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 ION/OFF ratio of over 109.