Dynamic Properties of SnO₂ Semiconductor Gas Sensors

Sensing of Hydrocarbons in Air

Abstract

The sensing mechanism of SnO₂ semiconductor gas sensors was studied by examining, via the pulse reaction method, the transient response characteristics of the conductivity of gas sensors for methane and isobutane, typical hydrocarbons. The study revealed the following facts:
(1) The relationship between gas sensor conductivity and inflammable gas concentration, both in steady and unsteady states, can be determined for hydrocarbons such as methane and isobutane, as for hydrogen using Equation (1) below: dσ/dt=aP_G+b/σ-cσ (1) σ: sensor conductivity P_G: atmospheric gas concentration a, b, c: constants t: time
(2) If atmosphere containing no inflammable gas is changed to one containing inflammable gas, the speed of change in sensor conductivity is highest in air containing hydrogen, followed by air containing isobutane, and is lowest in air containing methane. This order corresponds to the order of flammability, confirming the supposition that the change results from the reaction between flammable gas and adsorbed oxygen.
(3) If atmosphere containing flammable gas is changed to one containing no inflammable gas, the speed of change in sensor conductivity does not vary significantly with the kind and concentration of gas. This fact suggests that the change results from the adsorption of oxygen onto open sites on SnO₂.