PhD Thesis Arne Lüker final version V4 - Cranfield University

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PST directly on SiO2
Fig. 7.2: A slotted PST varactor to minimise the variation of the capacitor areas due to mask alignment
errors.
These two examples show clearly that sol-gel deposition of PST directly onto SiO2 is
possible without any limitations. In the following sections the growth of PST 40/60
doped with 3 mol% Mn directly onto SiO2 is studied in more detail using XRD-, SEM-,
AFM- and Auger analysis.
7.1 The growth of PST on SiO2
X-ray-diffractograms of PST deposited directly onto SiO2 and annealed at different
temperatures from 350°C to 650°C are depicted in Fig. 7.3. These are diffractograms of
just one layer PST (~ 40-50 nm), therefore the overall intensities are lower than in Fig.
5.3 for 6 layers. It is believed that if one layer is crystallised the subsequent layers will
crystallise as well using the same deposition process, thus the study in this section is
limited to one layer PST only.
It can be seen that the PST deposited directly onto SiO2 begins to crystallise around
550°C into the (110) phase. That is approximately 50°C higher compared to PST on
Ti/Pt. No other orientations of the perovskite crystal structure are visible. But that can be
a result of the low intensities.