Influence of atmosphere and material properties on damp heat stability of ZnO:Al

We report on electrical properties and corrosion of ZnO:Al thin films on glass after damp heat treatments under various atmospheric conditions. The ZnO:Al films were prepared by in-line magnetron sputtering onto glass substrates. Damp heat treatments took place at 90 °C in various humid atmospheres including air, nitrogen, and mixtures of argon and carbon dioxide. Dry heat did not affect the properties of ZnO:Al films. Humidity, however, led to a significant increase in resistivity depending on preparation conditions of the ZnO:Al and the composition of the atmosphere. Additionally, humid CO2 levels exceeding 5% significantly etched the ZnO:Al films with resistance increase by orders of magnitude. The only exception from degradation exhibited the damp heat stable ZnO:Al that had experienced the so-called high-mobility annealing under the protective layer before degradation. This unique behavior was related to bulk properties of the ZnO:Al rather than a barrier effect at the film surface