Dielectric permittivity and loss of hydroxyapatite screen-printed thick films

In this paper we did a study on the structural and electrical properties of bioceramic hydroxiapatite (HA) thick films. The films were prepared in two layers using the screen printing technique on Al2O3 substrates. Mechanical alloying has been used successfully to produce nanocrystalline powders of hydroxyapatite (HA) to be used in the films. We also look for the effect of the grain size of the HA in the final properties of the film. The samples were studied using X-ray diffraction, scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS) and electric measurements. We did a study of the dielectric permittivity and the loss of the films in the radio-frequency of the spectra. The X-ray diffraction (XRD) patterns of the films indicates that all the peaks associated to HA phase is present in the films. One can notice that, for all the films there is a decrease of the DC with the increase of the frequency. The values of the dielectric constant of the films are in between 4 and 9 (at 1 KHz), as a function of the flux material concentration. The loss is decreasing as we increase the frequency for all the films. These results strongly suggests that the screen-printing HA thick films are good candidates for applications in biocompatible coatings of implant materials but also for the insulating materials of electronic circuits and dielectric layer in bio-sensors. (C) 2003 Kluwer Academic Publishers.