Silicon Tungsten Research Articles

The AGILE gamma ray satellite

AGILE (Light Imager for Gamma-ray Astrophysics) will be launched on an equatorial orbit in 2007 by the PSLV Indian launcher. It is a small scientific satellite for the detection of γ -ray cosmic sources in the energy range 50 MeV–30 GeV with a field of view of 1 5 of the sky, and will become the only detector in that energy range till the launch of GLAST. Three different detectors and an anticoincidence system are the components of the scientific instrument. The main detector is a silicon–tungsten tracker. The second detector is a X-ray detector in the range 15–45 keV; its main aim is to highlight the X-ray emission associated to the gamma emissions. The third detector is a small calorimeter made of 30 CsI scintillating bars read out by photodiodes; its energy range is 150–300 keV. The large number of channels (about 37 000, with analog read out), requires very reliable components. Each part of the instrument has undergone several tests during the assembly phase; then the whole instrument has been calibrated on a dedicated photon tagged beam-line developed at the DAPHNE BTF (Beam Test Facility, INFN Frascati) and has been integrated with the satellite.

Front-end ASICs development for W–Si calorimeter at ILC (CALICE collaboration)

An ASIC (FLC_PHY3) has been developed to read out the test-beam prototype of the future international linear collider (ILC) tungsten–silicon calorimeter. It consists of 18 channels low-noise charge preamplifiers, bi-gain CRRC2 180 ns shapers, 12-bit track-and-hold, and a 5 MHz output multiplexer. It covers a dynamic range of 14 bits with a noise of 3500 e − with the 70 pF detector and a linearity at the per-mil level. The chip dissipates 6 mW/channel and 1000 chips have been produced in AMS 0.8 μm BiCMOS technology in 2003. One channel has recently been migrated into 0.35 μm, improving the series noise by 20% and the 1/ f noise by two. Besides, a power pulsing feature has been added in order to exploit the 1% duty cycle of the accelerator. This feature is a key parameter for ILC, as it is mandatory to embed the front-end inside the detector, without spoiling the Moliere radius with cooling pipes. Preliminary results indicate a good behavior in pulsing mode and several hundred channels have been produced of the recent version including this feature (FLC_PHY4), to be tested extensively in test beam at CERN in autumn 2006. FLC_PHY4 also includes a 12-bit ADC in order to take a step to the final version, which will send digital data out.

A method to distinguish extrinsic and intrinsic fracture-origin populations in monolithic ceramics

Fracture-stress data and fractographic examination for the identification of the fracture origin are presented for two types of brittle materials (tungsten carbide and silicon carbide (SiC)) tested either in three- or four-point bending. The results of the adjustment of a mixture of two Weibull distributions to the fracture-stress data through maximum likelihood estimates via R-software (version 1.8.1 2003, package MASS) agree quite well with the results of the fractographic examinations. Different flaw distributions (e.g. extrinsic and intrinsic) are observed, and each has its own strength distribution parameters.

Surface morphology of sputter deposited W–Si–N composite coatings characterized by atomic force microscopy

Tungsten–silicon–nitride (W–Si–N) composite coatings on Si(100) substrates were sputter deposited at various silicon target currents, and their surface morphology was studied with scaling analysis and fractal analysis based on atomic force microscopy (AFM). The root-mean-square (rms) roughness σ, roughness exponent α, the correlation length ξ and the average magnitude of the lateral surface slope ρ decrease with the silicon target current, which is caused by the impeding effect of amorphous Si 3N 4 on the grain growth of W 2N and W 5Si 3. The competition of surface diffusion and shadowing effect together with other processes drives the formation of columnar grains with mould-like tops. The fractal dimensions obtained using power spectrum method and the R/ S method are 2.16 ± 0.04 and 2.15 ± 0.01, respectively, and they both increase with the silicon target current.

Space qualification tests of the PAMELA instrument

PAMELA is a satellite-borne experiment which will measure the antiparticle component of cosmic rays over an extended energy range and with unprecedented accuracy. The apparatus consists of a permanent magnetic spectrometer equipped with a double-sided silicon microstrip tracking system and surrounded by a scintillator anticoincidence system. A silicon–tungsten imaging calorimeter, complemented by a scintillator shower tail catcher, and a transition radiation detector perform the particle identification task. Fast scintillators are used for Time-of-Flight measurements and to provide the primary trigger. A neutron detector is finally provided to extend the range of particle measurements to the TeV region. PAMELA will fly on-board of the Resurs-DK1 satellite, which will be put into a semi-polar orbit in 2005 by a Soyuz rocket. We give a brief review of the scientific issues of the mission and report about the status of the experiment few months before the launch.

EPR and XPS measurements of polymeric catalysts doped with hereopolyacids in oxygen adsorption studies

The goal of our studies was to determine the nature of interactions between catalytic active samples, such as polypyrrole (PPy) doped with: chloride anions, heteropolyacids such as H 5PMo 10V 2O 40, or H 4SiW 12O 40, and oxygen particles. In order to reveal the mechanism of the linkage between the catalysts and oxygen we provided the electron paramagnetic resonance (EPR) measurements of synthesized samples in O 2 and N 2 flow. Moreover, the X-ray photoelectron spectroscopy (XPS) measurements were performed to show the properties of doped heteropolyacids and the state of nitrogen in polypyrrole matrix. The results of EPR studies of PPy(Cl), PPy(H 4SiW 12O 40), PPy(H 5PMo 10V 2O 40) samples, show that the polypyrrole doped with chloride anions interacts much easier with oxygen than polypyrrole doped with heteropolyacids (in the above given order, of preference with the most active polypyrrole system first). It correlates with XPS results, which show that a molybdenium–vanadium anion is more reduced than a silicon–tungsten one. The redox reactions of heteropolyacids involve the oxidation–reduction of the conjugated polymer chain, leaving no or little place for interactions with oxygen. Polypyrrole doped with H 4SiW 12O 40 shows some oxygen sensitivity as observed in the EPR studies, as opposed to polypyrrole doped with H 5PMo 10V 2O 40, which is in line with the XPS results.

Improved nanotriode fabrication process for multiple gates and reduced leakage current

The nanotriode is a novel vacuum microelectronic device, in which electrons are emitted from a metal nanopillar with tip radius <1 nm in an integrated vacuum chamber, over a distance of about 100 nm. In this work, the nanotriode fabrication process has been revised, with the aim of creating nanotriode-type devices with additional gates. The resultant structure has smooth steps on the outer edges of the RF magnetron-sputtered tungsten–silicon dioxide multilayer stack, which aids the isolation of the electrode layers. This improved structure contributes reduced inter-electrode leakage currents. The form of the nanopillars has also been investigated by cross-sectional TEM.

Improved nanotriode fabrication process for multiple gates and reduced leakage current

The nanotriode is a novel vacuum microelectronic device, in which electrons are emitted from a metal nanopillar with tip radius <1 nm in an integrated vacuum chamber, over a distance of about 100 nm. In this work, the nanotriode fabrication process has been revised, with the aim of creating nanotriode-type devices with additional gates. The resultant structure has smooth steps on the outer edges of the RF magnetron-sputtered tungsten–silicon dioxide multilayer stack, which aids the isolation of the electrode layers. This improved structure contributes reduced inter-electrode leakage currents. The form of the nanopillars has also been investigated by cross-sectional TEM.

The space mission PAMELA

Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) is a satellite-borne experiment which will investigate the matter–antimatter (a)symmetry of the universe and other cosmological problems through precise cosmic-ray measurements. The primary objectives of the PAMELA mission include measurements of the energy spectra of cosmic-ray antiprotons and positrons over a large energy range (up to 190 GeV for antiprotons, 270 GeV for positrons) and with unprecedented accuracy, the search for an antimatter component with a sensitivity of 10 −7 in the He /He ratio, the measurement of the light nuclear components of cosmic rays up to 200 GeV/n and of the electron component up to at least 400 GeV. The apparatus is built around a permanent magnetic spectrometer equipped with a double-sided silicon microstrip tracking system and surrounded by a scintillator anticoincidence system. State-of-the-art detectors are used for particle identification: a silicon–tungsten imaging calorimeter, augmented by a scintillator shower tail catcher, and a transition radiation detector made up of carbon fibre radiators and proportional straw tubes. Fast scintillators are used for time-of-flight measurements and to provide the primary trigger. A neutron detector is finally provided to extend the range of particle measurements to energies as high as 10 11–10 13 eV. PAMELA will be operated on-board of the Resurs-DK1 satellite, which will be put into its semi-polar orbit in 2004. Here we illustrate the main features of the apparatus and its current status.

AGILE, a satellite for high energy γ-ray astrophysics: prospects for the Mini-Calorimeter

Astrorivelatore Gamma ad Immagini LEggero (AGILE) is an Italian Space Agency (ASI) small space mission for high energy astrophysics in the γ-ray energy range 30 MeV–50 GeV and in the X-ray band 10–40 keV. AGILE is composed of three scientific detectors: a Tungsten–Silicon Tracker, a CsI Mini-Calorimeter and a silicon based X-ray detector (Super-Agile), moreover, an anticoincidence system carries out background rejection. The satellite’s payload will have good imaging performances (with angular resolution of a few arc-minutes in the γ-ray band), good timing resolution and a large field of view (about 1/5 of the sky). AGILE detection principle is based on the pair production process, that arises from the interaction between high energy photons and the tungsten layers of the Silicon Tracker. The Silicon Tracker is designed to determine the direction of the incoming radiation, while the Mini-Calorimeter evaluates the energy of the interacting photons. The Mini-Calorimeter can also work as a stand-alone γ-ray detector in the energy range 250 keV–250 MeV, with no imaging capabilities, for the detection of transients and γ-ray burst events (in cooperation with Super-Agile) and for the evaluation of γ-ray background fluctuations. In this paper a description of the Mini-Calorimeter is done.

Simulation study of the silicon–tungsten calorimeter for ACCESS

The Advanced Cosmic-ray Composition Experiment for the Space Station (ACCESS) will perform a direct measurement of the elemental composition and energy spectra of cosmic-ray particles up to an energy of 10 15 eV. The detector complement of ACCESS consists of a TRD and a ionization calorimeter, and six different concepts for the ACCESS calorimeter design alone have been proposed in the recent past. In this work, we present the structure optimization analysis and the Monte Carlo simulation results on detector performance for the silicon–tungsten (Si–W) imaging calorimeter design for ACCESS, developed as part of the NASA-sponsored mission concept and detector assessment study for this experiment.

Sintering Behavior of Alumina-Niobium Carbide Ceramics from Polymer-Filler Mixtures

Studies have been developed in the literature to obtain alternative ceramic cutting tools with better properties as tungsten carbide and silicon nitride. Results have showed that the addition of titanium carbide, tungsten carbide or niobium carbide has improved the wear resistance and hardness of alumina. This work presents a study about preparation and characterization of an alumina reinforced with niobium carbide. The composite material is produced using polymer-filler mixtures. Samples with 60 wt.% polysiloxane and a mixture of 40 wt.% of niobium and alumina powder were mixed, uniaxially pressed at 200°C and sintered in flowing argon at 1200°, 1400° and 1600°C. The composite materials were characterized by X-ray diffraction (XRD), density measurements, fracture strength and microstructural analysis. The 60 wt% polymer + 40 wt% Nb showed the presence of new crystalline phases such as NbC, Nb 5 Si 3 and Nb 3 Si.

Microwave Sintering Process Model

In order to simulate and optimize the microwave sintering of a silicon nitride and tungsten carbide/cobalt too/bits process, a microwave sintering process model has been built. A cylindrical sintering furnace was used containing a heat insulating layer, a susceptor layer, and an alumina tube containing the green toolbit parts between parallel, electrically conductive, graphite plates. Dielectric and absorption properties of the silicon nitride green parts, the tungsten carbide/cobalt green parts, and an oxidizable susveptor material were measured using perturbation and waveg Hide transmission methods. Microwave absorption data Were measured over a temperature range from 20°C to 800°C. These data were then used in the microwave process model which assumed plane wave propagation along the radial direction and included the microwave reflection at each interlace between the materials and the microwave absorption in the bulk materials. Heal transfer between the components inside the cylindrical sintering furnace was also included in the model. The simulated heating process data for both silicon nitride and tungsten carbide/cobalt samples closely follow the experimental data. By varying the physical parameters of/lie sintering furnace model, such as the thickness of ihe susceptor layer, the thickness of the alumina tube wall, the sample load volume and the graphite plate mass, the model data predicts their effects which are helpful in optimizing those parameters in the industrial sintering process.

The AGILE silicon tracker: an innovative γ-ray instrument for space

Abstract AGILE (Light Imager for Gamma-ray Astrophysics) is the first small scientific mission of ASI, the Italian Space Agency. It is a light ( 100 kg for the scientific instrument) satellite for the detection of γ-ray sources in the energy range 30 MeV – 50 GeV within a large field of view ( 1 4 of the sky). It is planned to be operational in the years 2003–2006, a period in which no other gamma-ray mission in the same energy range is foreseen. AGILE is made of a silicon tungsten tracker, a CsI(Tl) minicalorimeter (1.5X0), an anticoincidence system of segmented plastic scintillators and a X-ray imaging detector sensitive in the 10– 40 keV range. The tracker consists of 14 planes, each of them made of two layers of 16 single-sided, AC coupled, 410 μm thick, 9.5×9.5 cm 2 silicon detectors with a readout pitch of 242 μm and a floating strip. The readout ASIC is the TAA1, an analog-digital, low noise, self-triggering ASIC used in a very low power configuration ( μW / channel ) with full analog readout. The trigger of the satellite is given by the tracker. The total number of readout channels is around 43 000. We present a detailed description of the tracker, its trigger and readout logic, its assembly procedures and the prototype performance in several testbeam periods at the CERN PS.

Performance of the Transition Radiation Detector of the PAMELA space mission

The performance of the Transition Radiation Detector (TRD) of the PAMELA telescope has been studied using beam test data and simulation tools. PAMELA is a satellite—borne magnetic spectrometer designed to measure particles and antiparticles spectra in cosmic rays. The particle identification at high energy will be achieved by combining the measurements by the TRD and a silicon—tungsten imaging calorimeter. The TRD is composed of 9 planes of straw tubes, interleaved with carbon fiber radiators. A prototype of the detector has been exposed to particle beams of electrons, pious and muons of various momenta at the CERN-PS and SPS accelerator facilities. In addition a dedicated Monte Carlo code has been developed to simulate the detector. Here we illustrate both simulation results and experimental data analysis procedures and we will discuss the estimated TRD performance.

The AGILE silicon tracker: testbeam results of the prototype silicon detector

AGILE (Light Imager for Gamma-ray Astrophysics) is a small scientific satellite for the detection of cosmic γ-ray sources in the energy range 30 MeV – 50 GeV with a very large field of view (1/4 of the sky). It is planned to be operational in the years 2003–2006, a period in which no other γ-ray mission in the same energy range is foreseen. The heart of the AGILE scientific instrument is a silicon–tungsten tracker made of 14 planes of single sided silicon detectors for a total of 43 000 readout channels. Each detector has a dimension of 9.5×9.5 cm 2 and a thickness of 410 μm . We present here a detailed description of the performance of the detector prototype during a testbeam period at the CERN PS in May 2000. The Tracker performance is described in terms of position resolution and signal-to-noise ratio for on and off-axis incident charged particles. The measured 40 μm resolution for a large range of incident angles will provide an excellent angular resolution for cosmic γ-ray imaging.

The PAMELA experiment on satellite and its capability in cosmic rays measurements

The PAMELA equipment will be assembled in 2001 and installed on board the Russian satellite Resurs. PAMELA is conceived mainly to study the antiproton and positron fluxes in cosmic rays up to high energy (190 GeV for p ̄ and 270 GeV for e +) and to search antinuclei, up to 30 GeV/n, with a sensitivity of 10 −7 in the He / He ratio. The PAMELA telescope consists of: a magnetic spectrometer made up of a permanent magnet system equipped with double sided microstrip silicon detectors; a transition radiation detector made up of active layers of proportional straw tubes interleaved with carbon fibre radiators; and a silicon–tungsten imaging calorimeter made up of layers of tungsten absorbers and silicon detector planes. A time-of-flight system and anti-coincidence counters complete the PAMELA equipment. In the past years, tests have been done on each subdetector of PAMELA; the main results are presented and their implications on the anti-particles identification capability in cosmic rays are discussed here.

Total reflection X-ray fluorescence spectrometers for multielement analysis: status of equipment

Multielement analysis by total reflection X-ray fluorescence spectrometry has evolved during two decades. At present commercial equipment is available for chemical analysis of all types of biological and mineral samples. The electronic industry has also benefited from scientific and technological developments in this field due to new instrumentation to determine contamination on the surface of silicon wafers (the equipment will not be covered in this paper). The basic components of the spectrometers can be summarized as follows: (a) excitation source; (b) geometric arrangement (optics) for collimation and monochromatization of the primary radiation; (c) X-ray detector; and (d) software for operation of the instrument, data acquisition and spectral deconvolution to determine the concentrations of the elements (quantitative analysis). As an optional feature one manufacturer offers a conventional 45° geometry for direct excitation. Personal communications of the author and commercial brochures available have allowed us to list the components used in TXRF for multielement analysis. Excitation source: high-power sealed X-ray tubes, output from 1300 to 3000 W, different mixed alloy anodes Mo/W are used but molybdenum, tungsten and copper are common; single anode metal ceramic low power X-ray tubes, output up to 40 W. Excitation systems can be customized according to the requirements of the laboratory. Detector: silicon–lithium drifted semiconductor detector liquid nitrogen cooled; or silicon solid state thermoelectrically cooled detector (silicon drift detector SDD and silicon-PIN diode detector). Optics: multilayer monochromator of silicon–tungsten, nickel–carbon or double multilayer monochromator. Electronics: spectroscopy amplifier, analog to digital converter adapted to a PC compatible computer with software in a Windows environment for the whole operation of the spectrometer and for qualitative/quantitative analysis of samples are standard features in the production of this instrument. The detection limits reported in the literature are presented; pricing, analytical capability, ease of operation, calibration and optical alignment as well as technical support are also discussed.

Effect of thinning a WSiN/WSi[sub x] barrier layer on its barrier capability

We investigated the effects of tungsten silicon nitride/tungsten silicide (WSiN/WSix) barrier layer thickness on its barrier capability. WSiN was obtained by nitridizing the WSix surface with electron cyclotron resonance nitrogen plasma. The total thickness of the WSiN/WSix barrier layer was reduced by thinning the initial WSix layer. When 5-nm-thick WSix was nitridized, the N and Si contents in the WSiN/WSix layer became smaller than when WSix initial thickness was 20 nm. This barrier layer diffused into the copper (Cu) layer when annealed, and did not act as a barrier layer. On the contrary, a WSiN/WSix barrier layer formed by nitridizing 10-nm-thick WSix showed good barrier capability against Cu diffusion. We evaluated the leakage current between Cu damascene interconnections with this barrier layer and found that this barrier layer formed on the trench side wall prevents Cu diffusion when the thickness on the side wall is over 10 nm.

Grain Boundary and Crystallographic Orientation Effects on Friction

Experimental results are presented that show relationships between grain structure and friction. In particular, grain boundaries cause changes in friction during single pass experiments using a diamond rip sliding on polycrystalline tungsten (polytungsten) and polycrystalline silicon (polysilicon). For polysilicon, the crystallographic orientation of individual grains is also shown to have n pronounced effect on friction. Since polysilicon is the major material used for microelectromechanical systems (MEMS), inter- and intragranular friction measurements are needed by scientists and engineers who hope to design and fabricate microminiature motors and other devicevs using polysilicon. For this reason, friction measurements were also made using an Atomic Force/Friction Force Microscope (AFM/FFM) which allows for measurements on a microscope. Presented as a Society of Tribologists and Lubrication Engineers Paper at the STLE/ASME Tribology Conference in Orlando, Florida, October 11–13, 1999