High-quality Micro-LED full-color display device and its fabrication method based on microfluidics technology

Abstract

This invention discloses a high-quality Micro-LED full-color display device and its fabrication method based on microfluidic technology. A patterned metal layer is formed on a transparent substrate. The patterned metal layer has light-transmitting openings arranged in an array. The arrayed light-transmitting metal layer is used as a quantum dot deposition area. Red and green quantum dots are filled into different arrays using microfluidic chip technology to serve as red and green sub-pixel color conversion layers. These layers are then bonded to blue Micro-LEDs to fabricate a Micro-LED full-color display device. The metal layer between the sub-pixels is made of opaque material. Red, green, and blue light between the sub-pixels can only be transmitted from the preset array area, reducing crosstalk between light emitted by sub-pixels of the same color and different colors, and improving the light quality of the Micro-LED device.

Description

Technical Field

[0001] This invention belongs to the field of quantum dot color conversion display technology, specifically relating to a high-quality Micro-LED full-color display device based on microfluidic technology and its fabrication method. Background Technology

[0002] Micro-LED display is a rapidly developing display technology in recent years, characterized by low power consumption, fast response, long lifespan, and wide color gamut. It can be applied in virtual / augmented reality, visible light communication, automotive displays, wearable devices, and backlight units in liquid crystal displays. The primary goal in display applications is full-color display. Currently, the mainstream methods include direct-color (red, green, blue) display technology and using ultraviolet or blue Micro-LEDs as excitation sources to excite the quantum dot array in the color conversion layer to achieve full-color display.

[0003] Currently, the main methods for preparing quantum dot color conversion layers include: ① Using inkjet printing technology to deposit quantum dots on pre-deposited patterned areas to achieve the color conversion layer requirement. However, the solution is prone to the coffee ring effect, affecting display performance and nozzle clogging, and the preparation speed is slow. ② Photolithography to prepare the color conversion layer. In this method, the solvents used in the photolithography process, including photoresist, developer, and thickener, can damage the quantum dot solution, resulting in low light extraction efficiency, poor quality, short lifespan, and high material cost. ③ Nanoimprint technology can achieve high-resolution micro-LED patterning, but this method has disadvantages such as contact contamination, difficulty in alignment, and difficulty in peeling off the nanoimprint primer.

[0004] In recent years, the method of preparing color conversion layers using microfluidics has received widespread attention from academia and industry due to its advantages such as low preparation cost and high material utilization. The method of preparing color conversion layers using microfluidics requires fabricating the color conversion layer on the device surface or substrate. The uniform distribution of quantum dot particles in the color conversion layer has a significant impact on the light extraction efficiency of the array excitation light source and the color conversion efficiency of the quantum dots, which in turn significantly affects the overall performance of Micro-LED full-color display devices. Furthermore, the simultaneous emission of red, green, and blue light from the photoexcited quantum dot pattern can easily lead to light crosstalk, affecting the light quality of the full-color display and reducing contrast. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by using an array of transparent metal layers as quantum dot deposition areas. It then uses microfluidic chip technology to fill different arrays with red and green quantum dots as red and green sub-pixel color conversion layers, which are then bonded to blue Micro-LEDs to prepare a high-quality Micro-LED full-color display device with low light crosstalk.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for fabricating a high-quality Micro-LED full-color display device based on microfluidic technology includes the following steps:

[0008] 1) A patterned metal layer is formed on a transparent substrate, wherein the patterned metal layer has a plurality of light-transmitting openings arranged in an array at intervals;

[0009] 2) Fabricate a microchannel device, wherein the microchannel device has a plurality of microchannels spaced apart, and each microchannel has an inlet and an outlet;

[0010] 3) The microchannel device is bonded to the patterned metal layer of the transparent substrate. After bonding, each microchannel is connected to multiple light-transmitting openings.

[0011] 4) Inject the red quantum dot solution and the green quantum dot solution into different microchannels until the quantum dot solution fills the microchannels and deposits in the corresponding light-transmitting openings;

[0012] 5) Excess quantum dot solution is removed by purging the microchannel with inert gas to obtain a quantum dot pattern located within the light-transmitting opening;

[0013] 6) The microchannel device is stripped and dried to obtain a quantum dot color conversion layer embedded in a patterned metal layer;

[0014] 7) Deposit a DBR layer covering the region where the quantum dot color conversion layer is located;

[0015] 8) Bond the transparent substrate to the blue Micro-LED chip array so that the chip units of the Micro-LED chip array correspond one-to-one with the light-transmitting openings of the patterned metal layer to obtain a Micro-LED full-color display device.

[0016] Optionally, the patterned metal layer is made of an opaque metal such as Cr, Al, Ti or Cu, and has a thickness of 2 to 5 micrometers.

[0017] Optionally, the method for forming the patterned metal layer is as follows: depositing a metal layer on the transparent substrate, coating the metal layer with photoresist, preparing a pattern of photoresist using photolithography, etching the metal layer using the photoresist pattern as a mask until the transparent substrate is exposed, and stripping the photoresist.

[0018] Optionally, the method for forming the patterned metal layer is as follows: coating photoresist on the transparent substrate, preparing a photoresist pattern using photolithography, depositing metal using the photoresist pattern as a mask, and then stripping the photoresist.

[0019] Optionally, the metal is deposited using magnetron sputtering PVD, electron beam evaporation, or thermal evaporation processes.

[0020] Optionally, in step 5), the pressure of the inert gas introduced is 10-400 mbar.

[0021] Optionally, the DBR layer comprises alternating stacked titanium dioxide and silicon dioxide layers, with a stacking period of 10.5-20.5 cycles. The maximum reflectivity in the blue light emission band is calculated based on different thicknesses of the two layers. Different thicknesses and stacking periods ensure a reflectivity of over 90% in the blue light band.

[0022] Optionally, the thickness of the titanium dioxide layer is 30-50 nm, and the thickness of the silicon dioxide layer is 50-80 nm.

[0023] The high-quality Micro-LED full-color display device prepared by the above preparation method includes a blue Micro-LED chip array and a transparent substrate bonded to the blue Micro-LED chip array. The transparent substrate has a patterned metal layer on its surface. The patterned metal layer has light-transmitting openings that correspond one-to-one with the chip units of the blue Micro-LED chip array. A quantum dot color conversion layer is provided in part of the light-transmitting openings. A DBR layer is covered above the area where the quantum dot color conversion layer is located.

[0024] The beneficial effects of this invention are as follows:

[0025] 1) Direct deposition of quantum dots within the openings of a metal layer array is a simple, cost-effective process with controllable thickness. Using a metal layer with a transparent opening array as the quantum dot deposition region eliminates the need for any pretreatment of the transparent substrate, reducing device fabrication costs. This method is suitable for both rigid substrates like glass and flexible polymer substrates. Excess liquid is drained after a certain deposition time, ensuring more complete quantum dot deposition within the metal layer array openings. The quantum dot thickness can be controlled by adjusting the deposition time.

[0026] 2) The opaque metal portion reduces light crosstalk between sub-pixels, improving the light quality of Micro-LED full-color displays. Red and green quantum dots deposited in the light-transmitting areas of the metal layer array can be excited by the blue light emitted from the bottom blue Micro-LED chip, emitting red and green light respectively. The un-deposited quantum dot array emits blue light, achieving full-color display. Simultaneously, the metal layer between sub-pixels is opaque, ensuring that red, green, and blue light from the sub-pixels can only be transmitted through the pre-defined array area, reducing crosstalk between sub-pixels of the same and different colors and improving the light quality of the Micro-LED device. Attached Figure Description

[0027] Figures 1 to 12 This is a schematic diagram of each step in the preparation method of Example 1, wherein... Figure 12This is a schematic diagram of the structure of the high-quality Micro-LED full-color display device obtained in Example 1. Detailed Implementation

[0028] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments. The accompanying drawings are merely illustrative to facilitate understanding of the invention, and their specific proportions can be adjusted according to design requirements. The vertical relationships of relative elements and the definitions of front / back in the graphics described herein should be understood by those skilled in the art to refer to the relative positions of the components; therefore, they can all be flipped to present the same component, and all of this should fall within the scope disclosed in this specification.

[0029] Example 1

[0030] refer to Figures 1 to 12 The fabrication method of the high-quality Micro-LED full-color display device based on microfluidic technology in this embodiment is as follows:

[0031] 1. Glass substrate cleaning. Using a glass substrate as the transparent base, immerse the transparent glass substrate in an acetone solution and sonicate it for 20 minutes at 100% power. Then, immerse it in an alcohol solution and sonicate it for another 20 minutes. Next, immerse it in a piranha solution (H₂SO₄:H₂O₂:H₂O = 5:1:1) at 80°C for 30 minutes. Rinse the surface with deionized water and dry it with nitrogen. Alternatively, the transparent substrate can also be a flexible polymer substrate or other transparent substrates with composite structures or composite layers.

[0032] 2. Deposition of an opaque chromium layer. A 2-5 micrometer metal layer is deposited on the glass substrate 1 using methods such as magnetron sputtering PVD, electron beam evaporation, or thermal evaporation. This technical solution uses magnetron sputtering to deposit the chromium layer 2, with the RF power set to 60W, argon flow rate at 120 / 60 sccm, gas pressure at 5 Pa, and pre-sputtering time set to 20 s.

[0033] The formal sputtering time was 1.5 hours, resulting in the deposition of a 3-micrometer-thick opaque chromium layer. The morphology after deposition is as follows: Figure 1 As shown.

[0034] 3. Photolithography to form a patterned mask. Photoresist 3 is spin-coated onto the surface of the chromium layer 2 using a spin coater. The mask then undergoes pre-baking, exposure, reverse baking, overexposure, and development to form a patterned photoresist mask. The patterned photoresist mask pattern is shown below. Figure 2 As shown.

[0035] 4. Preparation of etching solution. The chromium layer etching solution mainly consists of 200g of cerium ammonium nitrate, 35mL of acetic acid solution with a concentration of 98%, and 1000mL of deionized water, which are then added to ensure complete dissolution.

[0036] 5. Chromium layer etching. The unmasked areas of the patterned photoresist obtained in step 3 are immersed in the chromium etching solution prepared in step 4 until the chromium layer in the unmasked patterned areas is completely removed. The chromium layer at the bottom of the photoresist-masked areas is not etched. The etched areas form an array of light-transmitting openings 21 on the exposed glass substrate. For example... Figure 3 As shown.

[0037] 6. Photoresist Removal. The etched substrate is placed in an acetone solution and sonicated for 20 minutes at 100% power. It is then placed in an alcohol solution and sonicated for 10 minutes, followed by rinsing with deionized water for 2 minutes to ensure complete removal of the photoresist from the chromium layer. After removal, an array of light-transmitting openings 21 is formed on the chromium layer. The height difference between the bottom of the light-transmitting opening 21 and the surface of the chromium layer 2 is the thickness of the chromium layer; that is, the depth of the light-transmitting opening 21 is equal to the thickness of the chromium layer. Figure 4 As shown.

[0038] 7. Fabrication of Microfluidic Channel Devices. Microfluidic devices are fabricated using methods such as hot pressing, molding, and injection molding. This technical solution uses a transparent microchannel device 4 as an example for illustration. Figure 5 As shown, the microchannel device includes an inlet / outlet.

[0039] The outlet and microchannel 41, which can be injected with different quantum dot solutions respectively, are also included. The microchannel 41 is a strip-shaped groove structure with an inlet and an outlet at both ends. The width of the microchannel 41 can be greater than or equal to the width of the light-transmitting opening 21 in step 6. The microchannel is mainly used to pass red and green quantum dot solutions into the light-transmitting opening areas in the corresponding chromium layers.

[0040] 8. The microchannel device 4 is bonded to the glass substrate 1. The microchannels to be injected with red and green light are precisely bonded to the light-transmitting openings of the quantum dots to be deposited, so that each microchannel corresponds to a row or column of light-transmitting openings 21 for conduction.

[0041] 9. Microchannel quantum dot solution injection. Red quantum dot solution R and green quantum dot solution G are injected into two independent microchannels 41 using a pressure injector and flow controller. Excess quantum dot solution is discharged from the outlet for reuse, ensuring the entire microchannel is filled with quantum dot solution, and the corresponding light-transmitting opening 21 is also filled with quantum dot solution. Figure 6 As shown. Once the quantum dot solution fills the entire microchannel, allow it to stand to allow the quantum dot particles to fully deposit within the light-transmitting opening 21.

[0042] 10. Discharge of quantum dot solution. An inert gas (such as nitrogen or argon) at a pressure of 60 mbar is introduced into the inlet to discharge the quantum dot solution from the chromium layer surface in microchannel 41 without affecting the quantum dot solution deposited within the light-transmitting opening 21. Under appropriate gas pressure, the quantum dot solution can be uniformly deposited within the light-transmitting opening 21. Figure 7 As shown.

[0043] 11. Microchannel device 4 peeling. After excess quantum dot solution is drained from the microchannel, the microchannel device 4 is peeled off from the glass substrate 1. Red quantum dot solution R and green quantum dot solution G are uniformly deposited in the array of partially transparent openings 21 of the chromium layer, while no quantum dot solution is deposited in the array of partially transparent openings 21. Figure 8 As shown.

[0044] 12. Quantum dot deposition. After the solvent in the quantum dot solution evaporates by allowing it to stand naturally in the air for 24 hours or by baking at a low temperature of 40°C, a quantum dot color conversion layer is formed in the partially transparent opening, including red quantum dots R and green quantum dots G.

[0045] like Figure 9 As shown.

[0046] 13. Deposition of a Dip-Bracket Mirror (DBR). A DBR layer 5 is formed on the surface of a substrate with a quantum dot pattern. Specifically, two periods of 48nm thick titanium dioxide and 77nm thick silicon dioxide layers are alternately deposited on its surface using atomic layer deposition to form a layer that prevents blue light leakage, improves the conversion efficiency of the quantum dots, and also serves as an isolation and protective layer. Figure 10 As shown, the light-transmitting opening region without quantum dots does not have a DBR layer deposited on its surface.

[0047] 14. Fabrication of Blue Micro-LED Chip Array. Using transparent sapphire as a substrate, epitaxial thin films were fabricated sequentially via MOCVD, followed by typical fabrication processes including cleaning, photolithography, resist coating, development, etching, sputtering, evaporation, and bonding to prepare a blue Micro-LED chip array 6. The array's individual chips emit blue light with a peak wavelength of 450nm.

[0048] Micro-LED chip array structure such as Figure 11 As shown.

[0049] 15. The Micro-LED chip array 6 is bonded to the glass substrate 1 to fabricate a color-conversion Micro-LED full-color display device. For example... Figure 12As shown, a high-precision bonding machine utilizes the light transmittance of the blue light emitting area on the chromium layer as a benchmark (i.e., the light-transmitting opening 21 without quantum dots deposited). The Micro-LED chip unit 61 is then matched one-to-one with the light-transmitting opening 21, corresponding to the sub-pixels of the quantum dot deposition area and the blue light-transmitting area in the color conversion layer. The red and green quantum dots deposited in the light-transmitting area of ​​the metal layer array can be excited by the blue light emitted by the bottom blue Micro-LED chip to emit red and green light respectively, while the transparent metal array without quantum dots emits blue light, achieving full-color display. In areas shielded by the chromium layer 2, blue light cannot pass through the chromium layer to excite the residual quantum dot solution on the chromium layer surface.

[0050] refer to Figure 12 The resulting high-quality Micro-LED full-color display device includes a blue Micro-LED chip array 6 and a glass substrate 1 bonded to the blue Micro-LED chip array 6. A patterned metal layer 2 is provided on the surface of the glass substrate 1. The patterned metal layer 2 has light-transmitting openings 21 that correspond one-to-one with the chip units 61 of the blue Micro-LED chip array. A quantum dot color conversion layer, including red quantum dots R and green quantum dots G, is provided in part of the light-transmitting openings 21. A DBR layer 5 is covered above the area where the quantum dot color conversion layer is located.

[0051] In addition, there are conventional steps such as packaging.

[0052] The technology of this invention mainly consists of four parts:

[0053] I. Fabrication of an arrayed transparent metal layer. There are two main methods: (1) Deposit a metal layer on a transparent substrate, then use photolithography to prepare a photoresist pattern, and use this as a mask to etch the metal to expose the transparent substrate, thus obtaining an arrayed transparent metal layer. (2) Spin-coat photoresist on a transparent substrate, prepare an array pattern of photoresist through photolithography, then deposit metal, and further strip the photoresist to obtain an arrayed transparent metal layer.

[0054] II. Deposition of Quantum Dots in an Array of Transparent Metal Layers. The pattern of microchannels is aligned with the array of transparent metal layers, ensuring that red and green quantum dot solutions are injected into the pre-designed array of transparent metal layers through the microchannels. A syringe pump is used to inject the quantum dot solution into the microchannels, filling them completely. Once the quantum dot solution is uniformly deposited within the array of transparent metal layers, the excess solution is drained from the microchannels for reuse, and the microchannels are then peeled off. Due to the depth of the metal layer array, the quantum dots within the array cannot be drained; they remain until the solvent evaporates, forming the quantum dot pattern.

[0055] III. Fabrication of the Bragg Mirror (DBR). A number of titanium dioxide and silicon dioxide thin films with quantum dot-filled metal layers are deposited using atomic layer deposition to serve as a Bragg mirror. This prevents blue light leakage after bonding with the blue Micro-LED chip, reflecting excess blue light back into the quantum dot pattern, thus improving the color conversion efficiency of the quantum dots. Simultaneously, it can also serve as an isolation and protective layer.

[0056] IV. Bonding the color conversion layer to blue Micro-LEDs. A quantum dot color conversion Micro-LED full-color display device is fabricated by mapping the blue Micro-LED chip to the pixel array and the transparent array without quantum dots on the color conversion substrate. Using the metal between the sub-pixels as a barrier layer avoids light crosstalk between sub-pixels, thus improving light quality.

[0057] The patterned metal layer of this invention can be used to define the light transmission area to avoid light crosstalk. Due to its certain thickness, it can also be combined with microfluidic technology to define the quantum dot deposition area, which improves the quality, improves the process accuracy, simplifies the steps, and improves the manufacturing efficiency, thus having outstanding features.

[0058] The above embodiments are only used to further illustrate a high-quality Micro-LED full-color display device and its preparation method based on microfluidic technology according to the present invention. However, the present invention is not limited to the embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A method for fabricating a high-quality Micro-LED full-color display device based on microfluidic technology, characterized in that, Includes the following steps: 1) A patterned metal layer is formed on a transparent substrate, wherein the material of the patterned metal layer is Cr, Al, Ti or Cu, and the thickness is 2 to 5 micrometers, and the patterned metal layer has a plurality of light-transmitting openings arranged in an array at intervals; 2) Fabrication of a microchannel device, wherein the microchannel device has a plurality of microchannels spaced apart, and each microchannel has a liquid inlet and a liquid outlet; 3) The microchannel device is bonded to the patterned metal layer of the transparent substrate. After bonding, each microchannel is connected to multiple light-transmitting openings. 4) Inject the red quantum dot solution and the green quantum dot solution into different microchannels until the quantum dot solution fills the microchannels and deposits in the corresponding light-transmitting openings; 5) Excess quantum dot solution is removed by purging the microchannel with inert gas to obtain a quantum dot pattern located within the light-transmitting opening; 6) The microchannel device is peeled off and dried to obtain a quantum dot color conversion layer embedded in a patterned metal layer; 7) Deposit a DBR layer covering the region where the quantum dot color conversion layer is located; 8) Bond the transparent substrate to the blue Micro-LED chip array so that the chip units of the Micro-LED chip array correspond one-to-one with the light-transmitting openings of the patterned metal layer to obtain a Micro-LED full-color display device.

2. The preparation method according to claim 1, characterized in that: The method for forming the patterned metal layer is as follows: depositing a metal layer on the transparent substrate, coating the metal layer with photoresist, preparing a pattern of photoresist using photolithography, etching the metal layer using the photoresist pattern as a mask until the transparent substrate is exposed, and then peeling off the photoresist.

3. The preparation method according to claim 1, characterized in that: The method for forming the patterned metal layer is as follows: photoresist is coated on the transparent substrate, a pattern of photoresist is prepared using photolithography, metal is deposited using the photoresist pattern as a mask, and then the photoresist is stripped off.

4. The preparation method according to claim 2 or 3, characterized in that: The metal is deposited using magnetron sputtering PVD, electron beam evaporation, or thermal evaporation processes.

5. The preparation method according to claim 1, characterized in that: In step 5), the pressure of the inert gas introduced is 10-400 mbar.

6. The preparation method according to claim 1, characterized in that: The DBR layer comprises alternating stacked titanium dioxide and silicon dioxide layers, with a stacking period of 10.5-20.5 cycles.

7. The preparation method according to claim 6, characterized in that: The thickness of the titanium dioxide layer is 30-50 nm, and the thickness of the silicon dioxide layer is 50-80 nm.

8. A high-quality Micro-LED full-color display device prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The device includes a blue Micro-LED chip array and a transparent substrate bonded to the blue Micro-LED chip array. The transparent substrate has a patterned metal layer on its surface. The patterned metal layer has light-transmitting openings that correspond one-to-one with the chip units of the blue Micro-LED chip array. A quantum dot color conversion layer is provided in some of the light-transmitting openings. A DBR layer is covered above the area where the quantum dot color conversion layer is located.

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