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23 Oct 2000

Volume 77, Issue 17, pp. 2629-2769

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Structural distortion and ferroelectric properties of SrBi2(Ta1−xNbx)2O9

Y. Shimakawa, Y. Kubo, Y. Tauchi, T. Kamiyama, H. Asano, and F. Izumi

Appl. Phys. Lett. 77, 2749 (2000); http://dx.doi.org/10.1063/1.1319509 (3 pages) | Cited 49 times

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Ferroelectric materials of the SrBi2(Ta1−xNbx)2O9 solid-solution system were synthesized, and their structural and ferroelectric properties were investigated. Atomic displacements of the ions in the (Ta,Nb)O6 octahedron significantly increase as x increases, which leads to more structural distortion of the perovskite-type unit. The Bi2O2 layer, in contrast, is less distorted in SrBi2Nb2O9 than in SrBi2Ta2O9. The contribution of the perovskite-type unit to total ferroelectric polarization is greater in the SrBi2Nb2O9 sample, while that of the Bi2O2 layer is less; consequently, the total calculated polarization slightly increases. The ferroelectric Curie temperature also increases from 300 (SrBi2Ta2O9) to 440 °C(SrBi2Nb2O9). Three short (Ta,Nb)–O bonds in the (Ta,Nb)O6 octahedron, whose lengths are less than 2 Å, have a covalent character, and the substitution of Nb for Ta makes the bonds more covalent. The strong covalent interaction of the (Ta,Nb)–O bonds increases the structural distortion, resulting in the higher ferroelectric Curie temperature and the larger contribution of the perovskite-type unit to the total spontaneous ferroelectric polarization. © 2000 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.B- Phase transitions and Curie point
61.66.Fn Inorganic compounds
77.22.Ej Polarization and depolarization
61.50.Lt Crystal binding; cohesive energy

Ultrathin silicon nitride gate dielectrics prepared by catalytic chemical vapor deposition at low temperatures

Hidekazu Sato, Akira Izumi, and Hideki Matsumura

Appl. Phys. Lett. 77, 2752 (2000); http://dx.doi.org/10.1063/1.1319513 (3 pages) | Cited 7 times

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The feasibility of using ultrathin silicon nitride (SiNx) films, prepared by catalytic chemical vapor deposition (Cat-CVD) method, as an ultrathin gate dielectric is reported. The effects of postdeposition treatments carried out using hydrogen (H2)-decomposed species or NH3-decomposed species formed by catalytic cracking of H2 and NH3 are also studied. A small hysteresis loop is seen in the C–V curve of as-deposited Cat-CVD SiNx films. The leakage current in the case of these films with equivalent oxide thickness (EOT) of 3 nm is slightly larger than that in the conventional thermal SiO2 films of similar EOT. However, it is found that the properties of Cat-CVD SiNx films are markedly improved by the postdeposition H2 or NH3 treatments, that is, the hysteresis loop disappears and the leakage current decreases by three orders of magnitude. © 2000 American Institute of Physics.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Ng Insulators
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
85.30.Tv Field effect devices

Hysteresis loops of ferroelectric bilayers and superlattices

Khian-Hooi Chew, Lye-Hock Ong, Junaidah Osman, and D. R. Tilley

Appl. Phys. Lett. 77, 2755 (2000); http://dx.doi.org/10.1063/1.1320040 (3 pages) | Cited 32 times

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A ferroelectric superlattice with an antiferroelectric interfacial coupling is considered; the same model describes a bilayer with antiferroelectric coupling. By mapping minimum points in the Landau free energy expression and plotting them against the applied electric field, a triple hysteresis loop pattern is obtained. The loop patterns vary between typically ferroelectric and typically antiferroelectric depending on the layer thicknesses and the magnitude of the interfacial-coupling constant. This work suggests the possibility of designing multilayer elements for computer memories with four or more different storage states. © 2000 American Institute of Physics.
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77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization

Tandem injection of charge carriers across a metal-dielectric interface

V. I. Arkhipov and H. Bässler

Appl. Phys. Lett. 77, 2758 (2000); http://dx.doi.org/10.1063/1.1320456 (3 pages) | Cited 7 times

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A tandem mechanism of charge injection from a metal contact into an organic dielectric via an intermediate injection-facilitating layer is considered. It is shown that introducing such a layer can enhance charge injection considerably if the energy of transport states in this layer is in between the Fermi level of the contact and the energy of transport states in the bulk dielectric. The optimum energy of transport states in the intermediate layer and the minimum thickness thereof are calculated. © 2000 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
73.20.-r Electron states at surfaces and interfaces
85.60.Jb Light-emitting devices
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