The (MOSFET)-M-E as an oxygen sensor: constant current potentiometry

In a previous paper, a novel type of potentiometric dissolved oxygen sensor was introduced. The transduction principle of the sensor is based on the m odulation of the work function of an iridium oxide film by the ratio of Ir- III/Ir-IV oxide in the film. This ratio depends on the oxygen concentration in the solution, so that the work function of the iridium oxide is a measu re of the amount of dissolved oxygen. The work function changes are determi ned by using the iridium oxide film as the gate contact of a MOSFET. Becaus e the threshold voltage of:a MOSFET depends on the work function of the gat e contact, it can be used as a sensor signal. In the present paper, a reduc ing current of constant magnitude is in addition externally applied to the iridium oxide film, so that an overpotential is generated. The influence of this overpotential on the sensor signal is studied and it is shown that th e sensitivity towards oxygen increases compared to the equilibrium potentia l. Measurement results are shown and compared to the theory. The applied cu rrent leads to sensitivities to and pH that correspond well to the values t hat may be expected from the literature. (C) 1999 Elsevier Science S.A. All rights reserved.