Oxide Thin Film Transistor With a Novel Gate Insulator Stack to Suppress Photo-Excited Charge Injection

In this paper, a tri-layer gate insulator stack (SiO
₂
-SiN
_x
-SiO
₂
) is proposed for reducing a photo-excited charge injection in thin film transistors (TFTs). Since the bottom SiO
₂
layer in contact with the gate electrode has a conduction band offset (ΔEC) of 1.1 eV and a valence band offset (ΔE
_V
) of 2.4 eV larger than the SiN
_x
, it is expected that the photo-excited charge injection into SiN
_x
trap states is reduced in a certain range. In order to verify this phenomenon, the TFTs with the proposed structure are fabricated and characterized. The measured result shows that the threshold voltage (VT) shift induced by a photo-exited charge injection is remarkably reduced up to 75% with the use of the proposed tri-layer insulator stack.