Replications and analysis of microlens array fabricated by a modified LIGA process

Abstract

Microlens arrays were fabricated using a modified LIGA process based on the exposure of a PMMA (polymethylmethacrylate) sheet to deep X-rays from the synchrotron of PAL (Pohang Accelerator Laboratory) and a subsequent thermal treatment. A successful physical modeling and analyses for microlens formation were reviewed according to the experimental procedure of the modified LIGA process based on our previous study. A metallic nickel mold insert for the replication of microlens arrays was successfully fabricated by the nickel electroforming process on the PMMA microlens arrays fabricated by the modified LIGA process. For the replication of microlens arrays having various diameters with different foci on the same surface, the hot embossing and the microinjection molding processes have been successfully utilized with the nickel mold insert. The scanning electron microscope and atomic force microscope measurements showed that replicated microlenses have good surface quality with the surface roughness of the order of 1 nm. The injection-molded microlens arrays were also found to have very small birefringence. Finally, the focal lengths of the injection-molded microlenses were successfully measured experimentally and also estimated theoretically. The replicated microlens arrays with the good surface quality could be applied to various optical applications that require microlens arrays having the different foci on the same surface.