PhD Thesis Arne Lüker final version V4 - Cranfield University

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B Site Doping of PST 40/60 ........................................................................................... 110 6.1 Synthesis and Characterisation of (Pb0.4,Sr0.6)(Ti1-x,Mnx)O3 .......................... 110 6.2 Enhanced Tunability and Ferroelectricity in Mn doped PST ......................... 118 6.3 References ....................................................................................................... 123 PST directly on SiO2 ....................................................................................................... 127 7.1 The growth of PST on SiO2 ............................................................................ 128 7.1.1 The interface between SrTiO3 and Si .......................................................... 132 7.2 Auger Analysis of PST on SiO2 ...................................................................... 134 7.3 References ....................................................................................................... 139 PST as a buffer layer for PZT on SiO2 ........................................................................... 142 8.1 XRD-Studies ................................................................................................... 144 8.2 Microstructure Evaluation .............................................................................. 148 8.3 Electrical Characterisation of PZT with a PST buffer layer ........................... 151 8.4 References ....................................................................................................... 153 Final Discussions, Conclusions and Future Work .......................................................... 156 9.1 References ....................................................................................................... 160 Appendix A: PZT actuated Diamond Cantilever Technology ........................................ 162 A.1 Introduction ..................................................................................................... 162 A.2 Design ............................................................................................................. 163 A.2.1 Modes of operation ................................................................................. 163 A.2.2 Resonance Behaviour.............................................................................. 164 A.2.3 Cantilever deflection ............................................................................... 166 A.3 Technology ..................................................................................................... 168 A.4 Results ............................................................................................................. 169 A.5 Conclusions ..................................................................................................... 170 A.6 References ....................................................................................................... 171 Appendix B: Curriculum Vitae ....................................................................................... 172 vi
Sol-Gel derived Ferroelectric Thin Films for Voltage Tunable Applications Introduction and Motivation Ferroelectricity was discovered in the beginning of the last century by J. Valasek in Rochelle salt (potassium sodium tartrate) which was originally produced in France in 1665 by an apothecary Elie Seignette. Rochelle salt was originally used in medicine as a mild purgative. Crystals of Rochelle salt were easily grown and were subsequently used in piezoelectric devices such as crystal microphones and phonograph pickup cartridges. Historically, ferroelectricity was discovered after piezoelectricity and pyroelectricity. The ceramic BaTiO3 (Barium Titanate), was found by B. Wul and I. M. Goldman. This discovery triggered considerable efforts in search of additional ferroelectrics having the same perovskite structure. A significant progress in applications was made possible after the discovery of Lead Zirconate Titanate - Pb(Zr,Ti)O3 or PZT – which has a very strong piezoelectric response, and a large remnant ferroelectric polarization. Lead-based materials have since become the dominant compounds in this field. Later on it was discovered that one could decrease the Curie temperature (ferroelectric- paraelectric transition temperature) TC of pure BaTiO3 (TC ~ 120 °C) down to room temperature by adding Strontium (Sr). From there on Ba1-xSrxTiO3 (BST) began to rock the world. The initial interest in BST thin films was due to its high dielectric constant, low dielectric loss, high dielectric breakdown and composition dependent Curie temperature enabling it to be in the paraelectric state as well as in the ferroelectric state, all of which makes it a candidate for replacing SiO2 as charge storage dielectric for DRAMs (dynamic random access memories), MEMS-switches and varactors in phase shifters. It is worthwhile to define some basic physical characteristics within ferroelectrics: 1. Pyroelectricity Pyroelectricty was probably first observed in tourmaline by ancient Greeks, but quantitatively investigated only in the eighteenth century, during the early studies of electrostatics. Sir David Brewster, a Scottish scientist, was the first to use the term pyro-(fire)-electricity in 1824 when describing this phenomena in one of his numerous and famous contributions to the Encyclopaedia Britannica. Pyroelectric 7
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Intensity [arb. Units] (g) (f) (e)
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Relative diel. diel. constant Const
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Intensity [arb. Units] Intensity [a
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Tunability [%] 100 90 80 70 60 50 4
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(g) (f) (e) (d) (c) (b) (a) Sol-Gel
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Internships: Sol-Gel derived Ferroe
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PhD Thesis Arne Lüker final version V4 - Cranfield University

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