Fully Transparent and Rollable Electronics Mallory Mativenga, Di Geng, Byungsoon Kim, and Jin Jang* Advanced Display Research Center, Department of Information Display, Kyung Hee University, 26 kyungheedaero, Dongdaemun-gu, Seoul 130-701, Korea * S Supporting Information ABSTRACT: Major obstacles toward the manufacture of transparent and ﬂexible display screens include the diﬃculty of ﬁnding transparent and ﬂexible semiconductors and electrodes, temperature restrictions of ﬂexible plastic substrates, and bulging or warping of the ﬂexible electronics during processing. Here we report the fabrication and performance of fully transparent and rollable thin-ﬁlm transistor (TFT) circuits for display applications. The TFTs employ an amorphous indium-gallium-zinc oxide semiconductor (with optical band gap of 3.1 eV) and amorphous indium-zinc oxide transparent conductive electrodes, and are built on 15-μm-thick solution-processed colorless polyimide (CPI), resulting in optical transmittance >70% in the visible range. As the CPI supports processing temperatures >300 °C, TFT performance on plastic is similar to that on glass, with typical ﬁeld-eﬀect mobility, turn-on voltage, and subthreshold voltage swing of 12.7 ± 0.5 cm 2 /V·s, -1.7 ± 0.2 V, and 160 ± 29 mV/dec, respectively. There is no signiﬁcant degradation after rolling the TFTs 100 times on a cylinder with a radius of 4 mm or when shift registers, each consisting of 40 TFTs, are operated while bent to a radius of 2 mm. For handling purposes, carrier glass is used during fabrication, together with a very thin (∼1 nm) solution-processed carbon nanotube (CNT)/graphene oxide (GO) backbone that is ﬁrst spin-coated on the glass to decrease adhesion of the CPI to the glass; peel strength of the CPI from glass decreases from 0.43 to 0.10 N/cm, which eases the process of detachment performed after device fabrication. Given that the CNT/GO remains embedded under the CPI after detachment, it minimizes wrinkling and decreases the substrate’s tensile elongation from 8.0% to 4.6%. Device performance is also stable under electrostatic discharge exposures up to 10 kV, as electrostatic charge can be released via the conducting CNTs. KEYWORDS: transparent, rollable, ﬂexible, thin-ﬁlm transistor, amorphous oxide semiconductor ■ INTRODUCTION In displays, the combination of transparency and ﬂexibility can have interesting applicationsextending beyond displays like embedded windows (for example, in car windshields) or televisions (TVs) that will be invisible when not used. Being transparent, ﬂexible, conformal, and nonbreakable, all at the same time, a transparent and ﬂexible display can be wearable or used as a dynamic paint job in automobiles. 1-6 For a display to be ﬂexible, it should be built on a ﬂexible plastic substrate with ﬂexible components, which is a major challenge, given that plastic substrates cannot withstand the high processing temperatures required to fabricate nondefective semiconduc- tors or dielectrics. 7-10 For the display to be transparent, while being ﬂexible at the same time, all the ﬂexible display components, including the plastic substrate, should also be transparent. Because a large optical band gap (>3 eV) is required for a material to be transparent in the visible range, the choice of nonbrittle and transparent electrodes introduce additional challenges. An electronic device technology that can be fabricated at low temperature or a ﬂexible substrate that can withstand high temperatures is, therefore, required. Additionally, handling of ﬂexible substrates is an issue because the substrate can shrink, expand, or bulge during fabrication or be stretched, kinked, dimpled, or scratched during unwinding and winding movements. 11,12 These issues lead to loss of layer alignment in the processing and ultimately poor device yield. 12 There are three methods for manufacturing ﬂexible displays on plastic substrates: (1) processing on plastic substrate without using a substrate holder, which is typically used for roll-to-roll technology 13 ; (2) ﬁxing a plastic substrate on a glass substrate using adhesive material 14,15 ; and (3) coating a polymeric solution on a glass substrate and then detaching the glass later on. 16 The roll-to-roll process is restricted to materials that are solution-processed at low temperatures, while the laminating-type substrate technology suﬀers from drawbacks such as thermal expansion and thermal damage of adhesive glue. In (3), detachment from glass is very hard and often leads to cracking or wrinkling during the detachment process because the adhesion of the polymer to glass strengthens during device processing. Therefore, there has been considerable research involving the insertion of a release material between the carrier substrate and the ﬂexible substrate. 17-19 However, most of these release layers require lasers for the release process, which are very expensive to install. Received: October 9, 2014 Accepted: December 19, 2014 Research Article www.acsami.org © XXXX American Chemical Society A DOI: 10.1021/am506937s ACS Appl. Mater. Interfaces XXXX, XXX, XXX-XXX