Degradation of Zinc Oxide Thin Films in Carbonating Atmosphere

Abstract

Carbonation of ZnO thin film was investigated in order to understand degradation of ZnO-based transparent conductive films, gas sensors and other electronic devices. The ZnO thin film (thickness : 400 nm) sputter-deposited on a glass substrate was exposed to the atmosphere of carbon dioxide (1.0×10⁵ Pa) and saturated water vapor (2.3×10³ Pa) at 20°C until 8 weeks when an exfoliation of the film occurred remarkably. The X-ray diffraction analysis showed a degradation of ZnO and formation of ZnCO₃ and the basic carbonates. The crystal growth of ZnCO₃ occurred independent of the orientation of the original ZnO crystal. Zn₃CO₃ (OH) ₄·2H₂O was detected in the early stage (1-2 weeks) and disappeared quickly. Zn₃CO₃ (OH) ₄·2H₂O was estimated to exist mainly at the surface of the film. Zn₅ (CO₃) ₂ (OH) ₆ and Zn₂CO₃ (OH) ₂ increased during the present experiment. Zn₂CO₃ (OH) ₂ was expected to exist mainly at the inner part of the film.