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1 Nov 2004

Volume 85, Issue 18, pp. 3959-4247

Issue Cover Spotlight Figure

Appl. Phys. Lett. 85, 4142 (2004); http://dx.doi.org/10.1063/1.1811774 (3 pages)

Hong Jin Fan, Roland Scholz, Florian M. Kolb, and Margit Zacharias
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Abnormal temperature dependence of dielectric constant in (Ba0.7Sr0.3)TiO3 thin films

Hao Yang, Jun Miao, Bin Chen, Li Zhao, Bo Xu, Xiaoli Dong, Lixin Cao, Xianggang Qiu, and Bairu Zhao

Appl. Phys. Lett. 85, 4106 (2004); http://dx.doi.org/10.1063/1.1812575 (3 pages) | Cited 2 times

Online Publication Date: 3 November 2004

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Pt∕(Ba0.7Sr0.3)TiO3∕YBa2Cu3O7−x capacitors were fabricated on LaAlO3 substrates. Dielectric and ferroelectric properties were measured in the temperature range from 20 to 250 K. It was found that the dielectric constant decreased with decreasing temperature from 250 to ∼150 K but then increased as the temperature continued to decrease to 20 K. Considering this phenomenon along with the irregular temperature dependence of spontaneous polarization, it is indicated that such abnormal behavior originates in a second-order structural phase transition in the (Ba1−xSrx)TiO3 thin film in the vicinity of 150 K.
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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.B- Phase transitions and Curie point
77.22.Ch Permittivity (dielectric function)
77.80.Dj Domain structure; hysteresis
77.22.Ej Polarization and depolarization
84.32.Tt Capacitors
85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Epitaxially induced high temperature (>900 K) cubic-tetragonal structural phase transition in BaTiO3 thin films

Feiming Bai, Haimei Zheng, Hu Cao, L. E. Cross, R. Ramesh, Jiefang Li, and D. Viehland

Appl. Phys. Lett. 85, 4109 (2004); http://dx.doi.org/10.1063/1.1812579 (3 pages) | Cited 6 times

Online Publication Date: 3 November 2004

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For (001)c oriented BaTiO3 thin films, it has been found that epitaxial constraint can result in a dramatic increase in the temperature of a tetragonal (T) structural phase transition. For 2000-math-thick films grown directly on SrTiO3 substrates, a T→cubic (C) phase transition was found on heating at >950 K, where the lattice constant changed smoothly with temperature. It was also found for films of the same thickness that the T→C transition is nearly restored to that of bulk crystals by the use of a buffer layer, which relaxes the epitaxial constraint. These results provide evidence of an epitaxially induced high temperature structural phase transition in BaTiO3 thin films, where the ferroelectric (internal) and structural (external) aspects of the phase transition are decoupled.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
77.80.B- Phase transitions and Curie point
81.15.Fg Pulsed laser ablation deposition

High dielectric constant TiO2 thin films on a Ru electrode grown at 250 °C by atomic-layer deposition

Seong Keun Kim, Wan-Don Kim, Kyung-Min Kim, Cheol Seong Hwang, and Jaehack Jeong

Appl. Phys. Lett. 85, 4112 (2004); http://dx.doi.org/10.1063/1.1812832 (3 pages) | Cited 103 times

Online Publication Date: 3 November 2004

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TiO2 thin films with high dielectric constants (83–100) were grown on a Ru electrode at a growth temperature of 250 °C using the atomic-layer deposition method. The as-deposited films were crystallized with rutile structure. Adoption of O3 with a very high concentration (400 g∕m3) was crucial for obtaining the rutile phase and the high dielectric constant. The leakage current density of a TiO2 film with an equivalent oxide thickness of 1.0–1.5 nm was 10−6–10−8 A∕cm2 at ±1 V. All these electrical properties were obtained after limited postannealing where the annealing temperature was <500 °C, which is crucial to the structural stability of the Ru electrode. Therefore, these TiO2 films are very promising as the capacitor dielectrics of dynamic random access memories. TiO2 films grown on a bare Si wafer or Pt electrode by the same process had anatase structure and a dielectric constant of ∼40.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.22.Ch Permittivity (dielectric function)
81.40.Gh Other heat and thermomechanical treatments

Interfacial reaction depending on the stack structure of Al2O3 and HfO2 during film growth and postannealing

M.-H. Cho, K. B. Chung, H. S. Chang, D. W. Moon, S. A. Park, Y. K. Kim, K. Jeong, C. N. Whang, D. W. Lee, D.-H. Ko, S. J. Doh, J. H. Lee, and N. I. Lee

Appl. Phys. Lett. 85, 4115 (2004); http://dx.doi.org/10.1063/1.1807968 (3 pages) | Cited 8 times

Online Publication Date: 3 November 2004

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Interfacial reactions as a function of the stack structure of Al2O3 and HfO2 grown on Si by atomic-layer deposition were examined by various physical and electrical measurements. In the case of an Al2O3 film with a buffer layer of HfO2, reactions between the Al2O3 and Si layers were suppressed, while a HfO2 film with an Al2O3 buffer layer on the Si readily interacted with Si, forming a Hf–Al–Si–O compound. The thickness of the interfacial layer increased dramatically after an annealing treatment in which a buffer layer of Al2O3 was used, while no change in thickness was observed in the film in which a HfO2 buffer layer was used. Moreover, the stoichiometric change caused by a different reaction process altered the chemical state of the films, which affected charge trapping and the interfacial trap density.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
66.30.Ny Chemical interdiffusion; diffusion barriers
73.61.Ng Insulators
77.22.Ch Permittivity (dielectric function)
61.66.Bi Elemental solids
61.66.Dk Alloys
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
68.37.Lp Transmission electron microscopy (TEM)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

(Bi,La)4Ti3O12 (BLT) thin films grown from nanocrystalline perovskite nuclei for ferroelectric memory devices

N. K. Kim, S. J. Yeom, S. Y. Kweon, E. S. Choi, H. J. Sun, J. S. Roh, H. C. Sohn, D. W. Lee, H. S. Kim, B. H. Choi, J. W. Kim, K. J. Choi, N. J. Seong, and S. G. Yoon

Appl. Phys. Lett. 85, 4118 (2004); http://dx.doi.org/10.1063/1.1812840 (3 pages) | Cited 4 times

Online Publication Date: 3 November 2004

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Using nanocrystalline perovskite nuclei, (117) oriented-(Bi,La)4Ti3O12(BLT) thin films were grown using a noble bake process for nonvolatile ferroelectric memory devices. The c-axis oriented BLT thin films have a remanent polarization (2Pr) of 8.0 μC∕cm2 at a 3 V driving voltage, and the (117) oriented films have a 2Pr value of about 25 μC∕cm2. The BLT capacitors, grown on a platinum electrode via nanocrystalline perovskite nuclei, had fatigue and imprint free characteristics after applying 1×1011 switching cycles and for ten years at a 125 °C stress. The average sensing margin of the (117) oriented BLT thin films was approximately 700 mV for a 0.65 μm2 cell size and a sufficient signal margin for ten years was indicated, based on the extrapolation of the measured data for high density ferreoelectric random access memory applications.
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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.A- Nucleation and growth
77.22.Ej Polarization and depolarization
77.80.Dj Domain structure; hysteresis
77.80.Fm Switching phenomena
68.55.-a Thin film structure and morphology
84.32.Tt Capacitors
85.50.Gk Non-volatile ferroelectric memories
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Phase transitional behavior and piezoelectric properties of (Na0.5K0.5)NbO3–LiNbO3 ceramics

Yiping Guo, Ken-ichi Kakimoto, and Hitoshi Ohsato

Appl. Phys. Lett. 85, 4121 (2004); http://dx.doi.org/10.1063/1.1813636 (3 pages) | Cited 475 times

Online Publication Date: 3 November 2004

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Lead-free piezoelectric ceramics (1−x)(Na0.5K0.5)NbO3–xLiNbO3 {[Lix(Na0.5K0.5)1−x]NbO3} (x=0.04–0.20) have been synthesized by an ordinary sintering technique. The materials with perovskite structure is orthorhombic phase at x⩽0.05 and becomes tetragonal phase at x⩾0.07, a phase K3Li2Nb5O15 with tetragonal tungsten bronze structure begins to appear at x=0.08 and becomes dominant with increasing the content of LiNbO3. A morphotropic phase boundary between orthorhombic and tetragonal phases is found in the composition range 0.05<x<0.07. Analogous to Pb(Zr,Ti)O3, the piezoelectric and electromechanical properties are enhanced for compositions near the morphotropic phase boundary. Piezoelectric constant d33 values reach 200–235 pC∕N. Electromechanical coefficients of the planar mode and the thickness mode reach 38%–44% and 44%–48%, respectively. The Curie temperatures (TC) of [Lix(Na0.5K0.5)1−x]NbO3 (x=0.04–0.20) are in the range of 452–510 °C, at least 100 °C higher than that of conventional Pb(Zr,Ti)O3. Our results show that [Lix(Na0.5K0.5)1−x]NbO3 is a good lead-free high-temperature piezoelectric ceramic.
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81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Bn Piezoelectric and electrostrictive constants
64.70.K- Solid-solid transitions
77.22.Ch Permittivity (dielectric function)
77.80.B- Phase transitions and Curie point
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

Effect of thermal strain on the ferroelectric phase transition in polycrystalline Ba0.5Sr0.5TiO3 thin films studied by Raman spectroscopy

D. A. Tenne, A. Soukiassian, X. X. Xi, T. R. Taylor, P. J. Hansen, J. S. Speck, and R. A. York

Appl. Phys. Lett. 85, 4124 (2004); http://dx.doi.org/10.1063/1.1813625 (3 pages) | Cited 15 times

Online Publication Date: 3 November 2004

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We have applied Raman spectroscopy to study the influence of thermal strain on the vibrational properties of polycrystalline Ba0.5Sr0.5TiO3 films. The films were grown by rf magnetron sputtering on Pt∕SiO2 surface using different host substrates: strontium titanate, sapphire, silicon, and vycor glass. These substrates provide a systematic change in the thermal strain while maintaining the same film microstructure. From the temperature dependence of the ferroelectric A1 soft phonon intensity, the ferroelectric phase transition temperature, TC, was determined. We found that TC decreases with increasing tensile stress in the films. This dependence is different from the theoretical predictions for epitaxial ferroelectric films. The reduction of the ferroelectric transition temperature with increasing biaxial tensile strain is attributed to the suppression of in-plane polarization due to the small lateral grain size in the films.
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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
81.15.Cd Deposition by sputtering
78.66.Nk Insulators
78.30.Hv Other nonmetallic inorganics
68.60.Bs Mechanical and acoustical properties
77.22.Ej Polarization and depolarization

Alternative surface passivation on germanium for metal-oxide-semiconductor applications with high-k gate dielectric

Nan Wu, Qingchun Zhang, Chunxiang Zhu, D. S. H. Chan, M. F. Li, N. Balasubramanian, Albert Chin, and Dim-Lee Kwong

Appl. Phys. Lett. 85, 4127 (2004); http://dx.doi.org/10.1063/1.1812835 (3 pages) | Cited 44 times

Online Publication Date: 3 November 2004

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An alternative surface passivation process for high-k Ge metal-oxide-semiconductor (MOS) device has been studied. The surface SiH4 annealing was implemented prior to HfO2 deposition. X-ray photoelectron spectroscopy analysis results show that the SiH4 surface passivation can greatly prevent the formation of unstable germanium oxide at the surface and suppress the Ge out-diffusion after the HfO2 deposition. The electrical measurement shows that an equivalent oxide thickness of 13.5 math and a leakage current of 1.16×10−5 A∕cm2 at 1 V gate bias was achieved for TaN∕HfO2∕Ge MOS capacitors with the SiH4 surface treatment.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.55.-g Dielectric thin films
68.55.A- Nucleation and growth
68.55.-a Thin film structure and morphology
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
84.32.Tt Capacitors
81.65.Rv Passivation
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.40.Gh Other heat and thermomechanical treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.35.Fx Diffusion; interface formation
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Evolution of the chemical bonding nature of ferroelectric bismuth titanate upon cation substitution

Su Gil Hur, Dae Hoon Park, Tae Woo Kim, and Seong-Ju Hwang

Appl. Phys. Lett. 85, 4130 (2004); http://dx.doi.org/10.1063/1.1814818 (3 pages) | Cited 9 times

Online Publication Date: 3 November 2004

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The effect of cation substitution on the crystal and electronic structures of ferroelectric bismuth titanate has been systematically investigated. According to the x-ray diffraction analyses on Bi3.25A0.75Ti3O12 (A=Bi, La, Gd, and Y), it was found that the cation substitution gives rise to the contraction of the volume of the unit cell and to the decrease of the structural distortion of the bismuth titanate, as well. The present x-ray absorption spectroscopic results reveal that the local structural change upon chemical reduction is remarkably depressed by the cation substitution through the enhancement of (TiO) bonds. Such a stabilization of TiO6 octahedra can be understood by a competition between adjacent (BiO) and (TiO) bonds as well as the contraction of the unit cell.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
71.20.Ps Other inorganic compounds
61.50.Lt Crystal binding; cohesive energy
82.30.-b Specific chemical reactions; reaction mechanisms
61.66.Fn Inorganic compounds
78.70.Dm X-ray absorption spectra

Determination of energy barrier profiles for high-k dielectric materials utilizing bias-dependent internal photoemission

Julie Casperson Brewer, Robert J. Walters, L. Douglas Bell, Damon B. Farmer, Roy G. Gordon, and Harry A. Atwater

Appl. Phys. Lett. 85, 4133 (2004); http://dx.doi.org/10.1063/1.1812831 (3 pages) | Cited 9 times

Online Publication Date: 3 November 2004

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We utilize bias-dependent internal photoemission spectroscopy to determine the metal∕dielectric∕silicon energy barrier profiles for Au∕HfO2∕Si and Au∕Al2O3∕Si structures. The results indicate that the applied voltage plays a large role in determining the effective barrier height and we attribute much of the variation in this case to image potential barrier lowering in measurements of single layers. By measuring current at both positive and negative voltages, we are able to measure the band offsets from Si and also to determine the flatband voltage and the barrier asymmetry at 0 V. Our SiO2 calibration sample yielded a conduction band offset value of 3.03±0.1 eV. Measurements on HfO2 give a conduction band offset value of 2.7±0.2 eV (at 1.0 V) and Al2O3 gives an offset of 3.3±0.1 (at 1.0 V). We believe that interfacial SiO2 layers may dominate the electron transport from silicon for these films. The Au∕HfO2 barrier height was found to be 3.6±0.1 eV while the Au∕Al2O3 barrier is 3.5±0.1 eV.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
71.20.Ps Other inorganic compounds
72.40.+w Photoconduction and photovoltaic effects
79.60.Jv Interfaces; heterostructures; nanostructures
77.55.-g Dielectric thin films
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

[001]-poled Pb(Zn1∕3Nb2∕3)O3-(6-7)%PbTiO3k31-actuators: Effects of initial domain structure, length orientation, and poling conditions

K. K. Rajan, Y. S. Ng, J. Zhang, and L. C. Lim

Appl. Phys. Lett. 85, 4136 (2004); http://dx.doi.org/10.1063/1.1809278 (3 pages) | Cited 6 times

Online Publication Date: 3 November 2004

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Extremely high k31 and d31 values of 0.88 and −1850 pC∕N were obtained from [001]-poled PZN-(6-7)%PT single-crystal plates but of different length orientations and initial domain structures. This composition also exhibits dielectric constant of 5500–6500 and a high depolarization temperature of ≈100 °C.
Show PACS
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
77.65.Bn Piezoelectric and electrostrictive constants
77.22.Ch Permittivity (dielectric function)
77.22.Ej Polarization and depolarization
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