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19 Apr 2010

Volume 96, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 96, 163101 (2010); http://dx.doi.org/10.1063/1.3327831 (3 pages)

Ramesh Nath, Seungbum Hong, Jeffrey A. Klug, Alexandra Imre, Michael J. Bedzyk, Ram S. Katiyar, and Orlando Auciello
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Effect of postdeposition annealing on the structural and electrical characteristics of Yb2TiO5 charge trapping layers

Tung-Ming Pan, Ji-Shing Jung, and Xin-Chang Wu

Appl. Phys. Lett. 96, 162901 (2010); http://dx.doi.org/10.1063/1.3402774 (3 pages) | Cited 3 times

Online Publication Date: 20 April 2010

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In this letter, we proposed a metal-oxide-high-k-oxide-silicon-type (MOHOS) memory structure incorporating a high-k Yb2TiO5 charge trapping layer and the subsequent postdeposition annealing treatment. The effect of postdeposition annealing on the structural properties of Yb2TiO5 charge trapping layers was explored by x-ray diffraction, transmission electron microscopy, and x-ray photoelectron spectroscopy. The Yb2TiO5 MOHOS-type device annealed at 800 °C exhibited a larger memory window of 2.8 V and a smaller charge loss of 10% than did those prepared at other annealing temperatures. This outcome is attributed to the higher probability for trapping the charge carrier due to the formation of a well-crystallized Yb2TiO5 structure and a thin low-k interfacial layer.
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84.30.Sk Pulse and digital circuits
61.72.Cc Kinetics of defect formation and annealing
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
79.60.-i Photoemission and photoelectron spectra

Photoinduced charge-trapping phenomena in metal/high-k gate stack structures studied by synchrotron radiation photoemission spectroscopy

T. Tanimura, S. Toyoda, H. Kamada, H. Kumigashira, M. Oshima, T. Sukegawa, G. L. Liu, and Z. Liu

Appl. Phys. Lett. 96, 162902 (2010); http://dx.doi.org/10.1063/1.3409162 (3 pages) | Cited 3 times

Online Publication Date: 21 April 2010

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We have demonstrated photoinduced charge-trapping phenomena in metal/high-k gate stack structures using time-dependent photoemission spectroscopy with synchrotron radiation. Pt metal gate electrode with a large work function releases trapped negative charges near the surface of the HfSiON film while TiN metal gate electrode with a lower work function keeps negative charges in the HfSiON film. The release of negative trapped charges reveals a possibility of positive charge trapping at the interface in the HfSiON film. The location of energy level for negative charges is concluded to be between Pt and TiN Fermi-level in the band gap of the HfSiON film.
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77.55.D- High-permittivity gate dielectric films
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.-r Electrical properties of specific thin films
73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions
79.60.-i Photoemission and photoelectron spectra

Unusual dielectric response in B-site size-disordered hexagonal transition metal oxides

Debraj Choudhury, Adyam Venimadhav, Chandrasekhar Kakarla, Kris T. Delaney, P. Sujatha Devi, P. Mondal, R. Nirmala, J. Gopalakrishnan, Nicola A. Spaldin, Umesh V. Waghmare, and D. D. Sarma

Appl. Phys. Lett. 96, 162903 (2010); http://dx.doi.org/10.1063/1.3379293 (3 pages) | Cited 1 time

Online Publication Date: 21 April 2010

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We discover that hexagonal holmium copper titanate (Ho2CuTiO6), has a unique and highly desirable combination of high dielectric constant, low losses, very small temperature coefficient, and low frequency dependence. Our first-principles calculations indicate that these exceptional properties result from a size-difference at the Cu/Ti B-site that suppresses the expected ferroelectric transition, combined with the dominance of intermediate-frequency polar vibrational modes in the dielectric response. Our results suggest that the use of such B-site disorder in alloys of hexagonal transition-metal oxides should generally result in similar robust dielectrics.
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77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
77.84.Cg PZT ceramics and other titanates
63.20.-e Phonons in crystal lattices
77.80.B- Phase transitions and Curie point

Particle size reduction: A way to enhanced dielectric properties of magnetocapacitive La2/3Ca1/3MnO3

S. Yáñez-Vilar, J. Mira, M. Sánchez-Andújar, S. Castro-García, A. Fondado, J. Rivas, and M. A. Señarís-Rodríguez

Appl. Phys. Lett. 96, 162904 (2010); http://dx.doi.org/10.1063/1.3394004 (3 pages) | Cited 2 times

Online Publication Date: 21 April 2010

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We report the optimization of the dielectric properties of La2/3Ca1/3MnO3. This is achieved by synthesizing this material with small particle size, strategy that reduces the conductivity of the sample and its dielectric losses, while retaining a reasonably high dielectric permittivity and a good magnetocapacitive response. In order to further improve the properties of these nanoparticles, we have also prepared core-shell composites La2/3Ca1/3MnO3@SiO2 but in this case the magnetocapacitive effect is strongly reduced.
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77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.84.Lf Composite materials

Effect of intrinsic surface stress on single-vertex structure of polarization in ferroelectric nanoparticles

Yu Su and Jing-Na Du

Appl. Phys. Lett. 96, 162905 (2010); http://dx.doi.org/10.1063/1.3409122 (3 pages) | Cited 5 times

Online Publication Date: 23 April 2010

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Intrinsic surface stress forms due to the relatively high surface energy of nanoscale ferroelectrics. Such surface stress induces mechanical balancing stress below the curved free surfaces, and consequently affects the existence of singe-vertex structure of polarization within free-standing ferroelectric nanostructures. A thermodynamics-based continuum phase field approach is employed to investigate such surface effect in ferroelectric nanodisks. It has been observed that, for a given material, the minimum geometric limit for existence of single-vertex structure will generally be elevated upon the compressive surface-induced stress. Such increase is nonlinear, and highly depending on the energy exchange parameter in the model.
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77.22.Ej Polarization and depolarization
68.35.Md Surface thermodynamics, surface energies
62.25.-g Mechanical properties of nanoscale systems
05.70.Np Interface and surface thermodynamics

Effects of capping HfO2 with multivalent oxides toward reducing the number of charged defects

Naoto Umezawa

Appl. Phys. Lett. 96, 162906 (2010); http://dx.doi.org/10.1063/1.3409222 (3 pages) | Cited 3 times

Online Publication Date: 23 April 2010

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Electrical properties of field-effect transistors are significantly degraded by charged defects formed in dielectric oxides. Here, we propose a simple method for eliminating charged defects in HfO2. Our computational and thermodynamic investigations have revealed that multivalent oxides act as an oxygen reservoir when deposited on HfO2, playing an important role in keeping the oxygen chemical potential constant throughout the oxide film. This is due to the coexistence of two stoichiometric phases in the multivalent oxide, which allows absorption or desorption of oxygen atoms depending on the ambient conditions. Our theory predicts europium oxide is the best capping material for minimizing oxygen-related charged defects in HfO2.
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77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials

Giant dielectric constant dominated by Maxwell–Wagner relaxation in Al2O3/TiO2 nanolaminates synthesized by atomic layer deposition

Wei Li, Orlando Auciello, Ramesh N. Premnath, and Bernd Kabius

Appl. Phys. Lett. 96, 162907 (2010); http://dx.doi.org/10.1063/1.3413961 (3 pages) | Cited 10 times

Online Publication Date: 23 April 2010

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Nanolaminates consisting of Al2O3 and TiO2 oxide sublayers were synthesized by using atomic layer deposition to produce individual layers with atomic scale thickness control. The sublayer thicknesses were kept constant for each multilayer structure, and were changed from 50 to 0.2 nm for a series of different samples. Giant dielectric constant ( ∼ 1000) was observed when the sublayer thickness is less than 0.5 nm, which is significantly larger than that of Al2O3 and TiO2 dielectrics. Detailed investigation revealed that the observed giant dielectric constant is originated from the Maxwell–Wagner type dielectric relaxation.
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77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation
77.55.-g Dielectric thin films
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.65.Ac Multilayers
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