Comparative studies on ZnO thin-film transistors with inorganic versus polymer dielectric interfaces

Comparative studies of top-gate ZnO thin-film transistors (TFTs) that adopt a polymer/high-k oxide double-layer dielectric according to the sequence of polymer and high-k oxide deposition on a ZnO channel are reported. When the polymer gate dielectric was on a ZnO channel, an improved field-effect mobility of 0.50 cm²/Vs was achieved for the polymer/ZnO interface, which is superior to that of 0.02 cm²/Vs for the high-k oxide/ZnO interface. From the fact that a more negative value of the threshold voltage was observed with a polymer/ZnO channel in spite of the counter-clockwise hysteresis in the transfer characteristics, the sequence of polymer then high-k oxide deposition on ZnO can be concluded to be advantageous because the channel/dielectric interface is less defective relative to the high-k oxide then the polymer dielectric sequence, which suffers from a charge trap/de-trap instability owing to the poor dielectric/gate interface.