Fabrication of Hierarchical Pillar Arrays from Thermoplastic and Photosensitive SU‐8

Abstract

By exploiting the thermoplastic and photosensitive nature of SU-8 photoresists, different types of hierarchical pillar arrays with variable aspect ratios are fabricated through capillary force lithography (CFL), followed by photopatterning. The thermoplastic nature of SU-8 enables the imprinting of micropillar arrays with variable aspect ratios by CFL using a single poly(dimethylsiloxane) mold, simply by tuning the initial film thickness of SU-8 on a substrate. The pillar array is subsequently photopatterned through a photomask, followed by post-exposure baking above the glass transition temperature (T(g)) of SU-8. The pillars in the exposed region become highly crosslinked and, therefore, neither soluble nor able to reflow above T(g), whereas the pillars in the unexposed regions can reflow and flatten out. Two developing strategies are investigated after UV exposure of the SU-8 pillar arrays including i) solvent development and drying and ii) thermal reflow to create bilevel hierarchical structures with short pillars and single-level, dual-scaled, high-aspect-ratio (up to 7.7) pillars in a microdot array, respectively.

Replication of flexible polymer membranes with geometry-controllable nano-apertures via a hierarchical mould-based dewetting

“…The more important and unique feature of our method is the capability of generating non-residual layer and free-standing membranes by exploiting not only a highwettability difference but also a utilization of a hierarchical structure as a mould. Here, the two-level hierarchical mould can be made by a two-step moulding process utilizing oxygen inhibition effects 35,36 or conventional multilevel photolithography 37 .…”

Evaporative assembly of ordered microporous films and their hierarchical structures from amphiphilic random copolymers

“…40 SU-8 has been widely used to create micropillar arrays by photolithography, replica molding and capillary force lithography. 48 As discussed earlier, the polymer-acetone solution wets well on SU-8. By varying the pillar dimension (diameter, height and spacing) and symmetry together with the polymer concentration, we expect to create hierarchical structures with tunable pore size, symmetry and architecture.…”

High aspect ratio silicon and polyimide nanopillars by combination of nanosphere lithography and intermediate mask pattern transfer

“…With the advent of organic electronics the pillar process could also be applied to conductive polymers to shape them into nanoscale patterns for next generation devices. Polymer pillars are more commonly produced by replication of a master through moulding [33]. Our process does not require the fabrication of a master or the use of imprint equipment and the dimensions of the pillars are readily adjusted by the etch parameters.…”