Electrowetting Assisted Air Detrapping in Transfer Micromolding for Difficult-to-Mold Microstructures

Abstract

As a widely applicable process for fabricating micro- or nanostructures, micromolding in atmosphere would require the removal or minimization of air-trapping in mold cavities so as to fill the liquid prepolymer fully into the mold for generating an exact polymer duplicate. This has been difficult, if not impossible, especially for a mold with high aspect ratio, varying size/shape, or isolated cavities because the air can be trapped inside such mold cavities in most variants of the molding process. This paper presents an electrowetting assisted transfer micromolding process to solve this problem. A feeding blade continuously supplies a UV-curable prepolymer over a dielectric-coated conductive mold placed on a progressively advancing stage. A voltage applied to the electrode pair composed of the feeding blade and mold generates an electrowetting of the prepolymer to the mold. The electrowetting allows for the three-phase contact line to pass progressively along the sidewalls and bottoms of the cavities, completely pushing out the air initially occupying the cavities, or generates an electrocapillary force large enough to pull the prepolymer deeply into the mold by compressing the air already trapped inside the cavities to a minimized volume. An experiment has been performed for micromolding with deep cavities of various shapes and sizes, demonstrating an essential improvement in the structural integrity of the polymer duplicates.

Toward Scalable Flexible Nanomanufacturing for Photonic Structures and Devices

“…b) Electrowetting‐assisted transfer micromolding. Reproduced with permission . Copyright 2014, American Chemical Society.…”

“…Taking advantage of the electrocapillary force, Li et al further developed a robust and versatile filling process for nanoimprinting (Figure b) . In this kind of filling method, a feeding blade is not only used as an electrode, but also to supply UV‐curable prepolymer to the cavities of the template when it is moved over the surface of the template.…”

Parallel Near-Field Photolithography with Metal-Coated Elastomeric Masks

“…In particular, this experiment could be utilized to fabricate nanopatterns with a gradient in line width from 150 to 625 nm over 3 mm 2 areas ( Figure S8 in Supporting Information), which demonstrated one of the important methods in fabricating gradient patterns. 38,39 The gradient patterns are useful in the rapid and systematic screening of stem cell adhesion. 40 Importantly, the feature size can be controlled by tailoring the exposure dose.…”

Step-Controllable Electric-Field-Assisted Nanoimprint Lithography for Uneven Large-Area Substrates

“…[26][27][28][29][30][31] For example, Chou et al successfully utilize electrostatic attraction force, equivalent to an external applied mechanical pressure as in the case of a conventional nanoimprint process, to pattern nanogratings with high fidelity and excellent uniformity in a photocurable resist on a 4′′ Si wafer. 28 Experimental results show no visible damage to the structures on the substrate.…”

“…[26][27][28][29][30][31] For example, Chou et al successfully utilize electrostatic attraction force, equivalent to an external applied mechanical pressure as in the case of a conventional nanoimprint process, to pattern nanogratings with high fidelity and excellent uniformity in a photocurable resist on a 4′′ Si wafer. 28 Experimental results show no visible damage to the structures on the substrate. In our previous work, fabrication of high-aspect-ratio (>10:1) microstructures using dielectrophoresiselectrocapillary force-driven UV-imprinting is demonstrated, which prevents drawbacks seen in conventional imprinting lithography such as mechanically induced mold deformation and position shift thereby maximizing pattern uniformity.…”