Low-cost deposition methods for transparent thin-film transistors

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 cm 2/Vs. 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 HfO ₂ 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 μm. Lithography patterning of ZnO TTFTs is introduced as a means of assessing the effects of shrinking device dimensions on electrical performance.