A MOS (Metal-Oxide-Semiconductor) capacitor dissolved oxygen sensor, which has a thin porous Pt layer as a metal layer, was developed and its response characteristics to dissolved oxygen (DO) were examined in aqueous solutions containing 2.5×10-2-37 mass ppm DO at temperatures of 303-363K. It was found that the porous Pt-MOS capacitor DO sensor showed a linear relationship between the response voltage and log 〔DO concentration〕 in the range of 2.5×10-2-37 mass ppm DO at 303-363K. The responce voltage at a given DO concentration became large with decreasing thickness of Pt layer and also with increasing temperature. The response time of the sensor became short with increasing temperature. The 90% response time at a given DO concentration was less than 400s at 363 K. The slope of the linear relationship between the response voltage and the log 〔DO concentration〕 was 133mV/decade for the Pt layer 12nm thickness at 363K. The slope did not depend on the solution pH. The principle of this DO sensor was thought to be based on its Pt-EOS (Electrolyte-Oxide-Semiconductor) structure.
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