Shaping layer for stepped full-color micro-led pixel and preparation method thereof

Abstract

This invention discloses a shaping layer for stepped full-color microLED pixels and its fabrication method. The layer includes an optical shaping area disposed above the full-color MicroLED light-emitting structure. The optical shaping area is divided into multiple partitions along the planar direction, each partition corresponding to a sub-pixel region with a different light-emitting height, and each partition has a refractive index gradient structure along its thickness direction. By setting partitioned refractive index gradient structures corresponding to the pixel's geometric height on the pixel's light-emitting side, the emitted light from pixels of different heights can propagate along a preset principal optical axis or the normal direction of the display surface after passing through the shaping layer. This makes the emission direction and optical axis of pixels of different heights and colors tend to be consistent. Thus, without the need for fine microlenses or microstructure processing, and reducing reliance on complex optical packaging and micro-optical elements, passive collimation of emitted light is achieved, and the brightness consistency, viewing angle consistency, and light utilization efficiency of the full-color MicroLED display are improved.

Description

Technical Field

[0001] This invention belongs to the field of micro-light-emitting diode display and optical shaping technology, specifically relating to a shaping layer for stepped full-color micro-light-emitting diode pixels. This invention also relates to a method for fabricating the shaping layer for stepped full-color micro-light-emitting diode pixels. Background Technology

[0002] In full-color MicroLED displays, pixels of different colors or color conversion structures are typically integrated onto the same substrate. For example... Figure 1 As shown, due to differences in the epitaxial structure, color conversion layer thickness, or encapsulation method of different color pixels, the actual light-emitting surface of each pixel is often at different heights, forming a stepped pixel structure.

[0003] like Figure 2 As shown, in a stepped pixel structure, the light-emitting surfaces of different pixels are not geometrically coplanar, resulting in systematic differences in the initial propagation direction, optical axis offset, and divergence angle of the emitted light, making it difficult to achieve overall collimation of the emitted light. In full-color displays, this difference further leads to inconsistent brightness, inconsistent viewing angle characteristics, and reduced light utilization efficiency.

[0004] Existing technologies typically collimate or shape emitted light using microlens arrays, subwavelength microstructures, or complex optical packaging. However, these solutions rely on intricate microstructure fabrication, resulting in complex processes, high costs, and significant integration challenges in high-resolution MicroLED displays. Therefore, there is an urgent need for an optical solution that eliminates the need for intricate microstructure fabrication and can passively achieve stepped pixel-based light collimation at the structural level. Summary of the Invention

[0005] The purpose of this invention is to provide a shaping layer for stepped full-color micro light-emitting diode pixels, which solves the problem that it is difficult to achieve overall pixel light collimation due to the non-coplanar geometry of the light-emitting surfaces of the pixels.

[0006] Another object of the present invention is to provide a method for preparing a shaping layer for a stepped full-color micro light-emitting diode pixel.

[0007] The first technical solution adopted in this invention is: a shaping layer for stepped full-color micro LED pixels, including an optical shaping area disposed above the full-color MicroLED light-emitting structure. The optical shaping area is divided into multiple partitions along the plane direction, each partition corresponding to a sub-pixel region with a different light emission height and forming a refractive index gradient structure along the thickness direction.

[0008] The first technical solution of this invention is further characterized by: The refractive index gradient structure consists of 3 to 8 sublayers whose refractive index changes monotonically step by step along the light-emitting direction.

[0009] The thickness of each sublayer in the refractive index gradient structure is 0.5–3 μm, the refractive index of each sublayer is 1.45–1.80, and the refractive index difference between adjacent sublayers is 0.02–0.10.

[0010] The total refractive index gradient Δn within each partition and the light emission height difference Δh of the corresponding sub-pixel both satisfy the following conditions: The proportionality constant k ranges from 0.02 to 0.08 μm. -1 .

[0011] The refractive index gradient structure uses transparent inorganic materials or transparent resin materials.

[0012] Transparent inorganic materials are selected from SiO2 and SiN x Al2O3, TiO2 or HfO2.

[0013] The transparent resin material is selected from an acrylic transparent resin system and nanofillers are introduced.

[0014] The MicroLED light-emitting structure includes a p-type semiconductor layer, a light-emitting layer, and an n-type semiconductor layer arranged sequentially from bottom to top. An n-type transparent electrode layer is disposed between the n-type semiconductor layer and the refractive index gradient structure. The p-type semiconductor layer is electrically connected to the anode electrode in the CMOS backplane through a p-type contact electrode layer.

[0015] The second technical solution adopted in this invention is: a method for preparing a shaping layer for stepped full-color micro-light-emitting diode pixels, comprising the following steps: Step 1: Divide the upper part of the full-color MicroLED light-emitting structure into corresponding horizontal partitions based on each sub-pixel region; Step 2: Set the total refractive index gradient matching in each horizontal partition according to the light emission height difference of each sub-pixel, and configure transparent resin materials with different refractive indices accordingly; Step 3: Spin-coat transparent resin materials with increasing refractive index layer by layer on top of the MicroLED light-emitting structure. After each layer is spin-coated, perform pre-baking and UV exposure for preliminary curing in sequence, and finally perform overall post-baking to form a refractive index gradient structure in each horizontal partition.

[0016] The third technical solution adopted in this invention is: a method for preparing a shaping layer for stepped full-color micro-light-emitting diode pixels, comprising the following steps: Step 1: Divide the upper part of the full-color MicroLED light-emitting structure into corresponding horizontal partitions based on each sub-pixel region; Step 2: Based on the light emission height difference of each sub-pixel, set the total refractive index gradient matching in each horizontal partition, and configure transparent inorganic materials with different refractive indices accordingly; Step 3: Using thin film deposition technology, transparent inorganic materials with increasing refractive index are deposited layer by layer on top of the MicroLED light-emitting structure. After each layer is deposited, a low-temperature annealing process is performed to form a refractive index gradient structure in each lateral partition.

[0017] The beneficial effects of this invention are as follows: This invention relates to a shaping layer for stepped full-color micro-LED pixels and its fabrication method. By setting a partitioned refractive index gradient structure corresponding to the pixel's geometric height on the pixel's light-emitting side, the emitted light from pixels of different heights can propagate along a preset principal optical axis or the normal direction of the display surface after passing through the shaping layer. This makes the emission direction and optical axis of pixels of different heights and colors tend to be consistent. Thus, passive collimation of emitted light is achieved without the need for fine microlenses or microstructure processing, reducing reliance on complex optical packaging and micro-optical elements, and improving the brightness consistency, viewing angle consistency, and light utilization efficiency of full-color MicroLED displays. Furthermore, this invention has a simple structure, high reliability, is suitable for high-resolution MicroLED display integration, and is easily compatible with existing MicroLED manufacturing processes and packaging technologies. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a stepped full-color micro light-emitting diode pixel; Figure 2 This is a schematic diagram illustrating the difference in the direction of light emitted by pixels at different heights in a stepped full-color micro light-emitting diode pixel. Figure 3 This is a schematic diagram of the shaping layer for the pixels of a stepped full-color micro light-emitting diode according to the present invention; Figure 4 This is a schematic diagram illustrating how the refractive index gradient of different partitions in the shaping layer of the stepped full-color micro light-emitting diode pixel adjusts the direction of emitted light according to the present invention.

[0019] In the figure, 1. CMOS backplane, 2. MicroLED light-emitting structure, 3. Optical shaping area, 4. Refractive index gradient structure; 11. Anode electrode; 12. Cathode electrode; 2a. Green photon pixel, 2b. Red photon pixel, 2c. Blue photon pixel, 21. n-type semiconductor layer, 22. Light-emitting layer, 23. p-type semiconductor layer, 24. p-type contact electrode layer, 25. n-type transparent electrode layer, 26. Color conversion layer; 31. Green light shaping zone; 32. Red light shaping zone; 33. Blue light shaping zone; 41. First sub-layer, 42. Second sub-layer, 43. Third sub-layer. Detailed Implementation

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

[0021] Example 1 The present invention provides a shaping layer for stepped full-color micro light-emitting diode pixels. The shaping layer is disposed above a quantum dot photoresist structure or a micro display pixel, with a thickness of 3 to 15 μm, preferably 5 to 10 μm, and covers at least the entire effective light-emitting area of ​​the pixel.

[0022] The stepped MicroLED pixel has a height difference structure in the light emission direction. Different color sub-pixels (e.g., R, G, B) correspond to different light emission heights, with the height difference ranging from 0.5 to 5 μm, typically 1 to 3 μm. Based on this height difference, the passive optical shaping layer is divided into multiple partitions in the planar direction, each partition corresponding to a sub-pixel region or a region with the same light emission height. Preferably, three partitions are set within an RGB pixel unit, corresponding to the red, green, and blue sub-pixel regions respectively; in higher precision embodiments, it can be further subdivided into 3 to 6 sub-partitions to achieve finer optical correction.

[0023] A refractive index gradient structure is set within each partition, with the refractive index gradient forming along the thickness direction. This gradient can be achieved using a layered discrete structure or a continuous gradient structure. In the layered structure implementation, each partition contains 3 to 8 sub-layers with different refractive indices, each with a thickness of 0.5 to 2 μm, and the total thickness is consistent with the shaping layer thickness. The refractive index range of each layer is n = 1.45 to 1.80, the refractive index difference between adjacent layers is 0.02 to 0.08, and the difference monotonically increases or decreases along the light emission direction.

[0024] In the continuous gradient implementation, the refractive index varies continuously along the thickness direction, with a gradient range of dn / dz = 0.01–0.10 μm. -1 This forms an equivalent gradient refractive index (GRIN) structure.

[0025] A matching relationship is established between the refractive index gradient parameters of different partitions and the light emission height difference Δh of the corresponding sub-pixels. Preferably, the change in refractive index gradient, i.e., the total gradient Δn, and the height difference Δh satisfy the following relationship:

[0026] Where k is the adjustment coefficient, and its value ranges from 0.02 to 0.08 μm. -1 This matching relationship ensures that light emitted from different heights undergoes corresponding refraction deflection angles after passing through the shaping layer, thereby compensating for the optical axis shift caused by the height difference.

[0027] In the specific design, the lower light emission height region corresponds to a smaller refractive index gradient (e.g., Δn = 0.05 to 0.10), while the higher light emission region corresponds to a larger refractive index gradient (e.g., Δn = 0.10 to 0.25), thereby achieving differentiated correction for light rays with different initial emission angles.

[0028] The shaping layer material can be a transparent polymer system, and its refractive index can be controlled by the following methods: changing the material ratio (e.g., adjusting the ratio of high refractive index resin to low refractive index resin in the range of 20% to 80%), introducing nanofillers (such as TiO2, ZrO2, with a volume fraction of 1% to 15%), or forming a refractive index gradient structure by controlling the crosslinking density.

[0029] During the operation of MicroLED pixels, the initial emission angles differ due to the varying light emission starting heights of different sub-pixels. By employing the aforementioned partitioned refractive index gradient structure with quantitatively designed parameters, controlled refraction and path deflection of light occur within the shaping layer, causing light emitted from different regions to tend to propagate along a unified reference direction after leaving the shaping layer. This reference direction is either the normal direction of the display surface or a preset principal optical axis, with deviations controllable within ±2° to ±5°.

[0030] Based on optical simulation results (ray tracing model), it is shown that after introducing this structure, the difference in angular divergence of light emitted from different sub-pixels can be reduced by about 30% to 60%, and the overall beam divergence angle (FWHM) converges from about 20° to 30° to about 10° to 18%, thereby significantly improving light collimation and display efficiency.

[0031] When there is no height difference (Δh≈0) on the light-emitting surface of a MicroLED pixel, there is no need to set a differentiated refractive index gradient structure for each zone. In this case, the shaping layer can be simplified to a uniform refractive index layer.

[0032] Through the above-mentioned passive optical shaping layer design with a clear structural form, number of layers, refractive index range and matching relationship with pixel height difference, structural collimation of light emitted from pixels of multiple heights and colors can be achieved without additional optical components or active control.

[0033] Example 2 This invention provides a shaping layer for stepped full-color micro-light-emitting diode pixels, such as... Figure 3 and Figure 4 As shown, the structure includes a CMOS backplane 1, a MicroLED light-emitting structure 2 disposed on the CMOS backplane 1, and an optical shaping region 3 disposed above the MicroLED light-emitting structure 2. A refractive index gradient structure 4 is formed inside the optical shaping region 3.

[0034] The CMOS backplane 1 is used to drive pixels, and an anode electrode 11 and a cathode electrode 12 are formed on it, which are electrically connected to the MicroLED light-emitting structure 2. The MicroLED light-emitting structure 2 includes an n-type semiconductor layer 21, a light-emitting layer 22, and a p-type semiconductor layer 23 stacked sequentially, wherein the p-type semiconductor layer 23 is electrically connected to the anode electrode 11 through a p-type contact electrode layer 24. An n-type transparent electrode layer 25 is formed on the n-type semiconductor layer 21 for current spreading and light emission.

[0035] Since the MicroLED light-emitting structure 2 is a stepped structure, different color sub-pixels, such as green sub-pixel 2a, red sub-pixel 2b, and blue sub-pixel 2c, have different heights in the light-emitting direction. The height difference between the light-emitting surfaces of each sub-pixel and the same preset reference plane is Δh, which is 0.5 to 3 μm, preferably 1 to 2 μm. Among them, the red sub-pixel 2b can be obtained by converting the blue pixel through the top color conversion layer 26.

[0036] The optical shaping region 3 is disposed above the n-type transparent electrode layer 25 and covers the entire pixel light-emitting area, with a thickness of 5–12 μm. The optical shaping region 3 is divided into 3 partitions in the planar direction according to the stepped pixel structure. Each partition corresponds to a sub-pixel region with a different light emission height, namely, the green light shaping partition 31 corresponds to the green light sub-pixel 2a, the red light shaping partition 32 corresponds to the red light sub-pixel 2b, and the blue light shaping partition 33 corresponds to the blue light sub-pixel 2c.

[0037] The refractive index gradient structure 4 is the internal functional structure of the optical shaping region 3, and it is distributed along the thickness direction of the shaping structure. The refractive index gradient structure 4 can be realized through a multi-layered structure, with 3 to 6 sub-layers of different refractive indices set in each region. For example, when there are 3 sub-layers, they include a first sub-layer 41, a second sub-layer 42, and a third sub-layer 43 set in sequence. The thickness of each layer is 0.8 to 3 μm, the refractive index range is 1.45 to 1.80, the refractive index difference between adjacent sub-layers is 0.03 to 0.10, and it exhibits a monotonically changing relationship along the light emission direction (n). 41 <n 42 <n 43 This causes the light to be refracted and deflected step by step during its propagation.

[0038] A matching relationship is established between the refractive index gradient parameters within each partition and the light emission height difference Δh of the corresponding sub-pixels. The refractive index change, i.e., the total gradient Δn, satisfies the relationship Δn = k·Δh with Δh. The scaling factor k ranges from 0.03 to 0.08m. -1 Specifically, subpixels with lower light emission heights correspond to smaller refractive index gradients (Δn is 0.05 to 0.10), while subpixels with higher light emission heights correspond to larger refractive index gradients (Δn is 0.10 to 0.25).

[0039] During the operation of MicroLED pixels, due to the height difference in the light emission starting points of different sub-pixels 2a, 2b, and 2c, the emitted light has different propagation directions before shaping. Through the refractive index gradient structure 4 inside the optical shaping area 3, the light is continuously deflected along the direction of gradually increasing refractive index during propagation, causing the light emitted from different areas to tend to propagate along a unified reference direction after leaving the optical shaping area 3. The reference direction is the normal direction of the display surface, and its emission angle deviation can be controlled within the range of ±2° to ±5°.

[0040] When there is no height difference between the light-emitting surfaces of MicroLED pixels, the refractive index gradient structure 4 in each partition 31, 32, and 33 can be simplified into a uniform refractive index distribution structure.

[0041] Through the above structural design, the optical shaping area 3 and its internal refractive index gradient structure 4 are integrated, achieving passive collimation of light emitted from pixels of multiple heights and colors without the need for additional optical components or active control.

[0042] Example 3 This invention provides a shaping layer for the pixels of a stepped full-color micro light-emitting diode. The optical shaping area 3 can be made of a transparent polymer material system. Its refractive index gradient structure 4 can be prepared by spin coating different refractive index materials in layers, adjusting the proportion of high refractive index resin to 30% to 80%, and through multiple spin coating and exposure curing processes.

[0043] Example 4 This invention provides a method for fabricating a shaping layer for a stepped full-color microLED pixel as described in Embodiment 3. In this embodiment, the MicroLED pixel adopts a stepped full-color structure, with a single pixel unit size of 12μm×12μm. The red, green, and blue sub-pixels correspond to different light emission heights, with height differences Δh of approximately 2.0μm (red light), 1.2μm (green light), and 0.5μm (blue light), respectively. An n-type transparent electrode layer (ITO) with a thickness of 120nm is formed above the MicroLED light-emitting structure.

[0044] An integrated optical shaping layer is formed above the n-type transparent electrode layer. This shaping layer is made of a transparent polymer material system and is prepared by a multilayer spin coating and curing process, with a total thickness of approximately 8 μm. In the planar direction, the shaping layer is divided into three horizontal partitions according to the RGB sub-pixel regions. Each partition covers the light-emitting area of ​​the corresponding color sub-pixel and is aligned with it in the planar position.

[0045] A layered refractive index gradient structure is formed along the thickness direction within each partition. Specifically, each partition has four sublayers with different refractive indices, each approximately 2 μm thick, formed by spin-coating different proportions of optical resin material layer by layer. The material is an acrylic transparent resin system, and the refractive index is controlled by adjusting the ratio of high-refractive-index monomers (refractive index approximately 1.65–1.75) to low-refractive-index monomers (refractive index approximately 1.45–1.50). Furthermore, TiO2 nanoparticles (particle size approximately 20–50 nm, volume fraction 3%–10%) are introduced into some layers to further enhance the refractive index.

[0046] For different zones, the refractive index gradient parameters are designed to match the light emission height of the corresponding sub-pixels. In the blue sub-pixel region (Δh≈0.5μm), the refractive index increases stepwise from 1.46 to 1.55 along the thickness direction, with a total gradient Δn≈0.09; in the green sub-pixel region (Δh≈1.2μm), the refractive index increases from 1.46 to approximately 1.62, with a total gradient Δn≈0.16; and in the red sub-pixel region (Δh≈2.0μm), the refractive index increases from 1.48 to approximately 1.72, with a total gradient Δn≈0.24. The refractive index difference between adjacent layers is controlled within the range of 0.03 to 0.08, ensuring that light undergoes stepwise refraction rather than abrupt scattering during propagation.

[0047] The shaping layer is formed through the following process: First, a first layer of low-refractive-index resin is spin-coated onto the ITO surface at a spin speed of 3000 rpm for 40 seconds, forming a film layer of approximately 2 μm thickness, and then pre-baked at 90 °C for 2 minutes; subsequently, it is exposed to ultraviolet light (dose 200 mJ / cm²). 2 After initial curing, the next three layers of material are spin-coated sequentially. The refractive index of each layer is increased by adjusting the resin ratio or the content of nanoparticles. The pre-baking and exposure curing steps are repeated, and finally, a stable multi-layer gradient structure is formed by overall post-baking (110℃, 5min).

[0048] During the operation of MicroLEDs, due to their light-emitting characteristics approximating a Lambertian distribution, the emitted light spreads over a wide angular range, with typical energy mainly distributed within ±45°, exhibiting an overall wide-angle divergence characteristic. Simultaneously, due to the different light-emitting heights introduced by the stepped structure, the angular distribution and energy weight of each sub-pixel differ. Without optical shaping, the red sub-pixel, due to its higher light-emitting height, spreads its light distribution over a wide angular range, with its main energy covering approximately ±45° or even larger angles, and having a higher weight in the larger angular directions. The green sub-pixel's angular distribution is relatively convergent, mainly concentrated within the ±30° to ±40° range. The blue sub-pixel, due to its lower light-emitting height, has a relatively more concentrated distribution, but still exhibits typical Lambertian characteristics, mainly distributed within the ±25° to ±35° range. Overall, under unshaped conditions, all three color sub-pixels exhibit a wide-angle divergence distribution, and there are significant differences in angular distribution between different colors. Meanwhile, due to the different light emission heights of different sub-pixels, their initial emission angles vary. Under unshaped conditions, the emission angle of red sub-pixels deviates from the normal by approximately 15° to 20°, green by approximately 8° to 12°, and blue by approximately 3° to 6°.

[0049] After introducing the partitioned refractive index gradient shaping layer in this embodiment, the light propagates in the direction of gradually increasing refractive index inside the shaping layer and undergoes multiple refractions and deflections, thereby achieving a gradual deflection and redistribution of the light propagation direction, causing the originally wide-angle distributed outgoing light to converge towards the normal direction, thus achieving optical axis correction.

[0050] Based on ray tracing simulations (LightTools), the results show that under this structure, the average emission angle of the emitted light from each sub-pixel is compressed to within ±3°, and the energy distribution of the emitted light from each sub-pixel can be effectively compressed to within ±18°, achieving optimization from a Lambertian wide-angle distribution to a medium-angle concentrated distribution. With further optimization of design parameters, the energy distribution along the principal optical axis can be further converged to within ±3°. Simultaneously, the overall divergence angle (FWHM) is significantly reduced from the original large angle to approximately 14°–18°, a reduction of approximately 40%–60%. Furthermore, the angular distribution difference between different sub-pixels is reduced by approximately 60%, and the optical axis consistency is significantly improved.

[0051] Further optical efficiency calculations show that concentrating the light output direction increases the effective light utilization rate by about 20% to 30%. In particular, when coupled with subsequent waveguides or optical systems, it can significantly reduce angular loss and improve the overall optical efficiency of the system.

[0052] By using the aforementioned optical shaping layer with a clear partitioning structure, layer design, material system, and refractive index gradient parameters, passive collimation of the light emitted from the stepped MicroLED pixels is achieved without the need to introduce additional microlenses or active control structures. This effectively compresses the original wide-angle Lambertian light distribution to an engineering-acceptable range of ±18°, thereby significantly improving the brightness utilization efficiency and color consistency of the display system.

[0053] Example 5 This invention provides a shaping layer for the pixels of a stepped full-color micro light-emitting diode. The optical shaping area 3 can be realized using a transparent polymer material system, and its refractive index gradient structure 4 can be prepared by introducing high refractive index nanoparticles (TiO2 or ZrO2, volume fraction 2% to 15%) in layers.

[0054] Example 6 This invention provides a method for fabricating a shaping layer for a stepped full-color microLED pixel, as described in Example 5. In this example, the MicroLED pixel size is 8μm × 8μm, the pixel pitch is 4μm, and different color sub-pixels have a step height difference Δh in the light emission direction, with a value ranging from 0.8 to 2.0μm. An n-type transparent electrode layer (ITO) with a thickness of approximately 120nm is formed above the MicroLED light-emitting structure. An inorganic refractive index gradient optical shaping layer with a thickness of 6–10μm is deposited above the transparent electrode layer, covering the entire pixel light-emitting area.

[0055] The shaping layer employs an inorganic dielectric multilayer stacked structure to form a refractive index gradient along the thickness direction, and its material system is selected from SiO2 and SiN. x Transparent inorganic materials such as Al2O3, TiO2, or HfO2 are used. By combining low-refractive-index materials (such as SiO2, n≈1.45) with high-refractive-index materials (such as TiO2 or HfO2, n≈2.0~2.2), a gradient structure with an effective refractive index continuously varying in the range of 1.45~1.85 can be constructed.

[0056] In this embodiment, the refractive index gradient is approximated by a 5-layer discrete multilayer structure, with each layer having a thickness of 1.0–2.0 μm. The effective refractive index difference between adjacent layers is 0.05–0.10, and they satisfy a monotonically increasing relationship along the light emission direction. The effective refractive index of each layer is achieved by adjusting the volume fraction of SiO2 and high-refractive-index materials (TiO2 or HfO2), wherein the SiO2 content in the low-refractive-index layer is 70%–90%, and the TiO2 content in the high-refractive-index layer is 40%–70%.

[0057] For different sub-pixel regions, the refractive index gradient range is adjusted according to the light emission height difference Δh. In the region with lower light emission height, the refractive index ranges from 1.45 to 1.60, corresponding to Δn of 0.10 to 0.15; in the region with medium light emission height, the refractive index ranges from 1.48 to 1.70, corresponding to Δn of 0.15 to 0.22; and in the region with higher light emission height, the refractive index ranges from 1.50 to 1.85, corresponding to Δn of 0.20 to 0.30. The refractive index change Δn and the height difference Δh satisfy the relationship Δn = k·Δh, where k is 0.04 to 0.07 μm. -1 This allows for quantitative correction of light rays with different initial exit angles.

[0058] The inorganic refractive index gradient shaping layer is formed through a thin film deposition process. Specifically, a SiO2 and TiO2 (or HfO2) composite layer is deposited using alternating magnetron sputtering or atomic layer deposition (ALD). In the magnetron sputtering process, the sputtering power is 100–250 W, the working gas pressure is 2–5 mTorr, and the gas is an Ar / O2 mixture (O2 ratio 10%–30%). The composition ratio of different layers is controlled by adjusting the dual-target power ratio. After each layer is deposited, a low-temperature annealing treatment is performed (temperature 200℃–300℃, time 5–10 min) to improve the film density and optical stability. Through repeated deposition and controlled composition, a multilayer gradient structure along the thickness direction is formed.

[0059] During the operation of MicroLEDs, due to their light-emitting characteristics approximating the Lambertian distribution, the emitted light spreads over a wide angular range, with typical energy mainly distributed within ±45°, exhibiting an overall wide-angle divergence characteristic. Simultaneously, due to the light-emitting height difference Δh introduced by the stepped structure, the angular distribution and energy weight of different sub-pixels differ, with regions having higher light-emitting heights exhibiting a higher energy proportion over larger angular directions.

[0060] Through the inorganic refractive index gradient structure, light is continuously deflected along the direction of gradually increasing refractive index during propagation, causing the originally wide-angle distributed outgoing light to gradually converge towards the normal direction, thus achieving unified correction of light rays with different initial angle distributions.

[0061] Based on ray tracing simulation (Zemax) results, after introducing this inorganic gradient structure, the angular difference of the emitted light from different sub-pixels is reduced by approximately 45%–65%, the overall beam divergence angle (FWHM) significantly converges from the original wide-angle distribution to approximately 14°–18°, the principal energy distribution is compressed to within ±18°, and the principal optical axis deviation can be controlled within ±3°. Simultaneously, the light energy utilization efficiency is improved by approximately 15%–25%.

[0062] In experimental verification, no significant refractive index degradation or structural changes were observed in the sample using this inorganic gradient structure after 200 hours of continuous operation, and its optical performance stability was superior to that of the organic structure. Test results showed that the emitted light brightness was improved by approximately 18%–22%, and the viewing angle consistency was significantly improved.

[0063] Through the above-mentioned design of the refractive index gradient shaping layer based on the inorganic material system, passive collimation and optical shaping of the light emitted from the stepped MicroLED pixels are achieved while ensuring high thermal stability and long-term reliability. This effectively compresses the original Lambertian wide-angle (±45°) distribution to an engineering-usable range of ±18°, thereby significantly improving the brightness utilization efficiency and angle consistency of the display system.

Claims

1. A shaping layer for a stepped full-color micro-LED pixel, characterized in that, It includes an optical shaping area (3) set above the full-color MicroLED light-emitting structure (2). The optical shaping area (3) is divided into multiple partitions along the plane direction. Each partition corresponds to a sub-pixel region with a different light emission height and has a refractive index gradient structure (4) along the thickness direction.

2. The shaping layer for stepped full-color micro-LED pixels of claim 1, wherein, The refractive index gradient structure (4) includes 3 to 8 sub-layers whose refractive index changes monotonically along the light-emitting direction.

3. The shaping layer for stepped full-color micro-LED pixels of claim 2, wherein, The thickness of each sublayer in the refractive index gradient structure (4) is 0.5 to 3 μm, the refractive index of each sublayer is 1.45 to 1.80, and the refractive index difference between adjacent sublayers is 0.02 to 0.

10.

4. The shaping layer for stepped full-color micro-light-emitting diode pixels as described in claim 1, characterized in that, The total gradient of the refractive index Δn in each partition and the light-out height difference Δh of the corresponding sub-pixel satisfy The value range of the proportional coefficient k is 0.02-0.08 μm -1 .

5. The shaping layer for stepped full-color micro-light-emitting diode pixels as described in claim 1, characterized in that, The refractive index gradient structure (4) is made of transparent inorganic material or transparent resin material.

6. The shaping layer for stepped full-color micro-light-emitting diode pixels as described in claim 5, characterized in that, The transparent inorganic material is selected from SiO2, SiN x , Al2O3, TiO2or HfO2.

7. The shaping layer for stepped full-color micro-light-emitting diode pixels as described in claim 5, characterized in that, The transparent resin material is selected from acrylic transparent resin systems and nanofillers are introduced.

8. The shaping layer for stepped full-color micro-light-emitting diode pixels as described in claim 1, characterized in that, The MicroLED light-emitting structure (2) includes a p-type semiconductor layer (23), a light-emitting layer (22) and an n-type semiconductor layer (21) arranged sequentially from bottom to top. An n-type transparent electrode layer (25) is disposed between the n-type semiconductor layer (21) and the refractive index gradient structure (4). The p-type semiconductor layer (23) is electrically connected to the anode electrode (11) in the CMOS backplane (1) through the p-type contact electrode layer (24).

9. The method for preparing the shaping layer for stepped full-color micro-light-emitting diode pixels as described in claim 1, characterized in that, Includes the following steps: Step 1: Divide the upper part of the full-color MicroLED light-emitting structure into corresponding horizontal partitions based on each sub-pixel region; Step 2: Set the total refractive index gradient matching in each horizontal partition according to the light emission height difference of each sub-pixel, and configure transparent resin materials with different refractive indices accordingly; Step 3: Spin-coat transparent resin materials with increasing refractive index layer by layer on top of the MicroLED light-emitting structure. After each layer is spin-coated, perform pre-baking and UV exposure for preliminary curing in sequence, and finally perform overall post-baking to form a refractive index gradient structure in each horizontal partition.

10. The method for preparing the shaping layer for a stepped full-color micro-light-emitting diode pixel as described in claim 1, characterized in that, Includes the following steps: Step 1: Divide the upper part of the full-color MicroLED light-emitting structure into corresponding horizontal partitions based on each sub-pixel region; Step 2: Based on the light emission height difference of each sub-pixel, set the total refractive index gradient matching in each horizontal partition, and configure transparent inorganic materials with different refractive indices accordingly; Step 3: Using thin film deposition technology, transparent inorganic materials with increasing refractive index are deposited layer by layer on top of the MicroLED light-emitting structure. After each layer is deposited, a low-temperature annealing process is performed to form a refractive index gradient structure in each lateral partition.

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