Patent ID: 8373166

Claim:
A display device comprising: a pixel portion over a substrate, the pixel portion comprising a first thin film transistor and a pixel electrode electrically connected to the first thin film transistor; and a drive circuit comprising a second thin film transistor formed over the substrate wherein the drive circuit is operationally connected to the pixel portion, each of the first thin film transistor and the second thin film transistor comprising: a gate electrode formed over the substrate; a gate insulating film formed over the gate electrode; a first semiconductor layer comprising semi-amorphous silicon formed over the gate electrode with the gate insulating film interposed therebetween; a pair of third semiconductor layers comprising semi-amorphous silicon formed over the first semiconductor layer; a pair of second semiconductor layers having n-type conductive type formed over the first semiconductor layer with the pair of third semiconductor layers interposed at least between the first semiconductor layer and the pair of second semiconductor layers; a first conductive layer formed on one of the pair of second semiconductor layers; and a second conductive layer formed on the other one of the pair of second semiconductor layers, wherein the pair of third semiconductor layers are non-doped semiconductor layers, wherein the pair of third semiconductor layers have n-type conductive type, and wherein the pair of third semiconductor layers has a lower conductivity than the pair of second semiconductor layers.