In this study focuses on the dielectric layer materials of thin film transistors (TFTs). Gate oxide was deposited using a RF Magnetron Sputtering control system. The first studied the aluminium oxide (Al₂O₃) dielectric layer material deposited with different oxygen flow and annealed by the furnace tube. The study found that the properties of aluminium oxide (Al₂O₃) thin film transistors (TFTs) after furnace tube annealing reduced the interface trap density and the roughness of the thin film after annealing. The above dielectric layer is used to make thin film transistors (TFTs) with a bottom gate structure. The characteristics of thin film transistors (TFTs) are significantly improved by higher oxygen flow and additional thermal anneal. By analyzing the structure and electrical measurement of the thin film, the influence of the dielectric layer material on the thin film transistors (TFTs) is analyzed.