Limiting current and wide range air/fuel ratio sensors using the same ysz-al₂o₃ layers as electrolyte and diffusion barrier

A limiting current-type oxygen sensor using the same YSZ-Al₂O₃ layers as electrolyte and diffusion barrier was designed to increase thermal shock resistance, ease of fabrication, and long-term stability of the sensor. The limiting current of the sensor originated from the limited O₂ diffusion towards the cathode side from all directions of the sensor because the microstructures of the electrolyte and diffusion barrier are the same. The limiting current could be manipulated successfully by varying Al₂O₃ contents and sintering temperatures, which resulted from the microstructural change of the YSZ-Al₂O₃ layers. A new wide range air/fuel ratio (A/F) sensor was also suggested by placing an additional O₂ pumping cell under the present limiting current-type sensor. The sensing signal increased linearly with O₂ in O₂-CO₂-N₂ and decreased with CO in CO-CO₂-N₂. Thus the wide range of A/F can be measured with this simple sensor structure and operating algorithm.