A display panel includes a base substrate, a first transistor, and a second transistor. The first transistor and the second transistor are formed on the base substrate. The first transistor includes a first active layer, a first gate electrode, a first source electrode, and a first drain electrode. The first active layer includes silicon. The second transistor includes a second active layer, a second gate electrode, a second source electrode, and a second drain electrode. The second active layer includes oxide semiconductor. A length of a channel region of the first transistor is L1. Along a direction perpendicular to the base substrate, a distance between the first gate electrode and the first active layer is D1. A length of a channel region of the second transistor is L2. Along the direction perpendicular to the base substrate, a distance between the second gate electrode and the second active layer is D2.

A display device includes two or more transistors in one pixel, and the two or more transistors include a first transistor of which a channel semiconductor layer is polycrystalline silicon, and a second transistor of which a channel semiconductor layer is an oxide semiconductor.

Displays can be fabricated using driver transistors formed with high quality semiconductor channel materials, and switching transistors formed with low quality semiconductor channel materials. The driver transistors can require high forward current to drive emission of the OLED pixels, but might not require very low leakage current. The switching transistors can require low leakage current to allow the pixel capacitor to retain the signal level for accurate OLED device emission, preventing abnormal displays or cross talks.

Provided are a thin film transistor (TFT) substrate, a display device, and a method of forming the TFT. A TFT substrate includes: a first TFT including: a polycrystalline semiconductor (PS) layer, a first gate electrode (GE) overlapping the PS layer, a nitride layer (NL) on the first GE, an oxide layer (OL) on the NL, and a first source electrode and a first drain electrode on the OL, and a second TFT including: a second GE on a same layer as the first GE, a hydrogen collecting layer between the second GE and the NL, an oxide semiconductor (OS) layer on the OL, a second source electrode and a second drain electrode contacting respective sides of the OS layer, wherein the first TFT and the second TFT are disposed on a same substrate, and wherein the NL includes an opening exposing the hydrogen collecting layer of the second TFT.

At least one of a plurality of transistors which are highly integrated in an element is provided with a back gate without increasing the number of manufacturing steps. In an element including a plurality of transistors which are longitudinally stacked, at least a transistor in an upper portion includes a metal oxide having semiconductor characteristics, a same layer as a gate electrode of a transistor in a lower portion is provided to overlap with a channel formation region of the transistor in an upper portion, and part of the same layer as the gate electrode functions as a back gate of the transistor in an upper portion. The transistor in a lower portion which is covered with an insulating layer is subjected to planarization treatment, whereby the gate electrode is exposed and connected to a layer functioning as source and drain electrodes of the transistor in an upper portion.

An object is to provide a deposition method in which a gallium oxide film is formed by a DC sputtering method. Another object is to provide a method for manufacturing a semiconductor device using a gallium oxide film as an insulating layer such as a gate insulating layer of a transistor. An insulating film is formed by a DC sputtering method or a pulsed DC sputtering method, using an oxide target including gallium oxide (also referred to as GaO.sub.X). The oxide target includes GaO.sub.X, and X is less than 1.5, preferably more than or equal to 0.01 and less than or equal to 0.5, further preferably more than or equal to 0.1 and less than or equal to 0.2. The oxide target has conductivity, and sputtering is performed in an oxygen gas atmosphere or a mixed atmosphere of an oxygen gas and a rare gas such as argon.

An active device includes a poly-silicon semiconductor layer, a first insulating layer, a gate electrode, a second insulating layer, a first through hole, an oxide semiconductor layer, a first electrode and a second electrode. The poly-silicon semiconductor layer includes a first doped region, a channel region and a second doped region. The gate electrode is disposed on the first insulating layer covering the poly-silicon semiconductor layer, and corresponds to the channel region. The gate electrode is covered by the second insulating layer, where the first and second insulating layers have a first through hole. The oxide semiconductor layer is disposed on the second insulating layer and corresponds to the gate electrode. The first and second electrodes are oppositely disposed on the oxide semiconductor layer. The oxide semiconductor layer is electrically connected to the second electrode, and to the second doped region via the first through hole.

The present invention provides a display device and a manufacturing method thereof that can simplify manufacturing steps and enhance efficiency in the use of materials, and further, a manufacturing method that can enhance adhesiveness of a pattern. One feature of the invention is that at least one or more patterns needed for manufacturing a display panel, such as a conductive layer forming a wiring or an electrode or a mask for forming a desired pattern is/are formed by a method capable of selectively forming a pattern, thereby manufacturing a display panel.

The present invention provides a TFT substrate structure, comprising a Switching TFT and a Driving TFT, and the Switching TFT comprises a first active layer, and the Driving TFT comprises a second active layer, and the first active layer and the second active layer are made by the same or different materials and the electrical properties of the Switching TFT and the Driving TFT are different. According to the different functions of the different TFTs, the present invention employs different working structures for the Switching TFT and the Driving TFT to respectively implement deposition and photolithography, and employs different materials for the active layers of the Switching TFT and the Driving TFT to differentiate the electrical properties of different TFTs in the TFT substrate. Accordingly, the accurate control to the OLED with lowest cost can be realized.

The present invention provides a TFT substrate structure, comprising a Switching TFT and a Driving TFT, and the Switching TFT comprises a first active layer, and the Driving TFT comprises a second active layer, and the first active layer and the second active layer are made by the same or different materials and the electrical properties of the Switching TFT and the Driving TFT are different. According to the different functions of the different TFTs, the present invention employs different working structures for the Switching TFT and the Driving TFT to respectively implement deposition and photolithography, and employs different materials for the active layers of the Switching TFT and the Driving TFT to differentiate the electrical properties of different TFTs in the TFT substrate. Accordingly, the accurate control to the OLED with lowest cost can be realized.