Effects of plasma hydrogenation on characteristics of T-shaped gate polysilicon thin-film transistors with lightly-doped drain

We study the influences of plasma hydrogenation on the operation of a novel poly-Si thin-film transistor (TFT) featuring a T-shaped gate (T-gate), air spacers, and a lightly doped drain (LDD). The plasma treatments were done in a commercial chamber with a high plasma density (AMAT Centura 5200, Applied Materials Inc.). The results show that the threshold voltage can be reduced, while field-effect mobility and subthreshold swing can be greatly improved in just half an hour. Besides, the evolution trends of the above parameters for the T-gate device are close to those exhibited by the device with a conventional gate configuration. This indicates that the air spacers of the T-gate devices do not retard the plasma hydrogenation. The minimum drain current measured in the off-state at a high drain bias for the T-gate device reduces with increasing hydrogenation time. The conventional devices show an opposite trend due to a different and steeper source/drain doping profile than the LDD.