| Summary: | 碩士 === 國立臺灣大學 === 電子工程學研究所 === 100 === Zinc oxide (ZnO) thin film is a promising transparent oxide to replace amorphous silicon used in thin film transistor (TFT), but the ZnO thin film deposited by atomic layer deposition (ALD) has high electron concentration (1019~1020 cm-3). Thin film transistor could not be turned off and exhibited large leakage current. It is necessary to add acceptor into ZnO thin film to suppress electron concentration. For ZnO, nitrogen, phosphorus, and arsenic are acceptors. When choosing ammonia as the precursor of nitrogen, the best performance is achieved when delta doping concentration of NH3 is 50%. It can reduce electron concentration to 1017 cm-3 and has hall mobility around 15 cm2/V-sec.
TFT using the doping condition from above and using Ti as source and drain contact achieves the best on/off current ratio of 6 order of magnitude and the mobility could attain 20.7 cm2/V-sec with Vth=3 V. The ZnO:N TFT that use E-gun silicon oxide (SiOx) as passivation layer has good performance. The on/off current ratio can still remain 6 order of magnitude and the mobility could attain 18.6 cm2/V-sec after deposition SiOx as passivation layer. The electrical properties change very little when the passivated TFT was exposed to atmosphere for 30 days.
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