Flip micro-led circular polarizer based on homogeneous chiral metasurface and preparation method thereof

Abstract

The application discloses a flip Micro-LED circular polarization device based on a homogeneous chiral metasurface and a preparation method thereof, and relates to the technical field of semiconductor display. The preparation method of the device comprises the following steps: forming a first support layer on the surface of an electrode layer; performing thinning treatment and polishing treatment on an initial GaN substrate layer to prepare a metasurface structure layer; forming a chiral metasurface structure on the thinned GaN substrate layer by using a micro-nano processing process, and combining an etching process to realize a homogeneous GaN chiral metasurface structure and a transition layer which is not etched; forming a second support layer on the chiral metasurface structure; removing the first support layer to expose the electrode layer, and flip bonding the electrode layer with a control circuit; and removing the second support layer to obtain the flip Micro-LED circular polarization device. According to the application, the light loss can be reduced, the circular polarization conversion stability can be improved, and cracks, fragmentation or structural damage can be avoided during the preparation of the polarization device.

Description

Technical Field

[0001] This invention relates to the field of semiconductor display technology, specifically to a flip-chip Micro-LED circularly polarized device based on a homogeneous chiral metasurface and its fabrication method. Background Technology

[0002] As display technology advances towards higher resolution, lower power consumption, miniaturization, and multifunctional integration, Micro-LEDs, with their advantages of self-emission, high brightness, low power consumption, long lifespan, and pixel-level independent driving, are widely used in displays, near-eye displays, optical communications, optical sensing, and polarization imaging. However, conventional GaN-based Micro-LEDs typically rely on spontaneous emission from quantum well regions, resulting in emitted light that is mostly unpolarized or weakly polarized, making it difficult to directly meet the demand for stable circularly polarized light sources in applications such as 3D displays, AR / VR, and optical communications.

[0003] To achieve polarization state control of Micro-LED light output, existing technologies typically employ external polarizers, grating structures, microcavity structures, or additional integrated metasurface structures. However, external polarizers or additional optical components increase device thickness and packaging complexity, and introduce significant light intensity loss. Grating structures are mostly used for linearly polarized light screening or light output direction control, but their polarization conversion efficiency and circular polarization control capability are limited. Although heterogeneous material metasurfaces or metallic chiral structures can achieve certain light field control, they are prone to introducing problems such as interface reflection, thermal expansion mismatch, lattice mismatch, and additional absorption, affecting the light output efficiency and long-term reliability of Micro-LED devices.

[0004] Furthermore, for flip-chip Micro-LED devices, the electrode layer needs to be flip-bonded to the control circuit, while the light-emitting side needs to retain or form micro / nano structures for controlling the polarization state of the emitted light. Firstly, because the control circuit makes metasurface fabrication difficult after flip-chip bonding of Micro-LEDs, it is necessary to protect the unbonded Micro-LED chip with a support layer before fabricating the metasurface structure. Secondly, for pixelated Micro-LED array chips aiming to achieve different polarization states, directly fabricating chiral metasurface structures on the GaN substrate side is problematic. Due to the large thickness of conventional GaN-based epitaxial wafers and the significant distance between the quantum well layer and the light-emitting metasurface structure, lateral diffusion, crosstalk, and scattering losses easily occur in the GaN substrate, weakening the polarization control effect of the chiral metasurface structure on the emitted light. Therefore, the initial GaN substrate layer needs to be thinned to bring the subsequently formed chiral metasurface structure closer to the quantum well layer, thereby improving the coupling efficiency between the emitted light and the chiral structure units. However, GaN materials are hard and brittle. The mechanical strength of GaN-based epitaxial wafers is significantly reduced after thinning. They are prone to warping, cracking or fragmentation during grinding, polishing, nanoimprinting, etching and subsequent flip-chip bonding. Especially after the chiral metasurface structure has been formed, the flip-chip bonding pressure may also directly act on the micro-nano protrusion structure, leading to damage, collapse or deterioration of the polarization control performance of the chiral structural unit. Summary of the Invention

[0005] One objective of the first aspect of this invention is to provide a method for fabricating a flip-chip Micro-LED circularly polarized device based on a homogeneous chiral metasurface, thereby solving the technical problems in the prior art where it is difficult to reliably fabricate a homogeneous chiral metasurface structure on the light-emitting side of thinned GaN for flip-chip Micro-LED devices, resulting in the difficulty of converting unpolarized or weakly polarized light into circularly polarized light with low loss and high stability, and the easy generation of cracks, fragmentation or structural damage in the thinned chip and micro / nano chiral structure during metasurface fabrication and flip-chip bonding.

[0006] Another objective of the first aspect of this invention is to further improve the processing stability and device reliability during the fabrication of homogeneous GaN chiral metasurface structures.

[0007] The second aspect of this invention aims to provide a flip-chip Micro-LED circularly polarized device prepared by the above-described preparation method.

[0008] According to a first aspect of the present invention, the present invention provides a method for fabricating a flip-chip Micro-LED circularly polarized device based on a homogeneous chiral metasurface, comprising the following steps: An electrode layer is deposited on a p-type GaN layer of a GaN-based epitaxial wafer, wherein the GaN-based epitaxial wafer comprises an initial GaN substrate layer, an n-type GaN layer, a quantum well layer and the p-type GaN layer, which are stacked sequentially from top to bottom; A first buffer layer and a first temporary support layer are sequentially disposed on the surface of the electrode layer to form a first support layer, wherein the first buffer layer covers the electrode layer and bonds the first temporary support layer. With the support of the first support layer, the initial GaN substrate is thinned and polished sequentially from the side of the initial GaN substrate away from the n-type GaN layer to obtain a thinned GaN substrate for the preparation of metasurface structures. A patterned mask is formed on the surface of the thinned GaN substrate using micro-nano fabrication technology, and the patterned mask is used as an etching mask to partially etch the metasurface structure layer along the thickness direction, so that the thinned GaN substrate layer forms a chiral metasurface structure with multiple chiral structural units arranged periodically and an unetched transition layer. A second buffer layer and a second temporary support layer are sequentially disposed on the side of the chiral metasurface structure away from the transition layer to form a second support layer, and the second buffer layer covers the chiral structural unit and at least fills the gap between adjacent chiral structural units. With the chiral metasurface structure supported by the second support layer, the first support layer is removed to expose the electrode layer, and the electrode layer is flip-bonded to the control circuit. A light-absorbing material is filled between the electrode layer and the control circuit using the capillary effect; The second support layer is removed to expose the chiral metasurface structure, thereby obtaining a flip-chip Micro-LED circularly polarized device.

[0009] Optionally, the thickness of the thinned GaN substrate layer is any value between 5 μm and 100 μm, and the thickness of each chiral structural unit is any value between 0.5 μm and 1.5 μm.

[0010] Optionally, the thinning process includes sequentially grinding and polishing the substrate layer to make the surface roughness Ra of the thinned GaN substrate layer on the side away from the n-type GaN layer less than or equal to 5 nm.

[0011] Optionally, the cross-section of the chiral structural unit includes a first right trapezoid and a second right trapezoid arranged in a centrally symmetrical manner, wherein the midpoint of the short base of the first right trapezoid is the center of symmetry.

[0012] Optionally, the length of the long base of the first right trapezoid is any value between 0.18μm and 0.20μm, the length of the short base is any value between 0.06μm and 0.10μm, and the height is any value between 0.16μm and 0.20μm.

[0013] Optionally, the period of the multiple chiral structural units can be any value between 400nm and 800nm.

[0014] Optionally, the first buffer layer is a first removable buffer layer that can be removed by the first removal medium, and the second buffer layer is a second removable buffer layer that maintains structural integrity in the first removal medium. When removing the first support layer, the GaN-based epitaxial wafer with the second support layer formed thereon is placed in the first removal medium to remove the first buffer layer and separate the first temporary support layer. The second buffer layer in the first removal medium maintains coverage of the chiral structural units and fills the gaps between adjacent chiral structural units.

[0015] Optionally, the first buffer layer is a photoresist layer soluble in an organic solvent, and the first removal medium includes at least one of acetone, N-methylpyrrolidone, or photoresist stripping solution; The second buffer layer is a polymer sacrificial layer that has been treated with ultraviolet curing, thermal curing or cross-linking curing, and the swelling rate of the second buffer layer in the first removal medium is less than or equal to 10%.

[0016] According to a second aspect of the present invention, the present invention also provides a flip-chip Micro-LED circular polarization device prepared according to the above-described method for preparing a flip-chip Micro-LED circular polarization device based on a homogeneous chiral metasurface.

[0017] This invention utilizes the thinned GaN substrate layer formed after the initial GaN substrate layer is thinned to directly etch a homogeneous chiral metasurface structure. This allows the chiral metasurface structure and the unetched transition layer to be integrally formed from the same GaN material, thus avoiding interface reflection, thermal expansion mismatch, and additional optical losses introduced by external polarizers or heterogeneous metasurfaces. While ensuring the mechanical reliability and manufacturability of flip-chip Micro-LED circularly polarized devices, it achieves low-loss, high-integration, and stable circularly polarized light output. Furthermore, for pixelated Micro-LED array chips, the thinned transition layer shortens the propagation distance of light emitted from the quantum well layer to the chiral metasurface structure, reducing lateral diffusion, crosstalk, and scattering losses within the thick substrate. This allows unpolarized or weakly polarized light emitted from the quantum well layer to couple more effectively into the chiral metasurface structure. Furthermore, the periodically arranged chiral structural units, through their non-mirror-symmetric profiles, produce differentiated transmission, scattering, and phase modulation effects on the left-hand circularly polarized components and the right-hand circularly polarized components, thereby realizing on-chip conversion of Micro-LED emitted light from an unpolarized or weakly polarized state to a circularly polarized state, improving the stability and integration of circularly polarized light output.

[0018] Furthermore, the thickness of the GaN substrate layer thinned in this invention is any value between 5μm and 100μm, and the thickness of each chiral structural unit is any value between 0.5μm and 1.5μm. This achieves a match between optical control performance and structural mechanical reliability. That is, the thickness of the thinned GaN substrate layer and the thickness of the chiral structural unit complement each other, ensuring both the thinning, low-loss light emission, and circular polarization conversion effect of the flip-chip Micro-LED device, and improving the processing stability and device reliability during the fabrication of the homogeneous GaN chiral metasurface structure.

[0019] 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

[0020] The following sections will describe some specific embodiments of the invention in detail by way of example and not limitation, with reference to the accompanying drawings. The same reference numerals in the drawings denote the same or similar parts or portions. Those skilled in the art should understand that these drawings are not necessarily drawn to scale. In the drawings: Figure 1 This is a schematic flowchart of a method for fabricating a flip-chip Micro-LED circularly polarized device according to an embodiment of the present invention; Figure 2 This is a schematic structural diagram of a flip-chip Micro-LED circularly polarized device according to an embodiment of the present invention; Figure 3This is a schematic structural diagram of a GaN-based epitaxial wafer according to an embodiment of the present invention; Figure 4 This is a schematic structural distribution diagram of a chiral metasurface structure according to an embodiment of the present invention; Figure 5 This is a schematic cross-sectional view of a chiral structural unit according to an embodiment of the present invention; Figure 6 This is a schematic structural diagram of a chiral structural unit according to a first embodiment of the present invention; Figure 7 This is a schematic structural diagram of a chiral structural unit according to a second embodiment of the present invention; Figure 8 This is a schematic structural diagram of a chiral structural unit according to a third embodiment of the present invention; Figure 9 The XY plane field strength direction of the flip-chip Micro-LED circularly polarized device according to Embodiment 1 of the present invention under right-hand circularly polarized incident light; Figure 10 This describes the XY plane field strength distribution of the flip-chip Micro-LED circularly polarized device according to Embodiment 1 of the present invention under right-hand circularly polarized incident light. Figure 11 The XY plane field strength direction of the flip-chip Micro-LED circularly polarized device according to Embodiment 1 of the present invention under left-handed circularly polarized incident light; Figure 12 This describes the XY plane field strength distribution of the flip-chip Micro-LED circularly polarized device according to Embodiment 1 of the present invention under left-handed circularly polarized incident light. Figure 13 The transmission spectra of the flip-chip Micro-LED circularly polarized device according to Embodiment 1 of the present invention are corresponding to left-handed and right-handed circularly polarized incident light. Figure 14 This is a circular dichroism diagram of the chiral metasurface structure according to Embodiment 1 of the present invention; Figure 15 This refers to the ratio of left-handed to right-handed circular polarization conversion efficiency of the flip-chip Micro-LED circular polarization device according to Embodiment 1 of the present invention when right-handed circularly polarized light is incident. Figure 16 It is the ratio of left-handed to right-handed circular polarization conversion efficiency when left-handed circularly polarized light is incident on the flip-chip Micro-LED circular polarization device according to Embodiment 1 of the present invention.

[0021] Figure label: 100-Flip-chip Micro-LED circularly polarized device, 10-GaN-based epitaxial wafer, 20-Electrode layer, 30-Control circuit, 40-Bonding metal, 50-Black light-absorbing material, 11-Initial GaN substrate layer, 12-n-type GaN layer, 13-Quantum well layer, 14-p-type GaN layer, 111-Thinned GaN substrate layer, 112-Chiral structural unit, 113-Chiral metasurface structure, 114-Transition layer. Detailed Implementation

[0022] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0023] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, it should be noted that, for ease of description, only the parts relevant to this application are shown in the accompanying drawings, not the entire structure. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application.

[0024] The terms “comprising” and “having”, and any variations thereof, used in this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0025] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0026] Figure 1 This is a schematic flowchart of a method for fabricating a flip-chip Micro-LED circularly polarized device according to an embodiment of the present invention. Figure 2 This is a schematic structural diagram of a flip-chip Micro-LED circularly polarized device according to an embodiment of the present invention. Figure 3 This is a schematic structural diagram of a GaN-based epitaxial wafer according to an embodiment of the present invention.

[0027] like Figure 1As shown, the present invention provides a flip-chip Micro-LED circularly polarized device 100 based on a homogeneous chiral metasurface (refer to...). Figure 2 The preparation method of ) includes the following steps: Step S100: On GaN-based epitaxial wafer 10 (refer to...) Figure 3 Electrode layers 20 are deposited on the n-type GaN layer 12 and the p-type GaN layer 14 of the GaN-based epitaxial wafer 10, which includes an initial GaN substrate layer 11, an n-type GaN layer 12, a quantum well layer 13 and a p-type GaN layer 14 stacked from top to bottom. Step S200: A first buffer layer and a first temporary support layer are sequentially disposed on the surface of the electrode layer 20 to form a first support layer. The first buffer layer covers the electrode layer 20 and bonds the first temporary support layer. Step S300: With the support of the first support layer, the initial GaN substrate 11 is thinned and polished sequentially from the side of the initial GaN substrate 11 away from the n-type GaN layer 12 to obtain the thinned GaN substrate 111. Step S400: A patterned mask is formed on the surface of the thinned GaN substrate 111 using micro-nano fabrication processes such as nanoimprinting, mask exposure, or three-dimensional direct writing. The patterned mask is then used as an etching mask to partially etch the thinned GaN substrate 111 along the thickness direction, so that the thinned GaN substrate 111 forms a chiral metasurface structure 113 with multiple chiral structural units 112 arranged periodically and an unetched transition layer 114. Step S500: A second buffer layer and a second temporary support layer are sequentially disposed on the side of the chiral metasurface structure 113 away from the transition layer 114 to form a second support layer, and the second buffer layer covers the chiral structure unit 112 and at least fills the gap between adjacent chiral structure units 112. Step S600: With the chiral metasurface structure 113 supported by the second support layer, the first support layer is removed to expose the electrode layer 20, and the electrode layer 20 is flip-bonded to the control circuit 30. Step S700: Using capillary effect, fill the space between electrode layer 20 and control circuit 30 with light-absorbing material 50. The light-absorbing material 50 is any one of black photoresist, epoxy resin doped with carbon black or titanium black filler, and curable liquid organosilicon. Step S800: Remove the second support layer to expose the chiral metasurface structure 113 and prepare a flip-chip Micro-LED circularly polarized device 100.

[0028] In this embodiment, the fabrication method of the flip-chip Micro-LED circularly polarized device 100 based on a homogeneous chiral metasurface firstly deposits an electrode layer 20 on the p-type GaN layer 14 side of a GaN-based epitaxial wafer 10, which includes an initial GaN substrate layer 11, an n-type GaN layer 12, a quantum well layer 13, and a p-type GaN layer 14. A first buffer layer and a first temporary support layer are then sequentially deposited on the surface of the electrode layer 20 to form a first support layer, providing temporary support for the GaN-based epitaxial wafer 10 during subsequent metasurface structure fabrication. Subsequently, supported by the first support layer, the initial GaN substrate layer 11 is thinned from the side away from the n-type GaN layer 12 to obtain a thinned GaN substrate layer 111 close to the quantum well layer 13. Subsequently, a patterned mask is formed on the surface of the thinned GaN substrate 111 using micro-nano fabrication processes such as nanoimprint lithography, mask exposure, or 3D direct writing. This patterned mask is then used as an etching mask to partially etch the thinned GaN substrate 111 along its thickness direction, integrally forming a chiral metasurface structure 113 with a plurality of periodically arranged chiral structural units 112 and an unetched transition layer 114 on the side of the chiral metasurface structure 113 away from the transition layer 114, forming a second support layer. The second buffer layer covers the chiral structural units 112 and at least fills the gaps between adjacent chiral structural units 112. Next, with the chiral metasurface structure 113 supported by the second support layer, the first support layer is removed to expose the electrode layer 20, and the electrode layer 20 is flip-chip bonded to the control circuit 30. A light-absorbing material 50 is filled between the electrode layer 20 and the control circuit 30 using capillary effect. Finally, the second support layer is removed, exposing the chiral metasurface structure 113 to the light-emitting side, thereby fabricating a flip-chip Micro-LED circularly polarized device 100 capable of outputting circularly polarized light. Here, after the electrode layer 20 is flip-chip bonded to the control circuit 30, the N and P electrodes are in contact and conductive through the bonding metal 40, which can be any one of Au, In, or Cu.

[0029] In this embodiment, a homogeneous chiral metasurface structure 113 is obtained by directly etching the thinned GaN substrate 111 formed after thinning the initial GaN substrate 11. This allows the chiral metasurface structure 113 and the unetched transition layer 114 to be integrally formed from the same GaN material, thereby avoiding interface reflection, thermal expansion mismatch, and additional optical loss introduced by external polarizers or heterogeneous metasurfaces. While ensuring the mechanical reliability and manufacturability of the flip-chip Micro-LED circularly polarized device 100, it achieves low-loss, high-integration, and stable circularly polarized light output. Simultaneously, the thinned transition layer 114 shortens the propagation distance of the light emitted from the quantum well layer 13 to the chiral metasurface structure 113, reducing lateral diffusion, crosstalk, and scattering losses within the thick substrate. This allows unpolarized or weakly polarized light emitted from the quantum well layer 13 to be more effectively coupled into the chiral metasurface structure 113. Furthermore, the periodically arranged chiral structural units 112 exert differentiated transmission, scattering, and phase modulation effects on the left-hand circularly polarized components and the right-hand circularly polarized components through their non-mirror symmetric profiles, thereby realizing on-chip conversion of Micro-LED emitted light from an unpolarized or weakly polarized state to a circularly polarized state, improving the stability and integration of circularly polarized light output.

[0030] Furthermore, the first support layer formed by the first buffer layer and the first temporary support layer provides support and stress buffer for the GaN-based epitaxial wafer 10 and the electrode layer 20 during the thinning and metasurface preparation process. The second support layer formed by the second buffer layer and the second temporary support layer covers and fills the gaps between the chiral structural units 112 during the flip-chip bonding process, so as to disperse the bonding pressure and protect the micro-nano chiral structure, and prevent cracks, edge chipping or fragmentation of the thinned GaN chip and the chiral metasurface structure 113.

[0031] In step S200, by sequentially depositing a first buffer layer and a first temporary support layer on the surface of the electrode layer 20, the GaN-based epitaxial wafer 10 obtains stable mechanical support during the thinning, nanoimprinting, etching, and flip-chip bonding processes of the initial GaN substrate layer 11. The first buffer layer covers and protects the electrode layer 20, while also acting as a temporary bond and stress buffer between the electrode layer 20 and the first temporary support layer. The first temporary support layer provides overall load-bearing rigidity. The combination of the first buffer layer and the first temporary support layer reduces the risk of warping, cracking, or fragmentation of the thin GaN epitaxial wafer during the thinning process, providing a smooth and stable process foundation for the subsequent fabrication of micro / nano-scale chiral structures on the thin initial GaN substrate layer 11.

[0032] In this embodiment, the first buffer layer is made of at least one of photoresist, UV-curable adhesive, thermally release adhesive, or a solvent-removable polymer material, and the first temporary support layer is made of at least one of UV film, glass, quartz, silicon wafer, or sapphire. This allows the first support layer to simultaneously serve as a temporary bond, stress buffer, surface protection, and mechanical support. Through the synergistic effect of the first buffer layer and the first temporary support layer in the first support layer, the electrode side remains protected and supported throughout the entire process of thinning the GaN substrate 111 and fabricating the chiral metasurface structure 113. Furthermore, because the first buffer layer is removable, it can be removed along with the first temporary support layer after the second support layer takes over, thus smoothly exposing the electrode layer 20 and preventing residues from affecting subsequent flip-chip bonding.

[0033] In step S300, by thinning the initial GaN substrate 11 from the side away from the n-type GaN layer 12, the thinned initial GaN substrate 11 becomes a thinned GaN substrate 111. This shortens the light propagation distance between the quantum well layer 13 and the subsequent chiral metasurface structure 113, reducing lateral diffusion, crosstalk, and scattering losses of the light emitted from the quantum well layer 13 in the initial GaN substrate 11. This allows unpolarized or weakly polarized light emitted from the quantum well layer 13 to more effectively enter the chiral metasurface structure 113 for polarization state modulation. Simultaneously, the thinned initial GaN substrate 11 retains the unetched transition layer 114, achieving a balance between optical coupling distance and mechanical strength. This prevents the metasurface structure from being too close to the light-emitting layer or the overall chip from becoming too thin, which could lead to a decrease in structural reliability.

[0034] In step S400, a patterned mask is formed using micro / nano fabrication techniques such as nanoimprint lithography, photomask lithography, or 3D direct writing. Partial etching is then performed along the thickness direction on the thinned GaN substrate layer 111, causing the chiral metasurface structure 113 and the transition layer 114 to be integrally formed from the same GaN material layer. This method differs from external polarizers, external heterogeneous metasurfaces, or metal grating structures, as it eliminates the need for additional GaP, metal, or other heterogeneous material layers. This reduces lattice mismatch, thermal expansion mismatch, interface reflection, and reliability issues caused by heterogeneous interfaces. Furthermore, since the chiral metasurface structure 113 and the transition layer 114 are homogeneously connected, the high refractive index of the GaN material itself allows for better light field manipulation, while also improving the bonding stability between the micro / nano structure and the chip substrate. This facilitates long-term stable circularly polarized light output.

[0035] Furthermore, the periodically arranged multiple chiral structural units 112 can produce differentiated transmission, scattering, or conversion responses to the left-hand circularly polarized component and the right-hand circularly polarized component through their non-mirror-symmetric geometric profiles, so that the unpolarized or weakly polarized light emitted by the quantum well layer 13 of the flip-chip Micro-LED circularly polarized device 100 is converted into circularly polarized light with higher stability after passing through the chiral metasurface structure 113.

[0036] In step S500, after the chiral metasurface structure 113 is fabricated, a second buffer layer and a second temporary support layer are sequentially deposited on the side away from the transition layer 114 to form a second support layer. The second buffer layer covers the chiral structural unit 112 and at least fills the gap between adjacent chiral structural units 112, so that it can not only play a temporary bonding role, but also cover, fill gaps and buffer the protruding micro-nano chiral structure during flip bonding, avoiding the bonding pressure from being directly concentrated on the top or edge of the chiral structural unit 112. The second temporary support layer can disperse the external pressure during flip bonding, reducing the risk of cracks, edge chipping or breakage of the thinned GaN chip and the chiral metasurface structure 113 during the bonding process. Here, the material of the second buffer layer is at least one of photoresist, UV-curable adhesive, thermally release adhesive or a polymer material that can be removed by solvent, and the material of the second temporary support layer is at least one of UV film, glass, quartz, silicon wafer or sapphire.

[0037] In steps S600 and S800, by removing the first support layer and exposing the electrode layer 20 while the chiral metasurface structure 113 is supported by the second support layer, the support position can be transferred from the electrode side to the metasurface side. This ensures that the GaN-based epitaxial wafer 10 is always in a supported state before and after flip-chip bonding. After the electrode layer 20 and the control circuit 30 complete the flip-chip bonding, the second support layer is removed, and the chiral metasurface structure 113 is re-exposed to the light-emitting side. This ensures mechanical protection during the bonding process and avoids the support material from blocking or interfering with the circular polarization control function of the chiral metasurface.

[0038] In step S700, the light-absorbing material 50 is filled between the transition layer 114, the electrode layer 20 and the control circuit 30, so that the reflected light generated by the light-emitting device is absorbed, and the back-and-forth oscillation of the light is avoided from affecting the polarization conversion efficiency.

[0039] In a preferred embodiment, an absorption layer can be spin-coated or deposited on the non-light-emitting surface after the first support layer is removed to eliminate back light reflection and improve the extinction ratio.

[0040] In a further embodiment, the thickness of the thinned GaN substrate 111 is any value between 5 μm and 100 μm, and the thickness of each chiral structural unit 112 is any value between 0.5 μm and 1.5 μm. That is, the thickness of the thinned GaN substrate 111 can be 5 μm, 10 μm, 20 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 80 μm, or 100 μm, or any other value between 5 μm and 100 μm. Each chiral structural unit 112 can be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, or 1.5 μm, or any other value between 0.5 μm and 1.5 μm. In this embodiment, by controlling the thickness of the thinned GaN substrate 111 within the range of 5μm-100μm and the thickness of each chiral structural unit 112 along the thickness direction within the range of 0.5μm-1.5μm, a match can be achieved between optical control performance and structural mechanical reliability. That is, the thickness of the thinned GaN substrate 111 and the thickness of the chiral structural unit 112 complement each other, which not only ensures the thinning, low-loss light output and circular polarization conversion effect of the flip-chip Micro-LED device, but also improves the processing stability and device reliability during the fabrication of the homogeneous GaN chiral metasurface structure 113.

[0041] In this embodiment, the thinned GaN substrate layer 111 is formed by thinning the initial GaN substrate layer 11. When its thickness is controlled between 5μm and 100μm, it can not only significantly shorten the propagation distance of the light emitted from the quantum well layer 13 to the chiral metasurface structure 113, but also reduce the lateral diffusion, crosstalk and scattering loss of light in the thick GaN substrate, so that unpolarized light or weakly polarized light can be coupled into the chiral structure unit 112 more effectively. At the same time, it can retain a GaN transition layer 114 of sufficient thickness as a support part, and avoid warping, cracking or fragmentation of the chip during nanoimprinting, etching and flip bonding due to excessive thinning. Meanwhile, by controlling the thickness of the chiral structural unit 112 within the range of 0.5μm-1.5μm, the chiral structural unit 112 can have sufficient optical field interaction depth and phase modulation capability to enhance its differentiated transmission, scattering and conversion response to the left-hand circular polarization component and the right-hand circular polarization component. It can also avoid insufficient circular polarization modulation due to the thickness of the chiral structural unit 112 being too small, or increased etching difficulty, increased sidewall roughness and decreased stability of the micro-nano structure due to the thickness being too large.

[0042] In a further embodiment, the thinning process includes sequentially grinding and polishing the substrate layer to ensure that the surface roughness Ra of the thinned GaN substrate layer 111 on the side away from the n-type GaN layer 12 is less than or equal to 5 nm. In this embodiment, the grinding process can quickly remove the excess thickness of the initial GaN substrate layer 11, making the chiral metasurface structure 113 closer to the quantum well layer 13, thereby shortening the propagation distance of emitted light in the GaN layer; the polishing process can further reduce scratches, microcracks, and surface undulations formed after grinding, ensuring that the surface of the thinned GaN substrate layer 111 meets the flatness requirements for nanoimprinting and subsequent etching. When the surface roughness Ra is less than or equal to 5 nm, the patterned mask can be formed more uniformly and completely on the surface of the thinned GaN substrate layer 111, which is beneficial to improving the size consistency, boundary clarity, and array period accuracy of the chiral structural unit 112, and reducing local imprinting defects, etching deviations, and light scattering losses caused by surface roughness. Therefore, the fabrication precision and repeatability of the homogeneous GaN chiral metasurface structure 113 can be improved, enabling unpolarized or weakly polarized light emitted from the quantum well layer 13 to obtain a more stable circular polarization control effect when passing through the chiral metasurface structure 113, while reducing the negative impact of thinning processing on the mechanical strength and device reliability of the GaN-based epitaxial wafer 10.

[0043] Figure 4 This is a schematic structural distribution diagram of a chiral metasurface structure according to an embodiment of the present invention. Figure 5 This is a schematic cross-sectional view of a chiral structural unit according to an embodiment of the present invention. Figure 6 This is a schematic structural diagram of a chiral structural unit according to the first embodiment of the present invention. Figure 7 This is a schematic structural diagram of a chiral structural unit according to a second embodiment of the present invention. Figure 8 This is a schematic structural diagram of a chiral structural unit according to a third embodiment of the present invention.

[0044] like Figure 4 and Figure 5 As shown, in a further embodiment, the cross-section of the chiral structural unit includes a first right trapezoid and a second right trapezoid arranged in a centrally symmetrical manner. The midpoint of the short base of the first right trapezoid is the center of symmetry. Here, the cross-section refers to the plane intercepted by a plane parallel to the transition layer 114, thereby enabling the formation of a continuous and oriented geometrically asymmetrical profile within a single chiral structural unit 112, thus breaking the mirror symmetry of the structure in the plane.

[0045] Specifically, the short bases of the two right-angled trapezoids abutting each other can improve the overall continuity and mechanical stability of the structural unit, avoiding the formation of isolated gaps or weak connection areas between adjacent trapezoidal portions. This is beneficial for maintaining pattern integrity during nanoimprinting and etching. The two inclined sides extending in the same direction can create a continuously varying boundary profile and equivalent refractive index distribution within the structural unit, causing the incident light to generate an asymmetric local electromagnetic field distribution when passing through the chiral structural unit 112, and producing differentiated scattering, transmission, and phase responses for the left-hand and right-hand circularly polarized components. In other embodiments, the cross-section of the chiral structural unit 112 can also be other trapezoidal structures exhibiting chiral properties (see [reference]). Figure 6 ).

[0046] like Figure 7 As shown, in one embodiment, the chiral structural unit 112 is a twisted structure, comprising a columnar body extending along the thickness direction. The cross-sectional profile of the columnar body is gradually rotated along the height direction, resulting in a preset twist angle between its bottom and top sections. Adjacent twisted structures are arranged in an array according to a preset period P, with a height H for each individual twisted structure. In this embodiment, the twisted structure can form a continuously varying equivalent optical axis in the thickness direction, causing the incident light to undergo gradual chiral phase modulation during propagation. Compared to a simple upright columnar structure, the twisted structure can enhance the coupling between the electric dipole response and the magnetic dipole response, and cause the left-hand circularly polarized component and the right-hand circularly polarized component to produce different phase delays and transmission responses, thereby improving the stability of the conversion from unpolarized or weakly polarized light to circularly polarized light.

[0047] like Figure 8 As shown, in one embodiment, the chiral structural unit 112 is a ramp-shaped structure, which includes a wedge-shaped body with inclined sidewalls or an inclined top surface along the thickness direction. The wedge-shaped body extends in a plane along a predetermined direction and forms an asymmetric gradient profile in the height or lateral direction. Adjacent ramp-shaped structures are arranged in an array according to a predetermined period P, and the maximum height of a single ramp-shaped structure is H. In this embodiment, the ramp-shaped structure can introduce a spatial asymmetric refractive index distribution and phase gradient through the inclined surface, causing the incident light to generate an asymmetric propagation path and a local field enhancement region inside the structure. This structure is beneficial for adjusting the scattering direction, transmission phase, and energy distribution of different circularly polarized components, thereby enhancing the ability of the chiral structural unit 112 to distinguish between left-handed and right-handed circularly polarized components.

[0048] like Figure 5As shown, in a further embodiment, the length L1 of the longer base of the first right trapezoid is any value between 0.18 μm and 0.20 μm, the length L3 of the shorter base of the first right trapezoid is any value between 0.06 μm and 0.10 μm, and the distance L2 between the shorter base and the longer base is any value between 0.16 μm and 0.20 μm. That is, the length L1 of the longer base of the first right trapezoid can be 0.18 μm, 0.19 μm, or 0.20 μm, or it can be 0.18 μm. The short base length L3 can be any other value between m and 0.20 μm, and can be 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, or 0.10 μm, or any other value between 0.06 μm and 0.10 μm. The distance between the short base and the long base L2 can be 0.16 μm, 0.17 μm, 0.18 μm, 0.19 μm, or 0.20 μm, or any other value between 0.16 μm and 0.20 μm. In this embodiment, the short base, long base, and spacing of the first and second right-angled trapezoids are set within the above-mentioned range, so that the first right-angled trapezoid has both a sufficient light field modulation area and a significant non-mirror symmetric profile, and can form a stable chiral structural unit 112 together with the second right-angled trapezoid. This allows for differentiated modulation of the left-hand circular polarization component and the right-hand circular polarization component in transmission, scattering, and phase response, thereby improving the stability and selectivity of the conversion of unpolarized or weakly polarized light to circularly polarized light in the flip-chip Micro-LED circular polarization device 100.

[0049] like Figure 4 As shown, in a further embodiment, the period of the plurality of chiral structural units 112 is any value between 400nm and 800nm. That is, the period of the plurality of chiral structural units 112 can be 400nm, 500nm, 600nm, 700nm, 750nm, or 800nm, or any other value between 400nm and 800nm. By controlling the period of the plurality of chiral structural units 112 within the range of 400nm-800nm, the array period of the chiral metasurface structure 113 can be matched with the target emission wavelength of the Micro-LED and the geometric dimensions of the chiral structural units 112, thereby forming an effective periodic optical field modulation interface at the subwavelength or near-subwavelength scale. Specifically, when the period is within the above range, an appropriate optical field coupling distance can be maintained between adjacent chiral structural units 112, so that the asymmetric distribution of the local electromagnetic field generated by a single chiral structural unit 112 in the array forms a synergistic enhancement effect, which is beneficial to improving the differentiated transmission, scattering, and phase modulation capabilities of the left-hand circularly polarized component and the right-hand circularly polarized component. At the same time, it can avoid the problem of excessively strong coupling between adjacent structural units, excessively narrow processing gaps and difficulty in etching due to excessively small period, and it can also avoid the problem of insufficient array filling density, discontinuous local optical field modulation and decreased circular polarization conversion efficiency due to excessively large period.

[0050] In a further embodiment, the first buffer layer is a first removable buffer layer that can be removed by the first removal medium, and the second buffer layer is a second removable buffer layer that maintains structural integrity in the first removal medium. When removing the first support layer, the GaN-based epitaxial wafer with the second support layer is placed in the first removal medium to remove the first buffer layer and separate the first temporary support layer. The second buffer layer maintains its coverage of the chiral structural units and fills the gaps between adjacent chiral structural units in the first removal medium. This allows the first buffer layer to be fully dissolved or peeled off during the removal of the first support layer and exposure of the electrode layer, thereby achieving separation of the first temporary support layer from the GaN-based epitaxial wafer. Simultaneously, the second buffer layer will not dissolve, detach, or lose its filling and supporting function due to immersion in the first removal medium, continuing to cover the chiral structural units and maintain the filling of the gaps between adjacent chiral structural units. This ensures that the chiral metasurface structure remains protected before support transfer and flip-chip bonding, reducing the risk of cracks, fragmentation, or structural damage during the thinning of the GaN substrate and the micro / nano chiral structure.

[0051] In a preferred embodiment, the first buffer layer is a photoresist layer soluble in an organic solvent, the first removal medium includes at least one of acetone, N-methylpyrrolidone, or photoresist stripping solution, and the second buffer layer is a polymer sacrificial layer that has been treated with ultraviolet curing, thermal curing, or cross-linking curing. The swelling rate of the second buffer layer in the first removal medium is less than or equal to 10%, which can more thoroughly release the first temporary support layer and expose the electrode layer, facilitating subsequent flip bonding. At the same time, it can improve the tolerance of the second buffer layer to the first removal medium, avoiding significant swelling, deformation, or desorption when the first buffer layer is removed by immersion. This maintains its coating and gap filling morphology of the chiral structural unit, ensures the morphological integrity and support stability of the chiral metasurface structure before flip bonding, and improves the device fabrication yield and the consistency of circularly polarized light output.

[0052] In a further embodiment, before depositing the electrode layer 20 on the n-type GaN layer 12 and the p-type GaN layer 14, the GaN-based epitaxial wafer 10 undergoes surface pretreatment, which includes the following steps: GaN-based epitaxial wafer 10 was ultrasonically cleaned in acetone and isopropanol in sequence. After rinsing with deionized water and drying, it is then placed in an oxidizing cleaning solution for inorganic cleaning, and rinsed and dried again with deionized water.

[0053] In this embodiment, by sequentially performing ultrasonic cleaning with acetone and isopropanol, rinsing and drying with deionized water, and inorganic cleaning with an oxidizing cleaning solution on the GaN-based epitaxial wafer 10 before depositing the electrode layer 20, a clean, uniform surface of the n-type GaN layer 12 and p-type GaN layer 14 with low contaminant content can be obtained before the electrode layer 20 is prepared. Specifically, ultrasonic cleaning with acetone and isopropanol can effectively remove grease, organic residues, photoresist residues, and particulate contamination from the surface of the GaN-based epitaxial wafer 10, reducing localized poor adhesion or film defects caused by organic contamination during subsequent deposition; rinsing and drying with deionized water can remove cleaning solution residues, avoiding residual solvents from affecting subsequent inorganic cleaning and electrode deposition. Inorganic cleaning with an oxidizing cleaning solution can further remove metal ion contamination, oxide layers, and trace inorganic impurities from the surface, resulting in better cleanliness and interfacial activity of the n-type GaN layer 12 and p-type GaN layer 14. This improves the uniformity, adhesion, and electrical contact stability of the subsequent electrode layer 20 or transparent conductive layer on the p-type GaN layer 14, reducing problems such as increased contact resistance, local leakage, or uneven current spread caused by surface contamination. Simultaneously, a clean surface also helps improve the process stability during subsequent processes such as first buffer layer attachment, thinning, and the fabrication of the chiral metasurface structure 113.

[0054] like Figure 2 As shown, the present invention also provides a flip-chip Micro-LED circular polarization device 100 prepared according to the above-described method for preparing a flip-chip Micro-LED circular polarization device 100 based on a homogeneous chiral metasurface. The flip-chip Micro-LED circular polarization device 100 includes a control circuit 30 and a Micro-LED chip flip-bonded to the surface of the control circuit 30. The Micro-LED chip includes a GaN-based epitaxial wafer 10, an electrode layer 20, a transition layer 114, and a chiral metasurface structure 113. The electrode layer 20 is disposed on the side of the GaN-based epitaxial light-emitting structure close to the control circuit 30 and is electrically connected to the control circuit 30. The transition layer 114 is disposed on the side of the GaN-based epitaxial wafer 10 away from the control circuit 30. The chiral metasurface structure 113 is disposed on the side of the transition layer 114 away from the GaN-based epitaxial wafer 10. The chiral metasurface structure 113 includes a plurality of periodically arranged chiral structure units 112. The chiral structure units 112 are used to modulate the polarization state of unpolarized light or weakly polarized light emitted by the GaN-based epitaxial light-emitting structure so that the flip-chip Micro-LED circular polarization device 100 outputs circularly polarized light.

[0055] In this embodiment, through the aforementioned flip-chip Micro-LED circularly polarized device 100 structure, the electrode layer 20 is located on the side of the GaN-based epitaxial light-emitting structure closer to the control circuit 30 and is flip-bonded to the control circuit 30. This separates the electrical connection side of the device from the light emission control side, which helps reduce the obstruction of the light emission path by the electrode structure and improves the light emission utilization rate of the flip-chip Micro-LED circularly polarized device 100. Simultaneously, the transition layer 114 and the chiral metasurface structure 113 are disposed on the side of the GaN-based epitaxial light-emitting structure away from the control circuit 30, allowing unpolarized or weakly polarized light emitted from the quantum well layer 13 to directly enter the chiral metasurface structure 113 for polarization state control from the light emission side. Since the chiral metasurface structure 113 includes multiple periodically arranged chiral structural units 112, and the chiral metasurface structure 113 and the transition layer 114 can be integrally formed from the same GaN material layer, it can avoid interface reflection, material mismatch, thermal expansion mismatch and additional optical loss introduced by external polarizers or heterogeneous metasurface structures, thereby improving the structural stability and long-term reliability of the flip-chip Micro-LED circular polarization device 100.

[0056] Furthermore, the periodically arranged chiral structural units 112 form an asymmetric local electromagnetic field distribution on the light-emitting side through their non-mirror-symmetric geometric contours, thereby causing differential modulation of the left-hand circularly polarized component and the right-hand circularly polarized component in terms of transmission, scattering and phase response, thus converting the unpolarized or weakly polarized light emitted by the GaN-based epitaxial light-emitting structure into circularly polarized light output.

[0057] The technical solution of this application will be further described below with reference to specific embodiments.

[0058] Example 1 Step S100: Deposit an electrode layer 20 on the n-type GaN layer 12 and the p-type GaN layer 14 of the GaN-based epitaxial wafer 10. The GaN-based epitaxial wafer 10 includes an initial GaN substrate layer 11, an n-type GaN layer 12, a quantum well layer 13 and a p-type GaN layer 14, which are stacked sequentially from top to bottom. Step S200: A photoresist layer and a UV film are sequentially deposited on the surface of the electrode layer 20 to form a first support layer. The photoresist layer covers the ITO electrode layer 20 and bonds the UV film. Step S300: With the support of the first support layer, the initial GaN substrate 11 is thinned from the side away from the n-type GaN layer 12 to obtain a thinned GaN substrate 111 with a thickness of 50 μm, and the roughness of the thinned GaN substrate 111 after polishing is 4.2 nm. Step S400: A patterned mask is formed on the surface of the thinned GaN substrate 111 using nanoimprint lithography, and the patterned mask is used as an etching mask to partially etch the thinned GaN substrate 111 along the thickness direction, so that the thinned GaN substrate 111 forms a chiral metasurface structure 113 with a plurality of periodically arranged chiral structural units 112 and an unetched transition layer 114. The thickness of the chiral structural units 112 is 1.0 μm. Step S500: A photoresist sacrificial layer and a glass substrate are sequentially disposed on the side of the chiral metasurface structure 113 away from the transition layer 114 to form a second support layer, and the second buffer layer covers the chiral structure unit 112 and at least fills the gap between adjacent chiral structure units 112. Step S600: With the chiral metasurface structure 113 supported by the second support layer, the first support layer is removed to expose the electrode layer 20, and the electrode layer 20 is flip-bonded to the control circuit 30. Step S700: Fill the space between the electrode layer and the control circuit with black resin using capillary effect.

[0059] Step S800: Remove the second support layer to expose the chiral metasurface structure 113, and fabricate a flip-chip Micro-LED circularly polarized device 100. Here, the chiral structure unit 112 has a first right-angled cross-section comprising the same first right-angled trapezoid and second right-angled trapezoid. The short bases of the first and second right-angled trapezoids abut each other, and the inclined sides of the first and second right-angled trapezoids extend in the same inclined direction. The length of the short base of the first right-angled trapezoid is 0.08 μm, the length of the long base is 0.19 μm, and the distance between the short and long bases is 0.18 μm.

[0060] Figure 9 The XY plane field strength direction of the flip-chip Micro-LED circularly polarized device according to Embodiment 1 of the present invention is as follows: Figure 10 This describes the XY plane field strength distribution of the flip-chip Micro-LED circularly polarized device according to Embodiment 1 of the present invention under right-handed circularly polarized incident light. Figure 11 The XY plane field strength direction of the flip-chip Micro-LED circularly polarized device according to Embodiment 1 of the present invention is as follows: Figure 12 This describes the XY plane field strength distribution of the flip-chip Micro-LED circularly polarized device according to Embodiment 1 of the present invention under left-handed circularly polarized incident light. Figure 13 These are the transmission spectra of the flip-chip Micro-LED circularly polarized device according to Embodiment 1 of the present invention, corresponding to left-handed and right-handed circularly polarized incident radiation. Figure 14 This is a circular dichroism diagram of the chiral metasurface structure according to Embodiment 1 of the present invention. Figure 15This refers to the ratio of left-handed to right-handed circular polarization conversion efficiency of the flip-chip Micro-LED circular polarization device according to Embodiment 1 of the present invention when right-handed circularly polarized light is incident. Figure 16 It is the ratio of left-handed to right-handed circular polarization conversion efficiency when left-handed circularly polarized light is incident on the flip-chip Micro-LED circular polarization device according to Embodiment 1 of the present invention.

[0061] First, the field intensity distribution and direction in the XY plane of the flip-chip Micro-LED circularly polarized device 100 prepared in Example 1 were tested under left-hand and right-hand circularly polarized incident light, respectively, and the results were as follows: Figures 9 to 12 The test results are shown.

[0062] like Figures 9 to 12 As shown, when right-handed circularly polarized light is incident, the color bar shows that most of the pattern is close to pure circular polarization, indicating that the right-handed circularly polarized incident light maintains high spin purity in the structure and is less affected by scattering or depolarization. Furthermore, compared to right-handed circular polarization, the polarization vector distribution of left-handed circular polarization is much more complex, breaking the translational symmetry. The vector arrows no longer uniformly point in one direction, but instead exhibit a rotating, vortex-like, or complex grid pattern. The maximum value of the color bar is 0.702, much lower than the value for right-handed circular polarization, suggesting that the incident left-handed circular polarization undergoes significant linearization, depolarization, or conversion to other chiralities when passing through the structure; that is, the flip-chip Micro-LED circularly polarized device 100 of Example 1 strongly scatters left-handed circular polarization. In summary, the incident light is coupled to the chiral structure and its rotation direction is modulated in GaN. By comparing the incident light of the two polarized beams, the electric field generated by the right-hand circularly polarized light is stronger than that generated by the left-hand circularly polarized light, demonstrating the selective transmission of the polarization state of the incident light by the flip-chip Micro-LED circularly polarized device 100 in Example 1. Here, the XY plane refers to the horizontal plane when the flip-chip Micro-LED circularly polarized device 100 is placed horizontally.

[0063] Next, the circularly polarized light transmission test was performed on the flip-chip Micro-LED circularly polarized device 100 of Example 1, and the results were as follows: Figure 13 The transmission spectrum shown.

[0064] like Figure 13 As shown, when left-handed polarized light is incident, only a small portion of the energy is transmitted, i.e., the transmittance is less than 35% (refer to curve T). LCP When right-handed polarized light is incident, most of the energy is transmitted, meaning the transmittance is greater than 85% (refer to curve T). RCP This demonstrates that the chiral metasurface structure 113 in Example 1 has a strong selective control capability for left-handed / right-handed circularly polarized light, and can efficiently realize the conversion of unpolarized light to single circularly polarized light.

[0065] The circular dichroism of the flip-chip Micro-LED circularly polarized device 100 of Example 1 was tested, and the results were as follows: Figure 14 The circular dichroism diagram is shown.

[0066] like Figure 14 As shown, the circular dichroism is greater than 80% near a wavelength of 520nm and greater than 60% in the wavelength range of 515nm-525nm, demonstrating the absorption difference performance of the chiral metasurface structure 113 for left and right circularly polarized light.

[0067] Finally, the circular polarization conversion efficiency of the flip-chip Micro-LED circular polarization device 100 in Example 1 was tested, and the results were as follows: Figure 15 and Figure 16 The test results are shown.

[0068] like Figure 15 and Figure 16 As shown, when right-handed circularly polarized light is incident, over 80% of the outgoing energy remains right-handed circularly polarized. When left-handed circularly polarized light is incident, 50% of the outgoing energy is converted to right-handed circularly polarized light, indicating that this chiral metasurface possesses a certain selectivity and conversion capability for circularly polarized states. Here, RCP represents right-handed circularly polarized light incident, and LCP represents left-handed circularly polarized light incident.

[0069] In summary, Figures 9 to 16 The test results show that the flip-chip Micro-LED circularly polarized device 100 prepared in Example 1 has a significant ability to selectively control circular polarization. Specifically, when right-handed circularly polarized light is incident, its field intensity distribution in the chiral metasurface structure 113 is strong and its polarization state is well maintained, indicating that the structure has high transmission capability and spin retention capability for right-handed circularly polarized light. However, when left-handed circularly polarized light is incident, its field intensity distribution and polarization vector become significantly more complex, indicating that the left-handed circularly polarized light undergoes strong scattering, depolarization, or polarization conversion when passing through the chiral structural unit 112. Further combined with the transmission spectrum, circular dichroism, and polarization conversion efficiency test results, it can be seen that near the target wavelength, the transmittance of left-handed circularly polarized light is less than 35%, while the transmittance of right-handed circularly polarized light is greater than 85%. The circular dichroism near 520 nm is greater than 80%, and more than 80% of the energy of right-handed circularly polarized light remains as right-handed circularly polarized light after incident, while about 50% of the energy of left-handed circularly polarized light can be converted into right-handed circularly polarized light after incident. This indicates that the homogeneous GaN chiral metasurface structure 113 in Example 1 can produce significantly different responses to left and right circular polarization components, thereby achieving on-chip efficient conversion of unpolarized or weakly polarized light to single circularly polarized light in the flip-chip Micro-LED circular polarization device 100. This demonstrates that the flip-chip Micro-LED circular polarization device 100 of this application has good circular polarization output capability and polarization control stability.

[0070] 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.

[0071] 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 fabricating a flip-chip Micro-LED circularly polarized device based on a homogeneous chiral metasurface, characterized in that, Includes the following steps: Electrode layers are deposited on the n-type GaN layer and the p-type GaN layer of the GaN-based epitaxial wafer, respectively. The GaN-based epitaxial wafer includes an initial GaN substrate layer, an n-type GaN layer, a quantum well layer and the p-type GaN layer stacked from top to bottom. A first buffer layer and a first temporary support layer are sequentially disposed on the surface of the electrode layer to form a first support layer, wherein the first buffer layer covers the electrode layer and bonds the first temporary support layer. With the support of the first support layer, the initial GaN substrate is thinned and polished sequentially from the side of the initial GaN substrate away from the n-type GaN layer to obtain a thinned GaN substrate for the preparation of metasurface structures. A patterned mask is formed on the surface of the thinned GaN substrate using micro-nano fabrication technology, and the patterned mask is used as an etching mask to partially etch the thinned GaN substrate along the thickness direction, so that the thinned GaN substrate forms a chiral metasurface structure with multiple chiral structural units arranged periodically and an unetched transition layer. A second buffer layer and a second temporary support layer are sequentially disposed on the side of the chiral metasurface structure away from the transition layer to form a second support layer, and the second buffer layer covers all the chiral structural units and at least fills the gaps between adjacent chiral structural units. With the chiral metasurface structure supported by the second support layer, the first support layer is removed to expose the electrode layer, and the electrode layer is flip-bonded to the control circuit. A light-absorbing material is filled between the electrode layer and the control circuit using the capillary effect; The second support layer is removed to expose the chiral metasurface structure, thereby obtaining a flip-chip Micro-LED circularly polarized device.

2. The method for fabricating a flip-chip Micro-LED circularly polarized device based on a homogeneous chiral metasurface according to claim 1, characterized in that, The thickness of the thinned GaN substrate layer is any value between 5 μm and 100 μm, and the thickness of each chiral structural unit is any value between 0.5 μm and 1.5 μm.

3. The method for fabricating a flip-chip Micro-LED circularly polarized device based on a homogeneous chiral metasurface according to claim 2, characterized in that, The thinning process includes sequentially grinding and polishing the substrate layer to make the surface roughness Ra of the thinned GaN substrate layer on the side away from the n-type GaN layer less than or equal to 5 nm.

4. The method for fabricating a flip-chip Micro-LED circularly polarized device based on a homogeneous chiral metasurface according to claim 3, characterized in that, The cross-section of the chiral structural unit includes a first right trapezoid and a second right trapezoid arranged in a centrally symmetrical manner, with the midpoint of the short base of the first right trapezoid being the center of symmetry.

5. The method for fabricating a flip-chip Micro-LED circularly polarized device based on a homogeneous chiral metasurface according to claim 4, characterized in that, The first right trapezoid has a long base length of any value between 0.18μm and 0.20μm, a short base length of any value between 0.06μm and 0.10μm, and a height of any value between 0.16μm and 0.20μm.

6. The method for fabricating a flip-chip Micro-LED circularly polarized device based on a homogeneous chiral metasurface according to claim 5, characterized in that, The period of multiple chiral structural units is any value between 400nm and 800nm.

7. The method for fabricating a flip-chip Micro-LED circularly polarized device based on a homogeneous chiral metasurface according to any one of claims 1-6, characterized in that, The first buffer layer is a first removable buffer layer that can be removed by the first removal medium, and the second buffer layer is a second removable buffer layer that maintains structural integrity in the first removal medium; When removing the first support layer, the GaN-based epitaxial wafer with the second support layer formed thereon is placed in the first removal medium to remove the first buffer layer and separate the first temporary support layer. The second buffer layer in the first removal medium maintains coverage of the chiral structural units and fills the gaps between adjacent chiral structural units.

8. The method for fabricating a flip-chip Micro-LED circularly polarized device based on a homogeneous chiral metasurface according to claim 7, characterized in that, The first buffer layer is a photoresist layer soluble in organic solvents, and the first removal medium includes at least one of acetone, N-methylpyrrolidone, or photoresist stripping solution. The second buffer layer is a polymer sacrificial layer that has been treated with ultraviolet curing, thermal curing or cross-linking curing, and the swelling rate of the second buffer layer in the first removal medium is less than or equal to 10%.

9. A flip-chip Micro-LED circularly polarized device prepared by a method for fabricating a flip-chip Micro-LED circularly polarized device based on a homogeneous chiral metasurface according to any one of claims 1-8.

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