Influence of Applied Power in Microwave Hydrogen Plasma Annealing on Aluminum doped Zinc Oxide/Tin doped Indium Oxide Bilayer Films for Low Emissivity Application

Low emissivity (Low-E) glass shows not only high reflectivity in infrared light, but also high visible light transmission applied in energy saving buildings. The smaller low-e glass emissivity is, the higher infrared reflection is for low-e glass. Low electrical resistivity reduces emissivity of low e functional materials like transparent conductive oxides. Microwave hydrogen plasma annealing can lower the electrical resistivity of zinc oxide studied before. Applied power is one of key factors in plasma annealing. In this study, aluminum doped zinc oxide and tin doped indium oxide bilayer (AZO/ITO) films were sequentially deposited on glass substrates by in-line sputtering. The AZO/ITO films were post-annealed in microwave hydrogen plasma at 400W, 600W and 800W separately. The optimized power in microwave plasma with respect to plasma annealed AZO/ITO films as the good candidate of low-e glass was tried to be found. Experiment results indicates applied power in plasma annealing of AZO/ITO samples indeed influences the structure and electrical properties. The plasma power at 600W corresponds to lowest electrical resistivity and emissivity of AZO/ITO films among all test samples. The electrical resistivity of 400, 600 and 800W plasma annealed AZO/ITO samples are 4.68×10
^-4
, 4.22×10
^-4
and 4.47×10
^-4
Ω-cm respectively, which decreases 55%, 59% and 57% compared with that of the as-deposited ones. Decrease of electric resistivity for hydrogen plasma annealing could be ascribed to 1. desorption of negatively charged oxygen from grain boundary; 2. substitution of matrix atoms such as zinc and indium atoms with impurity atoms such as aluminum and tin atoms in AZO/ITO films. The lowest emissivity in all plasma annealed AZO/ITO films is 0.1 corresponding to 600W plasma annealed AZO/ITO films. Emissivity of 600W plasma annealed AZO/ITO films is 58% lower than that of as-deposited AZO/ITO films. The average transmittance in visible wavelength (380~780 nm) of all plasma annealed AZO/ITO films is over than 83%. This paper contributes to industry of energy saving buildings.