A novel metal oxide is provided. The metal oxide has a plurality of energy gaps, and includes a first region having a high energy level of a conduction band minimum and a second region having an energy level of a conduction band minimum lower than that of the first region. The second region comprises more carriers than the first region. A difference between the energy level of the conduction band minimum of the first region and the energy level of the conduction band minimum of the second region is 0.2 eV or more. The energy gap of the first region is greater than or equal to 3.3 eV and less than or equal to 4.0 eV and the energy gap of the second region is greater than or equal to 2.2 eV and less than or equal to 2.9 eV.

An oxide semiconductor layer which is intrinsic or substantially intrinsic and includes a crystalline region in a surface portion of the oxide semiconductor layer is used for the transistors. An intrinsic or substantially intrinsic semiconductor from which an impurity which is to be an electron donor (donor) is removed from an oxide semiconductor and which has a larger energy gap than a silicon semiconductor is used. Electrical characteristics of the transistors can be controlled by controlling the potential of a pair of conductive films which are provided on opposite sides from each other with respect to the oxide semiconductor layer, each with an insulating film arranged therebetween, so that the position of a channel formed in the oxide semiconductor layer is determined.

An object is to improve reliability of a light-emitting device. A light-emitting device has a driver circuit portion including a transistor for a driver circuit and a pixel portion including a transistor for a pixel over one substrate. The transistor for the driver circuit and the transistor for the pixel are inverted staggered transistors each including an oxide semiconductor layer in contact with part of an oxide insulating layer. In the pixel portion, a color filter layer and a light-emitting element are provided over the oxide insulating layer. In the transistor for the driver circuit, a conductive layer overlapping with a gate electrode layer and the oxide semiconductor layer is provided over the oxide insulating layer. The gate electrode layer, a source electrode layer, and a drain electrode layer are formed using metal conductive films.

A novel memory device is provided. The memory device includes a plurality of memory cells, and one memory cell includes a first transistor and a second transistor. One of a source and a drain of the first transistor is electrically connected to a gate of the second transistor through a node SN. Data written through the first transistor is retained at the node SN. When an OS transistor is used as the first transistor, formation of a storage capacitor is not needed. A region with a low dielectric constant is provided outside the memory cell, whereby noise from the outside is reduced and stable operation is achieved.

It is an object to provide a highly reliable semiconductor device including a thin film transistor with stable electric characteristics. In a semiconductor device including an inverted staggered thin film transistor whose semiconductor layer is an oxide semiconductor layer, a buffer layer is provided over the oxide semiconductor layer. The buffer layer is in contact with a channel formation region of the semiconductor layer and source and drain electrode layers. A film of the buffer layer has resistance distribution. A region provided over the channel formation region of the semiconductor layer has lower electrical conductivity than the channel formation region of the semiconductor layer, and a region in contact with the source and drain electrode layers has higher electrical conductivity than the channel formation region of the semiconductor layer.

An integrated circuit structure comprises one or more backend-of-line (BEOL) interconnects formed over a first ILD layer. An etch stop layer is over the one or more BEOL interconnects, the etch stop layer having a plurality of vias that are in contact with the one or more BEOL interconnects. An array of BEOL thin-film-transistors (TFTs) is over the etch stop layer, wherein adjacent ones of the BEOL TFTs are separated by isolation trench regions. The TFTs are aligned with at least one of the plurality of vias to connect to the one or more BEOL interconnects, wherein each of the BEOL TFTs comprise a bottom gate electrode, a gate dielectric layer over the bottom gate electrode, and an oxide-based semiconductor channel layer over the bottom gate electrode having source and drain regions therein. Contacts are formed over the source and drain regions of each of BEOL TFTs, wherein the contacts have a critical dimension of 35 nm or less, and wherein the BEOL TFTs have an absence of diluted hydro-fluoride (DHF).

A field-effect transistor includes a substrate, a source electrode, a drain electrode, a gate electrode, a gate-insulating film, and an active layer. The active layer contains an oxide having a transmittance of 70% or more in the wavelength range of 400 to 800 nm. A light-shielding member is provided as a light-shielding structure for the active layer, for example, on the bottom face of the substrate.

A transistor includes a vertical stack containing, in order from bottom to top or from top to bottom, a gate electrode, a gate dielectric, and an active layer and located over a substrate. The active layer includes an amorphous semiconductor material. A crystalline source region including a first portion of a crystalline semiconductor material overlies, and is electrically connected to, a first end portion of the active layer. A crystalline drain region including a second portion of the crystalline semiconductor material overlies, and is electrically connected to, a second end portion of the active layer.

The present invention discloses a metal oxide (MO) semiconductor, which is obtained by doping a small amount of rare-earth oxide (RO) as a photo-induced carrier transportion center into an indium-containing MO semiconductor to form a (In.sub.2O.sub.3).sub.x(MO).sub.y(RO).sub.z semiconductor material. According to the present invention, a charge transportion center can be formed by utilizing the characteristics that the radius of rare-earth ions is equal to that of indium ions, and 4f orbitals in the rare-earth ions and 5s orbitals of the indium ions, so as to improve the stability under illumination. The present invention further provides a thin-film transistor based on the MO semiconductor and application thereof.

The present invention discloses a metal oxide (MO) semiconductor, which is implemented by respectively doping at least an oxide of rare earth element R and an oxide of rare earth element R′ into an indium-containing MO semiconductor to form an In.sub.xM.sub.yR.sub.nR′.sub.mO.sub.z semiconductor. According to the present invention, the extremely high oxygen bond breaking energy in the oxide of rare earth element R is used to effectively control the carrier concentration in the semiconductor, and a charge transportation center can be formed by using the characteristic that the radius of rare earth ions is equivalent to the radius of indium ions, so that the electrical stability of the semiconductor is improved. The present invention further provides a thin-film transistor based on the MO semiconductor and application thereof.