Device Fabrications Using Multi-Dimensional Graphene Based Structures and Their Applications for Wearable, Transparent Electronics

Abstract

Remarkable growths in switching speeds of transistors and the number of transistors on a chip have mainly driven the evolution of micro-electronics during last 50 years. An alternative trend to increase overall area coverage of devices, rather than transistor size or speed, has established a relatively new market that now represented as macro-electronics. Recently, a natural extension of this large-area electronics technology derived strong demands on flexible electronics, and hence developments of electronic materials and processing suitable for flexible electronic devices are interesting research topics. Graphene has been explored as one of next-generation electronic materials due to its outstanding electrical, mechanical, and chemical properties. Conventional processes with multiple vacuum steps and metallization have been still used to fabricate electronic devices using this new nanomaterial. Here we report unconventional approaches to synthesize entire, integrated device array structures based on graphene and multi-dimensional nanomaterials. The conventional silicon-based process which has multiple vacuum deposition and etching steps has been used to in the most of the fabrication. However, this silicon process is not only complicated and expensive methods but also unsuitable for the non-planar substrates. To come close toward flexible electronics, it is necessary for simplify the entire process. For this reason, we suggested the one-step bottom-up synthesis of the entire circuit structures. The number of graphene layers can be adjusted in the synthesis step by using different catalyst metals. The deviation in the carbon solubility of each metals results in the variations of graphite thicknesses, after synthesis. These all-carbon based device arrays are transferrable onto different substrates, such as non-planar surfaces of insects, glass cylinder tubes, soft contact lens, live plants, etc. Furthermore we can demonstrate real-time chemical sensors using the integrated device arrays. As another approach, electrically conductive, transparent, and stretchable materials have been intensively studied to replace indium tin oxide (ITO) electrodes owing to its limited supply and brittleness. There are several potential alternatives such as carbon nanotubes, graphene, conducting polymers, metal nanowires (mNWs), and their hybrid structures. Among these, we studied on graphene-mNW hybrid structures which have attracted considerable attentions due to improvements of properties after hybridization as well as preservation of their own outstanding nature. Hybridization of graphene and Silver nanowires could resolve the critical disadvantages with such as high NW-NW junction resistance, low breakdown voltages, and oxidation of the Silver nanowire networks and relatively low sheet resistance of undoped synthesized graphene. Hybrid electrode shows low sheet resistance of ~33 Ω/sq with the transmittance at 94% and superb mechanical stretchability. Furthermore, the hybrid electrode based FET arrays as forms of integrated circuits were fabricated directly on very thin and flexible substrates, and then we investigated the mechanical flexibility of FET arrays. Lastly, we demonstrated real-time, multiplexed sensors for selective detection of mannan-binding lectin (MBL, Concanavalin A) by using these integrated FET arrays after synthesizing and characterizing of glycol-pyrene derivatives. Demonstration of stretchable, transparent transistors using all-carbon structures or graphene-Silver nanowire hybrid electrodes is the substantial progress towards producing future-oriented soft and wearable electronics.