Patent Application
20070041097
1. Field of Invention
The present invention relates to a method for fabricating micro-lens, and particularly to a method for fabricating micro-lens mold and concave micro-lens.
2. Related Art
In the development of photoelectric products, since the micro-optical lens can produce an optical effect in a small area, it has become a basic element greatly demanded in this industry. For example, an array of optical lenses is used in the backlight plate of a Liquid Crystal Display (LCD) to produce a uniform backlight. Moreover, the improving of photoelectric semiconductor elements, such as laser diodes, light emitting diodes, photo-detectors, a single element is substituted by an array, while its increasing application field, such as an optical computing and optical communication system, greatly needs the use of the micro-lens array. Therefore, those skilled in the art, such as manufacturers and academics, are chasing to develop the technologies of fabricating an optical micro-lens array. A brief introduction will be made below with regard to the conventional methods for fabricating a micro-lens array.
1. The Hot Melt Process:
The hot melt process is one of the methods for fabricating a refractive lens, in which a tiny cylinder of a photo-resist or polymer material is re-flowed by re-warming. When the polymer microstructure is above the glass transition temperature (Tg), the polymer material is semi-melted, and the polymeric chain between the macromolecules begins to slip, so that the polymer itself has flow ability. With the treatment at a high temperature for a long time, the microstructure will be deformed slowly by the diffusion because the microstructure is affected by semi-liquid surface tension. Finally, this material will be shaped as a semi-sphere, and thus the roughness of the surface will be improved, thereby meeting the requirements of optical grades. The disadvantage of this process is that it is necessary to use a thermoplastic polymer material, and the film made from this kind of material is typically thin, i.e., it is difficult to produce a lens with high curvature, and the mechanical properties of the material are relatively poor.
2. The Hot Press Meltback Process:
In this method, a circular mold is produced by a LIGA technology, and then is pressed to a micro-cylinder by a hot press on a polymer plastic sheet at a high pressure and temperature. The semi-sphere, formed on the top of the micro-cylinder during the hot press forming process and heating, thus fabricates a micro-lens. An advantage of the non-contact press molding is that the shapes of the finish product (semi-spherical micro-lens) and the mold (hollow cylinder) may be different, due to the hot melt effect. Thus, an approximately semi-spherical micro-lens may be obtained without a mold with a precise shape. Also, it is suggested that an optimal shape and surface of the micro-lens may be obtained at a particular draft angle of the mold. However, the disadvantage of this kind of lens is that a micro-lens with a large curvature cannot be formed, so that the numerical aperture will be diminished, and a very compact array structure cannot be produced due to the width of the mold itself.
3. The Droplets Process:
A technology similar to ink-jet printing is used in this method, in which a plurality of droplets is first sprayed onto the photo-resist layer, so as to form a reflective type micro-lens array. Also, according to this method it is difficult to control the precise appearance of the outer surface, including size, height, focus and so on.
4. The Grey-scale Mask Process:
Generally, the function of the mask used in a photolithography process is to pass or block the light source for exposure so as to achieve the purpose of replicating a pattern onto a photo-resist. However, different from the chrome (Cr)-plated mask of quartz glass which shields or transmits the exposure beam, the penetration of the exposure beam through the grey-scale mask are varied continuously. During developing, a significantly different effect of developing will be obtained due to the different exposure amount obtained by the different thicknesses of the photo-resist layer. Thus, the grey-scale mask may produce a multilevel height or continuous curved surface pattern by developing after the first exposure, and this property can also be utilized to design and fabricate a refractive micro-lens. Therefore, the fabrication cost of the grey-scale mask process is extremely high, and the cost of the bulk production cannot be reduced.
In the prior methods for mass-producing micro-lenses, take the convex lens as an example, a convex micro-lens array is obtained only by the methods of photo-resist hot melt, hot press meltback, droplet methods, then in conjunction with a concave micro-mold formed by the micro-electroforming, and finally by molding in a hot press manner. For the conventional methods for mass-producing micro-lens molds and micro-lenses, the processes are complex. Furthermore, the step of electroforming is a precise technology, and the parameters of the subsequent hot press process should also be determined carefully, thus increasing the instability of the conventional process.
In view of the above-mentioned problems, the object of the invention is to provide a method for fabricating a micro-lens (micro-lens array) mold, in which a LIGA-like process for a thick film photo-resist are utilized along with the application of a UV-curing glue to produce a concave micro-mold directly, and then a convex micro-lens (micro-lens array) product can be molded. Alternatively, since the concave micro-mold structure employs a material with suitable optical properties, if it can be released from the substrate, it can be directly used as a concave micro-lens (micro-lens array) product. Thereby the problems present in the prior art could be substantially eliminated.
In view of the above-mentioned problems, the object of the invention is to provide a method for fabricating a concave micro-lens (micro-lens array), in which the micro-capillary (micro-capillary array) fabricated by the method described above is used as a micro-lens (micro-lens array) mold, in which a UV-curing glue is filled. A micro-lens may be formed by the surface tension of the UV-curing material and the adhesion of the capillary, which are the most natural methods for forming a lens, such, that the liquid in the capillary presents an circular arc as a micro-lens. As for the curvature of the concave shape, it will depend on the amount of the filled curing glue. Thereby substantially eliminating the problems in the prior art.
Thus, in order to achieve the above-mentioned purposes, a method for fabricating a micro-lens mold disclosed in the present invention includes forming a thick film on a substrate, patterning the thick film to form a micro-capillary, filling the micro-capillary with a heat curing glue liquor, and curing and shaping the heat curing glue liquor by the irradiation of a light source or by heating.
Thus, in order to achieve the above-mentioned purposes, a method for fabricating a concave micro-lens disclosed in the invention includes forming a thick film on a substrate, patterning the thick film to form a micro-capillary, filling the micro-capillary with a heat curing glue liquor, curing and shaping the heat curing glue liquor by the irradiation of a light source or by heating, and releasing the thick film from the substrate as a concave micro-lens.
The above steps of forming and patterning the thick film are accomplished by utilizing a LIGA technology or a LIGA-like technology.
The thick film described above is a polymer material or a photo-resist with optical properties.
Detailed characteristics and advantages of the invention will be illustrated in detail in the detailed description below, and the content is sufficient for those skilled in the art to understand and utilize the technology content of the invention, to practice the invention. Moreover, the relevant objects and advantages of the invention may be readily understood by any of those skilled in the art according to the content, claims and drawings disclosed in the specification.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The present invention will become more fully understood from the detailed description given herein below for illustration only, and thus is not limitative of the present invention, wherein:
In order to illustrate the purposes, constructions, characteristics and functions of the invention, it will be described in detail below with reference to the embodiments. The abovementioned content of the invention and the detailed description below are intended to exemplify and explain the principle of the present invention, and also to provide a further explanation about the claims of the invention.
The object of the present invention is to simplify the conventional process for mass-producing micro-lens molds and micro-lenses, and to develop a new process for producing a micro-lens mold. A LIGA-like process for a thick film (photo resist) can be used along with the application of a UV-curing glue to directly produce a concave micro-mold 1 as shown in
According to the above conception, the invention designs an array micro-capillary structure with good transmissive optical property. This structure is made from a thick film polymer or photo-resist with optical properties and can be obtained by injecting a curable polymer flowing material with optical properties, such as UV-curing glue, heat curing glue into a micro-capillary, and forming the curing glue liquid in the micro-capillary into a circular arc as a lens, due to the surface tension effect, and then forming a concave micro-lens (micro-lens array) after curing by UV irradiation or by heating. Following this, a material with optical properties such as a polymer curing glue for molding as polydimethyl siloxane (PDMS) or a UV-curing glue may be used to mold a convex micro-lens (micro-lens array) optical film product. If necessary, the concave micro-lens (micro-lens array) master mold can also be released from the substrate, so as to be used as a concave micro-lens (micro-lens array) finish product.
As shown in
The substrate described above may be a silicon substrate.
The thick film described above may be a polymer material or a photo-resist material.
As shown in
As shown in
As shown in
As shown in
By utilizing changes of the surface tension of the photo-resist material itself and the adhesion of the micro-capillary, micro-lenses or micro-lens, arrays with different curvatures are obtained, and the formed micro-lenses may be cured by the UV light, which is the most convenient method for forming a lens.
With regard to the experiments of the invention, when it is desired to design a micro-capillary structure in an array pattern, since a hexagonal column can produce an array structure that is more closed (no seam) than a circular micro-capillary, i.e. a cellular structure, the design of a hexagonal micro-capillary array is employed in the experiments of the invention. In order to facilitate the experiments to prove the feasibility, two structures with diagonals of the hexagonal micro-capillary openings of 100 μm and 75 μm are respectively designed depending upon the different sizes, and additionally four sizes with spacing of 5 μm, 10 μm, 15 μm, and 20 μm are respectively designed depending upon the different gaps, i.e. wall thickness of the micro-capillary. Furthermore, while the UV-curing glue is spun, different spinning speeds are varied, which are three spinning speeds of 4500 rpm, 5000 rpm, 5500 rpm respectively in this experiment. This is done to seek for their effects on the subsequent process of forming the cavity of the concave micro-lens array at these three parameters.
Herein, the three experimental parameters are again listed out for illustration below.
(1) When the UV-curing glue is spun, different spinning speeds are varied, which are three spinning speeds of 4500 rpm, 5000 rpm, 5500 rpm respectively in this experiment, so as to seek for the effect of the spinning speed on its subsequent forming.
(2) In the process of yellow light, the mask design described above is used to make different spacing between the micro-capillary arrays being approximately 5 μm, 10 μm, 15 μm and 20 μm respectively, so as to seek for its effect on the subsequent forming at different spacing.
(3) The diagonal width of the hexagonal micro-capillary array is varied, to be openings of 75 μm and 100 μm respectively to seek its effect on the subsequent forming at different diagonal widths of the micro-capillary.
The radius of curvature (Rc) and the focus (f) are calculated respectively for each of the completed concave lens molds fabricated at the parameters by the depth (h) and the diameter (D) of the concave hole measured and the refractive index (n) of the curing glue, by the following formula (1) and (2)
Measurement results of the parameters in the experiments are shown in the tables 1 and 2 below, while the calculation results of the radius of the curvature are shown in the tables 3 and 4 below.
From the results of the experiments of the invention, the tendency may be apparent to those skilled in the art and is summarized as follows:
(1) with the same spinning speed of the glue and the same spacing of the hexagonal micro-column of the array, if the diagonal length of the hexagonal micro-column opening is larger, the concave micro-lens will be deeper, i.e., the micro-lens is higher after being molded.
(2) with the same spacing of the hexagonal micro-column and the same diagonal opening length of the hexagonal micro-capillary, it will be apparent that if the spinning speed of the glue is faster, the concave micro-lens will be deeper.
(3) with the fixed spinning speed of the glue and the fixed diagonal opening length of the hexagonal micro-capillary, if the spacing of the hexagonal micro-column array is smaller, the concave micro-lens will be deeper.
In addition to those basic measurements, observation for molding is also a good method to determine the quality of the shape of a mold. However, the present invention is not intended to discuss the conception of the subsequent molded final product, but to discuss whether the geometrical shape of the mold has achieved the expected shape of a micro-lens by using the molded final product, to observe and demonstrate the feasibility and integrity of the invention, in conjunction with background and summary of the invention described above. Therefore, a material with optical properties such a polymer curing glue for molding as a PDMS or a UV-curing glue is used for molding.
The benefits/advantages achieved in the present application include:
(1) Mass Replication:
By utilizing the present invention, array micro-lens molds can be mass-produced directly, and convex micro-lens or convex micro-lens array products can be molded with a polymer material such as a PDMS or a UV-curing glue, with or without the electroforming molding step. Moreover, since the micro-lens mold structure employs a material with suitable optical properties, if it is released from the substrate, it can also be used as a concave micro-lens or concave micro-lens array product.
(2) An Extremely Simple Process:
The shape and size of the micro-lens mold may be stably controlled by the spinning speed of the curing glue, the spacing between the micro-capillary arrays, and the opening size of the micro-capillary array.
(3) Low Cost of Production Equipment:
The invention employs a cheap spinner, vacuum equipment and heating plate or UV irradiation lamp, used for curing glue other than complex and expensive production equipment.
Knowing the invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
