New Gas‐Sensing Method for Detecting Carbon Monoxide by Use of the Complex Impedance of a CuO/ZnO Heterocontact under a dc Bias Voltage

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Abstract
The impedance characteristics of a CuO/ZnO oxide semiconductor heterocontact were investigated to study a new method of gas identification. This was done by applying a dc bias voltage in atmospheres of air‐balanced, flammable CO or H2 gas (4000 ppm). The frequency dependence of the reactance component showed a characteristic behavior that varied according to the testing atmosphere under the applied negative dc voltage at 400°C. The discrimination of CO gas from H2 gas in air was demonstrated as feasible by either varying the bias voltage in negative values at constant frequency or sweeping the frequency on a negative bias voltage. The new method of gas identification suggested by the present study uses a ceramic‐semiconductor heterocontact, on which a combination of dc bias voltage and ac signal is applied.