Sensor element for limiting current sensors to determine the lambda value of gas mixtures

A sensor element for limiting-current sensors for determining the lambda value of gas mixtures, in particular of exhaust gases of internal combustion engines, comprising:

• a ceramic substrate (1),
• a diffusion layer (5) on one side of said substrate (1) for producing a permeable diffusion barrier for reducing diffusion of a measurement gas, said diffusion layer (5) covering less than all of said side of said substrate,
• an inner pump electrode (2) on a portion of said diffusion layer and having a first conductor track (2') on a portion of said one substrate side which is not covered by said diffusion layer,
• a solid electrolyte gas-tight cover layer (9) directly covering said inner pump electrode (2) and portions of said diffusion layer (5) not covered by said inner pump electrode (2) and conformably covering said diffusion layer where it would otherwise be exposed to measurement gas except for a measurement gas inlet opening (12) located at an edge portion of said diffusion layer (5) which is opposite and remote from said inner electrode,
• an outer pump electrode (3) on said solid electrolyte gas-tight cover layer (9) connected to a second conductor track (3');
• an insulating layer (10) on said solid electrolyte gas-tight cover layer 9 and interposed between said solid electrolyte gas-tight cover layer (9) and said first conductor track (2'), whereby said second conductor track (3') is insulated from said first conductor track (2'), and
• a porous engobe layer (11) on said outer pump electrode (3),
• characterized in that
• said diffusion layer (5) has at the edge thereof at which said measurement gas inlet opening (12) is located, a series of outwardly tapered projections each oriented towards the measurement gas inlet opening (12), said solid electrolyte gas-tight cover layer (9) filling all gaps between said projections whereby the finished sensor element is calibratable by at least one mechanical or laser cutting operation which cuts off extremity portions of a plurality of said outwardly tapered projections and thereby reduces the diffusion resistance of the diffusion layer.