Modified Stoichiometry in Homogeneous Indium–Zinc Oxide System as Vertically Graded Oxygen Deficiencies by Controlling Redox Reactions

The present study suggests a way to improve electrical characteristics and stabilities by forming a different stoichiometry in a homogeneous system without using a multiple deposition process. Post treatment by sequential pressure annealing (SPA) of a homogeneous indium–zinc oxide system is carried out to fabricate vertically graded oxygen deficiencies via redox reactions. The SPA treatment consists of several steps. First, hydrogen pressure annealing is performed to chemically expedite the reduction reaction of weak chemical bonds in the overall channel region and thereby make the material highly conducting. Second, oxygen pressure annealing is performed to render the channel a poor conductor by gradually oxidizing the channel from the back to the front. Such SPA-treated devices have significantly more oxygen deficiencies in the front-channel region than in the back-channel region. The stoichiometry of the channel region modified in this manner provided enhanced mobility, a higher on/off ratio, and a decreased threshold voltage shift (under positive and negative bias stresses).