**3.1.2 Microstructural characterization of the infiltrated PZT thick films (SEM analysis)**

Following the crystallographic structural analysis, the microstructural analysis of standard and infiltrated PZT thick films reveals important aspects like: surface roughness, surface cracks, powder agglomeration, film thickness, porosity, among others. When the film is not infiltrated it is easy to observe cracks and small powder agglomerates in the surface of the films, while after few infiltrations the PZT thick films show a smoother and crack-free surface, as shown in Fig.4. It is visible that the infiltration process results in a decrease of the film porosity, increasing the connectivity of the composite films. This fact is extremely important in order to improve the dielectric and ferroelectric properties of the PZT thick films. Moreover, the infiltration process also reduces the film surface roughness, which is helpful for a good adhesion between the film and the top electrode and for a correct estimation of the thickness of the films that will be used in the further calculation of the dielectric and ferroelectric properties.

Fig. 4. SEM plan-view images of the PZT thick films with 0 (left) and 8 (right) top infiltrations (Pérez et al., 2007). (Copyright Elsevier)

Figure 5 shows the SEM cross-section microstructure images of the PZT thick films prepared with 0 and 8 top infiltrations. Relatively dense microstructure is observed in the film with 8

Fig. 5. SEM cross section images of the PZT thick films after 0 (left) and 8 (right) top infiltrations (Pérez et al., 2007). (Copyright Elsevier)

**3.1.2 Microstructural characterization of the infiltrated PZT thick films (SEM analysis)**  Following the crystallographic structural analysis, the microstructural analysis of standard and infiltrated PZT thick films reveals important aspects like: surface roughness, surface cracks, powder agglomeration, film thickness, porosity, among others. When the film is not infiltrated it is easy to observe cracks and small powder agglomerates in the surface of the films, while after few infiltrations the PZT thick films show a smoother and crack-free surface, as shown in Fig.4. It is visible that the infiltration process results in a decrease of the film porosity, increasing the connectivity of the composite films. This fact is extremely important in order to improve the dielectric and ferroelectric properties of the PZT thick films. Moreover, the infiltration process also reduces the film surface roughness, which is helpful for a good adhesion between the film and the top electrode and for a correct estimation of the thickness of the films that will be used in the further calculation of the

Fig. 4. SEM plan-view images of the PZT thick films with 0 (left) and 8 (right) top

Fig. 5. SEM cross section images of the PZT thick films after 0 (left) and 8 (right) top

Figure 5 shows the SEM cross-section microstructure images of the PZT thick films prepared with 0 and 8 top infiltrations. Relatively dense microstructure is observed in the film with 8

infiltrations (Pérez et al., 2007). (Copyright Elsevier)

infiltrations (Pérez et al., 2007). (Copyright Elsevier)

dielectric and ferroelectric properties.

infiltrations, while film without infiltration shows a porous structure mainly in the last deposited layer. It is also visible in the cross section images that the infiltration process results in a decrease of the film porosity; however, there is some remaining porosity that cannot be eliminated. It is called *internal or closed porosity* and results from a premature closing up of the pores channels.

Dorey et al., report a similar behavior in infiltrated PZT thick films using a high molecular weight precursor solution, as shown in Fig. 6 (Dorey et al., 2002). We can see that in films with four infiltrations of this solution, the internal porosity is higher than those reported by Pérez et. al., (Pérez, 2004). It is believed that the higher closed porosity observed in these films result from the increase of the density and viscosity of the precursor solution. Nevertheless, other factors like average grain size and shape and tortuosity of the pore channel should be also taken into account.

Fig. 6. SEM cross section images of the PZT thick films after 0 (left), 2 center and 4 (right) infiltrations using a high molecular weight precursor solution (Dorey et al., 2002). (Copyright Elsevier)

Surface roughness and porosity can be responsible for the possible deterioration of the dielectric constant and polarization values and the increase dielectric losses in PZT thick film. As mentioned, they are highly affected by the infiltration process. For this reason, in the next section one presents the dielectric, ferroelectric and piezoelectric behavior of the PZT thick films as a function of the number of infiltrations.
