CONTENTS Abstract………………………………………………………………………………I Contents ……………………………………………………………………………V Table Captions ……………………………………………………………………VIII Figure Captions ……………………………………………………………………IX Chapter 1 General Introduction ………………………………………………1 1-1 Perovskite-type Structure ……………………………………………1 1-2 Piezoelectricity ………………………………………………………1 1-3 Domain Structure…………………………………………………………2 1-4 Pb-based PZT Piezoelectric Material.………………………………3 1-4-1 PZT Piezoceramics ………………………………………………………4 1-4-2 PZT Thin Films ……………………………………………………………6 1-5 Fabrication Methods ……………………………………………………7 1-5-1 Bulks ………………………………………………………………7 1-5-2 Thin Films …………………………………………………………7 1-6 Outline of the Thesis …………………………………………………9 Chapter 2 Experimental Procedure……………………………………………11 2-1 Sol-Gel Processing ………………………………………………………11 2-1-1 Deposition Chemistry ……………………………………11 2-1-2 Drying and Firing…………………………………………12 2-2 Sample Preparation.………………………………………………………12 2-2-1 Sol-Gel Derived PZT Piezoceramics……………………13 2-2-2 Nb-Modified Solid-State Reaction PZT Piezoceramics………………………………………………14 2-2-3 Sol-Gel and Spin Coating Deposited PZT Ferroelectric Thin Films.......................................14 2-3 Electroding …………………………………………………………15 2-4 Poling ………………………………………………………………15 2-4-1 Bulk materials ……………………………………………15 2-4-2 Thin Films …………………………………………………16 2-5 Characterization Analyses ………………………………………16 2-5-1 Gel Powders Size Distribution…………………………16 2-5-2 Crystal Phase and Microstructure ……………………16 2-5-3 Domain Observation ………………………………………17 2-5-4 Measurements of Piezoelectric Properties …………17 2-5-4-1 Equivalent Circuits and Measurement Method……………………………17 2-5-4-2 Electromechanical Coupling Factors and Mechanical Quality Factor…………………………………19 2-6 Fabrication of Surface Acoustic Waves Resonator …………21 Chapter 3 Evaluation of PZT Piezoceramics from Gel-Derived Powders.....................................22 3-1 Introduction ………………………………………………………22 3-2 Results and Discussion……………………………………………24 3-3 Conclusions …………………………………………………………27 Chapter 4 Effect of Nb-Modified on Microstructures and Piezoelectric Properties of PZT Piezoceramics.........................29 4-1 Introduction ………………………………………………………29 4-2 Results and Discussion …………………………………………30 4-3 Conclusions …………………………………………………………32 Chapter 5 Crack Alleviation Process of PZT Ferroelectric Thin Films by Sol-Gel Deposition and Application for SAW Device …………………34 5-1 Introduction ………………………………………………………34 5-2 Fundamentals of Surface Acoustic Waves………………………35 5-2-1 Interdigital Transducer…………………………………35 5-2-2 General Equations for Surface Waves and Bulk Waves ……………………………………………36 5-2-3 Surface Acoustic Waves Parameters …………………37 5-2-4 Surface Acoustic Waves Resonator ……………………39 5-3 Results and Discussion …………………………………………40 5-3-1 Crystal Structure…………………………………………40 5-3-2 Microstructure and Surface Morphology………………42 5-3-3 Analysis of Electrical Properties……………………43 5-3-4 Analysis of Interdigital Transducer Structure……43 5-3-5 Performance of SAW Resonator …………………………44 5-4 Conclusions …………………………………………………………44 Chapter 6 Conclusions and Future Works……………………………………46 References …………………………………………………………………………50 Tables ………………………………………………………………………………55 Figures………………………………………………………………………………60 Acknowledgements ………………………………………………………………99 Table Captions Table 1 A comparison of the different deposition techniques ………55 Table 2 Constants varying with vibration modes used for calculating electromechanical coupling factors as a function of resonance frequency ………………………………………………………………56 Table 3 The device parameters of a SAW resonator………………………57 Table 4 The reflux time and Zr/Ti ratio ………………………………58 Table 5 Dielectric constant and dielectric loss of the PZT bulks calcined at 900oC for 4 h, sintered at various temperatures under f = 1KHz, 102 KHz ……………………………………………………59 Figure Captions Fig. 1.1 Schematic of ABO3 perovskite structure ………………………60 Fig. 1.2 Interrelationship of piezoelectricity and subgroups on the basis of crystal Symmetry ………………………………………61 Fig. 1.3 Dependence of grains and domains of piezoelectric ceramic…………………………………………………………………62 Fig. 1.4 Phase diagram of the PbTiO3 – PbZrO3 solid solution system …………………………………………………………………63 Fig. 2.1 Schematic of sol-gel routes………………………………………64 Fig. 2.2 Flow diagram for the processing of PZT ceramics with powders prepared by sol-gel processing………………………………………………65 Fig. 2.3 Equivalent electrical circuits of a piezoelectric vibrator ………………………………………………………………66 Fig. 2.4 Schematic of (a) modified Sawyer-Tower circuit and (b) typical P-E hysteresis loop………………………………………………………67 Fig. 2.5 Schematic of lift-off process for fabricating IDT pattern…………………………………………………………………68 Fig. 3.1 PZT as calcined gel powders size distribution………………69 Fig. 3.2 DTA/TG curves of the dried PZT gels……………………………70 Fig. 3.3 X-ray diffraction patterns for PZT powders calcined at 900oC as a function of calcining time ……………………………………71 Fig. 3.4 Density variations of the PZT ceramics calcined at 900oC for 4 h, then sintered at various temperatures for 2 h ……………………72 Fig. 3.5 SEM morphology of PZT ceramic calcined at 900oC for 4 h and sintered at (a) 1000oC (b) 1100oC (c) 1200oC for 2 h …………………73 Fig. 3.6 TEM observation of PZT ceramic calcined at 900oC for 4 h, and then sintered at 1100oC for 2 h (a) bright-field image of the 900a-c domain boundary. (b) selected-area diffraction pattern …………74 Fig. 3.7 P-E hysteresis curve of PZT ceramic calcined at 900oC for 4 h, and then sintered at 1100oC for 2 h ………………………………………75 Fig. 3.8 Variation of temperature coefficient of resonator frequency (TCF) as a function of sintering temperature with fixed firing time 2 h and poling conditions 3.0 kV/mm, 90oC for 30 min…………………………76 Fig. 3.9 Variation of impedance with frequency for the poled PZT ceramic calcined at 900oC for 4 h, sintered at 1100oC for 2 h……77 Fig. 4.1 Scanning electron micrographs of surface morphology of PZT ceramics doped with 1 mole% Nb2O5 calcined at 850oC for 2 h, and sintered at (a) 1100oC (b) 1200oC (c) 1250oC for 2 h …………………………78 Fig. 4.2 Grain size variations between doped and undoped PZT ceramics as a function of the sintering temperature from 1100oC to 1250oC for 2 h ………………………………………………………79 Fig. 4.3 Scanning electron micrographs showing surface morphology of PZT ceramics sintered 1200oC for 2h (a) undoped (b) doped with 1 mole% Nb2O5……………………………………………………………………80 Fig. 4.4 XRD spectra for Nb2O5 doped samples. All samples were calcined at 850oC for 2 h, and then sintered except (a) as a function of sintering temperature (b) 1100oC (c) 1200oC and (d) 1250oC …………81 Fig. 4.5 P-E hysteresis curve of doped with Nb2O5 PZT ceramic calcined at 850oC for 2 h, sintered at 1250oC for 2 h. (Pr and Ec were 8.63 μC/cm2 and 17.2 kV/cm, respectively)…………………………………………82 Fig. 4.6 The variation of impedance with frequency for the poled doped PZT ceramic calcined at 850oC for 2 h, sintered at various temperatures for 2 h…………………………………………………………………83 Fig. 4.7 The variation of piezoelectric properties for doped PZT ceramic calcined at 850oC for 2 h, sintered at various temperatures for 2 h…………………………………………………………………84 Fig. 4.8 Variation of impedance with frequency for the poled doped with Nb2O5 PZT calcined at 850oC for 2 h, sintered at 1250oC for 2 h…………………………………………………………………85 Fig. 5.1 Elementary structure for SAW/pseudo-SAW delay line on piezoelectric substrate comprising input and output IDTS with uniform finger spacing ………………………………………………………86 Fig. 5.2 Transfer function components for the SAW device……………87 Fig. 5.3 XRD patterns of PZT thin films (a) sintered at various temperature for 30 min at 50oC/min. (b) sintered at 650oC for 30 min at various heating rate ……………………………………………………………………88 Fig. 5.4 Volume fraction of pyrochlore of PZT thin films (a) sintered at various temperatures for 30 min at 50oC/min. (b) sintered at 650oC for 30 min at various heating rate……………………………………………89 Fig. 5.5 XRD patterns of 0.2 M PZT films with sintering at 700oC for 30 min (a) drying, pre-baking and sintering with heating rate 50oC/min repeatedly. (b) drying and pre-baking repeatedly, then sintering with heating rate 50oC/min. (c) drying and pre-baking repeatedly, then sintering with heating rate 5oC/min ………………………………………………90 Fig. 5.6 Scanning electron microscopy of cross-sections of 0.2 M PZT film with sintering at 700oC for 30 min (a) drying, pre-baking and sintering with 50oC/min repeatedly. (b) drying and pre-baking repeatedly, then sintering with heating rate 50oC/min. (c) drying and pre-baking repeatedly, then sintering with heating rate 5oC/min ……91 Fig. 5.7 SEM micrographs of PZT film surface obtained with different molar concentration and sintered at 700oC for 30 min with 50oC/min (a) 0.2 M (b) 0.3 M ………………………………………………………………92 Fig. 5.8 SEM micrographs of PZT film surface obtained at different heating rate and sintered at 700oC for 30 min (a) 50oC/min (b) 100oC/min (c) 150oC/min………………………………………………………………93 Fig. 5.9 P-E hysteresis curve of PZT thin film deposited at 0.2 M gel concentration with a drying at 150oC for 5 min and a pre-baking at 350oC for 10 min, and then sintering at 700oC for 30 min with a heating rate 50oC/min…………………………………………………………94 Fig. 5.10 Basic design structure of SAW delay line on PZT films …95 Fig. 5.11 Basic gadget of measured frequency for a SAW device on PZT films…………………………………………………………96 Fig. 5.12 Frequency response of a SAW delay line on PZT thin films……………………………………………………………97