Dynamic characteristics of leakage current in amorphous silicon thin‐film transistors

Abstract

AbstractThe transient off‐currents of thin‐film transistors (TFTs) have been characterized. The authors connected the TFT to a capacitor equivalent to an actual pixel capacitance and made accurate measurements of the voltage at the capacitor under a drive condition actually used for the TFT‐LCDs. The currents were calculated from the measured voltages. Inverted staggered‐type TFTs were used with the gate on‐voltage Vgs = 20 V and the drain voltage Vsig = Vsigc ± 5 V (Vsigc = 4 ± 10 V). It has been found that the off‐current shows an increase or decrease with a time delay of a few milliseconds. The change in the off‐current has been characterized as a relation between the gate bias voltage Vgs and the off‐current Ids. Comparing the results with the dc characteristics, it has been found that the Ids vs. Vgs curves approach the dc curves from the positive side of Vgs' i.e., the transient current curves shift from their dc curves in the positive direction of Vgs. The authors have verified that this behavior of the off‐current with time delay can be explained by introducing a trap level inside the TFT.