Research On Microlens Arrays Made By Contactless Embossing

Along with the development of micro-optics, micro-optical elements play an important role in many engineering applications, especially the microlens arrays. Currently there are many methods of fabricating microlens arrays, and contact hot embossing, one of which has many advantages and has become one of important research domains in the word, however it has shortcomings in high requirement of the molding tool, difficulty in de-molding and clean, high cost. In order to reduce the requirement of the molding tool used by hot embossing for fabricating microlens arrays, the method of fabricating microlens arrays by contact-less embossing is proposed. An independently developed nanoimprint machine and a stainless molding tool manufactured by photolithography with through-holes are used to fabricate microlens arrays on PMMA sheet. Meanwhile, vacuum support is unnecessary when using the molding tool with through-holes, which can reduce the requirement of the environment.In this study, a mold with through-holes is used to fabricate micro-lenses by employing the hot embossing technique. The experimental equipment used is an independently developed nanoimprint machine. An array of penetrating cylindrical holes is produced on a stainless steel plate by photolithography. The PMMA substrate is used for micro-lenses. The optical microscope is employed to examine the microstructures. The radius of curvature and f-number can be calculated. The influence of pressure, temperature and embossing time on the formation of micro-lenses having various radii is investigated.The micro-lenses manufactured using contact-less embossing generally have a larger height-to-width aspect ratio. In the process of de-molding, the difference in shrinkage between PMMA and steel mold due to temperature decrease will create a large contact force on the interface, which may pose a difficulty in de-molding. In the current research, in some cases the PMMA substrate is glued to a PCB plate, which will constrain the shrinkage of PMMA and the microstructures can be easily separated from the steel mold.