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Vendik, O. G.; Hollmann, E. K.; Kozyrev, A. B.; Prudan, A. M.

doi:10.1023/a:1007797131173

Cited by 237 publications

(99 citation statements)

References 29 publications

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“…The dielectric constant of ⑀ STO (300 K)Ϸ200-250 with a maximum of ⑀ STO,max Ϸ300-450 at 55-65 K of our STO films are comparable to literature data. [2][3][4] The dielectric loss of the STO layer are very low, i.e., tan ␦ STO (300 K)Ϸ0.002-0.004 with a maximum of tan ␦ STO Ϸ0.005-0.01 at 35-55 K. The losses are very small compared to typical literature data for STO films on sapphire 5 and comparable to the best values obtained via postannealing treatment of STO on LaAlO 3 . 4 The aim of this work was to develop and examine different capacity designs in order to improve the tunability of the capacities especially at low electric voltages.…”

supporting

confidence: 59%

“…Simple considerations demonstrate, that values K(U max )Ͼ45 are required for most microwave applications of tunable capacities. 5 In Fig. 4, the quality factor is shown as function of the applied bias voltage for our VC and PC type capacities.…”

mentioning

confidence: 99%

“…4, the quality factor is shown as function of the applied bias voltage for our VC and PC type capacities. For comparison, K values of representative planar STO capacitors obtained from literature 5,7 are added. The plot demonstrates, that ͑i͒ our STO films on CeO 2 -buffered sapphire possess a good quality ͑i.e., KϾ45 is obtained for both designs at relatively low voltages͒ and ͑ii͒ that the design shows extremely high quality at very low voltages ͑i.e., KϾ45 for U dc Ͼ18 V͒.…”

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confidence: 99%

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Improved designs of tunable ferroelectric capacities for microwave applications

Ott

Wördenweber

2002

Applied Physics Letters

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Epitaxial SrTiO 3 films are deposited by on-axis magnetron sputtering on CeO 2 -buffered r-cut sapphire. The ferroelectric films possess low losses ͑e.g., tan ␦Ϸ0.001-0.004 at 300 K͒ and a large tunability at small electric fields. Different complex designs for ferroelectric capacities are prepared via dry etching ranging from standard designs to those in which the ferroelectric material is restricted to the gap of the capacity. The resulting capacity data can be explained in terms of an analytic model for parallel capacities. Due to modifications and optimization of the design, the quality factors for an improved capacity design exceeds the requirement for most applications K Ͼ45 already for extremely small voltages UϷ18 V, which demonstrates the good properties of the design in combination with the quality of our ferroelectric films. © 2002 American Institute of Physics. ͓DOI: 10.1063/1.1459486͔The rapid development of microwave applications in, among others, communication technology has triggered a strong demand for frequency tunable resonators and filters operating in the GHz regime. Thin films of ferroelectrics such as BaTiO 3 , SrTiO 3 ͑STO͒ and several others provide high dielectric constants ⑀ and the possibility of tuning since their ⑀ depends on the electric field strength, ⑀ϭ⑀(E). For tunable electronic devices and circuits, such films are, therefore, used as dielectric material in capacitors ͑see Fig. 1͒. Especially, the combination with conductors of extremely low rf losses like high-T C superconductors ͑HTS͒ seems to be promising. However, up to the present, the disadvantage of ferroelectric films is given by ͑i͒ the relatively high dielectric loss, for instance represented by typical values of the loss tangent of tan ␦Ͼ0.01 for STO films, ͑ii͒ the large voltages Uу100 V necessary for the frequency tuning, and ͑iii͒ the degradation of either the ferroelectric or HTS film in hybrid structures. This calls for a careful production control and an intelligent design of the capacitors. In this work, we demonstrate that low losses can be obtained in STO films, that small bias voltages of UϽ20 V can lead to a considerable tuning of nϷ1.6, and that degradation problems in the ceramic components might be avoided by a special design of the capacity.250 to 500 nm thick STO films are grown on CeO 2 -buffered r-cut sapphire (Al 2 O 3 ). Sapphire possesses extremely low microwave losses (tan ␦Ϸ10 Ϫ7 -10 Ϫ8 ), whereas the CeO 2 -buffer layer ͑30 nm thickness͒ reduces the lattice mismatch between STO and substrate. Furthermore, this substrate system has proven to be ideal for the deposition of high-temperature superconducting films, 1 i.e., the combination of STO with YBa 2 Cu 3 O 7 for the tunable high-Q resonators is feasible for this system. The layers are deposited via on-axis magnetron rf sputtering technique. CeO 2 growths ͑200͒ oriented with a full width at half maximum of ⌬ Ϸ0.8°-1.3°. The structural orientation of STO depends strongly on gas pressure and substrate temperature during deposition. At low proc...

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confidence: 59%

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confidence: 99%

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confidence: 99%

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Improved designs of tunable ferroelectric capacities for microwave applications

Ott

Wördenweber

2002

Applied Physics Letters

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“…Figure 10 shows the temperature dependence of the apparent (measured) permittivity of a BSTO film grown at 585 C. The dependence differs from that of the single crystal counterpart, which reveals sharp maximum at T m ¼ 125 K and a room temperature permittivity of 460. 20,26 The apparent permittivity of the BSTO film is reduced and reveals a diffuse maximum shifted to a higher temperature T m ¼ 150 K. This is a typical effect of the ferroelectric material inhomogeneities. The inhomogeneities result in formation of the residual polar regions and, consequently, broaden the phase transition and shift T m to the higher temperature.…”

Section: Resultsmentioning

confidence: 97%

Correlations between microstructure and Q-factor of tunable thin film bulk acoustic wave resonators

Vorobiev

Gevorgian

Löffler

et al. 2011

Journal of Applied Physics

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Correlations between microstructure and Q-factor of tunable solidly mounted Ba 0.25 Sr 0.75 TiO 3 (BSTO) thin film bulk acoustic wave resonators are studied using analysis of test structures prepared at different growth temperatures of the BSTO films varying in the range 450-650 C. The observed changes in the Q-factor with growth temperature are correlated with related changes in microstructure, including the grain size, texture misalignment, interfacial amorphous layer, surface roughness, and deterioration of the Bragg reflector layers. The correlations are established through analysis of corresponding extrinsic acoustic loss mechanisms, including Rayleigh scattering at localized defects, acoustic attenuation by amorphous layer, generation of the shear waves leaking into the substrate, waves scattering by surface roughness, and resonance broadening by local thickness variations. It is shown that the waves scattering by surface roughness at the BSTO film interfaces is the main loss mechanism limiting the Q-factor of the BSTO thin film bulk acoustic wave resonators.

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“…Ba x Sr 1-x TiO 3 (BST) and its related materials have been intensively studied for practical applications because of ferroelectricity, high permittivity and reconfigurable permittivity (i.e., tunability) in the paraelectric phase by applying external electric fields [1,2]. However, for tunable thin film capacitors mostly used at microwave frequencies, the high permittivity of BST results in the great capacitance in the parallel plate configuration, which is not always suitable for applications from the viewpoint of the impedance matching in the circuit [2][3].…”

Section: Introductionmentioning

confidence: 99%

Self-assembled ferroelectric-dielectric nanocomposite films for tunable applications

Yamada

Sandu

Gureev

et al. 2010

IOP Conf. Ser.: Mater. Sci. Eng.

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Abstract. Nanocomposite films consisting of BaTiO 3 and CeO 2 have been grown by a selfassembled approach. The composite structure of those films varied with the volume fractions of BaTiO 3 and CeO 2 . A BaTiO 3 in the form of inclined nano-fibers embedded in CeO 2 matrix was obtained for CeO 2 -rich composition, which results in an appreciable tunability with a very low permittivity of 50. The observed tunable properties imply the competitive potential of BaTiO 3 -CeO 2 composite as an alternative tunable material.

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Untitled

Cited by 237 publications

References 29 publications

Improved designs of tunable ferroelectric capacities for microwave applications

Improved designs of tunable ferroelectric capacities for microwave applications

Correlations between microstructure and Q-factor of tunable thin film bulk acoustic wave resonators

Self-assembled ferroelectric-dielectric nanocomposite films for tunable applications

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