Improvement in the negative bias temperature stability of ZnO based thin film transistors by Hf and Sn doping

We assessed the performance of ZnO TFTs using Si₃N₄ gate dielectrics after various treatments. A remarkable improvement in the transfer characteristics was obtained for the O₂ plasma treated ZnO TFT and SiO₂ interlayer deposited ZnO TFT. Also, we developed amorphous hafnium-zinc-tin oxide (HZTO) thin film transistors (TFTs) and investigated the influence of hafnium (Hf) doping on the electrical characteristics of the hafnium-zinc oxide (HZO) thin film transistors. Doping with Hf can decrease the carrier concentration, which may result from a decrease of the field effect mobility, and reduce oxygen vacancy related defects in the interfacial layer. Adding tin (Sn) can suppress the growth of a crystalline phase in the HZTO films. The HZTO TFTs exhibited good electrical properties with a field effect mobility of 14.33 cm²/Vs, a subthreshold swing of 0.97 V/decade, and a high I_ON/OFF ratio of over 10⁹.