ZnO bilayer thin film transistors using H2O and O3 as oxidants by atomic layer deposition

This work demonstrates a novel design of thin film transistors composed of a bilayer structure of ZnO thin films (O-3 as oxidant/H2O as oxidant) prepared by atomic layer deposition. Based on this structure, a large I-ON/I-OFF ratio of 10(8) at V-DS = 0.1 V, a high field-effect mobility of 31.1 +/- 0.26 cm(2) V-1 s(-1), a low threshold voltage of 0.14 +/- 0.07 V and a proper subthreshold swing of 0.21 +/- 0.02 V/decade as well as an excellent positive bias stress stability have been obtained. The improved performance of the bilayer structured devices is attributed to the first channel layer of ZnO (H2O as oxidant) decreasing the interfacial trap density and providing high mobility, and the second channel layer of ZnO (O-3 as oxidant) suppressing the off-state current as well as a newly formed sub-channel at the interface between the two channel layers. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.