Citation:
R. A. Dorey; R. W. Whatmore. Apparent Reduction in the Value of the d 33 Piezoelectric Coefficient in PZT Thick Films. Integrated Ferroelectrics, Volume 50, Issue 1 2002 , pages 111-119
Abstract:
Thick PZT films (1 - 20 m) have been prepared using a composite sol gel
technique whereby PZT powder and a PZT producing sol are formed into a slurry
and spin coated onto silicon wafers. The maximum relative permittivity obtained
was approximately 80% of that exhibited by bulk PZT of comparable composition.
However, the d 33, f and e 31, f [1] piezoelectric coefficients were shown to be
significantly lower than that of bulk PZT. It has been proposed that the
measured value of d 33, f is affected appreciably by particle-particle rotation
and substrate clamping leading to reduced poling efficiency which may also
greatly reduce the value of e 31, f observed. Samples with high levels of
porosity have been shown to exhibit a reduced value of d 33 . This was
attributed to 31 and 51 mode piezoelectrically generated charges caused by the
bending and shearing of particle-particle bridges. The effect of substrate
clamping, on d 33, f and poling, has been studied by monitoring the changes in
position and intensity of the (200)/(002) X-ray diffraction (XRD) peaks of
composite films. The presence of the substrate was found to introduce tensile
stresses parallel to the film plane which distorted the unit cell. Subsequent
permanent polarisation following poling was found to be reduced due to the
presence of these stresses. The discrepancies between the values of d 33
measured on thick films and bulk ceramics were highlighted as being of
particular importance if thick film materials are to be modelled for device
applications. Thick film piezoelectric coefficients (i.e. those of the combined
film-substrate structure) should not be used in place of material piezoelectric
coefficients when attempting to model the behaviour of devices. Such actions
would inevitably lead to erroneous results.
