A semiconductor device for high power application in which a novel semiconductor material having high mass productivity is provided. An oxide semiconductor film is formed, and then, first heat treatment is performed on the exposed oxide semiconductor film in order to reduce impurities such as moisture or hydrogen in the oxide semiconductor film. Next, in order to further reduce impurities such as moisture or hydrogen in the oxide semiconductor film, oxygen is added to the oxide semiconductor film by an ion implantation method, an ion doping method, or the like, and after that, second heat treatment is performed on the exposed oxide semiconductor film.

An object is to improve reliability of a semiconductor device. A semiconductor device including a driver circuit portion and a display portion (also referred to as a pixel portion) over the same substrate is provided. The driver circuit portion and the display portion include thin film transistors in which a semiconductor layer includes an oxide semiconductor; a first wiring; and a second wiring. The thin film transistors each include a source electrode layer and a drain electrode layer. In the thin film transistor in the driver circuit portion, the semiconductor layer is sandwiched between a gate electrode layer and a conductive layer. The first wiring and the second wiring are electrically connected to each other in an opening provided in a gate insulating film through an oxide conductive layer.

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.

A substrate contact land for a first MOS transistor is produced in and on an active zone of a substrate of silicon on insulator type using a second MOS transistor without any PN junction that is also provided in the active zone. A contact land on at least one of a source or drain region of the second MOS transistor forms the substrate contact land.

Fabrication of radio-frequency (RF) devices involves providing a field-effect transistor (FET), forming one or more electrical connections to the FET, forming one or more dielectric layers over at least a portion of the electrical connections, and disposing an electrical element at least partially above the one or more dielectric layers, the electrical element being in electrical communication with the FET via the one or more electrical connections. RF device fabrication further involves applying an interface material over at least a portion of the one or more dielectric layers, removing at least a portion of the interface material to form a trench above at least a portion of the electrical element, and covering at least a portion of the interface material and the trench with a substrate layer to form a cavity, the electrical element being disposed at least partially within the cavity.

A method includes forming a first material stack above a first transistor region, a second transistor region, and a dummy gate region of a semiconductor structure, the first material stack including a high-k material layer and a workfunction adjustment metal layer. The first material stack is patterned to remove a first portion of the first material stack from above the dummy gate region while leaving second portions of the first material stack above the first and second transistor regions. A gate electrode stack is formed above the first and second transistor regions and above the dummy gate region, and the gate electrode stack and the remaining second portions of the first material stack are patterned to form a first gate structure above the first transistor region, a second gate structure above the second transistor region, and a dummy gate structure above the dummy gate region.

A method for manufacturing a semiconductor device includes the steps of forming a first insulating film over a first gate electrode over a substrate while heated at a temperature higher than or equal to 450 C. and lower than the strain point of the substrate, forming a first oxide semiconductor film over the first insulating film, adding oxygen to the first oxide semiconductor film and then forming a second oxide semiconductor film over the first oxide semiconductor film, and performing heat treatment so that part of oxygen contained in the first oxide semiconductor film is transferred to the second oxide semiconductor film.

A semiconductor device that can measure a minute current. The semiconductor device includes a first transistor, a second transistor, a node, and a capacitor. The first transistor includes an oxide semiconductor in a channel formation region. The node is electrically connected to a gate of the second transistor and a first terminal of the capacitor. The node is brought into an electrically floating state by turning off the first transistor after a potential V.sub.0 is supplied. Change in a potential V.sub.FN of the node over time is expressed by Formula (1). In Formula (1), t is elapsed time after the node is brought into the electrically floating state, is a constant with a unit of time, and is a constant greater than or equal to 0.4 and less than or equal to 0.6.

[00001]$\begin{array}{cc}{V}_{\mathrm{FN}}\left(t\right)=V_0{e}^{-{\left(\frac{t}{}\right)}^{}}& \left(1\right)\end{array}$

A display device includes a pixel including a thin film transistor, and an under layer below the thin film transistor. The thin film transistor includes a first gate electrode, a semiconductor layer and a second gate electrode. The semiconductor layer includes a channel region that overlaps at least one of the first gate electrode and the second gate electrode in a plan view. The channel region curves in a thickness direction of the semiconductor layer. The first gate electrode includes a first edge located on the side of an edge of the channel region in a direction of a channel length. The second gate electrode includes a second edge located on the side of the edge of the channel region. The position of the first edge is different from the position of the second edge in the direction of the channel length.

A semiconductor device which includes a transistor having a miniaturized structure is provided. A first insulator is provided over a stack in which a semiconductor, a first conductor, and a second conductor are stacked in this order. Over the first insulator, an etching mask is formed. Using the etching mask, the first insulator and the second conductor are etched until the first conductor is exposed. After etching the first conductor until the semiconductor is exposed so as to form a groove having a smaller width than the second conductor, a second insulator and a third conductor are formed sequentially.