Low-cost deposition methods for transparent thin-film transistors

Abstract

The objective of this dissertation is to introduce low-cost processing methods for the fabrication of ZnO transparent thin-film transistors (TTFTs). A novel method for depositing ZnO body layers via spin-coating of a zinc nitrate-based spin solution is presented. The processing conditions of spin-coated ZnO are optimized to produce continuous and polycrystalline thin-films. Optimal spin-coated ZnO thin-films are obtained for a 32 nm thick film which is converted to ZnO at 600±C in air. Spin-coated ZnO TTFT mobilities are consistently in the range of 0.1 - 0.2 cm2=V s. Spin-coating deposition methods for HfO2 are presented as a novel way to deposit low-cost gate insulators. Spin-coated HfO2 dielectric has a breakdown field, dielectric constant, loss tangent, and leakage current at 1 MV=cm of » 2:1 MV=cm, 12.1–13.5, 0.411%, and 17.37 nA=cm2, respectively. Additionally, ZnO TTFTs constructed using spin-coated HfO2 gate insulators possess electrical characteristics similar to those obtained with aluminum oxide and titanium oxide superlattice (ATO) gate dielectrics. A second objective of this dissertation is to demonstrate a novel photolithography processing method for ZnO TTFTs with critical dimensions as small as 25 ¹m. Lithography patterning of ZnO TTFTs is introduced as a means of assessing the effects of shrinking device dimensions on electrical performance.