Patent ID: 8818497

Claim:
A biological signal processing unit comprising: an electrode for at least one of detecting a biological signal from an inside of a living body and transmitting an electric signal to the inside of the living body; a plastic substrate having flexibility; an antenna over the plastic substrate having flexibility, wherein the antenna is configured to wirelessly communicate with a wireless memory configured to be attached to the living body, which is located outside the biological signal processing unit; an interface comprising a rectification circuit provided between the electrode and the antenna and over the plastic substrate having flexibility; and a processor over the plastic substrate having flexibility, wherein the processor comprises a transistor electrically connected to the antenna, the transistor comprising: a first insulating film; a first electrode over the first insulating film; a second insulating film over the first insulating film and the first electrode; a semiconductor layer over the second insulating film, so as to overlap with the first electrode, wherein the semiconductor layer comprises a channel region, a first impurity region, and a second impurity region between the channel region and the first impurity region, and wherein a concentration of an impurity element in the second impurity region is lower than a concentration of the impurity element in the first impurity region; a third insulating film over the semiconductor layer; a second electrode over the third insulating film, so as to overlap with the semiconductor layer; a third electrode over the second electrode, wherein a width of the third electrode is shorter than a width of the second electrode in a channel length direction; a fourth insulating film over the third insulating film, second electrode and the third electrode; and a fourth electrode over the fourth insulating film, the fourth electrode electrically connected to the first impurity region through a contact hole in the third insulating film and the fourth insulating film, wherein at least the antenna, the rectification circuit, and the processor are provided over the plastic substrate having flexibility with an adhesive agent interposed therebetween.