Numerical Results of Modeling Semiconductor Sensor Layers in SAW Gas Sensors

Abstract

The paper presents the numerical results of investigations of the layered gas surface acoustic waves sensor. The base electric load of the piezoelectric acoustic line is predicted by the effect of surface acoustic waves velocity changes vs. surface conductivity, which depends on the profile concentration by gas diffused molecules into the porous film. Inside the sensor layer Knudsen's model of gas diffusion was used.

The Application of Surface Acoustic Waves in Surface Semiconductor Investigations and Gas Sensors

“…The gas concentration profile was counted basing on the concentration of the profiles [58], which are different for gases, depending on Knudsen diffusion constants, temperature, molecular weight, the gas constants R and the thickness of the porous sensing materials with an assumed porous radius. A simple model of a structure consisting of porous sensing material is shown in Figure 19.…”

“…Molecular hydrogen dissociated to atomic hydrogen on the outer catalytic surface of Pd. Adsorbed hydrogen atoms then act as electrical dipoles at the metal semiconductor interface and involve changes in the work function in the surface conductivity of the semiconductor material [53,58]. The target gas, diffusing in the sensing layer, is gradually consumed in the surface reaction.…”

Analysis of Non-Steady Stage in SAW Gas Sensors with Semiconducting Sensor Layers

“…A high porosity ensures a high sensitivity to the impact of gas. As far as porosity is concerned, there are to be distinguished: surface diffusion at a diameter of the pores below 1 nm, Knudsen's diffusion when the diameter of the pores amounts to 1-100 nm, and molecular diffusion in the case of pores with diameters exceeding 100 nm [8,9]. Practically, Knudsen's diffusion is most essential in the application of sensors.…”

“…The distance of the charge carriers from the piezoelectric waveguide deserves special attention. This stationary phenomenon of interaction has been dealt with by Hejczyk et al [7][8][9][10]. At present the procedure described above is applied in the analysis of the phenomenon of the non-stationary acoustoelectric effect in the SAW gas sensors.…”

“…Of no less importance is also the matching of a mathematical model to the achieved experimental results. These papers suggest a theoretical model as well as numerical analyses of a gas sensor of surface acoustic wave (SAW) type [1][2][3][4][5][6][7][8][9][10], in its steady state. As the phenomenon of the acoustoelectric effect depends in the set of a semiconducting layer and piezoelectric acoustic waveguide on the profile of the distribution of concentrations of the charge carriers in the sensor layer, it has been suggested to divide the sensor layer into thin sublayers, assuming a constant concentration of the carriers in these sublayers, alternating in each subsequent sublayer situated at different distances from the acoustic waveguide.…”