Mobility and Stability Enhancement of Amorphous In-Ga-Zn-O TFTs With Atomic Layer Deposited Al₂O₃/SiO₂ Stacked Insulators

Amorphous In-Ga-Zn-O (a-IGZO) thin film transistors (TFTs) were fabricated with an atomic-layer-deposited (ALD) SiO2 buffer layer between the a-IGZO channel and the Al2O3 dielectric. Compared with the TFTs with a single Al2O3 dielectric, the a-IGZO TFTs with the Al2O3/SiO2 stacked insulator demonstrated improved performance. That is, the field-effect mobility increased from 12.3 to 16.2 cm2V-1s-1, the threshold voltage (Vth) and subthreshold swing (SS) decreased from 1.14 to 0.72 V and from 0.48 to 0.30 V/dec, respectively. Furthermore, the Al2O3/SiO2 device also exhibited better electrical stability under negative gate bias stress and negative bias illumination stress than the Al2O3 device. These are mainly attributed to improved interfacial properties between IGZO and SiO2. Such a buffer layer of ALD SiO2 in a-IGZO TFTs is very promising for practical applications.