80 research outputs found
Serengeti - Webbasierte Annotation semantischer Relationen
No full textDiewald N, Stührenberg M, Garbar A, Goecke D. Serengeti - Webbasierte Annotation semantischer Relationen. Journal for Language Technology and Computational Linguistics. 2008;24(2):74-93
The influence of BF2 and F implants on the 1/f noise in SiGe HBTs with a self-aligned link base
No full textA study is made of 1/f noise in SiGe HBTs fabricated using selective growth of the Si collector and non-selective growth of the SiGe base and Si emitter cap. The transistors incorporate a self-aligned link base formed by BF2 implantation into the field oxide below the p+ polysilicon extrinsic base. The influence of this BF2 implant on the 1/f noise is compared with that of a F implant into the polysilicon emitter. Increased base current noise SIB and base current are seen in transistors annealed at 975?C, compared with transistors annealed at 950 or 900?C. At a constant collector current, both the BF2 and F implants reduce SIB, whereas at a constant base current, only the BF2 implant reduces SIB. This result indicates that the BF2 implant decreases the intensity of the base current noise source whereas the F implant decreases the base current. The proposed explanation for the increased 1/f noise is degradation of the surface oxide by viscous flow at 975?C under the influence of stress introduced during selective Si epitaxy. The influence of the BF2 implant on the noise is explained by the relief of the stress and hence the prevention of viscous oxide flow
On the physical nature of the base current 1/f noise typical for SiGe HBTs and Si BJTs made by SEG/NSEG epitaxy
No full textIt is shown that the high base current and associated low-frequency noise typical for the SiGe HBTs prepared by the selective epitaxial growth of the collector and non-selective epitaxial growth of the base and emitter (SEG/NSEG technology), can be explained by the mechanical stress between the collector and the field oxide surrounding the collector in these devices. The reason is that such stress provokes the viscous flow of the surface oxide producing an ‘action-at-distance’ effect which results in the creation of additional fast and slow surface centers at the poly/single crystal emitter and passivating oxide interfaces respectively. The increase of fast center density increases the recombination base current component while the increase of the slow centers density increases the intensity of the 1/f noise source. As a result, any factor that promotes the reduction of the stress or the decrease of the intensity of the surface oxide viscous flow serves to decrease the base current and its 1/f noise. Thus we have found that we can mitigate the undesirable effects by the following solutions: increasing the temperature of the selective epitaxial growth of the collector TSEG, decreasing the temperature of the rapid thermal activation TRTA, implantation of the BF2 implant into the field oxide before the collector and base layers are being grown, replacement of the bulk substrate by SOI. It is shown that the maximal decrease of the base current IB and of the spectral density of the 1/f noise SIB are as high as factors of 30 and 8,000, respectively
1/f Noise and Generation/Recombination Noise in SiGe HBTs on SOI
No full textA study is made of 1/f and generation/recombination (GR) noise in SOI SiGe HBTs fabricated using selective growth of the Si collector and non-selective growth of the SiGe base and n-type low doped Si emitter. A range of devices is studied in which different etch processes are used for the field oxide and different temperatures for the selective collector epitaxy. The results obtained are interpreted using Gummel plot measurements and 2D device simulations. The 1/f noise dominates the base current noise spectra at high biases while the GR noise is the main noise component at low biases, and the noise levels in all devices are much lower than reported in previous bulk devices. The 1/f noise in small area devices shows a different base current dependence than in large area devices and this dependence correlates with a turnover of the collector characteristic at high biases. This turnover is also more marked in devices where the overlay of the polysilicon over the emitter window is large. The analysis of the 1/f noise in small area devices has shown that the collector current turn over effect observed is due to the voltage drop across the interfacial oxide layer resistance. Device simulations show two different current crowding mechanisms, with crowding in the centre of the device for large overlays and crowding at the periphery for small overlays. Analysis of the 1/f noise results indicates that the 1/f noise in small area devices has a signature consistent with transparency fluctuations in the interfacial oxide at the polysilicon/silicon interface and in large area devices a signature consistent with recombination at the oxide/silicon surface. The GR noise is visible because of the low values of 1/f noise obtained and is shown to be due to recombination at deep levels in the emitter/base depletion layer, possibly due to residual damage from the extrinsic base implant. The noise in SOI devices is found to be comparable to that in control bulk devices, indicating that the buried oxide in SOI devices does not degrade the noise
Low frequency noise in SOI SiGe HBTs made by selective growth of Si collector and non-selective growth of SiGe base
No full textThe base current and related 1/f noise for SiGe HBTs realized by SEG/NSEG technology on SOI and bulk substrates
No full textIt is shown that the high base current and associated low-frequency noise typical for the SiGe HBTs prepared by the selective epitaxial growth of the collector and non-selective epitaxial growth of the base and emitter (SEG/NSEG technology), can be related to the mechanical stress between the collector and the field oxide surrounding the collector in these devices. The reason is that such stress provokes the viscous flow of the surface oxide producing an “action-at-distance” effect which results in the creation of additional fast and slow surface centers at the single crystal emitter and passivating oxide interface and in the oxide, respectively. The increase of fast center density increases the recombination base current component while the increase of slow center density increases the intensity of the 1/f noise source. As a result, any factor that promotes the reduction of the stress or the decrease of the intensity of the surface oxide viscous flow serves to decrease the base current and its 1/f noise. Thus we have found that we can mitigate the undesirable effects by the following solutions: increasing the temperature of the selective epitaxial growth of the collector TSEG, decreasing the temperature of the rapid thermal activation TRTA, implantation of BF2 into the field oxide before the collector and base layers are grown, replacement of the bulk substrate by SOI. It is shown that the maximal decreases of the base current IB and of the spectral density of the 1/f noise SIB are as high as factors of 30 and 8,000, respectively. Therefore, the technology conditions have been identified to guarantee a sufficiently low level of both excess base current noise and base current
Polyploid races, genetic structure and morphological features of the earthworm Octodrіlus transpadanus (Rosa, 1884) (Oligohaeta: Lumbricidae) in the Ukraine
No full textKariological investigation of the earthworm Octodrilus transpada-nus
(Rosa, 1884) in the Ukraine showed that this species is represented by at least three
races of different ploidy with the basic chromosome number n=15. Strict geographic
heterogeneity of electrophoretic spectra of different populations was registered:
south-eastern populations (7n=105) are characterized by a clonal structure, whereas
western (from 3n = 45 to 4n = 60) and south-western (2n=30) ones have a high level
of polymorphism. The Crimea sample (4n=60) is well isolated, has no clonal
structure and is characterized by a series of specifi c alleles , which are absent in
forms from continental Ukraine. All the forms turned out to be wel
Karyotypes of european species of radix (Gastropoda: Pulmonata: Lymnaeidae) and their relevance to species distinction in the genus
No full textKaryotypes of Radix auricularia (Linnaeus, 1758) and three disputable taxa considered by
different authors as distinct species or assigned as forms of Radix peregra (Muller, 1774),
sensu lato - R. labiata (Rossmassler, 1835), R. balthica (Linnaeus, 1758), and R. ampla
(Hartmann, 1821) - were studied with preparations obtained from gonad tissues by the airdrying
method. The studied taxa have the same diploid number (2n = 34), but are characterized
by different morphology of some chromosome pairs. In particular, R. labiata (traditionally
identified as R. peregra, s. s.) and R. balthica (= R. ovata in traditional understanding) differ
in the number of subtelocentric chromosomes (1 and 5, respectively), species status of
these taxa being also supported by pronounced differences in centomeric indexes of chromosome
pairs 4 and 16. Species distinctness of R. ampla is supported by differences in
three chromosome pairs, and karyological similarity between this taxon and R. balthica is
also noted. FN values varied among the studied taxa from 56 in R. ampla to 66 in R. labiata.
The known karyological characters are traced on phylogenetic trees suggested by recent
molecular reconstructions. This study demonstrates that karyology can be an effective tool
for aiding taxonomic distinctions of historically problematic groups of molluscs
Karyotypes of two European species of the genus Lymnaea with disputable taxonomic status (Gastropoda: Pulmonata: Lymnaeidae)
No full textKaryotypes of Lymnaea corvus and L. occulta are studied for the first time and
compared to the original data on Ukrainian populations of L. palustris and L. stagnalis. While
all the studied species have the same diploid chromosome number (2n = 36), they differ in
chromosome morphology. Karyotypes of L. occulta and L. palustris include only biarmed
chromosomes (number of arms = 72). In contrast, L. corvus and L. stagnalis have also
uniarmed (acrocentric) chromosomes (number of arms = 60 and 62, respectively).
Karyological data confirm specific distinctness of L. occulta and L. corvus; however, similarity
in the chromosome morphology of the latter species to L. stagnalis is probably based on
symplesiomorphies and, thus, cannot support phylogenetic relationship suggested earlier
on the basis of anatomical characters.
Kurzfassung. Karyotypen von zwei europдischen Arten der Gattung Lymnaea mit
umstrittenem taxonomischen Status (Gastropoda: Pulmonata: Lymnaeidae). -
Karyotypen von Lymnaea corvus und L. occulta wurden erstmalig untersucht und mit den
originalen Daten fьr ukrainische Populationen von L. stagnalis und L. palustris verglichen.
Alle untersuchten vier Arten weisen dieselbe Anzahl diploider Chromosomen auf (2n =
36), kцnnen aber durch die Morphologie der Chromosomen unterschieden werden. Die
Karyotypen von L. occulta enthalten nur zweiarmige Chromosomen (Anzahl der Arme =
72). Im Gegensatz hierzu weisen L. corvus und L. stagnalis auch einarmige (akrozentrische)
Chromosomen auf (Anzahl der Arme = 60 beziehungsweise 62). Die karyologischen
Befunde bestдtigen die spezifische Verschiedenheit von L. occulta und L. corvus; jedoch ist
die Дhnlichkeit in der Chromosomenmorphologie der letzteren Art gegenьber L. stagnalis
wahrscheinlich auf Symplesiomorphien zurьckzufьhren, deshalb kann die frьher auf der
Basis anatomischer Merkmale behauptete phylogenetische Verwandtschaft von L. corvus
und L. stagnalis nicht unterstьtzt werden
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