Lead zirconate titanate composite film with high electro-optical coefficient, preparation method of lead zirconate titanate composite film and electro-optical modulator

Abstract

The invention provides a lead zirconate titanate composite film with a high electro-optical coefficient, a preparation method of the lead zirconate titanate composite film and an electro-optical modulator, the lead zirconate titanate composite film comprises an insulating substrate, a buffer layer and a ferroelectric main body layer which are sequentially stacked, and the buffer layer is a lanthanum-doped lead zirconate titanate film; the ferroelectric main body layer is a lead zirconate titanate thin film and has (001) / (100) orientation. The composite film has a relatively high electro-optical coefficient, relatively low driving voltage and relatively high thermal stability.

Description

Technical Field

[0001] This invention relates to the field of functional materials technology, specifically to a lead zirconate titanate composite thin film with a high electro-optic coefficient, its preparation method, and an electro-optic modulator. Background Technology

[0002] An electro-optic modulator (EOM) is a core device that utilizes the electro-optic effect of an electro-optic crystal thin film to modulate optical signals. Its performance directly depends on the electro-optic coefficient of the electro-optic crystal thin film. Lead zirconate titanate (PZT, e.g., PbZr) ferroelectric materials... 0.52 Ti 0.48 O3 has attracted much attention due to its high Curie temperature and potential high electro-optic effect, but its theoretical electro-optic coefficient (~13 pm / V) still falls short of the requirements of practical applications.

[0003] Therefore, it is urgent to improve the electro-optic coefficient of PZT thin films. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a lead zirconate titanate composite film with a high electro-optic coefficient, a method for preparing the same, and an electro-optic modulator, aiming to improve the electro-optic coefficient of PZT films.

[0005] In a first aspect, embodiments of this application provide a lead zirconate titanate composite thin film with a high electro-optic coefficient, comprising an insulating substrate, a buffer layer and a ferroelectric host layer stacked sequentially, wherein the buffer layer is a lanthanum-doped lead zirconate titanate thin film and the ferroelectric host layer is a lead zirconate titanate thin film having a (001) / (100) orientation.

[0006] Optionally, in some embodiments of this application, the material of the buffer layer is Pb. 0.9 La 0.1 Zr x Ti 1-x O3, the material of the ferroelectric host layer is PbZr y Ti 1-y O3, where x is 0.52~0.8 and y is 0.52~0.8.

[0007] Optionally, in some embodiments of this application, the thickness of the buffer layer is 5~20 nm, and the thickness of the ferroelectric host layer is 300~3000 nm.

[0008] Optionally, in some embodiments of this application, the insulating substrate is a Si substrate with an amorphous SiO2 layer, or a quartz glass substrate with an amorphous SiO2 layer.

[0009] Secondly, embodiments of this application provide a method for preparing the lead zirconate titanate composite thin film described above, comprising the following steps: Provide PbZr y Ti 1-y O3 precursor sol and Pb 0.9 La 0.1 Zr x Ti 1-x O3 precursor sol; The Pb is coated on an insulating substrate 0.9 La 0.1 Zr x Ti 1-x O3 precursor sol is subjected to a first heat treatment to obtain a buffer layer; The PbZr is coated on the side of the buffer layer opposite to the insulating substrate. y Ti 1-y O3 precursor sol is subjected to a second heat treatment to obtain the ferroelectric host layer; Where x is 0.52~0.8 and y is 0.52~0.8.

[0010] Optionally, in some embodiments of this application, the first heat treatment step includes: baking at 200~300℃ for 10~30 min, baking at 400~500℃ for 10~30 min, and finally annealing at 600~700℃ for 10~30 min.

[0011] Optionally, in some embodiments of this application, the second heat treatment step includes: first baking at 200~300℃ for 10~30 min, then baking at 400~500℃ for 10~30 min, and finally annealing at 600~700℃ for 10~30 min.

[0012] Optionally, in some embodiments of this application, the thickness of the buffer layer is 5~20 nm, and the thickness of the ferroelectric host layer is 300~3000 nm.

[0013] Optionally, in some embodiments of this application, the insulating substrate is a Si substrate with an amorphous SiO2 layer, or a quartz glass substrate with an amorphous SiO2 layer.

[0014] Optionally, in some embodiments of this application, PbZr is provided. y Ti 1-y O3 precursor sol and Pb 0.9 La 0.1 Zr x Ti 1-x The steps involved in producing the O3 precursor sol include: A first titanium source, a first zirconium source, a first solvent, and acetylacetone are mixed and stirred at 70–120°C for 1–3 h to obtain a first mixed solution. A first lead source, acetic acid, and ethylene glycol methyl ether are mixed and stirred at 70–110°C for 1–2 h to obtain a first lead solution. The first lead solution is added to the first mixed solution and stirred at 20–40°C for 1–2 h to obtain PbZr. y Ti 1-y O3 precursor sol; and A second titanium source, a second zirconium source, a second solvent, and acetylacetone are mixed and stirred at 70–120 °C for 1–3 h to obtain a second mixed solution. A second lead source, a lanthanum source, acetic acid, and ethylene glycol methyl ether are mixed and stirred at 70–110 °C for 1–2 h to obtain a third mixed solution. The third mixed solution is added to the second mixed solution and stirred at 20–40 °C for 1–2 h to obtain Pb. 0.9 La 0.1 Zr x Ti 1-x O3 precursor sol.

[0015] Optionally, in some embodiments of this application, the molar ratio of lead in the first lead source, zirconium in the first zirconium source, and titanium in the first titanium source is 1.2:y:(1-y).

[0016] Optionally, in some embodiments of this application, the molar ratio of lead in the second lead source, lanthanum in the lanthanum source, zirconium in the second zirconium source, and titanium in the second titanium source is 1.08:0.1:x:(1-x).

[0017] Optionally, in some embodiments of this application, the molar ratio of the chelating agent to lead is (1~2):1.

[0018] Optionally, in some embodiments of this application, the first titanium source and the second titanium source are tetrabutyl titanate, respectively.

[0019] Optionally, in some embodiments of this application, the first zirconium source and the second zirconium source are respectively zirconium n-propoxide.

[0020] Optionally, in some embodiments of this application, the first lead source and the second lead source are each independently selected from lead acetate or lead nitrate.

[0021] Optionally, in some embodiments of this application, the lanthanum source includes lanthanum nitrate.

[0022] Optionally, in some embodiments of this application, the first solvent and the second solvent each independently include one or more of acetic acid, ethylene glycol methyl ether, and N,N-dimethylformamide.

[0023] Thirdly, embodiments of this application propose an electro-optic modulator, including the lead zirconate titanate composite film described above, or the lead zirconate titanate composite film prepared by the preparation method described above.

[0024] The technical solution proposed in this application has the following beneficial effects: The lead zirconate titanate composite film proposed in this application has a three-layer composite structure of insulating substrate / lanthanum-doped PZT buffer layer / PZT ferroelectric host layer, and the ferroelectric host layer based on PZT material has a (001) / (100) mixed orientation, which makes the composite film have a high electro-optic coefficient, a low driving voltage and a high thermal stability. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of this application, the accompanying drawings used in this application will be briefly described below. Obviously, the drawings described below are merely some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0026] Figure 1 This is a schematic diagram of a method for preparing a lead zirconate titanate composite thin film according to an embodiment of this application; Figure 2 The image shows a cross-sectional SEM image of the composite film prepared in Example 3 of Experimental Example (I). Figure 3 The images show cross-sectional SEM images and detailed TEM images of the composite film prepared in Example 4 of Experimental Example (I). Figure 4 The XRD pattern of the composite film prepared in Example 1 of Experimental Example (II); Figure 5 The XRD pattern of the composite film prepared in Example 2 of Experimental Example (II); Figure 6 The XRD pattern of the composite film prepared in Example 3 of Experimental Example (II); Figure 7 The XRD pattern of the composite film prepared in Example 4 of Experimental Example (II); Figure 8 The XRD pattern of the composite film prepared in Example 5 of Experimental Example (II); Figure 9 The XRD pattern of the composite film prepared in Comparative Example 1 in Experimental Example (II); Figure 10The XRD pattern of the composite film prepared in Comparative Example 2 of Experimental Example (II); Figure 11 The XRD pattern of the composite film prepared in Comparative Example 3 in Experimental Example (II); Figure 12 The XRD pattern of the composite film prepared in Comparative Example 4 in Experimental Example (II); Figure 13 The XRD pattern of the composite film prepared in Comparative Example 5 in Experimental Example (II); Figure 14 The hysteresis loops of the composite films prepared in Examples 1-5, Comparative Examples 1, 4 and 5 in Experimental Example (III); Figure 15 The electro-optic coefficient fitting spectra of the composite films prepared in Examples 1 to 4 and Comparative Example 6 in Experimental Example (IV); Figure 16 Photographs of the spatial electro-optic effect testing devices used in Experiments (III) and (IV); Figure 17 The distribution of refractive index n and extinction coefficient k of the composite thin film prepared in Example 1 of Experimental Example (III) at different wavelengths; Figure 18 The distribution of refractive index n and extinction coefficient k of the composite thin film prepared in Example 4 of Experiment (III) at different wavelengths; Figure 19 The dielectric capacitance temperature spectrum of the composite thin film prepared in Example 1; Figure 20 An optical microscope image of the composite film prepared in Comparative Example 2. Detailed Implementation

[0027] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0029] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0030] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0031] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0032] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0033] In the description of the embodiments of this application, the term "at least one" refers to one or more, "more than one" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces). "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c," or "at least one of a, b, and c," can all represent: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0034] To improve the electro-optic coefficient of PZT thin films, the commonly used method is to optimize the film orientation to a single (100) orientation by preparing buffer layers such as La2O3 or La2O3CO3 on the substrate. However, the films prepared in this way are subject to interfacial stress, resulting in limited improvement in the electro-optic coefficient, which is far lower than that of barium titanate systems. In view of this, this application proposes a lead zirconate titanate composite thin film with a high electro-optic coefficient, its preparation method, and an electro-optic modulator. The optimization is achieved from the perspective of the composite structure and specific mixed orientation, breaking through the theoretical limit of the electro-optic coefficient of traditional single-orientation optimized or epitaxial PZT thin films.

[0035] In a first aspect, embodiments of this application provide a lead zirconate titanate composite thin film, comprising an insulating substrate, a buffer layer, and a ferroelectric host layer stacked sequentially, wherein the buffer layer is a lanthanum-doped lead zirconate titanate thin film, and the ferroelectric host layer is a lead zirconate titanate thin film having a (001) / (100) orientation.

[0036] The lead zirconate titanate composite thin film proposed in this application has a three-layer composite structure of an insulating substrate / lanthanum-doped PZT buffer layer / lead zirconate titanate ferroelectric host layer. The ferroelectric host layer based on lead zirconate titanate material has a (001) / (100) mixed orientation, which makes it easier to generate polarization reversal under an electric field, resulting in a large change in refractive index. This gives the composite thin film a high electro-optic coefficient, a low driving voltage, and high thermal stability (Curie temperature approximately 347℃). Specifically, the electro-optic coefficient reflects the rate of change of refractive index (Δn) with respect to the electric field E. The specific combination of ((001) / (100)) dual orientation mixing allows the thin film to undergo phase transition and domain polarization change under an in-plane electric field. The phase transition can generate 10... -1 A change in refractive index on the order of magnitude can produce domain polarization of 10. -2The refractive index change is on the order of magnitude, thus generating a large electro-optic effect overall; however, if the film has a single (001) orientation, a single (100) orientation, or a mixed orientation of other combinations (e.g., (100) and (110) main orientations), the electro-optic effect is poor. In some embodiments, the electro-optic coefficient of the composite film proposed in this application can reach 233.5 pm / V. In this embodiment, a lanthanum-doped PZT buffer layer is used, which can induce the orientation of the ferroelectric host layer and control the orientation to a (001) / (100) mixed orientation. If other lanthanum compounds or PZT doped with other elements are used as the buffer layer, the orientation may become uncontrollable. By performing lattice-matched growth on the lanthanum-doped PZT buffer layer / insulating substrate, the clamping effect caused by lattice mismatch is significantly reduced, which helps to reduce the polarization modulation coercivity voltage. The composite film proposed in this embodiment has a low driving voltage and an in-plane coercivity field of about 4.3 kV / cm, which is at least one order of magnitude lower than the polarization modulation coercivity voltage (>100 kV / cm) of traditional PZT films (grown on an epitaxial substrate with interfacial stress clamping), thus helping to reduce device power consumption. In addition, the design of the insulating substrate also makes the composite film highly compatible with the manufacturing process of electro-optic modulators.

[0037] In some specific embodiments of this application, the material of the buffer layer may be Pb. 0.9 La 0.1 Zr x Ti 1-x O3, the material of the ferroelectric host layer can be PbZr. y Ti 1-y O3, where x and y satisfy charge balance within their respective chemical formulas. Furthermore, x and y can both be any values ​​within the range of 0.52 to 0.8. It can be understood that x and y can have the same or different values.

[0038] In some embodiments of this application, the thickness of the buffer layer is 5~20nm, for example, it can be 5nm, 8nm, 10nm, 12nm, 15nm, 18nm, 20nm, or any value between any two of the above; the thickness of the ferroelectric host layer is 300~3000 nm, for example, it can be 300nm, 500nm, 700nm, 1000nm, 1300nm, 1500nm, 1700nm, 2000nm, 2300nm, 2500nm, 2800nm, 3000nm, or any value between any two of the above. By controlling the thickness of the buffer layer and the ferroelectric host layer within the above ranges, the induction effect on the crystal orientation of the ferroelectric host layer can be adjusted, stabilizing the crystal orientation in a (001) / (100) mixed orientation; if the thickness is too thin, for example, less than 100nm, it may lead to growth into a (001) preferred orientation.

[0039] In some embodiments of this application, the insulating substrate is a Si substrate with an amorphous SiO2 layer, or a quartz glass substrate with an amorphous SiO2 layer. The insulating substrate can be commercially available or prepared by using a single-crystal silicon substrate or a quartz glass substrate with a thickness of at least 0.5 mm, followed by thermal oxidation treatment of the substrate surface to form an amorphous SiO2 layer with a thickness of approximately 3000 nm.

[0040] Secondly, please refer to Figure 1 This application provides a method for preparing the lead zirconate titanate composite film described above, comprising the following steps: S10 provides PbZr y Ti 1-y O3 precursor sol and Pb 0.9 La 0.1 Zr x Ti 1-x O3 precursor sol; where x is 0.52~0.8 and y is 0.52~0.8.

[0041] S20, coating the Pb onto the insulating substrate. 0.9 La 0.1 Zr x Ti 1-x The O3 precursor sol is subjected to a first heat treatment to obtain a buffer layer.

[0042] S30, coating the buffer layer on the side facing away from the insulating substrate with the PbZr. y Ti 1-y The O3 precursor sol is subjected to a second heat treatment to obtain the ferroelectric host layer.

[0043] The method described in this application involves preparing a La-doped PZT buffer layer and a PZT ferroelectric host layer on an insulating substrate using a sol-gel method. Through method optimization and the design of a specific buffer layer, the orientation of the ferroelectric host layer is optimized, achieving the formation of a (001) / (100) mixed orientation. This composite film exhibits a high electro-optic coefficient, a low driving voltage, and high thermal stability.

[0044] In some embodiments of this application, step S10 may be implemented through the following steps: S11, the first titanium source, the first zirconium source, the first solvent, and acetylacetone are mixed to obtain a first mixed solution; the first lead source, acetic acid, and ethylene glycol methyl ether are mixed to obtain a first lead solution; the first lead solution is added to the first mixed solution to obtain PbZr. y Ti 1-y O3 precursor sol; and S12, the second titanium source, the second zirconium source, the second solvent, and acetylacetone are mixed to obtain a second mixed solution; the second lead source, lanthanum source, acetic acid, and ethylene glycol methyl ether are mixed to obtain a third mixed solution; the third mixed solution is added to the second mixed solution to obtain Pb. 0.9 La 0.1 Zr x Ti 1-x O3 precursor sol.

[0045] This application optimizes the preparation of precursor sols by controlling particle size and crystallinity, thereby regulating film orientation. Specifically, in the sol-gel preparation process, film orientation is affected by the sol (e.g., the rate of particle condensation and particle size). To synthesize the PZT phase, lead sources are often added in excess, which can easily affect the chelation process of the sol by mixing the three precursors. Adding Pb precursors to Zr / Ti precursors allows Pb to pair uniformly with Zr / Ti. The excess Pb can compensate for Pb volatilization during the sol baking process, thus tending to form a mixed orientation. Conversely, adding Zr / Ti precursors to Pb precursors makes Zr / Ti easier to separate, greatly increasing the probability of each Pb particle pairing with Ti. This results in Pb being uniformly dispersed within the Zr / Ti condensation network during sol volatilization and crystallization, potentially contributing to a single crystallization kinetic and resulting in a single crystallization orientation.

[0046] Furthermore, to achieve better mixing and improve film quality, the preparation temperature of the precursor solution can be optimized. In some embodiments, step S10 may specifically include: S11, the first titanium source, the first zirconium source, the first solvent, and acetylacetone are mixed and stirred at 70-120°C for 1-3 hours to obtain a first mixed solution; the first lead source, acetic acid, and ethylene glycol methyl ether are mixed and stirred at 70-110°C for 1-2 hours to obtain a first lead solution; the first lead solution is added to the first mixed solution and stirred at 20-40°C for 1-2 hours to obtain PbZr. y Ti 1-y O3 precursor sol; and S12, a second titanium source, a second zirconium source, a second solvent, and acetylacetone are mixed and stirred at 70-120°C for 1-3 hours to obtain a second mixed solution; a second lead source, a lanthanum source, acetic acid, and ethylene glycol methyl ether are mixed and stirred at 70-110°C for 1-2 hours to obtain a third mixed solution; the third mixed solution is added to the second mixed solution and stirred at 20-40°C for 1-2 hours to obtain Pb. 0.9 La 0.1 Zr x Ti 1-x O3 precursor sol.

[0047] In some embodiments of this application, the first titanium source and the second titanium source may be the same or different, and they may be independently selected from commonly used titanium salts or titanium oxides, such as tetrabutyl titanate.

[0048] In some embodiments of this application, the first zirconium source and the second zirconium source may be the same or different, and they may be independently selected from commonly used zirconium salts, such as zirconium n-propoxide.

[0049] In some embodiments of this application, the first lead source and the second lead source may be the same or different, and they may be independently selected from commonly used lead salts, such as lead acetate or lead nitrate.

[0050] In some embodiments of this application, the lanthanum source can be a commonly used lanthanum salt, such as lanthanum nitrate.

[0051] In some embodiments of this application, the first solvent and the second solvent may be the same or different, and may be independently selected from one or more of acetic acid, ethylene glycol methyl ether, and N,N-dimethylformamide. Using the above solvents helps to improve sol performance and film quality. It is understood that the first and second solvents are used to provide a liquid-phase reaction environment, and this application does not limit the specific amounts of the first and second solvents added, provided that their solute concentration is less than or equal to 0.1 mol / L.

[0052] As a preferred embodiment, when tetrabutyl titanate is used as the titanium source, zirconium propoxide as the zirconium source, lead acetate or lead nitrate as the lead source, and acetic acid, ethylene glycol methyl ether or N,N dimethylformamide is used, the resulting precursor sol is conducive to the formation of a perovskite film with a (001) / (100) mixed orientation.

[0053] In some embodiments of this application, the molar ratio of lead in the first lead source, zirconium in the first zirconium source, and titanium in the first titanium source is 1.2:y:(1-y), where y is 0.52~0.8.

[0054] In some embodiments of this application, the molar ratio of lead in the second lead source, lanthanum in the lanthanum source, zirconium in the second zirconium source, and titanium in the second titanium source is 1.08:0.1:x:(1-x), where x is 0.52~0.8.

[0055] In some embodiments of this application, the molar ratio of the chelating agent to lead is (1~2):1; for example, it can be 1:1, 1.2:1, 1.5:1, 1.7:1, 2:1, or any value between any two of the above.

[0056] In some embodiments of this application, the thickness of the buffer layer is 5-20 nm, and the thickness of the ferroelectric host layer is 300-3000 nm. Thickness optimization helps to control the orientation of the thin film.

[0057] In some embodiments of this application, the insulating substrate is a Si substrate with an amorphous SiO2 layer, or a quartz glass substrate with an amorphous SiO2 layer.

[0058] In some embodiments of this application, the first heat treatment step includes: baking at 200-300°C for 10-30 minutes, then baking at 400-500°C for 10-30 minutes, and finally annealing at 600-700°C for 10-30 minutes. In other embodiments of this application, the second heat treatment step includes: baking at 200-300°C for 10-30 minutes, then baking at 400-500°C for 10-30 minutes, and finally annealing at 600-700°C for 10-30 minutes. The embodiments of this application employ a three-stage heat treatment and regulate the crystallization temperature within the aforementioned range. This allows for control of the polycondensation rate, grain size, and selective generation of multiple crystal planes, facilitating the formation of mixed orientations. Furthermore, the annealing process and sol-gel process proposed in the embodiments of this application are compatible with silicon-based CMOS processes, suitable for wafer-level fabrication, resulting in high integration compatibility for the composite thin film of this application.

[0059] It is understandable that when preparing the buffer layer and the ferroelectric host layer, they can be prepared in multiple stages according to the target thickness. For example, a layer of sol can be coated first, and then baked and heat-treated. The above steps can be repeated multiple times until the target thickness is reached, and then annealing can be performed.

[0060] Thirdly, embodiments of this application propose an electro-optic modulator, which includes the lead zirconate titanate composite film described above, or the lead zirconate titanate composite film prepared by the preparation method described above, and has better modulation effect, lower device power consumption and better thermal stability.

[0061] The following are some specific embodiments. It should be noted that the embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0062] Example 1 (1) Surface thermal oxidation of 0.5 mm thick single crystal silicon until an amorphous SiO2 layer with a thickness of about 3000 nm is formed to obtain a SiO2 / Si insulating substrate.

[0063] (2) According to the molar ratio of Pb, Zr and Ti of 1.2:0.52:0.48 and the molar ratio of acetylacetone to Pb of 1:1, a first Ti / Zr mixed solution and a first Pb solution were prepared respectively. Then, the first Pb solution was added to the first Ti / Zr mixed solution and stirred at 25°C for 1.5 h to obtain PbZr. 0.52 Ti 0.48 O3 precursor sol.

[0064] The preparation steps of the Ti / Zr first mixed solution are as follows: Tetrabutyl titanate, zirconium propoxide, ethylene glycol methyl ether, acetic acid and acetylacetone are mixed and stirred at 100℃ for 2 hours to obtain the Ti / Zr first mixed solution. The amount of acetic acid and ethylene glycol methyl ether fed is such that the volume ratio of acetic acid to ethylene glycol methyl ether is 1.5:1, and the total molar concentration of titanium ions and zirconium ions in the Ti / Zr first mixed solution is 0.1 mol / L.

[0065] The preparation steps of the first Pb solution are as follows: lead acetate, ethylene glycol methyl ether, and acetic acid are mixed and stirred at 100°C for 1.5 h to obtain the first Pb solution. The amounts of acetic acid and ethylene glycol methyl ether added meet the following requirements: the volume ratio of acetic acid to ethylene glycol methyl ether is 1.5:1, and the molar concentration of Pb is 0.1 mol / L.

[0066] (3) According to the molar ratio of Pb, La, Zr and Ti of 1.08:0.1:0.52:0.48 and the molar ratio of acetylacetone to Pb of 1:1, a second Ti / Zr mixed solution and a second Pb solution were prepared respectively. Then, the second Pb solution was added to the second Ti / Zr mixed solution and stirred at 25°C for 1.5 h to obtain Pb. 0.9 La 0.1 Zr 0.52 Ti 0.48 O3 precursor sol.

[0067] The preparation steps of the Ti / Zr second mixed solution are as follows: Tetrabutyl titanate, zirconium n-propoxide, ethylene glycol methyl ether, acetic acid and acetylacetone are mixed and stirred at 100℃ for 2 hours to obtain the Ti / Zr second mixed solution. The amount of acetic acid and ethylene glycol methyl ether fed is such that the volume ratio of acetic acid to ethylene glycol methyl ether is 1.5:1, and the total molar concentration of titanium ions and zirconium ions in the Ti / Zr first mixed solution is 0.1 mol / L.

[0068] The preparation steps of the second Pb solution are as follows: lead acetate, lanthanum nitrate, ethylene glycol methyl ether, and acetic acid are mixed and stirred at 100°C for 1.5 h to obtain the second Pb solution. The amounts of acetic acid and ethylene glycol methyl ether added meet the following requirements: the volume ratio of acetic acid to ethylene glycol methyl ether is 1.5:1, and the molar concentration of Pb is 0.1 mol / L.

[0069] (4) Using Pb 0.9 La 0.1 Zr 0.52 Ti 0.48 O3 precursor sol was spin-coated on an insulating substrate at a spin speed of 4000 r / min for 20 s. The substrate was then baked at 200℃ for 10 min, followed by baking at 450℃ for 10 min. This process was repeated once, and finally annealed at 650℃ for 10 min to obtain a buffer layer with a thickness of approximately 10 nm.

[0070] (5) Using PbZr 0.52 Ti 0.48 O3 precursor sol was spin-coated onto a buffer layer at 300 rpm for 5 seconds, followed by high-speed spin-coating at 4000 rpm for 20 seconds. The mixture was then baked at 200°C for 10 minutes, then at 450°C for 10 minutes, and this process was repeated 10 times. Finally, the mixture was annealed at 650°C for 10 minutes to obtain a ferroelectric host layer with a thickness of approximately 960 nm. Figure 19 As shown, the Curie temperature of the composite film is approximately 347℃, as determined by the surface parallel interdigitated electrode dielectric capacitance temperature spectrum test method.

[0071] Example 2 The scheme of this embodiment is basically the same as that of embodiment 1. The only difference is that in this embodiment, the thickness of the ferroelectric main body layer is changed to 700nm. Correspondingly, in step (5), spin coating is repeated 6 times.

[0072] Apart from this, all other parameters and conditions remain unchanged.

[0073] Example 3 The scheme in this embodiment is basically the same as that in embodiment 1, except that in step (2) of this embodiment, the molar ratio of Pb, Zr and Ti is 1.2:0.8:0.2, and correspondingly: Step (2) is modified as follows: Prepare a Ti / Zr first mixed solution and a first Pb solution according to the molar ratio of Pb, Zr and Ti of 1.2:0.8:0.2 and the molar ratio of acetylacetone to Pb of 1:1. Then add the first Pb solution to the Ti / Zr first mixed solution and stir at 20°C for 2 hours to obtain PbZr. 0.8 Ti 0.2 O3 precursor sol; In step (5), PbZr is used. 0.8 Ti 0.2 The ferroelectric host layer was prepared by O3 precursor sol, and the thickness of the obtained ferroelectric host layer was approximately 968 nm.

[0074] Apart from this, all other parameters and conditions remain unchanged.

[0075] Example 4 The scheme in this embodiment is basically the same as that in embodiment 1, except that in this embodiment, the monocrystalline silicon in step (1) is replaced with quartz glass, and correspondingly, step (5) is changed to: Spin coating was performed on the buffer layer at a speed of 300 r / min for 5 s, followed by high-speed spin coating at a speed of 4000 r / min for 20 s. The layer was then baked at 250 °C for 30 min, then at 400 °C for 30 min. The above steps were repeated 10 times. Finally, the layer was annealed at 600 °C for 30 min to obtain a ferroelectric host layer with a thickness of approximately 968 nm.

[0076] Apart from this, all other parameters and conditions remain unchanged.

[0077] Example 5 The scheme in this embodiment is basically the same as that in embodiment 4. The only difference is that in this embodiment, the thickness of the ferroelectric main body layer is changed to 340nm. Accordingly, in step (5), spin coating is repeated 4 times.

[0078] Apart from this, all other parameters and conditions remain unchanged.

[0079] Comparative Example 1 The comparative example scheme is basically the same as that of Example 1, except that the buffer layer in this comparative example uses PbTiO3, and correspondingly: Step (3) is changed to: mix PbTiO3, ethylene glycol methyl ether and acetic acid, and stir at 25°C for 1.5 h to obtain PbTiO3 precursor sol.

[0080] And in step (4), Pb 0.9 La 0.1 Zr 0.52 Ti 0.48 The O3 precursor sol was replaced with a PbTiO3 precursor sol.

[0081] Apart from this, all other parameters and conditions remain unchanged.

[0082] Comparative Example 2 This comparative example is basically the same as Example 1, except that the step "baking at 200°C for 10 minutes" is removed from step (5) of this comparative example. Other than that, all other parameters and conditions remain unchanged.

[0083] Comparative Example 3 This comparative example is basically the same as Example 1, except that the thickness of the ferroelectric host layer is changed to 100 nm. All other parameters and conditions remain unchanged.

[0084] Comparative Example 4 This comparative example is basically the same as Example 1, except that in step (2) of this comparative example, the PbZr preparation is... 0.52 Ti 0.48 When preparing the O3 precursor sol, the feeding sequence is "adding the first Ti / Zr mixed solution to the first Pb solution". Other than this, all other parameters and conditions remain unchanged.

[0085] Comparative Example 5 This comparative example is basically the same as Example 1, except that the following adjustments are made in this comparative example: 1. In step (2), during the preparation of PbZr 0.52 Ti 0.48 When preparing O3 precursor sol, the feeding sequence is "add the first Ti / Zr mixed solution to the first Pb solution".

[0086] 2. The buffer layer material is changed to La2O3, and step (3) is changed to: mixing La2O3, ethylene glycol methyl ether, acetic acid, and citric acid, and stirring at 25°C for 1.5 h to obtain the La2O3 precursor sol. And in step (4), Pb... 0.9 La 0.1 Zr 0.52 Ti 0.48The O3 precursor sol was replaced with a La2O3 precursor sol.

[0087] 3. Remove the step “Bake at 200℃ for 10 min” from step (5).

[0088] Apart from this, all other parameters and conditions remain unchanged.

[0089] Experimental Example (1): SEM Detection The composite films prepared in Examples 3 and 4 were examined cross-sections using a field emission scanning electron microscope (SEM). The results are as follows: Figures 2 to 3 As shown.

[0090] Results analysis: As can be seen from the figures, the ferroelectric host layer in the films prepared in Examples 3 and 4 has a uniform thickness (968 nm and 340 nm, respectively), small uniformity deviation (1.8% and 1.8%, respectively), and exhibits columnar growth. Figure 3 The right image in the middle is a TEM image of a portion of the thin film, which shows that a buffer layer is placed between the ferroelectric host layer and the insulating substrate, and the thin film has a three-layer structure.

[0091] Experimental Example (II) Orientation Characterization The composite films prepared in each embodiment and comparative example were tested using X-ray diffraction (XRD). The test results are as follows: Figures 4 to 13 As shown in the figure, the horizontal axis represents the diffraction angle (2θ), and the vertical axis represents the diffraction intensity. Figure 4 , Figure 5 , Figure 7 , Figure 12 and Figure 13 The small image on the right is a magnified view of the details of the left image.

[0092] Results Analysis: The XRD patterns of each embodiment show that the composite film exhibits a predominant orientation of (100) and (001). Figure 5 In the magnified image, an asymmetrical protrusion appears on the left side of the peak, namely the (001) peak, indicating that the preparation method proposed in this application produces a composite film with (001) / (100) orientation; The composite film of Comparative Example 1 exhibits a (100) and (110) main orientation, while the composite film of Comparative Example 5 exhibits a (001) single orientation. This indicates that by using lanthanum-doped PZT as a buffer layer, it is helpful to control the film orientation and regulate it to a (100) and (110) main orientation.

[0093] Comparative Example 2's composite film exhibits predominantly (100) and (001) orientations, but observation using an optical microscope revealed that, as... Figure 20As shown, the presence of pores and microcracks on the film indicates that the heat treatment process lacks the step of "baking at 200~300℃ for 10~30 minutes", which affects the film formation effect and is not conducive to obtaining products with better electro-optical properties.

[0094] The orientation of the composite film in Comparative Example 3 was difficult to detect and was not obvious. In contrast, the composite films in Examples 1, 4 and 5 showed obvious dual orientations, indicating that controlling the thickness of the ferroelectric host layer at 300~3000 nm is more conducive to controlling the (100) and (001) main orientations.

[0095] Comparative Example 4 shows the main orientations as (100) and (001).

[0096] Experimental Example (III) Ferroelectric Performance Testing The composite films prepared in Examples 1 to 5, Comparative Examples 1, 4, and 5 were tested, and their hysteresis loops were measured (the composite films of Comparative Examples 2 and 3 showed significant defects in Experimental Example (II) and were not included in subsequent performance tests). The results are as follows: Figure 14 As shown in the figure, the horizontal axis E represents the electric field strength, and the vertical axis Q represents the polarization intensity.

[0097] The testing method is as follows: Two Au electrodes are connected to the composite film, and an external power supply is connected through the electrodes to build a test device. The structure of the device is as follows. Figure 16 As shown, when the device is powered on, the intensity change of polarization charge Q of the composite thin film under one electric field cycle is detected by a ferroelectric analyzer, and the hysteresis loop is plotted.

[0098] Results Analysis: The hysteresis loops of each embodiment show that the polarization intensity P and the electric field E of their respective composite films change nonlinearly under the action of an applied electric field, indicating that the preparation method proposed in this application has successfully prepared films with good ferroelectric polarization reversal effect; while the hysteresis loop of Comparative Example 1 shows that its in-plane ferroelectric polarization effect is not obvious, indicating that the composite films with (100) and (110) main orientations have poor ferroelectricity and do not have the basic conditions for good electro-optic effect; Comparative Example 4 has no obvious ferroelectricity, large leakage current and many defects, indicating that by adopting the feeding sequence of adding the first Pb solution to the first Ti / Zr mixed solution, not only can (100) and (001) main orientations be formed, but it is also more conducive to forming films with ferroelectric properties.

[0099] Experimental Example (IV) Thin Film Performance Testing (1) The in-plane coercive field Ec of the composite film was obtained according to the hysteresis loop of Experiment Example (3), and the results were recorded in Table 1.

[0100] (2) The composite films prepared in Examples 1 to 4 and Comparative Example 6 were tested using the Stocks vector method and the Teng-Man simple reflection method (780 nm). The curves of refractive index n versus polarization electric field intensity E were plotted to determine the electro-optic coefficient. The results are as follows: Figure 15 As shown in Table 1.

[0101] Table 1

[0102] Results analysis: Each embodiment exhibits a higher electro-optic coefficient and a lower in-plane coercive field than Comparative Example 6, indicating that the composite film prepared in this application has a higher electro-optic coefficient and a lower driving voltage, thus exhibiting good electro-optic performance.

[0103] Experimental Example (5): The composite films prepared in Examples 1 and 4 were used. The distribution of the refractive index n and extinction coefficient k of the composite films in the wavelength range of 300 nm to 2500 nm was detected by a refractometer and a spectrophotometer. The results are as follows. Figure 17 and Figure 18 As shown.

[0104] Results Analysis: The extinction coefficient of the composite film in Example 1 is less than 2 × 10⁻⁶ nm in the wavelength range of 1100–2000 nm. -6 In Example 4, the extinction coefficient of the composite film in the wavelength range of 1100~2000 nm is less than 1×10⁻⁶. -6 This indicates that the composite thin film proposed in this application has a small extinction coefficient and can be used for waveguide-type electro-optic modulation; the refractive index of Example 1 is close to 2.3 in the 1550nm band, which is in good agreement with commonly reported results.

[0105] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A lead zirconate titanate composite film with a high electro-optic coefficient, characterized in that, It includes an insulating substrate, a buffer layer and a ferroelectric host layer stacked in sequence. The buffer layer is a lanthanum-doped lead zirconate titanate film, and the ferroelectric host layer is a lead zirconate titanate film with (001) / (100) orientation.

2. The lead zirconate titanate composite film according to claim 1, characterized in that, The material of the buffer layer is Pb. 0.9 La 0.1 Zr x Ti 1-x O3, the material of the ferroelectric host layer is PbZr y Ti 1-y O3, where x is 0.52~0.8 and y is 0.52~0.

8.

3. The lead zirconate titanate composite film according to claim 1, characterized in that, The thickness of the buffer layer is 5~20nm, and the thickness of the ferroelectric host layer is 300~3000nm.

4. The lead zirconate titanate composite film according to claim 1, characterized in that, The insulating substrate is a Si substrate with an amorphous SiO2 layer, or a quartz glass substrate with an amorphous SiO2 layer.

5. A method for preparing a lead zirconate titanate composite thin film according to any one of claims 1 to 4, characterized in that, Includes the following steps: Provide PbZr y Ti 1-y O3 precursor sol and Pb 0.9 La 0.1 Zr x Ti 1-x O3 precursor sol; The Pb is coated on an insulating substrate 0.9 La 0.1 Zr x Ti 1-x O3 precursor sol is subjected to a first heat treatment to obtain a buffer layer; The PbZr is coated on the side of the buffer layer opposite to the insulating substrate. y Ti 1-y O3 precursor sol is subjected to a second heat treatment to obtain the ferroelectric host layer; Where x is 0.52~0.8 and y is 0.52~0.

8.

6. The preparation method according to claim 5, characterized in that, The first heat treatment steps include: first baking at 200~300℃ for 10~30 min, then baking at 400~500℃ for 10~30 min, and finally annealing at 600~700℃ for 10~30 min; The second heat treatment steps include: first baking at 200~300℃ for 10~30 min, then baking at 400~500℃ for 10~30 min, and finally annealing at 600~700℃ for 10~30 min.

7. The preparation method according to claim 5, characterized in that, Provide PbZr y Ti 1-y O3 precursor sol and Pb 0.9 La 0.1 Zr x Ti 1-x The steps involved in producing the O3 precursor sol include: A first titanium source, a first zirconium source, a first solvent, and acetylacetone are mixed and stirred at 70–120°C for 1–3 h to obtain a first mixed solution. A first lead source, acetic acid, and ethylene glycol methyl ether are mixed and stirred at 70–110°C for 1–2 h to obtain a first lead solution. The first lead solution is added to the first mixed solution and stirred at 20–40°C for 1–2 h to obtain PbZr. y Ti 1-y O3 precursor sol; and A second titanium source, a second zirconium source, a second solvent, and acetylacetone are mixed and stirred at 70–120 °C for 1–3 h to obtain a second mixed solution. A second lead source, a lanthanum source, acetic acid, and ethylene glycol methyl ether are mixed and stirred at 70–110 °C for 1–2 h to obtain a third mixed solution. The third mixed solution is added to the second mixed solution and stirred at 20–40 °C for 1–2 h to obtain Pb. 0.9 La 0.1 Zr x Ti 1-x O3 precursor sol.

8. The preparation method according to claim 7, characterized in that, The molar ratio of lead in the first lead source, zirconium in the first zirconium source, and titanium in the first titanium source is 1.2:y:(1-y); and / or, The molar ratio of lead in the second lead source, lanthanum in the lanthanum source, zirconium in the second zirconium source, and titanium in the second titanium source is 1.08:0.1:x:(1-x); and / or, The molar ratio of the chelating agent to lead is (1~2):

1.

9. The preparation method according to claim 7, characterized in that, The first titanium source and the second titanium source are both tetrabutyl titanate; and / or, The first zirconium source and the second zirconium source are respectively zirconium n-propoxide; and / or, The first lead source and the second lead source are each independently selected from lead acetate or lead nitrate; and / or, The lanthanum source includes lanthanum nitrate; and / or, The first solvent and the second solvent each independently comprise one or more of acetic acid, ethylene glycol methyl ether, and N,N-dimethylformamide.

10. An electro-optic modulator, characterized in that, The lead zirconate titanate composite film according to any one of claims 1 to 4, or the lead zirconate titanate composite film prepared by the preparation method according to any one of claims 5 to 9.

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