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4 Jun 2007

Volume 90, Issue 23, Articles (23xxxx)

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Appl. Phys. Lett. 90, 233105 (2007); http://dx.doi.org/10.1063/1.2747052 (3 pages)

Youhui Gao, Daisuke Shindo, Yuping Bao, and Kannan Krishnan
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Leakage currents at crystallites in ZrAlxOy thin films measured by conductive atomic-force microscopy

O. Bierwagen, L. Geelhaar, X. Gay, M. Piešiņš, H. Riechert, B. Jobst, and A. Rucki

Appl. Phys. Lett. 90, 232901 (2007); http://dx.doi.org/10.1063/1.2746058 (3 pages) | Cited 17 times

Online Publication Date: 4 June 2007

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The spatial distribution of the leakage current through ZrAlxOy thin films with different degrees of crystallinity was investigated at the nanometer-scale. Conductive atomic-force microscopy shows leakage currents at low electric fields in the polycrystalline but not in the amorphous films. Leakage occurs at large crystallites that protrude from the surface. Ring-shaped current distributions around some of the crystallites suggest a conduction at the boundary of crystalline grain and amorphous matrix, and not through the grain. In contrast, the leakage spots that are observed in amorphous films at high electric fields are not correlated to the morphology.
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73.61.-r Electrical properties of specific thin films
73.63.Bd Nanocrystalline materials
68.37.Ps Atomic force microscopy (AFM)
68.55.-a Thin film structure and morphology
61.46.Hk Nanocrystals
61.43.-j Disordered solids

High-density capacitors based on amorphous BaTiO3 layers grown under hydrogen containing atmosphere

P. Gonon and F. El Kamel

Appl. Phys. Lett. 90, 232902 (2007); http://dx.doi.org/10.1063/1.2746066 (3 pages) | Cited 11 times

Online Publication Date: 4 June 2007

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Addition of hydrogen (H2) during the sputter deposition of BaTiO3 amorphous thin films drastically modifies their dielectric properties. Films grown under hydrogen containing atmospheres display large capacitances (several μF/cm2 for 1 μm thick films), that are hundred times higher than capacitances measured for films grown without hydrogen. This is explained by the formation of a double-layer capacitor which arises from mobile protons (protonic conduction with an activation energy around 0.3 eV). These films could find applications for the elaboration of integrated supercapacitors.
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84.32.Tt Capacitors

Double hysteresis loop in Cu-doped K0.5Na0.5NbO3 lead-free piezoelectric ceramics

Dunmin Lin, K. W. Kwok, and H. L. W. Chan

Appl. Phys. Lett. 90, 232903 (2007); http://dx.doi.org/10.1063/1.2746087 (3 pages) | Cited 43 times

Online Publication Date: 4 June 2007

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In this letter the authors report the observation of double hysteresis loops in Cu-doped K0.5Na0.5NbO3 (KNN) ceramics. Unlike other ferroelectric titanates (e.g., BaTiO3), aging is not required for the ceramic to exhibit the double-loop-like characteristics. Based on the symmetry-conforming principle of point defects, it is suggested that defect dipoles are formed by the acceptor dopant ions-Cu2+ and O2− vacancies along the polarization direction after the diffuse tetragonal-orthorhombic phase transition of the ceramic. Because of the low migration rates of defects, the defect dipoles remain in the original orientation during the P-E loop measurement, providing a restoring force to reverse the switched polarization. The defect dipoles also provide “pinning” effects in the normal piezoelectric activities. As a result, the ceramic becomes “hardened,” exhibiting an extraordinarily high mechanical quality factor (2500), while the other piezoelectric properties remain reasonably good: electromechanical coupling coefficients kp = 39%, kt = 47%, and piezoelectric coefficient d33 = 82 pC/N.
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77.80.Dj Domain structure; hysteresis
77.65.Bn Piezoelectric and electrostrictive constants
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization

Structural and electrical characteristics of atomic layer deposited high κ HfO2 on GaN

Y. C. Chang, H. C. Chiu, Y. J. Lee, M. L. Huang, K. Y. Lee, M. Hong, Y. N. Chiu, J. Kwo, and Y. H. Wang

Appl. Phys. Lett. 90, 232904 (2007); http://dx.doi.org/10.1063/1.2746057 (3 pages) | Cited 32 times

Online Publication Date: 4 June 2007

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High κ HfO2 was deposited on n-type GaN (0001) using atomic layer deposition with Hf(NCH3C2H5)4 and H2O as the precursors. Excellent electrical properties of TiN/HfO2/GaN metal-oxide-semiconductor diode with the oxide thickness of 8.8 nm were obtained, in terms of low electrical leakage current density ( ∼ 10−6A/cm2 at VFB+1 V), well behaved capacitance-voltage (C-V) curves having a low interfacial density of states of 2×1011 cm−2 eV−1 at the midgap, and a high dielectric constant of 16.5. C-V curves with clear accumulation and depletion behaviors were shown, along with negligible frequency dispersion and hysteresis with sweeping biasing voltages. The structural properties studied by high-resolution transmission electron microscopy and x-ray reflectivity show an atomically smooth oxide/GaN interface, with an interfacial layer of GaON ∼ 1.8 nm thick, as probed using x-ray photoelectron spectroscopy.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Ch Permittivity (dielectric function)
77.80.Dj Domain structure; hysteresis
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices
85.30.Kk Junction diodes

Effects of Li content on the phase structure and electrical properties of lead-free (K0.46−x/2Na0.54−x/2Lix)(Nb0.76Ta0.20Sb0.04)O3 ceramics

Yunfei Chang, Zupei Yang, Yuting Hou, Zonghuai Liu, and Zenglin Wang

Appl. Phys. Lett. 90, 232905 (2007); http://dx.doi.org/10.1063/1.2746411 (3 pages) | Cited 31 times

Online Publication Date: 5 June 2007

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Lead-free (K0.46−x/2Na0.54−x/2Lix)(Nb0.76Ta0.20Sb0.04)O3 piezoelectric ceramics were prepared by the conventional solid state sintering method without cold-isostatic pressing process. The x-ray diffraction and Raman scattering results show that the phase structure of the ceramics undergoes a transition from pseudocubic to tetragonal phase with increasing x from 0 to 0.10. Significantly enhanced electrical properties (d33 = 259 pC/N, kp = 0.42, εr = 1653, and tan δ = 0.027) were obtained in the ceramics with x = 0.04 near the morphotropic phase boundary, and only the tetragonal-cubic phase transition was observed above the room temperature in the εr-T curve. The temperature stability of the ceramics with x = 0.04 was also investigated.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
64.70.K- Solid-solid transitions
77.65.-j Piezoelectricity and electromechanical effects
78.30.Hv Other nonmetallic inorganics
61.50.Ks Crystallographic aspects of phase transformations; pressure effects

Interface effect on dielectric constant of HfO2/Al2O3 nanolaminate films deposited by plasma-enhanced atomic layer deposition

Pan Kwi Park, Eun-Soo Cha, and Sang-Won Kang

Appl. Phys. Lett. 90, 232906 (2007); http://dx.doi.org/10.1063/1.2746416 (3 pages) | Cited 12 times

Online Publication Date: 5 June 2007

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The effect of the interface between Al2O3 and HfO2 sublayers on the dielectric constant was investigated in HfO2/Al2O3 nanolaminate films deposited using plasma-enhanced atomic layer deposition. After annealing at 700 °C, the dielectric constants of the nanolaminate films with a sublayer thickness of 40 Å or greater were the same as the calculated values for a series of capacitors consisting of amorphous Al2O3 and monoclinic or tetragonal HfO2. As the sublayer thickness was reduced to 10 Å, the dielectric constant increased up to 17.7 because a thin Hf–O–Al mixture layer, of which the number increases drastically in the nanolaminate films with thin sublayers, is formed at the interface.
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77.22.Ch Permittivity (dielectric function)
52.77.Dq Plasma-based ion implantation and deposition
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
77.55.-g Dielectric thin films

Effects of microwave irradiation on the dehydriding reaction of the composites of lithium borohydride and microwave absorber

Motoaki Matsuo, Yuko Nakamori, Keitaro Yamada, and Shin-ichi Orimo

Appl. Phys. Lett. 90, 232907 (2007); http://dx.doi.org/10.1063/1.2746061 (3 pages) | Cited 11 times

Online Publication Date: 6 June 2007

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Effects of microwave irradiation on the dehydriding reaction of the composites of LiBH4 and a microwave absorber such as TiH2, B, or C were experimentally investigated. The composites with TiH2 exhibited faster temperature increases than pure LiBH4; however, they took more than 30 min to release hydrogen. In contrast, the composites with B or C as efficient microwave absorbers were heated much more rapidly to release 6 mass % hydrogen within 5 min. The composites with C were superior to those with B, probably due to the higher thermal conductivity of C.
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84.60.-h Direct energy conversion and storage
84.90.+a Other topics in electronics, radiowave and microwave technology, and direct energy conversion and storage (restricted to new topics in section 84)

Ferroelectric and pyroelectric properties of highly (110)-oriented Pb(Zr0.40Ti0.60)O3 thin films grown on Pt/LaNiO3/SiO2/Si substrates

Yiping Guo, Daisuke Akai, Kzauaki Swada, and Makoto Ishida

Appl. Phys. Lett. 90, 232908 (2007); http://dx.doi.org/10.1063/1.2746949 (3 pages) | Cited 9 times

Online Publication Date: 6 June 2007

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Pb(Zr0.4Ti0.6)O3 thin films with a thickness of 500 nm were spin coated on (110) preferred Pt bottom electrodes using a sol-gel method, in which the (110) preferred Pt bottom electrode was developed by using a (100)-oriented conductive oxide electrode LaNiO3 film as an adhesion layer on a SiO2/Si substrate. X-ray diffraction analysis and field emission scanning electron microscopy show that the as-grown Pb(Zr0.4Ti0.6)O3 films are highly (110)-oriented with a columnar structure. It indicates that the (110) preferred Pt bottom electrode is effective for growing highly (110)-oriented Pb(Zr0.4Ti0.6)O3 films. The as-grown Pb(Zr0.4Ti0.6)O3 films show excellent dielectric and ferroelectric properties with dielectric constant ε33T/ε0 = 1620, loss tangent tan δ = 2.1%, spontaneous polarization 2Ps = 158 μC/cm2, and remnant polarization 2Pr = 92 μC/cm2. Excellent pyroelectric properties are also detected in the (110)-oriented films. At room temperature, the pyroelectric coefficient and the figure of merit for detectivity can reach up to 7.8×10−4 C m−2 K−1 and 1.79×10−5 Pa−0.5, respectively.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
77.70.+a Pyroelectric and electrocaloric effects
77.55.-g Dielectric thin films
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Effective thickness and dielectric constant of interfacial layers of Pt/Bi3.15Nd0.85Ti3O12/SrRuO3 capacitors

H. Yang, N. A. Suvorova, M. Jain, B. S. Kang, Y. Li, M. E. Hawley, P. C. Dowden, R. F. DePaula, Q. X. Jia, and C. J. Lu

Appl. Phys. Lett. 90, 232909 (2007); http://dx.doi.org/10.1063/1.2746953 (3 pages) | Cited 3 times

Online Publication Date: 6 June 2007

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Epitaxial c-axis-oriented Bi3.15Nd0.85Ti3O12 (BNT) thin films with thickness ranging from 150 to 350 nm were deposited on conductive SrRuO3 (SRO) on (001) SrTiO3 substrates by pulsed laser deposition. The top Pt electrode was deposited by sputtering to construct a capacitor Pt/BNT/SRO. The authors have evaluated the effective thickness (ti) and dielectric constant (εi) of interfacial layers at the Pt/BNT and BNT/SRO interfaces based on the optical refractive index of the BNT layer and the capacitance frequency as well as the current-voltage characteristics of the capacitors. Using a series capacitor model, they have found that the dielectric constant of bulk BNT and the ti/εi ratio are 586 and 1.46 nm, respectively. Knowing the optical dielectric constant (εopt) and the product of εoptti of BNT thin films, the authors have estimated that the effective thickness and dielectric constant of the interfacial layers are 20.1 nm and 13.7, respectively.
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84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Creating shifted resonances at favored optical frequencies

Chungpin Liao and Hsien-Ming Chang

Appl. Phys. Lett. 90, 232910 (2007); http://dx.doi.org/10.1063/1.2747176 (3 pages)

Online Publication Date: 7 June 2007

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In general, resonance absorption spectra are fixed properties of natural or man-made bulk materials. However, in optical and photonic applications, it will be celebrated if such spectral behaviors can be tailored at will. In particular, e.g., resonance peaks can be created at frequency locations desired. The authors demonstrated that, via the guidance of Clausius-Mossotti equation [ K. D. Bonin and V. V. Kresin, Electric-Dipole Polarizabilities of Atoms, Molecules and Clusters (World Scientific, New Jersey, 1997), p. 129 ] and the assistance of first-principles quantum mechanical simulations, the collective beating of multiple types of artificially implemented dipoles could render favorable resonance(s) originally in absence.
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33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility
32.30.-r Atomic spectra
03.65.-w Quantum mechanics

Characterization of high TC Pb(Mg1/3Nb2/3)O3–PbZrO3–PbTiO3 single crystals fabricated by solid state crystal growth

Shujun Zhang, S. M. Lee, D. H. Kim, H. Y. Lee, and Thomas R. Shrout

Appl. Phys. Lett. 90, 232911 (2007); http://dx.doi.org/10.1063/1.2746055 (3 pages) | Cited 12 times

Online Publication Date: 11 June 2007

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Ferroelectric crystals near the morphotropic phase boundary (MPB) in the Pb(Mg1/3Nb2/3)O3–PbZrO3–PbTiO3 ternary system were grown using the solid state crystal growth technique. A MPB composition with a Curie temperature of ∼ 205 °C was selected for characterization of the piezoelectric properties and temperature dependent behavior. The room temperature electromechanical coupling factors were found to be ≥ 90% for k33 and ∼ −87% for k32, respectively, comparable to Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) crystals. The coercive field, being on the order of 5 kV/cm, was found to be nearly double that of the pure PMN-PT. The temperature dependence of the piezoelectric and electromechanical properties showed temperature stability up to 160 °C, expanding the temperature usage range for actuator and ultrasonic transducer applications.
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77.80.B- Phase transitions and Curie point
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Bn Piezoelectric and electrostrictive constants
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