A protective film for a thin film device comprises a composite inorganic film that may be deposited on a parylene film or deposited directly on the device. Optionally, additional parylene and composite inorganic protective films may be added. The composite inorganic protective film is on the order of 1-100 nm thick and contains a material (e.g., Si) that forms a tenacious oxide at room temperature. When the device is exposed to air after deposition of the composite inorganic film, the oxidizable species oxidizes and fills voids to create an effective diffusion barrier.