Processing optimization of SiO2-capped aluminum-doped ZnO thin films for transparent heater and near-infrared reflecting applications

Abstract

In this study, a series of optimization steps were performed in the production of Al-doped ZnO (AZO) thin films to tailor their properties as efficient transparent heaters and for near-infrared (NIR) reflectance. The films were produced on 50 x 75 mm(2) glass substrates via magnetron sputtering and capped with a protective SiO2 layer. Processing parameters such as deposition temperature, film thickness, and annealing conditions were all optimized in terms of structure, morphology, optical/electrical properties, and heating/deicing behavior. Electro-thermal characteristics of the films were investigated using a thermal imaging infrared camera under various input voltages. The optimized AZO/SiO2 coatings displayed impressive room-temperature electrical conductivity (sigma) of nearly 3774 S/cm with a sheet resistance (R-s) of 3.53 Omega/square, carrier concentration (eta) of 1.14 x 10(21), and Hall mobility (mu) of 20.48 cm(2)/Vs. These films exhibited very high optical transmittance (above 96%) in the visible range and reflectance (73% at 2500 nm) in the NIR region. The highest figure of merit (FOM) was achieved as 237 (x 10(-3) omega(-1)). Deicing tests were performed with samples cooled to - 40 degrees C and resulted with complete removal of ice/water only within 3 min. In addition, the heater exhibited a high surface temperature of 161 degrees C (12 V), a good thermal resistance value (219 degrees C cm(2)/Watts) with stable and reversible heating behavior. More importantly, these results reveal the potential of optimized AZO/SiO2 coatings as alternatives to transparent tin-doped indium oxide heaters and NIR reflecting mirrors for vehicular applications. [GRAPHICS]