bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature Effect on Vapor Phase Etching of Ground Silicon Substrate and Surface Morphology
Authors: He Yifei , Zakaluk Gregory
Published: April 2011

We have been using the low-cost method of fabrication of epitaxial wafer for discrete devices for many years. This low-cost operation is done by eliminating the conventional but costly polishing procedure, instead of using grinding, cleaning and etching processes prior to epitaxy growth. The etching step is needed to remove any residual grinding scratches and possible remaining contamination. In this study, etching is accomplished with HCl gas at a temperature range from 1120 to 1150 °C, at atmospheric pressure. The surface analysis and inspection techniques were used to test residual grinding scratch removal and point defect density. It is found that the temperature effect on the etch rate is small, but the surface morphology with ground pattern is very sensitive to the etching temperature. The study revealed the presence of regions of temperature which the silicon surface has a minimum of grinding scratches and little etch pits. The etching temperature has strong effect on the substrate surface thereby strongly impacting subsequent epitaxial layer morphology. The different morphologies and their temperature dependence can be explained on the basis of the thermodynamics of the surface and role of surface diffusion and evaporation.
SOI Formation from Amorphous Silicon by Novel Gain Enhancement Method
Authors: Yuen C.Y. , Poon M.C. , Chan M. , Qin M. , Chan W.Y. , Shivani S. , Ko P.K.
Published: April 2011

Large grain (> 10 um) poly-Si film has been formed from nickel Metal Induced Lateral Crystallization (MILC) and subsequent high temperature annealing. The fabricated thin film transistors (TFT) have near SOI performance. The new technology has good potential to provide low cost SOI substrates, multi-layer devices and other novel applications.
Homogeneity of Thermally-Annealed Lightly Fe-Doped SI InP
Authors: Avella M. , Jimenez J. , Fornari R. , puente E. De La
Published: April 2011

Lightly Fe-doped semiconducting InP samples have been rendered semi-insulating by thermal annealing and subsequently studied by Hall effect, Scanning Photocurrent (SPC) and Scanning Photoluminescence (SPL). Hall measurement shows that the semi-insulating conversion is generally associated to an improvement of the mobility. SPL and SPC measurements show that the distribution of both electrically active iron and compensation ratio is homogeneous after annealing. The cooling rate was seen to influence the compensation ratio.
Micro-Raman Study of Charge Carrier Distribution and Cathodoluminescence Microanalysis of Porous gap Membranes
Authors: Tiginyanu I. M. , Kalceff M. A. Stevens , Sarua A. , Irmer G. , Monecke J. , Cojocari O. , Hartnagel H. L.
Published: April 2011

Porous layers and free-standing membranes were fabricated by anodic etching of n-GaP substrates in a sulphuric acid solution. Micro-Raman analysis of the interaction between the longitudinal optical phonons and plasmons in porous membranes allowed us to obtain specific information about the electro-optical properties of microstructured GaP. In particular, apart from the carrier exhausted areas surrounding the pores, the existence of conductive regions was demonstrated. A comparative analysis of the secondary electron and panchromatic cathodoluminescence (CL) images evidenced an increase in the emission efficiency caused by porosity. Data concerning the spectral distribution of CL in bulk and porous samples are presented.
Study of GaSb Junction Devices by Cathodoluminescence and Scanning Tunneling Spectroscopy
Authors: Hidalgo P. , Méndez B. , Piqueras J. , Dutta P. S.
Published: April 2011

GaSb p-n junctions formed by Zn diffusion in Te-doped n-GaSb single crystalline wafers have been characterized by cathodoluminescence (CL) microscopy and by scanning tunneling spectroscopy. CL plane-view observations of the Zn diffused side enable to study the homogeneity of the diffusion treatment. Spectra recorded by current imaging tunneling spectroscopy (CITS) in the n and p sides of the junction, clearly show the respective conductive behaviour and provide information on the local surface band gaps. Results are related to the diffusion profile measured by secondary ion mass spectrometry (SIMS).
Nondestructive Analysis of Current Gain of InP/InGaAs Heterojunction Bipolar Transistor Structures using Photoreflectance Spectroscopy
Authors: Sugiyama Hiroki , Watanabe Noriyuki , Watanabe Kazuo , Kobayashi Takashi , Wada Kazumi
Published: April 2011

InP/InGaAs heterojunction bipolar transistor (HBT) wafers grown by metal-organic vapor phase epitaxy (MOVPE) have been characterized by photoreflectance (PR) spectroscopy. The intensity of PR signals from the InP emitter and InGaAs collector layers of the HBT wafers decreased with increasing emitter growth temperature and showed a linear positive correlation with the HBT current gain. On the other hand, the intensity of PR signals from the n-InP single layers scarcely changed with increasing InP growth temperature. The change in the PR intensity of the emitter and collector layers is expected to reflect the crystal quality of the adjacent InGaAs:C base layer, which determines the HBT current gain. Thus, the present PR method is eminently suitable for the nondestructive analysis of the current gain of InP/InGaAs HBT wafers.
Investigation of Deep Levels in GaP Liquid Phase Epitaxial Layers on Substrates with Vapor Pressure Heat Treatment
Authors: Yu T. J. , Suto K. , Nishizawa J.
Published: April 2011

We fabricated GaP liquid phase epitaxial layers with temperature difference method under controlled vapor pressure (TDM-CVP), successively to GaP substrate annealing at growth temperature (1133K) under various phosphorus vapor pressures around the optimum one (150 torr) for stoichiometric crystallization of GaP. Photocapacitance (PHCAP) and photoluminescence measurements have been carried out for characterizing GaP substrate crystals and the LPE layers and for revealing the mechanism of defect formation. Over one order of magnitude decrease of deep level densities in PHCAP has been observed after substrate crystals are annealed. Compared to the layers on substrates without heat treatment, similar tendency of deep level density deduction has been found in GaP LPE layers on heattreated substrates. In photoluminescence measurements, an obvious decrease of 700nm-band intensity from heat-treated substrates, as well as increases of green band intensities from GaP LPE layers on heat treated substrates, have been observed at 77K. Phosphorus interstitial is suggested to be possibly related to the origin of deep level centers in the GaP substrate crystals. It is considered that during the process of heat treatment at growth temperature, under the optimum phosphorous pressure, the defects in GaP substrate crystals reach an equilibrium state, so that their diffusion to the growth layer decreases greatly.
Interplay of charge, orbital and magnetic order in Pr1−xCaxMnO3
Authors: Zimmermann M. v. , Hill J.P. , Gibbs Doon , Blume M. , Casa D. , Keimer B. , Murakami Y. , Tomioka Y. , Tokura Y.
Published: April 2011

We report resonant x-ray scattering studies of charge and orbital order in Prl−xCaxMnO3 with x=0.4 and 0.5. Below the ordering temperature, To=245 K, the charge and orbital order intensities follow the same temperature dependence, including an increase at the antiferromagnetic ordering temperature, TN. High resolution measurements reveal, however, that long range orbital order is never achieved. Rather, an orbital domain state is formed. Above To, the charge order fluctuations are more highly correlated than the orbital fluctuations. We conclude that the charge order drives the orbital order at the transition.
Synchrotron Small Angle X-ray Scattering Study of Melt Crystallized Polymers
Authors: Georgiev Georgi , Dai Patrick Shuanghua , Oyebode Elizabeth , Cebe Peggy , Capel Malcolm
Published: April 2011

In this paper we report a synchrotron small angle x-ray scattering (SAXS) study of development of structure in semicrystalline Poly(Ether Ether Ketone), (PEEK) and an 80/20 blend with amorphous Poly(Ether Imide) (PEEK/PEI). Samples were treated to dual stage melt crystallization scheme involving initial isothermal crystallization at T1 followed by a second isothermal period at T2 (T1 < T2). Intensity of small angle scattering was measured in real-time. Structural parameters characterizing the lamellar thickness, 1c, long period, L, and SAXS invariant were deduced from the one-dimensional electron density correlation function assuming an ideal, two-phase structural model.
Plastic Deformation and Recrystallization Studied by the 3-D x-ray Microscope
Authors: Jensen D. Juul , Kvick Å. , Lauridsen E.M. , Lienert U. , Margulies L. , Nielsen S.F. , Poulsen H.F.
Published: April 2011

A newly developed synchrotron instrument – the so-called 3D X-ray microscope – is presented. The instrument is placed at the Materials Science beamline at ESRF and dedicated to local μm scale structural characterization within bulk materials. In this paper, emphasis is onin situstudies of thermomechanical processing. The potential of the instrument for characterization of single nuclei and grains is described and discussed based on both first results and planned experiments.
Raman Characterization of Composition and Strain in Si1−xGex/Si Heterostructures
Authors: Liu Ran , Tillack B. , Zaumseil P.
Published: April 2011

High quality epitaxial Sil−xGex/Si (x= 0.09 to 0.27) samples were studied with polarized Raman scattering technique. The LO (longitudinal optical) -TO (transversal optical) phonon mode splitting due to the tetragonal strain imposed by the lattice mismatch between Sil−xGexand Si was observed for the first time in such structures. In contrast to the case of uniaxial stress, the biaxial stress induces a larger strain frequency shift for the LO mode than for the TO mode. The phonon strain shift coefficient for the LO mode was found to be 1010 cm−1, which is larger than most of the values reported in the literatures, and almost composition independent throughout the range ofx≤0.27. We argue that the smaller LO strain shift coefficients indicate that the Sil−xGexfilms used in previous work were partially relaxed.
Real-Time optical Characterization and Control of Heteroepitaxial GaxIn1−xP Growth by P-Polarized Reflectance
Authors: Dietz N. , Ito K. , Lauko I. , Woods V.
Published: April 2011

The characterization and control of thin film growth processes requires improved methods of characterization and understanding of decomposition pathways and surface reaction kinetics under steady-state epitaxial growth involving organometallic precursors. In this contribution we present the application of p-polarized reflectance spectroscopy (PRS) for real-time monitoring and control of pulsed chemical beam epitaxy (PCBE) during low temperature growth of epitaxial Ga1−xInxP heterostructures on Si(001) substrates by PCBE, where the growth surface is sequentially exposed to organometallic precursors. During the pulsed precursor supply the surface reaction kinetics can be followed by analyzing a periodically in composition and thickness modulated surface reaction layer (SRL), which is captured in the PR-signals as a fine structure that is superimposed to the interference fringes caused due to the underlying growing film. The optical response is linked to the growth process via a reduced order surface kinetics (ROSK) model and integrated as a control signal in the implementation of filter and control algorithms for closed-loop controlled growth of epitaxial Ga1−xInxP heterostructures on Si(001) substrates. The control concept has been applied for thickness and compositional graded multi-heterostructure GaxIn1−xP epilayers and validated by ex-situ post-growth analysis, showing superior tracking of composition and thickness targets under closed loop controlled conditions compared to films grown using pre-designed source injection profiles (open-loop conditions).
Development of Nondestructive Method for Prediction of Crack Instability
Authors: Schroeder J. L. , Eylon D. , Shell E. B. , Matikas T. E.
Published: April 2011

A method to characterize the deformation zone at a crack tip and predict upcoming fracture under load using white light interference microscopy was developed and studied. Cracks were initiated in notched Ti-6A1-4V specimens through fatigue loading. Following crack initiation, specimens were subjected to static loading during in-situ observation of the deformation area ahead of the crack. Nondestructive in-situ observations were performed using white light interference microscopy. Profilometer measurements quantified the area, volume, and shape of the deformation ahead of the crack front. Results showed an exponential relationship between the area and volume of deformation and the stress intensity factor of the cracked alloy. These findings also indicate that it is possible to determine a critical rate of change in deformation versus the stress intensity factor that can predict oncoming catastrophic failure. In addition, crack front deformation zones were measured as a function of time under sustained load, and crack tip deformation zone enlargement over time was observed.
Atomic-Scale Structure of the Si-SiO2 and SiC-SiO2 Interfaces and the Origin of Their Contrasting Properties
Authors: Buczko Ryszard , Pennycook Stephen J. , Pantelides Sokrates T.
Published: April 2011

One of the reasons for the dominance of Si in microelectronics is the quality of the Si-SiO2 interface. In contrast, development of SiC-based MOSFETs for power applications is hampered primarily by poor carrier mobility at the SiC-SiO2 interface. Here we review recent calculations that elucidate the reasons of the contrasting properties of the two interfaces. In the case of Si, the interface energy is in fact lower when the interface is abrupt and smooth because of the intrinisic geometry of the Si (001) surface and the softness of the Si-O-Si angle. However, two energe ically degenerate phases are possible, leading to domain boundaries, that are the cause of subcxide bonds, steps, and dangling bonds. In principle, these effects may be avoidable by low-temperature deposition. In contrast, the geometry and bond lengths of SiC surfaces are not suitable for abrupt and smooth interfaces, requiring the existence of a nonstoichiometric interlayer that may be the cause of the reduced mobility.
Mesoscopic Transport in Broken Down Ultrathin SiO2 Films
Authors: Miranda E. , Suñe J. , Rodriguez R. , Nafria M. , Aymerich X.
Published: April 2011

A common theoretical framework is presented to model the conduction characteristics of the two main dielectric breakdown modes in ultrathin SiO2 gate oxides, namely the soft and hard breakdown modes. The breakdown paths are considered to behave as mesoscopic quantum point contacts so that the conduction properties are controlled by energy funneling effects. An adiabatic approach to the modelling of these quantum point contacts is adopted to obtain an analytical approximation for the total transmission coefficient. In the limit of small breakdown spot areas, tunneling through a potential barrier associated with the lower electron transversal state at the narrowest part of the constriction explains the soft breakdown characteristics. For larger areas, such a barrier dissapears and conductance quantization is predicted. Experimental results are well explained by the model, including the conductance values after the hard breakdown and the oxide thickness independence of the current-voltage characteristic after the soft breakdown.
Mechanical Properties of Al Thin Films as Measured by Bulge Testing
Authors: Wang Yinmin , Edwards Richard L. , Hemker Kevin J.
Published: April 2011

Free-standing rectangular Al thin films have been fabricated using sputter deposition and standard micromachining techniques. Mechanical properties and residual stresses of both asdeposited and annealed Al films were measured by bulge testing. The films were loaded into the plastic deformation regime, and then unloaded and reloaded several times. The pressure and deflection of the thin films were recorded and used to generate stress-strain curves. The planestrain elastic modulus, flow stress and plastic behavior of the Al thin films were used to characterize the mechanical response of these films. The Al films were measured to have a plane-strain modulus that is slightly lower than the literature values for a {111} textured film. The Von-Mises equivalent yield stress was measured to be higher in the annealed films but much more significant strain hardening was observed in the as-deposited films. A plastic hysteresis was observed on unloading and reloading stress-strain curves of the as-deposited Al films but not the annealed films.
Bending Response of a 100nm Thick Free Standing Aluminum Cantilever Beam
Authors: Taher M. , Saif A. , Haque Aman
Published: April 2011

A micro instrument is developed to apply force on free standing cantilever samples with suborm thickness. The objective is to study the effect of small thickness on the strength of materials when subjected to bending. The instrument consists of a MEMS actuator, 2mm × 3mm in size, and 20μm deep. It is employed to study an annealed Al cantilever sample, 110nm thick, 2μm wide and 15μm long, fabricated by evaporation. The sample yields at 841M Pa during the first cycle of loading. It is then unloaded and reloaded, when yielding occurs at 1200M Pa. To the best of our knowledge, this is the first reported experiment on free standing submicron metal film subjected to bending.
Residual Stresses in MEMS Structures
Authors: Majumdar B. S. , Cowan W. D. , Pagano N. J.
Published: April 2011

The magnitude and origin of residual stresses in thin polysilicon MEMS structures are discussed in this article. The curvature of polysilicon beams were determined at different temperatures. An accurate method of analysis that avoids the thick substrate approximation is described. The polysilicon beams without an Au layer exhibited temperature-independent curvatures, indicating that their residual stresses were largely process related. Beams with an Au top-coat exhibited a strong temperaturedependent effect, and allowed derivation of a stress-free temperature of 143°C. The technique allowed an independent estimate of the thermal expansion coefficient of polysilicon, namely 2.5×10−6 to 3.1×10−6/°C.
Ion Implantation and Misfit Dislocation Formation in P/P+Silicon
Authors: Feichtinger Petra , Fukuto Hiroaki , Sandhu Rajinder , Poust Benjamin , Goorsky Mark S.
Published: April 2011

We determined that self implantation of pseudomorphically strained silicon epitaxial layers greatly attenuates strain relaxation. We employed highly boron doped 150 mm diameter silicon with a nominally un-doped, 2.5 μm thick epitaxial layer (p/p+). The compressively strained layer (mismatch ≈ 1.5 × 10−4) showed inhomogeneous relaxation after epitaxial growth, with misfits forming only near the wafer periphery. High temperature rapid thermal annealing was employed after ion implantation to study misfit dislocation nucleation and glide. Our results suggest that low dose ion implantation has a potential to reduce misfit dislocation propagation and nucleation in epitaxial thin films.
Analysis of Adhesion Strength of Interfaces Between Thin Films Using Molecular Dynamics Technique
Authors: Iwasaki T. , Miura H.
Published: April 2011

We have developed a molecular-dynamics technique for determining the adhesion strength of the interfaces between different materials. In this technique the extended Tersoff-type potential is applied to calculate the adhesive fracture energy defined as the difference between the total potential energy of the material-connected state and that of the material-separated state. The adhesion strength of metal/dielectric interfaces as well as metal/metal interfaces is discussed based on this fracture energy. We used this technique to determine the adhesion strength of the interfaces between ULSI-interconnect materials (Al and Cu) and diffusionbarrier materials (TiN and W). The calculated adhesive fracture energy shows that the adhesion strength increases in the order: Cu/TiN, Cu/W, Al/W, and Al/TiN. Because this result was confirmed by scratch testing on the film-laminated structure, this technique is considered to be effective for determining the adhesion strength.
Adsorption/Desorption Phenomena in Silicate Glasses: Modeling and Application to a Sub-Micron Bicmos Technology
Authors: Hoffmann T. , Senez V. , Leduc P.
Published: April 2011

In this study, we present a numerical model, implemented in our two-dimensional Finite-Element process simulator, allowing the evaluation of the mechanical stress generated by deposited oxides in case of adsorbing or desorbing of water. Using both in-situ and ex-situ measurements of stress, the model parameters (water diffusion, evaporation rate, viscosity) are calibrated. Moisture instability of doped silicate glasses, like borophosphosilicate (BPSG) and phosphosilicate (PSG), is investigated. Moreover, an extension of the present model to simulate the densification of Spin-On-Glass (SOG) will be demonstrated. A failure analysis of a specific structure in an industrial process will validate the capability of the model to evaluate and minimize the risk of cracking in SOG films during densification.
Stress Effects on Al and Al(Cu) Thin Film Grain-Boundary Diffusion
Authors: Liu X.-Y. , Liu C.-L.
Published: April 2011

Stress effects on grain-boundary diffusion in Al and Al(Cu) thin films are evaluated through atomistic simulations. Specifically, the grain-boundary vacancy formation and migration and interstitial migration energetics are obtained as a function of stress states in thin film. In general, the activation energies vary at a rate of 0.1 eV per 1.0 % strain at the grain boundary investigated, indicating the possible impact on electromigration phenomenon in these films.
Measurement of Residual Stresses by Load and Depth Sensing Spherical Indentation
Authors: Taljat B. , Pharr G. M.
Published: April 2011

The finite element method was used to determine whether load and depth sensing indentation with spherical indenters may be useful in the measurement of residual stresses in materials. The spherical indentation process for a wide range of elastic/ideal-plastic materials to which compressive and tensile biaxial stresses were applied was simulated using standard finite element techniques. The elastic moduli and yield stresses of the materials were varied systematically to model the behavior of a wide variety of metals and ceramics. Elastic-ideal-plastic materials were considered in the study with residual stress levels varied from zero up to the yield stress. All three indentation regimes - elastic, elastic-plastic, and plastic - were examined, with emphasis given to the elastic and the early part of the elastic-plastic regimes, where differences in the load-displacement characteristics caused by residual stress were found to have a significant effect. Systematic examination of the relationships among residual stress, contact pressure, and elastic recovery revealed a simple, measurable indentation parameter which correlates well with the residual stress. Using this parameter, an experimental technique is proposed by which residual stresses can be estimated from measurements of the load of an indentation in the elastic-plastic regime, the yield stress, and the elastic modulus of the material, all of which can be determined by load and depth sensing indentation methods. Based on a critical examination of the technique by finite element simulation, the technique appears promising.
Mechanical Characterization of Surfaces by Nanotribological Measurements of Sliding and Abrasive Terms
Authors: Enders S. , Grau P. , Berg G.
Published: April 2011

To investigate the fumdamentals of the behavior of the friction of surfaces, nanotribological experiments have been performed on coated systems with thin glass films (SiO2-structure) and bulk fused silica, increasing the load on a Berkovich indenter oriented in edge or face-forward direction, respectively. The results depend strongly on the normal load and the contact area. For interpreting these results a new method of data analysis is presented, which explains the load dependence of the friction coefficient comprehensively. Particular attention is also focused on the effect of adhesion forces between the moving pairs. The good agreement between theory and experiment and the reasonable values of the material parameters obtained by fitting prove the validity of the presented analytical model.
Activation Volume for Inelastic Deformation in Polycrystalline Ag Films at Low Temperatures
Authors: Kobrinsky Mauro J. , Thompson Carl V.
Published: April 2011

The low temperature (T < 100 °C) inelasticity of polycrystalline Ag thin films on thick substrates has been studied. In-situ Transmission Electron Microscopy and stress-relaxation experiments indicate that thermally-activated glide of dislocations through forest-dislocation obstacles is the dominant inelastic mechanism. Values of the activation volume for inelastic deformation obtained with both experiments are reported. The mean distance between obstacles along the length of moving dislocations was found to be significantly smaller than the thickness of the film and the average grain size, which explains why current models for dislocationmediated plasticity underestimate the strength of thin films. Results from these experiments on Ag are expected to be representative of other metallic thin films (e.g. Cu and Au) on substrates.
The Microstructure, Phase and Ferroelectric Properties of PZT Thin Films on Oriented Multilayer Electrodes
Authors: Li Tingkai , Hsu Sheng Teng , Gao Yufei , Engelhard Mark
Published: April 2011

Three kinds of oriented electrodes of Pt, Ir and Pt/Ir electrodes were prepared using electron beam evaporation techniques for deposition of PZT thin films. An oxide MOCVD reactor with liquid delivery system was used for the growth of PZT thin films. [Pb(thd)2], Zr(TMHD)4 and Ti(IPO)4 were dissolved in a mixed solvent of tetrahydrofuran or butyl ether, isopropanol and tetraglyme to form a precursor source. The deposition temperature and pressure were 500 - 650°C and 5 - 10 Torr, respectively. The experimental results showed PZT thin film deposited on various electrodes had different phase formation, microstructure and ferroelectric property. The X-ray patterns showed the perovskite phase of PZT was formed on both Ir and Pt/Ir electrodes at 550°C. The grain size of the PZT thin film increases after a further, higher temperature annealing. The as-deposited PZT thin film on Pt electrode exhibits pyrochlore phase at 550°C. The phase is transformed to perovskite phase after 650°C annealing. The experimental results also indicated that the MOCVD PZT thin film on Pt/Ir exhibits better ferroelectric and electrical properties compared to those deposited on Pt and Ir electrodes. A 300 nm thick PZT thin film on Pt/Ir electrode has a square, well saturated, and symmetrical hysteresis loop with 2Pr value of 40 μC/cm2 and 2Ec of 73 kV/cm at an applied voltage of 5 V. The hysteresis loop of the PZT thin film is almost saturated at 2 V. The leakage current of the film is 6.16 × 10−7 A/cm2 at 100 KV/cm. The electrode effects on ferroelectric properties of PZT thin films also have been investigated.
Effect of La Dopant on Electrical Properties of Pb(Zr,Ti)O3 Thin Film Capacitors
Authors: Kim Chang Jung , Chung Ilsub
Published: April 2011

Lanthanum doped lead zirconate titanate (PZT) thin films have been prepared on Pt/IrO2/Ir/SiO2/Si substrates to improve the ferroelectric and retention properties. The microstructure and electrical properties of the PZT capacitors were evaluated as a function of La content. The crystalline orientation was appreciably influenced by the addition of La in PZT thin films. The microstructures of films containing 0 and 0.5 mol% La were single phase perovskite, but for La = 1 mol%, a second phase was detected by SEM observation. The 0.5 mol% La doped PZT thin film capacitor showed the best ferroelectric and retention properties for ferroelectric random access memory compared to non-doped PZT.
Characterization of Ferroelectric BaTiO3 (100) Surfaces by Variable Temperature Scanning Surface Potential Microscopy and Piezoresponse Imaging
Authors: Kalinin Sergei V. , Bonnell Dawn A.
Published: April 2011

Variable temperature atomic force microscopy (AFM), scanning surface potential microscopy (SSPM) and piezoresponse imaging were applied to the characterization of a model BaTiO3(100) surface. The influence of the domain structure on surface topography, surface potential and piezoresponse image is discussed. The domain induced surface corrugations and piezoelectric response were found to disappear above the Curie temperature in full agreement with theoretical expectations. Relaxation of apparent surface potential after the transition to paraelectric state on heating and during the transition to ferroelectric state on cooling was observed. The kinetics of potential relaxation was orders of magnitude slower than that of the transition.
Domain Images and Retention Properties of Pb(Zr,Ti)O3 Thin Films Observed by Electrostatic Force Microscopy
Authors: Jo William , Kim D. C. , Hong J. W.
Published: April 2011

We report results on domain retention in preferentially oriented Pb(Zr,Ti)O3 (PZT) thin films on Pt and on LaNiO3 (LNO) electrodes. Effects of bottom electrodes on domain images and retention properties have been explored by detecting an electrostatic force exerted on the biased conductive probe. It was demonstrated that polarization loss of PZT crystallites on LNO appears to be less than that of PZT grains on Pt. Moreover, charge retention was controlled by a reverse-poling protocol during electrostatic force microscopy (EFM) measurements. The surface charge density of the PZT films was observed as a function of time in a selected area where a region is single-poled and another region is reverse-poled. The retention behavior of the regions is very different; the single-poled region shows a declined response and the reverse-poled region reveals a retained characteristic. Decay and retention mechanisms are explained by space-charge redistribution and trapping of defects in the films.
Microstructure and Electrical Properties of PZT Thin Film Heterostructures on Silicon by pulsed laser deposition
Authors: Chattopadhyay Soma , Sharma A. K. , Kvit Alex , Jin Chunming , Lee C. B. , Collis W. J. , Narayan J.
Published: April 2011

We have been successful in the fabrication of (001) oriented epitaxial PZT films on YBCO/SrTiO3/MgO/TiN/Si heterostructures by pulsed laser deposition. The films were observed to be single phase by X-ray diffraction. The deposition parameters were varied to obtain the best epitaxial layer for each of the compounds. Transmission electron microscopy was employed for understanding of the structure, crystallinity and interfaces for each of these epilayers. Dielectric and P-E hysteresis loop measurements were carried out with evaporated Ag electrodes. The dielectric constant for the films was found to be around 380–400. The value of saturation polarization Ps was between 40–50 μC/cm2 and the coercive field Ec varied from 45–55 kV/cm. Integration of PZT films with silicon will be useful for future memory and micromechanical devices.
Structure - Property Relationships of Thin Films of Epitaxial Ferroelectric Bismuth-Layered Perovskites with Even and Odd Aurivillius' Parameters
Authors: Pignolet A. , Harnagea C. , James A. R. , Senz S. , Zakharov N. D. , Hesse D.
Published: April 2011

Thin films of bismuth-layered perovskites with the generic formula (Bi2O2)2+(An- 1BnO3n+1)2- with an even Aurivillius' parameter n like SrBi2Ta2O9 (n = 2) and BaBi4Ti4O15 (n= 4) and with an odd Aurivillius' parameter like Bi4Ti3O12 (n= 3) and Ba2Bi4Ti5O18 (n=5) have been grown by pulsed laser deposition on epitaxial conducting LaNiO3 electrodes on single crystalline (100) SrTiO3 or on top of epitaxial buffer layers on (100) silicon. The films are shown to grow epitaxially, however, they do not have a single crystallographic orientation but several preferred orientations. The films consist of both c-axis-oriented regions and mixed (110)-, (100)- and (001)-oriented regions. The regions with mixed orientation feature rectangular as well as equiaxed crystalline grains embedded in a c-oriented matrix, protruding out of its smooth surface. Macroscopic as well as microscopic measurements of the ferroelectric properties of regions with pure c-orientation and of regions with mixed orientations showed a clear relationship between their ferroelectric properties and their morphology and crystallographic orientation. In the regions with mixed orientation, the films exhibited saturated ferroelectric hysteresis loops with well-defined remanent polarization Pr and coercive field Ec. The regions having c-axis orientation with a smooth surface morphology, in contrast, exhibited a linear P-E curve with no hysteretic behavior for SrBi2Ta2O9 and BaBi4Ti4O15, and weak ferroelectric behavior for Bi4Ti3O12. These results might have a technological impact due to the relevance of bismuth-layered ferroelectric oxides for the fabrication of non-volatile FeRAM memories.
MFMOS Capacitor with Pb5Ge3O11 Thin Film for One Transistor Ferroelectric Memory Applications
Authors: Li T. K. , Hsu S. T. , Lee J. J. , Gao Y. F. , Engelhard M.
Published: April 2011

A ferroelectric Pb5Ge3O11 thin film with a low dielectric constant is proposed for application in one transistor ferroelectric memories. A strong depolarization voltage on the ferroelectric capacitor with MIFSFET structures diminishes the remanent polarization significantly and, therefore, the low dielectric constant becomes very important to widen the memory window. A memory window of 3V was estimated for the MFMOS memory structure with 2000Å ferroelectric Pb5Ge3O11 and a 100Å gate oxide. In the second part of this paper, Pb5Ge3O11 films deposited on Ir/Ti/SiO2/Si substrates, by using MOCVD system, was demonstrated. Germanium ethoxide, Ge(OC2H5)4, and lead bis-tetramethylheptadione, Pb(thd)2, were used as the MOCVD precursors. The film composition, phase formation, microstructure and ferroelectric properties are reported. The c-axis oriented Pb5Ge3O11 thin films prepared by MOCVD and RTP post-annealing showed a square ferroelectric hysteresis loop with Pr of 2.83 μC/cm2 and EC of 49 kV/cm. A low leakage current of 7.5 × 10−7 A/cm2 at 100 kV/cm and low dielectric constant of 41 were also demonstrated.
Relaxor Pb(Mgl/3Nb2/3)O3 Thin Films: Processing, Dielectric and Electrostrictive Properties
Authors: Kighelman Z. , Damjanovic D. , Seifert A. , Gentil S. , Hiboux S. , Setter N.
Published: April 2011

Lead magnesium niobate, Pb(Mg1/3Nb2/3)O3, thin films were formed from alkoxide-based solution precursors. To obtain stable and reproducible PMN precursor solution, a special effort has been undertaken to optimize the precursor synthesis. The organic decomposition behavior and crystalline phase development in a dried gel powder are reported. The influence of different seeding layers on the microstructures is shown. Dielectric and electromechanical measurements were carried out. Films show relaxor-like behavior, but with dielectric permittivity which is low (4500 at peak) compared to bulk ceramics and single crystals. Several parameters which might be responsible for this lower permittivity are suggested. Large electric dc bias fields (up to 120 kV/cm) can be applied to the films. This dc field reduces the permittivity, suppresses the frequency dispersion and flattens the permittivity peak. The anomaly associated with the field induced transition into a ferroelectric phase was not observed. Electrostrictive strains versus amplitude of electric field were measured and are discussed.
Study of the Transverse Piezoelectric Coefficient of Pb(Zr,Ti)O3 Thin Films as a Function of Texture and Composition
Authors: Seifert A. , Ledermann N. , Hiboux S. , Muralt P.
Published: April 2011

The effective transverse piezoelectric coefficient was measured on 1 μm thick sol-gel processed Pb(Zr,Ti)O3 (PZT) thin films as a function of texture and composition. Optimal values were obtained with PZT films of {100} texture near the morphotropic phase boundary (53/47). The best value amounted to -12 C/m2
Excimer Laser Liftoff of Epitaxial Pb(Zr,Ti)O3 Thin Films and Heterostructures
Authors: Tsakalakos L. , Sands T.
Published: April 2011

Epitaxial (100) and (111)-oriented Pb(Zr,Ti)O3-based thin films and heterostructures have been transferred intact from their sapphire and MgO growth substrates to silicon and polymer substrates utilizing a novel laser liftoff process. The heterostructures, while on their growth substrate, were bonded to the receptor substrates using one of several bonding methods, including van der Waals bonding to an elastomer receptor, and transient liquid-phase Pd-In bonding to Si. A single 38 ns pulse from a KrF excimer laser (<,= 248 nm) directed through the transparent growth substrate induced localized heating of the perovskite interfacial layer. At fluences corresponding to the onset of vaporization (>300 mJ/cm2), the sapphire or MgO substrate was detached. Because of the short pulse length and the low thermal conductivity of Pb-based perovskite phases, heating of the top surface of the heterostructure was minimal, thus permitting film transfer to thermally-sensitive receptor substrates. X-ray rocking curves revealed slight broadening of the principal PLZT diffraction peaks (∼10–20%), suggesting local relaxation of film stress.
Tem Investigation of Growth Temperature Dependence in Pulsed-Laser Ablated PLZT Films for Pyroelectric Applications
Authors: Jacobs R. N. , Godfrey R. P. , Sarney W. L. , Tipton C. W. , Salamanca-Riba L.
Published: April 2011

Transmission electron microscopy is used to examine the structural characteristics of Pb0.9La0.1Zr0.2Ti0.8O3 (PLZT) films grown directly on single crystal LaAlO3 (LAO) substrates. In particular, the domain orientation and film epitaxial quality as a function of substrate deposition temperature are obtained in the range 500–650°C and compared to x-ray diffraction results. High-resolution cross sectional images and electron diffraction patterns confirm that domain orientation and overall epitaxial quality can be optimized with growth temperature. In addition, these results show a direct correlation with pyroelectric measurements obtained for capacitor structures incorporating La1−xSrxCoO3 (LSCO) top and bottom electrodes.
Thermal Stability of Ir/TaN Electrode/Barrier on Thin Gate Oxide for MFMOS one Transistor Memory Application
Authors: Zhang Fengyan , Hsu Sheng Teng , Li Tingkai , Ono Yoshi , Maa Jer-shen , Ying Hong , Stecker Lisa
Published: April 2011

The Metal-Ferroelectric-Metal-Oxide-Silicon (MFMOS) one transistor memory requires a metal electrode directly on top of the thin gate oxide. The gate oxide used in our present MFMOS one transistor memory processing is 30 Å SiO2. Ir has been chosen for the bottom electrode and TaN was used as the barrier layer between the Ir and thin gate oxide. It has been shown from previous studies that a TaN barrier layer can effectively prevent the formation of iridium silicide and can enhance the adhesion between Ir and Si or SiO2 substrates. But it is more important that the TaN itself is stable and will not react with the gate oxide during ferroelectric material deposition, annealing and subsequent processing. In this paper, TaN barriers with different deposition conditions have been deposited on 30 Å gate oxide. 1500 Å Ir was deposited on the TaN barrier layer. Capacitors of Ir/TaN/gate SiO2/Si were defined by dry etching. Series RTP annealing were performed in oxygen from 500 to 650 °C with annealing times from 5 min to 90 min. The capacitor was also annealed in a nitrogen ambient at 1000°C for 10s. C-V and I-V studies were used to characterize the stability of the Ir/TaN/Gate SiO2 structure. It was observed that the Ir/TaN/Gate SiO2 is very stable during the above mentioned annealing conditions. The consumption and further oxidation of the gate oxide is negligible and would depend on the deposition condition of the TaN barrier layer. With optimized deposition conditions, a 220 Å TaN barrier layer can effectively prevent any iridium silicide formation and will not degrade the gate oxide during annealing processing. The interfaces between the TaN and gate SiO2 and between the gate SiO2 and Si substrate can be further improved by forming gas annealing.
Preparation of SrRuO3 and CaRuO3 Films by Mocvd and its Application to Electrodes for Ferroelectric Thin Films
Authors: Okuda N , Higashi N , Ishikawa K , Nukaga N , Funakubo H
Published: April 2011

SrRuO3 and CaRuO3 thin films were successfully prepared by metalorganic chemical vapor deposition (MOCVD). Sr(C11H19O2)2(C8H23N5)x – Ru(C11H19O2)3–O2 and Sr(C11H19O2)2(C8H23N5)x. – Ru[(C5H4)(C2H5)]2 - O2 systems, and Ca(C11H19O2)2(C8H23N5)x, – Ru(C11H19O2)3–O2 and Ca(C11 H19O2)2(C8H23N5)x – Ru[(C5H4)(C2H5)]2– O2 systems were used as source materials for SrRuO3 and CaRuO3 thin film preparation, respectively. Sr and Ca source vapors were successfully obtained by bubbling N2 gas including C8H23N5 vapor through liquid sources. Self-composition limiting to keep single phase of SrRuO3 and CaRuO3 was observed under an excess input of the Ru source at 700 – 750 °C for both Ru sources. Epitaxlly grown films with high crystal perfection were grown on various kinds of substrates in this temperature range. Epitaxially grown SrRuO3 film with three kinds of orientation, (100), (110) and (111), were deposited on (100), (110) and (111)SrTiO3 substrates, respectively. By using these films as bottom electrodes, we measured the ferroelectric anisotropy of SrBi2Ta2O9 by preparing (001)- and (116)- oriented films.
Autostoichiometric Mocvd Of Multicomponent Thin Films LiTaO3, LiNbO3 and SrxBa1-xNbO6
Authors: Zhang R. , Xu R.
Published: April 2011

A novel stoichiometric vapor deposition process, Autostoichiometric MOCVD, was developed in this study to prepare stoichiometric thin films. Heterometallic alkoxides were used as single precursor for two different metal components in Autostoichiometric MOCVD. The molecular ratios of the metals were conserved through the precursor evaporation and the deposition reactions based on the chemical nature of precursors and the deposition reaction mechanisms. A non-stoichiometric factor K was defined to study the evaporation process of precursors. A precursor evaluation method using the K factor and the thermal decomposition analysis was introduced to quantitatively analyze the stoichiometric evaporation characteristic of a heterometallic alkoxide precursor. Single phase LiTaO3, LiNbO3, SrNb2O6 and BaNb2O6 films were successfully obtained using precursor LiTa(n-OBut)6 or LiTa(i-OBut)6, LiNb(n-OBut)6, SrNb2(n-OBut)12 and BaNb2(n-OBut)12, respectively. Solid solution Sr1-x.BaxNb2O6(SBN) films were also successfully obtained by a two-step Autostoichiometric MOCVD.
Preparation Of K3LI2NB5O15 (KLN) Thin Films by Rf-Magnetron Sputter Process
Authors: Kim Gwang-Tae , Park Myung-Sik , Lee Joon-Hyung , Cho Sang-Hee
Published: April 2011

In this study, the KLN thin films were prepared by RF-magnetron sputtering method onto Coming 1737 glass. The effect of working pressure, substrate temperature, RF-power, sputter gas ratio (Ar/O2) during deposition was investigated. For an optimum deposition condition, the postannealing, RTA(rapid thermal annealing) and IPA(in-situ post annealing)methods were employed. Both RTA and IPA processes, which were conducted at different deposition and annealing temperature influenced surface morphology and optical properties of the films. The films prepared by the IPA process showed a lower crystallization temperature and better optical transmittance.
Progress in Fully Functionalized Photorefractive Materials
Authors: Wang Qing , Wang Liming , Ng Man Kit , Yu Luping
Published: April 2011

Photorefractive (PR) materials are multifunctional materials which combine both photoconductivity and electro-optic response to show a new phenomenon: reversible modulation of the index of refraction by light. In the past years, our group has focused on the development of fully functionalized polymers, oligomers and small molecular materials. We have had success in identifying new materials and in gaining understanding in design principles of better materials. Several new PR material systems have been explored, including conjugated PR polymers containing transition metal complexes as photosensitizers, oligothiophene based PR systems and small molecular PR materials containing carbazole and methine dyes. Large net optical gain and minimized phase separation were achieved. The correlation between molecular structure and physical properties is the focal point of this paper.
A Study Towards the Design of Materials for Nonlinear Optical Applications Using First Principle Calculations
Authors: Nguyen Kiet A. , Day Paul N. , Pachter Ruth
Published: April 2011

Electronic structure calculations are carried out to predict properties of reverse saturable absorption (RSA) materials that are important in nonlinear optical (NLO) applications. The RSA dyes under investigation are zinc porphyrins with a combination of halogen and phenyl substituents. The computed data include electronic spectra for the ground and triplet excited states as well as ionization potentials. These properties are important in predicting the performance of NLO materials. Since comprehensive data are not available, we begin with the basic porphyrin unit, then systematically replace the peripheral hydrogens of porphin with halogen and phenyl groups to study the substituent effects. The results of halogenated porphyrins and halogenated tetraphenylporphyrins provide insightful accounts of effects of phenyl, fluoro, chloro, and bromo substituents on the spectra of these systems. The computed spectra and IPs are in excellent agreement with available experimental data.
Wavelength Dispersion of Optical Power Limiting in Stilbene3 Analyzed within a Three Level Model
Authors: Chollet P-A. , Somin A. , Paci B. , Hully V. , Nunzi J-M. , Morel Y. , Baldeck P.
Published: April 2011

Nonlinear transmission in a dye (stilbene3) exhibiting two-photon absorption (TPA) has been studied has a function of wavelength, in the visible range using nanosecond laser pulses. The results have been analyzed within a three level model: the first excited one is populated by TPA and is excited toward an upper level (excited state absorption, ESA). The TPA and ESA spectra obtained by optical limiting (δ∼10-46 cm4s photon-1molecule-1; δ∼ 10-16 cm2) are in good agreement with those determined by two-photon fluorescence and Kerr ellipsometry. Thus, nonlinear transmission appears as a useful technique to estimate the TPA and ESA contributions in optical limiting.
Porphyrin Dye Media for Optical Limiting
Authors: McEwan K. J. , Robertson J. M. , Anderson H. L.
Published: April 2011

In this report we study nine structurally similar porphyrins and show how the material parameters that control the optical limiting depend on the molecular structure. Optical limiting measurements at 532 nm on the metal-free, zinc and lead analogues of tetraphenyl porphyrin (TPP), tetra(trimethylsilyethynyl) porphyrin (TTMSAP) and tetra(4-n-butylphenylethynyl) porphyrin (TNBBAP) reveal a strong dependence on the molecular structure. A double pump/cw probe technique is used to measure the material parameters that control the optical limiting and the results give a strong insight into how the molecular structure influences the individual parameters. These measurements revealed that one of the materials TTMSAP(Pb) has a σex/σgrratio of ∼45 at 532 rim, which is one of the largest values ever reported. Finally, broadband measurements with a picosecond white-light source show that the excited state absorption profile for the porphyrins examined is much broader than the ground state features and is centred to the long wavelength side of the ground state Soret band.