US Patent 8115201 Semiconductor device with oxide semiconductor formed within

One of the objects of the present invention is to provide a thin film transistor using an oxide semiconductor film containing indium (In), gallium (Ga), and zinc (Zn), in which the contact resistance between the oxide semiconductor layer and a source and drain electrodes is reduced, and to provide a method for manufacturing the thin film transistor. An ohmic contact is formed by intentionally providing a buffer layer having a higher carrier concentration than the IGZO semiconductor layer between the IGZO semiconductor layer and the source and drain electrode layers.