Display devices such as EL elements or LED elements, are formed from thin film elements having banks of prescribed height and a thin film layer formed by an ink jet method in areas to be coated that are partitioned by those banks. The banks may be formed of an organic material on a bank formation surface configured of an inorganic material, plasma treatment is performed under conditions that the induction gas is fluorine-based and that fluorine is present excessively, and the areas enclosed by the banks subjected to surface treatment are filled with the liquid thin film material to form the thin film layer or layers.