The reliability of a transistor including an oxide semiconductor is improved. The transistor in a semiconductor device includes a first oxide semiconductor film over a first insulating film, a gate insulating film over the first oxide semiconductor film, a second oxide semiconductor film over the gate insulating film, and a second insulating film over the first oxide semiconductor film and the second oxide semiconductor film. The first oxide semiconductor film includes a channel region overlapping with the second oxide semiconductor film, a source region and a drain region each in contact with the second insulating film. The channel region includes a first layer and a second layer in contact with a top surface of the first layer and covering a side surface of the first layer in the channel width direction. The second oxide semiconductor film has a higher carrier density than the first oxide semiconductor film.

A retention circuit provided in a logic circuit enables power gating. The retention circuit includes a first terminal, a node, a capacitor, and first to third transistors. The first transistor controls electrical connection between the first terminal and an input terminal of the logic circuit. The second transistor controls electrical connection between an output terminal of the logic circuit and the node. The third transistor controls electrical connection between the node and the input terminal of the logic circuit. A gate of the first transistor is electrically connected to a gate of the second transistor. In a data retention period, the node becomes electrically floating. The voltage of the node is held by the capacitor.

A semiconductor device and method of formation are provided. The semiconductor device includes a substrate, a first active area over the substrate, a second active area over the substrate, a graphene channel between the first active area and the second active area, and a first in-plane gate. In some embodiments, the graphene channel, the first in-plane gate, the first active area, and the second active area include graphene. A method of forming the first in-plane gate, the first active area, the second active area, and the graphene channel from a single layer of graphene is also provided.

Even when a light shielding film is provided between a transistor and a substrate, a threshold voltage of the transistor can be prevented or suppressed from being shifted. A display device includes light shielding films provided between a substrate and a semiconductor layer of a transistor including a gate electrode and the semiconductor layer. The semiconductor layer includes a source region and a drain region. Both of the light shielding films overlap the semiconductor layer when seen in a plan view, and are spaced apart from each other in a direction.

A semiconductor device including an oxide conductor with high conductivity and high transmittance is provided. A manufacturing method for a semiconductor device includes the steps of: forming an oxide semiconductor over a first insulator; forming a second insulator over the first insulator and the oxide semiconductor; forming a first conductor over the second insulator; forming an etching mask over the first conductor; forming a second conductor including a region overlapping with the oxide semiconductor by etching the first conductor with use of the etching mask as a mask; removing the etching mask; and performing heat treatment after forming a hydrogen-containing layer over the second insulator and the second conductor.

An object is to provide a semiconductor device using an oxide semiconductor having stable electric characteristics and high reliability. A transistor including the oxide semiconductor film in which a top surface portion of the oxide semiconductor film is provided with a metal oxide film containing a constituent similar to that of the oxide semiconductor film and functioning as a channel protective film is provided. In addition, the oxide semiconductor film used for an active layer of the transistor is an oxide semiconductor film highly purified to be electrically i-type (intrinsic) by heat treatment in which impurities such as hydrogen, moisture, a hydroxyl group, or a hydride are removed from the oxide semiconductor and oxygen which is a major constituent of the oxide semiconductor and is reduced concurrently with a step of removing impurities is supplied.

A transistor with stable electrical characteristics is provided. Provided is a method for manufacturing a semiconductor device that includes, over a substrate, an oxide semiconductor, a first conductor, a first insulator, a second insulator, and a third insulator. The oxide semiconductor is over the first insulator. The second insulator is over the oxide semiconductor. The third insulator is over the second insulator. The first conductor is over the third insulator. The oxide semiconductor has a first region and a second region. To form the first region, ion implantation into the oxide semiconductor is performed using the first conductor as a mask, and then hydrogen is added to the oxide semiconductor using the first conductor as a mask.

A semiconductor device including an oxide semiconductor in which on-state current is high is provided. The semiconductor device includes a first transistor provided in a driver circuit portion and a second transistor provided in a pixel portion; the first transistor and the second transistor have different structures. Furthermore, the first transistor and the second transistor are transistors having a top-gate structure. In an oxide semiconductor film of each of the transistors, an impurity element is contained in regions which do not overlap with a gate electrode. The regions of the oxide semiconductor film which contain the impurity element function as low-resistance regions. Furthermore, the regions of the oxide semiconductor film which contain the impurity element are in contact with a film containing hydrogen. The first transistor provided in the driver circuit portion includes two gate electrodes between which the oxide semiconductor film is provided.

A semiconductor device capable of retaining data for a long time is provided. A semiconductor device includes a first transistor including a first insulator, a first oxide semiconductor, a first gate, and a second gate; a second transistor including a second oxide semiconductor, a third gate, and a fourth gate; and a node. The first gate and the second gate overlap with each other with the first oxide semiconductor therebetween. The third gate and the fourth gate overlap with each other with the second oxide semiconductor therebetween. The first oxide semiconductor and the second gate overlap with each other with the first insulator therebetween. One of a source and a drain of the first transistor, the first gate, and the fourth gate are electrically connected to the node. The first insulator is configured to charges.

A method for fabricating semiconductor device is disclosed. The method includes the steps of: providing a substrate having a first region and a second region; forming a gate layer on the substrate; forming a first gate dielectric layer on the gate layer; forming a first channel layer on the first region and a second channel layer on the second region; and forming a first source/drain on the first channel layer and a second source/drain on the second channel layer.