Development and Application of Rolling process based on soft-mold Micro-stamping Mechanism

With the rapid stride of electro-optical industry, the needs for minimized optical elements increase. One of them is micro-lens array, which is widely used in electro-optical instruments for optical fiber communication, image sensing, displaying, and medical inspections. They are now made with expensive facility. Therefore, this thesis is devoted to developing a rolling process based on soft-mold micro-stamping mechanism to replicate micro-structure with UV curable material. There are three major steps in the development process.
First, plastic micro-lens array has been fabricated using gas-assisted hot-embossing. In this method, a silica mold with micro-holes array is first fabricated by conventional photolithography and deep ion etching process. PC film is then placed on the top of the mold, and the stack is placed in a closed chamber. By heating above the characteristic temperature of the plastic film, and introducing nitrogen gas into the chamber, the polymer material is partially filled into the circular holes, and a hemispherical surface is formed due to surface tension. In addition, this study also employs factorial design to develop a precision linear regression for predicting of the height of the lens.
Second, a novel technique to produce a soft roller mold has been developed. A PC micro-lens mold is bent around a carved roller to form a shell-shaped cavity, and then PDMS is poured into it. After curing, a roller with micro-lens cavity array is obtained after PC mold is torn off.
Third, a roller stamping facility with UV exposure capacity has been designed, constructed, and tested. The system consists of a UV-lamp, a roller stamp, a movable platform, a slot-coating system and a pneumatic cylinder unit. During rolling operation, the soft roller mold with micro-lens cavity array uniformly coated with a layer of UV curable photopolymer is pressed against a transparent substrate with a slight pressure. At the same time, the photopolymer is cured by UV-irradiation at room temperature. As the platform moving on, micro-lens array pattern can be continuously fabricated. The lens array is of high quality and good uniformity. The root mean square roughness of the micro-lens is 9.73nm, and average surface roughness is 8.23nm.
These results prove the potential of the roller stamping process for rapid fabricating micro-lens array with high productivity and low cost.