New capabilities for optimizing SAW gas sensors

It is shown how the performances of SAW gas sensors can be optimized based on pure acoustic peculiarities of SAW propagation in anisotropic single cry stals. For a given gas and sensitive membrane, the calibration curve (depen dence of the response R versus gas concentration n), the sensitivity S (slo pe of the calibration curve: S = dR/dn), the detection limit n(thr) (cut-of f of the curve at the threshold R-thr), and the resolution Deltan of the se nsor (recognition of two close concentrations) can be controlled by a prope r choice of the substrate material and its crystallographic orientation (cu t and direction of the SAW propagation). An experimental test of this prope rty is performed on SAW devices implemented on different substrate material s and crystallographic orientations, both uncoated or coated, with a sorben t membrane of polycrystalline Pd or Pd:Ni film, upon exposure to humid air as a test analyte.