Dielectric spectroscopy of thin films by dual-channel impedance measurements on differential interdigitated electrode arrays

We report a new approach to measuring the dielectric behavior of thin films by means of differential interdigitated electrode (IDE) cells coupled with a dual-channel impedance measurement setup. The differential IDE cell consists of two identical IDE's on a common substrate. With one IDE loaded with sample and the other one empty, the complex permittivities of both capacitors are measured simultaneously by means of a dual-channel impedance measurement setup. The net dielectric response of the material under study is then obtained by the difference of the two permittivities, which corrects for the substrate contribution. The applicability of this approach is examined with bulk glycerol and a 600 nm indomethacin film and is evidenced by the results being consistent with those measured by conventional methods. The main advantages of this new approach include a simplified preparation technique for thin film samples and a straightforward correction for the substrate contribution by subtracting the empty IDE signal obtained at the same temperature and thermal history.