bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical Characterization of Undoped, N- and P-Type Thermal Annealed PECVD SiC Films Deposited on Transparent Insulator Substrates
Authors: Oliveira Alessandro R. , Pereyra Inés , Carreño Marcelo N.
Published: September 2009

Electrical characterization of undoped, n- and p-type doped, thermal annealed stoichiometric a-SiC:H films obtained in "silane starving plasma" condition by PECVD technique on transparent insulator substrates is presented. The electrical conductivity of the undoped SiC films demonstrates strong dependence on the increase of the structural order due to the thermal annealing process, which maximizes the heterogeneous Si-C bonds, providing larger spatial continuity for the electrical mobility by the crystallization process. The undoped 3C-SiC films show n-type conduction with conductivity, Hall mobility, and carrier concentration at room temperature of about 6.6×10-3 (Ω.cm)-1, 100 cm2/Vs, and 4×1016 cm-3, respectively. Different doping levels are exhibited for both, n- and p-type doping; highest conductivity values were obtained for doped samples with 5×1020 cm-3. In this case dark electrical conductivity values of 6.6×10-1 (Ω.cm)-1 and 9.8 (Ω.cm)-1 for p- and n-type doping, respectively, were observed.
Highly Effective Etching Using Excimer Irradiation and a Crossed-Form Tool
Authors: Pa P.S.
Published: September 2009

This study offers a new design module using excimer irra-diation and a crossed-form tool in a micro electroetching (μ-ECE) process, and, as a precise reuse modus, it offers faster performance in removing ITO thin-films from the surface of the color filters of defective displays of TFT-LCD. In the current study, the narrow width of the crossed-form tool, the small dis-tance between the crossed-form tool and the color filter surface of the display, or the small edge radius of the crossed-form tool provides an effective removal performance. The use of excimer irradiation is possible to efficiently promote the performance of the designed crossed-form tool in stripping away the ITO layers. The required machining time when irradiating with an excimer lamp before removing the ITO layers is shorter than that of the process without excimer irradiation under similar processing conditions.
Characterization of Cu/Cu0,4Ni0,4P0.2 Thermocouples Fabricated on Silicon Surfaces Using Electroless Deposition
Authors: Trevisan Fernando , Santos Filho Sebastião , Marques Angelo , Martini Sandro
Published: September 2009

In this work, it is presented the fabrication of Cu/Cu0.4Ni0.4 P0.2 thermocouples onto silicon wafer surfaces. Both Cu and CuNi films were plated onto silicon surfaces by electroless deposition. The aerial concentration and films compositions were obtained by means of Rutherford Backscattering Spectrometry (RBS). The thermoelectric power of the fabricated thermocouples was 86{plus minus}6 µV/oC, which is similar to the typical values reported in literature for Cu/CuNi.
Optical Diagnostics of SF6 Low Pressure Plasma Jet Applied to Silicon Etching
Authors: Pessoa Rodrigo S. , Tezani Leandro L. , Wakavaiachi Shirley M. , Maciel Homero S. , Petraconi Gilberto
Published: September 2009

In this work the applicability of a low pressure sulphur hexafluoride (SF6) plasma jet for silicon etching was investigated by optical emission spectroscopy (OES) technique. Through the use of actinometry method the density of atomic fluorine was obtained as a function of process parameters namely radio-frequency (rf) power, axial magnetic field, SF6 gas pressure and flow rate, and O2 concentration in the SF6+O2 mixture. The results indicate large fluorine concentrations (>10% in overall plasma volume) for the conditions studied. To confirm the applicability of these results for microelectronic material processing, we performed the etching of masked silicon (Si) substrates under some optimum process conditions. Etch rates of up to 1.2 µm/min were obtained for rf power of about 150W and operating pressures about 3.1 mTorr. These values of etching rates are comparable with those obtained in inductively coupled plasma (ICP) systems operating at similar process conditions.
A Study of the Geometrical Correction Factor on the Sensitivity of the Transversal Piezoresistive Sensors
Authors: Coraucci Guilherme D. , De Oliveira Rafael V. , Filho José G. , Fruett Fabiano
Published: September 2009

The sensitivity of four-terminal devices like Hall and piezoresistive sensors is very dependent on its geometric parameters. This dependence is modeled by the Geometrical Correction Factor (G). The majority of these studies take very time-consumption analytical calculations for the analysis of G. In order to simplify this analysis, we present numerical analysis for the most common geometrical forms of four-terminal devices and propose suitable aspect ratios of its geometric parameters for maximization of G. This result is general for any four-terminal-shaped sensors. Experimental result of a new topology of pressure sensor is also presented, which maximizes G in a comparison with conventional four-terminal devices and also improves its sensitivity.
Nanoparticle Floating Gate Flash Memories
Authors: Banerjee S. K. , Ferdousi F. , Liu H. , Ferrer D.
Published: September 2009

This work reports Si and SiGe(C) nanoparticle formation on high-k dielectrics to work as charge storage nodes in NC Flash memories. When applying high fields for programming or erase operations the bands for the high-k dielectric bend sufficiently to cause Fowler Nordheim (FN) tunneling through a narrow triangular barrier, while higher bandgap SiO2 remains in direct tunneling regime. In our proposed high-k based cells the memory operations are achieved at lower voltages and reduced charge loss. SiGe NCs possess a lower bandgap than Si NCs, and deeper potential wells when embedded in the gate dielectric and hence longer retention times. A different approach involves demonstrating that a chaperonin protein lattice can be used as a template to assemble nanocrystal (NC) arrays for Flash memory fabrication. Different types of NCs from colloidal suspensions can be incorporated into Flash memory fabrication.
Multiwall Carbon Nanotubes Decorated with Metal Oxide Nanoparticles for Gas Sensing Applications
Authors: Gelamo Rogerio V. , Abbaspourrad Ali , Verissimoa C. , Vaz Alfredo R. , Rouxinol F. P. , Alves O. L. , Moshkalev Stanislav A.
Published: September 2009

Experimental procedures have been developed to prepare carbon nanotubes (CNTs) decorated by metal oxides nanoparticles for gas sensing applications. For decoration of carbon nanotubes with Sn and Cu oxides, the concentration of precursors and time of sonication were found to be crucial parameters, to control the size and density of nanoparticles on the nanotubes surface. In the case of CNTs decorated with Ti oxides, the pH value of the solution was found to play a key role in the final size of the nanoparticles. The material decorated with SnO2 was tested with H2S and changes in the conductivity showed the potential of this material for gas sensing application.
Metallization Technologies and Strategies for Plastic Based Biochips, Sensors and Actuators for Healthcare and Medical Applications
Authors: Shacham-Diamand Yosi , Krylov Slava , Shmilovich Tsvi , Ofek Almog Rakefet , Fishelson Nikolai , Sverdlov Yelena , Torchinsky ILya , Rosenman Gil , Inberg Alexandra , Berkh Olga
Published: September 2009

Metallization on flexible MEMS is used for various applications such as interconnects, electrodes and flexible actuators, where the metal lines are embedded onto the polymeric structure. An important issue is the properties of the polymer/metal interface. We review various surface treatments and discuss in details functionalization using self assembled monolayer (SAM) and electron-beam irradiation that significantly improve metal/polymer adhesion. To demonstrate the highlights and problems of flexible MEMS metallization we review processes and structures of two applications: a. flexible electrodes on thin hard polyimide substrates and b. flexible actuators on thick soft PDMS.
Fabrication Process of Ag/AgCl Reference Pseudo-Electrode Based on Electrodeposition of Au on Pt Surfaces from Formaldehyde Baths: Chemical Stability and Adherence
Authors: Almeida Fernando L. , Cardoso Juliana L. , Igarashi Massaki O. , Dos Santos Filho Sebastião G. , Jiménez-Jorquera Cecilia , Fontes Marcelo B.
Published: September 2009

Adherence, homogeneity and chemical stability are key fabrication process parameters for Ag/AgCl reference pseudo-electrode. In this work, we were able to achieve reference electrodes over platinum, using an intermediated layer of gold to promote adhesion. The gold bath was prepared using sulfide and formaldehyde. The concentration of formaldehyde was adjusted to prevent electroless deposition during the electrodeposition. The obtained gold deposit was yellow, flat, 200 nm thick with good adherence and resistivity(6.02 μohms cm). Silver and silver chloride layers were deposited with a home-made galvanostatic equipment. The current density was ranged from 0.4 to 8.0 mA cm-2. Finally, a Nafion® 117 membrane was used to recover the AgCl film to avoid corrosion and to maximize lifetime of the reference electrode.
Electrochemical Migration on Lead-Free Soldering of Pcbs
Authors: Freire Mendes Luiz T. , Cardoso Valtemar F. , Da Silva Ana Neilde R.
Published: September 2009

It is well known that in printed circuits boards assembled by SMT technology may occur electrochemical migration (ECM). The electrochemical migration may become a potential reliability problem in electronic soldering when lead free technology is used in soldering electronic devices. Electrochemical migration is an electrochemical process where metal on an insulating material, in a humid environment and under an applied electric field, leaves its initial location in ionic form and redeposits. In a PCB two adjacents terminal may behave as electrodes so the dendrites grow from cathode to anode. A structure with a comb shape printed on FR4 substrate was used in the experiments. The distance between the fingers was 105 or 254 micron, in order to simulate a real distance between dispositive terminals. The parameters considered during the experiments were surface finishing, solder paste composition, distance between terminals and applied voltage. Al the experiments were performed two times. Tin was the main metal that migrates.
Radiation Effects on SOI Microrelays for Space Applications
Authors: Lozano Alex , Palumbo Felix , Alurralde Martín
Published: September 2009

Considerable effort has gone into the study of the failure mechanisms and reliability of micro-electro-mechanical-systems (MEMS) to extend its use to critical areas. In this paper a prototype of SOI microrelays is evaluated for space applications. The MEMS devices are subjected to uniform proton beam of 10MeV, while its response is monitored by electrical characteristics for successive irradiation pulses. Although the system shows a significant increase of positive trapped charge, it has not been found any limitation on the functionality based in the main parameters such as the actuation voltage, the leakage currents, and conduction mechanism of the switch.
Development of Optimal Symmetric Focused SAW Atomizers for Nanoliter Single Droplet Atomization
Authors: Balashov Sergey , Pavani Filho Aristides , Balashova Olga , De Almeida Maria
Published: September 2009

Symmetric point and inline focused SAW atomizers on 128 deg. YX cut of the LiNbO3 were designed and fabricated for atomization of nanoliter single water droplet. Developed focused atomizers were experimentally proven to double SAW energy density in the region of the droplet comparable to traditional atomizer. It was shown that RF pulses with low duty factor give stable atomization in such structures. Detailed procedure of optimum matching for such devices is described.
Ladder Type SAW Filters Using Quasi-Synchronous Resonators with Thinned Density of Randomly Distributed "Hot" Electrodes
Authors: Kim C. U. , Balashov Sergey , Plessky V.P. , Nam C. W. , Chul L. K.
Published: September 2009

The new method of design of relatively narrow band ladder type SAW filters is proposed. It consists of thinning procedure with consecutive randomization of positions of the remained transductive periods inside the IDT. The filter with 0.9% fractional bandwidth and with 3 dB insertion loss was designed on 42 deg. cut of LiTaO3, using this approach. The method completely suppresses undesirable additional passbands which appear if periodic thinning is used. Experimental results, confirming the validity of the method, are presented.
Performance Analysis of Single-electron NAND Gates
Authors: Silva Lorena , Guimaraes Janaina G.
Published: September 2009

In this work, three different circuit architectures implementing single-electron NAND gates are investigated by simulation. A complete behavior analysis of each architecture, considering critical aspects in SET-based circuits, such as co-tunnelling, temperature dependence and offset charges is performed. Power consumption and area estimations (critical for GSI and TSI realizations) are also taken into account.
A new fabrication technique of planar metallic microstructures on alumina substrate
Authors: Da Costa Juvenil S. , Flacker Alexander , Fruett Fabiano
Published: September 2009

This paper describes a new fabrication technique of planar metallic microstructures with geometries equal or smaller than 15m on 96% alumina substrates. This technique is based on both: chemical and electrolytic deposition. In order to evaluate this technique we design and fabricate a bridge of interdigited capacitors. The microscope inspection showed that the structures well reproduced the design of the masks. The adhesion of the film was tested by soldering metallic wires on the capacitor electrodes. The mean value and the standard deviation considering 16 capacitors with distance between interdigited electrodes of 15μm, fabricated in two runs, are 1,484pF and 0,053pF, respectively. The relative standard deviation amounts to 3,3%.
Thermal Effects in Fully-Depleted SOI Devices
Authors: Vasileska D. , Ralevab K. , Goodnick S. M.
Published: September 2009

In this paper we summarize our research work on electro-thermal modeling of different generations of fully-depleted SOI devices. We first discuss our electro-thermal device simulator that self-consistently couples the Monte Carlo solver for the electrons with the energy balance solver for acoustic and optical phonons. Afterwards we discuss simulation results for different technology fully-depleted SOI devices.
The Effect of Microstructure on Electromigration-Induced Failure Development
Authors: Lacerda de Orio Roberto , Ceric Hajdin , Cervenka Johann , Selberherr Siegfried
Published: September 2009

The effect of the microstructure on the electromigration failure development is analyzed. We investigate the influence of the statistical distribution of copper grain sizes on the electromigration time to failure distribution. Also, the effect of the microstructure on the formation and development of an electromigration-induced void is studied by simulation and the results are compared with experiments. It is shown that the lognormal distribution of the grain sizes resulted in lognormal distributions of the electromigration lifetimes. A close investigation has shown that the network of grain boundaries has a decisive impact in the determination of void nucleation sites and main features of void development.
Extraction of MOSFET Model Parameters from the Measured Source-to-drain Resistance
Authors: Garcia-Sanchez Francisco J. , Muci Juan , Lugo Muñoz Denise C. , Latorre Reya Alvaro A. , Ortiz-Conde Adelmo , Ho Ching S. , Liou Juin J.
Published: September 2009

We present the extraction of MOSFET model parameters as functions of the channel length by means of a procedure based on the use of the measured source-to-drain resistance, instead of the conventional direct fitting to the drain current characteristics. Doing so, allows to separately extract the two parameters, source-and-drain series resistance and mobility degradation factor, that give rise to comparable effects on the current-gate voltage characteristics. The procedure involves a bidimensional fitting of the source-to-drain resistance as obtained from the below-saturation output characteristics measured at several above-threshold gate voltages. Its application is illustrated on experimental DRAM MOSFET test devices with channel lengths ranging from 0.23 to 2.0 m. It is shown that the new procedure is able to overcome the common difficulty typically encountered when trying to separate the effects of these two parameters using more conventional extraction methods.
A Novel Overlapping Circular-Gate Transistor and its Application to Power MOSFETs
Authors: De Lima Jader A. , Gimenez Salvador P.
Published: September 2009

This paper introduces an Overlapping Circular-Gate Transistor (O-CGT) that allows gate overlaying between neighboring cells, enhancing layout packing with respect to conventional circular- and rectangular-gate structures. Although a section of gate annulus does not contribute to the drain current, a higher aspect-ratio is attained. Besides, both drain and source junctions have their area minimized, so that faster transients can be reached. A first-order model for the effective aspect-ratio of the proposed device is developed and its validity attested by a range of 3D-simulation of IDS x VDS characteristics obtained with ATLAS3D software. Error between analytical and 3D-simulation data was limited to only 4.7%, for different VGS values. With respect to a conventional circular-gate transistor (CGT), the O-CGT breakdown voltage BVDS is reduced by a factor of only 6.1%. A power FET with on-resistance in the interval of tens of mOhms is laid out having the O-CGT as elementary cell. To verify the benefits of the O-CGT, a comparison with a rectangular-geometry transistor (RCT) is carried out. Defining a figure-of-merit as n= (W/L)/cell_area, the O-CGT features a better efficiency on current driving capability, as nO-GCT/ nRCT = 22.9%. Unity cell size, drain and source junction areas are reduced by factors of 81.3%, 33.9% and 40.6%, respectively. The O-CGT approach allows a saving of 18.6% in the power FET size as compared to rectangular geometries.
The Influence of Poly-Si/SiGe Gate in Threshold, Sub-Threshold Parameters and Low Frequency Noise in p-MOSFETs
Authors: Jimenez Grados Hugo R. , Manera Leandro T. , Rautemberg Finardi Márcia , Alexandre Diniz José , Doi Ioshiaki , Jurgen Tatsch Peter , Enrique Figueroa Hugo , W. Swart Jacobus
Published: September 2009

DC performance and Low Frequency Noise in p-MOS transistor with poly-Si/SiGe Gate fabricated with the CMOS process entirely developed in the Center for Semiconductor Components at UNICAMP is presented. After deposition, films of poly-Si and poly SiGe were implanted by phosphorus ions. The transistor has a channel region with silicon oxide thickness of 30 nm and a poly-Si/SiGe gate region with self-aligned thick S/D region. The parameters on threshold, sub-threshold and low frequency noise (1/f) of poly-Si/SiGe p-MOS transistor are reported. The turn-on in the I-V characteristics increases and at a drain-to-source bias VDS of -0.1V p-MOSFETs with Lpoly=1.57µm gate length had peak transconductance (Gm) increased as well, compared with conventional p-MOS with poly-Si gate. The DC and 1/f characteristics of the p-MOS transistors are studied using several devices sizes. Devices show low 1/f and high values for Gm parameters and make them promising devices for RF and microwave circuit applications
On the Performance of Thin-Film Lateral SOI PIN Diodes as Thermal Sensors in a Wide Temperature Range
Authors: De Souza Michelly , Rue Bertrand , Flandre Denis , Pavanello Marcelo A.
Published: September 2009

This paper presents a study of lateral SOI PIN diodes as temperature sensors in the range of 100 K to 400 K. Experimental results indicate that PIN diodes can be used to implement temperature sensors with high accuracy in cryogenic regime, provided that a suitable temperature range is chosen. Numerical simulations using Atlas two-dimensional simulator were performed in order to confirm this hypothesis and extend this analysis, verifying the accuracy of the existing model.
Transformation Between Power-law and Polynomial Thin-Film Transistor Models
Authors: Ortiz-Conde Adelmo , Garcia-Sanchez Francisco J. , Muci Juan
Published: September 2009

A procedure is proposed to convert back and forth between two equations used to model the saturation current of thin film transistors. To demonstrate and determine the effectiveness of the proposed procedure, experimental data modeled by the traditional monomial (power-law) model is transformed into a recently proposed polynomial model. Conversely, another set of data, which was originally represented by the polynomial model, is transformed to the monomial model. This procedure is also applied to short-channel crystalline MOSFETs.
Reduction in On-resistance of LDMOS Transistor for Improved RF Performance
Authors: Kashif Ahsan U. , Sevensson Christer , Wahab Qamar U.
Published: September 2009

In an LDMOS transistor, a low doped drift (LDD) region at the drain side is created to enhance the breakdown voltage (BVDS), but this increases on-resistance (Ron) which degrades the transistor RF performance. In this paper, the LDD region of LDMOS transistor is optimized using two different techniques, (i) a dual implanted-layer p- and n-region in LDD and (ii) an excess interface charge at the RESURF of LDD. Both techniques are used to enhance the carrier density for lower Ron. The comparison revealed that excess interface charge provides 43 % reduction in Ron with BVDS of 70 V, while the dual-implanted region provides 26 % reduction in Ron together with BVDS of 64 - 68 V.
Equivalent Circuit for NBTI Evaluation in CMOS Logic Gates
Authors: Schuch Nivea , Dal Bem Vinícius , Reis André I. , Ribas Renato P.
Published: September 2009

As technology scales, effects such as NBTI increase their importance. The performance degradation in CMOS circuits caused by NBTI is being studied for many years and several models are available. In this work, an equivalent circuit representing one of these models is presented and evaluated through electrical simulation. The proposed circuit is process independent once the chosen model does not present any relation to technology parameters. Experimental results indicate that the equivalent circuit is valid to evaluate the degradation of PMOS transistors due to aging. Using the proposed circuit, threshold voltage degradation of each transistor may be simulated individually, which allows the evaluation of complex CMOS gates in a linear cost in relation to the number of transistors.
The Impact of CMOS Logic Gate Topologies on Performance Variability
Authors: Da Silva Digeorgia N. , Reis André I. , Ribas Renato P.
Published: September 2009

CMOS technology has presented aggressive scaling in the last few years, resulting in drastic variability of process parameters. Variations in physical, operational and modeling parameters of semiconductor device lead to discrepancies in its electrical behavior, such as transistor threshold voltage and logic gate drive strength. As a result, discrepancies in performance and power consumption of digital circuits are observed. Since different transistor networks present distinct electrical characteristics, even when they represent the same logic function, the purpose of this work is to evaluate the impact of process variability in CMOS gates performance. The goal of such study is to provide some design guidelines for cell parametric yield improvement while building standard cell libraries and full custom blocks.
Solution Processing of Polymer Photovoltaic Solar Cells in Air or Under Inert Atmosphere
Authors: Dang M. T. , Wantz G. , Hirsch L. , Parneix J. P.
Published: September 2009

Polymer photovoltaic solar cells based on a blend of poly(3-hexylthiophene) (P3HT) blended with [6,6]-phenyl-C61 butyric acid methyl ester (PCBM) have been manufactured in air under ambient conditions and under inert atmosphere in a nitrogen-filled glovebox (O2 and H2O < 0.1 ppm). The solution processing of the active layer, in air or nitrogen, affects the performances of the resulting devices. However, the air processed devices shows reasonable efficiencies implying that somehow large area processing of such materials using machinery in air under ambient conditions is realistic for the high throughput production of polymeric solar modules.
Fabrication and Characterization of Active Pixel Sensors (APS) Using Simple Metal Gate nMOS Technology
Authors: Furtado André S. , Alexandre Diniz José , De Lima Monteiro Davies William
Published: September 2009

Active pixel sensors (APS) based on simple nMOS technology with large feature size can offer good sensitivity for photodetection and be a low cost choice for imaging circuits. In this work, we present the design, fabrication and characterization of APSs with 200x200μm photodiodes, which presented an ideality factor of 1.05 and a dark current of -150pA at -VDD (-5V). The APS has worked similarly as the SPICE simulations (error below 7%), presenting a 2.3V output voltage range and total discharge time of 48s when in complete darkness. These results indicate that these sensors can have a good performance in application specific circuits, such as position sensitive detectors and wavefront sensors.
Resonance Optical Effects and Artificial Microphotonic Electromagnetic Materials
Authors: Barabanenkov Mikhail Y. , Kazmiruk Viacheslav V.
Published: September 2009

Brief historical background is given of appearing of unified exact approach, the so called transfer relations, to the theory of multiple scattering of wave fields in inhomogeneous discrete dielectric media. One dimensional (1D) diffraction gratings and two dimensional (2D) photonic crystals (PCs) are considered as particular types of inhomogeneous media with spatial periodicity. A few application oriented items are presented as a result of computations on the basis of transfer relations, regarding 2D PCs as a stack of 1D diffraction gratings and applying technique of matrix Riccati equation. Two first items are 2D PCs and hollow pin structure. The last two items are two methods of optical monitoring. The first is a quantitative approach to optical grating nanoshape control. The last item that is spatial spectroscopy of electromagnetic wave near fields definitely answered the question is it possible to retrieve subwavelength information in the near field microscopy.
Wavefront Sensor Using Double-efficiency Quad-cells for the Measurement of High-order Ocular Aberrations
Authors: Salles Luciana P. , De Oliveira Otávio G. , De Lima Monteiro Davies William
Published: September 2009

This paper presents a discussion about an alternative layout for optical wavefront sensors, which is composed of position-sensitive detectors (PSDs) of the quad-cell type with two different sensitivity regions (i.e. quantum efficiencies). This wavefront sensor can be used in the measurement of high-order ocular aberrations, associated with the Hartmann-Shack method. The proposed layout is compatible with the standard complementary metal-oxide-semiconductor (CMOS) technology. It provides smaller measurement errors than conventional wavefront sensors, once the quad-cell response can be better approximated to a linear response. In this article, some characteristic project parameters are discussed based on numerical simulation results, so as to make the sensor suitable for high-order ocular aberrations measurement.
Porous Silicon Heterostructures for Refractometer Device Application
Authors: Huanca Danilo R. , Salcedo Walter J.
Published: September 2009

Porous silicon heterostructure with very large photonic band gap with a cavity defect layer inside the structure had been fabricated and applied successfully as refractometer device of the organic solvent moieties by using the resonant peak shift due to solvent refractive index modulation effect. The results show that the optical performance of this structure is better than to the conventional porous silicon photonic crystal early reported. The relationship between the wavelength resonance peak shift and the solvent refractive index showed to be linear as desired for device sensor application.
Computational Intelligence Optimization Method for AlGaAs/GaAs Quantum Well Solar Cells
Authors: Singulani Anderson , De Souza Patricia L. , Vilela Neto Omar P. , Pires Mauricio P. , Pacheco Marco Aurélio C.
Published: September 2009

The benefits of using quantum wells as the active region of solar cells have already been proposed. Different models have been reported which quite accurately explain the behavior of this new device. In this work we propose minor modifications in the Lande model for solar cells containing quantum wells and we use a methodology based on genetic algorithms for designing optimized quantum well solar cells. Our proposed modifications have improved the agreement between the model and the experimental values. The proposed design methodology has proven to be fast and very helpful in obtaining an optimum AlGaAs/GaAs quantum well solar cell.
Intrinsically Self-Amplified CMOS Image Sensor
Authors: Santos Patrick M. , De Lima Monteiro Davies William
Published: September 2009

This paper introduces an alternative imager concept that employs the pixel matrix itself to intrinsically amplify its signal while kept compliant to standard CMOS processes. The amplification is achieved by attributing to one pixel at a time the control of a matricial transistor, which is built by adding a gate across the center of the pixel matrix to divide it into two large regions serving as drain and source. This imparts a considerable transimpedance gain and more accurate contrast information rendering a pre-amplifier unnecessary and providing a choice for direct coupling with a current processing circuitry. Simulation results present the effect of this architecture on the captured image.
A Possible Organic Solar Cell Based on Buriti Oil
Authors: Da Silva Elizete R. , Durães Jussara A. , Ceschin Artemis M.
Published: September 2009

This work proposes a new approach - the possible production of organic solar cells, based on Buriti oil. We propose the formation of an active layer, three types of mixture, always exploring the use of Buriti oil. The active layers were deposited by spin coating the mixture of Buriti oil: polystyrene (PS), Buriti oil: poly (3-hexylthiophene) (P3HT) and blend Buriti oil: PS plus P3HT. For the three devices investigated here, we use a glass substrate, coated with fluoride-doped tin oxide (FTO). An electrode of poly (3,4-ethylenedioxythiophene) / poly (4-styrenesulfonate) (PEDOT / PSS) was deposited by spin coating. The other electrode was painted on top, with silver conductive ink (Ag). We show two different illuminations for the characterization of the devices. For the acquisition of measures: resistance (Ω), open circuit voltage (VOC) and the short circuit current (ISC) a common digital multimeter was used.
Analysis of the Interface Trap Density in SOI FinFETs with Different TiN Gate Electrode Thickness through Charge Pumping Technique
Authors: Rodrigues Michele , Cho Moon , Martino João A. , Collaert Nadine , Mercha Abdelkarim , Simoen Eddy , Claeys Cor
Published: September 2009

This work presents the analysis of the interface trap density in triple-gate silicon-on-insulator FinFET gated-diode structures with different TiN gate electrode thickness and fin widths by using the charge pumping technique. It is shown that a thicker metal gate corresponds with more traps. The fin width comparison shows that narrow fin devices exhibit a higher interface trap density due to the (110) sidewall contribution.
Analysis of the Total Resistance in Standard and Strained FinFET Devices With and Without the Use of SEG
Authors: Nicoletti Talitha , Martino João A. , Simoen Eddy , Claeys Cor
Published: September 2009

In this work the total resistance (RT) behavior is experimentally studied in standard and strained (CESL and sSOI) triple-gate nFinFET devices with and without the use of Selective Epitaxial Growth (SEG). It was verified that the devices with SEG present a better behavior of RT even for standard devices if compared with strained ones without the use of SEG. For short channel FinFETs (L < 100 nm), the CESL ones present the lowest value of RT if SEG is used. However, for long channel FinFETs (L > 420 nm), sSOI shows the best behavior with and without the use of SEG. The effective mobility degradation factor (MDF) has also been analyzed showing that devices with SEG and sSOI present the lowest degradation.
Back-Gate Influence on the Mobility Behavior in Ultrathin FD SOI Devices
Authors: Dos Santos Carolina D. , Pham-Nguyen Loan , Cristoloveanu Sorin , Fenouillet-Béranger Claire , Martino João A.
Published: September 2009

The carrier mobility in advanced ultra-thin SOI transistors with n- and p-channels was measured using the Y-function and the transconductance peak methods. The mobilities at front channel and back channel were investigated as a function of the opposite gate bias and channel width. The results confirm that the mobility extracted from the Y-function is greatly overestimated when the opposite channel is activated. The experiments also show that the electron mobility is higher at the back channel than at the front channel. Finally, a decrease in mobility is observed in narrower channels.
DIBL Study Using Triple Gate Unstrained and Uniaxial/Biaxial Strained FinFETs
Authors: Santos Sara D. , Martino João A. , Simoen Eddy , Claeys Cor
Published: September 2009

The DIBL effect is studied in triple gate strained and unstrained FinFETs. Transistors with different channel lengths and fin widths were measured for two different drain voltages to extract the DIBL values. In all cases, the unstrained devices presented a better performance with lower VT variation than the strained ones. Although the effect of mechanical stress is more pronounced and the mobility is higher in the uniaxially strained devices, these devices have lower VT values in the saturation condition causing the highest DIBL values.
Application of the Symmetric Doped Double-Gate Model in Circuit Simulation Containing Double-Gate Graded-Channel Transistors
Authors: Contreras Esteban , Cerdeira Antonio , Alvarado Joaquin , Pavanello Marcelo A.
Published: September 2009

The development of models to simulate circuits containing new devices is an important task to allow for the introduction of these devices in practical applications. In this paper we show the advantages of using the Symmetric Doped Double-Gate Model recently developed and are already introduced in SmartSpice simulator, for modeling circuits containing Double-Gate Graded-Channel (GC) transistors. In this case there is no need to use two different models to represent the graded-channel device, as has been done up to now. A current-mirror circuit using GC devices has been simulated and the results were validated comparing them with those obtained in MIXED-MODE and two-dimensional ATLAS simulation of the GC devices.
Low Temperature and Silicon Thickness Influences on the Threshold Voltage of Double-Gate MOSFETs Considering a Charge Based Extraction Procedure
Authors: Doria Renan T. , Pavanello Marcelo A.
Published: September 2009

This work studies the influence of the temperature and the fin width (silicon thickness) on the threshold voltage of lightly doped double-gate MOSFETs. The evaluation was performed using tridimensional simulations, device measurements and model. The threshold voltage was defined considering the classical double derivative method and a charge based one, and the results were compared to an analytical model. The charge based definition has shown a better concordance with the analytical model for the influence of both temperature and fin width. The surface potentials extracted at the threshold condition have also exhibited that the charge-based criterion for threshold voltage definition results in closer values to those expected analytically. The variation of the threshold voltage with the temperature is overestimated if it is extracted using the double derivative method in comparison to the charge-based one. Experimental results confirmed the predictions obtained through simulations and model.
mTOR, AMPK, and GCN2 coordinate the adaptation of hepatic energy metabolic pathways in response to protein intake in the rat
Authors: Chotechuang Nattida , Azzout-Marniche Dalila , Bos Cécile , Chaumontet Catherine , Gausserès Nicolas , Steiler Tatiana , Gaudichon Claire , Tomé Daniel
Published: September 2009

Three transduction pathways are involved in amino acid (AA) sensing in liver: mammalian target of rapamycin (mTOR), AMP-activated protein kinase (AMPK), and general control nondepressible kinase 2 (GCN2). However, no study has investigated the involvement of these signaling pathways in hepatic AA sensing. To address the question of liver AA sensing and signaling in response to a high-protein (HP) dietary supply, we investigated the changes in the phosphorylation state of hepatic mTOR (p-mTOR), AMPKα (p-AMPKα), and GCN2 (p-GCN2) by Western blotting. In rats fed a HP diet for 14 days, the hepatic p-AMPKα and p-GCN2 were lower ( P < 0.001), and those of both the p-mTOR and eukaryotic initiation factor 4E-binding protein-1 phosphorylation (p-4E-BP1) were higher ( P < 0.01) compared with rats receiving a normal protein (NP) diet. In hepatocytes in primary culture, high AA concentration decreased AMPKα phosphorylation whether insulin was present or not ( P < 0.01). Either AAs or insulin can stimulate p-mTOR, but this is not sufficient for 4E-BP1 phosphorylation that requires both ( P < 0.01). As expected, branched-chain AAs (BCAA) or leucine stimulated the phosphorylation of mTOR, but both insulin and BCAA or leucine are required for 4E-BP1 phosphorylation. GCN2 phosphorylation was reduced by both AAs and insulin( P < 0.01), suggesting for the first time that the translation inhibitor GCN2 senses not only the AA deficiency but also the AA increase in the liver. The present findings demonstrate that AAs and insulin exert a coordinated action on translation and involved mTOR, AMPK, and GCN2 transduction pathways.
The Sso7d protein of Sulfolobus solfataricus: in vitro relationship among different activities
Authors: Guagliardi Annamaria , Cerchia Laura , Rossi Mosè
Published: September 2009

The physiological role of the nonspecific DNA‐binding protein Sso7d from the crenarchaeon Sulfolobus solfataricus is unknown. In vitro studies have shown that Sso7d promotes annealing of complementary DNA strands (Guagliardi et al. 1997), induces negative supercoiling (Lopez‐Garcia et al. 1998), and chaperones the disassembly and renaturation of protein aggregates in an ATP hydrolysis‐dependent manner (Guagliardi et al. 2000). In this study, we examined the relationships among the binding of Sso7d to double‐stranded DNA, its interaction with protein aggregates, and its ATPase activity. Experiments with 1‐anilinonaphthalene‐8‐sulfonic acid as probe demonstrated that exposed hydrophobic surfaces in Sso7d are responsible for interactions with protein aggregates and double‐stranded DNA, whereas the site of ATPase activity has a non‐hydrophobic character. The interactions of Sso7d with double‐stranded DNA and with protein aggregates are mutually exclusive events, suggesting that the disassembly activity and the DNA‐related activities of Sso7d may be competitive in vivo. In contrast, the hydrolysis of ATP by Sso7d is independent of the binding of Sso7d to double‐stranded DNA or protein aggregates.
Functional organization of a single nif cluster in the mesophilic archaeon Methanosarcina mazei strain Gö1
Authors: Ehlers Claudia , Veit Katharina , Gottschalk Gerhard , Schmitz Ruth A.
Published: September 2009

The mesophilic methanogenic archaeon Methanosarcina mazei strain Gö1 is able to utilize molecular nitrogen (N2) as its sole nitrogen source. We have identified and characterized a single nitrogen fixation (nif) gene cluster in M. mazei Gö1 with an approximate length of 9 kbp. Sequence analysis revealed seven genes with sequence similarities to nifH, nifI1
, nifI2
, nifD, nifK, nifE and nifN, similar to other diazotrophic methanogens and certain bacteria such as Clostridium acetobutylicum, with the two glnB‐like genes (nifI1
and nifI2
) located between nifH and nifD. Phylogenetic analysis of deduced amino acid sequences for the nitrogenase structural genes of M. mazei Gö1 showed that they are most closely related to Methanosarcina barkeri nif2 genes, and also closely resemble those for the corresponding nif products of the gram‐positive bacterium C. acetobutylicum. Northern blot analysis and reverse transcription PCR analysis demonstrated that the M. mazei nif genes constitute an operon transcribed only under nitrogen starvation as a single 8 kb transcript. Sequence analysis revealed a palindromic sequence at the transcriptional start site in front of the M. mazei nifH gene, which may have a function in transcriptional regulation of the nif operon.
Perspectives on biotechnological applications of archaea
Authors: Schiraldi Chiara , Giuliano Mariateresa , De Rosa Mario
Published: September 2009

Many archaea colonize extreme environments. They include hyperthermophiles, sulfur‐metabolizing thermophiles, extreme halophiles and methanogens. Because extremophilic microorganisms have unusual properties, they are a potentially valuable resource in the development of novel biotechnological processes. Despite extensive research, however, there are few existing industrial applications of either archaeal biomass or archaeal enzymes. This review summarizes current knowledge about the biotechnological uses of archaea and archaeal enzymes with special attention to potential applications that are the subject of current experimental evaluation. Topics covered include cultivation methods, recent achievements in genomics, which are of key importance for the development of new biotechnological tools, and the application of wild‐type biomasses, engineered microorganisms, enzymes and specific metabolites in particular bioprocesses of industrial interest.
Proteolysis in hyperthermophilic microorganisms
Authors: Ward Donald E. , Shockley Keith R. , Chang Lara S. , Levy Ryan D. , Michel Joshua K. , Conners Shannon B. , Kelly Robert M.
Published: September 2009

Proteases are found in every cell, where they recognize and break down unneeded or abnormal polypeptides or peptide‐based nutrients within or outside the cell. Genome sequence data can be used to compare proteolytic enzyme inventories of different organisms as they relate to physiological needs for protein modification and hydrolysis. In this review, we exploit genome sequence data to compare hyperthermophilic microorganisms from the euryarchaeotal genus Pyrococcus, the crenarchaeote Sulfolobus solfataricus, and the bacterium Thermotoga maritima. An overview of the proteases in these organisms is given based on those proteases that have been characterized and on putative proteases that have been identified from genomic sequences, but have yet to be characterized. The analysis revealed both similarities and differences in the mechanisms utilized for proteolysis by each of these hyperthermophiles and indicated how these mechanisms relate to proteolysis in less thermophilic cells and organisms.
Loss of genetic accuracy in mutants of the thermoacidophile Sulfolobus acidocaldarius
Authors: Bell Greg D. , Grogan Dennis W.
Published: September 2009

To investigate how hyperthermophilic archaea can propagate their genomes accurately, we isolated Sulfolobus acidocaldarius mutants exhibiting abnormally high rates of spontaneous mutation. Our isolation strategy involved enrichment for mutator lineages via alternating selections, followed by screening for the production of spontaneous, 5‐fluoro‐orotate‐resistant mutants in micro‐colonies. Several candidates were evaluated and found to have high frequencies of pyrE and pyrF mutation and reversion. Neither an increased efficiency of plating of mutants on selective medium, nor the creation of a genetically unstable pyrE allele, could be implicated as the cause of these high frequencies. The strains had elevated frequencies of other mutations, and exhibited certain phenotypic differences among themselves. A large increase in sensitivity to DNA‐damaging agents was not observed, however. These properties generally resemble those of bacterial mutator mutants and suggest loss of functions specific to genetic accuracy.
Biochemical evidence for the presence of two α‐glucoside ABC‐transport systems in the hyperthermophilic archaeon Pyrococcus furiosus
Authors: Koning Sonja M. , Konings Wil N. , Driessen Arnold J.M.
Published: September 2009

The hyperthermophilic archaeon Pyrococcus furiosus can utilize different carbohydrates, such as starch, maltose and trehalose. Uptake of α‐glucosides is mediated by two different, binding protein‐dependent, ATP‐binding cassette (ABC)‐type transport systems. The maltose transporter also transports trehalose, whereas the maltodextrin transport system mediates the uptake of maltotriose and higher malto‐oligosaccharides, but not maltose. Both transport systems are induced during growth on their respective substrates.
Characterization of the proteasome from the extremely halophilic archaeon Haloarcula marismortui
Authors: Franzetti B. , Schoehn G. , Garcia D. , Ruigrok R. W. H. , Zaccai G.
Published: September 2009

A 20S proteasome, comprising two subunits α and β, was purified from the extreme halophilic archaeon Haloarcula marismortui, which grows only in saturated salt conditions. The three‐dimensional reconstruction of the H. marismortui proteasome (Hm proteasome), obtained from negatively stained electron micrographs, is virtually identical to the structure of a thermophilic proteasome filtered to the same resolution. The stability of the Hm proteasome was found to be less salt‐dependent than that of other halophilic enzymes previously described. The proteolytic activity of the Hm proteasome was investigated using the malate dehydrogenase from H. marismortui (HmMalDH) as a model substrate. The HmMalDH denatures when the salt concentration is decreased below 2 M. Under these conditions, the proteasome efficiently cleaves HmMalDH during its denaturation process, but the fully denatured HmMalDH is poorly degraded. These in vitro experiments show that, at low salt concentrations, the 20S proteasome from halophilic archaea eliminates a misfolded protein.
Pyrobaculum calidifontis sp. nov., a novel hyperthermophilic archaeon that grows in atmospheric air
Authors: Amo Taku , Paje Maria Luz F. , Inagaki Akiko , Ezaki Satoshi , Atomi Haruyuki , Imanaka Tadayuki
Published: September 2009

A novel, facultatively aerobic, heterotrophic hyperthermophilic archaeon was isolated from a terrestrial hot spring in the Philippines. Cells of the new isolate, strain VA1, were rod‐shaped with a length of 1.5 to 10 μm and a width of 0.5 to 1.0 μm. Isolate VA1 grew optimally at 90 to 95 °C and pH 7.0 under atmospheric air. Oxygen served as a final electron acceptor under aerobic growth conditions, and vigorous shaking of the medium significantly enhanced growth. Elemental sulfur inhibited cell growth under aerobic growth conditions, whereas thiosulfate stimulated cell growth. Under anaerobic growth conditions, nitrate served as a final electron acceptor, but nitrite or sulfur‐containing compounds such as elemental sulfur, thiosulfate, sulfate and sulfite could not act as final electron acceptors. The G+C content of the genomic DNA was 51 mol%. Phylogenetic analysis based on 16S rRNA sequences indicated that strain VA1 exhibited close relationships to species of the genus Pyrobaculum. A DNA–DNA hybridization study revealed a low level of similarity (≤ 18%) between strain VA1 and previously described members of the genus Pyrobaculum. Physiological characteristics also indicated that strain VA1 was distinct from these Pyrobaculum species. Our results indicate that isolate VA1 represents a novel species, named Pyrobaculum calidifontis.