Microstructural and electrical characterisation of PZT thick films on LTCC substrates

Piezoelectric thick films based on Pb(Zr,Ti)O3 (PZT) were prepared on two types of LTCC tapes (Du Pont 951 and Electro Science Labs. 41020) and on relatively inert alumina substrates. The results obtained with the alumina were used as a reference. The microstructures of the cross-sections of the resistors were investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray (EDS) analysis. The dielectric permittivities, dielectric losses, remanent polarisation, coercive field and piezoelectric constant d33 were measured. The dielectric and piezoelectric characteristics of the PZT fired on the LTCC substrates deteriorated in comparison to the samples on alumina, due to interactions between the LTCC substrate and the PZT layer. Lower dielectric constants, remanent polarisations and piezoelectric constants indicate the formation of phases with a low permittivity. This was attributed to the diffusion of SiO2 from the LTCC into the active PZT layer and to the diffusion of PbO from the PZT layer into the LTCC substrate. The diffusion was confirmed by the SEM and EDS analysis.