Polycrystalline-Silicon CMOS Thin-Film Transistors With T-Shaped Gate and Lightly Doped Drain

Abstract

We report the implementation of both n- and p-channel polycrystalline-silicon (poly-Si) thin-film transistors (TFTs) with features of T-shaped gate (T-gate) of n+ poly-Si in combination with lightly doped drain (LDD) structure. The inclusion of the T-gate and LDD structures improves both the on-state current ( ${I}_{\text {on}}$ ) and off-state leakage ( ${I}_{\text {off}}$ ) of n-channel TFTs significantly in comparison to the conventional TFTs. For p-channel poly-Si TFTs, the LDD structure mitigates ${I}_{\text {off}}$ but leads to an ${I}_{\text {on}}$ degradation due to a potential barrier at the source junction underneath the T-gate’s wing. An additional boron channel doping not only improves ${I}_{\text {on}}$ but also adjusts the threshold voltage of p-channel TFTs. Based on our proposed poly-Si TFTs, the fabricated T-gate devices demonstrate full-swing switching of CMOS inverters.