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- Cho, Choong-Rae, 66-
(author)
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Ferroelectric Na0.5K0.5NbO3 Thin Films : Processing, Physical Properties and Applications
- 2001
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Doctoral thesis (other academic/artistic)abstract
- 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.
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| 2. |
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| 3. |
- Cho, Choong-Rae, et al.
(author)
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Na0.5K0.5NbO3 thin films for voltage controlled acoustoelectric device applications
- 2002
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 80:17, s. 3171-3173
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Journal article (peer-reviewed)abstract
- Perovskite Na0.5K0.5NbO3 (NKN) thin films have been prepared on Y+36degrees cut single crystal quartz substrates using the pulsed laser ablation technique. X-ray diffraction theta-2theta and omega-scan data demonstrate almost perfectly c-axis oriented film textures with narrow mosaic broadening. Radio frequency dielectric spectroscopy showed that the films possess relatively high dielectric permittivities, low dielectric losses, and low frequency dispersions. Capacitance-voltage (C-V) measurements for a 2 mum slot NKN/quartz interdigital capacitor yield 23.1% tunability by applying 40 V bias at 1 MHz, while C-V hysteresis indicates polarization reversal. The considerable voltage tunability with superior crystallinity in piezoelectric NKN films on quartz substrates suggests their potential use for novel voltage tunable acoustoelectric devices.
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| 4. |
- Cho, Choong-Rae, et al.
(author)
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Preparation of Na0.5K0.5NbO3/La0.6Sr0.2Mn1.2O3/LaAlO3 Thin Film Structures by Pulsed Laser Deposition
- 1999
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In: Multicomponent oxide films for electronics. - Warrendale, Pa : Materials Research Society. - 1558994815 - 9781558994812 ; , s. 249-254
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Conference paper (peer-reviewed)abstract
- We report on ferroelectric/giant magnetoresistive Nao.sKo.sNbCVLao.oSrojMniO} (NKN/LSMO) heterostructures gro\vn onto LaAlOj (001) single crystal using KrF pulsed laser ablation of stoichiometric ceramic target. Main processing parameters have been optimized to obtain smooth LSMO template layer, avoid NKN-LSMO interdiffusion, preserve NKN stoichiometry against the lost of volatile potassium and sodium and achieve reasonable reliability of NKN film performance. X-ray diffraction 0- 20 scans and rocking curves evidence for single-phase content and high c-axis orientation both in template LSMO and top NKN layers. Ferroelectric measurements yield remnant polarization P, of 1.5 (.iC/cm2 and spontaneous polarization Ps of 7 jiC/cm2 at electric field strength of 130 kV/cm. At room temperature, dielectric permittivity e' and dissipation factor tancJhave been found to vary from 595 to 555 and 0.046 to 0.029 respectively in the frequency range of 0.4 to 20 kHz. At 10 kHz dielectric permittivity linearly increases from 410 to 650 in the temperature range 77 K to 415 K while the dissipation factor below 320 K does not exceed 3%.
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