Abstract: In order to reduce exhaust gases impurities damaging of deposition and chemical reaction on the electrode of automobile lambda sensor chip，and to improve stability and longevity of chip，porous protective layer on electrode surface was made by the way of screen printing. The pores of protective layer were adjusted by optimizing pore former type，particle size，content and slurry formula. The optimum conditions were as below：Yixing 8YSZ was selected preferably as powder material，5 μm polymethyl methacrylate（PMMA） microspheres was selected preferably as pore former，pore former content was 15% ，resin content was 6% ，solid content was 39. 39% ，15% ethyl cellulose（EC4） and 10% ethyl cellulose （EC45） were selected preferably as adhesive resins. Protective layer slurry was prepared with the optimized conditions. It forms many and uniform size pores after sintering；average aperture was 2. 44 μm，and it is beneficial to make the protective layer play a better role of ″filtration″ for exhaust gases.

Key words: PMMA microspheres, pore former, lambda sensor, porous protective layer