A novel method for rapid fabrication of microlens arrays using micro-transfer molding with soft mold

This paper reports a novel technique for fabricating polymeric microlens arrays based on micro-transfer molding with soft mold. The soft mold with a micro-holes array is made by casting a pre-polymer of PDMS against a silicon master. The silicon master of the micro-cylinders array is prepared using photolithography and deep reactive ion etching. During the micro-transfer molding operation, the surface of the soft mold of the micro-holes array is filled with liquid UV curable photopolymer, and the soft mold is then pressed against the flat substrate with a slight pressure for a period of time. After the soft mold is removed from the substrate, surface tension causes the liquid photopolymer cylinders to assume a spherical shape. Finally, the liquid photopolymer is cured by UV irradiation at room temperature. A substrate with a microlens array pattern can be successfully fabricated. In this study, a micro-transfer molding facility with UV exposure capacity has been designed, constructed and tested. The 100 x 100 arrays of a polymeric microlens have been successfully produced. Under the condition of 50 kPa stamping pressure, 6 s duration and 500 mJ cm(-2) UV curing dose, the microlenses were successfully formed on the plastic substrate. Their optical properties were verified with a beam profiler. In addition, microlenses of different curvatures and focal lengths can be obtained by using substrates with different surface wettabilities. This study shows that micro-transfer molding can be used for the fabrication of polymeric microlens arrays with high productivity and low cost.