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29 Jan 2007

Volume 90, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 90, 052503 (2007); http://dx.doi.org/10.1063/1.2436715 (3 pages)

Biqin Huang, Igor Altfeder, and Ian Appelbaum
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Process-dependent defects in Si/HfO2/Mo gate oxide heterostructures

S. Walsh, L. Fang, J. K. Schaeffer, E. Weisbrod, and L. J. Brillson

Appl. Phys. Lett. 90, 052901 (2007); http://dx.doi.org/10.1063/1.2435585 (3 pages) | Cited 15 times

Online Publication Date: 29 January 2007

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The authors have used low energy electron-excited nanoscale-depth-resolved spectroscopy to probe the bulk and interface defect states of ultrathin Mo/HfO2/Si with conventional process sequences. Multiple deep level emissions are evident below the 5.9 eV HfO2 near band edge, including three associated with HfO2 oxygen vacancies in different charge states predicted theoretically. Defects resembling SiO2-related nonbonding oxygen hole centers and positively charged O vacancies increase with depth within the 4 nm HfO2 film suggesting Hf silicate formation at the HfO2/Si interface. These states vary dramatically between process sequences and can be understood in terms of known reactions at HfO2–Si interfaces.
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71.55.-i Impurity and defect levels
73.20.At Surface states, band structure, electron density of states
61.72.J- Point defects and defect clusters

Giant strain in PbZr0.2Ti0.8O3 nanowires

Z. H. Zhou, X. S. Gao, John Wang, K. Fujihara, S. Ramakrishna, and V. Nagarajan

Appl. Phys. Lett. 90, 052902 (2007); http://dx.doi.org/10.1063/1.2435941 (3 pages) | Cited 30 times

Online Publication Date: 29 January 2007

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The authors report a giant reversible piezoelectric strain of ∼ 4.2% achieved with single-crystalline PbZr0.2Ti0.8O3 nanowires of ∼ 70 nm in diameter, which is nearly 300% greater than the nominal values reported for ceramic perovskite single crystals. The giant strain arises from the reversible switching of ferroelastic domains. In the nanowires, there is a competition between surface tension, which forces in-plane polarization, and applied electric field, which stabilizes out-of-plane polarization, through the entire voltage cycle, the result of which is the reversible movement of ferroelastic domains.
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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
77.80.Dj Domain structure; hysteresis
61.46.-w Structure of nanoscale materials
77.22.Ej Polarization and depolarization
81.40.Jj Elasticity and anelasticity, stress-strain relations

Electrical properties of Bi2Mg2/3Nb4/3O7 (BMN) pyrochlore thin films deposited on Pt and Cu metal at low temperatures for embedded capacitor applications

Cheng-Ji Xian, Jong-Hyun Park, Kyung-Chan Ahn, Soon-Gil Yoon, Jeong-Won Lee, Woon-Chun Kim, Sung-Taek Lim, Seung-Hyun Sohn, Jin-Seok Moon, Hyung-Mi Jung, Seung-Eun Lee, In-Hyung Lee, Yul-Kyo Chung, Min-Ku Jeon, and Seong-Ihl Woo

Appl. Phys. Lett. 90, 052903 (2007); http://dx.doi.org/10.1063/1.2435336 (3 pages) | Cited 11 times

Online Publication Date: 29 January 2007

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200-nm-thick BMN films were deposited on Pt/TiO2/SiO2/Si and Cu/Ti/SiO2/Si substrates at various temperatures by pulsed laser deposition. The dielectric constant and capacitance density of the films deposited on Pt and Cu electrodes show similar tendency with increasing deposition temperature. On the other hand, dielectric loss of the films deposited on Cu electrode varies from 0.7% to 1.3%, while dielectric loss of films on Pt constantly shows 0.2% even though the deposition temperature increases. The low value of breakdown strength in BMN films on Pt compared to films deposited on Cu electrode was attributed to the increase of surface roughness by the formation of secondary phases at interface between BMN films and Pt electrodes.
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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)
77.22.Gm Dielectric loss and relaxation
77.22.Jp Dielectric breakdown and space-charge effects
68.55.-a Thin film structure and morphology

Cylinder-shaped ultrasonic motors 4.8 mm in diameter using electroactive piezoelectric materials

Laihui Luo, Hua Zhu, Chunsheng Zhao, Haixia Wang, and Haosu Luo

Appl. Phys. Lett. 90, 052904 (2007); http://dx.doi.org/10.1063/1.2437093 (3 pages) | Cited 25 times

Online Publication Date: 30 January 2007

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Two cylinder-shaped ultrasonic motors 4.8 mm in diameter were developed. This kind of motor was driven by four pieces of piezoelectric materials, which were used to excite the two first-bending vibrations. Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMNT) crystal and Pb(Zr,Ti)O3 (PZT) ceramic piezoelectric materials were used as drive elements. The motor based on PMNT crystals could operate at a voltage of 25 Vp-p (peak to peak). When driven by a 100 Vp-p voltage, the motor could run at frequency ranging from 26 to 68 kHz and the revolution speed reached 450 rpm. Its maximum output torque was 0.6 mN m. The motor based on the PZT ceramic did not exhibit high performance as the PMNT crystal motor. The piezoelectric materials affect the performance of the motors greatly.
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84.50.+d Electric motors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Electric field gating with ionic liquids

Rajiv Misra, Mitchell McCarthy, and Arthur F. Hebard

Appl. Phys. Lett. 90, 052905 (2007); http://dx.doi.org/10.1063/1.2437663 (3 pages) | Cited 36 times

Online Publication Date: 30 January 2007

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The authors show that ionic liquids are well suited to specialized electric field gating applications in which large surface charge densities can be induced on the surfaces of low-carrier density thin-film metals. Using either coplanar or overlay gate configurations, they demonstrate field-induced resistance changes on the order of a factor of 104 for thin conducting InOx films. The areal capacitances and field effect mobilities noticeably exceed those that can be achieved using AlOx dielectrics. In addition, the charge state can be frozen in by reducing the temperature, thus providing an opportunity for electric field tuning of metal-insulator transitions in a variety of thin-film systems.
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66.10.Ed Ionic conduction
68.15.+e Liquid thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
71.30.+h Metal-insulator transitions and other electronic transitions
73.50.Dn Low-field transport and mobility; piezoresistance

Soft chemical deposition of BiFeO3 multiferroic thin films

A. H. M. Gonzalez, A. Z. Simões, L. S. Cavalcante, E. Longo, J. A. Varela, and C. S. Riccardi

Appl. Phys. Lett. 90, 052906 (2007); http://dx.doi.org/10.1063/1.2433027 (3 pages) | Cited 22 times

Online Publication Date: 31 January 2007

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BiFeO3 thin films free of secondary phases were obtained by the soft chemical solution on Pt(111)/Ti/SiO2/Si substrates after annealing at 500 °C for 2 h. The film grown in the (100) direction presented a remanent polarization Pr of 31 μC/cm2 at room temperature. Electrical measurements using both quasistatic hysteresis and pulsed polarization confirm the existence of ferroelectricity with a switched polarization of 60–70 μC/cm2, ΔP = (P*−P̂). Low leakage conduction and an out-of-plane piezoelectric (d3) coefficient of 40 pm/V were obtained by the improvement of preparation technology.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
68.55.A- Nucleation and growth
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
81.40.Gh Other heat and thermomechanical treatments

Monodomain to polydomain transition in ferroelectric PbTiO3 thin films with La0.67Sr0.33MnO3 electrodes

Céline Lichtensteiger, Matthew Dawber, Nicolas Stucki, Jean-Marc Triscone, Jason Hoffman, Jeng-Bang Yau, Charles H. Ahn, Laurent Despont, and Philipp Aebi

Appl. Phys. Lett. 90, 052907 (2007); http://dx.doi.org/10.1063/1.2433757 (3 pages) | Cited 15 times

Online Publication Date: 31 January 2007

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Finite size effects in ferroelectric thin films have been probed in a series of epitaxial perovskite c-axis oriented PbTiO3 films grown on thin La0.67Sr0.33MnO3 epitaxial electrodes. The film thickness ranges from 480 down to 28 Å (seven unit cells). The evolution of the film tetragonality c/a, studied using high resolution x-ray diffraction measurements, shows first a decrease of c/a with decreasing film thickness followed by a recovery of c/a at small thicknesses. This recovery is accompanied by a change from a monodomain to a polydomain configuration of the polarization, as directly demonstrated by piezoresponse atomic force microscopy measurements.
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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.B- Phase transitions and Curie point
77.22.Ej Polarization and depolarization
68.55.-a Thin film structure and morphology

Observation of photoassisted polarization switching in BiFeO3 thin films probed by terahertz radiation

Kouhei Takahashi and Masayoshi Tonouchi

Appl. Phys. Lett. 90, 052908 (2007); http://dx.doi.org/10.1063/1.2437076 (3 pages) | Cited 5 times

Online Publication Date: 31 January 2007

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The authors have examined the effect of photoexcitation in a multiferroic BiFeO3 thin film using terahertz radiation as the probe. The illumination of femtosecond laser pulses with a center wavelength of 400 nm gave rise to a significant improvement in the polarization switching process by the application of bias electric field. This effect is attributed to the depinning of domain walls induced by carrier excitation as reported in ordinary ferroelectrics. The authors revealed that a significantly weak laser power in the order of submilliwatt is sufficient to invoke this effect.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
77.22.Ej Polarization and depolarization
78.47.-p Spectroscopy of solid state dynamics

Phase-field model for epitaxial ferroelectric and magnetic nanocomposite thin films

J. X. Zhang, Y. L. Li, D. G. Schlom, L. Q. Chen, F. Zavaliche, R. Ramesh, and Q. X. Jia

Appl. Phys. Lett. 90, 052909 (2007); http://dx.doi.org/10.1063/1.2431574 (3 pages) | Cited 39 times

Online Publication Date: 31 January 2007

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A phase-field model was developed for studying the magnetoelectric coupling effect in epitaxial ferroelectric and magnetic nanocomposite thin films. The model can simultaneously take into account the ferroelectric and magnetic domain structures, the electrostrictive and magnetostrictive effects, substrate constraint, as well as the long-range interactions such as magnetic, electric, and elastic interactions. As an example, the magnetic-field-induced electric polarization in BaTiO3–CoFe2O4 nanocomposite film was analyzed. The effects of the film thickness, morphology of the nanocomposite, and substrate constraint on the degree of magnetoelectric coupling were discussed.
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77.55.-g Dielectric thin films
75.80.+q Magnetomechanical effects, magnetostriction
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.55.-a Thin film structure and morphology
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization

Heat capacity in magnetic and electric fields near the ferroelectric transition in triglycine sulfate

J. C. Lashley, M. F. Hundley, B. Mihaila, J. L. Smith, C. P. Opeil, T. R. Finlayson, R. A. Fisher, and N. Hur

Appl. Phys. Lett. 90, 052910 (2007); http://dx.doi.org/10.1063/1.2435333 (3 pages) | Cited 4 times

Online Publication Date: 1 February 2007

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Specific-heat measurements are reported near the Curie temperature (TC = 320 K) on triglycine sulfate. Measurements were made on crystals whose surfaces were either nongrounded or short circuited, and were carried out in magnetic fields up to 9 T and electric fields up to 220 V/cm. In nongrounded crystals the authors find that the shape of the specific-heat anomaly near TC is thermally broadened. However, the anomaly changes to the characteristic sharp λ shape expected for a continuous transition with the application of either a magnetic field or an electric field. In crystals whose surfaces were short circuited with gold, the characteristic λ shape appeared in the absence of an external field. This effect enabled a determination of the critical exponents above and below TC, and may be understood on the basis that the surface charge originating from the pyroelectric coefficient, dP/dT, behaves as if shorted by external magnetic or electric fields.
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77.84.Jd Polymers; organic compounds
77.80.B- Phase transitions and Curie point
65.40.Ba Heat capacity
77.70.+a Pyroelectric and electrocaloric effects

Effect of (Li,Ce) doping in Aurivillius phase material Na0.25K0.25Bi2.5Nb2O9

Zhi-Gang Gai, Jin-Feng Wang, and Chun-Ming Wang

Appl. Phys. Lett. 90, 052911 (2007); http://dx.doi.org/10.1063/1.2450669 (3 pages) | Cited 11 times

Online Publication Date: 1 February 2007

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The effect of (Li,Ce) substitution for A site on the properties of Na0.25K0.25Bi2.5Nb2O9-based ceramics was investigated. The piezoelectric activity of Na0.25K0.25Bi2.5Nb2O9-based ceramics is significantly improved by the modification of lithium and cerium. The Curie temperature (TC) gradually increases from 668 to 684 °C with increasing the (Li,Ce) modification. The piezoelectric coefficient d33 of the [(Na0.5K0.5)Bi]0.44(LiCe)0.03[ ]0.03Bi2Nb2O9 ceramic was found to be 28 pC/N, the highest value among the Na0.25K0.25Bi2.5Nb2O9-based ceramics and also almost 50% higher than the reported d33 values of other bismuth layer-structured ferroelectric systems ( ∼ 5–19 pC/N). The planar coupling factors kp and kt were found to be 8.0% and 23.0%, together with the high TC ( ∼ 670 °C) and stable piezoelectric properties, demonstrating that the (Li,Ce) modified Na0.25K0.25Bi2.5Nb2O9-based material a promising candidate for high temperature applications.
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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
77.80.B- Phase transitions and Curie point
61.72.up Other materials

Low dielectric loss BaNd2Ti5O14 thick films prepared by an electrophoretic deposition technique

Zhi Fu, Aiying Wu, P. M. Vilarinho, A. I. Kingon, and R. Wördenweber

Appl. Phys. Lett. 90, 052912 (2007); http://dx.doi.org/10.1063/1.2435334 (3 pages) | Cited 9 times

Online Publication Date: 2 February 2007

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BaNd2Ti5O14 (BNT) films 12–52 μm thick were fabricated on platinum metallic foils by electrophoretic deposition (EPD). 52-μm-thick BNT film exhibits a dielectric constant and a loss tangent of 107 and 0.0006 (Q of 1600) at 1 MHz, respectively. Variation in permittivity is less than 0.02% at a bias voltage ±8 kV/cm. Change of film permittivity with temperature (30–120 °C) is below +58.5 ppm/°C, pointing to a good thermal stability. Preliminary microwave measurements indicate that the losses are not significantly increased up to the gigahertz regime. EPD derived BNT thick films on metallic foils are attractive candidates for microwave communication devices.
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77.22.Gm Dielectric loss and relaxation
81.15.Pq Electrodeposition, electroplating
77.22.Ch Permittivity (dielectric function)

Atomic transport and integrity of Al2O3(2.0 nm)/HfO2(2.5 nm) gate stacks on Si

L. Miotti, R. P. Pezzi, M. Copel, C. Krug, and I. J. R. Baumvol

Appl. Phys. Lett. 90, 052913 (2007); http://dx.doi.org/10.1063/1.2437708 (3 pages) | Cited 5 times

Online Publication Date: 2 February 2007

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The integrity of Al2O3(2.0 nm)/HfO2(2.5 nm)/SiO2(<1 nm)/Si(001) stacks after rapid thermal annealing at temperature up to 1025 °C was investigated. The structures were prepared by atomic layer deposition and atomic transport was accessed by profiling all elements in the system with subnanometric depth resolution, using medium and low energy ion scattering and narrow resonant nuclear reaction profiling. Al migration toward the stack/Si interface, Al loss by desorption from the surface, and Hf transport across the Al2O3 film layer toward the outermost surface were observed. The loss of oxygen from the stack is also noticeable, most probably caused by compound dissociation and desorption of oxygen containing species. The possible detrimental effects on device electrical properties of the observed presence of Hf at the outermost surface of the dielectric stack and of Al at the dielectric/Si interface are discussed.
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77.55.-g Dielectric thin films
61.72.Cc Kinetics of defect formation and annealing
68.43.Mn Adsorption kinetics
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
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