Buffer Layer Engineering of Indium Oxide Based Trench TFT for Ultra High Current Driving

Oxide thin-film transistors (TFTs) with high mobility that exceed 100 cm2/ $\text{V}\cdot \text{s}$ and appropriate turn-on voltage ( ${V}_{\text {on}}{)}$ are necessary to drive next-generation displays and memory devices. However, a trade-off relationship exists between mobility and ${V}_{\text {on}}$ , making it difficult to achieve both in the same oxide TFT. In this letter, we propose a buffer layer engineered trench-TFT (T-TFT) as a solution to this trade-off problem. Planar-TFT (P-TFT) with an Al2O3 buffer layer exhibits a high current level; however, its ${V}_{\text {on}}$ value is unsuitable. In contrast, P-TFT with an SiO2 buffer demonstrates a ${V}_{\text {on}}$ close to zero, although its mobility remains below 100 cm2/ $\text{V}\cdot \text{s}$ . The T-TFT, which incorporates both Al2O3 and SiO2 buffer layers, shows a high mobility of 129 cm2/ $\text{V}\cdot \text{s}$ and a suitable ${V}_{\text {on}}$ of −0.4 V, selectively utilizing the advantages of P-TFTs. Based on electrical measurements and material analyses, the active layer on each buffer layer performs a distinct role in the T-TFT; the active layer on SiO2 serves as the “ ${V}_{\text {on}}$ determiner,” owing to its low oxygen vacancy, whereas the active layer on Al2O3 enhances the mobility, through reduced electron trap sites and a smooth surface.