An airfoil includes a leading edge, a trailing edge downstream from the leading edge, a pressure surface between the leading and trailing edges, and a suction surface between the leading and trailing edges and opposite the pressure surface. A conventional four-row by three-column 12-key keypad is used to enter all of the letters of the alphabet using single key actuation. Gettering is performed in such a manner that a metallic element contained in the semiconductor film is caused to segregate in the impurity region by heat treatment.