Graphene is attractive for conventional semiconductor applications because of its flexibility, transparency, and high mobility. However, because the pristine graphene does not have a bandgap, many studies have been performed for an appropriate engineering a graphene bandgap for many semiconductor applications including transistors, making it challenging to take advantage of its extraordinary electronic properties in practical thin film transistors (TFTs). To enable predominant electrical performance of graphene-based TFTs, we report the fabrication of flexible and transparent TFTs using nitrogen-doped graphene films as the active layer for an electron channel based on transfer-free, large-scale, high-quality, monolayer graphene synthesized directly on polyethylene terephthalate (PET) substrates at 150 C. The flexible N-doped graphene TFTs with a channel width (800 m) and length (200 m) recorded the world's best results with an on/off current ratio of ~ 109, field-effect mobility of ~ 300 cm2 (Vs)-1, threshold voltage (VTH) of ~ 0.4 V, and a subthreshold swing (S.S.) of ~ 0.09 V dec-1 at room temperature. One important device performance for high-speed and low-power operation for switching transistors is the low S.S., in which the S.S. value of our TFTs is ideally approached the theoretical limit of ~ 0.06 V dec-1. These transparent transistors exhibited predominant flexibility, stable photoresponse, and thermal stability as well as sufficient stretchability. These results could pave the way for the development of flexible, stretchable, and transparent electronics for next-generation TFTs.

Soon-Gil Yoon received his Ph.D. from the Korea Advanced Institute of Science and Technology (KAIST), Korea in 1988. He is a professor in Department of Materials Science and Engineering, Chungnam National University, Republic of Korea. His current research interests are Thin film capacitor, Fusion technology of Solar cell, Thermoelectric, and Piezoelectric using one structure, In situ graphene growth with no transfer at 150 oC, Flexoelectric properties using Zn-Al:LDH nanosheets. Perovskite dye thin films such as MAPbI3, MASnI3, and MAPbCl3, etc by CVD. He had published SCI papers of about 330 including Nano Letters, Advanced Materials, J. Mater. Chem. A, and Scientific Reports.