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2 Apr 2007

Volume 90, Issue 14, Articles (14xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 142110 (2007); http://dx.doi.org/10.1063/1.2720640 (3 pages)

M. T. Björk, O. Hayden, H. Schmid, H. Riel, and W. Riess
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Asymmetry of domain forward switching and multilevel relaxation times of domain backswitching in antiferroelectric Pb0.99Nb0.02(Zr0.84Sn0.12Ti0.04)0.98O3 thin films

A. Q. Jiang, Y. Y. Lin, T. A. Tang, and Q. Zhang

Appl. Phys. Lett. 90, 142901 (2007); http://dx.doi.org/10.1063/1.2718506 (3 pages) | Cited 7 times

Online Publication Date: 2 April 2007

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Pb0.99Nb0.02(Zr0.84Sn0.12Ti0.04)0.98O3 thin films demonstrate a double hysteresis loop characteristic of antiferroelectric behavior with film thickness at above 150 nm, but only one branch of the loop is present in films that are 90 nm thick. The relaxation time of domain backswitching from ferroelectric into antiferroelectric is multistaged in a range of 100 ns–100 ms, but it is less than 100 ns in the films without Sn and Nb dopants. Electrical modeling of the films composed of elementary regions with inhomogeneities of dielectric constant, conductivity, and polarization embodies the essence of charge injection for the compensation of local backswitching field of domains.
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77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
77.22.Gm Dielectric loss and relaxation

Physical properties of multiferroic hexagonal HoMnO3 thin films

P. Murugavel, J.-H. Lee, D. Lee, T. W. Noh, Younghun Jo, Myung-Hwa Jung, Yoon Seok Oh, and Kee Hoon Kim

Appl. Phys. Lett. 90, 142902 (2007); http://dx.doi.org/10.1063/1.2718512 (3 pages) | Cited 20 times

Online Publication Date: 2 April 2007

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The authors investigated the magnetic and ferroelectric properties of hexagonally grown HoMnO3 thin films. The magnetic measurements revealed bulklike magnetic phase transitions with an additional spin-glass-like behavior feature below the Néel temperature. The ferroelectricity in the films was distinctly different from the suggested bulk behavior. Below 40 K, the HoMnO3 films showed typical ferroelectric character: their remnant polarization and coercive field values at 20 K were 3.7 μC/cm2 and 0.69 MV/cm. Above 40 K, however, the films exhibited an unusual antiferroelectriclike behavior, with more pronounced features appearing at higher temperatures. These intriguing physical properties make HoMnO3 films a potential candidate material for numerous future applications.
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75.80.+q Magnetomechanical effects, magnetostriction
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.80.-e Ferroelectricity and antiferroelectricity
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.22.Ej Polarization and depolarization

Phase transition in disordered ferroelectric ceramic Pb0.70Ca0.30TiO3 under pressure

Amreesh Chandra, Dhananjai Pandey, A. K. Tyagi, G. D. Mukherjee, and V. Vijayakumar

Appl. Phys. Lett. 90, 142903 (2007); http://dx.doi.org/10.1063/1.2719021 (3 pages) | Cited 4 times

Online Publication Date: 2 April 2007

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Pressure dependent synchrotron x-ray diffraction studies on Pb0.70Ca0.30TiO3 (PCT30) ferroelectric ceramic reveal a crossover in the nature of phase transition from first order nature observed at ambient pressures to second order at high pressures. It is shown that Ca2+ doping affects the transition temperature but does not change the transition pressure of PbTiO3 significantly. The values of bulk modulus and its pressure derivative are also given in this letter.
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64.70.K- Solid-solid transitions
62.50.-p High-pressure effects in solids and liquids
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Comparative study of passivation mechanism of oxygen vacancy with fluorine in HfO2 and HfSiO4

Qing-Qing Sun, Wei Chen, Shi-Jin Ding, Min Xu, Hong-Liang Lu, Hans-Cristian Lindh-Rengifo, David Wei Zhang, and Li-Kang Wang

Appl. Phys. Lett. 90, 142904 (2007); http://dx.doi.org/10.1063/1.2719177 (3 pages) | Cited 3 times

Online Publication Date: 2 April 2007

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It has been experimentally observed that the incorporated fluorine will greatly improve the reliability of high-permittivity gate dielectric based transistors, but the role of fluorine passivation on leakage current change through gate is still a debated issue. The authors performed first-principles calculations to study the role of fluorine in oxygen vacancies in HfO2 and HfSiO4. They found that fluorine behaves completely differently in these two gate dielectrics. Fluorine can passivate the gap states of HfO2 completely but has no effect on the passivation of oxygen vacancies in HfSiO4, which is a possible explanation to the controversy surrounding varying leakage current.
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61.72.J- Point defects and defect clusters
81.65.Rv Passivation
77.55.-g Dielectric thin films

Polaron relaxation related to localized charge carriers in CaCu3Ti4O12

C. C. Wang and L. W. Zhang

Appl. Phys. Lett. 90, 142905 (2007); http://dx.doi.org/10.1063/1.2719608 (3 pages) | Cited 18 times

Online Publication Date: 2 April 2007

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The dielectric properties of CaCu3Ti4O12 were studied in the frequency range from 100 Hz to 100 kHz at temperatures ranging from 23 K to room temperature. The properties can be perfectly described by the so-called universal dielectric response, indicating that they are intimately related to the hopping conductivity caused by localized carriers. A deviation from the Arrhenius behavior in the lower frequency (temperature) region has been attributed to Anderson localization. These results strongly indicate that the relaxation in CaCu3Ti4O12 might be a dipolar-type relaxation associated with the hopping localized carriers.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
71.38.-k Polarons and electron-phonon interactions
73.20.Fz Weak or Anderson localization
72.20.Ee Mobility edges; hopping transport

Modeling of nonlinearities in the capacitance-voltage characteristics of high-k metal-insulator-metal capacitors

P. Gonon and C. Vallée

Appl. Phys. Lett. 90, 142906 (2007); http://dx.doi.org/10.1063/1.2719618 (3 pages) | Cited 26 times

Online Publication Date: 2 April 2007

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Metal-insulator-metal capacitors using high-k oxides are known to display nonlinear capacitance-voltage (C-V) characteristics. In the present work it is proposed that such nonlinearities arise from an electrode polarization mechanism. By considering a field activated hopping conduction in the bulk (related to oxygen vacancies), a simple analytical expression is derived which relates the capacitance to the applied bias. The model is able to predict voltage coefficients of capacitance and is found to be in good agreement with experimental C-V.
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84.32.Tt Capacitors

Resonance-antiresonance electromagnetic behavior in a disordered dielectric composite

L. Zhen, J. T. Jiang, W. Z. Shao, and C. Y. Xu

Appl. Phys. Lett. 90, 142907 (2007); http://dx.doi.org/10.1063/1.2719023 (3 pages) | Cited 10 times

Online Publication Date: 4 April 2007

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In the present study, a kind of SiCw/wax composite was prepared and its electromagnetic properties were studied experimentally. It is found that Mie resonance can occur in this composite in spite of its disordered structure. The Mie resonance is believed to lead to the resonant-antiresonant electromagnetic behavior accompanied by a negative ε″ in the SiCw/wax composite in the 2–18 GHz band range. The resulted magnetic behavior in the current composite is believed to be weakened by the random orientation of the whiskers.
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77.84.Lf Composite materials
77.22.Ch Permittivity (dielectric function)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Kj Amorphous and quasicrystalline magnetic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Effects of octahedral thickness variance on the temperature coefficient of resonant frequency of the B-site deficient hexagonal perovskites

Fei Zhao, Zhenxing Yue, Jing Pei, Zhilun Gui, and Longtu Li

Appl. Phys. Lett. 90, 142908 (2007); http://dx.doi.org/10.1063/1.2719219 (3 pages) | Cited 4 times

Online Publication Date: 4 April 2007

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The temperature coefficient of resonant frequency (τf) and the structure of B-site deficient hexagonal perovskite materials have been assembled with the intention of understanding the structure-property relationship. Based on the refined structure data, the authors proposed a structure-related parameter v to characterize the octahedral thickness variance. Therefore, a correlation between the value of τf and the octahedral thickness variance has been established. This approach illustrates that the octahedral thickness variance plays an important role in the value and sign of τf. It also gives a satisfying explanation for the variation of τf in the Ba5Nb4O15–Ba5Ta4O15 system.
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61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling

High insulating quality CaF2 pseudomorphic films on Si(111)

N. S. Sokolov, A. K. Kaveev, A. V. Krupin, S. E. Tyaginov, M. I. Vexler, S. Ikeda, K. Tsutsui, and K. Saiki

Appl. Phys. Lett. 90, 142909 (2007); http://dx.doi.org/10.1063/1.2719610 (3 pages) | Cited 2 times

Online Publication Date: 4 April 2007

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Current-voltage characteristics of epitaxially grown Au/CaF2/Si(111) metal-insulator-semiconductor structures with thin (1.5–6 nm) pseudomorphic fluoride layer have been studied. It was found that CaF2 films in these structures are of better insulating quality than those in the devices reported previously. Typical breakdown field for the fluorite layers was about 8×106 V/cm and the tunnel current did not exceed the values predicted by simulations with realistic parameters.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Gk Tunneling

Effect of the thermal expansion matching on the dielectric tunability of (100)-one-axis-oriented (Ba0.5Sr0.5)TiO3 thin films

Shinichi Ito, Hiroshi Funakubo, Ivoyl P. Koutsaroff, Marina Zelner, and Andrew Cervin-Lawry

Appl. Phys. Lett. 90, 142910 (2007); http://dx.doi.org/10.1063/1.2719621 (3 pages) | Cited 9 times

Online Publication Date: 4 April 2007

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The impact of the residual strain induced by the thermal strain on the dielectric tunability was systematically studied for rf sputtered (100)-one-axis-oriented polycrystalline (Ba0.5Sr0.5)TiO3 films. These films were grown on various substrates with different thermal expansion coefficients [α(sub)] covered with a stack of (100)cSrRuO3/(100)cLaNiO3/(111)Pt layers. The residual strain was ascertained to linearly increase with the increase in α(sub) by enhancement of the surface-normal lattice spacing of (Ba0.5Sr0.5)TiO3 and Pt. Dielectric tunability of the films also linearly increased with the increase in α(sub). These results clearly demonstrate that dielectric tunability tailoring of the (Ba0.5Sr0.5)TiO3 films can be achieved by using residual thermal strain.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.60.Bs Mechanical and acoustical properties
65.40.De Thermal expansion; thermomechanical effects

Epitaxial growth of Ba0.3Sr0.7TiO3 thin films on Al2O3(0001) using ultrathin TiN layer as a sacrificial template

Tomoaki Yamada, Paul Muralt, Vladimir O. Sherman, Cosmin S. Sandu, and Nava Setter

Appl. Phys. Lett. 90, 142911 (2007); http://dx.doi.org/10.1063/1.2719673 (3 pages) | Cited 6 times

Online Publication Date: 4 April 2007

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Epitaxial Ba0.3Sr0.7TiO3 (BST) films with significantly improved tunable performance were grown on c-plane sapphire [Al2O3(0001)] substrates using ultrathin TiN seed layers by pulsed laser deposition. A very thin (111) epitaxial TiN layer deposited at room temperature acted as a sacrificial epitaxial template for the BST film in the initial growth stage. The BST films grew with (111) orientation having BST[2mathmath]‖Al2O3[11math0] and BST[2mathmath]‖Al2O3[2mathmath0] epitaxial relationships. Planar capacitors fabricated on the epitaxial BST film showed significantly higher tunability as compared to those on a polycrystalline BST film directly deposited on the substrate.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth

Separation of dielectric and space charge polarizations in CaCu3Ti4O12/CaTiO3 composite polycrystalline systems

Paulo R. Bueno, William C. Ribeiro, Miguel A. Ramírez, José A. Varela, and Elson Longo

Appl. Phys. Lett. 90, 142912 (2007); http://dx.doi.org/10.1063/1.2720301 (3 pages) | Cited 10 times

Online Publication Date: 5 April 2007

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The complex analysis of dielectric/capacitance is a very useful approach to separate different polarization contributions existing in polycrystalline ceramics. In this letter, the authors use this type of spectroscopic analysis to separate the bulk’s dielectric dipolar relaxation contributions from the polarization contribution due to space charge in the grain boundaries of a CaCu3Ti4O12/CaTiO3 polycrystalline composite system. The bulk dielectric dipolar relaxation was attributed to the self-intertwined domain structures from the CaCu3Ti4O12 phase coupled to the dipole relaxation from the CaTiO3 phase, while the space charge relaxation was attributed to the Schottky-type potential barrier responsible for the highly non-Ohmic properties observed in this composite polycrystalline system.
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77.84.Lf Composite materials
77.22.Ej Polarization and depolarization
77.22.Jp Dielectric breakdown and space-charge effects
77.22.Gm Dielectric loss and relaxation
77.80.Dj Domain structure; hysteresis
73.30.+y Surface double layers, Schottky barriers, and work functions

Frequency and temperature dependence of tunable dielectric properties of Ba(Zr0.2Ti0.8)O3 thin films grown on (001) MgO

X. H. Zhu, J. Li, and D. N. Zheng

Appl. Phys. Lett. 90, 142913 (2007); http://dx.doi.org/10.1063/1.2720303 (3 pages) | Cited 9 times

Online Publication Date: 5 April 2007

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High quality Ba(Zr0.2Ti0.8)O3 (BZT) thin films were epitaxially grown on MgO single-crystal substrates. No structural phase transition took place in the temperature range of 80–300 K, and the films displayed a typical behavior of relaxor ferroelectrics, which was demonstrated by micro-Raman spectroscopy. Frequency and temperature dependence of dielectric properties was systematically investigated for the BZT thin films. It was found that enhanced dielectric properties could be obtained over a wide frequency and temperature range. This is of great importance for practical microelectronic device applications. At room temperature, a high dielectric tunability of nearly 50% was achieved over the whole measurement frequency range of 10 kHz–1 MHz by applying an electric field with intensity as low as 40 kV/cm; meanwhile, a relatively low dielectric loss was obtained and the value could be further reduced significantly with the applied dc electric field, indicating an excellent figure of merit and promising applications in tunable microwave devices for the BZT films.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
77.80.-e Ferroelectricity and antiferroelectricity
78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics

Comment on the use of calcium as a dopant in X8R BaTiO3-based ceramics

Lei Zhang, Om Prakash Thakur, Antonio Feteira, Gillian M. Keith, Andrew G. Mould, Derek C. Sinclair, and Anthony R. West

Appl. Phys. Lett. 90, 142914 (2007); http://dx.doi.org/10.1063/1.2720305 (3 pages) | Cited 18 times

Online Publication Date: 6 April 2007

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BaTi1−xCaxO3−x ceramics, where 0 ⩽ x ⩽ 0.04, prepared by the mixed oxide route at 1500 °C display a strong suppression of the Curie temperature and a significant increase in grain conductivity with increasing x. The ramifications of these results on the applicability of using Ca2+ as a dopant to achieve X8R specification in BaTiO3-based formulations are discussed.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
61.72.up Other materials

Hot electron transport in Au–HfO2–SiO2–Si structures studied by ballistic electron emission spectroscopy

Yi Zheng, Andrew T. S. Wee, K. L. Pey, Cedric Troadec, S. J. O’Shea, and N. Chandrasekhar

Appl. Phys. Lett. 90, 142915 (2007); http://dx.doi.org/10.1063/1.2720346 (3 pages) | Cited 5 times

Online Publication Date: 6 April 2007

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Hot electron transport in Au–HfO2–SiO2–Si structures with 4 nm HfO2 and 1.5 nm SiO2 interfacial layer have been investigated by ballistic electron emission spectroscopy (BEES). By controlling the hot electron kinetic energy and injection current, distinctly different barrier heights can be measured. BEES sweeping below −5 V with 1 nA injection current yields high barrier heights ( ∼ 3.8 eV), attributable to the interfacial SiO2 layer. BEES sweeping from −6 V with high injection current (5 nA and above) induced localized breakdown of the SiO2 interfacial layer, allowing the barrier height of the HfO2 layer to be measured ( ∼ 1.9 eV). The energy-dependent effective mass of electrons in HfO2 is also determined by fitting oscillations in the BEES current.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
72.20.Ht High-field and nonlinear effects
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