A high-efficiency, low-loss barium titanate electro-optic modulator chip and its fabrication method

Abstract

This invention relates to the field of optoelectronic device fabrication technology, and particularly to a high-efficiency, low-loss barium titanate electro-optic modulator chip and its fabrication method. The barium titanate electro-optic modulator chip includes a substrate layer, a buffer thin film layer, a barium titanate thin film layer, a first protective layer, a silicon nitride thin film, a second protective layer, and two electrodes. A multilayer waveguide material structure of silicon nitride + barium titanate is formed by barium titanate waveguides on the barium titanate thin film layer and silicon nitride waveguides on the silicon nitride thin film. Light transmission is based on the low-loss characteristics of the silicon nitride waveguide. During modulation, the optical signal enters the barium titanate waveguide through interlayer coupling between the silicon nitride waveguide and the barium titanate waveguide. An electric field is applied through the electrodes to change the refractive index of the barium titanate waveguide, and the signal is modulated based on the high electro-optic coefficient characteristics of the barium titanate waveguide. After modulation, the signal enters the silicon nitride waveguide for transmission, outputting the modulated optical signal. This achieves low loss in the optical signal transmission process of the electro-optic modulator chip and improves the modulation efficiency of the optical signal.

Description

Technical Field

[0001] This invention relates to the field of optoelectronic device fabrication technology, and in particular to a high-efficiency, low-loss barium titanate electro-optic modulator chip and its fabrication method. Background Technology

[0002] An electro-optic modulator (EOM) is an optical signal modulation device based on the Pockels effect. By applying an electric field to an electro-optic material, the EOM can control the phase, intensity, or frequency of an optical signal. As a core device for electro-optic signal conversion, the EOM directly determines the performance of optical communication and optical interconnect networks.

[0003] Currently, the electro-optic material used in commercial electro-optic modulators is mainly lithium niobate (LiNbO3). The electro-optic coefficient of lithium niobate is about 30 pm / V, which is relatively low. Therefore, electro-optic modulators made with LiNbO3 as the core material have problems such as high driving voltage, high energy consumption, and low adjustment bandwidth limit, which seriously restricts the modulation efficiency of electro-optic modulators. Summary of the Invention

[0004] This invention provides a high-efficiency, low-loss barium titanate electro-optic modulator chip and its fabrication method, which solves the defects of high driving voltage and high energy consumption of existing electro-optic modulators, and realizes the fabrication of a low-loss, high-efficiency barium titanate electro-optic modulator based on multilayer materials.

[0005] This invention provides a high-efficiency, low-loss barium titanate electro-optic modulator chip, comprising a substrate layer, a buffer thin film layer, a barium titanate thin film layer, a first protective layer, a silicon nitride thin film, a second protective layer, and two electrodes. The buffer thin film layer is grown on the substrate layer; the barium titanate thin film layer is grown on the buffer thin film layer, and a barium titanate waveguide is formed on the barium titanate thin film layer; the first protective layer is deposited on the barium titanate thin film layer; the silicon nitride thin film is grown on the first protective layer, and the silicon nitride thin film is etched to form a silicon nitride waveguide above the barium titanate waveguide. The silicon nitride waveguide and the barium titanate waveguide each form a gradually narrowing trapezoidal portion towards the first protective layer to form an interlayer coupler; the second protective layer is deposited on the silicon nitride waveguide and the first protective layer; the two electrodes are deposited on the second protective layer and located on both sides of the barium titanate waveguide to form an electric field covering the barium titanate waveguide.

[0006] According to the present invention, a high-efficiency, low-loss barium titanate electro-optic modulator chip is provided, wherein the barium titanate waveguide is a ridge waveguide, and deposition trenches are etched on the barium titanate thin film layer at positions on both sides of the barium titanate waveguide, the deposition trenches being used to sequentially deposit the first protective layer, the second protective layer and the electrode.

[0007] According to the present invention, a high-efficiency, low-loss barium titanate electro-optic modulator chip is provided, wherein the buffer thin film layer is one of strontium titanate thin film, magnesium oxide thin film, lanthanum cerate thin film, and titanium oxide thin film.

[0008] According to the present invention, a high-efficiency, low-loss barium titanate electro-optic modulator chip is provided, wherein both the first protective layer and the second protective layer are silicon dioxide thin films.

[0009] According to the present invention, a high-efficiency, low-loss barium titanate electro-optic modulator chip is provided, wherein the electrode is a metal electrode, which is suitable for forming a GSG coplanar waveguide type planar electrode, so as to load the modulation signal onto the barium titanate waveguide through the electric field of the GSG coplanar waveguide type planar electrode.

[0010] According to the present invention, a high-efficiency, low-loss barium titanate electro-optic modulator chip is provided, wherein the electrode includes a titanium metal adhesion layer deposited on a second protective layer and a gold layer deposited on the titanium metal adhesion layer.

[0011] The present invention also provides a method for fabricating a high-efficiency, low-loss barium titanate electro-optic modulator chip, which is suitable for fabricating the high-efficiency, low-loss barium titanate electro-optic modulator chip described in any of the above-mentioned methods. The method for fabricating the high-efficiency, low-loss barium titanate electro-optic modulator chip includes the following steps S1 to S7.

[0012] S1. Use a piece of silicon dioxide as a substrate.

[0013] S2. A buffer film layer and a barium titanate film layer are sequentially grown on the substrate layer.

[0014] S3. A barium titanate waveguide is formed by etching the barium titanate thin film layer, and deposition trenches are formed on both sides of the barium titanate waveguide.

[0015] S4. Deposit a first protective layer on the barium titanate thin film layer.

[0016] S5. A silicon nitride thin film is deposited on the first protective layer, and the silicon nitride thin film is etched to form a strip-shaped silicon nitride waveguide.

[0017] S6. Deposit a second protective layer on the silicon nitride waveguide and the first protective layer.

[0018] S7. Etch the second protective layer at the position corresponding to the deposition tank and deposit an electrode.

[0019] According to the method for fabricating a high-efficiency, low-loss barium titanate electro-optic modulator chip provided by the present invention, in step S3, the barium titanate thin film layer is etched using one of wet etching, physical sputtering etching, reactive ion etching, and inductively coupled plasma etching.

[0020] In step S4, after the first protective layer is deposited and formed, the surface of the first protective layer is polished, and then step S5 is performed; the first protective layer is deposited and formed using a chemical vapor deposition method or a physical vapor deposition method.

[0021] In step S6, after the second protective layer is deposited and formed, the surface of the second protective layer is polished, and then step S7 is performed; the second protective layer is deposited and formed using a chemical vapor deposition method or a physical vapor deposition method.

[0022] According to the method for fabricating a high-efficiency, low-loss barium titanate electro-optic modulator chip provided by the present invention, in step S7, the etching process of the second protective layer is a partial etching process. After the etching is completed, a thin layer of the second protective layer remains in the deposition tank to isolate the barium titanate thin film layer and the electrode.

[0023] According to the method for fabricating a high-efficiency, low-loss barium titanate electro-optic modulator chip provided by the present invention, in step S7, the electrode is deposited by electron beam evaporation or magnetron sputtering.

[0024] The present invention provides a high-efficiency, low-loss barium titanate electro-optic modulator chip and its fabrication method. It utilizes a multilayer waveguide material structure of silicon nitride + barium titanate, formed by a barium titanate waveguide on a barium titanate thin film layer and a silicon nitride waveguide formed by a silicon nitride thin film. Light transmission is based on the low-loss characteristics of the silicon nitride waveguide. During modulation, the optical signal enters the barium titanate waveguide through interlayer coupling between the silicon nitride and barium titanate waveguides. An electric field is applied through electrodes to change the refractive index of the barium titanate waveguide, and the signal is modulated based on the high electro-optic coefficient characteristics of the barium titanate waveguide. After modulation, the signal is transmitted through the silicon nitride waveguide, outputting the modulated optical signal. This achieves low loss during the optical signal transmission process of the electro-optic modulator chip and improves the modulation efficiency of the optical signal. Attached Figure Description

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

[0026] Figure 1 This is a schematic diagram of the structure of the high-efficiency, low-loss barium titanate electro-optic modulator chip provided by the present invention.

[0027] Figure 2 This is a schematic diagram of the modulation principle of the high-efficiency, low-loss barium titanate electro-optic modulator chip provided by the present invention.

[0028] Figure 3 This is one of the process diagrams illustrating the fabrication method of the high-efficiency, low-loss barium titanate electro-optic modulator chip provided by the present invention.

[0029] Figure 4 This is the second schematic diagram of the process for fabricating the high-efficiency, low-loss barium titanate electro-optic modulator chip provided by the present invention.

[0030] Figure 5 This is the third schematic diagram of the process for fabricating the high-efficiency, low-loss barium titanate electro-optic modulator chip provided by the present invention.

[0031] Reference numerals: 1. Substrate layer; 2. Buffer thin film layer; 3. Barium titanate thin film layer; 31. Barium titanate waveguide; 4. First protective layer; 5. Silicon nitride waveguide; 6. Second protective layer; 7. Electrode; 8. Grating coupler; 9. Beam splitter; 10. Beam combiner; 11. Mode converter; 12. Photoresist; 13. Mask. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0033] In the description of the embodiments of the present invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of the present invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0034] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0035] In embodiments of the present invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "on top of," and "over" the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0036] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0037] The following is combined with Figures 1 to 5 This invention describes a high-efficiency, low-loss barium titanate electro-optic modulator chip and its fabrication method.

[0038] One embodiment of the present invention provides a high-efficiency, low-loss barium titanate electro-optic modulator chip, see [link to relevant documentation]. Figure 1 As shown, the barium titanate electro-optic modulator chip includes a substrate layer 1, a buffer thin film layer 2, a barium titanate thin film layer 3, a first protective layer 4, a silicon nitride thin film, a second protective layer 6, and two electrodes 7. The buffer thin film layer 2 is grown on the substrate layer 1; the barium titanate thin film layer 3 is grown on the buffer thin film layer 2, and a barium titanate waveguide 31 is formed on the barium titanate thin film layer 3; the first protective layer 4 is deposited on the barium titanate thin film layer 3; the silicon nitride thin film is grown on the first protective layer 4, and the silicon nitride thin film is etched to form a silicon nitride waveguide 5 above the barium titanate waveguide 31. The silicon nitride waveguide 5 and the barium titanate waveguide 31 each form a gradually narrowing trapezoidal portion towards the first protective layer 4 to form an interlayer coupler; the second protective layer 6 is deposited on the silicon nitride waveguide 5 and the first protective layer 4; the two electrodes 7 are deposited on the second protective layer 6 and located on both sides of the barium titanate waveguide 31 to form an electric field covering the barium titanate waveguide 31.

[0039] It is understood that the high-efficiency, low-loss barium titanate electro-optic modulator chip of this embodiment forms a multilayer waveguide material structure of silicon nitride + barium titanate through a barium titanate waveguide 31 formed on a barium titanate thin film layer 3 and a silicon nitride waveguide 5 formed on a silicon nitride thin film. Light transmission mainly occurs in the silicon nitride waveguide 5, while signal modulation occurs in the barium titanate waveguide 31. By applying an electric field through two electrodes 7 to change the refractive index of the barium titanate waveguide 31, phase modulation of the signal is achieved in the barium titanate waveguide 31, thereby modulating the intensity of the output light.

[0040] It is important to understand that the electro-optic coefficient of barium titanate (BaTiO3, BTO) is r. 33 =105 pm / V and r 42 =1300 pm / V, which is 30 times higher than the electro-optic coefficient of traditional LiNbO3, and has a wide transmission spectrum from visible light to mid-infrared, theoretically reducing the half-wave voltage length by an order of magnitude. Silicon nitride (SiN) material has lower loss in optical waveguides than silicon (Si): the band gap of silicon nitride is about 4.9 eV, which is much larger than that of silicon (1.1 eV), which means that the absorption loss of silicon nitride in the optical communication band is very low; the refractive index of silicon nitride waveguide 5 used in this embodiment (about 2.0) is lower than that of silicon (about 3.48). The lower refractive index makes the mode field of silicon nitride waveguide 5 more uniformly distributed, thereby reducing the scattering loss of light at the edge of the waveguide; the silicon nitride fabrication process (usually low-pressure chemical vapor deposition LPCVD) can achieve extremely low surface roughness and good material quality, thereby reducing the loss caused by surface scattering.

[0041] In this embodiment, a multilayer waveguide material structure of silicon nitride + barium titanate is formed by barium titanate waveguide 31 and silicon nitride waveguide 5 on barium titanate thin film layer 3. Light is transmitted based on the low loss characteristics of silicon nitride waveguide 5. During modulation, the optical signal enters barium titanate waveguide 31 through the interlayer coupler formed by silicon nitride waveguide 5 and barium titanate waveguide 31, and the signal is modulated based on the high electro-optic coefficient characteristics of barium titanate waveguide 31. After modulation, it enters silicon nitride waveguide 5 for transmission and outputs the modulated optical signal. This achieves low loss in the process of transmitting optical signals in the electro-optic modulator chip and improves the modulation efficiency of the optical signal.

[0042] In some embodiments of the high-efficiency, low-loss barium titanate electro-optic modulator chip of the present invention, the barium titanate waveguide 31 is a ridge waveguide, and deposition trenches are etched on the barium titanate thin film layer 3 at positions on both sides of the barium titanate waveguide 31. The deposition trenches are used to sequentially deposit the first protective layer 4, the second protective layer 6, and the electrode 7.

[0043] It is understood that the barium titanate waveguide 31 in this embodiment adopts a ridge waveguide structure. Compared with the traditional strip waveguide, the ridge waveguide reduces the leakage of the optical field at the sidewalls and reduces optical loss. A second etching is performed on both sides of the ridge waveguide to form deposition trenches. This structure not only optimizes the waveguide shape, but also enables the subsequent deposition of the first protective layer 4, the second protective layer 6, and the electrode 7 to be positioned more accurately, and improves the electric field distribution and increases the photoelectric coincidence factor.

[0044] The first protective layer 4, typically silicon dioxide (SiO2), is deposited in the barium titanate waveguide 31 and its two side deposition tanks. It protects the waveguide from damage during subsequent processes and isolates the metal electrode from the waveguide to reduce optical loss. The second protective layer 6, also made of silicon dioxide (SiO2), is deposited again on top of the silicon nitride waveguide 5 and the first protective layer 4. After partial etching, the second protective layer 6 exposes the underlying structure in specific areas to facilitate the subsequent deposition of the electrode 7. Finally, the electrode 7 deposits a metal electrode in the partially etched area of ​​the second protective layer 6. The electrode 7 loads a modulation signal onto the barium titanate waveguide 31 via a GSG (Ground-Signal-Ground) coplanar waveguide-type planar electrode, thus modulating the optical signal.

[0045] In the fabrication process of the barium titanate electro-optic modulator chip of the present invention, a buffer thin film layer 2 is first grown on a substrate layer 1 (usually silicon dioxide, SiO2), followed by the growth of a barium titanate thin film layer 3. The main function of the buffer thin film layer 2 is to reduce the lattice mismatch between the barium titanate (BTO) thin film and the substrate (usually silicon dioxide, SiO2). Since there may be a large difference in lattice constant between the barium titanate thin film layer 3 and the substrate layer 1, direct growth of the barium titanate thin film layer 3 may lead to epitaxial growth defects, affecting device performance. The buffer thin film layer 2 ensures that the barium titanate thin film layer 3 can be grown with high quality, reducing the negative impact of lattice mismatch and thus improving the overall performance of the electro-optic modulator chip.

[0046] In some embodiments of the high-efficiency, low-loss barium titanate electro-optic modulator chip of the present invention, the buffer thin film layer 2 may use materials including, but not limited to, strontium titanate thin film, magnesium oxide thin film, lanthanum cerate thin film, and titanium oxide thin film. It is understood that different buffer thin film layer 2 materials have their own advantages, specifically depending on the requirements of lattice matching (the lattice constant of the buffer thin film layer 2 material should be as close as possible to that of the barium titanate thin film layer 3 to reduce interface defects), coefficient of thermal expansion (the coefficient of thermal expansion of the buffer thin film layer 2 material should match that of the barium titanate thin film layer 3 and the substrate layer 1 to avoid stress caused by temperature changes), and growth process (different materials have different requirements for growth conditions, and the feasibility of the actual process needs to be considered). In this embodiment, the strontium titanate thin film has good dielectric properties and low leakage current, making it suitable as a high-dielectric material; the magnesium oxide thin film has a stable crystal structure and good high-temperature resistance, which helps to improve interface quality; the lanthanum cerate thin film has excellent chemical stability and resistance to reduction, making it suitable for applications in harsh environments; and the titanium oxide thin film is a wide-bandgap semiconductor with good optical transparency and chemical stability. By introducing an appropriate buffer thin film layer 2, the lattice mismatch problem can be effectively alleviated, and the quality of the barium titanate thin film layer 3 can be improved.

[0047] In some embodiments of the high-efficiency, low-loss barium titanate electro-optic modulator chip of the present invention, electrode 7 is a metal electrode, suitable for forming a GSG coplanar waveguide type planar electrode, so as to load the modulation signal onto the barium titanate waveguide 31 through the electric field of the GSG coplanar waveguide type planar electrode.

[0048] It is understood that the barium titanate electro-optic modulator chip of the present invention, when performing optical modulation, is generally based on a barium titanate thin-film modulator forming an MZ (Mach-Zehnder Modulator) structure, see [link to relevant documentation]. Figure 2 As shown, the key components of the barium titanate thin-film modulator include straight waveguides, curved waveguides, grating couplers / mode converters, beam splitters, silicon nitride-BTO interlayer couplers, and electrodes. The light beam needs to be split first, then phase modulated, and finally combined for output. Optical signal phase modulation requires simultaneous modulation of both beams. Therefore, the barium titanate electro-optic modulator chip used in this embodiment requires two sets of chips arranged side-by-side. The electrodes 7 of the two sets of chips form... Figure 2The electrode arrangement structure, namely the GSG coplanar waveguide type planar electrode, has a central electrode 7 as the signal electrode responsible for loading the modulation signal, and two side electrodes 7 as ground electrodes located on either side of the signal electrode, used for shielding and providing a stable reference potential. When the modulation signal is applied to the GSG electrode, a corresponding electric field change is generated within the barium titanate waveguide 31. Due to the high electro-optic coefficient of the BTO material, this electric field change leads to a change in the waveguide refractive index, thereby altering the phase or intensity of the optical signal passing through the waveguide. By adjusting the phase of the two optical signals, the phase difference between the two optical signals is controlled. After modulation of the two optical signals, the modulated two optical signals are recombined in the beam combiner and interfere, thus modulating the intensity of the output light.

[0049] In some specific examples, electrode 7 comprises a titanium metal adhesion layer deposited on the second protective layer 6 and a gold layer deposited on the titanium metal adhesion layer. It is understood that electrode 7 is formed as the final step after the first protective layer 4, silicon nitride waveguide 5, and second protective layer 6 are completed during the fabrication of the barium titanate electro-optic modulator chip. Partial etching is performed on the second protective layer 6 at the deposition trench locations corresponding to both sides of the barium titanate waveguide 31, exposing the areas where electrodes need to be deposited, while retaining a thin layer of the second protective layer 6 to avoid direct contact between the barium titanate waveguide 31 and the metal electrode, reducing light absorption loss. First, a titanium metal layer is deposited in the etched area using electron beam evaporation or magnetron sputtering as an adhesion layer to ensure good adhesion of the subsequent gold layer. The titanium metal layer serves primarily to improve the adhesion between the subsequent gold layer and the second protective layer 6. Since the adhesion of gold layers is poor when directly deposited on insulating materials such as silicon dioxide, the presence of the titanium metal layer can significantly improve this. Typically, the titanium metal layer is thin, approximately 50–200 nanometers, to ensure sufficient adhesion without increasing unnecessary resistance. Then, a gold layer is deposited in the same area. This gold layer is the actual conductive part, responsible for transmitting the modulated signal. Gold has excellent conductivity, chemical stability, and corrosion resistance, making it ideal for high-frequency signal transmission. The thickness of the gold layer is typically between 300 and 1000 nanometers to ensure low resistance and good current carrying capacity.

[0050] In some specific embodiments, a BTO thin-film modulator based on an MZ structure is fabricated using the high-efficiency, low-loss barium titanate electro-optic modulator chip described in the above embodiments. See also Figure 2 As shown, the key components of the BTO thin-film modulator include a straight waveguide, a curved waveguide, a grating coupler 8, a beam splitter 9, an MZ interferometer structure formed by two sets of barium titanate electro-optic modulator chips, a beam combiner 10, and a mode converter 11. Light transmission mainly occurs in the silicon nitride waveguide 5. During modulation, the optical signal is coupled to the barium titanate waveguide 31 for modulation via a silicon nitride-BTO interlayer coupler.

[0051] After the optical signal enters the waveguide through the grating coupler 8, it is first split into two optical waves at the beam splitter 9, which propagate along two independent optical paths. Upon entering the MZ interferometer structure, the optical signal first enters the silicon nitride waveguide 5 for transmission. During modulation, the optical signal is coupled to the barium titanate waveguide 31 through the silicon nitride-BTO interlayer coupler for modulation. After modulation, it re-enters the silicon nitride waveguide 5 for transmission. During modulation of the optical signal in the barium titanate waveguide 31, the electric field applied to the barium titanate waveguide 31 under the action of the electrode 7 changes the refractive index of the barium titanate waveguide 31. By applying different electric fields to the two optical paths, the phase difference between the two optical paths is changed. The greater the electric field strength, the greater the resulting phase difference. The two optical signals are re-merged at the beam combiner 10 and interfere, and are output by the mode converter 11. Since the phase difference between the two optical paths is controllable, this phase difference affects the interference result, thereby modulating the intensity of the output light.

[0052] In another aspect, this invention provides a method for fabricating a high-efficiency, low-loss barium titanate electro-optic modulator chip, suitable for fabricating any of the above-mentioned high-efficiency, low-loss barium titanate electro-optic modulator chips, combined with... Figure 3 , Figure 4 and Figure 5 As shown, the fabrication method of the high-efficiency, low-loss barium titanate electro-optic modulator chip includes the following steps S1 to S7.

[0053] S1. A silicon dioxide substrate is used as substrate layer 1. The silicon dioxide substrate provides a stable growth platform and is the basis for subsequent thin film deposition.

[0054] S2. A buffer thin film layer 2 and a barium titanate thin film layer 3 are sequentially grown on the substrate layer 1.

[0055] The buffer thin film layer 2 can be made of one or more materials such as strontium titanate (STO), magnesium oxide (MgO), lanthanum cerate (LCO), or titanium oxide (TiO2). The barium titanate thin film layer 3 is deposited on top of the buffer thin film layer 2 using epitaxial growth technology. The buffer thin film layer 2 is used to reduce the lattice mismatch between the barium titanate thin film layer 3 and the substrate layer 1, thereby improving the quality of the barium titanate thin film layer 3.

[0056] S3. Barium titanate waveguide 31 is formed by etching the barium titanate thin film layer 3, and deposition trenches are formed on both sides of the barium titanate waveguide 31.

[0057] See Figure 3As shown, photoresist 12 is coated on the barium titanate thin film layer 3 (leaving space for etching the barium titanate waveguide 31). Photolithography is performed using a mask 13 to remove the unexposed photoresist 12, exposing the areas to be etched. The barium titanate thin film layer 3 is then etched to form the barium titanate waveguide 31. The etching process can employ wet etching, physical sputtering (IBM), reactive ion etching (RIE), or inductively coupled plasma etching (ICP). The barium titanate waveguide 31 is formed as a ridge waveguide structure, reducing light leakage at the sidewalls and lowering optical loss.

[0058] See Figure 4 As shown, the barium titanate thin film layer 3 undergoes a second etching process. This second etching occurs on both sides of the barium titanate waveguide 31 formed in the first etching, maintaining a certain distance from the waveguide 31. Specifically, after determining the positions on both sides of the barium titanate waveguide 31, photoresist 12 is coated. Then, photolithography is performed using a mask 13 to remove the unexposed photoresist 12. Deposition trenches are then etched on both sides of the barium titanate waveguide 31, providing space for subsequent protective layer and electrode deposition.

[0059] S4. Deposit the first protective layer 4 on the barium titanate thin film layer 3.

[0060] See Figure 5 As shown, a layer of silicon dioxide (SiO2) is deposited on the barium titanate thin film layer 3 as the first protective layer 4. The first protective layer protects the waveguide from damage by subsequent processes and isolates the metal electrode from the waveguide to reduce optical loss. The deposition method can be chemical vapor deposition (CVD) or physical vapor deposition (PVD), and the surface needs to be polished (CMP) after deposition to ensure planarization.

[0061] S5, see below. Figure 5 As shown, a silicon nitride thin film is deposited on the first protective layer 4, and the silicon nitride thin film is etched to form a strip-shaped silicon nitride waveguide 5. The silicon nitride waveguide 5 is mainly used for optical transmission path, and its ultra-low optical loss characteristics help improve the overall performance. The deposition and etching processes also need to consider surface planarization.

[0062] S6, see also Figure 5 As shown, a second protective layer 6 is deposited on the silicon nitride waveguide 5 and the first protective layer 4. The second protective layer 6 further protects the entire structure and provides support for the subsequent deposition of the electrode 7. After deposition, a polishing process (CMP) is also required to ensure surface flatness.

[0063] S7. Etching is performed on the second protective layer 6 at the location corresponding to the deposition tank, and electrode 7 is deposited. See again. Figure 5As shown, partial etching is performed on the second protective layer 6 at the location corresponding to the deposition tank to expose the underlying structure. A metal electrode 7 is deposited in the etched area using electron beam evaporation or magnetron sputtering. First, a layer of titanium (Ti) is deposited as an adhesion layer, followed by a gold (Au) layer to form the electrode 7. An electric field is applied to the electrode 7 to modulate the optical signal within the barium titanate waveguide 31.

[0064] It is understood that the barium titanate electro-optic modulator chip prepared using this method of the present embodiment has a multilayer waveguide material structure of silicon nitride + barium titanate, consisting of a barium titanate waveguide 31 on the barium titanate thin film layer 3 and a silicon nitride waveguide 5. Light is transmitted based on the low loss characteristics of the silicon nitride waveguide 5. During modulation, the optical signal enters the barium titanate waveguide 31 through the interlayer coupling between the silicon nitride waveguide 5 and the barium titanate waveguide 31, and is modulated based on the high electro-optic coefficient characteristics of the barium titanate waveguide 31. After modulation, it enters the silicon nitride waveguide 5 for transmission and outputs the modulated optical signal, thus achieving low loss in the process of transmitting optical signals in the electro-optic modulator chip and improving the modulation efficiency of the optical signal.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-efficiency, low-loss barium titanate electro-optic modulator chip, characterized in that, include: Substrate (1); A buffer thin film layer (2) is grown on the substrate layer (1); A barium titanate thin film layer (3) is grown on the buffer thin film layer (2), and a barium titanate waveguide (31) is formed on the barium titanate thin film layer (3). The first protective layer (4) is deposited on the barium titanate thin film layer (3); A silicon nitride thin film is grown on the first protective layer (4). The silicon nitride thin film is etched to form a silicon nitride waveguide (5) above the barium titanate waveguide (31). The silicon nitride waveguide (5) and the barium titanate waveguide (31) form a trapezoidal portion that gradually narrows toward the first protective layer (4) to form an interlayer coupler. A second protective layer (6) is deposited on the silicon nitride waveguide (5) and the first protective layer (4); Two electrodes (7) are deposited on the second protective layer (6) and located on both sides of the barium titanate waveguide (31) to form an electric field covering the barium titanate waveguide (31).

2. The high-efficiency, low-loss barium titanate electro-optic modulator chip according to claim 1, characterized in that, The barium titanate waveguide (31) is a ridge waveguide. Deposition trenches are etched on the barium titanate thin film layer (3) at positions on both sides of the barium titanate waveguide (31). The deposition trenches are used to sequentially deposit the first protective layer (4), the second protective layer (6), and the electrode (7).

3. The high-efficiency, low-loss barium titanate electro-optic modulator chip according to claim 1, characterized in that, The buffer film layer (2) is one of strontium titanate film, magnesium oxide film, lanthanum cerate film and titanium oxide film.

4. The high-efficiency, low-loss barium titanate electro-optic modulator chip according to claim 1, characterized in that, Both the first protective layer (4) and the second protective layer (6) are silicon dioxide thin films.

5. The high-efficiency, low-loss barium titanate electro-optic modulator chip according to claim 1, characterized in that, The electrode (7) is a metal electrode, suitable for forming a GSG coplanar waveguide type planar electrode, so as to load the modulation signal onto the barium titanate waveguide (31) through the electric field of the GSG coplanar waveguide type planar electrode.

6. The high-efficiency, low-loss barium titanate electro-optic modulator chip according to claim 1, characterized in that, The electrode (7) includes a titanium metal adhesion layer deposited on the second protective layer (6) and a gold layer deposited on the titanium metal adhesion layer.

7. A method for fabricating a high-efficiency, low-loss barium titanate electro-optic modulator chip, characterized in that, Suitable for fabricating the high-efficiency, low-loss barium titanate electro-optic modulator chip according to any one of claims 1 to 6, wherein the fabrication method of the high-efficiency, low-loss barium titanate electro-optic modulator chip comprises: S1. Use a piece of silicon dioxide as a substrate (1). S2. A buffer thin film layer (2) and a barium titanate thin film layer (3) are sequentially grown on the substrate layer (1). S3. A barium titanate waveguide (31) is formed by etching the barium titanate thin film layer (3), and deposition trenches are formed on both sides of the barium titanate waveguide (31). S4. Deposit a first protective layer (4) on the barium titanate thin film layer (3). S5. A silicon nitride thin film is deposited on the first protective layer (4), and the silicon nitride thin film is etched to form a strip-shaped silicon nitride waveguide (5). S6. Deposit a second protective layer (6) on the silicon nitride waveguide (5) and the first protective layer (4). S7. Etch the second protective layer (6) at the position corresponding to the deposition tank and deposit an electrode (7).

8. The method for fabricating a high-efficiency, low-loss barium titanate electro-optic modulator chip according to claim 7, characterized in that, In step S3, the barium titanate thin film layer (3) is etched using one of the following methods: wet etching, physical sputtering etching, reactive ion etching, and inductively coupled plasma etching. In step S4, after the first protective layer (4) is deposited and formed, the surface of the first protective layer (4) is polished, and then step S5 is performed; the first protective layer (4) is deposited and formed using a chemical vapor deposition method or a physical vapor deposition method; In step S6, after the second protective layer (6) is deposited and formed, the surface of the second protective layer (6) is polished, and then step S7 is performed; the second protective layer (6) is deposited and formed using a chemical vapor deposition method or a physical vapor deposition method.

9. The method for fabricating a high-efficiency, low-loss barium titanate electro-optic modulator chip according to claim 7, characterized in that, In step S7, the etching process of the second protective layer (6) is partial etching. After the etching is completed, a thin layer of the second protective layer (6) remains in the deposition tank to isolate the barium titanate thin film layer (3) and the electrode (7).

10. The method for fabricating a high-efficiency, low-loss barium titanate electro-optic modulator chip according to claim 9, characterized in that, In step S7, the electrode (7) is deposited using electron beam evaporation or magnetron sputtering.

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