bluuebunny/crossref_metadata_2025 huggingface dataset:
The Boundary Between Hard- and Soft-Breakdown in Ultrathin Silicon Dioxide Films
Authors: Toriumi A. , Satake H.
Published: April 2011

The dielectric breakdown is an irreversible and transient process, and it is difficult to understand its dynamic characteristics. We notice that the post-breakdown electrical properties of silicon dioxide films may include much information on the dielectric breakdown mechanism. First, the resistance of silicon dioxide films after the dielectric breakdown is statistically investigated, and then this analysis is applied to differentiate the hard- from the soft-breakdown. In particular, we discuss the critical dependence of the boundary between the hard- and softbreakdown on the discharging time constant as well as the discharging energy at the breakdown, concerning the formation of the conductive filament in the insulator silicon dioxide films. It should be noted that the ratio of the soft- to the hard-breakdown changes in terms of the statistical distribution in the case that the growth parameters and the measurement conditions are changed. In partcular, the external inductance effect to modify the discharging time constant in the MOS circuit is discussed. The thickness limitation of the silicon dioxide film in the roadmap is in this transition region, and this fact will be of essential importance in the assessment of the reliability and the process control of silicon device fabrication in sub-5nm silicon dioxide regime.
A Study of Trap Profiles in Thin Silicon Dioxide Films at Dielectric Breakdown Using Percolation Model
Authors: Uno S. , Ishida A. , Okada K. , Sakura T. , Deguchi K. , Kamakura Y. , Taniguchi K.
Published: April 2011

A Monte Carlo simulation of wear-out process in thin silicon dioxide films is performed to investigate the correlation between the electron trap distribution and the dielectric breakdown. Non-uniformity of the trap generation and its dependence on the stress conditions are monitored by the measurements of the charge centroid. In order to include these experimental observations into Degraeve's percolation model [IEDM Tech. Dig., pp.863-866 (1995)], we introduce exponential trap profiles decaying from the Si/SiO2interface. Our new model successfully reproduces critical threshold voltage shifts from the information about critical charge centroids for various stress conditions. Finally, as a reasonable explanation of the stress dependent breakdown properties, we suggest that the bond strain caused by lattice mismatch at the interface is accelerated by the electric field.
Precise characterization of ultrathin nitride/oxide gate dielectrics by grazing x-ray reflectance and spectroscopic ellipsometry
Authors: Boher Pierre , Piel Jean Philippe , Stehle Jean Louis
Published: April 2011

Precise characterization of nitride/oxide gate structures becomes a challenging task due to the very thin thickness (<3-4nm), which will be needed in the next generation integrated circuits. Conventional techniques such as spectroscopic ellipsometry in the visible range becomes difficult to apply because of the great correlation between thickness and optical indices. To overcome this problem the following strategy is applied. First, grazing x-ray reflectance is used on all the samples to extract the different layer thicknesses using a simple model. Second, spectroscopi ellipsometry from deep UV 190nm to 850nm is applied and the results fitted with the structural models deduced from the x-ray results. In this conditions the nitrogen content of the films can be precisely determined. This kind of analysis has been made on a series of nitride/oxide gate structures with variable thicknesses and degree of nitridation. Regression results are discussed and compared to x-ray photoemission results obtained on the same samples.
Deposition and Characterization of Ultrathin Ta2O5 Layers Deposited on Silicon From a Ta(OC2H5)5 Precursor
Authors: Chaneliere C. , Autran J.L. , Reynard J.P. , Michailos J. , Barla K. , Ushikawa H. , Hiroe A. , Shimomura K. , Kakimoto A.
Published: April 2011

Ultra-thin tantalum pentoxide (Ta2O5) layers of thicknesses ranging from 6 to 10 nm were deposited by low pressure chemical vapor deposition from Ta(OC2 H5)5 on rapid thermal nitrided silicon substrates. Films were annealed in UV-O3 at 450°C, in dry O2 at 750°C or by using a combination of these two treatments. The physico-chemical properties were studied by TEM and SIMS. Results showed an oxidation of the interfacial region during annealing. The C and H contaminants are reduced during the O2 post-deposition treatment, and this step may also lead to a modification of the chemical state of C in Ta2O5. Both capacitance-voltage and current-voltage measurements were performed on Al/Ta2O5/Si structures. Excellent electrical properties were recorded: high dielectric constant (between 14.8 and 19 in the case of the double step annealing, which corresponds to an equivalent SiO2 thickness ranging from 2.0 to 2.3 nm), low leakage current densities (close to 5×10−9 A.cm−2 @ 1MV.cm−1) and promising long-term reliability.
Band Alignments of High-K Dielectrics on Si and Pt
Authors: Robertson J , Riassi E , Maria J-P , Kingon A I
Published: April 2011

Materials with a high dielectric constant (K) such as tantalum pentoxide (Ta2O5) and barium strontium titanate (BST) are needed for insulators in dynamic random access memory capacitors and as gate dielectrics in future silicon devices. The band offsets of these oxides must be over 1 eV for both electrons and holes, to minimise leakage currents due to Schottky emission. We have calculated the band alignments of many high K materials on Si and metals using the method of charge neutrality levels. Ta2O5 and BST have rather small conduction band offsets on Si, because the band alignments are quite asymmetric. Other wide gap materials Al2O3, Y2O3, ZrO2 and ZrSiO4 are found to have offsets of over 1.5 eV for both electrons and holes, suggesting that these are preferable dielectrics. Zirconates such as BaZrO3 have wider gaps than the titanates, but they still have rather low conduction band offsets on Si. The implications of the results for future generations of MOSFETs and DRAMS are discussed.
Influence of the Deposition Parameters on the Electrical and Mechanical Properties of Physically Vapor-Deposited Iridium and Rhodium Thin Films
Authors: Golecki Ilan , Eagan Margaret
Published: April 2011

Iridium and rhodium thin films have been formed by e-gun physical vapor deposition on thin-chromium-coated, thermally-oxidized, silicon substrates. Cr, Ir and Rh deposition rates and substrate temperature during deposition were measured and controlled. The effects of the latter deposition parameters on the sheet resistance and stress of the Ir and Rh films are presented and it is demonstrated that both stress and sheet resistance can be desirably minimized by proper choice of the process conditions. The resistivity of these Rh and Ir thin films has been measured at room temperature. Rh can be formed in a wider process window than Ir. Rh films with Rsh = 0.1 Ω/square have been obtained at a thickness of 0.6 ¼m.
The Influence of Thermal History and Alloying Elements on Temporary Strengthening of Thin Al-Cu Films
Authors: Lokker J. P. , Janssen G. C. A. M. , Radelaar S.
Published: April 2011

The influence of Cu on the response of Al-Cu thin films to thermally induced stress is studied. The copper concentration is varied between 0 and 1.15 at. %. It is proposed that copper atoms which have not formed precipitates, largely affect the mechanical behaviour. This idea is supported by the following observations. An isothermal hold results in temporary strengthening of the films. The extent of this strengthening increases with copper concentration, increases with decreasing isothermal hold temperature and saturates with increasing isothermal hold period. Based on these observations the large tensile stress increase below 200 °C is ascribed to the formation of Cottrell atmospheres.
In Situ Study of Dislocation Behavior in Columnar Al Thin Film on Si Substrate During Thermal Cycling
Authors: Allen Charles W. , Schroeder Herbert , Hiller Jon M.
Published: April 2011

In situ transmission electron microscopy (150 kV) has been employed to study the evolution of dislocation microstructures during relatively rapid thermal cycling of a 200 nm Al thin film on Si substrate. After a few thermal cycles between 150 and 500°C, nearly stable Al columnar grain structure is established with average grain less than a μm. On rapid cooling (3–30+ °C/s) from 500°C, dislocations first appear at a nominal temperature of 360–380°C, quickly multiplying and forming planar glide plane arrays on further cooling. From a large number of such experiments we have attempted to deduce the dislocation evolution during thermal cycling in these polycrystalline Al films and to account qualitatively for the results on a simple dislocation model.
Silicide Induced Mechanical Stress in Si: What are the Consequences for MOS Technology
Authors: Maex Karen , Steegen An
Published: April 2011

In this paper, a detailed analysis of silicide induced stress is presented. Micro-Raman spectroscopy measurements of the silicide induced stress in the silicon substrate are combined with simulations by Finite Element Modeling down to 0.1 μm MOS technologies. It is shown that the scaling possibilities of TiSi2 and of CoSi2 are both hampered by the increasing silicide stress, which can even result in the generation of dislocations in the silicon substrate. Because of the difference in material properties between TiSi2 and CoSi2, TiSi2 induces a higher stress in the silicon substrate than CoSi2. It is also proven that the silicide induced stress affects the performance of transistors and diodes. Therefore, the mechanical characteristics related to the silicide formation become a critical parameter in the optimization of the silicide for sub-0.25μm MOS technologies.
Influence of Nanometer-Scale Multilayered Thin Films on Fatigue Crack Initiation
Authors: Stoudt M. R. , Cammarata R. C. , Ricker R. E.
Published: April 2011

The hypothesis that a thin nanometer-scale multilayered surface film could delay crack initiation and extend fatigue lives was evaluated by electrodepositing a Cu-Ni multilayer on Cu fatigue samples. A significant improvement in fatigue lives resulted and this improvement is attributed to properties of the multilayer coating.
Stress Relaxation in Uniquely Oriented SiGe/Si Epitaxial Layers
Authors: Ware M. E. , Nemanich R. J.
Published: April 2011

This study explores stress relaxation of epitaxial SiGe layers grown on Si substrates with unique orientations. The crystallographic orientations of the Si substrates used were off-axis from the (001) plane towards the (111) plane by angles, θ = 0, 10, and 22 degrees. We have grown 100nm thick Si(1−x) Ge(x) epitaxial layers with x=0.3 on the Si substrates to examine the relaxation process. The as-deposited films are metastable to the formation of strain relaxing misfit dislocations, and thermal annealing is used to obtain highly relaxed films for comparison. Raman spectroscopy has been used to measure the strain relaxation, and atomic force microscopy has been used to explore the development of surface morphology. The Raman scattering indicated that the strain in the as-deposited films is dependent on the substrate orientation with strained layers grown on Si with 0 and 22 degree orientations while highly relaxed films were grown on the 10 degree substrate. The surface morphology also differed for the substrate orientations. The 10 degree surface is relatively smooth with hut shaped structures oriented at predicted angles relative to the step edges.
Coherent and Incoherent Relaxation in III-V Heterostructures
Authors: Rocher André , Snoeck Etienne
Published: April 2011

The relaxation for large lattice mismatch systems such as GaSb/GaAs and GaAs/InP has been studied by numerical analysis of HREM images. The GaSb/GaAs epitaxial system can be obtained with an interface constituted by a perfect square array of Lomer dislocations. GaSb appears to be coherently and homogeneously relaxed. For GaAs/InP grown at 450°C the GaAs layer becomes well relaxed at some distances from the interface by a network of randomly distributed partial and 60° dislocation segments with a limited length. At low temperature, the plastic relaxation appears directly at the growth front when the individual adatoms take a position different from the ideal pseudomorphic one. In this case, the relaxation mechanism is incoherent.
Wafer Scale Testing of MEMS Structural Films
Authors: Gally Brian J. , Abnet C. Cameron , Brown Stuart , Chui Clarence
Published: April 2011

Biaxial modulus and residual stress of silicon-rich silicon nitride (Si3 + xN4−x) films on silicon substrates were measured at multiple discrete locations across wafer surfaces using a versatile bulge testing method. An array of 0.2 μm thick silicon nitride membranes were fabricated across the surface of 100 mm diameter wafers. The membranes were 1 mm square. Material properties of the film were extracted by measuring the deflection of the silicon nitride membranes under controlled pressure loading conditions. Pressures from 0 to 12 psi were applied across the membranes, while their deflected shapes were measured with a white light interferometer. Numerical analysis of the measured pressure-deflection behavior of the membranes enabled the biaxial modulus and residual stress of the film to be mapped over the wafer surface. These initial results indicated that the technique was able to determine biaxial modulus to within ±1 % and residual stress within ±4 %. Furthermore, the technique can be applied to composite membranes, enabling the determination of biaxial modulus and residual stress of an additional film subsequently deposited upon the membrane film.
Nanoindentation Probing of Environmental Effects on Polymer Coating Properties
Authors: Xia X. , Rowenhorst D. , Yoder K. B. , Scriven L. E. , Gerberich W. W.
Published: April 2011

Humidity and temperature control accessories for Hysitron Triboscope have been developed to study the environmental influence on in situ properties of drying coatings. Mechanical properties of drying poly (vinyl alcohol) (PVOH) and poly (vinyl pyrrolidone) (PVP) coatings on silicon wafer were measured under different humidities. The modulus results were compared with outputs of elastic, plastic and viscoelastic theories of indentation testing.
Mechanical Properties and Toughening of a Polymethylsilsesquioxane Network
Authors: Zhu Bizhong , Katsoulis Dimitris E. , Zank Gregg A. , McGarry Frederick J.
Published: April 2011

Polysilsesquioxanes are finding wider uses in microelectronics. However these materials are brittle and their mechanical behaviors need to be better understood. In this paper the mechanical properties of a cured methyl silsesquioxane network are studied and they are found to vary strongly with curing conditions. In the investigated curing temperature range there seems to be a correlation between the fracture toughness (KIc) and the viscoelastic transitions, which are affected by the network crosslink density. A higher crosslink density suppresses the cc and β transitions and reduces the KIc. A toughening approach is designed and its applicability is demonstrated by the increased fracture toughness.
Mechanical Stress Measurements in Damascene-Fabricated Aluminum Interconnect Lines
Authors: Besser Paul R.
Published: April 2011

The mechanical stress state of damascene-fabricated Al interconnect lines was determined on an array of lines on the product die of a logic technology device. Narrow, unpassivated, damascene Al lines have a purely hydrostatic stress (108 MPa). The hydrostatic stress of damascene Al lines (411 MPa) is much larger once the dielectric is deposited. However, the maximum shear stress remains small in magnitude, compared to RIE Al lines of similar thermal history and aspect ratio. The stress of damascene lines was measured as a function of linewidth. Unpassivated, wide lines, have compressive stresses along the length and width and zero along the line height. Passivated wide lines have a biaxial, tensile stress in-plane and zero along the line height.
Passivated Interconnect Lines: Thermomechanical Analysis and Curvature Measurements
Authors: Wikström A. , Gudmundson P. , Suresh S.
Published: April 2011

It is well known that curvature measurements may be used to obtain volume averaged stresses in thin continuous films and unpassivated lines without knowledge of the material properties of the film or lines. However, recently a method was presented which makes it possible to use curvature measurements also for the determination of volume averaged stresses in passivated lines. Since the problem is statically indeterminate the method requires knowledge of the material properties of the lines and passivation. The sensitivity of the method to uncertainties in material properties and curvature data is here investigated by utilizing the finite element method for anisotropic Cu or Al lines embedded in SiO2 passivation. Furthermore, the method is extended to cover the case of different stress-free temperatures for the lines and passivation respectively.
Quantitative Study of Nanoscale Contact and Pre-Contact Mechanics Using Force Modulation
Authors: Asif S. A. Syed , Wahl K. J. , Colton R. J.
Published: April 2011

For submicron-scale mechanical property measurements, depth sensing nanoindentation techniques are very successful and gaining much attention. However, for ultra-small volumes of materials below a length scale of 10 nm, measuring the quantitative mechanical properties of materials is still a problem. The atomic force microscope (AFM) has very good surface sensitivity and has been shown to measure nanomechanical properties. However cantilever instability, conventional force detection and displacement sensing make contact area measurement difficult, hence the measured mechanical properties are usually only qualitative. In this article, we show that combining force modulation with depth sensing nanoindentation allows measurement of the mechanical properties of materials on the nanometer scale. With this technique we have studied the role of oxide layers on the mechanical response of Si surfaces. We also present a novel quantitative stiffness imaging technique, which can be used to directly map the mechanical properties of materials with submicron lateral resolution.
Hardness and Elastic Modulus Measurements of AIN and TiN Sub-Micron Thin Films Using the Continuous Stiffness Measurement Technique with Fem Analysis
Authors: Rawdanowicz T. A. , Sankar J. , Narayan J. , Godbole V.
Published: April 2011

The hardnesses and elastic moduli of aluminum nitride (AIN) and titanium nitride (TiN) sub-micron thin films pulsed laser deposited (PLD) on silicon (111) were measured using nanoindentation based on a continuous stiffness measurement (CSM) technique. Thin film thicknesses, based on profile measurements of simultaneously grown step samples, are 210 nm and 180 nm with surface roughnesses of 12 nm and 2 nm for AlN and TiN, respectively. X-ray diffraction showed AlN as a highly textured polycrystalline AlN wurzite structure with a (0001) orientation and TiN as a cubic structure with a (111) orientation. The CSM technique provided hardness and elastic modulus as a function of depth. Finite element modeling (FEM) aided in determining the optimum indenter contact depth at which the thin films behaved as a semi-infinite solid with negligible substrate induced artifacts. Hardnesses of these AlN and TiN thin films were, determined analytically, 25 GPa and 33 GPa, as compared to FEM results of 24 GPa and 30 GPa, respectively. The elastic moduli measured 320 GPa and 370 GPa for these AlN and TiN thin films, respectively.
Structural Characterization and Raman Studies of SrBi2Ta0.8Nb1.2O9 Thin Films
Authors: Srinivas S. , Das R. R. , Mercoda J. , Fachini E. R. , Perez W. , Katiyar R. S.
Published: April 2011

The effect of growth conditions such as substrate temperature and oxygen partial pressure on the microstructure and properties of pulsed laser deposited SBTN thin films on Si(100) and MgO(100) substrates have been studied. Crystallization of films begins at room temperature but, the obtained phase was non-ferroelectric. The influence of oxygen pressure (150 to 450 mTorr) on crystallinity of the films deposited on Si(100) at 750°C is negligible. XPS studies of as-deposited films reveal that the oxygen vacancies are preferably present near the Bi ions at the Bi2O2 layers and vary with substrate temperature and oxygen partial pressure. Also, XPS studies of Sr 3d core level for SBTN films suggest that the oxygen ions in the Sr(Ta/Nb)2O7 perovskite layers are much more stable than those in the Bi2O2 layers. Micro-Raman studies of SBTN films deposited below 700°C show Raman modes of a non -ferroelectric phase.
Effect of Crystallographic Texture on Ferroelectric Performance of PZT Thin Films
Authors: Fox G. R.
Published: April 2011

A large set of films with textures ranging from almost fully random to highly {111} textured were generated using an ULVAC ZX-1000 production sputter deposition machine. The PZT texture was altered by changing the {111} texture of the underlying Pt electrode, but the PZT thickness, composition, sputter deposition conditions, and crystallization anneals were held constant for all samples. X-ray diffraction peak intensities were used to calculate the volume fraction of {111}, {100}, and randomly oriented material composing the PZT films. All samples contained less than a 6% {100} textured volume fraction. It was found that the switchable polarization is linearly dependent on the {111} textured volume fraction. The voltage required to achieve 90% saturation of the switchable polarization also has a linear dependence on the {111} textured volume fraction. The rate of fatigue and degradation of the switchable polarization caused by same-state and opposite-state retention tests were independent of the {111} textured volume fraction.
Bottom Electrode Effects in Controlling Orientation of Lead Zirconate Titanate Films Deposited by Chemical Solution Deposition
Authors: Neumayer Deborah A. , Saenger Katherine L. , Laibowitz Robert B. , Shaw Thomas M. , Mih Rebecca , Grill Alfred
Published: April 2011

The microstructure and electrical properties of lead zirconate titanate Pb(Zr,Ti)O3 (PZT) films prepared by chemical solution deposition (CSD) with and without lead titanate (PT) seed layers were examined as a function of Ir/lr oxide electrode type. The novel PZT CSD solution was prepared from a mixture of zirconium and titanium butoxyethoxides and lead ethylhexanoate dissolved in butoxyethanol. The use of excess-lead (PbxsTi) and stoichiometric PT seed layers was found to promote PZT(111) orientation on Ir but not on Ir oxide. Ir substrate thickness was observed to influence orientation of PZT deposited on stoichiometric PT with greater PZT(111) texturing on thinner Ir(111) substrates. PZT with greater PZT(111) texturing tended to have greater remanent polarization (2Pr, μC/cm2). PZT deposited on stoichiometric PT seed layers on Ir(111) was of higher film quality than PZT deposited on PbxsTi seed layers on Ir(111). The PZT films deposited on stoichiometric PT on Ir(111) had enhanced PZT(111) orientation, a reduced pyrochlore content, and tended to saturate at lower coercive fields, have higher remanent polarization, squarer hysteresis loops with less tilt and greater fatigue endurance. The use of iridium oxide top electrode was demonstrated to significantly improve fatigue endurance compared to use of an iridium top electrode.
Stoichiometry and Interdiffusion in PZT Thin Films Studied by Transmission Electron Microscopy
Authors: Sagalowicz L. , Muralt P. , Hiboux S. , Maeder T. , Brooks K. , Kighelman Z. , Setter N.
Published: April 2011

Electrode stability, interdiffusion, phase purity and deviation from stoichiometry at the PZT-electrode interface are key issues in PZT thin film integration. This article highlights the use of transmission electron imaging combined with energy dispersive spectroscopy (EDS) for the investigation of these phenomena. The accuracy of the EDS analysis is discussed. It will be shown that using a standard PZT sample and controlled conditions, reliable analysis can be performed.

Diffusion mechanisms have been studied for Pt based electrode systems and RuO2-based electrode systems developed for direct integration onto silicon. The materials studied were composed of stacks of silicon-silicon oxide, an adhesion layer (Ti, Ta or TiOx), an electrode (Pt or RuG2) and PZT (45/55). The PZT was deposited by sol gel using the same parameters to allow for comparison of the different electrodes. Four different electrode / adhesion layer materials were compared (Pt/Ti, Pt/TiOx, Pt/Ta and RuO2 / TiO2). In the case of Pt, lead and oxygen diffusion through the electrode is observed. While the initial Ta layer transforms into a homogeneous pyrochlore phase, the Ti adhesion layer is heavily deformed. In the case of TiOx the lead is mainly incorporated at the interfaces with Pt and with SiO2. No lead diffusion to the adhesion layer is observed for the RuO2 electrode. In-situ sputtering and sol-gel deposition of PZT are also compared. The sol-gel films are close to the right stoichiometry for the perovskite while the sputtered films contained an excess of lead. No sign of second phase is found by X-ray diffraction (XRD), by EDS and by high resolution transmission electron microscopy (HRTEM) which suggests that the excess lead is accommodated in the perovskite lattice.
Phase Formation Studies and Structural Properties of Laser Ablated (Pb,La)(Zr, Ti)O3-Thin-Films on Stainless Steel
Authors: Klarmann R. , Kuhn M. , Schey B. , Lindner J. K. N. , Biegel W. , Stritzker B.
Published: April 2011

It is shown that high-quality La-doped PZT-films, (Pb,La)(Zr,Ti)O3, can be deposited by pulsed laser deposition (PLD) directly onto stainless steel substrates resulting in a very simple bicomponental system with high potential for sensor applications. This is an astonishing result, since there is quite a substantial lattice mismatch between the substrate and the PZT-film. Careful investigations revealed the existence of a thin oriented nickeloxide layer at the surface of the stainless steel. The formation of this interface layer leads to a reduction of the lattice mismatch thus affecting the subsequent phase formation of the perovskite PZT. The interface was examined by RBS, XRD, TEM / X-TEM studies and SIMS depth profiling. The phase formation and stoichiometry of the PZT films were investigated by XRD and EDX and their microstructure and texture by SEM and XRD pole figure measurements.
Measuring Bimodal Crystallographic Texture in Ferroelectric PbZrxTi1-x O3 Thin Films
Authors: Vaudin Mark D. , Fox Glen R.
Published: April 2011

A powder x-ray diffraction method has been developed to quantify textured volume fractions in thin films. It has been applied to {111}, {100} and randomly oriented PbZrxTi1-xO3 in 200 nm thick films used for ferroelectric random access memory applications. The integrated and peak intensities of 100, 110, 200 and 222 Bragg peaks from an untextured PZT film were determined by applying a thickness correction to a θ–2θ scan obtained from random powder of the same composition as the film. X-ray scans were made on the same peaks from the PZT film specimens. The distributions of grain orientation for the {111} and {100} populations in the films were determined from ω scans which were obtained from the films using 100, 200 and 222 scattering angles and corrected for defocussing and absorption. To determine the total volume fraction of each population of grains, the ratios of the integrated film peak intensities to the corrected powder integrated peak intensities were multiplied by the integrals of the corrected ω scans.
Low-Voltage Pb(Zr,Ti)O3 Film Capacitors: Control of Charge Relaxation at the Interfaces
Authors: Stolichnov I. , Tagantsev A. , Gentil S. , Hiboux S. , Muralt P. , Setter N. , Cross J. S. , Tsukada M.
Published: April 2011

It is suggested that the processes of charge injection and entrapment at the interfacial layer of Pb(Zr,Ti)O3 (PZT) film capacitors are responsible for both polarization fatigue and size effects on ferroelectric switching. The study of the charge injection by analyzing the dependence of coercive field on maximum polarization shows that there is a direct relationship between the charge injection properties and fatigue performance. Based on our results, we conclude that enhancement of charge relaxation at the interfaces of PZT capacitors results in two positive effects: improvement of polarization fatigue performance and suppression of size effects on ferroelectric switching, which are detrimental for low-voltage PZT film capacitors.

This idea has been implemented experimentally by introducing a thin RuO2 layer into the top-electrode interface of the Pt/PZT/Pt capacitor. PZT film capacitors of 100–170 nm thickness prepared in this way exhibited substantially improved fatigue in combination with weak size effects, which allows reduction of the operation voltage down to 0.8 V without degradation of the hysteresis properties. Our results show that the control of charge relaxation at the interface is a key issue for development of the low-voltage ferroelectric capacitors.
Ferroelectric and Piezoelectric Properties of MOCVD Pb(Mg1/3Nb2/3)O3-PbTiO3 Epitaxial Thin Films
Authors: Baumann P. K. , Bai G. R. , Streiffer S. K. , Auciello O. , Ghosh K. , Stemmer S. , Munkholm A. , Thompson Carol , Kim D.-J. , Maria J.-P. , Kingon A. I.
Published: April 2011

We have grown epitaxial Pb(Mg1/3Nb2/3)O3 (PMN) and (1-x)(Pb(Mg1/3Nb2/3)O3)- x(PbTiO3) (PMN-PT) thin films by metalorganic chemical vapor deposition at 700 - 780°C on (100) SrTiO3 and SrRuO3/SrTiO3 substrates. The zero-bias permittivity and loss measured at room temperature and 10 kHz for 220 nm thick pure PMN films were 900 and 1.5%, respectively. For PMN-PT films, the small-signal permittivity ranged from 1000 to 1500 depending on deposition conditions and Ti content; correspondingly low values for the zero-bias dielectric loss between 1 and 5% were determined for all specimens. For PMN-PT with x of approximately 0.30–0.35, polarization hysteresis with Pr,≈18μC/cm2 was obtained. Initial piezoresponse data are discussed.
Organic Light Emitting Diode Directly Fabricated on a Polymer Waveguide Device
Authors: Ohmori Yutaka , Ueta Hiroshi , Hikita Makoto , Yoshino Katsumi
Published: April 2011

Organic light emitting diodes (OLEDs) which consists of 8-hydroxyquinoline aluminum (Alq3) and diamine derivative (TPD) were directly fabricated on a polymer waveguide device. Polymer waveguide device consists of deuterated methacrylate polymer core and UV cured epoxy resin cladding. One of the edges of the polymer waveguide was cut in 45 degree, which was served as a mirror, in order to introduce the output light from OLED to the waveguide. Indium-tin oxide (ITO) or semi-transparent aluminum metal was deposited onto the polymer waveguide, which served as anode. The OLED was directly fabricated by evaporation technique at the edge of a waveguide, whose edge served as a mirror.

Emission and transmission characteristics of the light from red-light-emitting OLED are also discussed as a light source for the polymer based waveguide with low transmission loss.
Enhanced Electrooptic Activity of Nlo Polymers Via the Use of Conductive Polymers
Authors: Grote J. G. , Drummond J. P. , Zetts J. S. , Nelson R. L. , Hopkins F. K. , Zhang C. , Dalton L. R. , Steier W. H.
Published: April 2011

We have demonstrated a 3 to 13 times increase in the effective electro-optic (EO) coefficient of electrode poled nonlinear optical polymers using a conductive polymer cladding, compared to using passive polymer claddings. We have also demonstrated the lowest poling voltage to date, 300 V, for a 2 μm thick NLO polymer film. Since the cladding material is more conductive than the core material, the majority of the applied poling voltage is dropped across the core, realizing a higher EO coefficient than for conventional devices using passive polymer claddings and has the potential for in-situ poling. These results show promise for shorter, lower operating voltage devices.
Dynamic Response of the Electro-Optic Effect in Epitaxial Ferroelectric Thin Films
Authors: Hoerman B. H. , Majewski J. C. , Nichols B. M. , Teren A. , Wessels B. W.
Published: April 2011

The dynamic response of the electro-optic coefficients and the electronic polarizability for epitaxial thin films of KnbO3 and BaTiO3 are measured. For these two systems a logarithmic dependence of the electro-optic response and the polarization on time was observed after removal of an applied electric field. The dynamic response of the electro-optic effect and the polarization of the films are attributed to the same physical mechanism, which we associate with the dynamic response of ferroelectric nanodomains.
Waveguiding and 1.54 μm Er3+ Photoluminescence Properties of Erbium Doped Silicon Rich Silicon Oxide
Authors: Seo Se-Young , Han Hak-Seung , Shin Jung H.
Published: April 2011

The waveguiding and 1.54 μm Er3+ photoluminescent properties of Er doped silicon-rich silicon oxide (SRSO) are investigated. Erbium-doped SRSO films, which consist of nanocrystalline Si clusters embedded inside Si0 2 matrix, were deposited by electron cyclotron resonance plasma enhanced chemical vapor deposition of SiH4 and O2 with concurrent sputtering of erbium. The excess Si content of the SRSO films ranged from 0 to 10 at. %, and Er content ranged from 0.01 to 0.3 at. %. After deposition, films were rapid thermal annealed at temperatures between 750 and 1150°C for durations ranging from 2 to 20 min. to precipitate silicon nanoclusters. All films show strong room temperature 1.54 μm Er3+ photoluminescence. The luminescence lifetimes that can be > 6 msec. The refractive indices of the SRSO films range from 1.48 to 2.47, increasing with increasing excess Si content. Thus, waveguides can be formed easily by depositing erbium doped SRSO films on 1 μm thick SiO2 films. Furthermore, carrier-induced de-excitation mechanisms of excited erbium atoms in SRSO are nearly completely suppressed in such SRSO films, indicating that population inversion of Er3+ ions by carrier-mediated excitation is possible.
Exciting Erbium-Doped Planar Optical Amplifier Materials
Authors: Polman A.
Published: April 2011

Erbium-doped planar optical amplifiers can find numerous applications in photonic integrated circuits operating at 1.5 μm. The challenge is to fabricate these devices with high gain, operating at low pump power, and having small overall size. In this paper a review is given of our recent work in the area of Er-doped waveguide materials and amplifiers based on three materials classes: oxide films (A12O3, Y2O3, SiO2), polymers, and silicon.
Single State Absorption Spectra of Novel Nonlinear Optical Materials
Authors: Kirkpatrick Sean M. , Clark Casey , Sutherland Richard L.
Published: April 2011

During the absorption of a laser pulse of moderate length, the leading edge can experience excited state absorption out of the first singlet state. The measurement of this excited state absorption spectrum can only be accurately probed using short pulse pump-probe techniques. Specifically, we examine the excited state absorption of AF-380 in THF using ultrafast transient white light absorption spectroscopy (TWLA). This material has been the focus of several investigations due to it's purported large two-photon absorption cross-section, the discrepancies between long and short pulse measurements, and it's use in holographic twophoton induced photopolymerization. It is believed that a substantial excited state absorbance can account for the difference in two-photon cross section measurements. It is also possible that this excited state exhibits coherence for time scales that can affect further absorption of longer pump pulses. We examine the transient absorption of this species, as well as polarization and free carrier effects and discuss the possible implications with regards to measurement techniques.
Optical Power Limiters for Nanosecond Pulses: Design of New Dendritic Chromophores with Exceptionally Large Two-Photon Cross-Sections
Authors: Elandaloussi E. H. , Spangler C. , Casstevens M. , Kumar D. , Weibel J. , Burzynski R. , HE G.-S. , Prasad P.
Published: April 2011

Over the past five years there has been a renaissance in design studies of chromophores with the possibility of enhanced two-photon absorption (TPA). While two-photon absorption has been described for molecules such as laser dyes in solution for a number of years1, it has only been recently that researchers have attempted detailed structure-property relationships to elucidate how new chromophores with greatly enhanced two-photon cross-sections might be designed. Since the intrinsic cross-sections are related to the Im component of the third order optical nonlinearity, it should come as no surprise that much of the previous work in the literature which focused on structure-property relationships for molecules with enhanced NLO response might be applicable to the design of new TPA chromophores. In this presentation we will review our recent studies in this area, and our rationale for the applicability of dendritic strctures based on photonic-active repeat units for enhancment of two-photon absorption, particularly in the area of optical power limiting applications.
Fourier Transform Techniques for Measuring Absorption of Transient Species Inoptical Limiting Materials
Authors: Han Yanong , Sonnenberg Wendi , Short Kurt W. , Hyfield Amy , Spangler Lee H.
Published: April 2011

We have developed methods of measuring absorption of transient species utilizing both rapid scan and stepped-scan Fourier transform interferometery that allows a combination of broad spectral coverage (10,000 – 15,000 cm-1 per spectrum), good spectral resolution, and the ability to cover temporal ranges from minutes to nanoseconds. A wide range of pump sources are used including continuous, modulated, ns pulsed, and ultrafast lasers. The probe is provided by a broadband, incoherent source providing large spectral information in each experiment. This capability enables investigation of phenomena such as excited state absorption, charge transfer, formation of metastable species, and others. Extension of the technique to the ps realm is underway and will be discussed.
Syntheses and Optical Limiting Characterizations of a Series of Porphyrin-Buckminsterfullerene Dyads
Authors: Ang How-Ghee , Loh Zhi-Heng , Chng Leng-Leng , Lee Yiew-Wang , Yang Guo-Ying , McEwan Kenneth J. , Robertson John M. , Lewis Keith L.
Published: April 2011

We report herein the syntheses and optical limiting characterizations of a series of porphyrin-C60 dyads in which the porphyrin and C60 moieties are held within close proximity of one another by an o-phenylene bridge. The electron-donating ability of the porphyrin moiety in the dyads is systematically varied through chemical modification. This allows us to control the ease of electron transfer from the porphyrin to the C60 moiety in these dyads. Optical limiting measurements at 532 nm using 3-ns pulses show that the limiting performances of the dyads are poorer relative to their model compounds. This could be due to an ultra-short lifetime for the charge-separated species or a depopulation of the triplet states by photoinduced electron transfer. The optical limiting performances of the free-base porphyrin-C60 dyads are also related to the electron- donating abilities of the meso substituents of the porphyrin moieties. 12PorphyC60 displays better limiting performance at 532 nm (with 3-ns and 15-ns pulses) compared to Val12PorphyC60. This trend has been rationalized in terms of the relative energies of the first excited singlet and triplet states of the fullerene moiety and the charge-separated state of the dyads.
Design and Synthesis of a 33-Layer Narrow Bandpass Filter with Graded Refractive Index Profiles
Authors: Wang X. , Masumoto H. , Chen L. , Hirai T. , Someno Y.
Published: April 2011

A novel bandp ass filter consisting of graded refractive index profiles and a three-cavity stack was designed. It exhibits good optical characteristics, i.e., high transmittance (>99%) at the designated wavelength of 1550±25 nm and high reflectance (>99%) in wavelength regions of 1400±50 nm and 1780±100 nm. This designed 33-layer TiO2-SiO2 film with graded refractive index profiles was prepared by helicon plasma sputtering. The measured transmittance spectrum exhibited good agreement with the designed spectrum. The microstructure of this multilay er film was investigated using electron microscopy.
An Omnidirectional Reflector and Microcavity Resonatorvia the Sol-Gel Method
Authors: Chen Kevin M. , Sparks Andrew W. , Luan Hsin-Chiao , Lim Desmond R. , Wada Kazumi , Kimerling Lionel C.
Published: April 2011

Thin films of sol-gel SiO2 and TiO2 were used to fabricate two types of onedimensional photonic crystals: an omnidirectional reflector and microcavity resonator. The reflector consisted of six SiO2/TiO2 bilayers, designed with a stopband in the near infrared. Reflectance measurements over an incident angle range of 0–80° showed an omnidirectional band of 70 nm, which agrees with theoretical predictions for this materials system. The microcavity resonator consisted of a TiO2 Fabry-Perot cavity sandwiched between two SiO2/TiO2 mirrors of three bilayers each. We have fabricated a microcavity with resonance at λcavity = 1500nm and achieved a quality factor of Q=35. We measured a modulation in the cavity resonance frequency with a change of defect layer thickness and incident angle of light. This work demonstrates the feasibility of fabricating photonic crystals via the sol-gel method.
Carbonate Apatite-Bearing Pure Titanium Implant
Authors: Teraoka K. , Nonami T. , Taoda H. , Naganuma K. , Yokogawa Y. , Doi Y. , Kameyama T.
Published: April 2011

New bone formation around implants is one of preferable conditions for the successful implantation. In this study, formable carbonate apatite ceramics were prepared and implanted in cavities (φ 400 μm, depth 400 μm) on the surface of pure titanium implant (ASTMB348-GR2) to enhance new bone formation around the titanium implant.
Ceramic Thin Films on Organic Self-Assembled Monolayers: Synthesis and the Mechanism of Formation
Authors: Sampathkumaran U. , Supothina S. , Wang R. , De Guire M. R.
Published: April 2011

In recent years, several research groups have pursued biomimetic or bio-inspired techniques for the synthesis of ceramic thin films from aqueous solutions at low temperatures. The substrates range from inorganic materials (metals, glass, single-crystal silicon) without special surface preparation, to functionalized organic surfaces such as self-assembled organic monolayers (SAMs). Our results on the deposition of tin (IV) oxide (SnO2, cassiterite) and hydroxyapatite (Ca10(PO4)6(OH)2) thin films on SAMs will be reviewed. The former system forms films via assembly of nano-scale particles on the substrate, while the latter system appears to form films via heterogeneous nucleation. In both cases, the role of the substrate in film formation is discussed.
Morphology of Mesoporous Silica Grown on Organic Surfaces: Effects of Surface Functional Groups and Microstructures
Authors: Hozumi Atsushi , Yokogawa Yoshiyuki , Kameyama Tetsuya , Hiraku Katsumasa , Sugimura Hiroyuki , Takai Osamu , Okido Masazumi
Published: April 2011

Through organized surfactant templating, mesoporous silica (MPS) was prepared on two different types of substrates with a hydrophilic or hydrophobic surface. In this study, a Si substrate covered with photochemically-grown surface oxide was served as the hydrophilic surface. The hydrophobic surfaces were prepared by forming an organosilane self-assembled monolayer (SAM) on Si substrates through chemical vapor deposition. Octadecyltrimetoxysilane or (heptadecafluoro-1,1,2,2-tetrahydro-decyl) trimethoxysilane was used as a precursor. The morphologies of the deposited MPS on these surfaces were found to be quite different. The MPS formed on the hydrophilic Si substrate consisted of small disk-like features of 2∼5 μm in diameter, while those on the hydrophobic SAM surfaces were continuous thin films. These morphological differences of the deposited MPS were ascribable to the differences in the supramolecular template structure formed on each of the surfaces. Furthermore, in order to study microstructure effects on the MPS growth, a micropatterned SAM/Si, on which hydrophobic regions were spaced alternately with hydrophilic regions at a 5 μm-wide interval, was employed as a sample substrate. On this substrate, MPS was preferentially grown on the hydrophobic regions while the hydrophilic regions remained almost undeposited. The spatial control of surfactant-assembling using the micropatterned SAM surface was successfully accomplished.
Involvement of Cellular Membranes and their Lipids in Nucleation of Stone Forming Crystals
Authors: Khan S. R. , Fasano J. M. , Backov R. , Talham D. R.
Published: April 2011

More than 80% of human kidney stones consist of calcium oxalate and/or calcium phosphate. Human urine is generally metastable with respect to these salts and their nucleation is heterogeneous. Based on: 1. ultrastructural and immunohistochemical studies of stones in which cellular degradation products and lipids were commonly seen in association with calcific crystals and 2. in vivo studies of nephrolithiasis in rat models where calcium oxalate (CaOx) and calcium phosphate (CaP) crystals almost always formed and seen in association with cell membranes, we proposed that membranes and their lipids are involved in crystallization of these salts. To test our hypothesis we isolated organic matrix of kidney stones, its lipid contents and membrane vesicles from epithelial cells of rat kidney and incubated them in metastable solution of CaOx. Both membrane vesicles and matrix from the stones supported crystallization of CaOx and crystals formed in association with the membranes. Lipids of the stone matrix appeared better nucleators than whole matrix. Urine spends only minutes within the kidneys thus any nucleation which can lead to stone formation has to occur rapidly. In studies described here, we demonstrate that under specific circumstances relevant to conditions in the kidney, membrane vesicle- supported CaOx crystallization can occur within seconds, demonstrating the possibility of such events happening in the kidneys. We also studied CaOx monohydrate (COM) precipitation at Langmuir monolayers of dipalmitoylphosphatidylglecerol (DPPG), dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylserine (DPPS) showed precipitation to be heterogeneous and selective with a majority of crystals orienting with the 101 face of COM facing the monolayer. Our results show that membrane lipids can initiate nucleation of calcium oxalate crystals in solutions similar to those present in the kidneys. In addition these crystals form within the time urine spends inside the renal tubules demonstrating for the first time the likelihood of occurrence of such a phenomenon in the kidneys during stone formation.