PhD Thesis Arne Lüker final version V4 - Cranfield University

Sol-Gel derived Ferroelectric Thin Films for Voltage Tunable Applications
deposited on SiO2/Si substrates under different annealing conditions, the surface of the
films was found to be smooth without any discontinuities in terms of crazing and
microcracks, see Fig. 7.4, 7.11.
Based on these results and the finding of the last section, that the XRD analysis of the
PZT/PST composites with underneath PST grown at 700°C exhibited lower peak intensity
of perovskite (111) phase in comparison to PZT/PST structure with PST layer at 550°C, an
AFM surface analysis of PZT films on platinised structures, i.e. Pt/Ti/PST/SiO2/Si with
buffer PST deposited at 550°C was carried out. The result is illustrated in Figure 8.7(a) and
was also compared with PZT surface having the
same PZT film thickness, grown on a different
template, in this case a PZT/Pt/Ti/TiO2/SiNx/Si
device structure with TiO2 as a barrier deposited
at 700°C as shown in Figure 8.7(b).
The estimated RMS surface roughness was 0.7
nm and 0.9 nm in these platinised PZT/PST/SiO2
and PZT/TiO2/SiNx transducer stacks
respectively. These results indicate that a
homogenous film surface with lower roughness
can be achieved by employing PST as a
diffusion barrier in the PZT device structures,
similar to commonly used barrier TiO2 layer.
The apparent variation in texture of the PZT
films in these two device structures as depicted
in Figure 8.7 can be explained in terms of the
effect of incorporating different types of
templates in device structural layer design,
properties of the barrier materials, the different
deposition techniques and thermal treatment of
the barrier layers which altered the film density,
porosity and crystalline phase nucleation, thus having an impact on final PZT
microstructures. There are several contributing factors in determining quality of the PZT
(a)
(b)
Fig. 8.7: AFM surface imagines of PZT on Pt/Ti on (a)
PST/SiO2/Si and (b) TiO2/SiN. The roughness rms is (a)
0.7 and (b) 0.9 nm
149