A novel semiconductor device or a highly reliable semiconductor device is provided. The on/off state of a transistor which functions as a switch for writing data is controlled using the potential of a potential hold portion. The potential of the potential hold portion is controlled using a plurality of capacitors, whereby both a positive potential and a negative potential can be held in the potential hold portion. Accordingly, deterioration of the transistor which functions as the switch for writing data can be prevented and the characteristics of the transistor can be maintained. Therefore, the highly reliable semiconductor device can be provided.

A display device with a narrow bezel is provided. The display device includes a pixel circuit and a driver circuit provided on one plane. The driver circuit includes a selection circuit and a buffer circuit. The buffer circuit includes a first transistor and a second transistor. Sources of the first and second transistors are electrically connected with each other. Drains of the first and second transistors are electrically connected with each other. Gates of the first and second transistors are electrically connected with each other. The first transistor and the second transistor are stacked so that the direction of the current flow in the first transistor is parallel to that in the second transistor.

A novel metal oxide or a novel sputtering target is provided. A sputtering target includes a conductive material and an insulating material. The insulating material includes an oxide, a nitride, or an oxynitride including an element M1. The element M1 is one or more kinds of elements selected from Al, Ga, Si, Mg, Zr, Be, and B. The conductive material includes an oxide, a nitride, or an oxynitride including indium and zinc. A metal oxide film is deposited using the sputtering target in which the conductive material and the insulating material are separated from each other.

A novel metal oxide is provided. The metal oxide has a plurality of energy gaps, and includes a first region having a high energy level of a conduction band minimum and a second region having an energy level of a conduction band minimum lower than that of the first region. The second region comprises more carriers than the first region. A difference between the energy level of the conduction band minimum of the first region and the energy level of the conduction band minimum of the second region is 0.2 eV or more. The energy gap of the first region is greater than or equal to 3.3 eV and less than or equal to 4.0 eV and the energy gap of the second region is greater than or equal to 2.2 eV and less than or equal to 2.9 eV.

The semiconductor device comprises a gate electrode, a first gate insulating film overlapping a part of the side surface and the upper surface of the gate electrode, a second gate insulating film overlapping the upper surface of the gate electrode, a semiconductor film provided on the upper surface of the second gate insulating film and overlapping the gate electrode and a first terminal and a second terminal overlapping the upper surface of the semiconductor film. In a plan view, a first region is a region where the semiconductor film overlaps the upper surface of the first gate insulating film and the second gate insulating film between the first terminal and the second terminal, and a third region is a region that overlaps both a part of the upper surface of the gate electrode and the second gate insulating film and does not overlap the first gate insulating film.

An oxide semiconductor layer which is intrinsic or substantially intrinsic and includes a crystalline region in a surface portion of the oxide semiconductor layer is used for the transistors. An intrinsic or substantially intrinsic semiconductor from which an impurity which is to be an electron donor (donor) is removed from an oxide semiconductor and which has a larger energy gap than a silicon semiconductor is used. Electrical characteristics of the transistors can be controlled by controlling the potential of a pair of conductive films which are provided on opposite sides from each other with respect to the oxide semiconductor layer, each with an insulating film arranged therebetween, so that the position of a channel formed in the oxide semiconductor layer is determined.

A display device is disclosed that may include a first active layer disposed on a substrate, a scan line disposed on the first active layer, extending in a first direction and including a first protruding portion protruding in a second direction crossing the first direction, a first compensation control line disposed on the first active layer, extending in the first direction and spaced apart from the scan line in the second direction, and a second active layer disposed on the scan line and the first compensation control line, overlapping the scan line and the first compensation control line and including a second protruding portion protruding in the first direction. The first protruding portion may be positioned outside the second active layer in the first direction in a plan view.

An object is to provide a display device which operates stably with use of a transistor having stable electric characteristics. In manufacture of a display device using transistors in which an oxide semiconductor layer is used for a channel formation region, a gate electrode is further provided over at least a transistor which is applied to a driver circuit. In manufacture of a transistor in which an oxide semiconductor layer is used for a channel formation region, the oxide semiconductor layer is subjected to heat treatment so as to be dehydrated or dehydrogenated; thus, impurities such as moisture existing in an interface between the oxide semiconductor layer and the gate insulating layer provided below and in contact with the oxide semiconductor layer and an interface between the oxide semiconductor layer and a protective insulating layer provided on and in contact with the oxide semiconductor layer can be reduced.

An object is to improve reliability of a light-emitting device. A light-emitting device has a driver circuit portion including a transistor for a driver circuit and a pixel portion including a transistor for a pixel over one substrate. The transistor for the driver circuit and the transistor for the pixel are inverted staggered transistors each including an oxide semiconductor layer in contact with part of an oxide insulating layer. In the pixel portion, a color filter layer and a light-emitting element are provided over the oxide insulating layer. In the transistor for the driver circuit, a conductive layer overlapping with a gate electrode layer and the oxide semiconductor layer is provided over the oxide insulating layer. The gate electrode layer, a source electrode layer, and a drain electrode layer are formed using metal conductive films.

An imaging device having a three-dimensional integration structure is provided. A first structure including a transistor including silicon in an active layer or an active region and a second structure including an oxide semiconductor in an active layer are fabricated. After that, the first and second structures are bonded to each other so that metal layers included in the first and second structures are bonded to each other; thus, an imaging device having a three-dimensional integration structure is formed.