Semiconductor gas sensor stability and selectivity can be improved by using catalytic filtering membranes to avoid interference of various gas molecules. The deposition of dielectric thin films doped with catalytic metals directly on the surface of semiconductor sensing element allows to increase the selectivity without considerable decrease of the sensitivity and increase of the response time.
The films were obtained by aerosol pyrolysis method. The filtering membranes of pure and Pt or Ru doped Al₂O₃ with various thickness (6-160 nm) were deposited on the surface of SnO₂(Pd) films. Phase composition and microstructure of the films were studied by X-ray diffraction, Atomic Force Microscopy, Transmission Electron Microscopy and Electron Probe MicroAnalysis.
Sensors properties of SnO₂(Pd)/Al₂O₃ and SnO₂(Pd)/Al₂O₃(Me) structures (Me = Pt, Ru) were studied under H₂, CH₄, C₃H₈ and CO-air gas mixtures in a temperature range 100-300C. The use of the membranes increases the response time of the sensors. All membranes reduce significantly the sensitivity to CO in the temperature range and increase the sensitivity to CH₄ and C₃H₈ at 200C. Ru-doped membranes significantly reduce the sensitivity to H₂. Sensitivity and response time considerably depend on membrane thickness.

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