Substrate current and Its correlation with degradation of poly-Si thin film transistors

Substrate current (I
_sub
) in poly-Si thin film transistors (TFTs) is first investigated by considering their specific substrate contact configuration. When the substrate bias is very small, I
_sub
is driven by the recombination process in the channel region and is related to the trap density (D
_t
) wherein. Controlled by the gate bias (V
_g
), the recombination region varies from the whole channel area to a localized region near the drain, source or substrate terminal. Based on such observation, I
_sub
is used to monitor the hot carrier degradation in TFTs. The I
_sub
-V
_g
curve is applied to sensitively reflect the location of the hot carrier-induced damage region and evaluate the local Dt increase wherein.