Micro light emitting diode display integrated with light guide structure and preparation method thereof

Abstract

The application discloses a micro light emitting diode display integrated structure with a light guide and a preparation method thereof, comprising a MicroLED pixel array, a color conversion or light emitting modulation layer is arranged on the light emitting side of each sub-pixel of the MicroLED pixel array, and a mode-restricted light guide layer structure is arranged above the color conversion or light emitting modulation layer as a whole. According to the application, a conformal mode-restricted light guide layer is formed on the light emitting surface of the MicroLED pixel, so that the pixel emitted light enters the restricted propagation mode at the instant of emission, thereby realizing the pixel-level integrated integration of the display and the light guide system, significantly improving the optical coupling efficiency between the MicroLED and the light guide system, eliminating the dependence on independent optical components such as collimation lenses, coupling gratings or prisms, simplifying the overall structure of the display-light guide system, reducing the system thickness, reducing the system alignment freedom requirement, and relaxing the manufacturing and assembly tolerance.

Description

Technical Field

[0001] This invention belongs to the field of micro-light-emitting diode (LED) display and light-conductor integration technology, specifically relating to an integrated structure combining an LED display and a light-conductor. This invention also relates to a method for fabricating this integrated structure. Background Technology

[0002] In augmented reality (AR), virtual reality (VR), and other near-eye display systems, MicroLED displays are considered one of the next-generation core display technologies due to their advantages such as high brightness, high contrast, and long lifespan. To achieve thinner and lighter designs and high luminous efficiency, MicroLED displays typically require efficient coupling with optical waveguide systems to transmit the displayed image to the human eye.

[0003] In existing technologies, MicroLED displays and optical waveguide systems are typically coupled via a free-space propagation path. Specifically, light emitted from MicroLED pixels first propagates in free space before being injected into the optical waveguide system via a collimating lens, coupling grating, prism, or other independent optical components. This approach generally suffers from the following problems: the emitted light from the pixels must propagate through free space, resulting in light divergence and energy loss during propagation, limiting coupling efficiency; collimating lenses or coupling optical elements are required, complicating the system structure and increasing thickness; the large emission angle of MicroLED pixels makes it difficult to directly meet the mode injection conditions of optical waveguides or fibers; high alignment accuracy is required between the display module and the optical waveguide system, leading to complex assembly and adjustment processes; in high-PPI MicroLED displays, the system's optical tolerance is further tightened, hindering large-scale manufacturing. Furthermore, most existing solutions treat the display and the optical waveguide as two independent subsystems, connecting them through subsequent coupling, failing to address the fundamental problems caused by free-space propagation at the pixel emission interface level.

[0004] Therefore, there is an urgent need for a structural solution that can achieve restricted light propagation at the light-emitting interface of MicroLED pixels, thereby eliminating free-space coupling paths from the propagation paradigm and realizing efficient integrated display and light guide system. Summary of the Invention

[0005] The purpose of this invention is to provide an integrated structure that combines micro-light-emitting diode display and light guide, solving the problem that the emitted light from existing MicroLED pixels must propagate through free space before being coupled into the light guide.

[0006] Another objective of this invention is to provide a method for fabricating an integrated structure combining a micro-light-emitting diode display and a light guide.

[0007] The first technical solution adopted in this invention is: an integrated structure of micro LED display and light guide, including a MicroLED pixel array, wherein each sub-pixel on the light-emitting side of the MicroLED pixel array is provided with a color conversion or light emission modulation layer, and a mode-restricted light guide layer structure is provided above the color conversion or light emission modulation layer as a whole.

[0008] The first technical solution of the present invention is further characterized in that, The mode-restricted light guide layer structure is a planar light waveguide structure, including a lower cladding layer, a light guide core layer and an upper cladding layer formed sequentially along the thickness direction. The lower cladding layer is located near the color conversion or light emission modulation layer and has a refractive index of 1.45 to 1.65. The refractive index of the light guide core layer is 1.75 to 2.2, and the refractive index of the upper cladding layer is 1.45 to 1.65.

[0009] The mode-restricted light guide layer structure is a segmented refractive index structure, consisting of 2 to 5 thin film stacks, with the refractive index of each thin film stack increasing stepwise along the light emission direction.

[0010] The mode-restricted optical guide layer structure is a graded refractive index structure, consisting of a structure in which the refractive index changes continuously along the thickness direction, with the overall refractive index variation range Δn being 0.2 to 0.5.

[0011] The mode-restricted light guide layer structure is an image fiber structure, consisting of several fiber units whose length direction corresponds one-to-one with the light output direction of each sub-pixel. Each fiber unit includes a core layer with a refractive index of 1.6 to 1.9 and a cladding layer with a refractive index of 1.45 to 1.55.

[0012] The mode-restricted light guide layer structure is a conical or wedge-shaped transition structure with a sidewall tilt angle of 10° to 45°.

[0013] The second technical solution adopted in this invention is: a method for fabricating an integrated structure of micro-light-emitting diode display and light guide, comprising the following steps: Step 1: Fabricate a micro-LED pixel array; Step 2: Deposit a refractive index matching layer on the micro-LED pixel array; Step 3: Sequentially deposit the cladding layer and the light guide core layer on the refractive index matching layer; Step 4: Photolithographic patterning and etching of the light guide core layer; Step 5: Deposit the cladding layer on the optical core layer and anneal it to obtain the mode-confined optical guide layer structure of the planar optical waveguide structure.

[0014] The third technical solution adopted in this invention is: a method for fabricating an integrated structure of micro-light-emitting diode display and light guide, comprising the following steps: Step 1: Fabricate a micro-LED pixel array; Step 2: Sequentially sputter and deposit a multilayer inorganic thin film stack with progressively increasing refractive index on the micro-LED pixel array, including a SiO2 layer, a SiO2 / SiN layer, etc. x Composite layer, SiN x Layer, SiN x / TiO2 composite layer; Step 3: Annealing treatment to obtain the mode-constrained optical guide layer structure with segmented refractive index structure.

[0015] The fourth technical solution adopted in this invention is: a method for fabricating an integrated structure of micro-light-emitting diode display and light guide, comprising the following steps: Step 1: Fabricate a micro-LED pixel array; Step 2: Using SiO2 and SiN on the micro-light-emitting diode pixel array x Dual-target co-sputtering is used to deposit an optical guide layer with a continuously varying refractive index in the thickness direction by continuously adjusting the power ratio of the two targets. Step 3: Annealing treatment to obtain a mode-confined optical guide layer structure with a gradient refractive index.

[0016] The fifth technical solution adopted in this invention is: a method for fabricating an integrated structure of micro-light-emitting diode display and light guide, comprising the following steps: Step 1: Fabricate a micro-LED pixel array; Step 2: Prepare a periodic aperture array template and sequentially fill it with a high refractive index core layer and a low refractive index cladding material to form an image fiber array; Step 3: Cut and polish the incident end face of the image fiber array; Step 4: Align and attach the incident end face of the image fiber array with the micro light-emitting diode pixel array so that the fiber and the pixel correspond one-to-one, thus obtaining the mode-constrained light guide layer structure of the image fiber structure.

[0017] The beneficial effects of this invention are as follows: The integrated structure and fabrication method of the micro-LED display and light guide of this invention, by forming a conformal mode-restricted light guide layer on the light-emitting surface of the MicroLED pixel, enables the emitted light from the pixel to enter a restricted propagation mode at the moment of emission. This solves the problems of low optical coupling efficiency, complex system structure, increased thickness, and limited assembly tolerance caused by the need for the emitted light from the pixel to propagate through free space and rely on subsequent coupling optical components during the integration of existing MicroLED display and light guide systems. This achieves pixel-level integrated integration of the display and light guide system, significantly improves the optical coupling efficiency between the MicroLED and the light guide system, eliminates the dependence on independent optical components such as alignment lenses, coupling gratings, or prisms, simplifies the overall structure of the display-light guide system, reduces system thickness, reduces the system assembly and adjustment freedom requirements, and relaxes manufacturing and assembly tolerances. It is suitable for high PPI, thin and light AR / VR MicroLED display systems and is conducive to achieving pixel-level integrated integration and large-scale manufacturing of the display and light guide system. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the integrated structure of micro-light-emitting diode display and light guide of the present invention; Figure 2 This is a schematic diagram of the mode-restricted light guide layer structure with a tapered or wedge-shaped transition structure in the integrated structure of micro-light-emitting diode display and light guide of the present invention.

[0019] In the figure, 1. substrate, 2. CMOS backplane, 3. MicroLED pixel array, 4. color conversion or light emission modulation layer, 5. mode-restricted light guide layer structure, 6. optical waveguide system, 7. human eye observation area; 51. Light guiding functional area; 52. Mode control area; 53. Incident coupling interface area; 61. Light output coupling structure. Detailed Implementation

[0020] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0021] Example 1 This invention provides an integrated structure combining a micro-light-emitting diode (LED) display and a light guide, comprising a CMOS backplane, a MicroLED pixel structure disposed thereon, a transparent electrode layer covering the light-emitting surface of the pixel, and a conformal mode-restricted light guide layer disposed on the transparent electrode layer. The light guide layer is directly attached to the light-emitting surface of the MicroLED pixel or connected to it through a refractive index matching layer, so that the light emitted from the pixel enters a restricted propagation mode at the emission interface.

[0022] The conformal mode-restricted light guide layer is composed of transparent inorganic or inorganic-organic composite optical materials with a refractive index ranging from 1.45 to 2.05 and a thickness ranging from 0.5 to 20 μm, spatially covering at least 80% of the pixel light-emitting area. The interface roughness between the light guide layer and the MicroLED light-emitting surface is preferably less than 50 nm to reduce interface scattering loss.

[0023] In one embodiment, the mode-confined optical guide layer is a planar optical waveguide structure, and its core layer is made of SiN. x The core layer is a high-refractive-index core layer, and the cladding layer is a TiO2 (n≈1.8~2.0) or TiO2 (n≈2.0~2.2) thin film with a thickness of 1~5μm. The upper and lower cladding layers are made of SiO2 or Al2O3 (n≈1.45~1.65) with a thickness of 0.5~3μm each, thus forming a typical waveguide structure of high-refractive-index core layer + low-refractive-index cladding layer. This structure is formed by magnetron sputtering or atomic layer deposition (ALD), and the waveguide region is defined by photolithography and etching, so that the light emitted from the MicroLED satisfies the total internal reflection condition (critical angle of about 40°~60°) at the interface and is directly coupled into the waveguide mode.

[0024] In another embodiment, the mode-confined photoconductor layer is a segmented refractive index structure, composed of 2 to 5 layers of inorganic thin films stacked together. The refractive index of each layer changes progressively along the light emission direction, ranging from 1.50 to 1.65 to 1.80 to 1.95, and the thickness of each layer is 0.5 to 2 μm. This structure is achieved through multiple depositions (SiO2 / SiN...). x The method utilizes TiO2 to gradually compress the divergence angle of the emitted light from the pixel during propagation, thereby improving coupling efficiency. Each layer is formed through a layer-by-layer deposition and patterning process, and its density is improved by annealing at 200℃~300℃.

[0025] In another embodiment, the mode-confined light guide layer is a gradient refractive index structure. This is achieved by continuously adjusting the gas ratio (e.g., Ar / O2 or Ar / N2) or the dual-target power ratio during deposition, resulting in a continuous change in refractive index along the thickness direction (gradient range Δn ≈ 0.2–0.5, gradient thickness 2–10 μm). This structure can be achieved through co-sputtering or ALD gradient deposition processes, allowing the mode to gradually converge during light propagation and reducing interface reflection and mode mismatch losses.

[0026] In another embodiment, the mode-restricted light guide layer forms a conical or wedge-shaped transition structure on the light-emitting surface of the MicroLED pixel. The structure has a height of 1–10 μm, a lateral dimension of 2–10 μm, and a tilt angle of 10°–45°. This structure is initially formed using photoresist reflow or grayscale lithography, and then the final structure is obtained through inorganic material transfer (such as etching or deposition replication). This structure is used to adjust the incident angle distribution of light to match the numerical aperture (NA≈0.3–0.7) of the subsequent light guide system.

[0027] In another embodiment, the mode-restricted light guide layer is an image fiber structure composed of multiple microfiber units, each with a diameter of 2–10 μm, a core refractive index of 1.6–1.9 (e.g., doped with SiO2 or polymer / inorganic composite material), and a cladding refractive index of 1.45–1.55. The fiber array is formed by drawing or template filling processes, and the incident end face is formed by cutting and polishing to correspond one-to-one with the MicroLED pixel array. The incident end face and the MicroLED light-emitting surface are connected by a refractive index matching layer (n≈1.5–1.6, thickness 0.1–1 μm) to reduce interface reflection loss.

[0028] In all the above embodiments, the mode-restricted light guide layer is directly formed on the light-emitting side of the MicroLED pixel through processes such as thin film deposition, photolithography patterning, etching or nanoimprinting, and forms a continuous or equivalent continuous interface with the subsequent light guide system in terms of refractive index and structure.

[0029] The above structure enables the light emitted from MicroLED pixels to meet waveguide or confined propagation conditions at the emission interface, achieving a direct conversion from free-space divergence mode to confined propagation mode, thereby avoiding light loss caused by collimation and recoupling processes in traditional structures.

[0030] Example 2 This invention provides an integrated structure for micro-light-emitting diode (LED) display and light guide, including a substrate 1, a CMOS backplane 2 disposed on the substrate 1, a MicroLED pixel array 3 disposed on the CMOS backplane 2, a color conversion or light emission modulation layer 4 disposed on the light-emitting side of the MicroLED pixel array 3, and a mode-restricted light guide layer structure 5 disposed above the color conversion layer. The mode-restricted light guide layer structure 5 is used to achieve integrated display and light transmission functions at the device level, so that the light emitted from the pixel enters a restricted propagation path after emission.

[0031] The CMOS backplane 2 integrates a driving circuit and is electrically connected to each sub-pixel in the MicroLED pixel array 3 through metal interconnects and conductive via structures. The MicroLED pixel array 3 includes multiple sub-pixel units arranged along a planar direction. Each sub-pixel unit includes an n-type semiconductor layer, a light-emitting layer, and a p-type semiconductor layer, and forms a driving circuit with the CMOS backplane 2 through an electrode structure. A color conversion or light emission modulation layer 4 is disposed on the light-emitting side of the MicroLED pixel array 3 and corresponds to each sub-pixel in a planar position to achieve full-color display output. Its material can be quantum dot photoresist or a multi-color light-emitting material structure, and it covers the light-emitting area of ​​the pixel in the thickness direction.

[0032] The mode-restricted light guide layer structure 5 is disposed above the color conversion layer and extends along the planar direction. Its interior forms a restricted propagation structure in the thickness direction, including a light-guiding functional area 51, a mode control area 52, and an incident coupling interface area 53. The incident coupling interface area 53 is located near the color conversion layer, forming a direct or equivalently bonded optical interface with it. This allows light emitted from the MicroLED pixel array 3 to directly couple into the mode-restricted light guide layer structure 5 through this incident coupling interface area 53 without needing to propagate in free space after passing through the color conversion layer. The incident coupling interface area 53 and the light-guiding functional area 51 are structurally continuous and integrated, ensuring that light transitions from a free-diffusion mode to a restricted propagation mode upon entering the mode-restricted light guide layer structure 5.

[0033] After entering the mode-restricted light guide layer structure 5, light first undergoes propagation path reconstruction and mode redistribution within the mode control region 52. The mode control region 52, through refractive index distribution design, structural morphology changes, or equivalent optical path control, enables spatial rearrangement of light from different pixel positions during lateral propagation, thereby improving the uniformity of light distribution in the planar direction and providing mode-matching conditions for subsequent stable coupling into the light guide functional region 51. Subsequently, the controlled light enters the light guide functional region 51 and undergoes restricted propagation along the planar direction within this region. The light guide functional region 51 is continuous with the incident coupling interface region 53 in the thickness direction, together forming the core light guide channel of the light guide structure. This continuous interface is also a key structure for achieving optical coupling between the display area and the light guide area.

[0034] On the side furthest from the MicroLED pixel array 3, the mode-restricted light guide layer structure 5 extends to the optical waveguide system 6. The light-exit coupling structure 61 of the optical waveguide system 6 guides the light propagating within the light guide layer to the external space through the coupling structure, and finally into the human eye observation area 7. Thus, a continuous light path is formed in the overall structure: MicroLED pixel array 3 → color conversion or light emission modulation layer 4 → incident coupling interface region 53 → mode control region 52 → light guide functional region 51 → optical waveguide system 6 → light-exit coupling structure 61 → human eye observation area 7. This path is structurally continuous and does not require additional free space coupling or external optical components.

[0035] The mode-constrained light guide layer structure 5 can be implemented using different specific structural forms. In one embodiment, the structure forms an incident coupling interface region 53, a mode control region 52, and a light guiding functional region 51 through a layered refractive index matching design, allowing light to be coupled into the light guide channel step by step. In another embodiment, the structure introduces a light field expansion structure on the incident side, causing the light to expand laterally and redistribute before entering the light guide region. In yet another embodiment, the structure forms a continuously gradient refractive index distribution in the thickness direction, allowing the light to smoothly complete mode compression and direction adjustment during propagation. In yet another embodiment, the structure achieves a spatially gradual transition through a wedge-shaped or conical geometry, allowing the light to gradually transition from divergent propagation to confined mode propagation.

[0036] All the above-described different implementations satisfy a unified structural relationship: the incident coupling interface region 53 is responsible for the initial coupling of light, the mode control region 52 is responsible for light field reconstruction and mode matching, and the light guiding functional region 51 is responsible for planar confined propagation, thereby achieving a continuous conversion from pixel light emission to light guiding transmission within the same structure. For example, in the implementation of a high refractive index core layer + low refractive index cladding layer, the low refractive index cladding layer and its interface region near the MicroLED side can jointly constitute the light guiding functional region 51 and the incident coupling interface region 53, while the high refractive index core layer mainly participates in the mode control region 52 to achieve mode confinement and propagation mode adjustment; in the implementation of 2 to 5 layers of inorganic thin film stack, different film layers form light guiding and mode confinement functions through refractive index differences, wherein some high refractive index film layers, periodic modulation film layers, or micro / nano structure layers form the mode control region 52, while the light guiding film layer, coupling film layer, or interface region near the MicroLED side jointly form the light guiding functional region 51 and the incident coupling interface region 53.

[0037] Through the above structural arrangement, the mode-restricted light guide layer structure 5 not only serves as a light transmission channel but also undertakes the functions of mode conversion and spatial redistribution of light emitted from pixels, enabling the MicroLED display unit and the light guide system to be integrated at the device level. This structure allows the light emitted from the pixels to enter a restricted propagation state immediately after leaving the pixel, thereby effectively avoiding the coupling loss, increased system complexity, and decreased luminous efficiency problems existing in traditional display and waveguide separation structures.

[0038] Example 3 This invention provides a method for fabricating an integrated structure of micro-light-emitting diode (LED) display and light guide, employing a monolithic full-color MicroLED and planar waveguide integrated structure. The MicroLED pixel array is disposed above a CMOS backplane, with a pixel size of 8×8μm and a pixel pitch of 4μm. A color conversion layer with a thickness of 4–6μm is disposed above the display area. The MicroLED pixel array has a resolution of 640×480, corresponding to a total of approximately 307,200 pixels, and an effective display area size of approximately 7.68×5.76mm. A refractive index-matched planar waveguide structure is further disposed above the color conversion layer, allowing the light emitted from the MicroLED pixels to directly couple into the planar waveguide propagation mode after leaving the color conversion layer.

[0039] The planar waveguide structure includes a core layer, a lower cladding layer, and an upper cladding layer. The lower cladding layer is located between the upper surface of the color conversion layer and the core layer, and is made of SiO2 or Al2O3 with a refractive index of 1.45–1.62 and a thickness of 0.3–1.5 μm. The core layer is made of SiN. x Alternatively, an inorganic dielectric material doped with TiO2 can be used, with a refractive index of 1.75–2.00 and a thickness of 1.5–4.0 μm; the upper cladding material can be SiO2, Al2O3, or a low-refractive-index composite oxide, with a refractive index of 1.45–1.60 and a thickness of 0.5–2.0 μm. This structure forms a typical combination of a high-refractive-index core and a low-refractive-index cladding, enabling the planar waveguide to meet confined propagation conditions within the indicated wavelength range.

[0040] To reduce interface reflection loss between the MicroLED emission side and the waveguide structure, a refractive index matching layer is placed between the top of the color conversion layer and the lower cladding layer. The refractive index matching layer can be made of SiO₂. x N The material used is an AlON or low-refractive-index nanocomposite medium, preferably with a refractive index of 1.58–1.72 and a thickness of 100–800 nm, more preferably 200–500 nm. The refractive index of the matching layer is located between the effective refractive index of the color conversion layer and the refractive index of the waveguide cladding, thereby reducing Fresnel reflection at the interface and improving coupling efficiency.

[0041] In one specific embodiment, the effective refractive index of the color conversion layer is approximately 1.68, and the refractive index matching layer is made of SiO₂. x N The material has a refractive index of 1.63 and a thickness of approximately 350 nm; the lower cladding layer uses SiO2 with a thickness of 0.8 μm and a refractive index of 1.46; the light guide core layer uses SiN. xThe core layer is 2.5 μm thick with a refractive index of 1.92; the top cladding is made of SiO2 with a thickness of 1.2 μm and a refractive index of 1.46. Under this parameter combination, the emitted light from the MicroLED can be directly coupled into the planar waveguide core layer after color conversion and propagates along the planar direction within the waveguide.

[0042] The waveguide structure is formed through thin-film deposition and patterning processes. First, after fabricating the MicroLED array and color conversion layer, the sample surface undergoes plasma cleaning treatment with an oxygen plasma power of 50–100 W for 30–60 s to improve interfacial adhesion. Subsequently, a refractive index matching layer is deposited using PECVD or ALD processes. The PECVD deposition temperature is 180℃–280℃, the cavity pressure is 0.5–2 Torr, and the deposition rate is 10–40 nm / min. Afterward, the cladding layer and the light-guiding core layer are deposited. The SiO2 cladding layer can be deposited using PECVD, and the SiN... x The core layer can be formed using PECVD or LPCVD processes at a deposition temperature of 250℃ to 400℃. When it is necessary to define the waveguide propagation area, the core layer can be patterned by photolithography followed by dry etching, preferably using CHF3 / O2 or CF4 / O2 as the etching gas. Finally, the cladding layer is deposited and subjected to low-temperature annealing at 250℃ to 350℃ for 10 to 30 minutes to reduce film defects and improve optical uniformity.

[0043] Based on ray tracing and waveguide mode field simulation results, without a refractive index matching layer, the reflection loss at the interface between the color conversion layer and the waveguide is approximately 8%–15%, and the effective coupling efficiency incident on the waveguide core is approximately 55%–68%. After introducing the refractive index matching layer in this embodiment, the interface reflection loss can be reduced to 2%–6%, and the effective coupling efficiency can be increased to 72%–85%. Simultaneously, the light introduced into the waveguide maintains stable transmission over a propagation distance of 5–15 mm, and the waveguide transmission loss is controlled within the range of 0.5–2.0 dB / cm.

[0044] In the experimental samples, using blue MicroLEDs to excite the quantum dot color conversion layer, it was measured that under the same driving current density, the introduction of a refractive index-matched planar waveguide structure increased the total luminous flux at the waveguide emission end by approximately 18%–28%, and the brightness of the far-end emission region by approximately 15%–22%. Simultaneously, due to reduced interface reflection, the reflected stray light above the pixel area was significantly reduced, resulting in an improvement in display uniformity of approximately 10%–18%.

[0045] Through the above structural and process design, a refractive index-matched planar waveguide structure continuously coupled with the light-emitting surface of the MicroLED is formed, enabling the emitted light from the pixel to be directly coupled into the confined propagation mode under low interface loss conditions. This is suitable for the integrated application of monolithic full-color MicroLED and waveguide display system.

[0046] Example 4 This invention provides a method for fabricating an integrated structure of micro-light-emitting diode display and light guide. A segmented refractive index-type mode-restricted light guide layer is set on the light-emitting side of the MicroLED pixel. A structure with gradually changing refractive index along the light-emitting direction is formed by stacking multiple inorganic materials, so that the light emitted from the pixel gradually transitions from a divergent mode to a restricted propagation mode during the propagation process.

[0047] The MicroLED pixel array has a resolution of 640×480, corresponding to a total of approximately 307,200 pixels. Each pixel is 8×8μm in size, with a pixel pitch of 4μm and a center-to-center distance of approximately 12μm. Therefore, the effective display area of ​​the array is approximately 7.68×5.76mm.

[0048] The segmented refractive index light guide layer covers the light-emitting area of ​​the pixel array and forms a continuous light guide structure throughout the entire effective display area. The total thickness of the light guide layer is approximately 6–8 μm, and it consists of four inorganic thin films, which are stacked sequentially along the light-emitting direction.

[0049] In one specific embodiment, the materials and parameters of each layer are as follows: the first layer is a SiO2 thin film (refractive index n≈1.46, thickness approximately 1.5μm), and the second layer is a SiO2 / SiN film. x The composite layer (n≈1.60, thickness approximately 1.5μm) and the third layer are SiN. x The thin film (n≈1.75, thickness approximately 1.5μm), the fourth layer is SiN. x / TiO2 composite layer (n≈1.90, thickness approximately 1.5μm). The refractive index of each layer increases progressively, forming a segmented gradient structure with a total refractive index change Δn≈0.4.

[0050] The structure was formed by full-coverage deposition on the entire 640×480 pixel array using magnetron sputtering. During the deposition process, the SiO2 layer was sputtered using radio frequency (RF) sputtering (power 150–200W, gas pressure 3–5 mTorr), and the SiN layer was sputtered using... x The layers were deposited using reactive sputtering (Ar / N2 ratio 70 / 30 to 50 / 50), and the TiO2 composite layer was achieved through dual-target co-sputtering. After deposition, each layer was annealed at 200℃ to 300℃ (for 5 to 10 minutes) to ensure the consistency and stability of the large-area film.

[0051] Under large-area array conditions, through process optimization, the film thickness uniformity can be controlled within ±3%, and the refractive index fluctuation can be controlled within ±0.02, thereby ensuring the consistency of mode conversion throughout the entire display area.

[0052] After the structure is formed, the photoconductor layer forms a continuous coverage over the entire pixel array and is connected to the underlying transparent electrode layer through a refractive index matching interface, so that the interface reflection loss when light enters the photoconductor layer is controlled to be below 5%.

[0053] Based on optical simulation results (average statistics for the 640×480 full array), it is shown that under the above segmented refractive index structure, the average coupling efficiency of MicroLED emitted light is increased from about 55% to about 75% to 82%, the divergence angle (FWHM) is reduced from about 30° to about 15° to 20%, and the difference between the array edge and the center region is less than 10%.

[0054] During the experimental test, no obvious brightness unevenness or optical degradation was observed in the entire array after 100 hours of continuous operation, indicating that the structure has good consistency and reliability in large-area high-resolution MicroLED displays.

[0055] By using the segmented refractive index-type mode-restricted light guide layer, a stable transition from pixel-level outgoing light to waveguide mode was achieved at a resolution of 640×480, while ensuring consistent performance of the large-area array.

[0056] Example 5 This invention provides a method for fabricating an integrated structure of micro-light-emitting diode display and light guide. A gradient refractive index type mode-restricted light guide layer is set on the light-emitting side of the MicroLED pixel, so that the light emitted from the pixel gradually transitions from a divergent mode to a restricted propagation mode as it enters the light guide structure.

[0057] MicroLED pixels have a size of 8×8μm and a pixel pitch of 4μm, with an initial divergence angle of emitted light of approximately ±20° to ±30°. A gradient refractive index light guide layer with a thickness of approximately 4 to 8μm is formed above its light-emitting surface, and is in direct contact with the underlying transparent electrode layer (such as ITO) or connected through a refractive index matching layer (thickness of approximately 0.2 to 0.5μm, n≈1.5 to 1.6).

[0058] The graded refractive index photoconductor layer employs an inorganic material system, forming a structure where the refractive index changes monotonically along the thickness direction by continuously adjusting the material composition. In one specific embodiment, the refractive index at the bottom of the photoconductor layer is n≈1.50 (SiO2 main body), and the refractive index at the top is n≈1.90 (SiN2 main body). x (or TiO2 enriched layer), the overall refractive index varies in the range of Δn≈0.3~0.4, corresponding to a gradient thickness of about 5μm.

[0059] The structure was achieved through a co-sputtering process using SiO2 and SiN. x Simultaneous deposition of two targets (or TiO2) is performed, with refractive index gradient control achieved by continuously adjusting the power ratio of the two targets. The sputtering power ranges from 120 to 250 W, the working gas pressure is 2 to 5 mTorr, and the reactant gas is an Ar / O2 or Ar / N2 mixture. During deposition, the SiO2 target power is gradually reduced, while the SiN2 target power is increased. x Alternatively, the TiO2 target power can be gradually increased to create a continuous refractive index change along the thickness direction. After deposition, annealing at 200℃~300℃ (5~10min) is performed to improve the film density and stability.

[0060] In terms of optical effects, the gradient refractive index structure changes the refraction path of light during propagation, causing the original large-angle divergent light to gradually converge toward the normal direction, and satisfies the waveguide mode propagation conditions at the top of the optical guide layer.

[0061] Based on ray tracing simulation results, under the conditions of Δn≈0.35 and a thickness of about 5μm, the effective divergence angle of the pixel emitted light converges from the initial about 28° to about 15° to 18°, and the efficiency of coupling into the subsequent waveguide structure is improved by about 20% to 35%. At the same time, the interface reflection loss is reduced by about 10% to 20%.

[0062] Experimental results show that, under continuous operation for 150 hours, the gradient refractive index structure did not exhibit significant delamination or refractive index degradation, and its light output stability was good. Compared to the ungradient structure, the light output uniformity was improved by approximately 15%, and the overall brightness was improved by approximately 18%.

[0063] By using the aforementioned gradient refractive index-type mode-restricted light guide layer, a smooth transition from MicroLED pixel-emitted light to the restricted propagation mode is achieved without introducing complex microstructures, making it suitable for highly integrated MicroLED-waveguide integrated display systems.

[0064] Example 6 This invention provides a method for fabricating an integrated structure of micro-light-emitting diode display and light guide. An image fiber-type mode-restricted light guide structure is integrated on the light-emitting side of the MicroLED pixel array, so that the light emitted from each pixel is directly coupled into the corresponding fiber unit at the emission interface, thereby achieving pixel-level restricted propagation.

[0065] The MicroLED pixels are 8×8μm in size with a pixel pitch of 4μm. The image fiber structure consists of multiple fiber units, each arranged in a planar manner corresponding to the MicroLED pixel array, with a center-to-center spacing of 10–12μm. The core diameter of each fiber unit is 6–10μm, the cladding thickness is 1–3μm, and the overall diameter is 8–14μm.

[0066] The fiber core uses a high-refractive-index material (n≈1.60~1.85), such as doped SiO2, SiON, or inorganic-organic composite materials; the cladding uses a low-refractive-index material (n≈1.45~1.55), such as pure SiO2 or fluorine-doped SiO2, thus forming a confined light-guiding structure with a numerical aperture NA≈0.3~0.6. The fiber length is 50~500μm, used to realize the spatial transmission of pixel optical signals.

[0067] A refractive index matching layer with a thickness of 0.2–1 μm and a refractive index of 1.50–1.60 is placed between the MicroLED and the fiber array to reduce interface reflection loss. The matching layer is formed by spin coating or thin film deposition and cured at a low temperature of 100℃–150℃.

[0068] Image fiber structures can be formed through template-assisted filling or drawing processes. In one specific process, a template with a periodic array of holes (aperture diameter 6–10 μm, spacing 10–12 μm) is first prepared, then filled with a high-refractive-index core material and cured, followed by filling with a low-refractive-index cladding material to form a complete fiber unit. The structure is then cut and polished to achieve an incident end-face roughness of less than 50 nm, and aligned and bonded to a MicroLED pixel array (alignment error <1 μm).

[0069] During coupling, the light emitted from the MicroLED pixels directly enters the corresponding fiber core and propagates through total internal reflection at the core-cladding interface, thus avoiding free-space divergence. Based on optical simulation results, under the condition of fiber NA≈0.45, the pixel-emitter light coupling efficiency can reach 70%–85%, which is about 30%–50% higher than that of fiberless structures. At the same time, crosstalk during light transmission is reduced by more than 40%.

[0070] Experimental tests show that, with a fiber length of 100 μm, the output light spot maintains a one-to-one correspondence with the input pixel, with a positional offset of less than 1 μm, and the brightness uniformity is improved by about 20%. Under continuous operation for 200 hours, no significant decrease in coupling efficiency or interface failure was observed.

[0071] The above structure enables the light emitted from the MicroLED pixels to enter a confined propagation mode at the emission interface, achieving integrated display unit and light guide structure, suitable for high-resolution near-eye display and waveguide display systems.

[0072] Example 7 This invention provides a method for fabricating an integrated structure combining a micro-light-emitting diode (LED) display and a light guide. A conical or wedge-shaped transition structure is formed on one side of the light-emitting surface of the MicroLED pixel array to serve as part of the mode-restricted light guide layer. Specifically, a transparent planarization layer or a low-refractive-index dielectric layer is first formed above the MicroLED pixel array. The transparent planarization layer can be made of SiO2 or SiN. x Al2O3, polyimide, or other transparent insulating materials are used. Photoresist is then coated onto the transparent planarization layer, and the patterned areas corresponding to each MicroLED pixel are defined by photolithography.

[0073] In a specific process, a photoresist reflow process can be used to form an initial conical or wedge-shaped morphology. That is, after photolithography and development, a heat treatment process causes controlled softening and surface tension-driven morphology reconstruction of the photoresist pattern, thereby forming a conical or wedge-shaped structure with continuously sloping sidewalls. The heat treatment temperature can be selected according to the photoresist material, for example, 100℃ to 180℃, and the treatment time can be 1 to 10 minutes. By adjusting the photoresist thickness, pattern opening size, heat treatment temperature, and time, the height, lateral dimension, and tilt angle of the conical or wedge-shaped transition structure can be controlled.

[0074] In another specific process, grayscale photolithography can also be used to form the initial morphology. This involves using a grayscale mask or multi-dose exposure to allow the photoresist to have different exposure doses and development depths at different locations, thereby directly forming a conical, wedge-shaped, or curved transition structure with a target height distribution. The height of this initial morphology can be 1–10 μm, the lateral dimension can be 2–10 μm, and the sidewall tilt angle can be 10°–45°.

[0075] Subsequently, the initial morphology of the photoresist is transferred to an inorganic material structure. This transfer process can employ an etching transfer method, for example, by pre-forming SiO2 or SiN beneath the photoresist pattern. x A layer of TiO2, Ta2O5, Al2O3, or other transparent inorganic materials is formed, and then the photoresist morphology is transferred to the underlying inorganic material layer through reactive ion etching, inductively coupled plasma etching, or ion beam etching. Alternatively, a deposition replication method can be used, for example, depositing a transparent inorganic material layer on the surface of the initial photoresist morphology, and then obtaining an inorganic conical or wedge-shaped transition structure corresponding to the initial photoresist morphology through resist removal, reverse etching, or planarization processes.

[0076] The formed conical or wedge-shaped transition structure is located between the light-emitting surface of the MicroLED pixel and the subsequent light guide system. It is used to adjust the angular distribution and spatial mode distribution of the MicroLED emitted light. By controlling the height, lateral dimensions, tilt angle, and refractive index of the material of this structure, the main propagation direction and divergence angle range of the MicroLED emitted light can be better matched with the numerical aperture of the subsequent light guide system. For example, when the numerical aperture NA of the subsequent light guide system is approximately 0.3 to 0.7, the tilt angle of the conical or wedge-shaped structure can be set to 10° to 45°, allowing more emitted light to fall within the acceptable angle range of the subsequent light guide system, thereby improving the incident coupling efficiency, reducing large-angle stray light, and improving the uniformity of light output.

Claims

1. A micro-LED display integrated with a light guide, characterized in that, The microLED pixel array (3) includes a color conversion or light emission modulation layer (4) on the light-emitting side of each sub-pixel, and a mode-restricted light guide layer structure (5) is provided on the top of the color conversion or light emission modulation layer (4).

2. The integrated structure of micro-light-emitting diode display and light guide as described in claim 1, characterized in that, The mode-restricted light guide layer structure (5) is a planar light waveguide structure, including a lower cladding layer, a light guide core layer and an upper cladding layer formed sequentially along the thickness direction. The lower cladding layer is located near the color conversion or light emission modulation layer (4) and has a refractive index of 1.45 to 1.

65. The refractive index of the light guide core layer is 1.75 to 2.2 and the refractive index of the upper cladding layer is 1.45 to 1.

65. 3.The micro-LED display and light guide integrated structure of claim 1, wherein, The mode-restricted light guide layer structure (5) is a segmented refractive index structure, consisting of 2 to 5 thin film stacks, with the refractive index of each thin film stack increasing gradually along the light output direction. 4.The micro-LED display and light guide integrated structure of claim 1, wherein, The mode-restricted light guide layer structure (5) is a gradient refractive index structure, which is composed of a structure whose refractive index changes continuously along the thickness direction, and the overall refractive index variation range Δn is 0.2 to 0.

5.

5. The integrated structure of micro-light-emitting diode display and light guide as described in claim 1, characterized in that, The mode-restricted light guide layer structure (5) is an image fiber structure, consisting of several fiber units whose length direction corresponds one-to-one with the light output direction of each sub-pixel. Each fiber unit includes a core layer with a refractive index of 1.6 to 1.9 and a cladding layer with a refractive index of 1.45 to 1.

55. 6.The micro-LED display and light guide integrated structure of claim 1, wherein, The mode-restricted light guide layer structure (5) is a conical or wedge-shaped transition structure with a sidewall inclination angle of 10° to 45°. 7.The method of claim 1, wherein the method further comprises: forming a plurality of micro-LEDs on the substrate; and forming a plurality of micro-LEDs on the substrate. Includes the following steps: Step 1: Fabricate a micro-LED pixel array; Step 2: Deposit a refractive index matching layer on the micro-LED pixel array; Step 3: Sequentially deposit the cladding layer and the light guide core layer on the refractive index matching layer; Step 4: Photolithographic patterning and etching of the light guide core layer; Step 5: Deposit the cladding layer on the optical core layer and anneal it to obtain the mode-confined optical guide layer structure of the planar optical waveguide structure. 8.The method of claim 1, wherein the method further comprises: forming a micro-LED array on the substrate; and forming a plurality of micro-LEDs on the micro-LED array. Includes the following steps: Step 1: Fabricate a micro-LED pixel array; Step 2: Sequentially sputter and deposit a multilayer inorganic thin film stack with progressively increasing refractive index on the micro-LED pixel array, including a SiO2 layer, a SiO2 / SiN layer, etc. x Composite layer, SiN x Layer, SiN x / TiO2 composite layer; Step 3: Annealing treatment to obtain the mode-constrained optical guide layer structure with segmented refractive index structure. 9.The method of claim 1, wherein the method further comprises: forming a plurality of micro-LEDs on the substrate; and forming a plurality of micro-LEDs on the substrate. Includes the following steps: Step 1: Fabricate a micro-LED pixel array; Step 2, SiO2 and SiN are used on the micro-LED pixel array x Double-target co-sputtering, the light guide layer with continuously graded refractive index in thickness direction is formed by continuously adjusting the power ratio of double targets Step 3: Annealing treatment to obtain a mode-confined optical guide layer structure with a gradient refractive index. 10.The method of claim 1, wherein the method further comprises: forming a micro-LED array on the substrate; and forming a plurality of micro-LEDs on the micro-LED array. Includes the following steps: Step 1: Fabricate a micro-LED pixel array; Step 2: Prepare a periodic aperture array template and sequentially fill it with a high refractive index core layer and a low refractive index cladding material to form an image fiber array; Step 3: Cut and polish the incident end face of the image fiber array; Step 4: Align and attach the incident end face of the image fiber array with the micro light-emitting diode pixel array so that the fiber and the pixel correspond one-to-one, thus obtaining the mode-constrained light guide layer structure of the image fiber structure.

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