Highly Improved Quasi-Two-Dimensional Oxide Transistors via Non-centrosymmetric Nitrogen Dioxide Treatment, toward Extremely Low Process Temperature and Operant Self-Aligned Coplanar Structure.

Rapid degradations are typically encountered in low-temperature processed oxide thin-film transistors (TFTs) with a high indium composition and quasi-two-dimensional (Q2D) thin channel, owing to the breaking of numerous surface bonds of the Q2D oxide and the ineffectiveness of oxidation treatment. Strategically, a novel approach is proposed for the effective use of non-centrosymmetric nitrous oxide (NO2) as a reactive oxidizer gas for realizing the highly robust and rapid field-effect mobility properties of low-temperature-processed Q2D amorphous indium zinc oxide (a-IZO) TFTs. From the surface chemical analysis, it is found that NO2 stably reconstructs surface chemical bonding with NO3- ions by capturing the charged electrons and oxygen and the regions with and without NO2 treatment display extreme differences in their electrical conductivity. Thus, a new process design can be suggested for the fabrication of self-aligned coplanar Q2D transistors, with the aim of scaling down and replacing conventional hydrogen treatment or ultraviolet irradiation. This concept is tactically designed considering the problematic aging effect and impact of the NO2 treatment. The self-aligned coplanar top-gate Q2D a-IZO TFTs exhibit outstanding device performance with a field-effect mobility of 30.1 cm2 V-1 s-1 and a relatively low positive bias stress shift of 1.3 V at an extremely low process temperature of 80 °C.