Preparation method of thin-film lithium niobate electro-optical modulator and electro-optical modulator

Abstract

The invention discloses a preparation method of a thin-film lithium niobate electro-optical modulator and the electro-optical modulator, relates to the technical field of optical communication, and can be used for preparing the electro-optical modulator which is relatively small in size, relatively low in preparation difficulty and low in waveguide transmission loss. The method comprises a first substrate, a grating layer located on the first substrate, a target second dielectric film located on the grating layer, the grating layer is formed by etching a first dielectric film, the surface roughness of the target second dielectric film is smaller than 1 nm, and the refractive index of the target second dielectric film is smaller than that of the first dielectric film; the lithium niobate substrate comprises a lithium niobate thin film formed by ion implantation and a target third dielectric film located on the lithium niobate thin film, and the surface roughness of the target third dielectric film is smaller than 1 nm; bonding the target second dielectric film and the target third dielectric film to obtain a bonding structure; stripping the lithium niobate substrate in the bonding structure; and etching the lithium niobate film to form a ridge-shaped waveguide structure layer, and then forming a waveguide transmission covering layer.

Description

Technical Field

[0001] The present application relates to the field of optical communication technology, and in particular to a method for preparing a thin-film lithium niobate electro-optic modulator and the electro-optic modulator. Background Art

[0002] Electro-optic modulators (EOMs) are key devices in optical communications and quantum computing systems. In particular, ultra-compact EOMs are necessary for highly integrated photonic chips. Thin-film lithium niobate materials have many technical advantages in high-efficiency EOMs.

[0003] At present, the lithium niobate electro-optic modulator based on the traditional waveguide structure is still at the millimeter scale, and it is very challenging to further reduce the size, which greatly hinders its integration ability on silicon photonic chips. Therefore, how to prepare a thin-film lithium niobate electro-optic modulator with a smaller size, lower preparation difficulty and low waveguide transmission loss has become an urgent problem to be solved. Summary of the invention

[0004] The present application provides a method for preparing a thin-film lithium niobate electro-optic modulator and an electro-optic modulator, which can prepare a thin-film lithium niobate electro-optic modulator with a smaller size, lower preparation difficulty and lower waveguide transmission loss, thereby improving the integration capability of the thin-film lithium niobate electro-optic modulator on a silicon photonic chip.

[0005] In order to achieve the above objectives, this application adopts the following technical solutions: In a first aspect of an embodiment of the present application, a method for preparing a thin-film lithium niobate electro-optic modulator is provided, the method comprising: Acquire a first structure, wherein the first structure comprises: a first substrate, a grating layer located on the first substrate, the grating layer being formed by etching a first dielectric film, and a target second dielectric film located on the grating layer, the surface roughness of the target second dielectric film being less than 1 nm (RMS), and the refractive index of the target second dielectric film being less than that of the first dielectric film; Acquire a second structure, the second structure comprising: a lithium niobate substrate, the lithium niobate substrate comprising a lithium niobate film formed by ion implantation, a target third dielectric film located on the lithium niobate film, the surface roughness of the target third dielectric film being less than 1 nm (RMS), and the refractive index of the target third dielectric film being the same as the refractive index of the target second dielectric film; Bonding the target second dielectric film and the target third dielectric film to obtain a bonding structure; peeling off the lithium niobate substrate in the bonding structure to obtain a peeling structure; After etching the lithium niobate film in the peeling structure to form a ridge waveguide structure layer, a covering layer for waveguide transmission is formed on the ridge waveguide structure layer.

[0006] As a possible implementation manner, obtaining the first structure includes: obtaining a first substrate; Depositing a first dielectric film on a first substrate, wherein the thickness of the first dielectric film is 1000-3000 nm; Etching the first dielectric film to form the grating layer, wherein the etching depth of the grating layer is 20-500 nm; Depositing a second dielectric film on the grating layer, wherein the thickness of the second dielectric film is greater than 60 nm; After chemical mechanical polishing is performed on the second dielectric film, the target second dielectric film is obtained, and the thickness of the target second dielectric film is greater than 10 nm.

[0007] As a possible implementation manner, obtaining the second structure includes: Obtaining a lithium niobate substrate; Performing ion implantation on the first surface of the lithium niobate substrate to form a lithium niobate film, wherein the depth of the ion implantation is 200-800 nm; Depositing a third dielectric film on the lithium niobate film; The third dielectric film is subjected to chemical mechanical polishing to obtain the target third dielectric film, wherein the target third dielectric film has a thickness of 100-1000 nm.

[0008] As a possible implementation manner, the step of peeling off the lithium niobate substrate in the bonding structure to obtain a peeled structure includes: The bonding structure is heated to separate the lithium niobate film from the lithium niobate substrate. The lithium niobate substrate is removed from the bonding structure to obtain the peeling structure.

[0009] As a possible implementation manner, etching the lithium niobate film in the peeling structure to form a ridge waveguide structure layer includes: Etching the lithium niobate film in the peeling structure to obtain a target lithium niobate film, wherein the target lithium niobate film has a thickness of 50-500 nm and a roughness of 4-6 nm (RMS); Depositing a chromium metal film on the target lithium niobate film; Etching the chromium metal film into a mask structure corresponding to the ridge waveguide structure to obtain a mask layer; The target lithium niobate film is etched using the mask layer to form the ridge waveguide structure layer, and the thickness of the ridge waveguide structure layer is 50-500 nm.

[0010] As a possible implementation manner, forming a covering layer for waveguide transmission on the ridge waveguide structure layer includes: A fourth dielectric film is deposited on the ridge waveguide structure layer to form the cover layer.

[0011] As a possible implementation manner, after forming a covering layer for waveguide transmission on the ridge waveguide structure layer, the method further includes: forming a signal electrode and a ground electrode on the fourth dielectric film to form a modulation structure; After cutting and polishing the first side surface and the second side surface of the modulation structure, an anti-reflection film is plated on the first side surface and the second side surface to obtain a lithium niobate electro-optic modulator.

[0012] As a possible implementation manner, the first substrate is a silicon-based substrate, a germanium substrate, or a gallium arsenide substrate; The first dielectric film is SiN x Dielectric film, titanium dioxide, hafnium dioxide, tantalum oxide or yttrium oxide: The second dielectric film and the third dielectric film are silicon dioxide; The fourth dielectric film is one of silicon dioxide, silicon nitride, magnesium fluoride or aluminum oxide.

[0013] As a possible implementation, the signal electrode and the ground electrode are made of a titanium bonding layer and a gold film on the titanium bonding layer, the thickness of the titanium bonding layer is 5-10 nm, and the thickness of the gold film is 300-800 nm.

[0014] According to a second aspect of the embodiments of the present application, a thin film lithium niobate electro-optic modulator is provided. The electro-optic modulator is prepared by the method for preparing a thin film lithium niobate electro-optic modulator according to the first aspect of the embodiments of the present application.

[0015] The beneficial effects brought by the technical solution provided by the embodiment of the present application include at least: The method for preparing a thin-film lithium niobate electro-optical modulator provided in an embodiment of the present application comprises: obtaining a first structure, the first structure comprising: a first substrate, a grating layer located on the first substrate, the grating layer being formed by etching a first dielectric film, a target second dielectric film located on the grating layer, the surface roughness of the target second dielectric film being less than 1 nm (RMS), and the refractive index of the target second dielectric film being less than that of the first dielectric film; obtaining a second structure, the second structure comprising: a lithium niobate substrate, the lithium niobate substrate comprising a lithium niobate thin film formed by ion implantation, a target third dielectric film located on the lithium niobate thin film, the surface roughness of the target third dielectric film being less than 1 nm (RMS), and the refractive index of the target third dielectric film being the same as that of the target second dielectric film; bonding the target second dielectric film to the target third dielectric film to obtain a bonding structure; stripping the lithium niobate substrate in the bonding structure to obtain a stripping structure; etching the lithium niobate thin film in the stripping structure to form a ridge waveguide structure layer, and then forming a covering layer for waveguide transmission on the ridge waveguide structure layer. In the preparation method of the thin-film lithium niobate electro-optic modulator provided by the present application, the coupling strength of the grating and the waveguide can meet the strict performance requirements of the device by precisely controlling the grating etching duty cycle, the grating etching depth and the distance between the grating and the lithium niobate waveguide. This method uses conventional semiconductor processes and avoids the need to etch special profile gratings on ridge waveguides. Conventional ridge waveguide forms can be used, thereby significantly reducing waveguide transmission losses, significantly reducing the manufacturing cost of slow-light thin-film lithium niobate electro-optic modulators, and improving the electro-optical performance of the device. The thin-film lithium niobate electro-optic modulator made by this method can be easily integrated with other silicon optical devices because it can use silicon-based substrates and compact areas, and can meet the requirements of next-generation communication equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 A structural diagram of an existing fishbone waveguide provided in an embodiment of the present application; Figure 2 A ridge waveguide structure diagram provided in an embodiment of the present application; Figure 3 The preparation method of the thin film lithium niobate electro-optic modulator provided in the embodiment of the present application Figure 1 ; Figure 4 The preparation method of the thin film lithium niobate electro-optic modulator provided in the embodiment of the present application Figure 2 ; Figure 5 A structural diagram of a first structure provided in an embodiment of the present application; Figure 6 A structural diagram of a second structure provided in an embodiment of the present application; Figure 7 A structural diagram of a bonding structure provided in an embodiment of the present application; Figure 8A structural diagram of a peeling structure provided in an embodiment of the present application; Fig. 9 A schematic diagram of a modulation structure provided in an embodiment of the present application; Fig.10 Schematic diagram of a lithium niobate electro-optic modulator provided in an embodiment of the present application. DETAILED DESCRIPTION

[0017] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0018] In the following, the terms "first" and "second" are used for descriptive purposes only and are not to be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present disclosure, unless otherwise specified, "plurality" means two or more.

[0019] Additionally, the use of “based on” or “according to” is meant to be open and inclusive, in that a process, step, calculation, or other action “based on” or “according to” one or more conditions or values ​​may, in practice, be based on additional conditions or beyond values.

[0020] Electro-optic modulators are key devices in optical communications and quantum computing systems. In particular, ultra-compact electro-optic modulators are necessary for highly integrated photonic chips. Thin-film lithium niobate materials have many technical advantages in high-efficiency electro-optic modulators. However, electro-optic modulators based on traditional waveguide structures are still at the millimeter scale, and further reducing their size is very challenging, which greatly hinders their integration capabilities on silicon photonic chips.

[0021] By using cavity structures such as microring (MR) resonators and photonic crystal (PC) waveguides, the device footprint can be reduced. Although these cavity-based modulators are more compact, their operating wavelength is limited to a narrow passband (<1nm), requiring specialized wavelength tuning mechanisms. In addition, cavity-based modulators usually have an inherent trade-off between driving voltage and modulation speed.

[0022] The slow light (SL) effect is a fundamental physical phenomenon that can reduce the group velocity of light by using special structures on photonic integrated circuits. The slow light effect can also enhance the interaction between light and the electric field in electro-optic modulators, thereby helping to improve the modulation efficiency. Slow light modulators based on photonic crystal (PC) waveguides have been realized on silicon-on-insulator (SOI) platforms. A bandwidth of more than 10nm and a high optical group refractive index of 34 have been achieved. However, photonic crystal waveguides face challenges such as small manufacturing tolerances, so high-precision manufacturing processes are required.

[0023] Bragg grating coupled waveguide is another periodic waveguide structure, and its slow light structure design is much simpler than that of photonic crystal waveguide. Slow light Mach-Zehnder modulator (SL-MZM) assisted by coupled waveguide Bragg resonator can achieve a compact footprint of several hundred microns, with higher modulation efficiency and power consumption of sub-femtojoule / bit, as well as better stability over a wide temperature range. On the thin-film lithium niobate technology platform, a slow light waveguide with coupled Bragg resonator structure is used. High-speed modulation under high bandwidth can be achieved. However, in order to achieve good coupling efficiency, the Bragg resonator structure needs to etch the grating on the side of the ridge waveguide. This method uses electron beam lithography to form a zigzag edge on the waveguide, and subsequent ion beam etching forms a grating on the side of the lithium niobate waveguide. Direct etching on lithium niobate material itself is very difficult, and etching a waveguide structure with a grating structure is particularly difficult. At the same time, the grating quality and coupling effect will be affected by the non-steep side of the grating. Etching fishbone gratings on both sides of the ridge waveguide requires controlling multiple etching side walls at the same time, so the production cost is expensive, the efficiency and yield are low, and it is difficult to accurately control the quality and duty cycle of the grating structure. In addition, its transmission loss is still as high as 2.9dB / cm, which affects the modulation performance of the device.

[0024] That is to say, Figure 1 As shown, the existing fishbone waveguide structure includes a silicon substrate 200, a low-refractive index dielectric film 210 on the substrate, a thin-film lithium niobate waveguide 220, and a low-refractive index dielectric film covering layer 230 on the waveguide. Although this fishbone waveguide structure can meet the requirements of grating coupling, it is very difficult to manufacture, has high cost, and low yield. More importantly, the grating on the ridge side also causes a large waveguide insertion loss, thereby affecting the electro-optical performance of the modulator.

[0025] Based on the above problems, the present application can obtain the following by directly bonding the silicon-based substrate containing the grating and the lithium niobate thin film substrate and the subsequent process. Figure 2The ridge waveguide structure includes a silicon substrate 130, a high refractive index dielectric film 141 containing an etched grating, a low refractive index dielectric film 123 covering the high refractive index dielectric film 141, a thin-film lithium niobate ridge waveguide 112, and a low refractive index dielectric film 150 covering the lithium niobate ridge waveguide. The method can reduce the difficulty of manufacturing the current thin-film lithium niobate electro-optic modulator and improve the yield. The high-contrast and precisely controllable grating formed at the bottom of the lithium niobate thin-film waveguide can reduce the waveguide transmission loss to less than 0.5dB / cm while obtaining high reflection, thereby obtaining a high-bandwidth, high-speed, compact thin-film lithium niobate electro-optic modulator.

[0026] Specifically, the present application provides a method for preparing a thin film lithium niobate electro-optic modulator, such as Figure 3 As shown, the method comprises the following steps: Step A1: obtaining a first structure, the first structure comprising: a first substrate, a grating layer located on the first substrate, the grating layer being formed by etching a first dielectric film, and a target second dielectric film located on the grating layer, the surface roughness of the target second dielectric film being less than 1 nm (RMS), and the refractive index of the target second dielectric film being less than that of the first dielectric film; Step A2: obtaining a second structure, the second structure comprising: a lithium niobate substrate, the lithium niobate substrate comprising a lithium niobate film formed by ion implantation, a target third dielectric film located on the lithium niobate film, the surface roughness of the target third dielectric film being less than 1 nm (RMS), and the refractive index of the target third dielectric film being the same as the refractive index of the target second dielectric film; Step A3: bonding the target second dielectric film and the target third dielectric film to obtain a bonding structure; Step A4: peeling off the lithium niobate substrate in the bonding structure to obtain a peeling structure; Step A5: After etching the lithium niobate film in the peeling structure to form a ridge waveguide structure layer, a covering layer for waveguide transmission is formed on the ridge waveguide structure layer.

[0027] The method for preparing a thin-film lithium niobate electro-optical modulator provided in an embodiment of the present application comprises: obtaining a first structure, the first structure comprising: a first substrate, a grating layer located on the first substrate, the grating layer being formed by etching a first dielectric film, a target second dielectric film located on the grating layer, the surface roughness of the target second dielectric film being less than 1 nm (RMS), and the refractive index of the target second dielectric film being less than that of the first dielectric film; obtaining a second structure, the second structure comprising: a lithium niobate substrate, the lithium niobate substrate comprising a lithium niobate thin film formed by ion implantation, a target third dielectric film located on the lithium niobate thin film, the surface roughness of the target third dielectric film being less than 1 nm (RMS), and the refractive index of the target third dielectric film being the same as that of the target second dielectric film; bonding the target second dielectric film to the target third dielectric film to obtain a bonding structure; stripping the lithium niobate substrate in the bonding structure to obtain a stripping structure; etching the lithium niobate thin film in the stripping structure to form a ridge waveguide structure layer, and then forming a covering layer for waveguide transmission on the ridge waveguide structure layer. In the preparation method of the thin-film lithium niobate electro-optic modulator provided by the present application, the coupling strength of the grating and the waveguide can meet the strict performance requirements of the device by precisely controlling the grating etching duty cycle, the grating etching depth and the distance between the grating and the lithium niobate waveguide. This method uses conventional semiconductor processes and avoids the need to etch special profile gratings on ridge waveguides. Conventional ridge waveguide forms can be used, thereby significantly reducing waveguide transmission losses, significantly reducing the manufacturing cost of slow-light thin-film lithium niobate electro-optic modulators, and improving the electro-optical performance of the device. The thin-film lithium niobate electro-optic modulator made by this method can be easily integrated with other silicon optical devices because it can use silicon-based substrates and compact areas, and can meet the requirements of next-generation communication equipment.

[0028] like Figure 4 As shown, step A1 in the above embodiment may include the following steps: Step A11: Obtain a first substrate.

[0029] The first substrate may be a silicon-based substrate, a germanium substrate or a gallium arsenide substrate. If the thin-film lithium niobate electro-optic modulator needs to be integrated into a silicon photonic chip, a silicon-based substrate may be used. This application takes a silicon-based substrate as an example.

[0030] Step A12: depositing a first dielectric film on the first substrate, wherein the thickness of the first dielectric film is 1000-3000 nm.

[0031] The first dielectric film may be SiN x Dielectric film, titanium dioxide, hafnium dioxide, tantalum oxide or yttrium oxide such high refractive index film, this application is SiN x A dielectric film is shown as an example.

[0032] In the actual preparation process, a plasma enhanced chemical vapor deposition (PECVD) method may be used to deposit the first dielectric film on the first substrate.

[0033] Step A13: Etching the first dielectric film to form a grating layer, wherein the etching depth of the grating layer is 20-500 nm.

[0034] For example, SiN x A grating pattern is formed on the film by photolithography, and a grating layer is formed by etching.

[0035] It should be noted that since only a planar grating needs to be etched, in addition to electron beam lithography, conventional semiconductor lithography technology can also be used, such as contact lithography, i-line / DUV-line stepper lithography, or nanoimprint technology, which can greatly improve manufacturing efficiency and save costs.

[0036] In the actual preparation process, the grating etching can be carried out by conventional reactive plasma etching or inductively coupled plasma process, and the chemical reaction gas can be fluorine-containing gas, argon, nitrogen and helium and the combination of these gases. x Dry etching process and high SiN x / photoresist etching selectivity, so no cumbersome hard mask process is required. Especially important is the dry etching of SiN x , it is easy to obtain a grating sidewall close to 90° and a 50 / 50 duty ratio, so that the grating duty ratio can be easily controlled to improve the grating quality. According to the coupling strength requirements, the etching depth range can be controlled between 20nm-500nm.

[0037] Step A14: depositing a second dielectric film on the grating layer, wherein the thickness of the second dielectric film is greater than 60 nm; Step A15: After chemical mechanical polishing is performed on the second dielectric film, a target second dielectric film is obtained, and the thickness of the target second dielectric film is greater than 10 nm.

[0038] Optionally, the second dielectric film may be a silicon dioxide film, the refractive index of the second dielectric film is smaller than the refractive index of the first dielectric film, and the target surface roughness of the second dielectric film is smaller than 1 nm (RMS).

[0039] In the actual preparation process, a second SiO2 dielectric film can be deposited on the grating layer by plasma enhanced chemical vapor deposition (PECVD) and then chemical mechanical polishing is performed to obtain a target second dielectric film.

[0040] The first structure prepared by the above preparation method is as follows Figure 5 As shown, Figure 5130 is the first substrate, 141 is the grating layer, and 122 is the target second dielectric film.

[0041] Please continue to refer to Figure 4 In the above embodiment, step A2 may include the following steps: Step A21: Obtain a lithium niobate substrate.

[0042] Step A22: performing ion implantation on the first surface of the lithium niobate substrate to form a lithium niobate film, wherein the depth of the ion implantation is 200-800 nm.

[0043] It should be noted that the lithium niobate thin film is an implantation layer formed in a lithium niobate substrate by ion implantation.

[0044] Step A23: depositing a third dielectric film on the lithium niobate film.

[0045] The third dielectric film may be a silicon dioxide film.

[0046] It is understandable that, since the target second dielectric film needs to be bonded with the target third dielectric film in the subsequent processing, in order to improve the stability after bonding, the second dielectric film and the third dielectric film can be prepared using the same material.

[0047] In the actual preparation process, a plasma enhanced chemical vapor deposition method is used on the lithium niobate film to deposit a third dielectric film and perform chemical mechanical polishing (SB3). The thickness of the third dielectric film is determined by comprehensive factors such as the grating coupling strength and the bottom cover layer of the lithium niobate waveguide. According to the device performance design requirements, chemical mechanical polishing + chemical reaction plasma etching can also be used to meet the precise thickness requirements. The initial thickness of the third dielectric film is generally not less than 200nm.

[0048] Step A24: chemically mechanically polish the third dielectric film to obtain a target third dielectric film, wherein the target third dielectric film has a thickness of 100-1000 nm.

[0049] The third dielectric film is subjected to chemical mechanical polishing. The roughness of the surface of the polished third dielectric film must be less than 1 nm (RMS) to meet the subsequent SiO2-SiO2 bonding requirements.

[0050] The second structure prepared by the above preparation method is as follows Figure 6 As shown, Figure 6 100 is a lithium niobate substrate, 110 is a lithium niobate film, and 120 is a target third dielectric film.

[0051] Please continue to refer to Figure 4 , the process of the above step A3: bonding the target second dielectric film and the target third dielectric film to obtain the bonding structure may be: Step A31: Bonding the first surface of the target second dielectric film and the first surface of the target third dielectric film to obtain a bonding structure.

[0052] like Figure 7 Shown is a schematic diagram of the bonding structure, where Figure 7 130 is a first substrate, 141 is a grating layer, 122 is a target second dielectric film, 100 is a lithium niobate substrate, 110 is a lithium niobate thin film, and 120 is a target third dielectric film.

[0053] Please continue to refer to Figure 4 In the above step A4: peeling off the lithium niobate substrate in the bonding structure, the process of obtaining the peeling structure may be: Step A41: After heating the bonding structure to separate the lithium niobate film from the lithium niobate substrate, the lithium niobate substrate is removed from the bonding structure to obtain a peeling structure.

[0054] The heating rate during heating is 1-2°C / min, and the temperature is heated to 220-300°C.

[0055] It should be noted that during the heating process, the lithium niobate film is separated from the wafer of the lithium niobate substrate as a lithium niobate single crystal thin film waveguide material, and the SiO2-SiO2 interface bonding formed by the target second dielectric film and the target third dielectric film is also strengthened during the heating process.

[0056] In addition, after the lithium niobate film is peeled off, the surface of the lithium niobate substrate can be reused after chemical mechanical polishing to reduce the production cost.

[0057] like Figure 8 Shown is a schematic diagram of a peeling structure, wherein: Figure 8 130 is a first substrate, 141 is a grating layer, 123 is a target second dielectric film and a target third dielectric film after bonding, and 112 is a target lithium niobate film.

[0058] Please continue to refer to Figure 4 In the above step A5: after etching the lithium niobate film in the peeling structure to form a ridge waveguide structure layer, the process of forming a covering layer for waveguide transmission on the ridge waveguide structure layer can be: Step A51: Etching the lithium niobate film in the peeling structure to obtain a target lithium niobate film, the target lithium niobate film has a thickness of 50-500 nm, and a roughness of 4-6 nm (RMS).

[0059] In the actual preparation process, the second lithium niobate film after stripping is etched to make the surface of the second lithium niobate film flat. In the specific implementation, because the stripped lithium niobate waveguide film has considerable surface roughness, it is necessary to use argon ions to etch the lithium niobate surface material greater than 70nm to reduce the surface roughness to 4-6nm (RMS), which can reduce the transmission loss of the lithium niobate waveguide.

[0060] Step A52: depositing a chromium metal film on the target lithium niobate film.

[0061] Step A53: Etching the chromium metal film into a mask structure corresponding to the ridge waveguide structure to obtain a mask layer.

[0062] Step A54: using the mask layer to etch the target lithium niobate film to form a ridge waveguide structure layer, the thickness of the ridge waveguide structure layer is 50-500nm.

[0063] In the actual preparation process, a metal film is deposited on the surface of the target lithium niobate film as a hard mask layer of the ridge waveguide structure. For example, metal materials such as chromium metal can be used. Then, the ridge waveguide structure pattern is transferred to the metal film by photolithography and inductively coupled plasma etching. Finally, the lithium niobate film is etched by inductively coupled plasma under the metal mask to form a ridge waveguide structure layer. The chemical reaction gas can be chlorine-containing gas, argon gas and helium gas and a combination of these gases.

[0064] Step A55: depositing a fourth dielectric film on the ridge waveguide structure layer to form a covering layer.

[0065] Wherein, the fourth dielectric film is silicon dioxide, silicon nitride, magnesium fluoride or aluminum oxide.

[0066] A fourth dielectric film is deposited on the surface of the ridge waveguide structure layer to form a covering layer of the lithium niobate ridge waveguide structure to reduce waveguide transmission loss. Other low refractive index dielectric materials, such as silicon nitride, magnesium fluoride, aluminum oxide and other dielectric films, can also be used according to waveguide performance requirements.

[0067] Please continue to refer to Figure 4 , after step A55, the method further comprises: Step A6: Forming a signal electrode and a ground electrode on the fourth dielectric film to form a modulation structure. like Fig. 9 The schematic diagram of the modulation structure is shown in FIG. Fig. 9 130 is the first substrate, 141 is the grating layer, 123 is the target second dielectric film and the target third dielectric film after bonding, 112 is the ridge waveguide structure layer, 150 is the fourth dielectric film, 161 is the signal electrode, and 162 is the ground electrode.

[0068] Step A7: After cutting and polishing the first side surface and the second side surface of the modulation structure, an anti-reflection film is plated on the first side surface and the second side surface to obtain a lithium niobate electro-optic modulator.

[0069] In the actual preparation process, the first side and the second side of the modulation structure are cut by a grinding wheel and polished by end face or laser cut to form the light input and output end faces, and an anti-reflection film is plated on the end faces to complete the production of the entire device and obtain a lithium niobate electro-optic modulator. The schematic diagram of the lithium niobate electro-optic modulator is shown in FIG. Fig.10 As shown, Fig.10 130 is the first substrate, 141 is the grating layer, 123 is the target second dielectric film and the target third dielectric film after bonding, 112 is the ridge waveguide structure layer, 150 is the fourth dielectric film, 161 is the signal electrode, and 162 is the ground electrode.

[0070] The present application can prepare a thin-film lithium niobate electro-optic modulator by the preparation method of the thin-film lithium niobate electro-optic modulator provided. The slow light effect of the electro-optic modulator is realized on a thin-film lithium niobate platform using a coupled Bragg resonator structure, and an ultra-compact modulator is constructed at the same time. The prepared slow light waveguide shows a wide optical passband, low insertion loss, and an optical group refractive index that is three times greater than that of an ordinary ridge waveguide.

[0071] The feature of the present application is that a special grating formation and surface flattening process is performed on a silicon-based substrate, and a lithium niobate wafer with an ion-cut lithium niobate film is directly combined to form a lithium niobate waveguide and an electro-optical modulation device with bottom grating coupling. In addition, high-contrast grating materials can be flexibly used according to design requirements to adapt to production line equipment capabilities and product cost requirements. Furthermore, the coupling strength of the grating and the waveguide can meet the strict performance requirements of the device by precisely controlling the grating etching duty cycle, the grating etching depth, and the distance between the grating and the lithium niobate waveguide. The preparation method of the thin-film lithium niobate electro-optical modulator provided in the embodiment of the present application adopts conventional semiconductor processes and avoids the need to form a grating on a special profile of the ridge waveguide, significantly reducing the cost of the slow-light thin-film lithium niobate electro-optical modulator, reducing waveguide transmission loss, and improving the electro-optical performance of the device. The slow-light thin-film lithium niobate electro-optical modulator made by this method can be easily integrated with other silicon optical devices due to the use of a silicon-based substrate and a compact area to meet the requirements of the next generation of communication equipment.

[0072] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0073] The above embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for preparing a thin film lithium niobate electro-optic modulator, characterized in that: The method comprises: Acquire a first structure, wherein the first structure comprises: a first substrate, a grating layer located on the first substrate, the grating layer being formed by etching a first dielectric film, and a target second dielectric film located on the grating layer, the surface roughness of the target second dielectric film being less than 1 nm (RMS), and the refractive index of the target second dielectric film being less than that of the first dielectric film; Acquire a second structure, the second structure comprising: a lithium niobate substrate, the lithium niobate substrate comprising a lithium niobate film formed by ion implantation, a target third dielectric film located on the lithium niobate film, the surface roughness of the target third dielectric film being less than 1 nm (RMS), and the refractive index of the target third dielectric film being the same as the refractive index of the target second dielectric film; Bonding the target second dielectric film and the target third dielectric film to obtain a bonding structure; peeling off the lithium niobate substrate in the bonding structure to obtain a peeling structure; After etching the lithium niobate film in the peeling structure to form a ridge waveguide structure layer, a covering layer for waveguide transmission is formed on the ridge waveguide structure layer.

2. The method according to claim 1, characterized in that The obtaining of the first structure comprises: obtaining a first substrate; Depositing a first dielectric film on a first substrate, wherein the thickness of the first dielectric film is 1000-3000 nm; Etching the first dielectric film to form the grating layer, wherein the etching depth of the grating layer is 20-500 nm; Depositing a second dielectric film on the grating layer, wherein the thickness of the second dielectric film is greater than 60 nm; After chemical mechanical polishing is performed on the second dielectric film, the target second dielectric film is obtained, and the thickness of the target second dielectric film is greater than 10 nm.

3. The method according to claim 1, characterized in that The obtaining of the second structure comprises: Obtaining a lithium niobate substrate; Performing ion implantation on the first surface of the lithium niobate substrate to form a lithium niobate film, wherein the depth of the ion implantation is 200-800 nm; Depositing a third dielectric film on the lithium niobate film; The third dielectric film is subjected to chemical mechanical polishing to obtain the target third dielectric film, wherein the target third dielectric film has a thickness of 100-1000 nm.

4. The method according to claim 1, characterized in that: The step of peeling off the lithium niobate substrate in the bonding structure to obtain a peeled structure comprises: The bonding structure is heated to separate the lithium niobate film from the lithium niobate substrate. The lithium niobate substrate is removed from the bonding structure to obtain the peeling structure.

5. The method according to claim 1, characterized in that: The etching of the lithium niobate film in the peeling structure to form a ridge waveguide structure layer comprises: Etching the lithium niobate film in the peeling structure to obtain a target lithium niobate film, wherein the target lithium niobate film has a thickness of 50-500 nm and a roughness of 4-6 nm (RMS); Depositing a chromium metal film on the target lithium niobate film; Etching the chromium metal film into a mask structure corresponding to the ridge waveguide structure to obtain a mask layer; The target lithium niobate film is etched using the mask layer to form the ridge waveguide structure layer, and the thickness of the ridge waveguide structure layer is 50-500 nm.

6. The method according to claim 1, characterized in that The covering layer for waveguide transmission is formed on the ridge waveguide structure layer, comprising: A fourth dielectric film is deposited on the ridge waveguide structure layer to form the cover layer.

7. The method according to claim 6, characterized in that After forming a covering layer for waveguide transmission on the ridge waveguide structure layer, the method further comprises: forming a signal electrode and a ground electrode on the fourth dielectric film to form a modulation structure; After cutting and polishing the first side surface and the second side surface of the modulation structure, an anti-reflection film is plated on the first side surface and the second side surface to obtain a lithium niobate electro-optic modulator.

8. The method according to claim 6, characterized in that The first substrate is a silicon-based substrate, a germanium substrate or a gallium arsenide substrate; The first dielectric film is SiN x Dielectric film, titanium dioxide, hafnium dioxide, tantalum oxide or yttrium oxide: The second dielectric film and the third dielectric film are silicon dioxide; The fourth dielectric film is silicon dioxide, silicon nitride, magnesium fluoride or aluminum oxide.

9. The method according to claim 7, characterized in that: The signal electrode and the ground electrode are made of a titanium bonding layer and a gold film on the titanium bonding layer. The thickness of the titanium bonding layer is 5-10 nm, and the thickness of the gold film is 300-800 nm.

10. A thin film lithium niobate electro-optic modulator, characterized in that: The electro-optic modulator is prepared by the method for preparing a thin-film lithium niobate electro-optic modulator according to any one of claims 1 to 9.

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