Gallium nitride photoelectron integrated turbidity sensor using visible light signal and preparation method thereof

Abstract

The present invention proposes a gallium nitride optoelectronic integrated turbidity sensor in the semiconductor field that utilizes visible light signals. The sensor comprises an optoelectronic chip disposed on the inner wall of a liquid container. The optoelectronic chip includes a silicon substrate layer and a nitride epitaxial layer. A micro-LED device serving as a visible light signal light source and a photodetector for receiving the visible light signal are disposed on the nitride epitaxial layer. The nitride epitaxial layer is provided with a positive electrode and a negative electrode connecting the micro-LED device and the photodetector. The silicon substrate layer is partially bonded to a circuit board, and an encapsulation layer is provided on the outside of the nitride epitaxial layer. The present invention has a high degree of integration and can use a low-cost, small-volume integrated system to effectively and accurately monitor physical parameters such as turbidity of the liquid to be measured.

Description

Technical Field

[0001] The present invention relates to a gallium nitride optoelectronic chip, in particular to a gallium nitride optoelectronic integrated turbidity sensor, belonging to the technical field of semiconductors. Background Art

[0002] Water turbidity has long been a primary criterion for determining water quality. China, a country with relatively limited natural resources and the urgent task of environmental pollution control, has seen an increasing demand for water monitoring. Improving water quality monitoring and disseminating water quality monitoring equipment are crucial tasks. Turbidity sensors measure the turbidity of liquids. Besides being used for environmental monitoring, they can also be used to monitor the turbidity of water used in household appliances such as washing machines and cleaning machines. By monitoring the turbidity of discharged water, the cleanliness of items being cleaned can be determined, thereby determining cleaning procedures for electrical equipment. Currently, there are three main types of turbidity sensors. The first involves visual inspection, where the user directly observes water turbidity with the naked eye. These methods include visual turbidimetry and nephelometers. However, these methods are subject to subjective factors and personal visual experience, making it difficult to obtain stable turbidity data. The second method involves spectrophotometry, where a white polymer, formed by mixing holmium hydrazine sulfate and 6-methylenetetramine polymer at a specific temperature, is used as a turbidity standard solution and compared with the turbidity of a water sample under specific conditions. The disadvantage is that it uses transmitted light measurement, which cannot accurately reflect water turbidity. The third method is instrumental analysis, which uses the principles of light scattering or transmission to convert the turbidity of the water sample into photovoltaic current information to measure the water turbidity value. Specifically, it can be divided into transmission method, divergent light method, transmitted light ratio method, and scattered light method. Of these, the scattered light method has the highest sensitivity and measurement accuracy.

[0003] The emergence of advanced miniature light sources and the improvement of electronic circuit accuracy have gradually refined photoelectric measurement methods. Therefore, dual-beam monitoring technology can reduce interference with the light source. Alternatively, the light generated by the light source can be split into two beams using a spectrometer, and the contrast between the two beams can be used to reduce the impact of ambient lighting. Fiber optic sensors can replace photoelectric sensors, increasing monitoring accuracy and sensitivity. Laser illumination sources can replace conventional tungsten lamps, improving light source performance and lifespan. In addition to traditional photoelectric measurement techniques, new methods such as image processing turbidity measurement are also attracting industry interest. However, the sample distribution and coverage of these methods are inconsistent and incomplete, requiring further improvement. Among domestic turbidity sensors, the application of photoelectric methods has greatly improved sensitivity and accuracy, but there are challenges with the device's form factor, installation method, and manual cleaning. Domestic turbidity sensors are limited to flow-through types, lacking other test device configurations such as immersion and insertion types. There is room for improvement in domestic turbidity sensors in terms of cost-effective integration, compact size, and real-time monitoring.

[0004] Currently, the most advanced transmission turbidity monitoring methods follow the Lambert-Beer law, which states that when a beam of monochromatic parallel light is projected along a specific direction into a homogeneous medium, the attenuation of the light intensity is proportional to the product of the light intensity and the thickness of the medium. The Lambert-Beer law states that in gases or certain substances, the amount of light absorbed is proportional to the concentration of the absorbing substance. These substances are those that can dissolve in non-light-absorbing solvents. Because visible light signals have strong penetration and low absorption in water, changes in water turbidity, based on the Lambert-Beer law, can produce very sensitive changes in light intensity. Based on this principle, we can exploit the intensity modulation effect of visible light signals for turbidity sensing and develop integrated photonic chips for turbidity sensing applications.

[0005] In recent years, gallium nitride (GaN), a new generation of semiconductor materials, has emerged. GaN semiconductor materials offer unique properties such as wide bandgap, high breakdown electric field, high electron saturation drift velocity, low dielectric constant, strong radiation resistance, and excellent chemical stability. These materials hold broad application prospects in optoelectronic devices such as optical displays, optical storage, and optical detection, as well as in microelectronic devices for high-temperature, high-frequency, and high-power electronics. InGaN / GaN multiple quantum well (MQW) materials exhibit simultaneous emission and detection capabilities in the visible light band. Using these materials, micro-LED devices that emit visible light signals and photodetectors that receive visible light signals can be fabricated on a single, homogeneous integrated chip with high integration density. Through monolithic integration, a single chip can simultaneously transmit and detect visible light signals, enabling the development of compact, functional optical microsystems with applications in various fields, such as on-chip visible light communications, light-induced neuromorphic devices, and synaptic transistors. This patent, leveraging the simultaneous emission and detection capabilities of InGaN / GaN multiple quantum well materials, describes a GaN optoelectronic integrated turbidity sensor utilizing visible light signals. Summary of the Invention

[0006] The purpose of the present invention is to provide a gallium nitride photoelectric integrated turbidity sensor using visible light signals and a preparation method thereof. The prepared sensor has the advantages of high integration, high sensitivity, small size and easy operation.

[0007] The objective of the present invention is achieved as follows: A gallium nitride optoelectronic integrated turbidity sensor utilizing visible light signals, characterized in that it includes an optoelectronic chip arranged on the inner wall of a liquid container, the optoelectronic chip including a silicon substrate layer and a nitride epitaxial layer, the nitride epitaxial layer is provided with a micro LED device serving as a visible light signal light source and a photodetector for receiving the visible light signal, the nitride epitaxial layer is provided with a positive electrode and a negative electrode connecting the micro LED device and the photodetector, the silicon substrate layer is partially combined with a circuit board, and an encapsulation layer is provided on the outside of the nitride epitaxial layer.

[0008] As a further limitation of the present invention, the encapsulation layer is formed by waterproof encapsulation using polydimethylsiloxane.

[0009] As a further limitation of the present invention, a high reflective mirror is attached to the inner wall of the liquid container.

[0010] A method for preparing a gallium nitride optoelectronic integrated turbidity sensor comprises the following steps:

[0011] Step (1) using PECVD technology to deposit a layer of silicon dioxide as a hard mask on the upper surface of the silicon substrate nitride wafer;

[0012] Step (2) using photolithography technology to spin-coat a photoresist on the surface of the hard mask to define the pattern structure of the micro LED device serving as the visible light signal light source and the photodetector receiving the visible light signal, and using reactive ion etching technology to transfer the pattern on the photoresist layer to the hard mask layer;

[0013] Step (3) using the III-V material inductively coupled plasma etching technology, based on the pattern structure on the silicon dioxide hard mask, etching away the P-type GaN layer and the multi-quantum well structure to expose the n-type GaN;

[0014] Step (4) Spin-coating photoresist on the top nitride surface of the silicon substrate nitride wafer, performing optical lithography to define the pattern structure of the isolation groove, and using III-V material inductively coupled plasma etching technology to etch through the entire nitride epitaxial layer to the top surface of the silicon substrate to achieve electrical isolation between each micro LED device and the photodetector;

[0015] Step (5) performing photolithography on the top nitride surface of the silicon substrate nitride wafer to define the pattern structure of the positive and negative electrodes of the micro LED device and the photodetector, and depositing a nickel / gold composite metal layer using electron beam evaporation technology;

[0016] Step (6) using an organic reagent, acetone, to peel off the nickel / gold composite metal layer deposited on the surface of the photoresist in an ultrasonic cleaning environment to obtain positive and negative electrodes of the micro LED device and the photodetector;

[0017] Step (7) bonding the lower surface of the silicon substrate nitride wafer, i.e., the silicon substrate surface, to the circuit board to form a whole, and connecting the positive and negative electrodes of the micro LED device and the photodetector to the electrodes on the circuit board by wires;

[0018] Step (8) waterproof packaging the whole with PDMS material to produce a gallium nitride optoelectronic integrated chip for turbidity sensor;

[0019] Step (9) packaging the gallium nitride optoelectronic integrated chip;

[0020] Step (10) preparing a liquid container, and electroplating chromium metal on the inner wall of the liquid container to prepare a high-reflectivity mirror surface;

[0021] Step (11) mounts the packaged gallium nitride optoelectronic integrated chip on the inner wall of the liquid container to obtain the gallium nitride optoelectronic integrated turbidity sensor.

[0022] As a further limitation of the present invention, step (9) specifically includes:

[0023] Step (9-1) performs a glue preparation operation, dividing the PDMS glue into glue A and glue B, and mixing glue A and glue B evenly until the mixed glue is milky white overall;

[0024] Step (9-2) performs defoaming treatment; the mixed PDMS glue is placed in a vacuum drying oven and kept under vacuum until the bubbles inside the mixed PDMS glue are completely eliminated; the defoamed PDMS glue is ready for molding;

[0025] Step (9-3) Molding: Use tin foil to make a mold for encapsulating the gallium nitride optoelectronic integrated chip, pour the mixed PDMS glue into the container, and place it in a vacuum drying oven for defoaming and pre-curing;

[0026] Step (9-4) drying in an oven;

[0027] Step (9-5) cleaning and drying: rinse the GaN optoelectronic integrated chip coated with PDMS material with alcohol and purified water, blow away the remaining liquid with compressed air, and place the GaN optoelectronic integrated chip coated with PDMS material in an oven for drying;

[0028] In step (9-6), a micro-drill is used to drill holes in the PDMS material on the back of the GaN optoelectronic integrated chip that has been waterproofed and coated with PDMS material, leaving space for electrical connection to the chip to complete the package.

[0029] As a further limitation of the present invention, the preparation of the liquid container in step (10) is specifically as follows:

[0030] Step (10-1) uses ABS material and performs drying treatment, and then dries it before processing;

[0031] Step (10-2) melting the dried ABS material at high temperature;

[0032] Step (10-3) uses a symmetrical two-part mold and a standard injection molding machine for injection molding. A time-switched pressure-holding method is used, and the injection time is used to adjust the defects of the product to produce an ultra-thin liquid container divided into two parts. The structure of the container is a rectangular parallelepiped cavity with liquid inlet and outlet holes at both ends.

[0033] In step (10-4), the injection molded product is cooled to form an ultra-thin liquid container divided into two parts.

[0034] As a further limitation of the present invention, the preparation of the high reflectivity mirror in step (10) specifically includes:

[0035] Step (10-5) using a degreasing agent to degrease the cavity of the manufactured ultra-thin container, and using a chemical etching agent to roughen the plastic surface inside the cavity, so that the surface changes from hydrophobic to hydrophilic;

[0036] After the roughening step (10-6), the plastic surface inside the cavity is sensitized with a sensitizer, a stannous chloride solution, and activated with a silver nitrate solution to cause an oxidation-reduction reaction between the stannous chloride and the silver nitrate, thereby reducing and depositing a silver film on the surface;

[0037] Step (10-7) is to perform alkaline chemical copper plating to further plate a copper film on the silver film through an oxidation-reduction reaction to enhance its conductivity in the subsequent chromium electroplating process;

[0038] In step (10-8), a chromium electroplating process is performed to obtain a cavity of an ultra-thin liquid container with two inner surfaces having high reflectivity mirrors.

[0039] The GaN material involved in the present invention is a wide bandgap semiconductor with a direct bandgap of 3.4eV. It has broad application prospects in long-life, low-energy consumption, short-wavelength semiconductor light-emitting diodes (LEDs), laser diodes (LDs), ultraviolet detectors, and high-temperature microelectronic devices. The quantum well structure involved is a potential well for electrons or holes with a significant quantum confinement effect, and has the excellent characteristic of integrated transmission and reception of visible light signals. The present invention proposes a gallium nitride optoelectronic integrated turbidity sensor that utilizes visible light signals, in which a photonic integrated chip with a waterproof package is placed inside an ultra-thin liquid container with a high-reflectivity mirror. When the integrated turbidity sensor is in operation, the liquid to be tested is placed in the container, and the integrated photonic chip for transmission and reception is used for light emission and reception. The micro-LED device emits a visible light signal that penetrates the liquid to be tested. Under the reflection of the high-reflectivity mirror electroplated inside the container, the visible light signal is returned to the photodetector through multiple optical paths modulated by the liquid to be tested. The modulated visible light signal is received by the photodetector and converted into a photocurrent. Because the intensity of the visible light signal is modulated by the turbidity of the liquid being tested, the more turbid the liquid being tested, the greater the visible light signal absorption. The lower the intensity of the modulated visible light signal transmitted back to the photodetector, the lower the corresponding photocurrent intensity. By analyzing the intensity of the photocurrent, the turbidity of the liquid being tested can be tested.

[0040] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects: the present invention has high integration and small volume, and can effectively and quickly monitor the turbidity parameters of the liquid to be tested. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 Schematic top view of the optoelectronic integrated chip in the gallium nitride optoelectronic integrated turbidity sensor using visible light signals of the present invention.

[0042] Figure 2 Schematic diagram of the optoelectronic integrated chip in the gallium nitride optoelectronic integrated turbidity sensor using visible light signals of the present invention.

[0043] Figure 3 This is a diagram of the internal structure of the ultra-thin cavity of a gallium nitride optoelectronic integrated turbidity sensor that utilizes visible light signals.

[0044] Figure 4 Cross-sectional view of a GaN optoelectronic integrated turbidity sensor utilizing visible light signals.

[0045] Figure 5 The figure is a flow chart of the preparation process of the gallium nitride optoelectronic integrated turbidity sensor using visible light signals of the present invention.

[0046] Figure 6 Schematic diagram of the working process of the GaN photoelectric integrated turbidity sensor using visible light signals.

[0047] Among them, 1 is the positive electrode of the micro LED device, 2 is the positive electrode of the photodetector, 3 is the negative electrode of the micro LED device, 4 is the negative electrode of the photodetector, 5 is the silicon substrate wafer, 6 is the circuit board, 7 is the PDMS microfluidic channel, 8 is the internal electroplated high-reflectivity mirror, 9 is the liquid to be tested, 10 is the inlet of the liquid to be tested, and 11 is the liquid outlet. DETAILED DESCRIPTION

[0048] The technical solution of the present invention is further described in detail below with reference to the accompanying drawings:

[0049] like Figure 1-4 As shown, the present invention designs a gallium nitride optoelectronic integrated turbidity sensor that utilizes visible light signals. This gallium nitride optoelectronic integrated turbidity sensor utilizes a silicon substrate nitride wafer as a carrier, comprising a silicon substrate layer 5 and a nitride epitaxial layer. A micro-LED device (light source) and a photodetector are disposed on the nitride epitaxial layer. The nitride epitaxial layer is provided with a positive electrode 1 for the micro-LED device, a negative electrode 3 for the micro-LED device, a positive electrode 2 for the photodetector, and a negative electrode 4 for the photodetector. Each of the micro-LED device's negative electrode 3, positive electrode 2, and negative electrode 4 are ring-shaped. The silicon substrate layer is wire-connected and bonded to a circuit board 6. After waterproof packaging, the sensor is integrated with a transparent, thin liquid container with a high-reflectivity mirror. Nitride materials are chemically stable, have a wide bandgap, and exhibit excellent optoelectronic and mechanical properties. Gallium nitride is a representative third-generation semiconductor material. The band gap of gallium nitride material is 3.4eV, and it can form a ternary or quaternary solid solution alloy system with indium nitride (band gap is 1.9eV) and aluminum nitride (band gap is 6.2eV). Its corresponding direct band gap wavelength covers the region from red light to ultraviolet light, and can be used as the main material for optoelectronic devices such as visible light sources and photodetectors.

[0050] In a specific application scenario, a GaN optoelectronic integrated turbidity sensor utilizing visible light signals incorporates an optoelectronic chip that integrates a micro-LED device for emitting visible light signals and a photodetector for receiving light signals. The liquid to be measured is introduced into a thin, transparent liquid container. A positive voltage visible light signal is applied to the optoelectronic chip's micro-LED device. The visible light signal propagates through the liquid to be measured. After reflection from the highly reflective mirror surface inside the thin, transparent liquid container, it is modulated by the liquid's turbidity and enters the photodetector, where it is converted into a photocurrent. The photocurrent value can be used to monitor the turbidity of the liquid to be measured, thus enabling the GaN optoelectronic integrated chip to be used to construct a turbidity sensor, improving performance and efficiency. After testing, the measured liquid is discarded. The thin, transparent liquid container of the turbidity sensor can be cleaned using ultrasonic methods. The specific steps are as follows: First, hot immersion or spray cleaning softens, separates, and dissolves contaminants within the turbidity sensor, reducing the load on subsequent cleaning steps. The second step is ultrasonic cleaning: The intense cavitation and vibration generated by ultrasound removes dirt from the inner and outer surfaces of the turbidity sensor, while also breaking down and emulsifying greasy dirt. The third step is ultrasonic rinsing: The turbidity sensor is immersed in clean water and ultrasonic waves are used to clean away dirt stuck to the edges, corners, and crevices of the sensor. This completes the cleaning of the turbidity sensor and prepares it for the next use.

[0051] like Figure 5 A gallium nitride optoelectronic integrated turbidity sensor using visible light signals and a manufacturing method thereof are shown, comprising the following specific steps:

[0052] Step (1) using PECVD (plasma enhanced chemical vapor deposition) technology to evaporate a layer of silicon dioxide as a hard mask on the upper surface of the silicon substrate nitride wafer;

[0053] Step (2) using photolithography technology to spin-coat a photoresist on the surface of the hard mask to define the pattern structure of the micro LED device serving as the visible light signal light source and the photodetector receiving the visible light signal, and using reactive ion etching technology to transfer the pattern on the photoresist layer to the hard mask layer;

[0054] Step (3) using the III-V material inductively coupled plasma etching technology, based on the pattern structure on the silicon dioxide hard mask, etching away the P-type GaN layer and the multi-quantum well structure to expose the n-type GaN;

[0055] Step (4) Spin-coating photoresist on the top nitride surface of the silicon substrate nitride wafer, performing optical lithography to define the pattern structure of the isolation groove, and using III-V material inductively coupled plasma etching technology to etch through the entire nitride epitaxial layer to the top surface of the silicon substrate to achieve electrical isolation between each micro LED device and the photodetector;

[0056] Step (5) performing photolithography on the top nitride surface of the silicon substrate nitride wafer to define the pattern structure of the positive and negative electrodes of the micro LED device and the photodetector, and depositing a nickel / gold composite metal layer using electron beam evaporation technology;

[0057] Step (6) using an organic reagent, acetone, to peel off the nickel / gold composite metal layer deposited on the surface of the photoresist in an ultrasonic cleaning environment to obtain positive and negative electrodes of the micro LED device and the photodetector;

[0058] Step (7) bonding the lower surface of the silicon substrate nitride wafer, i.e., the silicon substrate surface, to the circuit board to form a whole, and connecting the positive and negative electrodes of the micro LED device and the photodetector to the electrodes on the circuit board by wires;

[0059] Step (8) waterproof packaging the above whole with PDMS material to produce a gallium nitride optoelectronic integrated chip for turbidity sensor.

[0060] The waterproof packaging using PDMS material includes the following steps:

[0061] Step (9) performs a glue preparation operation, dividing the PDMS glue into glue A and glue B, and mixing glue A and glue B in a ratio of 10:1, with the mass of glue A being 25-30 grams and the mass of glue B being 2.5-3 grams. Glue A and glue B are mixed evenly until the mixed glue is milky white overall;

[0062] Step (10) is to perform defoaming treatment. The mixed PDMS glue is placed in a vacuum drying oven and kept under vacuum for half an hour until the bubbles inside the mixed PDMS glue are completely eliminated. The defoamed PDMS glue is placed in an environment of 4 degrees Celsius and prepared for molding;

[0063] Step (11) Molding. Use tin foil to make a mold for the GaN optoelectronic integrated chip, pour the mixed PDMS glue into the container, and place it in a vacuum drying oven for defoaming and pre-curing;

[0064] Step (12) baking in an oven at 65°C for 3 hours;

[0065] Step (13) Cleaning and drying. Rinse the GaN optoelectronic integrated chip coated with PDMS material with alcohol and pure water, blow away the remaining liquid with compressed air, and place the GaN optoelectronic integrated chip coated with PDMS material in an oven for drying;

[0066] Step (14) uses a micro-drill to drill holes in the PDMS material on the back of the gallium nitride optoelectronic integrated chip that has been waterproofly encapsulated and coated with the PDMS material, leaving space for electrical connection to power the chip.

[0067] The preparation of an ultra-thin liquid container with a highly reflective mirror includes the following steps:

[0068] Step (15) ABS plastic is a terpolymer of acrylonitrile (A), butadiene (B), and styrene (S). ABS material is used and dried. Before processing, it is dried in an oven at 80-85°C for 24 hours or in a drying hopper at 80°C for 1-2 hours.

[0069] Step (16) melting the dried ABS material at a temperature of 210-280°C;

[0070] Step (17) Take a symmetrical two-part mold, maintain the mold temperature at 40-80°C, select a standard injection molding machine to perform injection molding at an injection pressure of 90-150 MPa, use a time-switching pressure-holding method, and use the injection time to adjust the defects of the product to produce an ultra-thin liquid container divided into two parts. The structure of the container is a rectangular cavity with liquid inlet and outlet holes at both ends. The internal dimensions of the cavity are 20 mm * 50 mm * 100 mm, the internal diameter of the liquid inlet and outlet holes is 10 mm, the length is 15 mm, and the thickness of the ABS cavity is 2 mm;

[0071] In step (18), the injection molded product is cooled and the cooling time is adjusted to 18 seconds, which can effectively prevent the top white defect. After cooling, an ultra-thin liquid container divided into two parts is produced.

[0072] The steps of preparing a high reflectivity mirror by electroplating chromium metal on the inner side of an ultra-thin cavity include the following:

[0073] Step (19) Degreasing the cavity of the ultra-thin container using a degreasing agent at a temperature of 70°C for 5 minutes. Roughening the plastic surface inside the cavity using a chemical etchant to change the surface from hydrophobic to hydrophilic at a temperature of 60°C for 10 minutes.

[0074] Step (20) After roughening, the plastic surface inside the cavity is sensitized using a sensitizer, stannous chloride (SnCl2) solution. Activation treatment is performed using a silver nitrate solution to cause an oxidation-reduction reaction between the stannous chloride and the silver nitrate, thereby reducing and depositing a silver film on the surface.

[0075] Step (21) performs alkaline chemical copper plating to continuously plate a copper film on the silver film through an oxidation-reduction reaction to enhance its conductivity in a subsequent chromium electroplating process;

[0076] Step (22) performs a chromium electroplating process to obtain a cavity of an ultra-thin liquid container with two inner surfaces having high reflectivity mirrors;

[0077] Step (23) bonding the gallium nitride optoelectronic integrated chip for the turbidity sensor manufactured in step (8) to the center position inside the ultra-thin sensor cavity with a high reflective mirror of any one petal manufactured in step (22);

[0078] Step (24) uses adhesive such as ABS seam glue to bond the two cavity petals to make a gallium nitride optoelectronic integrated turbidity sensor using visible light signals.

[0079] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person familiar with the technology can understand and think of any changes or replacements within the technical scope disclosed by the present invention, which should be included in the scope of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A method for preparing a gallium nitride optoelectronic integrated turbidity sensor using visible light signals, characterized in that: The following steps are involved: Step (1) using PECVD technology to deposit a layer of silicon dioxide as a hard mask on the upper surface of the silicon substrate nitride wafer; Step (2) using photolithography technology to spin-coat a photoresist on the surface of the hard mask to define the pattern structure of the micro LED device serving as the visible light signal light source and the photodetector receiving the visible light signal, and using reactive ion etching technology to transfer the pattern on the photoresist layer to the hard mask layer; Step (3) using the III-V material inductively coupled plasma etching technology, based on the pattern structure on the silicon dioxide hard mask, etching away the P-type GaN layer and the multi-quantum well structure to expose the n-type GaN; Step (4) Spin-coating photoresist on the top nitride surface of the silicon substrate nitride wafer, performing optical lithography to define the pattern structure of the isolation groove, and using III-V material inductively coupled plasma etching technology to etch through the entire nitride epitaxial layer to the top surface of the silicon substrate to achieve electrical isolation between each micro LED device and the photodetector; Step (5) performing photolithography on the top nitride surface of the silicon substrate nitride wafer to define the pattern structure of the positive and negative electrodes of the micro LED device and the photodetector, and depositing a nickel / gold composite metal layer using electron beam evaporation technology; Step (6) using an organic reagent, acetone, to peel off the nickel / gold composite metal layer deposited on the surface of the photoresist in an ultrasonic cleaning environment to obtain positive and negative electrodes of the micro LED device and the photodetector; Step (7) bonding the lower surface of the silicon substrate nitride wafer, i.e., the silicon substrate surface, to the circuit board to form a whole, and connecting the positive and negative electrodes of the micro LED device and the photodetector to the electrodes on the circuit board by wires; Step (8) waterproof packaging the whole with PDMS material to produce a gallium nitride optoelectronic integrated chip for turbidity sensor; Step (9) packaging the gallium nitride optoelectronic integrated chip; Step (10) preparing a liquid container, and electroplating chromium metal on the inner wall of the liquid container to prepare a high-reflectivity mirror surface; Step (11) mounts the packaged gallium nitride optoelectronic integrated chip on the inner wall of the liquid container to obtain the gallium nitride optoelectronic integrated turbidity sensor.

2. The preparation method according to claim 1, characterized in that Step (9) specifically includes: Step (9-1) performs a glue preparation operation, dividing the PDMS glue into glue A and glue B, and mixing glue A and glue B evenly until the mixed glue is milky white overall; Step (9-2) performs defoaming treatment; the mixed PDMS glue is placed in a vacuum drying oven and kept under vacuum until the bubbles inside the mixed PDMS glue are completely eliminated; the defoamed PDMS glue is ready for molding; Step (9-3) Molding: Use tin foil to make a mold for encapsulating the gallium nitride optoelectronic integrated chip, pour the mixed PDMS glue into the container, and place it in a vacuum drying oven for defoaming and pre-curing; Step (9-4) drying in an oven; Step (9-5) cleaning and drying: rinse the GaN optoelectronic integrated chip coated with PDMS material with alcohol and purified water, blow away the remaining liquid with compressed air, and place the GaN optoelectronic integrated chip coated with PDMS material in an oven for drying; In step (9-6), a micro-drill is used to drill holes in the PDMS material on the back of the GaN optoelectronic integrated chip that has been waterproofed and coated with PDMS material, leaving space for electrical connection to the chip to complete the package.

3. The preparation method according to claim 1, characterized in that The preparation of the liquid container in step (10) is specifically as follows: Step (10-1) uses ABS material and performs drying treatment, and then dries it before processing; Step (10-2) melting the dried ABS material at high temperature; Step (10-3) uses a symmetrical two-part mold and a standard injection molding machine for injection molding. A time-switched pressure-holding method is used, and the injection time is used to adjust the defects of the product to produce an ultra-thin liquid container divided into two parts. The structure of the container is a rectangular parallelepiped cavity with liquid inlet and outlet holes at both ends. In step (10-4), the injection molded product is cooled to form an ultra-thin liquid container divided into two parts.

4. The preparation method according to claim 1, characterized in that The preparation of the high reflectivity mirror in step (10) specifically includes: Step (10-5) using a degreasing agent to degrease the cavity of the manufactured ultra-thin container, and using a chemical etching agent to roughen the plastic surface inside the cavity, so that the surface changes from hydrophobic to hydrophilic; After the roughening step (10-6), the plastic surface inside the cavity is sensitized with a sensitizer, a stannous chloride solution, and activated with a silver nitrate solution to cause an oxidation-reduction reaction between the stannous chloride and the silver nitrate, thereby reducing and depositing a silver film on the surface; Step (10-7) is to perform alkaline chemical copper plating to further plate a copper film on the silver film through an oxidation-reduction reaction to enhance its conductivity in the subsequent chromium electroplating process; In step (10-8), a chromium electroplating process is performed to obtain a cavity of an ultra-thin liquid container with two inner surfaces having high reflectivity mirrors.

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