Mechanisms of dislocation generation and methods of crystal growth are two historically rich areas of scientific study. These two fields converge in the area of metamorphic epitaxial materials, where the goal is to produce high-performance devices that contain high densities of crystal defects in regions of the engineered material away from the active areas. Metamorphic epitaxy is a form of thin-film growth, where the lattice structure of the layer and substrate are mismatched, and its defining characteristic is that any elastic strain in the overlayer has been relaxed by the deliberate introduction of dislocations at the film–substrate interface. Metamorphic growth enables novel combinations of relaxed single-crystal materials to realize novel functionality and performance in numerous technological areas, including lasers, photovoltaics, transistors, and quantum computing. Many of the devices described in this issue are impossible to realize using the traditional approach of avoiding dislocation generation; instead, they rely on metamorphic epitaxy to attain high performance.

The microstructures, interfacial reactions, and bonding strength properties of the Ti–Cu dissimilar joints using a commercially available Ag–28Cu–2Ti filler were studied, particularly as they relate to the role of an Ag barrier layer at the Ti interface. A joint microstructure and interfacial reactions closely related to the formation of brittle interfacial Ti–Cu intermetallics were fully dominated by the presence of the Ag layer at the Ti interface. Reliable Ti(base)/TiAg/Ag/Ag–Cu eutectic/Cu(base) joints without any detrimental Ti–Cu intermetallics were achieved at low brazing temperatures below 810 °C by applying an Ag interlayer of suitable thickness. It was notable that their bonding strengths were strong enough to exceed the strength of a Cu bulk base metal. This research demonstrates the potential application of an Ag interlayer for the reliable Ti–Cu dissimilar joints.

Void formation in lead-free solder joints, away from the joint interface, has been observed after solid-state aging. These voids are attached to intermetallic precipitates in the solder matrix, especially to those that are adjacent to the layered intermetallic at the joint interface. Two potential void formation mechanisms are discussed. The mechanism proposed to describe void formation is that a flux of vacancies is created due to volume contraction during solid-state reaction. The ripening process among the intermetallics also assists this process. Using the suggested mechanisms, the void size was estimated. This phenomenon differs from the classical Kirkendall void formation because it is a nonequilibrium state of void formation and stress generation.

In this study, the effect of addition of Nb on glass formation in Ni–Ti–Zr–Si–Sn alloys has been studied. The composition range for bulk glass formation with Dmax > 2 mm (Dmax, maximum diameter for glass formation by injection cast method) becomes wider when compared with the non-Nb–containing alloy. The ΔTx (= Tx – Tg; Tx, crystallization onset temperature; Tg, glass transition temperature), Trg (= Tg/Tl; Tl, liquidus temperature) and γ [= Tx/(Tl + Tg)] values for the alloys Dmax > 2 mm are in the range of 40–59, 0.638–0.651, and 0.410–0.419, respectively. The compositions of the alloys (Dmax > 2 mm) are closer to pseudo-eutectic composition than that of the alloy without Nb, showing an improved glass forming ability. The critical cooling rate for glass formation (Dmax = 5 mm) is estimated to be order of approximately 40 K/s.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

The deformation behavior of Ti-based bulk metallic glass (BMG) and metallic glass matrix composite (MGMC), both having a multistep crystallization behavior upon heating, has been investigated in the supercooled liquid region. The BMG deforms homogeneously and exhibits moderate elongation to failure due to its multistep crystallization behavior, but shows a significant variation of the flow stress during deformation. For the MGMC containing an in situ β-phase, a stress-overshoot characteristic, observed in the BMG, is not presented, but elongation to failure is rather limited because the crystalline β-phase prevents the viscous flow of the amorphous phase. The different presence of the crystalline phases in the metallic glasses can differently affect the flow behavior of metallic glass in the supercooled liquid region.

In this work we show the feasibility of producing silicon nanocrystals by means of a new method based on the oxi-reduction of silicon dioxide induced by the presence of an impurity and annealing. The choice of magnesium as the impurity relies on its chemical properties of oxireducing the SiO2 matrix while avoiding the formation of Si-based compounds. The samples were obtained by 3×1016 and 1×1017 at/cm2 ion implantation into fused silicon dioxide followed by annealing in vacuum at 900 °C for 2 or 10 h. Rutherford backscattering spectrometry (RBS) characterized the chemical content and the Mg depth distribution. In all cases, photoluminescence measurements that showed a broad band starting around 1.8 eV with increasing emission intensity for lower energies, indicating the presence of Si nanocrystals. The analysis of the photoluminescence data in the framework of the quantum confinement theory suggests the existence of relatively large Si nanocrystals. The presence of these nanocrystals was also confirmed by Raman spectroscopy.

CdSe/ZnSe based semiconductor quantum dot (Q D) structures are a promising candidate for optoelectronic device applications. However, key to the luminescence properties is the cation distribution and ordering on the atomic level within the CdSe QDs/agglomerates. Here the Z contrast imaging technique in the scanning transmission electron microscope (STEM) is employed to study multisheet (Cd,Zn,Mn)Se QD structures. Since Z-contrast is an incoherent imaging technique, problems associated with strain contrast in conventional TEM are avoided an accurate size and composition determinations can be made.

For this work we used a JEOL JEM 201 OF field emission STEM/TEM. The sample was grown by molecular beam epitaxy in order to achieve vertical self-ordering of Cd rich quasi-2D platelet This sample comprises 8 sequences of 10 ML (2.83 nm)Zn0.9Mn0.1Se cladding layer and 0.3 ML (0.09 nm) CdSe sheet, a further 10 ML of Zn0.9Mn0.1Se, and a 50 nm ZnSe capping layer.

Pyroelectric effect on ferroelectricity was examined for PZT capacitors with diodes in series. It was observed that the magnitude of the polarization reversal increases as heating rate increases. The polarization reversal begins to decrease as heating rate becomes very high, which may stem from the fact that pyroelectric charges flow through the PZT film at high temperature as the film loses its resistance at the elevated temperature. A pure remanent polarization reversal model is suggested for the polarization reversal caused by pyroelectric charges. Based on the above results, a thermal shock test method is proposed for quality control of FRAM products. The thermal shock test reveals that pyroelectric effect can be minimized by controlling process for 1T-1C FRAM. It was also observed, by the thermal shock test, that imprint dominates pyroelectric effect in 1Tr cell with MFIS structure.

New methodologies are being developed in our laboratory that allow measurements of the Young's modulus (E) and thermal expansion coefficient (TEC) for materials that cannot be prepared as free standing films. The first employs a bending beam measurement of stress versus temperature. We measure the thermal stress of a given film on two substrates, Si and GaAs. The use of two substrates allows the determination of both E and TEC. A TEOS film is used to demonstrate the technique. Another technique is a variation of the stress-strain measurement of E. The brittle material of interest is coated onto a polymer substrate, and the composite film is elongated to obtain the stress-strain curve of the composite film. Subtraction of the polymer substrate contribution to this curve yields the stress-strain behavior of the brittle film and allows calculation of E.

The in-plane dielectric constants of potential interlayer dielectrics (ILD) are determined from the interline capacitance between metal lines passivated with the material. We have developed a finite difference simulation to account for the fringe capacitance, and it allows the extraction of the in-plane dielectric constant from the measured capacitance. The method was used to measure the anisotropies in two polymer ILDs. A flexible chain polymer showed the same anisotropy in both a blanket film and on patterned lines, but a rigid rod-like polymer was found to be much less anisotropic on the patterned lines relative to the blanket film. This result indicates that the molecular orientation of the film is different on the patterned lines.

The effects of top-insulator on the instability problems of hydrogenated amorphous silicon (a-Si:H) thin film transistors (TFTs) have been studied. In a-Si:H TFT with top-insulator (E/S type), charge trapping into the both of top-insulator and gate insulator has been shown under the bias stress.

In order to investigate the charge trapping effects of top-insulator, we proposed a new method of Measurement. By this Method, we observed that trapped charges in top-insulator increased drain currents for positive gate bias stress, and this increment of drain currents was more serious with increasing the ratio of source/drain overlap length to channel length. It has founded that the instability problems of a-Si:H TFTs was attributed to the effects of top-insulator as well as that of gate insulator.

PZT (Zr/Ti = 53/47), PNZT (4% Nb doped PZT), PSZT (2% Sc doped PZT), and PSNZT (1% Sc and 1% Nb doped PZT) thin films were prepared by a sol-gel process. They were characterized by XRD, SEM and TEM. Both crystallographic orientation and grain size of PZT films can be changed by doping. Pt/PZT/Pt capacitors were fabricated for the measurement of ferroelectric properties. By doping with both Sc and Nb, the fatigue performance of the PZT films was considerably improved and the coercive field was decreased, while the remanent polarization was not changed. In addition, the effect of dopants on the leakage current level of PZT films was studied.

The ferroelectric properties of PZT on RuO2 electrodes were compared to those on RuOStudy on Multilayered Electrodes for Ferroelectric Thin Film Capacitors. It seems that the microstructure of PZT film plays an important role in the improvement of electrical properties. In particular, the change in the grain size of PZT film is responsible for the enhancement of the electrical properties. It was found in this study that films with smaller grain size had larger coercive fields. The exact dependence of the grain size on the hysteretic property is not fully understood at present. However, it is believed that the grain size affects both domain formation and domain pinning because of the influence of grain boundaries. The change in physical properties of PZT films due to the bottom electrode is understood in terms of interfacial modifications. Here we report on a method to modify physical properties of PZT films utilizing interfacial engineering.

BPSG films show good flow characteristics with the increase of boron and phosphorus concentration. As–deposited BPSG films with high boron and phosphorus concentration, however, have a dopant instability which results in film bursts, cracks, and precipitates, due to water absorption. Elimination of dopant instabilities of BPSG films by N2O plasma treatment is investigated. Film structure, composition and flow properties are evaluated by FT-IR, SIMS, and SEM, respectively. Dopant stability is examined after H2SO4 boiling. After H2SO4 boiling without N2O plasma treatment, BPSG films with high boron and phosphorus concentration show poor flow characteristics. Boron and phosphorus are leached out of the BPSG films by reaction with absorbed water during the H2SO4 boil. N2O plasma treatment results in a thin surface layer composed of Si-O-B bonds. These bonds do not dissolve in water. It is proposed that the thin layer consisting of Si-O-B bonds prevents the penetration of water into BPSG film during H2SO4 boiling.

High tensile stresses develop in passivated aluminum line metallizations on silicon substrates after excursion to elevated temperatures. The principal mechanisms to relax these stresses at room temperature are plastic deformation and grain boundary void growth. It is shown that stress relaxation and void growth are intimately connected.

EDISON is a large-aperture telescope under study for the second generation of infrared space observatories, whether in orbit or on the moon. The optics equilibrate via radiative cooling to temperatures between 40 and 80 K, depending upon, for example, telescope structure and location. At these temperatures, telescope emission is below that of the astronomical background at all wavelengths shortward of 20-40 μm. The detector components can be cooled via mechanical refrigerators now in an advanced stage of development. A mixture of radiative and mechanical cooling means that there is no natural limit to EDISON’s lifetime. In addition, the upper stage rocket fairing can be almost filled with light-collecting optics and alternative low-emissivity optical designs, such as off-axis systems, can be easily engineered. We are presently evaluating a design for a 2.5 m observatory to be launched in collaboration with European astronomers as part of the NASA Explorer program. In this presentation, we describe possible spectroscopic and spectrophotometric studies of very faint infrared sources that will require large-aperture space telescopes working at the celestial background limit.

We report the epitaxial growth of GaAs films on bulk Si, Ge and Ge coated Si substrates by MOCVD. This work is directed at comparing the structural, electrical, optical and optoelectronic properties of the GaAs films grown on these substrates. The quality of the GaAs films was evaluated by a number of techniques including X-ray, TEM, RBS, I-V and C-V. We have also obtained good photoresponse for Au-GaAs/Si, Au-GaAs/Ge and Au-GaAs/Ge/Si Schottky diodes at 0.87μm. We have observed significant differences in defect density, strain, crystalline quality, structural order, doping density depth-profile, dark current, diode ideality factor, photoresponse, inter-diffusion and interface structure among these three different structures. The GaAs/Ge structure exhibited the best structural and electrical characteristics of all. The GaAs/Ge/Si structure showed material properties and Schottky diode performance that are better than those of the GaAs/Si stucture. Although Ge and Si both out-diffuse into GaAs, that the out-diffusion of Si into GaAs appears to cause more degradation in the electrical and optoelectronic properties of GaAs.