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5 Dec 2011

Volume 99, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 233701 (2011); http://dx.doi.org/10.1063/1.3651756 (3 pages)

Melis Hazar, Robert L. Steward, Jr., Chia-Jung Chang, Cynthia J. Orndoff, Yukai Zeng, Mon-Shu Ho, Philip R. LeDuc, and Chao-Min Cheng
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Piezoresponse force microscopy of domains and walls in multiferroic HoMnO3

Edward B. Lochocki, S. Park, Nara Lee, S.-W. Cheong, and Weida Wu

Appl. Phys. Lett. 99, 232901 (2011); http://dx.doi.org/10.1063/1.3665255 (3 pages) | Cited 6 times

Online Publication Date: 5 December 2011

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We report ambient piezoresponse force microscopy (PFM) studies of the multiferroic hexagonal manganite HoMnO3 performed on the cleaved (110) surface of a single-crystal specimen. By changing the sample orientation with respect to the cantilever, we observed an unexpected out-of-plane PFM signal at domain walls, which depends on domain wall orientation, in addition to the expected in-plane PFM signal in domains. Further studies confirmed that the domain wall PFM signal results from an out-of-plane displacement, which can be explained by a simple model of local elastic response with the conservation of unit cell volume at head-on domain walls.
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77.80.Dj Domain structure; hysteresis
81.40.Jj Elasticity and anelasticity, stress-strain relations
77.65.-j Piezoelectricity and electromechanical effects

Titania/alumina bilayer gate insulators for InGaAs metal-oxide-semiconductor devices

Jaesoo Ahn, Irina Geppert, Marika Gunji, Martin Holland, Iain Thayne, Moshe Eizenberg, and Paul C. McIntyre

Appl. Phys. Lett. 99, 232902 (2011); http://dx.doi.org/10.1063/1.3662966 (3 pages) | Cited 3 times

Online Publication Date: 5 December 2011

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We describe the electrical properties of atomic layer deposited TiO2/Al2O3 bilayer gate oxides which simultaneously achieve high gate capacitance density and low gate leakage current density. Crystallization of the initially amorphous TiO2 film contributes to a significant accumulation capacitance increase (∼33%) observed after a forming gas anneal at 400 °C. The bilayer dielectrics reduce gate leakage current density by approximately one order of magnitude at flatband compared to Al2O3 single layer of comparable capacitance equivalent thickness. The conduction band offset of TiO2 relative to InGaAs is 0.6 eV, contributing to the ability of the stacked dielectric to suppress gate leakage conduction.
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85.30.Tv Field effect devices
61.72.Cc Kinetics of defect formation and annealing

X-ray nanodiffraction of tilted domains in a poled epitaxial BiFeO3 thin film

S. O. Hruszkewycz, C. M. Folkman, M. J. Highland, M. V. Holt, S. H. Baek, S. K. Streiffer, P. Baldo, C. B. Eom, and P. H. Fuoss

Appl. Phys. Lett. 99, 232903 (2011); http://dx.doi.org/10.1063/1.3665627 (3 pages) | Cited 3 times

Online Publication Date: 6 December 2011

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We present measurements of crystallographic domain tilts in a (001) BiFeO3 thin film using focused beam x-ray nanodiffraction. Films were ferroelectrically pre-poled with an electric field orthogonal and parallel to as-grown tilt domain stripes. The tilt domains, associated with higher energy (010) vertical twin walls, displayed different nanostructural responses based on the poling orientation. Specifically, an electric field applied perpendicular to the as-grown domain stripe allowed the domain tilts and associated vertical twin walls to persist. The result demonstrates that thin film ferroelectric devices can be designed to maintain unexpected domain morphologies in working poled environments.
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77.80.Dj Domain structure; hysteresis
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.35.bt Other materials
77.55.Nv Multiferroic/magnetoelectric films
77.55.Px Epitaxial and superlattice films
77.22.Ej Polarization and depolarization

Study of slow oxide trap creating random telegraph noise within a gate edge overlap region in inversion mode

Heung-Jae Cho, Younghwan Son, Seunghyun Jang, and Hyungcheol Shin

Appl. Phys. Lett. 99, 232904 (2011); http://dx.doi.org/10.1063/1.3665628 (3 pages)

Online Publication Date: 6 December 2011

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We investigated a slow oxide trap causing a random telegraph noise (RTN) within a gate edge overlap region in an inversion mode at metal/high-k dielectric nMOSFETs. The oxide trap was observed to generate RTN only in gate leakage current (Ig RTN) without in drain current (Id RTN) in the inversion mode. Through the analysis of the RTN dependence on drain, source, and body bias, we found that the oxide trap in the dielectric exists not within the channel area but within the gate edge overlap region, resulting in the absence of Id RTN.
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85.30.Tv Field effect devices

Suppression of vacancy defects in epitaxial La-doped SrTiO3 films

D. J. Keeble, B. Jalan, L. Ravelli, W. Egger, G. Kanda, and S. Stemmer

Appl. Phys. Lett. 99, 232905 (2011); http://dx.doi.org/10.1063/1.3664398 (3 pages) | Cited 4 times

Online Publication Date: 6 December 2011

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Variable energy positron annihilation lifetime spectroscopy of high-mobility La-doped SrTiO3 grown by molecular beam epitaxy found that the films contained sufficiently low concentrations of Sr vacancies and vacancy cluster defects to allow the observation of positron annihilation events from the perfect lattice. This enabled the concentrations of charged cation vacancies to be estimated, and these were found to be at least an order of magnitude below the La-dopant concentrations.
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68.55.aj Insulators
61.72.jd Vacancies
78.70.Bj Positron annihilation
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Antiferroelectric–ferroelectric phase boundary enhances polarization extension in rhombohedral Pb(Zr,Ti)O3

Anirban Ghosh and Dragan Damjanovic

Appl. Phys. Lett. 99, 232906 (2011); http://dx.doi.org/10.1063/1.3666233 (3 pages)

Online Publication Date: 7 December 2011

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The main mechanism of properties enhancement in the morphotropic phase boundary region separating tetragonal and rhombohedral phases of Pb(Zr1-xTix)O3 (PZT) is related to polarization rotation. It is shown here that in proximity of the morphotropic phase boundary separating antiferroelectric and rhombohedral phases (near x = 0.1) and at elevated temperatures the properties are dominated by polarization extension. These results may provide a guideline for developing alternative piezoelectric materials to PZT.
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77.80.B- Phase transitions and Curie point
77.22.Ej Polarization and depolarization
61.66.Fn Inorganic compounds
81.30.Dz Phase diagrams of other materials

Influence of lattice parameters on the dielectric constant of tetragonal ZrO2 and La-doped ZrO2 crystals in thin films deposited by atomic layer deposition on Ge(001)

C. Wiemer, A. Debernardi, A. Lamperti, A. Molle, O. Salicio, L. Lamagna, and M. Fanciulli

Appl. Phys. Lett. 99, 232907 (2011); http://dx.doi.org/10.1063/1.3666237 (3 pages) | Cited 1 time

Online Publication Date: 7 December 2011

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In ZrO2 crystals, the highest dielectric constant (k) is ascribed to the tetragonal phase. By the use of density functional theory and synchrotron radiation x-ray diffraction, we show how the a and c lattice parameters of the tetragonal phase influence the resulting k. Highest k values are obtained at increasing both a and c, while k is reduced for compressive strained cells. The determination of a and c on La-doped ZrO2 and ZrO2 thin films deposited by atomic layer deposition on Ge (001) allowed us to elucidate the influence of La doping and Ge diffusion on the k value.
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77.22.Ch Permittivity (dielectric function)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.up Other materials
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
68.55.aj Insulators

Decoupling electrocaloric effect from Joule heating in a solid state cooling device

M. Quintero, L. Ghivelder, F. Gomez-Marlasca, and F. Parisi

Appl. Phys. Lett. 99, 232908 (2011); http://dx.doi.org/10.1063/1.3665949 (3 pages) | Cited 1 time

Online Publication Date: 7 December 2011

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We report a heat dynamics analysis of the electrocaloric effect (ECE) in commercial multilayer capacitors based on BaTiO3 dielectric, a promising candidate for applications as a solid state cooling device. Direct measurements of the time evolution of the sample’s temperature changes under different applied voltages allow us to decouple the contributions from Joule heating and from the ECE. Heat balance equations were used to model the thermal coupling between different parts of the system. Fingerprints of Joule heating and the ECE could be resolved at different time scales. We argue that Joule heating and the thermal coupling of the device to the environment must be carefully taken in to account in future developments of refrigeration technologies employing the ECE.
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84.32.Tt Capacitors

Threshold shift observed in resistive switching in metal-oxide-semiconductor transistors and the effect of forming gas anneal

W. H. Liu, K. L. Pey, X. Wu, N. Raghavan, A. Padovani, L. Larcher, L. Vandelli, M. Bosman, and T. Kauerauf

Appl. Phys. Lett. 99, 232909 (2011); http://dx.doi.org/10.1063/1.3669525 (3 pages) | Cited 2 times

Online Publication Date: 8 December 2011

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The resistive switching mechanism, which is crucial for the operations of resistive random access memory (RRAM) devices, is investigated using HfO2 based MOSFETs. After the SET operation, MOSFETs exhibit a threshold voltage (VT) shift that is found to be closely related to the formation of conductive filaments in the gate oxide. The RESET operation performed through a forming gas anneal treatment is found to have the same effect of applying a reverse polarity gate voltage sweep, as usually done in bipolar switching RRAM devices. After RESET, the gate current and VT measured shift back to their pristine levels, indicating the passivation of oxygen vacancies (forming the conductive path) as the most likely physical mechanism responsible for RRAMs RESET operation. Transmission electron microscopy analysis and physical simulations support these conclusions.
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85.30.Tv Field effect devices

Defects control for improved electrical properties in (Ba0.8Sr0.2)(Zr0.2Ti0.8)O3 films by Co acceptor doping

Jun Miao, Khian Hooi Chew, and Yong Jiang

Appl. Phys. Lett. 99, 232910 (2011); http://dx.doi.org/10.1063/1.3666021 (3 pages) | Cited 4 times

Online Publication Date: 8 December 2011

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(Ba0.8Sr0.2)(Zr0.2Ti0.8)O3 (BSZT) films were grown on La0.5Sr0.5CoO3 buffered (001) SrTiO3 substrates by pulsed laser deposition. Effects of Co doping on electrical properties of the films were investigated to establish material design through defects control. The doping led to a significant improvement in the electrical properties with reduction in leakage current and dielectric loss. In addition, the dielectric tunability and figure of merit were enhanced, implying that Co-doped BSZT films are promising materials for tunable microware applications. Our detail studies suggest that the improved electrical properties of Co-doped BSZT films are closely related to defect concentrations in the films.
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73.61.Ng Insulators
77.22.Gm Dielectric loss and relaxation
81.15.Fg Pulsed laser ablation deposition
61.72.sd Impurity concentration
68.55.at Other materials
77.55.-g Dielectric thin films
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