In a thin film integrated device wherein thin film elements, such as thin film condensers, thin film field effect type transistors and thin film electroluminescent elements, which include insulating films (3, 7, 13, 15, 16) as one of their constitution elements, are formed on an insulating substrate; the insulating films are made of sputtered composite oxide films with at least tantalum and aluminum as major constituents. Since this sputtered composite oxide film has characteristics with a large dielectric constant and a breakdown field intensity and a small leakage current, if it is applied in the thin film elements, their operation characteristics can be increased and their reliability can be remarkably improved.