Deposition Rate Effect on Optical and Electrical Properties of Thermally Evaporated WO_3−x/Ag/WO_3−x Multilayer Electrode for Transparent and Flexible Thin Film Heaters

We investigated the deposition rate effect on the optical, electrical, and morphological characteristics of thermally evaporated WO_3−x/Ag/WO_3−x (WAW) multilayer electrodes. By controlling the deposition rate of the WO_3−x and Ag layers, we can control the interface structure between WO_3−x and Ag and improve both the optical and electrical properties of the thermally evaporated WAW multilayer electrodes. At the optimized deposition rate of WO_3−x (2.5 Å/sec) and Ag (10 Å/sec), the symmetric WAW multilayer exhibited a high optical transmittance of 92.16% at a 550 nm wavelength and low sheet resistance of 3.78 Ω/square. During repeated bending, rolling, and twisting, there was no resistance change indicating the superior flexibility of WAW multilayer electrodes. As a promising application of the WAW multilayer electrodes, we suggested the transparent and flexible thin film heaters (TFHs) to substitute the high cost indium tin oxide-based TFHs. In comparison to the ITO-based TFHs, the WAW based TFHs showed higher convective heat transfer property and higher saturation temperatures are achieved at lower input voltages due to lower sheet resistance. This indicates that the WAW multilayer is suitable as the electrode for high performance transparent and flexible TFHs.