| Summary: | 碩士 === 國立臺灣大學 === 機械工程學研究所 === 103 === Transparent conductive oxides (TCO) thin films have drawn great interests and have been widely studied in recent years because of their important role as electrodes in various optoelectronic devices. One of the most widely used TCOs is tin-doped indium oxide (ITO) due to its high electrical conductivity, wide band gap, and high transparency in the visible spectral range. However, indium is rare in the Earth’s crust, which increases the production cost of ITO. Owing to its high chemical and mechanical stability, high abundance, nontoxicity, and exceptionally high electron mobility, zinc oxide (ZnO) thin film has become one of the popular alternatives to ITO films. ZnO is a well-known II-VI transparent semiconductor with a wide direct band gap of ~3.37 eV at room temperature, and a high exciton binding energy of 60 meV. ZnO heavily doped with metals, such as Al, Ga and In, shows Fermi level degeneration and thus behaves metallic along with its high transparency.
Atmospheric pressure plasma jet (APPJ) technology provides a relatively simple and cost-effective method to deposit gallium-doped zinc oxide (GZO or ZnO:Ga) films onto large-area glass substrates in atmosphere. APPJ is simple and compatible with a wide range of precursor materials, facilitating the incorporation of suitable dopants without the need of heating the substrate over 200 C.
We prepare GZO thin films on 185 mm × 117 mm glass substrates by APPJ,
and study the effects of deposition parameter and trajectory on film sheet resistance
uniformity. In this study, we find that during the deposition, the plasma jet deposition
becomes more stable over time, and is able to deposit films with lower sheet
resistance. By adjusting the substrate temperature and scanning speed, we find that
films deposited with a higher substrate temperature and a lower scanning speed exhibit lower sheet resistance. The lowest sheet resistance of 49.4 Ω/□ and uniformity
of 7% is obtained. In the external flow experiment, we observe that the flow field
between the plasma jet chamber and the tool enclosure has a significant effect on the
film quality and uniformity. The films near the exhaust of the enclosure tend to exhibit
higher resistivity. The exact mechanism is still unclear and is a topic for future work.
Using the concentric trajectory we can obtain films with the lowest sheet resistance in
the central area. By using a raster scan on top of a concentric scan, we obtain a
two-layer film with better uniformity.
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