A Micromachined Chemical Sensor for Sea Floor Environments: Initial Results

This paper reports a micromachined chemical sensor intended for harsh environments such as those near hydrothermal vents at the sea floor. The sensor is intended to measure the pH, dissolved H2 and H2S, and temperature. The device is 12 mm in diameter and 6 mm in effective length, including packaging. A YSZ|HgO|Hg solid electrode is used as a common electrode for measurement of the three chemical quantities. The YSZ diaphragm used for this electrode is <500 μm thick, allowing sufficient ion conductance at temperatures >35°C. The other electrodes are thin-film metal electrodes fabricated on the same YSZ diaphragm: an Ag|AgCl reference electrode for pH sensing, an Ag|Ag2S electrode for H2S sensing, and a Pt electrode for H2 sensing. The two temperature sensors are thin film Pt resistors. Initial tests have been performed to test the functionality of the pH and H2S sensors; measurements are in line with expectations.