Miniaturized and Integrated On-Chip Ag/AgCl Micro-electrodes for Chemical Detection

This work proposes a fabrication and optimization process of miniature Ag/AgCl reference electrodes (RE) at a micrometer (μm) scale for the miniaturized chemical sensors, and these electrodes could also be integrated into a single CMOS chip with solid-state sensors, e.g., ISFET. The thin silver films are first grown by magnetron sputtering and chemically chloridized afterward to form the Ag/AgCl microelectrodes. Different chlorination durations and current densities have been applied to investigate the best fabrication recipe. Both scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) have been used to analyze the physical composition of electrodes under different recipes. The electrical performance of the proposed micro-electrode has been compared with a standard saturated calomel electrode (SCE), and it is observed that the electrode fabricated with an optimized recipe could provide less than 4 mV accuracy within the pH range from 4 to 10 and more than 200 minutes product life even with only 1.95 × 10⁵μm² area.