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15 Feb 2012

Volume 111, Issue 4, Articles (04xxxx)

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J. Appl. Phys. 111, 043501 (2012); http://dx.doi.org/10.1063/1.3680881 (8 pages)

Gregory J. McGraw and Stephen R. Forrest
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back to top Dielectrics and Ferroelectricity

X-ray diffraction, dielectric, conduction and Raman studies in Na0.925Bi0.075Nb0.925Mn0.075O3 ceramic

Chiheb Chaker, Y. Gagou, N. Abdelmoula, J.-L. Dellis, C. Masquelier, H. Khemakhem, and M. El Marssi

J. Appl. Phys. 111, 044101 (2012); http://dx.doi.org/10.1063/1.3684961 (8 pages)

Online Publication Date: 17 February 2012

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Ceramic with composition Na0.925Bi0.075Nb0.925Mn0.075O3 (NNBM0075) was synthesized by high temperature solid state reaction technique. It was studied using X-ray diffraction (XRD), dielectric measurements and Raman spectroscopy. The sample crystallizes in orthorhombic perovskite structure with space group Pbma at room temperature. Dielectric properties of the ceramic was investigated in a broad range of temperatures (−150 to 450 °C) and frequencies (0.1–103 kHz), and show two different anomalies connected to the symmetry change and electrical conductivity. Dielectric frequency dispersion phenomena in the NNBM0075 ceramic was analyzed by impedance spectroscopy in the temperature range from 55 to 425 °C. The Cole-Cole analysis based on electrical circuit and least square method was used to characterize the conduction phenomenon. A separation of the grain and grain boundary properties was achieved using an equivalent circuit model. The different parameters of this circuit were determined using impedance studies. Four conduction ranges, with different activation energies, were determined using the Arrhenius model. Raman spectra were studied as a function of temperatures and confirmed the X-ray and dielectric results. This composition is of interest for applications due to his physical properties and environmentally friendly character.
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77.22.Ch Permittivity (dielectric function)
78.30.Hv Other nonmetallic inorganics
72.80.Sk Insulators
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
82.80.Fk Electrochemical methods
61.72.Mm Grain and twin boundaries

Tuned dielectric, pyroelectric and piezoelectric properties of ferroelectric P(VDF-TrFE) thin films by using mechanical loads

G. Bai, R. Li, Z. G. Liu, Y. D. Xia, and J. Yin

J. Appl. Phys. 111, 044102 (2012); http://dx.doi.org/10.1063/1.3685750 (4 pages) | Cited 1 time

Online Publication Date: 22 February 2012

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Using the phenomenological Landau thermodynamic theory, we have investigated the effect of external mechanical loads on the phase transition and physical properties of poly(vinylidene fluoride-trifluorethylene) [P(VDF-TrFE)] thin films. Quantitative calculation shows that the phase transition temperature, polarization, dielectric, pyroelectric, and piezoelectric properties are highly sensitive to external mechanical loads. External compressive stress increases the phase transition temperature and the out-of-plane polarization and decreases the out-of-plane dielectric constant below Tc, pyroelectric coefficient, and piezoelectric coefficient (absolute value) and vice versa. Compared with pervoskite-type ferroelectrics, the calculated results are opposite due to the different intrinsic parameters between pervoskite and polymer ferroelectrics, especially, electrostrictive constants. The ability to tailor the properties in ferroelectric P(VDF-TrFE) thin films with the mechanical load can offer a tremendously promising future for applications in multifunctional devices, such as agile mechanical sensors and transducers.
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77.84.Jd Polymers; organic compounds
77.55.hn Other piezoelectric or electrostrictive films
77.80.B- Phase transitions and Curie point
77.22.Ej Polarization and depolarization
81.40.Lm Deformation, plasticity, and creep
77.22.Ch Permittivity (dielectric function)

Controllable chemical vapor deposition of large area uniform nanocrystalline graphene directly on silicon dioxide

Jie Sun (孙捷), Niclas Lindvall, Matthew T. Cole, Teng Wang (王腾), Tim J. Booth, Peter Bøggild, Kenneth B. K. Teo (张谋瑾), Johan Liu, and August Yurgens

J. Appl. Phys. 111, 044103 (2012); http://dx.doi.org/10.1063/1.3686135 (6 pages) | Cited 6 times

Online Publication Date: 23 February 2012

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Metal-catalyst-free chemical vapor deposition (CVD) of large area uniform nanocrystalline graphene on oxidized silicon substrates is demonstrated. The material grows slowly, allowing for thickness control down to monolayer graphene. The as-grown thin films are continuous with no observable pinholes, and are smooth and uniform across whole wafers, as inspected by optical-, scanning electron-, and atomic force microscopy. The sp2 hybridized carbon structure is confirmed by Raman spectroscopy. Room temperature electrical measurements show ohmic behavior (sheet resistance similar to exfoliated graphene) and up to 13% of electric-field effect. The Hall mobility is ∼40 cm2/Vs, which is an order of magnitude higher than previously reported values for nanocrystalline graphene. Transmission electron microscopy, Raman spectroscopy, and transport measurements indicate a graphene crystalline domain size ∼10 nm. The absence of transfer to another substrate allows avoidance of wrinkles, holes, and etching residues which are usually detrimental to device performance. This work provides a broader perspective of graphene CVD and shows a viable route toward applications involving transparent electrodes.
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81.07.Bc Nanocrystalline materials
81.05.ue Graphene
81.16.-c Methods of micro- and nanofabrication and processing
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.48.Gh Structure of graphene
72.20.My Galvanomagnetic and other magnetotransport effects

Phase transition hysteresis of ferroelectric Sr5EuTi3Nb7O30 ceramics with tetragonal tungsten bronze structure

Xiao Li Zhu and Xiang Ming Chen

J. Appl. Phys. 111, 044104 (2012); http://dx.doi.org/10.1063/1.3686644 (5 pages)

Online Publication Date: 23 February 2012

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The first-order ferroelectric transition of Sr5EuTi3Nb7O30 tungsten bronze ceramics was investigated together with the thermal history dependence of dielectric properties and differential scanning calorimetry (DSC) analysis. Moreover, the diffuse dielectric maximum appeared at a temperature above the ferroelectric transition, and this phenomenon had been reported in ferroelectrics with perovskite structure, but had never been observed in tungsten bronzes. Large hysteresis in the ferroelectric transition and severe depression of T0 were observed in both the permittivity-temperature and DSC curves, and were attributed to the complex nature of the tetragonal tungsten bronze structure. The DSC measurements were also used to get better insight into the gradual stability of the ferroelectric phase after cooling from the high temperature paraelectric phase. The abnormal splitting of the endothermic peaks was observed during the DSC measurements with lower start temperature or longer aging time. Two possible mechanisms were suggested. One was the separation of ferroelectric phase due to the compositional inhomogeneity. In another possible mechanism, the polar nanoregions coexisting with the ferroelectric domains were suggested and would possibly transit into the paraelectric phase at temperature below the ferroelectric transition.
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77.80.B- Phase transitions and Curie point
77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
81.40.Cd Solid solution hardening, precipitation hardening, and dispersion hardening; aging
77.84.Lf Composite materials
77.22.Ch Permittivity (dielectric function)

Effect of annealing ambient and temperature on the electrical characteristics of atomic layer deposition Al2O3/In0.53Ga0.47As metal-oxide-semiconductor capacitors and MOSFETs

Jenny Hu and H.-S. Philip Wong

J. Appl. Phys. 111, 044105 (2012); http://dx.doi.org/10.1063/1.3686628 (8 pages) | Cited 5 times

Online Publication Date: 28 February 2012

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In this work, we investigate the effect of forming gas annealing (FGA) on n-type and p-type In0.53Ga0.47As MOS capacitors with atomic layer deposition (ALD) Al2O3 high-κ dielectric. The as-deposited samples have a significant amount of fixed charge in the bulk of the gate dielectric and at the dielectric/semiconductor interface, which causes the flatband voltage (VFB) to have an oxide thickness dependent shift. Through FGA, we successfully (1) reduce the amount of bulk and interface fixed charge in the Al2O3, and (2) improve the Al2O3/InGaAs interface. The reduction in fixed charge is verified through an alignment of the VFB across all dielectric thicknesses. The gate stack improvement is qualitatively illustrated through a sharper capacitance-voltage (C-V) curve and quantitatively verified through a reduction of the interface trap density (DIT). The effect of the annealing temperature (300–400 °C) and ambient (N2 and forming gas (FG)) are investigated in detail through electrical characterization by C-V, I-V, DIT, fixed charge density (QF), and interface sheet charge (QIT) measurements. We find that there exists a trade-off where higher annealing temperatures result in a lower DIT, but comes at the cost of higher gate leakage. Furthermore, by comparing the effect of annealing in inert N2 versus FG, we are able to distinguish the effect of hydrogen in the FGA from the purely thermal effects of annealing. We discover that hydrogen passivation of dangling bonds and border traps is responsible for improving the interfacial properties, while the thermal budget is responsible for minimizing the fixed charge. Finally, we study the benefit of FGA on InGaAs nMOSFET device performance and demonstrate that the on-current increases by 25% after annealing at 350 °C for 30 min. A thorough understanding of the impact of FGA is crucial for threshold voltage tuning and improvement of the InGaAs MOSFET gate stack.
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85.30.Tv Field effect devices
84.32.Tt Capacitors
81.40.Gh Other heat and thermomechanical treatments
77.55.dj For nonsilicon electronics (Ge, III-V, II-VI, organic electronics)
85.40.Sz Deposition technology

Optical properties of amorphous high-k LaGdO3 films and its band alignment with Si

S. P. Pavunny, R. Thomas, A. Kumar, E. Fachini, and R. S. Katiyar

J. Appl. Phys. 111, 044106 (2012); http://dx.doi.org/10.1063/1.3688256 (9 pages) | Cited 1 time

Online Publication Date: 29 February 2012

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Optical properties of pulsed laser ablated amorphous high-k LaGdO3 (LGO) thin films on quartz (0001) substrates and its conduction/valance band offset with Si were studied. Complex refractive index and bandgap were extracted from the transmission spectra. An increase in the bandgap with decreasing film thickness was observed. The degree of structural disorder frozen in the network was estimated using Urbach model and found that the amorphousness increased with decreasing thickness. The analysis of refractive index dispersion with wavelength confirmed the single-effective-oscillator model for the direct inter-band transition. The calculated conduction and valance band offset of LGO with silicon were 2.57 ± 0.15 eV and 1.91 ± 0.15 eV, respectively, and are high enough to suppress the electron or hole injection into the conduction and valence band of LGO from the Si substrate, hence, can be of use as new high-k dielectric for the Si based CMOS technology.
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78.66.Nk Insulators
78.40.Ha Other nonmetallic inorganics
77.55.-g Dielectric thin films
73.20.At Surface states, band structure, electron density of states
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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