A multi-focal microlens array and a preparation method and application thereof

Abstract

The present application belongs to the field of micro-nano machining manufacturing and lens processing technology, and relates to a multi-focal microlens array and a preparation method and application thereof, the method comprising the following steps: 1) preparing a substrate; 2) performing hydrophilic and hydrophobic patterning modification on the surface of the substrate, and forming a pattern corresponding to the shape and position of the microlens array; and 3) forming a multi-focal microdroplet array on the pattern through inkjet printing. The method of the present application can change the volume of ink by changing the number of ink drops through inkjet printing of different numbers of ink drops on a patterned wettability substrate, so as to cause different curvature angles and lens focal lengths. The present application utilizes the surface energy difference, designability and other characteristics of the patterned substrate.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano fabrication and lens processing technology, and relates to a multifocal microlens array, its preparation method and application, specifically a multifocal microlens array prepared by inkjet printing, its preparation method and application. Background Technology

[0002] In contemporary optics and optoelectronics, multifocal microlens arrays (MLAs) are becoming a key technology, playing a crucial role in many applications such as high-resolution imaging, depth sensing, and medical imaging. Their application effects are particularly significant in areas like 3D microscopy, integrated imaging, and machine vision, demonstrating their broad potential applications. With the rapid development of micro-nano optics technology, the demand for precise and efficient microlens manufacturing methods is increasing. Traditional microlens array manufacturing technologies, such as photolithography and injection molding, have significant limitations in terms of cost, efficiency, and design flexibility. Based on this, invention patent application number 202310064177.7 discloses an aperture array for a multifocal curved microlens array and its fabrication method. This method obtains the microlens array through 3D printing of resin. However, the resulting microlens array suffers from poor surface smoothness, structural complexity, and slow fabrication speed. Therefore, the development of new manufacturing technologies is urgently needed. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the inventors have for the first time introduced inkjet printing technology into the fabrication of multifocal microlens arrays. Inkjet printing, as an advanced digital manufacturing method, possesses unique advantages—low cost, high precision, and extremely high design freedom—providing a new solution for fabricating multifocal microlens arrays. Specifically, the inventors discovered that by precisely controlling the position and number of ink droplets, inkjet printing can fabricate microlenses with different optical properties at the microscale, achieving the goal of integrating lenses with different focal lengths on the same platform.

[0004] Specifically, the present invention provides the following technical solution:

[0005] A method for fabricating a multifocal microlens array, the method comprising the following steps:

[0006] 1) Prepare the substrate;

[0007] 2) The substrate surface is modified with hydrophilic and hydrophobic patterns, and the resulting patterns correspond to the shape and position of the microlens array;

[0008] 3) Multifocal microdroplet arrays are formed on the pattern by inkjet printing.

[0009] According to the present invention, step 2) specifically includes:

[0010] S1. Patterning photolithography is performed on a substrate with a hydrophilic surface to transfer a microlens array including several microlens patterns onto the substrate to form a patterned substrate;

[0011] S2. The patterned substrate is hydrophobically treated to remove the photoresist on the substrate surface, forming a micron-scale patterned wettable surface.

[0012] The present invention also provides a multifocal microlens array, which is prepared by the above method, and the surface roughness of the multifocal microlens array is less than 1.5 nm.

[0013] The present invention also provides applications of the above-described multifocal microlens array in the fields of three-dimensional microscopy, integrated imaging, and machine vision.

[0014] The present invention achieves the following beneficial effects:

[0015] The method of this invention first prepares a substrate with a micron-scale patterned wettable surface. The areas corresponding to the microlens patterns on the substrate are hydrophilic regions, while other areas are hydrophobic regions. Particularly within the microlens patterns, the non-hydrophilic areas are hydrophobic, forming a structure where hydrophobic regions enclose hydrophilic regions. When ink droplets are added to the hydrophilic regions, the hydrophobic boundary has a confinement effect. When the droplet volume does not exceed the confinement capacity of the hydrophilic / hydrophobic boundary, the droplet ultimately exhibits a process where the bottom radius remains constant while the height increases, i.e., the curvature angle gradually increases. This invention utilizes the surface energy differences and designability of the patterned substrate by inkjet printing different numbers of ink droplets onto the patterned wettable substrate. By changing the number of ink droplets, the ink volume is altered, resulting in different curvature angles and lens focal lengths.

[0016] This invention enables the low-cost, high-precision fabrication of multifocal microlens arrays, with a highly flexible, controllable, and rapid fabrication process. This is of great significance given the rapid development of micro-nano optics technology, especially the increasing demand for precise and efficient microlens manufacturing methods.

[0017] This invention is based on micron-scale patterned hydrophilic and hydrophobic surfaces, combining the surface energy differences and designability of patterned substrates with the programmable, high-throughput, and precise deposition characteristics of inkjet printing. By inkjet printing different numbers of ink drops onto a patterned wettable substrate, the varying volumes and hydrophilic / hydrophobic confinement result in different curvature angles, ultimately leading to differences in lens focal lengths. Furthermore, the use of photocurable inks effectively solves the problem of droplet evaporation. This method also offers the advantage of programmable substrate design, allowing for the design of different shapes, densities, and arrangements.

[0018] This invention differs from traditional multifocal microlens array manufacturing technologies, such as photolithography and injection molding, effectively addressing limitations in cost, efficiency, and design flexibility. Furthermore, because the surface shape of the microlens formed by this invention is driven by surface tension, the surface smoothness is extremely high, reaching sub-nanometer levels, effectively improving the imaging quality of the microlens.

[0019] Due to the precise control over the position and number of ink droplets achieved by inkjet printing, this invention can fabricate microlenses with different optical properties at the microscale, realizing the goal of integrating lenses with different focal lengths on the same platform. This multifocal-length microlens array plays an important role in fields such as three-dimensional microscopy, integrated imaging, and machine vision, demonstrating its wide range of potential applications. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the present invention.

[0021] Figure 2 It is a component of multifocal microlens array ink.

[0022] Figure 3 These are the optical characterization results of multifocal microlens arrays with different densities and arrangements.

[0023] Figure 4 These are the characterization results from a multifocal microlens array microscope.

[0024] Figure 5 It relates the curvature angle and base radius of the microlenses formed by inks with different droplet numbers.

[0025] Figure 6 These are the results of atomic force microscopy characterization of the microlens surface. Detailed Implementation

[0026] As mentioned above, the present invention provides a method for fabricating a multifocal microlens array, the method comprising the following steps:

[0027] 1) Prepare the substrate;

[0028] 2) The substrate surface is modified with hydrophilic and hydrophobic patterns, and the resulting patterns correspond to the shape and position of the microlens array;

[0029] 3) Multifocal microdroplet arrays are formed on the pattern by inkjet printing.

[0030] According to an embodiment of the present invention, in step 1), the substrate is glass, selected from any one of JGS2 quartz glass sheet, JGS1 quartz glass sheet, and JGS3 type quartz glass sheet. The substrate has good light transmittance in the visible light region.

[0031] According to an embodiment of the present invention, step 1) includes a step of cleaning the substrate.

[0032] According to an embodiment of the present invention, the cleaning reagent is selected from at least one of detergent aqueous solution, water, ethanol, acetone, and isopropanol.

[0033] Specifically, the substrate can be cleaned using the aforementioned reagents in sequence. More specifically, ultrasonic cleaning can be employed. For example, the cleaning time can be more than 10 minutes.

[0034] According to an embodiment of the present invention, step 2) specifically includes:

[0035] S1. Patterning photolithography is performed on a substrate with a hydrophilic surface to transfer a microlens array including several microlens patterns onto the substrate to form a patterned substrate;

[0036] S2. The patterned substrate is hydrophobically treated to remove the photoresist on the substrate surface, forming a micron-scale patterned wettable surface.

[0037] According to an embodiment of the present invention, in step S1, the microlens array is located in the middle of the substrate, forming a central lens pattern area, and the edge portion of the substrate is an edge marking pattern area.

[0038] According to an embodiment of the present invention, after cleaning the substrate and before performing patterning photolithography on the substrate, the following step is further included: performing an adhesion-enhancing treatment on the substrate.

[0039] According to an embodiment of the present invention, the adhesion enhancement treatment of the substrate includes the following steps: applying an adhesion enhancer to the substrate surface by means of chemical deposition, spin coating, or blade coating.

[0040] According to an embodiment of the present invention, the tackifier is selected from any one of hexamethyldisilazane, AR 300-80 (a tackifier), and TIPRIME (a tackifier), for example, hexamethyldisilazane is used to perform vapor phase chemical deposition on the substrate.

[0041] According to an embodiment of the present invention, in step S1, the substrate having a hydrophilic surface includes hydrophilic treatment of the substrate after cleaning and thickening treatment.

[0042] According to an embodiment of the present invention, hydrophilic treatment of the substrate includes the following steps: sputtering the substrate surface using an air plasma treatment instrument to increase the hydroxyl density of the surface.

[0043] According to an embodiment of the present invention, in step S1, the sputtering power of sputtering the substrate surface using an air plasma processor is 20-200W, and the sputtering time is 15-300s.

[0044] According to an embodiment of the present invention, the contact angle of the hydrophilic surface is less than 5°, preferably less than 3°.

[0045] According to an embodiment of the present invention, step S1 specifically includes the following steps: a photoresist is disposed on the substrate surface, a photolithography machine is used to irradiate the photoresist containing the target pattern information on the substrate surface, and after exposure and development, a micron-scale patterned region is formed on the hydrophilic substrate surface to form a patterned substrate.

[0046] According to an embodiment of the present invention, in step S1, the photoresist is selected as a positive photoresist.

[0047] According to an embodiment of the present invention, in step S1, the lithography machine can be a maskless direct-write lithography machine or a mask lithography machine.

[0048] According to an embodiment of the present invention, in step S1, the microlens pattern can be circular, square, triangular or hexagonal.

[0049] According to an embodiment of the present invention, the spacing between the microlens patterns is set according to actual needs, and can be 10 to 50 micrometers, for example, 10 micrometers, 20 micrometers, 30 micrometers, 40 micrometers or 50 micrometers.

[0050] According to an embodiment of the present invention, in step S2, the hydrophobic treatment includes the following steps: first, air plasma sputtering is performed on the substrate surface, and then the substrate is soaked and dried with a hydrophobic solution.

[0051] According to an embodiment of the present invention, the hydrophobic water solution is selected from perfluorodecyltrimethoxysilane, perfluorodecyltriethoxysilane, hexadecyltrimethoxysilane, perfluorodecyltrichlorosilane, n-octyltrimethoxysilane, etc., preferably one or more of perfluorodecyltrimethoxysilane and perfluorodecyltriethoxysilane, for example, perfluorodecyltrimethoxysilane.

[0052] According to an embodiment of the present invention, the sputtering power of the air plasma sputtering is 100-300W and the sputtering time is 100-500s.

[0053] According to an embodiment of the present invention, soaking and drying with a hydrophobic solution includes the following steps: placing the plasma-sputtered substrate in a container with a drop of hydrophobic solution, removing it and drying it.

[0054] According to an embodiment of the present invention, the drying includes the following steps: placing the substrate soaked in the hydrophobic solution in a vacuum oven for 1-5 hours, followed by oven treatment at 40-100°C for 5-30 minutes.

[0055] According to an embodiment of the present invention, after the substrate surface is hydrophobically treated, the contact angle of the hydrophobic region is not less than 105°, preferably not less than 110°.

[0056] According to an embodiment of the present invention, the micron-scale patterned wettable surface refers to a region on the substrate corresponding to the microlens pattern being a hydrophilic region and other regions being hydrophobic regions. In particular, within the microlens pattern, the non-hydrophilic region is a hydrophobic region, forming a structure in which the hydrophobic region encloses the hydrophilic region. When an ink droplet is added to the hydrophilic region, the hydrophobic boundary has a confinement effect. When the volume of the droplet does not exceed the confinement ability of the hydrophilic and hydrophobic boundary, the droplet eventually exhibits a process in which the bottom radius remains unchanged and the height increases, that is, the curvature angle gradually increases.

[0057] According to an embodiment of the present invention, in step S2, removing the photoresist includes soaking the substrate in a removal solvent, wherein the removal solvent may be one or more of acetone, ethanol, isopropanol, etc.

[0058] According to an embodiment of the present invention, after step S2 and before step 3), the following step is also included: marking the edge marking pattern area to form a clearly visible patterned mark, which facilitates the alignment of the printhead with the substrate during inkjet printing.

[0059] According to an embodiment of the present invention, marking the edge marking pattern area includes the following steps: scraping the edge marking pattern area with a polymer solution of a certain solid content.

[0060] According to an embodiment of the present invention, the polymer solution is selected from at least one of polyvinylpyrrolidone, cellulose, polyacrylic acid, polyvinyl alcohol, starch, hydroxymethyl cellulose, polyacrylamide, polymaleic anhydride, and polyethylene glycol, for example, polyacrylic acid can be used.

[0061] According to an embodiment of the present invention, the polymer solution contains a polymer mass fraction of 0.1-10%, preferably 0.5-5%.

[0062] According to an embodiment of the present invention, in order to improve the visualization of the marked area, a small amount of dye can be added to the polymer solution. The dye is selected from any one of sodium fluorescein, fluorescein isothiocyanate, imino succinate AF488, imino succinate BODIPYFL, green fluorescent protein, cyanine dye Cy3, cyanine dye Cy5, cyanine dye Cy5.5, cyanine dye Cy7, and rhodamine, for example, rhodamine.

[0063] According to an embodiment of the present invention, the polymer solution coating includes the following steps: drawing up the polymer solution, allowing a small droplet to move in the edge marking pattern area, leaving polymer solution in the hydrophilic area of ​​the edge marking pattern area, and drying to form a clear pattern consistent with the photolithographic shape.

[0064] According to an embodiment of the present invention, step 3) includes: inkjet printing ink on a patterned wettable surface at the micrometer scale, printing different numbers of ink droplets in different areas.

[0065] According to an embodiment of the present invention, the ink in step 3) includes a photocurable monomer and an initiator, wherein the photocurable monomer and the initiator are selected from any photocurable monomer and corresponding initiator capable of polymerization and curing under light.

[0066] According to an embodiment of the present invention, the photocurable monomer is selected from one or more of 4-acryloylmorpholine, acrylate, and vinyl monomers.

[0067] According to an embodiment of the present invention, the initiator is selected from one or more of (2,4,6-trimethylbenzoyl)diphenylphosphine oxide, diaryliodomonium salt, and methyl benzoylformate, for example, (2,4,6-trimethylbenzoyl)diphenylphosphine oxide (TPO).

[0068] According to an embodiment of the present invention, the ink further includes a crosslinking agent selected from any one or more of divinylbenzene, diisocyanate, N,N-methylenebisacrylamide, dicumyl peroxide, benzoyl peroxide, dicumyl hydrogen peroxide, diethylenetriamine, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-isopropylimidazole, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, triethylenetetramine, dimethylaminopropylamine, and diethylaminopropylamine.

[0069] According to an embodiment of the present invention, the ink further includes a solvent selected from good solvents of photocurable monomers, initiators and crosslinking agents, preferably selected from one or more of water, ethanol, ethylene glycol, glycerol, propanol and butanol.

[0070] According to an embodiment of the present invention, the initiator in the ink has a mass concentration of 1-20%, preferably 5-15%, for example, the initiator in the ink has a mass concentration of 1%, 3%, 5%, 7%, 9%, 11%, 13%, 15%, 17%, or 19%.

[0071] According to an embodiment of the present invention, the surface tension of the ink is 26-55 mN / m, preferably 30-40 mN / m.

[0072] According to an embodiment of the present invention, the viscosity of the ink is 2-15 mPa·s, preferably 5-10 mPa·s.

[0073] According to an embodiment of the present invention, the method for preparing the ink includes the following steps: adding or not adding a solvent to a photocurable monomer and an initiator, and stirring in a light-protected environment until fully dissolved.

[0074] According to an embodiment of the present invention, after preparing the ink, the following steps are further included: testing the surface tension and viscosity of the ink, and adding it to the printing system if it meets the requirements.

[0075] According to an embodiment of the present invention, printing ink on a micron-scale patterned wettable surface includes the following steps: filtering the ink with an organic filter head, loading it into an ink cartridge and installing a printhead, printing with a printer, and printing different numbers of ink droplets in different areas.

[0076] According to an embodiment of the present invention, when printing with a printer, the printer's alignment function is used to align the substrate with the nozzle movement direction.

[0077] According to an embodiment of the present invention, the voltage of the printer is such that it can form a better inkjet state, and the droplets can fall vertically into the hydrophilic region with a hydrophobic edge.

[0078] As an example, the printing forms a circular pattern arranged in a hexagonal array. The bottom diameter of the circular pattern is 30-300 μm, and the center distance between adjacent circular patterns is 40-1000 μm. 1-50 layers of liquid are printed on the circular pattern. The number of printed droplets gradually increases from the center of the hexagonal array outwards, thereby forming a microdroplet array with a gradually increasing curvature angle.

[0079] According to an embodiment of the present invention, after printing ink in step 3), the method further includes: using ultraviolet light to photocur the ink on the substrate surface to obtain a multifocal microlens array, wherein the photocuring time is preferably 0.1-50 min.

[0080] According to an embodiment of the present invention, after step 3), the following steps are further included:

[0081] 4) Characterize the prepared multifocal microlens array, preferably by surface characterization, and the surface characterization equipment includes, for example, an optical microscope, an electron microscope, etc.

[0082] As mentioned above, the present invention also provides a multifocal microlens array prepared by the method described above, wherein the surface roughness of the multifocal microlens array is less than 1.5 nm, preferably less than 1.0 nm, for example 0.9 nm.

[0083] According to an embodiment of the present invention, the microlenses in the microlens array have different optical properties at the microscale, that is, different focal lengths are integrated on the same platform, forming a multifocal-length microlens array.

[0084] Furthermore, the present invention also provides applications of the multifocal microlens array, which are used in fields such as three-dimensional microscopy, integrated imaging, and machine vision.

[0085] The structure and application of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0086] In the description of the invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the invention.

[0087] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0088] Example 1

[0089] Cleaning quartz plates: Place JGS2 type quartz glass plates with lengths of 10-20mm, widths of 10-20mm, and thicknesses of 0.2-1.5mm in a polytetrafluoroethylene cleaning basket. Clean them ultrasonically for about 15 minutes in a room temperature ultrasonic environment with detergent solution, water, ethanol, acetone, and isopropanol in sequence. After cleaning, dry the surface with dry high-purity nitrogen gas and place them in a clean plastic petri dish.

[0090] Hydrophilic patterning modification and characterization of substrate surface: The substrate surface was subjected to plasma sputtering hydrophilic treatment using an air plasma treatment instrument with a sputtering power of 100-200W and a sputtering time of 60-200s to obtain a hydrophilic substrate. The contact angle of the hydrophilic area was measured to be less than 5° using a contact angle tester, which showed that the hydrophilic area has excellent hydrophilicity and is beneficial to the spread of ink in the hydrophilic area.

[0091] A positive photoresist is applied to the surface of a hydrophilic substrate. A micron-scale patterned direct-write lithography machine is used to illuminate the photoresist on the surface of the hydrophilic substrate using a mask containing the target pattern information. After exposure and development, a micron-scale patterned region is formed on the surface of the hydrophilic substrate, resulting in a patterned substrate. The target pattern information refers to a microlens array.

[0092] The patterned substrate was surface-treated using perfluorodecyltrimethoxysilane: the substrate surface was first subjected to plasma sputtering using an air plasma treatment instrument with a sputtering power of 100-300W and a sputtering time of 200-500s, which generated a large number of active hydroxyl groups on the patterned substrate surface. The substrate was then placed in a glass petri dish, and 2-100 μL of perfluorodecyltrimethoxysilane was added to the dish. The dish was then placed in a vacuum oven and dried under vacuum to obtain a hydrophobic substrate.

[0093] After hydrophobication treatment, acetone is used to remove the photoresist on the surface of the hydrophobic substrate. For areas with residual photoresist that are difficult to remove, a lint-free cloth soaked in an appropriate amount of acetone or ethanol can be used to wipe the substrate surface to form a substrate with hydrophilic regions (the photoresist-covered parts of the hydrophobic substrate) and hydrophobic regions (the parts of the hydrophobic substrate that are not covered by photoresist). The hydrophilic regions correspond to the microlens array. After wiping, the surface is dried with high-purity nitrogen to prevent foreign matter residues in the droplets, resulting in a patterned substrate.

[0094] During the hydrophobic treatment, a clean glass plate without photolithography was also hydrophobically treated as a comparative example. After the treatment, the contact angle of the hydrophobic area was measured using a contact angle meter, thus proving that when the ink is printed on the hydrophilic and hydrophobic patterned area, it can form a higher curvature angle, which is beneficial to improving the imaging quality and imaging resolution of the microlens.

[0095] Printing microlenses: Since inkjet printing is performed on a patterned substrate, the direction of the printhead movement needs to be aligned with the substrate pattern. However, before printing, the edges of the glass substrate need to be marked with patterns. The markings are squares with a side length of 100-500 micrometers, and the spacing between adjacent squares is 100-300 micrometers. The pattern markings are located on both sides of the outermost edge of the substrate. The squares in the edge marking pattern area exhibit excellent hydrophilic properties. A polyacrylic acid solution with a certain solid content is used to scrape the edge marking area to form clearly visible patterned markings for alignment during printing.

[0096] The ink was filtered using an organic filter, loaded into an ink cartridge, and fitted with a 10pL printhead. It was then printed using a Fujifilm printer.

[0097] Example 2

[0098] Ink formulation: In order to form a highly adjustable multifocal microlens array through inkjet printing, it is important to select and configure inks suitable for inkjet printing.

[0099] In this embodiment, 4-acryloylmorpholine (ACMO) is selected as the photocurable monomer and (2,4,6-trimethylbenzoyl)diphenylphosphine oxide (TPO) is selected as the initiator. The mass concentration of the initiator in the ink is 5%. 4-acryloylmorpholine and diphenylphosphine oxide are stirred in a light-protected environment until fully dissolved to obtain the ink. The surface tension of the ink at room temperature is 43.6 mN / m and the viscosity is 12.0 mPa·s.

[0100] The surface tension and viscosity of ACMO monomers are suitable for inkjet printing. At room temperature, the surface tension is 43.58 mN / m and the viscosity is 12.04 mPa·s, which allows for good inkjet printing when using a Fujifilm printer. Furthermore, ACMO has an ultra-low vapor pressure (7.73 × 10⁻⁶) at room temperature. -3 (mmHg) helps reduce monomer evaporation in micron-sized microdroplets, minimizing the uncontrollability of liquid volume due to evaporation. Furthermore, curing occurs immediately after each printing cycle, using a 365nm UV LED point light source placed 2–3 cm above the substrate surface for approximately 10–500 seconds. ACMO monomers cure quickly, are resistant to acids, alkalis, and solvents, are insensitive to the presence of acids and alkalis, are difficult to hydrolyze, and exhibit good stability. They also have good heat resistance, offering significant advantages under stringent high-temperature conditions. The curing shrinkage is low, providing toughness while maintaining hardness, making it suitable for fabricating microlenses.

[0101] Example 3

[0102] Printing of multifocal microlens arrays: Using the ink prepared in Example 2, different numbers of ink droplets were printed at different positions (patterns in the array) on the patterned substrate surface. Due to the confinement effect of the hydrophilic and hydrophobic boundary, when the droplet volume does not exceed the confinement capability of the hydrophilic and hydrophobic boundary, the droplet eventually exhibits a process in which the bottom radius remains unchanged and the height increases, that is, the curvature angle gradually increases.

[0103] In this embodiment, the array is a hexagonal circular pattern with a bottom diameter of 30-300 μm and a center distance of 40-1000 μm between adjacent circular patterns. The number of printed droplets is increased sequentially from the center of the hexagonal arrangement outwards, with 1-50 layers of liquid printed on the circular patterns respectively, thereby forming a microdroplet array with a gradually increasing curvature angle. Since the droplet shape is driven by surface tension, this microdroplet has a good light focusing effect, thus forming a multifocal microlens array.

[0104] Characterizing the curvature angle and base radius of each microlens revealed that within a range of 20 ink droplets, the curvature angle gradually increased while the base radius remained essentially constant. Furthermore, due to the surface tension driving the droplet surface, the surface roughness was extremely low; AFM results showed a surface roughness of approximately 0.9 nm, indicating an extremely smooth surface, which is beneficial for high-quality imaging of the microlens.

[0105] See Figure 5 and Figure 6 As shown, the distribution of the radius of curvature and height of microlenses formed by different numbers of ink droplets is shown. It can be seen that as the number of droplets gradually increases from 1 to 8, the curvature angle gradually increases, while the ground radius remains basically unchanged.

[0106] Example 4

[0107] Due to the programmable substrate design, multifocal microlens arrays with different shapes, densities, and arrangements can be flexibly fabricated. For example... Figure 3 As shown, this invention can fabricate microlens arrays of different shapes, such as circles, hexagons, squares, and triangles, providing more possibilities for optical imaging. Furthermore, the arrangement is diverse, such as hexagonal and tetragonal arrangements. The density can also be changed to form high fill factor multifocal microlens arrays.

[0108] See Figure 3 As shown, different arrangements of the microlens array are illustrated. Figure 3 The left image shows a hexagonal arrangement (partial view). The printed pattern design can use two square array printing methods to divide the columns on different horizontal lines into two groups; alternatively, a simple array pattern can be drawn on the computer provided with the printer and the ink droplets can be deposited on the corresponding substrate according to the normal operating procedures of the printer. Figure 3 The right side uses a square arrangement to integrate microlenses with different aspect ratios. The overall design consists of nine groups, with ink droplets ranging from 1 to 9, printed in a square array format.

[0109] The method of this invention is used to prepare microlens arrays. Since the microlens surface is formed by surface tension, the surface is extremely smooth and the roughness can reach the sub-nanometer level, with a roughness of 0.9 nm, which is beneficial to the improvement of optical imaging quality.

[0110] The specific embodiments of the present invention have been described above by way of example. However, the scope of protection of the present invention is not limited to the above exemplary embodiments. Any modifications, equivalent substitutions, improvements, etc., made by those skilled in the art within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for fabricating a multifocal microlens array, characterized in that, The method includes the following steps: 1) Prepare the substrate; 2) The substrate surface is modified with hydrophilic and hydrophobic patterns, and the resulting patterns correspond to the shape and position of the microlens array; 3) Multifocal microdroplet arrays are formed on the pattern through inkjet printing; Step 3) includes: inkjet printing ink on a patterned wettable surface at the micrometer scale, printing different numbers of ink droplets in different areas; Step 2) specifically includes: In step S1, before performing patterned photolithography on the substrate, the following step is also included: performing an adhesion enhancement treatment on the substrate; S1. Patterning photolithography is performed on a substrate with a hydrophilic surface to transfer a microlens array including several microlens patterns onto the substrate to form a patterned substrate; the substrate with a hydrophilic surface is obtained by hydrophilic treatment of a substrate after cleaning and adhesion enhancement. S2. The patterned substrate is hydrophobically treated to remove the photoresist on the substrate surface, forming a micron-scale patterned wettable surface.

2. The method for fabricating a multifocal microlens array according to claim 1, characterized in that, In step S1, the adhesion enhancement treatment of the substrate includes the following steps: applying the adhesion enhancer to the substrate surface by at least one of chemical deposition, spin coating or blade coating.

3. The method for fabricating a multifocal microlens array according to claim 1, characterized in that, In step S1, the hydrophilic treatment of the substrate includes the following steps: sputtering the substrate surface using an air plasma treatment instrument to increase the hydroxyl density on the surface.

4. The method for fabricating a multifocal microlens array according to claim 1, characterized in that, The contact angle of the hydrophilic surface is less than 5°.

5. The method for fabricating a multifocal microlens array according to claim 1, characterized in that, In step S2, the hydrophobic treatment includes the following steps: first, air plasma sputtering is performed on the substrate surface, and then the substrate is soaked and dried using a vapor-phase hydrophobic solution.

6. The method for fabricating a multifocal microlens array according to claim 5, characterized in that, The hydrophobic water solution is selected from at least one of perfluorodecyltrimethoxysilane, perfluorodecyltriethoxysilane, hexadecyltrimethoxysilane, perfluorodecyltrichlorosilane, and n-octyltrimethoxysilane.

7. The method for fabricating a multifocal microlens array according to claim 5, characterized in that, After hydrophobic treatment of the substrate surface, the contact angle of the hydrophobic region is greater than or equal to 105°.

8. The method for fabricating a multifocal microlens array according to claim 1, characterized in that, The surface tension of the ink is 26-55 mN / m.

9. The method for fabricating a multifocal microlens array according to claim 1, characterized in that, The viscosity of the ink is 2-15 mPa·s.

Images