Amorphous IGZO TFT with High Mobility of ~70 cm2/Vs via Vertical Dimension Control using PEALD.

Amorphous InGaZnOx (a-IGZO) thin film transistors (TFTs) are currently used in flat-panel displays due to their beneficial properties. However, conventional a-IGZO TFT has a mobility of ~10 cm2/Vs, which is not satisfactory for high-resolution display applications such as virtual and augmented reality (VR and AR, respectively) applications. Although increasing the fraction of Indium (In) can achieve high mobilities exceeding 50 cm2/Vs, the TFT stability is significantly reduced due to the intrinsically high carrier density of In-rich amorphous oxides. Therefore, development of effective way to carrier density suppression in In-rich oxides will be a key strategy to realization ofhigh-mobility a-IGZO. In this study, we report that In-rich IGZO TFTs consisting of vertically stacked InOx and GaZnOx atomic layers fabricated at a low deposition temperature (200 oC) exhibit significantly high mobilities of ~80 cm2/Vs while keeping a reasonable carrier density of ~1017 cm-3. We found that the ratio of InOx to GaZnOx is critical to TFT performance parameters such as mobility and threshold voltage. This study illustrates the potential advantages of ALD processes for fabricating ultra-high mobility oxide TFTs.

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