Fabrication process design for embedded type metal-mesh patterned flexible transparent conducting electrode

Abstract

With the recent emergence of flexible or wearable optoelectronic devices, the achievement of sufficient bendability and stretchability of transparent and conducting electrodes (TCEs) became an important requirement, which cannot be satisfied by oxide-based transparent conducting materials. Among several approaches, metal-mesh-based structures have been actively investigated because of excellent performances and reliability. Nevertheless, the fabrication of mesh or grid structures with a sub-micron line width is still complex and cumbersome due to the requirements of lithography and pattern transfer steps. In this thesis, we introduce an extremely facile fabrication technique for metal patterns embedded in flexible substrate based on sub-micron replication and area-selective lift-off process. The high-yield, area-specific lift-off process consists of the novel principle of solvent-assisted delamination of deposited metal thin films and mechanical triggering effect by soft wiping or ultrasonication. Our fabrication process is highly simple, convenient, and cost-effective in that it does not require any lithography/etching steps or sophisticated facilities. These transparent electrodes composed of submicron silver metal mesh have outstanding optical and electrical properties (e.g. sheet resistances of 0.43 Ω/sq. at 94% transmittance or 2.27 Ω/sq. at 97% transmittance depending on the width and height of mesh patterns), which are markedly superior to other flexible TCEs such as graphene, Ag nanowires, or hybrid-type electrodes. Moreover, there was no significant change of resistance for over 1,000 repeated bending cycles with a bending radius of 5 mm and for the storage in various solvents such as salt water and organic solvents, which confirms the stable bendability and chemical reliability of our embedded-type transparent electrodes.