Abnormal ${C}$ – ${V}$ Hump Effect Induced by Hot Carriers in Gate Length-Dependent p-Type LTPS TFTs

We investigate the abnormal current-voltage (C-V) hump effect of p-type low-temperature polysilicon (LTPS) thin-film transistors (TFTs) which have undergone high current operations. Experimental results indicate localized electron trapping in the gate insulator (GI), which is carried out near the drain. The ON-current (ION) enhancement is due to the reduction of effective length, and the O
_FF
-current (I
_OFF
) decrease as the electron tunneling path distance increases. These can be observed after hot carrier stress in current characteristics. The C-V measurements demonstrate that the threshold voltage (V
_th
) shift is associated with the gate length. In addition, capacitance-voltage measurements also show that this localized trapping region remains the same in length, regardless of channel length. Hence, a model is proposed to explain how the electric field, which is gate length-dependent, affects the source side of the device, and then lowers the source barrier height. This leads to bulk leakage, which causes the subthreshold swing degradation at device scale down.