bluuebunny/crossref_metadata_2025 huggingface dataset:
Broadband scattering from spherical shells in a waveguide: modeling and classification
Authors: Fawcett John A.
Published: May 2008

In this presentation, the exact expression for scattering from a sphere in a Pekeris waveguide (e.g., Sammelmann and Hackman, J. Acoust. Soc. Am., 𝟠𝟚, 1987) is discussed. The importance of the sphere/interface rescattering terms is considered. A computationally faster multipath expansion approach is derived and its accuracy compared with the exact approach. For sufficiently high frequencies and in the case where the rescattering terms can be ignored, the multipath approach yields accurate predictions. The broadband scattering from an elastic-shelled sphere in a Pekeris waveguide is considered as a function of the frequency (or time for a pulse) and the sphere's range and depth in the waveguide. The classification problem is also discussed. The echos (time series or spectra) from a large set of spheres with varying parameters are generated and grouped into six classes corresponding to the various shell thicknesses and materials. Simple classifiers based upon temporal or spectral representations are considered for the spheres in free space and in a waveguide
Backscattering from an elastic target near a water-sediment interface at oblique incidence: First results of tank experiments
Authors: Sessarego Jean-Pierre , Ivakin Anatoliy N. , Guillermin Régine
Published: May 2008

Sound scattering from a target situated near a water-sediment interface was studied in laboratory conditions in order to control separately all the parameters involved in the scattering process. Targets of different sizes were ensonified with wide band transducers covering the frequency range 200 kHz to 1 MHz. First, the target scattering strength was measured in the free space conditions, and the scattering strength of the water-sediment interface was measured at oblique incidence. These characteristics were used to provide a rough estimate for the signal-to-noise ratio for the second set of experiments where the target was situated near the interface to study effects of target-boundary interactions. The intensity of the total scattered field was measured as a function of the beamwidth, transducer/object and object/interface distances, frequency, grazing angle, target size and the interface roughness parameters. The interface considered here is a flattened sand surface which was studied earlier [Ivakin and Sessarego, High frequency scattering from flattened sand sediments: effects of granular structure, J. Acoust. Soc. Am., 122, (5) 2007]. The targets were spherical glass beads of different size. Side scan sonar images are presented and possibilities of their qualitative interpretation are discussed.
A track-before-detect algorithm for active sonar based on a hidden Markov model
Authors: Parsons Nigel H.
Published: May 2008

An active sonar track-before-detect algorithm is described. It is based on a hidden Markov model which uses a Viterbi algorithm to estimate the log-likelihood ratio of the presence or absence of a target in tracks within a state space representing a set of ranges, bearings, range rates and bearing rates, assuming a set of transition probabilities of changes in range rate and bearing rate. A detection is declared if the log-likelihood ratio exceeds a certain threshold and subsequently an HMM tracker, operating on a much smaller state space, is then employed. The performance of this algorithm on simulated data is evaluated. It is shown that, for moving and manoeuvring targets, the detection performance is significantly better than that of a conventional algorithm.
Evaluation of portable high-frequency sonars for diver identification
Authors: Crawford Anna , Crowe Vance , Pastore Thomas , Kessel Ronald
Published: May 2008

Obtaining a positive identification is a critical step in most tiered harbour protection strategies for countering underwater intruders. It is generally recognised that sonar is one of the best tools for underwater imaging, however operating in a harbour environment presents challenges. As part of an on-going harbour protection research project, small easily portable high-frequency sonar systems are being investigated as a means to equip small response craft with intruder identification capability. Several systems are being considered, with the most comprehensive testing by DRDC to date being done on small Canadian-made sonars. Tests were conducted in local harbour waters in Halifax, Canada, and in La Spezia, Italy, through participation in the NATO Undersea Research Centre Response Against Diver Intrusions (RADI) joint trial, conducted in November 2007. A variety of small sonars and manned and unmanned response craft were used during the RADI trial. Evaluation of the performance of these devices for the task of diver identification in realistic conditions will be discussed.
Elimination of corner-turning in FFT-based sonar array beamforming
Authors: Barhen Jacob , Humble Travis , Traweek Michael
Published: May 2008

The expected availability, in the near future, of an ultralow power version of the revolutionary IBM CELL multicore processor opens unprecedented opportunities for implementing sophisticated signal processing algorithms faster and within a much lower energy budget. The concept of “corner turning” has been, for many decades, at the heart of array beamforming via Fourier transforms. As widely reported in the open literature (both for sonars and radars), the computational sequence involving corner turning operations, i.e., the sequence: temporal Fourier transforms --> data cube corner turning --> spatial Fourier transforms, constitutes one of the primary obstacles to achieving high-performance and lower power dissipation (by reducing the number of times memory is accessed). Even with the emergence of novel multicore processors, leading providers (e.g., Mercury Computers) still include explicit corner turning stages in their computational flow architectures for multidimensional array processing. The primary innovation reported in this paper addresses the development of a computational scheme that avoids altogether the corner turning stage. We discuss its implementation on currently available CELL technology (65 nm SOI) and demonstrate close to an order of magnitude speed-up compared to the scheme with corner turning implemented on the same processor.
Robust capon beamformer for port/starboard discrimination of twin-line array
Authors: Gong Zaixiao
Published: May 2008

Compared with the single-line array, the twin-line array have the potential to solve the port/starboard discrimination problem. Conventional method of geometric phase shifting has been used to distinguish the port/starboard of the target. But it can only be used to solve the problem when the frequency bandwidth is limited. The method based on optimum beamforming for hydrophone triplets can hardly be applied with the twin-line arrays. Aimed at the twin-line arrays port/starboard discrimination problem, a method based on the robust capon beamformer is proposed in this paper, which has advantages of concise algorithm and robustness against the aberration of the array shape. And the method works better with wider frequency bandwidth. Simulation and on sea experiment data are analyzed to verify the method.
Improving spatial resolution of interferometric bathymetry in multibeam echosounders
Authors: Llort-Pujol Gerard , Sintes Christophe , Lurton Xavier
Published: May 2008

Most multibeam echosounders used in seafloor mapping use the interferometry method for bathymetry measurement, based on the zero-crossing of the phase difference between two sub-arrays. In this approach, only one sounding is computed per formed beam, and the spatial resolution is linked to the beam footprint extent. Using the whole content of the phase difference signal vs time makes it possible ideally to get a bathymetry data sampled at the very resolution of the digitised signal. A trade-off is however to be found between this resolution improvement and the increase in the measurement noise. The performances of interferometric bathymetry are presented, together with the constraints of the resolution-accuracy trade-off, and a presentation of a high-resolution algorithm for interferometric bathymetry applicable to multibeam systems. This is illustrated by results obtained on a wreck, showing the remarkable improvement achievable in resolution over a real target. The potentialities for this method are promising, since it allows to process, in the same beam, targets on the seafloor and inside the water column; simplifications in multibeam sounders array structure and processing are also to consider.
A dynamic simulation of loblolly pine (Pinustaeda L.) seedling establishment based upon carbon and water balances
Authors: Blake John I. , Hoogenboom Gerrit
Published: May 2008

A generalized simulation model, ROOTSIMU, which utilizes dynamic carbon and water balance algorithms, was modified to simulate loblolly pine (Pinustaeda L.) seedling growth and water uptake for a 100-day transplant period. The modifications included an allowance for time-dependent changes in photosynthesis and carbon allocation. Heat sums were used to control the initiation of growth. Additional compartments were added to separate the physiological functions of suberized and nonsuberized roots and secondary woody tissues. Values used to initialize the model were largely derived from the published literature. The predicted results of a simulation run using 1985 and 1986 weather data are reported. Changes in simulated plant water potential were closely related to periods of rainfall or high evaporative demand. Midday values were occasionally less than −7 MPa when evaporative demand was high. Simulated responses to the 1986 drought indicated that initial soil water potentials at planting affected survival at values of less than −0.064 MPa in a sandy soil. Simulated growth was very sensitive to the photosynthetic rate, less sensitive to initial soluble carbohydrate concentration, and insensitive to instantaneous carbon allocation in relation to drought stress. The predicted increase in total root length for 1985 corresponded to the responses reported in several controlled environmental studies, but these were generally higher than those reported under field conditions. The results suggest that the carbon balance algorithm represents potential root growth within the constraints imposed by the model assumptions. The extreme diurnal fluctuations in plant water potential indicate that one or more important components of the plant system used to regulate short-term drought stress are not represented. Both stem tissue capacitance and the hydraulic conductance of mycorrhizal mycelia at low soil moisture contents may be important in controlling short-term water deficits. Further advances in the application of similar models depend upon an evaluation of these variables and a better theoretical and experimental determination of the effects of the geometry of the transplanted root system.
Initial Pinustaeda seedling height relationships with early survival and growth
Authors: Tuttle C. L. , South D. B. , Golden M. S. , Meldahl R. S.
Published: May 2008

Initial planting height of loblolly pine (Pinustaeda L.) seedlings from several nurseries and seed sources was related to survival and height growth on "good" and "poor" planting chances in Alabama. A planting chance was classified as poor if 2-year survival was less than 75% and total 2-year height growth was less than 75 cm. Seedling height (measured immediately following planting) was negatively related to survival, and the slope of the regression was four times greater when the planting chance was classified as poor than when it was classified as good. Initial height was also negatively related to 2-year height growth on poor planting chances, with shorter seedlings at planting reaching the same total height as taller ones after two seasons. As a result, initial field height on poor planting chances had little impact on total seedling height after two growing seasons. Therefore, there was no height growth advantage gained by planting seedlings taller than 20 cm when survival was less than 75%. Planting seedlings with heights of 20–34 cm was less of a problem when the planting chance was good. The use of shorter seedlings on planting chances where low survival may be expected may significantly increase loblolly pine seedling survival in the southern United States.
Biological species of Armillaria in the mixedwood forest of northern Ontario
Authors: Dumas M. T.
Published: May 2008

The Armillaria complex of the mixedwood forest of northern Ontario is composed of four intersterile species. Single-spore isolates of these biological species were compatible with Anderson and Ullrich's biological species I (Armillariaobscura), III, V, and VII (Armillariabulbosa). Armillariaobscura and biological species V were the most common. Armillariamellea sensu stricto was not collected.
Climatic reconstruction from tree rings at Banff
Authors: Robertson E. O. , Jozsa L. A.
Published: May 2008

This study describes new techniques of tree-ring data preparation and data analysis for deriving proxy climate data from senescent Douglas-fir (Pseudotsugamenziesii var. glauca (Beissn.) Franco) trees from the Canadian Rockies, near Banff, Alberta. Fifteen annual tree-ring variables were measured by X-ray densitometry for 429 years (1550–1978) for 12 increment cores. Ring variable data were reduced to standard indexes using a 99-year normally weighted digital filter. Missing ring values were estimated using correlation with younger and more vigorous specimens, and each ring variable data set (12 cores × 429 years) was reduced to its first and second principal component score, to be used in the development of response and transfer functions. Factor analysis identified six subsets of ring variable principal component scores. The best multiple regression equations for transferring tree-ring variable principal components into reconstruction of climate were identified by screening all possible combinations of principal component scores between factor groups. Annual climate variables, such as total precipitation, did not transfer as successfully as did the shorter-term climate variables like June–July precipitation (R2 = 0.36 compared with 0.51). Verified transfer functions were developed for five climate variables which can now be reconstructed to 1550 a.d. (429 years).
The effects of Velpar L (hexazinone) on seedling growth and ectomycorrhizal symbiosis of Pinusresinosa
Authors: Chakravarty P. , Chatarpaul L.
Published: May 2008

We investigated the effects of Velpar L (hexazinone) on ectomycorrhizal (Laccarialaccata) and nonmycorrhizal Pinusresinosa seedlings in the greenhouse and in the field. In both greenhouse and field studies, seedling growth was reduced by Velpar L at 1, 2, and 4 kg/ha application rates in the short term (2 months' exposure) with significant recovery occurring afterwards. Seedling mortality occurred only with herbicide treatments and was higher in the greenhouse than in the field. The 4 kg/ha Velpar L treatment caused the highest mortality and toxicity was most pronounced in the mycorrhizal (Laccarialaccata inoculated) seedlings. In both experiments mycorrhizal infection was significantly reduced by 2 and 4 kg/ha Velpar L treatments during the 0- to 2-month and 2- to 6-month exposure periods, with significant recovery occurring in the latter. Although seedlings not infected with Laccarialaccata became mycorrhizal through unidentified indigenous species, their infection rates were also affected by Velpar L at all levels during the 0- to 2-month period and at the 2 and 4 kg/ha levels after 2–6 months of exposure to the herbicide.
Element loss and retention during litter decay in a red spruce stand in Maine
Authors: Rustad Lindsey E. , Cronan Christopher S.
Published: May 2008

Litter decay in a Maine red spruce ecosystem was examined to determine the importance of decomposition as a recycling pathway for the trace metals Al, Mn, and Fe versus the major nutrients N, P, Ca, and Mg. The experimental design included litterbags containing the following species: red spruce (Picearubens Sarg.), red maple (Acerrubrum L.), white pine (Pinusstrobus L.), and mixtures of all three. Although decomposing litter was an important source of P, Mg, and Mn, the litter acted as a sink for Al, Fe, and N. Calcium showed a variable, species-dependent pattern. During the 2-year study, there was no net mineralization of Al, Fe, or N. The estimated net accumulations of Al and Fe during the first 24 months of litter decomposition were 0.58 and 0.50 kg ha−1, respectively. By comparison, the net accumulation of N during the same period was approximately 3.43 kg ha−1. Evidence suggests that Al and Fe accumulation are controlled by abiotic adsorption on humified litter, whereas N retention is controlled by microbial immobilization.
Effects of fertilization on wood density and tracheid length of 70-year-old lodgepole pine in west-central Alberta
Authors: Yang R. C. , Wang E. I. C. , Micko M. M.
Published: May 2008

Fertilization with nitrogen, phosphorus, and sulfur had relatively minor and overall negligible effects on both basic wood density and tracheid length of 70-year-old lodgepole pine (Pinuscontorta Dougl. var. latifolia Engelm.) on both Coalspur and Mercoal soil types in west-central Alberta. Wood density declined moderately 1–5 years after treatment on both soil types, but the decrease was offset by an increase in density 6–10 years after fertilization. Tracheid length of the pine decreased moderately after fertilization; high sulfur levels were generally associated with greater decreases in tracheid length.
Herbaceous weed control in young conifer plantations with formulations of nitrogen and simazine
Authors: White Diane E. , Newton Michael
Published: May 2008

Weed control and 2nd-year survival and growth of newly planted Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco) and noble fir (Abiesprocera Rehd.) seedlings were measured after application of herbicide and fertilizer in a replicated complete factorial experiment with four levels of simazine (0, 2.2, 4.4, 8.8 kg/ha), three levels of nitrogen (0, 110, 220 kg/ha), two types of nitrogen (urea prill; urea + trimamino-s-triazine (TST) prill), and two kinds of formulations (cogranular prill of simazine + nitrogen; nitrogen prill followed by liquid simazine). For the first growing season, total weed and grass control increased with increasing simazine rates. Total weed control was better when urea + TST, rather than urea alone, was applied in conjunction with simazine. Formulation and nitrogen rate were not significant. After plot treatment with 1.1 kg/ha of liquid hexazinone at the beginning of the second growing season, Douglas-fir survival decreased as rate of urea alone increased; survival decreased with little or no weed control and remained constant or increased with good weed control as rate of urea + TST increased. Noble fir height and diameter and Douglas-fir diameter declined with poor weed control but increased at least to the levels of untreated seedlings with good weed control. Noble fir diameter responded positively to added nitrogen. Although simazine may be toxic to 1st-year conifers, this study suggests that more complete weed control in conjunction with fertilization may benefit young conifer plantations.
Evaluation of morphological attributes as response variables to perennial competition for 4-year-old black spruce and jack pine seedlings
Authors: Morris D. M. , MacDonald G. B. , McClain K. M.
Published: May 2008

The sensitivity of seedling morphological attributes to changing competition levels was evaluated on 4-year-old black spruce (Piceamariana (Mill.) B.S.P.) and jack pine (Pinusbanksiana Lamb.) seedlings to determine the most appropriate response variables to be used in the assessment of early plantation performance. A total of 720 seedlings (360 per species) were sampled between 1987 and 1989, covering a range of stock types, soil textures, and competition levels. A competition index, derived from hemispherical photographs, provided an estimate of incident radiation received by each sampled seedling. Seedling stem volume at time of planting was used as a covariate in the regression analyses. Stratification by plantation was done to account for variations in site quality. The results from this study demonstrated that total height or current height increment were not reliable for quantifying individual seedling response to inter specific competition for 4-year-old black spruce or jack pine plantations. Overall, the most consistent response variable was total seedling dry weight. Coefficients of determination ranged from 0.116 to 0.534 for black spruce and from 0.601 to 0.810 for jack pine across the range of sites and stock types. If it is inappropriate to determine total seedling dry weight, root collar diameter would be the best substitute. Correlation coefficients between these two variables were 0.897 for black spruce and 0.912 for jack pine.
Devising sampling methods for inventory of receptive seed cones of jack pine
Authors: Fleming R. A. , Groot P. de , Obarymskyj A. , Burns T.
Published: May 2008

Open-grown jack pine (Pinusbanksiana Lamb.) in northern Ontario, ranging in age from 9–20 years, bore an average of 311 receptive seed cones, with the greatest number in the upper midcrown. Generally, counts of receptive seed cones varied more among trees than among directions; most of the variation among trees occurred in the mid to upper crown. The expression F(H) = Hb+1[b + 2 − (b + 1)H], with b = 3.12 (P < 0.001, R2 = 0.94), described the cumulative proportion of receptive seed cones occurring up to relative crown height, H. Significant directional differences in the parameter estimates for b showed that the open-grown jack pines initiated seed cones at slightly lower heights on the south side than on the other sides. For monitoring the crop, a procedure for randomly selecting receptive seed cones with respect to their vertical distribution in the crown was developed. The construction of simple, cost-effective sampling plans for estimating yields of receptive seed cones in jack pine seed orchards is explained. This involves determining the cost of conducting the sampling necessary to achieve a desired precision of estimation. It also involves determining the precision attainable with limited resources to conduct the sampling. With this focus, simple random sampling and two types of stratified random sampling were compared. Stratified random sampling based on relative crown height with equal stratum widths was cost-effective and should be relatively easy to implement operationally.
Effects of seed provenance and mycorrhizal fungi on early seedling growth in Piceamariana
Authors: Thomson J. , Matthes-Sears U. , Peterson R. L.
Published: May 2008

The importance of provenance and fungal species effects on mycorrhiza formation in Piceamariana was determined. Seed was collected from two sites near Chapleau, Ontario. One provenance was collected from an upland site with sandy soil, the second from a lowland site with peaty soil. Seedlings were grown under aseptic conditions in test tubes. Two experiments were performed: in the first, seedlings were inoculated with Hebelomacylindrosporum, Laccarialaccata, or Paxillusinvolutus, whereas in the second, seedlings were inoculated with Laccariabicolor, Laccarialaccata, Laccariaproximo or noninoculated agar plugs. Counts of ectomycorrhiza and lateral root formation were analyzed for significance with two-way factorial ANOVAS. When inoculated with L. laccata, seedlings from the lowland seed source had significantly more mycorrhizal second order lateral roots than seedlings from the upland seed source. Lowland seedlings also had greater shoot dry weight and foliage length values. However, overall differences between provenances were small. In contrast, differences between fungal treatments were pronounced. Both L. laccata and L. bicolor initiated good ectomycorrhiza formation and increased seedling growth.
Armillariaostoyae in young spruce plantations
Authors: Livingston William H.
Published: May 2008

Black spruce (Piceamariana (Mill.) B.S.P.) and white spruce (P. glauca (Moench) Voss) plantations, 4–10 years old, were examined for Armillaria root disease. The disease was found in 89% of 27 sample locations, and up to 2% of the trees were recently killed. Armillariaostoyae (Romagn.) Herink was the cause of the disease. Spruce show little reduction in stem height and diameter prior to being killed by the fungus. Lethal infections of A. ostoyae develop primarily at the root collar and are associated with root deformities and small diameters of lateral roots. Root deformities, frequently associated with growing conifer seedlings in containers, are hypothesized to predispose planted spruce to Armillaria root disease.
The nitrogen budget of a hybrid poplar plantation in Minnesota
Authors: Updegraff Karen L. , Zak Donald R. , Grigal David F.
Published: May 2008

The nitrogen (N) dynamics within short-rotation intensive-culture forest plantations are poorly understood. We developed a N budget for a 3-year-old hybrid poplar plantation under short-rotation intensive-culture management in northwestern Minnesota. Measured pools and fluxes of N included plant content, atmospheric input, litter fall, microbial biomass, mineralization, nitrification, and denitrification. Total aboveground tree biomass represented only 1.6% of the total N capital. Stable soil organic N was the largest pool, 5670 kg N•ha−1, and constituted 93% of all N within the site. Labile soil organic N and microbial N represented 5.6 and 1.6% of stable soil organic N, respectively. Nitrogen mineralization averaged 56 kg N•ha−1•year−1, and 66% of that production was oxidized to NO3−. Losses of N by denitrification and leaching were small compared with the magnitude of the other fluxes. Results suggest that a relatively high rate of plant uptake and production maintained NH4+ and NO3− pools at low levels, minimizing N exports to the atmosphere and groundwater.
Plant Viruses as Biotemplates for Materials and Their Use in Nanotechnology
Authors: Young Mark , Debbie Willits , Uchida Masaki , Douglas Trevor
Published: May 2008

In recent years, plant virus capsids, the protein shells that form the surface of a typical plant virus particle, have emerged as useful biotemplates for material synthesis. All virus capsids are assembled from virus-coded protein subunits. Many plant viruses assemble capsids with precise 3D structures providing nanoscale architectures that are highly homogeneous and can be produced in large quantities. Capsids are amenable to both genetic and chemical modifications allowing new functions to be incorporated into their structure by design. The three capsid surfaces, the interior surface, the exterior surface, or the interface between coat protein subunits, can be independently functionalized to produce multifunctional biotemplates. In this review, we examine the recent advances in using plant virus capsids as biotemplates for nanomaterials and their potential for applications in nanotechnology, especially medicine.
Gas Sensing Devices Based on 1D Metal-Oxide Nanostructures: Fabrication, Testing and Device Integration
Authors: Romano-Rodriguez Albert , Hernandez-Ramirez Francisco , Jimenez-Diaz Roman , Prades Joan Daniel , Casals Olga , Barth Sven , Mathur Sanjay
Published: May 2008

Individual tin oxide (SnO2) nanowires were electrically contacted with Focused Ion Beam (FIB) nanolithography techniques, their properties were characterized and their behavior as gas and ultraviolet light sensing devices was evaluated. These nanowires exhibited outstanding and reproducible responses to carbon monoxide and ultraviolet light, demonstrating that gas sensors and photodetectors based on this technology can be obtained. The combination of these nanowires with suspended microhotplates with integrated heaters is presented as a good solution to develop new nanowire-based devices.
Photoemission Study of Metal/HfSiON Gate Stack
Authors: Miyazaki Seiichi , Yoshinaga Hiromichi , Ohta Akio , Akasaka Yasushi , Shiraishi Kenji , Yamada Keisaku , Inumiya Seiji , Kadoshima Masaru , Nara Yasuo
Published: May 2008

Chemical bonding features in metal (TiN or Ru)/HfSiON gate stacks and electrical potential changes due to dipoles at the metal/dielectric interfaces have been studied by back-side x-ray photoemission measurements of the samples after wet-chemical removal of Si substrate. The photoemission threshold of the metal gate measured through the ultrathin dielectric layer confirms that the potential change of the gate metals, which is nearly equivalent to the difference in the flat-band voltage shift between capacitors with SiO2 and HfSiON, is caused by electron transfer from the HfSiON layer to the metal gate near the interface. From the recovery in the gate potential induced by oxygen incorporation into HfSiON, oxygen vacancies in the HfSiON layer are likely to be possible origin of the gate potential change. Also, from the experimental fact that the gate potential change becomes significant with decreasing thickness of the interfacial SiO2 layer below 3.5nm in Ru/HfSiON/SiO2 gate stacks, it is suggested that the generation of oxygen vacancies in HfSiON caused by oxidation reaction of Si substrate through ultrathin SiO2 layer plays an important role on the electron transfer near the Ru/HfSiON interface.
The Challenge of Measuring Defects in Nanoscale Dielectrics
Authors: Cheung Kin P. , Suehle John S.
Published: May 2008

Defects in nanoscale gate dielectric of MOS devices can exchange charges with the substrate via quantum mechanical tunneling. This characteristic has been utilized in many measurement methods to measure the defects and its spatial distribution. In some cases, the quantitative relationship between tunneling time and defect depth can be established. In other cases, this is not yet possible due to the lack of knowledge about the interface trap-fill time. As gate dielectrics reaches less than 1 nm equivalent oxide thickness, the measurement techniques must be made at higher speeds. Measurement into the GHz range will be needed.
In Situ Gas Phase Diagnostics for Hafnium Oxide Atomic Layer Deposition
Authors: Maslar James E. , Hurst W.S. , Burgess D.R. , Kimes William , Nguyen Nhan V. , Moore E.F. , Hodges J.T.
Published: May 2008

Atomic layer deposition (ALD) is an important method for depositing the nanometer-scale, conformal high k dielectric layers required for many nanoelectronics applications. In situ monitoring of ALD processes has the potential to yield insights that will enable efficiencies in film growth, in the development of deposition recipes, and in the design and qualification of reactors. This report will describe the status of a project to develop in situ diagnostics for hafnium oxide ALD processes. The focus is on an examination of the utility of Fourier transform infrared spectroscopy and diode laser spectroscopy for optimizing deposition conditions, rather than simply monitoring precursor delivery. Measurements were performed in a single-wafer, warm-wall, horizontal-flow reactor during hafnium oxide ALD involving tetrakis(ethylmethylamino) hafnium and water. Measurements were performed near the wafer surface under a range of deposition conditions in an effort to correlate gas phase measurements with surface processes.
A New Physics Effect, Phonon-Energy-Coupling Enhancement, and Its Applications for Leakage Current Reduction of Gate Dielectrics
Authors: Chen Zhi , Guo Jun , Samantaray Chandan B. , Ong Pangleen
Published: May 2008

Since discovery of the phonon-energy coupling enhancement (PECE) effect, significant progress has been made in understanding of this new physics effect. Extensive evidence showed that all chemical bonds in SiO2/Si, including Si-D, Si-O, and Si-Si bonds are strengthened due to the PECE effect. To our great surprise, the quantum tunneling current of SiO2 is also reduced by 2-5 orders of magnitude. The key factors for generation of the PECE effect are the structure change at high temperature and repairing of defects by trace O2. There is a strong correlation between the leakage current reduction of high-k HfSiON and concentration of Si-O bonds suggesting that it is the PECE effect that causes the leakage current reduction of high-k oxides.
Advanced Metal Gate FinFET CMOS TEchnology
Authors: Liu Yongxun , Matsukawa Takashi , Endo Kazuhiko , Masahara Meishoku , Ouchi Shinichi , Ishii Kenichi , Sakamoto Kunihoro , Suzuki Eiichi
Published: May 2008

We have developed the advanced metal gate technologies for materializing FinFET CMOS circuits. Using the developed titanium nitride (TiN) gate technologies, we demonstrate the fin-height controlled FinFET CMOS with accurate current matching and the flexible threshold voltage (Vth) asymmetric gate insulator thickness four-terminal (4T) FinFETs with a greatly improved subthreshold slope (S-slope). Furthermore, the newly developed nitrogen gas flow ratio, RN = N2/(Ar + N2), controlled PVD TiN gate and the tantalum (Ta)/molybdenum (Mo) interdiffusion gate technologies to set the symmetrical and lower Vth's for FinFET CMOS are presented.
Growth of Fluoride Quantum Well Heterostrucutres for Resonant Tunneling Devices on Si Substrates
Authors: Tsutsui Kazuo , Oshita Takao , Watanabe So , Maeda Motoki
Published: May 2008

Heteroepitaxial fluoride structures are candidates of material systems for quantum well devices such as resonant tunneling devices on Si substrates. Resonant tunneling diodes composed of CaF2/CdF2/CaF2 on Si(111) have been demonstrated and they exhibited large potential for high performance quantum effect devices based on high energy barrier and abrupt hetero-interface. However, this material system has significant problem of the pin-hole defects in CaF2 and strong chemical reaction of CdF2 with Si. Fluoride alloys such as CaxCd1-xF2 and CaxMg1-xF2, as well as the post oxidation technique, are effective to overcome these problems.
Evaluation and Control of Strain in Si Induced by Patterned SiN Stressor
Authors: Saitoh Hiroyuki , Kosemura Daisuke , Kakemura Yasuto , Yoshida Tetsuya , Takei Munehisa , Ogura Atsushi , Koganezawa Tomoyuki , Hirosawa Ichiro , Kohno Masayuki , Nishita Tatsuo , Nakanishi Toshio
Published: May 2008

We evaluated the strain introduced in the Si-substrate by the patterned SiN film using UV-Raman spectroscopy. We confirmed that the tensile/compressive strain was induced under the SiN film with compressive/tensile inner stress. The density of the SiN film was evaluated using X-ray reflectometry. The inner stress of the SiN film was proportional to the film density. Therefore, the induced strain can be control by changing SiN CVD conditions. Furthermore, the film density was increased and induced strain was changed after annealing.
Metal Surface Characterization for Understanding of Electrical Properties on Aluminum Interconnects
Authors: Otake Atsushi , Aoki Tomoko
Published: May 2008

Wet cleaning technology in the semiconductor manufacturing process is required to provide reliable electrical properties as well as wafer cleanliness. The high density connections of ULSI devices require low resistance contacts with extreme via hole cleanliness being a major factor in achieving this. In this study, metal surfaces that are commonly exposed during wet chemical cleaning of a via structure after plasma etch were characterized by X-ray photoelectron spectroscopy. XPS surface characterization and surface resistance measurement were used to understand the correlation between via cleaning and the resulting electrical properties of the device. Results support the advantages of hydroxylamine cleaning on wafer cleanliness and electrical properties.
Measurement of the Stability and Investigation of the Rupture Behavior of Semiconductor Line Nanostructures by AFM
Authors: Peter Daniel , Dalmer Michael , Kruwinus Hans , Lechner Alfred , Archer Leo , Gaulhofer Ernst , Bensch Wolfgang
Published: May 2008

The measured lateral stability of polysilicon line structures on a Silicon Oxy-Nitride layer is presented. This has been measured by Lateral Force Microscopy (LFM) in order to understand how much force can be applied to the structure during a wet cleaning process with subsequent drying. The measured values in the lateral dimension are between 2 and 5 µN which is in the same range as expected by mechanical calculations. SEM micrographs of the damaged sites confirm a round breaking shape. The length of the broken line is around 0.5 to 1 µm with a lower limit of 0.5 µm which is similar to previously reported results on real damage produced by cleaning processes supported with Megasonic energy. The rupture in the AFM experiments occurs clearly in the polysilicon and not at the interfaces of the structure.
The Role of Borophosphosilicate Chemistry in Heterogeneous Nucleation
Authors: Sokolov Yuri V. , Wang Qi
Published: May 2008

This study aims to solve the conflict between two important features of PECVD BPSG film: good flow ability and low defectiveness, which can ultimately alter the electrical characteristics of devices. The film flow associates with the amount of phosphorus and boron dopants, which, in their turn, are a source of boron phosphate imperfections. The films' compounds SiO2-B2O3-P2O3/P2O5 have to be thus kept appropriately to satisfy both requirements. Unstable glass structure carries an excessive amount of hydrogen related species, especially H2O, which is a catalyst for defects. Such films are also vulnerable to additional moisture from the air. The as-deposited film instability brings on defect generation and out-gassing / counterdoping problems during the relaxation process when film is being stored and heated. This work studies the film structure that is modulated by the deposition parameters in order to get optimized ratios of N2O/SiH4, P2O3/P2O5 and SiO2/P2O5. Special attention is paid to the oxygen-rich film's composition with low SiH4 precursor.
Sp2 Carbon Phases in Nano Diamond.
Authors: Ballutaud Dominique , Jomard François , Pinault Marie-Amandine , Frangieh Georges , Simon Nathalie
Published: May 2008

Hot filament and microwave plasma CVD nanocrystalline diamond films are analysed by visible and ultra-violet excitation source Raman spectroscopy. The analysis of the shape and relative intensity of the different Raman features due to the sp2 phases, i.e. the sp2 1550 cm-1 G band attributed to C=C sp2 bond stretching mode, the D band (collective breathing mode of aromatic rings) and the shoulder observed at about 1150 cm-1 (assigned to transpolyacetylene segments) gives some information on the local structure of the sp2 phases. The surface of the samples is analysed by X-ray Photoelectron Spectroscopy (XPS). The evolution of the sp2 phases is analysed at the surface and in the bulk when the diamond films are submitted to thermal annealing under ultra-high vacuum or acidic surface oxidation. The decomposition of the C1s peak evidences graphitic phases attributed to the high density of grain boundaries.
In-situ Monitoring of Si Wafer Temperature during Millisecond Rapid Thermal Annealing
Authors: Furukawa Hirokazu , Higashi Seiichiro , Okada Tatsuya , Kaku Hirotaka , Murakami Hideki , Miyazaki Seiichi
Published: May 2008

An in-situ mnitoring technique for the temperature profile of a Si wafer during millisecond rapid thermal annealing has been developed. By analyzing the oscillation observed in transient reflectivity of the Si wafer during annealing, we obtain a transient temperature profile with a millisecond time resolution. Since this measurement is based on optical interference, a highly sensitive temperature measurement with an accuracy of 2 K is expected. Using this measurement technique, we controlled Si wafer sutface temperature during thermal plasma jet irradiation with the heating and cooling rates in the order of 10^4 to 10^5 K/s.
Physical Modeling of Layout-Dependent Transistor Performance
Authors: Knutson Karson L. , Cea Stephan , Giles Martin , Keys Patrick , Davids Paul , Weber Cory , Shifren Lucian , Kotlyar Roza , Hwang Jack , Talukdar Suddha , Stettler Mark
Published: May 2008

Design for Manufacturability (DFM) is a phrase that often accompanies discussion of layout optimization for lithography process effects, particularly Optical Proximity Correction (OPC). In an environment where process technology and circuit design are developed together, many other process-layout co-optimization strategies can be investigated. In this paper we discuss physical modeling to enable co-optimization strategies from a device performance point of view by examining layout-induced variation in front-end manufacturing processes used to engineer transistor strain and dopant diffusion/activation.
Crystalline Structure of HfZrO Thin Films and ZrO2 / HfO2 bi-Layers Grown by AVD for MOS Applications
Authors: Lhostis Sandrine , Gaumer Clement , Bonafos Caroline , Schamn Sylvie , Cherkashin Nikolay , Pierre Francois , Fanton Aurélien , Morin Christine , Ferrieu F. , Casse Mikael , Garros Xavier , Leroux Charles
Published: May 2008

The downscaling in CMOS transistors requires the introduction of new materials with a higher dielectric constant. The electrical properties of HfxZryOz films and ZrO2 / HfO2 bi-layers grown by Atomic Vapor Deposition were analyzed for their integration as gate oxides. While crystallinity of those layers was found to be dependent on their zirconium concentration, the electrical performance was shown to depend mainly on the growth temperature of the high-k films.
Investigation of VT Shift Mechanism of High-K Dielectrics caused by Lanthanum Capping for NMOS and Tantalum Capping for PMOS Devices
Authors: Lee Bongmook , Lichtenwalner Daniel , Agustin Melody , Arghavani Reza , Tang Xianmin , Gandikota Srinivas , Ku Victor , Misra Veena
Published: May 2008

The role of LaO capping or TaO capping in the VFB shift of two different high-K dielectrics was investigated. It was found that the formation of La-O-Si and its location correlates with the VFB modulation in NMOS devices. When more La atoms are present at the high-K/SiOx interface, a larger shift in VFB is observed, consistent with net directional La-O-Si bonding. In the case of a TaO capping layer, the bulk property of Ta d states in an Al2O3 matrix is attributed as the mechanism responsible for enhancing VFB for PMOS devices.
The Study of Workfunction Measurement Method for Bilayer Metal Gate Electrode using XPS
Authors: Jung Eunjae , Yim C. J. , Yang I. S. , Chang Hyun-Jin , Cho S. W. , Cho Mann-Ho , Ko Dae-Hong
Published: May 2008

An Al-Ti bi-layer was deposited by D.C. magnetron sputtering and annealed by RTA at 500oC 10s in an N2 ambient. After RTA, the Al3Ti alloy layer was formed at the Al/Ti interface. The XPS/UPS depth-profile was performed in other to measure workfunction. The workfunction of Al3Ti layer is measured to be about 4.67 eV.
Si Nanowire CMOS Transistors and Circuits by Top-Down Technology Approach
Authors: Balasubramanian Narayanan , Singh Navab , Rustogi Subhash C. , Buddharaju Kavitha D. , Fu J , Hui Z. , Balakumar Subramanian , Agarwal A. , Manhas S. K. , Lo Guo Qiang , Kwong D. L.
Published: May 2008

For the end of the roadmap CMOS scaling, the non-classical device architecture, Gate All Around (GAA) FET with nanowire (NW) channel body offers the ultimate electro-static control and thus has the potential to push the gate length to few nanometers. The key challenge for NWs to be widely adopted in CMOS IC industry is that they have to be formed by large scale manufacturing methods and devoid of contamination issues. Top-down methods using lithography and etching suit CMOS applications in general and also provides a well-established CMOS based platform for creating devices for other applications. We have developed such a technology platform for Si NW fabrication with NW diameter down to 3 nm. This paper gives an overview of our technology approach, GAA Transistors, CMOS inverters, logic gates, ring oscillators, nanocrystal embedded SONOS memory devices and an introduction to high Ge content SiGe nanowires.
Ge Enrichment Technique on SiGe/SOI Mesa Islands: a Localized GeOI Structures Fabrication Method
Authors: Vincent Benjamin , Damlencourt Jean-Francois , Morand Yves , Rouchon D. , Mermoux Michel
Published: May 2008

This paper presents a review of the mechanisms involved in the oxidation of SiGe/SOI mesa structures. This method, called local Ge enrichment technique is proposed to carry out GeOI structures on SOI wafers to allow planar SOI-GeOI co-integration. Two types of mechanisms have been identified, defined by their respective scale. Small scaled mechanisms (nanometer range) involve additional oxidations critical for mesa size and shape preservation. Large scaled mechanisms (micrometer range) involve non homogeneous Ge spatial distributions on the enriched mesa.
Growth of Strain InAs-Channel Quantum Well FETs on Si Substrate Using SiGe buffer
Authors: Chang Edward Yi , Tang Shih-Hsuan , Lin Yueh-Chin , Hsieh Yen-Chang
Published: May 2008

The growth of the AlGaSb/InAs quantum well field effect transistor(QWFET) epitaxial structure on the Si substrate has been investigated. Buffer layers consisted of UHV/chemical vapor deposited grown Ge/GeSi and molecular beam epitaxy-grown AlGaSb/AlSb/GaAs were used to accommodate the strain induced by the large lattice mismatch between the AlGaSb/InAs QWFET structure and the Si substrate. A very high room-temperature electron mobility of 27300 cm2 /V s was achieved. Strained QWFET was also grown on the GaAs substrate, it is found that the strained QWFET grown on the Si substrate has higher electron mobility due to high strain induced in this structure.
CMOS Scaling For the Next Decade: Trends, Challenges and Opportunities
Authors: Majhi Prashant , Oh Jungwoo , Lee Se-Hoon , Harris Rusty , Tseng Hsing-Huang , Jammy Raj
Published: May 2008

The advent of high-k/metal gates into production for CMOS gate stacks has marked the onset of MOSFET scaling that has clearly become reliant on new materials and / or new device architecture. Additionally, new approaches to form ultra-shallow junctions with high active-dopant concentrations and low schottky barrier height silicides with novel materials to reduce contact resistance have been reported by many groups and will continue to facilitate MOSFET scaling with increasing performance. It is becoming clear that Si (as the channel) may not be able to provide for the high performance combined with low power technologies that would be needed in future. Over several years, there has been a lot of research on high mobility channels: group IV for pMOSFETs and III-V for NMOSFETs. However, there appears to be little consensus on a) the choice of high mobility channels for P and N channel MOSFETs, b) its potential compared to short channel strained-Si, and 3) potential technology node for insertion. In this work, trends, challenges and opportunities related to several of the aforementioned modules (gate stack, junctions, contacts, and high mobility Ge based channels) will be briefly presented and discussed.
Uniaxially Strained Si/SiGe Wire-Channel Transistors
Authors: Tezuka Tsutomu , Irisawa Toshifumi , Toyoda Eiji , Sugiyama Naoharu , Takagi Shin-ichi
Published: May 2008

A novel fabrication process and electrical characteristics of uniaxially strained Si and SiGe wire-channel transistors are presented. The uniaxial stress was introduced into the wire channels by anisotropic relaxation of biaxially strained SOI (SSOI) and SGOI (SiGe-on-insulator) substrates. Ge-condensation and hydrogen thermal etching techniques were also employed. The fabricated SSOI-wire n- and SGOI-wire p-MOSFETs exhibited mobility enhancements against both (100)Si surface and control SOI-wire devices due to the uniaxial strain.