Gas sensor and method for manufacturing the same

A prismatic multilayer gas sensor element (200) having substantially a rectangular cross section comprising:

• a gas-sensing cell portion (401) formed at a distal end portion of the prismatic gas sensor element (200), the gas-sensing cell portion (401) comprising first and second zirconia solid electrode layers (103, 107) each having metallic electrodes (102a, 104a), (106c, 108a) formed thereon;
• a posterior lead portion (402) adjoining the gas-sensing cell portion (401) and extending to a rear end portion of the prismatic gas sensor element (200), comprising first and second zirconia solid electrolyte layers (103, 107) each extending from the gas-sensing cell portion (402) to a rear end portion of the prismatic gas sensor element (200), first top and bottom metallic leads (104b, 102b) sandwiching the extended first zirconia solid electrolyte layer (103), second top and bottom metallic leads (108b, 106b) sandwiching the extended second zirconia solid electrolyte layer (107), a first non-porous alumina layer (101) covering the bottom surface of the first solid electrolyte layer (103) and the first bottom lead (102b), an insulating alumina spacer (105) arranged between the first and second zirconia solid electrolyte layers (103, 107) and between the first bottom metallic lead (104b) and the second bottom metallic lead (106d), and a second non-porous alumina layer (109a) covering the top surface of the second solid electrolyte layer (107) and the top metallic lead (108b);
• and
• a heating resistor (116a) sandwiched by insulating layers (111, 112) and positioned in the vicinity of the metallic electrodes (102a, 104a) (106c, 108a) so as to heat the gas sensing cell portion (401) to a temperature of more than 600° C.;
• wherein longitudinal lateral surfaces of the posterior lead portion (401), which lateral surfaces are substantially perpendicular to top and bottom planer surfaces of the prismatic multilayer gas sensor element (200), and which lateral surfaces are heated by the heating resistor (116a) to a temperature not exceeding 600° C., are coated with a third non-porous alumina layer (114).

A method of manufacturing a multilayer prismatic gas sensor having a substantially rectangular cross section, which comprises:

• forming a plurality of unfired metallic electrodes on a top surface of a green zirconia solid electrolyte sheet;
• forming a plurality of unfired metallic reference electrodes on the bottom surface of the green solid electrolyte sheet so as to obtain a plurality of gas sensing cells;
• forming a plurality of unfired first and second metallic leads on the bottom and top surfaces of the green solid electrolyte layer, respectively, the first metallic leads connecting to respective reference electrodes and the second metallic electrodes connected to respective measuring electrodes to form a plurality of posterior lead portions each adjoined to a gas sensing portion;
• forming an unfired laminate sheet by laminating a first green alumina sheet on the bottom surface of the green solid electrolyte layer and the first metallic leads and laminating a second green alumina sheet on the top surface of the green solid electrolyte layer and the second metallic leads;
• cutting the unfired laminate sheet into a plurality of unfired prismatic multilayer gas sensor elements;
• forming on cut-surfaces of the posterior lead portions constituting unfired prismatic gas sensor elements, a first paste layer comprising alumina particles and a solvent and then drying the first paste layer to form a joining layer;
• forming on the first dried paste layer, a second paste layer comprising alumina particles and a solvent and then drying the second paste layer to form a surface layer;
• and
• firing the unfired prismatic multilayer gas sensor elements at a temperature of 1350-1550° C. so as to obtain plurality of fired prismatic gas sensor elements.