Optical waveguide structure based on ferroelectric film and preparation method thereof

Abstract

According to the optical waveguide structure based on the ferroelectric film and the preparation method thereof provided by the invention, the aluminum sacrificial layer is constructed on the surface of the ferroelectric film on the insulating substrate, so that the aluminum sacrificial layer can be used as a conductive layer to effectively discharge charges accumulated in the electron beam exposure process in the electron beam exposure process; the problems of electron beam deflection, positioning misalignment and the like caused by a charge accumulation effect are fundamentally eliminated, so that high fidelity of an exposure pattern is ensured, global distortion and writing field splicing dislocation during large-area exposure are avoided, complex and high-precision waveguide pattern preparation can be realized on an insulating substrate, and the production cost is reduced. In addition, the metal aluminum is low in price and easy to obtain, the aluminum sacrificial layer can be removed synchronously through an alkaline solution used in the electron beam glue removing step and the re-sediment removing step, the charge accumulation effect and pollution to the side wall of the optical waveguide structure are finally solved, and meanwhile the cost is reduced. And the cost of the whole process flow is reduced.

Description

Technical Field

[0001] This invention relates to the field of integrated optoelectronic device technology, and in particular to an optical waveguide structure based on ferroelectric thin films and its fabrication method. Background Technology

[0002] Integrated photonic chips, as core hardware in cutting-edge systems such as modern optical communication, optical computing, and high-bandwidth signal processing, rely primarily on optical waveguides to fabricate various functional devices on the chip, such as micro-ring resonators, Mach-Zehnder interferometers, and on-chip filters, to generate, transmit, modulate, and process optical signals. As a micro / nano-scale structure, the core function of a photonic waveguide is to confine the light field within a tiny cross-sectional area and transmit it along a predetermined path with low loss. The performance of a photonic waveguide is determined on the one hand by the intrinsic optical properties of the constituent materials (such as refractive index, absorption coefficient, and nonlinear coefficient), and on the other hand by the precision and perfection of the micro / nano fabrication process. Excessive process defects can directly lead to problems such as rough sidewalls and dimensional deviations in the photonic waveguide, introducing severe scattering loss and thus degrading device performance.

[0003] Among numerous material systems, ferroelectric materials, represented by lithium niobate and lithium tantalate, are considered ideal platforms for fabricating high-performance active photonic devices such as high-speed electro-optic modulators and tunable filters due to their excellent electro-optic, acousto-optic, and nonlinear optical properties. To achieve the high performance of these devices, ferroelectric thin films are typically fabricated on insulating substrates such as quartz, sapphire, and silicon carbide. This effectively prevents the light field from leaking into the high-refractive-index substrate and reduces microwave signal loss during transmission. Furthermore, it achieves phase velocity matching between light waves and microwaves, significantly improving the modulation bandwidth and efficiency of the device.

[0004] However, for existing fabrication processes, especially in high-precision electron beam lithography, the surface of the insulating substrate experiences severe charge accumulation under electron beam irradiation. This accumulated charge forms a non-uniform local electric field, interfering with subsequent incident electron beams and causing unexpected deflection and misalignment. Ultimately, this leads to global geometric distortion of the exposure pattern, particularly during multi-write field stitching exposures of large-area, high-precision patterns. This results in pattern misalignment at write field boundaries, causing stitching errors and severely limiting the fabrication accuracy and yield of complex photonic devices.

[0005] Furthermore, contaminants are inevitably generated during the dry etching process of transferring resist patterns to the ferroelectric thin film layer. On the one hand, atoms of the etched material adhere to the sidewalls of the formed waveguide as redeposition deposits; on the other hand, the resist (usually an organic polymer) acting as a mask undergoes denaturation and cross-linking due to bombardment by high-energy ions, becoming difficult to remove. These residual contaminants roughen the waveguide sidewalls, significantly increasing scattering loss during light propagation within the waveguide, thereby severely degrading device performance. Existing technologies typically require additional, complex cleaning steps to separately treat these contaminants with different properties, which undoubtedly increases process complexity, processing time, and production costs. Summary of the Invention

[0006] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an optical waveguide structure based on ferroelectric thin films and its fabrication method, which solves the problems of low fabrication accuracy and process yield caused by the charge accumulation effect generated during electron beam irradiation in existing fabrication processes, as well as the high waveguide loss and complex process flow caused by the difficulty in removing contaminants generated after dry etching.

[0007] To achieve the above and other related objectives, this invention provides a method for fabricating an optical waveguide structure based on a ferroelectric thin film, comprising the following steps:

[0008] A substrate is provided, the substrate comprising an insulating substrate and a ferroelectric thin film layer located on the insulating substrate;

[0009] An aluminum sacrificial layer and an electron beam resist layer are formed on the ferroelectric thin film layer, and the electron beam resist layer is subjected to electron beam exposure to form an exposed area and an unexposed area on the electron beam resist layer. A pattern of a preset optical waveguide structure is defined in the exposed area.

[0010] The electron beam resist layer is developed using a developer to remove the electron beam resist layer and the aluminum sacrificial layer from the unexposed areas.

[0011] Using the electron beam resist layer in the exposure area as a mask, the ferroelectric thin film layer is dry etched to transfer the pattern of the preset optical waveguide structure to the ferroelectric thin film layer. The electron beam resist layer and the aluminum sacrificial layer in the exposure area are then removed to form the optical waveguide structure.

[0012] Optionally, the step of removing the electron beam resist layer and the aluminum sacrificial layer in the exposed area includes: performing wet etching on the electron beam resist layer and the aluminum sacrificial layer in the exposed area using a wet etching solution.

[0013] Optionally, the wet etching solution includes at least one of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonia water or tetramethylammonium hydroxide aqueous solution, and the wet etching solution and the developer are of the same type or different types.

[0014] Optionally, the optical waveguide structure based on ferroelectric thin film further includes a buried silicon dioxide layer, which is located between the insulating substrate and the ferroelectric thin film layer, and the thickness of the buried silicon dioxide layer is 0.2~20μm.

[0015] Optionally, the material of the ferroelectric thin film layer includes lithium tantalate, lithium niobate, barium titanate, strontium titanate, or lead zirconate titanate, and the thickness of the ferroelectric thin film layer is 100~1000 nm.

[0016] Optionally, the insulating substrate includes a high-resistivity silicon substrate, a sapphire substrate, a silicon carbide substrate, a quartz substrate, or a strontium titanate substrate, and the thickness of the insulating substrate is 0.1~1mm.

[0017] Optionally, the thickness of the aluminum sacrificial layer is 5~50nm, and the thickness of the electron beam resist layer is 200~2000nm.

[0018] Optionally, the pattern of the preset optical waveguide structure includes a straight waveguide, a curved waveguide, a polarization beam splitter rotator, a micro-ring resonator, a racetrack-shaped resonator, a multimode interference coupler, a directional coupler, a Y-shaped beam splitter, a grating coupler, or an edge coupler.

[0019] The present invention also provides an optical waveguide structure based on a ferroelectric thin film, wherein the optical waveguide structure based on the ferroelectric thin film is obtained by the above-described preparation method and comprises, from bottom to top, a substrate and an optical waveguide structure stacked sequentially. The substrate comprises an insulating substrate and a ferroelectric thin film layer located on the insulating substrate, and the optical waveguide structure is disposed on the ferroelectric thin film layer.

[0020] Optionally, the optical waveguide structure based on ferroelectric thin film further includes a buried silicon dioxide layer, which is located between the insulating substrate and the ferroelectric thin film layer, and the thickness of the buried silicon dioxide layer is 0.2~20μm.

[0021] Optionally, the optical waveguide structure includes a straight waveguide, a curved waveguide, a polarization beam splitter rotator, a micro-ring resonator, a racetrack-shaped resonator, a multimode interference coupler, a directional coupler, a Y-shaped beam splitter, a grating coupler, or an edge coupler.

[0022] As described above, the optical waveguide structure based on ferroelectric thin film and its fabrication method of the present invention have the following beneficial effects: By constructing an aluminum sacrificial layer on the surface of the ferroelectric thin film on an insulating substrate, the aluminum sacrificial layer can effectively dissipate the charge accumulated during electron beam exposure as a conductive layer, fundamentally eliminating problems such as electron beam deflection and positioning inaccuracy caused by charge accumulation effect, thereby ensuring high fidelity of the exposure pattern and avoiding global distortion and write field splicing misalignment during large-area exposure. This enables the fabrication of complex and high-precision waveguide patterns on an insulating substrate, significantly improving the fabrication accuracy and process yield of complex photonic devices. In addition, aluminum is inexpensive and readily available, and the alkaline solution used in the electron beam resist removal and redeposition removal steps can simultaneously remove the aluminum sacrificial layer without introducing any additional special equipment or complex steps such as high temperature and plasma, which reduces the cost of the entire process to a certain extent. It can also thoroughly remove various contaminants that cause optical scattering, thereby obtaining very smooth waveguide sidewalls and significantly reducing optical transmission loss. Attached Figure Description

[0023] Figure 1 The diagram shown is a process flow chart of the ferroelectric thin film-based optical waveguide structure of the present invention.

[0024] Figure 2 The diagram shown is a cross-sectional view of the insulating substrate, the buried oxide layer of silicon dioxide, and the ferroelectric thin film layer formed in Example 1.

[0025] Figure 3 The diagram shown is a cross-sectional view of the aluminum sacrificial layer formed in Example 1.

[0026] Figure 4 The diagram shown is a cross-sectional view of the electron beam resist layer formed in Example 1.

[0027] Figure 5 The diagram shown is a cross-sectional view of the electron beam resist layer after exposure and development, as illustrated in Example 1.

[0028] Figure 6 The diagram shown is a cross-sectional view of the ferroelectric thin film layer after dry etching, as described in Example 1.

[0029] Figure 7 The diagram shown is a cross-sectional view of the electron beam resist layer and the aluminum sacrificial layer after wet etching, as illustrated in Example 1.

[0030] Figure 8 The diagram shows the structural topography of the optical waveguide structure in Example 1, where (a) is a straight waveguide, (b) is a multimode interference coupler, (c) is a grating coupler, and (d) is a micro-ring resonator.

[0031] Component designation explanation

[0032] 10. Insulating substrate; 11. Silica buried oxide layer; 12. Ferroelectric thin film layer; 13. Aluminum sacrificial layer; 14. Electron beam resist layer; 131. Unexposed area; 132. Exposed area; 15. Optical waveguide structure; S1~S4, steps. Detailed Implementation

[0033] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0034] For ease of description, spatial relation terms such as “below,” “under,” “lower than,” “below,” “above,” and “upper” may be used herein to describe the relationship between one element or feature shown in the accompanying drawings and other elements or features. It will be understood that these spatial relation terms are intended to include directions other than those depicted in the drawings for devices in use or operation. Furthermore, when a layer is referred to as being “between” two layers, it may be the only layer between the two layers, or there may be one or more layers in between.

[0035] Please see Figures 1 to 8 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the illustrations only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0036] Example 1

[0037] This embodiment provides a method for fabricating an optical waveguide structure based on a ferroelectric thin film, such as... Figure 1 The diagram shown is a process flow chart of the fabrication method of the optical waveguide structure based on ferroelectric thin films, which specifically includes the following steps:

[0038] S1: A substrate is provided, the substrate comprising an insulating substrate 10 and a ferroelectric thin film layer 12 located on the insulating substrate 10;

[0039] S2: An aluminum sacrificial layer 13 and an electron beam resist layer 14 are formed on the ferroelectric thin film layer 12, and the electron beam resist layer 14 is subjected to electron beam exposure to form an exposed region 132 and an unexposed region 131 on the electron beam resist layer 14. The exposed region 132 is defined with a pattern of a preset optical waveguide structure 15.

[0040] S3: The electron beam resist layer 14 is developed using a developer to remove the electron beam resist layer 14 and the aluminum sacrificial layer 13 from the unexposed area 131.

[0041] S4: Using the electron beam resist layer 14 in the exposure area 132 as a mask, dry etching is performed on the ferroelectric thin film layer 12 to transfer the pattern of the preset optical waveguide structure 15 to the ferroelectric thin film layer 12, and the electron beam resist layer 14 and the aluminum sacrificial layer 13 in the exposure area 132 are removed to form the optical waveguide structure 15.

[0042] The fabrication method of the optical waveguide structure based on ferroelectric thin films is further described below with reference to the accompanying drawings:

[0043] In step S1, please refer to Figure 2 A substrate is provided, the substrate comprising an insulating substrate 10 and a ferroelectric thin film layer 12 located on the insulating substrate 10.

[0044] In some embodiments, the insulating substrate 10 has a front side and a back side disposed opposite to each other. The insulating substrate 10 includes one of a high-resistivity silicon substrate, a sapphire substrate, a silicon carbide substrate, a quartz substrate, or a strontium titanate substrate. The shape and size of the insulating substrate 10 can be selected according to actual needs and are not limited herein.

[0045] In some embodiments, the thickness of the insulating substrate 10 ranges from 0.1 to 1 mm, and is not limited thereto. A suitable thickness of the insulating substrate 10 can ensure the mechanical strength of the optical waveguide structure 15 based on the ferroelectric thin film, while also avoiding the problem of increased light loss during propagation due to a larger thickness.

[0046] Specifically, in this embodiment, the insulating substrate 10 is a silicon carbide substrate with a thickness of 500 μm.

[0047] In some embodiments, the substrate further includes a silicon dioxide buried oxide layer 11 located between the insulating substrate 10 and the ferroelectric thin film layer 12, the thickness of the silicon dioxide buried oxide layer 11 being 0.2~20μm.

[0048] Specifically, a silicon dioxide buried oxide layer 11 is formed on the front side of the insulating substrate 10 by thermal oxidation or plasma-enhanced chemical vapor deposition. The silicon dioxide buried oxide layer 11 has good insulation and low dielectric constant, which can effectively prevent mutual interference between different layers. Furthermore, the silicon dioxide buried oxide layer 11, as a lower cladding layer, can confine the light field in the upper optical waveguide structure 15, thereby reducing the transmission loss of the optical signal.

[0049] In some embodiments, the thickness of the buried silica layer 11 is 0.2~20μm, and is not limited here. Setting an appropriate thickness for the buried silica layer 11 can reduce the microwave loss of the optical waveguide structure 15 and further avoid interactions between different layers.

[0050] Specifically, in this embodiment, the thickness of the buried oxide layer 11 in silica is 2 μm.

[0051] In some embodiments, the material of the ferroelectric thin film layer 12 includes lithium tantalate, lithium niobate, barium titanate, strontium titanate, or lead titanate. This embodiment takes the lithium tantalate thin film layer as an example to describe the formation process of the ferroelectric thin film layer 12 in detail.

[0052] In this embodiment of the application, the steps for forming a lithium tantalate thin film layer are as follows: First, a single-crystal lithium tantalate wafer is provided, and ion implantation is performed on the single-crystal lithium tantalate wafer to form a damaged layer. The single-crystal lithium tantalate wafer is then flip-chip hydrophilic bonded to the silicon dioxide buried oxide layer 11. The damaged layer is then removed by a separation process, thereby forming a lithium tantalate thin film layer on the silicon dioxide buried oxide layer 11. The size of the single-crystal lithium tantalate wafer is equal to the size of the substrate.

[0053] Specifically, hydrogen or helium ions are implanted into a single-crystal lithium tantalate wafer to form a damage layer at a specific depth below the surface of the single-crystal lithium tantalate wafer. The single-crystal lithium tantalate wafer with the damage layer is then hydrophilically bonded to the insulating substrate 10 forming the silicon dioxide buried oxide layer 11, so that the single-crystal lithium tantalate wafer and the silicon dioxide buried oxide layer 11 are tightly bonded by intermolecular forces. The bonded structure is then heat-treated. The implanted hydrogen or helium ions form tiny bubbles after heating, causing the single-crystal lithium tantalate wafer to fracture at the damage layer. Finally, a lithium tantalate thin film layer is formed on the silicon dioxide buried oxide layer 11. Then, the surface of the lithium tantalate thin film layer is annealed to repair part of the ion implantation damage, and the lithium tantalate thin film layer is chemically and mechanically polished to thin the lithium tantalate thin film layer to the target thickness and reduce the surface roughness of the lithium tantalate thin film layer to less than 0.5 nm.

[0054] In some embodiments, the thickness of the ferroelectric thin film layer 12 is 100~1000 nm, which is not limited here. In this embodiment, the thickness of the lithium tantalate thin film layer can be adjusted by adjusting the ion implantation depth. Generally, the greater the ion implantation depth, the greater the thickness of the lithium tantalate thin film layer; conversely, the smaller the ion implantation depth, the smaller the thickness of the lithium tantalate thin film layer.

[0055] In this embodiment, the thickness of the lithium tantalate thin film is 300 nm.

[0056] In step S2, please refer to Figure 3 and Figure 4 An aluminum sacrificial layer 13 and an electron beam resist layer 14 are formed on the ferroelectric thin film layer 12, and the electron beam resist layer 14 is subjected to electron beam exposure to form an exposed region 132 and an unexposed region 131 on the electron beam resist layer 14. The exposed region 132 is defined with a pattern of a preset optical waveguide structure 15.

[0057] In some embodiments, before forming the aluminum sacrificial layer 13 on the ferroelectric thin film layer 12, the insulating substrate 10, the silicon dioxide buried oxide layer 11, and the ferroelectric thin film layer 12 can be cleaned first. For example, organic solvents such as acetone and deionized water can be used sequentially to clean the surface contaminants, followed by drying. Alternatively, a diluted acid solution can be used to remove the natural oxide layer on the surface, followed by cleaning with deionized water, and finally drying, to obtain a contamination-free, hydrophilic ferroelectric thin film layer 12 surface.

[0058] In some embodiments, such as Figure 3 As shown, an aluminum sacrificial layer 13 is formed on the ferroelectric thin film layer 12 by magnetron sputtering. The thickness of the aluminum sacrificial layer 13 is 5~50nm. The aluminum sacrificial layer 13 can serve as a conductive layer, which can effectively dissipate the charge accumulated during subsequent electron beam exposure. This fundamentally suppresses the formation of an uneven local electric field due to the charge accumulation effect, thereby preventing the electron beam from deflecting unexpectedly and becoming inaccurate in positioning.

[0059] In this embodiment, the thickness of the aluminum sacrificial layer 13 is 20 nm.

[0060] In some embodiments, before forming the electron beam resist layer 14 on the aluminum sacrificial layer 13, the above structure is subjected to a heating process, such as baking at 180°C for 30 minutes, to completely remove the moisture adsorbed on the aluminum sacrificial layer 13, thereby enhancing the adhesion of the subsequently formed electron beam resist layer 14.

[0061] In some embodiments, such as Figure 4As shown, an electron beam resist layer 14 is formed on the aluminum sacrificial layer 13. The thickness of the electron beam resist layer 14 is 200-2000 nm. Electron beam lithography is a technique that uses an electron beam to directly draw on a wafer coated with an electron beam photoresist layer. After exposing the electron beam resist layer 14 with electron beam lithography, the pattern of the optical waveguide structure 15 can be transferred to the surface of the ferroelectric thin film layer 12.

[0062] Optionally, the electron beam resist layer 14 includes two types: positive photoresist and negative photoresist. When the electron beam resist layer 14 is a positive photoresist, the positive photoresist in the area irradiated by the electron beam is dissolved after development, while the positive photoresist in the unirradiated area is retained. When the electron beam resist layer 14 is a negative photoresist, the negative photoresist in the area irradiated by the electron beam is retained after development, while the negative photoresist in the unirradiated area is dissolved.

[0063] In this embodiment, the electron beam resist layer 14 is used as a negative photoresist for detailed explanation.

[0064] In the embodiments of this application, such as Figure 4 As shown, a photoresist layer 14 is first formed by spin-coating photoresist onto the surface of a lithium tantalate thin film layer. The selected photoresist is a negative photoresist. The thickness of the electron beam resist layer 14 is 600 nm. Then, electron beam exposure technology is used to perform a first exposure and development on the electron beam resist layer 14, thereby forming an exposed area 132 and an unexposed area 131 on the electron beam resist layer 14. A pattern of a preset optical waveguide structure 15 is defined in the exposed area 132.

[0065] In some embodiments, the pattern of the preset optical waveguide structure 15 includes a straight waveguide, a curved waveguide, a polarization beam splitter rotator, a micro-ring resonator, a racetrack-shaped resonator, a multimode interference coupler, a directional coupler, a Y-shaped beam splitter, a grating coupler, or an edge coupler, which can be selected according to actual needs.

[0066] In step S3, please refer to Figure 5 The electron beam resist layer 14 is developed using a developer to remove the electron beam resist layer 14 and the aluminum sacrificial layer 13 from the unexposed area 131.

[0067] In this embodiment, the developing solution is a potassium hydroxide solution with a volume ratio of 30% and a concentration of 30%.

[0068] In the embodiments of this application, such as Figure 5As shown, after the photoresist layer is exposed and developed for the first time using electron beam lithography, an exposed region 132 and an unexposed region 131 are formed on the electron beam resist layer 14. Then, the electron beam resist layer 14 is developed using a developer, which dissolves the electron beam resist layer 14 irradiated by the electron beam in the unexposed region 131, while the photoresist layer that has not been irradiated by the electron beam in the exposed region 132 is retained. At the same time, the aluminum sacrificial layer 13 in the unexposed region 131 is removed.

[0069] In step S4, please refer to Figures 6 to 8 Using the electron beam resist layer 14 in the exposure area 132 as a mask, the ferroelectric thin film layer 12 is dry etched to transfer the pattern of the preset optical waveguide structure 15 to the ferroelectric thin film layer 12. The electron beam resist layer 14 and the aluminum sacrificial layer 13 in the exposure area 132 are removed to form the optical waveguide structure 15.

[0070] In the embodiments of this application, such as Figure 6 As shown, an ion beam etching process is used to etch the lithium tantalate thin film layer using the remaining electron beam resist layer 14 and the aluminum sacrificial layer 13 as etching masks. The etching depth is 200 nm. The ions used in the ion beam etching process are pure argon ions, thereby removing the part of the lithium tantalate thin film layer exposed in the unexposed area 131, and retaining the lithium tantalate thin film layer in the area covered by the electron beam resist layer 14 and the aluminum sacrificial layer 13 in the exposed area 132. The pattern of the preset optical waveguide structure 15 is transferred to the ferroelectric thin film layer 12. The shape of the optical waveguide structure 15 is a ridge waveguide.

[0071] In the embodiments of this application, such as Figure 6 As shown, when the lithium tantalate thin film layer is ion-beam etched, the electron beam resist layer 14 in the exposure area 132 will undergo denaturation and cross-linking, thereby generating redeposited material on the sidewall of the optical waveguide structure 15. The redeposited material is difficult to remove with conventional resist remover.

[0072] In some embodiments, the wet etching solution includes at least one of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonia or tetramethylammonium hydroxide aqueous solution, and the wet etching solution and the developer may be of the same type or different type.

[0073] In the embodiments of this application, such as Figure 7As shown, the wet etching solution is a mixed aqueous solution of potassium hydroxide solution (concentration of 30%) and hydrogen peroxide solution (concentration of 30%) at 80°C and a volume ratio of 3:1. The above structure is subjected to wet etching process to remove the redeposited material generated by the ion beam etching process and to completely remove the aluminum sacrificial layer 13, thereby achieving more effective stripping of the electron beam resist layer 14 after denaturation and crosslinking.

[0074] In the embodiments of this application, such as Figure 8 As shown, it is displayed that the optical waveguide structure 15 is a straight waveguide ( Figure 8 a) Multimode interference coupler ( Figure 8 b) Grating coupler ( Figure 8 c) and micro-ring resonator ( Figure 8 The structural morphology diagram in d) shows that when the optical waveguide structure 15 based on ferroelectric thin film is prepared using the preparation method in this embodiment, pattern distortion and write field splicing misalignment during large-area exposure can be avoided.

[0075] This embodiment describes a method for fabricating an optical waveguide structure 15 based on a ferroelectric thin film. By constructing an aluminum sacrificial layer 13 on the surface of the ferroelectric thin film on an insulating substrate 10, the aluminum sacrificial layer 13 can effectively dissipate the charge accumulated during electron beam exposure as a conductive layer. This fundamentally eliminates problems such as electron beam deflection and positioning inaccuracy caused by charge accumulation effects, thereby ensuring high fidelity of the exposure pattern and avoiding global distortion and write field splicing misalignment during large-area exposure. As a result, complex and high-precision waveguide patterns can be fabricated on the insulating substrate 10, significantly improving the fabrication accuracy and process yield of complex photonic devices.

[0076] Example 2

[0077] This embodiment provides an optical waveguide structure 15 based on a ferroelectric thin film, such as... Figure 8 As shown, the optical waveguide structure based on ferroelectric thin film is obtained by the above-described preparation method. From bottom to top, it includes a substrate and an optical waveguide structure 15 stacked sequentially. The substrate includes an insulating substrate 10 and a ferroelectric thin film layer 12 located on the insulating substrate 10. The optical waveguide structure 15 is disposed on the ferroelectric thin film layer 12.

[0078] In this embodiment, the insulating substrate 10 is a silicon carbide substrate with a thickness of 0.5 mm. Silicon carbide is a good thermal conductor with a large thermal conductivity, which can effectively dissipate the heat accumulated in the optical waveguide structure 15 during operation. Furthermore, silicon carbide has low dielectric loss and a dielectric constant that can match the refractive index of the optical group in the high-frequency band, thereby reducing the optical loss of the optical waveguide structure 15.

[0079] In another embodiment, the optical waveguide structure based on ferroelectric thin film further includes a silicon dioxide buried oxide layer, which is located between the insulating substrate and the ferroelectric thin film layer. The thickness of the silicon dioxide buried oxide layer is 0.2~20μm. Silicon dioxide has good insulation and low dielectric constant, which can effectively prevent mutual interference between different layers and reduce the transmission loss of optical signals.

[0080] In this embodiment, the thickness of the ferroelectric thin film layer 12 is 300 nm, and the refractive index of the ferroelectric thin film layer 12 is greater than that of the silicon dioxide buried oxide layer 11. This allows the light field of the optical waveguide structure 15 to be confined within the ferroelectric thin film layer 12, thereby reducing the transmission loss of the optical signal.

[0081] In some embodiments, the optical waveguide structure 15 includes a straight waveguide, a curved waveguide, a polarization beam splitter rotator, a micro-ring resonator, a racetrack-shaped resonator, a multimode interference coupler, a directional coupler, a Y-shaped beam splitter, a grating coupler, or an edge coupler, and the optical waveguide structure 15 is used to provide a transmission path for optical signals.

[0082] In this embodiment, the optical waveguide structure 15 is a straight waveguide with a thickness of 200nm and a ridge waveguide shape. The tilt angle of the ridge waveguide is 60-75 degrees, which can support single-mode transmission of optical signals.

[0083] In summary, the optical waveguide structure based on ferroelectric thin films and its fabrication method of this invention constructs an aluminum sacrificial layer on the surface of a ferroelectric thin film on an insulating substrate. During electron beam exposure, the aluminum sacrificial layer acts as a conductive layer to effectively dissipate the charge accumulated during electron beam exposure, fundamentally eliminating problems such as electron beam deflection and positioning misalignment caused by charge accumulation effects. This ensures high fidelity of the exposure pattern and avoids global distortion and write field splicing misalignment during large-area exposure. Therefore, it enables the fabrication of complex, high-precision waveguide patterns on insulating substrates, significantly improving the fabrication accuracy and process yield of complex photonic devices. Furthermore, aluminum is inexpensive and readily available, and the alkaline solution used in the electron beam resist removal and re-deposition removal steps can simultaneously remove the aluminum sacrificial layer without introducing any additional specialized equipment or complex steps such as high temperature and plasma. This reduces the overall process cost to a certain extent and thoroughly removes various contaminants that cause optical scattering, resulting in very smooth waveguide sidewalls and significantly reducing optical transmission loss. Therefore, this invention effectively overcomes the various shortcomings of existing technologies and has high industrial applicability.

[0084] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for fabricating an optical waveguide structure based on a ferroelectric thin film, characterized in that, Includes the following steps: A substrate is provided, the substrate comprising an insulating substrate and a ferroelectric thin film layer located on the insulating substrate; An aluminum sacrificial layer and an electron beam resist layer are formed on the ferroelectric thin film layer, and the electron beam resist layer is subjected to electron beam exposure to form an exposed area and an unexposed area on the electron beam resist layer. A pattern of a preset optical waveguide structure is defined in the exposed area. The electron beam resist layer is developed using a developer to remove the electron beam resist layer and the aluminum sacrificial layer from the unexposed areas. Using the electron beam resist layer in the exposure area as a mask, the ferroelectric thin film layer is dry etched to transfer the pattern of the preset optical waveguide structure to the ferroelectric thin film layer. The electron beam resist layer and the aluminum sacrificial layer in the exposure area are then removed to form the optical waveguide structure.

2. The method for fabricating an optical waveguide structure based on a ferroelectric thin film according to claim 1, characterized in that, The step of removing the electron beam resist layer and the aluminum sacrificial layer in the exposed area includes: performing wet etching on the electron beam resist layer and the aluminum sacrificial layer in the exposed area using a wet etching solution.

3. The method for fabricating an optical waveguide structure based on a ferroelectric thin film according to claim 2, characterized in that: The wet etching solution includes at least one of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, ammonia or tetramethylammonium hydroxide aqueous solution, and the wet etching solution and the developer may be of the same type or different type.

4. The method for fabricating an optical waveguide structure based on a ferroelectric thin film according to claim 1, characterized in that: The substrate further includes a buried silicon dioxide layer located between the insulating substrate and the ferroelectric thin film layer, the thickness of which is 0.2~20μm.

5. The method for fabricating an optical waveguide structure based on a ferroelectric thin film according to claim 1, characterized in that: The ferroelectric thin film layer is made of lithium tantalate, lithium niobate, barium titanate, strontium titanate, or lead titanate, and the thickness of the ferroelectric thin film layer is 100~1000 nm.

6. The method for fabricating an optical waveguide structure based on a ferroelectric thin film according to claim 1, characterized in that: The insulating substrate includes a high-resistivity silicon substrate, a sapphire substrate, a silicon carbide substrate, a quartz substrate, or a strontium titanate substrate, and the thickness of the insulating substrate is 0.1~1mm.

7. The method for fabricating an optical waveguide structure based on a ferroelectric thin film according to claim 1, characterized in that: The thickness of the aluminum sacrificial layer is 5~50nm, and the thickness of the electron beam resist layer is 200~2000nm.

8. The method for fabricating an optical waveguide structure based on a ferroelectric thin film according to claim 1, characterized in that: The pattern of the preset optical waveguide structure includes straight waveguides, curved waveguides, polarization beam splitters, micro-ring resonators, racetrack-shaped resonators, multimode interference couplers, directional couplers, Y-shaped beam splitters, grating couplers, or edge couplers.

9. An optical waveguide structure based on a ferroelectric thin film, characterized in that, The optical waveguide structure based on ferroelectric thin film is obtained by the fabrication method according to any one of claims 1 to 8, and includes a substrate and an optical waveguide structure stacked sequentially from bottom to top. The substrate includes an insulating substrate and a ferroelectric thin film layer located on the insulating substrate, and the optical waveguide structure is disposed on the ferroelectric thin film layer.

10. The optical waveguide structure based on ferroelectric thin films according to claim 9, characterized in that: The optical waveguide structure based on ferroelectric thin film further includes a silicon dioxide buried oxide layer, which is located between the insulating substrate and the ferroelectric thin film layer, and the thickness of the silicon dioxide buried oxide layer is 0.2~20μm.

11. The optical waveguide structure based on ferroelectric thin films according to claim 9, characterized in that: The optical waveguide structure includes a straight waveguide, a curved waveguide, a polarization beam splitter rotator, a micro-ring resonator, a racetrack-shaped resonator, a multimode interference coupler, a directional coupler, a Y-shaped beam splitter, a grating coupler, or an edge coupler.

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