| 摘要 |
PROBLEM TO BE SOLVED: To provide a display device composed of a transistor having stable electrical characteristics (e.g., off-current is extremely reduced).SOLUTION: By using a semiconductor material having a wider forbidden band width (band gap) than a silicon semiconductor as a semiconductor material for forming a transistor, and favorably, by decreasing a concentration of an impurity serving as a carrier donor of the semiconductor material, reduced off-current is achieved. For this purpose, an oxide semiconductor having energy gap of 2 eV and over, favorably of 2.5 eV and over and more favorably of 3 eV and over is used as a semiconductor layer (layer for forming a channel region) of the transistor thereby to reduce a concentration of an impurity contained in the oxide semiconductor and serving as a carrier donor. By doing this, off-current of the transistor can be reduced to an extremely low level of less than 10 zA/μm per channel width of 1 μm at a room temperature, and less than 100 zA/μm at 85°C. |
