High directional emission Micro-LED chip, preparation method thereof and display device

Abstract

The invention discloses a high directional emission Micro-LED chip, a preparation method thereof and a display device. The Micro-LED chip sequentially comprises a conductive second substrate, a composite metal layer, a transparent conductive layer, an epitaxial layer and a composite enhancement layer from bottom to top, the composite enhancement layer comprises a low-refractive-index dielectric layer, a metal nanopillar array and a fluorescent powder layer, the metal nanopillar array is arranged at the upper end of the low-refractive-index dielectric layer, and the fluorescent powder layer covers the low-refractive-index dielectric layer and the metal nanopillar array. The composite enhancement layer is arranged on the epitaxial layer of the chip, the guided wave mode intensity of emitted light in the fluorescent powder is enhanced, the photoluminescence efficiency of the fluorescent powder is improved, and therefore the forward emission intensity of the chip is remarkably improved. Meanwhile, according to the display panel based on the high directional emission Micro-LED chip, the n-type electrodes are arranged between the adjacent chips and at the edge of the driving substrate, transverse propagation of light emitted by the chips can be effectively restrained, and light crosstalk is prevented.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor chips, and particularly to a highly directional emission Micro-LED chip, a preparation method thereof, and a display device. Background Art

[0002] In recent years, Micro-LED production technology has attracted extensive attention in related fields. Compared with LCD and OLED, Micro-LED has huge advantages of low power consumption, fast response, and high luminous efficiency, and has great commercial value in technical fields such as high-resolution displays, virtual reality, and augmented reality. The light-emitting characteristics of traditional Micro-LEDs usually follow Lambertian distribution, resulting in uniform diffusion of the emitted light in all directions, limited front brightness, and poor brightness and color consistency at different viewing angles. These problems limit the wide application of Micro-LEDs in scenarios with extremely high optical performance requirements such as high-brightness displays, wide-view applications, and AR / VR.

[0003] To overcome these challenges, in recent years, researchers have begun to explore Micro-LED chips with highly directional emission characteristics. Highly directional emission Micro-LEDs significantly improve the front brightness and luminous efficiency by concentrating light energy in a specific direction, while reducing light scattering and energy loss. This characteristic can not only meet the requirements of high-brightness displays, but also simplify the optical design, reduce power consumption, and improve the overall performance of the display panel. However, existing highly directional emission Micro-LED technologies still face problems such as complex preparation processes, high costs, and low yields. Especially in large-scale mass production and display panel integration, further optimization and innovation are still needed. In addition, the phenomenon of optical crosstalk between Micro-LED light-emitting pixel points has an important impact on display saturation. The emitted light of blue LEDs will exhibit photoluminescence after propagating to green LEDs and red LEDs, thus affecting the purity of display emission.

[0004] Therefore, there is an urgent need to develop a method for highly directional emission Micro-LED chips and display panels that is efficient, low-cost, and scalable for preparation. Summary of the Invention

[0005] To solve the problems existing in the prior art, the present invention provides a highly directional emission Micro-LED chip, which sequentially includes a conductive second substrate, a composite metal layer, a transparent conductive layer, an epitaxial layer, and a composite enhancement layer from bottom to top; The composite enhancement layer includes a low refractive index dielectric layer, a metal nanorod array, and a phosphor layer. The metal nanorod array is disposed at the upper end of the low refractive index dielectric layer, and the phosphor layer covers the low refractive index dielectric layer and the metal nanorod array.

[0006] Further, the height of the metal nanocolumns in the metal nanocolumn array is 10 - 100 nm, the diameter is 20 - 150 nm, and the period is 200 - 600 nm.

[0007] Further, the thickness of the low refractive index dielectric layer is 0.5 - 1.5 μm.

[0008] Further, the thickness of the phosphor layer is 300 - 800 nm.

[0009] Further, the epitaxial layer includes a p-type GaN layer, a multi-quantum well active region layer, and an n-type GaN layer arranged in sequence from bottom to top.

[0010] The present invention also provides a method for fabricating a highly directionally emitting Micro-LED chip, including: Obtaining a Micro-LED wafer, which sequentially includes a first substrate, an epitaxial layer, a transparent conductive layer, and a p-type electrode layer from bottom to top; Obtaining a bonding substrate, which includes a conductive second substrate and a bonding metal layer on the upper part of the second substrate; Bonding the p-type electrode layer of the Micro-LED wafer with the bonding metal layer of the bonding substrate to form a composite metal layer, obtaining an intermediate product; Removing the first substrate of the intermediate product, sequentially fabricating a low refractive index dielectric layer and a metal nanocolumn array on the exposed surface of the epitaxial layer, and covering a phosphor layer on the low refractive index dielectric layer and the metal nanocolumn array, obtaining a composite enhancement layer.

[0011] Further, the bonding adopts Au-In eutectic bonding.

[0012] Further, the removal adopts laser lift-off, and the wavelength of the laser is 200 - 280 nm, and the energy density is 0.6 - 1.0 J / cm 2 。

[0013] The present invention also provides a display device, including a driving substrate with a plurality of conductive contacts, and further including the above-mentioned highly directionally emitting Micro-LED chip, a transparent polymer layer, an n-type electrode, and a cover plate; The conductive second substrate of the highly directionally emitting Micro-LED chip is disposed on the conductive contacts and electrically connected to the conductive contacts; The transparent polymer layer is disposed on the edge of the driving substrate, between the edge of the driving substrate and the conductive contacts, and between adjacent conductive contacts, and the transparent polymer layer has electrode through holes; The n-type electrode is disposed in the electrode through holes and electrically connected to the driving substrate; On the driving substrate, the n-type electrode is higher than the transparent polymer layer and the highly directionally emitting Micro-LED chip, and the cover plate is disposed on the n-type electrode.

[0014] Further, the conductive contact array is disposed on the driving substrate.

[0015] It should be noted that the material of the first substrate of the present invention is not strictly limited. Exemplarily, it can be sapphire, silicon, silicon-on-insulator, silicon carbide, etc.; the material of the second substrate is also not strictly limited, but since the P electrode is led out by bonding, it is necessary to ensure that the substrate material has conductivity while meeting the preparation process. The material of the metal in the metal nanorod array is not strictly limited. Exemplarily, it can be at least one of gold, silver, copper, etc. The material of the low refractive index dielectric layer can be at least one of silicon dioxide, aluminum oxide, etc., and preferably silicon dioxide. The phosphor layer is a polystyrene phosphor thin film. The preparation method is to first mix the phosphor and polystyrene, then add toluene solvent, and drop the ground mixed solution onto the metal nanorod array, and form a polystyrene phosphor thin film through spin coating and solvent evaporation. The phosphor can be one of perylene-based dyes, CsPbBr 3 , copper(I) halide complexes, ZnS(Ag), etc.

[0016] Compared with the prior art, the present invention has the following beneficial effects: By inserting a low refractive index dielectric layer and a metal nanorod array between the epitaxial layer and the phosphor layer of the Micro-LED chip, the present invention enhances the intensity of the guided wave mode of the emitted light in the phosphor, improves the photoluminescence efficiency of the phosphor, and thus significantly increases the forward emission intensity of the Micro-LED.

[0017] Meanwhile, for the display panel based on the highly directionally emitting Micro-LED chip of the present invention, the n-type electrode is disposed between adjacent Micro-LED chips and at the edge of the driving substrate, which can effectively suppress the lateral propagation of the light emitted by the Micro-LED chip and prevent light crosstalk. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0019] Figure 1 Shows a preparation flow chart of a preparation method of a highly directionally emitting Micro-LED chip; Figure 2Shows a schematic structural diagram of each display structure on the Micro-LED wafer; Figure 3 Shows a schematic structural diagram after depositing a transparent conductive layer and a p-type electrode layer on the p-type GaN layer; Figure 4 Shows a schematic structural diagram of the bonding substrate; Figure 5 Shows a schematic diagram of bonding the bonding substrate to the p-type electrode layer; Figure 6 Shows a schematic structural diagram of the intermediate product; Figure 7 Shows a schematic diagram of peeling off the first substrate of the intermediate product; Figure 8 Shows a schematic structural diagram after depositing a low-refractive-index dielectric layer on the exposed n-type GaN layer; Figure 9 Shows a schematic structural diagram of the metal nanocolumn array on the low-refractive-index dielectric layer; Figure 10 Shows a schematic structural diagram of the composite enhancement layer; Figure 11 Shows a schematic structural diagram of the highly directionally emitting Micro-LED chips distributed on the driving substrate; Figure 12 Shows a schematic structural diagram of the transparent polymer layer; Figure 13 Shows a schematic structural diagram of the n-type electrode; Figure 14 Shows a schematic structural diagram of the display device; Figure 15 Shows a comparison diagram of the light distribution curves of the Micro-LED chips prepared in Example 1 and Comparative Example 1 of the present invention Explanation of reference numerals: 201, first substrate; 202, n-type GaN layer; 203, multi-quantum well active region layer; 204, p-type GaN layer; 205, transparent conductive layer; 206, p-type electrode layer; 207, second substrate; 208, bonding metal layer; 209, composite metal layer; 210, low-refractive-index dielectric layer; 211, metal nanocolumn array; 212, phosphor layer; 213, driving substrate; 214, conductive contact; 215, transparent polymer layer; 216, n-type electrode; 217, cover plate. Detailed implementation manners

[0020] In the ranges disclosed in the present invention, the endpoints and any values of the ranges are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values, they can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in the present invention.

[0021] In the description of the present application, it should be understood that the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of the said features. In the description of the present application, the meaning of "a plurality" is two or more, unless otherwise specifically defined.

[0022] In the description of the present application, it should be noted that unless otherwise clearly specified and defined, the terms "mounted", "connected" and "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection or an integral connection; it may be a mechanical connection, an electrical connection or a connection capable of mutual communication; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0023] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the specific embodiments of the present invention and the accompanying drawings of the specification. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0024] Embodiment 1 A preparation method of a highly directionally emitting Micro-LED chip is as follows. S101. Prepare a Micro-LED wafer, and the Micro-LED wafer has a plurality of display structures, such as Figure 2 shown. Each display structure sequentially includes a first substrate 201 made of sapphire, an n-type GaN layer 202, a multi-quantum well active region layer 203, and a p-type GaN layer 204 from bottom to top. S102. Use the ion beam sputtering process to sequentially deposit indium tin oxide (ITO) and Ag / Ti / W on the surface of the p-type GaN layer, as Figure 3As shown, a transparent conductive layer 205 and a p-type electrode layer 206 are formed; and high-temperature annealing is performed in a nitrogen environment at 600 °C for 4 minutes, so that a good ohmic contact is formed between the p-type GaN layer 206 and the transparent conductive layer 205; S103. Prepare a second substrate 207 made of conductive silicon, and deposit Ti / Pt / Au / In on the second substrate 207 by an ion beam sputtering process to form a bonding metal layer 208, obtaining a bonding substrate as Figure 4 shown; as Figure 5 shown, use the Au-In eutectic bonding technology to bond the p-type electrode layer 206 of the Micro-LED wafer to the bonding metal layer 208 of the bonding substrate, form a composite metal layer 209 and then turn it over, obtaining an intermediate product as Figure 6 shown; S104. Adopt a laser lift-off technology, as Figure 7 shown, use a laser with a wavelength of 248 nm and an energy density of 0.9 J / cm 2 emitted by a KrF excimer laser to strip the first substrate 201 of the intermediate product, so that the n-type GaN layer 202 is exposed; S105. Through a plasma-enhanced chemical vapor deposition technology, deposit a 1.5-μm-thick silicon dioxide layer on the exposed n-type GaN layer 202 to form a low-refractive-index dielectric layer 210, as Figure 8 shown; S106. Use a photolithography process and an ion beam sputtering process to deposit periodically distributed silver on the low-refractive-index dielectric layer to form a metal nanocolumn array 211, as Figure 9 shown. The height of the silver nanocolumns in the metal nanocolumn array 211 is 40 nm, the diameter is 80 nm, and the period is 400 nm; S107. Prepare a phosphor layer 212 on the surface of the metal nanocolumn array 211. The phosphor layer is a polystyrene phosphor thin film. The preparation method is to first mix 2 wt% phosphor with polystyrene, then add toluene solvent, and drop the ground mixed solution onto the metal nanocolumn array, and form a polystyrene phosphor thin film through spin coating and solvent evaporation. The phosphor is Oracet FL Red 305, which belongs to perylene-based dyes. As Figure 10 shown, a phosphor layer 212 with a thickness of 500 nm is formed on the low-refractive-index dielectric layer and the metal nanocolumn array to form a composite enhancement layer; S108. Perform dicing to obtain a number of high-directional emission Micro-LED chips.

[0025] Example 2 A method for preparing a display device, using the high-directional emission Micro-LED chips prepared in Example 1, the steps are as follows, S201. Transfer the highly directional emission Micro-LED chips onto the driving substrate 213 with the array-structured conductive contacts 214, such that the second substrate 207 is electrically connected to the conductive contacts 214, as Figure 11 shown; S201. Prepare a transparent polymer layer 215 on the driving substrate 213 by using photolithography and spin coating processes, as Figure 12 shown. The transparent polymer layer 215 is disposed at the edge of the driving substrate 213, between the edge of the driving substrate 213 and the conductive contacts 214, and between adjacent conductive contacts 214, and there are electrode trenches between the transparent polymer layers 215; the transparent polymer layer 215 is flush with the height of the highly directional emission Micro-LED chips; S203. Deposit Cr / Al / Ti / Pt / Au in the electrode trenches of the patterned polymer layer by using photolithography and ion beam sputtering processes to form an n-type electrode 216, as Figure 13 shown. The n-type electrode 216 is higher than the transparent polymer layer 215 and is electrically connected to the driving substrate 213 and the n-type GaN layer 202; place a cover plate 217 on the n-type electrode 216 to obtain a display device as Figure 14 shown.

[0026] Comparative Example 1 A method for preparing a Micro-LED chip, compared with Example 1, the difference is that steps S105 and S106 are not included, that is, the highly directional emission Micro-LED chip prepared compared with Example 1 does not have a low refractive index dielectric layer and a metal nanorod array, and the phosphor layer is directly disposed on the top of the n-type GaN layer.

[0027] Comparative Example 2 A method for preparing a Micro-LED chip, compared with Example 1, the difference is that step S105 is not included, that is, the highly directional emission Micro-LED chip prepared compared with Example 1 does not have a low refractive index dielectric layer.

[0028] Comparative Example 3 A method for preparing a Micro-LED chip, compared with Example 1, the difference is that step S106 is not included, that is, the highly directional emission Micro-LED chip prepared compared with Example 1 does not have a metal nanorod array.

[0029] Comparative Example 4 A method for preparing a display device, using the Micro-LED chip prepared in Comparative Example 1, the steps refer to Example 2 and will not be elaborated here.

[0030] The light distribution curves of the Micro-LED chips prepared in Example 1, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were analyzed, and the results are as Figure 15 shown. It can be seen that a single metal nanocolumn array (Comparative Example 2) and a single low refractive index dielectric layer (Comparative Example 3) have no obvious effect on enhancing the emission spectral intensity and beam collimation of the Micro-LED chip. Through the synergistic effect between the low refractive index dielectric layer and the metal nanocolumn array for mode extraction, a guided wave mode is generated in the phosphor layer, making Example 1 exhibit a greater forward emission spectral intensity than Comparative Example 1, Comparative Example 2, and Comparative Example 3.

[0031] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A highly directional emission Micro-LED chip, characterized in that: It includes, from bottom to top, a conductive second substrate, a composite metal layer, a transparent conductive layer, an epitaxial layer and a composite reinforcement layer; The composite enhancement layer comprises a low refractive index medium layer, a metal nanocolumn array and a phosphor layer, wherein the metal nanocolumn array is arranged on the upper end of the low refractive index medium layer, and the phosphor layer covers the low refractive index medium layer and the metal nanocolumn array.

2. The highly directional emission Micro-LED chip according to claim 1, characterized in that: The metal nano-columns in the metal nano-column array have a height of 10-100 nm, a diameter of 20-150 nm, and a period of 200-600 nm.

3. The highly directional emission Micro-LED chip according to claim 1, characterized in that: The thickness of the low refractive index medium layer is 0.5-1.5 μm.

4. The highly directional emission Micro-LED chip according to claim 1, characterized in that: The thickness of the phosphor layer is 300-800nm.

5. The highly directional emission Micro-LED chip according to claim 1, characterized in that: The epitaxial layer comprises a p-type GaN layer, a multi-quantum well active region layer, and an n-type GaN layer which are arranged in sequence from bottom to top.

6. A method for preparing a highly directional emission Micro-LED chip, characterized in that: include, Obtaining a Micro-LED wafer, wherein the Micro-LED wafer includes, from bottom to top, a first substrate, an epitaxial layer, a transparent conductive layer, and a p-type electrode layer; Obtaining a bonding substrate, wherein the bonding substrate comprises a conductive second substrate and a bonding metal layer on an upper portion of the second substrate; Bonding the p-type electrode layer of the Micro-LED wafer to the bonding metal layer of the bonding substrate to form a composite metal layer to obtain an intermediate product; The first substrate of the intermediate product is peeled off, a low refractive index medium layer and a metal nanocolumn array are sequentially prepared on the exposed epitaxial layer surface, and a phosphor layer is covered on the low refractive index medium layer and the metal nanocolumn array to obtain a composite enhancement layer.

7. The method for preparing a highly directional emission Micro-LED chip according to claim 6, characterized in that: The bonding adopts Au-In eutectic bonding.

8. The method for preparing a highly directional emission Micro-LED chip according to claim 6, characterized in that: The peeling is performed by laser peeling, the wavelength of the laser is 200-280nm, and the energy density is 0.6-1.0J / cm 2 .

9. A display device comprising a driving substrate with a plurality of conductive contacts, characterized in that: It also includes the highly directional emission Micro-LED chip, a transparent polymer layer, an n-type electrode and a cover plate according to any one of claims 1 to 5; The conductive second substrate of the highly directional emission Micro-LED chip is disposed on the conductive contact and electrically connected to the conductive contact; The transparent polymer layer is arranged at the edge of the driving substrate, between the edge of the driving substrate and the conductive contact, and between adjacent conductive contacts, and the transparent polymer layer has electrode grooves; The n-type electrode is disposed in the electrode groove and is electrically connected to the driving substrate and the epitaxial layer; On the driving substrate, the n-type electrode is higher than the transparent polymer layer and the highly directional emission Micro-LED chip, and the cover plate is disposed on the n-type electrode.

10. The display device according to claim 9, characterized in that The conductive contact array is disposed on the driving substrate.

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