| 1. |
- Blomqvist, Mats, et al.
(författare)
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High-performance epitaxial Na0.5K0.5NbO3 thin films by magnetron sputtering
- 2002
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 81:2, s. 337-339
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial Na0.5K0.5NbO3 (NKN) thin films have been grown on LaAlO3 substrates by rf magnetron sputtering of a stoichiometric, high-density, ceramic target. X-ray diffraction analysis showed c-axis oriented cube-on-cube growth. Micrometer size interdigital capacitor (IDC) structures were defined on the surface of the NKN film using photolithography. The electrical characterization at 1 MHz showed dissipation factor tan delta of 0.010, tunability 16.5% at 200 kV/cm and dielectric permittivity epsilon(r)=470. The frequency dispersion of epsilon(r) between 1 kHz and 1 MHz was 8.5% and the IDCs showed very good insulating properties with leakage current density on the order of 30 nA/cm(2) at 400 kV/cm. The polarization loop exhibits weak ferroelectric hysteresis with maximum polarization 23.5 muC/cm(2) at 600 kV/cm. These results are promising for tunable microwave devices based on rf sputtered NKN thin films.
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| 2. |
- Blomqvist, Mats, et al.
(författare)
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Rf-magnetron sputtered ferroelectric (Na,K)NbO3 films
- 2002
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Ingår i: Proceedings of the 13th IEEE International Symposium on Applications of Ferroelectronics. - 0780374142 ; , s. 195-198
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Konferensbidrag (refereegranskat)abstract
- Sodium potassium niobate (Na,K)NbO3 (NKN) thin films were grown by rf-magnetron sputtering from stoichiometric Na0.5K0.5NbO3 target on LaAlO3 (LAO) single crystals and polycrystalline Pt80Ir20 (PtIr) substrates. NKN films on polycrystalline PtIr substrates were found to be preferentially (004 oriented while XRD measurements reveal epitaxial quality of NKN/LaAlO3 film structures. The ferroelectric state in NKN/PtIr films at room temperature is indicated by polarization loops with polarization as high as 33.4 muC/cm(2) at 700 kV/crn, remnant polarization of 9.9 muC/cm(2), and coercive field of 91 kV/cm. I-V characteristics of vertical Au/NKN/PtIr capacitive cells and planar Au/NKN/LAO interdigital capacitors (IDCs) showed very good insulating properties. For NKN IDC the leakage current density was in the order of 30 nA/cm(2) at 400 kV/cm. Rf dielectric spectroscopy demonstrates low loss, low frequency dispersion, and high voltage tunability both for vertical Au/NKN/PtIr and planar interdigital Au/NKN/LAO capacitors.
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| 3. |
- Cho, Coong-Rae, et al.
(författare)
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Na0.5K0.5NbO3/SiO2/Si Thin Film Varactor
- 2000
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 76, s. 1761-
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Tidskriftsartikel (refereegranskat)abstract
- Perfectly c-axis oriented micrometer thickNa 0.5 K 0.5 NbO 3 (NKN) films have been prepared on a thermally grown ultrathinSiO 2 template layer onto a Si(001) wafer by the pulsed laser deposition technique. A x-ray diffraction θ–2θ scan reveals multiple-cell structuring of single phase NKN film along the polar axis, while filmsgrown onto amorphous ceramic (Corning) glass show a mixture of slightly c-axis oriented NKN and pyrochlore phases. This implies a small amount ofSiO 2 crystallites distributed in an amorphous matrix inherit Si(001) orientation and promotes highly oriented NKN film growth. NKN filmdielectric permittivityε ′ was found to vary from 114.0 to 107.2 in the frequency range 1 kHz–1 MHz, while the resistivity was on the order of2.6×10 10 Ω cm @ 20 kV/cm. The planar interdigital variable reactance device (varactor) based on theNKN/SiO 2 /Si thin film structure possesses a dissipation factor of 0.8% at 1 MHz and zero bias, electrical tunability of 3.1%, and nA order leakage current at 20 V bias at room temperature.
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| 4. |
- Cho, Nam-Hyuk, et al.
(författare)
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The Orientia tsutsugamushi genome reveals massive proliferation of conjugative type IV secretion system and host–cell interaction genes
- 2007
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 104:19, s. 7981-7986
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Tidskriftsartikel (refereegranskat)abstract
- Scrub typhus is caused by the obligate intracellular rickettsia Orientia tsutsugamushi (previously called Rickettsia tsutsugamushi). The bacterium is maternally inherited in trombicuid mites and transmitted to humans by feeding larvae. We report here the 2,127,051-bp genome of the Boryong strain, which represents the most highly repeated bacterial genome sequenced to date. The repeat density of the scrub typhus pathogen is 200-fold higher than that of its close relative Rickettsia prowazekii, the agent of epidemic typhus. A total of 359 tra genes for components of conjugative type IV secretion systems were identified at 79 sites in the genome. Associated with these are >200 genes for signaling and host–cell interaction proteins, such as histidine kinases, ankyrin-repeat proteins, and tetratrico peptide-repeat proteins. Additionally, the O. tsutsugamushi genome contains >400 transposases, 60 phage integrases, and 70 reverse transcriptases. Deletions and rearrangements have yielded unique gene combinations as well as frequent pseudogenization in the tra clusters. A comparative analysis of the tra clusters within the genome and across strains indicates sequence homogenization by gene conversion, whereas complexity, diversity, and pseudogenization are acquired by duplications, deletions, and transposon integrations into the amplified segments. The results suggest intragenomic duplications or multiple integrations of a massively proliferating conjugative transfer system. Diversifying selection on host–cell interaction genes along with repeated population bottlenecks may drive rare genome variants to fixation, thereby short-circuiting selection for low complexity in bacterial genomes.
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| 5. |
- Kim, Jang-Yong, et al.
(författare)
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Magnetically and electrically tunable devices using ferromagnetic/ferroelectric ceramics
- 2004
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Ingår i: Physica status solidi. B, Basic research. - : Wiley. - 0370-1972 .- 1521-3951. ; 241:7, s. 1714-1717
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Tidskriftsartikel (refereegranskat)abstract
- There has been a growing interest in tunable devices applications such as filters, phase shifters, and resonators. Both of ferromagnetic and ferroelectric materials have strong advantages in the high tunability and stability. Therefore many reports have been published by employing ferrite or dielectric materials for high frequency devices applications. Both of controllable dielectric permittivity and magnetic permeability were considered one of the solutions for impedance matching in tunable devices. In this experiment ferromagnetic/ferroelectric composite ceramics were successfully fabricated without any cracking or shrinkage. Fabricated ferromagnetic/ferroelectric composite ceramic showed ferroelectric properties of P-E hysteresis and magnetic properties of B-H hysteresis loops.
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| 6. |
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| 7. |
- Koh, Jung-Hyuk, 1969-
(författare)
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Processing and Properties of Ferroelectric Ag(Ta,Nb)O3 Thin Films
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- High tunability and low loss tangent of ferroelectric thinfilms offer unique opportunity for the development of variousmicrowave devices. Silver tantalate niobate, which showsexcellent microwave properties, was selected for this study.Ag(Ta,Nb)O3(ATN) showed week dielectric dispersion in a widefrequency range from 1 kHz up to 100 GHz, negligible losses upto 30 GHz, and ease to tailor paraelectric state in a widetemperature range by Ta:Nb ratio.This thesis is mainly based on the synthesis andcharacterization of niobate ferroelectric ATN thin films. Thinfilms for various measurements were prepared by pulsed laserdeposition and rf-magnetron sputtering techniques.X-ray diffraction (XRD) pattern show that ATN/Pt80Ir20films have been found to be (001) preferentiallyoriented, while the epitaxial quality of ATN/LaAlO3heterostructures have been ascertained. Dielectricproperties were analyzed by measuring the relationship betweendielectric permittivity and frequency as well as dielectricpermittivity and temperature. Reliable tracing of theferroelectric hysteresis polarization versus electric loopsindicate the ferroelectric state in ATN films at temperaturebelow 125 K and yields the remanant polarization of 0.4µC/cm2@ 77 K.The fundamental current-voltage behavior in Ag(Ta,Nb)O3ferroelectric films was measured usingMe/Ag(Ta,Nb)O3/Pt80Ir20, Me = Pd, Au, Cr, and Al, vertical capacitivecell structures with different top electrodes. Various kinds ofconduction mechanisms such as Schottky emission, Poole-Frenkel,Fowler-Nordheim, and ionic conduction were classified.Finally, by fabricating interdigital capacitors on the oxidesubstrates, the characteristics and performances of Ag(Ta,Nb)O3varactors were examined. Au/Cr/ATN/LaAlO3interdigital capacitors exhibited loss tangent aslow as 0.0033 @ 1 MHz, weak frequency dispersion of 5.8 % in 1kHz to 1 MHz range, tunability as high as 16.4 %,K-factor (tunability/tanδ) higher than 48.
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