Design, Fabrication and Characterization of ZnO based Thin Film Schottky Diodes and Transistors

Abstract

The thesis focuses on the development of thin film Schottky diodes and thin film transistors (TFTs) based on ZnO. ZnO has been recognized as a promising candidates for the next generation of transparent and flexible electronics for displays. Some of the interesting properties of ZnO include the variation from insulating to semiconducting nature by change of stoichiometry, the relative low toxicity enabling its use in edible materials, the presence of a reasonably high electron mobility and its high transmission to visible light. All of these properties have increased interest for the development of ZnO-TFTs and diodes. This work focuses on process development of thin film Schottky diodes( Al-ZnO-Ag) and transistors(Al-ZnO-ZrO2). The Schottky diodes were developed with thermally evaporated Aluminium ohmic contact and silver Schottky contact. The fabricated diodes had cut-in voltage between 1-2 V with mean reverse saturation current of 1.0 x 10^-7 A and an excellent rectification ratio of 10^6. Thin film transistors were developed with thermally evaporated Aluminium contacts for Gate, Source and Drain. Zinc oxide was used as semiconductor channel material. For process development of thin film transistors, Zinc oxide was used as semiconductor and a transparent thin film with transmittance of 83.45 % at 450 nm was deposited using DC Reactive sputtering of zinc in oxygen ambient of 1 x 10^-3 mbar. The optical bandgap was found to be around 3.15 eV. ZrO2 was selected as Gate dielectric because of its high dielectric constant, wide band gap and excellent chemical and thermal stability. The ZrO2 thin film was deposited by DC reactive sputtering in an oxygen ambient of 1.5 x 10^-3 mbar. The maximum drain to source current was found to be 25.45 mA and maximum leakage gate current was found to be 0.22 mA.