An on-chip integrated ring-shaped conductive polymer waveguide photodetector based on photo-thermal-electric energy conversion

Abstract

An on-chip integrated ring-shaped conductive polymer waveguide photodetector based on photo-thermal-electric energy conversion belongs to the field of functional photonic chip technology. It consists of a substrate layer, a barrier layer, a cladding layer, a core layer, and a detection electrode layer. The core layer is embedded in the cladding layer, with its upper surface and the upper surface of the cladding layer located on the same plane. The core layer is a ring-shaped racetrack waveguide structure composed of five sequentially linked parts: an input Y-branch waveguide, a first straight waveguide, a first semi-ring feedback waveguide, a second straight waveguide, and a second semi-ring feedback waveguide. The core layer is obtained by doping gold nanoparticle-modified metal-organic framework powder into a polymer material and then curing it under ultraviolet light. This invention alters the photothermal effect of the gold nanoparticle-doped waveguide core layer by changing the excitation light power, and uses an external detection electrode based on the Seebeck effect to monitor the thermoelectric potential. The detector of this invention features low cost, small size, high integration, and fast response.

Description

Technical Field

[0001] This invention belongs to the field of functional photonic chip technology, specifically relating to an on-chip integrated ring conductive polymer waveguide photodetector based on optical-thermal-electric energy conversion. Background Technology

[0002] A photodetector is a detection element that converts optical signals into electrical signals. As an important component of the receiver in fiber optic transmission networks, it is widely used in optical communication systems. Especially in the construction of photonic integrated transceiver modules, traditional on-chip semiconductor photodetectors must be formed through heterojunction epitaxial growth and ion implantation doping to create the basic structure of the photodetector. This not only limits the integration density and flexibility of the photodetector but also increases the difficulty of fabricating silicon photonic integrated chips. How to achieve on-chip integrated photodetectors with small size, high integration, fast response, and good cost-effectiveness has become a research hotspot in the field of photonic integration. Compared with other waveguide structures, microring resonators, as important optical signal processing units, can effectively realize functions such as filtering, multiplexing / demultiplexing, modulation, switching, delay, routing, sensing, and amplification. In particular, the racetrack-shaped microring waveguide structure has advantages such as large bandwidth, good compatibility, and high precision, making it suitable for designs involving optical storage, wavelength selection, and optical cascading. This invention utilizes a racetrack-shaped micro-ring to form a feedback optical loop structure. Through the photothermal effect generated between the conductive polymer waveguide and the optical signal, light energy is first converted into heat energy. Then, the Seebeck effect, generated by the temperature gradient in different regions of the active polymer waveguide, is used to convert heat energy into electrical energy. By detecting changes in voltage and dark current between the electrodes, the intensity of light of different power levels can be detected. This invention innovatively proposes an on-chip integrated optical-thermal-electric conversion conductive polymer waveguide photodetector. The related technology can meet the important requirements of my country for high-speed, high-density photoelectric detection systems and is of great significance for the establishment of all-optical communication networks. Summary of the Invention

[0003] The purpose of this invention is to provide an on-chip integrated ring-shaped conductive polymer waveguide photodetector based on photo-thermal-electric energy conversion. This invention employs a ring-shaped feedback waveguide structure to improve the detection efficiency of optical signals. By incorporating gold nanoparticle-modified metal-organic frameworks (Au-MOFs), highly efficient photo-thermal-electric energy conversion is achieved in the conductive polymer waveguide core. The polymer waveguide incorporating gold nanoparticles interacts with the optical signal, generating surface plasmon resonance. Under the influence of an electric field, the electron clusters of the entire gold nanoparticle system will shift relative to the original positions of the nanoparticles and oscillate with the fluctuations of the electromagnetic field, thereby causing resonance in the internal lattice and obtaining a large amount of thermal energy to achieve photo-thermal energy conversion. Based on the Seebeck effect generated by the temperature gradient in different regions of the conductive polymer waveguide, thermoelectric energy conversion is achieved through thermoelectric response. The changes in voltage and dark current are detected using overlapping metal electrodes, realizing an on-chip integrated photo-thermal-electric conversion ring-shaped conductive polymer waveguide photodetector.

[0004] The present invention discloses an on-chip integrated ring conductive polymer waveguide photodetector based on optical-thermal-electric energy conversion, which employs a ring waveguide structure, as shown in the attached figure. Figure 1 (a) shows a three-dimensional waveguide structure, consisting from bottom to top of a substrate layer 1, a barrier layer 2, a cladding layer 3, a core layer 4, and a probe electrode layer 5; the core layer 4 is embedded in the cladding layer 3, and the upper surface of the core layer 4 and the upper surface of the cladding layer 3 are located on the same plane; as shown in the attached diagram. Figure 1 As shown in (b), along the optical transmission direction, the core layer 4 is a ring-shaped racetrack waveguide structure composed of five parts connected in sequence: an input Y-branch waveguide 41, a first straight waveguide 42, a first semi-ring feedback waveguide 43, a second straight waveguide 44, and a second semi-ring feedback waveguide 45; the probe electrode 5 is composed of a strip electrode with its front end embedded between the first straight waveguide 42 and the cladding 3 and its rear end located on the cladding 3, which is connected to a square plate probe electrode through electrode leads.

[0005] As attached Figure 1 (c) An on-chip integrated conductive polymer waveguide photodetector based on photo-thermal-electric energy conversion. Figure 1 (a) is a cross-sectional schematic diagram at point a. From bottom to top, it consists of a substrate layer 1, a barrier layer 2, a cladding layer 3, a core layer 4, and a detection electrode layer 5. Air is used as the upper cladding layer of the core layer 4. The cladding layer 3 and the core layer 4 are made of different materials. The core layer 4 is obtained by ultraviolet light curing. Its refractive index is greater than that of the cladding layer 3, which allows the light to be better confined and transmitted in the core layer.

[0006] The substrate layer 1 material described in this invention is any one of indium phosphide, gallium arsenide, and silicon.

[0007] The barrier layer 2 described in this invention is made of SiO2;

[0008] The cladding material 3 described in this invention is either PMMA or P(MMA-GMA).

[0009] The metal detection electrode 5 described in this invention is made of any one of gold, aluminum, or chromium.

[0010] The core layer 4 material of the present invention is obtained by doping gold nanoparticle-modified metal-organic framework powder (Au-MOFs) into a polymer material and then curing it under ultraviolet light. The polymer material is either conductive SU-8 or conductive FSU-8.

[0011] As attached Figure 2 As shown, the on-chip integrated ring-shaped conductive polymer waveguide photodetector based on optical-thermal-electric energy conversion of the present invention uses a 532nm laser as the signal light λ. The signal light λ is input through the lower branch of the Y-shaped branch waveguide (the upper branch waveguide of the Y-shaped branch waveguide partially overlaps with the second semi-ring feedback waveguide 45), sequentially passes through the first straight waveguide section 42 of the ring racetrack waveguide, the first semi-ring feedback waveguide 43, the second straight waveguide 44, and the second semi-ring feedback waveguide 45, and then re-enters the first straight waveguide 42. This process repeats continuously; optical power accumulates within the ring-shaped waveguide, generating a certain photothermal effect. The presence of doped gold nanoparticles further enhances this effect, making it easier to detect. According to the Seebeck effect, the significant thermal potential difference in the waveguide generates a potential difference across the two ends of the first straight waveguide 42. The doped metal-organic framework allows particles of different polarities to accumulate at both ends of the waveguide, achieving a large potential difference gain. A pair of metal detection electrodes are introduced at both ends of the first straight waveguide 42, and the potential difference is measured using an external voltammeter. When signal light of different powers is passed through the waveguide, different potentials are measured on the same electrodes, thus achieving photoelectric detection.

[0012] The role of gold nanoparticle-modified metal-organic frameworks is twofold:

[0013] 1. When gold nanoparticles interact with light waves, surface plasmon resonance occurs. Under the action of an electric field, the electron gas cluster of the entire gold nanoparticle will be displaced relative to the original position of the nanoparticle and oscillate with the fluctuation of the electromagnetic field, thereby causing resonance of the internal lattice and obtaining a large amount of heat energy to achieve light-to-heat conversion.

[0014] 2. Metal-organic frameworks are metal ion compound materials with high specific surface area and porosity. They can add the required functional groups to organic ligands. In this invention, they serve as carriers for gold nanoparticles, increasing light absorption and enabling the gold nanoparticles to be uniformly distributed in the core material.

[0015] Compared with existing device structures and fabrication techniques, the significant advantages of this invention are:

[0016] (1) Compared with existing waveguide photodetectors, the present invention is based on low-cost polymer waveguide materials, and the preparation method is simple, which greatly simplifies the process flow. Waveguides can be formed by reactive ion etching and waveguide material infusion, and the waveguide morphology is easy to control.

[0017] (2) Compared with traditional material waveguide photodetectors, the present invention uses doped Au-MOFs to greatly improve its photo-thermal conversion efficiency and achieve high Seebeck effect thermoelectric gain.

[0018] (3) Compared with the traditional method of fabricating electrodes on the upper layer of the waveguide, the method of fabricating the probe electrode in the groove on the lower side of the waveguide and covering it can effectively reduce heat loss and make the thermoelectric potential more significant.

[0019] (4) Compared with existing waveguide photodetectors, the device fabricated in this invention is based on a ring feedback waveguide structure, which greatly improves the light utilization rate. Attached Figure Description

[0020] Figure 1 Figure 1 is a schematic diagram of the structure of an on-chip integrated optical-thermal-electric conversion conductive polymer waveguide photodetector according to the present invention; wherein Figure 2) is a three-dimensional structural schematic diagram of an on-chip integrated optical-thermal-electric conversion conductive polymer waveguide photodetector; Figure 3) is a top view of an on-chip integrated optical-thermal-electric conversion conductive polymer waveguide photodetector; and Figure 4) is a cross-sectional schematic diagram of an on-chip integrated optical-thermal-electric conversion conductive polymer waveguide photodetector.

[0021] Figure 2 This invention describes the optical transmission path of an on-chip integrated photo-thermal-electric conversion conductive polymer waveguide photodetector with an input light wavelength of λ = 532 nm.

[0022] Figure 3 This is a schematic diagram of the waveguide cross-sectional dimensions of an on-chip integrated optical-thermal-electric conversion conductive polymer waveguide photodetector according to Embodiment 1 of the present invention.

[0023] Figure 4 This is a schematic diagram of the device dimensions according to Embodiment 1 of the present invention;

[0024] Figure 5 The absorption spectrum of the core material used in Example 1 of this invention is shown in the 500-600nm wavelength range, and a significant absorption peak can be observed at a wavelength of 532nm.

[0025] Figure 6 The curve shows the change in waveguide core temperature with the input 532nm wavelength excitation light power in Embodiment 1 of the present invention.

[0026] Figure 7The simulated thermoelectric potential versus waveguide core temperature curve in Embodiment 1 of this invention shows that the two are directly proportional, with a slope of 6.5 μV / ℃.

[0027] Figure 8 The potential variation curve with excitation optical power in Embodiment 1 of the present invention is calculated based on the waveguide core temperature variation curve with excitation optical power and the thermoelectric potential variation curve with waveguide core temperature, with a slope of 33.28 μV / mW.

[0028] Figure 9 This is a flowchart illustrating the fabrication process of the device in Embodiment 1 of the present invention. Detailed Implementation

[0029] The present invention will now be described more clearly and comprehensively with reference to the accompanying drawings. Those skilled in the art will gain a deeper understanding of the advantages and functions of the present invention from this description. However, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] Example 1:

[0031] In this embodiment, the substrate layer 1 is a silicon substrate with a thickness of 730 μm;

[0032] In this embodiment, the barrier layer 2 is a 5μm thick SiO2.

[0033] In this embodiment, the cladding layer 3 is an 8μm thick PMMA.

[0034] In this embodiment, the detection electrode 5 is an aluminum electrode with a thickness of 100 nm.

[0035] The chemical formula of the metal-organic framework nanoparticles modified with gold nanoparticles used in this embodiment is as follows: the spheres are doped gold nanoparticles bound in the metal-organic framework shown in the following formula. For the preparation method and experimental spectra, please refer to the reference (Ke Wu, Xiaoya Miao, Yunlong Yu, et al. Highly Sensitive Humidity Sensor Based on Proton Conducting Au Nanoparticles-Modified Metal–OrganicFrameworks[J].IEEE SENSORS JOURNAL,2023,23(3):1867-1874.).

[0036]

[0037] In this embodiment, the core layer 4 is made of conductive SU-8, which is a metal-organic framework powder modified with gold nanoparticles synthesized in-house.

[0038] In this embodiment, the mass of the gold nanoparticle-modified metal-organic framework powder used in the core layer 4 material is 0.166% of the sum of the mass of the gold nanoparticle-modified metal-organic framework powder and the conductive SU-8 material, wherein the mass of the gold nanoparticles accounts for approximately 5% of the mass of the gold nanoparticle-modified metal-organic framework powder.

[0039] As attached Figure 3 As shown, in this embodiment, the core layer 4 has a thickness of 3.6 μm, the barrier layer 2 has a thickness of 8 μm, the core layer 4 is embedded in the cladding layer 3, and the upper surface of the core layer 4 and the upper surface of the cladding layer 3 are located on the same plane; as shown in the attached figure. Figure 4 As shown, in this embodiment, the width of all waveguide core layers 4 is 10 μm, the length of the Y-branch waveguide 41 is 20000 μm, and its radius of curvature r is 1500 μm (to maintain shape symmetry with the second semi-ring waveguide). The length of the first and second straight waveguide sections of the ring racetrack waveguide is 8000 μm. The inner diameter of the first semi-ring feedback waveguide 43 and the second semi-ring feedback waveguide 45 is 1500 μm, and the outer diameter is 1510 μm. The probe electrode 5 is composed of a strip electrode (1200 μm long and 30 μm wide) embedded between the first straight waveguide 42 and the cladding 3, the width of the part of the probe electrode 5 embedded between the first straight waveguide 42 and the cladding 3 is 5 μm, and the width of the part of the probe electrode 5 located above the cladding 3 is 25 μm) connected to a square plate probe electrode (1000 μm side length) through an electrode lead (1000 μm long and 20 μm wide).

[0040] The basic synthesis method of the conductive SU-8 material doped with gold nanoparticle-modified metal-organic framework powder used in this embodiment is as follows:

[0041] 1. Take 2.9989g of conductive SU-8 photoresist and place it in a clean weighing bottle. Then add 5mg of gold nanoparticle-modified metal-organic framework powder (the specific synthesis principle and route have been published in Ke Wu, Xiaoya Miao, Yunlong Yu, et al. Highly Sensitive Humidity Sensor Based on Proton Conducting Au Nanoparticles-Modified Metal–Organic Frameworks[J].IEEE SENSORSJOURNAL,2023,23(3):1867-1874.).

[0042] 2. Wrap the weighing bottle in tin foil and place it in an ultrasonic cleaner in a dark environment. Stir it ultrasonically at 45°C for 6 hours (to ensure that the gold nanoparticle-modified metal-organic framework powder is completely and evenly dispersed in the conductive SU-8 solution). This will yield a conductive SU-8 core material doped with gold nanoparticle-modified metal-organic framework powder.

[0043] This embodiment selects a center wavelength of 532nm. Although this embodiment can realize the detection of optical power of signals in multiple bands, as shown in the attached... Figure 5 The absorption spectrum of Au-MOFs measured by UV-3600 shows that the core material has a significant absorption peak at a wavelength of 532nm. Therefore, the test results are better under signal light at this wavelength. Thus, 532nm signal light was selected as the probe light in this embodiment.

[0044] The refractive index of the core material used in this embodiment is 1.596 at a wavelength of 532 nm.

[0045] This embodiment simulates the photo-thermal-electric conversion effect of conductive SU-8 doped with Au-MOFs when it absorbs 532nm wavelength excitation light using COMSOL software. (See attached image) Figure 6 Simulated by R-soft software, and attached Figure 6 It can be seen that as the 532nm excitation power gradually increases, the temperature of waveguide core layer 4 generally shows an upward trend. Figure 7 Simulated by COMSOL software, and attached Figure 7 It can be seen that the potential difference between the hot and cold ends of the first straight waveguide of the Au-MOFs-doped SU-8 proposed in this embodiment is proportional to the temperature difference between the two ends of the waveguide. Since the waveguide core temperature increases with the increase of optical power in the above simulation, it can be seen that the potential difference between the hot and cold ends of the first straight waveguide increases with the increase of excitation optical power, and the rate of change is about 6.5μV / K.

[0046] The fabrication method of the on-chip integrated optical-thermal-electric conversion conductive polymer waveguide photodetector in this embodiment is as follows: Figure 8 As shown, the specific description is as follows:

[0047] A. Using a silicon dioxide layer grown on a silicon substrate 1 as barrier layer 1, the silicon dioxide surface is first cleaned. The silicon substrate 1 with barrier layer 2 is placed in a beaker containing acetone solution and ultrasonically cleaned for 10 minutes. After removal, it is placed in a beaker containing isopropanol solution and ultrasonically cleaned for 10 minutes. After removal, it is placed in a beaker containing deionized water and ultrasonically cleaned for 10 minutes. After removal, the deionized water on the silicon wafer surface is dried with a nitrogen gun. Finally, the silicon substrate 1 with barrier layer 2 is placed in a glass container and dried in an oven (150℃, 30min) to remove surface moisture and organic impurities. PMMA is spin-coated (2500 rpm, 20 seconds) onto the cleaned silicon dioxide surface. Immediately after spin-coating, it is thermally cured on a hot plate (120℃, 30min) to form a PMMA coating.

[0048] B. Evaporate a 200nm thick aluminum protective layer onto the PMMA surface;

[0049] C. Spin-coat BP212 (3000 rpm, 20 seconds) onto the surface of the aluminum protective layer, and immediately heat-cure it on a hot plate (pre-baking: 87°C, 10 minutes; post-baking: 92°C, 20 minutes) as a mask 7;

[0050] D. Expose the circular racetrack-shaped negative photomask to ultraviolet light (exposure time 3.5 seconds) to expose the aluminum in the groove area to be etched, and wash away the exposed aluminum protective layer with sodium hydroxide solution (sodium hydroxide powder mass: water mass = 2g: 500g);

[0051] E. Expose again with ultraviolet light (exposure time 15 seconds) to remove the remaining BP212 mask, leaving only the waveguide part exposed and the other part covered by the aluminum protective layer of the PMMA cladding.

[0052] F. The prepared PMMA cladding was used to prepare a 3.6 μm deep PMMA groove by reactive ion etching (O2:Ar volume ratio of 4:1, time 200 seconds);

[0053] G. Use sodium hydroxide of the same concentration as described in D to wash away the aluminum protective layer 6 and immerse in alcohol for 30 seconds to wash away impurities on the surface of the PMMA groove;

[0054] H. A 100 nm thick aluminum electrode layer is deposited on the surface of the prepared PMMA groove 5';

[0055] I. Spin-coat BP212 (3000 rpm, 20 seconds) onto the surface of aluminum, and immediately heat-cure on a hot plate (pre-baking: 87°C, 10 minutes; post-baking: 92°C, 20 minutes) as a mask;

[0056] J. Uses and attachments Figure 4The original electrode plate of the same shape as the middle electrode is exposed to ultraviolet light (exposure time 3.5 seconds) to remove the mask 8, so that the aluminum electrode layer 5' other than the aluminum electrode to be prepared is exposed;

[0057] K. Use sodium hydroxide of the same concentration as in step D to wash away the exposed aluminum electrode layer 5', rinse with deionized water, dry with a nitrogen gun, and then expose to ultraviolet light again (exposure time 15 seconds) to remove the BP212 mask 8. The aluminum detection electrode 5 is now prepared.

[0058] L. The conductive SU-8 core layer material, modified with gold nanoparticles and doped with metal-organic framework powder, was ultrasonicated for 30 minutes (to ensure uniform dispersion of the nanoparticles). Then, it was spin-coated (3000 rpm, 20 seconds) onto the cleaned PMMA groove surface on which the aluminum detection electrode 5 was prepared. Immediately after spin-coating, it was exposed to ultraviolet light for 5 seconds, and then thermally cured on a hot plate (pre-baking: 65°C, 10 minutes; post-baking: 95°C, 40 minutes) to obtain the conductive SU-8 core layer material coating 4, modified with gold nanoparticles and doped with metal-organic framework powder. At this point, the device fabrication process was completed.

Claims

1. An on-chip integrated ring-conductive polymer waveguide photodetector based on optical-thermal-electrical energy conversion, employing a ring waveguide structure, characterized in that: From bottom to top, it consists of a substrate layer (1), a barrier layer (2), a cladding layer (3), a core layer (4), and a probe electrode (5); the core layer (4) is embedded in the cladding layer (3), and the upper surface of the core layer (4) and the upper surface of the cladding layer (3) are on the same plane; along the optical transmission direction, the core layer (4) is a ring-shaped racetrack waveguide structure composed of five parts connected in sequence: an input Y-branch waveguide (41), a first straight waveguide (42), a first semi-ring feedback waveguide (43), a second straight waveguide (44), and a second semi-ring feedback waveguide (45). The upper branch waveguide of the Y-branch waveguide partially overlaps with the second semi-ring feedback waveguide (45); the probe electrode (5) consists of a front end... The strip electrode, which is embedded between the first waveguide (42) and the cladding (3) and whose rear end is located on the cladding (3), is connected to a square plate detection electrode through an electrode lead; the substrate layer (1) is made of any one of indium phosphide, gallium arsenide, and silicon; the barrier layer (2) is made of SiO2; the cladding layer (3) is made of any one of PMMA and P (MMA-GMA); the detection electrode (5) is made of any one of gold, aluminum, and chromium; the core layer (4) is made of metal-organic framework powder modified with gold nanoparticles, which is doped into a polymer material and then cured under ultraviolet light. The polymer material is any one of conductive SU-8 and conductive FSU-8.

2. The on-chip integrated ring-shaped conductive polymer waveguide photodetector based on optical-thermal-electrical energy conversion as described in claim 1, characterized in that: The substrate (1) is a silicon substrate with a thickness of 730 μm, the barrier layer (2) is SiO2 with a thickness of 5 μm, the cladding layer (3) is PMMA with a thickness of 8 μm, the detector electrode (5) is an aluminum electrode with a thickness of 100 nm; the core layer (4) is a metal-organic framework powder modified with gold nanoparticles doped in conductive SU-8 and then cured by ultraviolet light. The core layer (4) has a thickness of 3.6 μm and a width of 10 μm.

3. The on-chip integrated ring-shaped conductive polymer waveguide photodetector based on photo-thermal-electric energy conversion as described in claim 1, characterized in that: The Y-branch waveguide (41) has a length of 20,000 μm and a radius of curvature r of 1,500 μm; the first straight waveguide (42) and the second straight waveguide (44) both have a length of 8,000 μm; the first semi-ring feedback waveguide (43) and the second semi-ring feedback waveguide (45) both have an inner diameter of 1,500 μm and an outer diameter of 1,510 μm; the five strip electrodes of the detection electrode have a length of 1,200 μm and a width of 30 μm, the width of the part of its front end embedded between the first straight waveguide (42) and the cladding (3) is 5 μm, and the width of the part of its rear end located above the cladding (3) is 25 μm; the electrode lead has a length of 1,000 μm and a width of 20 μm; the side length of the square plate detection electrode is 1,000 μm.

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