Self-Aligned Metal Electrodes in Fully Roll-to-Roll Processed Organic Transistors

Marja Vilkman,Elina Jansson,Johanna Hiitola-Keinänen,Teemu Ruotsalainen,Kimmo Solehmainen

doi:10.3390/electronics5010002

Marja Vilkman, Elina Jansson + Show 3 more

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https://doi.org/10.3390/electronics5010002

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Abstract

We demonstrate the production of organic bottom gate transistors with self-aligned electrodes, using only continuous roll-to-roll (R2R) techniques. The self-alignment allows accurate <5 µm layer-to-layer registration, which is usually a challenge in high-speed R2R environments as the standard registration methods are limited to the millimeter range—or, at best, to tens of µm if online cameras and automatic web control are utilized. The improved registration enables minimizing the overlap between the source/drain electrodes and the gate electrode, which is essential for minimizing the parasitic capacitance. The complete process is a combination of several techniques, including evaporation, reverse gravure, flexography, lift-off, UV exposure and development methods—all transferred to a continuous R2R pilot line. Altogether, approximately 80 meters of devices consisting of thousands of transistors were manufactured in a roll-to-roll fashion. Finally, a cost analysis is presented in order to ascertain the main costs and to predict whether the process would be feasible for the industrial production of organic transistors.

Highlights

Organic thin film transistors (OTFTs) are a promising candidate for low-cost flexible electronics due to their potential for low-temperature processing by printing, allowing plastic substrates and high-speed R2R processes to be used
We have shown that the self-alignment process, which uses a metallic gate electrode as a photolithography mask, can be transferred to a continuous R2R process
Self-alignment is especially important in transistors since the channel area is small and the printing machines are not capable of such accurate μm-scale registration

Summary

Introduction

Organic thin film transistors (OTFTs) are a promising candidate for low-cost flexible electronics due to their potential for low-temperature processing by printing, allowing plastic substrates and high-speed R2R processes to be used. In addition to high performance, the whole process has to be scalable to industrial high-speed production. Fully R2R-processed transistors are still less frequently demonstrated [7,8,9,10,11,12]. The production of fully printed OTFTs faces two main challenges: resolution and registration—especially in the R2R environment. High resolution is needed for minimizing the foot print of the transistor, which is important, e.g., in flexible display applications, and for decreasing the channel length, which would lead to higher switching speeds. Traditional printing processes are limited to a resolution of a few tens of μm [13]. Special R2R-compatible methods are needed, e.g., UV-nanoimprint lithography (UV-NIL) [14] or attoliter gravure printing [15]

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