High-Performance Unannealed a-InGaZnO TFT With an Atomic-Layer-Deposited SiO2 Insulator

Amorphous In-Ga-Zn-O (a-IGZO) thin-film transistor with an atomic-layer-deposited (ALD) SiO
₂
gate insulator was fabricated under a maximum processing temperature of 250 °C and compared with the counterpart with a plasmaenhanced chemical vapor deposited (PECVD) SiO
₂
gate insulator. It was demonstrated that the ALD SiO
₂
insulator could generate much better device performance than the PECVD one. This is attributed to a lower density of interfacial traps, weaker surface roughness scattering, and enhanced passivation of oxygen vacancies in the a-IGZO channel atop the ALD SiO
₂
film with more OH groups. Without the need of post-annealing, the ALD SiO
₂
device exhibited very good stability under a negative gate bias stress (-15 V), while maintaining superior performance such as quite high field effect mobility of 63.6 cm
²
V
^-1
s
^-1
, a low threshold voltage of -0.10 V, a small subthreshold swing of 0.14 V/decade, and a large ON/OFF current ratio of ~10
⁸
.