Electrical linewidth test structures fabricated in monocrystallinefilms for reference-material applications

The physical widths of reference features incorporated into electrical linewidth test structures patterned in films of monocrystalline silicon have been determined from Kelvin voltage measurements. The films in which the test structures are patterned are electrically insulated from the bulk-silicon substrate by a layer of silicon dioxide provided by SIMOX (Separation by the IMplantation of OXygen) processing. The motivation is to facilitate the development of linewidth reference materials for critical-dimension (CD) metrology-instrument calibration. The selection of the (110) orientation of the starting silicon and the orientation of the structures' features relative to the crystal lattice enable a lattice-plane-selective etch to generate reference-feature properties of rectangular cross section and atomically planar sidewalls. These properties are highly desirable for CD applications in which feature widths are certified with nanometer-level uncertainty for use by a diverse range of CD instruments. End applications include the development and calibration of new generations of CD instruments directed at controlling processes for manufacturing devices having sub-quarter-micrometer features     

Fatty acid compositions of lipids from corn and grain sorghum kernels

Summary Characteristics and fatty acid compositions of the lipid components of the main fractions (germ, starch, gluten, and fiber) obtained in the wet milling of corn and grain sorghum kernels have been determined. The various lipids exhibited differences in chemical characteristics and fatty acid composition. These differences were found to be similar in both grains. Germ fats were the most unsaturated, contained the least free fatty acids and the least unsaponifiable matter. Starch fats were 70 to 90% free fatty acids and contained large amounts of palmitic acid. Gluten and fiber fats contained up to 32% unsaponifiables and about 20% free fatty acids.     

Distribution and sequence analysis of a novel Ty3-like element in natural Saccharomyces paradoxus isolates

Little is known about the transposable elements of species closely related to Saccharomyces cerevisiae. We present a novel transposable element in Saccharomyces paradoxus, a close congener of S. cerevisiae. Sequence analysis of this element, designated Ty3-1p, indicates that it is a homologue of the S. cerevisiae Ty3 element. Ty3-1p shares 82% nucleotide identity with an S. cerevisiae Ty3 element and appears to be structured identically to Ty3, containing two overlapping open reading frames, six retroviral-like domains, a J domain, and flanking sigma-like elements. A sigma element from Ty3-1p is 75% identical to a Ty3 sigma element. There is no evidence of horizontal transfer of Ty3 in Saccharomyces sensu stricto. We assess the distributions of Ty3p and Ty3 element insertions in natural population samples of S. paradoxus and S. cerevisiae. The S. paradoxus population sample exhibits Ty3p insertions present at a variety of sites at low frequency; this suggests that Ty3p elements are active in the sampled population. The S. cerevisiae population sample exhibits a uniform Ty3 hybridization profile in which all element insertions appear to be fixed. We comment on the possible causes of these contrasting observed distributions (GenBank Accession Nos AY198186 and AY198187).     

Genomic mutation rates that neutralize adaptive evolution and natural selection

When mutation rates are low, natural selection remains effective, and increasing the mutation rate can give rise to an increase in adaptation rate. When mutation rates are high to begin with, however, increasing the mutation rate may have a detrimental effect because of the overwhelming presence of deleterious mutations. Indeed, if mutation rates are high enough: (i) adaptive evolution may be neutralized, resulting in a zero (or negative) adaptation rate despite the continued availability of adaptive and/or compensatory mutations, or (ii) natural selection may be neutralized, because the fitness of lineages bearing adaptive and/or compensatory mutations—whether established or newly arising—is eroded by excessive mutation, causing such lineages to decline in frequency. We apply these two criteria to a standard model of asexual adaptive evolution and derive mathematical expressions—some new, some old in new guise—delineating the mutation rates under which either adaptive evolution or natural selection is neutralized. The expressions are simple and require no a priori knowledge of organism- and/or environment-specific parameters. Our discussion connects these results to each other and to previous theory, showing convergence or equivalence of the different results in most cases.     

Design of Compliant Mechanisms: Applications to MEMS

Compliant mechanisms are single-piece flexible structures that deliver the desired motion by undergoing elastic deformation as opposed to jointed rigid body motions of conventional mechanisms. Compliance in design leads to jointless, no-assembly (Fig. 1), monolithic mechanical devices and is particularly suited for applications with small range of motions. The compliant windshield wiper shown in Fig. 1 illustrates this paradigm of no-assembly. Conventional flexural mechanisms employ flexural joints that connect relatively rigid links as depicted in Fig. 2. Reduced fatigue life, high stress concentration and difficulty in fabrication are some of the drawbacks of flexural joints. Our focus is on designing compliant mechanisms with distributed compliance which employs flexural links (see Fig. 3) and have no joints (neither pin nor flexural joints) for improved reliability, performance, and ease of manufacture. Distributed compliant mechanisms derive their flexibility due to topology and shape of the material continuum rather than concentrated flexion at few regions. This paper focuses on the unique methodology employed to design jointless mechanisms with distributed compliance. The paper also illustrates a compliant stroke amplification mechanism that was recently designed, fabricated and tested for MEMS application.     

Failure modes in surface micromachined microelectromechanical actuation systems

In order for the rapidly emerging field of MicroElectroMechanical Systems (MEMS) to meet its extraordinary expectations regarding commercial impact, issues pertaining to how they fail must be understood. We identify and address failure modes common to a broad range of MEMS actuation systems, including adhesion (stiction) and friction-induced failures caused by improper operational methods, mechanical instabilities, and electrical instabilities. Demonstrated methods to mitigate these failure modes include implementing optimized designs, model-based operational methods, and chemical surface treatments.     

Surface-micromachined gear trains driven by an on-chipelectrostatic microengine

Test results for a polysilicon, surface-micromachined, electrostatically-actuated microengine driving multiple gears are presented. The microengine provides output in the form of a continuously rotating output gear (50 μm in diameter) that is capable of delivering torque to additional geared mechanisms. The microengine can be operated at varying speeds and its motion can be reversed. A rotational speed of up to 200000 r/min while driving multiple gears has been obtained. Drive of a 1600 μm diameter optical shutter has also been demonstrated. The resultant microengine and gear train, produced by polysilicon surface-micromachining techniques, are completely batch-fabricated without the need for piece-part assembly     

Fatty acid compositions of corn oils in relation to oil contents of the kernels

Summary The fatty acid compositions of 13 oils from corns having oil contents over the range of 1.6 to 11.5% oil, d.b., were determined either by a spectrophotometric technique applied to the whole oil or by the methyl ester fractional distillation technique. Linear relationships between iodine values and fatty acid compositions, between oil contents of the corns and iodine values, and between oil contents and fatty acid compositions were determined. An increase in oil content of the corn is accompanied by a decrease in iodine value and linoleic acid content of the oil and by an increase in oleic acid and saturated acids.     

Real time forecasting of near-future evolution

A metaphor for adaptation that informs much evolutionary thinking today is that of mountain climbing, where horizontal displacement represents change in genotype, and vertical displacement represents change in fitness. If it were known a priori what the ‘fitness landscape’ looked like, that is, how the myriad possible genotypes mapped onto fitness, then the possible paths up the fitness mountain could each be assigned a probability, thus providing a dynamical theory with long-term predictive power. Such detailed genotype–fitness data, however, are rarely available and are subject to change with each change in the organism or in the environment. Here, we take a very different approach that depends only on fitness or phenotype–fitness data obtained in real time and requires no a priori information about the fitness landscape. Our general statistical model of adaptive evolution builds on classical theory and gives reasonable predictions of fitness and phenotype evolution many generations into the future.     

汽车电子封装趋势,考量及生产的特殊性

汽车电子是半导体行业成长较快的领域。安全、舒适、互联,和个性化是未来十年成长的主要动力。可靠性和性价比优势使支架封装仍占主导,而其它封装,如PBGA、堆叠式芯片尺寸封装(SCSP),和晶圆级封装(WLP)等,也正得到启用。MLF誖(QFN)应用广泛,具有很好的热电性能和设计灵活性。类似凹槽侧面可湿性焊点技术的创新,让MLF誖这种传统封装更具吸引力。更多传感器和MEMS用于汽车应用,封装形式主要为MLF誖,LGA和"凹槽MEMS"。资讯娱乐系统需要采用更多类型的封装形式。汽车电子封装生产所涉及的供应商管理、可靠性测试等因素必须与严格的汽车标准保持一致。