Sensor element, gas sensor, and method for manufacturing sensor element

A plate-shaped, stacked sensor element extending in an axial direction and comprising:

• a first ceramic layer;
• and
• a pair of electrodes disposed on opposing surfaces of the first ceramic layer,
• the pair of electrodes being disposed on one end side of the sensor element in the axial direction and including a measurement electrode which comes into contact with a gas under measurement so as to detect a specific gas, and a porous reference electrode which comes into contact with a reference gas,
• the sensor element further comprising:
• a through hole formed in at least the first ceramic layer at a position on the other end side of the sensor element and extending in a stacking direction of the sensor element;
• a through hole conductor provided on an inner wall which defines the through hole;
• a porous reference lead connected to the reference electrode, extending toward the other end side of the sensor element, and connected to the through hole conductor;
• and
• a gas impermeable second ceramic layer disposed to face the first ceramic layer and sandwich the reference electrode and the reference lead in cooperation with the first ceramic layer, the second ceramic layer extending to a region which overlaps the entirety of the through hole as viewed in the stacking direction,
• the sensor element being characterized by further comprising:
• a gas flow chamber which is provided between the first ceramic layer and the second ceramic layer and which faces the through hole and is in communication with the reference lead;
• and
• a gas flow passage which is connected to the through hole or the gas flow chamber and is open to a second region of an outer surface of the sensor element, different from a region to which the through hole is open, thereby establishing communication between the gas flow chamber and an outside atmosphere.