Thin-film sensors for industrial electronics: performance evaluation by circuit model simulation

Thin-films of pure and Li- or Au-doped iron oxide have been realized by liquid phase deposition (LPD). Supporting them over alumina substrates provided with gold interdigitated contacts, gas sensor devices in a layered configuration have been obtained. The sensor electrical response to CO and humidity in air was evaluated. Furthermore, an impedance spectroscopy characterization over the whole 0-100% RH humidity range was carried out. The results have been employed to extract accurate circuit models of the sensing films. Since each element of the equivalent circuit has a direct and univocal relationship with the different parts of the physical structure, such models have shown to be a basic tool for a deeper knowledge of the sensor performance by relating structural to electrical properties. In addition, their implementation gives useful indications on the changes that can be made to improve the sensor response. In the paper, the performance of the sensors and the most interesting results of the model simulation are presented and discussed.