Abstract

High-current level ZnO thin-film transistors (TFTs) on transparent substrates are demonstrated using low-temperature RF sputtering. Oxygen passivation induced fill of oxygen vacancies within the sputtered n-type ZnO thin films on glass substrates is investigated to manipulate the performance of top-gate ZnO TFTs. The surface oxygen passivation effectively enlarges grain size of the ZnO on glass substrates from 7 nm to 20 nm and increases the oxygen composition ratio from 30% to 35%, which essentially yields a TFT with its significantly increase of drain-source current and $I_{\rm on}/I _{\rm off}$ ratio, as compared with a typical ZnO based TFT. The optimum duration of oxygen passivation in this study yields a device with a drain-source current level 0.87 mA under a bias condition $V _{\rm GS} =5~{\hbox{V}}$ and $V_{\rm DS} =15~{\hbox{V}}$, $I_{\rm on} /I_{\rm off}$ ratio ${\hbox{1.4}}\times {\hbox{10}} ^{6}$. We further demonstrate high-performance top-gate ZnO TFTs by applying similar low-temperature process on a flexible polymer substrate. The device shows an $I _{\rm DS}$ 26 $\mu{\hbox{A}}$ under a bias condition $V _{\rm GS} =15~{\hbox{V}}$ and $V_{\rm DS} =25~{\hbox{V}}$ with gate size $W/L=600~\mu {\hbox{m}}/300~\mu {\hbox{m}}$. The average optical transmission of the entire flexible TFT structure in the visible spectrum range is about 82% while the transmission at 550 nm is 88%.

© 2009 IEEE

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