A data line and an amorphous silicon pattern are formed on a substrate. The first electrode pattern is extended from the data line and overlaps an edge of the amorphous silicon pattern. The second electrode pattern is made of the same metal as the first electrode pattern and overlaps the edge of the amorphous silicon pattern at an opposite side of the first electrode pattern. Edges of the first and the second electrode patterns are sharply formed so that a tunneling effect easily occurs through the amorphous silicon pattern. An indium-tin-oxide pattern for a capacitor is formed at the end of the second electrode pattern. The capacitor is formed between the ITO pattern and a common electrode.