS1 = 5 mm, and RS2 = 5 mm. For the measurement, a slit was set up with an incident solar slit of 5°, an IS longitudinal side of 2 mm, a PSA of 0.5°, and a measurement solar slit of 5°, and a scintillation counter (Rigaku, SC-70) was used as the detector. The obtained XRD intensity data was subjected to peak search using integrated powder X-ray analysis software (PDXL2, Rigaku). In the evaluation of XRD intensity, the integrated intensity I of the PLZT(100) peak appearing between 21.00° and 23.00° was used. XY We measured it.

[0062] When measuring the in-plane distribution of XRD intensity of the PLZT film, the orientation flat of the substrate (wafer) was placed on the front side of the stage, and mapping measurements were taken at nine points along a line parallel to the orientation flat, with the center coordinates set to (0mm,0mm): (-40mm,0mm), (-20mm,0mm), (0mm,0mm), (20mm,0mm), (40mm,0mm), (0mm,40mm), (0mm,20mm), (0mm,-20mm), and (0mm,-40mm).

[0063] These integrated intensity I XY We calculate the standard deviation [Counts·degree] and further calculate the integrated intensity I of the 9 points. XY Of these, the maximum value [Counts·degree] was identified, and the ratio of the standard deviation to the maximum value was calculated.

[0064] The orientation of the PLZT film was evaluated as follows: a standard deviation / maximum value of 0.18 or less was considered to indicate high uniformity of PLZT orientation throughout the substrate, while a standard deviation / maximum value exceeding 0.18 was considered to indicate large variation in the degree of PLZT orientation throughout the substrate, resulting in a poor evaluation.

[0065] Table 1 shows the appearance and XRD intensity ratio (standard deviation / maximum value) of each sample.

[0066] [Table 1]

[0067] As shown in Table 1, samples 2-4, 7-9, 11, and 12 (amount of water added to the nitrate solution: 5%-20% by mass, total water volume: 5.4%-20.4% by mass, lanthanum nitrate concentration: 1.2%-3.5% by mass) all had good or very good appearance, and the standard deviation / maximum value of the XRD intensity was 0.03-0.17, indicating the formation of a uniform dielectric orientation film. In particular, samples 3 and 7, with a water addition amount of 10% by mass, a total water volume of 10.2%-10.4% by mass, and a lanthanum nitrate concentration of 1.2%-1.8% by mass, had very good appearance and the standard deviation / maximum value of the XRD intensity was 0.04 or less. Furthermore, as shown in samples 11 and 12, it can be seen that this method is suitably applicable not only to Pt but also to metal layers using Cu and Au.

[0068] In contrast, sample 1, which did not have water added to the lanthanum nitrate solution, resulted in a non-uniform film with visible unevenness, and the standard deviation / maximum XRD intensity was high at 0.24. Sample 5 had too much water added to the lanthanum nitrate solution, resulting in a radial pattern (color unevenness) on the surface and a poor appearance. The standard deviation / maximum XRD intensity was also high at 0.27. Sample 6 had a low lanthanum nitrate concentration, which prevented uniform film formation and resulted in a film with color unevenness. The standard deviation / maximum XRD intensity was also high at 0.25. Furthermore, sample 10 had a high lanthanum nitrate concentration of 4.7 mass%, resulting in color unevenness, and the standard deviation / maximum XRD intensity was also high at 0.22.

[0069] From these results, it can be seen that if the ratio of XRD intensities of the PLZT film (standard deviation / maximum value) is 0.18 or less, a uniform laminated film without appearance defects can be formed even on a metal layer. [Explanation of Symbols]

[0070] 1. Thin-film coated substrate (multilayer coated substrate) 10 Main board 20 Multilayer film 210 buffer layers 220 Ferroelectric Thin Film

Claims

1. The device comprises a buffer layer made of an oxide mainly composed of La formed on a metal layer, and a PZT-based ferroelectric thin film made of PZT or PLZT formed on the buffer layer, The integral intensity of the peak of the PZT-based ferroelectric thin film (100) at each of the nine XRD intensities in the plane of the PZT-based ferroelectric thin film is I ＸＹ [Counts・degree] is the integrated intensity I in the plane. ＸＹ A laminated film characterized in that the ratio of the standard deviation to the maximum value (standard deviation / maximum value) is 0.18 or less.

2. A substrate with a laminated film, characterized by comprising a substrate body, a metal layer formed on the substrate body, and a laminated film according to claim 1 formed on the metal layer.

3. The laminated substrate according to claim 2, characterized in that the metal layer contains platinum (Pt), gold (Au), or copper (Cu).

4. An electro-optical device comprising a laminated substrate according to claim 2 or 3.

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