Bionic micro-nano composite light extraction structure and preparation method

Abstract

The invention discloses a bionic micro-nano composite light extraction structure, which relates to the field of photoelectric display and comprises a plurality of periodic micro line top polygonal pyramids and periodic nano salient point array structures which are applied to the micro line top polygonal pyramids and have long-range orderliness. The micro line top polygonal pyramid is of a three-dimensional structure with a polygonal bottom surface and a line top formed by two top ends, and the bionic micro-nano composite structure is used for reducing total reflection and improving the light extraction efficiency of the light-emitting element by changing the light propagation direction; the bottom surface of the miniature line top polygonal pyramid is polygonal, and the top end position and the distance are variable, so that the miniature line top polygonal pyramid is asymmetric along the vertical plane where the line top of the miniature line top polygonal pyramid is located or the middle vertical plane of the line top of the miniature line top polygonal pyramid. The bionic micro-nano composite structure can effectively improve the light extraction efficiency of the light-emitting element and save energy.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic display technologies, and particularly to a bionic micro-nano composite light extraction structure and a preparation method thereof. Background Art

[0002] Micro-LED is a new display technology that uses a panel composed of tiny LED chips to achieve high-resolution and high-brightness display effects. Compared with traditional liquid crystal display (LCD) and organic light-emitting diode (OLED) technologies, Micro-LED has higher peak brightness, excellent dark state, high resolution density, longer service life, and faster response time. These characteristics make Micro-LED show great potential in high-end display applications, such as wearable devices, smart phones, augmented reality (AR) / virtual reality (VR) devices, micro projectors, and ultra-high-resolution TVs.

[0003] Although Micro-LED technology has broad development prospects, there are still many deficiencies and challenges at present, which limit its large-scale application and commercial promotion. Light extraction efficiency is one of the important indicators to measure the display performance of Micro-LED. It refers to the proportion of the light emitted from the Micro-LED chip that can be effectively extracted and transmitted to the surface of the display screen. Improving the light extraction efficiency means that the light energy can be more fully utilized, thereby providing a brighter and more energy-efficient display effect. However, the existing Micro-LED chip has low light extraction efficiency, resulting in excessive energy loss and energy waste. Therefore, researching and developing efficient external light extraction technologies is of great significance for improving the display performance of Micro-LED. Summary of the Invention

[0004] In view of the above-mentioned partial defects of the prior art, the technical problem to be solved by the present invention is to provide a bionic micro-nano composite light extraction structure and a preparation method thereof, aiming to improve the light extraction efficiency of light-emitting elements.

[0005] To achieve the above object, the first aspect of the present invention discloses a preparation method of a bionic micro-nano composite light extraction structure, and the method includes:

[0006] Step S1, uniformly coating a first photoresist on a first substrate, and forming a plurality of periodic micro wire-top multi-edge pyramid concave die micron structures on the first photoresist by grayscale lithography; and developing and drying the first photoresist after lithography to obtain a micron pattern master.

[0007] Step S2: Uniformly mix the polydimethylsiloxane monomer and the crosslinking agent according to a first preset ratio, evacuate and degas the first mixture, and uniformly spin-coat it on the micron pattern master; then heat-cure and peel the first mixture in sequence to obtain a first PDMS template with a structure opposite to that of the micron pattern master; wherein, the first PDMS template includes a plurality of periodic micro wire-top multi-sided pyramid convex die micron structures;

[0008] Step S3: Horizontally stretch the first PDMS template through a stretching displacement stage, etch the horizontally stretched first PDMS template by reactive ion etching, and then restore the first PDMS template to form a periodic horizontal nanostructure grating on the first PDMS template;

[0009] Step S4: Treat the first PDMS template with a hydrophobic modifier for hydrophobic treatment; uniformly mix the polydimethylsiloxane monomer and the crosslinking agent according to a second preset ratio, evacuate and degas the second mixture, and uniformly spin-coat it on the first PDMS template; then heat-cure and peel the second mixture in sequence to obtain a second PDMS template with a structure opposite to that of the first PDMS template; wherein, the second PDMS template includes a plurality of periodic micro wire-top multi-sided pyramid concave die micron structures and the horizontal nanostructure grating;

[0010] Step S5: Vertically stretch the second PDMS template through the stretching displacement stage, etch the vertically stretched second PDMS template by reactive ion etching, and then restore the second PDMS template to form a periodic vertical nanostructure grating on the second PDMS template; wherein, the horizontal nanostructure grating and the vertical nanostructure grating constitute a periodic nano bump array structure with long-range order;

[0011] Step S6: Obtain a light-emitting element, spin-coat ultraviolet imprinting glue on the light-emitting surface of the light-emitting element, place the second PDMS template on the ultraviolet imprinting glue, and by pressing and ultraviolet irradiating the second PDMS template, make the ultraviolet imprinting glue form a bionic micro-nano composite structure on the light-emitting surface of the light-emitting element; peel the second PDMS template to obtain a light-emitting element assembly with a bionic micro-nano composite structure.

[0012] Optionally, step S3 includes:

[0013] According to the first period and the first height required for the horizontal nanostructure grating, obtain the first horizontal stretching degree and the first reactive ion etching parameters; wherein, the first reactive ion etching parameters at least include etching power, etching time, etching flow rate, etching pressure, and etching gas type;

[0014] According to the first lateral stretching degree, the first PDMS template is laterally stretched by a stretching displacement stage; according to the first reactive ion etching parameters, the laterally stretched first PDMS template is subjected to reactive ion etching;

[0015] The etched first PDMS template is restored to form a periodic lateral nanostructure grating on the first PDMS template.

[0016] Optionally, in step S3, the first lateral stretching degree is 0%-500%, the reactive ion etching power of the reactive ion etching is 50-250 W, the reactive ion etching time is 40-240 s, the reactive ion etching flow rate is 10-300 sccm, the reactive ion etching pressure is 1-100 pa, the reactive ion etching gas at least includes oxygen, argon or a mixed gas of the two, the first period of the lateral nanostructure grating is 100 nm-2000 nm, and the first height of the lateral nanostructure grating is 50 nm-1000 nm.

[0017] Optionally, step S5 includes:

[0018] According to the second period and the second height required for the longitudinal nanostructure grating, the second longitudinal stretching degree and the second reactive ion etching parameters are obtained; wherein, the second reactive ion etching parameters at least include etching power, etching time, etching flow rate, etching pressure and etching gas type;

[0019] According to the second longitudinal stretching degree, the second PDMS template is longitudinally stretched by a stretching displacement stage; according to the second reactive ion etching parameters, the longitudinally stretched second PDMS template is subjected to reactive ion etching;

[0020] The etched second PDMS template is restored to form a periodic longitudinal nanostructure grating on the second PDMS template.

[0021] Optionally, in step S5, the second longitudinal stretching degree is 0%-500%, the reactive ion etching power of the reactive ion etching is 50-250 W, the reactive ion etching time is 40-240 s, the reactive ion etching flow rate is 10-300 sccm, the reactive ion etching pressure is 1-100 pa, the reactive ion etching gas at least includes oxygen, argon or a mixed gas of the two, the second period of the longitudinal nanostructure grating is 100 nm-2000 nm, and the second height of the longitudinal nanostructure grating is 50 nm-1000 nm.

[0022] Optionally, step S1 includes:

[0023] A first photoresist is uniformly coated on a first substrate, and one or more of laser direct writing, photolithography, laser etching, and nanoimprinting are used to form a plurality of periodic micro wire-top multi-sided pyramid concave die microstructures on the first photoresist, thereby obtaining the micro pattern master; wherein, the periodicity of the micro wire-top multi-sided pyramid concave die microstructures of the micro pattern master is one-dimensional or two-dimensional.

[0024] Optionally, in the step S1, the period of the micro pattern master is 1 - 100 um, and the height is 0.5 - 10 um.

[0025] Optionally, the ratio of polydimethylsiloxane monomer to crosslinking agent in the first preset ratio and the second preset ratio is 100:1 - 1:1.

[0026] Optionally, the micro wire-top multi-sided pyramid is a three-dimensional structure with a polygonal bottom surface and two tops.

[0027] Optionally, the method further includes:

[0028] According to the first light extraction efficiency required for the micro-nano composite structure, determine the first position of the midpoint between the two tops of the micro wire-top multi-sided pyramid and the first distance between the two tops; wherein, the first position and the first distance are used to adjust the light extraction efficiency of the micro-nano composite structure.

[0029] A second aspect of the present invention discloses a bionic micro-nano composite light extraction structure, characterized in that the bionic micro-nano composite structure includes a plurality of periodic micro wire-top multi-sided pyramids and a periodic nano bump array structure with long-range order applied on the micro wire-top multi-sided pyramids. The micro wire-top multi-sided pyramid is a three-dimensional structure with a polygonal bottom surface and a wire top formed by two tops. The bionic micro-nano composite structure is used to change the light propagation direction to reduce total internal reflection and improve the light extraction efficiency of the light-emitting element; the bottom surface of the micro wire-top multi-sided pyramid is polygonal, and the top position and spacing are variable, so that the micro wire-top multi-sided pyramid is asymmetric along the vertical plane where the wire top of the micro wire-top multi-sided pyramid is located or the mid-perpendicular plane of the wire top.

[0030] Advantages of the present invention: 1. By referring to the lantern structure of the abdomen of fireflies and further improving it into a micro-line-top multi-sided pyramid composite with a periodically nanostructured array with long-range order, it is verified by simulation that the external light extraction efficiency is effectively improved. The bionic micro-nano composite structure prepared by the present invention has an ordered micro-structured pattern nested with periodic nano-structures, which can avoid light loss at the interface between the device substrate and air, improve the light extraction efficiency of the light-emitting element without changing the viewing angle characteristics of the light-emitting element, and has a strong light extraction effect. 2. When preparing the lateral nanostructured grating and the longitudinal nanostructured grating in the present invention, the period and height of the nanostructured grating can be controlled by adjusting parameters such as the stretching direction, degree, etching power, time, flow rate, pressure, and gas of reactive ion etching, so that the light extraction efficiency of light in different directions can be controlled according to requirements. 3. The present invention forms a periodically nanostructured array with long-range order through two stretches and reactive ion etching. Compared with the prior art which only performs one stretch, the corresponding bionic micro-nano composite structure of the present invention can more effectively improve the divergence angle of the light field emitted by the device. 4. Using the PDMS micro-nano composite pattern opposite to the desired bionic micro-nano composite structure obtained as a template, the desired bionic micro-nano composite structure can be obtained only by a simple replication method later, with high production efficiency and low cost.

[0031] In summary, the present invention can effectively improve the light extraction efficiency of the light-emitting element, reduce energy loss, and avoid energy waste. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a schematic flow chart of a method for preparing a bionic micro-nano composite light extraction structure provided by a specific embodiment of the present invention;

[0033] Figure 2 is a schematic diagram of the formation process of a micro-structured master provided by a specific embodiment of the present invention;

[0034] Figure 3 is a schematic diagram of a micro-line-top multi-sided pyramid concave die structure provided by a specific embodiment of the present invention;

[0035] Figure 4 is a schematic diagram of the formation process of a first PDMS template provided by a specific embodiment of the present invention;

[0036] Figure 5 is a schematic diagram of a micro-line-top multi-sided pyramid convex die structure provided by a specific embodiment of the present invention;

[0037] Figure 6 is a 3D schematic diagram of a micro-line-top multi-sided pyramid convex die structure provided by a specific embodiment of the present invention;

[0038] Figure 7It is a schematic diagram of the preparation process of the lateral nanostructure grating of the first PDMS template provided by a specific embodiment of the present invention;

[0039] Figure 8 It is a schematic diagram of the formation process of the second PDMS template provided by a specific embodiment of the present invention;

[0040] Figure 9 It is a schematic diagram of the preparation process of the longitudinal nanostructure grating of the second PDMS template provided by a specific embodiment of the present invention;

[0041] Figure 10 It is a schematic diagram of the periodic nano bump array structure with long-range order provided by a specific embodiment of the present invention;

[0042] Figure 11 It is a schematic diagram of the preparation process of the bionic micro-nano composite structure provided by a specific embodiment of the present invention;

[0043] Figure 12 It is a schematic diagram of the structure of the Micro-LED chip provided by a specific embodiment of the present invention;

[0044] Figure 13 It is a schematic diagram of the existing single-top pyramid structure provided by a specific embodiment of the present invention;

[0045] Figure 14 It is a relationship diagram of the light extraction efficiency varying with the number of sides of the single-top pyramid structure provided by a specific embodiment of the present invention;

[0046] Figure 15 It is a relationship diagram of the light enhancement ratio varying with the number of sides of the single-top pyramid structure provided by a specific embodiment of the present invention;

[0047] Figure 16 It is a relationship diagram of the light extraction efficiency varying with the height and radius of the single-top pyramid provided by a specific embodiment of the present invention;

[0048] Figure 17 It is a relationship diagram of the light enhancement ratio varying with the height and radius of the single-top pyramid provided by a specific embodiment of the present invention;

[0049] Figure 18 It is a relationship diagram of the light extraction efficiency varying with the vertex spacing of the micro wire-top multi-sided pyramid structure provided by a specific embodiment of the present invention;

[0050] Figure 19 It is a relationship diagram of the light enhancement ratio varying with the vertex spacing of the micro wire-top multi-sided pyramid structure provided by a specific embodiment of the present invention;

[0051] Figure 20It is a relationship diagram showing the variation of the light extraction efficiency with the grating period and height of the micro-line-top multi-sided pyramid structure provided by a specific embodiment of the present invention;

[0052] Figure 21 It is a relationship diagram showing the variation of the light enhancement ratio with the grating period and height of the micro-line-top multi-sided pyramid structure provided by a specific embodiment of the present invention. Specific embodiments

[0053] The present invention discloses a bionic micro-nano composite light extraction structure and a preparation method. Those skilled in the art can draw on the content of this article and appropriately improve the technical details to achieve it. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments. Relevant personnel can obviously make changes or appropriate changes and combinations to the methods and applications described in this article without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0054] After research by the applicant, it is found that: through long-term evolution, organisms in nature have many structures with excellent optical properties, which provide new ideas and methods for solving the problem of the light extraction efficiency of light-emitting elements. A bionic structure refers to an artificial structure designed by imitating the microscopic or macroscopic structures of organisms in nature. These structures usually have fine dimensions, complex shapes and special materials, and can achieve some excellent properties of organisms, such as efficient light absorption, reflection, scattering, refraction, etc. For example, the scales on the wings of butterflies show gorgeous colors, which benefits from the reflection, scattering and interference of light by their unique micro-nano structures; the micro-nano structures on the surface of lotus leaves endow the lotus leaves with superhydrophobic and self-cleaning properties, and also have an impact on the propagation of light. The luminous cuticle with a tiny stepped structure on the abdomen of fireflies enhances Lambert emission, thereby improving the wide-angle illuminance. These bionic micro-nano structures provide brand-new ideas and methods for improving the light extraction efficiency of light-emitting elements. Traditional single periodic micro-nano structures often change the spectral characteristics and angular distribution of devices. In this embodiment, the light-emitting element uses a Micro-LED. In practical applications, the type of the light-emitting element is not limited; the light-emitting element includes but is not limited to: LED, LCD, PDP plasma display, FED field emission, OLED organic display, quantum dot display, etc.

[0055] Therefore, the embodiment of the present invention provides a method for preparing a bionic micro-nano composite light extraction structure, as Figure 1 shown, the method includes:

[0056] Step S1: Uniformly coat a first photoresist on a first substrate, and use gray-scale lithography on the first photoresist to form a plurality of periodic micron-scale structures of micro-line-top multi-sided pyramid concave dies; then develop and dry the lithographed first photoresist to obtain a micron pattern master.

[0057] In this specific embodiment, step S1 includes:

[0058] Uniformly coat a first photoresist on a first substrate, and use one or more of laser direct writing, lithography, laser etching, and nanoimprinting to form a plurality of periodic micron-scale structures of micro-line-top multi-sided pyramid concave dies on the first photoresist, thereby obtaining a micron pattern master.

[0059] Among them, the periodicity of the micron-scale structures of the micro-line-top multi-sided pyramid concave dies of the micron pattern master is one-dimensional or two-dimensional.

[0060] It should be noted that the micron pattern master can be prepared alone or in combination through a variety of different methods.

[0061] In this specific embodiment, in step S1, the period of the micron pattern master is 1 - 100 μm, and the height is 0.5 - 10 μm.

[0062] In this specific embodiment, the micro-line-top multi-sided pyramid is a three-dimensional structure with a pentagonal base and two tops. Specifically, the three-dimensional structure of the micro-line-top multi-sided pyramid corresponding to the concave die can be as shown in Figure 3 shown. The three-dimensional structure of the micro-line-top multi-sided pyramid convex die corresponding to the convex film can be as shown in Figure 5 shown, and the 3D three-dimensional structure of the micro-line-top multi-sided pyramid convex die corresponding to the convex film can be as shown in Figure 6 shown. Figure 6 In [figure], 601 is the first angle, 602 is the second angle, and 603 is the third angle. The position and height of the top of the micro-line-top multi-sided pyramid can be controlled according to the bottom radius of the micro-line-top multi-sided pyramid and these three angles.

[0063] Furthermore, the method further includes:

[0064] Determine a first position at the midpoint between the two tops and a first distance between the two tops of the micro-line-top multi-sided pyramid according to the first light extraction efficiency required for the micro-nano composite structure; wherein, the first position and the first distance are used to adjust the light extraction efficiency of the micro-nano composite structure.

[0065] In a specific application process, step S1 specifically includes:

[0066] S101: Spin-coat AZ4620 photoresist on a glass substrate (first substrate) with spin-coating parameters of 2000 revolutions for 40 seconds, and then dry it at 120 degrees for 10 minutes after spin-coating.

[0067] S102. Then, produce a grayscale image using PS, and lithographically pattern the desired pattern on the photoresist through the grayscale function of laser direct writing.

[0068] Since three replications are to be carried out (two PDMS replications and one replication to the light-emitting surface of the chip), the pattern initially produced by laser direct writing should be the opposite one. After directly obtaining the corresponding grayscale image through the color inversion function, the corresponding pattern can be laser direct written.

[0069] S103. Then, perform development. Immerse it in the rzx3038 developer for one minute, then immerse it in deionized water for one minute, and perform drying at 100 degrees for 90 seconds.

[0070] The formation process of the micron pattern master corresponding to S101 - S103 can be as Figure 2 shown, Figure 2 where 201 is the glass substrate and 202 is the photoresist. Meanwhile, the micro wire top multi-sided pyramid concave die structure in the micron pattern master can be as Figure 3 shown.

[0071] Step S2: Uniformly mix the polydimethylsiloxane monomer and the crosslinking agent according to the first preset ratio, evacuate and remove bubbles from the first mixture, and uniformly spin coat it on the micron pattern master; then heat and cure and peel the first mixture in sequence to obtain a first PDMS template with a structure opposite to that of the micron pattern master.

[0072] Among them, the first PDMS template includes a plurality of periodic micro wire top multi-sided pyramid convex die micron structures.

[0073] In a specific application process, step S2 specifically includes:

[0074] Prepare the first PDMS template using the soft printing method. Uniformly mix the polydimethylsiloxane monomer and the crosslinking agent at a ratio of 10:1, add a magnetic stirrer and rotate at 800 revolutions per minute for 3 minutes to evacuate and remove bubbles, then uniformly pour it on the micron pattern master, let it stand for half an hour, then heat and cure at 80 degrees for 1 hour and then peel. After peeling, a polydimethylsiloxane micron structure opposite to the micron pattern master is obtained, that is, the first PDMS template with an ordered micron structure.

[0075] The formation process of the first PDMS template corresponding to step S2 is as Figure 4 shown, Figure 4 where 201 is the glass substrate, 202 is the photoresist, and 403 is the first PDMS template. The micro wire top multi-sided pyramid convex die is as Figure 5 shown.

[0076] Step S3: Horizontally stretch the first PDMS template by a stretching displacement stage, etch the horizontally stretched first PDMS template by reactive ion etching, and then restore the first PDMS template to form a periodic horizontal nanostructure grating on the first PDMS template.

[0077] In this specific embodiment, step S3 includes:

[0078] Obtain a first horizontal stretching degree and first reactive ion etching parameters according to the first period and first height required for the horizontal nanostructure grating; wherein, the first reactive ion etching parameters at least include etching power, etching time, etching flow rate, etching pressure, and etching gas type;

[0079] Horizontally stretch the first PDMS template by a stretching displacement stage according to the first horizontal stretching degree; perform reactive ion etching on the horizontally stretched first PDMS template according to the first reactive ion etching parameters;

[0080] Restore the etched first PDMS template to form a periodic horizontal nanostructure grating on the first PDMS template.

[0081] Further, in step S3, the first horizontal stretching degree is 0%-500%, the reactive ion etching power of the reactive ion etching is 50-250 W, the reactive ion etching time is 40-240 s, the reactive ion etching flow rate is 10-300 sccm, the reactive ion etching pressure is 1-100 Pa, the reactive ion etching gas at least includes oxygen, argon, or a mixed gas of the two, the first period of the horizontal nanostructure grating is 100 nm-2000 nm, and the first height of the horizontal nanostructure grating is 50 nm-1000 nm.

[0082] In a specific application process, step S3 includes:

[0083] S301: Horizontally stretch the first PDMS template obtained above by 20% (0%-500%) by a stretching displacement stage.

[0084] S302: Place the first PDMS template into a RIE (reactive ion etching) device, introduce oxygen (argon) as the gas, the radio frequency power is 200 w (50-250 w), the etching time is 120 s (40-240 s), the air pressure is 10 Pa (1-100 Pa), and the gas flow rate is 50 sccm (10-300 sccm).

[0085] S303: Obtain that the grating period corresponding to the first PDMS template is 600 nm (100-2000 nm), and the undulation (height) is 250 nm (50-1000 nm).

[0086] The change process corresponding to step S3 for the first PDMS template is as follows Figure 7 shown Figure 7 where a, b, and c respectively correspond to the first PDMS template before stretching, after stretching, and after etching restoration

[0087] Step S4: Hydrophobically treat the first PDMS template with a hydrophobic modifier; uniformly mix the polydimethylsiloxane monomer and the crosslinking agent according to a second preset ratio, evacuate and defoam the second mixture, and uniformly spin-coat it on the first PDMS template; and sequentially heat-cure and peel the second mixture to obtain a second PDMS template with a structure opposite to that of the first PDMS template

[0088] Among them, the second PDMS template includes a plurality of periodic micro wire-top multi-sided pyramid concave die micron structures and transverse nanostructure gratings

[0089] It should be noted that in the embodiment of the present invention, through the hydrophobic treatment, the second PDMS template can be directly prepared through the first PDMS template

[0090] In this specific embodiment, the hydrophobic modifier can be trimethylchlorosilane

[0091] In this specific embodiment, the ratios of the polydimethylsiloxane monomer and the crosslinking agent in the first preset ratio and the second preset ratio are both 100:1 - 1:1

[0092] In a specific application, step S4 specifically includes

[0093] S401: Uniformly spray TMCS (trimethylchlorosilane, hydrophobic modifier) on the first PDMS template, spray it again after standing for 1 hour, and spray it three times in total, so that the structure will not deform during the secondary replication

[0094] S402: Uniformly mix the polydimethylsiloxane monomer and the crosslinking agent according to a ratio of 10:1, add a magnetic stirrer and rotate at 800 revolutions per minute for 3 minutes for evacuation and defoaming, then uniformly pour it on the hydrophobically treated first PDMS template, stand for half an hour, then heat-cure at 80 °C for 1 hour and then peel off. After peeling, a second PDMS template opposite to the above-mentioned first PDMS template is obtained

[0095] The process of preparing the second PDMS template in step S4 can be as follows Figure 8 shown. As shown in 8, 403 is the first PDMS template for the first replication, 805 is TMCS, and 806 is the second PDMS template poured on for the second replication

[0096] Step S5: Vertically stretch the second PDMS template through a stretching displacement stage, etch the vertically stretched second PDMS template by reactive ion etching, and then restore the second PDMS template to form a periodic longitudinal nanostructure grating on the second PDMS template.

[0097] Among them, the transverse nanostructure grating and the longitudinal nanostructure grating

[0098] have a periodic nano bump array structure with long-range order, and the periodic nano bump array structure with long-range order can be as Figure 10 shown.

[0099] In this specific embodiment, step S5 includes:

[0100] According to the second period and the second height required for the longitudinal nanostructure grating, obtain the second longitudinal stretching degree and the second reactive ion etching parameters; wherein, the second reactive ion etching parameters at least include etching power, etching time, etching flow rate, etching pressure, and etching gas type;

[0101] Vertically stretch the second PDMS template through a stretching displacement stage according to the second longitudinal stretching degree; perform reactive ion etching on the vertically stretched second PDMS template according to the second reactive ion etching parameters;

[0102] Restore the etched second PDMS template to form a periodic longitudinal nanostructure grating on the second PDMS template.

[0103] Further, in step S5, the second longitudinal stretching degree is 0%-500%, the reactive ion etching power of the reactive ion etching is 50-250W, the reactive ion etching time is 40-240s, the reactive ion etching flow rate is 10-300sccm, the reactive ion etching pressure is 1-100pa, the reactive ion etching gas at least includes oxygen, argon, or a mixed gas of the two, the second period of the longitudinal nanostructure grating is 100nm-2000nm, and the second height of the longitudinal nanostructure grating is 50nm-1000nm.

[0104] In a specific application process, step S5 specifically includes:

[0105] S501: Vertically stretch the second PDMS template obtained above by 20% (0%-500%) through a stretching displacement stage.

[0106] S502. Place the second PDMS template into the RIE (Reactive Ion Etching) equipment. The gas introduced is oxygen (argon), the radio frequency power is 200 w (50 - 250 w), the etching time is 120 s (40 - 240 s), the air pressure is 10 pa (1 - 100 pa), and the gas flow rate is 50 sccm (10 - 300 sccm).

[0107] S503. The grating period corresponding to the obtained second PDMS template is 600 nm (100 - 2000 nm), and the undulation (height) is 250 nm (50 - 1000 nm).

[0108] The change process of step S5 corresponding to the first PDMS template is as Figure 9 shown. Figure 9 In it, a, b, and c respectively correspond to the second PDMS template before stretching, after stretching, and after etching restoration.

[0109] Step S6. Obtain a Micro-LED chip. Spin-coat a UV imprinting adhesive on the light-emitting surface of the Micro-LED chip. Place the second PDMS template on the UV imprinting adhesive. By pressing and UV irradiating the second PDMS template, the UV imprinting adhesive forms a bionic micro-nano composite structure on the light-emitting surface of the Micro-LED chip; peel off the second PDMS template to obtain a Micro-LED chip with a bionic micro-nano composite structure. It should be noted that here the light-emitting element is temporarily described by the Micro-LED chip, and the present invention does not limit the specific type of the light-emitting element.

[0110] In a specific application process, step S6 specifically includes:

[0111] S601. Spin-coat NOA63 UV curable adhesive on the light-emitting surface of the Micro-LED chip at a spin-coating speed of 4000 revolutions for 60 seconds, and let it stand for half an hour after spin-coating.

[0112] S602. Carefully attach the second PDMS template obtained above to the UV curable adhesive, slightly press it and then irradiate it with a UV lamp at a power of 25 w for 15 minutes, and then peel off the PDMS template to obtain a Micro-LED chip with a light extraction structure (bionic micro-nano composite structure).

[0113] The preparation process of step S6 corresponding to the bionic micro-nano composite structure can be as Figure 11 shown, Figure 11 where 1107 is the Micro-LED chip, 1108 is the UV curable adhesive, 1109 is the UV lamp, and 806 is the second PDMS template.

[0114] An embodiment of the present invention also provides a bionic micro-nano composite structure for improving the light extraction efficiency of Micro-LEDs. The bionic micro-nano composite structure for improving the light extraction efficiency of Micro-LEDs includes: a Micro-LED chip array, the Micro-LED chip array includes a plurality of Micro-LED chips, the light-emitting surface of the Micro-LED chips is covered with a bionic micro-nano composite structure, the bionic micro-nano composite structure includes a plurality of periodic micro wire-top multi-sided pyramids and a periodic nano bump array structure with long-range order applied on the micro wire-top multi-sided pyramids. The micro wire-top multi-sided pyramid is a three-dimensional structure with a polygonal bottom surface and two tops. The bionic micro-nano composite structure improves the light extraction efficiency of Micro-LEDs by changing the light propagation direction and reducing total internal reflection.

[0115] In this specific embodiment, the preparation process of the Micro-LED chip is as follows:

[0116] 1. Substrate preparation

[0117] Substrate selection: Sapphire (Al 2 O 3 ), because of its low cost and good lattice matching with GaN.

[0118] Substrate cleaning:

[0119] Use acetone and isopropyl alcohol for ultrasonic cleaning to remove organic substances.

[0120] Pickling (H 2 SO 4 :H 3 PO 4 = 3:1) to remove surface oxides.

[0121] Rinse with deionized water and dry with nitrogen.

[0122] 2. Buffer layer growth

[0123] Low-temperature GaN nucleation layer:

[0124] Grow a low-temperature (~500 °C) GaN nucleation layer (20 - 50 nm) on the sapphire substrate to relieve lattice mismatch (the lattice mismatch between sapphire and GaN is about 16%).

[0125] High-temperature GaN buffer layer:

[0126] Raise the temperature to 1000 - 1100 °C and grow a high-temperature GaN buffer layer (1 - 2 um) to improve crystal quality.

[0127] 3. N-type GaN layer growth

[0128] Doping parameters: Use silane (SiH 4)As a doping source, grow an Si-doped N-type GaN layer (1 - 3 um) with the electron concentration controlled at 1×10 18 ~1×10 19 cm -3 。

[0129] Quality control: Verify the crystal quality through XRD (full width at half maximum < 300 arcsec) and PL spectroscopy.

[0130] 4. Growth of multiple quantum wells (MQWs)

[0131] Structure design: InGaN / GaN multiple quantum wells (5 - 10 periods), and for each period:

[0132] InGaN well layer: 2 - 5 nm, In content 15 - 30% (control the wavelength by adjusting the TMIn flow rate and growth temperature, with the target wavelength for green light being 520 - 560 nm).

[0133] GaN barrier layer: 5 - 15 nm, with a slightly higher growth temperature (~800 °C) to maintain the crystal quality.

[0134] Key control: Precisely control the In composition uniformity (±1%) and the steepness of the well / barrier interface.

[0135] 5. p-AlGaN electron blocking layer

[0136] Function: Prevent electrons from spilling out of the quantum wells and improve the radiative recombination efficiency.

[0137] Growth parameters:

[0138] Al composition 10 - 20%, thickness 10 - 30 nm, Mg doping concentration 1×10 19 cm -3 。

[0139] The growth temperature is slightly lower than that of the GaN barrier layer (~900 °C) to reduce In evaporation.

[0140] 6. p-type GaN layer

[0141] Doping parameters: Grow an Mg-doped p-type GaN layer (100 - 300 nm) with a doping concentration of 1×10 19 ~5×10 19 cm -3 。

[0142] Activation annealing: Anneal at 700 - 800 °C for 10 - 30 minutes in an N 2 or O 2 atmosphere to activate the Mg acceptors (hole concentration reaches 1×10 17 cm -3 )。

[0143] 7. ITO Transparent Conductive Layer

[0144] Deposition method: Magnetron sputtering or electron beam evaporation, thickness 50 - 200 nm.

[0145] Annealing treatment: Anneal at 400 - 600 °C to optimize the transmittance (>90% @ 550 nm) and sheet resistance (<10 Ω / sq).

[0146] 8. Ag Reflective Layer

[0147] Function: Reflect the light propagating downward and improve the light extraction efficiency of the N side.

[0148] Deposition process:

[0149] Deposit an Ag layer (100 - 200 nm) by electron beam evaporation, reflectivity >95% (in the green light band).

[0150] Cover with a protective layer (such as SiO 2 50 nm) to prevent Ag oxidation.

[0151] After the preparation of the Ag reflective layer

[0152] 1. Lithography and Etching

[0153] mesa etching:

[0154] Lithography defines the mesa pattern, and ICP dry etching (Cl 2 / BCl 3 gas) penetrates through Ag, ITO, p-GaN to the N-type GaN layer to form independent light-emitting units.

[0155] Etching depth control: Keep 50 - 100 nm of the N-type GaN layer to avoid damaging the MQWs.

[0156] Cleaning: O 2 Plasma ashing, dilute HCl to remove etching residues.

[0157] 2. Electrode Preparation

[0158] N-type electrode (Ti / Al / Ni / Au):

[0159] Deposit Ti / Al / Ni / Au (20 / 100 / 20 / 100 nm) by electron beam evaporation and form a pattern by lift-off lithography.

[0160] Anneal (400 - 500 °C, N 2 atmosphere) to optimize the ohmic contact (specific contact resistance <1×10 -4 Ω·cm 2 ).

[0161] P-type electrode (Ni / Au):

[0162] Deposit Ni / Au (20 / 100 nm) on the ITO surface and anneal to form a low-resistance contact.

[0163] 3. Passivation layer and opening

[0164] Passivation layer deposition: Grow SiO 2 / SiN x (200 nm) to protect the sidewalls.

[0165] Opening process: Lithography + dry etching (CF 4 / O 2 ) to expose the electrode area.

[0166] 4. Sapphire substrate peeling

[0167] Laser lift-off (LLO):

[0168] Irradiate the sapphire substrate with a KrF excimer laser (248 nm), and the laser energy (500 - 800 mJ / cm 2 ) decomposes the GaN / sapphire interface.

[0169] Mechanically separate the sapphire substrate and retain the complete GaN epitaxial layer.

[0170] Surface treatment:

[0171] Chemical mechanical polishing (CMP) or KOH etching (50 - 80 °C) to reduce the surface roughness of N-type GaN (Ra < 1 nm).

[0172] Optional: Nanoimprinting or wet etching to form a surface roughening structure to improve the light extraction efficiency by 10 - 30%.

[0173] The Micro-LED chip is obtained through the above steps as Figure 12 shown.

[0174] In a specific application process, the present invention conducts simulation experiments on the Figure 12 Micro-LED chip and the bionic micro-nano composite structure shown, and the simulation experiment data results are as follows:

[0175] The simulation structure is as Figure 12 , and the thicknesses of each layer from the GaN buffer layer to the AG reflective layer are 0.03 um, 1.5 um, 0.2 um, 0.03 um, 0.3 um, 0.08 um, 0.2 um respectively. The scanning diameter is 10 * 10 um. When the bionic micro-nano composite structure is not added, the light extraction efficiency of the pure Micro-LED is 0.153864.

[0176] First, for the one as Figure 13The base number of the existing single-top pyramid structure (light extraction efficiency improvement structure) shown in the figure was simulated. The radius was set to 5 μm and the height was set to 2 μm. The simulation results are shown in Table 1. It can be seen that the 5-sided structure has the best light extraction efficiency, with a light extraction efficiency of 0.259943812 and an enhancement ratio of 1.6894388. The relationship diagram of the light extraction efficiency varying with the number of sides is as shown in Figure 14 shown, and the relationship diagram of the light enhancement ratio varying with the number of sides is as shown in Figure 15 shown.

[0177] Table 1 Simulation Results Table of the Number of Sides

[0178]

[0179] Then, a joint parameter sweep was performed on the height and radius of the pentagonal pyramid. The radius ranged from 2 μm to 5 μm, and the height ranged from 0 to 2 μm. It was found that when the radius was 4 μm and the height was 1.6 μm, the light extraction efficiency was the highest, at 0.26142731, and the enhancement ratio was 1.699080419. The simulation results are shown in Tables 2 and 3. The relationship diagram of the light extraction efficiency varying with the height and radius is as shown in Figure 16 shown, and the relationship diagram of the light enhancement ratio varying with the height and radius is as shown in Figure 17 shown.

[0180] Table 2 Simulation Results Table of the Height and Radius of the Light Extraction Efficiency

[0181]

[0182] Table 3 Simulation Results Table of the Height and Radius of the Light Enhancement Ratio

[0183]

[0184]

[0185] A simulation experiment was carried out on the bionic micro-nano composite structure without a grating. Then, the radius of the micro wire top multi-sided pyramid was set to 4 μm, the height was set to 1.6 μm, and the number of sides of the base was five. A parameter sweep was performed on the offset between the center positions of its two vertices and the center of the polygon and the distance between the two vertices. When the offset was 0 μm and the distance was 2 μm, the light extraction efficiency was the highest, at 0.279451306, and the enhancement ratio was 1.816222807. The simulation results are shown in Tables 4 and 5. The relationship diagram of the light extraction efficiency varying with the vertex distance is as shown in Figure 18 shown, and the relationship diagram of the light enhancement ratio varying with the vertex distance is as shown in Figure 19 shown.

[0186] Table 4 Simulation Results Table of the Offset and Vertex Distance of the Light Extraction Efficiency

[0187]

[0188] Table 5 Simulation Results Table of Offset and Vertex Spacing Enhancement Ratio

[0189]

[0190] The bionic micro-nano composite structure with a grating was subjected to a simulation experiment. The period and height of the grating were swept. The period ranged from 0.3 um to 1.2 um, and the height ranged from 100 nm to 500 nm. It was found that when the period was 0.6 um and the height was 250 nm, the effect was the best, the light extraction efficiency was 0.282547937225147, and the enhancement ratio was 1.83634857552869. The simulation results are shown in Table 6 and Table 7, and the relationship diagrams of the light extraction efficiency varying with the period and height are as shown in Figure 20 shown, and the relationship diagrams of the light enhancement ratio varying with the period and height are as shown in Figure 21 shown.

[0191] Table 6 Simulation Results Table of Period and Height Light Extraction Efficiency

[0192]

[0193]

[0194] Table 7 True Results Table of Period and Height Light Enhancement Ratio

[0195]

[0196] Through simulation experiments, the present invention compared the light extraction efficiency and light enhancement ratio of the corresponding structure of the present invention, the existing structure, and the structure without application corresponding to Micro-LED, and learned that the five-sided pyramid single-top structure has the highest light extraction efficiency. Based on the five-sided pyramid single-top structure, the corresponding structure of the embodiment of the present invention was obtained. Through simulation experiments, it can be found that compared with the prior art, the corresponding structure of the embodiment of the present invention has a very significant improvement in the light extraction efficiency and light enhancement ratio of Micro-LED.

[0197] By referring to the lantern structure of the abdomen of fireflies, the bionic micro-nano composite structure prepared in the embodiment of the present invention can avoid the light loss at the interface between the device substrate and air by nesting periodic nanostructures in the ordered micro-structure pattern, and improve the light extraction efficiency of Micro-LED while not changing the viewing angle characteristics of the Micro-LED device, and has a strong light extraction effect.

[0198] When preparing the lateral nanostructure grating and the longitudinal nanostructure grating in the embodiment of the present invention, the period and height of the nanostructure grating can be controlled by adjusting parameters such as the stretching direction, degree, etching power, time, flow rate, pressure, and gas of the reactive ion etching, so that the light extraction efficiency of light in different directions can be controlled according to requirements.

[0199] In the embodiments of the present invention, a periodic nano bump array structure with long-range order is formed through two stretching processes and reactive ion etching. Compared with the prior art which only performs one stretching process, the bionic micro-nano composite structure corresponding to the embodiments of the present invention has a better effect of improving the light extraction efficiency.

[0200] In the embodiments of the present invention, the PDMS micro-nano composite pattern obtained, which is opposite to the desired bionic micro-nano composite structure, is used as a template. Subsequently, the desired bionic micro-nano composite structure can be obtained simply by replication, with high production efficiency and low cost.

[0201] In summary, the embodiments of the present invention can effectively improve the light extraction efficiency of Micro-LEDs, reduce energy loss, and avoid energy waste.

[0202] It is worth mentioning that the present invention does not limit the application fields of the bionic micro-nano composite light extraction structure. It can be used for Micro-LEDs or other light sources such as OLEDs, PDP plasma displays, FED field emission displays, LCD liquid crystal displays, etc.

[0203] In the second embodiment of the present invention, a bionic micro-nano composite light extraction structure is further provided. It is characterized in that the bionic micro-nano composite structure includes a plurality of periodic micro wire-top multi-sided pyramids and a periodic nano bump array structure with long-range order applied on the micro wire-top multi-sided pyramids. The micro wire-top multi-sided pyramid is a three-dimensional structure with a polygon as the bottom surface and a wire-top formed by two top ends. The bionic micro-nano composite structure is used to change the light propagation direction to reduce total reflection and improve the light extraction efficiency of Micro-LEDs. The bottom surface of the micro wire-top multi-sided pyramid is a polygon, and the top position and spacing are variable, so that the micro wire-top multi-sided pyramid is asymmetric along the vertical plane where the wire-top of the micro wire-top multi-sided pyramid is located or the mid-perpendicular plane of the wire-top. The specific structure and its principle can refer to the first embodiment and will not be elaborated here.

[0204] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, method, article or device including the element.

[0205] Each embodiment in this specification is described in a related manner. For the same or similar parts among the embodiments, reference can be made to each other. Each embodiment focuses on the differences from other embodiments. In particular, for the system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and for the related parts, reference can be made to the corresponding description in the method embodiment.

[0206] The above are only the preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are all included in the protection scope of the present invention.

Claims

1. A bionic micro-nano composite light extraction structure, characterized in that: The bionic micro-nano composite structure includes a plurality of periodic micro-wire-top polygonal pyramids and a periodic nano-bump array structure with long-range order applied to the micro-wire-top polygonal pyramid. The micro-wire-top polygonal pyramid is a three-dimensional structure with a polygonal bottom surface and a wire top formed by two tops. The bionic micro-nano composite structure is used to improve the light extraction efficiency of the light-emitting element by reducing total reflection by changing the light propagation direction. The bottom surface of the micro-wire-top polygonal pyramid is a polygon, and the top position and spacing are variable, so that the micro-wire-top polygonal pyramid is asymmetric along the vertical plane where the wire top of the micro-wire-top polygonal pyramid is located or the mid-vertical plane of the wire top.

2. A method for preparing a bionic micro-nano composite light extraction structure, characterized in that: The method comprises: Step S1, uniformly coating a first photoresist on a first substrate, using grayscale photolithography to form a plurality of periodic micro-line-top polygonal pyramid concave mold micron structures on the first photoresist; and developing and drying the first photoresist after photolithography to obtain a micron pattern master; Step S2, uniformly mixing the polydimethylsiloxane monomer and the cross-linking agent in a first preset ratio, vacuuming and defoaming the first mixture, and uniformly spin-coating the mixture on the micron pattern master; and sequentially heating, curing and peeling the first mixture to obtain a first PDMS template with a structure opposite to the micron pattern master; wherein the first PDMS template includes a plurality of periodic micro-wire-top polygonal pyramid convex micro-structures; Step S3, stretching the first PDMS template transversely by a stretching displacement stage, etching the first PDMS template after transverse stretching by reactive ion etching, and then restoring the first PDMS template to form a periodic transverse nanostructure grating on the first PDMS template; Step S4, using a hydrophobic modifier to perform hydrophobic treatment on the first PDMS template; and uniformly mixing the polydimethylsiloxane monomer and the cross-linking agent according to a second preset ratio, vacuuming and debubbling the second mixture, and uniformly spin-coating it on the first PDMS template; and sequentially heating, curing and peeling the second mixture to obtain a second PDMS template with a structure opposite to the first PDMS template; wherein the second PDMS template includes a plurality of periodic micro-line-top polygonal pyramid concave mold micron structures and the lateral nanostructure grating; Step S5, longitudinally stretching the second PDMS template by the stretching displacement stage, etching the longitudinally stretched second PDMS template by reactive ion etching, and then restoring the second PDMS template to form a periodic longitudinal nanostructure grating on the second PDMS template; wherein the transverse nanostructure grating and the longitudinal nanostructure grating constitute a periodic nano-bump array structure with long-range order; Step S6, obtaining a light-emitting element, spin-coating a UV embossing glue on the light-emitting surface of the light-emitting element, placing the second PDMS template on the UV embossing glue, and pressing and UV-irradiating the second PDMS template so that the UV embossing glue forms a bionic micro-nano composite structure on the light-emitting surface of the light-emitting element; peeling off the second PDMS template to obtain a light-emitting element assembly with a bionic micro-nano composite structure.

3. The method for preparing a bionic micro-nano composite light extraction structure according to claim 2, characterized in that: The step S3 comprises: According to the first period and the first height required by the lateral nanostructure grating, a first lateral stretching degree and a first reactive ion etching parameter are obtained; wherein the first reactive ion etching parameter includes at least etching power, etching time, etching flow rate, etching pressure and etching gas type; According to the first lateral stretching degree, the first PDMS template is stretched laterally by a stretching translation stage; according to the first reactive ion etching parameters, the first PDMS template after the lateral stretching is subjected to reactive ion etching; The first PDMS template after etching is restored to form a periodic transverse nanostructure grating on the first PDMS template.

4. The method for preparing a bionic micro-nano composite light extraction structure according to claim 3, characterized in that: In the step S3, the first lateral stretching degree is 0%-500%, the reactive ion etching power of the reactive ion etching is 50-250W, the reactive ion etching time is 40-240s, the reactive ion etching flow rate is 10-300sccm, the reactive ion etching pressure is 1-100pa, the reactive ion etching gas includes at least oxygen, argon or a mixture of the two, the first period of the lateral nanostructure grating is 100nm-2000nm, and the first height of the lateral nanostructure grating is 50nm-1000nm.

5. The method for preparing a bionic micro-nano composite light extraction structure according to claim 2, characterized in that: The step S5 comprises: According to the second period and the second height required by the longitudinal nanostructure grating, a second longitudinal stretching degree and a second reactive ion etching parameter are obtained; wherein the second reactive ion etching parameter includes at least etching power, etching time, etching flow rate, etching pressure and etching gas type; According to the second longitudinal stretching degree, the second PDMS template is longitudinally stretched by a stretching translation stage; according to the second reactive ion etching parameters, the longitudinally stretched second PDMS template is reactive ion etching; The second PDMS template after etching is restored to form a periodic longitudinal nanostructure grating on the second PDMS template.

6. The method for preparing a bionic micro-nano composite light extraction structure according to claim 5, characterized in that: In the step S5, the second longitudinal stretching degree is 0%-500%, the reactive ion etching power of the reactive ion etching is 50-250W, the reactive ion etching time is 40-240s, the reactive ion etching flow rate is 10-300sccm, the reactive ion etching pressure is 1-100pa, the reactive ion etching gas includes at least oxygen, argon or a mixture of the two, the second period of the longitudinal nanostructure grating is 100nm-2000nm, and the second height of the longitudinal nanostructure grating is 50nm-1000nm.

7. The method for preparing a bionic micro-nano composite light extraction structure according to claim 2, characterized in that: The step S1 comprises: A first photoresist is uniformly coated on a first substrate, and one or more methods selected from the group consisting of laser direct writing, photolithography, laser etching, and nanoimprinting are used to form a plurality of periodic micro-wire-top polygonal pyramid concave mold micro-structures on the first photoresist to obtain the micro-pattern master; wherein the periodicity of the micro-wire-top polygonal pyramid concave mold micro-structures of the micro-pattern master is one-dimensional or two-dimensional.

8. The method for preparing a bionic micro-nano composite light extraction structure according to claim 2, characterized in that: In the step S1, the period of the micron pattern master is 1-100 um, and the height is 0.5-10 um.

9. The method for preparing the bionic micro-nano composite light extraction structure according to claim 2, characterized in that: The micro wire-top polygonal pyramid is a three-dimensional structure with a polygonal bottom surface and two top ends.

10. The method for preparing a bionic micro-nano composite light extraction structure according to claim 9, characterized in that: The method further comprises: According to the first light extraction efficiency required by the micro-nano composite structure, the first position of the midpoints of the two vertices of the micro-wire-top polygonal pyramid and the first spacing between the two vertices are determined; wherein the first position and the first spacing are used to adjust the light extraction efficiency of the micro-nano composite structure.

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