bluuebunny/crossref_metadata_2025 huggingface dataset:
Finite Element Analysis of Thermal-Mechanical Stress Induced Failure in Interconnects
Authors: Yu X. , Weide K.
Published: April 2011

In this work a study of the nature as well as an evalution of the thermal-mechanical stress in aluminum interconnects was carried out. A theoretical model discribes the atom flux which can be induced by the relaxation of the stress. Based on this theory an algorithm has been developed and integrated into the finite element simulation software. This algorithm allows the calculation of the mass flux divergence and prediction of the failure location before the damage occurs. For the verification of this algorithm an aluminum pad structure sputtered on thermal oxide layer was used. The failure location was correlated with in situ observation during the long term stress tests. Experimental results confirm that the observed structure degradations correspond with the simulations very well.
Effect of Crack Blunting on the Ductile-Brittle Response of Crystalline Materials
Authors: Lipkin D.M. , Beltz G.E. , Fischer L.L.
Published: April 2011

We propose a self-consistent criterion for crack propagation versus dislocation emission, taking into account the effects of crack-tip blunting. Continuum concepts are used to evaluate the evolving competition between crack advance and dislocation nucleation as a function of crack- tip curvature. This framework is used to classify crystals as intrinsically ductile or brittle in terms of the unstable stacking energy, the surface energy, and the peak cohesive stresses achieved during opening and shear of the atomic planes. We find that ductile-brittle criteria based on the assumption that the crack is ideally sharp capture only two of the four possible fracture regimes. One implication of the present analysis is that a crack may initially emit dislocations, only to reinitiate cleavage upon reaching a sufficiently blunted crack-tip geometry.
Chemical Vapor Deposition (CVD) of Iridium and Platinum Films and Gas-Phase Chemical Etching of Iridium Thin Films
Authors: Xu Chongying , Dimeo Frank , Baum Thomas H. , Russell Michael
Published: April 2011

Chemical vapor deposition (CVD) of noble metal thin-films is increasingly important for future memory storage applications. Integration of ferroelectric perovskites and/or high permittivity oxides requires specialized metal interconnect technologies. Platinum and iridium are two preferred metal electrode materials being explored since they are highly resistant to corrosion and exhibit excellent stability at high temperatures. Further, the formation of stable oxides (IrO2) provides a mechanism for decreased inter-diffusion of oxygen and elemental film constituents, and provides improved reliability in silicon-based devices. CVD provides conformal electrode films that are required to achieve high-densities; high purity films of both platinum and iridium were deposited in this research, using (β-diketonate)Ir(I)L and (MeCp)Me3Pt(IV) as the precursors.

Concurrently, chemical etching of these metals is highly desirable for creating patterns of the electrical contacts and for CVD reactor cleaning. To date, etching of noble metal electrodes has relied upon physical sputtering or chemically assisted etching. In this paper, we also report the first chemical etching of iridium films under ambient conditions, such as room temperature.
Nonlinear Dielectric Relaxation of Mn Doped Polycrystalline (Ba,Sr)TiO3 Thin Films Over the Temperature Range of 4.2 - 473 K
Authors: Baniecki J.D. , Laibowitz R.B. , Shaw T.M. , Duncombe P.R. , Kotecki D.E , Shen H. , Lian J. , Mat Q.Y.
Published: April 2011

We have investigated the dielectric relaxation currents of Mn doped polycrystalline Ba0.7Sr0.3TiO3 (BSTO) thin films as a function of applied electric field and temperature (4.2 - 473 K). The dielectric relaxation currents followed a power law time dependence, J(t) = Jot-n, over the entire temperature range. Plots of log(Jo) vs. reciprocal temperature were not linear and showed slopes approaching values of 0.35 eV at high temperatures which rapidly decreased to 0.25 meV at lower temperatures. The relaxation currents were found to be nonlinear with applied field. The observed nonlinearity of the field dependence of the relaxation currents can be understood in terms of the nonlinear relaxation component of the total capacitance. An equivalent circuit model for a paraelectric BSTO thin film capacitor is presented and possible polarization mechanisms are briefly discussed.
Correlations Between Composition, Texture, and Polarization in SrxBiyTa2O5+x+3y/2 Thin Films Deposited by MOCVD
Authors: Hendrix Bryan C. , Hintermaieri Frank , Desrochers Debra A. , Roeder Jeffrey F. , Baum Thomas H. , Dehm Christine , Nagel Nikolas , Honlein Wolfgang , Mazure Carlos
Published: April 2011

SrxBiyTa2O5+x+3y/2 (SBT) is a promising material for ferroelectric random access memories (FeRAM's) because of its inherently high resistance to fatigue and imprint. Metalorganic chemical vapor deposition (MOCVD) offers the ability to produce high quality, conformal SBT films for both high and low density memory applications. An MOCVD process based on liquid delivery and flash vaporization has been developed which allows precise control of film stoichiometry and thickness. In this study, wavelength dispersive x-ray fluorescence and x-ray diffractometry have been used to survey composition and preferred crystallographic orientation (texture) relationships. It is shown that as-deposited film composition can be used to influence the texture of the Aurivillius phase in the annealed film. The polarization of the films increases with increasing (115) and (200)/(020) peak intensity due to the relationship of the electric field direction with the polarization direction in the film. The highest values of polarization are found with Sr content, x<0.8 and Bi content, 2.1 <y<2.6.
Ultra-Thin PZT Films for Low-Voltage Ferroelectric Non-Volatile Memories
Authors: Wouters D.J. , Norga G.J. , Maes H.E.
Published: April 2011

For the possible application of PZT thin films in ferroelectric non-volatile memories, the potential of low-voltage switching is a major requirement. By straightforward thickness scaling down to 75nm, operation voltage can be reduced to 1.5V without degradation of the hysteresis properties. However, interface effects increase the coercive field for thinner films, so that operation voltage does not scale linearly with thickness. In view of the large difference in coercive field between bulk and thin-films, on the other hand, material (and interface) optimization may constitute an interesting alternative route for further voltage scaling. By optimizing the composition and stoichiometry, less than 1.5V switching has indeed been obtained even for 150nm films. It is argued that an important material parameter affecting low-voltage switching behavior is the ferroelectric domain configuration and presence/absence of mobile domain walls in the PZT film.
Study of Rf-Sputtered Ba(ZrxTi1−x)O3 Thin Films for Ulsi Dram Application
Authors: Lee Jian-Hung , Chen Tung-Sheng , Balu Venkatasubramani , Han Jeong , Mohammedali Razak , Gopalan Sundar , Wong Chun-Hui , Lee Jack C.
Published: April 2011

Barium zirconate-titanate (Ba(ZrxTi1−x)O3, BZT) films with thickness around 60 nm were deposited on Ir substrates using RF magnetron sputtering. The effect of zirconium atomic fraction (x = 0.14 to 0.7), substrate temperature (380 °C to 550 °C) and oxygen partial pressure (0 to 5 mTorr with total pressure 30 mTorr) on leakage current, dielectric constant and dielectric dispersion (capacitance reduction with increasing frequency) was studied. We found that the Zr/Ti ratio played a crucial role in determining the dielectric constant and dispersion. The dielectric constant varies from 26 to 168 while dispersion ranges from 0.80 to 2.58 % loss in capacitance (dielectric constant) per decade of frequency. Low leakage currents (< 1× 10−7 A/cm2) were observed.
PMN Based Thin Film Capacitor for Decoupling Applications in High Speed Digital Circuits
Authors: Fukumaru F. , Nagakari S. , Konushi S. , Nishikawa H. , Kamigaki K. , Nambu S.
Published: April 2011

A new type of Pb(Mgl1/3Nb2/3)O3 (PMN) based thin film decoupling capacitor for high speed digital circuits is presented. The thin film capacitor fabricated on a ceramic Al2O3 substrate with Ball Grid Array (BGA) terminations showed low impedance and low inductance characteristics in the 100MHz – 1GHz range. The sol-gel derived Pb(Mg1/3Nb2/3)O3-PbTiO3(PMN-PT) thin film showed a high dielectric constant (k=3000) with broad temperature dependence. The capacitor consists of a PMN-PT thin film (0.8 µm thickness), Au electrodes, and solder balls mounted on the upper electrode as terminals. Numerical simulations based on the Partial Element Equivalent Circuit (PEEC) model were conducted for the design of electrodes, which gives low inductance of the capacitor. It was shown that the thin film 1.2mm × 1.2mm capacitor mounted on a board exhibits high capacitance of 20 nF, low ESR of 100 mΩ, and low inductance of 135 pH. These values are in good agreement with the results of numerical simulations.
Investigation of PZT//LSCO/IPT//Aerogel Thin Film Composites for Uncooled Pyroelectric Ir Detectors
Authors: Clem P.G. , Tuttle B.A. , Ruffner J.A. , Brinker C.J. , Schwartz R.W. , Rodriguez M. , Warren W.L.
Published: April 2011

A monolithic thin film structure for uncooled pyroelectric infrared detector arrays was developed to integrate thermally isolated Pb(Zr,Ti)O3-based thin films on silicon, with a low thermal conductivity, aerogel thin film interlayer. Aerogel thin films of 0.4-1.2μm thickness and 70-85% porosity were deposited on silicon substrates by dip coating to form a thermal isolation layer. 200-400nm thick Pb(Zr0.4Ti0.6)O3 films deposited on (La,Sr)CoO3[LSCO]//Pt electrodes atop these aerogel films displayed a remanent polarization Pr = 28μ C/cm2, pyroelectric coefficient p = 30 nC/cm2K, and calculated noise equivalent temperature difference NETD = 0.07°C. Processing of Pb(Zr,Ti)O3 thin films atop the aerogel interlayer structure required modifications to deposition and heat treatment methods to minimize tensile stress accumulation. Effects of thermal processing and thin film stress state on ferroelectric properties are also reported.
Epitaxial Giant Magnetoresistive/Ferroelectric La0.7Ca0.3MnO.3/PbZr0.52Ti0.48O3 Thin Film Heterostructures
Authors: Grishin A. , Khartsev S. , Johnsson P. , Maneikis A.
Published: April 2011

Recently, doped rare-earth manganates exhibiting colossal magnetoresistivity have been proposed to be used as the semiconductor channel material for a Ferrolectric Field Effect Transistor. Although the feasibility of epitaxial magnetoresistive/ferroelectric heterostructures have been demonstrated, the leakage in the ferrolectric layer and the strain induced degradation of the magnetoresitive layer remain a principal problem. We present results on fabrication and characterization of epitaxial giant magnetoresistive/ferrolectric La0.7Ca0.3MnO3(LCMO)/PbZr0.52TiO.48O3(PZT) heterostructures. The films have been prepared in situ by a KrF pulsed laser deposition technique on single crystal LaAlO3 substrates from stoichiometric LCMO and PZT targets. The main processing parameters have been optimized to preserve the existence of giant magnetoresitivity in the LCMO films after deposition of the top ferrolectric layer. A high degree of c-axis orientation and a strong in-plane texture coherent with the substrate both in template LCMO and PZT layers, high dielectric permittivity of 1800, remanent polarization of 0.2 C/m2 and a magnetoresistivity of 28% at H=0.5 T indicate excellent characteristics of coexisting magnetoresistive and ferroelectric properties.
Pulsed Laser Deposition of BaxSr1−xTiO3 Films on MgO, LaAlO3 and SrTiO3 for Tunable Microwave Applications
Authors: Chang Wontae , Horwitz James S. , Kim Won-Jeong , Pond Jeffrey M. , Kirchoefer Steven W. , Gilmore Charles M. , Qadri Syed B. , Chrisey Douglas B.
Published: April 2011

Single phase BaxSr1−xTiO3 (BST) films (∼0.5-7 μm thick) have been deposited onto single crystal substrates (MgO, LaAlO3, SrTiO3) by pulsed laser deposition. Silver interdigitated electrodes were deposited on top of the ferroelectric film. The room temperature capacitance and dielectric Q (1/tanδ) of the film have been measured as a function of electric field (≤80 kV/cm) at 1 - 20 GHz. The dielectric properties of the film are observed to strongly depend on substrate type and post-deposition processing. After annealing (≤1000° C), it was observed that the dielectric constant and % tuning decreased and the dielectric Q increased for films deposited onto MgO, and the opposite effect was observed for films deposited onto LaA1O3. Presumably, this change in dielectric properties is due to the changes in film stress. Very thin (∼50 Å) amorphous BST films were successfully used as a stress-relief layer for the subsequently deposited crystalline BST (∼5000 Å) films to maximize % tuning and dielectric Q. Films have been deposited from stoichiometric targets and targets that have excess Ba and Sr. The additional Ba and Sr has been added to the target to compensate for deficiencies in Ba and Sr observed in the deposited BST (x=0.5) films. Films deposited from compensated targets have higher dielectric constants than films deposited from stoichiometric targets. Donor/acceptor dopants have also been added to the BST target (Mn, W, Fe ≤4 mol.%) to further improve the dielectric properties. The relationship between the dielectric constant, the dielectric Q, the change in dielectric constant with electric field is discussed.
Interconnect-Related Degradation of PZT Capacitor for FeRAM
Authors: Kobayashi S. , Amanuma K. , Hada H.
Published: April 2011

Ferroelectric properties of a Pb(Zr,Ti)O3 (PZT) thin film capacitor with a conventional Al/TiN/Ti interconnect are seriously degraded by annealing at around 400°C. The degradation of the PZT capacitor is reduced as the interconnects are narrowed while the total area of the interconnects on the capacitor is fixed. This result cannot be understood by supposing that Ti diffusion into PZT degrades the ferroelectric properties. A possible cause for the degradation is stress placed on the PZT film during the 400°C annealing.
Depth and Time Dependence of Polystyrene Chain Diffusion Near the Polystyrene/Silicon Interface
Authors: Trzhemechny Y. , Hapovalov V. , Hou K. G. , Chwarz S. A. , Sokolov J. , Rafailovich M. H.
Published: April 2011

We report on the results for the diffusion coefficient (D*) of polystyrene (PS) chains near the PS/Silicon interface. The present study employs secondary ion mass spectrometry (SIMS) to examine diffusion from a deuterated marker layer in thin PS films on silicon. The observed SIMS depth profiles are fit to numerical simulations of the diffusion process. The best fit is obtained for a super-linear dependence of D* vs. distance from the silicon wall. A non-trivial time dependence extending over tens of hours is observed for all the models tested.
Buckling Dynamics of Tethered Membranes
Authors: Moldovan Dorel , Golubovic Leonardo
Published: April 2011

We investigate the dynamics of the classical Euler buckling of compressed solid membranes. We relate the membrane buckling dynamics to phase ordering phenomena. Membrane develops a wavelike pattern whose wavelength grows, via coarsening, as a power of time. Evolving membrane is similar to rough growing surfaces (“growing interfaces”) whose roughness grows as a power of time. Membrane buckling dynamics is characterized by a distinct scaling behavior not found in other coarsening phenomena
Studies Of The Polymer Thin Film Glass Transition Temperature Monitored With The Complex Viscoelastic Cofficients
Authors: White C. C. , Wu W. L.
Published: April 2011

In integrated circuit manufacturing, the gaps between metal lines are a critical parameter, and polymer films are being evaluated as low k dielectric materials for VLSI. Desire to maximize the number of elements within a given area to increase clock speed and decrease power consumption have forced the gaps to become increasingly smaller. Currently, 0.25–0.18 micron line widths are the subject of much commercial interest. A line width of 0.25 microns is within a factor of 5 of the molecular dimension of most commercial polymers. Experiments have suggested polymer films slightly smaller than these dimensions may not have the expected bulk mechanical properties. This deviation from the expected behavior (i.e., Change in the glass transition temperature) would present significant technical challenges to the manufacturing and reliability of integrated circuits. These effects are extremely difficult to determine experimentally with requisite precision. Recently, an experimental technique, based on a highly modified quartz crystal microbalance, has been developed to study the mechanical properties of these ultra-thin polymer films with high precision. The experimental details and preliminary results from this recently developed state-of-the-art experimental technique will be presented.
Extended Tomlinson Model for Rheological Response
Authors: Zaloj V. , Urbakh M. , Klafter J.
Published: April 2011

We investigate the response of a confined harmonic chain to an external harmonic driving force. A model is introduced which extends the one-dimensional Tomlinson model to include motion in the normal direction. This model with lateral-normal coupling mimics recent measurements on friction, using surface forces apparatus (SFA). The model predicts a critical driving amplitude below which the response is linear. For higher amplitudes the system exhibits a nonlinear behavior and an apparent shear thinning. We discuss the effects of shear induced dilatancy, which results from the lateral-normal coupling, on the energy dissipation, and therefore on the frictional properties. It is demonstrated that measurements of response in the normal direction provide additional information on the mechanisms of friction.
Anomalous Surface Diffusion of Water in Nanopores
Authors: Korb J.-P. , Bryant R. G.
Published: April 2011

Proton nuclear magnetic relaxation dispersion experiments show remarkable differences between water and aprotic liquids in contact with microporous glass surfaces containing trace paramagnetic impurities. Proton surface diffusion permits long range effectively 1-dimensional exploration along the pores for water. This gives a direct measurement of the translational diffusion coefficient at the pore surface.
Vacuum Ultraviolet Irradiation of Polymers
Authors: Fozza A. C. , Bergeron A. , Klemberg-Sapieha J. E. , Wertheimer M. R.
Published: April 2011

The interest in incoherent sources for wavelength selective photochemistry has increased lately, but little is still known about the behavior of polymers when exposed to far UV and vacuum UV (VUV) radiation, for example that emitted from low-pressure plasmas. In order to study VUV-UV effects on several polymers (polyethylene - PE, polystyrene - PS, hexatriacontane - HTC, polymethylmethacrylate - PMMA and polycarbonate - PC), we used the wellcharacterized emissions from hydrogen and hydrogen/argon mixture plasmas as light sources. Mass changes were measured in-situ using a quartz crystal microbalance (QCM); irradiated samples were analyzed ex-situ by XPS, spectroscopic ellipsometry, and AFM.
Preparation of SiC Thin Film Using Organosilicon by Remote Plasma CVD Method
Authors: Xu Ying-Yu , Muramatsu Takahiro , Aoki Toru , Nakanishi Yoichiro , Hatanaka Yoshinori
Published: April 2011

An organosilicon compound, hexamethyldisilane (HMDS) was incorporated for SiC thin film preparation by remote plasma enhanced CVD method. We investigated how plasma excited radicals react with source monomers using two kinds of gas mixtures. It was found that film component and formation mechanism depends on stronger on plasma gases. Using a mixture of nitrogen and hydrogen gases as plasma gas source, deposited films contained large amounts of nitrogen. When uing an argon and hydrogen mixture, deposited film was a SiC with large hydrogen contents. In this research, we found that hydrogen radicals are very active for decomposition of monomer source gas and this can be related to precursors for film deposition. When using a mixture of argon and hydrogen as plasma gas, the film deposition speed was influenced by substrate temperature. The estimated activation energy was larger than the case of using nitrogen and hydrogen gases. Different reaction mechanisms were observed for different plasma gas source
Precise and Smooth Removal from Polymer Surfaces by VUV Excimer Laser Ablation at 157 nm: PMMA.
Authors: Padeletti G. , Lapczyna M. , Stuke M.
Published: April 2011

Smooth polymer surfaces can be generated by VUV laser ablation at 157 nm. This has been demonstrated for poly-methyl-metacrylate (PMMA) by atomic force microscopy (AFM) analysis of laser-exposed surfaces. At excimer laser fluences below 30 mJ/cm2 the mean roughness (Ra) remains below 10 nm for both single and 10 shot exposures.

A detailed characterization of the surface nano-morphology distribution carried out by the “power spectral density” (PSD) analysis, shows that the surface is smoothened by the VUV laser for lateral scales smaller than 20 μm.
Conjugation of DNA to Plasma-Treated Polymer Surfaces and Their Application to Multiplex DNA Sequencing
Authors: Lambert Stephen M. , Chen Jer-Kang , Chiesa Claudia , Fry George A. , Furniss Vergine C. , Mehrpouyan Majid A. , O'Neill Roger A.
Published: April 2011

Plasma treatment and deposition techniques have been used to facilitate the covalent attachment of DNA to polymer surfaces. The variety of surface functional groups that can be created by plasma techniques enables different chemical conjugation routes to be explored. For example, a phosphodiester linkage can be used for surfaces with hydroxyl groups. Likewise, a carboxyamide linkage can be used for surfaces with carboxyl or amine groups. The primary application of the engineered materials has been the hybridization-based separation of multiplexed DNA sequencing products. Traditionally, sequencing reactions are performed individually on single templates. Multiplex sequencing offers reagent and time savings by permitting multiple sequencing reactions on single or multiple templates. The method developed uses recoverable DNA sequencing primers with additional “capture sequences” attached to the 5' end. The capture sequences are designed to be complementary to “binding sequences” covalently attached to the plasma-treated polymer supports. When a solution of the extended recoverable primers is exposed to a polymer support, primers with complementary capture sequences hybridize to the immobilized binding sequences. Contacting a multiplexed sample with a series of solid supports (each having a different binding sequence) selectively removes each set of sequencing products from the mixture. Washing each solid support, followed by releasing the hybridized DNA, results in isolated and purified sequencing products that are amenable to analysis by gel or capillary electrophoresis.
Silicon Quantum Dots in Silica
Authors: Henderson D. O. , Wu M. H. , Mu R. , Ueda A. , White C. W. , Meldrum A.
Published: April 2011

Silicon ions were implanted into fused silica substrates at doses of 1×1021, 2×1021, 5×1021, and 1×1022 ions/cm3. The implanted substrates were annealed at 1100°C for one hour in a reducing atmosphere (95% Ar+5% H2). Optical absorption spectra recorded after the annealing treatment showed absorption onsets at 3.86, 3.73, 2.86 and 2.52 eV for substrates implanted with 1×1021, 2×1021, 5×1021, and 1×1022 ions/cm3, respectively. Static photoluminescence (PL) measurements indicated red emission between 1.72 and 1.61 nm with a slightly increasing red shift with ion dose. Time resolved PL at room temperature revealed slow (∼50 μs) and fast (×20 μs) lifetimes which increased with decreasing temperature. TEM studies showed that the particle size increased with increasing ion dose. Typical particle sizes ranged between 2 and 5 nm indicating quantum confinement of the exciton, which can account for the blue shift in the absorption edge with decreasing ion dose. However, the maxima in the PL spectra for all ion doses are relatively independent of the ion dose and are strongly shifted from the absorption spectra. This suggests that radiative recombination occurs from a common luminescent center, possibly a surface or interfacial state in thexs SiOx, layer surrounding the nanocrystal.
Development of Metallic Closed Cellular Materials Containing Polymers
Authors: Kishimoto S. , Shinya N.
Published: April 2011

A new material for structures in space, which have a high energy absorbability has been developed using a powder particle assembling technique. Powder particles of polystyrene coated with nickel-phosphorus alloy layers using electroless plating were sintered at high temperature. A metallic closed cellular material containing polystyrene was then constructed.

The mechanical and ultrasonic properties of this material were measured at both room and high temperatures. The compressive tests of this material show a low Young's modulus and high energy absorption. Ultrasonic measurement shows that the attenuation coefficient of this cellular material is very large and would change due to increasing temperature. These results indicate that this metallic closed cellular material can be used for the space applications.
The Dependence of Tensile Ductility on Investment Casting Parameters in Gamma Titanium Aluminides
Authors: Raban R. , L. L. , M. T.
Published: April 2011

Plates of three gamma titanium aluminide alloys have been investment cast with a wide variety of casting conditions designed to influence cooling rates. These alloys include Ti-48Al-2Cr-2Nb, Ti- 47Al-2Cr-2Nb+0.5at%B and Ti-45Al-2Cr-2Nb+0.9at%B. Cooling rates have been estimated with the use of thermal data from casting experiments, along with the UES ProCAST simulation package. Variations in cooling rate significantly influenced the microstructure and tensile properties of all three alloys.
Effect of Thermal Residual Stress on the Mechanical Properties of NiAl-Based Composites
Authors: Choo Hahn , Bourke Mark , Nash Philip
Published: April 2011

NiAl-based hybrid composites containing 5, 15 and 30 volume percent of A12O3 fibers in addition to AIN dispersion particles were fabricated via a powder metallurgy route. The strengthening mechanisms associated with the short A12O3 fiber in NiAl-(A1N)dispersion,-(A12O3)fiber, composite were studied with an emphasis on the effect of thermal residual stress on the compressive strength at room temperature and 1300K. At 300K, the yield strength of the composites was predicted using a linear superposition of the monolithic yield strength, direct fiber strengthening and tensile matrix residual stresses. The prediction shows good agreement with the measured data. The majority of the room temperature strengthening is attributable to the residual stress. At 1300K, the strengthening was achieved only by the load sharing of the fibers and there is no direct influence from the process-induced thermal residual stresses since they were completely relaxed at this temperature.
Creep Mechanisms in Niobium-Silicide Based In-Situ Composites
Authors: Bewlay B. P. , Whiting P. W. , Davis A. W. , Briant C. L.
Published: April 2011

This paper will discuss the relationship between microstructure and creep behavior in hightemperature niobium-silicide based in-situ composites. The creep behavior of composites generated from binary Nb-Si alloys, and higher order alloys containing Mo, Hf and Ti additions, will be described. In-situ composites were tested in compression at temperatures up to 1200°C and stress levels in the range 70 to 280MPa. It was found that the Hf concentration can be increased to 7.5 with little increase in creep rate, over that for the binary Nb3Si-Nb composite, but at higher concentrations the creep rate is increased at stress levels higher than 21OMPa. At stresses less than 21OMPa the Ti concentration can be increased to 21 without a detrimental effect on creep performance, but at higher concentrations there is a substantial increase in the creep rate.
Microstructures and Mechanical Properties of Two-Phase Alloys Based on NbCr2
Authors: Chen Katherine C. , Kotula Paul G. , Cady Carl M. , Mauro Michael E. , Thoma Dan J.
Published: April 2011

A two-phase, NbCrTi alloy (bce + C15 Laves phase) has been developed using several alloy design methodologies. In efforts to understand processing-microstructure-property relationships, different processing routes were employed. The resulting microstructures and mechanical properties are discussed and compared. Plasma arc melted (PAM) samples served to establish baseline, as-cast properties. In addition, a novel processing technique, involving decomposition of a supersaturated and metastable precursor phase during hot isostatic pressing (HIP), was used to produce a refined, equilibrium two-phase microstructure. Quasi-static compression tests as a function of temperature were performed on both alloy types. Different deformation mechanisms were encountered based upon temperature and microstructure.
Microstructural Evolution during Superplastic Deformation in Large-grained Iron Aluminides
Authors: Lin Dongliang , Liu Yi
Published: April 2011

Superplastic behavior has been found in Fe3A1 and FeAl alloys with grain sizes of 100–600μm. The large-grained Fe3Al and FeAl alloys exhibit all deformation characteristics of conventional fine size superplastic alloys. However, superplastic behavior was found in large-grained iron aluminides without the usual pre-requisites for superplasticity of a fine grain size and grain boundary sliding. The metallographic examinations have shown that the average grain size of large-grained iron aluminides decreased during superplastic deformation. Transmission electron microscopy (TEM) observations have shown that there were a great number of subgrain boundaries which formed a network and among which the proportion of low and high angle boundaries increased with increased strain. The observed superplastic phenomenon is explained by continuous recovery and recrystallization. During superplastic deformation, an unstable subgrain network forms and these subboundaries absorb gliding dislocations and transform into low and high angle grain boundaries. A dislocation glide and climb process accommodated by subboundary sliding, migration and rotation, allows the superplastic flow to proceed
Plasticity Of Quasicrystals
Authors: Feuerbacher M. , Klein H. , Schall P. , Bartsch M. , Messerschmidt U. , Urban K.
Published: April 2011

Results of plastic deformation experiments on two quasicrystalline phases of different structure, icosahedral Al-Pd-Mn and decagonal Al-Ni-Co, and of an approximant phase, ξ'-Al-Pd-Mn, are described. They are interpreted on the basis of a model for the deformation process, the clusterfriction model, which is discussed in a number of modifications.
Modulated Photocurrent Measurements On Icosahedral Quasicrystals Of AI-Pd-Re System
Authors: Sakairi Yoshiko , Takeda Masatoshi , Tamura Ryuji , Edagawa Keiichi , Kimura Kaoru
Published: April 2011

Modulated photocurrent method originally developed for analyzing the electronic states of semiconductor has been applied to an Al-Pd-Re quasicrystal having high electrical resistivity. The measured DC component of the photocurrent has indicated that the mobility of the photocarrier is approximately the same as that of the dark carrier at the Fermi level. The data of the amplitude and phase shift of the AC component can be explained well by a simple model in which only the two processes, carrier generation and recombination, are involved. The recombination time obtained by fitting is by about six orders larger than those reported for semiconductors. The long recombination time as well as the energy independent mobility of carriers are discussed in view of a spiky structure in electron density of states expected for the quasicrystals.
Polymer Ultrathin Films Via Alternate Self-Assembly Adsorption of Polyelectrolyte and Azo-Dye Molecules: Photo-Induced Alignment and Lc Display Properties
Authors: Advincula R.C. , Baba A. , Kaneko F.
Published: April 2011

In this report, we describe the fabrication and photo-induced alignment of ultrathin films of small molecular azobenzene dyes and polyelectrolytes using the alternate polyelectrolyte deposition (APD) technique. The molecular self-assembly process were investigated by QCM, ellipsometry, UV-vis spectroscopy, X-ray reflectometry, and other surface sensitive spectroscopic and microscopic methods to correlate with film formation parameters. The importance of layer ordering and dye aggregation phenomena is emphasized. We then utilized polarized UV-light to induce photo-alignment of these ultrathin films and observed high anisotropies dependent on the dye, layer preparation and thickness. Fabrication of hybrid LC cells using a nematic LC reveal that in-plane homogeneous alignment is influenced by the anisotropy of the dye aggregates.
Electrical Properties of Liquid-Crystal Materials for Display Applications
Authors: Naemura S.
Published: April 2011

Both dielectric permittivity and AC conductivity are important properties of LC materials for use in displays. By taking typical LC substances as examples, quantitative data are presented on these properties. From microscopic point of view, permanent dipole of LC molecules and ions contained in LC materials play important roles in these electric properties. Quantitative discussions are also presented on these microscopic characteristics. Theoretical understandings of these properties are reviewed, providing good explanations of the relation between these microscopic and macroscopic properties.
Effect of Side Chain Substitution on the Field-Dependent Birefringence in a Series Of Chiral Smectic a Liquid Crystals
Authors: Lindle J. R. , Bartoli F. J. , Flom S. R. , Selinger J. V. , Shashidhar R. , Ratna B. R.
Published: April 2011

The field dependent birefringence and the tilt angle are measured for a series of four electroclinic liquid crystals. The zero-field birefringence decreased significantly and monotonically with the length of the siloxane side chain. For all four samples, the birefringence and the electroclinic tilt angle increased substantially with the application of a field. At 10 V/µm, the electroclinic tilt angle in DSiKN65 and TSiKN105 exceeded 22.5 degrees and the phase retardation due to the change in the birefringence exceeded a quarter wave. In all four liquid crystals, the electroclinic tilt angle and the field-dependent birefringence were shown to be strongly correlated, suggesting a common origin. Moreover, this correlation persists even at high fields where both processes undergo saturation. A simple orientational model, based on a distribution in the molecular optical axis, was developed to explain the large change in birefringence in the substituted compounds as well as the dependence of δn on electric field.
An Analysis of the Photo-Polymerization Induced Phase Separation Process in Liquid Crystal/Polymer Composite Films
Authors: Fujisawa Toru , Hayasi Masanao , Nakada Hidetoshi , Matumoto Sigeru , Tani Yuitiro , Yada Makoto , Aizawa Masao
Published: April 2011

We have analyzed the micro-phase separation during photo-polymerization in the liquid crystal/polymer composite films for a variety of light-control applications. The photo-polymerization induced phase separation process is remarkably affected by the reactivity in diacrylates and the fraction volume in liquid crystals. It is presumed that the nematic transition in a liquid crystal-rich phase and the reactivity play an important role to determine the morphology.
Deposition Kinetics and Microstructural Evolution in Sputtered TA Films: a Real-Time/In-Situ Study
Authors: Whitacre J. F. , Yalisove S. M. , Bilello J. C.
Published: April 2011

Ta films were grown using sputter gas (Ar) pressures ranging from 1.7 to 20 mTorr. This produced growth environments where incoming adatom kinetic energies ranged from over 100 eV to less than 1 eV. Film development was monitored in-situ using a x-ray diffraction set-up that allowed complete diffraction patterns to be rapidly collected without interrupting the growth process. Traditional x-ray diffraction methods, transmission electron microscopy (TEM), and transmission electron diffraction (TED) were used to examine film microstructure after growth. It was found that lower Ar pressures, which allow higher adatom kinetic energies, produced films that displayed significant grain growth, texturing, and a smooth surface morphology. Those films grown at increasingly higher Ar pressures displayed smaller grain sizes, less texturing, and increasingly porous microstructures. To further explore this effect, the Ar pressure was varied during deposition for several films. The in-situ probe allowed the effects of each pressure increment to be analyzed and compared with previous x-ray and microscopy results. It was found that the microstructure of any particular film layer depended more on the deposition conditions during its formation rather than the structure or crystallography of previous layers.
Stress Development in Mo/Si and Ru/Si Multilayers
Authors: Freitag J. M. , Clemens B. M.
Published: April 2011

The stress evolution of Mo/Si and Ru/Si multilayers sputtered under the same processing conditions has been investigated. A series of Mo/Si multilayers was also prepared with varying sputtering pressures. The stress evolution of each multilayer displays a well-defined modulation concurrent with the deposition of Mo (Ru) and Si. Large stress develops during the early stages of deposition of each successive layer with Mo (Ru) exhibiting apparent tension and Si exhibiting apparent compression. In the Mo/Si multilayers, these initial transients cause curvature changes of, ∼ 2.5 to 4.5 N/m depending on the sputtering pressure. For Ru/Si the transients exceed 8 N/m and extend across a larger fraction of the total layer thickness. Intermixing and reaction at the interfaces of Mo/Si and Ru/Si multilayers lead to a volume contraction and consequently a contraction of the bilayer period. Moreover, volume contraction due to intermixing is a stress generating mechanism that may explain the initial transients in the stress evolution. The volume of the interdiffused regions of Mo/Si and Ru/Si multilayers was estimated by measuring the contraction of the bilayer period using x-ray diffraction. The results show a strong correlation with the size of the initial stress transients suggesting that intermixing may cause them.
Highly Oriented Co Soft Magnetic Films on Si Substrates
Authors: Gong Heng , Yang Wei , Rao Maithri , Laughlin David E. , Lambeth David N.
Published: April 2011

Thin Co and Co based alloy films with the face centered cubic (FCC) structure have been epitaxially grown on single crystal Si wafers by sputter deposition. Epitaxial orientation relationships have been determined by x-ray diffraction, x-ray pole figure scans and TEM. Magnetic properties have been characterized using vibrating sampling magnetometer (VSM), torque magnetometer and BH loop tracer. Soft magnetic properties have been observed for the pure Co films.
Permanent Magnetism In Exchange-Coupled Nanocomposites
Authors: Skomski R. , Liu J. P. , Sellmyer D. J.
Published: April 2011

The magnetic properties of permanent magnetic nanocomposites are investigated both experimentally and by model calculations. Rare-earth transition-metal films and nanocomposite thin films containing a L10hard phase (PtFe) have been prepared by plasma sputtering and heat treatment. By choosing suitable heat-treatment processes a nearly ideal nanostructure and high energy products of up to about 50 MGOe have been achieved for the Fe-Pt system. The behavior of the nanocomposites is discussed in terms of a model applicable to nearly ideal magnets, where there are no pronounced shoulders in the hysteresis loops. Analytic expressions for M(H) are obtained for a number of cases, and it is discussed how the loops depend on the micromagnetic parameters of the involved phases. A novel aspect of magnetic nanostructures is that very small magnetic grains exhibit very large energy products, even if they are intrinsically soft-magnetic.
Epitaxial Co/NiAl Thin Film Growth on Si Substrates
Authors: Gong Heng , Yang Wei , Lambeth David N. , Laughlin David E.
Published: April 2011

Quad-crystal Co/NiAI/Ag thin films were epitaxially grown on hydrofluoric acid etched Si(111) single crystal substrates by sputter deposition. The orientation relationship was studied by x-ray θ;/2θ; diffraction and pole figure Φ-scan, and it was determined to be Co(image1) 11 NiAI(1 10) 11 Ag(111) 11 Si(1 11). The Ag layer contains two twin-related orientations of grains. NiAI grows with three variants of grains on the Ag(1 11) layer. Since Co(image1) contains grains with four possible easy axis directions when grown on each NiAl variant, the quad-crystal media consist of grains with twelve easy axis directions and exhibit nearly isotropic in-plane magnetic properties. Meanwhile, uni-crystal Co(image2)/NiAl(1 12) films were also epitaxially grown on Ag(110)/HF-Si(110) templates. The orientation relationships determined from these epitaxial films were very useful in understanding the texture evolution of the Co alloys on NiAl. It indicates that the Co (image2) texture evolution on the (110) texture of NiAl on amorphous substrates, such as NiP/A1Mg or glass, is due to a difficult to observe NiA1 (112) texture on the top of the (110) texture.
The Influence of Microstructure on the Magnetic Properties in Nanostructured Copt Li0Thin Films
Authors: Jeong S. , Mchenry M. E. , Laughlin D. E.
Published: April 2011

We have applied the Neel's spin pair potential model to model the dependence of magnetocrystalline anisotropy on the long range order parameter. We have produced CoPt nanoscale thin films, with and without an immiscible second phase, by RF and DC magnetron sputtering. These thin films showed a shoulder in their magnetic hysteresis, indicative of a disordered soft magnetic phase for samples annealed above 600 °C while it was barely detectable in 500–600 °C annealed samples. A (111) texture is observed in as-deposited and annealed films is identified as one of the possible contributions to the lower coercivity squareness S* and perpendicular magnetic properties. Micromagnetic calculations confirmed a poor exchange interaction, identified rotational energy barriers and inferred that the ordered region was not fully ordered. The initial stage of ordering clearly showed a discontinuous type transformation.
Spin-Valve GMR Films Based on Antiferromagnetic NiMn
Authors: Anderson Geoff , Huai Yiming , Miloslavsky Lena
Published: April 2011

In this work we have investigated the magnetic and structural properties of spin-valve films exchange biased by CoFe/NiMn compared to CoFe/lrMn spin valves. A spin-valve film of structure Ta/NiFe/CoFe/Cu/CoFe/NiMnITa showed a giant-magnetoresistance of 5.5% with a Hex∼850 Oe after annealing. Structural ordering of the NiMn in an fct phase after annealing has been observed using x-ray diffraction, with the data exhibiting pure fct(111) texture. The thermal stability of both the exchange pinning and magnetoresistance of NiMn spin-valves was evaluated. The blocking temperature (Tb) of this film is 400°C, compared to 225°C for IrMn based spin-valve films (IrMn thickness ∼50 Å). Blocking temperature distribution and remnant blocking temperature measurements also suggest that NiMn based spin-valves have far superior pinning stability with temperature than IrMn based spin-valves. Magnetoresistance measurements show a linear decrease with temperature due to electron-phonon scattering with the ∆R/R being reduced by 33% at 150°C (as compared to a 50% decrease for IrMn based spinvalves). Extended annealing at 150°C did not effect spin-valve performance, with ∆R/R and R being constant over 60 hours, suggesting that no appreciable interdiffusion is occurring.
Aggressively Scaled P-Channel Mosfets With Stacked Nitride-Oxide-Nitride, N/O/N, Gate Dielectrics
Authors: Wu Yider , Lucovsky Gerald
Published: April 2011

Ultrathin (tox,eq < 2.0 nm) Si3N4/SiO2(hereafter N/O) gate dielectrics with improved interface characteristics compared to devices with thermal oxides have been formed by remote plasma enhanced CVD of Si3N4onto oxides. If the Si-Si02 interface is intentionally nitrided prior to the Si3N4deposition, the increased physical thickness of the N/O stack combined with the interfacial nitridation reduces the direct tunneling current by more than two orders of magnitude. The ensuing device structure can then be characterized as N/O/N. The top nitride layer is also an effective boron diffusion barrier improving short channel characteristics in p+-poly PMOSFETs. In addition, nitrogen can also be transported to the silicon/dielectric interface during post-deposition RTAs, and this reduces degradation of transconductance during hot carrier stressing.
A Tale of Two Precursors: UHV-CVD of TiO2 From Titanium Nitrate and Titanium Isopropoxide
Authors: Gladfelter Wayne L. , Taylor Charles J. , Gilmer David C. , Colombo Daniel G. , Wilk G. D. , Campbell Stephen A. , Roberts Jeff
Published: April 2011

A side-by-side comparison of the TiO2 deposition kinetics and the corresponding film microstructures using titanium(IV) isopropoxide and anhydrous titanium(IV) nitrate was conducted at low pressures (< 10−4 Torr) in an ultrahigh vacuum chemical vapor deposition reactor. Titanium(IV) nitrate exhibited a lower activation energy of reaction (Er= 98 kJ/mol) which allowed deposition at lower temperatures compared to titanium(IV) isopropoxide (Er= 135 kJ/mol). Comparison of the microstructures of films deposited at similar temperatures revealed significant differences in the reaction rate limited kinetic regime. As the growth rates of the two precursors converged in the flux-limited regime, the respective microstructures became indistinguishable.
Characterization of the Seed SiO2 Layer in Stacked SiO2-Ta2O5 Gate Dielectrics
Authors: Roy Pradip K. , Laughery Michael A. , Chacon Carlos M. , Kanan Ayman M. , Daugherty Thomas
Published: April 2011

A major hurdle in the gate dielectric scaling using conventionally grown SiO2 has been excessive tunneling that occurs in ultra-thin (<25Å) SiO2. High dielectric constant materials have high concentrations of bulk fixed charge, unacceptable levels of Si-Ta2O5 interface trap states, and low Silicon interface carrier mobilities. Stacked Ta2O5 gate dielectrics have alleviated these issues with significant improvements in leakage, tunneling, charge trapping behavior, and interface substructure. Transistors fabricated using this stacked gate dielectric exhibit excellent sub threshold, saturation, and drive currents. In this study, we have characterized the first SiO2 (8-12Å) layer of the SiO2-Ta2O5 stack by ThermaWave (TWI 5240SE) absolute ellipsometry (AE) using He-Ne (λ= 630nm) laser light source and by corona oxide semiconductor (COS) non-contact techniques. We have also monitored the kinetics of a thin hydrocarbon layer deposition on top of these films that can be removed by simple heat treatments (250°C - 400°C). Electrical thickness (Tox) of these oxides measured by COS indicates this hydrocarbon layer has no impact on Tox. Stacked Ta2O5 was synthesized by metal organic chemical vapor deposition (MOCVD) of a 50-75Å thick Ta2O5 layer at 480°C, 300mTorr followed by an in-situ 550°C UV-03 anneal to densify the Ta2O5 film and grow an additional 5Å SiO2 layer underneath the first grown SiO2 layer resulting in an effective SiO2 thickness of 25-30Å (process 1). We have done exactly the same deposition schedule after chemically removing the first LP grown SiO2 layer resulting in an effective SiO2 thickness of 15-20Å (process 2). Transistors are now fabricated for our sub-0.16μm CMOS technologies. These stacked films indicated excellent charge trapping (Dit, Vfb, Qtot), leakage and tunneling characteristics from COS electrical measurements.