Flexible Metal/Oxide/Metal Transparent Electrodes Made of Thermally Evaporated MoO₃/Ag/MoO₃ for Thin Film Heaters

The authors report on thermally-evaporated MoO₃/Ag/MoO₃ multilayer films as a flexible and transparent electrode for high performance flexible thin film heaters (TFHs). Using thermal evaporation, the authors obtain highly flexible MoO₃/Ag/MoO₃ multilayer films on colorless polyimide substrate without plasma damage. To optimize the thickness of the Ag interlayer, the authors investigate the electrical, optical, morphological, and mechanical properties of MoO₃/Ag/MoO₃ multilayers as a function of Ag interlayer thickness. Based on a figure of merit value, the authors obtain an optimal MoO₃/Ag/MoO₃ electrode with a low sheet resistance of 3.17 Ohm/square, a high optical transmittance of 77.85%, and critical bending radius of 1 mm, which are acceptable for fabrication of TFHs. The flexible TFHs (25 × 25 mm²) fabricated on a thermally evaporated MoO₃/Ag/MoO₃ electrode shows a high saturation temperature of 118 °C even at a low input power of 2.5 W (input voltage 2.5 V) due to very low sheet resistance. Successful operation of the flexible TFHs indicate that the thermally-evaporated MoO₃/Ag/MoO₃ film is a promising alternative transparent electrode to substitute sputtered Sn-doped In₂O₃ (ITO) films for highly transparent and flexible TFHs.