Improved solid-state planar Ti/Pd/Ag/AgCl/KCl-gel microreference electrode by silicon cap sealing package

Although solid-state microreference electrodes (mu REs) have been developed for electrochemical and biomedical sensing applications for more than one decade, there are very few studies devoted to improving their performance through packaging. Using planar technology and a silicon cap sealing method, we implement a packaged Ti/Pd/Ag/AgCl/KCl-gel mu RE with a total dimension of only 9 mm (L) x 6 mm (W) x 1 mm (H), a hundredfold less than the commercial Ag/AgCl reference electrode (RE). Compared with the unpackaged mu RE, the presented chip-level packaged mu RE demonstrates many improved characteristics, including a very stable cell potential (5-mV drift voltage in 30,000 s), an approximately zero offset voltage (-7 mV), a very low impedance (1.50 k Omega) and phase shift (8.98 deg) at 1-kHz operation frequency, a very small double-layer capacitance (0.04 mu F), and a very high reproducibility (+/- 3.1-mV). (C) 2009 Society of Photo-Optical Instrumentation Engineers. [DOI: 10.1117/1.3196547]