The use of high aspect ratio photoresist (SU-8) for super-hydrophobic pattern prototyping

Abstract

In this work we present a reliable technique for the production of large areas of high aspect ratio patterns and their use as model super-hydrophobic systems. The high thickness and straight sidewalls possible with SU-8 were used to generate dense patterns of small pillars. The photoresist patterns could be used directly, without the need for micromoulding. A method is given allowing resist thickness to be varied over a wide range and a bottom antireflective layer was used to ease patterning on reflective substrates. This patterning technique allows rapid testing of wetting theories, as pattern size and depth can be varied simply and samples can be produced in sufficient numbers for laboratory use. We show how the static contact angle of water varies with pattern height for one sample-pattern and how static and dynamic contact angles vary with dimension using high aspect-ratio patterns.

Lithographically fabricated SU8 composite structures for wettability control

“…In order to establish the effect of both the ridge structure and bead inclusions upon the wettability of SU8 an unpatterned SU8 sample, with no glass bead inclusions, was prepared by using the same protocol as described above except that the exposure to UV radiation was not performed in the presence of a photomask. This yielded a surface which exhibited a water contact angle of 77.3 ± 1.1° which is in good agreement with the literature [2], [15] and provided a control to firstly determine the effect of the ridged structure on the wettability of SU8 and then the effect that the inclusion of the glass beads within the SU8 has on the ridged structure.…”

“…SU8 is a commonly used negative resist for the fabrication of sub-micron scale structures based on a novolak epoxy resin [1] and is capable of producing structures of high aspect ratios [2]. The versatility of SU8 is highlighted by the range of applications for which it can be used.…”

“…The versatility of SU8 is highlighted by the range of applications for which it can be used. For example sensors [3] and microlenses [4] have been fabricated out of SU8 as have templates for soft lithographic techniques [5,6] and functional surfaces displaying properties such as superhydrophobicity [2]. The inclusion of particles in SU8 can be done to impart greater functionality on the final structure, an example of this being the inclusion of SiO 2 particles in an SU8 matrix to increase wear resistance [7].…”

Dual‐Scale Roughness Produces Unusually Water‐Repellent Surfaces

“…The upward component of the surface tension between the columns allowing suspension of the drop on a surface of lower roughness (at the base of the pillars) than would otherwise be the case. Patterns of this type reach a maximum contact angle when the aspect ratio of the pattern exceeds 1 [17] ; when the contact angle on a pattern of tall SU-8 pillars (15 jum diameter and separation, 30 |um height) was measured the contact angle was the same as that observed on the pillars on a rough base (147(±3)°). For a pattern of smooth pillars, as the pillars grow in height, the influence of the base decreases until the drop is suspended solely by the pillars and the observed contact angle is independent of pillar height.…”

Advances in Bio-inspired Tribology for Engineering Applications

“…Of all these, the most commonly used is the lithography process which can be of two methods-photolithography, where layers are illuminated through a patterned mask to activate soft areas; and soft lithography, which is a simplified version of contact printing. Although relatively higher cost is involved in soft lithography it can produce a well-defined surface with excellent repeatability [74][75][76][77][78][79].…”