A thin film transistor array substrate includes a bottom gate disposed on a substrate and a bottom gate insulating layer covering the bottom gate, a semiconductor oxide layer disposed on the bottom gate insulating layer and an etch blocking layer covering the semiconductor oxide layer and including a first via, a drain disposed on the etch blocking layer and contacting with the semiconductor oxide layer through the first via and an insulating protection layer covering the drain, a second via arranged in the insulating protection layer, the etch blocking layer and the bottom gate insulating layer, a top gate disposed on insulating protection layer and contacting with the bottom gate through the second via. A method for manufacturing the thin film transistor array substrate is also disclosed. The thin film transistor prevents the threshold voltage thereof from being drifted in a case of negative bias illumination stress (NBIS).

With an image sensor in which the amplifier circuit is disposed at each pixel, there is such an issue that the threshold voltage of the transistor fluctuates so that the signal voltage fluctuates because a voltage is continuously applied between the source and the gate of the transistor at all times when using the amorphous thin film semiconductor as the transistor that constitutes an amplifier circuit. The gate-source potential of the TFT that constitutes the amplifier circuit is controlled so that the gate terminal voltage becomes smaller than the source terminal voltage in an integrating period where the pixels accumulate the signals, and controlled so that the gate terminal voltage becomes larger than the source terminal voltage in a readout period where the pixels output the signals.

A change in electrical characteristics is suppressed and reliability in a semiconductor device using a transistor including an oxide semiconductor is improved. Oxygen is introduced into a surface of an insulating film, and then, an oxide semiconductor, a layer which is capable of blocking oxygen, a gate insulating film, and other films which composes a transistor are formed. For at least one of the first gate insulating film and the insulating film, three signals in Electron Spin Resonance Measurement are each observed in a certain range of g-factor. Reducing the sum of the spin densities of the signals will improve reliability of the semiconductor device.

Provided is a transistor containing a semiconductor with low density of defect states, a transistor having a small subthreshold swing value, a transistor having a small short-channel effect, a transistor having normally-off electrical characteristics, a transistor having a low leakage current in an off state, a transistor having excellent electrical characteristics, a transistor having high reliability, or a transistor having excellent frequency characteristics. An insulator is formed, a layer is formed over the insulator, oxygen is added to the insulator through the layer, the layer is removed, an oxide semiconductor is formed over the insulator to which the oxygen is added, and a semiconductor element is formed using the oxide semiconductor.

An object is to control composition and a defect of an oxide semiconductor, another object is to increase a field effect mobility of a thin film transistor and to obtain a sufficient on-off ratio with a reduced off current. A solution is to employ an oxide semiconductor whose composition is represented by InMO.sub.3(ZnO).sub.m, where M is one or a plurality of elements selected from Ga, Fe, Ni, Mn, Co, and Al, and m is preferably a non-integer number of greater than 0 and less than 1. The concentration of Zn is lower than the concentrations of In and M. The oxide semiconductor has an amorphous structure. Oxide and nitride layers can be provided to prevent pollution and degradation of the oxide semiconductor.

An object is to obtain a semiconductor device having a high sensitivity in detecting signals and a wide dynamic range, using a thin film transistor in which an oxide semiconductor layer is used. An analog circuit is formed with the use of a thin film transistor including an oxide semiconductor which has a function as a channel formation layer, has a hydrogen concentration of 510.sup.19 atoms/cm.sup.3 or lower, and substantially functions as an insulator in the state where no electric field is generated. Thus, a semiconductor device having a high sensitivity in detecting signals and a wide dynamic range can be obtained.

A semiconductor device in which parasitic capacitance is reduced is provided. A first oxide insulating layer and a first oxide semiconductor layer are sequentially formed over a first insulating layer. A first conductive layer is formed over the first oxide semiconductor layer and etched to form a second conductive layer. The first oxide insulating layer and the first oxide semiconductor layer are etched with the second conductive layer as a mask to form a second oxide insulating layer and a second oxide semiconductor layer. A planarized insulating layer is formed over the first insulating layer and the second conductive layer. A second insulating layer, a source electrode layer, and a drain electrode layer are formed by etching the planarized insulating layer and the second conductive layer. A third oxide insulating layer, a gate insulating layer, and a gate electrode layer are formed over the second oxide semiconductor layer.

An object is to improve field effect mobility of a thin film transistor using an oxide semiconductor. Another object is to suppress increase in off current even in a thin film transistor with improved field effect mobility. In a thin film transistor using an oxide semiconductor layer, by forming a semiconductor layer having higher electrical conductivity and a smaller thickness than the oxide semiconductor layer between the oxide semiconductor layer and a gate insulating layer, field effect mobility of the thin film transistor can be improved, and increase in off current can be suppressed.

A manufacturing method of a semiconductor device comprises the steps of: providing a transparent substrate; forming a gate electrode on the transparent substrate; forming a gate insulation layer covering the gate electrode; forming an oxide semiconductor layer on the gate insulation layer and at least partially over the gate electrode; forming an etching stop layer over the gate electrode and at least covering a part of the oxide semiconductor layer, wherein the etching stop layer includes an opening; forming an electrode layer at the opening and on a part of the etching stop layer; and applying a low-resistance treatment to a part of the oxide semiconductor layer uncovered by the etching stop layer and the electrode layer to form a pixel electrode.

A display device includes a display element, a transistor configured to drive the display element, the transistor including a channel region, and a retention capacitor. An oxide semiconductor film is provided in areas across the transistor and the retention capacitor, the oxide semiconductor film including a first region formed in the channel region of the transistor, and a second region having a lower resistance than that of the first region. The second region is formed in the areas of the transistor and retention capacitor other than in the channel region.