Additive-free solution processing of high-quality ZnO thin films for TFT applications
Alexander Sadlo, Inorganic Materials Chemistry, Faculty of Chemistry and Biochemistry, Ruhr-University Bochum, Bochum, GermanyDaniel Peeters, Inorganic Materials Chemistry, Faculty of Chemistry and Biochemistry, Ruhr-University Bochum, Bochum, GermanyRene Albert, Faculty of Engineering and Center for Nanointegration Duisburg-Essen (CENIDE), University Duisburg-Essen, Duisburg, GermanyDetlef Rogalla, RUBION, Ruhr-University Bochum, Bochum, GermanyHans-Werner Becker, RUBION, Ruhr-University Bochum, Bochum, GermanyRoland Schmechel, Faculty of Engineering and Center for Nanointegration Duisburg-Essen (CENIDE), University Duisburg-Essen, Duisburg, GermanyAnjana Devi , Inorganic Materials Chemistry, Faculty of Chemistry and Biochemistry, Ruhr-University Bochum, Bochum, Germany
Metal oxide semiconductor (MOS) based thin film transistors (TFTs) have been widely studied considering their potential application in electronic devices. Among them, zinc oxide (ZnO) has received significant attention in the last decades, due to its excellent features such as high charge carrier mobility, chemical and thermal stability and high optical transparency in the visible range . It is a promising low-cost material for the utilization in TFTs . The deposition of ZnO thin films via various routes, including physical and chemical vapor deposition, has been thoroughly studied during the last years.
However, these techniques commonly require high vacuum and/or high deposition temperatures, which increase the manufacturing costs significantly and thus are major obstacles for realizing large-area, inexpensive electronics. In contrast, chemical solution deposition (CSD) based processes, e.g. spin coating, can be performed at ambient conditions and facilitate simple, inexpensive and highly controllable processes .
Within the scope of this work, a facile, straightforward and additive-free spin coating process for ZnO thin films was developed and the resulting films were thoroughly investigated in terms of structure, morphology, composition, optical properties and the capability to serve as active layer in TFTs. Therefore, a zinc ketoiminate precursor was employed which is easily accessible, decomposes cleanly and yields high-purity polycrystalline ZnO nanostructures upon annealing.
Further, single-step spin coating with subsequent curing in ambient air was sufficient to fabricate TFT test structures. By extending the curing process, using UV-ozone and laser irradiation treatment, TFT performances could even be enhanced, resulting in average electron mobilities of 1.2 cm2/Vs and excellent on/off current ratios (107), indicating the high potential of the presented route.
 Ü. Özgür, Y. I. Alivov, C. Liu, A. Teke, M. A. Reshchikov, S. Doğan, V. Avrutin, S.-J. Cho and H. Morkoç, J. Appl. Phys., 2005, 98, 41301.
 T. Guo, M.-S. Yao, Y.-H. Lin and C.-W. Nan, CrystEngComm, 2015, 17, 3551–3585.
 R. C. Hoffmann and J. J. Schneider, Eur. J. Inorg. Chem., 2014, 2014, 2241–2247.