PhD Thesis Arne Lüker final version V4 - Cranfield University

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136 PST directly on SiO2 rate of approximately 0.029 nm/(mW·s) and 0.033 nm/(mW·s) for SiO2 and PST respectively. Fig. 7.13: Depth profile of one layer PST on SiO2/Si. The interface regions are clearly visible. The diffusion area of the PST-SiO2 interface is relatively small. After ten etching steps the diffusion of titanium and lead stops. Only strontium diffuses further on until it is not traceable anymore after the 14 th etching step (inset in Fig. 7.13). The silicon diffuses strongly into the PST layer due to the large Si-source. The broad SiO2 area is the dominant feature in this graph and the SiO2-Si interface is clearly distinguishable. As a comparison a sample with a single layer of PZT directly onto SiO2/Si was prepared. It is well known that PZT suffers from a strong lead diffusion into the substrate, therefore 10% Pb excess is normally given to the solution to compensate the Pb loss during the heat treatment of the thin film. Although PZT needs a lower annealing temperature and time (≤ 600°C for 5 min, depending on the composition) the film was annealed at 650°C for 15 min for better comparison. The depth profile of this sample is shown in Fig. 7.14.
Sol-Gel derived Ferroelectric Thin Films for Voltage Tunable Applications Fig. 7.14: Depth profile of one layer PZT on SiO2/Si. The interface regions are blurred. The etch rates in this system are considerably lower compared to the PST sample. The etching parameters were adjusted to 100 s, 2 kV and 0.9 µA (1.8 mW) for each etch step. Although that means a higher ion beam output more etch cycles were needed to reach a comparable depth. Assuming the same layer thicknesses than above this leads to an etch rate of 0.009 nm/(mW·s) for PZT and 0.012 nm/(mW·s) for the SiO2 interdiffusion layer. The lower etch rate of the latter layer was explained by a formation of some lead silicate (PbSiO3), which is harder to etch than SiO2 using the ion sputtering unit [7]. Fig. 7.15 shows the details of the Auger analysis for the Pb, O and Si traces. The first two traces after etch cycles 15 and 32 (top blue and magenta in the Pb and O spectra) show that Pb and O are present in a similar way like in Fig. 7.11, viz a Pb double peak at 140 and 146 eV and an OPZT peak at 536 eV. The Si is not really traceable in this region. After etch cycle 54 (thick black curve) a second O peak begins to appear at 539 eV and the Si shows two weak peaks at 102 and 107 eV. At the same time the Pb double peak moves slightly to lower energies and begins to “wobble” around with increasing depth until it vanishes after the 94 th etch cycle (blue curve). After the Pb is not traceable anymore O shows only one peak at higher energy and the Si only one at lower energy. 137
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Sol-Gel derived Ferroelectric Thin
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Abstract Ferroelectric perovskite t
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Table of Content Introduction and M
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Page 87 and 88: Sol-Gel derived Ferroelectric Thin
Page 99 and 100: Intensity [arb. Units] (g) (f) (e)
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PhD Thesis Arne Lüker final version V4 - Cranfield University

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