Nanotechnology in paper electronics

Abstract

The ability to put cutting edge technology on paper—not in words but in a working physical form—has been attracting an increasing number of researchers over the past decade. Paper has many advantages that make it attractive for flexible electronics: it is relatively environmentally benign; it is renewable; it can be recycled; it is light weight; production processes for paper are well advanced; and it is inexpensive. This special issue, with guest editors Ronald Österbacka from Åbo Akademi University in Finland and Jin-Woo Han from the NASA AMES Research Center, features some of the latest in paper electronics research, including developments towards applications in displays, sensing and alternative energy sources, as well as fundamental studies to further our understanding of how paper can be most effectively used in electronics.As Andrew Steckl and colleagues in the US point out, ‘Cellulose-based paper substrates were implemented as an electronic substrate as early as 1969, with most advancement occurring in the past decade largely due to technology improvements in thin film deposition and organic materials’ [1, 2]. They report a detailed comparison between paper, standard liquid crystal display rigid glass and flexible glass for hosting pentacene organic thin film transistors, and obtain promising results for future paper-based devices. As most meaningful electronic devices rely on transistors to function, transistors feature quite prominently in this special issue. Rodrigo Martins and colleagues in France and Portugal study the effect of fibre type, structure and dimension on paper-based transistors and reveal further insights into how paper properties affect device performance [3]. Qing Wan and colleagues in China bring the state of the art in transistor technology to paper substrates [4], fabricating indium-zinc-oxide (IZO)-based protonic/electronic hybrid thin film transistors on paper and showing that they can be used as artificial synapses. Like the connections in the nervous system, these synaptic transistors can mimic synaptic stimulation response and short-term synaptic plasticity.The idea of harnessing paper electronics for display applications seems a natural update on the familiar traditional uses of paper to host text and images. Jong-Man Kim and Bora Yoon at Hanyang University in Korea screen print a flexible paper-based display for representing the digits 0–9 [5]. The device exploits the electrochromothermic properties of five different polydiacetylenes to allow a range of activation temperatures and operational voltages for the display. A number of other applications also feature in the special issue, including two different supramolecular recognition architectures for DNA hybridization in sensing applications [6] and all-solid flexible micro-supercapacitors with excellent cycling stability [7]. The demonstrated potential in the alternative energy industry seems particularly fitting given the environmental recommendations of paper electronics.Despite the promising outlook demonstrated for fabricating on paper by screen or ink-jet printing, as Henrik A Andersson and colleagues point out, it may be some time before devices can be printed with the functionality of even the most inexpensive microcontroller or other integrated circuit [8]. In their report they consider different methods to mount and contact standard surface mount device components to ink-jet printed conductive tracks on paper substrates. ‘If paper is used as a substrate for printed hybrid electronics, it opens the possibility of integrating low-cost electronic functions directly on packages, even possibly directly in the production line’, they add.A blank sheet of paper can be considered useful for making notes, convenient for slipping in a purse or pocket and enormously inspiring for the infinity of ideas not yet written on it. As this special issue demonstrates [2–14] all three attributes are at least as valid when using paper for electronics devices. If ‘writing is thinking on paper’ [15], it seems researchers are finding yet more powerful means of putting their ideas on paper.