Impacts of Stress Voltage and Channel Length on Hot-Carrier Characteristics of Tunnel Field-Effect Thin-Film Transistor

Hot-carrier stress (HCS) characteristics of polycrystalline-silicon (poly-Si) tunnel field-effect thin-film transistors are investigated and compared with the conventional poly-Si thin-film transistors (TFTs). After HCS with V
_DS
= 2V
_GS
= 20 V for 1000 s, poly-Si TFT exhibits significant ON-state current (Ion) degradation ~85% and two-step subthreshold swing (SS) behavior due to the serious lattice damage between the pinch-off point and the drain. For the poly-Si tunnel field-effect transistor (TFET), less I
_on
degradation 70% is observed. In addition, the stress drain voltage (V
_DS
) effect of the HCS is also studied. When the stress V
_DS
is increased from 10 to 15 V, the poly-Si TFETs exhibit more obvious stressed Ion degradation (~24.4%) than that of poly-Si TFTs ( 6.5%). When the stress V
_DS
is further increased from 15 to 20 V, the poly-Si TFETs exhibit less stressed Ion degradation (~62.4%) than that of polySi TFTs (~85%). Because the increase in the stress drain voltage is dropped in the pinch-off region of the poly-Si TFETs after the pinch-off phenomenon occurs, resulting in less impact on the stress field at the tunnel junction. When the channel length is decreased, the results show that the HCS effect of poly-Si TFETs is insensitive to the channel length, and the poly-Si TFTs show more serious electrical degradation and breakdown behavior with the scaling down of the channel length. The stronger HCS immunity of poly-Si TFETs would be an important advantage to replacing poly-Si TFTs for applications of 3-D integrated circuits.