General considerations for interpreting junction capacitance in complex systems

Many attempts have been made to provide theoretical and experimental methods to achieve a simple interpretation of the measurement of the capacitance of a junction as a function of reverse bias voltage. In this paper we present a quite general but simple formulation that includes all of these previous cases and is useful for describing experimental results in complex systems both conceptually and quantitatively. The results are useful especially for materials containing a high density of deep imperfection levels.     

Interdiffusion and compound formation in the Mo/Pd/Si thin film metallization system

The process of interdiffusion and compound formation in Mo/Pd/Si thin films was studied between 250 and 750°C via sheet resistance measurements, X-ray diffraction, Rutherford backscattering spectrometry and Auger electron spectroscopy. The results indicate that thermal annealing of the Mo/Pd/Si thin film couples between 250 and 475°C lead to PdSi interaction, Pd₂Si compound formation and consequently a small increase in the sheet resistance. In contrast, exposure of the Mo/Pd/Si thin films to temperatures higher than 475°C lead to MoPd₂Si interaction in addition to PdSi interaction, MoSi₂ compound formation and a dramatic increase in the sheet resistance. The influence of interdiffusion and compound formation on the interface morphology in the Mo/Pd/Si system was studied, and the implications of these observations to a very-large-scale integration contact metallization utilizing an Mo/Pd₂Si/Si system are discussed.     

Optimum design,redundancy and reliability of structural systems

The need for structural safety under a variety of loading and accident conditions has focused attention on redundancy, ductility and reliability of structural systems. The concepts of component reserve strength and system residual strength, system reliability and system residual reliability and their application are described. Several different structural configuration examples are illustrated in which component sizes are optimized. Design models for extreme loading and accident conditions for both brittle and ductile models are developed. System design methods are recommended.     

Technology transfer: Biotechnology industry perspectives

Gabriel Schmergel is President and Chief Executive Officer of Genetics Institute and also serves as President of the Industrial Biotechnology Association. The importance of foreign capital for equity investments and supporting contract research is cited as crucial to the development of the newer biotechnology firms. The author addresses the potential impact of export controls on the international biotechnology network of people, money, information flow, and markets. He cincludes by noting that the key to industrial leadership is assembling the relevant capital and scientific and managerial talent that can organize the research for developing products.     

Calibration of Si(Li) detectors for X-ray astronomy

The characterization of a high performance, energy dispersive Si(Li) solid-state detector is presented. The response of the detector to K and L lines in the energy range 0.7–9.0 keV is obtained by using a Van de Graaff accelerator to bombard selected targets having 12 ⩽ Z ⩽ 50 with a high energy proton beam. In addition to the channel-to-energy calibration and resolution vs energy plot, an empirical relation is presented for line yield as a function of energy for the K lines. Further, spectral data are used to estimate the silicon dead layer thickness. Finally, a detailed characterization of the detector's response function, including deviations from a simple Gaussian form due to effects such as incomplete charge collection, is given. From these results, a procedure is indicated by which X-ray spectrometers used in X-ray astrophysics applications may be calibrated.     

Scanning electron microscopy of coal macerals

Individual macerals separated from some United Kingdom coals of Carboniferous age and bituminous rank were examined by scanning electron microscopy. In each case a specific morphology characteristic of the macerals studied could be recognized. Collinite (a member of the vitrinite maceral group) was recognizable in all samples by its angular shape and characteristic fracture patterns, the particles (30–200 μm) frequently showing striated or laminated surfaces. Sporinite particles had no well defined shape and were associated with more detrital material than were the other macerals studied. This detritus was shown by conventional light microscopy to be the maceral micrinite. Fusinite was remarkable in having a ‘chunky’ needle form, with lengths of up to 200 μm.     

Electropolishing of horizontal tubes under conditions of natural convection mass transfer control

The kinetics of electropolishing of the inside surface of horizontal copper tubes in phosphoric acid was studied by measuring the limiting current of the process under natural convection conditions. Phosphoric acid concentration and tube diameter were varied to provide a range of ScGr extending from 3.3 × 10⁹ to 1.6 × 10¹¹. Under these conditions, the mass transfer coefficient of the electropolishing process was correlated to other variables by the dimensionless equation Sh = 0.62(ScGr)^0.28. Limiting current distribution measurement inside the tube revealed that the rate of polishing decreases from the top of the tube to the bottom.     

Gain clamping in two-stage L-band EDFA using a broadband FBG

A gain-clamped long wavelength band erbium-doped fiber amplifier (L-band EDFA) with an improved gain characteristic is demonstrated by simply adding a broadband conventional band (C-band) fiber Bragg grating (FBG) in a two-stage amplifier system. The FBG reflects backward C-band amplified spontaneous emission (ASE) from the second stage back into the system to clamp the gain. The gain is clamped at about 22.4 dB with a gain variation below 0.4 dB for input signal powers of -40 to -15 dBm. Compared with an unclamped amplifier of similar noise figure values, the small signal gain has improved by 2.4 dB due to the FBG which blocks the backward propagating ASE. At wavelengths from 1570 to 1600 nm, gain of the clamped amplifier varies from 19.4 to 26.7 dB. The corresponding noise figure varies by /spl plusmn/0.35 dB around 5 dB, which is not much different compared to that of the unclamped amplifier.     

Raman spectroscopy as process analytical tool in downstream processing of biotechnology

Downstream processing or product recovery plays a vital role in the development of bioprocesses. To improve the bioprocess efficiency, some unconventional methods are much required. The continuous manufacturing in downstream processing makes the Process Analytical Technologies (PATs) as an important tool. Monitoring and controlling bioprocess are an essential factor for the principles of PAT and quality by design. Spectroscopic methods can apply to monitor multiple analytes in real-time with less sample processing with significant advancements. Raman spectroscopy is an extensively used technique as an analytical and research tool owing to its modest process form, non-destructive, non-invasive optical molecular spectroscopic imaging with computer-based analysis. Generally, its application is essential for the analysis and characterization of biological samples, and it is easy to operate with minimal sample. The innovation on various types of enhanced Raman spectroscopy was designed to enhance the Raman analytical technique. Raman spectroscopy could couple with chemometrics to provide reliable alternative analysis method of downstream process analysis. Thus, this review aims to provide useful insight on the application of Raman spectroscopy for PAT in downstream processing of biotechnology and Raman data analysis in biological fields.     

Die attach properties of Zn–Al–Mg–Ga based high-temperature lead-free solder on Cu lead-frame

Several candidate alloys have been suggested as high-temperature lead-free solder for Si die attachment by different researchers. Among them, Zn–Al based alloys have proper melting range and excellent thermal/electrical properties. In this study, Zn–Al–Mg–Ga solder wire was used to attach Ti/Ni/Ag metallized Si die on Cu lead-frame in an automatic die attach machine. Die attachment was performed in a forming gas environment at temperature ranging from 370 to 400 °C. At the interface with Cu lead-frame, CuZn₄, Cu₅Zn₈ and CuZn intermetallic compound (IMC) layers were formed. At the interface with Si, Al₃Ni₂ IMC formed when 200 nm Ag layer was used at the die back and AgZn and AgZn₃ IMC layers when the Ag layer was 2,000 nm thick. Microstructure of the bulk solder consists of mainly two phases: one with a brighter contrast (about 80.9 wt% Zn) and the other one is a mixture of light (about 73.7 wt% Zn) and dark phases (about 45 wt% Al). Zn–Al–Mg–Ga solder wetted well on Cu lead-frame, covered entire die area and flowed in all directions under the Si die. Less than 10% voids were found in the die attach samples at die attach temperatures of 380 and 390 °C. Die shear strength was found within the acceptable limit (21.8–29.4 MPa) for all the die attach temperatures. Die shear strength of standard Pb–Sn solder was also measured for comparison and was found to be 29.3 MPa. In electrical test, maximum deviation of output voltage after 1,000 thermal cycles was found 12.1%.