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.