Abstract: An object is to provide a memory device including a memory element that can be operated without problems by a thin film transistor with a low off-state current. Provided is a memory device in which a memory element including at least one thin film transistor that includes an oxide semiconductor layer is arranged as a matrix. The thin film transistor including an oxide semiconductor layer has a high field effect mobility and low off-state current, and thus can be operated favorably without problems. In addition, the power consumption can be reduced. Such a memory device is particularly effective in the case where the thin film transistor including an oxide semiconductor layer is provided in a pixel of a display device because the memory device and the pixel can be formed over one substrate.

Abstract: To reduce a leakage current of a transistor so that malfunction of a logic circuit can be suppressed. The logic circuit includes a transistor which includes an oxide semiconductor layer having a function of a channel formation layer and in which an off current is 1×10?13 A or less per micrometer in channel width. A first signal, a second signal, and a third signal that is a clock signal are input as input signals. A fourth signal and a fifth signal whose voltage states are set in accordance with the first to third signals which have been input are output as output signals.

Abstract: The band tail state and defects in the band gap are reduced as much as possible, whereby optical absorption of energy which is in the vicinity of the band gap or less than or equal to the band gap is reduced. In that case, not by merely optimizing conditions of manufacturing an oxide semiconductor film, but by making an oxide semiconductor to be a substantially intrinsic semiconductor or extremely close to an intrinsic semiconductor, defects on which irradiation light acts are reduced and the effect of light irradiation is reduced essentially. That is, even in the case where light with a wavelength of 350 nm is delivered at 1×1013 photons/cm2·sec, a channel region of a transistor is formed using an oxide semiconductor, in which the absolute value of the amount of the variation in the threshold voltage is less than or equal to 0.65 V.

Abstract: To reduce a leakage current of a transistor so that malfunction of a logic circuit can be suppressed, a semiconductor device includes a first conductive layer over an insulating layer, a semiconductor layer over the first conductive layer, a second conductive layer over the semiconductor layer, a gate insulating layer over the second conductive layer, and a gate electrode over the gate insulating layer. The semiconductor device may further include wiring layers. The logic circuit includes a transistor which includes an oxide semiconductor layer having a function of a channel formation layer and in which an off current is 1×10?13 A or less per micrometer in channel width, and may be 1×10?17 A or less per micrometer. A first signal, a second signal, and a third signal that is a clock signal are input as input signals. A fourth signal and a fifth signal whose voltage states are set in accordance with the first to third signals which have been input are output as output signals.

Abstract: A change in electrical characteristics is suppressed and reliability in a semiconductor device using a transistor including an oxide semiconductor is improved. The semiconductor device includes an oxide semiconductor film over an insulating surface, an antioxidant film over the insulating surface and the oxide semiconductor film, a pair of electrodes in contact with the antioxidant film, a gate insulating film over the pair of electrodes, and a gate electrode which is over the gate insulating film and overlaps with the oxide semiconductor film. In the antioxidant film, a width of a region overlapping with the pair of electrodes is longer than a width of a region not overlapping with the pair of electrodes.

Abstract: In a liquid crystal display device including a plurality of pixels in a display portion and configured to performed display in a plurality of frame periods, each of the frame periods includes a writing period and a holding period, and after an image signal is input to each of the plurality of pixels in the writing period, a transistor included in each of the plurality of pixels is turned off and the image signal is held for at least 30 seconds in the holding period. The pixel includes a semiconductor layer including an oxide semiconductor layer, and the oxide semiconductor layer has a carrier concentration of less than 1×1014/cm3.

Abstract: To suppress a decrease in on-state current in a semiconductor device including an oxide semiconductor. A semiconductor device includes an insulating film containing silicon, an oxide semiconductor film over the insulating film, a gate insulating film containing silicon over the oxide semiconductor film, a gate electrode which is over the gate insulating film and overlaps with at least the oxide semiconductor film, and a source electrode and a drain electrode which are electrically connected to the oxide semiconductor film. In the semiconductor device, the oxide semiconductor film which overlaps with at least the gate electrode includes a region in which a concentration of silicon distributed from an interface with the insulating film is lower than or equal to 1.1 at. %. In addition, a concentration of silicon contained in a remaining portion of the oxide semiconductor film except the region is lower than the concentration of silicon contained in the region.

Abstract: It is an object to provide a manufacturing method of a structure of a thin film transistor including an oxide semiconductor film, in which threshold voltage at which a channel is formed is positive and as close to 0 V as possible. A protective insulating layer is formed to cover a thin film transistor including an oxide semiconductor layer that is dehydrated or dehydrogenated by first heat treatment, and second heat treatment at a temperature that is lower than that of the first heat treatment, in which the increase and decrease in temperature are repeated plural times, is performed, whereby a thin film transistor including an oxide semiconductor layer, in which threshold voltage at which a channel is formed is positive and as close to 0 V as possible without depending on the channel length, can be manufactured.

Abstract: An object is to reduce leakage current and parasitic capacitance of a transistor used for an LSI, a CPU, or a memory. A semiconductor integrated circuit such as an LSI, a CPU, or a memory is manufactured using a thin film transistor in which a channel formation region is formed using an oxide semiconductor which becomes an intrinsic or substantially intrinsic semiconductor by removing impurities which serve as electron donors (donors) from the oxide semiconductor and has larger energy gap than that of a silicon semiconductor. With use of a thin film transistor using a highly purified oxide semiconductor layer with sufficiently reduced hydrogen concentration, a semiconductor device with low power consumption due to leakage current can be realized.

Abstract: 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.

Abstract: A semiconductor device includes a first oxide semiconductor film, a second oxide semiconductor film over the first oxide semiconductor film, a source electrode in contact with the second oxide semiconductor film, a drain electrode in contact with the second oxide semiconductor film, a metal oxide film over the second oxide semiconductor film, the source electrode, and the drain electrode, a gate insulating film over the metal oxide film, and a gate electrode over the gate insulating film. The metal oxide film contains M (M represents Ti, Ga, Y, Zr, La, Ce, Nd, or Hf) and Zn. The metal oxide film includes a portion where x/(x+y) is greater than 0.67 and less than or equal to 0.99 when a target has an atomic ratio of M:Zn=x:y.

Abstract: An object is to provide a method for manufacturing a semiconductor device without exposing a specific layer to moisture or the like at all. A thin film element is manufactured in such a manner that a first film, a second film, and a third film are stacked in this order; a resist mask is formed over the third film; a mask layer is formed by etching the third film with the use of the resist mask; the resist mask is removed; a second layer and a first layer are formed by performing dry etching on the second film and the first film with the use of the mask layer; a fourth film is formed to cover at least the second layer and the first layer; and sidewall layers are formed to cover at least the entire side surfaces of the first layer by performing etch back on the fourth film.

Abstract: A crystalline oxide semiconductor film which can be used as a semiconductor film of a transistor or the like is provided. In particular, a crystalline oxide semiconductor film with less defects such as grain boundaries is provided. One embodiment of the present invention is a crystalline oxide semiconductor film which is provided over a substrate and has a region including five or less areas where a transmission electron diffraction pattern showing discontinuous points is observed when an observation area is changed one-dimensionally within a range of 700 nm, using a transmission electron diffraction apparatus with an electron beam having a probe diameter of 1 nm.

Abstract: Reducing hydrogen concentration in a channel formation region of an oxide semiconductor is important in stabilizing threshold voltage of a transistor including an oxide semiconductor and improving reliability. Hence, hydrogen is attracted from the oxide semiconductor and trapped in a region of an insulating film which overlaps with a source region and a drain region of the oxide semiconductor. Impurities such as argon, nitrogen, carbon, phosphorus, or boron are added to the region of the insulating film which overlaps with the source region and the drain region of the oxide semiconductor, thereby generating a defect. Hydrogen in the oxide semiconductor is attracted to the defect in the insulating film. The defect in the insulating film is stabilized by the presence of hydrogen.

Abstract: It is an object to provide a manufacturing method of a structure of a thin film transistor including an oxide semiconductor film, in which threshold voltage at which a channel is formed is positive and as close to 0 V as possible. A protective insulating layer is formed to cover a thin film transistor including an oxide semiconductor layer that is dehydrated or dehydrogenated by first heat treatment, and second heat treatment at a temperature that is lower than that of the first heat treatment, in which the increase and decrease in temperature are repeated plural times, is performed, whereby a thin film transistor including an oxide semiconductor layer, in which threshold voltage at which a channel is formed is positive and as close to 0 V as possible without depending on the channel length, can be manufactured.

Abstract: An object is to provide a memory device including a memory element that can be operated without problems by a thin film transistor with a low off-state current. Provided is a memory device in which a memory element including at least one thin film transistor that includes an oxide semiconductor layer is arranged as a matrix. The thin film transistor including an oxide semiconductor layer has a high field effect mobility and low off-state current, and thus can be operated favorably without problems. In addition, the power consumption can be reduced. Such a memory device is particularly effective in the case where the thin film transistor including an oxide semiconductor layer is provided in a pixel of a display device because the memory device and the pixel can be formed over one substrate.

Abstract: A change in electrical characteristics is suppressed and reliability in a semiconductor device using a transistor including an oxide semiconductor is improved. The semiconductor device includes an oxide semiconductor film over an insulating surface, an antioxidant film over the insulating surface and the oxide semiconductor film, a pair of electrodes in contact with the antioxidant film, a gate insulating film over the pair of electrodes, and a gate electrode which is over the gate insulating film and overlaps with the oxide semiconductor film. In the antioxidant film, a width of a region overlapping with the pair of electrodes is longer than a width of a region not overlapping with the pair of electrodes.

Abstract: When a transistor having bottom gate bottom contact structure is manufactured, for example, a conductive layer constituting a source and a drain has a three-layer structure and two-step etching is performed. In the first etching process, an etching method in which the etching rates for at least the second film and the third film are high is employed, and the first etching process is performed until at least the first film is exposed. In the second etching process, an etching method in which the etching rate for the first film is higher than that in the first etching process and the etching rate for a “layer provided below and in contact with the first film” is lower than that in the first etching process is employed. The side wall of the second film is slightly etched when a resist mask is removed after the second etching process.

Abstract: The concentration of impurity elements included in an oxide semiconductor film in the vicinity of a gate insulating film is reduced. Further, crystallinity of the oxide semiconductor film in the vicinity of the gate insulating film is improved. A semiconductor device includes an oxide semiconductor film over a substrate, a source electrode and a drain electrode over the oxide semiconductor film, a gate insulating film which includes an oxide containing silicon and is formed over the oxide semiconductor film, and a gate electrode over the gate insulating film. The oxide semiconductor film includes a region in which the concentration of silicon is lower than or equal to 1.0 at. %, and at least the region includes a crystal portion.

Abstract: It is an object to manufacture a highly reliable display device using a thin film transistor having favorable electric characteristics and high reliability as a switching element. In a bottom gate thin film transistor including an amorphous oxide semiconductor, an oxide conductive layer having a crystal region is formed between an oxide semiconductor layer which has been dehydrated or dehydrogenated by heat treatment and each of a source electrode layer and a drain electrode layer which are formed using a metal material. Accordingly, contact resistance between the oxide semiconductor layer and each of the source electrode layer and the drain electrode layer can be reduced; thus, a thin film transistor having favorable electric characteristics and a highly reliable display device using the thin film transistor can be provided.