Investigations on temperature controlled monolithic integrated surface acoustic wave (SAW) gas sensors

The paper presents examinations on temperature behavior of mass sensitive surface acoustic wave (SAW) gas sensors. The investigations were realized on dual-delay-line SAW-devices based on AlN as piezoelectric layer. In order to measure temperature, a thin film resistor was placed on the surface of the SAW-device. To heat up the sensor device a monolithic integrated polysilicon heating resistor was used. As mass sensitive layers different polymers were deposited using a spin-on-process. For the detection of aromatic compounds like benzene, toluene and xylene suitable imprinted polymers were used. To examine sensitivity and selectivity of alcoholic compounds a polyurethane was deposited as mass sensitive layer. In our investigations, the effect of gas adsorption on the SAW transmission behavior was studied. Different atmospheres caused varying damping behavior and thus energy losses of the transmission line influenced the surface temperature of the mass sensitive layer. Growing demands on quality standards demand improvements in sensitivity, selectivity and stability of gas sensors. Because of the temperature influence on physical properties of surface acoustic waves, the temperature behavior of the SAW-devices was examined. Further on, the effects of cross sensitivity were studied according to different temperature behavior of adsorption. As a result, a higher sensitivity and stability could be achieved by controlling and changing temperature during the measurement in comparison to uncontrolled devices. (C) 2003 Elsevier Science B.V. All rights reserved.