An oxygen sensor element with a ceramic heater, having a cylindrical element body formed of an oxygen ion permeable solid electrolyte with one end closed, inner and outer electrodes formed on the inner and outer surfaces of the element body, and an electrode protective layer covering at least one of...http://www.google.de/patents/US4540479?utm_source=gb-gplus-sharePatent US4540479 - Oxygen sensor element with a ceramic heater and a method for manufacturing it
