Spl Sim Research Articles

Anomalous variations of OFF-State leakage current in poly-Si TFT under static stress

Studies the anomalous variations of the OFF-state leakage current (I/sub OFF/) in n-channel poly-Si thin-film transistors (TFTs) under static stress. The dominant mechanisms for the anomalous I/sub OFF/ can be attributed to (1) I/sub OFF/ increases due to channel hot electrons trapping at the gate oxide/channel interface and silicon grain boundaries and (2) I/sub OFF/ decreases due to hot holes accumulated/trapped near the channel/bottom oxide interface near the source region. Under the stress of high drain bias, serious impact ionization effect will occur to generate hot electrons and hot holes near the drain region. Some of holes will be injected into the gate oxide due to the vertical field (/spl sim/(V_Gstress V_Dstress)/T/sub OX/) near the drain and the others will be migrated from drain to source along the channel due to lateral electric field (/spl sim/V_Dstress/L/sub CH/).

On the complexity of bounded distance decoding for the AWGN channel

Earlier work has derived the storage complexity of the bounded distance decoder (BDD) for binary channel convolutional codes. We extend this work to the Gaussian noise channel and to partial-response codes. We show that the storage requirement /spl sim/(2/sup 1-R/ - 1)/sup -t/ paths for rate-R convolutional codes over the binary channel becomes /spl sim/2/sup 2Rt/ over the Gaussian channel, where the decoder must correct t errors. Thus, convolutional coding over the Gaussian channel is not only 3 dB more energy efficient, but its decoding is simpler as well. Next, we estimate the path storage for partial-response codes, i.e., real-number convolutional codes, over the Gaussian channel. The growth rate depends primarily on the bandwidth of the code. A new optimization procedure is devised to measure the maximum storage requirement in Gaussian noise for these two code types. An analysis based on difference equations predicts the asymptotic storage growth for partial response codes.

Downscaling limit of equivalent oxide thickness in formation of ultrathin gate dielectric by thermal-enhanced remote plasma nitridation

The gate-oxide downscaling limit in thermal-enhanced remote plasma nitridation (RPN) process for forming ultrathin gate dielectric has been extensively investigated. In this work, the radical-induced re-oxidation effect has been observed as the base-oxide thickness less than 20 /spl Aring/. Nevertheless, for the base-oxide thickness thicker than 17 /spl Aring/, the RPN process still can effectively reduce the equivalent oxide thickness (EOT) and almost no transconductance degradation is observed. Further thinning of the base oxide will degrade the reduction of EOT and the transconductance with the RPN process, due to the penetration of nitrogen radicals into the active region. The physical and electrical properties of the ultrathin oxides (10 /spl sim/ 20 /spl Aring/) affected by this radical penetration have been studied extensively as well. Finally, the thinnest thickness has been estimated by compromising the feasible base-oxide thickness, the degradation of device performance, and the gate leakage criteria. Based on the forementioned criteria, we rind the 14 /spl Aring/ EOT to be the downscaling limit of the gate-oxide thickness.

High-level triggers in ATLAS

The trigger and data-acquisition system of ATLAS, a general-purpose experiment at the Large Hadron Collider (LHC), will be based on three levels of online selection. Starting from the bunch-crossing rate of 40 MHz (an interaction rate of 1 GHz at design luminosity-/spl sim/ 10/sup 34/ cm/sup -2/s/sup -1/), the first level trigger (LVL1) will reduce the rate to about 75 kHz using purpose-built hardware. An additional factor of about 10/sup 3/ in rate reduction is to be provided by the high-level triggers (HLTs) system, with two main functional components: the second-level trigger (LVL2) and the event filter(EF). LVL2 has to provide a fast decision (guided by the information from LVL1), using only a fraction of the full event, however, already at full granularity and can combine all subdetectors. At the EF, a refined selection is made with the. capability of full event reconstruction and the use of detailed calibration and alignment parameters. The HLT software architecture will provide a common and rather lightweight framework, able to execute the various selection algorithms and to control the sequence of execution according to the event properties and configuration parameters. System flexibility is a strong requirement in order to adapt to changes, e.g., in luminosity and background conditions. This paper will present the approach chosen for the software design of the HLT selection framework and of the algorithm interface, giving examples for selection sequences and algorithms. Based on currently existing prototypes, results for both the expected physics (signal efficiency, background rejection) and system (execution time) performance will also be shown.

Prolonged plasma production at current-driven implosion of wire arrays on Angara-5-1 facility

Results of experimental investigation and modeling of prolonged plasma production during implosion of cylindrical wire arrays are presented. Results of the radiography of dense cores of imploding wire array and the measurements of internal azimuthal magnetic field in wire array give new experimental evidences of prolonged plasma production phenomenon. This phenomenon is an important property of current-driven implosion of the wire arrays at current rise rates /spl sim/(0.5-1)10/sup 14/ A/s. The prolonged plasma production can determine the current and the density profiles before final stage of a Z pinch compression, and also in the moment of Z pinch stagnation. From this point of view, the requirement that residual uncompressed plasma should not shunt the current at the discharge periphery becomes of the greatest importance. The conditions exist when the prolonged plasma production isn't an obstacle for the achievement of high-power X-ray emission from Z pinch. Presented experimental results on multiwire array implosion can be explained on the basis of prolonged plasma production without referring to multiwire array azimuthal structure.

Simulation of electromagnetic induction scattering from targets with negligible to moderate penetration by primary fields

The problem of numerical modeling of electromagnetic induction (EMI) responses by metallic objects is complicated by the fact that transmitted fields may penetrate the target, but will often only do so slightly. The effect cannot be ignored, yet it is often grossly impractical to discretize the entire surface or volume of a target in space increments only on the order of a fraction of the skin depth. To deal with this problem, we retain a simple integral equation formulation in scalar potential for the region outside the target, where magnetic fields are quasi-static and irrotational. Within the target we apply only the divergence relation, /spl nabla//spl middot/H = 0. When the skin depth is small relative to the radius of curvature of the target (e.g., <0.1), we use the thin skin depth approximation (TSA), /spl part/H/sub n///spl part/n as /spl sim/-ikH/sub n/, just inside the target's surface, where k is the electromagnetic wavenumber inside the metal and n is the normal direction on the surface and pointing inside of metallic object. Examination of analytical solutions for the sphere suggests the parameter range in which this approximation might perform well and suggests ways of improving accuracy over an extended range. The fundamental TSA formulation appears to be relatively robust. Analysis indicates that it is insensitive to variation over the target's surface of primary field orientation relative to that surface, and that it is only dependent on the target's magnetic permeability through induction number. Implementing the TSA numerically, within the above divergence relation, allows us to express all quantities in terms of tangential magnetic field components and their tangential derivatives over the target surface. In principle, this closes the system completely in terms of the exterior scalar potential. Broad-band numerical simulations based on the TSA compare favorably with analytical and other numerical solutions.

Low-threshold strain-compensated InGaAs(N) (/spl lambda/ = 1.19-1.31 μm) quantum-well lasers

Highly strained (/spl Delta/a/a /spl sim/ 2.5%) In/sub 0.4/Ga/sub 0.6/As and In/sub 0.4/Ga/sub 0.6/As/sub 0.995/N/sub 0.005/-quantum-well (QW) active lasers utilizing strain-compensating InGaP-GaAsP buffer layers and GaAs/sub 0.85/P/sub 0.15/ barrier layers, grown by metal-organic chemical vapor deposition (MOCVD), are demonstrated with lasing emission wavelength of 1.185 and 1.307 μm, respectively. Threshold and transparency current density for the strain compensated InGaAsN QW lasers, with emission wavelength of 1.295 μm, are measured to be as low as 290 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> (L = 1500 μm) and 110 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , respectively, with characteristic temperature of T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> and T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> of 130 K and 400 K.

Thermal conductivity, thermal diffusivity and thermoelectric power of Sm-based bulk superconductors

The ab-plane thermal conductivity /spl kappa//sub ab/(T), thermal diffusivity /spl alpha//sub ab/(T) and thermoelectric power S/sub ab/(T) were measured for the highly-oriented Ag-doped superconducting materials Sm/sub 1+2x/Ba/sub 2+x/Cu/sub 3+x/O/sub 7+5x/ (X = 0.1 /spl sim/ 0.4) prepared by a melt process. The absolute value of /spl kappa//sub ab/ and its characteristic enhancement below T/sub c/ were suppressed with increasing content X of the Sm/sub 2/BaCuO/sub 5/ (Sm211) secondary phase, while they were enhanced with increasing content of doped-Ag. The application of the magnetic field up to 10 T clarified that the phonon scattering by vortices was most enhanced with the applied field perpendicular to the ab-plane. The trapped magnetic field also seriously suppressed the /spl kappa//sub ab/(T) enhancement.

Current transport in metal/hafnium oxide/silicon structure

Based on the experimental results of the temperature dependence of gate leakage current and Fowler-Nordheim tunneling characteristics at 77 K, we have extracted the energy band diagrams and current transport mechanisms for metal/HfO/sub 2//Si structures. In particular, we have obtained the following quantities that will be useful for modeling and simulation: i) HfO/sub 2//Si conduction band offset (or barrier height): 1.13 /spl plusmn/ 0.13 eV; ii) Pt/HfO/sub 2/ barrier height: /spl sim/ 2.48 eV; iii) Al/HfO/sub 2/ barrier height: /spl sim/ 1.28 eV; iv) electron effective mass in HfO/sub 2/: 0.1 m/sub o/, where m/sub o/ is the free electron mass and v) a trap level at 1.5 /spl plusmn/ 0.1 eV below the HfO/sub 2/ conduction band which contributes to Frenkel-Poole conduction.

Temperature dependence of electron and hole signals in irradiated p/sup +/-n-n/sup +/ diodes in the presence of continuous carrier injection

The temperature dependence of electron and hole signals in irradiated p/sup +/-n-n/sup +/ diodes was studied in the presence of carrier injection. Diodes fabricated on high-resistivity (15 k/spl Omega/cm) silicon wafers were irradiated with neutrons up to a 1 MeV-neutron equivalent fluence of 2 /spl times/ 10/sup 14/ /cm/sup 2/. The detector signal after illumination with a fast (full-width at half-maximum /spl sim/ 1 ns) red (/spl lambda/ = 670 nm) light pulse was amplified with a fast amplifier (f/sub t/ = 1 GHz) and recorded with a fast digitizing oscilloscope. During measurements, the electron or hole densities were changed by illuminating the detector with light of short penetration depth. The effect of charge trapping was studied by observing the change in effective space-charge density as the flux of injected carriers was varied. The effect of continuous carrier injection on signal decay at cryogenic temperatures was also observed.

Slat collimator design issues for dual-head coincidence imaging systems

This paper investigates optimum slat collimator design parameters for dual-head coincidence imaging (DHCI) systems. The noise equivalent count (NEC) rate was examined with respect to the activity concentration under various system conditions. All results are derived from Monte Carlo simulations with a digital anthropomorphic (Zubal) phantom. The DHCI system was modeled after the Millennium VG gamma camera (GEMS, Waukesha, WI). The dead-time characteristics of the camera were experimentally determined. Our results suggests that substantial NEC gains can be achieved by varying the slat-to-slat separation, such that the peak of the NEC curve is located at clinically relevant levels (i.e., 0.07 /spl sim/ 0.10 /spl mu/Ci/cc). The NEC was also found to increase with the use of longer slats with appropriately selected slat-to-slat separation. Furthermore, the NEC performance also depends on the count-rate performance (i.e., dead-time losses) of the system. Therefore, as improvements are made to the count-rate capabilities of DHCI systems, the slat geometry should be modified. Further study is required to determine the effect that slat collimator design has on image quality and lesion detection for clinically realistic imaging situations.

Design of the collective Thomson scattering diagnostics for Large Helical Device using a quasi-optical frequency tunable gyrotron as a radiation source

Summary form only given. Development of the Collective Thomson Scattering (CTS) diagnostic system for LHD is presented. High frequency, tunable (87-97 GHz), medium power ( /spl sim/100 kW) quasi-optical gyrotron will be used as a radiation source. We will show the detailed description of the system as well as initial calculations of the scattered microwave power from the LHD plasma. Using the quasi-optical gyrotron as a radiation source was inspired by the fact that this particular device has the ability of tuning of the operational frequency. Which is made it very attractive for using under the various scenarios for LHD plasmas. It is planned that the system utilize 'forward scattering schema' of the experimental set-up. The calculation of the expected scattered power shows that (in the chosen frequency range and chosen values of the scattered angle) the dominant part of it came from the so-called 'ion-feature'. This is a situation when the incident radiation is mainly scattered by the 'shielded ions' (by electron cloud). Other advantage for using gyrotron (not 10.6 /spl mu/m CO/sub 2/ laser) as a power source is as follows. Since for the typical scattering experiments under consideration scattered wave number is k /spl sim/ k/sub i/ sin(/spl theta//sub B//2). Thus for coherent scattering to occur, it is possible to significantly increase the scattered angle /spl theta//sub B/ as a wave length of the incident radiation increases from the short wavelength (CO/sub 2/ laser) through far-infra-red (FIR) wavelength to the millimeter wavelength of gyrotrons.

Trimming phase and birefringence errors in photosensitivity-locked planar optical circuits

A strong and stable photosensitivity response was permanently locked into hydrogen-loaded Mach-Zehnder planar waveguide circuits by 248-nm KrF-laser preirradiation. The photosensitivity enhancement survived thermal annealing up to 225 /spl deg/C. Post-laser trimming at 248 nm induced an unsaturated refractive index increase of 0.002, and a birefringence change of /spl utri/n /spl sim/ 0.0001. This combination of photosensitivity locking and post-laser tuning affords wide latitude for precise and stable tuning of waveguide phase errors and birefringence.

Proton-induced CCD charge transfer degradation at low-operating temperatures

Measurements of charge transfer inefficiency (CTI) at charge-coupled device temperatures /spl sim/-100/spl deg/C show that proton-induced E-centers can be kept filled but other traps with energies 0.22-0.34 eV limit the achievable improvement in CTI. Estimates of trap energy levels and concentrations are made from CTI and emission time measurements. It is found that the CTI can be reduced for low signal levels. Implications for spaceborne astronomical instruments are discussed.

Microlenses self-aligned to optical fibers fabricated using the hydrophobic effect

We report a means of fabricating microlenses on transparent spacers that are self-aligned to optical fibers. The lenses so formed have f-numbers (f/sup /s) as low as f/1.55 and can be fabricated with minimal processing steps. Lenses can be fabricated desirably over-sized, with input apertures larger than operational beam diameters, The lenses deviate from spherical by as little as /spl plusmn/80 nm over the middle 90% of their surfaces, and are diffraction limited when used in their paraxial regions. Previous work suggests that arrays of such lenses can be fabricated in parallel with good uniformity (/spl Delta/f/f/spl sim//spl plusmn/5.9% for a 15/spl times/15 array of 500 /spl mu/m f/1.4 lenses), stability, and reproducibility (average f/sup /s are reproducible to within 3.5%). Although coupling efficiencies have not been measured, these values suggest that the lenses are of sufficient quality for a variety of multimode fiber applications.

Computational modeling of medium spiny projection neurons in nucleus accumbens: toward the cellular mechanisms of afferent stream integration

The nucleus accumbens (Nacc) regulates the major feedback pathways linking prefrontal cortex, hippocampus, and amygdala. We describe simulations of a biophysical level model of a single medium spiny projection (MSP) neuron, the principle cell of the Nacc. The model suggests that the unusual bistable membrane potential of MSP cells arises from the interplay between two potassium currents, K/sub IR/ and K/sub A/. We find that the transition from the membrane potential down state (/spl sim/-85 mV) to the upstate (/spl sim/-60 mV) requires a significant barrage of synchronized inputs, and that ongoing afferent stimulation is required to maintain the cell in the up state. The Nacc receives the densest dopominergic innervation in the brain, and the model demonstrates, in agreement with recent experimental evidence, that dopamine acts to increase the energy barrier to membrane potential state transitions. Through its action on K/sub IR/ and L-type Ca/sup 2+/ channels, dopamine selectively lowers cell gain in the down state and increases it in the up state, a mechanism for context-dependent gain control. These findings suggest a mechanism of afferent pattern integration in the accumbens arising from transient synchronization among ensembles of MSP neurons. We attempt to relate these findings to possible origins of abnormalities of sensory gating in schizophrenia.

Effects of substrate temperature on the magnetic properties of as-sputtered FeTaN films

We investigated the magnetic properties of as-sputtered FeTaN films as a function of deposition temperature and composition. At the deposition temperature higher than 200/spl deg/C, both soft magnetism and magnetic moments can be fully achieved. While the Ta and N contents in the films affect the magnetic properties, the N content exhibits stronger effects. The magnetic properties are affected by the film microstructures via, crystallinity, grain size, and formation of Fe/sub x/N phases. An excessive N incorporation into the films causes incomplete crystallization and/or formation of Fe/sub 3/N phases in the as-deposited state, leading to a poor soft magnetic property. As-deposited FeTaN film at the optimum composition of Fe/sub 91.7/Ta/sub 4.2/N/sub 4.1/ gives the best soft magnetic properties; coercivity of /spl sim//sub 2/ Oe and permeability of /spl sim/1600 stable up to the frequency of 100 MHz.

Media thermal robustness (MTR) test to quantify lifetime for media thermal decay

A media thermal robustness (MTR) test has been developed to quantify lifetime for media thermal decay. In this test, erasing currents produced by the write coil of a head were used to stress a written track. Amplitude was monitored as a function of log(time) to and beyond the failure point of 85% of initial amplitude. The lifetime with current =0 can be obtained by extrapolating [log(f/sub o//spl middot/lifetime)]/sup 2/3/ versus current to current =0, where f/sub o//spl sim/10/sup 9/ Hz is the attempt frequency. This MTR test procedure allows the media thermal decay lifetime to be determined in /spl sim/ hours. Consistency of short and long media lifetime predictions by MTR test was found to be quite good. Repeatability of lifetime prediction was demonstrated to be within a reasonably narrow range.

Magnetic properties, structure and shape-memory transitions in Ni-Mn-Ga thin films grown by ion-beam sputtering

Ni/sub 1-2x/Mn/sub x/Ga/sub x/ (x/spl sim/0.2 and 0.25) alloys in thin film form were prepared by ion-beam sputtering from alloy targets. For Si[001] substrates the structure/texture of the films are a function of the growth temperature (T/sub g/). The tetragonal martensite structure with a [220] texture was obtained for an optimal T/sub g//spl sim/300-350/spl deg/C. At higher temperatures a cubic silicide (Mn/sub 12/Ni/sub 4/Si/sub 3/) was obtained. At room temperature, optimal films with the stoichiometric composition (x /spl sim/ 0.2) showed a ferromagnetic hysteresis behavior characterized by significant in-plane rotation. The coercivity of the films was 310 Oe and temperature-dependent measurements confirmed a Curie temperature, T/sub c//spl sim/340 K. At room temperature the films show a modulated 7M martensite structure which was observed in in situ heating experiments to transforms to the cubic austenite phase at 500/spl deg/C.

Design and analysis of a portable high-speed clock generator

A new portable clock generator with full pull-in range and fast acquisition is presented in this paper, where it can be developed at hardware description language (HDL) to reduce design cycle as well as improve system-level integration simulation. In the proposed design, frequency tracking is performed by the Prune-and-Search algorithm, and the digital-controlled ring oscillator is constructed by CMOS standard cells. In order to reduce propagation delay of the loop divider, a novel structure is developed to provide a constant delay at any divider setting. In addition, input jitter can be isolated to avoid coupling by digital processing. Hence, the generated clock output becomes more clean and robust. Based on the proposed methodology, a test chip has been designed and verified on 0.6-/spl mu/m CMOS process with frequency range of (360 /spl sim/ 800) MHz at 3.3 V and peak-to-peak jitter of less than 60 ps at 800 MHz/3.3 V.