1. Field of the Invention
The present invention relates to a semiconductor structure. More particularly, the present invention relates to a thin film transistor (TFT) having an oxide semiconductor material.
2. Description of Related Art
By virtue of the rising awareness of environmental protection, flat panel displays featuring superior properties including low power consumption, optimal space utilization, no radiation, and high definition have gradually become the mainstream products in the market of the displays. Common flat panel displays include liquid crystal displays (LCDs), plasma displays, organic electroluminescent displays, and so forth. The prevailing LCD is mainly comprised of a thin film transistor (TFT) array substrate, a color filter substrate, and a liquid crystal layer sandwiched between the two substrates, for instance. Amorphous silicon (a-Si) TFTs or low temperature polysilicon TFTs on a conventional TFT array substrate often serve as switch elements of sub-pixels. According to the recent researches, the oxide semiconductor TFT, in comparison with the a-Si TFT, is characterized by favorable carrier mobility and, in comparison with the low temperature polysilicon TFT, is characterized by desired threshold voltage (Vth) uniformity. Hence, an oxide semiconductor TFT has the potential to be the key element in the next generation flat panel display.
However, under the atmospheric environment, the oxide semiconductor material is apt to be affected by moisture and oxygen, such that electrical properties of the oxide semiconductor material are varied together with time. As such, electrical performance and reliability of the oxide semiconductor TFT are deteriorated.