The influence of the SiO_2 gate insulator thickness to the performance and Bias-voltage stress stability of ZnO thin-film-transistors

摘要

Top-contact thin film transistors using radio frequency sputtering ZnO and SiO_2 films as channel layer and gate insulator are fabricated in this work. The performance of ZnO-TFTs with different thickness SiO_2 dielectrics are compared. The experiment results show that the SiO_2 dielectric thickness plays an important role on enhancing both the field effect mobility and bias stability of the devices. The device with 150 nm thick SiO2 insulator has much better performances: its mobility reaches 6.1cm~2/V.S, subthreshold swing is 1.6 V/Dec, bias-voltage stress induced Δ V_(th) is 3V. Comparison of 150 nm thickness with 200 nm thickness and 300 nm thickness SiO_2 insulator based devices shows that the field effect mobility improved by 250% and 150% and sub-threshold swing decreased by 60% and 25%, respectively, while bias-voltage stress instability reduced from 6V and 9.4V to 3V. The improved performance can be attributed to that the thinner insulator has larger capacitance and contains smaller amounts of total trap centers compared with the thicker dielectrics.