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9 May 2005

Volume 86, Issue 19, Articles (19xxxx)

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Appl. Phys. Lett. 86, 191102 (2005); http://dx.doi.org/10.1063/1.1922084 (3 pages)

Nir Dahan, Avi Niv, Gabriel Biener, Vladimir Kleiner, and Erez Hasman
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Equivalent oxide thickness of a thin oxide interlayer in gate insulator stacks on silicon

Feliciano Giustino, Angelo Bongiorno, and Alfredo Pasquarello

Appl. Phys. Lett. 86, 192901 (2005); http://dx.doi.org/10.1063/1.1923185 (3 pages) | Cited 13 times

Online Publication Date: 2 May 2005

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We investigate the equivalent oxide thickness of a thin oxide interlayer in gate insulator stacks on silicon. Through the use of a first-principles approach, we map the profile of the local permittivity across two interface models showing different suboxide structures. These models incorporate the available atomic-scale experimental data and account for the amorphous nature of the oxide. The equivalent oxide thickness of the interfacial oxide layer is found to be smaller than the corresponding physical thickness by 0.2–0.3 nm. We discuss implications of these results for future device scaling.
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85.30.De Semiconductor-device characterization, design, and modeling
85.40.Ls Metallization, contacts, interconnects; device isolation
73.61.-r Electrical properties of specific thin films

Polarization reversal and capacitance-voltage characteristic of epitaxial Pb(Zr,Ti)O3 layers

L. Pintilie, M. Lisca, and M. Alexe

Appl. Phys. Lett. 86, 192902 (2005); http://dx.doi.org/10.1063/1.1926403 (3 pages) | Cited 16 times

Online Publication Date: 2 May 2005

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Capacitance-voltage (C–V) measurements were performed on epitaxial layers of Pb(Zr0.2Ti0.8)O3 (PZT) with top and bottom SrRuO3 (SRO) electrodes. It is shown that the sharp capacitance peak∕discontinuity which is present in the C–V characteristics at different frequencies is directly associated with the polarization reversal. The ferroelectric film is assumed as a large band-gap semiconductor with Schottky contacts at the metal-ferroelectric interfaces. The capacitance discontinuity at the reversal (coercive) voltage is associated with a discontinuity in the built-in potential at the PZT∕SRO interfaces. The C–V characteristics for voltage ranges outside the coercive values can be used to extract the free carrier concentrations as in the case of Schottky metal-semiconductor contacts. The carrier concentration was found to be (2–4)×1018 cm−3, independent of measuring frequency and temperature up to 1 MHz and 170 °C, respectively, suggesting completely ionized shallow impurities.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Fm Switching phenomena
73.40.Sx Metal-semiconductor-metal structures

Domain rearrangement during nanoindentation in single-crystalline barium titanate measured by atomic force microscopy and piezoresponse force microscopy

G. A. Schneider, T. Scholz, J. Muñoz-Saldaña, and M. V. Swain

Appl. Phys. Lett. 86, 192903 (2005); http://dx.doi.org/10.1063/1.1920410 (3 pages) | Cited 17 times

Online Publication Date: 2 May 2005

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Nanoindentation tests in an aa-in-plane domain area of an {001} oriented barium titanate single crystal were performed using a conical indenter with a tip radius of 800 nm. The topography and the polarization vectors of the area after indentation were imaged afterwards by both atomic force and piezoresponse force microscopy (PFM), respectively. Two perpendicular oriented cracks in the {110} planes were identified in the topographic image. An unexpected considerable uplift occurs inside the residual impression, which was correlated with a sharp pop-out-like behavior observed in the force-displacement curve just prior to unloading. Furthermore, PFM revealed an almost a twofold symmetric arrangement of the domains around the indent, which can be explained by residual circumferential tensile stresses around a residual impression and was unambiguously correlated to the crystal orientation.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
68.37.Ps Atomic force microscopy (AFM)
77.22.Ej Polarization and depolarization
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
62.20.Qp Friction, tribology, and hardness
68.35.Gy Mechanical properties; surface strains

Chemical and dielectrical characteristics of ultrathin oxides grown by atomic force microscopy and scanning electron beam

X. N. Xie, H. J. Chung, C. H. Sow, and A. T. S. Wee

Appl. Phys. Lett. 86, 192904 (2005); http://dx.doi.org/10.1063/1.1901814 (3 pages) | Cited 4 times

Online Publication Date: 2 May 2005

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We report a comparative study on the chemical and dielectrical properties of ultrathin oxides grown by atomic force microscopy (AFM) and scanning electron beam (SEB) techniques. Oxide grown by AFM (AFM oxide) shows preferential etching as compared to oxide grown by SEB (SEB oxide). The structural and chemical features of these oxides were probed using time-of-flight secondary ion mass spectrometry (TOF-SIMS) time profiling. It was found that AFM oxide is richer in Si–H and Si–OH content, while SEB oxide is oxygen rich and relatively dense in structure. The dielectric strength of AFM and SEB oxides were further evaluated by conducting AFM (c-AFM). The current–voltage characteristics and dielectric breakdown probability of these oxides were compared. The correlation between Si–H and Si–OH site formation and its impact on the chemical and dielectrical stability of AFM and SEB oxides was discussed.
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81.65.Mq Oxidation
81.05.Cy Elemental semiconductors
77.22.Jp Dielectric breakdown and space-charge effects
82.80.Rt Time of flight mass spectrometry
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.37.Ps Atomic force microscopy (AFM)

Effects of nonequally biaxial misfit strains on the phase diagram and dielectric properties of epitaxial ferroelectric thin films

Jie Wang and Tong-Yi Zhang

Appl. Phys. Lett. 86, 192905 (2005); http://dx.doi.org/10.1063/1.1923765 (3 pages) | Cited 25 times

Online Publication Date: 2 May 2005

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The effects of nonequally biaxial in-plane misfit strains on the equilibrium polarization states and the dielectric properties of single-domain epitaxial ferroelectric thin films are investigated by a nonlinear thermodynamic theory. The “misfit strain-misfit strain” and “temperature-misfit strain” phase diagrams for single-domain BaTiO3 (BT) and PbTiO3 (PT) thin films grown on tetragonal substrates are developed by minimizing the Helmholtz free energy. The nonequally biaxial misfit strains cause the presence of two in-plane tetragonal ferreoelectric phases, a1 (P1 ≠ 0,P2 = P3 = 0) and a2 (P2 ≠ 0,P1 = P3 = 0), in both BT and PT thin films, which do not exist if the misfit strains are equally biaxial.
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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.Dj Domain structure; hysteresis
68.60.Bs Mechanical and acoustical properties
81.30.Dz Phase diagrams of other materials
77.22.Ej Polarization and depolarization
65.40.G- Other thermodynamical quantities

Intergrowth Bi2WO6–Bi3TiNbO9 ferroelectrics with high ionic conductivity

Z. G. Yi, Y. X. Li, Z. Y. Wen, S. R. Wang, J. T. Zeng, and Q. R. Yin

Appl. Phys. Lett. 86, 192906 (2005); http://dx.doi.org/10.1063/1.1925760 (3 pages) | Cited 18 times

Online Publication Date: 3 May 2005

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Two dielectric relaxation loss peaks associated with oxygen-ion diffusion in the intergrowth Bi2WO6–Bi3TiNbO9(Bi5TiNbWO15) bismuth layered ferroelectrics were observed. The activation energy and the relaxation time at infinite temperature, for these two peaks, were determined to be (0.89 eV, 1.3×10−13 s) and (0.84 eV, 3.6×10−10 s). The ac impedance spectroscopy indicated that the Bi5TiNbWO15 ceramic is an ionic conductor with an electrical conductivity of approximately 2.6×10−2 S/cm at a temperature of 1073 K.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.-e Ferroelectricity and antiferroelectricity
77.22.Gm Dielectric loss and relaxation
66.30.H- Self-diffusion and ionic conduction in nonmetals

Study of orientation effect on nanoscale polarization in BaTiO3 thin films using piezoresponse force microscopy

Il-Doo Kim, Ytshak Avrahami, Harry L. Tuller, Young-Bae Park, Matthew J. Dicken, and Harry A. Atwater

Appl. Phys. Lett. 86, 192907 (2005); http://dx.doi.org/10.1063/1.1923173 (3 pages) | Cited 13 times

Online Publication Date: 3 May 2005

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We have investigated the effect of texture on in-plane (IPP) and out-of plane (OPP) polarizations of pulsed-laser-deposited BaTiO3 thin films grown on Pt and La0.5Sr0.5CoO3 (LSCO) buffered Pt electrodes. The OPP and IPP polarizations were observed by piezoresponse force microscopy (PFM) for three-dimensional polarization analyses in conjunction with conventional diffraction methods using x-ray diffraction and reflection high energy electron diffraction measurements. BaTiO3 films grown on Pt electrodes exhibited highly (101) preferred orientation with higher IPP component whereas BaTiO3 film grown on LSCO/Pt electrodes showed (001) and (101) orientations with higher OPP component. Measured effective d33 values of BaTiO3 films deposited on Pt and LSCO/Pt electrodes were 14.3 and 54.0 pm/V, respectively. Local piezoelectric strain loops obtained by OPP and IPP-PFM showed that piezoelectric properties were strongly related to film orientation.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
77.65.-j Piezoelectricity and electromechanical effects
68.37.Ps Atomic force microscopy (AFM)
81.15.Fg Pulsed laser ablation deposition
68.35.B- Structure of clean surfaces (and surface reconstruction)

Priority of domain wall pinning during the fatigue period in bismuth titanate ferroelectric thin films

Wei Li, Aiping Chen, Xiaomei Lu, Jinsong Zhu, and Yening Wang

Appl. Phys. Lett. 86, 192908 (2005); http://dx.doi.org/10.1063/1.1925308 (3 pages) | Cited 7 times

Online Publication Date: 4 May 2005

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The switching current densities of pure Bi4Ti3O12 thin films were measured during a fatigue process. The peak switching current density and switching time decrease with the increase of switching cycles, which indicates a domain wall pinning effect by defects inside thin films. Through the fitting of the switching current density using the modified Kolmogorov-Avrami theory, it is found that the percentage of two-dimensional (2D) domain growth decreases during the fatigue period, which reveals that 2D domain growth has an absolute priority to be pinned compared with one-dimensional domain growth. The mechanism of the increased activation field during the fatigue process is briefly discussed based on the domain wall pinning effect. These results are of great importance in the switching kinetics and fatigue mechanisms in ferroelectric films.
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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.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

Memory effect in [001] poled 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 single crystals

Mingrong Shen and Wenwu Cao

Appl. Phys. Lett. 86, 192909 (2005); http://dx.doi.org/10.1063/1.1922575 (3 pages) | Cited 5 times

Online Publication Date: 4 May 2005

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We have conducted dielectric and pyroelectric measurements in [001] poled rhombohedral phase 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 single crystals from room temperature to 250 °C. An interesting poling history dependence has been revealed from the experimental results. Compared with room-temperature poled samples, crystals poled via the field-cooling method have a much lower rhombohedral-to-tetragonal phase transition temperature and have enhanced spontaneous polarization while heating up to the tetragonal phase. Such phenomena may be explained by the memory effect of dipolar defect alignment in the sample poled by the field-cooling method.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.70.+a Pyroelectric and electrocaloric effects
64.70.K- Solid-solid transitions

Misfit dislocations in nanoscale ferroelectric heterostructures

V. Nagarajan, C. L. Jia, H. Kohlstedt, R. Waser, I. B. Misirlioglu, S. P. Alpay, and R. Ramesh

Appl. Phys. Lett. 86, 192910 (2005); http://dx.doi.org/10.1063/1.1922579 (3 pages) | Cited 52 times

Online Publication Date: 6 May 2005

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We present a quantitative study of the thickness dependence of the polarization and piezoelectric properties in epitaxial (001) PbZr0.52Ti0.48O3 films grown on (001) SrRuO3-buffered (001) SrTiO3 substrates. High-resolution transmission electron microscopy reveals that even the thinnest films ( ∼ 8 nm) are fully relaxed with a dislocation density close to 1012 cm−2 and a spacing of approximately 12 nm. Quantitative piezoelectric and ferroelectric measurements show a drastic degradation in the out-of-plane piezoelectric constant (d33) and the switched polarization (ΔP) as a function of decreasing thickness. In contrast, lattice-matched ultrathin PbZr0.2Ti0.8O3 films that have a very low dislocation density show superior ferroelectric properties. Supporting theoretical calculations show that the variations in the strain field around the core of the dislocation leads to highly localized polarization gradients and hence strong depolarizing fields, which result in suppression of ferroelectricity in the vicinity of a dislocation.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.55.-g Dielectric thin films
77.65.Bn Piezoelectric and electrostrictive constants
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Fabrication of wide-band-gap MgxZn1−xO quasi-ternary alloys by molecular-beam epitaxy

Hiroshi Tanaka, Shigeo Fujita, and Shizuo Fujita

Appl. Phys. Lett. 86, 192911 (2005); http://dx.doi.org/10.1063/1.1923762 (3 pages) | Cited 28 times

Online Publication Date: 6 May 2005

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A series of wurtzite MgZnO quasi-ternary alloys, which consist of wurtzite MgO/ZnO superlattices, were grown by molecular-beam epitaxy on sapphire substrates. By changing the thicknesses of ZnO layers and/or of MgO layers of the superlattice, the band-gap energy was artificially tuned from 3.30 to 4.65 eV. The highest band gap, consequently realized by the quasi-ternary alloy, was larger than that of the single MgZnO layer, we have ever reported, keeping the wurtzite structure. The band gap of quasi-ternary alloys was well analyzed by the Kronig–Penny model supposing the effective masses of wurtzite MgO as 0.30m0 and (1–2)m0 for electrons and holes, respectively.
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81.05.Hd Other semiconductors
81.05.Dz II-VI semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
73.21.Cd Superlattices
71.20.Nr Semiconductor compounds
68.65.Cd Superlattices
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
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