Gas mixture analysis using silicon micro-reactor systems

A novel way of operating metal-oxide gas sensors is demonstrated that exten ds the gas-analyzing facilities of conventional thin-film gas sensors. In o ur approach, thin-film metal-oxide gas sensors on micro-machined heater sub strates are embedded into tiny silicon micro-chambers to form micro-reactor devices. Analyzing samples of polluted air, such micro-reactors can be ope rated either in constant-flow or no-flow modes. Whereas in the first mode, essentially normal sensor behavior is observed, gas depletion reactions are observed in the latter. Such depletion reactions are shown to provide, in a straightforward way, analytical information about gas mixtures which is d ifficult to obtain under normal sensor operating conditions. As an applicat ion example, we demonstrate how a micro-reactor device fan be used to analy ze samples of polluted air for their O-3 and NO2 contents.