1. Field of the Invention
The present invention relates to an object, a method, or a manufacturing method. In addition, the present invention relates to a process, a machine, manufacture, or a composition of matter. One embodiment of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a storage device, a driving method thereof, or a manufacturing method thereof. In particular, one embodiment of the present invention relates to a semiconductor device, a display device, or a light-emitting device each including an oxide semiconductor.
In this specification and the like, a semiconductor device generally means a device that can function by utilizing semiconductor characteristics. A display device, an electro-optical device, a semiconductor circuit, and an electronic device include a semiconductor device in some cases.
2. Description of the Related Art
A technique in which a transistor is formed using a semiconductor material has attracted attention. The transistor is used in a wide range of electronic devices such as an integrated circuit (IC) or an image display device (also simply referred to as a display device). A silicon-based semiconductor material is widely known as a semiconductor material applicable to the transistor. As another material, an oxide semiconductor has attracted attention.
Patent Document 1 discloses an example in which a transistor including an oxide semiconductor in a channel formation region (hereinafter referred to as an oxide semiconductor transistor) is used in a dynamic random access memory (DRAM). The oxide semiconductor transistor has extremely low leakage current in an off state (off-state current); thus, a low-power DRAM having a low refresh frequency can be formed.
Patent Document 2 discloses a nonvolatile memory including an oxide semiconductor transistor. Unlike the flash memory, the nonvolatile memory has unlimited cycling capability, can easily operate at high speed, and consumes less power.
Patent Document 2 discloses an example in which an oxide semiconductor transistor has a second gate to control the threshold voltage of the transistor so that the off-state current of the transistor is lowered.
Patent Documents 2 and 3 each disclose a structure example of a circuit for driving the second gate.