Abstract

We report channel length $L$ ( $L$ ranging from 2 to 40 $ \mu{{m}}$ ) dependence of the electrical stability of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs). The a-IGZO TFTs employ a coplanar structure with a ${{SiN}}_{x}$ interlayer used to dope the source/drain regions. After application of positive gate bias stress (PBS), short-channel devices ( $L = 2~ \mu {{m}}$ ) exhibit smaller threshold voltage shifts ( $\Delta {\rm V} _{\rm th}$ ) compared to longer-channel devices ( $L \ge {4}~ \mu{{m}}$ ). It is proposed that carrier diffusion takes place from the high carrier concentration regions under the ${{SiN}}_{x}$ interlayer to the intrinsic channel region, thereby shifting the Fermi level closer to the conduction band. Higher Fermi levels mean less defect states available for carrier trapping – hence the small $\Delta {\rm V} _{\rm th}$ in short devices under PBS.

© 2013 IEEE