A covering layer (240) is formed by atomic layer deposition (ALD) and contains an insulating inorganic material. An intermediate layer (220) contains a material having a linear expansion coefficient different from that of a material of the covering layer (240). A buffer layer (230) has a surface in contact with the intermediate layer (220), that is, a first surface. The buffer layer (230) has a surface in contact with the covering layer (240), that is, a second surface. A linear expansion coefficient difference between a material of the buffer layer (230) and the inorganic material of the covering layer (240) is less than a linear expansion coefficient difference between the material of the intermediate layer (220) and the inorganic material of the covering layer (240).