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30 May 2005

Volume 86, Issue 22, Articles (22xxxx)

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Appl. Phys. Lett. 86, 223902 (2005); http://dx.doi.org/10.1063/1.1938253 (3 pages)

Philip J. Lee, Paul J. Hung, Robin Shaw, Lily Jan, and Luke P. Lee
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Critical thickness for ferroelectricity of BaTiO3 by first-principles calculations

Ryo Nakao, Keisuke Ishizumi, Isao Takahashi, Hikaru Terauchi, Yoshinori Hayafuji, and Kaoru Miura

Appl. Phys. Lett. 86, 222901 (2005); http://dx.doi.org/10.1063/1.1915508 (3 pages) | Cited 3 times

Online Publication Date: 24 May 2005

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The critical thickness for ferroelectricity of a BaTiO3 film was determined by the first-principles discrete variational-Xα molecular orbital method and population analysis. Under the assumption that most ferroelectric perovskite oxides are predominantly ionic, a series of model clusters were developed for a BaTiO3 particle consisting of a Ba8Ti7O6 cluster constructed on the basis of the crystal structure of BaTiO3 phase and point charges surrounding the Ba8Ti7O6 cluster. The size of the model cluster was exactly defined by the size of a three-dimensional point-charge array. By comparing the dependence of the net charge of Ba, Ti, and O ions and of the overlap population between Ti 3d and O 2p orbitals on particle thickness in tetragonal and cubic BaTiO3 particles, the critical thickness for ferroelectricity was calculated to be about 12 nm for a BaTiO3 particle with a basal area of 20×20 nm.
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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
77.55.-g Dielectric thin films
61.66.Fn Inorganic compounds

Domain resonance in two-dimensional periodically poled ferroelectric resonator

I. V. Ostrovskii and A. B. Nadtochiy

Appl. Phys. Lett. 86, 222902 (2005); http://dx.doi.org/10.1063/1.1940726 (3 pages) | Cited 7 times

Online Publication Date: 24 May 2005

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A two-dimensional periodically poled ferroelectric resonator is reported. The theoretical calculations, computer simulations by the finite element method and experimental data from the lithium tantalite samples reveal a domain acoustoelectric resonance. A polarization inversion in a y-rotated cut of a ferroelectric chip is done. A distribution of an electric potential over crystal surface may be an effective experimental tool for characterization of the periodically poled ferroelectrics.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
77.80.Dj Domain structure; hysteresis

Epitaxially grown La-modified BiFeO3 magnetoferroelectric thin films

Dongeun Lee, Min G. Kim, Sangwoo Ryu, Hyun M. Jang, and Sang G. Lee

Appl. Phys. Lett. 86, 222903 (2005); http://dx.doi.org/10.1063/1.1941474 (3 pages) | Cited 122 times

Online Publication Date: 25 May 2005

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Effects of the La modification on the structure and magnetoferroelectric properties of BiFeO3 (BFO)-based films were examined. On SrTiO3 (001) planes, all the BFO-based films (for x between 0 and 0.15 in Bi1−xLaxFeO3 with the film thickness of 300 nm) were grown epitaxially along [001] direction of tetragonal symmetry. However, the La modification gradually changes the film structure from a monoclinically tilted state to a nontilted tetragonal-like state. Both extended x-ray absorption fine structure and x-ray absorption near edge structure spectra revealed the presence of a strong in-plane compressive stress. Room-temperature magnetization-field curves indicated that the saturation magnetization of these BFO-based epitaxial films increased with the degree of La modification. La-modified BFO film capacitors fabricated on SrRuO3-buffered SrTiO3 (001) substrates showed fatigue-free ferroelectric switching characteristics up to 4×1010 read∕write cycles at a frequency of 1 MHz.
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61.05.cj X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc.
75.70.Ak Magnetic properties of monolayers and thin films
77.55.-g Dielectric thin films
77.80.Fm Switching phenomena

Electrical properties of 0.5 nm thick Hf-silicate top‐layer/HfO2 gate dielectrics by atomic layer deposition

Satoshi Kamiyama, Takayoshi Miura, Yasuo Nara, and Tsunetoshi Arikado

Appl. Phys. Lett. 86, 222904 (2005); http://dx.doi.org/10.1063/1.1941455 (3 pages) | Cited 16 times

Online Publication Date: 25 May 2005

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The electrical properties have been studied for hafnium (Hf)-based gate stack structures, fabricated using atomic layer deposition (ALD) technology. The very thin ALD Hf-silicate layers on the top of HfO2 gate structures were very important in obtaining good electrical properties, because these surface films prevented a reaction between the polysilicon electrodes and HfO2 films during high temperature activation annealing. From subthreshold characteristic measurements, Ioff values were less than about 10 pA/μm and Ion values at ∣Vg∣ = 1.1 V were greater than 350 and 120 μA/μm for n- and p- metal oxide semiconductor field effect transistors, respectively. The effective mobility curves for the Hf-based gate stack structures were at the same level as those of 1.6 nm SiON reference films at 0.8 MV/cm. Furthermore, the interfacial trap densities were less than 5*1010 cm−2 for the Hf-based gate stack structures, achieving the same level as in the 1.6 nm SiON reference films.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
85.30.Tv Field effect devices
81.40.Gh Other heat and thermomechanical treatments
72.20.Fr Low-field transport and mobility; piezoresistance
73.20.At Surface states, band structure, electron density of states

Characterization of CF4-plasma fluorinated HfO2 gate dielectrics with TaN metal gate

Chao Sung Lai, Woei Cherng Wu, Jer Chyi Wang, and Tien sheng Chao

Appl. Phys. Lett. 86, 222905 (2005); http://dx.doi.org/10.1063/1.1944230 (3 pages) | Cited 12 times

Online Publication Date: 26 May 2005

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In this paper, fluorine incorporation into the HfO2 gate dielectrics by post CF4 plasma treatment was proposed to improve the electrical characterization. TaN–HfO2–p-Si capacitors were demonstrated in this work. The characteristics of fluorinated HfO2 gate dielectrics were improved, including the capacitance-voltage hysteresis and current-voltage behaviors. This may be attributed to the fluorine incorporated into the HfO2 gate dielectrics as revealed by secondary ion mass spectroscopy. Moreover, the formation of Hf-F bonding was observed through electron spectroscopy for chemical analysis spectra.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
84.32.Tt Capacitors
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
77.80.Dj Domain structure; hysteresis

Nickel-silicide phase effects on flatband voltage shift and equivalent oxide thickness decrease of hafnium silicon oxynitride metal-silicon-oxide capacitors

Chang Yong Kang, Pat Lysaght, Rino Choi, Byoung Hun Lee, Se Jong Rhee, Chang Hwan Choi, M. S. Akbar, and Jack C. Lee

Appl. Phys. Lett. 86, 222906 (2005); http://dx.doi.org/10.1063/1.1942633 (3 pages) | Cited 14 times

Online Publication Date: 26 May 2005

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This Letter reports the nickel-silicide phase effects on the electrical characteristics of high-k and silicon dioxide (SiO2) metal-oxide-semiconductor devices. It was found that the silicon-deficient nickel-silicided gate electrode on the hafnium silicon oxynitride (HfSiON) led to a positive flatband voltage (Vfb) shift and a reduction in the equivalent oxide thickness (EOT). However, negligible Vfb shift and EOT decrease were observed in the case of control hafnium oxide and SiO2 structures. It was believed that Si dissociation from the HfSiON layer was the main reason for the positive Vfb shift and the EOT decrease.
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84.32.Tt Capacitors
85.30.Tv Field effect devices
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Relaxation of induced polar state in relaxor PbMg1/3Nb2/3O3 thin films studied by piezoresponse force microscopy

V. V. Shvartsman, A. L. Kholkin, M. Tyunina, and J. Levoska

Appl. Phys. Lett. 86, 222907 (2005); http://dx.doi.org/10.1063/1.1942635 (3 pages) | Cited 29 times

Online Publication Date: 26 May 2005

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Polarization state in epitaxial thin films of relaxor ferroelectric PbMg1/3Nb2/3O3 (PMN) was experimentally studied at the nanoscale using a piezoresponse force microscopy (PFM). In the absence of a dc bias applied to the PFM tip, no piezoelectric activity could be found on most of the surface of the film. Under a moderate voltage (>1.5–2 V), a polar state with a nonzero piezoresponse could be induced. Longer poling resulted in a significant reduction of the initial piezoresponse. After removing the bias field, a long-term relaxation of the piezoelectric signal obeying a Kohlrausch-Williams-Watt dependence was observed.
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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.Ej Polarization and depolarization
77.55.-g Dielectric thin films
77.80.-e Ferroelectricity and antiferroelectricity
77.65.-j Piezoelectricity and electromechanical effects
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