A seed and bridge layer method for inkjet printing of narrow traces on receding ink-substrate combinations

Abstract

Inkjet printing of electronic materials is of interest for digital printing of flexible electronics and sensors, but the width of the inkjet-printed lines is still large, limiting device size and performance. Decreasing the drop volume, increasing the drop spacing, and increasing the ink-substrate contact angle are all approaches by which the line width can be lowered, however these approaches are limited by the nozzle geometry, ink coalescence and bead instabilities, and contact angle hysteresis, respectively. Here we demonstrate a novel approach for stable inkjet printing of very narrow lines on ink-substrate combinations with a high contact angle, utilizing the de-wetting of the ink due to the decreased contact angle hysteresis. After printing and drying an initial layer of disconnected seed drops of silver nanoparticle ink, we print an additional layer of bridging drops of the same ink in between the dried seed drops. The bridging drops expand to touch the dried seed drops and then retract into a line, due to the pinning of the wet ink on the dried seed ink but not on the substrate, forming a continuous silver trace. The trace width is decreased from 60 μm with a traditional printing approach down to 12.6 μm with this seed-bridge approach. The electrical conductivity of the silver trace is similar to that of a conventionally printed trace. Due to poor adhesion on the print substrate, the trace was transferred to a separate polymer substrate with a simple hot-pressing procedure, which preserves the electrical conductivity of the trace.