PURPOSE:To improve a surface flatness of a ZnO layer and a nonlinearity in a current-and-voltage characteristic by constituting the ZnO layer by a polycrystal film which is not dominantly oriented to a C axis. CONSTITUTION:A ZnO layer 11 is a polycrystal film which is not dominantly oriented to a C axis. The ZnO layer is formed by using an opposed type sputter in which targets face to each other. Ions come in from the plasma between the targets, forming the film. Since the film is a polycrystal film which is a random aggregate of minute single crystals which are aligned in different directions, the surface of the ZnO layer 11 is made flat. By this, a nonlinearity in a current-and-voltage characteristic can be improved.
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