A silicon-based heterogeneously integrated barium strontium niobate electro-optic modulator and a method of fabricating the same

Abstract

The application discloses a silicon-based hetero-integrated barium strontium niobate electro-optical modulator and a preparation method thereof, and belongs to the field of silicon photoelectronic. The electro-optical modulator comprises a silicon substrate base sheet, a silicon waveguide layer obtained by etching the silicon substrate base sheet and constituting an MZI waveguide structure, a KSBN film covering the silicon waveguide layer and exposed parts of the silicon substrate base sheet, a functional layer arranged on the buffer layer and comprising a SBN film with a c-axis preferred orientation, an electrode layer arranged on the functional layer and used for applying a modulation electric field to change the refractive index of the functional layer, and a protective layer covering the electrode layer and the exposed functional layer and used for preventing electrode arc damage. The method does not need complex wafer bonding, directly grows a high-preferred-orientation SBN film on the silicon waveguide by using a magnetron sputtering, realizes monolithic integration of the SBN and the silicon-based waveguide, improves the modulation efficiency, simplifies the preparation process, reduces the cost and realizes large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of silicon optoelectronics, specifically relating to a silicon-based hetero-integrated barium strontium niobate electro-optic modulator and its fabrication method, which is applicable to fields such as high-speed optical communication, data center interconnection, and photonic computing. Background Technology

[0002] With the rapid development of artificial intelligence, cloud computing, and big data technologies, unprecedented demands are being placed on the communication bandwidth and energy efficiency within and between data centers. According to International Data Corporation (IDC), the global data volume is projected to reach 393.8 zettabytes by 2028, a 9.8-fold increase compared to 2018. Traditional electrical interconnects are nearing their physical limits in terms of transmission bandwidth, distance, and energy efficiency, making silicon photonics integration technology the core solution for next-generation optical interconnects.

[0003] Electro-optic modulators, as core devices that convert electrical signals into optical signals, are crucial for high-speed optical interconnects. Existing mainstream electro-optic modulators have several limitations: silicon-based electro-optic modulators lack the Pockels effect and rely on carrier plasma dispersion mechanisms, resulting in weak and nonlinear electro-optic effects. This leads to an unresolved trade-off between modulation bandwidth, insertion loss, and drive power, failing to meet the demands of high-speed communication. While thin-film lithium niobate (TFLN) modulators possess good electro-optic performance, their main conduction-optic coefficient r33 is only 31 pm / V, limiting performance improvement potential. Furthermore, their fabrication relies on crystal ion slicing and wafer bonding processes. Lithium niobate insulator (LNOI) wafers are nearly 10 times more expensive than silicon insulator (SOI) wafers, making the fabrication of large-size, high-quality substrates difficult, resulting in high costs, significant challenges in large-scale production, and substantial obstacles to monolithic integration with silicon photonics platforms.

[0004] Therefore, there is an urgent need for a novel electro-optic material and device integration solution that combines high electro-optic coefficient with CMOS process compatibility. Strontium barium niobate (Sr...) x Ba 1-x Nb₂O₆ (SBN) is an important ferroelectric oxide material belonging to the tetragonal tungsten bronze structure system. Its component x typically varies between 0.25 and 0.75. Research on SBN materials dates back to the 1960s. Due to its unique properties, such as an adjustable Curie temperature Tc ranging from 50 to 120°C depending on the component x; a large electro-optic coefficient; excellent photorefractive properties; piezoelectric properties; and a non-centrosymmetric structure, it shows broad application prospects in multiple high-tech fields such as optoelectronics, storage, sensing, and microwaves.

[0005] The electro-optic coefficient of SBN crystal is 10-100 times that of lithium niobate crystal. From the perspective of the material's inherent properties, SBN has significant research value in the application of high-efficiency electro-optic modulators. However, current research on SBN is mostly limited to the material's growth and performance, with research on its application in practical electro-optic modulators, especially thin-film micro / nano devices, being almost nonexistent. The main technical challenges are: first, the growth of high-quality SBN thin films. The material's performance is closely related to the degree of crystallinity and the consistency of crystal orientation, therefore, high-quality SBN thin films have stringent requirements for the substrate, environment, and conditions for growth; second, the design of SBN thin film devices and their compatibility with fabrication processes. The stringent fabrication conditions, such as high temperature and substrate requirements, greatly limit the flexibility of device design. Furthermore, the vertical crystal orientation and high dielectric constant of SBN thin films also pose significant challenges to the design and fabrication of modulator electrodes. Summary of the Invention

[0006] To address the shortcomings of existing electro-optic modulators, such as low modulation efficiency, complex fabrication processes, high costs, difficulty in large-scale production, and the inability to effectively integrate SBN materials with silicon substrates, difficulties in high-quality orientation growth, weak effective electric fields in functional layers due to high dielectric constants, and low coupling efficiency between electric and optical fields, this invention provides a silicon-based hetero-integrated barium strontium niobate electro-optic modulator and its fabrication method. This method eliminates the need for complex wafer bonding, utilizing magnetron sputtering to directly grow highly oriented SBN thin films on silicon waveguides. Through device architecture and buffer layer control schemes, it solves bottlenecks such as lattice mismatch between SBN and silicon integration, difficulties in growing high-quality thin films on patterned substrates, and difficulties in applying current to high-dielectric-constant materials, significantly improving modulation efficiency, simplifying the fabrication process, reducing costs, and enabling large-scale production.

[0007] To achieve the above-mentioned objectives, an embodiment provides a silicon-based heterogeneous integrated barium strontium niobate electro-optic modulator, comprising: A silicon substrate, comprising, from bottom to top, a silicon substrate, a buried oxide layer, and a top silicon device layer; Silicon waveguide layer: Mach-Zehnder interferometer (MZI) waveguide structure is constructed by etching the top silicon device layer; The buffer layer is made of potassium-doped barium strontium niobate (KSBN) film, which covers the surface of the patterned silicon waveguide layer and buried oxide layer; The functional layer is a barium strontium niobate (SBN) thin film with a preferred c-axis orientation, which is disposed on the buffer layer; The electrode layer, which is a Ground-Signal-Ground (GSG) coplanar waveguide structure electrode located directly above the MZI modulation arm, is used to apply a modulation electric field to the SBN thin film to change the refractive index.

[0008] Preferably, the MZI waveguide structure includes an input grating coupler, a tapered waveguide, a 50:50 multimode interference (MMI) coupler, two asymmetric modulation arm waveguides, an output MMI coupler, and an output grating coupler. The sidewall angle of the modulation arm waveguide is ≥80°, and there is a 100 μm asymmetric arm length difference between the two modulation arm waveguides, which is used to achieve free spectral range (FSR) modulation.

[0009] Preferably, the thickness of the KSBN film is 20-100 nm, and more preferably, the thickness of the KSBN film is 40-70 nm. The buffer layer composed of the KSBN film can solve the problems of lattice mismatch between the functional layer and the buried oxide layer composed of SBN films with preferred c-axis orientation, the unevenness of the silicon waveguide surface leading to film orientation disorder, and high defect density. It precisely induces the SBN film to achieve preferred orientation growth with the c-axis perpendicular to the surface, providing a crystallographic basis for efficiently exciting the r33 electro-optic coefficient.

[0010] Preferably, the thickness of the SBN film with c-axis preferred orientation is 0.3-2 μm, wherein the molar ratio of Sr to Ba is 75:25, and the ordinary refractive index n at a wavelength of 1550 nm is [missing information]. o = 2.21, Extreme refractive index n e = 2.206. More preferably, the thickness of the SBN film is 1-1.5 μm. As the upper cladding of the silicon waveguide layer, the SBN film, together with the electrode layer, forms an integrated structure of electro-optic material and electrode, replacing the traditional multilayer structure of "electrode-insulating layer-electro-optic material". This shortens the electric field interaction distance and improves the electro-optic overlap integral by combining the high proportion of TM mode optical field in the cladding, thus overcoming the electric field voltage division problem caused by the high dielectric constant of SBN; the effective electro-optic coefficient r33 of the SBN film is ≥145 pm / V.

[0011] Preferably, the GSG metal electrode adopts push-pull modulation, with opposite electric fields applied to the two modulation arms. The electrode material is gold or copper, and the electrode sheet thickness is 300-1000 nm. The width of the center electrode sheet used as the signal line is 2-3 μm, and the electrode sheet gap is 2-4 μm. It is used to apply an electric field perpendicular to the SBN film surface, match the c-axis orientation of the SBN crystal, and directly excite the r33 main conduction optical coefficient. This subverts the traditional transverse electric field modulation mode of GSG electrodes and maximizes the utilization rate of the Pockels effect.

[0012] Preferably, the electro-optic modulator further includes a protective layer made of SiO2, which covers the surface of the electrode layer and the surface of the SBN film to prevent electrode arc damage. Its breakdown field strength is ≥10 MV / cm. Electrode through holes are provided on the protective layer for testing electrode contact.

[0013] Preferably, the electro-optic modulator operates in the C+L band (1500-1630 nm) and uses TM (transverse magnetic) polarized light to ensure that the electric field direction is parallel to the Z-axis of the SBN thin film, making full use of the r33 electro-optic coefficient of SBN; the half-wave voltage-length product (VL) of the electro-optic modulator is ≤2.3V‧cm, the extinction ratio is ≥38 dB, and the waveguide group refractive index is 3.507±0.003.

[0014] The embodiment provides a method for fabricating the above-mentioned silicon-based hetero-integrated barium strontium niobate electro-optic modulator, comprising the following steps: Step 1: Pre-treat the silicon substrate; Step 2: Perform photolithography and etching operations on the top silicon device layer of the silicon substrate obtained after the preprocessing in Step 1 to construct the MZI waveguide structure as the silicon waveguide layer; Step 3: Using the sol-gel method, spin-coat the surface of the MZI waveguide structure prepared in step 2 with KSBN precursor solution, and perform rapid annealing to form a KSBN thin film as a buffer layer; Step 4: Using magnetron sputtering, deposit an SBN thin film on the buffer layer prepared in step 3 at a substrate temperature of 500-650℃ to form an SBN thin film with a preferred c-axis orientation as a functional layer. Step 5: On the functional layer obtained in step 4, a GSG metal electrode structure is fabricated as the electrode layer using an overlay process; Step 6: A protective layer is deposited on the surface of the functional layer prepared in step 4 and the electrode layer prepared in step 5 using plasma-enhanced chemical vapor deposition. Then, electrode vias are opened on the protective layer by photolithography and etching processes to expose the electrode pads, thus completing the fabrication of the electro-optic modulator.

[0015] Preferably, the pretreatment in step 1 includes: ultrasonically cleaning the silicon substrate sequentially with acetone, ethanol, and deionized water to remove surface oil and impurities, and then drying it for later use. The drying temperature is 100-120℃, and the drying time is 10-15 minutes. The silicon substrate can be 6 / 8 / 12 inches in size; Preferably, the photolithography and etching operations in step 2 include: photolithography on the top silicon device layer of the silicon substrate to obtain an MZI waveguide pattern; and inductively coupled plasma reactive ion etching to form an MZI waveguide structure with a waveguide sidewall angle ≥80°.

[0016] Further, in step 2, a KrF stepper lithography system (Canon FPA-3030EX6) is used to perform photolithography on the top silicon device layer of the silicon substrate, and the MZI waveguide pattern is obtained by development. The photolithography process includes three steps: resist coating, exposure, and development. The resist coating thickness is 400 nm, and the exposure dose is 250-270 J / m.2 The development time is 30-60 s. Then, etching is performed using inductively coupled plasma reactive ion etching (ICP-RIE, Oxford Plasmalab System 100, Cobra 300) with an ICP power of 300-500 W. The etching gas is a mixture of CHF3 and SF6 with a flow rate ratio of 17:5. The RIE etching power is 40-80 W and the etching time is 40-80 s. Preferably, the ICP etching power is 300-400 W and the RIE power is 40-50 W. After etching, a silicon-based MZI waveguide structure with a waveguide sidewall angle ≥80° is formed. After etching, plasma microwave cleaning is performed to remove the photoresist. Preferably, in step 3, the KSBN precursor solution concentration is 0.05-0.2 mol / L, and the spin coating speed is 1000-4000 rpm. Then, rapid thermal annealing (RTP500) is used for annealing at a temperature of 800-1000℃ for 10-60 s to crystallize and stabilize the KSBN buffer layer, providing a high-quality substrate for the subsequent c-axis preferred orientation growth of the SBN thin film and solving the problem of silicon-SBN lattice mismatch. Preferably, the KSBN precursor solution concentration is 0.1-0.15 mol / L, and the spin coating speed is 1500-2000 rpm. A certain concentration of precursor solution and an appropriate speed ensure the uniformity of spin coating, while the formed buffer layer can fully cover the surface and sidewalls of the structure, reducing the influence of the structure on the growth of the SBN thin film.

[0017] Preferably, in step 4, the target material for magnetron sputtering is an SBN ceramic target with a Sr to Ba molar ratio of 75:25 and a magnetron sputtering pressure of 0.2-0.5 Pa.

[0018] Furthermore, the sputtering target used in magnetron sputtering is an SBN target with a Sr:Ba ratio of 75:25. The sputtering equipment is equipped with a Kurt J. Lesker magnetron sputtering source and an Advanced Energy CESAR RF power supply. The RF power of magnetron sputtering is 200-300 W, and the sputtering rate is 1.5-3 nm / min, ensuring the uniformity and crystal quality of the SBN film. The substrate temperature during sputtering is 500-650℃, and the sputtering gas is a mixture of 35 sccm Ar and 10 sccm O2. The vacuum level is maintained at 0.2-0.5 Pa during sputtering to ensure the preferred orientation growth of the SBN film along the

[001] direction (c-axis perpendicular to the film surface). Sufficient sputtering power and substrate temperature provide enough particle energy for sputtered particles to migrate and diffuse on the substrate surface, significantly improving the degree of crystallinity and growth uniformity. The lower vacuum level increases the mean free path of the sputtered particles, reducing energy loss and impurity effects.

[0019] Preferably, in step 5, a GSG electrode pattern is photolithographically patterned on the surface of the SBN thin film using laser direct writing (Heidelberg Instruments DWL66+), and then a 300-1000 nm thick metal layer is deposited using magnetron sputtering technology. After deposition, a metal stripping process is performed using acetone to form the GSG surface electrode layer. Preferably, in step 6, the protective layer consists of a SiO2 protective layer with a thickness of 500-800 nm, a PECVD deposition temperature of 300-350℃, and a deposition power of 50 W; the via etching is performed using ICP-RIE process, with Ar and CHF3 as the etching gases, and an etching time of 3-5 min, to ensure that the electrode pins are fully exposed.

[0020] Compared with the prior art, the beneficial effects of the present invention include at least the following: Utilizing the high effective electro-optic coefficient of SBN material (up to 145 pm / V), a low half-wave voltage length product of 2.3 V‧cm was achieved, with modulation efficiency comparable to the most advanced lithium niobate modulators. An integrated electro-optic material-electrode structure was employed to overcome the voltage division problem caused by the high dielectric constant of SBN. The application of the GSG vertical electric field, combined with the large proportion of the cladding optical field in TM mode, enabled efficient cladding optical modulation. Precise control of the KSBN buffer layer solved the problems of silicon-SBN lattice mismatch, uneven silicon waveguide surface leading to film orientation disorder, and high defect density, achieving high-quality SBN film growth with c-axis preferred orientation. The process is simplified, low-cost, and scalable: SBN films are grown directly on silicon using magnetron sputtering, avoiding expensive ion slicing and wafer bonding processes. The entire process is CMOS compatible and can be adapted for mass production of 6 / 8 / 12-inch large-size wafers, significantly reducing device costs and providing a feasible path for large-scale photonic integration. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present 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 only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of the overall structure of the electro-optic modulator of silicon-based heterogeneous integrated SBN provided in the embodiment; Figure 2 This is a cross-sectional schematic diagram of the modulation region of the electro-optic modulator function of the silicon-based heterogeneous integrated SBN provided in the embodiment; Figure 3 This is a schematic diagram of the fabrication process of the electro-optic modulator of silicon-based heterogeneous integrated SBN provided in the embodiment; Figure 4 This is the DC modulation result of the electro-optic modulator of the silicon-based heterogeneous integrated SBN provided in the embodiment. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of this invention.

[0024] The embodiment provides a silicon-based heterogeneously integrated barium strontium niobate electro-optic modulator, such as Figure 1 Overall structure diagram of the device and Figure 2 The schematic diagram of the cross-section of the modulation region is shown, including: The silicon substrate comprises, from bottom to top, a silicon substrate, a buried oxide layer, and a top silicon device layer; a silicon waveguide layer, which forms a Mach-Zehnder interferometer (MZI) waveguide structure by etching the top silicon device layer; a buffer layer, which is a potassium-doped barium strontium niobate (KSBN) thin film, covering the surfaces of the silicon waveguide layer and the buried oxide layer; a functional layer, which is a barium strontium niobate (SBN) thin film with a c-axis preferred orientation, disposed on the buffer layer; an electrode layer, which adopts a coplanar waveguide GSG (ground-signal-ground) metal electrode structure, used to apply a modulation electric field to the functional layer to change the refractive index of the functional layer; and a SiO2 protective layer, disposed on the electrode layer and the exposed functional layer, used to prevent electrode arc damage.

[0025] The embodiment provides a method for fabricating a silicon-based heterogeneous integrated barium strontium niobate electro-optic modulator, which adopts a CMOS-compatible process throughout, eliminates the need for wafer bonding, and achieves seamless integration between SBN and standard silicon photonics manufacturing processes. It is adaptable to large-scale mass production of 6 / 8 / 12-inch wafers. The specific steps are as follows: Step 1: Pre-treat the silicon substrate, specifically by ultrasonically cleaning the silicon substrate with acetone, ethanol and deionized water in sequence to remove surface oil and impurities, and then drying it for later use. The drying temperature is 100-120℃ and the drying time is 10-15 min. Step 2: Perform photolithography and etching operations on the top silicon device layer of the silicon substrate obtained after the preprocessing in Step 1 to fabricate a silicon waveguide layer, forming an MZI waveguide structure. The specific operations are as follows: perform photolithography on the top silicon device layer of the silicon substrate and develop it to obtain an MZI waveguide pattern; use inductively coupled plasma reactive ion etching to form an MZI waveguide structure with a waveguide sidewall angle ≥80°. Step 3: Using the sol-gel method, spin-coat the surface of the MZI waveguide structure prepared in step 2 with KSBN precursor solution, and then perform rapid thermal annealing treatment at a temperature of 800-1000℃ and an annealing time of 10-60 s to allow KSBN to crystallize and stabilize to form a buffer layer. Step 4: Using magnetron sputtering, a 1-2 μm thick functional layer is deposited on the buffer layer prepared in step 3. The sputtering target is an SBN target with Sr:Ba=75:25. The substrate temperature during sputtering is 500-650℃. The sputtering gas is a mixture of Ar at 35 sccm and O2 at 10 sccm. The vacuum degree is maintained at 0.2-0.5 Pa during sputtering to ensure that the SBN film is preferentially oriented and grown along the

[001] direction (c-axis is perpendicular to the film surface). Step 5: Using laser direct writing (Heidelberg Instruments DWL66+), the GSG electrode pattern is photolithographically patterned on the surface of the functional layer prepared in Step 4. Then, a gold layer with a thickness of 300-1000 nm is deposited using magnetron sputtering technology. After deposition, a metal lift-off process using acetone is performed to form the electrode layer. Step 6: SiO2 is deposited on the surface of the functional layer prepared in step 4 and the electrode layer prepared in step 5 as a protective layer using plasma-enhanced chemical vapor deposition. Then, electrode vias are opened on the protective layer by photolithography and etching processes to expose the electrode pads, thus completing the fabrication of the electro-optic modulator.

[0026] Furthermore, in step 2, the photolithography process includes three stages: resist coating, exposure, and development. The resist coating thickness is 400 nm, and the exposure dose is 250-270 J / m. 2 The development time is 30-60 s; during the etching process, the gas flow ratio of CHF3 and SF6 is 17:5, the ICP power is 300-500 W, the etching power is 40-80 W, and the etching time is 40-80 s.

[0027] Furthermore, in step 4, the RF power of magnetron sputtering is 200-300 W, and the sputtering rate is 1.5-3 nm / min to ensure the uniformity and crystal quality of the SBN film.

[0028] Furthermore, in step 6, the thickness of the SiO2 protective layer is 500-800 nm, the PECVD deposition temperature is 300-350℃, and the deposition power is 50 W; the etching of the via uses ICP-RIE process, the etching gases are Ar and CHF3, and the etching time is 3-5 min to ensure that the electrode pins are fully exposed.

[0029] Based on the above-described method for fabricating a silicon-based heterogeneously integrated barium strontium niobate electro-optic modulator, the following specific embodiments illustrate the method for fabricating a silicon-based heterogeneously integrated barium strontium niobate electro-optic modulator.

[0030] Example 1 like Figure 1 The overall structure diagram of the device and Figure 2 As shown in the schematic diagram of the cross-section of the modulation region, the electro-optic modulator of this embodiment includes a silicon substrate, a silicon waveguide layer, a buffer layer, a functional layer, an electrode layer, and a protective layer. The device fabrication process is as follows: Figure 3 As shown, the specific process is as follows: A 6-inch silicon substrate was selected. The substrate consisted of a bottom silicon layer, a buried oxide layer, and a top silicon device layer. The thickness of the silicon substrate was 600 μm, the thickness of the buried oxide layer was 2 μm, and the thickness of the top silicon device layer was 220 nm. The substrate was ultrasonically cleaned with acetone, ethanol, and deionized water for 10 min each to remove surface oil and impurities. Then it was dried in a 110℃ oven for 12 min and cooled to room temperature for later use.

[0031] MZI waveguide structures were fabricated by etching the top silicon device layer on a silicon substrate. These structures included an input grating coupler, a tapered waveguide, a 50:50 multimode interference coupler, two asymmetric modulation arm waveguides, an output multimode interference coupler, and an output grating coupler. The arm length difference between the two modulation arm waveguides was 100 μm to ensure a free spectral range of 6.85 nm. The top silicon device layer on the silicon substrate was lithographically etched and developed using a Canon KrF stepper lithography system with a resist thickness of 400 nm and an exposure dose of 270 J / m. 2 The development time was 60 s. The patterned silicon waveguide was etched using Oxford inductively coupled plasma reactive ion etching (ICP-RIE). The etching gas was a mixture of CHF3 (17 sccm) and SF6 (5 sccm). The ICP power was 300 W and the etching power was 40 W. After etching, the waveguide sidewall angle was 82°. After etching, plasma microwave cleaning was performed for 1 min to remove the photoresist.

[0032] KSBN precursor solution was spin-coated onto the surface of MZI waveguide structure using the sol-gel method. The precursor solution concentration was 0.1 mol / L, the spin-coating speed was 2000 rpm, and after rapid thermal annealing at 1000℃ for 10 s, KSBN crystallized. KSBN exhibited a preferred orientation in the

[001] direction and a thickness of about 60 nm, serving as a buffer layer.

[0033] SBN was deposited as a functional layer on the surface of a buffer layer using magnetron sputtering. The molar ratio of Sr to Ba was 75:25. The substrate temperature during sputtering was 600℃, and the sputtering gas was a mixture of Ar (35 sccm) and O2 (10 sccm). The vacuum level was maintained at 0.2 Pa, the RF power was 300 W, and the thickness of the functional layer was 1.2 μm. The refractive index of the functional layer at a wavelength of 1550 nm was n o = 2.21、n e = 2.206, effective electro-optic coefficient r33 = 145 pm / V, preferential orientation growth along the

[001] direction.

[0034] The electrode layer was fabricated on the surface of the functional layer. The alignment of the coplanar waveguide GSG structure electrode with the MZI waveguide structure was achieved by overlaying with a Heidelberg laser direct writing device. After photoresist patterning, a gold film with a thickness of 300 nm was deposited by magnetron sputtering. The metal electrode was peeled off and formed by immersion in acetone and sonication for 30 min. The width of the center electrode was 2 μm and the electrode gap was 3 μm.

[0035] The protective layer, composed of SiO2, was deposited using PECVD and has a thickness of 600 nm, covering the surfaces of the electrode layer and the functional layer. Electrode vias with a diameter of 80 μm were formed in the protective layer for connecting the test probes to the electrodes. Finally, the sample was cleaned and dried to complete the fabrication of the electro-optic modulator.

[0036] The electro-optic modulator in this embodiment operates in the C+L band (1500-1630 nm), uses TM polarized light, and has a half-wave voltage-length product V. π With L = 2.3 V‧cm, an extinction ratio of 38 dB, and a waveguide group refractive index of 3.507, the resonant wavelength shift is 5.86 nm under a bias scan from -4 V to +4 V, exhibiting excellent electro-optic modulation performance. The electrical modulation results are as follows: Figure 4 As shown.

[0037] The specific embodiments described above illustrate the technical solution and beneficial effects of the present invention in detail. It should be understood that the above description is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A silicon-based heterogeneously integrated barium strontium niobate electro-optic modulator, characterized in that, include: A silicon substrate, which from bottom to top includes a silicon substrate, a buried oxide layer and a top silicon device layer; A silicon waveguide layer is used to construct a Mach-Zehnder interferometer waveguide structure by etching the top silicon device layer. A buffer layer, which is a potassium-doped barium strontium niobate thin film, is applied to the surface of the silicon waveguide layer and the buried oxide layer. The functional layer is a barium strontium niobate thin film with a preferred c-axis orientation, disposed on the buffer layer; The electrode layer, which employs a Ground-Signal-Ground coplanar waveguide structure electrode located directly above the modulation arm of the Mach-Zehnder interferometer, is used to apply a modulation electric field to the barium strontium niobate thin film to change its refractive index.

2. The silicon-based heterogeneous integrated barium strontium niobate electro-optic modulator according to claim 1, characterized in that, The Mach-Zehnder interferometer waveguide structure includes an input grating coupler, a tapered waveguide, a multimode interference coupler, two asymmetric modulation arm waveguides, an output multimode interference coupler, and an output grating coupler. The sidewall angle of the modulation arm waveguide is ≥80°, and there is a 100 μm asymmetric arm length difference between the two modulation arm waveguides, which is used to achieve free spectral range control.

3. The silicon-based heterogeneous integrated barium strontium niobate electro-optic modulator according to claim 1, characterized in that, The thickness of the potassium-doped barium strontium niobate film is 20-100 nm.

4. The silicon-based heterogeneous integrated barium strontium niobate electro-optic modulator according to claim 1, characterized in that, The thickness of the barium strontium niobate film is 0.3-2 μm.

5. The silicon-based heterogeneous integrated barium strontium niobate electro-optic modulator according to claim 1, characterized in that, The Ground-Signal-Ground metal electrode adopts push-pull modulation, with opposite electric fields applied to the two modulation arms. The electrode material is gold or copper, and the electrode thickness is 300-1000 nm. The width of the center electrode used as the signal line is 2-3 μm, and the electrode gap is 2-4 μm.

6. The silicon-based heterogeneous integrated barium strontium niobate electro-optic modulator according to claim 1, characterized in that, The electro-optic modulator also includes a protective layer, which is made of SiO2, covering the surface of the electrode layer and the surface of the barium strontium niobate thin film.

7. A method for fabricating a silicon-based heterogeneous integrated barium strontium niobate electro-optic modulator according to any one of claims 1-6, characterized in that, Includes the following steps: Step 1: Pre-treat the silicon substrate; Step 2: Perform photolithography and etching operations on the top silicon device layer of the silicon substrate obtained after the preprocessing in Step 1 to construct the Mach-Zehnder interferometer waveguide structure as the silicon waveguide layer; Step 3: Using the sol-gel method, a potassium-doped barium strontium niobate precursor solution is spin-coated onto the surface of the Mach-Zehnder interferometer waveguide structure prepared in Step 2, and then rapidly annealed to form a potassium-doped barium strontium niobate thin film as the buffer layer. Step 4: Using magnetron sputtering, a barium strontium niobate thin film is deposited on the buffer layer prepared in step 3 at a substrate temperature of 500-650℃ to form a barium strontium niobate thin film with a preferred c-axis orientation as the functional layer. Step 5: On the functional layer obtained in step 4, a Ground-Signal-Ground metal electrode structure is fabricated as the electrode layer using an overlay process; Step 6: A protective layer is deposited on the surface of the functional layer prepared in step 4 and the electrode layer prepared in step 5 using plasma-enhanced chemical vapor deposition. Then, electrode vias are opened on the protective layer by photolithography and etching processes to expose the electrode pads, thus completing the fabrication of the electro-optic modulator.

8. The method for fabricating a silicon-based heterogeneous integrated barium strontium niobate electro-optic modulator according to claim 7, characterized in that, The photolithography and etching operations in step 2 include: photolithography on the top silicon device layer of the silicon substrate, development to obtain the Mach-Zehnder interferometer waveguide pattern; and inductively coupled plasma reactive ion etching to form a Mach-Zehnder interferometer waveguide structure with a waveguide sidewall angle ≥80°.

9. The method for fabricating a silicon-based heterogeneous integrated barium strontium niobate electro-optic modulator according to claim 7, characterized in that, In step 3, the concentration of the potassium-doped barium strontium niobate precursor solution is 0.05-0.2 mol / L, the spin coating speed is 1000-4000 rpm, the rapid annealing temperature is 800-1000℃, and the rapid annealing time is 10-60 s.

10. The method for fabricating a silicon-based heterogeneously integrated barium strontium niobate electro-optic modulator according to claim 7, characterized in that, In step 4, the target material for magnetron sputtering is a barium strontium niobate ceramic target with a molar ratio of Sr to Ba of 75:25 and a magnetron sputtering pressure of 0.2-0.5 Pa.

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