Low-temperature embossing technique for fabrication of large-area polymeric microlens array with supercritical carbon dioxide

This study reports an effective process for low temperature replication of polymeric microlens array using carbon dioxide (CO"2) as softening solvent and then as embossing pressure. Supercritical CO"2 is employed to soften the surface of polymer substrate and then apply pressure on it. Accordingly, microlens can be formed on the polymer substrate at low temperature. Using gas as embossing pressure can provide uniform pressure for large-area replication. During the embossing process, an array of convex microlenses is generated by partial protrusion of the substrate into the micro-holes of the mold under the action of embossing pressure and surface tension. The uniformity of large-area fabrication and optical property of the fabricated refractive microlens array on a 260mmx110mm poly (methyl methacrylate) (PMMA) substrate have been verified. Little residual stress can be observed by polariscope. With the proposed method, the large-area embossing can be performed without heating and cooling. Moreover, the problems of non-uniform pressure and residual stress can be overcome.