Abstract: A conventional DRAM needs to be refreshed at an interval of several tens of milliseconds to hold data, which results in large power consumption. In addition, a transistor therein is frequently turned on and off; thus, deterioration of the transistor is also a problem. These problems become significant as the memory capacity increases and transistor miniaturization advances. Another problem is that an increase in memory capacity leads to an increase in the area, despite an attempt at integration through advancement of transistor miniaturization. A transistor is provided which includes an oxide semiconductor and has a trench structure including a trench for a gate electrode and a trench for element isolation. In addition, a plurality of memory elements each including the transistor having a trench structure and including an oxide semiconductor is stacked in a semiconductor device, whereby the circuit area of the semiconductor device can be reduced.

Abstract: An object is to reduce to reduce variation in threshold voltage to stabilize electric characteristics of thin film transistors each using an oxide semiconductor layer. An object is to reduce an off current. The thin film transistor using an oxide semiconductor layer is formed by stacking an oxide semiconductor layer containing insulating oxide over the oxide semiconductor layer so that the oxide semiconductor layer and source and drain electrode layers are in contact with each other with the oxide semiconductor layer containing insulating oxide interposed therebetween; whereby, variation in threshold voltage of the thin film transistors can be reduced and thus the electric characteristics can be stabilized. Further, an off current can be reduced.

Abstract: A conventional DRAM needs to be refreshed at an interval of several tens of milliseconds to hold data, which results in large power consumption. In addition, a transistor therein is frequently turned on and off; thus, deterioration of the transistor is also a problem. These problems become significant as the memory capacity increases and transistor miniaturization advances. A transistor is provided which includes an oxide semiconductor and has a trench structure including a trench for a gate electrode and a trench for element isolation. Even when the distance between a source electrode and a drain electrode is decreased, the occurrence of a short-channel effect can be suppressed by setting the depth of the trench for the gate electrode as appropriate.

Abstract: An intrinsic or substantially intrinsic semiconductor, which has been subjected to a step of dehydration or dehydrogenation and a step of adding oxygen so that the carrier concentration is less than 1×1012/cm3 is used for an oxide semiconductor layer of an insulated gate transistor, in which a channel region is formed. The length of the channel formed in the oxide semiconductor layer is set to 0.2 ?m to 3.0 ?m inclusive and the thicknesses of the oxide semiconductor layer and the gate insulating layer are set to 15 nm to 30 nm inclusive and 20 nm to 50 nm inclusive, respectively, or 15 nm to 100 nm inclusive and 10 nm to 20 nm inclusive, respectively. Consequently, a short-channel effect can be suppressed, and the amount of change in threshold voltage can be less than 0.5 V in the range of the above channel lengths.

Abstract: The reliability of a semiconductor device is increased by suppression of a variation in electric characteristics of a transistor as much as possible. As a cause of a variation in electric characteristics of a transistor including an oxide semiconductor, the concentration of hydrogen in the oxide semiconductor, the density of oxygen vacancies in the oxide semiconductor, or the like can be given. A source electrode and a drain electrode are formed using a conductive material which is easily bonded to oxygen. A channel formation region is formed using an oxide layer formed by a sputtering method or the like under an atmosphere containing oxygen. Thus, the concentration of hydrogen in a stack, in particular, the concentration of hydrogen in a channel formation region can be reduced.

Abstract: An object is to provide a transistor in which light deterioration is suppressed as much as possible and electrical characteristics are stable, and a semiconductor device including the transistor. The attention focuses on the fact that light is reflected by a film used for forming a transistor and multiple interaction occurs. When the optical thickness of the film which causes the reflection is roughly an odd multiple of ?0/4 or roughly an even multiple of ?0/4, reflectance in a wavelength region of light which is absorbed by an oxide semiconductor is increased without a loss of a function of the film with respect to the transistor, whereby the amount of light absorbed by the oxide semiconductor is reduced and an effect of reducing light deterioration is increased.

Abstract: Provided is a field-effect transistor (FET) having small off-state current, which is used in a miniaturized semiconductor integrated circuit. The field-effect transistor includes a thin oxide semiconductor which is formed substantially perpendicular to an insulating surface and has a thickness of greater than or equal to 1 nm and less than or equal to 30 nm, a gate insulating film formed to cover the oxide semiconductor, and a strip-like gate which is formed to cover the gate insulating film and has a width of greater than or equal to 10 nm and less than or equal to 100 nm. In this structure, three surfaces of the thin oxide semiconductor are covered with the gate, so that electrons injected from a source or a drain can be effectively removed, and most of the space between the source and the drain can be a depletion region; thus, off-state current can be reduced.

Abstract: Disclosed is a semiconductor device including: an insulating layer; a source electrode and a drain electrode embedded in the insulating layer; an oxide semiconductor layer in contact and over the insulating layer, the source electrode, and the drain electrode; a gate insulating layer over and covering the oxide semiconductor layer; and a gate electrode over the gate insulating layer, where the upper surfaces of the insulating layer, the source electrode, and the drain electrode exist coplanarly. The upper surface of the insulating layer, which is in contact with the oxide semiconductor layer, has a root-mean-square (RMS) roughness of 1 nm or less, and the difference in height between the upper surface of the insulating layer and the upper surface of the source electrode or the drain electrode is less than 5 nm. This structure contributes to the suppression of defects of the semiconductor device and enables their miniaturization.

Abstract: Disclosed is a semiconductor device including an insulating layer, a source electrode and a drain electrode embedded in the insulating layer, an oxide semiconductor layer in contact with the insulating layer, the source electrode, and the drain electrode, a gate insulating layer covering the oxide semiconductor layer, and a gate electrode over the gate insulating layer. The upper surface of the surface of the insulating layer, which is in contact with the oxide semiconductor layer, has a root-mean-square (RMS) roughness of 1 nm or less. There is a difference in height between an upper surface of the insulating layer and each of an upper surface of the source electrode and an upper surface of the drain electrode. The difference in height is preferably 5 nm or more. This structure contributes to the suppression of defects of the semiconductor device and enables their miniaturization.

Abstract: A semiconductor device which includes an oxide semiconductor layer, a source electrode and a drain electrode electrically connected to the oxide semiconductor layer, a gate insulating layer covering the oxide semiconductor layer, the source electrode, and the drain electrode, and a gate electrode over the gate insulating layer is provided. The thickness of the oxide semiconductor layer is greater than or equal to 1 nm and less than or equal to 10 nm. The gate insulating layer satisfies a relation where ?r/d is greater than or equal to 0.08 (nm?1) and less than or equal to 7.9 (nm?1) when the relative permittivity of a material used for the gate insulating layer is ?r and the thickness of the gate insulating layer is d. The distance between the source electrode and the drain electrode is greater than or equal to 10 nm and less than or equal to 1 ?m.

Abstract: An object is to reduce to reduce variation in threshold voltage to stabilize electric characteristics of thin film transistors each using an oxide semiconductor layer. An object is to reduce an off current. The thin film transistor using an oxide semiconductor layer is formed by stacking an oxide semiconductor layer containing insulating oxide over the oxide semiconductor layer so that the oxide semiconductor layer and source and drain electrode layers are in contact with each other with the oxide semiconductor layer containing insulating oxide interposed therebetween; whereby, variation in threshold voltage of the thin film transistors can be reduced and thus the electric characteristics can be stabilized. Further, an off current can be reduced.

Abstract: In a transistor including an oxide semiconductor film, a metal oxide film which has a function of preventing electrification and covers a source electrode and a drain electrode is formed in contact with the oxide semiconductor film, and then, heat treatment is performed. Through the heat treatment, impurities such as hydrogen, moisture, a hydroxyl group, or hydride are intentionally removed from the oxide semiconductor film, whereby the oxide semiconductor film is highly purified. By providing the metal oxide film, generation of a parasitic channel on the back channel side of the oxide semiconductor film in the transistor can be prevented.

Abstract: The light-emitting display device comprises first and second thin film transistors. The first thin film transistor includes a first gate electrode; a first oxide semiconductor film; and a first electrode and a second electrode which are electrically connected to the first oxide semiconductor film. The second thin film transistor includes a second gate electrode electrically connected to the second electrode; a second oxide semiconductor film; a third electrode; a light-emitting layer and a fourth electrode over the second oxide semiconductor film. A work function of the second oxide semiconductor film is higher than a work function of the fourth electrode.

Abstract: Disclosed is a semiconductor device including: an insulating layer; a source electrode and a drain electrode embedded in the insulating layer; an oxide semiconductor layer in contact and over the insulating layer, the source electrode, and the drain electrode; a gate insulating layer over and covering the oxide semiconductor layer; and a gate electrode over the gate insulating layer, where the upper surfaces of the insulating layer, the source electrode, and the drain electrode exist coplanarly. The upper surface of the insulating layer, which is in contact with the oxide semiconductor layer, has a root-mean-square (RMS) roughness of 1 nm or less, and the difference in height between the upper surface of the insulating layer and the upper surface of the source electrode or the drain electrode is less than 5 nm. This structure contributes to the suppression of defects of the semiconductor device and enables their miniaturization.

Abstract: An intrinsic or substantially intrinsic semiconductor, which has been subjected to a step of dehydration or dehydrogenation and a step of adding oxygen so that the carrier concentration is less than 1×1012/cm3 is used for an oxide semiconductor layer of an insulated gate transistor, in which a channel region is formed. The length of the channel formed in the oxide semiconductor layer is set to 0.2 ?m to 3.0 ?m inclusive and the thicknesses of the oxide semiconductor layer and the gate insulating layer are set to 15 nm to 30 nm inclusive and 20 nm to 50 nm inclusive, respectively, or 15 nm to 100 nm inclusive and 10 nm to 20 nm inclusive, respectively. Consequently, a short-channel effect can be suppressed, and the amount of change in threshold voltage can be less than 0.5 V in the range of the above channel lengths.

Abstract: Disclosed is a semiconductor device including an insulating layer, a source electrode and a drain electrode embedded in the insulating layer, an oxide semiconductor layer in contact with the insulating layer, the source electrode, and the drain electrode, a gate insulating layer covering the oxide semiconductor layer, and a gate electrode over the gate insulating layer. The upper surface of the surface of the insulating layer, which is in contact with the oxide semiconductor layer, has a root-mean-square (RMS) roughness of 1 nm or less. There is a difference in height between an upper surface of the insulating layer and each of an upper surface of the source electrode and an upper surface of the drain electrode. The difference in height is preferably 5 nm or more. This structure contributes to the suppression of defects of the semiconductor device and enables their miniaturization.

Abstract: A semiconductor device which includes an oxide semiconductor layer, a source electrode and a drain electrode electrically connected to the oxide semiconductor layer, a gate insulating layer covering the oxide semiconductor layer, the source electrode, and the drain electrode, and a gate electrode over the gate insulating layer is provided. The thickness of the oxide semiconductor layer is greater than or equal to 1 nm and less than or equal to 10 nm. The gate insulating layer satisfies a relation where ?r/d is greater than or equal to 0.08 (nm?1) and less than or equal to 7.9 (nm?1) when the relative permittivity of a material used for the gate insulating layer is ?r and the thickness of the gate insulating layer is d. The distance between the source electrode and the drain electrode is greater than or equal to 10 nm and less than or equal to 1 ?m.

Abstract: To suppress deterioration in electrical characteristics in a transistor including an oxide semiconductor layer or a semiconductor device including the transistor. In a transistor in which a channel layer is formed using an oxide semiconductor, a silicon layer is provided in contact with a surface of the oxide semiconductor layer. Further, the silicon layer is provided in contact with at least a region of the oxide semiconductor layer, in which a channel is formed, and a source electrode layer and a drain electrode layer are provided in contact with regions of the oxide semiconductor layer, over which the silicon layer is not provided.

Abstract: An object is to provide a semiconductor device including an oxide semiconductor in which miniaturization is achieved while favorable characteristics are maintained. The semiconductor includes an oxide semiconductor layer, a source electrode and a drain electrode in contact with the oxide semiconductor layer, a gate electrode overlapping with the oxide semiconductor layer, a gate insulating layer provided between the oxide semiconductor layer and the gate electrode, and an insulating layer provided in contact with the oxide semiconductor layer. A side surface of the oxide semiconductor layer is in contact with the source electrode or the drain electrode. An upper surface of the oxide semiconductor layer overlaps with the source electrode or the drain electrode with the insulating layer interposed between the oxide semiconductor layer and the source electrode or the drain electrode.

Abstract: A thin film transistor is provided, which includes a gate insulating layer covering a gate electrode, a microcrystalline semiconductor layer provided over the gate insulating layer, an amorphous semiconductor layer overlapping the microcrystalline semiconductor layer and the gate insulating layer, and a pair of impurity semiconductor layers which are provided over the amorphous semiconductor layer and to which an impurity element imparting one conductivity type is added to form a source region and a drain region. The gate insulating layer has a step adjacent to a portion in contact with an end portion of the microcrystalline semiconductor layer. A second thickness of the gate insulating layer in a portion outside the microcrystalline semiconductor layer is smaller than a first thickness thereof in a portion in contact with the microcrystalline semiconductor layer.