1. Field of the Invention
The present invention relates to semiconductor devices, display devices, light-emitting devices, and methods for manufacturing these devices. In particular, the present invention relates to semiconductor devices, display devices, and light-emitting devices each including a transistor, and methods for manufacturing these devices. The present invention relates to electronic devices including the semiconductor devices, the display devices, or the light-emitting devices.
2. Description of the Related Art
It is known that the on-state current of a transistor including gate electrodes above and below with a semiconductor layer provided therebetween can be increased and that the off-state current of the transistor can be decreased by control of the threshold voltage. A transistor with such a structure is referred to as a double-gate transistor or a dual-gate transistor. In the following description, a transistor with such a structure is also referred to as a bottom-gate transistor with a back gate electrode.
A bottom-gate transistor with a back gate electrode can be used in, for example, a display device (see FIG. 7 in Patent Document 1).