Improved performances in low-voltage-driven InGaZnO thin film transistors using a SiO2 buffer layer insertion

Abstract

In this paper, we report the device characteristics of indium gallium zinc oxide (IGZO) thin film transistors (TFTs) with high-kappa lanthanum aluminate (LaAlO3) based gate insulators. The IGZO TFT with single LaAlO3 gate insulator has an operation voltage as low as 1.5 V but suffers a low on-off-state drive current ratio (I (on)/I (off)) of 1x10(3), a large subthreshold swing (SS) of 0.405 V/dec and a small field effect mobility (mu (FE)) of 0.84 cm(2)/V sec. Inserting a SiO2 buffer layer between IGZO active channel layer and LaAlO3 gate insulator results in a reduced effective dielectric constant but with significant improved characteristics including a high I (on)/I (off) of 6.2x10(4), a small SS of 0.113 V/dec and a large mu (FE) of 5.2 cm(2)/V sec. Such good performances can be attributed to the lowered gate leakage and reduced interface trap issue owing to the smooth SiO2 buffer layer insertion.