1. Field of the Invention
The present invention relates to a semiconductor device having a functional circuit. In particular, the invention relates to a lightweight, thin, high-functional and low-cost semiconductor device. Further, the invention relates to a display device having a functional circuit on the same substrate, in particular to a lightweight, thin, high-functional and low-cost display device.
2. Description of the Related Art
In recent years, a technology development regarding a thin film transistor (hereinafter referred to as a TFT) using polycrystalline silicon thin film as an active layer has been rapidly advanced. For example, a display device having a pixel portion of which switching element is formed of a TFT and an active matrix display device having a circuit for driving a pixel, which is formed of a TFT are actively researched and developed. Such display devices have major advantages in low-cost, thin design, lightweight, high definition, low power consumption and the like.
Further, research and development for forming a functional circuit by a TFT and mounting it on the same substrate as a display device are advanced as a TFT becomes higher in function. A central processing unit (CPU), an image processing unit, a memory and the like are included in a functional circuit, which are required to be formed without spoiling the advantages of a display device using a TFT as described above.