R-reliable intervals and confidences for the lifetime of a parallel system

In this discussion, R-reliable intervals for the life-time of a parallel system, based on order statistics, are obtained. The failure distributions for the individual components are assumed to have densities of the form 1/θ_Xif(x_iθ_Xi) where X_i, for i = 1, 2, …, n, are the failure times for the components in the parallel system and θ_Xis are the scale parameters for the failure times X_i. A relationship between the confidence of the R-reliable interval for the total lifetime of the parallel system and the confidences of the R-reliable intervals for the lifetimes of the individual components is investigated. A bound for the confidence of the R-reliable interval for the total lifetime of the system is obtained. Examples for n=3 are presented.     

Comparison of Insulated with Bare Au Bonding Wire: HAZ Length,HAZ Breaking Force,and FAB Deformability

Two types (A and B) of 25-μm-diameter bare Au bonding wire and their corresponding insulated wire were used to produce 50-μm-diameter free-air balls (FABs) for heat-affected zone (HAZ) and FAB deformability analyses. Insulated wires showed no significant difference in HAZ length compared with bare wire for type A, while their difference lay in the range of 4% to 12% longer for type B. The HAZ breaking load of bare wire is 0.3% to 1.8% smaller than that of insulated wire for type A and not significantly different for type B even though the HAZ length is shown to be larger for insulated wire B. The deformability of the FAB from insulated wires is 1.0% to 2.1% smaller than that from bare wires for type A and 2.1% to 3.4% larger for type B.     

Defect chemistry and intrinsic carrier concentration for Hg1−x Cdx Te(s) for x = 0.20, 0.40, and 1.0

The theoretical equations governing the crystal-vapor equilibrium for Hg_1−x Cd_x Te(s) are summarized for a model with doubly-ionized native defects and applied to the data for x = 0.20, 0.40, and 1. The basic equations (Eq. (1) or (19)) are shown to contain those used elsewhere as special cases. Allowing the intrinsic carrier concentration, n₁, to vary, but under constraints, to obtain an optimum fit and assuming a non-degenerate semiconductor, the hole con-centration-mercury pressure isotherms can be fitted satis-factorily and better than before with standard deviations between 22 and 24% for x = 0.20 and 0.40. A number of sets of model parameters give these fits, some of which give values as large as 10/cm at 500δC for the square root of the Schottky constant for ionized vacancies. In agreement with experiment, each of these parameter sets for x = 0.20 and 0.40 predicts a negligible dependence of the 77 and 192 K Hall mobilities upon equilibration temperature and predicts that metal saturation between 250 and 300δC with foreign donors in the 10¹⁵/cm³ range will result in elec-tron concentrations in the same range and dependent on saturation temperature to less than 26%. The enthalpy to create a “Hg-vacancy” and two holes is an invariant of the fits and is 2.00 ± 0.04 eV for x = 0.40 and 1.94 ± 0.02 eV for x = 0.20. Then n_i is calculated independently assuming a parabolic valence band and a Kane conduction band. With an exact density of states for the latter obtained here, the momentum matrix element, P = 8.5 × 10₋₈ eV-cm, the spin-orbit splitting, Δ = 1 eV, and E (x, T) from Hansen et al., the experimental values below 300 K for 0 ≤x = 0.3 and at high temperature for x = 1 are fitted well with m _h ^∗ /m = 0.70. With these independently calculated values for n_i the electron concentration-cadmium pressure isotherms for CdTe can be fitted to about 7% for either of two incon-sistent data sets assuming 2 × 10¹⁶ /cm³ foreign donors. However data for x = 0.40 can be fitted to only 42% and that for x = 0.20, which is degenerate, to only 28%.     

Linking Glass-Transition Behavior to Photophysical and Charge Transport Properties of High-Mobility Conjugated Polymers

The measurement of the mechanical properties of conjugated polymers can reveal highly relevant information linking optoelectronic properties to underlying microstructures and the knowledge of the glass transition temperature (T_g) is paramount for informing the choice of processing conditions and for interpreting the thermal stability of devices. In this work, we use dynamical mechanical analysis to determine the T_g of a range of state-of-the-art conjugated polymers with different degrees of crystallinity that are widely studied for applications in organic field-effect transistors. We compare our measured values for T_g to the theoretical value predicted by a recent work based on the concept of effective mobility ζ. The comparison shows that for conjugated polymers with a modest length of the monomer units, the T_g values agree well with theoretically predictions. However, for the near-amorphous, indacenodithiophene–benzothiadiazole family of polymers with more extended backbone units, values for T_g appear to be significantly higher, predicted by theory. However, values for T_g are correlated with the sub-bandgap optical absorption suggesting the possible role of the interchain short contacts within materials’ amorphous domains.     

Dual-Color InAs/GaSb Superlattice Focal-Plane Array Technology

Within a very few years, InAs/GaSb superlattice technology has proven its suitability for high-performance infrared imaging detector arrays. At the Fraunhofer Institute for Applied Solid State Physics (IAF) and AIM Infrarot-Module GmbH, efforts have been focused on developing mature fabrication technology for dual-color InAs/GaSb superlattice focal-plane arrays for simultaneous, colocated detection at 3 μm to 4 μm and 4 μm to 5 μm in the mid-wavelength infrared atmospheric transmission window. Integrated into a wide-field-of-view missile approach warning system for an airborne platform, a very low number of pixel outages and cluster defects is mandatory for bispectral detector arrays. Process refinements, intense root-cause analysis, and specific test methodologies employed at various stages during the process have proven to be the key for yield enhancements.     

CCGA packages for space applications

Commercial-off-the-shelf (COTS) area array packaging technologies in high reliability versions are now being considered for applications, including use in a number of NASA electronic systems being utilized for both the Space Shuttle and Mars Rover missions. Indeed, recently a ceramic package version specifically tailored for high reliability applications was used to provide the processing power required for the Spirit and Opportunity Mars Rovers built by NASA-JPL. Both Rovers successfully completed their 3-months mission requirements and continued exploring the Martian surface for many more moths, providing amazing new information on previous environmental conditions of Mars and strong evidence that water exists on Mars.Understanding process, reliability, and quality assurance (QA) indicators for reliability are important for low risk insertion of these newly available packages in high reliability applications. In a previous investigation, thermal cycle test results for a non-functional daisy-chained peripheral ceramic column grid array (CCGA) and its plastic ball grid array (PBGA) version, both having 560 I/Os, were gathered and are presented here. Test results included environmental data for three different thermal cycle regimes (−55/125 °C, −55/100 °C, and −50/75 °C). Detailed information on these—especially failure type for assemblies with high and low solder volumes—are presented. The thermal cycle test procedure followed those recommended by IPC-9701 for tin–lead solder joint assemblies. Its revision A covers guideline thermal cycle requirements for Pb-free solder joints. Key points on this specification are also discussed.In a recent investigation a fully populated CCGA with 717 I/Os was considered for assembly reliability evaluation. The functional package is a field-programmable gate array that has much higher processing power than its previous version. This new package is smaller in dimension, has no interposer, and has a thinner column wrapped with copper for reliability improvement. This paper will also present thermal cycle test results for assemblies of this and its plastic package version with 728 I/Os, both of which were exposed to four different cycle regimes. Two of these cycle profiles are specified by IPC-9701A for tin–lead, namely, −55 to 100 °C and −55 to 125 °C. One is a cycle profile specified by Mil-Std-883, namely, −65/150 °C, generally used for ceramic hybrid packages screening and qualification. The last cycle is in the range of −120 to 85 °C, a representative of electronic systems directly exposed to the Martian environment without use in a thermal control enclosure. Per IPC-9701A, test vehicles were built using daisy chain packages and were continuously monitored and/or manually checked for opens at intervals. The effects of many process and assembly variables—including corner staking commonly used for improving resistance to mechanical loading such as drop and vibration loads—were also considered as part of the test matrix. Optical photomicrographs were taken at various thermal cycle intervals to document damage progress and behavior. Representative samples of these are presented along with cross-sectional photomicrographs at higher magnification taken by scanning electron microscopy (SEM) to determine crack propagation and failure analyses for packages.     

Determination of the fractal dimension for the epitaxial <Emphasis Type="Italic">n</Emphasis>-GaAs surface in the local limit

Atomic-force microscopy studies of epitaxial n-GaAs surfaces prepared to deposit barrier contacts showed that major relief for such surfaces is characterized by a roughness within 3–15 nm, although “surges” up to 30–70 nm are observed. Using three independent methods for determining the spatial dimension of the surface, based on the fractal analysis for the surface (triangulation method), its section contours in the horizontal plane, and the vertical section (surface profile), it was shown that the active surface for epitaxial n-GaAs obeys all main features of behavior for fractal Brownian surfaces and, in the local approximation, can be characterized by the fractal dimension D _f slightly differing for various measuring scales. The most accurate triangulation method showed that the fractal dimensions for the studied surface of epitaxial n-GaAs for measurement scales from 0.692 to 0.0186 μm are in the range D _f = 2.490?2.664. The real surface area S _real for n-GaAs epitaxial layers was estimated using a graphical method in the approximation δ → 0 δ is the measurement scale parameter). It was shown that the real surface area for epitaxial n-GaAs can significantly (ten times and more) exceed the area of the visible contact window.     

Derivation of power gain for three types of three dimensional photovoltaics cells

In order to quantify the higher power output seen from solar cells with a three‐dimensional (3D) topology due to the increased interactions between photons and the cell surface, we have derived a formula for the average number of interactions, Γ, between a photon and the cell surface for 3D cells with vertical sidewalls and flat tops. We have derived Γ for three different cell morphologies, an infinite trench in the x‐ or y‐direction, an enclosed box, and an infinite two‐dimensional (2D) array of towers. Monte Carlo simulations were carried out in order to compare computational results for Γ with those derived. For varying distance between features, d, and photon azimuthal angle, the data fits the derived expressions quite well for a large range of values. For varying tower height, the data fits theory well for both the trench and box morphologies, however, theory overestimates the value of Γ for the 2D array of towers. This is due to simplifications made when deriving Γ. However, the error associated with Γ is small enough that it propagates to a measured power output error of less than 1% for cells with an absorbance efficiency of at least 25%. Even with simplifications, the derived expression for Γ should be usable for predicting the increased power output for 3D cells with vertical sidewalls and flat tops. Copyright © 2011 John Wiley & Sons, Ltd.     

Current–voltage curve translation by bilinear interpolation

By means of bilinear interpolation and four reference current–voltage (I–V) curves, an I–V curve of a photovoltaic (PV) module is translated to desired conditions of irradiance and PV module temperature. The four reference I–V curves are measured at two irradiance and two PV module temperature levels and contain all the essential PV module characteristic information for performing the bilinear interpolation. The interpolation is performed first with respect to open‐circuit voltage to account for PV module temperature, and second with respect to short‐circuit current to account for irradiance. The translation results over a wide range of irradiances and PV module temperatures agree closely with measured values for a group of PV modules representing seven different technologies. Root‐mean‐square errors were 1·5% or less for the I–V curve parameters of maximum power, voltage at maximum power, current at maximum power, short‐circuit current, and open‐circuit voltage. The translation is applicable for determining the performance of a PV module for a specified test condition, or for PV system performance modeling. Copyright © 2004 John Wiley & Sons, Ltd.     

Pd-Ge contact to n-GaAs with the TiW diffusion barrier

Pd-Ge based ohmic contact to n-GaAs with a TiW diffusion barrier was investigated. Electrical analysis as well as Auger electron spectroscopy and the scanning electron microscopy were used to study the contact after it was subjected to different furnace and rapid thermal annealing and different aging steps. All analyses show that TiW can act as a good barrier metal for the Au/Ge/Pd/n-GaAs contact system. A value of 1.45 × 10⁻⁶ Ω-cm² for the specific contact resistance was obtained for the Au/TiW/Ge/Pd/n-GaAs contact after it was rapid thermally annealed at 425°C for 90 s. It can withstand a thermal aging at 350°C for 40 h with its ρ_c increasing to 2.94 × 10⁻⁶Ω-cm² and for an aging at 410°C for 40 h with its ρ_c increasing to 1.38 × 10⁻⁵ Ω-cm².     

Reliability calculation of redundant systems with non-identical units

The present paper develops mathematical models for evaluating the exact reliability and mean time to failure of k-out-of-m: G systems with different unit failure probabilities. The ith unit is assumed to be characterized by a general hazard rate h_i(t) = λ_it^b.The models are based on the concepts of tie sets; they are fairly simple and can be used for any values of m and k. The algorithm developed for these models is suitable for adoption for a computer code.     

Grid-Enabled BLASTZ: Application to Comparative Genomics

BLASTZ is a sequence alignment tool designed mainly for aligning neutrally evolved bio-sequences and has been the choice for aligning noncoding sequences. However, its running time is impractical for high throughput alignment of long sequences, for example, for the alignment of human and mouse genomes. In order to improve the performance and efficiency for alignment at genome scale, BLASTZ was implemented using the GLOBUS toolkit on a computing grid. A dynamic load balancing technique was introduced to achieve enhanced performance on a grid which consists of sources of heterogeneous characteristics, such as resources of different computational powers. The robustness of the implementation to disturbances due to other processes on the grid is demonstrated.

Contractor selection criteria: a cost-benefit analysis

This paper describes an empirical study aimed at ranking prequalification criteria on the basis of perceived total cost-benefit to stakeholders. A postal questionnaire was distributed to 100 client and contractor organizations in Australia in 1997. Forty-eight responses were analyzed for scores on 38 categories of contractor information in terms of “value to client” “contractor costs,” “client costs,” and “value for money.” The client and contractor responses for “value to client” and “client costs” of processing were found to be homogeneous. Those for “contractor costs” and “value for money” differed significantly between the clients and the contractors. A simple linear regression analysis was used to model the responses, and an index of cost-benefit was derived for each of the categories. This was found to be superior to all of the nonlinear alternatives examined. The model was also found to have greater intuitive value than the equivalent raw “value for money” responses     

Nearly equilibrium growth of In1−x Gax Asy P1−y (0 ≤ y ≤ 1) Lattice-Matched to <100> InP

Data for nearly-equilibrium LPE growth at 626°C of InGaAs lattice-matched to the <100> face of InP are presented and the modeling of phase equilibria in this system is discussed. Because the simple solution approximation, which is useful for modeling binary (InP) and ternary (InGaAs) growth, is found to be unsatisfactory for the quaternary, a semi-empirical model suitable for determining the phase equilibria for LPE growth of any lattice-matched composition over a wide temperature range is proposed. The model is based on a simple scaling of data for lattice-matched growth at one liquidus temperature, 626°C, to other temperatures using data for the two lattice-matching compositions, InP and InGaAs, for which the temperature dependencies can be calculated. Using this ‘model’, melt compositions for growth with 600 < T_ℓ < 660°C are calculated and compared with expermental results. The nearly-equilibrium growth technique is fully described and empirical techniques for adjusting melt compositions to improve the degree of lattice-match are also given.     

Using d-limonene as the non-aromatic and non-chlorinated solvent for the fabrications of high performance polymer light-emitting diodes and field-effect transistors

Aiming to environment protection, green solvents are crucial for commercialization of solution-processed optoelectronic devices. In this work, d-limonene, a natural product, was introduced as the non-aromatic and non-chlorinated solvent for processing of polymer light-emitting diodes (PLEDs) and organic field effect transistors (OFETs). It was found that d-limonene could be a good solvent for a blue-emitting polyfluorene-based random copolymer for PLEDs and an alternating copolymer FBT-Th₄(1,4) with high hole mobility (μ_h) for OFETs. In comparisons to routine solvent-casted films of the two conjugated polymers, the resulting d-limonene-deposited films could show comparable film qualities, based on UV–vis absorption spectra and observations by atomic force microscopy (AFM). With d-limonene as the processing solvent, efficient blue PLEDs with CIE coordinates of (0.16, 0.16), maximum external quantum efficiency of 3.57%, and luminous efficiency of 3.66 cd/A, and OFETs with outstanding μ_h of 1.06 cm² (V s)⁻¹ were demonstrated. Our results suggest that d-limonene would be a promising non-aromatic and non-chlorinated solvent for solution processing of conjugated polymers and molecules for optoelectronic device applications.     

IC vs VBE law in double diffused bipolar transistors

It is shown that non-unity values for m in the I_C = _co exp (V_BE/mV_t) law for double diffused transistors can be caused by the graded emitter base junction. A simple analytic expression is derived for the linearly graded case. Tabulated results are given for this case and for measured and computed results on an actual double diffused transistor.     

Wide and narrow bandgap semiconductors for power electronics: A new valuation

An advantage for some wide bandgap materials that is often overlooked is that the thermal coefficient of expansion (CTE) is better matched to the ceramics in use for electronic-packaging technology. The optimal choice for unipolar devices is GaN and the associated material system of GaN/AlGaN. The future optimal choice for bipolar devices at all power levels is C (diamond). New expressions, ɛ _c=1.73×10⁵ (E_G)^2.5 for direct-gap and ɛ _c=2.38×10⁵ (E_G)² for indirect-gap semiconductors, relating the critical-electric field for breakdown in abrupt junctions to the material bandgap energy, and associated new expressions for specific on-resistance in power semiconductor devices is shown to further support the use of wide bandgap materials. Some low-voltage, power-electronics applications are shown to benefit by the use of Ge, C, and GaSb.     

Developments of new concept analytical instruments for failure analyses of sub-100 nm devices

We have developed analytical instruments based on new concepts for failure analyses of devices of 100 nm dimensions or less. They are a sputtered neutral mass spectrometer with focused ion beam for highly sensitive element analysis in microarea (10¹⁸ atoms/cm³ in 30 nm area), transmission electron microscope (TEM) with electron energy loss spectrometer for chemical bond analysis in less than 2 nm area, Nanoprober for electrical characteristics inspection in actual circuits, computed tomography-TEM for three-dimensional observation of crystalline defect with 1 nm spatial resolution, atmospheric pressure ionization mass spectrometer for trace impurities ppq (parts per quadrillion) analysis in gases, and glow discharge optical emission spectrometer for rapid and precise composition analysis. Using these instruments, it was found that the formation of SiO₂ or TiO_x film by water from titanic acid (TiO_x·H₂O) is the cause of the high resistivity in a contact (CVD-W/CVD-TiN/Ti/Si) and vaporization of silicon dioxide by phosphorus trifluoride (PF₃) is the cause of voids in interlayer dielectric film borophosphosilicate glass.     

Investigation of Alkali‐Ion (Li,Na, and K) Intercalation in KxVPO4F (x ∼ 0) Cathode

This work compares the intercalation of K, Na, and Li in K_xVPO₄F (x ～ 0). The K_xVPO₄F (x ～ 0) cathode delivers reversible capacities of ≈90–100 mAh g^?1 in K, Na, and Li cells, at an average voltage of ≈4.33 V for K, ≈3.98 V for Na, and ≈3.96 V for Li. This is so far the highest average voltage known for a K‐intercalation cathode. The lower voltage of Li insertion compared to Na is attributable to undercoordinated Li ions in the K_xVPO₄F (x ～ 0) framework. While the material shows high rate capability for all the alkali ions, Li migration in K_xVPO₄F (x ～ 0) is more difficult than with Na and K. This work suggests that a large cavity is not always good for insertion of alkali ions and cathode materials need to be suitably tailored to each intercalating ion species.     

Highly transparent polyimide/nanocrystalline-zirconium dioxide hybrid materials for organic thin film transistor applications

A solution-processable high k dielectric materials based on polyimide/zirconium dioxide (PI-ZrO₂) for organic thin film transistors (OTFTs) is demonstrated. To study the effect of the ZrO₂ content on the properties of the dielectric layer, a series of PZn films (n = 0, 2, 5, 8, 10, 12, and 15, which are the weight percentage of ZrO₂ in the film) were prepared. The results showed that all of the prepared hybrid films had a high transmittance of 96–99%. The nondestructive Zr K-edge XANES analysis revealed that the absorption intensity was proportional to the ZrO₂ content. EXAFS analysis indicated that the ZrO₂ formed bigger clusters in the film than in the solution state. Water and diiodomethane contact angle analysis found that the PZ12 film had the largest contact angles, lowest surface energy, and lowest water absorbance, which results in the least structural defects and highest carrier mobility. Electrical property analysis indicated that the dielectric constant of the films increased from 4.04 for the PZ0 film to 8.10 for the PZ12 film, but then dropped for the PZ15 film. All current leakages (−2 MV/cm) were less than 10⁻⁹ A/cm. The carrier mobility in the PZ0 film was 2.78 × 10⁻¹, up to 4.15 × 10⁻¹ for the PZ12 film, but down to 3.34 × 10⁻¹ for the PZ15 film. The I_on/I_off ratio was 2.3 × 10³ for PZ0, up to 1.4 × 10⁵ for PZ12, but down to 1.8 × 10⁴ for PZ15. The hybrid dielectric devices showed better performance. This work reveals great potential for hybrid dielectric materials for OTFT applications.