Improving Inkjet Printing Processes for  Achieving Stretchable and Flexible Traces with Small Linewidths

Pratt, Nicholas

Etd

Improving Inkjet Printing Processes for Achieving Stretchable and Flexible Traces with Small Linewidths

Public Deposited

Inkjet printing is a digital process suitable for the rapid prototyping and manufacturing of flexible and stretchable electronics and sensors that have uses in applications such as wearable devices. This work focuses on the inkjet printing of traces of silver nanoparticle inks onto polymeric substrates and addresses limitations including poor understanding and control of the widths of narrow traces printed at high substrate temperatures, and poor stretchability of the printed silver traces. The first part of the work improves the understanding of how advection-driven particle agglomeration induces pinning of the advancing edges of these inks, and how this results in narrower traces with rough edges. It also explores how microfeature arrays patterned uniformly over the substrate surface modify the pinning of the ink, with sufficiently dense microfeature arrays enhancing pinning at high substrate temperatures. The second part of the work explores printing onto high-contact-angle substrates on which the ink can recede (de-wet). This phenomenon is utilized to develop a “seed-bridge” approach for printing extremely narrow traces. This process achieves the smallest printed trace width that has been reported to date with a purely digital inkjet printing approach. The third part of the work improves our understanding of the process of using the printed silver traces to template the formation of eutectic gallium-indium (EGaIn) liquid metal traces through a wetting and alloying process. This process allows for the printed silver traces to be made stretchable, enabling the fabrication of devices that can be comfortably worn on the skin or in clothing. While several wetting and alloying approaches have been reported, this work investigates the influence of the chemical agents used, the alloying time, and the width and thickness of the silver traces on the process and on the resulting EGaIn trace morphology. This work contributes to society by providing better understanding and control of the inkjet printing process for electronics and sensors, enabling users to predict the outcome of their prints, greatly reducing the trial and error typically necessary. These advances will move inkjet printing of electronics and sensors towards becoming realized as a rapid prototyping technology that is accessible to industry and the public, similar to 3D printing, and will enable faster development of manufacturable flexible and stretchable wearable devices.

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