An object is to provide a structure of a transistor which has a channel formation region formed using an oxide semiconductor and a positive threshold voltage value, which enables a so-called normally-on switching element. The transistor includes an oxide semiconductor stack in which at least a first oxide semiconductor layer and a second oxide semiconductor layer with different energy gaps are stacked and a region containing oxygen in excess of its stoichiometric composition ratio is provided.

A preparation method of a poly-silicon thin film transistor (TFT) array substrate and an array substrate thereof are provided. The preparation method includes: forming a photoresist layer on a poly-silicon layer, and exposing and developing the photoresist layer with a gray tone mask to form patterns of a photoresist completely-reserved region, a photoresist partially-reserved regions and a photoresist completely-removed region; removing part of the poly-silicon layer located in the photoresist completely-removed region, to form patterns of active layers; ashing the photoresist so as to expose part of the active layer located in the photoresist partially-reserved regions and inject P+ions of high concentration into the part of the active layer, to form doping regions of patterns of source-drain electrodes of a P-type TFT; and stripping off remaining photoresist.

There is provided a thin film transistor having improved reliability. A gate electrode includes a first gate electrode having a taper portion and a second gate electrode with a width narrower than the first gate electrode. A semiconductor layer is doped with phosphorus of a low concentration through the first gate electrode. In the semiconductor layer, two kinds of n.sup.-type impurity regions are formed between a channel formation region and n.sup.+-type impurity regions. Some of the n.sup.-type impurity regions overlap with a gate electrode, and the other n.sup.-type impurity regions do not overlap with the gate electrode. Since the two kinds of n.sup.-type impurity regions are formed, an off current can be reduced, and deterioration of characteristics can be suppressed.

The present disclosure provides a TFT, a method for manufacturing the same, an array substrate and a display device, so as to effectively reduce a TFT edge leakage current I.sub.OFF (edge). The TFT includes an active layer and a silicon oxide layer arranged at a lateral side of the active layer.

The present disclosure provides a method for forming a transistor, including: forming a base structure, containing a first gate structure, an active layer covering the first gate structure, and an insulating structure in the active layer; forming a second gate structure on the active layer; forming a source-drain region, including a source region and a drain region in the active layer each on a different side of the second gate structure; and forming a first interlayer dielectric layer covering the base structure and the second gate structure. The method also includes: forming a first contact hole that exposes the first gate structure by etching the first interlayer dielectric layer and the insulating structure; and forming a second contact hole that exposes the second gate structure and a third contact hole that exposes the drain region by etching the first interlayer dielectric layer.

In a semiconductor device including an oxide semiconductor, a change in electrical characteristics is suppressed and reliability is improved. A miniaturized transistor including an oxide semiconductor is provided. A method for manufacturing a semiconductor device including an oxide semiconductor film includes the following steps: forming an oxide semiconductor film; forming an insulating film over the oxide semiconductor film; forming a conductive film over the insulating film; forming a first protective film over the conductive film; and forming a second protective film over the first protective film. The first protective film, the conductive film, and the insulating film are processed using the second protective film as a mask. After the second protective film is removed, the conductive film and the insulating film are processed using the first protective film as a mask to have a smaller area than that of the second protective film.

A reduction in contaminating impurities in a TFT, and a TFT which is reliable, is obtained in a semiconductor device which uses the TFT. By removing contaminating impurities residing in a film interface of the TFT using a solution containing fluorine, a reliable TFT can be obtained.

According to one embodiment, a method of manufacturing a semiconductor device comprises forming a semiconductor layer on a substrate, forming a first insulating film on the semiconductor layer, forming a metal layer on the first insulating film, forming a first portion and a second portion in the metal layer, implanting an impurity into the semiconductor layer by using the first portion and the second portion as masks, forming a gate electrode by reducing the second portion in addition to removing the first portion, and implanting an impurity into the semiconductor layer by using the gate electrode as a mask.

An array substrate includes a substrate and data lines and scan lines arranged on the substrate. The data lines and the scan lines define plural pixel regions. A thin film transistor is arranged in each pixel region and includes a gate electrode, a source electrode, a drain electrode, and an active region. The gate electrode is arranged above the active region. The source electrode and the drain electrode are arranged at two opposite sides of the active region respectively. A light shielding metal layer is further arranged in each pixel region. The light shielding metal layer and the data lines are arranged in the same layer on the substrate. The light shielding metal layer is arranged under the active region and at least partially overlaps with the active region. The data line is close to the source electrode and does not overlap with the active region at least partially.

A variable capacitor is formed from a pair of electrodes and a dielectric interposed between the electrodes over a substrate, and an external input is detected by changing capacitance of the variable capacitor by a physical or electrical force. Specifically, a variable capacitor and a sense amplifier are provided over the same substrate, and the sense amplifier reads the change of capacitance of the variable capacitor and transmits a signal in accordance with the input to a control circuit.