| Summary: | 博士 === 國立臺灣大學 === 電子工程學研究所 === 102 === Thin-film transistors (TFTs) using oxide semiconductors have been regarded as a promising next-generation TFT technology for displays and flexible electronics because of their merits in performance and production. Despite the great success in the development of n-type oxide TFTs in recent years, only few p-type oxide semiconductors were reported for TFTs and their properties and fabrication techniques are still far from practical applications. However, p-type oxide TFTs are strongly demanded in general so that low-power and high-performance complementary circuits can be realized by oxide TFTs and better compatibility with circuits of active-matrix organic light-emitting diode displays may be achieved. Among all p-type oxides reported, tin monoxide (SnO) is considered one of the most promising candidates for realizing practical p-channel devices. However, the properties of SnO-based TFTs and fabrication techniques are not yet good enough for practical applications, necessitating further studies.
In this dissertation, we investigated the SnO system from the material properties to the device characteristics, and developed industry-compatible sputtering targets as well as processing techniques. The research results in this study can facilitate the practical application of SnO in the next-generation display technology.
Firstly, we fabricated p-type SnO thin-films and TFTs by an industry-compatible sputtering technique with the pure SnO ceramic target as the benchmark for further study. The post-annealing effects on SnO films were studied by physical and chemical analysis, and the transmission line method (TLM) was adopted to characterize the contact resistance between SnO layers and various metal electrodes. Lastly, p-type SnO TFTs using practical metal electrodes were successfully fabricated.
In view of the difficulty related to the preparation of pure SnO targets at high temperatures, we further proposed use of Sn/SnO2 mixed target for sputtering deposition of p-type SnO films. The Sn/SnO2 mixed targets can be fabricated by the high-temperature high-pressure pressing/sintering technique and have higher density and robustness more suitable for real uses. The deposited films can be tuned from pure n-type SnO2 to p-type SnO by controlling the sputtering conditions with pure Ar sputtering.
Next, we further investigated sputtering deposition of p-type SnO thin films and TFTs by using the robust Sn/SnO2 mixed target and the hydrogen-containing atmosphere. The effects of the hydrogen gas ratio and post-annealing were studied. Pure polycrystalline SnO films with unified preferential orientation could be readily obtained by appropriate process conditions, and decent p-type SnO TFTs were also demonstrated.
Finally, we investigated the sputtering deposition of p-type SnO using the widely used and robust SnO2 target in a hydrogen-containing reducing atmosphere. The effects of the hydrogen gas ratio on structures, compositions, optical, and electrical properties of deposited SnOx films were studied, and p-type SnO thin-film transistors using such SnO-dominant films were also demonstrated, showing the feasibility and industrial compatibility of this method.
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