Showing papers in "Materials Science & Engineering R-reports in 2000"
TL;DR: In this article, a review of polymer-layered silicate nanocomposites is presented, where the polymer chains are sandwiched in between silicate layers and exfoliated layers are more or less uniformly dispersed in the polymer matrix.
Abstract: This review aims at reporting on very recent developments in syntheses, properties and (future) applications of polymer-layered silicate nanocomposites. This new type of materials, based on smectite clays usually rendered hydrophobic through ionic exchange of the sodium interlayer cation with an onium cation, may be prepared via various synthetic routes comprising exfoliation adsorption, in situ intercalative polymerization and melt intercalation. The whole range of polymer matrices is covered, i.e. thermoplastics, thermosets and elastomers. Two types of structure may be obtained, namely intercalated nanocomposites where the polymer chains are sandwiched in between silicate layers and exfoliated nanocomposites where the separated, individual silicate layers are more or less uniformly dispersed in the polymer matrix. This new family of materials exhibits enhanced properties at very low filler level, usually inferior to 5 wt.%, such as increased Young’s modulus and storage modulus, increase in thermal stability and gas barrier properties and good flame retardancy.
5,901 citations
TL;DR: The most widely used Pb-free solders have the eutectic composition as mentioned in this paper, which has been identified as a major factor affecting alloy selection, since this will have a major impact on the other polymeric materials used in microelectronic assembly and encapsulation.
Abstract: Practically all microelectronic assemblies in use today utilize Pb–Sn solders for interconnection. With the advent of chip scale packaging technologies, the usage of solder connections has increased. The most widely used Pb–Sn solder has the eutectic composition. Emerging environmental regulations worldwide, most notably in Europe and Japan, have targeted the elimination of Pb usage in electronic assemblies, due to the inherent toxicity of Pb. This has made the search for suitable “Pb-free” solders an important issue for microelectronics assembly. Approximately 70 Pb-free solder alloy compositions have been proposed thus far. There is a general lack of engineering information, and there is also significant disparity in the information available on these alloys. The issues involved can be divided into two broad categories: manufacturing and reliability/performance. A major factor affecting alloy selection is the melting point of the alloy, since this will have a major impact on the other polymeric materials used in microelectronic assembly and encapsulation. Other important manufacturing issues are cost, availability, and wetting characteristics. Reliability related properties include mechanical strength, fatigue resistance, coefficient of thermal expansion and intermetallic compound formation. The data available in the open literature have been reviewed and are summarized in this paper. Where data were not available, such as for corrosion and oxidation resistance, chemical thermodynamics was used to develop this information. While a formal alloy selection decision analysis methodology has not been developed, less formal approaches indicate that Sn-rich alloys will be the Pb-free solder alloys of choice, with three to four alloys being identified for each of the different applications. Research on this topic continues at the present time at a vigorous pace, in view of the imminence of the issue.
1,786 citations
TL;DR: In this paper, a review of the fabrication, microstructure and mechanical properties of in situ metal matrix composites reinforced with in situ ceramic phases is presented, with particular attention paid to the mechanisms responsible for the formation of the in situ reinforcements.
Abstract: During the past decade, considerable research effort has been directed towards the development of in situ metal matrix composites (MMCs), in which the reinforcements are formed in situ by exothermal reactions between elements or between elements and compounds. Using this approach, MMCs with a wide range of matrix materials (including aluminum, titanium, copper, nickel and iron), and second-phase particles (including borides, carbides, nitrides, oxides and their mixtures) have been produced. Because of the formation of ultrafine and stable ceramic reinforcements, the in situ MMCs are found to exhibit excellent mechanical properties. In this review article, current development on the fabrication, microstructure and mechanical properties of the composites reinforced with in situ ceramic phases will be addressed. Particular attention is paid to the mechanisms responsible for the formation of in situ reinforcements, and for creep failure of the aluminum-based matrix composites.
1,474 citations
TL;DR: In this paper, the development of fabrication processes for these devices and the current state-of-the-art in device performance, for all of these structures, are discussed. And the authors also detail areas where more work is needed, such as reducing defect densities and purity of epitaxial layers, the need for substrates and improved oxides and insulators, improved p-type doping and contacts and an understanding of the basic growth mechanisms.
Abstract: GaN and related materials (especially AlGaN) have recently attracted a lot of interest for applications in high power electronics capable of operation at elevated temperatures. Although the growth and processing technology for SiC, the other viable wide bandgap semiconductor material, is more mature, the AlGaInN system offers numerous advantages. These include wider bandgaps, good transport properties, the availability of heterostructures (particularly AlGaN/GaN), the experience base gained by the commercialization of GaN-based laser and light-emitting diodes and the existence of a high growth rate epitaxial method (hydride vapor phase epitaxy) for producing very thick layers or even quasi-substrates. These attributes have led to rapid progress in the realization of a broad range of GaN electronic devices, including heterostructure field effect transistors (HFETs), Schottky and p–i–n rectifiers, heterojunction bipolar transistors (HBTs), bipolar junction transistors (BJTs) and metal-oxide semiconductor field effect transistors (MOSFETs). This review focuses on the development of fabrication processes for these devices and the current state-of-the-art in device performance, for all of these structures. We also detail areas where more work is needed, such as reducing defect densities and purity of epitaxial layers, the need for substrates and improved oxides and insulators, improved p-type doping and contacts and an understanding of the basic growth mechanisms.
437 citations
TL;DR: In this paper, the synthesis, processing and properties of non-oxide silicon-based ceramic materials derived from silazanes and polysilazanes are discussed and a comprehensive review of the preparation of precursor compounds containing Si-N-Si units, including commercially available materials, is provided.
Abstract: This review highlights the synthesis, processing and properties of non-oxide silicon-based ceramic materials derived from silazanes and polysilazanes. A comprehensive summary of the preparation of precursor compounds containing Si–N–Si units, including commercially available materials, is followed by the discussion of various processing techniques. The fabrication of dense bulk ceramics in the Si/E/C/N systems is reported which involves cross-linking of the polymeric ceramic precursor followed by a polymer-to-ceramic transformation step. The cross-linked precursor can be milled, compacted and pyrolysed to form dense, additive-free, amorphous silicon carbonitride monoliths or polycrystalline composites which withstand oxidation in air at 1600°C. Furthermore, an overview is given on the fabrication of silazane derived powders and coatings involving chemical vapour deposition (CVD) methods utilising volatile precursors. Fibre spinning and fibre properties, as well as other processing techniques like infiltration of preforms, the preparation of porous ceramics and joining are briefly discussed. A state of the art of the mechanical properties of polymer derived amorphous Si/C/N and Si/B/C/N ceramics with respect to hardness as well as high-temperature creep and oxidation resistance is summarised. Finally, some important aspects of industrial applications will be considered. The review is in part based on our own work related to the polysilazane derived ceramics, but will also cover a comprehensive state of the art including the published literature in this field.
427 citations
TL;DR: The development of nonlinear optical borate crystals for generation of visible and UV light is reviewed in this article, where the main considerations are focused on the discussion of crystals like CsLiB6O10 (CLBO), GdxY1−xCa4O(BO3)3 (GdYCOB) and K2Al2B2O7 (KAB).
Abstract: The development of nonlinear optical (NLO) borate crystals for generation of visible and UV light is reviewed. We first discussed on the basic principles of laser frequency conversion. Then, we examine the trends in research on NLO crystals. The background and present status of NLO borate crystals are summarized. The main considerations are focused on the discussion of crystals like CsLiB6O10 (CLBO), GdxY1−xCa4O(BO3)3 (GdYCOB) and K2Al2B2O7 (KAB). Properties of related materials like β-BaB2O2 (BBO), LiB3O5 (LBO), KBe2BO3F2 (KBBF), Sr2Be2BO7 (SBBO), CsB3O5 (CBO), GdCa4O(BO3)3 (GdCOB) and YCa4O(BO3)3 (YCOB) are included for comparison. We aim to provide a complete view of developing a new NLO borate material for actual laser applications. This review covers various aspects including the search for new materials, the growth of bulk crystals, the characterization of crystal properties as well as the development of new techniques to overcome obstacles in actual laser application, namely, thermal dephasing and laser-induced damage. Finally, perspectives on NLO borate crystals and all-solid-state UV lasers are evaluated.
409 citations
TL;DR: In this paper, a device model for PLEDs is proposed in which the light generation is due to bimolecular recombination between the injected electrons and holes, which gives rise to a bias dependent efficiency.
Abstract: Since the discovery of electroluminescence in conjugated polymers it has been recognized that charge transport is a key ingredient for the efficiency of the polymer light-emitting diodes (PLEDs). This review focuses on the charge transport properties of these materials. From temperature dependent current density–voltage characteristics it has been obtained that the hole transport in poly(dialkoxy-p-phenylene vinylene) (PPV) is governed by a combination of space-charge effects and a field- and temperature-dependent mobility. The origin of the hole mobility, which seems to be generic for a large class of disordered materials, arises from hopping in a system with both energetic and structural disorder. The response time of PPV-based PLEDs is governed by the dispersive transport of holes towards the cathode. Based on the results of the electron- and hole-transport a device model for PLEDs is proposed in which the light generation is due to bimolecular recombination between the injected electrons and holes. The unbalanced electron and hole transport gives rise to a bias dependent efficiency. By comparison with experiment it is found that the bimolecular recombination process is of the Langevin-type, in which the rate-limiting step is the diffusion of electrons and holes towards each other. The occurrence of Langevin recombination explains why the conversion efficiency of current into light of a PLED is temperature independent. The understanding of the device operation of PLEDs indicates directions for further improvement of the performance.
353 citations
TL;DR: A review of the up-to-date experimental studies on amorphization transition, which results in the formation of amorphous alloys or metallic glasses, by ion irradiation of multiple metal layers in the binary metal systems is presented in this paper.
Abstract: This review attempts to present first a brief summary of the up-to-date experimental studies on amorphization transition, which results in the formation of amorphous alloys or metallic glasses, by ion irradiation of multiple metal layers in the binary metal systems Secondly, based on the framework of Miedema’s theory, thermodynamic modeling of metallic glass formation is described with consideration of the significant role of interfacial free energy of the multilayers in amorphization Thirdly, results of molecular dynamics simulations for some representative systems are presented to show the calculation of the intrinsic glass-forming ability from interatomic potential of the binary metal systems
202 citations
TL;DR: In this paper, the basic mechanisms responsible for the formation and growth of cavities and bubbles in single-crystalline silicon are reviewed, starting from the loading (ion implantation) and having in mind the formation of the cavities.
Abstract: Hydrogen is a quite common impurity in semiconductor-silicon technology: it is unintentionally but unavoidably added to the silicon after crystal growth during wafer processing, and continues to be present during wet oxidation, film depositions, etching and annealing steps. The effects of hydrogen in single crystal silicon at low concentration have been the subject of many papers, books and conference proceedings. Much less considered is the case of hydrogen at massive concentration. One final effect of heavy hydrogen loading is the formation of cavities and bubbles, with size up to 100 nm. Cavities and bubbles are also observed after helium loading by high-fluence ion implantation. This article reviews the basic mechanisms responsible for the formation and growth of such structures in single-crystalline silicon. In particular, starting from the loading (ion implantation) and having in mind the formation of the cavities, this paper will cover: the effects of substrate temperature, the interaction of vacancies and self-interstitials with the impurity, the mechanisms of gas segregation inside the cavities, the pressure which arises because of the segregation and the subsequent displacement field in the crystal, the stability against heat treatments of the gas in the cavities and of the cavities themselves. The understanding of the physical processes should lead to gain more insight in the processes of cleavage of the Si–Si bond and vacancy agglomeration which can induce not only the formation of cavities and bubbles, but also planar cutting or explosion.
151 citations
TL;DR: In this paper, the authors describe modeling efforts based on the dynamics of native point defects in silicon during crystal growth, which are aimed at developing comprehensive and robust tools for predicting microdefect distribution as a function of operating conditions.
Abstract: Modern microelectronic device manufacture requires single-crystal silicon substrates of unprecedented uniformity and purity, As the device feature lengths shrink into the realm of the nanoscale, it is becoming unlikely that the traditional technique of empirical process design and optimization in both crystal growth and wafer processing will suffice for meeting the dynamically evolving specifications. These circumstances are creating more demand for a derailed understanding of the physical mechanisms that dictate the evolution of crystalline silicon microstructure and associated electronic properties. This article describes modeling efforts based on the dynamics of native point defects in silicon during crystal growth, which are aimed at developing comprehensive and robust tools for predicting microdefect distribution as a function of operating conditions. These tools are not developed independently of experimental characterization but rather are designed to take advantage of the very detailed information database available for silicon generated by decades of industrial attention. The bulk of the article is focused on two specific microdefect structures observed in Czochralski crystalline silicon, the oxidation-induced stacking fault ring (OSF-ring) and octahedral voids; the latter is a current limitation on the quality of commercial CZ silicon crystals and the subject of intense research. (C) 2000 Published by Elsevier Science S.A.
119 citations
TL;DR: The formation of amorphous interlayer (a-interlayer) by solid-state diffusion in diffusion couples has been one of the most challenging problems in condensed matter physics in recent years.
Abstract: The formation of amorphous interlayer (a-interlayer) by solid-state diffusion in diffusion couples has been one of the most challenging problems in condensed matter physics in recent years. The a-interlayer has been found to occur in all refractory metal/Si and a number of rare-earth (RE) metal and platinum group metal and crystalline silicon systems. A systematic survey and review of extensive studies on the subject in the past years showed that (1) a negative heat of mixing provides the driving force for the reaction and fast diffusion of one component in the other preempts the formation of crystalline compounds, (2) the growth follows a linear law at the initial stage with activation energy around 1–1.5 eV for refractory metal/Si systems and 0.5 eV for RE metal/Si systems, (3) the dominant diffusing species is Si, (4) the stability of amorphous interlayer depends on the composition, (5) simultaneous presence of multiphases in the initial stage of metal/Si interaction, and (6) good correlations between physical parameters and kinetic data. From the investigation of amorphous interlayers, mechanisms of roughing of epitaxial RE silicide/(0 0 1)Si interface, formation of stacking faults and pinholes in RE silicides have gained in basic understanding. The insight led to successful growth of pinhole-free epitaxial RE silicide layer on (1 1 1)Si. Furthermore, the enhanced formation of technologically important C54-TiSi 2 by high temperature sputtering, a thin interposing Mo layer and tensile stress can all be explained involving some aspects of the amorphous interlayers.
TL;DR: In this article, the authors reviewed the microscopic physics, device physics, and system performance of quantum well infrared photodetectors (QWIPs) without the use of an optical grating.
Abstract: The microscopic physics, device physics, and system performance of quantum well infrared photodetectors (QWIPs) are reviewed. QWIPs which respond to normally incident radiation without the need for an optical grating are of particular interest because they can be fabricated with fewer process steps. Recent demonstrations of n-type QWIPs (n-QWIPs) which show a significant detectivity of 4×1010 cm Hz /W without the use of an optical grating are discussed here. This detectivity is significant because it is large enough for focal plane array (FPA) performance to be limited by the uniformity of processing rather than the size of the single pixel detectivity. Studies of the microscopic physics of quantum wells are summarized to elucidate the physical origin of the intersubband absorption of normally incident radiation. The selection rules for intersubband absorption by holes in a p-doped QWIP (p-QWIP) and electrons in an n-QWIP are reviewed. In particular, it is shown that the hole intersubband absorption is typically weaker than both the conduction intersubband absorption and the valence band-to-conduction band absorption. It is also shown that uniaxial strain does not have a large effect on the strength or the selection rules of intersubband absorption because the Hamiltonian describing uniaxial strain has the same (tetragonal) symmetry as that describing the confinement of carriers in the quantum wells along the growth direction. Also reviewed are device models which yield analytical expressions for the number of, and the distance over which, carriers are depleted from quantum wells under conditions of insufficient carrier injection. This carrier depletion becomes important when the incident photon flux is large or when the QWIP operating temperature is low. Uniformity of QWIP device parameters is important in determining the ultimate array signal-to-noise ratio (SNR). Examples of high-resolution X-ray diffraction methods used to find the layer width variations of QWIPs grown by molecular beam epitaxy are reviewed. The spread of the measured full-width at half-maxima (FWHM) of superlattice diffraction peaks with the diffraction order was used with Bragg’s Law to obtain the measured layer width variation in the growth direction. A theoretical study of different noise mechanisms which contribute to QWIP performance was carried out. A key result is that, when the SNR is limited by either fixed pattern noise or thermal leakage arrival noise, the largest expected QWIP SNR occurs when the number of quantum wells in the QWIP is at the optimal value of about η1−1, where η1 is the quantum efficiency of a QWIP having only one quantum well. Common QWIP designs used in industry are evaluated. In particular, different physical models for the leakage (sequential tunneling, thermionic and thermionic field assisted leakage) are reviewed. A new result is a physical model, derived from the Kronig–Penney model, for the tunneling leakage in existing QWIP designs in which the confinement barrier is a semiconductor superlattice. The tunneling leakage in such QWIPs is shown to vary exponentially with the average (rather than the full) height of the superlattice barrier.
TL;DR: In this article, the fabrication and characterization of ferroelectric/superconductor heterostructures such as Pb(ZrxTi1−x)O3/YBa2Cu3O7−δ (YBCO), BaTiO 3/YBCo and BaxSr 1−xTiO3 /YBC O7−ε etc on various single crystal substrates are compared.
Abstract: This review covers the fabrication and characterization of ferroelectric/superconductor heterostructures such as Pb(ZrxTi1−x)O3/YBa2Cu3O7−δ (YBCO), BaTiO3/YBCO and BaxSr1−xTiO3/YBCO etc on various single crystal substrates Pulsed laser deposition, laser molecular beam epitaxy, and magnetron-sputtering methods are compared This report shows that pulsed laser deposition equipped with in situ reflection high-energy electron diffraction is a good method to control the growth mode of YBCO thin films Furthermore, laser molecular beam epitaxy is a superb method for research of complex oxide films and their superlattices Atomic force microscopy and transmission electron microscopy showed the ferroelectric films grown on the rough surface of the YBCO films produced high-density planar defects in the film and is detrimental to the ferroelectric/dielectric properties of the heterostructures Therefore, for device usage, it is more advantageous to use SrRuO3 than YBCO as the bottom electrode material For growing atomically smooth surface films step-flow mode is highly recommended Prospects of microwave device application of the ferroelectric/superconductor heterostructures are discussed, and proposed the BSTO films as the best candidate for passive microwave components