Showing papers in "Materials Science & Engineering R-reports in 1999"

Wafer direct bonding: tailoring adhesion between brittle materials

Abstract: It is a well-known phenomenon that two solids with sufficiently flat surfaces can stick to each other when brought into intimate contact in ambient air at room temperature. The attraction between the two bodies is primarily mediated through van der Waals forces or hydrogen bonding. Without a subsequent heating step, that type of bonding is reversible. Annealing may increase the energy of adhesion up to the cohesive strength of the materials concerned. The wafer bonding phenomena in brittle materials systems, especially in silicon, is reviewed in the experiment. The focus is on low temperature bonding techniques. The pivotal influence chemical species on the surfaces have on the subsequent type of bonding (van der Waals, hydrogen, covalent bonding, mechanical interlocking) is discussed. Methods of modifying the surface chemistry for tailoring bonding properties are addressed. The paper is aimed at providing an overview of the current understanding of the factors determining the bondability and strength of the bonding obtainable. The authors assess the present state of the experimental methods for determining basic parameters governing the adhesion. A number of examples illustrate the applicability of fusion bonding for as diverse fields as opto-electronics, microsystems technology, and fabrication of advanced substrates like silicon-on-insulator wafers.

Recent progress in field emitter array development for high performance applications

Abstract: This article discusses the current status of the rapidly evolving area of field emitter arrays. The development of field emitter arrays is reviewed in the context of major applications of the devices, such as flat panel displays and cathodes for microwave power amplifiers. State-of-the art technologies for fabrication of field emitter arrays as well as recently reported results on electrical performance of the devices are reviewed. Remaining challenges in the major applications in conjunction with some of the potential pathways to device improvement are discussed.

CVD diamond films: nucleation and growth

Abstract: In the last decade, we have seen rapid developments in metastable diamond synthesis by means of low-pressure chemical vapor deposition. Concurrently, a fast growing interest in diamond technology has emerged. This review discusses the various low-pressure growth methods of diamond films. Particular attention is paid to recent advances in the understanding of the mechanism of diamond nucleation and metastable growth. These advances are discussed in connection with the advances in diamond heteroepitaxy, which raises hopes that single crystalline diamond films are not far beyond reach. Modern surface science techniques applied to diamond study have played an essential role in these achievements and their contributions are discussed.

Control of the charge inhomogeneity and high-Tc superconducting properties in homologous series of multi-layered copper oxides

Abstract: A systematic view stemmed for the most important parts from the authors’ own research results is presented for tailoring high-Tc superconductive copper oxides from the standpoint of materials chemistry. The present article first elucidates that, in the multi-layered superconductive copper-oxide structures presently known to exist, the distribution of charge/charge carriers is inhomogeneous over several different spatial dimensions throughout the crystal. At the same time useful guiding rules are derived based on the concepts of tolerance parameter and bond-valence for controlling the charge distribution. Then experimental and semi-experimental evidences are presented to establish the relationships between the inhomogeneous distribution of holes and superconducting properties. To reach this goal, phenomenological aspects of the high-Tc superconductive copper oxides are described systematically, and selected important techniques for estimating the local carrier concentration and distribution are discussed. That is, the following points are included in the present article: (i) general crystallographic categorization and naming scheme of multi-layered copper oxides based on the concept of homologous series, (ii) crystallographic and chemical factors to control the oxygen non-stoichiometry and charge distribution, (iii) techniques for probing the charge/carrier distribution in the layered copper-oxide crystal, and (iv) empirical relationships between the carrier distribution and superconducting properties including the superconductivity transition temperature, Tc, the magnetic irreversibility field, Hirr, and the so-called peak effect/fishtail phenomenon. Finally, the unified view is summarized and some indespensable questions to be still answered in future work are mentioned.

The future of atomic resolution electron microscopy for materials science

Abstract: The field of atomic-resolution transmission electron microscopy and its application to materials science is reviewed. This technique, whose spatial resolution is now about one Angstrom, is valuable wherever nanoscale characterization of materials is needed. The history of the subject is briefly outlined, followed by a discussion of experimental techniques. Resolution-limiting factors are summarized, together with the underlying theory of image formation. Seven promising approaches to super-resolution are reviewed. The statistical principles of quantitative image analysis and defect modelling are outlined for both HREM and STEM. Methods for obtaining defect energies from images are discussed. The review ends with a summary of some recent applications, including such topics as the Fullerenes, nanotubes, dislocation kink imaging, superconductors, atomic-resolution imaging of whole semiconductor devices, the study of atomic defects in mediating first-order phase transitions, collosal magnetoresistance, ceramic interfaces, quasicrystals, imaging of surfaces, glasses, catalysts and magnetic materials.

Organometallic vapor phase epitaxy (OMVPE)

Abstract: Organometallic vapor phase epitaxy (OMVPE) has emerged in this past decade as a flexible and powerful epitaxial materials synthesis technology for a wide range of compound–semiconductor materials and devices. Despite its capabilities and rapidly growing importance, OMVPE is far from being well understood: it is exceedingly complex, involving the chemically reacting flow of mixtures of organometallic, hydride and carrier-gas precursors. Recently, however, OMVPE technologies based on high-speed rotating disk reactors (RDRs) have become increasingly common. As fluid flow in these reactors is typically cylindrically symmetric and laminar, its effect on the overall epitaxial growth process is beginning to be unraveled through quantitative computer models. In addition, over the past several years, a combination of well-controlled surface science and RDR-based growth-rate measurements has led to a richer understanding of some of the critical gas and surface chemistry mechanisms underlying OMVPE. As a consequence, it is becoming increasingly possible to develop a quantitative and physically based understanding of OMVPE in particular chemical systems. In this article, we review this understanding for the important specific case of AlGaAs OMVPE in an RDR under conditions used for growing typical device heterostructures. Our goal is to use typical growth conditions as a starting point for a discussion of fundamental physical and chemical phenomena, beginning with the fluid flow through an RDR and ending with the chemical reactions on the surface. By focusing on one particularly important yet relatively simple specific case, this review differs from more comprehensive previous reviews. Viewed as a case study, though, it complements these previous reviews by illustrating the wide diversity of research that is related to OMVPE. It can also serve as a good starting point for the development and transfer of insights into other more complex cases, such as: OMVPE of materials families containing Sb, P or N species, of other devices types, and in other more complex reactor geometries.

SiGe field effect transistors

Abstract: Starting from a brief review of the basics of FETs and BJTs, we discuss typical applications of the two types of transistors, which is followed by a FET performance analysis including the transconductance, speed, power consumption, and packing density. These sections form the foundations for the understanding of the pros and cons of strained SiGe FETs. Based on this foundation, we scrutinize the perceived advantages of using SiGe, review the array of SiGe FET structures, and look at material and processing challenges.

Recent developments and applications in electroabsorption semiconductor modulators

Abstract: State of the art developments in electroabsorption modulators that utilize quantum well-semiconductors are reviewed. Special emphasis is given to recent progress made in materials for modulators. On technological grounds, optimized Multiple Quantum Well modulators in the GaAs/AlGaAs system have been driven by applications in photonic switching and optical interconnects. Surprisingly, these same structures exhibit a wealth of new behavior that ranges from Bloch oscillations to excitons in Coupled Well, Wannier–Stark and Shallow Well superlattices. Several types of excitonic phases have been identified, optically and found to transform as the system dimensionality changes from 2D to 3D. In addition, new material systems have shown that quantum well excitonic absorption quality can be transferred to technologically important wavelengths at 1.06 or 1.55 μm.