Ferroelectric Na0.5K0.5NbO3 Thin Films: Processing, Physical Properties and Applications
2001 (English)Doctoral thesis, comprehensive summary (Other scientific)
This thesis presents the results on the fabrication offerroelectric Na0.5K0.5NbO3(NKN) thin films by pulsed laser deposition (PLD)technique, comprehensive characterization of film properties,and various applications of NKN films. To preparestoichiometric single phase ferroelectric NKN films andovercome high volatility of Na and K constituents through thecomplete thermalization of plasma plume and forming a shockwave, NKN ceramic target was ablated at sufficiently highambient oxygen pressure. On the other hand, Na deficient filmsdeposited at low ambient pressure exhibited superparaelectricbehavior with very low frequency dispersion and uniquetemperature stability in the range 77 K to 420 K. Highly polaraxis oriented textures (XRD reflection ratio>100) areobserved in the films on polycrystalline Pt80Ir20, amorphous SiO2/Si, hexagonal Al2O3and trigonal quartz substrates. Smooth filmssurface (average roughness = 6 Å), significantly narrowermosaic broadenings than those in substrates (more than 6times), and abnormally large grain sizes (up to several µm2) indicateself-asembling phenomenon. From the analysis of bi-axialtextures observed in NKN films on MgO substrates, effect of theself-assembling has been attributed to strong interactionbetween NbO6octahedra and two-dimensional film growthmode.
Superior crystalline properties correlate with highperformances of electrical properties. High remnantpolarization of µC/cm2, low dielectric loss less than 1 %, highresistivity in the order of 1010Ω -cm, very low leakage currents, and highbreakdown voltages (>500 kV/cm) are observed in NKN films.Polarization fatigue resistant properties in Au/NKN/Ptstructures and wide memory window with long retention time inAu/NKN/SiO2/Si/Au MFIS-diode, as well as high degree ofpreferential orientations indicate NKN is a suitable materialfor next generation ferroelectric non-volatile memories. Highvoltage tunability (>40 %) with very low loss (<1 %)observed in NKN varactors both at radio and microwavefrequencies evidence this material is a promising candidate forvarious voltage tunable microwave devices. Considerable voltagetunability combined by high piezoelectricity in polar-axisoriented NKN films on various substrates suggest novel voltagetunable acoustic wave devices.
Place, publisher, year, edition, pages
Stockholm: Fysik , 2001. , 101 p.
Ferroelectric thin film, Pulsed Laser Deposition
IdentifiersURN: urn:nbn:se:kth:diva-3110ISBN: OAI: oai:DiVA.org:kth-3110DiVA: diva2:8872
NR 201408052001-03-212001-03-21Bibliographically approved