We fabricated the electrolyte-insulator-metal (EIM) sensor on the base of anodic aluminum oxide (AAO) template for capacitive pH sensors. For the change of the thickness of AAO template, the second anodizing time was varied from 1 min to 10 min. With increasing the second anodizing time from 1 min to 10 min, the thickness of AAO template increased from 90 nm to 1.3 μm. And the surface area compared to planar structure increased from 3 times to 25 times. The pH sensitivity of sensors with the second anodizing time of 10 min showed the highest value of 56.8 mV/pH in the concentration range from pH 3 to pH 11, a large hysteresis voltage of 7.6 mV in a cycle of pH 7→ 11→ 7→ 3→ 7. The EIM sensor with the second anodizing time of 1 min exhibited the best long-term stability of 2.5 mV/h.

Keywords: AAO, EIM, pH sensors.