Amorphous oxide semiconductors (AOS) based thin film transistors (TFTs) find potential applications in the field of large area electronics. Among the various AOS, amorphous Indium Gallium Zinc Oxide (a-IGZO) based TFTs have been broadly researched in the display industry. The characteristics such as high mobility, large-area uniformity, transparency, and low-temperature processing make a-IGZO TFTs suitable for next generation Active Matrix Liquid Crystal Displays (AMLCDs) and Active Matrix Organic Light Emitting Diode (AMOLED) displays. The advancement of a-IGZO TFT based applications relies on a thorough understanding of the impact of the material properties and process integration on the performance and reliability of a TFT. The objective of this thesis is to fabricate a-IGZO TFTs with different architectures and to understand the impact of different materials and process integration variables on device performance.