Design method of flip structure micro-led unit on gan homo-substrate, flip micro-led device

Abstract

This invention relates to the field of optoelectronic device design and manufacturing technology, specifically to a design method for a flip-chip Micro-LED unit on a GaN homogeneous substrate and a flip-chip Micro-LED device. The design method includes: growing an epitaxial structure on a GaN homogeneous substrate using MOCVD; subsequently fabricating a reflector cup structure on the GaN homogeneous substrate; bonding a microlens with a free-form surface to the rim of the reflector cup; fabricating the light-emitting surface of the microlens as an even-order aspherical surface; optimizing the surface shape parameters of the light-emitting surface using a collimation evaluation function to obtain a basic quadratic surface shape; sequentially optimizing the 2n-order aspherical parameters in batches to obtain even-order aspherical microlenses; and finally obtaining a flip-chip Micro-LED unit on a GaN homogeneous substrate. By integrating the reflector cup and free-form surface structure on the GaN homogeneous substrate, the beam collimation and light extraction efficiency of the flip-chip Micro-LED device are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of display chip manufacturing technology, specifically to a flip-chip Micro-LED (Micro Light Emitting Diode) unit and flip-chip Micro-LED device on a GaN homogeneous substrate. Background Technology

[0002] Micro-LEDs are optoelectronic devices based on gallium nitride (GaN) semiconductor materials. As one of the core directions of next-generation display technologies, they are gradually becoming an important candidate display solution for future augmented reality, virtual reality, wearable devices, and automotive displays due to their advantages such as high brightness, high contrast, fast response speed, low power consumption, and the ability to achieve ultra-high pixel density. However, current mainstream GaN-based Micro-LEDs typically use sapphire substrates. Due to the significant disadvantages of sapphire substrates in terms of lattice constant and thermal conductivity, the devices are prone to wavelength drift, efficiency degradation, and heat accumulation under high brightness and high power density operating conditions, which seriously restricts the performance of the devices and the large-scale commercialization process.

[0003] In optical packaging, LED reflector cup packaging is a common structure. By arranging a high-reflectivity cup-shaped structure around the chip, it can enhance light extraction efficiency and control the light emission direction, and is widely used in high-power LEDs, lighting LEDs, and Micro-LED integrated applications. Freeform lenses, with their higher degrees of freedom, can more precisely control incident light from various angles. Combining LED reflectors with freeform lenses can fully leverage the synergistic advantages of both in light field control. Although existing patents disclose combined designs of reflectors and microlenses, none have effectively solved the defects caused by lattice mismatch at heterogeneous interfaces and differences in thermal expansion coefficients, and their light extraction efficiency, beam collimation, and uniformity still need improvement. In addition, traditional freeform surface design methods are complex and involve numerous formulas, which are not conducive to practical applications. Summary of the Invention

[0004] The purpose of this invention is to provide a flip-chip Micro-LED unit and a flip-chip Micro-LED device on a GaN homogeneous substrate. By integrating a reflector cup and a freeform surface on a GaN homogeneous substrate (GaN-on-GaN) and fabricating an epitaxial structure on the GaN homogeneous substrate, the luminous efficiency and device uniformity of the flip-chip Micro-LED device are improved.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a design method for a flip-chip Micro-LED unit on a GaN homogeneous substrate, comprising the following steps:

[0006] An epitaxial structure with a quantum well structure is grown by MOCVD on a GaN homogeneous substrate. From bottom to top, the epitaxial structure includes an n-GaN layer, a quantum well structure, and a p-GaN layer stacked sequentially.

[0007] Micro-nano structures are designed and fabricated on the GaN homogeneous substrate, the micro-nano structures including a reflector cup and a microlens with a free-form surface;

[0008] The reflective cup has its rim facing downwards, and the diameter of its rim is larger than the diameter of its bottom.

[0009] The microlens with a free-form surface is glued to the rim of the reflector cup to integrate the reflector cup and the microlens on the GaN homogeneous substrate;

[0010] A planar receiver is placed at a predetermined distance from the microlens on the side away from the reflector cup to receive illuminance and energy distribution;

[0011] The light-emitting surface of the microlens is set as a quadratic surface. The intermediate thickness, surface curvature, and surface coefficient of the microlens are used as optimization variables. Based on the emitted light illuminance and energy distribution received by the planar receiver, a collimation evaluation function is used as the evaluation function to perform the first round of optimization. The optimized size parameters corresponding to the basic surface shape with preliminary collimation effect are obtained. The optimized size parameters include optimized intermediate thickness, optimized surface curvature, and optimized surface coefficient.

[0012] The light-emitting surface is set as an even-order aspherical surface. The optimized size parameters and the evaluation function are kept unchanged. The second round of optimization is performed with the 2n-order aspherical surface parameters as the optimization variables to further collimate the beam.

[0013] The surface shape formula for the even-order aspherical surface is as follows:

[0014] ;

[0015] Where z is the sagitta of the surface, c is the curvature of the surface, k is the surface coefficient, r is the radial coordinate, x and y are the rectangular coordinates in the plane perpendicular to the optical axis, and n is a positive integer. The parameters are 2n-order aspherical surfaces;

[0016] Based on the optimization results, the optimized design parameters of the flip-chip Micro-LED unit on the GaN homogeneous substrate were determined.

[0017] Furthermore, the diameter of the microlens is not less than the diameter of the cup opening, to ensure that all the light reflected by the reflective cup passes through the microlens. During the first and second rounds of optimization, the refractive index of the microlens is limited to the range of 1-2.4.

[0018] Furthermore, the interior of the reflector cup is filled with optical adhesive that provides cushioning.

[0019] During the first and second rounds of optimization, the refractive index of the optical adhesive is not lower than that of the microlens, so that the refractive indices of the GaN homogeneous substrate, the optical adhesive, and the microlens that the light passes through on the propagation path gradually decrease.

[0020] Furthermore, the size of the GaN homogeneous substrate is controlled within the range of (10μm-100μm)×(10μm-10μm)×(10μm-500μm);

[0021] The height of the reflector cup is 0.7-0.95 times the thickness of the GaN homogeneous substrate.

[0022] Furthermore, the diameter of the cup opening of the reflector is set to 0.3-0.85 times the width of the GaN homogeneous substrate, and the diameter of the cup bottom is set to 0.3-0.8 times the diameter of the cup opening, so that the tilt angle of the sidewall of the reflector is controlled within the range of 84°-88°.

[0023] Furthermore, the GaN homogeneous substrate is etched to form a cup-shaped structure with the cup opening facing downward at a position relative to the epitaxial structure, and a metal reflective film is prepared on the sidewall of the cup-shaped structure.

[0024] Furthermore, during the first and second rounds of optimization, the emission angle of the flip-chip Micro-LED unit on the GaN homogeneous substrate is set to ±(40°-60°), and the emission angle distribution is set to a Lambertian distribution.

[0025] Furthermore, during the first and second rounds of optimization, the divergence angle of the flip-chip Micro-LED unit on the GaN homogeneous substrate reaches ±(16°-20°), and the light extraction efficiency is not less than 25%.

[0026] This application also provides a flip-chip Micro-LED device, which is designed and fabricated using the design method described in any one of claims 1-8.

[0027] Furthermore, the flip-chip Micro-LED device includes multiple flip-chip Micro-LED units on the GaN homogeneous substrate. Each flip-chip Micro-LED unit on the GaN homogeneous substrate includes one GaN homogeneous substrate. The epitaxial structure is disposed on the GaN homogeneous substrate. The epitaxial structure includes, from bottom to top, an n-GaN layer, a quantum well structure, and a p-GaN layer. Metal electrodes are respectively fabricated on the GaN homogeneous substrate and the epitaxial structure.

[0028] The beneficial effects of this invention are as follows: The design method of the flip-chip Micro-LED unit on the GaN homogeneous substrate provided in this application integrates a reflector cup and a freeform surface into the flip-chip Micro-LED unit on the GaN homogeneous substrate. Compared with sapphire heterogeneous substrates, this method has a lower dislocation density and fewer heterogeneous interface defects. At the same time, the reflector cup micro-nano structure is prepared using a thicker GaN homogeneous substrate. The reflector cup constrains the light path to achieve initial collimation of the emitted light. Then, the excellent modulation characteristics of the freeform surface are used to complete the secondary adjustment of the light, which significantly improves the beam collimation and light extraction efficiency of the flip-chip Micro-LED device. This enables the flip-chip Micro-LED device to meet the requirements of high-brightness display and effectively expands its application prospects in cutting-edge fields such as ultra-high-definition display and optical communication.

[0029] By setting the diameter of the microlens to be no less than the diameter of the cup opening, it is ensured that all the light beam reflected by the reflector cup passes through the microlens, thereby further improving the light extraction efficiency.

[0030] By filling the reflector with optical adhesive, a buffering effect is achieved, adjusting the light propagation path and reducing the total internal reflection angle when light exits the GaN substrate into the air, thereby effectively reducing light energy loss. By designing the refractive index of the optical adhesive to be no lower than that of the microlens, the refractive indices of the GaN substrate, optical adhesive, and microlens gradually decrease along the light propagation path. This allows the microlens to act as a secondary buffer, further adjusting the light propagation path while preventing total internal reflection when the beam reaches the microlens, significantly improving the device's light extraction efficiency.

[0031] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of a flip-chip Micro-LED unit on a GaN homogeneous substrate according to an embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of the overall structure of a 10×10 array of flip-chip Micro-LED units on a GaN homogeneous substrate according to an embodiment of the present invention.

[0034] Figure 3 This is an enlarged view of the epitaxial structure on a GaN homogeneous substrate shown in an embodiment of the present invention;

[0035] Figure 4This is a three-dimensional structural schematic diagram of the micro / nano structure unit on the GaN homogeneous substrate shown in Embodiment 1 of the present invention;

[0036] Figure 5 This is a light illuminance distribution diagram of a flip-chip Micro-LED unit on a single GaN homogeneous substrate as shown in Embodiment 1 of the present invention;

[0037] Figure 6 This is a two-dimensional Cartesian coordinate light intensity cross-section of a flip-chip Micro-LED unit on a single GaN homogeneous substrate as shown in Embodiment 1 of the present invention.

[0038] Figure 7 This is a two-dimensional polar coordinate cross-sectional view of the light intensity of a flip-chip Micro-LED unit on a single GaN homogeneous substrate as shown in Embodiment 1 of the present invention.

[0039] Figure 8 This is a light illuminance distribution diagram of the entire array shown in Embodiment 1 of the present invention;

[0040] Figure 9 This is a two-dimensional Cartesian cross-sectional view of the overall array intensity shown in Embodiment 1 of the present invention;

[0041] Figure 10 This is a two-dimensional polar coordinate light intensity cross-section of the entire array shown in Embodiment 1 of the present invention;

[0042] Figure label:

[0043] 1. GaN homogeneous substrate; 2. Epitaxial structure; 21. n-GaN layer; 22. Quantum well structure; 221. Buffer layer; 222. Quantum well; 223. AlGaN layer; 23. p-GaN layer; 3. Reflector cup; 4. Microlens; 5. Optical adhesive; 6. ITO layer; 71. p electrode; 71. n electrode. Detailed Implementation

[0044] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0045] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0046] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0047] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0048] A preferred embodiment of this application illustrates a design method for a flip-chip Micro-LED device on a composite GaN homogeneous substrate, comprising the following steps:

[0049] An epitaxial structure 2 with a quantum well structure 22 is grown by MOCVD on a GaN homogeneous substrate 1, such as... Figure 1 As shown, from bottom to top, the epitaxial structure 2 includes an n-GaN layer 21, a quantum well structure 22, and a p-GaN layer 23 stacked sequentially. A micro / nano structure is designed and fabricated on the GaN homogeneous substrate 1. This micro / nano structure includes a reflector cup 3 and a microlens 4 with a free-form surface. Specifically, the reflector cup 3 is constructed on the bottom surface of the GaN homogeneous substrate 1 at a position opposite to the epitaxial structure 2. The mouth of the reflector cup 3 faces downwards, and its diameter is larger than its bottom diameter, used to reflect light out of the reflector cup 3. A microlens 4 with a free-form surface is glued to the mouth of the reflector cup 3 to integrate the reflector cup 3 and the microlens 4 onto the GaN homogeneous substrate.

[0050] A planar receiver is placed at a predetermined distance behind the microlens to receive the illuminance and energy distribution of the light beam transmitted through the microlens. The light-emitting surface of the microlens is set as a quadratic surface. Using the thickness, curvature, and surface coefficient of the microlens as optimization variables, and based on the illuminance and energy distribution received by the planar receiver, a collimation evaluation function is used to optimize its surface parameters, resulting in optimized dimensional parameters corresponding to the basic surface shape with preliminary collimation effect. These optimized dimensional parameters include optimized intermediate thickness, optimized surface curvature, and optimized surface coefficient.

[0051] The light-emitting surface is set to an even-order aspherical surface. The optimized size parameters and the evaluation function are kept unchanged. The second round of optimization is performed using the 2n-order aspherical surface parameters as optimization variables to further collimate the beam.

[0052] The surface shape formula for the even-order aspherical surface is as follows:

[0053] ,

[0054] Where z is the sagitta of the surface, c is the curvature, k is the surface coefficient, r is the radial coordinate, x and y are the rectangular coordinates in the plane perpendicular to the optical axis, and n is a positive integer;

[0055] Based on the optimization results, the optimized design parameters of the flip-chip Micro-LED unit on the GaN homogeneous substrate were determined.

[0056] After designing the flip-chip Micro-LED unit on the GaN homogeneous substrate using the above design method, multiple qualified flip-chip Micro-LED units can be precisely fabricated based on the set and optimized parameters. Subsequently, these units are arranged into an array according to specific rules, thus successfully fabricating a flip-chip Micro-LED device.

[0057] The flip-chip Micro-LED unit on the GaN homogeneous substrate is patterned on the GaN homogeneous substrate, specifically by integrating a reflector cup and a freeform surface onto the GaN homogeneous substrate. An epitaxial structure is fabricated on the other side of the GaN homogeneous substrate, followed by a flip-chip bonding process. From a structural perspective, this flip-chip Micro-LED unit on the GaN homogeneous substrate uses a high-quality self-supporting GaN substrate as an epitaxial growth platform. First, an epitaxial structure is grown using MOCVD, then the flip-chip Micro-LED unit is fabricated on the GaN homogeneous substrate, and finally, a Micro-LED device is constructed. By transferring the Micro-LED structure to an n-GaN homogeneous epitaxial layer (GaN-on-GaN), the dislocation density of the Micro-LED device itself is significantly reduced, effectively eliminating lattice mismatch and thermal expansion coefficient differences at the heterogeneous interface. This alleviates the electric field shielding and redshift problems caused by the quantum confinement Stark effect in traditional structures, fundamentally improving luminous efficiency and device uniformity.

[0058] In this embodiment and some other embodiments, the size of the GaN homogeneous substrate is designed to be (10μm-100μm)×(10μm-100μm)×(10μm-500μm); and when constructing the reflector on the GaN homogeneous substrate, the height of the reflector is set to 0.7-0.95 times the thickness of the GaN homogeneous substrate.

[0059] By setting the diameter of the reflector's opening to be larger than its bottom diameter, total internal reflection of the light source can be maximized. After multiple reflections within the reflector, the light is reflected as completely as possible, significantly improving light extraction efficiency and reducing light loss within the device.

[0060] A microlens with a free-form surface is glued to the rim of the reflector cup, enabling precise refraction and focusing of light. When the light beam reflected from the reflector cup reaches the rim, it passes smoothly through the microlens. This fully leverages the synergistic advantages of the reflector cup and microlens in light field manipulation, precisely controlling the output angle to ensure the beam propagates in a predetermined direction and range, while further enhancing light extraction efficiency and providing the optical system with higher quality and more efficient light output.

[0061] A planar receiver is placed at a predetermined distance away from the reflector on the side of the microlens, i.e., a rectangular planar receiver is placed behind the microlens. Its main function is to efficiently receive the light signal transmitted after modulation by the microlens, thereby accurately measuring and visually presenting the illuminance and energy distribution of the transmitted light. This provides crucial data support for subsequent optimization of the microlens' surface shape. Based on this data, the optical parameters of the microlens are dynamically adjusted to gradually approach ideal optical performance. Furthermore, in this embodiment and some other embodiments, to ensure stable operation of the optical system within a reasonable operating range, the predetermined distance between the microlens and the receiver is controlled within the range of 150μm-300μm. This distance range is set based on a comprehensive consideration of factors such as optical system aberrations and light transmission efficiency, effectively balancing the relationship between optical performance and system compactness. In this embodiment and some other embodiments, the preferred size of the rectangular planar receiver is (250μm-450μm) × (250μm-450μm).

[0062] In the first round of optimization, the purpose of selecting the collimation evaluation function as the evaluation function is to make the outgoing light as accurate as possible to the normal direction of the receiving surface, and quickly obtain a basic surface shape with preliminary collimation effect, that is, a basic surface shape with good optical properties, so as to lay a solid foundation for subsequent more refined optimization.

[0063] The collimation evaluation function described above is the root mean square value of the angle between all ray directions and the normal direction of the rectangular receiver. The smaller this value, the better the light collimation effect. When the root mean square value reaches its minimum, a basic surface shape can be obtained. At this point, the intermediate thickness, surface curvature, and surface coefficient of the microlens are at their optimal values, and these values ​​remain unchanged in subsequent optimization processes.

[0064] The specific formula for the collimation evaluation function is as follows:

[0065] ;

[0066] in, Let be the angle between the i-th actual ray and the z-axis. The angle between the normal and the z-axis, where N is the actual number of rays.

[0067] During the first and second rounds of optimization, considering factors such as optical performance, manufacturing process, and cost, the edge thickness of the microlens is preferably limited to 1 μm. In this embodiment and some other embodiments, during the first and second rounds of optimization, the spot diameter of the flip-chip Micro-LED unit on the GaN homogeneous substrate is controlled within the range of 1 μm-20 μm, preferably within the range of 3 μm-8 μm, the emission angle is set to ±(40°-60°), and the emission angle distribution is set to a Lambertian distribution. In this embodiment and some other embodiments, the divergence angle of the flip-chip Micro-LED unit on the GaN homogeneous substrate can reach ±(16°-20°), and the light extraction efficiency can reach 25% or higher.

[0068] In one embodiment, the diameter of the reflector's rim is set to 0.3-0.85 times the width of the GaN homogeneous substrate, and the diameter of its bottom is set to 0.3-0.8 times the rim diameter. By setting these parameters, the tilt angle of the reflector's sidewall can be controlled within the range of 84°-88°, allowing light to be reflected as completely as possible at this sidewall, thereby significantly improving light extraction efficiency and effectively reducing light loss within the device.

[0069] In one embodiment, the diameter of the microlens is set to be no less than the diameter of the reflector cup's opening to ensure that all light reflected from the reflector cup can pass through the microlens, thereby further improving light extraction efficiency. Furthermore, during the first and second rounds of optimization, the refractive index of the microlens is limited to the range of 1-2.4.

[0070] In one embodiment, the process of constructing the reflective cup includes first etching a GaN homogeneous substrate to form a cup-shaped structure with its opening facing downwards at the position opposite to the epitaxial structure on the GaN homogeneous substrate; then coating or chemically depositing a film on the sidewalls of the cup-shaped structure to prepare a reflective film, thereby enabling the cup-shaped structure to have reflective function and forming a reflective cup. The reflective film is preferably a metal reflective film.

[0071] In one embodiment, the reflector cup is filled with an optical adhesive that acts as a buffer. Because the GaN homopolymer substrate has a high refractive index, when light is directly emitted into the air, the significant refractive index difference at the interface between the air and the GaN homopolymer substrate leads to significant total internal reflection. This prevents large-angle light from passing through the interface, resulting in substantial light energy loss. Filling the reflector cup with optical adhesive, whose refractive index is much higher than that of air, acts as a buffer, adjusting the light propagation path and reducing the angle of total internal reflection when light exits the GaN homopolymer substrate into the air, thereby effectively reducing light energy loss. Furthermore, in the first and second rounds of optimization, the refractive index of the optical adhesive was controlled within the range of 1-2.4.

[0072] In one embodiment, during the first and second rounds of optimization, the refractive index of the microlens is set to be no higher than that of the optical adhesive. This allows the refractive indices of the GaN homopolymer substrate, optical adhesive, and microlens that the light beam passes through sequentially along the propagation path to gradually decrease. Under this refractive index distribution, the microlens can act as a secondary buffer, reducing the impact of total internal reflection when the light beam reaches the microlens, improving the light extraction efficiency of the device, and effectively reducing light energy loss.

[0073] In one embodiment, the flip-chip Micro-LED cells on the GaN homogeneous substrate are replicated and arranged into an array, such as... Figure 2 As shown, the light efficiency and beam collimation were verified by ray tracing using a planar receiver.

[0074] This application also provides a flip-chip Micro-LED device, which is designed and fabricated using the above-described design method.

[0075] In one embodiment, the flip-chip Micro-LED device includes multiple flip-chip Micro-LED units on a GaN homogeneous substrate, arranged in an array. Each flip-chip Micro-LED unit on the GaN homogeneous substrate includes a GaN homogeneous substrate on which a reflector and a microlens are integrated. An epitaxial structure is also disposed on the GaN homogeneous substrate, and the epitaxial structure, from bottom to top, includes an n-GaN layer, a quantum well structure, and a p-GaN layer. The quantum well structure includes a buffer layer (SRL), quantum wells (MQWs), and an AlGaN layer, and a transparent conductive (ITO) layer is stacked on the p-GaN layer. Metal electrodes are fabricated on the GaN homogeneous substrate and the epitaxial structure, specifically a p-electrode disposed on the p-GaN layer and an n-electrode disposed on the n-GaN layer. The p-electrode and the n-electrode can have the same structure or material, namely Ti / Al / Ti / Au, or they can be different.

[0076] Example 1

[0077] A 50μm × 50μm × 120μm GaN homogeneous substrate was used. Figure 3 As shown, an epitaxial structure 2 is fabricated on a GaN homogeneous substrate 1. This epitaxial structure 2 includes an n-GaN layer 21, a quantum well structure 22, and a p-GaN layer 23, stacked sequentially from bottom to top. The quantum well structure 22 includes, from bottom to top, an SRL layer 221, a quantum well structure 222, and an AlGaN layer 223. An ITO layer 6 is also disposed on the p-GaN layer 23. A p-electrode 71 is disposed on the ITO layer 6, and an n-electrode 72 is disposed on the n-GaN layer.

[0078] A cup-shaped structure with its rim facing downwards is constructed on the GaN homogeneous substrate 1, opposite the epitaxial structure 2. The height of the cup-shaped structure is set to 100 μm, and the bottom surface of the cup-shaped structure is 20 μm from the front surface of the GaN homogeneous substrate. The diameter of the bottom of the cup-shaped structure is set to 12 μm, and the diameter of the rim is set to 24 μm, with the inclination angle of the sidewall of the cup-shaped structure being approximately 86°. A metal reflective film is deposited on the sidewall of the cup-shaped structure to form a reflective cup 3.

[0079] The interior of the reflector cup 3 is filled with optical adhesive 5 with a refractive index of 1.7. Subsequently, a freeform microlens 4 with the same refractive index of 1.7 is glued to the rim of the reflector cup 3. Figure 4 As shown, the reflector cup 3 and the microlens 4 are integrated on the GaN homogeneous substrate 1.

[0080] The light-emitting unit of the flip-chip Micro-LED cell on the GaN homogeneous substrate is a quantum well. In this embodiment, a light spot with a diameter of 5 μm is used as the light-emitting unit, the emission angle is set to ±40°, the emission angle distribution is set to a Lambertian distribution, the wavelength is set to 436 nm, and the power is set to 1 W. A planar receiver with a size of 400 μm × 400 μm is placed 200 μm behind the microlens to receive the illuminance and energy distribution of the light beam transmitted through the microlens.

[0081] First, the light-emitting surface of the microlens is set as a quadratic surface. Using the microlens thickness, surface curvature, and surface coefficient as optimization variables, and based on the illuminance and energy distribution received by the planar receiver, a collimation evaluation function is used as the evaluation function to optimize its surface parameters. This first round of optimization yields a relatively good basic surface shape. Next, the surface shape of the microlens is set as an even-order aspherical surface. Keeping the microlens thickness, surface curvature, surface coefficient, and evaluation function unchanged, the 2n-order aspherical parameters are optimized in batches. Each time, one or two 2n-order aspherical coefficients are selected for optimization until each parameter is optimized. The surface parameters obtained during the optimization process are shown in Table 1.

[0082] The formula for the face shape is: ,

[0083] Where z is the sagitta of the surface, c is the curvature, k is the surface coefficient, r is the radial coordinate, x and y are the rectangular coordinates in the plane perpendicular to the optical axis, and n is a positive integer.

[0084] After parameter optimization, a Micro-LED structural unit on a GaN homogeneous substrate is obtained.

[0085] Table 1. Optimization results of surface parameters for Micro-LED structural units on GaN homogeneous substrates

[0086]

[0087] The above structural units were replicated and arranged into a 10×10 array. A rectangular receiver with a size of 300μm×300μm was placed 200μm behind the microlens, and ray tracing was performed through the rectangular receiver.

[0088] Ultimately, the flip-chip Micro-LED device was obtained.

[0089] After parameter optimization, the flip-chip Micro-LED unit receives a total energy of 0.297W on the receiving surface of its rear planar receiver. Given a set light source luminous power of 1W, the luminous efficiency of this flip-chip Micro-LED device can be calculated to be 29.7%. Figure 5 As shown, based on the two-dimensional illuminance distribution on the receiving surface of the planar receiver and the one-dimensional illuminance distribution in the x and y directions, it can be seen that the flip-chip structure Micro-LED unit on the single GaN homogeneous substrate forms a specific illuminance distribution on the rectangular receiver, its energy is concentrated to a certain extent, and the light spot shape is good.

[0090] Simultaneously, far-field angle analysis was performed on the light rays from a single flip-chip Micro-LED unit on the aforementioned GaN homogeneous substrate. This involved statistically analyzing the number of light rays at different angles and representing them in terms of intensity, primarily to observe the collimation of the flip-chip Micro-LED unit on the GaN homogeneous substrate. Figure 6 , Figure 7 As shown in the figure, it can be clearly seen that the flip-chip Micro-LED unit on the GaN homogeneous substrate exhibits excellent collimation performance, with the light intensity distribution displaying a distinct peak. The full width at half maximum (FWHM) of the two-dimensional light intensity distribution of the flip-chip Micro-LED unit on the GaN homogeneous substrate is 36.875°, and the divergence angle defined by the FWHM is ±18.436°.

[0091] After replicating and arranging the flip-chip Micro-LED units on the aforementioned GaN homogeneous substrate into a 10×10 array, the main purpose of ray tracing of this array was to verify whether the overall light extraction efficiency of the array remained consistent with that of a single unit, and to evaluate the beam collimation performance under the synergistic effect of multiple units. Specifically, using the refraction law of geometric optics, the angular deflection of light at the interface of the structure was calculated, and finally, the number and distribution of light rays arriving at the rectangular receiver were statistically analyzed to obtain the spot energy and spot intensity distribution. Experimental data showed that the total energy received on the receiving surface of the receiver was 29.921W, and the total energy of 100 circular light sources was 100W. The calculated light extraction efficiency was 29.921%, which highly agrees with the 29.7% light extraction efficiency of a single unit, indicating that its optical performance remains highly stable even after the array is expanded. Figure 8 As shown, based on the two-dimensional illuminance distribution on the receiver surface and the one-dimensional illuminance profile analysis in the x and y directions, it can be seen that the 10×10 array forms an illuminance distribution with highly concentrated energy and regular light spot shape on the rectangular receiver, proving that the arrangement of multiple units does not lead to energy diffusion or shape distortion.

[0092] Similarly, such as Figure 9 , Figure 10 As shown, the overall light intensity distribution of the array exhibits excellent collimation characteristics. The overall two-dimensional light intensity distribution of the array shows a sharp single-peak shape, with a full width at half maximum (FWHM) of 36.875°, and the defined outgoing light divergence angle is ±18.436°. This result not only matches the collimation performance of a single unit but also confirms that the array design maintains high efficiency without introducing additional light divergence or angle broadening, fully meeting the stringent requirements of high-precision optical systems for the directionality of outgoing light.

[0093] Therefore, the design method provided in this application, by combining the growth of epitaxial structures on GaN homogeneous substrates with composite optical structures, can significantly improve the luminous efficiency and beam collimation of flip-chip Micro-LED devices, achieving a light extraction efficiency of 29.921% and a divergence angle of ±18.436°, meeting the requirements of high-brightness displays and having broad application prospects.

[0094] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0095] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for designing a flip structure Micro-LED unit on a GaN homo-substrate, characterized in that, Includes the following steps: An epitaxial structure with a quantum well structure is grown by MOCVD on a GaN homogeneous substrate. From bottom to top, the epitaxial structure includes an n-GaN layer, a quantum well structure and a p-GaN layer stacked sequentially. Micro-nano structures are designed and fabricated on the GaN homogeneous substrate, the micro-nano structures including a reflector cup and a microlens with a free-form surface; The reflective cup has its rim facing downwards, and the diameter of its rim is larger than the diameter of its bottom. The microlens with a free-form surface is glued to the rim of the reflector cup to integrate the reflector cup and the microlens on the GaN homogeneous substrate; A planar receiver is placed at a predetermined distance from the microlens on the side away from the reflector cup to receive illuminance and energy distribution; The light-emitting surface of the microlens is set as a quadratic surface. The intermediate thickness, surface curvature, and surface coefficient of the microlens are used as optimization variables. Based on the emitted light illuminance and energy distribution received by the planar receiver, a collimation evaluation function is used as the evaluation function to perform the first round of optimization. The optimized size parameters corresponding to the basic surface shape with preliminary collimation effect are obtained. The optimized size parameters include optimized intermediate thickness, optimized surface curvature, and optimized surface coefficient. The light-emitting surface is set as an even-order aspherical surface. The optimized size parameters and the evaluation function are kept unchanged. The second round of optimization is performed with the 2n-order aspherical surface parameters as the optimization variables to further collimate the beam. The surface shape formula for the even-order aspherical surface is as follows: ； Where z is the sagitta of the surface, c is the curvature of the surface, k is the surface coefficient, r is the radial coordinate, x and y are the rectangular coordinates in the plane perpendicular to the optical axis, and n is a positive integer. The parameters are 2n-order aspherical surfaces; Based on the optimization results, the optimized design parameters of the flip-chip Micro-LED unit on the GaN homogeneous substrate were determined.

2. The design method as described in claim 1, characterized in that, The diameter of the microlens is not less than the diameter of the cup opening, so as to ensure that all the light reflected by the reflective cup passes through the microlens; During the first and second rounds of optimization, the refractive index of the microlens was limited to the range of 1-2.

4.

3. The design method as described in claim 2, characterized in that, The reflector cup is filled with optical adhesive that acts as a buffer. During the first and second rounds of optimization, the refractive index of the optical adhesive is not lower than that of the microlens, so that the refractive indices of the GaN homogeneous substrate, the optical adhesive, and the microlens that the light passes through on the propagation path gradually decrease.

4. The design method as described in claim 2, characterized in that, The size of the GaN homogeneous substrate is limited to the range of (10μm-100μm)×(10μm-100μm)×(10μm-500μm); The height of the reflector cup is 0.7-0.95 times the thickness of the GaN homogeneous substrate.

5. The design method as described in claim 4, characterized in that, The diameter of the cup opening of the reflector is set to 0.3-0.85 times the width of the GaN homogeneous substrate, and the diameter of the cup bottom is set to 0.3-0.8 times the diameter of the cup opening, so that the tilt angle of the sidewall of the reflector is controlled within the range of 84°-88°.

6. The design method as described in claim 4, characterized in that, The preparation process of the reflective cup includes: etching the GaN homogeneous substrate to form a cup-shaped structure with the cup opening facing downwards, and preparing a metal reflective film on the sidewall of the cup-shaped structure.

7. The design method as described in claim 1, characterized in that, During the first and second rounds of optimization, the emission angle of the flip-chip Micro-LED unit on the GaN homogeneous substrate is set to ±(40°-60°), and the emission angle distribution is set to a Lambertian distribution.

8. The design method as described in claim 1, characterized in that, During the first and second rounds of optimization, the divergence angle of the flip-chip Micro-LED unit on the GaN homogeneous substrate reached ±(16°-20°), and the light extraction efficiency was not less than 25%.

9. A flip-chip Micro-LED device, characterized in that, The sample was designed and prepared using the design method described in any one of claims 1-8.

10. The flip-chip Micro-LED device as described in claim 9, characterized in that, The device includes multiple flip-chip Micro-LED units on GaN homogeneous substrates. Each flip-chip Micro-LED unit on a GaN homogeneous substrate includes one GaN homogeneous substrate. An epitaxial structure is disposed on the GaN homogeneous substrate. The epitaxial structure includes an n-GaN layer, a quantum well structure, and a p-GaN layer from bottom to top. Metal electrodes are respectively fabricated on the GaN homogeneous substrate and the epitaxial structure.

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