Microlens array and method for manufacturing the same

Abstract

This invention discloses a microlens array and its manufacturing method. The manufacturing method of the microlens array includes the following steps: sequentially coating a bottom polymer layer and a top polymer layer on a substrate surface; foaming the bottom and top polymer layers using a supercritical CO2 micro-foaming process to form a porous structure, with some of the porous structure penetrating the interfaces of the polymer layers; selectively dissolving the top polymer layer using a solvent to obtain a microlens array template with a concave structure; replicating the concave microlens array template using a polydimethylsiloxane precursor, curing, and peeling it off to obtain the microlens array. The microlens array prepared by this invention can be applied to inorganic and organic light-emitting diodes (LEDs) to improve the light extraction efficiency of the devices. Simultaneously, the microlens array has a significant light diffusion effect, improving the uniformity of the light-emitting surface and reducing glare when applied to lighting systems using inorganic LEDs.

Description

Technical Field

[0001] This invention relates to the field of display lighting technology, and more specifically to a microlens array and its manufacturing method. Background Technology

[0002] Inorganic light-emitting diodes (LEDs) are highly efficient light-emitting light sources, with GaN-based LEDs becoming indispensable for lighting and display in daily life. Traditional LED devices consist of an LED chip and a packaging frame. Due to the high refractive index of the LED chip material and packaging medium, light emitted from inside the LED chip undergoes total internal reflection, making it difficult to effectively extract it into the outside air. This greatly limits the efficiency of LED devices. Furthermore, LED devices are typical point light sources, which can easily cause strong glare for users in practical applications, and are detrimental to their eye health. Therefore, when assembling LED devices into actual lighting systems, a light diffusion film needs to be installed on the light-emitting surface of the lighting system. The light diffusion film can play a role in homogenizing light, making the light source system a surface light source, and reducing the glare effect of LED lamps. One type of high-efficiency light diffusion film is a microstructure film composed of a microlens array.

[0003] Organic light-emitting diodes (OLEDs) are also an emerging light source. In particular, as a pixelated self-emissive light source, OLEDs have significant application prospects in the display field. Currently, OLEDs have achieved representative applications in scenarios such as mobile phone displays. OLEDs generally adopt a multi-layer stacked structure, including a substrate, cathode, anode, hole injection layer, electron injection layer, hole transport layer, electron transport layer, electron blocking layer, hole blocking layer, and light-emitting layer. Because the core component material of OLEDs is a high-refractive-index organic material, surface polariton modes, waveguide modes, and substrate modes exist inside the device. This greatly limits the light extraction efficiency of OLED devices. To improve the luminous efficiency of OLED devices, introducing a microlens array on the surface of the device substrate is an effective method.

[0004] In summary, microlens arrays are a highly efficient optical functional structure for improving the efficiency and luminous uniformity of LED and OLED devices. Currently, the main manufacturing methods for microlens arrays include inkjet printing, laser direct writing, screen printing, photolithography, photopolymerization, and hot melt reflow. However, most of these methods rely on expensive equipment and have complex operating processes, resulting in high costs for the microlenses manufactured using these methods, which limits their application in LED and OLED. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides a microlens array and a method for manufacturing the same, which is simple and has low manufacturing cost.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The first aspect of this invention provides a method for manufacturing a microlens array, comprising the following steps:

[0008] (1) A bottom polymer layer and a top polymer layer are sequentially coated on the substrate surface;

[0009] (2) The bottom polymer layer and the top polymer layer are foamed using supercritical CO2 micro-foaming process to form a porous structure, and some of the porous structure penetrates the interface of the polymer layer.

[0010] (3) The top polymer layer is selectively dissolved using a solvent to expose the concave structure of the bottom polymer layer, thereby obtaining a microlens array template with a concave structure;

[0011] (4) The concave microlens array template is replicated and cured using a polydimethylsiloxane precursor. The polydimethylsiloxane film with the replicated concave microlens array structure is peeled off from the bottom template to obtain a polydimethylsiloxane convex microlens array.

[0012] The porous structure penetrating the interface between the two polymer layers in step (2) of the manufacturing method of the microlens array of the present invention is the key structure for obtaining the microlens template. It should be noted that the bilayer polymer is the core configuration for achieving selective etching, while the single-layer polymer is difficult to selectively etch and therefore cannot obtain a microlens template.

[0013] Preferably, in step (1), the substrate is a hard substrate, including either a glass substrate or a silicon substrate.

[0014] Preferably, in step (1), the polymer materials coated on the bottom polymer layer and the top polymer layer are selected from polymethyl methacrylate and polystyrene, and the polymer materials coated on the bottom polymer layer and the top polymer layer are different.

[0015] More preferably, in step (3), when the polymer material coated on the top polymer layer is polystyrene, cyclohexane is used as a solvent to dissolve the polystyrene; when the polymer material coated on the top polymer layer is polymethyl methacrylate, acetic acid is used as a solvent to dissolve the polymethyl methacrylate.

[0016] Preferably, in step (1), the total thickness of the bottom polymer layer and the top polymer layer is ≥4μm. When the thickness of the two polymer layers is less than 4μm, due to the diffusion effect present in the supercritical CO2 micro-foaming process, the polymer layer cannot effectively form a bubble structure, so the total thickness of the polymer layer needs to be greater than 4μm.

[0017] The supercritical CO2 mentioned in step (2) of this invention refers to the transformation of gaseous CO2 into supercritical CO2 under high temperature and high pressure. The supercritical CO2 dissolves into the polymer layer and forms a stable and uniform saturated layer with the polymer layer. After maintaining a certain saturation time, the pressure drop process is used to induce the nucleation and growth of bubbles in the polymer layer, thereby forming a porous polymer in the polymer layer.

[0018] The specific operation of the supercritical CO2 microfoaming process of this invention is as follows: Materials coated with a bottom polymer layer and a top polymer layer are placed in a sealed foaming cavity. CO2 gas is filled into the sealed cavity, and the pressure and temperature within the cavity are controlled and maintained for a certain period. Then, using a pressure drop method, the CO2 within the sealed cavity is rapidly released to the outside, causing the internal pressure to quickly drop to atmospheric pressure. During this process, the uniform saturated layer of CO2 and polymer reaches a supersaturated state, resulting in the nucleation and growth of bubbles, thus forming a porous structure within the polymer. Some of the porous structure extends through the interface between polymethyl methacrylate and polystyrene.

[0019] Preferably, in step (2), the supercritical CO2 foaming parameters are: foaming temperature of 40-90℃, foaming pressure of 10-50MPa, and saturation time ≥1min.

[0020] Preferably, in step (4), the polydimethylsiloxane precursor comprises polydimethylsiloxane and a curing agent; the mass ratio of polydimethylsiloxane to curing agent is (8-12):1; more preferably, the mass ratio of polydimethylsiloxane to curing agent is (9-11):1; even more preferably, the mass ratio of polydimethylsiloxane to curing agent is 10:1.

[0021] More preferably, the curing agent includes one or more of silane crosslinking agents and platinum catalysts.

[0022] Preferably, in step (4), the curing conditions are: curing temperature of 60-100℃ and curing time of 30-120min; more preferably, the curing conditions are: curing temperature of 70-90℃ and curing time of 50-80min.

[0023] A second aspect of the present invention provides a microlens array, which is prepared by the manufacturing method of the microlens array.

[0024] Preferably, the microlens array is a polydimethylsiloxane convex microlens array; the diameter of the microlens array is 300nm-10μm, and the height-to-diameter ratio of the microlens array is ≥0.1.

[0025] Preferably, the polydimethylsiloxane convex microlens array is randomly distributed on the plane, and there is no mutual interference between the polydimethylsiloxane convex microlens arrays.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] The microlens array fabrication method of this invention is simple and low-cost. It utilizes a bilayer polymer composed of polymethyl methacrylate and polystyrene to achieve a core configuration for selective etching, resulting in a randomly distributed microlens template. Compared to traditional regularly arranged microlenses, the randomly distributed microlenses exhibit superior light diffusion effects. In particular, their light diffusion effect is not sensitive to incident light at different angles, making them suitable for improving the extraction and diffusion of light incident at various angles. The fabricated microlens array can be applied to inorganic and organic light-emitting diodes (LEDs) to improve the light extraction efficiency of the devices. Simultaneously, the significant light diffusion effect of the microlens array allows it to be applied to LED lighting systems to improve the uniformity of the emitting surface and reduce glare. Attached Figure Description

[0028] Figure 1 Flowchart for the fabrication of microlens arrays;

[0029] Figure 2 This is a schematic diagram illustrating the application of microlens arrays in LED devices.

[0030] Figure 3 This is a schematic diagram illustrating the application of microlens arrays in OLED devices.

[0031] Figure 4 This is a schematic diagram of the application of microlens arrays in LED lighting fixtures. Detailed Implementation

[0032] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0034] Example 1

[0035] In this embodiment of the invention, the manufacturing method of the polydimethylsiloxane convex microlens array is as follows: Figure 1 As shown, the specific steps include:

[0036] (1) A layer of polymethyl methacrylate (PMMA) with a thickness of 4 μm is coated onto the surface of a glass substrate using a spin-coating process; a 4 μm thick polystyrene coating is then spin-coated onto the 4 μm thick PMMA coating using the same process. A clear interface is present between the PMMA and the polystyrene coating.

[0037] (2) The above-mentioned double-layer polymer coating is placed in a foamed sealed cavity. The temperature of the sealed cavity is 80°C. CO2 gas is filled into the sealed cavity until the gas pressure in the sealed cavity reaches 50MPa. The cavity is kept in the high temperature and high pressure for 30 minutes to achieve the full dissolution of the polymer by supercritical CO2 and form a uniform saturated layer of CO2 and polymer. Using the pressure drop method, the CO2 in the sealed cavity is quickly released to the outside of the cavity, so that the pressure inside the cavity drops rapidly to the atmospheric pressure level, i.e., 0.1MPa. During this process, the uniform saturated layer of CO2 and polymer reaches a supersaturated state, thereby the nucleation and growth process of bubbles occurs, realizing the formation of a porous structure inside the polymer. Some porous structures penetrate the interface between polymethyl methacrylate and polystyrene, that is, some bubbles appear in both polymethyl methacrylate and polystyrene. These bubbles are the key structure for the subsequent formation of the microlens replica template.

[0038] (3) Polystyrene was dissolved using cyclohexane (excluding polymethyl methacrylate) for 10 minutes. After dissolving the polystyrene with cyclohexane, the concave structure of the underlying polymer layer was exposed, resulting in a polymethyl methacrylate microlens array template with a concave structure. It should be noted that the bilayer polymer composed of polymethyl methacrylate and polystyrene is the core configuration for achieving selective etching. Single-layer polymers composed of either polymethyl methacrylate or polystyrene alone are difficult to selectively etch, and therefore cannot yield a microlens template.

[0039] (4) Take a polydimethylsiloxane precursor and a curing agent with a mass ratio of 10:1, mix them evenly, and eliminate air bubbles; pour the prepared polydimethylsiloxane liquid polymer onto the surface of the polymethyl methacrylate microlens array concave template obtained in step (3) to replicate its structure, and cure the polydimethylsiloxane liquid polymer at 80°C for 1 hour. After the polydimethylsiloxane polymer has cured, peel the polydimethylsiloxane film with the replicated concave microlens array structure from the surface of the polymethyl methacrylate microlens array concave template to obtain the final polydimethylsiloxane convex microlens array.

[0040] The microlens array in this embodiment is a polydimethylsiloxane (PDMS) convex microlens array; the diameter of the microlens is between 1-2 μm, the average diameter is 1.6 μm, the height-to-diameter ratio of the hemispherical microlens is ≥0.1, the distribution of the hemispherical microlenses on the plane is random, and there is no mutual interference between the microlenses.

[0041] The microlens array exhibits a random diameter distribution, meaning that different microlenses have different diameters. The ratio of microlens height to diameter is also random, and the spacing between microlenses is also randomly distributed. This random, disordered structure provides excellent diffusion for incident light, such as... Figure 4 As shown, after passing through the microlens array, the perpendicularly incident light rays are distributed in a hemispherical space, which can play a role in homogenizing the light.

[0042] like Figure 2 As shown, for planar LEDs, when the angle between the light emitted from the LED chip and the silicone-air interface exceeds a critical angle, total internal reflection occurs, preventing the light from being extracted into the outside air. Transferring the obtained polydimethylsiloxane microlens array film to the surface of the planar LED device can extract the totally internally reflected light into the outside air, thereby improving the light extraction efficiency of the LED device. The working principle is as follows: when large-angle light is incident on the microlens array, the curved surface of the lens reduces the incident angle of the large-angle light, ensuring that the incident angle on the curved surface of the microlens is within the critical angle, thus extracting the light that would otherwise undergo total internal reflection into the external environment.

[0043] Example 2

[0044] The difference between this embodiment and Example 1 is that the bottom polymer is polystyrene with a thickness of 5 μm, and the top polymer is polymethyl methacrylate with a thickness of 5 μm. The supercritical CO2 foaming parameters in this embodiment are: temperature 90℃, pressure 50 MPa, and saturation time 1 h. The difference between this embodiment and Example 1 is that the top polymer is polymethyl methacrylate, which needs to be dissolved in acetic acid without damaging the bottom polystyrene polymer. Finally, the other steps in the embodiment are repeated to obtain the final polydimethylsiloxane convex microlens array.

[0045] like Figure 3As shown, this polydimethylsiloxane convex microlens array can be used in OLEDs to improve the light extraction efficiency of OLED devices. OLEDs exhibit three light modes: surface polariton mode, waveguide mode, and substrate mode. The substrate mode occurs primarily because the substrate's refractive index is greater than that of air, similar to the LED device in Example 1. When the light emission angle from the substrate exceeds the critical angle, total internal reflection occurs, preventing light from reaching the outside air. By introducing a polydimethylsiloxane microlens array film onto the substrate surface of the OLED device, this microlens array can effectively reduce total internal reflection within the substrate, thereby improving the light extraction efficiency of the OLED device.

[0046] In addition, polydimethylsiloxane microlens arrays can also be applied to the light-emitting surface of LED lamps (such as...). Figure 4 As shown in the figure, by uniformly dispersing light from a certain direction throughout the entire hemispherical space, the point light source distribution of LEDs can be transformed into a surface light source distribution, thereby reducing the glare effect of the LED light source system.

[0047] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for manufacturing a microlens array, characterized in that, Includes the following steps: (1) A bottom polymer layer and a top polymer layer are sequentially coated on the substrate surface; (2) The bottom polymer layer and the top polymer layer are foamed using supercritical CO2 micro-foaming process to form a porous structure, and some of the porous structure penetrates the interface of the polymer layer. (3) The top polymer layer is selectively dissolved using a solvent to expose the concave structure of the bottom polymer layer, thereby obtaining a concave microlens array template; (4) The concave microlens array template is replicated and cured using a polydimethylsiloxane precursor. The polydimethylsiloxane film that replicates the concave microlens array template is peeled off from the bottom template to obtain a polydimethylsiloxane convex microlens array.

2. The method for manufacturing a microlens array according to claim 1, characterized in that, In step (1), the polymer materials coated on the bottom polymer layer and the top polymer layer are selected from polymethyl methacrylate and polystyrene, and the polymer materials coated on the bottom polymer layer and the top polymer layer are different.

3. The method for manufacturing a microlens array according to claim 2, characterized in that, In step (3), when the polymer material coated on the top polymer layer is polystyrene, cyclohexane is used as a solvent to dissolve the polystyrene; when the polymer material coated on the top polymer layer is polymethyl methacrylate, acetic acid is used as a solvent to dissolve the polymethyl methacrylate.

4. The method for manufacturing a microlens array according to claim 1, characterized in that, In step (1), the total thickness of the bottom polymer layer and the top polymer layer is ≥4 μm.

5. The method for manufacturing a microlens array according to claim 1, characterized in that, In step (2), the supercritical CO2 micro-foaming parameters are: foaming temperature of 40-90 ℃, foaming pressure of 10-50 MPa, and saturation time ≥1 min.

6. The method for manufacturing a microlens array according to claim 1, characterized in that, In step (4), the polydimethylsiloxane precursor comprises polydimethylsiloxane and a curing agent; the mass ratio of polydimethylsiloxane to curing agent is (8-12):

1.

7. The method for manufacturing a microlens array according to claim 1, characterized in that, In step (4), the curing conditions are: curing temperature of 60-100 ℃ and curing time of 30-120 min.

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