Fabrication of flexible electrode with sub-tenth micron thickness using heat-induced peelable pressure-sensitive adhesive containing amide groups

In response to the increasing demand for flexible devices, there is increasing effort to manufacture flexible electrodes. However, the difficulty of handling a thin film is an obstacle to the production of flexible electrodes. In this study, a heat-induced peelable pressure-sensitive adhesive (h-PSA) was fabricated and used to manufacture a flexible electrode with sub-tenth micron thickness. Unlike the control PSA, the incorporation of amide groups made the h-PSA fail through adhesive failure at temperatures ranging from 20 to 80^◦C. Compared to the peeling adhesion (1719 gf/in) of h-PSA measured at 20^◦C, the value (171 gf/in) measured at 80^◦C was decreased by one order of magnitude. Next, the 8 µm thick polyethylene terephthalate (PET) film was attached on a thick substrate (50 µm) via h-PSA, and Mo/Al/Mol patterns were fabricated on the PET film through sputtering, photolithography, and wet-etching processes. The thick substrate alleviated the difficulty of handling the thin PET film during the electrode fabrication process. Thanks to the low peel force and clean separation of the h-PSA at 80^◦C, the flexible electrode of metal patterns on the PET (8 µm) film was isolated from the substrate with little change (<1%) in electrical conductivity. Finally, the mechanical durability of the flexible electrode was evaluated by a U-shape folding test, and no cracking or delamination was observed after 10,000 test cycles.