3D Shape Control of Printed Micro-Electrodes with Substrate Reshaping

Abstract

Additive manufacturing (AM) techniques based on liquid precursors, including inkjet printing or laser-induced forward transfer (LIFT), are emerging as the tool-of-choice for the on-demand fabrication of printed electronic devices on flat and flexible substrates. However, the aspect ratio of the printable structures, which is key for determining electrical properties, is typically determined by the wettability between printed ink and substrate. Higher aspect-ratio structures can only be achieved by multi-pass printing, with the consequent loss of fabrication throughput and increase in complexity. Here, these issues are addressed by using print-n-release, a method based on printing micro-electrodes on pre-stretched elastomeric substrates. Upon stress release, the liquid-printed electrodes shrink while increasing their aspect-ratio. As a result, their final shape can be tailored beyond the limitations imposed by wetting constraints, enabling intentional miniaturization by design. The principle and practical implementation of print-n-release are described, and show how electrodes with up to an 8 fold increase in aspect-ratio and a 4 fold reduction in sheet resistance can be produced in a single-pass compared to traditional printing methods. As a proof-of-concept, functional interdigitated electrodes that serve as sensors for drop volume and electrolyte concentration, delivering enhanced sensitivity and a reduced footprint not achievable with standard printing techniques are fabricated.