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24 Sep 2007

Volume 91, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 132501 (2007); http://dx.doi.org/10.1063/1.2786856 (3 pages)

V. Rose, X. M. Cheng, D. J. Keavney, J. W. Freeland, K. S. Buchanan, B. Ilic, and V. Metlushko
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Resistive magnetodielectric property of polycrystalline γ-Fe2O3

T. Bonaedy, Y. S. Koo, K. D. Sung, and J. H. Jung

Appl. Phys. Lett. 91, 132901 (2007); http://dx.doi.org/10.1063/1.2790474 (3 pages) | Cited 10 times

Online Publication Date: 24 September 2007

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We have systematically investigated the magnetodielectric property of polycrystalline γ-Fe2O3. The dielectric constants of γ-Fe2O3 seem to follow the Maxwell-Wagner model, i.e., their large enhancement and strong temperature and frequency dependences. Positive magnetodielectric property is observed with negative magnetoresistance, at least above 180 K. The value of magnetodielectric effect is maximized at the specific frequency, which is inversely proportional to resistivity. Based on the Maxwell-Wagner model and the magnetoresistance, we can reproduce the magnetodielectric effect of γ-Fe2O3.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
77.22.Ch Permittivity (dielectric function)

Critical radii of ferroelectric domains for different decay processes in LiNbO3 crystals

Yi Kan, Xiaomei Lu, Huifeng Bo, Fengzhen Huang, Xiaobo Wu, and Jinsong Zhu

Appl. Phys. Lett. 91, 132902 (2007); http://dx.doi.org/10.1063/1.2790475 (3 pages) | Cited 9 times

Online Publication Date: 24 September 2007

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The LiNbO3 crystals were polarized at fixed points and characterized by means of scanning probe microscope. The growth evolution and the decay process of the fabricated domains were carefully studied. Two critical radii rC and Rc that determine a different decay behavior of domains were put forward, where rC is considered to correspond to the point when the domains just penetrate the crystal. Those domains with radius larger than rC could exist beyond 5 days, those between rC and Rc experienced a distinct metastable state before completely disappearing, while those smaller than Rc were even invisible under piezoresponse force mode.
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77.80.Dj Domain structure; hysteresis
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ej Polarization and depolarization
77.65.-j Piezoelectricity and electromechanical effects
42.70.Mp Nonlinear optical crystals

Observation of inhomogeneous domain nucleation in epitaxial Pb(Zr,Ti)O3 capacitors

D. J. Kim, J. Y. Jo, T. H. Kim, S. M. Yang, B. Chen, Y. S. Kim, and T. W. Noh

Appl. Phys. Lett. 91, 132903 (2007); http://dx.doi.org/10.1063/1.2790485 (3 pages) | Cited 44 times

Online Publication Date: 25 September 2007

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We investigated domain nucleation process in epitaxial Pb(Zr,Ti)O3 capacitors under a modified piezoresponse force microscope. We obtained domain evolution images during polarization switching process and observed that domain nucleation occurs at particular sites. This inhomogeneous nucleation process should play an important role in an early stage of switching and under a high electric field. We found that the number of nuclei is linearly proportional to log(switching time), suggesting a broad distribution of activation energies for nucleation. The nucleation sites for a positive bias differ from those for a negative bias, indicating that most nucleation sites are located at the ferroelectric/electrode interfaces.
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77.55.-g Dielectric thin films
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
77.22.Ej Polarization and depolarization
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Suppression of oxygen vacancy formation in Hf-based high-k dielectrics by lanthanum incorporation

N. Umezawa, K. Shiraishi, S. Sugino, A. Tachibana, K. Ohmori, K. Kakushima, H. Iwai, T. Chikyow, T. Ohno, Y. Nara, and K. Yamada

Appl. Phys. Lett. 91, 132904 (2007); http://dx.doi.org/10.1063/1.2789392 (3 pages) | Cited 14 times

Online Publication Date: 25 September 2007

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The effects of lanthanum incorporation into HfO2 dielectrics were studied using first-principles total energy calculations. The author’s computational result clearly showed that the formation energy of a neutral oxygen vacancy (VO0) in the vicinity of substitutional La atoms at Hf sites is 0.7 eV larger than that in pure HfO2, indicating that the concentration of VO0’s is drastically reduced by La incorporation. This effect is understood to be caused by the decrease in the local dielectric constant κL around La atoms due to the strong ionic character of the La–O bond compared to the Hf–O bond.
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61.72.J- Point defects and defect clusters
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)

Spectroscopic study of dielectric barrier discharges in cellular polypropylene ferroelectrets

Xunlin Qiu, Axel Mellinger, Werner Wirges, and Reimund Gerhard

Appl. Phys. Lett. 91, 132905 (2007); http://dx.doi.org/10.1063/1.2786597 (3 pages) | Cited 5 times

Online Publication Date: 25 September 2007

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The transient light emission from the dielectric barrier discharges (DBDs) in cellular polypropylene ferroelectrets subjected to high electric poling fields was spectroscopically measured. The spectrum shows strong emission from the second positive system of molecular nitrogen, N2(C 3Πu)→N2(B 3Πg), and the first negative system of N2+, N2+(B 2Σu+)→N2+(X 2Σg+), consistent with a DBD in air. When a dc voltage is applied stepwise to the ferroelectret film, light emission starts above a threshold, coinciding with the threshold voltage in obtaining piezoelectricity. From selected vibronic band strength ratios, the electric field in the discharge was determined and found to agree with Townsend breakdown.
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52.80.-s Electric discharges
77.22.Ej Polarization and depolarization

Ab initio study on intrinsic defect properties of germanium nitride considered for gate dielectric

M. Yang, S. J. Wang, G. W. Peng, R. Q. Wu, and Y. P. Feng

Appl. Phys. Lett. 91, 132906 (2007); http://dx.doi.org/10.1063/1.2790075 (3 pages) | Cited 2 times

Online Publication Date: 25 September 2007

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First-principles calculations based on density-functional theory and local-density approximation were carried out to investigate intrinsic defect properties in β-Ge3N4. It was found that nitrogen vacancies are the main source of intrinsic defects in Ge3N4 due to their low formation energy. The N vacancies might become charge trapping centers since they induce energy levels near the Ge conduction band edge and in the middle of the Ge3N4 band gap. The formation energy of intrinsic defects in Ge3N4 is sensitive to N chemical potential, and N-rich ambient is favorable to reduce the concentration of N vacancies.
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71.55.Ht Other nonmetals
71.20.Ps Other inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.J- Point defects and defect clusters
65.40.G- Other thermodynamical quantities

Metal-insulator-metal capacitors’ current instability improvement using dielectric stacks to prevent oxygen vacancies formation

J.-P. Manceau, S. Bruyere, S. Jeannot, A. Sylvestre, and P. Gonon

Appl. Phys. Lett. 91, 132907 (2007); http://dx.doi.org/10.1063/1.2790478 (3 pages) | Cited 8 times

Online Publication Date: 26 September 2007

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Current instability in metal-oxide-semiconductor and metal-insulator-metal (MIM) capacitors has been previously reported to be a potential reliability issue. This letter intends to study a particular way to reduce these current instabilities with time in high-κ MIM capacitors. It consists in the introduction of a stable dielectric layer between the high-κ dielectric and the electrodes in order to prevent oxygen vacancy formation at interfaces. When applied to Ta2O5 capacitors, the deposition of a thin layer of Al2O3 in the range of a few tens of angstroms enables the strong reduction of current instabilities while maintaining good electrical performances.
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84.32.Tt Capacitors
85.30.Tv Field effect devices

The electronic structure change with Gd doping of HfO2 on silicon

Ya. B. Losovyj, Ihor Ketsman, A. Sokolov, K. D. Belashchenko, P. A. Dowben, Jinke Tang, and Zhenjun Wang

Appl. Phys. Lett. 91, 132908 (2007); http://dx.doi.org/10.1063/1.2787967 (3 pages) | Cited 17 times

Online Publication Date: 26 September 2007

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Gd-doped HfO2 films deposited on silicon substrates undergo a crystallographic change from monoclinic to fluorite (cubic) phase with increasing Gd concentrations. The crystallographic phase change is accompanied by a small increase in the valence bandwidth and in the apparent band offset in the surface region. Electrical measurements show pronounced rectification properties for lightly doped Gd:HfO2 films on p-Si and for heavily-doped Gd:HfO2 films on n-Si, suggesting a crossover from n-type to p-type behavior with increasing doping level.
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71.20.Ps Other inorganic compounds
73.20.At Surface states, band structure, electron density of states
61.72.up Other materials
77.55.-g Dielectric thin films
61.50.Ks Crystallographic aspects of phase transformations; pressure effects

Improved dielectric properties of Al2O3-doped Pb0.6Ba0.4ZrO3 thin films for tunable microwave applications

Lin-Jung Wu and Jenn-Ming Wu

Appl. Phys. Lett. 91, 132909 (2007); http://dx.doi.org/10.1063/1.2785130 (3 pages) | Cited 4 times

Online Publication Date: 26 September 2007

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The effect of doping Al2O3 on the Pb0.6Ba0.4ZrO3 thin films was investigated. With increasing Al2O3 content, the dielectric constant, tunability, and dissipation factor decrease while the figure of merit (FOM) increases. After doping with the optimal content of 1.5 at. % Al2O3, the Pb0.6Ba0.4ZrO3 films have a dielectric constant of 190, a tunability of 30%, a dissipation factor of 0.0067, a FOM value of 49, and a temperature coefficient of capacitance value of 1.13×10−4. The loss mechanism is discussed in order to provide information, which could be useful for further improvement of the material performance.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
77.22.Gm Dielectric loss and relaxation

An active energy harvesting scheme with an electroactive polymer

Kailiang Ren, Yiming Liu, H. Hofmann, Q. M. Zhang, and John Blottman

Appl. Phys. Lett. 91, 132910 (2007); http://dx.doi.org/10.1063/1.2793172 (3 pages) | Cited 14 times

Online Publication Date: 26 September 2007

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We investigate the energy harvesting with an electrostrictive polymer, possessing high electromechanical response and elastic energy density, which make it possible to generate high electric energy density and attractive for the active energy harvesting scheme. It is shown that combining the active energy harvesting scheme and high electromechanical response of the polymer yields a harvested electric energy density of ∼ 40 mJ/cm3 with a 10% efficiency.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices
84.90.+a Other topics in electronics, radiowave and microwave technology, and direct energy conversion and storage (restricted to new topics in section 84)

Incipient ferroelectricity and microwave dielectric resonance properties of CaCu2.85Mn0.15Ti4O12 ceramics

Ming Li, Antonio Feteira, Derek C. Sinclair, and Anthony R. West

Appl. Phys. Lett. 91, 132911 (2007); http://dx.doi.org/10.1063/1.2769954 (3 pages) | Cited 14 times

Online Publication Date: 26 September 2007

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Mn-doped CaCu3Ti4O12 ceramics with nominal composition CaCu2.85Mn0.15Ti4O12 (CCMTO) have been prepared and their radio- and micro-wave dielectric properties established. At 300 K, dense CCMTO ceramics have appreciable grain resistivity, ∼ 20 MΩ cm, and exhibit microwave dielectric resonance with εr ∼ 93, Qf ∼ 3950 GHz (at 3.95 GHz) and temperature coefficient of resonant frequency ∼ +657 ppm/K. εr decreases smoothly from ∼ 150 to 90 in the range of 10–300 K, obeys the Curie-Weiss law in the range of ∼ 60–180 K, and is consistent with incipient ferroelectricity. The source of the incipient ferroelectricity and potential applications of CCMTO ceramics are discussed.
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77.80.-e Ferroelectricity and antiferroelectricity
77.65.Fs Electromechanical resonance; quartz resonators
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.22.Ch Permittivity (dielectric function)

Fermi level pinning by defects in HfO2-metal gate stacks

J. Robertson, O. Sharia, and A. A. Demkov

Appl. Phys. Lett. 91, 132912 (2007); http://dx.doi.org/10.1063/1.2790479 (3 pages) | Cited 50 times

Online Publication Date: 28 September 2007

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Various mechanisms for the Fermi level pinning of p-gate metals on HfO2 are analyzed in detail. It is found that for Fermi energies below the Si valence band, HfO2 can oxidize Si by creating positively charged O vacancies. The band bending due to this vacancy concentration can account for the observed Fermi level pinning of p metals on HfO2.
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71.55.-i Impurity and defect levels
85.30.Tv Field effect devices
73.20.Hb Impurity and defect levels; energy states of adsorbed species

Modified (K0.5Na0.5)NbO3 based lead-free piezoelectrics with broad temperature usage range

Shujun Zhang, Ru Xia, and Thomas R. Shrout

Appl. Phys. Lett. 91, 132913 (2007); http://dx.doi.org/10.1063/1.2794400 (3 pages) | Cited 81 times

Online Publication Date: 28 September 2007

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(K0.5Na0.5)NbO3 (KNN) based lead-free materials exhibit arguably, comparable piezoelectric properties to conventional Pb(Zr,Ti)O3 ceramics owing to an orthorhombic to tetragonal polymorphic phase transition (TO-T) occurring near room temperature. However, this transition correspondingly results in a strong temperature dependence of the dielectric and piezoelectric properties, being limited further by domain instability, during thermal cycling between the two ferroelectric phases. Analogous to BaTiO3 based piezoelectrics, the addition of CaTiO3 in KNN materials was found to shift the TO-T well below room temperature. Piezoelectric and electromechanical values of KNN–LiSbO3–CaTiO3 material were found to be d33 ∼ 210 pC/N, d15 ∼ 268 pC/N and k33 ∼ 61%, k15 ∼ 56%, respectively, with greatly improved temperature stability over the temperature range of −50–200 °C, demonstrating practical potential for actuator and/or ultrasonic transducer applications.
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77.65.-j Piezoelectricity and electromechanical effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
77.80.Dj Domain structure; hysteresis

Effects of Ag content on the phase structure and piezoelectric properties of (K0.44−xNa0.52Li0.04Agx)(Nb0.91Ta0.05Sb0.04)O3 lead-free ceramics

Jiagang Wu, Yuanyu Wang, Dingquan Xiao, Jianguo Zhu, and Zhaohui Pu

Appl. Phys. Lett. 91, 132914 (2007); http://dx.doi.org/10.1063/1.2793507 (3 pages) | Cited 46 times

Online Publication Date: 28 September 2007

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(K0.44−xNa0.52Li0.04Agx)(Nb0.91Ta0.05Sb0.04)O3 lead-free piezoelectric ceramics were prepared by normal sintering. The effects of Ag content on the phase structure and piezoelectric properties of the ceramics were mainly studied. These results show that the phase structure undergoes a transition from orthorhombic to tetragonal phase with increasing x from 0.00 to 0.06. The optimum Ag content enhances the piezoelectric properties, and the Curie temperature increases with increasing x. The ceramics with x = 0.02 exhibit enhanced electrical properties (d33 ∼ 263 pC/N, kp ∼ 45.3%, TC ∼ 353 °C, εr ∼ 1478, and tan δ ∼ 2.3%) and good aging characteristics. These results show that the ceramic with x = 0.02 is a promising lead-free piezoelectric material.
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77.65.-j Piezoelectricity and electromechanical effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
64.70.K- Solid-solid transitions
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