PhD Thesis Arne Lüker final version V4 - Cranfield University

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146 PST as a buffer layer for PZT on SiO2 expected to provide favourable growth conditions for high quality PZT device layer in PZT transducer stacks. Relative PZT Intensity (Approach 1) 1.2 1 0.8 0.6 0.4 0.2 0 550 575 600 625 650 675 700 725 0 Fig. 8.4: The relative PZT PST (111) Annealing intensity calculated Temperature by two [°C] different approaches A further experimental study was undertaken to compare the performance of the PST layer with other widely employed materials as a barrier in the design of PZT transducers. In this case TiO2 was chosen as a buffer layer, as it was successfully integrated to realise PZT FBAR devices (Thin Film Bulk Acoustic Resonator) and FBAR filters for mobile phones [10]. In this study different combinations of structural layer and barrier were selected, e.g. PST/SiO2/Si and TiO2/SiN/Si templates with PST and TiO2 layer deposited at 550°C and 700°C respectively to develop a better understanding of their influences on PZT microstructures and grain orientations. Fig. 8.5 (a) and (b) show XRD spectra of PZT composites without a bottom Pt/Ti electrode, produced on both types of templates with a buffer PST and TiO2 respectively. XRD patterns of PZT stacks on both types of buffer layers exhibited similar polycrystalline nature of the PZT film having random orientations that comprised of (100), (110), (111), (200), (210) and (211) peaks and having low peak intensity. It was noted that the PZT (110) peak has slightly higher intensity compared to (100) and (111) peaks but broader, whereas the PZT (111) peak was sharper. It is evident from XRD spectra that the PZT stacks were not completely 0.1 0.09 0.08 0.07 0.06 0.05 0.04 0.03 0.02 0.01 Relative PZT Intensity (Approach 2)
Intensity [arb. Units] Sol-Gel derived Ferroelectric Thin Films for Voltage Tunable Applications crystallised into perovskite structures resulting in a mixture of nanocrystalline and amorphous phases in both cases. This is not quite surprising and reflects the need of a seed layer, in most cases a Pt seed layer with Pt (111) grains that enhances the PZT phase transformation introducing nucleation sites with the formation of intermetallic phase, Pt3Pb and reducing the surface energy [3, 11]. (100) (110) (d) (c) (b) (a) (111) (200) (210) (211) 20 25 30 35 40 45 50 55 60 In fact, the XRD analysis of the PZT device structures having platinised bottom electrode along with PST and TiO2 barrier configurations exhibited a preferred (111) phase with higher peak intensity and less preferred (110) peaks that confirmed the well- crystalline PZT grain formation. It was further noted that the PZT/Pt/Ti/TiO2/SiN stacks showed also a diminished (100) peak and introduced a slight shift in Pt (111) and PZT (111) peaks towards lower angles in contrast to PZT/Pt/Ti/PST/SiO2 device structure. The relative shift in Pt and PZT peak positions reflects an incremental change in lattice parameters, when PZT films were deposited on different types of barrier layer and templates. XRD patterns of PZT films deposited on PST/Pt/Ti/Si templates look very similar to those obtained from the PZT device structures incorporating barrier TiO2 layer. Pt 2-Theta [°] Fig.8.5: X-ray diffractograms of PZT on (a) PST/SiO2, (b)TiO2/SiN, (c) Pt/PST/SiO2, and (d)Pt/TiO2/SiN 147
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Sol-Gel derived Ferroelectric Thin
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Abstract Ferroelectric perovskite t
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Acknowledgements I want to take thi
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Table of Content Introduction and M
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Page 97 and 98: Sol-Gel derived Ferroelectric Thin
Page 99 and 100: Intensity [arb. Units] (g) (f) (e)
Page 103 and 104: Relative diel. diel. constant Const
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Page 121 and 122: Tunability [%] 100 90 80 70 60 50 4
Page 131 and 132: (g) (f) (e) (d) (c) (b) (a) Sol-Gel
Page 147: Sol-Gel derived Ferroelectric Thin
Page 175 and 176: Internships: Sol-Gel derived Ferroe
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PhD Thesis Arne Lüker final version V4 - Cranfield University

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