bluuebunny/crossref_metadata_2025 huggingface dataset:
Curvature Model for an Ion-Machined Free-Standing Thin Film MEMS Device
Authors: Johnson H.T. , Bierden P. , Bifano T. G.
Published: April 2011

The connection between processing effects and curvature of a free-standing poly-Si thin film MEMS structure is analyzed theoretically and compared to experimental data. Estimates are made for the strain resulting from processing and post-processing effects including Phosphorus implantation and chemically neutral ion-beam machining. The inferred strain distribution is used to predict the curvature of the free-standing structure upon release from its host substrate. Curvature predictions agree closely with experimental measurements for particular choices of the processing strain magnitudes. The analysis procedure is proposed as a means to determine the through-thickness stress distribution in a free-standing structure. The ion-beam machining procedure is found to be a useful method for planarizing free-standing thin film structures with undesirable curvature due to process-induced stress.
Asymmetrical Polysilicon Electrothermal Microactuators for Achieving Large In-Plane Mechanical Forces and Deflections
Authors: Kolesar Edward S. , Allen Peter B. , Boydston Noah C. , Howard Jeffery T. , Ko Simon Y. , Ruff Matthew D. , Wilken Josh M. , Wilks Richard J.
Published: April 2011

This research focuses on the design and experimental characterization of two types of asym- metrical MEMS electrothermal microactuators. Both MEMS polysilicon electrothermal microac- tuator designs use resistive (Joule) heating to generate thermal expansion and movement. Deflection and force measurements as a function of applied electrical power are presented.
Phenomenological Model of Non-Evaporated Getter for Micro-electromechanical Systems (MEMS) Applications
Authors: Kondoleon Caroline A. , Marinis Thomas F.
Published: April 2011

There has been increasing interest in the development and use of micro-electromechanical systems (MEMS) for various applications. Some MEM devices such as gyroscopes, accelerometers and bolometers, must be sealed under vacuum, at pressures below 10 millitorr, for efficient operation. A gas absorbing material (getter) is placed in the packages of these devices, to help maintain vacuum levels over service lives of many years. Heating under vacuum, just prior to sealing the package, activates getter, of this type. This study was undertaken to develop a model that could be used to estimate the quantity of getter needed as well as optimize the activation process subject to process constraints on time and temperature.

The material studied was a titanium and zirconium-based alloy (7:3 by weight) non-evaporable getter in the form of strips produced by SAES Getters. The zirconium alloy consisted of zirconium (70.0%), vanadium (24.6%) and iron (5.4%) by weight. The getter was analyzed under different ambient conditions of temperature, time and atmospheric pressure. Auger electron spectroscopy (AES) depth profiling was used to analyze the diffusion depth of the contaminant gases absorbed by the getter material under each condition. The data acquired from the depth profiles were fit to a simple diffusion model. This model is currently being validated, by activating the getter material under various ambient conditions, and measuring pressures and gas compositions inside packages using a residual gas analyzer (RGA). The utility of this model for optimization of getter activation and estimating package vacuum levels over time will be discussed.
R&D of Coated Conductors in Japan
Authors: Shiohara Yuh , Izumi Toru
Published: April 2011

The recent achievements of critical current densities in excess of 1MA/cm2 at 77K in YBCO films deposited over appropriate bi-axially textured buffer layers/metal substrates have stimulated interest in the potential future applications of coated conductors at liquid nitrogen temperature and high magnetic fields, which are called as the next/second generation tape conductors. Several different processes for obtaining the bi-axially textured buffer layers/metal substrates as well as thicker film deposition processes and non-vacuum processes are reviewed. This paper reviews the research goals of the project including the recent development of the related research by individual research group in Japan.
Trapped Magnetic Field of a Mini - Bulkmagnet using YBaCuO Superconductors
Authors: Fujimoto Hiroyuki , Kamijo Hiroki
Published: April 2011

We fabricated a mini-superconducting bulk magnet of 200 mm × 100 mm, consisting of 18 square bulks, 33 mm on a side and 10 mm in thickness, and magnetized the mini-magnet by field cooling. The mini-magnet showed the trapped magnetic field of larger than 0.1 T on the surface of the outer vessel of the magnet. The present preliminary study discusses the possibility of superconducting bulk magnets for the Maglev system, and trapped magnetic field properties of the mini-bulkmagnet using YBaCuO superconductors at 77K.
Fabrication of Large Melt-textured RE-Ba-Cu-O (RE = Gd, Dy) Superconductors and Their Trapped Magnetic Fields
Authors: Nariki Shinya , Sakai Naomichi , Murakami Masato
Published: April 2011

We have succeeded in synthesizing RE-Ba-Cu-O (RE = Gd and Dy) bulk superconductors with excellent field trapping properties. Large c-axis oriented single-domain Gd-Ba-Cu-O bulk samples with Ag addition were melt-textured under controlled oxygen partial pressure of 1.0%. The Gd-Ba-Cu-O sample 50 mm in diameter could trap a high flux density of 2.4 T at 77 K. In addition, we measured the trapped field between two Gd-bulks in order to minimize the demagnetizing effect and found that it reached 3.3 T. The single-domain Dy-Ba-Cu-O/Ag bulk 48 mm in diameter was also fabricated in air and its trapped field was 1.9 T at 77 K.
High Pressure Synthesis of RuSr2MeCu2O8 (Me = Ho or Y)
Authors: Ruiz-Bustos R. , Gallardo-Amores J. M. , Morán E. , Attfield J. P. , Sáez-Puche R. , Alario-Franco M. A.
Published: April 2011

The synthesis at high pressures ( ∼60 Kbar) and high temperatures (∼1100 °C) of the title new ruthenates has been achieved and the materials compared to the gadolinium analogue. The structure remains tetragonal (S.G. P4/mmm) and the cell parameters linearly decrease following the lanthanide contraction. Preliminary results concerning the complex magnetic properties of these materials, where superconductivity, antiferromagnetism and a superimposed ferromagnetic ordering coexist, are presented.
La2-xSrxCuO4-σ ceramics: synthesis, oxygen mobility and perspectives of catalytic applications
Authors: Mazo Galina N. , Shlyakhtin Oleg A. , Savvin Stanislav N.
Published: April 2011

Two special processing procedures based on freeze-drying synthesis have been developed in order to obtain fine (100nm) single phase LaSrCuO4−σ powders and dense ceramics. The rate of phase formation is strongly influenced by the composition of the salt precursor while the most crucial factors are heating rate and PO2 during decomposition. Studies of oxygen mobility in La2−xSrxCuO4−σ performed by dynamic-thermal O18-isotope exchange method revealed that all ceramic samples possess substantial catalytic activity in the isotope exchange reaction between oxygen molecules 32O2 and 36O2. Besides, substitution of La for Sr in La2−xSrxCuO4−σ (x =1) results in the decrease of oxygen release onset temperature from 460 to 380°C. Such a dependence correlates quite well with data on diffusion coefficients calculated for various x from the results of coulometric titration experiments. Samples with x=1 demonstrated also good catalytic activity in the reaction of CO oxidation.
Proton Beam Texturing of Superconducting YBaCuO Ceramics
Authors: Kalanov Makhmud , Ibragimova Elvira M.
Published: April 2011

Resistive superconducting (SC) transition, current-voltage characteristics, and X-ray diffraction (XRD) of YBaCuO ceramics have been studied after exposure to 18 MeV proton beam at 300 K. In the interval of 1013 −5×1014 cm−2 the irradiation induced oxygenation of weak intergrain contacts and grain alignment, anisotropy and broadening of SC-transition measured along and across the proton beam, and residual magnetization were found. The proton induced anisotropic texture is responsible for the critical current increase at 77 K and the resistivity decrease at 90–200 K. In a higher dose interval of 1013 −1015 cm−2 the SC-transition parameters degrade and the resistivity increases, depending on a texture degree, weak intergrain links become deoxygenated and no texture occurs. The magnetization (pinning) and the anisotropy of SC-transition can be due to localization of charges at the proton induced defects (mostly in oxygen sublattices).
A mesoscale strength model for silica-filled PDMS
Authors: Hanson D. E.
Published: April 2011

We present a mesoscale model that describes the tensile stress of silica-filled polydimethylsiloxane (PDMS) under elongation. Atomistic simulations of a single chain of PDMS, interacting with itself and/or a hydroxylated silica surface provide estimates of the microscopic forces required to stretch or uncoil a chain of PDMS, or detach it from a silica surface Using these results, we develop a mesoscale, inter-particle strength model for uncrosslinked, silica-filled PDMS. The strength model includes these atomistic forces, as determined from the simulations, a small entropic component, and a Gaussian probability distribution to describe the distribution of chain lengths of PDMS strands connecting two silica particles and the chain lengths in the free ends. We obtain an analytic stress/strain expression whose predictions agree with experiment.
Fractal Shape Analysis of Tire Debris Particles: Preliminary Results and Applications
Authors: Camatini Marina , Crosta Giovanni F , Corbetta Gaia M , Ottin-Bocat Mara , Ambrosio Stefano , Giuliani Gianpaolo , Cencetti Simone , Regazzoni Claudia
Published: April 2011

Particles of tread rubber debris produced by laboratory wear tests are imaged by light microscopy. The fractal dimension, DF, of the image perimeter is estimated. The sensitivity of DF with respect to the image acquisition and processing parameters is determined. Particles belonging to two types of undifferentiated debris, low severity (LS) and rasping (R), respectively, are analyzed. The values of DF have distributions, which, if suitably interpreted, allow the identification of either debris type with the following conditional probabilities: pLS|LS = 0.71 and pR|R = 0.81. The procedure can be eventually applied to environmental impact studies.
Design of pH Sensitive Materials for On/Off Release of Thrombolytic and Anticoagulant Drugs
Authors: Thornton Angela M. , Brazel Christopher S.
Published: April 2011

An experimental study was conducted to determine the mechanisms of transport for delivery of cardiovascular agents using a pH-sensitive hydrogel as the carrier. Copolymer gels based on hydrophilic (2-hydroxyethyl methacrylate) and polybasic (N,N-diethylaminoethyl methacrylate) monomers were formed as membranes and analyzed for their potential to control the diffusion of model solutes as well as heparin and streptokinase. The polybasic materials were selected because they would allow drug delivery to be triggered by microenvironmental pH fluctuations around the site of a blood clot. In slightly basic solutions, the polymers remained in a thermodynamic state of phase-separation, while the polymer absorbed more solution and the mesh size increased once the pH was less than the pKb of the polybasic moiety. The hydrogels' equilibrium swelling ratios were determined as a function of pH, and the mesh sizes were determined by rubber elasticity measurements. Diffusion of model solutes, as well as heparin, was studied using side-by-side diffusion cells to determine the influence of gel morphology and mesh size on the screening of the solutes. Streptokinase release from these gels was modulated by environmental pH.
Microstructural Characterization of Polyanhydride Blends for Controlled Drug Delivery
Authors: Shen Elizabeth E. , Chen Hsin-Lung , Narasimhan Balaji
Published: April 2011

This research examines the microstructure of polyanhydride blends for use in drug delivery devices. Atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS) studies were performed on the homopolymers and blends of the polyanhydrides poly(1,6-carboxyphenoxy hexane) (CPH) and poly(sebacic anhydride) (SA). AFM of the CPH/SA blends 20:80, 50:50, and 80:20 showed distinct patterns indicating spinodal decomposition and phase separation on the micron-scale. Because it has been shown that incorporated drugs will thermodynamically partition into phase-separated domains depending on their hydrophobicity, polyanhydride blends will be able to encapsulate larger bioactive compounds including nucleotides, proteins, and vaccines. Preliminary SAXS studies of the CPH/SA blend systems provide information on the crystalline morphology of the polymer. A peak shift to a lower q from poly(SA) to the blends indicates that the poly(CPH) is incorporated into and causes swelling of the interlamellar amorphous regions of poly(SA).
Functional Recovery Following Spinal Cord Hemisection Mediated by a Unique Polymer Scaffold Seeded with Neural Stem Cells
Authors: Lavik Erin , Teng Yang D. , Zurakowski David , Qu Xianlu , Snyder Evan , Langer Robert
Published: April 2011

A dual scaffold structure made of biodegradable polymers and seeded with neural stem cells has been developed to address the issues of spinal cord injury including axonal severance and the loss of neurons and glia. The general design of the scaffold is derived the structure of the spinal cord with an outer section which mimics the white matter with long axial pores to provide axonal guidance and an inner section seeded with neural stem cells to address the issues of cell replacement and mimic the general character of the gray matter. The seeded scaffold leads to improved functional recovery as compared with the lesion control or cells alone following spinal cord injury.
Tunable Optical Gain from Soluble Thiophene-Based Oligomers
Authors: Anni M. , Gigli G. , Zavelani-Rossi M. , Gadermaier C. , Lanzani G. , Barbarella G. , Favaretto L. , Cingolani R.
Published: April 2011

Tunable optical gain is demonstrated, through pump and probe measurements, in spin coated neat films of soluble S,S-dioxide oligothiophenes with different functionalization pattern. The molecular functionalization with alkyl and aryl groups allows us to obtain photoluminescence efficiency up to 70%, good chemical stability, high solubility and tunable gain along the visible range from 470 nm to 660 nm. The gain cross section is up to 9*10-18 cm2. The gain relaxation dynamic is studied through time resolved pump and probe measurements. A comparison with some of the best organic materials for laser application is presented. From these results we conclude that thienyl-S,S-dioxide oligothiophenes are interesting materials for applications to organic lasers and amplifiers.
The Effect of Surface Preparation on the Structure and Electrical Transport in an Organic Semiconductor
Authors: Kosbar Laura L. , Dimitrakopoulos Christos D. , Mascaro Debra J.
Published: April 2011

Self-assembled monolayers (SAMs) with a variety of structures and terminal groups were evaluated as underlayers for pentacene deposition. It was found that the most critical factor in the formation of highly oriented thin film pentacene with large grain size was the geometric structure of the monolayer. Monolayers with terminal bonds parallel to the surface produce large pentacene grains with an angular rather than the dendridic structure normally observed on octadecyltrichlorosilane (OTS) coated substrates. The grain size, X-ray scattering, carrier mobility, and current on/off ratios are all improved with monolayers of the appropriate geometry.
The First Example of a Polythiophene Bearing Fused Tetrathiafulvalene Units
Authors: Skabara Peter J. , Roberts Donna M. , Ray Asim K. , Umare Suresh S. , Hassan Aseel K. , Nabok Alexey V. , Müllen Klaus
Published: April 2011

The polymerization of a fused 2,5-dibromothieno-TTF derivative by Yamamoto procedures gave a highly electroactive polymer; doping the material with TCNQ increased the conductivity of the polymer by approximately two orders of magnitude.
Polarized Electroluminescence in Double Layer LEDs with Perpendicularly Oriented Polymers
Authors: Bolognesi A. , Botta C. , Facchinetti D , Jandke M. , Strohriegl P. , Kreger K. , Blumstengel S.
Published: April 2011

We have prepared and characterized a light emitting diode (LED) with the active film formed by two polymers emitting in two different regions: in the yellow-green and in the red range of the visible spectrum. The two polymers are polyparaphenylenevinylene (PPV) and poly[3-(6-methoxyhexyl)thiophene] (P6OMe) respectively. P6OMe was spin coated on a PPV layer previously oriented and was also oriented by means of the rubbing technique in the direction perpendicular to the PPV orientation. The polarized electroluminescence obtained from this device shows yellow-green emission from PPV, or red from P6OMe depending on the orientation of the analyzer.
Synthesis and Characterization of Poly(N-alkyl-2,7-carbazole)s: Blue Light-Emitting Materials
Authors: Morin J.-F. , Leclerc M. , Lévesque I. , D'Iorio M.
Published: April 2011

The synthesis of a new class of π-conjugated based on N-alkyl-2,7-carbazole is reported. Two different synthetic pathways were used to obtain 2,7-functionalized carbazole units. The first pathway leads to N-alkyl-2,7-dichlorocarbazole which undergoes a Yamamoto coupling to obtain the homopolymer. The second synthetic method provides N-alkyl-2,7-diiodocarbazole. This monomer allows the utilization of more versatile synthetic tools such as Suzuki and Stille couplings to obtain highly regioregular copolymers. Poly(N-(2-ethylhexyl)-2,7-carbazole) (PEHC) prepared using Yamamoto coupling shows strong pure blue photoluminescence (437 nm) and electroluminescence (432 nm, 225 cd/m2) with no excimer formation.
Silole Derivatives with a High and Non-dispersive Electron Mobility, and a 100 % Photoluminescence Quantum Efficiency
Authors: Murata H. , Malliaras G. G. , Uchida M. , Shen Y. , Kafafi Z. H.
Published: April 2011

Non-dispersive and fast electron transport was realized for an amorphous, vapor deposited film of 2,5-bis(2',2''-bipyridin-6-yl)-1,1-dimethyl-3,4-diphenylsilacyclopentadiene in ambient and inert atmospheres. An electron mobility of 2×10−4cm2/Vs was measured by time-of-flight at an electric field of 6×105V/cm. This mobility is more than two orders of magnitude larger than that of the most widely used electron transporter, tris(quinolin-8-olato) aluminum (III), in molecular organic light-emitting devices (MOLEDs). Another silole derivative, namely 1,2-bis (1-methyl-2,3,4,5,-tetraphenylsilacyclopentadienyl)ethane, exhibits bright fluorescent blue-green light with an absolute quantum yield close to 100 % in the solid state. MOLEDs composed of stacked neat films of these two silole derivatives and a hole transporter show a significantly low operating voltage and an external quantum efficiency of 4.8 %, close to the theoretical limit.
Thiophene Oligomer and NTCDI Semiconductors with High Field-effect Transistor On/off Ratios
Authors: Katz Howard E. , Lovinger Andrew J. , Hong X. Michael , Johnson Jerainne
Published: April 2011

Organic semiconductors are of continued interest for low-cost display drivers and logic elements. Field-effect transistors (FETs) with organic semiconductor channels have been fabricated in arrays to drive electrophoretic display pixels[1] and polymer dispersed liquid crystals (http://www.research.philips.com/pressmedia/releases/000901a.html). Complementary logic elements and shift registers containing hundreds of organic-based FETs have been produced[2], and high-speed organic circuits have been fabricated on polyester substrates.[3] The source and drain electrodes of individual FETs have been patterned using microcontact printing and inkjet methods[4] to give extraordinary aspect ratios. Inorganic[5] and hybrid[6] materials have been deposited as FET semiconductors using the methods of “organic electronics”. Organic FET channels have been harnessed to demonstrate ambipolar transport[7], chemical sensitivity[8], superconductivity[9], and electrically pumped lasers[10].
Role of Surfaces and Interfaces for the Electronic Properties of Conducting Oxides
Authors: Klein Andreas
Published: April 2011

Transparent conductive oxides (TCOs) are generally considered as degenerate semiconductors doped intrinsically by oxygen vacancies and by intentionally added dopants. For some applications a high work function is required in addition to high conductivity and it is desired to tune both properties independently. To increase the work function, the distance between the Fermi energy and the vacuum level must increase, which can be realized either by electronic surface dipoles or by space charge layers. Photoelectron spectroscopy data of in-situ prepared samples clearly show that highly doped TCOs can show surface band bending of the order of 1 eV. It is further shown that the band alignment at heterointerfaces between TCOs and other materials, which are crucial for many devices, are also affected by such band bending. The origin of the band bending, which seems to be general to all TCOs, depends on TCO thin film and surface processing conditions. The implication of surface band bending on the electronic properties of thin films and interfaces are discussed.
A Combinatorial Approach to TCO Synthesis and Characterization
Authors: Perkins John , Readey Dennis , Alleman Jeff , del Cueto Joe , Li Xiaonan , Coutts Tim , Stauber Renaud , Duncan Chris , Young David , Parilla Phil , Keyes Brian , Gedvilas Lynn , Balzar Davor , Wang Qi , Ginley David
Published: April 2011

We have developed the deposition, characterization and analysis tools necessary for a combinatorial approach to thin film metal oxides, with a special focus on transparent conducting oxides (TCOs). We are presently depositing compositionally graded libraries using mutli-target sputtering and CVD. The initial collection of characterization tools includes UV/VIS/NIR transmission/reflection, FTIR reflectance, Raman scattering, 4-point conductivity, thickness, xray diffraction and electron microprobe. In addition to allowing for a more complete empirical optimization of TCO properties, we expect to develop an improved basic understanding of TCOs, especially in the area of p-type TCOs. This paper provides an overview of our current combinatorial material science program as applied specifically to TCOs.
An X-ray Diffraction Investigation of Tin Oxide Deposition and Annealing
Authors: Robbins Joshua J. , Huang Yen-Jung , Bai Mailasu , Vincent Tyrone , Wolden Colin A.
Published: April 2011

Tin oxide thin films were deposited by plasma-enhanced chemical vapor deposition (PECVD) for applications as a transparent conductor. X-ray diffraction (XRD) and atomic force microscopy (AFM) were used to quantify the crystal structure and morphology of these films both as-deposited and after annealing conditions. Annealing was performed in an argon environment as a function of time and temperature. Although annealing was found to significantly improve electrical properties, the structure as measured by XRD remained largely unchanged. Hall effect measurements show that the improvements in resistivity are due to increases in carrier concentration. XRD did reveal that films deposited on the powered electrode had a film orientation that was distinctly different than films deposited on the grounded electrode. These changes suggest the importance of ion bombardment energy. The structural changes were correlated with improved electrical properties.
A Theoretical Study of p-Type Doping of ZnO: Problems and Solutions
Authors: Yan Yanfa , Zhang S.B. , Pennycook S.J. , Pantelides S.T.
Published: April 2011

We present results of a comprehensive set of first-principles total-energy calculations of native and impurity-defect complexes in ZnO and use these results to elucidate the problems that occur in efforts to achieve p-type doping. The analysis naturally leads to new approaches that are likely to overcome the difficulties. The results provide detailed explanations of recent puzzling observations made in attempts to produce p-type ZnO.
Deep-UV Transparent Conductive β-Ga2O3 Film
Authors: Orita Masahiro , Ohta Hiromichi , Hirano Masahiro , Hosono Hideo
Published: April 2011

Deep ultraviolet transparent and electrical conductive β-Ga2O3 film was prepared on SiO2 glass substrate. The film had electric conductivity of 1 Scm−1, carrier density of 1.4 × 1019cm−3 and mobility of 0.44 cm2V−1s−1. Internal transmittance at wavelength of 248 nm exceeded 50 %. Conductivity was enhanced at an oxygen pressure less than 10−4 Pa, and transparency appeared at a substrate temperature over 800 °C.
Structural, Optical, and Electron Transport Qualities of Zinc-Stannate Thin Films
Authors: Young David L. , Coutts Timothy J. , Williamson Don L.
Published: April 2011

Single-phase, spinel zinc stannate (ZTO = Zn2SnO4) thin films were grown by rf magnetron sputtering onto glass substrates. Uniaxially oriented films with resistivities of 10−2 -10−3 ωcm, mobilities of 16 - 26 cm2/V-s, and n-type carrier concentrations in the low 1019 cm−3 range were achieved. X-ray diffraction peak intensity studies established the films to be in the inverse spinel configuration. 119Sn Mössbauer studies identified two octahedral Sn sites, each with a unique quadrupole splitting, but with a common isomer shift consistent with Sn+4. A pronounced Burstein-Moss shift moved the optical bandgap from 3.35 eV to as high as 3.89 eV.

Density-of-states effective mass, relaxation time, mobility, Fermi energy level, and a scattering parameter were calculated from transport data. Effective-mass values increased with carrier concentration from 0.16 to 0.26 me as the Fermi energy increased from 0.2 to 0.9 eV above the conduction-band minimum. First-order nonparabolic conduction-band theory was applied to extrapolate a bottom-of-the-band effective mass of 0.15 me. Calculated scattering parameters and temperature-dependent transport measurements correlated well with ionized impurity scattering with screening by free electrons for highly degenerate films.
Niobate Films for Microwave Applications
Authors: Cho C.-R. , Koh J.-H. , Grishin A.M. , Abadei S. , Gevorgian S.
Published: April 2011

Submicron thick niobate films, Na0.5K0.5NbO3 (NKN) and Ag0.9Ta0.42Nb0.58O3-δ (ATN), have been pulsed laser deposited on MgO, Pt80Ir20, and Si substrates for microwave device applications. Strong bi-axial (001)-(011) texture observed in both films on MgO substrates indicates that there are major similarities in the growth mechanisms in these films. The dielectric permittivity ε′ of NKN film increases monotonously with temperature, while that of ATN shows a weak temperature dependence (about 21% of variation) in a wide temperature range from 77 K to 400 K. Measured tunability Δε′/ε′ and dielectric loss tanδ for niobate/MgO interdigital capacitors have been found to be (Δε′/ε′)NKN = 40%, tanδNKN = 1.4-2.3% and (Δε′/ε′)ATN = 4.3%, tanδATN = 0.23-0.25% at 1 MHz under maximum electric field of 100 kV/cm. Microwave spectroscopy studies for NKN/Si varactors show (Δε′/ε′)NKN/Si of 13% and tanδNKN/Si = 1.2-6.6% at 40 GHz @ 200 kV/cm.
Thin PZT Film Pressure Microsensor
Authors: Khartsev S.I. , Grishin M.A. , Nilsson Kenth , Grishin A.M.
Published: April 2011

We report on a ferroelectric film pressure sensor fabricated on the top of 4 mm long and 1.4 mm in diameter Pt80Ir20 (PtIr) rod-shaped tip. It consists of a PZT(0.5μm)/LSMO(0.1μm) film heterostructure, deposited by pulsed laser ablation of stoichiometric ceramic targets PbZr0.52Ti0.48O3 and La0.67Sr0.33MnO3, and a circular, ø= 1.2 mm, Au electrode on the top of the PZT film. The Au/PZT/LSMO/PtIr thin-film capacitor demonstrates good ferroelectric properties: dielectric constant of 762 and loss tanσ =0.008 @ 5 kHz, induced polarization as high as 32 μC/cm2 at electric field of 250 kV/cm. Piezoelectric test, performed in a hydrostatic pressure chamber, exhibits the piezoelectric constant to be as high as 67 pC/N. This is 20% higher than 56 pC/N shown by a polarized bulk PZT sensor fabricated from the ceramics used as the target in the pulsed laser deposition process. Such an increase of the piezoelectric constant we attribute to the preferential (001) orientation of the PZT film grown on the PtIr bulk substrate. The resolution of the thin PZT film pressure microsensor was found to be about 1 mbar.
Computer Modeling of Luminescence in ABO3 Perovskites
Authors: Eglitis R. I. , Kotomin E. A. , Borstel G.
Published: April 2011

We suggest theoretical interpretation to a long-debated discussion on a nature of the intrinsic “green” luminescence observed in many ABO3 perovskites. For this purpose we performed quantum chemical calculations using the Intermediate Neglect of the Differential Overlap combined with the Large Unit Cell periodic model. Triplet exciton which is very likely responsible for the “green” luminescence is shown to be in a good approximation a pair of nearest Jahn-Teller electron and hole polarons (a bipolaron).
Analysis of Tungstates and Sesquioxides, Two of the Best Yb3+-Doped Laser Crystals According to Different Evaluations.
Authors: Boulon Georges , Brenier Alain , Laversenne Laetitia , Guyot Yannick , Goutaudier Christelle , Cohen-Adad Marie-Thérèse , Métrat Gérard , Muhlstein Noelle
Published: April 2011

The development of reliable InGaAs laser diode pump sources emitting in the 900-980 nm spectral range is stongly influencing the field of lasers based on Yb3+-doped solid state crystals. Ca5(PO4)3F (C-FAP) and S-FAP (Sr5(PO4)3F) were soon recognized to be favourable hosts for Yb3+ lasing in the nanosecond pulse regime. This fact was supported by an evaluation of the spectroscopic properties of several Yb3+-doped crystals useful for laser action. This evaluation is based on two parameters known from spectroscopy, the emission cross-section at the laser wavelength and the minimum pump intensity required to achieve transparency at the laser wavelength.We think there is a need of a new evaluation of Yb3+-doped crystals in order to predict the laser efficiency in a more realistic manner in different kinds of regimes. We present here the main spectroscopic properties of two Yb3+-doped laser crystals which are grown in our Group: (i) KY(WO4)2 double tungstates by the Floating Crystal method and (ii) Y2O3sesquioxides by the Laser Heated Pedestal Growth method. The approach, based on a quasi-three level laser model, leads to compare all known Yb3+-doped crystals in a two-dimensional diagram considering the laser extracted power and the slope efficiency. We shall show that tungstates and sesquioxides belong to the highest laser crystal potential in CW-end pumping configuration.
High Pressure Studies of Sm2+-Doped Sol-Gel Glasses
Authors: Costa Vilma C. , Shen Yongrong , Bray Kevin L. , Santos Ana M. M.
Published: April 2011

Glasses containing nominally 1, 2, 5, and 10 wt% Sm2O3 in Na2O-Al2O3-SiO2 and Al2O3-SiO2 were prepared from metal alkoxide solution using the sol-gel process. After low temperature heat treatment in air, the glasses were heated up to 800 °C under a flowing H2 atmosphere to reduce Sm3+ into Sm2+. Samarium ions in the divalent and trivalent states were identified by fluorescence measurements. The fluorescence properties of Sm2+ions are discussed in relation to concentration of Sm2O3 and the glass matrix composition. Preliminary results of pressure studies on the luminescence spectra and lifetime of Sm2+ in the glasses are presented as well.
InGaAs-InP Quantum Wire Stark Effect Modulators: Effect of Wire Width in the Optimization of Changes in Excitonic Absorption and Index of Refraction
Authors: Xu M. , Huang W. , Jain F.
Published: April 2011

Quantum wire/dot modulators offer superior performance over their quantum well counterpart due to enhanced excitonic binding energy. This paper presents simulations on InGaAs-InP quantum wire Stark effect optical modulators showing a novel trend. While the excitonic binding energies and absorption coefficients increase as the width of the wire is decreased, the refractive index change Δn is maximized at a wire width depending on the magnitude of the applied electric field. For example, Δn is maximized at a width of about 100Å for an external electric field of 120kV/cm in an InGaAs quantum wire. This behavior is explained by considering the opposing effects of the wire width on binding energy and changes in the electron-hole overlap function in the presence of an external electric field. Practical InGaAs-InP modulators using V-groove structures are also presented.
Strong ultraviolet electroluminescence from porous silicon light-emitting diodes
Authors: Tam H. L. , Yuan J. , Li K. F. , Wong W. K. , Cheah K. W.
Published: April 2011

Porous silicon light-emitting diodes were found to emit strong line-shaped ultraviolet under a forward bias driving voltage of about 20 volts. The intensity was sufficiently strong to pump an organic crystal, Tb-dipicolinic acid, producing clear Tb 4f intra-shell transition photoluminescence spectrum. The current-voltage characteristics of the devices also showed negative differential resistance, which was frequency dependent. In addition, purging of the device with various gases could quench the electroluminescence but the intensity recovered partially after each purging, but with no change in emission spectrum. Both results indicate the transport was influenced strongly by local space charge. From the results, the electroluminescence mechanism is tentatively attributed to core recombination in the porous layer, and the spectral characteristics is due to the microcavity effect between the top Au contact and silicon substrate. The present study shows that porous silicon has the potential as UV source in optoelectronics applications.
Photoluminescence study of defects induced by B10H14 ions
Authors: Toyoda Noriaki , Aoki Takaaki , Matsuo Jiro , Yamada Isao , Wada Kazumi , Kimerling Lionel C.
Published: April 2011

Defect formation in Si by B10H14 (decaborane) ion implantation has been investigated with photoluminescence measurement. An intense W-line was observed at photon energy of 1.018eV from as-implanted FZ-Si by 30keV B10H14+ implantation. W-line center is considered as an interstitial aggregate and usually observed after ion implantation with subsequent low-temperatureannealing in the case of atomic ion implantation. As W-line is observed from as-implanted Si, the defect formation with B10H14 is expected to be different from that of B+ implantation with the same energy per atom. The energy dependence of W-line intensity is similar to that of diffusivity enhancement after rapid thermal annealing. Molecular dynamics simulation and Rutherford backscattering spectrometry channeling experiment suggest that one B10H14 implantation creates a larger number of dislocated Si atoms than that of B+ implantation with the same energy per atom. This characteristic of B10H14 implantation may cause the different defect reactions in subsequent annealing process.
Accurate Modeling of Residual recoil-mixing during SIMS Measurements
Authors: Yang Ming Hong , Odom Robert
Published: April 2011

Secondary ion mass spectrometry (SIMS) is an effective and powerful analytical technique, widely used in accurately determining dopant distributions (depth profiles). However, primary ion beam induced mass transport (ion mixing), especially the residual effect during SIMS profile measurements, greatly limits theaccuracy at nanometer depth resolutions by displacing and broadening the measured depth profile. In this paper, we present a simple deconvolution algorithm based on the general characteristics of the experimentally observed SIMS response function to reduce this broadening effect, thereby providing more accurate depth profiles. The results for several specific applications of this approach are presented and its strengths and limitations are discussed.
Characterization of Damage Induced by Cluster Ion Implantation
Authors: Aoki Takaaki , Matsuo Jiro , Takaoka Gikan
Published: April 2011

Molecular dynamics simulations of boron monomer and small clusters (B4 and B10) impacting on Si(001) were performed in order to investigate the damage formation by monomer/cluster impact. These monomer and clusters show similar implant depth and efficiency, but different damage structures. At the impact of B monomer with 230eV of incident energy, some point-defects such as vacancy-interstitial pairs are mainly formed. On the other hand B10 produces several times larger number of vacancies and interstitials compared with B1, This damage structure is different from one by B1 implantation and due to high yield amorphization of implanted region. This characteristic damage formation process is expected to cause different annihilation process.
A Comprehensive Model for Carbon Suppression of Boron Transient Enhanced Diffusion
Authors: Ngau Julie L. , Griffin Peter B. , Plummer James D.
Published: April 2011

In this work, the time evolution of B transient enhanced diffusion (TED) suppression due to the incorporation of 0.018% substitutional carbon in silicon was studied. The combination of having low C concentrations, which reduce B TED without completely eliminating it, and having diffused B profiles for several times at a single temperature provides much data upon which various models for the suppression of B TED can be tested. Recent work in the literature has indicated that the suppression of B TED in C-rich Si is caused by non-equilibrium Si point defect concentrations, specifically the undersaturation of Si self-interstitials, that result from the coupled out-diffusion of carbon interstitials via the kick-out and Frank-Turnbull reactions. Attempts to model our data with these two reactions revealed that the time evolved diffusion behavior of B was not accurately simulated and that an additional reaction that further reduces the Si self-inter- stitial concentration was necessary. In this work, we incorporate a carbon interstitial, carbon substitutional (CiCs) pairing mechanism into a comprehensive model that includes the C kick-out reaction, C Frank-Turnbull reaction, {311} defects, and boron interstitial clusters (BICs) and demonstrate that this model successfully simulates C suppression of B TED at 750 °C for anneal times ranging from 10 s to 60 min.
A Quantitative Model of the Electrical Activity of Metal Silicide Precipitates in Silicon Based on the Schottky Effect
Authors: Tan Teh Y. , Plekhanov Pavel S.
Published: April 2011

A quantitative model of the electrical activity of metallic precipitates in Si is presented. An emphasis is placed on the properties of the Schottky junction at the precipitate-Si interface, as well as the carrier diffusion and drift in the Si space charge region. Carrier recombination rate is found to be primarily determined by the thermionic emission charge transport process across the Schottky junction rather than the surface recombination process. It is shown that the precipitates can have a very large minority carrier capture cross-section.
Influence of low thermal budget pre-anneals on the high temperature redistribution of low energy boron implants in silicon
Authors: Boucard F. , Schott M. , Mathiot D. , Rivallin P. , Holliger P. , Guichard E.
Published: April 2011

It is now well established that the transient enhanced diffusion (TED) of ion implanted boron in silicon limits the formation of the ultra-shallow junctions required for the extreme deep sub- micron devices. It is also known that this TED is linked to the fate (elimination and agglomeration) of ion implantation related excess self-interstitials. Thus it can be expected that the final high temperature redistribution is at least partly governed by the effective initial point defect distribution at the onset of the high temperature plateau.

In this contribution we present the experimental evidence that low thermal pre-anneals, by affecting the initial self-interstitials distribution, affects boron redistribution during a subsequent high temperature anneal. Samples implanted with high dose boron at 3 keV were first annealed at 700°C for various durations. These samples, as well as reference samples without the pre-anneal, were then RTA annealed at various high temperatures around 1000°C. The resulting B profiles were measured by SIMS. It is found that the pre-annealed samples exhibits a clear reduction of the TED as compared with the reference ones.
Resolving the Origin of a Cmp-Associated Yield/Reliability Issue “Center Spike”– Film Thickness Bulge in the Wafer Center. is CMP to Be Held Responsible for Its Appearance?
Authors: Wei David , Gotkis Yehiel , Boyd John , Kistler Rodney
Published: April 2011

A long-standing CMP related yield/reliability puzzle - film thickness spike, frequently appearing at the wafer center after it is processed by CMP, was studied. Optical film thickness measurements for pre- and post-CMP film were compared with surface topography profiles. Wafer surface profiles were also studied after the oxide film was HF-etched out. It was found that the post-CMP film thickness spike actually is not caused by CMP malfunctioning, but originates to a specific bare silicon wafer defect and occurs when the bare silicon wafer has a narrow dip-like defect (depression) in its center. The dielectric film, deposited over the wafer, follows the underlying center-dipped topography, and, being planarized by CMP, is transformed into a top-flat film with a thick pattern in the wafer center, filling the silicon dip. In-line and end-of-line yield related issues are discussed.
Synthesis of Model Alumina Slurries for Damascene Patterning of Copper
Authors: Lee Byung-Chan , Duquette David J. , Gutmann Ronald J.
Published: April 2011

Model alumina slurries for chemical-mechanical planarization (CMP) of copper have been studied using fundamental electrochemical concepts together with modification of surface tension and zeta-potential. A model slurry was established containing 3 wt% alumina (50 nm nominal size), 2 wt% potassium dichromate (K2Cr2O7) and 1 vol % DOWFAX, as abrasive, oxidizer and anionic surfactant, respectively, which resulted in blanket copper removal rates of 130 nm/min with smooth, low-particulate defect density surfaces without aggressive post-CMP cleaning. When used with a model silica-abrasive slurry to remove the Ta liner, well-defined damascene-patterned structures were achieved with low-particulate defect densities.

Open circuit potential measurement, potentiodynamic polarization, surface tension measurement, and zeta-potential measurement were used in developing the model slurries. The variations obtained with alternative abrasives, alternative oxidizers and alternative surfactants illustrate the principles of synthesizing slurries for Cu and Ta.
Effect of Copper Film Surface Properties on CMP Removal Rate
Authors: Wang Yuchun , Bajaj Rajeev , Lam Gary , Dordi Yezdi , Bennet Doyle
Published: April 2011

It has been observed that CMP removal rate of copper varies for films from different sources. While the film hardness and static wet etch rate in the absence of inhibitors are similar for various films, the static etch rate in the presence of inhibitors is significantly different. Analysis by AFM, XPS, and ion beam sputtering showed the film roughness and surface composition were different for different Cu films within 160 angstroms of the surface. Thus the different in Cu CMP removal rates can be explained by a synergetic effect of copper film roughness (grain size), surface composition, and effective adsorption of inhibitors. This explanation suggests that if polishing is initiated by an aggressive polishing step, removal rate of the remaining bulk copper films become more consistent. Based on these findings, the polishing slurry and process were further optimized.
Analysis of CMP planarization performance for STI process
Authors: Tsujimura Manabu , Corporation Ebara , Ohta-ku Kamata , Japan Tokyo
Published: April 2011

It has recently been reported that some waviness may affect STI CMP yield. CMP is designed primarily to planarize relatively with large r scale than small topography. However, there may be a range of wafer topographies in which STI patterns are over-polished, depending on peak-to-valley variations and frequencies. Permissible peak-to-valley variations and frequencies are calculated by determining whether the difference in polish quantities between the peak and valley is less than permissible values, such as 10 nm, 20 nm, and 30 nm. Reports indicate that slurry selectivity can decrease this effect, although with certain disadvantages.
Fixed Abrasive Technology for STI CMP on a Web Format Tool
Authors: Simpson Alexander , Economikos Laertis , Jamin Fen-Fen , Ticknor Adam
Published: April 2011

Shallow trench isolation (STI) requires a high quality oxide with superior fill capability provided by High Density Plasma (HDP) oxide. Unfortunately, the HDP deposition process can create large within die topographies that are difficult to polish directly using conventional silica slurries. As a result, etch back integration schemes have traditionally been incorporated for STI polish. A more revolutionary approach is the use of Fixed Abrasive (FA) CMP [1]. FA CMP allows direct STI polish with good planarization/process stability, eliminating the need for prior etch back. The planarization efficiency is strongly dependent on the shape of the pad composites that hold the CeO2 mineral. Fixed abrasive pads with pyramid and pole shapes are available. In this work, three different fixed abrasive pads supplied by 3M corporation were evaluated for STI CMP polish performance using the Obsidian 8200C web format CMP tool. Basic polish characteristics such as planarity (dependence on sub-pad/pattern density), selectivity to topography, oxide dishing and nitride erosion are presented. The FA pads discussed here have been classified as “slow”, “medium” or “fast” depending on blanket oxide removal rate.

The slow rate pad had a very high selectivity to topography and very low dishing of the down area oxide. The removal rate of blanket oxide was less than 100 Å/min. The pad was best suited to the polish of isolation trench structures with small, controlled overfill (> 200 Å) across the wafer. A large process window was demonstrated. The removal rate of the “medium” pad also decreased significantly at the onset of planarization with a blanket oxide removal rate of ca. 200 Å/min. Unlike the slow rate pad, the medium rate pad did not provide a suitable overpolish process window required for a manufacturable STI process. It is believed this pad would be a good choice for BPSG polish. In contrast to the slow and medium rate pads, the blanket oxide removal rate of the fast pad was ca. 2000 Å/min with no self-stopping capability at the onset of planarization. The removal rate was extremely center fast, such that it could not be compensated by adjustment of tool parameters. Use of a modified process developed within the DRAM development alliance (DDA) at East Fishkill (IBM/ Infineon) enabled the fast pad to polish deep STI structures that would otherwise be impossible using the slow or medium rate pads.
Modeling the Effects of Polishing Pressure and Speed on CMP Rates
Authors: Paul Ed
Published: April 2011

In a previous CMP model, the effects of the slurry concentration of chemicals and abrasives on the polishing rate were quantitatively explained, for constant polishing pressure and velocity. That model is extended here to consider specific descriptions of mechanical abrasion, involving polishing pressures and speeds. Predictions of behavior are compared to literature data, leading to an improved understanding of the abrasive process in CMP.