1. Field of the Invention
The present invention relates to a display device and a manufacturing method thereof. In addition, the present invention relates to an electronic apparatus provided with the display device.
2. Description of the Related Art
There are many kinds of metal oxide and there are various applications of metal oxide. Indium oxide, which is a well-known material, is used as a material for a transparent electrode which is needed for a liquid crystal display or the like.
Some metal oxides have semiconductor characteristics. Metal oxide having semiconductor characteristics is a kind of a compound semiconductor. The compound semiconductor is a semiconductor formed using two or more kinds of elements bonded together. In general, metal oxides become insulators. However, it is known that metal oxides become semiconductors depending on the combination of elements included in the metal oxides.
It is known that some kinds of metal oxide, for example, tungsten oxide, tin oxide, indium oxide, and zinc oxide have semiconductor characteristics. A thin film transistor whose channel formation region is a transparent semiconductor layer formed from such metal oxide is disclosed (see Patent Documents 1, 2, 3, and 4 and Non-Patent Document 1).
Multi-component oxide is known as one of metal oxide having semiconductor characteristics in addition to the above single-component oxide. For example, InGaO3(ZnO)m (m: a natural number) including a homologous series is a known material (Non-Patent Documents 2, 3, and 4).
Further, it has been demonstrated that such a homologous thin film described above can be used as a channel layer of a thin film transistor (see Patent Document 5 and Non-Patent Documents 5 and 6).
In addition, Patent Documents 6 and 7 disclose techniques by which a thin film transistor is manufactured using zinc oxide or an In—Ga—Zn—O-based oxide semiconductor as a thin film transistor using a metal oxide semiconductor, and is used as a switching element or the like of an image display device.