Fabrication of 3-D Superhydrophobic Micro-Ratchets via Combined Thermal Imprint Lithography and Photolithography

Ratcheted structures with superhydrophobicity have potential to drive motion of liquid drops in microfluidic devices. We report development of a new process to integrate microscale pillars with varied periods of ratchets from sub-micrometer to 1.5 mm in SU-8. For the fabrication, an hierarchical mixed process of thermal imprint lithography and optical UV-lithography was employed. Use of Ni ratchets as stamps and a hydrophobic silane coating on the stamp surfaces significantly improved imprinting performance into SU-8. We have successfully demonstrated fabrication of ratcheted micropillars as well as submicrometer ratchets integrated into micropillars. In addition, we will discuss optimization of the SU-8 imprinting process and the air gap compensation for photolithography of ratcheted SU-8 layers, which are essential for the fabrication.