A method of forming a passivation film in a flat panel display device includes forming the flat panel display device on a substrate, bringing the flat panel display device into a chamber in order to form the passivation film, injecting precursors containing constituent elements of the passivation film into the chamber where the precursors include at least oxygen plasma, ammonia plasma, or nitrogen plasma, and forming the passivation film of an inorganic insulating material at a temperature of 20-220° C. through a surface chemical reaction between the precursors by a plasma enhanced atomic layer deposition method.