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13 Nov 2006

Volume 89, Issue 20, Articles (20xxxx)

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Appl. Phys. Lett. 89, 202101 (2006); http://dx.doi.org/10.1063/1.2388049 (3 pages)

J. H. Lee, Zh. M. Wang, N. W. Strom, Yu. I. Mazur, and G. J. Salamo
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Improvement on the temperature coefficient of resonant frequency of hexagonal perovskites through intergrowth structures

Fei Zhao, Zhenxing Yue, Jing Pei, Hao Zhuang, Zhilun Gui, and Longtu Li

Appl. Phys. Lett. 89, 202901 (2006); http://dx.doi.org/10.1063/1.2388141 (3 pages) | Cited 5 times

Online Publication Date: 13 November 2006

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Cation-deficient hexagonal perovskites Ba5Nb4O15, Ba6Nb4TiO18, and their intergrowth compounds were prepared by solid-state reaction method. Dielectric measurements showed that the intergrowth compounds had a relatively low temperature coefficient of resonant frequency (τf) compared to that of the simple terms Ba5Nb4O15 and Ba6Nb4TiO18. On the basis of the structure data, the authors proposed a structural parameter d, the degree of atomic displacements, to evaluate the structural dependence of the temperature coefficient of resonant frequency. The reduced τf value of intergrowths was considered to be resulted from the decreased degree of atomic displacements in the hexagonal perovskite structure.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
68.37.Lp Transmission electron microscopy (TEM)

Enhanced piezoresistive characteristics of Nb2O5 modified La0.8Sr0.2MnO3 ceramics

Vaneet Sharma, Maria R. Hossu, Woo Ho Lee, Ali R. Koymen, and Shashank Priya

Appl. Phys. Lett. 89, 202902 (2006); http://dx.doi.org/10.1063/1.2387567 (3 pages) | Cited 5 times

Online Publication Date: 13 November 2006

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This letter reports the giant piezoresistance phenomenon in Nb2O5 modified La0.8Sr0.2MnO3 (LSMO) polycrystalline ceramics. LSMO modified with 2 mol % Nb exhibited ∼ 2% change in resistivity at 19.2 MPa pressure as compared to 0.5% for the pure LSMO. A dramatic improvement was obtained for 5 mol % Nb-modified LSMO composition, which exhibited a linear change in resistivity with uniaxial stress and the fractional change was of the order of 3% at 19.2 MPa stress. The origin of the giant piezoresistance was found to be related to Nb substitution on the Mn sites which distorts the Mn–O bond, lowering the magnitude of stress required for the manganite lattice transformation.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.-j Piezoelectricity and electromechanical effects
72.20.Fr Low-field transport and mobility; piezoresistance

Aluminum oxynitride interfacial passivation layer for high-permittivity gate dielectric stack on gallium arsenide

Ming Zhu, Chih-Hang Tung, and Yee-Chia Yeo

Appl. Phys. Lett. 89, 202903 (2006); http://dx.doi.org/10.1063/1.2388246 (3 pages) | Cited 31 times

Online Publication Date: 13 November 2006

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The authors demonstrate a passivation technique for GaAs substrate by employing an aluminum oxynitride (AlON) interfacial passivation layer. X-ray photoelectron spectroscopy and transmission electron microscopy results show that the AlON interfacial passivation layer effectively suppresses the formation of Ga or As oxide during the gate dielectric deposition process. This enabled the fabrication of high quality GaAs n-channel metal-oxide-semiconductor capacitors with HfO2 gate dielectric and TaN metal gate electrode. The metal gate/high-k gate dielectric stack on GaAs demonstrated an equivalent SiO2 thickness of 2.2 nm and low leakage current density of 4.27×10−4 A/cm2 at a gate bias equal to Vfb−1 V. Excellent capacitance-voltage characteristics with low frequency dispersion ( ∼ 4%) were also obtained.
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85.30.Tv Field effect devices
84.32.Tt Capacitors
81.65.Rv Passivation

Effects of O vacancies and C doping on dielectric properties of ZrO2: A first-principles study

Gargi Dutta, K. P. S. S. Hembram, G. Mohan Rao, and Umesh V. Waghmare

Appl. Phys. Lett. 89, 202904 (2006); http://dx.doi.org/10.1063/1.2388146 (3 pages) | Cited 11 times

Online Publication Date: 14 November 2006

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The authors determine electronic properties, structural stability, and dielectric response of zirconia (ZrO2) with oxygen vacancies (O vacancies) and carbon doping (C doping) using first-principles density functional theory calculations based on pseudopotentials and a plane wave basis. They find significantly enhanced static dielectric response in zirconia with oxygen vacancies arising from a softened phonon mode. They also find that effects of carbon doping on the dielectric response are anisotropic.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Ch Permittivity (dielectric function)
61.72.J- Point defects and defect clusters
61.72.up Other materials
63.70.+h Statistical mechanics of lattice vibrations and displacive phase transitions

High performance Aurivillius phase sodium-potassium bismuth titanate lead-free piezoelectric ceramics with lithium and cerium modification

Chun-Ming Wang and Jin-Feng Wang

Appl. Phys. Lett. 89, 202905 (2006); http://dx.doi.org/10.1063/1.2388253 (3 pages) | Cited 30 times

Online Publication Date: 14 November 2006

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The piezoelectric properties of the lithium and cerium modified A-site vacancies sodium-potassium bismuth titanate (NKBT) lead-free piezoceramics are investigated. The piezoelectric activity of NKBT ceramics is significantly improved by the modification of lithium and cerium. The Curie temperature TC, piezoelectric coefficient d33, and mechanical quality factor Qm for the NKBT ceramics modified with 0.10 mol % (LiCe) are found to be 660 °C, 25 pC/N, and 3135, respectively. The Curie temperature gradually decreases from 675 to 650 °C with the increase of (LiCe) modification. The dielectric spectroscopy shows that all the samples possess stable piezoelectric properties, demonstrating that the (LiCe) modified NKBT-based ceramics are the promising candidates for high temperature applications.
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77.65.-j Piezoelectricity and electromechanical effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.72.J- Point defects and defect clusters
77.80.B- Phase transitions and Curie point

Resistive hystersis effects in perovskite oxide-based heterostructure junctions

M. P. Singh, L. Méchin, W. Prellier, and M. Maglione

Appl. Phys. Lett. 89, 202906 (2006); http://dx.doi.org/10.1063/1.2388145 (3 pages) | Cited 13 times

Online Publication Date: 16 November 2006

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The electrical and structural properties of the oxide-based metal/ferroelectric/metal (MFM) junctions are reported. The heterostructures are composed of ultrathin layers of La0.7Ca0.3MnO3 (LCMO) as a metallic layer and BaTiO3 (BTO) as a ferroelectric layer. Junction based devices, having the dimensions of 400×200 μm2, have been fabricated upon LCMO/BTO/LCMO heterostructures by photolithography and Ar-ion milling technique. The dc current-voltage (I-V) characteristics of the MFM junctions were carried out. At 300 K, the devices showed the linear (I-V) characteristics, whereas at 77 K, (I-V) curves exhibited some reproducible switching behaviors with well-defined remnant currents. The resulting resistance modulation is very different from what was already reported in ultrathin ferroelectric layers displaying resistive switching. A model is presented to explain the data.
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73.40.Rw Metal-insulator-metal structures

Impact of thin SrTiO3 seed layer to achieve low-temperature crystallization below 300 °C and ferroelectricity of lead zirconate titanate thin film

Ji-Won Moon, Shogo Tazawa, Kazuo Shinozaki, Naoki Wakiya, and Nobuyasu Mizutani

Appl. Phys. Lett. 89, 202907 (2006); http://dx.doi.org/10.1063/1.2390671 (3 pages) | Cited 8 times

Online Publication Date: 16 November 2006

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The authors report low-temperature preparation of Pb(Zr0.6,Ti0.4)O3 (PZT) thin films below 300 °C using SrTiO3 seed layers on (111)Pt/IrO2/SiO2/(001)Si substrates by metal-organic chemical vapor deposition. The critical parameters contributing low-temperature preparation for PZT were crystallinity and orientation of SrTiO3 seeds and deposition rate of PZT films. Using 1–2 nm of SrTiO3 with (h00) and (hh0) mixed orientations, polycrystalline PZT films could be obtained at 290 °C with deposition rate of 0.5–1.0 nm/min. The remanent polarization (2Pr) and coercive field (2Ec) of PZT films on SrTiO3 seeds with deposition rate of 0.5 nm/min were 42.4 μC/cm2 and 256 kV/cm, respectively.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
77.22.Ej Polarization and depolarization

Low leakage current—stacked MgO/Bi1.5Zn1.0Nb1.5O7 gate insulator— for low voltage ZnO thin film transistors

Mi-Hwa Lim, KyongTae Kang, Ho-Gi Kim, Il-Doo Kim, YongWoo Choi, and Harry L. Tuller

Appl. Phys. Lett. 89, 202908 (2006); http://dx.doi.org/10.1063/1.2387985 (3 pages) | Cited 14 times

Online Publication Date: 16 November 2006

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The authors report on the role of MgO capping layers in notably reducing leakage currents and improving mobility in ZnO thin film transistors (TFTs) utilizing compatible high-k Bi1.5Zn1.0Nb1.5O7 (BZN) gate insulators. All room temperature processed ZnO based TFTs with stacked MgO/BZN gate insulator exhibited a much enhanced field effect mobility of 5.4 cm2/V s with excellent saturation characteristics as compared to that (μFE = 1.13 cm2/V s) of ZnO based TFTs with BZN gate insulator. This work demonstrates the suitability of MgO/BZN stacked gate insulators in the fabrication of low voltage ZnO based TFTs on plastic substrates.
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73.40.Ns Metal-nonmetal contacts
72.20.Fr Low-field transport and mobility; piezoresistance
85.30.Tv Field effect devices

Internal photoemission of electrons at interfaces of metals with low-κ insulators

S. Shamuilia, V. V. Afanas’ev, P. Somers, A. Stesmans, Y.-L. Li, Zs. Tőkei, G. Groeseneken, and K. Maex

Appl. Phys. Lett. 89, 202909 (2006); http://dx.doi.org/10.1063/1.2360893 (3 pages) | Cited 8 times

Online Publication Date: 17 November 2006

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Energy barriers for electrons at interfaces of several low-permittivity insulators with metals (Ta, TaNx, TiNx, Au, and Al) are characterized using internal photoemission spectroscopy. In sharp contrast to thermal SiO2, the barriers show little sensitivity to the Fermi energy of the metal, suggesting that the uppermost occupied electron revels at the interface are states localized in the near-interfacial insulator layer. Moreover, despite large differences in the defect spectrum of the studied low-κ materials as revealed by electron spin resonance, all the measured energy barriers are found to be close to 4.5 eV. The latter indicates an extrinsic nature of the corresponding common electron state, which is tentatively ascribed to traces of moisture at the interface.
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73.20.At Surface states, band structure, electron density of states
79.60.Jv Interfaces; heterostructures; nanostructures
76.30.-v Electron paramagnetic resonance and relaxation
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
85.40.Ls Metallization, contacts, interconnects; device isolation

Nanocrystalline barium titanate films on flexible plastic substrates via pulsed laser annealing

Evangelos D. Tsagarakis, Connie Lew, Michael O. Thompson, and Emmanuel P. Giannelis

Appl. Phys. Lett. 89, 202910 (2006); http://dx.doi.org/10.1063/1.2387964 (3 pages) | Cited 5 times

Online Publication Date: 17 November 2006

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The drive towards ubiquitous electronics requires fundamental shifts in our approach to microelectronic fabrication as well as advances in materials and processing technologies. For large area electronics, low cost manufacturing, including roll-to-roll and printing technologies, will be required. These techniques present continuing challenges to develop processing technologies compatible with the low thermal budgets required for flexible polymeric substrates. The authors report here the deposition and dielectric properties of nanocrystalline BaTiO3 films on polyethylene terephthalate utilizing laser annealing as part of their effort to develop methods and tools for depositing various functional coatings and films on flexible substrates.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
81.07.Bc Nanocrystalline materials
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.16.-c Methods of micro- and nanofabrication and processing
42.62.-b Laser applications
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