Dielectric response of interdigital chemocapacitors: the role of the sensitive layer thickness

The most important characteristics of a chemical sensor are its sensitivity and selectivity. In choosing a sorbent material for a chemical sensor all possible interactions with the vapour of interest should be understood if our goal is to obtain a desirable sensitivity or/and selectivity. In this work, an analytical model for the capacitance of interdigital capacitive sensors was used to explain the relationship between the sensor response and its geometrical parameters. This study reveal the strong link between the sensor response (sensitivity and selectivity) and the sensor geometric parameters, in particular what concerns the sensitive layer (sorbent material) thickness for a given electrode geometry. The knowledge of these relationships enables the right choice of a sensor in order to obtain the desired sensitivity and/or selectivity to a set of analytes. This can be done not only by the correct choice of the sorbent material but as well by the right choice of its thickness and sensor geometry. On the other hand, the understanding of the sensor response opens the possibility of making sensors or a combination of sensors with a reduced sensitivity to unwanted analytes. The dynamic of the response was studied as well, to identify the physical process involved which can be used to understand the sensing mechanisms and as well to increase the number of features to be extracted from the sensors.