Patent ID: 7477222

Claim:
An active matrix display device comprising: a substrate having an insulating surface; a pixel portion comprising a pixel comprising: a switching TFT over the substrate; and a display element over the substrate, electrically connected to the switching TFT; and a driver circuit comprising a shift register comprising an inverter circuit comprising: an input terminal; a first TFT over the substrate; a second TFT over the substrate; a third TFT over the substrate; a fourth TFT over the substrate; and an output terminal, wherein a first terminal of the first TFT is electrically connected to the input terminal, wherein a second terminal of the first TFT is electrically connected to a first terminal of the second TFT, and to a gate terminal of the third TFT, wherein a first terminal of the third TFT is electrically connected to a first power source, wherein a second terminal of the third TFT is electrically connected to a second power source, via a first resistance element, wherein a first terminal of the fourth TFT is electrically connected to the first power source, wherein a second terminal of the fourth TFT is electrically connected to the second power source, via a second resistance element, wherein a second terminal of the second TFT is electrically connected to the second terminal of the fourth TFT, wherein the output terminal is electrically connected to the second terminal of the third TFT, and to a gate terminal of the fourth TFT, wherein a clock signal is inputted to a gate terminal of the first TFT, wherein an inverted clock signal is inputted to a gate terminal of the second TFT, and wherein each of the switching TFT, the first TFT, the second TFT, the third TFT and the fourth TFT comprises an active layer having a channel forming region comprising an impurity element having a same conductivity type.