Fabrication of high fill-factor microlens array using spatially constrained thermal reflow

In this paper, we introduce a simple method for fabricating high fill-factor microlens array using a novel spatially constrained thermal reflow process. The major difference with the conventional methods is that the proposed thermal reflow is conducted in polydimethylsiloxane (PDMS) solution instead of in the air. During the reflow process, PDMS would serve as a barrier to prevent the merging of adjacent microlenses which is usually a big obstacle of achieving high fill-factor in conventional thermal reflow methods. Moreover, for the microlenses are spatially constrained by the PDMS, the reflow process is very stable and much easier to control. To give a good understanding of the process, theoretical models are also established. Experimental results showed that almost 100% fill-factor and relative PDMS soft mold could be obtained efficiently and easily, and the microlens was good in both shape and surface quality. The proposed method may provide a low-cost and accurate method for fabricating high fill-factor microlens array in a very simple way.