Browsing by Subject "Bias reversal"

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Pushing the limits of Marangoni-driven patterning
(2020-08-17) Stanley, Steven Kenneth; Bonnecaze, R. T. (Roger T.); Willson, Carlton G; Ellison, Christopher J; Baldea, Michael; Lynd, Nathaniel A
Marangoni-driven patterning (MDP) is a relatively new technique that harnesses surface tension-driven flows to create topography in thin polymer films with potential uses in generating flexible electronics, metamaterials, and functional coatings for light capture, adhesive, and antibiofouling applications. To determine which applications MDP is best suited for, it is important to understand the fundamental limits of achievable pattern pitch and aspect ratio. To date, the maximum reported aspect ratio for MDP is roughly 0.05 and the minimum reported feature pitch is roughly 1.5 μm. To determine how much these metrics could be improved, we perform a numerical analysis to predict the maximum aspect ratio and minimum feature pitch for MDP. Our analysis shows that the maximum aspect ratio is roughly 0.5, which is roughly ten times better than what has been demonstrated to date. We also show that the pattern pitch is fundamentally limited by light-imaging capabilities and engineering constraints. One issue facing MDP is the leftover residual layer that blocks access to the substrate and necessitates a breakthrough etch for subsequent patterning. To avoid this extra processing step, we investigate the possibility of inducing a dewetting event during MDP, which could expose the underlying substrate during the annealing step and even improve the aspect ratio of the resulting pattern. Through modelling and simulation, we predict the conditions necessary to induce a dewetting event in MDP. Another issue in MDP is pattern control. When generating two-dimensional shapes like squares, simulations show that the corners and edges of the shape are significantly rounded. To improve pattern quality, we implement an algorithm to optimize the initial exposure to generate more favorable flow patterns and sharper topography. We also experimentally validate this work using a polystyrene polymer system. Finally, we investigate the root cause of unexpected bias reversal in spin-coated, conformal polymer films. Our model and simulation results show that Marangoni-driven flow could be responsible for this observation.