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13 Jul 2009

Volume 95, Issue 2, Articles (02xxxx)

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Appl. Phys. Lett. 95, 023701 (2009); http://dx.doi.org/10.1063/1.3173808 (3 pages)

G. Devès, S. Roudeau, A. Carmona, S. Lavielle, K. Gionnet, G. Déléris, and R. Ortega
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Grazing incidence small angle x-ray scattering study of the structure of nanoporous ultralow-k dielectrics prepared by plasma enhanced chemical vapor deposition

V. Jousseaume, O. Gourhant, A. Zenasni, M. Maret, and J.-P. Simon

Appl. Phys. Lett. 95, 022901 (2009); http://dx.doi.org/10.1063/1.3168521 (3 pages) | Cited 1 time

Online Publication Date: 13 July 2009

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This paper focuses on the structure of nanoporous SiOCH thin films deposited using a porogen approach by plasma enhanced chemical vapor deposition (PECVD). The grazing incidence small angle x-ray scattering signal demonstrates the existence of a biphase pattern in hybrid films, deposited by PECVD. After porogen removal, there are few differences between pore pattern of optimized ultraviolet (UV) illuminated and thermally treated samples: anisotropy of the pore pattern is observed in both samples, probably due to the porogen degradation. Finally, a kinetic study of porogen degradation by UV shows that the porous structure develops in only a few minutes.
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77.55.-g Dielectric thin films
78.70.Ck X-ray scattering
61.43.Gt Powders, porous materials
81.05.Rm Porous materials; granular materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.-c Methods of micro- and nanofabrication and processing
78.66.Qn Polymers; organic compounds
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Dielectric characteristics of poly(ether ketone ketone) for high temperature capacitive energy storage

Jilin Pan, Kun Li, Junjun Li, Tim Hsu, and Qing Wang

Appl. Phys. Lett. 95, 022902 (2009); http://dx.doi.org/10.1063/1.3176219 (3 pages) | Cited 10 times

Online Publication Date: 14 July 2009

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The dielectric constant and loss of poly(ether ketone ketone) have been investigated over a range of frequency and temperature. A linear correlation between the ac conductance and the angular frequency implies that the hopping as a dominant conduction process contributes to the dielectric loss. The energy density and discharged efficiency of the polymer were measured at various temperatures. High dielectric strengths (>400 MV/m) at temperatures up to 150 °C have been achieved. The increase of the dielectric loss and reduction in the breakdown field with increasing temperature could be attributed to thermally enhanced conduction of charge carriers in the polymer.
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81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
77.22.Gm Dielectric loss and relaxation
84.32.Tt Capacitors
77.22.Ch Permittivity (dielectric function)
77.84.Jd Polymers; organic compounds
77.22.Jp Dielectric breakdown and space-charge effects
72.20.Ee Mobility edges; hopping transport
72.80.Le Polymers; organic compounds (including organic semiconductors)

Oxygen vacancies in high dielectric constant oxides La2O3, Lu2O3, and LaLuO3

Ka Xiong and John Robertson

Appl. Phys. Lett. 95, 022903 (2009); http://dx.doi.org/10.1063/1.3176214 (3 pages) | Cited 9 times

Online Publication Date: 15 July 2009

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We present first principles calculations of the energy levels of the oxygen vacancy in La2O3, Lu2O3, and LaLuO3. The levels are found to lie above the Si gap when aligned using the experimental band offsets. In hexagonal La2O3, Lu2O3, and LaLuO3, oxygen vacancies with four neighbors behave similarly to those in HfO2, which are identified as the main electron trap, while oxygen vacancies with six neighbors have no negative charged state so that they are less important for charge trapping. Oxygen vacancies in perovskite LaLuO3 only have positive charge state so they do not act as electron trap.
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77.22.Ch Permittivity (dielectric function)
71.20.Ps Other inorganic compounds
61.72.jd Vacancies
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Interface-induced piezoelectricity in an unpoled Na0.5Bi0.5TiO3-based composite ceramic

M. L. Zhao, L. H. Wang, C. L. Wang, J. L. Zhang, Z. G. Gai, C. M. Wang, and J. C. Li

Appl. Phys. Lett. 95, 022904 (2009); http://dx.doi.org/10.1063/1.3182794 (3 pages) | Cited 2 times

Online Publication Date: 16 July 2009

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Composite ceramics containing Bi12TiO20 and Na0.5Bi0.5TiO3 grains were fabricated by an ordinary sintering technique. An anomalous piezoelectric response consistent with triclinic symmetry was found in unpoled samples and could be detected up to at least 765 °C. This piezoelectric effect appears concurrently with macroscopic cellular interfaces in as-sintered ceramics, suggesting that it may originate from an interface effect. Since these kinds of composites also have near-zero temperature coefficients of the resonance frequencies over the temperature range from 400 to 520 °C, they have potential as high-temperature piezoelectric materials.
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77.65.-j Piezoelectricity and electromechanical effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.05.Mh Cermets, ceramic and refractory composites
77.22.Ch Permittivity (dielectric function)

Bulk and Interface effects on voltage linearity of ZrO2–SiO2 multilayered metal-insulator-metal capacitors for analog mixed-signal applications

S. D. Park, C. Park, D. C. Gilmer, H. K. Park, C. Y. Kang, K. Y. Lim, C. Burham, J. Barnett, P. D. Kirsch, H. H. Tseng, R. Jammy, and G. Y. Yeom

Appl. Phys. Lett. 95, 022905 (2009); http://dx.doi.org/10.1063/1.3182856 (3 pages) | Cited 3 times

Online Publication Date: 16 July 2009

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Quadratic voltage coefficient of capacitance (VCC) for ZrO2–SiO2 multilayered dielectric metal-insulator-metal capacitors depends strongly on the stacking sequence of the layered dielectrics. The quadratic VCC of an optimized SiO2/ZrO2/SiO2 stack and ZrO2/SiO2/ZrO2 stack were +42 and −1094 ppm/V2, respectively, despite the same total SiO2 and ZrO2 dielectric thickness in the stack. The observed difference in quadratic VCC depending on dielectric stacking sequence is explained by taking into account both the interface and bulk dielectric responses to the applied voltage.
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84.32.Tt Capacitors

Transmission electron microscopy and scanning transmission electron microscopy study on B-site cation ordered structures in a (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 single crystal

Yukio Sato, Teruyasu Mizoguchi, Naoya Shibata, Hiroki Moriwake, Tsukasa Hirayama, and Yuichi Ikuhara

Appl. Phys. Lett. 95, 022906 (2009); http://dx.doi.org/10.1063/1.3183508 (3 pages)

Online Publication Date: 16 July 2009

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Transmission electron microscopy and scanning transmission electron microscopy were performed to investigate B-site cation-ordered structures in a (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3 (x ∼ 0.30) single crystal. Selected-area diffraction patterns showed presence of F-spots corresponding to 1:1 order. Besides, the F-spots were elongated to be “X”-like in shape. Transmission electron microscopy dark-field images revealed that size of ordered domains was about a few nanometers, and they were dispersed within disordered matrix. Scanning transmission electron microscopy indicated the presence of 1:1 ordered domains. Presence of 1:2 ordered structures was also indicated. These are consistent with features of the selected-area diffraction patterns.
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61.66.Fn Inorganic compounds
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ma Scanning transmission electron microscopy (STEM)

Epitaxial, cation-ordered, ferroelectric PbSc0.5Ta0.5O3 thin films prepared by pulsed laser deposition

Anuj Chopra, Balaji I. Birajdar, Yunseok Kim, Ionela Vrejoiu, Marin Alexe, and Dietrich Hesse

Appl. Phys. Lett. 95, 022907 (2009); http://dx.doi.org/10.1063/1.3180812 (3 pages) | Cited 3 times

Online Publication Date: 17 July 2009

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We report on growth and ferroelectric properties of cation-ordered, epitaxial PbSc0.5Ta0.5O3 (100) films. Single phase epitaxial films were grown on vicinal SrTiO3 (100) substrates with a layer of SrRuO3 as bottom electrode by pulsed laser deposition. Their crystal orientation, topography, and microstructure were analyzed by x-ray diffraction, atomic force microscopy, and transmission electron microscopy (TEM), respectively. The in-plane and out-of-plane epitaxial relationships were studied by ϕ and θ-2θ scans, respectively. Superstructure reflections obtained in TEM diffraction patterns of the films confirm cation ordering. Polarization-field and switching current-voltage hysteresis curves demonstrate ferroelectric behavior of the films at room temperature.
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77.55.-g Dielectric thin films
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.47.Gh Oxide surfaces
77.22.Ej Polarization and depolarization

Characterization and comparison of nanoscale domain boundary in congruent and stoichiometric LiTaO3 with scanning nonlinear dielectric microscopy

Dae-Yong Jeong and Yasuo Cho

Appl. Phys. Lett. 95, 022908 (2009); http://dx.doi.org/10.1063/1.3182713 (3 pages)

Online Publication Date: 17 July 2009

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The domain boundary of congruent LiTaO3 (CLT) and stoichiometric LiTaO3 (SLT) were characterized on the nanoscale using scanning nonlinear dielectric microscopy. SLT exhibited a smooth domain boundary but CLT showed an irregular domain boundary. The nonlinear dielectric constant ε333 in the domain boundary of SLT changed abruptly from the domain but there was a gradual change in ε333 in the boundary of CLT. The linear dielectric constant in the domain boundary of SLT was slightly higher than that in the domain itself. In addition, the topography showed that only SLT had <1 nm dimensional deformation in the domain boundary.
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61.66.Bi Elemental solids
61.66.Dk Alloys
77.22.Ch Permittivity (dielectric function)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
61.72.-y Defects and impurities in crystals; microstructure

Polymorphic phase transition and excellent piezoelectric performance of (K0.55Na0.45)0.965Li0.035Nb0.80Ta0.20O3 lead-free ceramics

J. L. Zhang, X. J. Zong, L. Wu, Y. Gao, P. Zheng, and S. F. Shao

Appl. Phys. Lett. 95, 022909 (2009); http://dx.doi.org/10.1063/1.3182725 (3 pages) | Cited 33 times

Online Publication Date: 17 July 2009

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A lead-free ceramic with the composition (K0.55Na0.45)0.965Li0.035Nb0.80Ta0.20O3 was found having an outstanding piezoelectric performance. It possesses high piezoelectric properties of d33 = 262 pC/N, kp = 0.53, k33 = 0.63, and k31 = 0.31 with ε′ = 1290 and tan δ = 0.019 at room temperature. In spite of the orthorhombic-tetragonal polymorphic phase transition around 30 °C, temperature stability of the electromechanical coupling coefficients is very good over the common usage temperature interval between −40 and 85 °C. Furthermore, the piezoelectric properties remain almost unchanged in the severe thermal aging test down to −150 °C and up to about 300 °C. It is suggested that the outstanding piezoelectric performance of this ceramic can be largely ascribed to the phase coexistence in a wide temperature range and the Ta-rich composition.
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64.70.K- Solid-solid transitions
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
77.65.-j Piezoelectricity and electromechanical effects

Wide-bandgap high-k Y2O3 as passivating interlayer for enhancing the electrical properties and high-field reliability of n-Ge metal-oxide-semiconductor capacitors with high-k HfTiO gate dielectric

C. X. Li and P. T. Lai

Appl. Phys. Lett. 95, 022910 (2009); http://dx.doi.org/10.1063/1.3182741 (3 pages) | Cited 8 times

Online Publication Date: 17 July 2009

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High-k and wide-bandgap Y2O3 was proposed as an interlayer in n-Ge metal-oxide-semiconductor (MOS) capacitor with HfTiO gate dielectric for passivating its dielectric/Ge interface, and thus improving its electrical properties and high-field reliability. Results showed that as compared to the Ge MOS capacitor with HfTiO dielectric, the sample with HfTiO/Y2O3 dielectric had better electrical properties such as higher dielectric constant (k = 24.4), lower interface-state density, and less frequency-dependent C-V dispersion, and also better reliability with less increases in gate leakage and interface states after high-field stressing. This should be attributed to the excellent interfacial quality of Y2O3/Ge with no appreciable growth of unstable GeOx at the interface as confirmed by transmission electron microscopy. Moreover, Y2O3 can also act as a barrier against the diffusions of Ge, Hf, and Ti, thus further improving the interface quality.
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84.32.Tt Capacitors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.65.Rv Passivation

Evolution of relaxor ferroelectric behavior of poly(vinylidene fluoride trifluoroethylene chlorofluoroethylene) terpolymer nanorods

Jun-Hong Lin, S. G. Lu, M. Lin, Markus Geuβ, and Q. M. Zhang

Appl. Phys. Lett. 95, 022911 (2009); http://dx.doi.org/10.1063/1.3182786 (3 pages) | Cited 3 times

Online Publication Date: 17 July 2009

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The evolution of relaxor ferroelectric behavior of poly(vinylidene fluoride trifluoroethylene chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer nanorods with diameters reduced from 200 to 25 nm was investigated. It was observed that all the nanorods studied exhibited relaxor ferroelectric behavior, as characterized by the dielectric peak shifting toward high temperatures with increasing frequency. The frequency-permittivity peak temperature characteristics fit well with the Vogel–Fulcher (VF) relation. Moreover, the freezing temperature in the VF relation decreased with the reduction of nanorod diameter, indicating that the scaling down of the lateral size of nanorods influenced the relaxor ferroelectric behavior of the terpolymer.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Jd Polymers; organic compounds
77.22.Ch Permittivity (dielectric function)

Photovoltaic mechanisms in ferroelectric thin films with the effects of the electrodes and interfaces

Meng Qin, Kui Yao, and Yung C. Liang

Appl. Phys. Lett. 95, 022912 (2009); http://dx.doi.org/10.1063/1.3182824 (3 pages) | Cited 19 times

Online Publication Date: 17 July 2009

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It was discovered that the dielectric constant of the electrodes substantially determines the photovoltaic output in (Pb0.97La0.03)(Zr0.52Ti0.48)O3 ferroelectric thin films. With the screening charges distributed extensively away from the electrode interfaces, the use of the electrodes with a high dielectric constant gives rise to dramatically enhanced magnitude of photocurrent in photovoltaic thin films, and extremely high photovoltaic efficiency is theoretically predicted to be possible in ferroelectric ultrathin films or nanostructures.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
73.50.Pz Photoconduction and photovoltaic effects
77.22.Ch Permittivity (dielectric function)
77.80.-e Ferroelectricity and antiferroelectricity
73.40.Ns Metal-nonmetal contacts
77.22.Ej Polarization and depolarization

A hexadomain vortex in tetragonal ferroelectrics

I. Münch and J. E. Huber

Appl. Phys. Lett. 95, 022913 (2009); http://dx.doi.org/10.1063/1.3183577 (3 pages) | Cited 10 times

Online Publication Date: 17 July 2009

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We study internal flux closures in tetragonal ferroelectric crystals using a phase-field model and demonstrate the existence of a stable polarization vortex of six domains. This hexadomain vortex exhibits a threefold rotation axis and appears as a minimum energy equilibrium state over a narrow range of aspect ratios in freestanding cuboidal nanodots. Square polarization vortices of four domains represent lower energy solutions for a wide range of aspect ratios. The hexadomain vortex offers significant potential in memory storage applications as it has eight stable states.
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77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
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