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10 Mar 2008

Volume 92, Issue 10, Articles (10xxxx)

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Appl. Phys. Lett. 92, 102101 (2008); http://dx.doi.org/10.1063/1.2890735 (3 pages)

Qing Wan, Jin Huang, Zhong Xie, Taihong Wang, Eric N. Dattoli, and Wei Lu
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Tunable work functions of platinum gate electrode on HfO2 thin films for metal-oxide-semiconductor devices

Yong-Mu Kim and Jang-Sik Lee

Appl. Phys. Lett. 92, 102901 (2008); http://dx.doi.org/10.1063/1.2892045 (3 pages) | Cited 7 times

Online Publication Date: 10 March 2008

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The change in work function of a platinum gate electrode on a HfO2 dielectric layer was examined as a function of the annealing conditions and thickness of the HfO2 layers. HfO2 thin films with a platinum gate electrode were deposited at various thicknesses to form metal-oxide-semiconductor capacitors. An analysis of the capacitance-voltage responses, equivalent oxide thickness, and flatband voltage variations revealed effective work functions of the platinum gate electrode ranging from 4.24 to 4.98 eV. This result will provide guidelines for process-dependent metal work function modulation and integration of high-k dielectric/metal gate stacks.
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84.32.Tt Capacitors
77.55.-g Dielectric thin films
73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices

Unusual thickness dependence of permittivity and elastic strain in Sc modified epitaxial (Ba,Sr)TiO3 thin films

Woo Young Park, Cheol Seong Hwang, John D. Baniecki, Masatoshi Ishii, Kazuaki Kurihara, and Kazunori Yamanaka

Appl. Phys. Lett. 92, 102902 (2008); http://dx.doi.org/10.1063/1.2883973 (3 pages) | Cited 4 times

Online Publication Date: 11 March 2008

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Undoped and Sc doped epitaxial (Ba0.6,Sr0.4)Ti1+xO3 (BST and SBST) thin films were grown by sputtering on epitaxial Pt/SrTiO3 substrates. The in-(a∥) and out-of-(an) lattice parameters of the BST films were relaxed with increasing thickness, but a∥ of the SBST films was independent of thickness. The dielectric constant (k) of the BST films decreased as the thickness decreased, whereas k of the SBST film was markedly larger and a maximum was observed at a certain thickness. This unusual behavior correlated with increased cell volume of the SBST and demonstrates doping can be used to adjust the thickness dependence of k.
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77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
68.55.aj Insulators
68.55.-a Thin film structure and morphology
77.22.Ch Permittivity (dielectric function)
68.60.Bs Mechanical and acoustical properties

Constrained ferroelectricity in BaTiO3/BaZrO3 superlattices

Palash Roy Choudhury and S. B. Krupanidhi

Appl. Phys. Lett. 92, 102903 (2008); http://dx.doi.org/10.1063/1.2894185 (3 pages) | Cited 6 times

Online Publication Date: 11 March 2008

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BaTiO3/BaZrO3 superlattices with varying periodicities were grown on SrRuO3 buffered MgO (001) substrates by pulsed laser ablation. Ferroelectric measurements were done and correlated to the strain in the heterostructures. The results of ferroelectric measurements indicate an apparent suppression of polarization in the low period superlattices and the onset of weakly ferroelectric behavior in higher period superlattices. Measured switchable polarization values indicate that contribution is primarily from the BaTiO3 in the structure. These results have been correlated to the interfacial strain and the critical thickness of BaTiO3 when grown over tensile substrates such as MgO.
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77.80.Fm Switching phenomena
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
68.65.Cd Superlattices
81.15.Fg Pulsed laser ablation deposition
68.35.Gy Mechanical properties; surface strains

Flatband voltage instability characteristics of HfO2-based GaAs metal-oxide-semiconductor capacitors with a thin Ge layer

Hyoung-Sub Kim, I. Ok, M. Zhang, F. Zhu, S. Park, J. Yum, H. Zhao, Jack C. Lee, Jungwoo Oh, and Prashant Majhi

Appl. Phys. Lett. 92, 102904 (2008); http://dx.doi.org/10.1063/1.2844883 (3 pages) | Cited 3 times

Online Publication Date: 11 March 2008

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This work investigates the flatband voltage instability of HfO2-based GaAs metal-oxide-semiconductor (MOS) capacitor with a thin germanium (Ge) interfacial passivation layer (IPL). Both positive and negative dc gate biases are used as stress condition. By studying various samples such as the devices with extremely thin equivalent oxide thickness of 8.7 Å, with optimum, thick Ge IPLs, and without Ge IPL at a given HfO2 thickness, as well as the devices with varying thicknesses of HfO2 on the optimum Ge IPLs, it is found that both the interface trap and the bulk trap of HfO2 are crucial in affecting the flatband voltage instability characteristics of HfO2 GaAs MOS capacitors. The results indicate that the minimum flatband voltage instability requires a higher quality interface and a thinner HfO2 layer, which can be achieved by employing Ge IPL technique in GaAs system.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.61.Ey III-V semiconductors
84.32.Tt Capacitors

Grain size effect of phase coexistence around morphotropic phase boundary in ferroelectric polycrystalline ceramics

Wei-Feng Rao and Yu U. Wang

Appl. Phys. Lett. 92, 102905 (2008); http://dx.doi.org/10.1063/1.2896612 (3 pages) | Cited 4 times

Online Publication Date: 12 March 2008

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Computer modeling and simulation reveals a grain size- and composition-dependent behavior of phase coexistence around the morphotropic phase boundaries in polycrystals of ferroelectric solid solutions. It shows that the width of phase coexistence composition range increases with decreasing grain sizes; phase-coexisting domain microstructures effectively reduce elastostatic, electrostatic, and domain wall energies; and grain boundaries impose internal mechanical and electric boundary conditions, which affect the phase-coexisting domain microstructures in the grains and give rise to the grain size effect of phase coexistence.
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77.80.-e Ferroelectricity and antiferroelectricity
61.72.Mm Grain and twin boundaries

Studies of two distinct types of (Ba,Sr)TiO3/Pt interfaces

Yidong Xia, Kuibo Yin, Chun Xu, Yi Zhang, Bo Xu, Weiye He, Xiangkang Meng, Jiang Yin, and Zhiguo Liu

Appl. Phys. Lett. 92, 102906 (2008); http://dx.doi.org/10.1063/1.2896990 (3 pages) | Cited 4 times

Online Publication Date: 12 March 2008

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High resolution transmission electron microscopy is used to investigate the interfacial layer at interfaces between (001) (Ba,Sr)TiO3 (BST) films and (111) Pt electrodes. Two distinct types of interfaces are observed. One case is the presence of interfacial layer with distorted structure, whereas another case is the good interfacial match without any interfacial layer. Based on the analyses of crystallographic relationships between BST and Pt, it is proposed that the in-plane lattice structure plays an important role in determining the feature of the interface. The impact of A-O and B-O terminations of BST films on the interfacial layer is also discussed.
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68.35.Ct Interface structure and roughness
77.55.-g Dielectric thin films
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates

Structurally frustrated polar nanoregions in BaTaO2N and the relationship between its high dielectric permittivity and that of BaTiO3

R. L. Withers, Y. Liu, P. Woodward, and Y.-I. Kim

Appl. Phys. Lett. 92, 102907 (2008); http://dx.doi.org/10.1063/1.2890052 (3 pages) | Cited 9 times

Online Publication Date: 12 March 2008

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This letter presents direct evidence for the existence of the same inherently polar one-dimensional (1D), displacive disorder in BaTaO2N as occurs in paraelectric BaTiO3 as well as in doped BaTiO3 relaxor ferroelectric systems. The inherently polar, off-center and oppositely directed displacements of Ta and neighboring O/N ions along ⟨001⟩ give rise to 1D polar nanoregions (PNRs) and are responsible for the dielectric properties of BaTaO2N. A bond valence sum analysis of the underlying crystal chemistry of BaTaO2N shows clearly that O/N ordering is not directly responsible for inducing the observed 1D PNRs.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)
77.80.-e Ferroelectricity and antiferroelectricity

Impact of germanium related defects on electrical performance of hafnium oxide

Qing-Qing Sun, Yu Shi, Lin Dong, Han Liu, Shi-Jin Ding, and David Wei Zhang

Appl. Phys. Lett. 92, 102908 (2008); http://dx.doi.org/10.1063/1.2883944 (3 pages) | Cited 8 times

Online Publication Date: 13 March 2008

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Germanium is known to diffuse into high-k dielectrics during germanium-based metal oxide semiconductor transistor process, which causes the degradation of gate dielectrics. In order to explore the origins of the degradation, we performed first-principles calculation based on density functional theory to study germanium related defects in HfO2. According to calculation, Ge at oxygen vacancy is responsible for the experimentally observed negative charge, gate leakage, and hysteresis enlargement while interstitial Ge in HfO2 is only responsible for the increased gate leakage. The results indicate that the passivation of oxygen vacancy is extremely important during germanium-based metal oxide semiconductor transistor processing.
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61.72.jd Vacancies
61.72.jj Interstitials
85.30.Tv Field effect devices

Low voltage performance of epitaxial BiFeO3 films on Si substrates through lanthanum substitution

Y. H. Chu, Q. Zhan, C.-H. Yang, M. P. Cruz, L. W. Martin, T. Zhao, P. Yu, R. Ramesh, P. T. Joseph, I. N. Lin, W. Tian, and D. G. Schlom

Appl. Phys. Lett. 92, 102909 (2008); http://dx.doi.org/10.1063/1.2897304 (3 pages) | Cited 32 times

Online Publication Date: 14 March 2008

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We have probed the role of La substitution on the ferroelectric properties of epitaxial BiFeO3 films on SrTiO3-templated Si. This provides a mechanism to engineer the rhombohedral distortion in the crystal and, thus, control domain structure and switching. With a 10% La substitution, the (Bi0.9La0.1)FeO3 film showed well-saturated ferroelectric hysteresis loops with a remanent polarization of 45 μC/cm2, a converse piezoelectric coefficient d33 of 45 pm/V, and a dielectric constant of 140. Over this range of La substitution, the coercive field systematically decreases such that a coercive voltage of 1 V can been obtained in a 100 nm thick film. These results show promise for the ultimate implementation of this lead-free multiferroic operating at voltages in the range of 2–3 V.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
77.65.Bn Piezoelectric and electrostrictive constants
77.22.Ch Permittivity (dielectric function)

Magnetoelectric properties of BixCo2−xMnO4 (0 ⩽ x ⩽ 0.3)

N. E. Rajeevan, P. P. Pradyumnan, Ravi Kumar, D. K. Shukla, S. Kumar, A. K. Singh, S. Patnaik, S. K. Arora, and I. V. Shvets

Appl. Phys. Lett. 92, 102910 (2008); http://dx.doi.org/10.1063/1.2894518 (3 pages) | Cited 17 times

Online Publication Date: 14 March 2008

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We present the structural, dielectric and magnetization study of single phase polycrystalline BixCo2−xMnO4 (0 ⩽ x ⩽ 0.3), synthesized by a conventional solid state route. All the samples have the cubic spinel structure with Fd3m space group. Bi-substitution in Co2MnO4 stabilizes the ferroelectric transition at a temperature of ∼ 350 K and enhances the dielectric constant with a relaxor behavior. The capacitance-voltage (C-V) measurements confirm the ferroelectric nature at room temperature. Ferrimagnetic nature of the Co2MnO4 is preserved in the Bi-substituted samples. Magnetocapacitive coupling proves candidature of these materials from an application point of view.
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61.66.Fn Inorganic compounds
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.22.Ch Permittivity (dielectric function)
77.80.B- Phase transitions and Curie point
75.50.Gg Ferrimagnetics
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