Vertical incidence silicon photon electric field sensor structure and heterogeneous integration method thereof

Abstract

The invention relates to the technical field of miniature optical voltage sensing, in particular to a vertical incidence silicon photon electric field sensor structure and a heterogeneous integration method thereof.The vertical incidence silicon photon electric field sensor structure comprises a laser coupling module, an optical sensing unit, a light detection coupling module and a lower layer substrate which are sequentially integrated from left to right; the laser coupling module and the light detection coupling module are integrated on the surface of the substrate in an inverted heterogeneous manner through a BCB film. The optical sensing unit is arranged on the substrate, laser emitted by the VCSEL laser is vertically coupled into the SOI waveguide structure through the vertical incidence grating coupled by a space light field, light waves are split through the unbalanced MZI, the initial phase difference of two arms is compensated, the resonant micro-ring is used for assisting in sensing the arms, the laser interferes at the end of the unbalanced MZI, and the interference is generated at the end of the unbalanced MZI. And finally, the light is emitted into the photoelectric detector through the vertical emitting grating. According to the invention, the packaging size of the platform can be greatly reduced, and a highly flexible and extensible implementation path is provided for application scenes such as an on-chip integrated optical system, a photoelectric hybrid integrated module, an electric field optical sensor and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of micro optical voltage sensing, and in particular to a vertically incident silicon photon electric field sensor structure and a heterogeneous integration method thereof. Background Art

[0002] Electricity is the core of modern energy systems. With the sustained and stable development of my country's economy, demand for electricity from industry and public consumption is increasing. In addition to building a flexible, stable, and secure energy network, smart grids require real-time measurement, feedback, and dynamic adjustment of grid state variables to rapidly achieve intelligent information perception and self-healing of faults. Sensors, as crucial nodes connecting physical and digital space, struggle with existing technologies to meet the demands of global electromagnetic perception and achieve the "comprehensive perception and ubiquitous Internet of Things" digital grid requirements. Therefore, in-depth research in coupling methods, material properties, and topological structures is urgently needed to overcome the limitations of existing technologies and enhance the holographic perception capabilities of energy and power conversion nodes.

[0003] Optical electric field sensors leverage the electro-optic effect of electro-optically sensitive materials to convert minute changes in the external electric field into optical signals, which are then coupled to an on-chip SOI waveguide. Compared to traditional electric field sensors, this approach offers not only higher sensitivity but also a wider measurement bandwidth, possessing enormous potential for application. However, current optical electric field sensors suffer from issues such as poor stability and large size, significantly limiting their application. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: In order to overcome the above technical problems, the present invention provides a vertically incident silicon photonic electric field sensor structure and a heterogeneous integration method thereof.

[0005] The technical solution adopted by the present invention to solve its technical problems is: a vertically incident silicon photonic electric field sensor structure based on SOI (silicon on insulator) wafer integration, the working layer is an SOI waveguide structure, the sensor structure includes a substrate, a laser coupling module, an optical sensitive unit and an optical probe coupling module are integrated on the substrate from left to right, the laser coupling module and the optical probe coupling module are flip-chip heterogeneously integrated on the substrate surface through BCB (polybenzocyclobutene) film, the laser coupling module and the optical probe coupling module are electrically connected through metal electrodes, and the optical probe coupling module receives and converts optical signals.

[0006] The laser coupling module includes a VCSEL laser and a vertical incidence grating;

[0007] The optical probe coupling module includes a photodetector and a vertical emission grating;

[0008] The optical sensitive unit is arranged on the substrate, and the optical sensitive unit includes an unbalanced MZI (Mach Zehnder structure) and a resonant microring;

[0009] The laser emitted by the VCSEL laser is vertically coupled into the SOI waveguide structure through a vertical incidence grating coupled with spatial light field. The light wave is split into two beams by an unbalanced MZI, and the initial phase difference between the two arms is compensated. A resonant microring is used to assist the sensing arm, and the sensing arm is covered with an electro-optic polymer film. The laser that changes with the electric field interferes at the end of the unbalanced MZI, converting the phase change into power change, and finally entering the photodetector through a vertical emission grating, thereby establishing a linear change in the external electric field and optical power.

[0010] The vertical incidence grating is used to couple the 1550nm laser emitted by the VCSEL laser to the SOI waveguide structure.

[0011] The vertical incidence grating and the vertical emission grating are both blazed gratings, which redistribute the originally backward reflected power to the first-order diffraction direction through the sawtooth "blazed surface", significantly reducing the VCSEL cavity surface reflection feedback at vertical incidence, and ultimately achieving vertical incidence.

[0012] One end of the unbalanced MZI is connected to the vertical incidence grating, and the other end is connected to the vertical emission grating. Laser light with altered intensity is injected into the photodetector to measure the electric field. The unbalanced MZI includes two unbalanced waveguide channels, which are used to compensate for phase differences caused by coupling to a microring on one side, thereby adjusting the initial phase.

[0013] Furthermore, an electro-optic polymer is covered on the resonant microring. Under the action of an external electric field, the refractive index of the electro-optic polymer film changes, thereby causing a phase change affected by the external electric field in the sensing arm of the unbalanced MZI, and finally converting the phase change into a power change at the unbalanced MZI interference point.

[0014] The laser coupling module and the optical probe coupling module are integrated on the surface of the SOI chip via gold or silver metal electrodes. The BCB film is placed at a corner of the laser coupling module away from the optical probe coupling module to ensure balance at both ends of the laser coupling module, allowing the laser to be vertically incident on the blazed grating (vertical incidence grating) and the vertical exit grating. Electrodes are located on both the front and back sides of the laser coupling module. These positive and negative electrodes are led out via metal electrodes and wires, ultimately integrated into the base plate of the SOI chip.

[0015] The electro-optic polymer film is only coated on the surface of the resonant microring and covers the SOI waveguide structure, that is, it only covers the local SOI waveguide area where the microring is located. An SU-8 protective film is provided at the straight waveguide coupling point between the resonant microring and the SOI waveguide structure, thereby ensuring that the coupling coefficient and the transmission coefficient remain unchanged.

[0016] The shape of the resonant micro-ring is circular, elliptical or racetrack, and the SOI waveguide structure is a strip waveguide, a slot waveguide or a sub-wavelength waveguide.

[0017] The electro-optic polymer film has a thickness ranging from 2um to 4um.

[0018] A heterogeneous integration method of a vertically incident silicon photonic electric field sensor structure comprises the following steps:

[0019] Step 1: heterogeneously integrate the laser coupling module and the optical probe coupling module on the substrate through metal electrodes and the BCB film;

[0020] Step 2: Prepare a laser coupling module, an optical sensing unit, and an optical probe coupling module on the SOI waveguide structure, including a vertical incidence grating, an unbalanced MZI, a resonant microring, an electro-optic polymer film, an SU-8 protective film, and a vertical emission grating;

[0021] Step 3: Couple the 1550nm laser into the SOI waveguide structure through a vertical incidence grating, and use the unbalanced MZI to split the beam and compensate for the phase difference;

[0022] Step 4: The electric field change is converted into phase change through the resonant microring and electro-optic polymer film, and then interfered into optical power change at the end of the unbalanced MZI;

[0023] Step 5: The light signal is emitted into the photodetector through the vertical emission grating to complete the electric field measurement.

[0024] The preparation of the electro-optical polymer film comprises the following steps:

[0025] Prepare dye solution and matrix solution, mix them and then spin-coat them on SOI chip;

[0026] After drying, the chromophore molecules are oriented and arranged through polarization treatment to form a film with electro-optical response capability.

[0027] The present invention has the following advantages over the prior art:

[0028] 1. A vertical-incidence blazed grating is used to efficiently couple a 1550nm VCSEL laser into a SOI waveguide. The electro-optic energy coupling of the evanescent field effect is achieved through a triple modulation structure of "unbalanced MZI + resonant microring + electro-optic polymer." Using electro-optic polymer materials with high electro-optic coefficients, the resonator's ultra-linear phase response compensates for the intermodulation distortion caused by the MZI structure, effectively improving the sensor's electric field sensitivity.

[0029] 2. The VCSEL laser and photodetector functional modules are heterogeneously integrated on the SOI chip to realize the emission-detection closed loop on the SOI chip. This package is compatible with the mainstream CMOS processing flow. The proposed silicon photonic integration solution provides a highly integrated and low-cost solution for on-chip high-voltage monitoring. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The present invention will be further described below with reference to the accompanying drawings and examples.

[0031] Figure 1 Schematic diagram of the structure of the vertically incident silicon photon electric field sensor of the present invention;

[0032] Figure 2 Schematic diagram of the structure of the laser coupling module in the present invention;

[0033] Figure 3 Schematic diagram of the silicon photonic surface film distribution in the present invention;

[0034] Figure 4 A flow chart for preparing the optical sensitive unit of the present invention;

[0035] Figure 5 This is a structural diagram of the blazed grating with a sawtooth blazed surface in the present invention.

[0036] In the figure: 1. Unbalanced MZI, 2. Electro-optic polymer film, 3. Resonant microring, 4. Upper metal electrode, 5. Laser coupling module, 51. VCSEL laser, 6. Lower metal electrode, 7. Substrate, 8. BCB film, 9. Laser emission port, 10. Vertical incidence grating, 11. Optical probe coupling module, 12. SU-8 protective film, 13. Vertical emission grating, 14. Laser positive electrode on substrate, 15. Laser negative electrode on substrate, 16. Photodetector positive electrode on substrate, 17. Photodetector negative electrode on substrate, 18. Optical sensitive unit. DETAILED DESCRIPTION

[0037] The present invention will now be described in further detail with reference to the accompanying drawings. It should be emphasized that the following description is merely exemplary and is not intended to limit the scope of the present invention and its application.

[0038] like Figure 1As shown, the vertical-incidence silicon photonic electric field sensor structure of the present invention includes a substrate 7 on which are integrated, from left to right, a laser coupling module 5, an optical sensing unit 18, and an optical probe coupling module 11. Substrate 7 is a SiO2 plate. The laser coupling module 5 and the optical probe coupling module 11 are flip-chip heterogeneously integrated on the surface of substrate 7 via a BCB film 8. Metal electrodes electrically connect the laser coupling module 5 and the optical probe coupling module 11, which receives and converts optical signals. Figure 1 In the figure, the metal electrodes are the laser positive electrode 14 on the substrate, the laser negative electrode 15 on the substrate, the photodetector positive electrode 16 on the substrate and the photodetector negative electrode 17 on the substrate.

[0039] like Figure 2 As shown, the laser coupling module 5 includes a VCSEL laser 51 and a vertical incidence grating 10. The optical probe coupling module 11 includes a photodetector and a vertical emission grating 13. The optical sensitive unit 18 is provided on the substrate 7 and includes an unbalanced MZI 1 and a resonant microring 3.

[0040] The 1550nm laser emitted by the VCSEL laser 51 is vertically coupled into the SOI waveguide structure through the vertical incidence grating 10 of spatial light field coupling. The light wave is split into two beams through the unbalanced MZI1, and the initial phase difference between the two arms is compensated. The resonant microring 3 is used to assist the sensing arm, and the sensing arm is covered with an electro-optic polymer film 2. The laser light that changes with the electric field interferes at the end of the unbalanced MZI1, converting the phase change into power change, and finally entering the photodetector through the vertical emission grating 13.

[0041] Both the vertical incidence grating 10 and the vertical emission grating 13 are blazed gratings, which redistribute the power originally reflected backward to the first-order diffraction direction through the sawtooth blazed surface. Figure 4 Figure 2 shows the structure of a blazed grating with a zigzag blazed surface.

[0042] One end of the unbalanced MZI 1 is connected to a vertical incidence grating 10, while a vertical emission grating 13 is connected to the other end of the unbalanced MZI 1, directing the laser light after varying its intensity into a photodetector. The unbalanced MZI 1 includes two unbalanced waveguide channels to compensate for the phase difference introduced by coupling to the microring on one side. The laser coupling module 5 and the optical probe coupling module 11 are integrated onto the surface of the SOI chip via gold or silver metal electrodes. A BCB film 8 is positioned at a corner of the laser coupling module 5 away from the optical probe coupling module 11. The electro-optic polymer film 2 is applied only to the surface of the resonant microring 3, covering the SOI waveguide structure. An SU-8 protective film 12 is applied at the direct waveguide coupling point between the resonant microring 3 and the SOI waveguide structure.

[0043] The shape of the resonant micro-ring 3 is circular, elliptical or racetrack, and the SOI waveguide structure is a strip waveguide, a slot waveguide or a sub-wavelength waveguide.

[0044] The electro-optic polymer film 2 has a thickness of 2um to 4um. The refractive index of the electro-optic polymer film 2 changes under the influence of the external electric field, which ultimately causes the phase of the sensing arm to change, expressed as:

[0045]

[0046] Among them L g Represents the optical path of the microring as a whole, n eff is the effective refractive index of the waveguide, η is the conversion efficiency between the refractive index of the polymer film and the effective refractive index of the waveguide, r 33 is the electro-optic coefficient, R r is the radius of the microring structure, E is the external electric field to be measured, △θ is the phase change of the light wave around the microring, and △n is the change in the effective refractive index of the resonant microring waveguide.

[0047] The sensor of the present invention is integrated on-chip using a silicon-on-insulator (SOI) platform. The working layer is a typical two-dimensional waveguide structure: from bottom to top, a 500μm silicon substrate, a 3μm silicon dioxide buried layer (BOX), and a 220nm top silicon layer. The approximately two-fold difference in refractive index between silicon and silicon dioxide creates strong optical confinement both laterally and vertically, allowing the guided mode to be stably confined to the top silicon waveguide and transmitted with low loss along the chip plane. This lays the foundation for high-Q resonance and efficient optoelectronic modulation. Furthermore, the outer layer of the optical waveguide is covered with a SU-8 protective film 12, which has a refractive index of 1.57 at 1550nm, effectively limiting the transmission of light waves within the waveguide.

[0048] In order to achieve high-precision measurement of the electric field, the device connects an "unbalanced MZI-resonant microring" composite structure in series on the SOI waveguide structure: the unbalanced MZI first splits the incident light field and eliminates the initial phase difference, and the resonant microring covers the high r 33 Electro-optic polymer films amplify refractive index perturbations induced by external electric fields into significant phase shifts. After the two beams are recombined at the interferometer output, the phase information is linearly converted into variations in light intensity. This establishes a calibrated and highly consistent linear mapping between the measured spatial electric field and the output optical power, enabling broadband, highly sensitive on-chip electric field detection.

[0049] The preparation and coating process of electro-optical polymers mainly includes:

[0050] In the first step, prepare the dye solution and matrix solution separately. Weigh the chromophore and dissolve it in tetrahydrofuran. Sonicate or mix thoroughly, and store in the dark. Separately, dissolve 1g of matrix particles in 10mL of tetrahydrofuran and stir or sonicate until completely dissolved, forming a uniform polymer solution with a concentration of 10% (wt).

[0051] In the second step, mix the chromophore and matrix solution at a ratio of 5, 10, or 15 ppm (i.e., 0.05g, 0.10g, or 0.15g chromophore per 1g matrix). Mix at 2000 / 3000 rpm for 12 minutes to ensure full dispersion of the dye. The mixed solution should be clear and homogeneous, with no visible particles or stratification.

[0052] In the third step, a 1cm×1cm SOI chip was prepared and ultrasonically cleaned with deionized water, acetone, and anhydrous ethanol, followed by drying. A 0.1-0.2mL drop of the mixed solution was placed on the center of the substrate and spin-coated on a spin coater at 1000-2000 rpm for 60 seconds to form a uniform, transparent polymer film.

[0053] The spin-coated substrate is then placed in an oven and dried at 50-60°C for 12 hours to completely remove any residual tetrahydrofuran. If necessary, further annealing can be performed under vacuum to improve the density and uniformity of the film, with the film thickness controlled to approximately 2 μm.

[0054] The fifth step involves polarizing the dried sample using a polarization platform. The sample is heated to the glass transition temperature of the substrate (approximately 100-120°C) and a vertical electric field is applied, resulting in a leakage current of 5-10 μA. This is maintained for 10-30 minutes to orient the chromophore molecules within the polymer. The sample is then cooled to room temperature while maintaining the electric field, completing the polarization process and endowing the film with macroscopic electro-optical responsiveness.

[0055] By flip-chipping the VCSEL laser 51 onto the surface of the SOI chip, the laser light emitted from its bottom surface is vertically incident on the blazed grating structure of the electric field sensitive chip, significantly improving the incident coupling efficiency and suppressing reflection feedback. The blazed grating is designed as a periodic tilted etched structure, which uses the Bragg diffraction principle to redistribute the main energy to the first-order diffraction direction. The first-order diffraction angle satisfies the formula:

[0056] Λ(sinθ i +sinθ m )=mλ

[0057] Where Λ is the grating period, θ i is the vertical incidence angle, θ mis the first-order diffraction angle, and λ is the operating wavelength. Through the geometric design of the inclined "blazed surface", the energy is mainly concentrated in the first-order emission direction, while suppressing the feedback of the -1st order and the reflected zeroth order, thus adapting to the vertical incidence of the VCSEL.

[0058] The present invention uses a flip-package process to flip the VCSEL laser 51 chip and the photodetector chip onto the top of the SOI chip, significantly improving device integration and system compactness. After flipping, the metal electrodes of the VCSEL laser 51 and the photodetector, which originally faced upward, face downward and connect one-to-one with the electrode pads on the surface of the SOI chip through micron-scale metal bumps, such as AuSn or SnAg. At the same time, to achieve a through-hole connection between the entire circuit, the bottom of the SOI chip forms a complete electrical path with the circuit of the PCB substrate through through-holes or back leads.

[0059] BCB is used as a bonding material to form reliable dielectric insulation and mechanical fixation between the VCSEL laser 51 and the SOI chip. BCB has a low dielectric constant, a low coefficient of thermal expansion (CTE), and good chemical stability. A bonding layer thickness of about 5 to 10 μm can be formed by precisely controlling spin coating and photolithography. An additional BCB buffer column structure is provided in the diagonal areas of the VCSEL laser 51 and the photodetector chip to alleviate the thermal stress concentration caused by chip flipping. These buffer layers can evenly distribute expansion and deformation during thermal cycling, preventing chip warping, metal layer peeling, or cracking, thereby ensuring the thermomechanical stability of the overall packaging structure.

[0060] With the above-described preferred embodiments of the present invention as a guide, and with reference to the above description, relevant personnel are fully capable of making various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the contents of the specification and must be determined according to the scope of the claims.

Claims

1. A vertically incident silicon photonic electric field sensor structure, characterized in that: Based on SOI chip integration, the working layer is an SOI waveguide structure, and the sensor structure includes a substrate (7). A laser coupling module (5), an optical sensitive unit (18), and an optical probe coupling module (11) are sequentially integrated on the substrate (7) from left to right. The laser coupling module (5) and the optical probe coupling module (11) are flip-chip heterogeneously integrated on the surface of the SOI chip through a BCB film (8). The laser coupling module (5) and the optical probe coupling module (11) are electrically connected through metal electrodes, and the optical probe coupling module (11) receives and converts optical signals. The laser coupling module (5) includes a VCSEL laser (51) and a vertical incidence grating (10); The optical probe coupling module (11) includes a photodetector and a vertical emission grating (13); The optical sensitive unit (18) is arranged on a substrate (7), and the optical sensitive unit (18) includes an unbalanced MZI (1) and a resonant microring (3); The laser light emitted by the VCSEL laser (51) is vertically coupled to the SOI waveguide structure through a vertical incidence grating (10) coupled with a spatial light field. The light wave is split into two beams through an unbalanced MZI (1), and the initial phase difference between the two arms is compensated. A resonant microring (3) is used to assist the sensing arm, and an electro-optic polymer film (2) is covered on the sensing arm. The laser light that changes with the electric field interferes at the end of the unbalanced MZI (1), converting the phase change into a power change, and finally entering the photodetector through a vertical emission grating (13).

2. The vertically incident silicon photonic electric field sensor structure according to claim 1, wherein: The vertical incidence grating (10) is used to couple the 1550nm laser emitted by the VCSEL laser (51) to the SOI waveguide structure.

3. The vertically incident silicon photonic electric field sensor structure according to claim 1, wherein: The vertical incident grating (10) and the vertical exit grating (13) are both blazed gratings, which redistribute the backward reflected power to the first-order diffraction direction through the sawtooth blazed surface.

4. The vertically incident silicon photonic electric field sensor structure according to claim 1, wherein: One end of the unbalanced MZI (1) is connected to the vertical incidence grating (10), and the vertical emission grating (13) is connected to the other end of the unbalanced MZI (1), so that the laser light with changed light intensity is emitted into the photodetector. The unbalanced MZI (1) includes two unbalanced waveguide channels, which are used to compensate for the phase difference caused by coupling the microring on one side.

5. The vertically incident silicon photonic electric field sensor structure according to claim 1, wherein: The laser coupling module (5) and the optical probe coupling module (11) are integrated on the surface of the SOI chip via gold or silver metal electrodes, and the BCB film (8) is arranged at a corner of the laser coupling module (5) away from the optical probe coupling module (11).

6. The vertically incident silicon photonic electric field sensor structure according to claim 1, wherein: The electro-optic polymer film (2) is only coated on the surface of the resonant micro-ring (3), covering the waveguide structure of the micro-ring, and a SU-8 protective film (12) is provided at the straight waveguide coupling portion between the resonant micro-ring (3) and the SOI waveguide structure.

7. The vertically incident silicon photonic electric field sensor structure according to claim 1, wherein: The shape of the resonant micro-ring (3) is circular, elliptical or racetrack, and the SOI waveguide structure is a strip waveguide, a slit waveguide or a sub-wavelength waveguide.

8. The vertically incident silicon photonic electric field sensor structure according to claim 1, wherein: The electro-optic polymer film (2) has a thickness ranging from 2um to 4um.

9. A heterogeneous integration method for a vertically incident silicon photonic electric field sensor structure according to any one of claims 1 to 8, characterized in that: The following steps are involved: Step 1: heterogeneously integrate the laser coupling module (5) and the optical probe coupling module (11) on the substrate (7) through the metal electrode and the BCB film (8); Step 2: preparing a laser coupling module (5), an optical sensitive unit (18) and an optical probe coupling module (11) on the SOI waveguide structure, including a vertical incidence grating (10), an unbalanced MZI (1), a resonant microring (3), an electro-optic polymer film (2), an SU-8 protective film (12) and a vertical emission grating (13); Step 3: Couple the 1550 nm laser into the SOI waveguide structure through the vertical incidence grating (10), and use the unbalanced MZI (1) to split the beam and compensate for the phase difference; Step 4: The electric field change is converted into a phase change through the resonant microring (3) and the electro-optic polymer film (2), and the interference is converted into an optical power change at the end of the unbalanced MZI (1); Step 5: The optical signal is emitted into the photodetector through the vertical emission grating (13) to complete the electric field measurement.

10. The heterogeneous integration method of a vertically incident silicon photonic electric field sensor structure according to claim 9, wherein: The preparation of the electro-optic polymer film (2) comprises the following steps: Prepare dye solution and matrix solution, mix them and then spin-coat them on SOI chip; After drying, the chromophore molecules are oriented and arranged through polarization treatment to form a film with electro-optical response capability.

Images