A comparison study was performed on radio frequency sputtered amorphous In-Zn-O transparent thin-film transistors (a-IZO TTFTs) using Y2O3 and Y2O3/Al2O3 dielectrics. Y2O3 has strong affinity for water and carbon dioxide molecules present in the air, which would induce a great deal of Y-O center dot electron traps at the Y2O3/a-IZO interface and ruin the device performance eventually. It is proposed that an Al2O3 capping layer is utilized to avoid chemical reaction on the surface of Y2O3, then the detrimental effects that yield electron trap states are circumvented. (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3519412] All rights reserved.