Accurate extraction of the temperature of the heating element in micromachined gas sensors

The sensitivity and selectivity of micromachined gas sensors strongly depend on the temperature of the heating element; therefore an accurate determination of this temperature is required. In this paper, a simple analytical model of the thermal behavior of a heating element placed onto a thermally insulated dielectric membrane is presented. It is demonstrated that simple resistance vs. power measurements are sufficient for a precise determination of the sensor temperature. These measurements performed "once and for all" at the wafer-level on the statistically relevant number of heaters, allowed us to determine a "universal" temperature vs. power curve.

1. Introduction

Solid-state gas detectors usually depend on the properties of wide-gap semiconductive metal oxides, such as SnO₂, deposited on suitable substrates [1],[2],[3]–. Typically, a thermally activated reaction occurs between a given gas and the sensing layer, thus producing a change in the conductance of the latter [4],[5]. It is therefore of primary importance to have a good knowledge of the actual temperature of the sensing layer.