Current status of capacitive type gas sensor were reviewed in this paper. Although the number of publications on capacitive type sensors has been limited so far, capacitive type sensors have good prospects given that the capacitor structure is so simple enabling miniaturization and achieving high reliability and low cost. Among the reported capacitive type sensors, detection of gas based on a change in dielectric layer thickness is most promising. On this point of view, capacitive type CO2 and NO sensors using depletion layer formed at p-n junction of oxide semiconductor were introduced in detail. In addition, commercial capacitive type sensors for monitoring CO2 based on this principle were mentioned. CO2 concentration in office can be successfully monitored by the developed capacitive type CO2 sensor.
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