Calorimetric Sensing Mode for Operation at Constant Temperature

5 Calorimetric Sensing Mode for Operation at Constant Temperature 

The microhotplate was coated with a thick-film tin-oxide droplet as described in Sect. 4.1.2. To characterize the chemical-sensor performance, the chip was exposed to CO concentrations from 5 to 50 ppm in humidified air at 40% relative humidity (23.4 °C water vaporization temperature) (see Sect. 5.1.8 for a description of the gas test measurement setup). 

A control experiment was performed with an uncoated microhotplate in the gas test measurement setup with the same measurement program and at the identical microhotplate temperature. No changes in the source-gate voltage could be measured. Therefore, the changes in the microhotplate heat budget are clearly related to the interaction of the analyte with the tin oxide. 

A problem of the calorimetric sensing mode is its cross-sensitivity to changes in ambient temperature. The realization of an additional temperature sensor on the bulk chip solves this problem. The signal-to-noise ratio of the calorimetric mode 

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