Flexible and Printed Electronics

Abstract

Significant advances have been made to the flexible electronics in the past two decades. A thin-film transistor (TFT) backplane is a generic component in an active-matrix electronic surface. TFT backplane technologies which have been developed for the flexible electronics applications can be mainly categorized into (a) hydrogenated amorphous silicon TFTs, (b) low-temperature polycrystalline silicon TFTs, (c) oxide TFTs, and (d) organic TFTs. The TFT fabrication usually involves accurate registrations between device layers. To mitigate misalignment issues caused by the handling of compliant substrates, built-in stress of deposited films, and mismatch strains between the device layers and substrates, lamination-debonding or coat (deposit)-release approaches for direct fabrication and transfer technique are developed. To further reduce the fabrication cost and improve the throughput, roll-to-roll compatible and printable processes are adopted. Gravure printing, offset printing, and flexography printing are commonly used contact printing technologies. Microcontact printing, nanoimprint, and transfer printing are emerging printing methods, which are of particular interest for the flexible electronics based on inorganic monocrystalline semiconductors. Non-contact printing methods, such as screen printing, inkjet printing, and slot-die printing, have also been widely investigated for the fabrication of flexible electronics. Depending on the roles of the printed materials, printing processes can be divided into two types: subtractive and additive. A subtractive printing process is similar to the conventional photolithography process, except the etch-mask material is applied by a printing method. In an additive printing process, the material waste is greatly reduced via direct “writing” of functional materials.