bluuebunny/crossref_metadata_2025 huggingface dataset:
Defect Cluster Formation in High Energy Displacement Cascades in Copper
Authors: Osetsky Yuri N. , Bacon David J.
Published: April 2011

Primary radiation damage in displacement cascades in metals has been studied extensively by atomistic simulation during the last decade. The variety of defect types observed in cascade simulation is not entirely consistent with experimental data. For example, experiments on copper show a very effective production of stacking fault tetrahedra (SFTs) but this was not observed systematically in cascade simulation. To clarify this and related issues, extensive simulation of displacement cascades in copper have been performed using two different interatomic potentials, a short-range many-body potential and a long-range pair potential. We have studied the damage created by primary knock-on-atoms of energy up to 20keV, i.e. below the energy range for formation of subcascades, at temperatures 100 and 600K. Special attention was paid to cascade statistics and the accuracy of simulation in the collision stage. The former required many simulations for each temperature whereas the latter involved a modification of the simulation method. The results on variety of clusters observed, e.g. SFTs, glissile and sessile interstitial clusters, and faulted and perfect interstitial dislocation loops, lead to conclusions on the effect of the potentials and the significant variation of the number of Frenkel pairs and clustering effects produced in different cascades under the same conditions.
Reordering and Crystallization of Silicon Carbide Amorphized by Neutron Irradiation
Authors: Snead Lance L. , Balden Martin
Published: April 2011

Densification and crystallization kinetics of bulk SiC amorphized by neutron irradiation is studied. The temperature of crystallization onset of this highly pure, fully amorphous bulk SiC was found to be between 875-885°C and crystallization is nearly complete by 950°C. In-situ TEM imaging confirms the onset of crystallization, though thin-film effects apparently alter the kinetics of crystallization above this temperature. It requires >1125°C for complete crystallization of the TEM foil. Annealing at temperatures between the irradiation and crystallization onset temperature is seen to cause significant densification attributed to a relaxation, or reordering, of the as-amorphized structure.
Unusual Change in Columnar Defect Morphology in YBCO upon Annealing
Authors: Yan Y. , Kirk M. A. , Petrean A. , Paulius L.
Published: April 2011

We show evidence from transmission electron microscopy of an unusual change in columnar defect morphology in YBCO upon annealing to 600°C. The disappearance of the nanotwinned, but not the larger scaled thermal twinned, structure is found. A removal of the large fluctuations in the diameter of the amorphous column, preserving a narrow continuous column, is surprisingly discovered. Correlations with magnetization measurements demonstrate the greater efficiency of vortex pinning at 77 K by the annealed defect structure.
Comparison of Experimental and Computational Aspects of Grain Growth in Al-Foil
Authors: Demirel Melik C. , Kuprat Andrew P. , George Denise C. , El-Dasher Bassem S. , Carlson Neil N. , Straub Galen K. , Rollett Anthony D.
Published: April 2011

Grain boundary and crystallographic orientation information of an Al-foil with a columnar grain structure is characterized by Electron Backscattered Diffraction (EBSD) technique. The starting microstructure and grain boundary properties are implemented as an input for the three- dimensional grain growth simulation. In the computational model, minimization of the interface energy is the driving force for the grain boundary motion. The computed evolved microstructure is compared with the final experimental microstructure, after annealing at 550 °C. Good agreement is observed between the experimentally obtained microstructure and the simulated microstructure. The constitutive description of the grain boundary properties was based on a 1- parameter characterization of the variation in mobility with misorientation angle.
Atomic and Electronic Structure of High Purity SiC Grain Boundary
Authors: Takuma Eriko , Ichinose Hideki
Published: April 2011

Fully relaxed SiC grain boundaries were produced by the sublimation re-crystallization method. Several kinds of grain boundaries of bi- and tri-crystals were investigated applying an atomic resolution high-voltage transmission electron microscopy (ARHVTEM). The rotation axis and the rotation angle were common tofrequently observed grain boundaries, which were, respectively, 70.5 degrees and <1120>. But boundary planes differed from each other. It was shown that the atomic bonding direction was continuous across the stable grain boundary.
Mechanism of Deformation by Intervariant Boundary Motion in Shape-Memory Materials
Authors: Pond Robert C. , Celotto Steven
Published: April 2011

The shape-memory effect relies on deformation in the martensitic state by motion of intervariant boundaries in response to an applied stress. A mechanism for this process in terms of interfacial defect generation, motion and interaction is proposed. This mechanism is conservative and is expected to operate with modest applied stresses and without thermal activation. Experimental observations of intervariant boundaries are discussed and atomistic simulations of the mechanism in such boundaries in hexagonal metals are presented.
Dendritic Growth Dynamics: Steady And Oscillatory States
Authors: Frei J.E. , Glicksman M.E. , LaCombe J.C. , Koss M.B. , Giummarra C. , Lupulescu A.O.
Published: April 2011

Microgravity dendritic growth experiments, conducted aboard the space shuttle Columbia (STS-87) in November/December 1997, are analyzed and discussed. In-situ video images now reveal that pivalic acid (PVA) dendrites growing in the diffusion-controlled environment of low-earth orbit exhibit a range of growth behaviors, including steady, transient, and oscillatory states. The observed transient features of the growth process are being studied with the objective of understanding their physical mechanisms. Some transients in the observed growth speed are thought to arise as an intrinsic aspect of the evolving dendritic pattern. Variability in the growth speed observed from a sequence of identical runs at equal supercooling suggests that self-interactions of the dendrite remain important throughout the development of the dendritic pattern. A Greens function analysis of the near-tip diffusion sources contributing to the local field at the tip suggests that strong non-local interactions exist well into the time-dependent side-branch region of real dendrites. Video data obtained at 30 fps allow the first application of discrete Fourier transform methods (Lomb periodograms) to the digitized images of dendritic growths under quiescent microgravity conditions. These observations provide evidence for the appearance of characteristic frequencies in the tip shape and its dynamical behavior. Some of the frequency bands observed coincide closely with the ratio of the dendritic tip growth speed divided by the side branch spacing. Other observed lower frequencies remain as yet unexplained. These data, and their interpretations, are discussed in this paper.
Dislocations in a Partially-Filled Skutterudite
Authors: Harper Jennifer S. , Gronsky Ronald
Published: April 2011

The partially filled skutterudite structure is a candidate thermoelectric material with the capacity for phonon scattering by the decoupled rattling of filling ions. In this transmission electron microscopy investigation of a 1.6%Ce, 1.6%Ni, 4.9%Ge, 22.8%Co, and 69.1%Sb alloy, the structure is confirmed to be of a partially-filled skutterudite, but with a number of defects. Isolated dislocation dipoles, arrays of dislocation dipoles, and a subgrain boundary are observed and characterized. An atomic structure of a dislocation dipole is also proposed, and the effect of such dislocations on thermoelectric properties is discussed.
High-resolution Electron Microscopy of grain Boundary Structures in Yttria-stabilized Cubic Zirconia
Authors: Merkle K. L. , Thompson L. J. , Bai G.-R. , Eastman J. A.
Published: April 2011

The atomic-scale structure of grain boundaries (GBs) in yttria-stabilized cubic zirconia (YSZ) was investigated by high-resolution electron microscopy (HREM). Non-stoichiometric oxides have found a wide range of applications and therefore it is of importance to explore the role of GBs and their atomic-scale relaxation modes. [001] and [110] tilt GBs were examined by HREM in highly textured thin films of YSZ grown by metal-organic chemical vapor deposition (MOCVD). In addition, a special technique was developed to also allow the HREM study of twist and general GBs. GBs and triple junctions show quite dense arrangements of cation atomic columns. The GB core structures in YSZ can be contrasted to the more open structures in stoichiometric cubic oxides, such NiO, which are characterized by a relatively large GB excess volume. This appears to be due to several factors, including the necessary rearrangement of the oxygen sublattice near GBs in a CsCl2 type structure, the redeployment of oxygen vacancies near GBs, and the segregation of Y to the GB. Relative to stoichiometric oxides, such mechanisms provide additional degrees of freedom for atomic relaxations at GBs and the development of low-energy GBs. These additional relaxation modes, which result in GB cation arrangements more akin to metallic systems, are also reflected by Burgers vector dissociations observed in low-angle YSZ GBs.
Channeling Studies of CeO2 and Ce1-xZrxO2 Films on Yttria-Stabilized ZrO2(111)
Authors: Shutthanandan V. , Thevuthasan S. , Kim Y. J. , Peden C.H.F.
Published: April 2011

Rutherford backscattering spectrometry and channeling techniques have been used to investigate the crystalline quality and interfacial properties of epitaxially grown CeO2 and Ce0.7Zr0.3O2 films on yttria-stabilized ZrO2(111) substrates. Both films appear to have high crystalline quality with minimum yield of Ce in the CeO2and Ce0.7Zr0.3O2 films determined to be 4.7% and 12.1% respectively. Visibility of more Ce atoms to the ion beam at the interface compared to the bulk of the film indicates that both films show significant disorder at the interface. The normalized angular yield curves obtained from Ce and Zr indicate that the Ce atomic rows in the CeO2 film are parallel to the Zr atomic rows in the substrates. Approximately 88% of the Zr atoms substitutionally occupy the Ce cation lattice sites in the Ce0.7Zr0.3O2 film.
Oxides Influence on Electrical Properties of Si and A2B6 Materials.
Authors: Andrukhiv Andrii , Khlvap Galina , Andrukhiv Mikhail , Belosertseva Violetta
Published: April 2011

It has been shown for the first time how atmospheric oxygen eff ects maj or electrical characteristics of MBE grown CdTe thin f ilms and CVD grown p-/p+ Si junction. I-V and C--V barrier-like characteristics indicate presence of CdO/CdTe quasi-3D microheteroj unctions and complexes at p/p+ interface.
Microstructural Effects in the Thermochromic Behavior of VO2/Al/Si Thin Film Heterostructures
Authors: Dovidenko K. , Beasor S. , Topol A. , Efstathiadis H. , Oktyabrsky S. , Shokhor S. , Naar S. , Kaloyeros A.E.
Published: April 2011

We present the results of detailed chemical and structural characterization of the VO2/Al/Si(100) thin film heterostructures fabricated by chemical vapor deposition and physical vapor deposition methods. The presence of the thermochromic behavior in the VO2 layer around 68°C and its correlation with the layer composition and structure are discussed. The study compares the structural and chemical properties of the two types of thin VO2 layers: one which exhibits a metal-insulator phase transition around 68°C, and another which fails to undergo the temperature-induced transition. The study of interfaces was carried out by transmission electron microscopy, and showed the existence of an aluminum oxide interfacial layer between VO2 and Al for the samples with the metal-insulator phase transition. The smooth VO2/Al interface and the presence of more than one VO2 monoclinic polytypes were observed for the CVD films exhibiting no phase transition.
Time Dependent Debonding of Aluminum/Alumina Interfaces under Cyclic and Static Loading
Authors: Kruzic J. J. , McNaney J. M. , Cannon R. M. , Ritchie R. O.
Published: April 2011

The structural integrity of oxide/metal interfaces is important in many applications. While most attention has focused on the debonding of oxide/metal interfaces by conducting strength and fracture toughness tests, very few investigations have looked at time dependant failure of interfaces under cyclic or static loading. Tests have been conducted on sandwich specimens consisting of 5 - 100 micron thick aluminum layers bonded between either polycrystalline or single crystal Al2O3 to determine cyclic fatigue-crack growth, as well as static loaded moisture- assisted crack-growth, properties of Al/Al2O3 interfaces. Under cyclic loading, crack growth was observed to occur predominantly by interfacial debonding, but was also observed to make excursions into the Al2O3. Static loading in a moist environment also caused interfacial cracks to deviate into the Al2O3 or alternatively to arrest. Due to the poor crack growth resistance of the Al2O3, cracks leaving the interface grew at faster rates than those at the interface. Trends in crack trajectories and crack growth rates are explained in terms of the degree of plastic constraint in the aluminum layer, the modulus mismatch, and the effects of environmental mechanisms.
Semiempirical Correlation between the Optical Band Gap of Oxides and Hydroxides and the Electronegativity of Their Constituents
Authors: Quarto Francesco Di , Santamaria Monica , Piazza Salvatore , Sunseri Carmelo
Published: April 2011

On the basis of new experimental results a previous proposed correlation between the optical band gap of oxides and the difference of electronegativity of their constituents is extended to mixed crystalline and amorphous TiO2-Fe2O3 (d,d-metal oxides) as well as to amorphous passive films grown on Al-Ta, Al-Ti, Al-Nb and Al-W alloys (sp,d-metal oxides). Moreover in analogy with previous results on anhydrous oxides, a correlation is proposed between the optical band gap of hydroxides and the electronegativities of their constituents after substituting the electronegativity of hydroxilic group to that of the oxygen. Like in the case of anhydrous oxides, two different interpolation lines have been found for sp-metal and d-metal hydroxides, respectively.
Electronic Structure of Titanium Oxide Crystal Surface with Lithium Atom on the Surface
Authors: Oshikiri M. , Aryasetiawan F. , Boerol M.
Published: April 2011

The electronic structure of the bulk TiO2 in the rutile structure, geometric and electronic structure of two dimensional titanium oxide and lithium titanium oxide layers have been investigated. Not only density functional approach within the local density approximation (LDA) but also GW approach has been tried and the LDA electronic band structures have been compared with the quasiparticle energy structures. The unit cells which include a few atomic layers and open space of more than several angstroms have been used as geometric model of the surface. The surface geometric relaxation has been investigated by the Car-Parrrinello quantum molecular dynamics method based on the plane wave basis with pseudo potential within Becke-Lee-Yang-Parr (BLYP) generalized gradient approximation (GGA) and the quasiparticle energy structure has been obtained by the GW method based on the linearized muffin tin orbital (LMTO) basis with the atomic sphere approximation (ASA). Good applicability of this hybridized first principles approach has been confirmed.
Nanoporous Ceria Films Prepared from Colloidal Suspension
Authors: Petrovsky Vladimir , Gorman Brian , Anderson Harlan U. , Petrovsky Tatiana
Published: April 2011

The influence of porosity and densification on optical properties of films on sapphire substrates that were prepared from water colloidal suspensions of small (∼5nm) particles of ceria was investigated. The colloidal ceria films have initially very porous structure (porosity about 50%) and densification starts at about 600°oC accompanied by grain growth. The concurrence of these two processes makes it difficultto interpret the results of the optical spectrophotometry, but the combination of transmittance and reflectance measurements provides enough data to separate these two influences and to calculate the porosity, particlesize and energy band gap separately. XRD, SEM, ellipsometry and mechanical profilometry were used to confirm the results obtained from the specrophotometric measurements. All these methods gave results, which are in good agreement: the change in the porosity from 50% to 15% and the particle size increased from 5 to 65nm in the temperature region from 400 to 1000°oC. An important result of the investigation is the fact that the main optical properties of the coating such as refractive index and band gap energy depend only on the porosity, but not on the grain size. The grain size influences the scattering properties of the coating, which allows the grain size to be estimated from optical measurements.
An Overview of FeRAM Technology for High Density Applications
Authors: Nagel Nicolas , Mikolajick Thomas , Kasko Igor , Hartner Walter , Moert Manfred , Pinnow Cay-Uwe , Dehm Christine , Mazure Carlos
Published: April 2011

Ferroelectric random access memories (FeRAMs) are new types of memories especially suitable for mobile applications due to their unique properties such as nonvolatility, small DRAM - like cell size, fast read and write as well as low voltage / low power behavior. Although standard CMOS processes can be used for frontend and backend / metallization processes, FeRAM technology development has to overcome major challenges due to new materials used for capacitor formation. In this paper, advantages and disadvantages of different ferroelectric materials and major development issues for high density applications are discussed. Results of a 0.5μm ferroelectric process using SrBi2Ta2O9 (SBT) as ferroelectric layer, Pt as electrode material, and 2-layer tungsten / aluminum metallization are discussed.
Surface and Size Effects in TGS, NaNO2, and DKDP Nanocrystals
Authors: Romero Juan D. , Fonseca Luis F. , Ramos Rafael , Marqués Manuel I. , Gonzalo Julio A.
Published: April 2011

Monte Carlo simulations of some typical order-disorder ferroelectrics such as TGS, NaNO2 and DKDP nanocrystals were studied using a Transverse Ising Model Hamiltonian with four-spins interactions. The microscopic parameters corresponding to this Hamiltonian were adjusted to fit the experimental polarization-temperature curves for each one of the materials in the bulk phase. Then the dependences of the ferroelectric-paraelectric phase transition temperatures, Tc, on the sizes of those crystals were studied with Monte Carlo simulations of the order-disorder system. We report a weak dependence of Tc on the size of the crystal (d) for these materials above d∼6nm. The addition of surface effects showed that the expected lowtemperature shift of Tc due to size effects, can be reverted.
Piezoresponse Measurements for Pb(Zr,Ti)O3 Island Structure Using Scanning Probe Microscopy
Authors: Fujisawa H. , Morimoto K. , Shimizu M. , Niu H. , Honda K. , Ohtani S.
Published: April 2011

Piezoresponse measurements using scanning probe microscopy (SPM) were performed for island structures at the initial growth stage of Pb(Zr,Ti)O3 (PZT) (Zr/Ti=0/100, 24/76 and 74/26) thin films prepared by metalorganic chemical vapor deposition(MOCVD). Deposition times were varied from 5s to 7min to control the size of PZT islands. When deposition times were shorter than 3min, (111)-oriented triangular-shaped PZT islands were observed before forming a continuous film. The width and height of PZT islands deposited at 3min were 160 and 70nm for Zr/Ti = 0/100, 100 and 30nm for Zr/Ti = 24/76, and 80 and 20nm for Zr/Ti = 74/26, respectively. The size of islands decreased with increasing the Zr composition. Hysteresis loops due to polarization switching were observed in the phase difference and displacement of piezoresponse measured using scanning probe microscopy (SPM). This result proves that nano-size PZT islands have weak ferroelectricity. The minimum width and height of PZT islands which showed ferroelectricity were 70 and 30nm for Zr/Ti=24/76.
Sensing Properties of Ba1划xLaxNbyTi1划yO3 (x=0.25%, y=0.25%) Thin-Film on SiO2/Si Substrate
Authors: Li B. , Lai P. T. , Li G. Q. , Zeng S. H. , Huang M. Q.
Published: April 2011

Barium lanthanum titanate-niobate (Ba1划xLaxNbyTi1划yO3) film deposited on a SiO2/Si substrate by the argon ion-beam sputtering technique has been used to fabricate a thin-film resistor and a metal-insulator-semiconductor (MIS) capacitor by standard integrated-circuit technology. Measurements show that the film resistor has superior sensitivity for visible light and a thermal sensitivity within the range 28∼400 °C, while the MIS capacitor is highly sensitive to relative humidity. The optical absorption spectrum of the film has been measured and the bandgap of the film determined. The effects of test frequency on the impedance of the film resistor at various temperatures and on the humidity-sensitive characteristics of the MIS capacitor have been investigated.
Dielectric and Piezoelectric Properties of PZT 52/48 Thick Films with (100) and Random Crystallorgraphic Orientation
Authors: Zhou Q. F. , Hong E. , Wolf R. , Trolier-McKinstry S.
Published: April 2011

Ferroelectric Pb(Zr1划xTix)O3 (PZT) films have been extensively studied for active components in microelectromechanical systems. The properties of PZT films depend on many parameters, including composition, orientation, film thickness and microstructure. In this study, the effects of crystallographic orientation on the dielectric and transverse piezoelectric properties of Pb(Zr0.52Ti0.48)O3 (PZT 52/48) films are reported. Crack free random and highly (100) oriented PZT(52/48) films up to ∼ 7 μm thick were deposited using a sol-gel process on Pt (111)/Ti/SiO2/Si and Pt(100)/SiO2/Si substrates, respectively. The dielectric permittivity (at 1kHz) for the (100) oriented films was 980-1000, and for the random films ∼ 930-950. In both cases, tanä was less than 0.03. The remanent polarization (∼ 30 μC/cm2) of random PZT films was larger than that of (100) oriented PZT films. The transverse piezoelectric coefficient (d31(eff)) of PZT films was measured by the wafer flexure method. The d31(eff) coefficient of random PZT thick films (-80pC/N) was larger than that of (100) oriented films (-60pC/N) when poled at 80 kV/cm for 15 min.
Hydrothermal Fabrication of Barium Strontium Titanate Ceramics for High-Frequency Wireless Communication Networks
Authors: Zelonka K. , Sayer M. , Hammad H. , Freundorfer A.P.
Published: April 2011

Thin films of barium strontium titanate are fabricated on alumina by a hydrothermal method. Crystalline films are produced at temperatures as low as 60°C. The relative dielectric permittivity of films with the composition Ba0.15Sr0.85TiO3 lies in the range between 150 and 220 for low frequencies (100 kHz to 1 MHz), decreasing with frequency. The loss tangent for the films increases from 0.05 to 0.15 over the same frequency range. Relative concentrations of barium and strontium in the film are controllable through the hydrothermal reaction conditions. The surface microstructure of the films is examined.
Oxide Films for Integrated Capacitors in Thin Film Functional Modules
Authors: Klee M. , Wissen D. , Keur W. , Kiewitt R. , Bausen D. , Lok P.
Published: April 2011

Single oxide films as well as complex oxide films are intensively studied for multi-chip modules with integrated passive functions. In this paper the processing and properties of oxide films such as Ta2O5, TiO2, Nb2O5, Ta2O5 -Al2O3, Ta2O5–Nb2O5 as well as complex oxide films such as BiNbO4 and Ba1划xSrxTiO3 films will be discussed with respect to their integration into thin film functional modules.
Theoretical and Experimental Studies on Retention Characteristics of Metal-Ferroelectric-Insulator-Semiconductor and Metal-Insulator -Ferroelectric-Insulator-Semiconductor Structures
Authors: Okuyama Masanori , Takahashi Mitsue , Kodama Kazushi , Nakaiso Toshiyuki , Noda Minoru
Published: April 2011

Retention characteristics of Metal-Ferroelectric-Insulator-Semiconductor(MFIS) and Metal-Insulator-Ferroelectric-Insulator-Semiconductor(M-I-FIS) structures have been investigated both theoretically and experimentally. The simulated time dependence of capacitance for the MFIS has indicated that reducing currents through the ferroelectric and the insulator layers improves the retention characteristics more effectively than choosing the insulators with larger dielectric constants. The M-I-FIS structure has been studied in order to reduce the charge injection between the metal and the ferroelectric layer in the MFIS. The simulations have indicated that the M-I-FIS can provide much longer retention time than the original MFIS, although the experimental retention time of the M-I-FIS have almost the same as that of the MFIS.
Microstructural and Electrical Properties of La Doped Ba1划xSrxTiO3 Thin Films For Tunable Microwave Device Applications
Authors: Cole M.W. , Joshi P.C. , Ngo E. , Hubbard C.W. , Lee U. , Ervin M.H.
Published: April 2011

We have investigated the structural, compositional, interfacial, surface morphological and dielectric properties of Ba0.6Sr0.4TiO3 solid solution thin films La doped from 0 to 10 mol%. The doped thin films were prepared by the metalorganic solution deposition technique using carboxylate-alkoxide precursors. After post-deposition annealing in oxygen ambient at 750 °C the films were characterized via x-ray diffraction, Auger electron microscopy, field emission scanning electron microscopy, and atomic force microscopy. The electrical measurements were achieved in the metal-insulator-metal (MIM) configuration with Pt as the top and bottom electrode. Our results demonstrated that La doping had a strong effect on the films microstructural, dielectric and insulating properties. Specifically, 1 mol% La doped BST films exhibited a lower dielectric constant, 283 and higher resistivity 31.4×1013 W-cm with respect to that of undoped BST. The loss tangent and tunability (at 100 kHz) of the 1 mol% La doped BST films were 0.019 and 21% (at E=300kV/cm) respectively.
Electrodes and Barriers for Dram and Feram: Processing, Integration, and Fundamentals
Authors: Saenger K.L. , Andricacos P.C. , Athavale S.D. , Baniecki J.D. , Cabral C. , Costrini G. , Kwietniak K.T. , Laibowitz R.B. , Lian J.J. , Limb Y. , Neumayer D.A. , Wise M.L.
Published: April 2011

Materials requirements for electrodes and barriers in high density dynamic random access memory (DRAM) and ferroelectric random access memory (FERAM) are reviewed, and some approaches to barrier materials and device geometries are described. Electrode/barrier topics covered in more detail include Pt reactivity with Si-containing barriers and dielectric overlayers, the application of a Bragg-Brentano x-ray diffraction technique to quantitatively probe Pt and Ir electrode morphology and thickness changes during ferroelectric processing, the stability of metal oxide electrode materials in reducing ambients, electrode patterning techniques (including Pt electroplating), and electrical properties of 3-D capacitors in 256k arrays as a function of top electrode annealing treatments.
200 °C Preparation of SiNx Passivation Films for PZT Ferroelectric Capacitors by Catalytic CVD
Authors: Minamikawa Toshiharu , Yonezawa Yasuto , Fujimori Yoshikazu , Nakamura Takashi , Masuda Atsushi , Matsumura Hideki
Published: April 2011

Feasibility of SiNx passivation films at low substrate temperatures prepared by catalytic chemical vapor deposition (Cat-CVD) is studied for ferroelectric nonvolatile random access memories (FRAMs). SiNx films were prepared at low substrate temperatures of 100 °C, 175 °C and 200 °C using Cat-CVD. Adjusting on flow rate ratio of SiH4/NH3, the refractive index of SiNx film, deposited at 175 °C and 200 °C, measured by ellipsometry is controlled around 2.0. SiNx films, with the refractive index around 2.0, deposited at only 200 °C show the following properties. 1) No oxidation during air exposure for 3 months was observed for the films. 2) Etching rate of the films in buffered HF is 20 nm/min. The dense SiNx film, which is resistive for oxidation in air exposure and dissolution in buffered HF, is prepared at 200 °C and the film is suitable to the passivation of ferroelectric capacitors.
Highly Stable Ir-Ta-O Electrode for Ferroelectric Material Deposition
Authors: Zhang Fengyan , Hsu Sheng Teng , Maa Jer-shen , Ono Yoshi , Hong Ying , Zhuang Weiwei , Ohnishi Shigeo , Zhen Wendong , Fujiwara Norito
Published: April 2011

Ir-Ta-O composite bottom electrode has extraordinary high temperature stability. It can maintain good conductivity and integrity even after 5min annealing at 1000 °C in oxygen ambient. The thermal stability of Ir-Ta-O on different substrates has been studied. It shows that Ir-Ta-O is also very stable on Si and SiO2 substrates. No hillock formation and peelings of the bottom electrode were observed after high temperature and long time annealing in O2 ambient. SEM, TEM, XRD, and AES have been used to characterize the Ir-Ta-O film and the interfaces between Ir-Ta-O bottom electrode and Si or SiO2 substrate. The composition and conductivity changes of the electrode during oxygen ambient annealing and the interdiffusion issue will be discussed. Furthermore, Ir-Ta-O/SiO2/Si capacitor with 30Å gate oxide was fabricated and the C-V and I-V characteristics were measured to confirm the stability of Ir-Ta-O on thin gate oxide.
Degradation of Ferroelectric Pb(Zr,Ti)O3 Under Reducing Conditions
Authors: Shimakawa Yuichi , Kubo Yoshimi
Published: April 2011

The degradation mechanism of Pb(Zr,Ti)O3 (PZT) under reducing conditions was revealed. In contrast to the significant decrease in the sample weight of SrBi2Ta2O9 due to decomposition, the weight of Pb(Zr,Ti)O3 samples change little during H2-annealing at typical process temperatures. Although no apparent changes were detected by thermogravimetric and x-ray diffraction measurements after annealing, the PZT material did actually change. The main mechanism of the degradation is introduction of oxygen defects into the materials. The oxygen defects produce a donor level within the band gap, and light absorption by this donor level accounts for the change in sample appearance from white to black. Different endurance behaviors of materials against reducing conditions were also found: PbZrO3 decomposes through oxygen dissociation more easily than PbTiO3. Oxygen atoms in PbZrO3 are more weakly bonded to Zr than to Ti in PbTiO3 because of a significant anti-bonding component in the hybridized orbitals.
The Properties of Mfmos and MFOS Capacitors with High K Gate Oxides for one Transistor Memory Applications
Authors: Li Tingkai , Hsu Sheng Teng , Ying Hong , Ulrich Bruce
Published: April 2011

MFMOS and MFOS (M: Metal, F: Ferroelectrics, O: Oxide, S: Silicon) capacitors with high k gate oxides, such as ZrO2, HfO2 thin films, have been fabricated for one transistor memory applications. Experimental results showed that ZrO2 and HfO2 have no serious reaction or diffusion into silicon substrate. Due to their high dielectric constant, the operation voltages of MFMOS capacitors are reduced. The MFMOS capacitor exhibits 2V memory window. For lead germanium oxide (PGO) on ZrO2 and PGO on HfO2 MFOS memory cells the memory windows are 1.8 V and 1.6 V, respectively, which are large enough for one-transistor memory applications. The basic mechanism for one-transistor memory applications was also discussed.
Investigation of Dead Layer Thickness in SrRuO3/Ba0.5Sr0.5TiO3/Au Thin Film Capacitors
Authors: Sinnamon L. J. , Bowman R. M. , Gregg J. M.
Published: April 2011

Thin film capacitors with barium strontium titanate (BST) dielectric layers of 7.5 to 950 nm were fabricated by Pulsed Laser Deposition. XRD and EDX analyses confirmed a strongly oriented BST cubic perovskite phase with the desired cation stoichiometry. Room temperature frequency dispersion (ε100 kHz / ε100 Hz) for all capacitors was greater than 0.75. Absolute values for the dielectric constant were slightly lower than expected. This was attributed to the use of Au top electrodes since the same sample showed up to a threefold increase in dielectric constant when Pt was used in place of Au. Dielectric constant as a function of thicknesses greater than 70 nm, was fitted using the series capacitor model. The large interfacial parameter ratio di / εi of 0.40 ± 0.05 nm implied a significant dead-layer component within the capacitor structure. Modelled consideration of the dielectric behaviour for BST films, whose total thickness was below that of the dead layer, predicted anomalies in the plots of d/ ε against d at the dead layer thickness. For the SRO/BST/Au system studied, no anomaly was observed. Therefore, either (i) 7.5 nm is an upper limit for the total dead layer thickness in this system, or (ii) dielectric collapse is not associated with a distinct interfacial dead layer, and is instead due to a through-film effect.
Characterization of Conductive RuO2 Thin Film as Bottom electrodes for Ferroelectric Thin Films
Authors: Bhaskar S. , Dobal P. S. , Majumder S. B. , Katiyar R. S.
Published: April 2011

Ruthenium Oxide (RuO2) thin films were prepared on silicon substrates by solution chemistry technique. X-ray Diffraction (XRD), Atomic Force Microscopy (AFM), micro-Raman, X-ray photoelectron spectroscopy (XPS), and four probe Van-der-paw technique were used for the film characterization. X-ray analysis shows a rutile structure in these films. The films annealed at 700°C showed lowest resistivity of 29 × 10−5 ohm-cm. The presence of Eg, A1g, and B2g modes is consistent with the Raman spectrum of rutile phase. These modes as well as additional unidentified band at about 477 cm−1 were investigated by temperature dependent Raman studies. Based on the result, band at 477 cm−1 that disappears above 370 K is attributed to hydrated RuO2 present in the films. XPS analysis show stoichiometric rutile RuO2 present in the films. Small concentrations of RuCl3, RuO3 and hydrated RuO2 were also detected. Pb0.9La0.15TiO3 (PLT15) thin films were deposited on RuO2/Si substrates and characterized for its ferroelectric properties to demonstrate that solution deposition technique offers an alternative approach for preparing high quality RuO2 bottom electrodes.
Properties of Au/Pb(Zr0.52Ti0.48)O3/ Bi4Ti3O12/p-Si Ferroelectric Memory Diodes
Authors: Yu Jun , Wang Hua , Dong Xiaomin , Zhou Wenli , Wang Yunbo , Zhu Lili
Published: April 2011

A ferroelectric memory diodes that consists of Au/Pb(Zr0.52Ti0.48)O3/Bi4Ti3O12/p-Si multilayer configuration was fabricated by pulsed laser deposition (PLD) technique. The ferroelectric properties and the electrical characteristics of the ferroelectric film system were investigated. The polarization-voltage curve of Pb(Zr0.52Ti0.48)O3/Bi4Ti3O12 thin films system had an asymmetry hysteresis loop with Pr=20μC/cm2 and Ec=48 kV/cm, and the decay in remnant polarization was only 10% after 109 switching cycles. The C-V curve and the I-V curve showed memory effects derived from the ferroelectric polarization of PZT/BIT films. The current density was 6.7×10−8A/cm2 at a voltage of +4V, and the conductivity behavior is discussed. The results suggested that the growth of the BIT ferroelectric layer is helpful to good ferroelectric properties, fatigue and capacitance retention characteristics.
The Effect of Forming Gas Annealing on Pt/(Ba,Sr)TiO3/Pt Thin Film Capacitors for Future Dram Applications: Electrical Properties and Degradation Mechanisms
Authors: Baniecki J. D. , Parks C. , Laibowitz R.B. , Shaw T. M. , Lian J.
Published: April 2011

We have used electrical characterization and secondary ion mass spectroscopy (SIMS) to investigate the influence of hydrogen or deuterium (H/D) on the degradation of the electrical properties of Pt/Ba0.7Sr0.3TiO3/Pt thin film capacitors after forming gas exposure. Deuterium SIMS depth profiling shows that high deuterium concentrations can be incorporated into Pt/BSTO/Pt capacitors after forming gas annealing. The increase in H/D concentration in the film is accompanied by an increase in the leakage and dielectric relaxation current density. Voltage offsets in the capacitance-applied voltage (C-VA) characteristics after forming gas exposure at lower temperatures (20 °C) and a suppression in the capacitance density near zero applied D.C. bias after forming gas exposure at higher temperatures, suggests that one effect of forming gas exposure to Pt/BSTO/Pt thin film capacitors is to introduce positive space charge into the BSTO film. Using an equivalent model for a ferroelectric thin film capacitor, which incorporates lower permittivity interfacial layers and a nonlinear electric field-electric displacement relationship for the film interior, the effects of a uniform distribution of positive space charge on the theoretical C-VA and current density applied voltage (J-VA) characteristics are investigated. It is shown the model can account for many of the observed changes that occur in the experimental C-VA and J-VA characteristics after forming gas exposure.
Room Temperature ZnO/Zn0.8Mg0.2O Resonant Tunneling Devices For Microwave Applications
Authors: Inumpudi Aravind , Iliadis Agis A. , Choopun Supab , Vispute R. D. , Venkatesan T.
Published: April 2011

A ZnO/Zn0.8Mg0.2O double barrier resonant tunneling device (DBRTD) is reported here for the first time. The structure consists of 6 nm ZnO quantum wells and 7 nm Zn0.8Mg0.2O barriers grown by pulsed laser deposition (PLD) on c-cut sapphire substrates. Negative differential resistance (NDR) peaks were obtained at room temperature. The structure is developed by using an indium-tin oxide (ITO) layer both as the back contact electrode and as an etch-stopping layer. The PLD growth quality, wet etching processing for developing the mesa structure, and the I-V characteristics of the device are reported.
Ferroelectric Na0.5K0.5NbO3 Films for Voltage Tunable Microwave Devices
Authors: Cho Choong-Rae , Grishin Alex , Andrèasson Johanna , Lindbäck Ture , Abadei Saeed , Gevorgian Spartak
Published: April 2011

Single phase Na0.5K0.5NbO3 (NKN) thin films have been pulsed laser deposited on Al2O3(0112), LaAlO3(001), and MgO(001) single crystal substrates as well as on the SiO2/Si(001) wafers to demonstrate films feasibility for voltage tunable microwave device applications. NKN film texture has been found to be quite different on three different single crystals: highly c-axis oriented on Al2O3, “cube-on-cube” epitaxial quality on LaAlO3, bi-axial textures on MgO, while NKN films grown on Si substrate with various thickness of SiO2 buffer layer possess highly c-axis oriented quadrupled structure. NKN film interdigital capacitors fabricated onto single crystal oxide substrates showed tunability of 30-40 % and dissipation factor of 0.01-0.02 at 1 MHz and applied electric field of 100kV/cm. Microwave frequency measurements for NKN/Si varactors yield 13 % tunability and dielectric loss tanδ as low as 0.012 at 40 GHz under 200 kV/cm applied bias.
Characteristics of Microwave Absorption of Ni-Zn-Ferrite/Sic Hemi-Crystallized Composites
Authors: Nakanishi Makoto , Shibuya Tomonori , Fujii Tatsuo , Takada Jun
Published: April 2011

In order to develop wide-band microwave absorbers we tried to prepare composite absorbers between the magnetic loss (Ni-Zn-ferrite) and the dielectric loss (SiC) materials. The dry or wet mixtures of Ni-Zn-ferrite and polycarbosilane (PCS) were cured in air and were then subjected to pyrolysis forming of the ferrite composites. The composites produced by the wet mixing had granular structure: the PCS surrounding the ferrite particles suppressed the sintering and the grain growth of the ferrite composites during pyrolysis. The matching frequency due to the magnetic loss linearly increased with increasing the PCS content. Moreover the ferrite/SiC hemi-crystallized composite cured at 473 K for 24 hours showed wide-band absorption spectrum having the both magnetic and dielectric losses.
Processing and Characterization of Pure and Doped Ba0.6Sr0.4TiO3 Thin Films for Tunable Microwave Applications
Authors: Joshi P. C. , Cole M. W. , Ngo E. , Hubbard C. W.
Published: April 2011

Ba1−xSrxTiO3 thin films are being developed for high-density DRAM devices. The nonlinearity of its dielectric properties with respect to applied dc voltage makes it attractive for tunable microwave devices. For successful integration into microwave devices, extremely reliable Ba1−xSrxTiO3 thin films with enhanced dielectric and insulating properties are desired. Properties of Ba1−xSrxTiO3are typically varied by changing the Ba/Sr ratio and/or doping. In this paper, we reports on the effects of acceptor and donor doping on the microstructural and electrical properties of Ba0.6Sr0.4TiO3 (BST) thin films deposited by metalorganic solution deposition technique on platinum coated silicon substrates. The effects of doping on structure, dielectric permittivity, dielectric loss tangent, and leakage current have been analyzed. The structure of the films was analyzed by x-ray diffraction (XRD). The surface morphology of the films was examined by field emission scanning electron microscope (FESEM) and atomic force microscope (AFM). The electrical measurements were conducted on MIM capacitors using Pt as the top and bottom electrode. It was possible to significantly improve the dielectric loss and leakage current characteristics, and control the dielectric tunability by doping the BST thin films.
Temperature-Dependent Internal Friction in Silicon Nanoelectromechanical Systems
Authors: Evoy Stephane , Olkhovets Anatoli , Carr Dustin W. , Parpia Jeevak M. , Craighead Harold G.
Published: April 2011

The mechanical properties of micro- and nanomechanical systems are of interest from both fundamental and technological standpoints. High-frequency mechanical resonators presenting high quality factors are of interest for the development of sensitive force detecting devices, and highly efficient RF electromechanical filters and oscillators. Internal losses are the combination of both extrinsic and intrinsic issues that must be well understood for the optimization of resonator quality, and for the experimental access to fundamental nanoscopic mechanical phenomena. The temperature dependent internal friction in 1-10 MHz paddle oscillators is reported. Quality factors as high as 1000 and 2500 are observed at room temperature in metallized and non-metallized devices, respectively. Internal friction peaks are observed in all devices in the T = 160-180 K range. The position of those peaks is consistent with the Debye relaxation of previously reported surface and near-surface phenomena.
On the Fracture Toughness of Polysilicon MEMS Structures
Authors: Kahn H. , Ballarini R. , Heuer A.H.
Published: April 2011

The mechanical properties of micromachined polysilicon are of great interest to designers of microelectromechanical systems (MEMS) devices. Numerous investigations have been carried out to determine the strength of MEMS-fabricated polysilicon structures, and the experimental results vary widely, depending on the experimental techniques, specimen geometries, and processing conditions. In order to determine whether these variations are inherent to all mechanical properties of MEMS materials, the fracture toughness, Kcrit, of micromachined polysilicon has been investigated, using a wide range of material microstructures (microstructure is used here in the Materials Science sense to mean the grain structure visible in a microscope, and not in the MEMS sense to mean small structures). Since fracture toughness is a fundamental materials property, whether or not it varies with microstructure and processing is an interesting question. We have confirmed that Kcrit is not a microstructure-sensitive property, using surface-micromachined specimens with sharp pre-cracks which are integrated with electrostatic actuators. The measured Kcrit is 1.0±0.1 MPa √m for a wide range of miscrostructures.
The Influence of Fabrication Governed Surface Conditions on the Mechanical Strength of Thin Film Materials
Authors: Chasiotis Ioannis , Knauss Wolfgang G.
Published: April 2011

The mechanical strength of thin polysilicon films has been examined in connection with exposure to Hydrofluoric Acid (HF). It is found that surface roughness as characterized by groove formation at grain boundaries depends on the HF release time. Surface undulations and crevasses related to grain structure result in reduced fracture strength and induced errors into the effective elastic modulus measurements - especially when the latter is determined from flexure configurations. Extensive exposure to HF results in material degradation, as evidenced by a transition from a transgranular to an intergranular failure manner and a corresponding drastic drop of the film strength with attendant increase of porosity.
Anelastic Creep Phenomena in Thin Metal Plated Cantilevers for MEMS
Authors: Vickers-Kirby Deborah J. , Kubena Randall L. , Stratton Frederic P. , Joyce Richard J. , Chang David T. , Kim Jinsoo
Published: April 2011

During the past several years, we have developed high displacement sensitivity tunneling accelerometers using surface micromachining and metal electroplating techniques. These devices consist of a Au tunneling tip fabricated below a 1-2 μm thick metal cantilever beam of electroplated Ni or Au. A thin film of e-beam evaporated Au on the underside of the cantilever serves as the tunneling counter electrode. In operation, a 100mV bias is applied across the tunneling gap. A larger turn-on voltage is also applied between the cantilever and a control electrode, located on the substrate, to deflect the cantilever and maintain a constant tunneling current of 1 or 10 nA. Typical deflections of the end of 100 μm-long and 250 μm-long cantilevers are 0.5μm during operation. We have observed that the turn-on voltage decreases over time for most devices with a larger drop observed for the Au cantilevers. In all cases, the initial decay of the turn-on voltage was almost completely recoverable after the device was turned off for 24 hrs. This decay was not found to be strongly dependent on the magnitude of the tunneling current, but could be significantly reduced by pre-stressing the cantilever before operation. Finally, a vacuum anneal at 100°C influences the measured temperature dependence of the turn-on voltage. The observed effects appear to be consistent with fatigue and creep phenomena in the cantilevers. These effects are reversible at room temperature and are dependent on the stress and temperature history of the devices. A comparison is made between metal plated and all-Si structures.
Defects and Failure Modes in PZT Films for a MEMS Microengine
Authors: Bahr D.F. , Crozier B.T. , Richards C.D. , Richards R.F.
Published: April 2011

Piezoelectric films for a MEMS microengine have been deposited using solution deposition routines onto platinized silicon wafers. These films are used as membranes above a bulk micromachined cavity. A dynamic bulge tester and interferometer were used to characterize the deformation of the films when pressurized. The mechanical strain at failure, as well as the fatigue behavior, have been characterized. Membranes between 300 and 500 nm thick have been shown to sustain mechanical fatigue damage over approximately 10 million cycles at strains of 30% of the monotonic failure strain. Defects in the films due to growth and thermal stresses during processing, and their role in membrane failure, are identified. Crack growth is demonstrated in these films by compliance measurements during fatigue testing, and interfacial failure is identified between the PZT and Pt layers.