Reverse-Offset Printing of Polymer Resist Ink for Micrometer-Level Patterning of Metal and Metal-Oxide Layers.

Asko Sneck,Jaakko Leppäniemi,Henri Ailas,Feng Gao

doi:10.1021/acsami.1c08126

Asko Sneck, Jaakko Leppäniemi + Show 2 more

Open Access

https://doi.org/10.1021/acsami.1c08126

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Abstract

Printed electronics has advanced during the recent decades in applications such as organic photovoltaic cells and biosensors. However, the main limiting factors preventing the more widespread use of printing in flexible electronics manufacturing are (i) the poor attainable linewidths via conventional printing methods (≫10 μm), (ii) the limited availability of printable materials (e.g., low work function metals), and (iii) the inferior performance of many printed materials when compared to vacuum-processed materials (e.g., printed vs sputtered ITO). Here, we report a printing-based, low-temperature, low-cost, and scalable patterning method that can be used to fabricate high-resolution, high-performance patterned layers with linewidths down to ∼1 μm from various materials. The method is based on sequential steps of reverse-offset printing (ROP) of a sacrificial polymer resist, vacuum deposition, and lift-off. The sharp vertical sidewalls of the ROP resist layer allow the patterning of evaporated metals (Al) and dielectrics (SiO) as well as sputtered conductive oxides (ITO), where the list is expandable also to other vacuum-deposited materials. The resulting patterned layers have sharp sidewalls, low line-edge roughness, and uniform thickness and are free from imperfections such as edge ears occurring with other printed lift-off methods. The applicability of the method is demonstrated with highly conductive Al (∼5 × 10–8 Ωm resistivity) utilized as transparent metal mesh conductors with ∼35 Ω□ at 85% transparent area percentage and source/drain electrodes for solution-processed metal-oxide (In2O3) thin-film transistors with ∼1 cm2/(Vs) mobility. Moreover, the method is expected to be compatible with other printing methods and applicable in other flexible electronics applications, such as biosensors, resistive random access memories, touch screens, displays, photonics, and metamaterials, where the selection of current printable materials falls short.

Highlights

Novel printing methods such as micro-contact printing,[1] high-resolution gravure,[2] adhesion contrast planography,[3] and reverse-offset printing (ROP)[4] have advanced the minimum attainable line resolution toward micrometer-level printing, well beyond that available with conventional printing methods such as gravure, flexography, and inkjet printing (>30 μm). From these high-resolution printing methods, ROP in particular shows great promise for the fabrication of electronic components and circuits as it can deliver high-quality patterns with a submicrometer printing resolution,[5] micrometer-level overlay printing accuracy,[6] uniform layer thickness, and rectangular cross section with steep sidewalls, producing features resembling those obtained with photolithography.[4]
There is a fundamental dearth in the availability of electronic materials as printable inks, which limits the more universal utilization of printing methods in electronics manufacturing
The semi-dry ink needs to enable patterning at high resolution with sharp, vertical sidewalls and undergo perfect transfer to the printing platé from the PDMS

Summary

Introduction

Novel printing methods such as micro-contact printing (μCP),[1] high-resolution gravure,[2] adhesion contrast planography,[3] and reverse-offset printing (ROP)[4] have advanced the minimum attainable line resolution toward micrometer-level printing, well beyond that available with conventional printing methods such as gravure, flexography, and inkjet printing (>30 μm). From these high-resolution printing methods, ROP in particular shows great promise for the fabrication of electronic components and circuits as it can deliver high-quality patterns with a submicrometer printing resolution,[5] micrometer-level overlay printing accuracy,[6] uniform layer thickness, and rectangular cross section with steep sidewalls, producing features resembling those obtained with photolithography.[4] there is a fundamental dearth in the availability of electronic materials as printable inks, which limits the more universal utilization of printing methods in electronics manufacturing. The use of cheaper metals such as Al would be highly beneficial in cost-conscious applications

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