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30 Jul 2007

Volume 91, Issue 5, Articles (05xxxx)

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Appl. Phys. Lett. 91, 052901 (2007); http://dx.doi.org/10.1063/1.2767146 (3 pages)

Wei-Feng Rao and Yu U. Wang
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Microstructures of coherent phase decomposition near morphotropic phase boundary in lead zirconate titanate

Wei-Feng Rao and Yu U. Wang

Appl. Phys. Lett. 91, 052901 (2007); http://dx.doi.org/10.1063/1.2767146 (3 pages) | Cited 10 times

Online Publication Date: 30 July 2007

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Microstructures of coherent phase decomposition near morphotropic phase boundary in lead zirconate titanate are investigated by using computer modeling and simulation. The model is based on the recently proposed incoherent equilibrium phase diagram [ G. A. Rossetti, Jr. et al., Appl. Phys. Lett. 88, 072912 (2006) ] and takes into account the coherency strain energy and electrostatic energy. It reveals characteristic multidomain microstructures, where nanoscale lamellar domains of tetragonal and rhombohedral phases coexist with well-defined crystallographic orientation relationships and produce coherent diffraction effects. The simulated microstructures provide important information for interpretation of diffraction data and identification of phases near morphotropic phase boundary.
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64.70.K- Solid-solid transitions
81.30.Dz Phase diagrams of other materials
61.50.Ks Crystallographic aspects of phase transformations; pressure effects

Electrical properties of HfTiON gate-dielectric metal-oxide-semiconductor capacitors with different Si-surface nitridations

F. Ji, J. P. Xu, P. T. Lai, C. X. Li, and J. G. Guan

Appl. Phys. Lett. 91, 052902 (2007); http://dx.doi.org/10.1063/1.2767177 (3 pages) | Cited 5 times

Online Publication Date: 30 July 2007

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Electrical properties of HfTiON gate-dielectric metal-oxide-semiconductor (MOS) capacitors with different Si-surface nitridations in N2O, NO, and NH3 prior to high-k film deposition are investigated and compared. It is found that the NO-nitrided sample exhibits low interface-state density and gate leakage current, and high reliability. This is attributed to formation of a SiON interlayer with suitable proportions of N and O. The MOS capacitor with Hf0.4Ti0.6OxNy/SiON gate dielectric stack (capacitance equivalent thickness of 1.52 nm and k value of 18.9) prepared by NO surface nitridation has an interface-state density of 1.22×1011 cm−2 eV−1 and gate leakage current density of 6×10−4 A cm−2 (Vg = 1 V). Moreover, only a small degradation of electrical properties after a stressing at 10 MV/cm for 3000 s is observed for the NO-nitrided sample.
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84.32.Tt Capacitors
81.65.Lp Surface hardening: nitridation, carburization, carbonitridation
85.30.-z Semiconductor devices

Dielectric abnormities in BaTi0.9(Ni1/2W1/2)0.1O3 giant dielectric constant ceramics

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

Appl. Phys. Lett. 91, 052903 (2007); http://dx.doi.org/10.1063/1.2767190 (3 pages) | Cited 13 times

Online Publication Date: 30 July 2007

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BaTi0.9(Ni1/2W1/2)0.1O3 ceramics were fabricated and their dielectric properties were investigated. With the sintering temperature increasing from 1250 to 1280 °C, the grain size abruptly increases from 1–2 to 20–40 μm, accompanying significant changes in dielectric response. The samples with larger grains exhibit giant dielectric constant characteristics, which are considered to be mainly attributed to the domain boundary effect. The activation energies of the dielectric relaxation Erelax = 0.325 eV reveal the existence of microdomains in larger grains. The ac conductivity results also give the evidence of the domain boundary effect in the present ceramics.
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77.22.Ch Permittivity (dielectric function)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Balanced charge injection in multilayer polymer light-emitting diode with water soluble nonconjugated polymer dispersed by ionic compounds

Dong-Kyu Park, A-Rum Chun, Soo-Hong Kim, Min-Sook Kim, Choong-Gi Kim, Tae-Woo Kwon, Seong-Jin Cho, Hyung-Suk Woo, Jae-Gyoung Lee, Suck-Hyun Lee, and Zhi-Xin Guo

Appl. Phys. Lett. 91, 052904 (2007); http://dx.doi.org/10.1063/1.2767212 (3 pages) | Cited 5 times

Online Publication Date: 30 July 2007

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The authors have fabricated highly efficient polymeric light-emitting diode (PLED) from ionic compound dispersed water soluble nonconjugated polymer, polyurethane (PU), which was used as an ultrathin hole blocking and electron injection layer (HB-EIL) on the top of commercially available blue-emitting polymer, polyfluorene. The device with HB-EIL showed a maximum quantum efficiency of 1.7%, while the one without HB-EIL showed an efficiency of 0.6%. They propose that the better performance in PLED with PU layer was due to a well balanced charge injection in emitting layer after the enhanced electron injection due to ionic compound in the insulating PU layer.
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85.60.Jb Light-emitting devices

Formation of TaN nanocrystals embedded in silicon nitride by phase separation methods for nonvolatile memory applications

Hyejung Choi, Seung-Jae Jung, Hokyung Park, Joon-Myung Lee, Moonjae Kwon, Man Chang, Musarrat Hasan, Sangmoo Choi, and Hyunsang Hwang

Appl. Phys. Lett. 91, 052905 (2007); http://dx.doi.org/10.1063/1.2760181 (3 pages) | Cited 6 times

Online Publication Date: 30 July 2007

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TaN nanocrystals (NCs) embedded in silicon nitride were investigated as a new charge-trapping layer of a silicon-oxide-nitride-oxide-silicon-type nonvolatile memory device. After annealing at 900 °C, TaN NCs with average size of 3.5 nm were formed by the phase separation method. Compared with a control sample without NC, memory devices with TaN NCs exhibit superior memory characteristics, such as a larger window of capacitance-voltage hysteresis and a lower charge loss rate. The improvement can be explained by the formation of high density TaN NCs with a deeper trap energy level.
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81.16.-c Methods of micro- and nanofabrication and processing
64.75.-g Phase equilibria

Local surface potential distribution in oriented ferroelectric thin films

Yunseok Kim, Simon Bühlmann, Jiyoon Kim, Moonkyu Park, Kwangsoo No, Yong Kwan Kim, and Seungbum Hong

Appl. Phys. Lett. 91, 052906 (2007); http://dx.doi.org/10.1063/1.2761502 (3 pages) | Cited 12 times

Online Publication Date: 31 July 2007

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Using Kelvin force microscopy, the authors have investigated the potential distribution on ferroelectric films. The local distribution of potential was observed on downward, prepoled areas. The polarity of the potential corresponds to the screen charge. It was found that the electrical properties of the grain boundary affect the potential distribution. Most of the grain boundaries show a lower potential than the area inside the grain. The authors identified certain regions at the grain boundary with a very low potential. Such potential pits may act as efficient screen charge draining paths and may lead to important perturbations on the device level.
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77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Ej Polarization and depolarization
61.72.Mm Grain and twin boundaries

Rearrangement of the oxide-semiconductor interface in annealed Al2O3/4H-SiC structures

M. Avice, S. Diplas, A. Thøgersen, J. S. Christensen, U. Grossner, B. G. Svensson, O. Nilsen, H. Fjellvåg, and J. F. Watts

Appl. Phys. Lett. 91, 052907 (2007); http://dx.doi.org/10.1063/1.2757608 (3 pages) | Cited 4 times

Online Publication Date: 31 July 2007

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Al2O3 films with different thicknesses have been deposited on n-type (nitrogen-doped) 4H-SiC(0001) epitaxial samples by atomic layer chemical vapor deposition at 300 °C and subsequently annealed in Ar atmosphere at temperatures up to 1000 °C. The Al2O3/4H-SiC structures were analyzed by x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry (SIMS), and transmission electron microscopy (TEM). The XPS and SIMS results indicate that the average composition in the wider interface area does not significantly change due to the annealing. However, as revealed by the TEM investigations in combination with XPS, the as-grown samples exhibit a double interface created by an intermediate suboxide SiOx layer (x<2). After annealing, this intermediate suboxide layer breaks up and transforms into SiO2 islands, resulting in a rather rough interface region and a high concentration of pure Si in the Al2O3 film. Furthermore, a pronounced accumulation of H is found in the rough interface region and this may play a key role for the low density of shallow electron states reported for annealed Al2O3/4H-SiC structures.
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68.35.Ct Interface structure and roughness
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.Cc Kinetics of defect formation and annealing
79.60.Jv Interfaces; heterostructures; nanostructures
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Modified atomic layer deposition of RuO2 thin films for capacitor electrodes

Jin-Hyock Kim, Deok-Sin Kil, Seung-Jin Yeom, Jae-Sung Roh, Noh-Jung Kwak, and Jin-Woong Kim

Appl. Phys. Lett. 91, 052908 (2007); http://dx.doi.org/10.1063/1.2767769 (3 pages) | Cited 10 times

Online Publication Date: 1 August 2007

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The authors investigated the modified atomic layer deposition (ALD) of RuO2 films using bis(ethylcyclopentadienyl)ruthenium [Ru(EtCp)2] at a deposition temperature of 265 °C. Oxygen gas diluted with argon was supplied throughout all of the ALD steps. The growth rate of the modified ALD RuO2 was about 1.4 Å/cycle, which is higher than that of conventional Ru ALD due to the increase in the amount of Ru(EtCp)2 adsorption per cycle, as well as the difference in the unit cell volumes of Ru and RuO2. The film thickness increased linearly with the number of cycles, and the incubation cycle in the initial stage was negligible.
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81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
68.43.Mn Adsorption kinetics

Spectroscopic determination of phase in tetragonally strained Ba0.5Sr0.5TiO3 films at room temperature

L. M. B. Alldredge, J. C. Woicik, Wontae Chang, Steven W. Kirchoefer, and Jeffrey M. Pond

Appl. Phys. Lett. 91, 052909 (2007); http://dx.doi.org/10.1063/1.2766668 (3 pages) | Cited 1 time

Online Publication Date: 2 August 2007

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Sputter-deposited Ba0.5Sr0.5TiO3 thin films on MgO(001) substrates with either in-plane (c<a) or out-of-plane (c>a) tetragonal lattice structure distortions were characterized by polarization-dependent Ti K-edge x-ray absorption fine-structure (XAFS) spectroscopy and microwave dielectric measurements. Anisotropy between the in-plane and out-of-plane directions in the films as determined by XAFS provided evidence of spontaneous polarization, and the anisotropy varied with the type of structural distortion. These results explain microwave measurements in which the dielectric properties were significantly affected by lattice distortions and exhibited hysteresis in the in-plane dielectric constant with dc bias at room temperature, suggesting the presence of permanent dipoles.
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68.55.-a Thin film structure and morphology
78.70.Dm X-ray absorption spectra
68.60.Bs Mechanical and acoustical properties
77.22.Ch Permittivity (dielectric function)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Ti-rich and Cu-poor grain-boundary layers of CaCu3Ti4O12 detected by x-ray photoelectron spectroscopy

C. Wang, H. J. Zhang, P. M. He, and G. H. Cao

Appl. Phys. Lett. 91, 052910 (2007); http://dx.doi.org/10.1063/1.2768006 (3 pages) | Cited 10 times

Online Publication Date: 2 August 2007

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Cleaved and polished surfaces of CaCu3Ti4O12 ceramics have been investigated by x-ray photoelectron spectroscopy (XPS) and energy dispersive x-ray spectroscopy (EDX), respectively. While EDX technique shows the identical CaCu3Ti4O12 stoichiometry for the two surfaces, XPS indicates that the cleaved surface with grain-boundary layers is remarkably Ti-rich and Cu-poor. The core-level spectrum of Cu 2p unambiguously shows the existence of monovalent copper only for the cleaved surface. Possible grain-boundary structure and its formation are discussed.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.72.Mm Grain and twin boundaries
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
73.20.At Surface states, band structure, electron density of states

Experimental study for the conditions of analog switching in ferroelectric liquid crystal cells

V. Manjuladevi, Yu. P. Panarin, and J. K. Vij

Appl. Phys. Lett. 91, 052911 (2007); http://dx.doi.org/10.1063/1.2767210 (3 pages) | Cited 6 times

Online Publication Date: 3 August 2007

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The authors study the effect of the spontaneous polarization (PS) of a ferroelectric liquid crystal mixture with compensated helix and of the thickness of the alignment layer (da) on the analog switching in a cell. The quality of analog switching is established in terms of its contrast ratio, texture in the dark state, and the electrostatic energy. The latter approximates to PS2da for da⪡d (thickness of the ferroelectric liquid crystal cell layer).
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77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
77.80.Fm Switching phenomena
77.22.Ej Polarization and depolarization

Superionic PbSnF4: A giant dielectric constant material

Mohamad M. Ahmad and Koji Yamada

Appl. Phys. Lett. 91, 052912 (2007); http://dx.doi.org/10.1063/1.2766849 (3 pages) | Cited 7 times

Online Publication Date: 3 August 2007

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In this letter, the authors report on the giant dielectric constant properties in a hitherto unexplored material, the superionic conductor lead tin fluoride PbSnF4. Despite its superionic behavior, PbSnF4 is surprisingly found to exhibit extraordinary high dielectric constant (ε′ ∼ 105). ε′ is almost independent of temperature and frequency over wide ranges. The authors find that the high value of ε′ originates from an internal effect, such as internal barrier layer capacitor, rather than from a surface barrier layer capacitor formed at the electrode/sample interface.
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77.22.Ch Permittivity (dielectric function)
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
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