Patent ID: 8610180

Claim:
A gas sensor comprising: a detection portion including a first transistor and a circuit portion including a second transistor over one insulating surface, wherein the first transistor comprises: a first gate electrode layer over the insulating surface; a gate insulating layer over the first gate electrode layer; a first oxide semiconductor layer, one surface of which is in contact with the gate insulating layer and the other surface of which is in contact with an atmosphere; and a first source electrode layer and a first drain electrode layer that are in contact with the first oxide semiconductor layer, and wherein the second transistor comprises: a second gate electrode layer over the insulating surface; the gate insulating layer over the second gate electrode layer; a second oxide semiconductor layer, one surface of which is in contact with the gate insulating layer and the other surface of which is in contact with a protective insulating layer; and a second source electrode layer and a second drain electrode layer that are in contact with the second oxide semiconductor layer.