Capillary-filling-regulated direct soft imprint lithography for coffee-ring- and residue-free stacked-layer patterning

Abstract

Direct soft imprint lithography (DSIL) provides a simple, high-resolution, and low-cost patterning alternative to photolithography. However, the imprint residues, thickness nonuniformity, and overlay printing problems of DSIL limit its practical applications. Here, we report a capillary-filling-regulated DSIL strategy that enables high-fidelity, residue-free, and coffee-ring-free stacked-layer patterning. Through capillary filling regulation, a 2-methoxyethanol (2-ME)/ethylene glycol (EG) co-solvent ink was formulated to tune ink properties, ensuring sufficient ink filling in the plasma-treated PDMS stamp microchannels. We develop a simplified quantitative framework to link ink properties and stamp wettability to the filling behavior during imprinting. The proposed framework is consistent with the experimental results and enables thicknesstunable patterning. Furthermore, evaporation-driven solute-transport analysis supports a solute-redistribution mechanism that suppresses the coffee-ring effect, while EG eliminates imprint residues by delaying solidification. Finally, this method is employed to fabricate stacked-layer thin-film transistors (TFTs) with ITO electrodes and In0.8Ga0.2Ox active layers, achieving mobilities up to 5.1 cm2 V-1 s-1. This simple and low-cost DSIL strategy provides a general and scalable route for high-precision stacked-layer patterning in printed electronics and microelectronic integration.