bluuebunny/crossref_metadata_2025 huggingface dataset:
XPS Studies of the Si/SiO2Interface With Synchrotron Radiation
Authors: Rochet F. , Jolly F. , Dufour G. , Grupp C. , Taleb-Ibrahimi A.
Published: April 2011

Si 2pcore-level spectroscopy is a unique tool to determine the chemical composition and spatial extension of the suboxide layer present at the Si/SiO2interface. In the case of ultra-thin oxide films (thickness <10 Å), the high surface sensitivity provided by the tunability of synchrotron radiation allows the observation of four energetically well-separated oxidation states, generally attributed to a silicon atom with an increasing number of oxygen first neighbors, and hence often denoted Sin+(withn=1,…,4). After a brief review of two decades of XPS studies on the Si/SiO2interface, we give an account of the recent debate concerning the possible contribution of the second oxygen neighbor shell to the chemical shift, which, if effective, would modify the picture of the interface. Then, we examine the benefit derived from the use of very high energy resolution (70 meV athv=130 eV), and we try to determine, for this system, what are the limits of this spectroscopy. To illustrate the latter point, among various case studies (thermal oxides, room temperature adsorption etc.), we treat in more detail the case of the H-terminated Si(1 11) surface oxidized by atomic oxygen, and discuss our data in the light of previous XPS and vibrational spectroscopy studies.
Diffusional Hillock Formation in Al Thin Films Controlled by Creep
Authors: Kim Deok-kee , Nix William D. , Arzt Eduard , Deal Michael D. , Plummer James D.
Published: April 2011

Thermal hillocks in sputter-deposited Al films have been studied as a part of a broad study of stress-induced diffusional processes in Al. Trace amounts of the impurities Ti, W, and O were incorporated into the films during deposition, causing them to be much stronger than most sputter deposited Al films. Stress measurement during thermal cycling, using the wafer curvature method, showed that these Al films are very strong; this finding was corroborated by hardness measurements. Microstructural studies using TEM and FIB showed that the hillocks start to form at the Al/SiO2 interface and grow under the original Al film, with its columnar grain structure. In some cases, the film fails as hillocks grow completely through the original film. The Al film on top of the hillocks appears to inhibit hillock growth by creating a back pressure associated with power law creep of the film. We modeled this form of hillock formation by modifying the boundary conditions in Chaudhari's hillock model [1]. Our model describes hillock formation by diffusion of Al atoms from the surrounding area into isolated hillocks, assuming that the original Al film on top of hillocks deforms following power law creep. Our model can be applied to many different situations by using different creep laws for the top Al film.
Phase Formation and Mechanical Properties of Multiphase Carbide Coatings
Authors: Krzanowski J. E. , Koutzaki S. H. , Nainaparampil J. , Zabinski J. S.
Published: April 2011

We have investigated nano-structured multiphase coatings consisting of mixed carbide components. Two ternary carbide systems, Ti-Mo-C and Ti-Si-C, were examined. Coatings were fabricated by co-sputtering from carbide targets, thereby allowing a complete range of film compositions to be obtained in each system. Films were deposited on Si and sapphire substrates at temperatures ranging from room temperature to 650°C. Film compositions were determined using XPS, and x-ray diffraction and TEM analysis were used to examine the films for texture, grain size, phase stability and the potential for creating nano-structured multiphase films. Mo was found to be soluble in TiC up to about 80% Mo, and between 85–95% Mo a multiphase structure was obtained. The hardness of these films generally did not improve due to the Mo additions. For the Ti-Si-C films, X-ray diffraction results were consistent with the formation of cubic SiC and TiC phases. In these films, the hardness was found to improve with SiC additions optimally giving hardness values of about twice that of TiC alone.
Strain and Mosaic Structure in Si0.7Ge0.3 Epilayers Grown on Si (001) Substrates Characterized by High Resolution X-Ray Diffraction
Authors: Li J. H. , Moss S. C.
Published: April 2011

X-ray double- and triple-axis diffractometries were employed to characterize the strain status and structural deformation in Si0.7Ge0.3 alloy layers grown on Si (001) substrates. We show that, at low levels of strain relaxation, x-ray peaks of the Si0.7Ge0.3 alloy layers contain two components, a narrow one superimposed on a broad one. Such a peak profile corresponds to a layer structure consisting of mosaic regions laterally separated by more perfect regions. With the increase in the degree of strain relaxation and consequently in the dislocation density, the narrow component of the x-ray peak gradually disappears as a result of expansion of the mosaic regions and shrinkage or even vanishing of the perfect regions in the layer. Moreover, our results indicate that the conventional method of estimating dislocation density from the x-ray rocking curve width fails in our case.
Film Stress Influence of Bilayer Metallization on the Structure of RF MEMS Switches
Authors: Strawser R. E. , Cortez R. , O'Keefe M. J. , Leedy K. D. , Ebel J. L. , Henderson H. T.
Published: April 2011

The performance of microelectromechanical systems (MEMS) switches is highly dependent on the switches' constituent materials. The switch material must be able to provide both structural integrity and high electrical conductivity. Cantilever beams, doubly clamped beams, and membranes are typical MEMS structures used in microwave/millimeter wave applications. In this study, cantilever and doubly clamped beam microswitches were fabricated on GaAs substrates using evaporated bilayers of titanium and gold metallization in which the total thickness was held constant at 1.5 μm while the gold thickness varied from 0.5 μm to 1.5 μm. The lengths of the cantilevers varied from 300 to 500 μm and the doubly clamped beams varied from 600 to 800 μm. An upward deflection of the gold dominated cantilever beams indicated an increasing tensile stress gradient. Results of microwave characterization demonstrated higher switch isolation (off-resistance) for shorter beam switches at the expense of higher insertion loss (on-resistance) and actuation voltage. A discussion of the observed released microswitch structure within the context of the measured film stresses and electrical performance will be presented.
Stress and Stress Relaxation Study of Sputtered PZT Thin Films for Microsystems Applications
Authors: Defaÿ E. , Malhaire C. , Dubois C. , Barbier D.
Published: April 2011

Residual stresses in thin films play an important role in the mechanical behaviour of MEMS. In this paper we present a study of the stress and its relaxation for the PZT films, and associated electrodes, deposited on oxidized silicon substrates. The stresses were calculated from the bending plate method and the Stoney's equation. The radius of curvature were measured by optical profilometry before and after films deposition. The substrates (180 μm Si + 0.66 μm thermal SiO2) were coated with sputtered Ti (20 nm) and Pt (200 nm) used as bottom electrode. The global stress in the Ti/Pt layer was found compressive (−1.29 GPa) after deposition and tensile (465 MPa) after annealing (400°C, 30s, Ar). A 0.55 μm thick PZT layer was RF-magnetron sputtered and crystallized by a RTA (700°, 30s, Air). The as-deposited PZT films exhibited a little tensile stress of 43 MPa. After annealing, a tensile stress value of 363 MPa was found. Finally, we observed that the stress of the whole multilayer showed a decrease as a function of time. In order to explain this phenomenon, depth profile of each component of the PZT layer were obtained by Secondary Ion Mass Spectrometry (SIMS). This time-dependent stress relaxation was then correlated to a lead and oxygen migration across the PZT layer.
Viscoelastic Behavior of Polymer Films During Scratch Test: a Quantitative Analysis
Authors: Jardret Vincent D. , Oliver Warren C.
Published: April 2011

Dynamic properties of polymer surfaces affect their ability to withstand abrasive actions. Kinetic conditions, like velocity, penetration depth and shape of the abrasive particles, change the abrasion mechanisms and the morphology of the abraded surface. Using the scratch technique, along with profilometry measurement across the scratches, we have been able to completely characterize the residual scratch morphology. Pile-up deformation and visco-plastic relaxation are key phenomena that characterize the importance of ductility in the scratch resistance of polymer surfaces. Cross profilometry aids in studying the relaxation of the scratch morphology for different time and temperature history after the scratch is made. The effect of scratch velocity, penetration depth and indenter geometry on the contact pressure and friction coefficient estimated during a scratch test can also be analyzed. Following Eyring's law, a good correlation, was found between normal indentation and scratch testing in the evolution of the contact pressure with the applied strain rate. This work results in a better understanding of the stresses and the strains applied by an abrasive particle, and especially relates the dynamic mechanical properties of viscous materials, like stress exponent, to their scratch behavior. The method presented can provide for the measurement of dynamic properties of polymer surfaces or thin films under a very large range of strain rates.
Tensile Properties of Amorphous Diamond Films
Authors: LaVan D.A. , Hohlfelder R.J. , Sullivan J.P. , Friedmann T.A. , Mitchell M. , Ashby C.I.H.
Published: April 2011

Amorphous diamond is a new material for surface micromachined microelectromechanical systems (MEMS) and sensors. Its strength and modulus was tested in uniaxial tension by pulling laterally on a specially designed sample with a flat tipped diamond in a nanoindenter. Several sample designs were attempted. Of those, only the single layer specimen with a 1 by 2 μm gage cross section and a fixed end rigidly attached to the substrate was successful. Tensile load was calculated by resolving the measured lateral and normal forces into the applied tensile force and frictional losses. Displacement was corrected for machine compliance using the differential stiffness method. Post-mortem examination of the samples was performed to document the failure mode. The load-displacement data from those samples that failed in the gage section was converted to stress-strain curves using carefully measured gage cross section dimensions. Mean fracture strength was found to be 8.5 ± 1.4 GPa and the modulus was 831 ± 94 GPa. Tensile results are compared to hardness and modulus measurements made using a nanoindenter.
Stress in Spin Valve Multilayers During Antiferromagnetic Phase Transformation
Authors: Daniels B. J. , Bozeman S. P. , HA H
Published: April 2011

The stresses in sputter-deposited, NiMn- and PtMn-pinned top spin valve multilayers were measured using a laser-based wafer curvature technique. As-deposited stresses were 150 to 180 MPa in compression for NiMn- and 970 to 1020 MPa in compression for PtMn-pinned spin valves. Following deposition and stress measurement, these films were annealed in an applied magnetic field of 250 Oe for 2 hours at 300°C. This anneal causes the antiferromagnetic layer to undergo a phase transformation from the face-centered cubic (fcc) to the face-centered tetragonal (fct) crystal structure. This phase transformation increases the average stresses in the spin valves to 740–800 MPa in tension for the NiMn-pinned spin valves and to 475–580 MPa for the PtMnpinned spin valves. Stress changes during the antiferromagnetic phase transformation were also observed as a function of annealing temperature and time during substrate heating, annealing, and cooling. The stress varied nearly linearly with temperature during the heating and cooling of the substrate, indicating that the bulk of the phase transformation occurs during the isothermal portion of the anneal. By monitoring stress vs time during the isothermal anneal, the progression of the antiferromagnetic phase transformation was observed. Final stress data obtained from the wafers annealed in the wafer curvature system (no applied magnetic field) are within 10% of those obtained using the magnetic annealing process.
Microcrystalline and Nanocrystalline Diamond Film Deposition on Cobalt Chrome Alloy
Authors: Fries Marc D. , Vohra Yogesh K.
Published: April 2011

The cobalt chrome alloy Co-28Cr-6Mo is widely used in human joint replacement applications. These joints are highly sensitive to wear and are usually replaced after approximately ten years of use. In order to extend these implants' service lifetimes, a thin film of diamond may be applied to the implant wear surfaces by microwave plasma chemical vapor deposition (MPCVD) following MPCVD nitridation. Diamond films often delaminate from cobalt chrome due to a high thermal expansion mismatch. Additionally, under most conditions diamond films degrade into graphite by dissolution of nuclei into solvents like Co and Cr. By nitriding the cobalt chrome through MPCVD prior to diamond deposition, a usable diamond film may be achieved. It may be possible to merge both the nitriding and deposition steps into a single process, since both nitridation and deposition will be performed by MPCVD. In addition, controlled amounts of nitrogen in hydrogen/methane plasma under CVD conditions result in a nanostructured diamond coating. We have investigated the formation of both micro- and nanocrystalline diamond formation on cobalt chrome.
Intrinsic Stress Measurements in CVD Diamond Films
Authors: Yu Jin , Kim J. G. , Sohn Y. C. , Lee Y. S.
Published: April 2011

Diamond films were grown over Si substrate at 1253K by the hot filament chemical vapor deposition method using CH4/H2 gas mixture, and intrinsic stresses in the film were deduced from the ex-situ curvature measurements. In order to account for the creep deformation of the Si substrate, an elastic/plastic stress and strain analysis were conducted. Results showed that intrinsic stresses were generally several times larger than the average film stresses and always positive increasing with the film thickness. For the film thickness larger than 10μm, stress relaxation by creep of the substrate became significant, and must be considered for the accurate assessment of the film stress in diamond. Later, an analysis based on the grain growth accounted for the development of intrinsic stresses reasonably well.
Evaluation of Mechanical Properties of DLC-TiC Microlaminate Coatings
Authors: Bahl R. , Vedawyas M. , Patel D. , Kumar Ashok , Shamsuzzoha M.
Published: April 2011

Microlaminate coatings are made of many alternating layers of two hard materials that, when combined in very thin layer on the nanometer scale, produce coatings with hardness that approaches diamond. In this report, we address these properties, from our investigations on the multilayer structures of titanium carbide (TIC) and diamond-like carbon (DLC) deposited on Si (100) substrates using pulsed laser deposition (PLD) technique. X-ray diffraction and Raman spectroscopy were used for the structural studies and the mechanical properties were analysed by the nano-indention technique. Microlaminate coatings of TiC/DLC and DLC/TiC coatings with varying layers were deposited on Si(100) substrates. Analysis of mechanical properties revealed that the hardness and modulus values of the multi-layers lie between those of monolithic coatings of TIC and DLC.
Effects of Seeding Over the Microstructure and Stresses of Diamond Thin Films
Authors: Gupta S. , Morell G. , Katiyar R. S. , Gilbert D. R. , Singh R. K.
Published: April 2011

We have studied diamond films grown by electron cyclotron resonance-assisted chemical vapor deposition (ECR-CVD) at low pressure (1.0 Torr) and temperatures (550–700 °C). These films were grown on seeded Si (111) substrates with different diamond seed densities (0.225, 1.5, 2.3, and 3.1 × 109 nuclei/cm2). Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy (RS) were employed to investigate the crystalline quality, diamond yield, and stresses developed in the films as a function of seeding density. Thermal interfacial stress, interactions across grain boundaries, and internal stress were considered in order to account for the total stress observed from the Raman band. We present correlations among seed density, relative amount of non-sp3 phase, O/C ratio, and total intrinsic stress.
Micromechanical Analysis of Residual Stress Effect in CVD-Processed Diamond Wafer
Authors: Jeong J.-H. , Kwon D. , Lee J.-K. , Lee W.-S. , Bai Y.-J.
Published: April 2011

Diamond wafer, considered as promising material for electronic substrate, thermal spreader, etc., has been made using deposition technology such as microwave plasma assisted CVD (MPACVD). However, high residual stress of diamond film induces bowing and throughthickness cracking in thick diamond wafer, and so hampers the economic fabrication of the wafer. Thus, to investigate the causes of bowing and cracking, the measurement of residual stress is very important. Of the residual stress, in particular, growth stress is one of the most important research topics because its effect on wafer-related problems is strong though the magnitude is relatively small. Quantification of growth stress is limited because of hightemperature plastic deformation of Si substrate. In this study, the initial growth stress without contribution of plastic deformation of substrate can be predicted through proposed beam bending stress model and numerical calculation in that plastic deformation of Si is considered. Finally, growth stress of film can be calculated from the apparent curvature of substrate measured just after deposition and the plastic curvature after diamond film removal.
On the Robustness of Scratch Testing for Thin Films: the Issue of Tip Geometry for Critical Load Measurement
Authors: Jardret Vincent D. , Oliver Warren C.
Published: April 2011

Scratch and abrasion resistance of hard protective thin films and polymer coatings is often related to their ability to withstand abrasive conditions without fracturing. Wear particles generate catastrophic and severe wear for hard films, and fractured scratches are often very visible on shiny polymer surfaces. Using a particular abrasive particle shape, the fracture resistance of a surface can be characterized by the load required to create fracture damages. The scratch technique has demonstrated its ability to create these damage mechanisms and characterize the critical load for coatings failure. However, this technique does not yet have the reproducibility and robustness required to be implemented in an industrial environment. The major reason for this lack of robustness is the great influence of the indenter geometry on critical load results and the non-reproducibility of the geometry of conical indenters. This paper addresses this issue and presents a fast and robust method to characterize the indenter geometry based on the indentation technique. Indenters, with radii smaller than 1 micron, were used to characterize thin films of different nature and thickness. The influence of tip geometry on the critical load results is presented for paint coatings. The reproducibility of the critical load measurement using different indenter tips of identical geometry, as shown in this paper, represents a considerable technological breakthrough in abrasion testing and demonstrates the scratch test's ability to control the manufacturing quality of thin films in an industrial environment.
Stress, Microstructure and Temperature Stability of Reactive Sputter Deposited Ta(N) Thin Films
Authors: Leedy K. D. , O'Keefe M. J. , Grant J. T.
Published: April 2011

Interest in tantalum nitride thin films for use as diffusion barriers in Cu-based microelectronic interconnects merits the study of tantalum nitride thin film properties as a function of deposition conditions and elevated temperature exposure. In this investigation, the influence of nitrogen content and post deposition annealing on the stress, microstructure and resistivity of Ta(N) films was analyzed. Ta(N) thin films were deposited by reactive dc magnetron sputtering of a Ta target in Ar/N2 gas mixtures. With an increasing N2 to Ar flow ratio, the as-deposited crystal structure of the films changed from ß-Ta to bcc Ta with N in solid solution to TaN0.1 to Ta2N and finally to TaN. The as-deposited Ta(N) stress, grain size and resistivity of the films were found to be strongly dependent on the phase(s) present. Films with less than 20 at. % nitrogen concentration displayed large compressive stress increases during 650°C anneals in flowing N2. Phase transformations to Ta2N occurred after 650°C anneals in films with nitrogen concentrations from ∼ 15 to 25 at. %. Microstructural characterization using transmission electron microscopy and x-ray diffraction, and chemical analysis by x-ray photoelectron spectroscopy and Auger electron spectroscopy of the Ta(N) films were used to identify the as-deposited and transformed phases.
Room Temperature Deposition of Silicon Oxynitride Films with Low Stress Using Sputtering-Type Electron Cyclotron Resonance Plasmas
Authors: Gao D. , Furukawa K. , Nakashima H. , Gao J. , Wang J. , Muraoka K.
Published: April 2011

Silicon oxynitride (SiOxNy) films with low stress were deposited successfully at room temperature using sputtering-type electron cyclotron resonance (ECR) plasmas. Films were deposited for a wide range of flow rate ratio of O2 to N2 at a constant Ar flow rate. Film properties were verified by characterizations of refractive index (ellipsometry), structural properties (Fourier transform infrared and Auger electron spectroscopy), intrinsic stress, and barrier strength of water penetration (thermal desorption spectroscopy). A near-stoichiometric SiOxNy (x = 1.44 and y = 0.41) film with low stress could be formed at the optimum deposition condition, under which the SiOxNy film had a refractive index of 1.54. The results of thermal desorption spectroscopy measurements showed that the SiOx Ny film had a higher barrier against moisture penetration relative to deposited SiOx and SiNy films. The SiOxNy film was directly deposited on the organic EL device and the applicability was shown clearly. These results indicate that this SiOxNy film deposited using a sputtering-type ECR plasma has the potential to be utilized as a passivation layer of organic EL devices, which are required to be formed at low temperature.
Studies of Plasticity in Thin Al Films Using Picosecond Ultrasonics
Authors: Antonelli G. A. , Maris H. J.
Published: April 2011

We have developed a new technique for the study of the onset of plastic flow in thin metal films. A sub-picosecond light pulse is absorbed at the upper surface of the film. This generates a strain pulse that propagates through the film to the substrate and then back to the upper surface of the film where it is detected. When the temperature of the film is changed, there is a change in the transit time of the strain pulse. This change arises from the variation of the sound velocity with temperature, and also has a contribution from thermal stress in the film. By making accurate measurements of the transit time, we are able to identify the onset of plastic flow in the film.
Hydrogen Induced Plastic Deformation of Thin Films
Authors: Pundt A. , Laudahn U. , Hüilsen U. v. , Geyer U. , Wagner T. , Getzlafft M. , Bode M. , Wiesendanger R. , Kirchheim R.
Published: April 2011

The mechanical behavior of a thin film that is clamped to an elastically hard substrate can be compared to a bulk metal by studying the absorption of hydrogen. Since hydrogen is dissolved in interstitial sites and exerts force on neighboring metal atoms, the in-plane stresses increase with increasing hydrogen concentration. In the case of Nb-films covered with a thin Pd layer, stresses of several GPa were measured. Nb and Pd films prepared by evaporation were loaded with hydrogen. Out-of-plane strain and in-plane stresses during electrolytic loading with hydrogen were determined by performing x-ray diffraction and substrate curvature measurements. At low H-concentrations the developing stresses correspond to a clamped film expanding elastically out-of-plane only. Above a critical H-concentration the films deform plastically. In some cases the critical hydrogen concentration corresponds to the terminal H-solubility, above which the hydride precipitates by emission of extrinsic dislocation loops. For the remaining cases a critical stress is reached before passing the phase boundary, which leads to the formation of misfit dislocations at the interface between film and substrate. The concomitant slip lines were observed on the surface of a Gd (0001) film using Scanning Tunneling Microscopy. An additional surface pattern that can be correlated with emitted dislocation loops was observed.
Plasticity in Copper Thin Films
Authors: Weihnacht V. , Brückner W.
Published: April 2011

Plastic deformation in thin Cu films was studied by stress measurements with the wafercurvature technique during thermal cycling and in combination with four-point bending. The results from 0.5 ¼m and 1 ¼m thick Cu films are compared. In thermal cycling experiments, strengthening during cooling and a Bauschinger-like effect during reheating were observed. The stress-strain behavior investigated by four-point bending showed to be asymmetric regarding tension and compression at lower temperatures. These phenomenons are explained by a dislocation arrangement at the film-substrate interface which has formed during a previous thermal cycle.
Relation Between Macro- and Microstress in Thin Metallic Layers
Authors: Seijbel Léon J. , Delhez Rob
Published: April 2011

X-ray diffraction has been used to measure the stress in thin nickel films. In addition to the stress value, information is obtained about the elastic interaction between grains. Various models exist to calculate the stress from the strain. A model that uses the mechanical elastic constants has been used. From this model it can be concluded that the model by Hill is applicable for the layers analyzed. Annealing experiments between 300 and 500 K show that the initially present growth stress reduces to zero at 500 K. The microstrain inside the grains is obtained from the broadening of the diffraction lines measured. During annealing the diffraction lines narrow. This is caused by two effects: grain growth and reduction of the dislocation density.
Crystal Structures, Ferroelectric Properties, and Chemical Reactions of SrBi2Ta2O9: Solid-State Chemistry of SBT Materials for FeRAMs
Authors: Shimakawa Y , Kubo Y
Published: April 2011

We discuss some aspects of solid-state chemistry concerning ferroelectric SrBi2Ta2O9, (SBT). Crystal structure analysis by high-resolution neutron diffraction revealed considerable structural distortion in the SBT materials. This distortion, which consists of large atomic displacements of constituent ions, causes large ferroelectric spontaneous polarization. The structural distortion is more pronounced in Sr-deficient-and-Bi-excess material Sr0.8Bi2.2Ta2O9 than in stoichiometric SBT, leading to the larger remanent polarization. The enhanced structural distortion is explained in terms of an “ionic size effect” at the A-cation site. This effect was apparently observed in a series of compounds of ABi2Ta2O9 (A=Ca, Sr, and Ba) with different size A-site cations. On the other hand, analysis of chemical reactions of SBT gave important information on the degradation of the SBT capacitors and on the reaction between the SBT materials and a Pt electrode during device fabrication. The degradation of SBT in an H2- containing reducing atmosphere and its recovery by subsequent annealing in oxygen have been reproduced experimentally by using bulk ceramics and analyzed by thermogravimetric and x-ray- diffraction measurements. SBT decomposes into Bi metal or Bi-Pt alloy in H2 by oxygen dissociation. In the presence of Pt, the SBT degradation and the re-crystallization processes differ from those for SBT alone.
Low-Temperature Processing Using Triple Alkoxide Precursors for Layer-Structured Perovskite Thin Films: Preparation and Characterization of Mbi2Ta2O9 (M: Ca or Ba) Thin Films
Authors: Kato K.
Published: April 2011

CaBi2Ta2O9 and BaBi2Ta2O9 thin films were successfully prepared by using triple alkoxide precursors such as Ca[BiTa(OC2H5)9]2 and Ba[BiTa(OC2H5)9]2, respectively. As-deposited films were amorphous and crystallized below 500°C by rapid thermal annealing in oxygen. The crystallinity improved with annealing temperature. The development of the crystal structure and surface topography of the thin films were investigated. Additionally, some electrical properties were evaluated.
Preparation of Al Doped PZT Thin Films Using a Sol-Gel Method
Authors: Iijima T. , Sanada N. , Hiyama K. , Tsuboi H , Okada M.
Published: April 2011

Al substitution for Zr/Ti site of PZT was attempted using a sol-gel method, and the ferroelectric properties of 200nm-thick Al doped PZT thin films were compared with those of non- doped PZT film. The leakage current of the thin films decreased with increasing Al content. Ps and Pr also decreased with increasing Al content, whereas Ec did not show a significant change. Furthermore, a simple capacitor cell structure like FeRAM was prepared using a seed layer process. The capacitor structure was Pb(Ti0.975Al0.025)O3/ Pb1.1((Zr0.52Ti0.48)0. 975Al0.025)O3/ Pb(Ti0.975Al0.025)O3, and 2Pr was 26μC/cm2. The fatigue properties of the A1 doped PZT capacitor cell showed a little improvement, because the reduction rate of the fatigue was smaller than that of non-doped PZT thin film.
Effect of Pb Excess Content on Microstructure and Electrical Properties of Sol Gel Derived PZT Thin Films
Authors: Wang Zhan-jie , Maeda Ryutaro , Kikuchi Kaoru
Published: April 2011

Lead zirconate titanate (PZT) thin films were fabricated by a three-step heat-treatment process which involves the addition of -10, 0 and 10 mol% excess Pb to the starting solution and spin coating onto Pt/Ti/SiO2/Si substrates. Crystalline phases as well as preferred orientations in PZT films were investigated by X-ray diffraction analysis (XRD). The microstructure and composition of the films were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA), respectively. The well-crystallized perovskite phase and the (100) preferred orientation were obtained by adding 10% excess Pb to the starting solution. It was found that PZT films to which 10% excess Pb was added had better electric properties. The remanent polarization and the coercive field of this film were 34.8 μC/cm2 and 41.7 kV/cm, while the dielectric constant and loss values measured at 1 kHz were approximately 1600 and 0.04, respectively. Dielectric and ferroelectric properties were correlated to the microstructure of the films.
Sputtered Pb(Zr, Ti)O3 Thin Films for Ferroelectric Capacitors
Authors: Sakoda T. , Aoki K. , Fukuda Y.
Published: April 2011

Sputtered Pb(Zr, Ti)O3 thin films with superior ferroelectric properties were successfully obtained by controlling the grain structure and the film compositions. We found that amorphous PbTiO3 buffer layers are effective in forming PZT thin films with fine dense grains. The sputtered PZT thin films with Ti-rich phase showed excellent ferroelectric properties. The polarization retention properties of PZT capacitors with Ti-rich phase are remarkable, and the value of the retained polarization density after 10 years is expected to be larger than 40 μC/cm2. Further, 150-nm-thick PZT capacitors with Zr/Ti=30/70 showed 2P, at 1.5 V of more than 30 μC/cm2, and good retention property. These results indicate the potential of the lower voltage operation of sputtered PZT capacitors by optimizing the film composition and thickness.
Temperature Dependence of the Reversible and Irreversible Polarization Contributions in Ferroelectric Thin Films
Authors: Bolten D. , Böttger U. , Grossmann M. , Lohse O. , Waser R. , Kastnert M. , Schindlert G. , Dehmo C.
Published: April 2011

In this paper the temperature dependence of reversible and irreversible polarization contributions in the temperature range between 223 K and 473 K is investigated to elucidate the microscopic mechanism responsible for reversible and irreversible changes of the ferroelectric polarization. Small signal capacitance measurements under dc-bias are used to measure the reversible contributions. Quasi-static hysteresis measurements are used to obtain the total polarization, i.e. the sum of the reversible and irreversible contributions. The combination of both measurements allows the separation of the reversible and irreversible parts. The reversible and irreversible contributions are demonstrated for SrBi2Ta2O9 (SBT), SrBi2Ta2-xNbxO9 (SBTN) thin films and compared to tetragonal PbZr0.3Ti0.7O3 (PZT) thin film capacitors.
Structural and Electrical Characterization of Rare Earth Doped Pb0.85La0.15TiO3 Ferroelectric Thin Films
Authors: Dobal P. S. , Das R. R. , Roy B. , Katiyar R. S. , Jain S. , Agrawal D. C.
Published: April 2011

Rare earth (Gd+3 and Ce+3) substitution on La+3 sites of the sol-gel prepared Pb0.85La0.15TiO3 films is studied using x-ray diffraction, atomic force microscopy, Raman scattering, and electrical characterization techniques. With increasing content of rare earths an increase in the lattice tetragonality was evidenced from x-ray data. Raman spectra obtained form Pb0.85La0.15-xCexTiO3 (x=0.0–0.07) and Pb0.85La0.15-xGdxTiO3 (x=0.0–0.15) films show features characteristics of PbTiO3 perovskite. Frequency variations of the lowest soft mode as a function of the composition x and temperature corraborate the increased tetragonality in these films. The ferroelectric transition temperature, dielectric constant, and coercive field was found to increase with Gd content. The phase transition temperature and polarization values increase up to 5 at.% Ce doping while they decrease above that composition due to the reduced domain wall mobility caused by Ce precipitation. A slight increase in the surface roughness was observed with increasing rare earth content in these films.
Depth Profiling of Solution-Deposited Lead Zirconate Titanate Thin Films by Radio Frequency Glow Discharge Atomic Emission Spectroscopy (RF-GDAES)
Authors: Brinkman K. S , Schwartz R. W. , Marcus R. K , Anfone A.
Published: April 2011

Compositional depth profiles have been obtained on chemical solution deposited lead zirconate titanate (PZT) thin films using radio-frequency glow discharge atomic emission spectroscopy. The technique is very rapid, requiring less than one minute for complete multi-element depth profiling of films and multilayer substrates. In the present study, the method was employed to obtain compositional profiles of the various metallic (Pb, Zr, Ti, Si) and organic-related (C, H, O) species that are present in the films and underlying device. Preliminary results using this relatively new technique are reported for PZT films deposited by an aqueous acetate process and heat treated at temperatures ranging from 300 and 700°C. The initial results from these investigations suggest that Pb volatilization occurs at temperatures as low as those typically encountered during the pyrolysis step. Significant interdiffusion of the Pb into the underlying Pt electrode at this temperature is also suggested. Effects of modifying ligand on film thickness and organic decomposition behavior were also observed.
Effects of In-Situ DC-Bias on the Composition, Microstructures and Dielectric Properties of RF Magnetron Reactive Sputtered (Ba,Sr)TiO3 Films
Authors: Chan Wen-Hao , Shen Hui-Ling , Chou Lih-Hsin , Wang Jinn-Lung , Tsai Jyi-Ching
Published: April 2011

Thin films of (Ba,Sr)TiO3 (BST) have been prepared by rf magnetron reactive sputtering using single alloy target, and in-situ negative DC-bias. Post annealing was applied to the asdeposited films at 620°C for 2 hours in 1 atm oxygen atmosphere. Thin film microstructures
and grain sizes were studied and calculated by means of X-ray diffraction, while the film composition was analyzed by Electron Probe X-ray Microanalyzer (EPMA). The dielectric constant of the films was also studied. As the applied DC-bias increased, the dielectric constant increased from 176 to 912, the x-ray diffraction patterns became more intense and narrower, and the (Ba+Sr)/Ti molar ratio increased from 0.70 to 0.83. In-situ DC-bias was observed to be a feasible fabrication process to increase the grain size and relative permittivity of sputtered BST films.
Gate Stacks for Low Voltage Ferroelectric Field Effect Devices Based on Pt/SBT/CeO2/Si(100)
Authors: Haneder T. , Hönlein W. , Bachhofer H. , Ullmann M. , von Philipsborn H. , Waser R.
Published: April 2011

METS (Metal Ferroelectric Insulator Semiconductor) capacitors were fabricated using CSD (Chemical Solution Deposition). Thin layers of CeO2 were deposited as an insulating buffer layer on Si(100) substrates and SrBi2Ta2O9 (SBT) was used as a ferroelectric layer. Pt electrodes were deposited by evaporation on top of the SBT layer. At constant SBT thickness the thickness of the CeO2 layer was varied to investigate the effects of the change in capacitance ratio between the ferroelectric and the buffer layer. XRD spectra were used to determine the phase of the SBT and the quality of the CeO2 layer. C(V) measurements showed the ferroelectric nature of the SBT. Additional information was provided by TEM and EDX analysis.

Some samples showed a memory window as big as 1.6 Volt at a moderate voltage sweep from −3.5 to +3.5 Volt. Interface state density is approximately 2×1011/cm2 eV and remanent polarization was found to be in the range of 0.3 μC/cm2. These results are already very promising in terms of fabricating a Ferroelectric FET. Some basic considerations with respect to the development of IT memory cells on the basis of this kind of transistor will also be presented.
Effect of Y-Doping on the Dielectric Properties of BatiO3 Films Deposited in Reducing Atmospheres Using Pulsed Laser Deposition
Authors: Choi Won-Youl , Tsur Yoed , Randall Clive A. , Trolier-McKinstry Susan
Published: April 2011

BaTiO3-based multilayer capacitors with Ni electrodes are fired at low Po2 to prevent the oxidation of Ni. Amphoteric dopants such as Y, Ho and Dy are used to prevent electrical degradation due to oxygen vacancy migration. This paper describes use of this approach in preparing thin film BaTiO3 capacitors. Tolerance of reducing atmospheres is particularly important in films which are co-processed with resistors such as TaN for integrated resistor-capacitor networks. To assess this approach, films with and without Y-doping were grown in pure N2 atmospheres by pulsed laser deposition from undoped and 0.2wt% Y2O3 doped BaTiO3 targets, respectively. Films were deposited onto Pt/Ti/SiO2/Si substrates using a 5∼10Hz laser repetition rate, an energy density of 4.2J/cm2 and a working pressure of 100mTorr. It was found that polycrystalline perovskite films could be grown at 700°C and that Y-doped films had better crystallinity than the undoped ones. The dielectric constants of films without and with Y-doping are ∼1100 and ∼1300 at lkHz, respectively. The dielectric losses of Y-doped films were lower than for undoped films, possibly because the concentration of mobile charges including oxygen vacancies was decreased. Y-doped films also have a smaller coercive field (25kV/cm) and higher maximum polarization (∼20μC/cm2) than undoped films. The defect chemistry of the system is also discussed.
Orientation and Composition Dependence of Piezoelectric-Dielectric Properties of Sputtered Pb(Zrx,Ti1-x)O3 Thin Films
Authors: Hiboux S. , Muralt P. , Setter N.
Published: April 2011

In-situ, reactively sputter deposited 300 nm thick Pb(Zrx,Ti1-x)O3 films on Pt/Si based substrates are investigated as a function of composition and texture. (111) PZT is grown on a (111) oriented Pt bottom electrode covered with a very thin TiO2 film. Highly {100} oriented PZT is grown on Pt (111) by means of a 10 nm thick PbTiO3 seed layer. Pronounced deviations from known bulk PZT behavior are observed for the (111) texture. Maximum of d33 and ε are shifted to 40/60 and 45/55 compositions, respectively. (100) textured films exhibit a higher d33. 1.3 μm (100) thick films attain the predicted d33 value of clamped bulk ceramics. Coercive fields and voltage offsets increase strongly with increasing Ti content. In parallel, the as-grown polarization increases. Polarization switching is not possible for x ≤ 0.1. Post-anneals in O2 and hot poling show that oxygen vacancies play an important role in this phenomenon. Ti-rich (100) oriented films exhibit very high and stable pyroelectric and piezoelectric coefficients whithout poling treatments.
Epitaxial PMN-PT Relaxor Thin Films: Dependence of Dielectric and Piezoelectric Properties on Film Thickness
Authors: Nagarajan V. , Alpay S. P. , Ganpule C. S. , Nagaraj B. , Aggarwal S. , Roytburd A. L. , Williams E. D. , Ramesh R.
Published: April 2011

The effect of substrate induced constraint and misfit strain on the structure and piezoelectric properties of epitaxial relaxor ferroelectric lead magnesium niobate-lead titanate (PMN-PT) films were investigated. Relaxor PMN-PT epitaxial 100–400 nm thick films with top and bottom oxide electrodes were grown by pulsed laser deposition on (100) LaAlO3 substrates. A systematic decrease in the temperature of the dielectric maximum with increasing film thickness was observed. This is accompanied by an increase in the room temperature relative dielectric constant. The longitudinal piezoelectric coefficient measured using a scanned probe microscope, increases by almost an order of magnitude with increasing film thickness.
Integrated (Pb,La)(Zr,Ti)O3 Heterostructure Waveguide Devices Fabricated by Solid-Phase Epitaxy
Authors: Nashimoto K. , Nakamura S. , Moriyama H. , Haga K. , Watanabe M. , Morikawa T. , Osakabe E. , Takeda T.
Published: April 2011

Heterostructures of a Pb(Zr,Ti)O3 (PZT) waveguide/(Pb,La)(Zr,Ti)O3 (PLZT) system buffer layer were grown on a Nb-doped SrTiO3 (Nb:ST) substrate by solid-phase epitaxy. The propagation loss in the PLZT heterostructure waveguides was on the order of I dB/cm. An electro-optic beam deflection device with an ITO prism electrode on the surface of the PLZT heterostructure waveguide presented efficient deflection of the coupled laser beam by applying a voltage between the electrode and the substrate. A beam deflection greater than 10 mrad at 5 V and frequency response as fast as 13 MHz were observed. An apparent electro-optic coefficient as large as 39 pmJV was estimated from the deflection characteristics for the TE mode and TM mode suggesting the polarization independent nature of the PZT waveguide. For integrating the electrooptic PLZT heterostructure waveguides, channel waveguides were fabricated in the PZT waveguides using a simple wet-etching process. Based on a low-voltage drive structure, lowloss waveguide process, and fine patterning process, a fabricated digital matrix switch showed a – 10 dB cross-talk at a voltage as low as 7.5 V.
Rotating Disk Reactor-Low Pressure Metal Organic Chemical Vapor Deposition (Mocvd) of Optical Films
Authors: McAleese John , Provost L. Gary , Tompa Gary S. , Colibaba-Evulet Andrei , Gulmac Nick G. , Doyle John J.
Published: April 2011

Over the past 30 years, the need for transparent conducting oxide coatings has been met almost exclusively by tin doped indium-oxide. As the display market advances in complexity, the demand for alternative transparent materials exhibiting high conductivity and stability has become greater. In this paper, we discuss briefly the merits of using doped ZnO as a superior transparent conducting oxide. We report here our results in scaling our ZnO MOCVD reactor technology from 5° to 12° diameter susceptors. Using Rotating Disk Reactor-Low Pressure Metal Organic Chemical Vapor Deposition, we have been able to obtain large area uniformity on multiple (14 cm × 9 cm) glass sheets per deposition run. Promising film characteristics suggest significant application in the field of flat panel displays and other optical systems may be possible.
Pdlc-Based Device for Optical Limiting
Authors: Feneyrou P. , Genty F. , Chastaing E. , Barny P. Le , Delboulbe A. , Dentan V. , Loiseaux B. , Huignard J P.
Published: April 2011

The scattering properties of polymer dispersed liquid crystal (PDLC) composites are studied and applied to optically addressed devices for the protection against continuous wave laser. The geometry of the device is chosen with respect to its scattering efficiency, linear transmission and response time. The optical limiting performances of this PDLC-based device are measured at 514 nm.
Liquid Crystal Devices for Light Limiting Applications
Authors: Patel J. S. , Zhuang Zhizhong , Kim Young Jin
Published: April 2011

In this paper, we introduce a novel liquid crystal structure, the Inverse Twisted Smectic Structure (ITSS), which has several advantages over the previously reported twisted smectic structure. Both these structures are capable of high-speed, gray scale modulation and phase modulation capability. Additionally, the easy fabrication of the ITSS makes it more attractive for practical applications. We discuss the use of this structure and the fabrication devices using the ITSS. Possible applications, such as the birefringence wavelength filter (BWF), and the digital wavelength filter (DWF) are also discussed and demonstrated experimentally.
Non Linear Optical Properties of Singlewall Carbon Nanotubes for Optical Limiting
Authors: Vivien L. , Anglaret E. , Riehl D. , Hache F.
Published: April 2011

Optical limiting properties of singlewall carbon nanotubes suspended in water have been evaluated with 7 ns pulses at 532 and 1064 nm and compared with those of other materials. In order to determine the origin of optical limiting, we carried out a Z-scan experiment at 532 nm and 1064nm at different input energies. We evidenced strong nonlinear scattering and a refractive effect with a negative nonlinear index. The kinetics of nonlinear transmission, from the nanosecond to millisecond time scale, was studied using a pump-probe set-up at 1064nm. We observed cavitation bubbles growth at low input energy. The different nonlinear effects evidenced are discussed in terms of physical origin and in terms of broadband optical limiting efficiency.
Improved Characteristic Temperature (TO) of a 1.3-μm GaInNAs/GaAs Single-Quantum-Well Laser Diode Through Thermal Annealing
Authors: Kitatani T. , Kondow M. , Nakahara K. , Uomi K. , Tanaka T.
Published: April 2011

Through optimal thermal annealing of the active region of a 1.3 μm GaInNAs/GaAs single-quantum-well laser diode, we obtained a characteristic temperature (T0) of 215 K under pulsed operation from 20°C to 80°C. This is the highest yet reported value for a 1.3-μm semiconductor laser. Even under continuous-wave operation, the T0 was as high as 147 K. The lasing-wavelength change with temperature was as small as 0.39 nm/°C, indicating the excellent stability for a GalnNAs laser diode with T0 of over 200 K. These results demonstrate that GaInNAs is a promising material for fabricating long-wavelength laser diodes used for opticalfiber communications.