Gas sensor element and method for producing gas sensor element

A gas sensor element comprising:

• a measurement chamber into which a gas under measurement is introduced;
• a pumping cell including a first solid electrolyte body having oxygen ion conductivity and a pair of pumping electrodes formed on the first solid electrolyte body, the pumping cell pumping oxygen into or out of the gas under measurement that has been introduced into the measurement chamber when a pumping current flows between the pair of pumping electrodes;
• an oxygen concentration detection cell including a plate-shaped cell member which includes at least a second solid electrolyte body having oxygen ion conductivity, a detection electrode formed on an upper surface of the second solid electrolyte body, and a reference electrode having oxygen permeability and formed on a lower surface of the second solid electrolyte body, the detection electrode being exposed to the measurement chamber, the oxygen concentration detection cell generating an electromotive force corresponding to a difference in oxygen concentration between the detection electrode and the reference electrode;
• a first lead portion having oxygen permeability and formed on a lower surface of the plate-shaped cell member so as to extend from the reference electrode to a through hole formed in the plate-shaped cell member and further extend from the lower surface of the plate-shaped cell member through the through hole to an upper surface of the plate-shaped cell member so as to cover an inner circumferential wall of the through hole and a portion of the upper surface around the through hole;
• and
• a second lead portion formed so as to extend from the upper surface of the plate-shaped cell member through the through hole to the lower surface of the plate-shaped cell member so as to cover the first lead portion along the inner circumferential wall of the through hole and a portion of the lower surface around the through hole, wherein
• an insulating substrate is disposed below the plate-shaped cell member so as to face the plate-shaped cell member and thereby form a space along the lower surface of the plate-shaped cell member extending across the through hole and a periphery of the through hole;
• the first lead portion has a section exposed to the space below the lower surface of the plate-shaped cell member;
• the second lead portion is spaced apart from the insulating substrate with the space therebetween;
• the first lead portion is in communication with the outside of the gas sensor element via the space and the through hole;
• the gas sensor element is configured such that oxygen accumulating in the reference electrode that flows to the outside of the gas sensor flows through the first lead portion;
• an insulating layer is disposed between the insulating substrate and the plate-shaped cell member;
• a surface of the insulating layer faces the space;
• and
• a part of the first lead portion on the lower surface of the plate-shaped cell member, which is not covered by the second lead portion and which does not face the space, is in contact with the insulating layer.