Roll-to-roll patterning of Al/Cu/Ag electrodes on flexible poly(ethylene terephthalate) by oil masking: a comparison of thermal evaporation and magnetron sputtering

Here we show in-line-patterning of Al (37 nm)/Cu (58 nm)/Ag (55 nm) electrodes on flexible poly(ethylene-terephthalate) at 1-25 m min(-1), using a flexography printing apparatus retrofitted to a commercial roll-to-roll vapor deposition system. A Krytox (R) 1506 lift-off mask was printed for simultaneous evaporation during metal deposition. Heat through Al thermal evaporation facilitated single-step patterning with 99.99% masking efficiency, and 5% area shrinkage compared to the 4 x 6 mm photopolymer stamp. Al with nominal line widths of 28-58 mu m (average. 47 mu m) was also demonstrated using a commercial nitrile sleeve. Sputtering was trialed using powers 1-2 kW, substrate speeds of 1-25 m min(-1), and was unable to achieve mask lift-off, leading to metallic over-coating, removed via secondary isopropanol cleaning. Dynamic deposition rates of thermal evaporation exceeded sputtering (928 vs. 775 nm.m min(-1) respectively, with ten inline/confocal sputtering sources theoretically required). Resistivities of Al/Cu/Ag were 7.2 x 10(-8)/8.2 x 10(-7)/6.8 x 10(-8) Omega.m; 2.6/48.2/4.2x greater than respective bulk values whilst work functions of electrodes varied 4.21/4.93/5.22 eV. Resistivities were critically impaired in proximity/on sputtered Cu/Ag. Electrodes were printed without inks/post-deposition heat-treatments, and whilst challenges remain, selective metallization is ready for high-throughput flexible electronics whilst sputtering may be used in a two-step process, requiring additional development for single-step patterning.