| 1. |
- Koh, J. H., et al.
(författare)
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Dielectric properties and Schottky barriers in silver tantalate-niobate thin film capacitors
- 2001
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Ingår i: Integrated Ferroelectrics. - 1058-4587 .- 1607-8489. ; 39:1-4, s. 1361-1368
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Tidskriftsartikel (refereegranskat)abstract
- Submicron thick ferroelectric Ag(Ta,Nb)O-3 films have been pulsed laser deposited on the bulk Pt80Ir20 polycrystalline substrates. They are ferroelectric at temperatures below 125 K with the remnant polarization of 0.4 muC/cm(2) @ 77K and paraelectric at higher temperatures with tandelta @ 100 kHz as low as 0.015. Extensive I-V characterization has been performed in a wide temperature range 77 K to 350 K for vertical Me/Ag(Ta,Nb)O-3/Pt80Ir20 capacitive cells, where the metals Me = Pd, Au, Cr, and Al have been used as a top electrode. The electronic transport in thin Me/Ag(Ta,Nb)O-3/Pt80Ir20 capacitors follows the Schottky emission mechanism with the barrier height for the Pd, Au, Cr, and Al of 0.85, 0.8, 0.74, and 0.69 eV, respectively.
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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- Khartsev, Sergiy, et al.
(författare)
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Comparative characteristics of Na0.5K0.5NbO 3 films on Pt by pulsed laser deposition and magnetron sputtering
- 2003
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Ingår i: Integrated Ferroelectrics. - : Informa UK Limited. - 1058-4587 .- 1607-8489. ; 55, s. 769-779
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Tidskriftsartikel (refereegranskat)abstract
- Ferroelectric Na0.5K0.5NbO3 (NKN) thin films were grown on the Pt80Ir20 polycrystalline substrates by pulsed laser deposition (PLD) and radio frequency-magnetron sputtering (RF) technique using the same stoichiometric Na0.5K 0.5NbO3 ceramic target. X-ray diffraction proved both PLD- and RF-made Na0.5K0.5NbOj/Pt80Ir20 films are single phase and have preferential c-axis orientation. Temperature dependence of dielectric permittivity reveals the presence of two phase transitions around 210 and 410°C. Capacitance vs. applied voltage C-V @ 100 kHz, I-V, and P-E hysteresis characteristics recorded for the vertical capacitive structures yielded loss tan δ = 0.026 and 0.016, tunability about 44.5 and 30% @ 100 kV/cm, Ohmic resistivity 6.7 × 1012 Ω·cm and 0.2 × 1012 Ω·cm, remnant polarization 11.7 and 9.7 μC/cm2, coercive field 28.0 and 94.6 kV/cm for PLD- and RF-films, respectively. Piezoelectric test carried out in hydrostatic conditions showed piezoelectric coefficient dH = 21 for PLD-NKN and 15 pC/N for RF-NKN film.
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| 6. |
- 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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| 7. |
- Koh, J. H., et al.
(författare)
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Ag(Ta, Nb)O-3 thin-film low-loss variable interdigital capacitors
- 2001
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 79:14, s. 2234-2236
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Tidskriftsartikel (refereegranskat)abstract
- Epitaxial silver tantalate-niobate Ag(Ta, Nb)O-3 (ATN) films have been grown on LaAlO3(001) MgO(001), and Al2O3(011_2) single crystals by pulsed ablation of stoichiometric AgTa0.38Nb0.62O3 ceramic target. Rutherford backscattering spectroscopy has revealed Ag0.9Ta0.42Nb0.58O3-delta composition of fabricated films. Micrometer size interdigital capacitor structures have been defined photolithographically on the top surface of ATN films. ATN/LaAlO3 thin-film capacitors exhibit superior overall performance: loss tangent as low as 0.0033 @1 MHz, dielectric permittivity 224 @1 kHz, weak frequency dispersion of 5.8% in 1 kHz to 1 MHz range, tunability as high as 16.8%, factor K=tunability/tan delta higher than 48, and leakage current as low as 230 nA/cm2 @100 kV/cm. ATN films on MgO show the lowest loss factor of 0.0025 @1 MHz and the weakest frequency dispersion of 2.5x10(-8) Hz(-1).
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| 8. |
- Koh, J. H., et al.
(författare)
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Dielectric relaxation behavior of Ag(Ta,Nb)O-3 interdigital capacitors on oxide substrates
- 2004
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Ingår i: Japanese Journal of Applied Physics. - : IOP Publishing. - 0021-4922 .- 1347-4065. ; 43:4A, s. 1434-1437
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Tidskriftsartikel (refereegranskat)abstract
- The time-dependent dielectric relaxation behavior of Ag(Ta,Nb)O-3 interdigital capacitors was investigated for tunable device applications. Ag(Ta,Nb)03 thin films, which have high k-factor (tunability/ loss tangent), were deposited on the oxide substrates by pulsed laser deposition technique. Ag(Ta,Nb)03 thin film on the LaAlO3 substrate has an epitaxial relationship with the substrate. The observed tunabilities and K-factors of Ag(Ta,Nb)O-3/LaAlO3 and Ag(Ta,Nb)O-3/AI(2)O(3) interdigital capacitors were 5.9% and 17.8 and 3.8% and 9.9, respectively, at 40 V (maximum electric field of 100 kV/cm), 300 K, and 1 MHz. Capacitance relaxation follows the power law C(t) = C-infinity + C-0(t/ls)-(beta) with a very small exponent negligibly fitted in the time domain. Due to this small exponent, the capacitance was changed by less than 0.05% in 2V in 71 s. Time-dependent leakage current was measured by employing the Ag(Ta,Nb)O-3(0.4mum)/Al2O3 interdigital capacitor. The time-dependent relaxation current follows the power law j(t) = j(leak) +j(0)(t/ls)-(alpha) with an exponent alpha = 0-98, j(leak) = 1.14 x 10(-14), and j(0) = 11.42s.
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| 9. |
- Koh, J. H., et al.
(författare)
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Electrically tunable Ag(Ta,Nb)O-3 thin film structures on oxide substrates
- 2001
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Ingår i: Integrated Ferroelectrics. - 1058-4587 .- 1607-8489. ; 39:1-4, s. 1281-1288
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Tidskriftsartikel (refereegranskat)abstract
- We report on design, fabrication, and comparative test of three different types of voltage-variable interdigital capacitors made on ferroelectric Ag(Ta,Nb)O-3 films deposited on MgO and Al2O3 substrates. X-ray diffraction patterns show that ATN films pulsed laser deposited on MgO(001) and Al2O3(01 (1) under bar2) single crystals have preferential (00l) and (0kk) orientation. Capacitance and loss tangent in interdigital capacitors were measured as the functions of frequency and applied dc voltage bias, Loss tangent was as low as 0.0025 and 0.0034 and K-factor (tunability/tandelta) was around 26.2 and 20.0 for MgO and Al2O3, respectively, @ +/- 40 V (maximum electric field 200 kV/cm), 300 K, and I MHz. Both of polarization and steady leakage currents were observed in the current-time domain measurements. 0.1 pF interdigital capacitors have pA leakage current level @ +/- 40 V.
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| 10. |
- Koh, J. H., et al.
(författare)
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Ferroelectric silver niobate-tantalate thin films
- 2000
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Ingår i: Applied Physics Letters. - 0003-6951 .- 1077-3118. ; 77:26, s. 4416-4418
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Tidskriftsartikel (refereegranskat)abstract
- Submicron thick ferroelectric AgTa0.38Nb0.62O3 (ATN) films have been prepared by pulsed laser deposition technique onto Pt80Ir20 polycrystalline and La0.7Sr0.3CoO3/LaAlO3 single crystal substrates. ATN/Pt80Ir20 films have been found to be (001) preferentially oriented, while the epitaxial quality of ATN/La0.7Sr0.3CoO3/LaAlO3 heterostructures has been ascertained. Comparative analysis of the temperature and frequency dependencies of the dielectric permittivity epsilon' and loss tan delta in ATN films and bulk ceramics shows that in films: the coupled structural-ferroelectric monoclinic M-1-to-monoclinic M-2 phase transition occurs at the temperature 60 degrees lower than in ceramics, thus the temperature stability of epsilon' and tan delta in films is improved and occurs in extended temperature range. Reliable tracing of the ferroelectric hysteresis polarization versus electric loops indicates the ferroelectric state in ATN films at temperatures below 125 K and yields the remnant polarization of 0.4 muC/cm2 @77 K. Weak frequency dispersion, high temperature stability of the dielectric properties, as well as low processing temperature of 550 degreesC, are the most attractive features of ATN films.
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