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There are many advantages of LEDs in energy and environmental conservation, but their short life in many outdoor applications prompt a necessity to have a detailed understanding of their degradations to prolong their lifetime, which can also conserve LED material and even expand their applications. Using ab initio density functional theory formulation, we identify the detail paths of the LED degradation in outdoor applications. We discovered that the main stressors are humidity and the light that is emitted from the LED chip itself. This is rather ironical. A mathematical model is developed based on the ab initio study, and excellent experimental agreements are found. With this model, we can predict the situations where no and slow degradations can be achieved, and these are verified experimentally here. We can also predict quantitatively the time to a specific degradation severity. Quality index of the housing material for LEDs can also be determined.

The mechanical properties—Young’s modulus (E) and hardness (H)—of diamond-like carbon (DLC) thin films deposited on p2+ Si (100) by filtered cathodic vacuum arc with different substrate bias voltage have been studied by nanoindentation measurement, where the substrate effect is included. Their intrinsic properties [including E,H, and yield strength (Y)] without the substrate effect are then derived by finite element analysis. The results show that the intrinsic mechanical properties of the DLC thin films are not affected by the film thickness, but significantly affected by change of sp3 bonding fraction caused by varied substrate bias. An empirical relationship among E, Y, and H for DLC thin films has been built, where E, Y, and H are intrinsic properties of DLC thin films. It is also confirmed that, as an empirical rule, the measured H could be used to represent its intrinsic value when the indentation depth is limited to 10% of the film thickness. However, the measured E with the substrate effect does n...

Band structures of n‐i‐n‐i doping superlattices are found using a self‐consistent calculation based on the envelope function formalism. The modulation potentials, the charge density distributions, the dispersion relationships, and the occupation of the subbands in the n‐i‐n‐i superlattices are computed and their dependence on temperature and the structural parameters of the superlattices are studied. It is found that the modulation potentials of n‐i‐n‐i doping superlattices are weak, and quantum effects are, therefore, also weak. The density of states in n‐i‐n‐i superlattices can be adjusted by varying the structural parameters of the superlattices. As a result, the n‐i‐n‐i doping superlattices behave like uniformly doped semiconductors with an adjustable density of states. The density of states is found to be temperature dependent. Electron mobilities of the n‐i‐n‐i doping superlattices are also computed. It is found that both impurity scattering processes that are observed in uniform lightly doped semic...

A numerical procedure for the calculation of the electron tunneling current through an arbitrary potential profile has been developed. It involves subdividing the profile into a number of strips for which a linear approximation of the potential is appropriate. A solution of the Schrodinger equation in the form of Airy functions is obtained. These functions are linked through boundary conditions at the interface of the strips. An expression for the transmission coefficient of the structure is obtained. The approach is found to accelerate the calculation of the electrical characteristic of resonant tunneling devices. An analysis is performed of tunneling through parabolic quantum‐well and half‐parabolic quantum‐well structures in the presence of an electric field. The room‐temperature current‐voltage characteristic for the half‐parabolic quantum‐well structure is calculated and is found to be rectifying with multiple peaks and regions of negative differential resistance. It is also found to have a relatively high peak‐to‐valley ratio and high peak current density.

Electromigration (EM) is an important failure mechanism in integrated circuit interconnections. Various models have been proposed to study the interconnect degradation due to EM from different perspectives. As the interconnect linewidth shrinks to submicrometer and below, a small growth in void size after void nucleation can sever the conduction path, and hence void nucleation time becomes the dominant part of the time to failure of an interconnect and the primary damage mechanism in EM failure. In this work, an alternative concept of EM modeling is proposed, and the EM lifetime of an interconnect during void nucleation is derived theoretically. A physics-based predictive Monte Carlo simulation methodology is used to model the void nucleation process during EM. To demonstrate the modeling concept and the simulation methodology developed in the present study, Al interconnect test structure is chosen as an illustration and it is shown that the model can predict the voiding location in the interconnect and estimate the median time to failure as verified experimentally.

In this paper, we present quantitative analyses of the impact of Joule heating on the package level electromigration (EM) test of copper dual damascene (DD) interconnects with linewidths of 0.28 and 0.7 μm. A total of 120 samples are tested with a maximum current density of 8 MA/cm2. It is found that high test current density has a negligible impact on the estimation of activation energy and offers an opportunity to shorten the test time. However, the current density exponent is found to be a strong function of test current density, especially for interconnects with a larger linewidth. Correction due to Joule heating on the estimation of the current density exponent is described.

The supersaturated and metastable boron produced by laser anneal could deactivate during post-laser-thermal-cycles and lead to undesirable performance degradation. The effect of tin incorporation on the thermal stability of boron was studied for the first time and suppressed boron deactivation during post-laser-rapid-thermal-anneal was observed with tin coimplantation. High resolution x-ray diffraction measurement indicates that the tensile strain caused by a high boron concentration was reduced by the introduction of tin, which effectively reduces the strain energy and therefore, enhances the thermal stability of boron in post-laser-anneal rapid thermal processing.

Electromigration (EM) is an important reliability concern in ultralarge-scale integration interconnects. A refined EM model based on a driving force approach is proposed in this work. The distribution of atomic flux divergence is computed by an finite element method to predict the void nucleation site in interconnects. It is demonstrated that the proposed model is more accurate than the conventional counterpart for narrow interconnects. The validity of the proposed model is verified through the study of the reservoir effect in EM. The predicted critical reservoir length agrees well with the reported values.

Electromigration (EM) is a major failure mechanism in ultralarge-scale integration interconnections. Various atomic migration mechanisms due to the electron wind force, temperature gradients, and thermomechanical stress gradients are involved during an EM failure process. In this study, a methodology that combines a Monte Carlo algorithm and finite element analysis is developed to study the underlying dynamic physical processes of EM, including void nucleation and void growth. The microstructure inhomogeneity of an interconnect thin film and the different atomic diffusivities along various diffusion paths in interconnections are also considered in this three-dimensional dynamic simulation.

The charge‐transfer (CT) interactions in electroactive polymeric complexes formed by nonconjugated polymers: poly‐2‐vinylpyridine, poly‐4‐vinylpyridine, and various halobenzoquinone electron acceptors such as: o‐chloranil, p‐chloranil, o‐bromanil, and p‐fluoranil have been investigated by means of x‐ray photoelectron spectroscopy (XPS). In spite of the relatively high degree of CT interactions, the conductivity of the complexes remains low and in the range of 10−11–10−6 S cm−1. XPS core‐level spectra for halogens, nitrogen, and oxygen allow the steric hindrance to CT interactions in the various complexes to be investigated and compared. In all the complexes, the presence of a halogen anion, a positively charged pyridinium nitrogen, and an oxygen anion is observed. This is indicative that CT interactions may have resulted in adducts arising from the formation of linkages between the polymers and the acceptors.