| Summary: | 博士 === 國立清華大學 === 動力機械工程學系 === 101 === This thesis presents a simulation and experimental investigation focusing on the fabrication of aspheric glass microlens array using thermal imprinting process with micro-hole molds, and establishes a theoretical model based on the theory of fully developed flow. In the simulation, a physical model for analyzing the formation of microlens array was constructed. The commercial finite element software ANSYS with four-node 141 fluid elements was adopted to model the imprinting process of glass microlenses and represent the glass flow. The mold was viewed as a rigid body and the glass material was regarded as Newtonian viscous flow when heated over the glass transition temperature. In order to realize the process-parameter and geometry-parameter effects on the imprinting of microlens array, six types of cases were simulated, including different imprinting temperatures of 630 and 635 K, hole-diameters of 50 and 100 μm, and duty ratios of 0.5 and 0.25. The simulation results indicated that imprinting temperature, micro-hole diameter, and duty ratio were important parameters to influence the imprinting of microlens array.
In the experiment, K-PG375 was used as a glass substrate and micro-hole molds were fabricated by electroforming technology and precision micro-drilling. Some experiments were implemented by a self-developed thermal imprinting equipment, including the formation of microlenses with diameters of 50 and 100 μm. The imprinting results were analyzed by 3D confocal laser microscope, white light interferometer, and scanning electron microscope (SEM). The experimental results indicated that various focal lengths of microlens were obtained by using the identical micro-hole mold with specified imprinting conditions and the fabrication of small-size microlens array became difficult as the hole diameter gradually decreased, which showed good agreement with the simulation results. Additionally, comparing the imprinting quality by micro-hole molds fabricated using various technologies, such as electroforming technology and precision micro-drilling process, we can clear know that the micro-drilling process is unsuitable to fabricate micro-hole mold for the imprinting of microlens array unless the serious burr problem around the micro-hole can be resolved. In the analysis of uniformity, small-area imprinting can obtain excellent uniformity because the pressure distribution between the middle and border of micro-pattern area has a slight difference.
Ultimately, some future works were pointed out in order to enhance the quality of this thesis and extend this study. Combining the FEM analysis and imprinting experiments, this study can assist us in profoundly apprehending numerous issues, such as the estimation of process parameters, the formability of microstructures for glass material, the filling condition of glass flow, and the uniformity after imprinting.
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