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15 Nov 2004

Volume 85, Issue 20, pp. 4561-4807

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 4768 (2004); http://dx.doi.org/10.1063/1.1818331 (3 pages)

G. Walter, N. Holonyak, M. Feng, and R. Chan
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Microwave characterization of (Pb,La)TiO3 thin films integrated on ZrO2∕SiO2∕Si wafers by sol-gel techniques

Z. T. Song, Y. Wang, H. L. W. Chan, C. L. Choy, and S. L. Feng

Appl. Phys. Lett. 85, 4696 (2004); http://dx.doi.org/10.1063/1.1823038 (3 pages) | Cited 6 times

Online Publication Date: 16 November 2004

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Polycrystalline perovskite lead lanthanum titanate (PLT) thin films were prepared by a sol-gel method on ZrO2∕SiO2∕Si substrates. The structure of the films was studied by x-ray diffraction and scanning electron microscopy, and the microwave dielectric properties characterized on a network analyzer. A strong dependence of the dielectric constant of PLT films and, correspondingly, the resonance frequency of PLT-based interdigital capacitor on the sample preparation conditions were observed. They resulted from the structural transformation of PLT from a layered structure to a uniform film as the annealing temperature was raised from 550 to 700 °C, suggesting a possible way to modify the device performance by controlling the layered structure of the ferroelectric film.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.32.Tt Capacitors
81.40.Gh Other heat and thermomechanical treatments
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Film and interface layer properties of ultraviolet-ozone oxidized hafnia and zirconia gate dielectrics on silicon substrates

David Chi and Paul C. McIntyre

Appl. Phys. Lett. 85, 4699 (2004); http://dx.doi.org/10.1063/1.1814799 (3 pages) | Cited 14 times

Online Publication Date: 16 November 2004

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We report on the use of ultraviolet-ozone (UVO) oxidation of thin film hafnium and zirconium to fabricate high-dielectric constant (high-k) gate oxides with chemically modified silicon dioxide-based interface layers on silicon (100) substrates. Using x-ray photoelectron spectroscopy and high-resolution transmission electron microscopy, the oxidation state and thickness of the interfacial layer are characterized before and after UVO exposure. Reduction of the chemical oxide followed by reoxidation is observed. The reoxidized silicon is found to be substoichiometric. Thickness series fabricated by repeating the UVO process multiple times for the same substrate indicate a constant interface layer thickness. Inverse capacitance density versus physical thickness plots were used to determine that the dielectric constants for the UVO HfO2 and UVO ZrO2 are 17.3 and 24.8, respectively.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
77.22.Ch Permittivity (dielectric function)
81.65.Mq Oxidation
61.66.Bi Elemental solids
61.66.Dk Alloys
78.66.Nk Insulators
78.40.Ha Other nonmetallic inorganics
79.60.Dp Adsorbed layers and thin films
79.60.Jv Interfaces; heterostructures; nanostructures
68.37.Lp Transmission electron microscopy (TEM)

Dielectric properties of epitaxial Ba0.6Sr0.4TiO3 films on SiO2∕Si using biaxially oriented ion-beam-assisted-deposited MgO as templates

B. S. Kang, Jang-Sik Lee, L. Stan, J.-K. Lee, R. F. DePaula, P. N. Arendt, M. Nastasi, and Q. X. Jia

Appl. Phys. Lett. 85, 4702 (2004); http://dx.doi.org/10.1063/1.1812573 (3 pages) | Cited 12 times

Online Publication Date: 16 November 2004

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We have epitaxially deposited Ba0.6Sr0.4TiO3 (BST) thin films on SiO2∕Si substrates using pulsed laser deposition by introducing biaxially oriented ion-beam-assisted-deposited MgO as templates. The structural properties of the BST films were strongly affected by the crystallinity of the templates. The dielectric loss of the BST film was found to decrease as its in-plane texture alignment was improved. As a result, a relatively larger figure of merit K value, defined as tunability∕loss, was obtained for the films with better in-plane crystallinity. The K factor ranged between 7.5 and 3.5 when the in-plane alignment of the MgO templates was varied from 5.0° to 10.5°. This work demonstrates that the crystalline quality of the template layers plays a critical role in monolithic integration of BST with SiO2∕Si for frequency agile devices.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
77.22.Gm Dielectric loss and relaxation
81.15.Fg Pulsed laser ablation deposition

High tunability (Ba,Sr)TiO3 thin films grown on atomic layer deposited TiO2 and Ta2O5 buffer layers

Il-Doo Kim, Harry L. Tuller, Hyun-Suk Kim, and Jin-Seong Park

Appl. Phys. Lett. 85, 4705 (2004); http://dx.doi.org/10.1063/1.1821656 (3 pages) | Cited 37 times

Online Publication Date: 16 November 2004

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In this letter, we report on increased tunability of Ba0.6Sr0.4TiO3 (BST) thin films by use of Ta2O5 and TiO2 films as buffer layers between BST and Si substrates. Ta2O5 and TiO2 buffer layers were grown by atomic layer deposition (ALD) onto Si substrates followed by pulsed laser deposition of Ba0.6Sr0.4TiO3 thin films onto the buffer layers. The randomly oriented BST films deposited on TiO2∕Si substrates exhibited a broader grain size distribution than the (110) textured BST films grown on Ta2O5∕Si substrates. At an applied voltage of 10 V, the BST films grown on Ta2O5∕Si and TiO2∕Si substrates showed much enhanced tunability values of 53.1% and 72.9%, respectively, as compared to the 20.7% value obtained with BST films grown on MgO single crystal substrates. Successful integration of BST low voltage microwave tunable devices onto Si substrates thus appears possible with the aid of ALD grown Ta2O5 or TiO2 buffer layers.
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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
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Fg Pulsed laser ablation deposition
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.35.B- Structure of clean surfaces (and surface reconstruction)

Interface-related thickness dependence of the tunability in BaSrTiO3 thin films

U. Ellerkmann, R. Liedtke, U. Boettger, and R. Waser

Appl. Phys. Lett. 85, 4708 (2004); http://dx.doi.org/10.1063/1.1824173 (3 pages) | Cited 14 times

Online Publication Date: 16 November 2004

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The thickness dependence of the tunability of Ba0.7Sr0.3TiO3 thin films is investigated. The capacitance–voltage curves, revealing the tunability of the films with thickness from 30 to 370 nm, show a strong thickness dependence. This is attributed to a bias-independent interface capacity. The interface suppresses the permittivity of the film with increasing influence for decreasing film thickness, whereas the tunability of the bulk of the film remains constant. Calculations are performed from a thermodynamic model based on the Landau–Ginzburg–Devonshire theory leading to the assumption of the bias-independent interface capacity. The bias dependence of the bulk of the films derived from measurement data are in very good agreement with the theoretically derived values.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.55.-a Thin film structure and morphology
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)

Two-dimensional planar size effects in epitaxial PbTiO3 thin films

Kilho Lee, Keewon Kim, Soon-Ju Kwon, and Sunggi Baik

Appl. Phys. Lett. 85, 4711 (2004); http://dx.doi.org/10.1063/1.1823033 (3 pages) | Cited 15 times

Online Publication Date: 16 November 2004

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In order to test a critical lateral dimension in two-dimensional (2D) planar ferroelectrics, epitaxial PbTiO3 thin films are patterned into discrete islands lithographically with different lateral sizes. As the pattern size decreases, the substrate clamping effect is significantly reduced and thus the misfit strain in the films could be relaxed further. Evolution of 90° domain structures as a function of lateral dimensions was characterized extensively by reciprocal space mapping using synchrotron x ray. As the lateral 2D planar size decreases in the PbTiO3 patterns on MgO(001), some of the a domains turned into c domains due to the relaxed tensile strain. In the PbTiO3 patterns on Pt(001)∕MgO(001), on the other hand, the formation of 90° domains is enhanced by the reduction in compressive misfit strain. Equilibrium domain structures in the PbTiO3 thin film islands are also analyzed by the finite element simulation and found to be consistent with the experimental observation.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
68.60.Bs Mechanical and acoustical properties
77.80.-e Ferroelectricity and antiferroelectricity
77.80.Dj Domain structure; hysteresis
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Raman study of Bi site-occupancy effect on orientation and polarization in Bi4Ti3O12 thin films

C. Y. Yau, R. Palan, K. Tran, and R. C. Buchanan

Appl. Phys. Lett. 85, 4714 (2004); http://dx.doi.org/10.1063/1.1819507 (3 pages) | Cited 10 times

Online Publication Date: 16 November 2004

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Our Raman study of 0–6 mol % Bi excess Bi4Ti3O12 (BIT) films implies that symmetry breaking effect occurs in 0 mol % Bi excess film, which is restored to BIT symmetry in 2–6 mol % Bi excess films. The “rigid layer” mode at 59.22 cm−1 implies a higher stability of Bi in the Bi2O2 layer than the perovskite layer and that Bi has high preference to incorporate into the Bi2O2 layer. Increasing Bi incorporation in the A site enhances the Jahn–Teller distortion of TiO6 octahedra and the c orientation. This implies that doping by an ion without an outer orbital like La can decrease the TiO6 distortion, change the orientation, and tilt the polarization vector.
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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
68.55.-a Thin film structure and morphology
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
77.80.B- Phase transitions and Curie point
78.30.Hv Other nonmetallic inorganics
78.66.Nk Insulators

Correlation among oxygen vacancies in bismuth titanate ferroelectric ceramics

Wei Li, Kai Chen, Yangyang Yao, Jinsong Zhu, and Yening Wang

Appl. Phys. Lett. 85, 4717 (2004); http://dx.doi.org/10.1063/1.1823583 (3 pages) | Cited 20 times

Online Publication Date: 16 November 2004

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Pure Bi4Ti3O12 ceramics were prepared using the conventional solid-state reaction method and their dielectric properties were investigated. A dielectric loss peak with the relaxation-type characteristic was observed at about 370 K at 100 Hz frequency. This peak was confirmed to be associated with the migration of oxygen vacancies inside ceramics. The Cole–Cole fitting to this peak reveals a strong correlation among oxygen vacancies and this strong correlation is considered to commonly exist among oxygen vacancies in ferroelectrics. Therefore, the migration of oxygen vacancies in ferroelectric materials would demonstrate a collective behavior instead of an individual one due to this strong correlation. Furthermore, this correlation is in proportion to the concentration and in inverse proportion to the activation energy of oxygen vacancies. These results could be helpful to the understanding of the fatigue mechanisms in ferroelectric materials.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
61.72.J- Point defects and defect clusters
77.22.Gm Dielectric loss and relaxation

Dielectric nonlinearity in relaxor and ferroelectric thin films of chemically ordered PbSc0.5Nb0.5O3

M. Tyunina and J. Levoska

Appl. Phys. Lett. 85, 4720 (2004); http://dx.doi.org/10.1063/1.1823591 (3 pages) | Cited 7 times

Online Publication Date: 16 November 2004

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Dynamic nonlinear dielectric response of pulsed laser deposited epitaxial thin films of chemically ordered perovskite PbSc0.5Nb0.5O3 was experimentally studied and analyzed. Films deposited at 925 K exhibited relaxor-like behavior indicated by frequency dispersion of temperature of dielectric maxima Tm, maximum in third-order dynamic nonlinear permittivity ε3(T), and increase of scaled dynamic third-order nonlinear permittivity asc below Tm. With decreasing deposition temperature, relaxor behavior was suppressed. Results are discussed in terms of film microstructure and random field strength.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)

Effects of denuded zone of Si(111) surface on current conduction and charge trapping of HfOxNy gate dielectric in metal-oxide-semiconductor devices

Chin-Lung Cheng, Kuei-Shu Chang-Liao, Ching-Hung Huang, and Tien-Ko Wang

Appl. Phys. Lett. 85, 4723 (2004); http://dx.doi.org/10.1063/1.1819994 (3 pages) | Cited 5 times

Online Publication Date: 16 November 2004

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This work investigated the effects of interstitial oxygen [Oi] defects at the Si(111) surface on current conduction and charge trapping of metal-oxide-simiconductor devices with HfOxNy gate dielectric. Smaller gate leakage current, stress-induced leakage current (SILC) and defect generation rate, attributable to the decrease of [Oi] defect concentration at the HfOxNy∕Si interface, were observed for devices with denuded zone. The current-conduction mechanism of the HfOxNy films at the low- and high-electrical field was dominated by the Schottky and Frenkel–Poole emissions, respectively. The trapped charges in HfOxNy dielectric were positive. The mechanism related to the SILC at low-electrical field can be explained using the interface trap-assisted tunneling.
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84.32.Tt Capacitors
77.55.-g Dielectric thin films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Ng Insulators
61.72.J- Point defects and defect clusters
78.30.Hv Other nonmetallic inorganics
72.20.Ht High-field and nonlinear effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.30.+y Surface double layers, Schottky barriers, and work functions
78.66.Nk Insulators

Low voltage lead titanate/Si one-transistor ferroelectric memory with good device characteristics

C. L. Sun, S. Y. Chen, C. C. Liao, and Albert Chin

Appl. Phys. Lett. 85, 4726 (2004); http://dx.doi.org/10.1063/1.1814440 (3 pages) | Cited 6 times

Online Publication Date: 16 November 2004

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We have developed one-transistor ferroelectric memory using lead titanate (PTO) as a gate dielectric directly formed on Si without any buffer layer. The PTO/Si metal–oxide–semiconductor field-effect transistor memory has shown a large threshold voltage shift of 1.6 V at only ±4 V program/erase voltages. The corresponding good interface was achieved by lowering the anneal temperature to 450 °C. Besides the sharp capacitance change of 0.17 μF∕V cm2, it was also evidenced by the high mobility of 169 cm2∕V s close to high-κ HfO2. In addition, long retention >1000 s and endurance >1011 stress cycles in the device suggested good memory characteristics.
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85.50.Gk Non-volatile ferroelectric memories
85.30.Tv Field effect devices
84.32.Tt Capacitors
61.72.Cc Kinetics of defect formation and annealing
72.20.Fr Low-field transport and mobility; piezoresistance
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