Semiconducting Metal Oxide Gas Sensors

In the next section, a variety of solid state environment gases sensors (NO,, CO2, CO, SO2, O2, etc.) are reviewed, and attention is also paid to semiconducting metal oxide type. Also discussed are the extension of the operating temperature to the near-human temperature regimes and better sensing properties derived from the nanostructured semiconducting metal oxide gas sensors. 

Various types of solid-state NO2 sensors have been proposed based on semiconducting metal oxides (including heterocontact materials) [42-50,58,59,234-238], solid electrolytes [1,239,240], metal phthalocyanine [241], and SAW devices [242]. Among these NO2 sensors, the semiconducting metal oxides and solid electrolytes appear to be the best. Specifically, semiconducting metal oxide gas sensors are most attractive because they are compact, sensitive, of low cost, and have low-power consumption. Their basic mechanism is that the NO2 gas is adsorbed on the surface of the material this decreases the free electron density into the space-charge layer and results in a resistance increase [243]. 

General discussion about sensing with semiconducting metal oxide gas sensors... 

The operation of a metal-oxide gas sensor relies on the change in resistance of an n- or p-type semiconducting layer - mainly Sn02 - when exposed to reducing or oxidizing gases. 

Kanan, S.M., El-Kadri, O.M., Abu-Yousef, LA., and Kanan, M.C. 2009. Semiconducting metal oxide based sensors for selective gas pollutant detection. Sensors 9 8158-8196. 

Figure 5. A methodological approach for simultanemis spectrtscopic and electrical (phenoiwnological) characterization of gas sensors based on semiconducting metal oxides [15].

Heterogeneous layers based on semiconducting metal oxides are known to show gas-sensing features different as compared to single oxides [1,2], The mentioned synergetic phenomenon can be provided by two effects i) the presence of active centers with diverse adsorption and catalytic behavior ii) the efficient separation of the sensor functions, receptor and transducer, between different oxide phases. 

With the increase in needs to monitor a variety of gases in our environment, the solid-state gas sensors based on electrical parameters are widely studied, including silicon-based chemical sensors, semiconducting metal oxide sensors, catalysis. 

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