Water transfer ferroelectric thin film silicon-based waveguide modulator

Abstract

The application discloses a water transfer ferroelectric thin film silicon-based waveguide modulator. Taking barium titanate material as an example, the water transfer method is to immerse the grown strontium aluminate / strontium titanate heterojunction into deionized water to dissolve the strontium aluminate layer to obtain a barium titanate layer, and then transfer the barium titanate layer to the silicon-based waveguide modulator. At present, the existing barium titanate silicon-based waveguide modulator is mostly prepared by the method of epitaxially depositing barium titanate on the strontium titanate oxide layer. Compared with the existing method of preparing barium titanate thin film by an oxide buffer layer, the water transfer method can prepare high-quality barium titanate thin film with good ferroelectricity and epitaxy, excellent flexibility and can be transferred to the substrate without damage. In the application, an embodiment of a barium titanate electro-optic silicon-based waveguide modulator is listed, and it can be found that the barium titanate prepared by the water transfer method can be used in the silicon-based waveguide modulator to obtain a modulator with excellent electro-optic performance, which proves the feasibility and high efficiency of the water transfer barium titanate method for modulation.

Description

Technical Field

[0001] This invention belongs to the field of optical information processing and relates to a water-transfer barium titanate silicon-based waveguide modulator. Background Technology

[0002] Optical modulators are devices in optical communication systems that generate high-speed digital pulse optical signals, essentially acting as the heart of the optical information system. The working principle of an optical modulator is to modulate the physical characteristics of the optical signal channel with a high-speed microwave electrical signal, thereby transforming a continuous laser beam into a synchronously alternating optical pulse signal. Silicon-based waveguide modulators are a particularly important type of optical modulator. Currently, silicon-based, silicon nitride-based, and lithium niobate crystal waveguide modulators are widely used in optical communication, but their electro-optical properties limit further increases in bandwidth, which remains a major challenge. Therefore, new electro-optical materials are needed to fabricate silicon-based waveguide modulators.

[0003] For electro-optic materials, generally speaking, the refractive index inside the material can be changed by applying a modulating electric field, thereby changing the phase of the light wave and achieving the purpose of light modulation. Therefore, the higher the electro-optic coefficient of the material, the more sensitive it is to the electric field of the applied voltage, and the better the modulator effect. As is well known, barium titanate ferroelectric crystal (BaTiO3, BTO) has the advantages of ultra-high electro-optic coefficient, good stability and good compatibility, making it very suitable for use in modulators to solve the problem of insufficient bandwidth.

[0004] Due to the lattice mismatch between silicon and barium titanate surfaces, barium titanate layers cannot be directly deposited on silicon layers. Existing methods for fabricating barium titanate crystals to create silicon-based waveguide modulators primarily involve first growing a layer of STO as an oxide buffer layer using molecular beam epitaxy (MBE), and then epitaxially depositing a BTO thin film on this buffer layer using off-axis sputtering. During deposition, a layer of silicon dioxide is formed between the BTO and STO layers. While this method can produce high-speed BTO / Si hybrid electro-optic modulators, the volume of the BTO unit cells on the resulting STO is larger than that of bulk BTO unit cells, indicating defects generated during growth. To obtain higher-quality barium titanate thin films, this patent provides a barium titanate crystal thin film silicon-based waveguide modulator fabricated using a water transfer method. The water transfer method is an environmentally friendly, non-destructive method that synthesizes a BTO / SAO heterostructure on an STO substrate through pulsed laser deposition, followed by etching a water-soluble SAO layer to synthesize an independent epitaxial inorganic thin film. By directly immersing the sample in deionized water to dissolve the sacrificial SAO layer, a large-size suspended epitaxial BTO film with good ferroelectricity and flexibility can be obtained. Due to its high dielectric constant, it can be transferred onto a silicon substrate to fabricate a silicon waveguide modulator with excellent electro-optic performance.

[0005] Barium titanate (BaTiO3, BTO), strontium aluminate (Sr3Al2O6, SAO), strontium titanate (SrTiO3, STO) Summary of the Invention

[0006] Technical Problem: To address the aforementioned problems in existing technologies, this invention proposes a water-transfer ferroelectric thin-film silicon-based waveguide modulator. An ultra-high bandwidth silicon-based waveguide modulator is achieved by integrating barium titanate material prepared via a water transfer method onto a waveguide structure.

[0007] Technical solution: The present invention provides a water-transfer ferroelectric thin-film silicon-based waveguide modulator comprising a silicon substrate, a buried oxide layer, a silicon waveguide, a ferroelectric thin film layer, and electrodes; wherein, a buried oxide layer is disposed on the silicon substrate, a silicon waveguide is disposed in the buried oxide layer, a ferroelectric thin film layer is disposed on the buried oxide layer and the silicon waveguide, and electrodes are disposed on the ferroelectric thin film layer.

[0008] The silicon waveguide is embedded in the buried oxide layer, and the upper surface of the silicon waveguide is flush with or slightly lower than the upper surface of the buried oxide layer.

[0009] The middle section of the silicon waveguide is a Mach-Zehnder interferometer (MZI) structure, and the two ends of the silicon waveguide are symmetrical straight waveguide structures located at both ends of the MZI structure.

[0010] The electrode is a traveling wave electrode structure or a differential electrode structure, deposited on a ferroelectric thin film layer.

[0011] The ferroelectric thin film layer is made of barium titanate and has a high electro-optic coefficient.

[0012] The ferroelectric thin film layer was fabricated on a silicon-based waveguide modulator using a water transfer method.

[0013] The ferroelectric thin film layer is prepared using a water transfer method. This involves immersing the grown layered BTO / SAO / STO heterojunction in deionized water to dissolve the SAO layer, thereby obtaining the ferroelectric thin film layer, which is then transferred to the target substrate. The method for transferring this layer to the target substrate using barium titanate material specifically includes the following steps:

[0014] Step 1: SAO / BTO structure is synthesized by sintering in air at 1400℃ for 5 hours and at 1300℃ for 2 hours through conventional solid-state reaction.

[0015] Step 2: Using a laser, SAO / BTO thin films are deposited on an STO substrate by pulsed laser deposition (PLD) to obtain a layered BTO / SAO / STO heterojunction at a temperature of 800°C.

[0016] Step 3: A photoresist film is spin-coated as a protective layer on the grown layered BTO / SAO / STO heterojunction at a rotation speed of 3000 rpm.

[0017] Step 4: Dry the BTO / SAO / STO heterojunction in a vacuum oven at 115℃ for 15 minutes;

[0018] Step 5: Immerse the BTO / SAO / STO heterojunction in deionized water to dissolve the SAO layer;

[0019] Step 6: Dissolve the SAO layer;

[0020] Step 7: Transfer the stripped photoresist / BTO film onto the target substrate;

[0021] Step 8: After transfer, dissolve the photoresist film in acetone solvent.

[0022] Furthermore, electrodes are deposited on barium titanate crystal material, and different voltages are applied to influence the refractive index distribution by changing the electric field.

[0023] The working principle is as follows: Utilizing the refractive index change and the rotation of the principal axis of the refractive index ellipsoid caused by the electro-optic effect of barium titanate, many active waveguide devices, especially electro-optic modulators, can be constructed. In barium titanate crystals, r... 51 Barium titanate has the largest electro-optic constant, but the linear electro-optic effect it produces depends on the direction of the applied electric field and the crystal axis. Because barium titanate has a different refractive index and exhibits birefringence, its phase velocities differ. Although propagating in the same direction, one is on the fast axis and the other on the slow axis, resulting in two beams of light rather than one. If two linearly polarized beams with electric vectors, each perpendicular to its own direction, simultaneously enter the crystal with the same phase along the same direction perpendicular to the optical axis, their different propagation velocities will cause them to exit the crystal with different phases, creating a phase difference between the two beams. Upon exiting the crystal, they will become an elliptically polarized beam. The voltage applied to the crystal to produce the electro-optic effect is called the modulation voltage. When a modulation voltage is applied, the light passing through the crystal will generate a phase difference, thus modulating the beam.

[0024] Beneficial effects: Compared with existing technologies, this invention innovatively proposes to fabricate a silicon-based waveguide modulator using barium titanate crystals prepared by the water transfer method, which can yield large-size, high-quality suspended epitaxial barium titanate thin films with good ferroelectric properties. Applying an electric field to the barium titanate significantly changes the effective refractive index distribution of the structure, improving the electro-optic characteristics and modulation efficiency of the modulator. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the present invention.

[0026] Figure 2This is a schematic diagram of the cross-sectional structure of the waveguide modulator of the present invention.

[0027] Figure 3 The transmission curves under different voltages are shown in the waveguide modulator example of this invention.

[0028] Figure 4 This is a test curve of the optical modulation signal versus voltage in an example of the waveguide modulator of the present invention.

[0029] The diagram shows: 1. Silicon substrate; 2. Buried oxide layer; 3. Silicon waveguide; 4. Ferroelectric thin film layer; 5. Electrode. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example: Refer to Figure 1 , Figure 2 As shown, a buried oxide layer 2 is disposed on a silicon substrate 1, a silicon waveguide 3 is disposed within the buried oxide layer 2, a ferroelectric thin film layer 4 is disposed on the buried oxide layer 2 and the silicon waveguide 3, and an electrode 5 is disposed on the ferroelectric thin film layer 4. The silicon waveguide 3 is embedded in the buried oxide layer 2, and the upper surface of the silicon waveguide 3 is flush with the upper surface of the buried oxide layer 2. The middle section of the silicon waveguide 3 is a MZI structure, and the two ends of the silicon waveguide 3 are straight structures symmetrically located at both ends of the hollow MZI structure. There are three electrodes 5 arranged side by side. The middle electrode 5 is located above the middle of the MZI structure in the middle section of the silicon waveguide 3 and is placed on the ferroelectric thin film layer 4; the two side electrodes 5 are symmetrically placed on the ferroelectric thin film layer 4 about the waveguide layer 3. The ferroelectric thin film layer 4 is made of barium titanate and has a high electro-optic coefficient.

[0032] The buried oxide layer 2 is made of silicon dioxide. The ferroelectric thin film layer 4 is barium titanate crystal transferred onto silicon-on-insulator (SOI) using a water transfer method. The electrode 5 is made of titanium with a thickness of 5 nm and gold with a thickness of 70 nm, and consists of GSG electrodes. By applying an external voltage to the electrodes, the refractive index of the barium titanate material in the upper layer of the waveguide changes; the light wave transmitted in the waveguide, due to the evanescent field, is affected by the change in the refractive index of the upper layer, resulting in a phase change, thereby carrying modulation information.

[0033] Figure 3 , Figure 4 Showing Figure 1 The modulator shown has the following performance parameters during actual testing. Figure 3The figures show the transmission curves under different voltages. It can be observed that when the applied voltage changes, the transmission at the same wavelength changes, meaning the overall transmission curve shifts. The greater the shift, the better the modulation performance of the electro-optic modulator. Figure 4 The curve shows the change in optical modulation intensity as a function of voltage. The output intensity changes when different bias voltages are applied. The active region length of this silicon-based waveguide modulator is 286 μm, and the half-wave voltage V0... π The voltage is 55V, so V can be calculated. π With an L of 1.57 V·cm, the modulation performance is good, demonstrating the feasibility and efficiency of the water-transfer barium titanate method for modulation.

[0034] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A water-transfer ferroelectric thin-film silicon-based waveguide modulator, characterized in that... The modulator includes a silicon substrate (1), a buried oxide layer (2), a silicon waveguide (3), a ferroelectric thin film layer (4), and electrodes (5); wherein, a buried oxide layer (2) is provided on the silicon substrate (1), a silicon waveguide (3) is provided in the buried oxide layer (2), a ferroelectric thin film layer (4) is provided on the buried oxide layer (2) and the silicon waveguide (3), and an electrode (5) is provided on the ferroelectric thin film layer (4); there are three electrodes (5) arranged side by side, the middle electrode (5) is located above the middle of the Mach-Zehnder interferometer (MZI) structure in the middle section of the silicon waveguide (3), and is placed on the ferroelectric thin film layer (4); the two electrodes (5) on both sides are symmetrically placed on the ferroelectric thin film layer (4) about the silicon waveguide (3); The middle section of the silicon waveguide (3) is a Mach-Zehnder interferometer (MZI) structure, and the two ends of the silicon waveguide (3) are respectively straight waveguide structures symmetrically located at both ends of the Mach-Zehnder interferometer (MZI) structure; The ferroelectric thin film layer (4) is made of barium titanate and has a high electro-optic coefficient.

2. The water-transfer ferroelectric thin-film silicon-based waveguide modulator according to claim 1, characterized in that... The silicon waveguide (3) is embedded in the buried oxide layer (2), and the upper surface of the silicon waveguide (3) is flush with the upper surface of the buried oxide layer (2).

3. A water-transfer ferroelectric thin-film silicon-based waveguide modulator according to claim 2, characterized in that... The aforementioned The electrode (5) is a traveling wave electrode structure or a differential electrode structure, deposited on the ferroelectric thin film layer (4).

4. A water-transfer ferroelectric thin-film silicon-based waveguide modulator according to claim 3, characterized in that, The ferroelectric thin film layer (4) is prepared on a silicon-based waveguide modulator using a water transfer method.

5. A water-transfer ferroelectric thin-film silicon-based waveguide modulator according to claim 4, characterized in that, The method of transferring the ferroelectric thin film layer (4) to the target substrate by immersing the grown layered BTO / SAO / STO heterojunction in deionized water to dissolve the SAO layer and obtaining BTO, specifically includes the following steps: Step 1: SAO / BTO structure was synthesized by sintering in air at 1400℃ for 5 h and at 1300℃ for 2 h through conventional solid-state reaction. Step 2: Using a laser, the SAO / BTO thin film is deposited onto the STO substrate by pulsed laser deposition, and a layered BTO / SAO / STO heterojunction is obtained at a temperature of 800℃. Step 3: A photoresist film is spin-coated as a protective layer on the grown layered BTO / SAO / STO heterojunction at a rotation speed of 3000 rpm. Step 4: Dry the BTO / SAO / STO heterojunction in a vacuum oven at 115°C for 15 minutes; Step 5: Immerse the BTO / SAO / STO heterojunction in deionized water to dissolve the SAO layer; Step 6: Dissolve the SAO layer; Step 7: Transfer the stripped photoresist / BTO film onto the target substrate; Step 8: After transfer, dissolve the photoresist film in acetone solvent.

Images