Fabrication of flexible microlens arrays through vapor-induced dewetting on selectively plasma-treated surfaces†
Microlens arrays have been increasingly employed as key components in building micro-optical systems. Conventional fabrication methods, such as grayscale lithography, ink-jet printing, and photoresist thermal reflow, are often constricted by certain drawbacks, including mask resolution, high fabrication cost, and complexity of processes. In this paper, we present a low-temperature dewetting method that enables fabrication of microlens arrays on polymeric surfaces in a rapid and cost-effective way. As the demonstration of such a technique, vapor-induced dewetting of SU-8 thin films has been carried out on heterogeneous polydimethylsiloxane (PDMS) substrates that were selectively pre-treated with low-energy sulfur hexafluoride (SF6) or oxygen (O2) plasma. The dewetted SU-8 droplets are self-organized to directly form well-aligned microlens arrays on the O2-plasma-treated regions, with various lens curvatures ranging from ∼27° to ∼47° as the processing temperature rises from 20 °C to 80 °C. The exposure to the solvent vapor allows for the realization of dewetting at low temperatures. The optical performance of such microlens arrays has been characterized by testing their imaging capabilities.