Influence of NF(3) Plasma-Treated HfO(2) Gate Insulator Surface on Tin Oxide Thin-Film Transistors

We studied the impact of NF(3) plasma treatment on the HfO(2) gate insulator of amorphous tin oxide (a-SnO(x)) thin-film transistors (TFTs). The plasma treatment was for 0, 10, or 30 s. The HfO(2) insulator demonstrated a slightly higher breakdown voltage, whereas the capacitance value remained almost constant (~150 nF/cm(2)). The linear mobility slightly increased from ~30 to ~35 cm(2)/Vs when the treatment time increased from 0 to 10 s, whereas a 30 s-treated TFT demonstrated a decreased mobility of ~15 cm(2)/Vs. The subthreshold swing and the threshold voltage remained in the 100–120 mV/dec. range and near 0 V, respectively. The hysteresis dramatically decreased from ~0.5 V to 0 V when a 10 s treatment was applied, and the 10 s-treated TFT demonstrated the best stability under high current stress (HCS) of 100 μA. The analysis of the tin oxide thin film crystallinity and oxygen environment demonstrated that the a-SnO(x) remained amorphous, whereas more metal–oxygen bonds were formed with a 10 s NF(3) plasma treatment. We also demonstrate that the density of states (DOS) significantly decreased in the 10 s-treated TFT compared to the other conditions. The stability under HCS was attributed to the HfO(2)/a-SnO(x) interface quality.