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8 Oct 2007

Volume 91, Issue 15, Articles (15xxxx)

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Appl. Phys. Lett. 91, 153101 (2007); http://dx.doi.org/10.1063/1.2793688 (3 pages)

B. J. Lee, K. Park, and Z. M. Zhang
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Chemical composition changes across the interface of amorphous LaScO3 on Si (001)

F. Liu and G. Duscher

Appl. Phys. Lett. 91, 152901 (2007); http://dx.doi.org/10.1063/1.2798246 (3 pages)

Online Publication Date: 8 October 2007

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An amorphous, high-dielectric-constant LaScO3 film was deposited directly on Si (001) by molecular-beam deposition at ∼ 100 °C. Various transmission electron microscopy techniques were applied to study the interface at atomic resolution. We observed an ∼ 3.5-nm-thick interfacial layer that was not previously detected with other techniques. The interfacial layer contained defects and its density changes gradually. The interface was not only structurally sharp but also chemically sharp within the detection limit of the experimental methods. The chemical composition of the bulk oxide film was stoichiometric, but the interfacial layer was oxygen poor.
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68.35.Dv Composition, segregation; defects and impurities
68.35.Ct Interface structure and roughness
61.43.Er Other amorphous solids
61.66.Bi Elemental solids
61.66.Dk Alloys
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Enhanced quality factors in aperiodic reflector resonators

Jonathan Breeze, Jerzy Krupka, and Neil McN Alford

Appl. Phys. Lett. 91, 152902 (2007); http://dx.doi.org/10.1063/1.2798055 (3 pages) | Cited 3 times

Online Publication Date: 9 October 2007

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Cavity resonators that employ the high reflectivity of periodic arrays of dielectric layers exhibit enhanced quality factors compared with dielectric resonators. Their quality factor is limited by the exponential decay of the electric field penetrating the structure. We show that an aperiodic reflector array with dielectric layers thinner than a quarter-wave near the defect site and asymptotically approaching quarter-wave thickness distant from the site can exhibit very high quality factors. A spherical aperiodic reflector resonator consisting of nested alumina shells is simulated and shown to exhibit quality factors greater than 107 at 10 GHz and room temperature.
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84.40.Az Waveguides, transmission lines, striplines
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Dynamic magnetoelectric coupling in “electronic ferroelectric” LuFe2O4

Ji Yong Park, Jung Hwan Park, Young Kyu Jeong, and Hyun M. Jang

Appl. Phys. Lett. 91, 152903 (2007); http://dx.doi.org/10.1063/1.2798597 (3 pages) | Cited 26 times

Online Publication Date: 9 October 2007

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Magnetoelectric (ME) coupling characteristics of LuFe2O4 were examined by monitoring the electrical voltage induced by an oscillating magnetic field under a static bias field (H0). Interestingly, the room-temperature dynamic ME output exhibited a constant plateau behavior up to a certain static-field strength but showed a sudden drop above this critical value. In addition, two evidences of the intrinsic ME coupling were obtained by monitoring the pyroelectric response near the ferrimagnetic ordering temperature ( ∼ 250 K) and by examining the temperature-dependent magnetization near the ferroelectric transition point ( ∼ 345 K) between the two-dimensional charge-density-wave (CDW) state and the three-dimensional CDW state.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Gg Ferrimagnetics
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
77.80.B- Phase transitions and Curie point
77.70.+a Pyroelectric and electrocaloric effects
71.45.Lr Charge-density-wave systems

Effect of kerf filler on the electromechanical coupling coefficient of an ultrasonic transducer array element

Jungsoon Kim, Moojoon Kim, and Wenwu Cao

Appl. Phys. Lett. 91, 152904 (2007); http://dx.doi.org/10.1063/1.2795333 (3 pages)

Online Publication Date: 10 October 2007

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Electromechanical coupling coefficient directly reflects the electromechanical energy conversion capability of a piezoelectric device. We show theoretically that the kerf filler in the ultrasonic array transducer can degrade this coupling coefficient. A closed form expression has been derived that can quantitatively describe the electromechanical coupling coefficient of an ultrasonic transducer array element with arbitrary aspect ratio and having polymer kerf filler in between transducer elements.
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43.38.Hz Transducer arrays, acoustic interaction effects in arrays
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Improved electrical properties of metal-oxide-semiconductor capacitor with HfTiON gate dielectric by using HfSiON interlayer

J. P. Xu, F. Ji, C. X. Li, P. T. Lai, J. G. Guan, and Y. R. Liu

Appl. Phys. Lett. 91, 152905 (2007); http://dx.doi.org/10.1063/1.2798248 (3 pages) | Cited 4 times

Online Publication Date: 10 October 2007

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Metal-oxide-semiconductor (MOS) capacitor with HfTiON/HfSiON stack structure as high-k gate dielectric is fabricated, and its electrical properties are compared with those of a similar device with HfTiON only as gate dielectric. Experimental results show that the device with HfTiON/HfSiON gate dielectric exhibits better interface properties, lower gate leakage current, and enhanced high-field reliability. All these improvements should be attributed to the fact that the HfSiON buffer layer effectively blocks the diffusion of Ti atoms to the Si substrate, thus resulting in a SiO2/Si-like HfSiON/Si interface.
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84.32.Tt Capacitors

Thermal annealing effect on the interface structure of high-κ LaScO3 on silicon

F. Liu and G. Duscher

Appl. Phys. Lett. 91, 152906 (2007); http://dx.doi.org/10.1063/1.2799177 (3 pages) | Cited 1 time

Online Publication Date: 10 October 2007

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The thermal stability of LaScO3 on Si was examined by various transmission electron microscopy techniques. The film remained amorphous up to 700 °C and became polycrystalline at 800 °C. All samples showed an interfacial layer about 3.5 nm thick, except for the 1000 °C-annealed sample, which had a thicker interfacial layer containing a thin silicate layer close to the interface with the substrate. Although the chemical composition of the bulk film was stoichiometric, the interfacial layer was oxygen-rich after postannealing. The interfacial layer remained amorphous up to 1000 °C, indicating that this interfacial layer itself may be used as a gate dielectric.
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68.35.Ct Interface structure and roughness
77.55.-g Dielectric thin films
61.66.Bi Elemental solids
61.66.Dk Alloys

Structurally frustrated polar nanoregions in BaTiO3-based relaxor ferroelectric systems

Y. Liu, R. L. Withers, B. Nguyen, and K. Elliott

Appl. Phys. Lett. 91, 152907 (2007); http://dx.doi.org/10.1063/1.2790481 (3 pages) | Cited 9 times

Online Publication Date: 11 October 2007

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This letter presents direct electron diffraction evidence that structurally frustrated one-dimensional polar nanoregions arising from anticorrelated displacements of Ti and nearest neighboring O ions are responsible for the relaxation behavior observed in doped BaTiO3 relaxor ferroelectrics, rather than chemical short range ordering. The role of the dopant ions is not to directly induce polar nanoregions but rather to set up random local strain fields preventing homogeneous strain distortion, thereby suppressing transverse correlation from one ⟨001⟩ chain dipole to the next and hence the development of long range ferroelectric order.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Gm Dielectric loss and relaxation
77.22.Ch Permittivity (dielectric function)
77.80.B- Phase transitions and Curie point

5-nm-thick TaSiC amorphous films stable up to 750 °C as a diffusion barrier for copper metallization

Ting-Yi Lin, Huai-Yu Cheng, Tsung-Shune Chin, Chin-Fu Chiu, and Jau-Shiung Fang

Appl. Phys. Lett. 91, 152908 (2007); http://dx.doi.org/10.1063/1.2799245 (3 pages) | Cited 15 times

Online Publication Date: 12 October 2007

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Ultrathin TaSiC amorphous films prepared by magnetron cosputtering using TaSi2 and C targets on Si(100), in a sandwiched scheme Si(100)/TaSiC(5 nm)/Cu, were evaluated for barrier performance in copper metallization. Optimizing carbon content maximizes thermal stability of the films as depicted by sheet-resistance, x-ray diffraction, and transmission electron microscopy examination. The stability temperatures of 700 °C (24 at. % C) and 750 °C (34 at. % C) have been systematically verified and discussed. Since Ta, Si, and C are compatible with integrated circuit (IC) processing, the TaSiC films are readily applicable for sub-65-nm IC production.
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68.55.-a Thin film structure and morphology
73.61.-r Electrical properties of specific thin films
66.30.-h Diffusion in solids

Thickness dependency of 180° stripe domains in ferroelectric ultrathin films: A first-principles-based study

Bo-Kuai Lai, Inna Ponomareva, Igor Kornev, L. Bellaiche, and Greg Salamo

Appl. Phys. Lett. 91, 152909 (2007); http://dx.doi.org/10.1063/1.2799252 (3 pages) | Cited 12 times

Online Publication Date: 12 October 2007

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A first-principles-based scheme is used to investigate the thickness dependency of domain width of 180° stripe domains in Pb(Zr,Ti)O3 ultrathin films. Our study shows that (1) more metastable states with energy closer to the 180° stripe domain ground state occur in thicker films, (2) the Kittel law is valid for 180° stripe domains when the film thickness is above 1.6 nm, and (3) below 1.2 nm, the Kittel law cannot be applied anymore due to the disappearance of domains. The thickness dependency of the domain morphology is also discussed.
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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
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