In a transistor including an oxide semiconductor film, field-effect mobility and reliability are improved. A semiconductor device includes a gate electrode, an insulating film over the gate electrode, an oxide semiconductor film over the insulating film, and a pair of electrodes over the oxide semiconductor film. The oxide semiconductor film includes a first oxide semiconductor film, a second oxide semiconductor film over the first oxide semiconductor film, and a third oxide semiconductor film over the second oxide semiconductor film. The first oxide semiconductor film, the second oxide semiconductor film, and the third oxide semiconductor film include the same elements. The second oxide semiconductor film includes a region having a higher carrier density than the first oxide semiconductor film and the third oxide semiconductor film.

To provide a transistor with favorable electrical characteristics, a transistor with stable electrical characteristics, or a highly integrated semiconductor device. By covering a side surface of an oxide semiconductor layer in which a channel is formed with an oxide semiconductor layer, diffusion of impurities into the inside from the side surface of the oxide semiconductor layer is prevented. By forming a gate electrode in a damascene process, miniaturization and high density of a transistor are achieved. By providing a protective layer covering a gate electrode over the gate electrode, the reliability of the transistor is increased.

A semiconductor device that can operate at high speed or having high strength against stress is provided. One embodiment of the present invention is a semiconductor device including a semiconductor film including a channel formation region and a pair of impurity regions between which the channel formation region is positioned; a gate electrode overlapping side and top portions of the channel formation region with an insulating film positioned between the gate electrode and the side and top portions; and a source electrode and a drain electrode in contact with side and top portions of the pair of impurity regions.

Provided is an in-wiring-layer active element (component) which allows for electrical isolation between a gate electrode and a channel in a top gate structure. A semiconductor device includes a first wiring layer, a second wiring layer, and a semiconductor element. The first wiring layer has a first interlayer insulating layer, and a first wire embedded in the first interlayer insulating layer. The second wiring layer has a second interlayer insulating layer, and second wires embedded in the second interlayer insulating layer. The semiconductor element is provided at least in the second wiring layer. The semiconductor element includes a semiconductor layer provided in the second wiring layer, a gate insulating film provided in contact with the semiconductor layer, a gate electrode provided on the opposite side of the semiconductor layer via the first gate insulating film, and a first side wall film provided over a side surface of the semiconductor layer.

The present invention proposes a TFT switch and a method for manufacturing the same. The TFT switch includes a gate, a drain, a source, a semiconductor layer and a fourth electrode. The drain is connected to a first signal, the gate is connected to a control signal to control the switch on or off. The source outputs the first signal when the switch turns on. The fourth electrode and the gate are respectively located at two sides of the semiconductor layer. The fourth electrode is conductive and is selectively coupled to different voltage levels, thereby reducing leakage current in a channel to improve switch characteristic when the switch turns off.

To provide a semiconductor device that includes an oxide semiconductor and is miniaturized while keeping good electrical properties. In the semiconductor device, an oxide semiconductor layer filling a groove is surrounded by insulating layers including an aluminum oxide film containing excess oxygen. Excess oxygen contained in the aluminum oxide film is supplied to the oxide semiconductor layer, in which a channel is formed, by heat treatment in a manufacturing process of the semiconductor device. Moreover, the aluminum oxide film forms a barrier against oxygen and hydrogen, which inhibits the removal of oxygen from the oxide semiconductor layer surrounded by the insulating layers including an aluminum oxide film and the entry of impurities such as hydrogen in the oxide semiconductor layer. Thus, a highly purified intrinsic oxide semiconductor layer can be obtained. The threshold voltage is controlled effectively by gate electrode layers formed over and under the oxide semiconductor layer.

A display device includes a substrate, a first insulating layer having a first side wall, an oxide semiconductor layer on the first side wall, a gate electrode facing the oxide semiconductor layer, a gate insulating layer between the oxide semiconductor layer and the gate electrode, a first transparent conductive layer between the oxide semiconductor layer and the substrate, the first transparent conductive layer being connected with a first portion of the oxide semiconductor layer, a first electrode on the first insulating layer on the side opposite to the substrate, the first electrode being connected with a second portion of the oxide semiconductor layer, and a second transparent conductive layer connected with the first transparent conductive layer, the second transparent conductive layer forming the same layer with the first transparent conductive layer.

An enhancement-mode n-type field effect transistor is disclosed to have a metal oxide channel layer, a gate dielectric layer, a gate electrode, a source electrode, and a drain electrode. The metal oxide channel layer has a material selected from SnO.sub.2, ITO, ZnO, SnO.sub.2 and In2O.sub.3. The metal oxide channel layer has a thickness less than a threshold value to exhibit pinch-off behavior in transfer characteristics and has a mobility trend without saturation under positive operational voltage.

A semiconductor device (100) includes, on a substrate, a plurality of oxide semiconductor TFTs including a first gate electrode (12), a first insulating layer (20) which is in contact with the first gate electrode, an oxide semiconductor layer (16) arranged so as to oppose the first gate electrode via the first insulating layer, and a source electrode (14) and a drain electrode (15) which are connected with the oxide semiconductor layer, and an organic insulating layer (24) covering only some of the plurality of oxide semiconductor TFTs, wherein the plurality of oxide semiconductor TFTs include a first TFT (5A) which is covered with the organic insulating layer and a second TFT (5B) which is not covered with the organic insulating layer, and the second TFT includes a second gate electrode (17) arranged so as to oppose the oxide semiconductor layer via a second insulating layer (22), when viewed in a direction normal to the substrate, the second gate electrode (17) being arranged so as to overlap with at least part of the first gate electrode with the oxide semiconductor layer interposed therebetween.

The TFT array substrate and the manufacturing method thereof are disclosed. The dual-layer structure having the bottom gate electrode, including the metal layer and the transparent metal oxide layer, and the common electrode, including the common electrode, may be formed by the same masking process. In this way, the number of masking processes may be decreased so as to enhance the manufacturing efficiency and the cost.