Effect of Nitrogen Doping on Elevated-Metal Metal-Oxide (EMMO) Thin-Film Transistors

Nitrogen doping is introduced in elevated-metal metal-oxide (EMMO) thin-film transistors (TFTs) by sputtering amorphous indium gallium zinc oxide (a-IGZO) channel in Ar and N₂ gas mixture. The electrical characteristic and reliability of TFTs under negative/positive bias illumination stress (N/PBIS) are systematically investigated on TFTs of different channel lengths ( ${L}\text{s}$ ). Compared with undoped TFTs, the short-channel effect (SCE) of the N-doped TFTs is significantly suppressed, the persistent photoconductivity (PPC) effect is weakened, and N/PBIS reliability is largely improved. Short- and long-channel N-doped TFTs have about the same reliability performance. X-ray photoelectron spectroscopy (XPS) analysis shows that N-doping forms Zn=N bonds in the channel and oxygen vacancies ( ${V}_{O}$ ) are reduced. Based on a group of TFTs with different ${L}\text{s}$ , channel mobility ( $\mu _{{\mathrm {ch}}}$ ) and source–drain series resistance ( ${R}_{{\mathrm {sd}}}$ ) are correctly extracted. In N-doped TFTs, $\mu _{{\mathrm {ch}}}$ has a limited decrease owing to the increase in ${R}_{{\mathrm {sd}}}$ . N-doped TFTs with different Ar/N₂ gas-flow ratios show similar electrical and reliability performance, indicating a wide process window.