Semiconductor Sensor Layer in SAW Gas Sensors Configuration

Abstract

A Rayleigh acoustic wave travelling on the surface of a semi-infinite piezoelectric medium may be changed by interaction with carriers and diffused gas in an adjacent semiconductor. The configuration, which uses a thin semiconductor film supported by a catalytic layer (Pd), is described in detail and the theoretical results of gas-sensor layer interaction are presented.

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

“…The space-charge potential satisfies the general form of Laplace. For this region Laplace's equation is reduced to [30]:…”

“…This effect depends on the electromechanical coupling factor K 2 . The Ingebrigtsen formula for electrical surface perturbations of SAW Rayleigh waves is reduced to the form [23,30]: …”

“…The electric effect has one very interesting feature, namely it causes significant changes in the propagation velocity of the SAW only in some particular range, which depends only on the properties of the piezoelectric substrate (which was LiNbO3, Y-Z); the metal layer shortens the electric field associated with the surface wave [22,30]. According to this theory we can prove that surface conductivity influences the detection features of SAW gas sensors.…”

“…The analysis summarizes the acoustoelectric theory, i.e. Ingebrigtsen's formula [23,29], the impedance transformation law and gas concentration profiles, and predicts the influence of a thin semiconductor sensor layer with Knudsen's gas diffusion model on the SAW wave velocity in a piezoelectric acoustic waveguide in steadystate and non-steady-state conditions [30]. Basing on these results the sensor structure can be optimized.…”

Analytical model of a SAW gas sensor

“…This resultant impedance applies the Ingebrigtsen formula to calculate changes in the propagation velocity of the surface wave. The transformation impedance law is derived from the general expressions for φ' and D y ' in the region 0>y>-h [5,11].…”