Improved Power Performance Research Articles

In situ SiN passivation of AlGaN/GaN HEMTs by molecular beam epitaxy

To improve the passivation process of AlGaN/GaN HEMTs, a unique passivation process has been developed in which an SiN passivation layer is deposited by MBE immediately following epitaxial growth of the HEMT structure. The effectiveness of this in situ passivation process is evaluated by comparing devices fabricated with this process to the conventional PECVD passivation process in which the SiN is deposited after gate metallisation. The improved material quality and the protection offered by the MBE-grown SiN may contribute to the significantly reduced dispersion and improved power performance measured for the wafer fabricated with the in situ passivation process.

Improvement of PEMFC's Power Performance by Electrophoretic Deposition of Pt/MWNT Nanocatalysts

The multi-walled carbon nanotubes (MWNTs) were treated through a chemical oxidation by mixture of nitric acid and sulfuric acid. Nearly monodispersed nanosized platinum catalysts (2-3 nm) for PEM fuel cells were synthesized by the reduction of hexachloroplatinic acid precursor with ethylene glycol solvent, which were simultaneously distributed over the surface of MWNT carriers. In the preparation of Pt/MWNT nanocatalysts, ethylene glycol solvent, as compared to formaldehyde, was an ideal chemical to obtain improved dispersivity, narrower particle size distribution, and platinum loading capability on MWNT carriers (18.6 wt% Pt on MWNT). The evenly distributed loading of Pt/MWNT nanocatalysts on the carbon-based gas diffusion layers (GDLs) for the PEM fuel cells was carried out via the electrophoretic deposition (EPD). The cell performance of PEMFC with both synthesized Pt/MWNT and Pt/C (E-TEK, XC-72) nanocatalysts and the influence of hydrophobicity by using MWNTs and carbon black carriers for the Pt nanoparticles on GDLs were evaluated by cyclic voltammetry and contact angle measurement, respectively. The power density (mW/cm2) of PEMFC fabricated by electrophoretic deposition of Pt/MWNT nanocatalysts was increased by ~36% as compared to the same Pt loading (0.16 mg- Pt/cm2) of Pt/C nanocatalysts.

Nanopowders of spinel-type electrode materials for Li-ion batteries

Nanomaterials are becoming important for use in Li-ion battery electrodes as these can deliver increased capacity and improved power performance. Our work is focused on Mg-doped high-voltage spinel materials, such as LiNi 0.5Mn 1.5O 4, in order to improve its stability. LiMg δ Ni 0.5− δ Mn 1.5O 4 with δ = 0.05, having the cubic spinel structure ( P4 332) were made via four different synthesis routes – a solid-state route, a sol–gel method, a xerogel route and an auto ignition method. The powders were investigated with SEM and TEM analysis. XRD was used to determine the crystallographic structure. Electrochemical tests were performed in CR2320 coin cells built with 1 M LiPF 6 in EC/EMC/DMC 1:2:2 as electrolyte and metallic Li as negative electrode – cells were measured with a MACCOR cycler. LiMg 0.05Ni 0.45Mn 1.5O 4 made via the sol–gel and xerogel routes revealed agglomerated nanoparticles with sizes ranging from 10 to 200 nm, whereas the auto ignition method gives particle sizes between 10 and 50 nm. Although agglomerated, often residual LiMn 2O 4 is observed, with increasing concentration going from solid-state, sol–gel, xerogel to auto ignition. Hence, thanks to these different synthesis routes, we are able to obtain particle sizes reaching from 10 to 200 nm, with a narrow particle size distribution. The electrochemical tests of the xerogel particles showed promising results. The auto ignition method show also promising results, however, the impurity phase needs to be suppressed significantly. The sol–gel method, the xerogel route and the auto ignition method show increased capacity retention at high power rates compared to the solid state method.

Improvement of PEMFC's Power Performance by Electrophoretic Deposition of Pt/MWNT Nanocatalysts

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Design and analysis for a miniature CMOS SPDT switch using body-floating technique to improve power performance

A low insertion-loss single-pole double-throw switch in a standard 0.18-/spl mu/m complementary metal-oxide semiconductor (CMOS) process was developed for 2.4- and 5.8-GHz wireless local area network applications. In order to increase the P/sub 1dB/, the body-floating circuit topology is implemented. A nonlinear CMOS model to predict the switch power performance is also developed. The series-shunt switch achieves a measured P/sub 1dB/ of 21.3 dBm, an insertion loss of 0.7 dB, and an isolation of 35 dB at 2.4 GHz, while at 5.8 GHz, the switch attains a measured P/sub 1dB/ of 20 dBm, an insertion loss of 1.1 dB, and an isolation of 27 dB. The effective chip size is only 0.03 mm/sup 2/. The measured data agree with the simulation results well, including the power-handling capability. To our knowledge, this study presents low insertion loss, high isolation, and good power performance with the smallest chip size among the previously reported 2.4- and 5.8-GHz CMOS switches.

Improved Power Performance for a Recessed-Gate AlGaN–GaN Heterojunction FET With a Field-Modulating Plate

A recessed-gate AlGaN-GaN field-modulating plate (FP) field-effect transistor (FET) was successfully fabricated on an SiC substrate. By employing a recessed-gate structure on an FP FET, the transconductance was increased from 150 to 270 mS/mm, leading to an improvement in gain characteristics, and current collapse was minimized. At 2 GHz, a 48-mm-wide recessed FP FET exhibited a record output power of 230 W (4.8 W/mm) with 67% power-added efficiency and 9.5-dB linear gain with a drain bias of 53 V.

A design flow for partially reconfigurable hardware

This paper presents a top-down designer-driven design flow for creating hardware that exploits partial run-time reconfiguration. Computer-aided design (CAD) tools are presented, which complement conventional FPGA design environments to enable the specification, simulation (both functional and timing), synthesis, automatic placement and routing, partial configuration generation and control of partially reconfigurable designs. Collectively these tools constitute the dynamic circuit switching CAD framework. A partially reconfigurable Viterbi decoder design is presented to demonstrate the design flow and illustrate possible power consumption reductions and performance improvements through the exploitation of partial reconfiguration.

Elimination of current instability and improvement of RF power performance using Si 3N 4 passivation in SiC lateral epitaxy MESFETs

SiC lateral epitaxy (LE) MESFETs demonstrated a dramatic reduction of output conductance. Despite elimination of current injection into the substrate, a severe problem of current instability remained. Using PECVD Si 3N 4 passivation, the current instability phenomenon has been completely eliminated resulting in improved RF power performance. RF output power measured after passivation exceeded 90% of the theoretical maximum values that were derived from the DC characteristics. Further enhanced performance in class B operation was observed.

Performance-optimized microstrip coupled VCOs for 40-GHz and 43-GHz OC-768 optical transmission

We present 40- and 43-GHz voltage-controlled oscillators (VCOs) for use in SONET/SDH optical transmission systems operating at OC-768 rates. SONET system jitter requirements are explained, as are methods for achieving the requisite performance in manufacturable oscillators. We describe in detail a technique for using quadrature-coupled VCOs to achieve a fundamental improvement in jitter power performance. The 40-GHz oscillator has a tuning range of 5 GHz, a single-sideband phase-noise power spectral density of -99 dBc/Hz at 1-MHz offset from the carrier, and consumes 207 mW in the oscillator core. Total power consumption is 363 mW (including biasing and output buffers) from a 3-V supply. The oscillator occupies 0.189 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of die area and is implemented in a 120-GHz f/sub T/ SiGe BiCMOS process.

Improvement of power performance in planar type AlGaAs/GaAs MESFET by substrate surface oxidation

The purpose of this study is to improve the output power ( P out) and third-order inter-modulation distortion (IM3) of planar type GaAs power FET, which is used for RF power amplifiers for base stations of digital wireless communications systems. We focused on the GaAs surface state and attempted to improve the FET performance by intentional GaAs surface oxidation just prior to SiN cap deposition. Thermal or plasma oxidation has been found to improve P out and IM3 characteristics. Distinct improvement of FET performance was observed in intentionally oxidized FET, and the highest P out = 34 dB m and P out (@IM3=−55 dB c) = 23 dB m was measured on plasma oxidized FET with W g=5.2 mm. These results are shown in this article together with the results of photoelectron analysis.

Slow transients observed in AlGaN HFETs: Effects of SiN/sub x/ passivation and UV illumination

Very slow drain current and surface potential transients have been observed in AlGaN/GaN heterostructure field effect transistors that are subjected to high bias stress. Simultaneous measurements of drain current and surface potential indicate that large change in surface potential after stress is responsible for the reduction in drain current in these devices. Measurements of surface potential profile from the gate edge toward the drain as a function of time indicate that surface potential changes occur mostly near the gate. It is proposed that the surface potential changes are caused by electrons which tunnel from the gate under high bias stress and get trapped at the surface states near the gate. Passivation of the surface with SiN/sub x/ reduces the transient magnitudes to a large extent. This correlates with a large improvement in microwave power performance in these devices after passivation. UV illumination of these devices totally eliminates the drain current and surface potential transients.

Optimization of inlet air cooling systems for steam injected gas turbines

The cooling of the inlet air in gas turbines is a practice used to improve power performances. In the past, the authors suggested extending this practice to STIG turbines, using some of the heat generated in the back boiler to supply the absorption systems. Positive results have prompted further developments. For the purpose of verifying the positive effects of compression air cooling in STIG turbines, a calculation model has been developed and studied specifically for gas turbines and STIG turbines. The model has been applied to the Allison 501 KH turbine. In addition to focusing on the two traditional techniques used to cool the air of the compression system through an absorption unit and an intercooling unit, the present work emphasizes the advantages of using an ejection cooling system. The availability of exhaust heat from the STIG turbines prompted the idea of cooling through a double ejection system. Water cannot be used as a primary refrigerant in compression cooling systems because of the very low pressures that have to be reached, whereas the ejection system used for steam compression allows for the use of water. Moreover, the ejection system is relatively easy to design and construct. The use of this cooling system, enables good results to be obtained in terms of the ejection system's coefficient of performance and consequently of the STIG turbine's performance.

Thermal effects on light emission in Yb3+-sensitized rare-earth doped optical glasses

The temperature effect upon infrared-to-visible frequency upconversion fluorescence emission in off-resonance infrared excited Yb3+-sensitized rare-earth doped optical glasses is theoretically and experimentally investigated. We have examined samples of Er3+/Yb3+-codoped Ga2S3:La2O3 chalcogenide glasses and germanosilicate optical fibers, and Ga2O3:La2O3 chalcogenide and fluoroindate glasses codoped with Pr3+/Yb3+, excited off-resonance at 1.064mum. The experimental results revealed thermal induced enhancement in the visible upconversion emission intensity as the samples temperatures were increased within the range of 20°C to 260°C. The fluorescence emission enhancement is attributed to the temperature dependent multiphonon-assisted anti-Stokes excitation process of the ytterbium-sensitizer. A theoretical approach that takes into account a sensitizer temperature dependent effective absorption cross-section, which depends upon the phonon occupation number in the host matrices, has proven to agree very well with the experimental data. As beneficial applications of the thermal enhancement, a temperature tunable amplifier and a fiber laser with improved power performance are presented.

Conceptual design of a high temperature superconducting generator

This paper describes the conceptual design of a high temperature superconducting (HTS) generator for mobile radar (MR) applications. The power system for MR consists of a diesel engine, a generator and power conditioning electronics. Significant improvements in power density, performance and system efficiency result if the generator and the power electronics are cryogenically cooled. The generator supplies power to the radar and the auxiliaries of the system. The generator output required is less than 50 volt AC (RMS phase to neutral) to maximize the efficiency of the cryogenically cooled power electronics. The auxiliaries of the system consume power at 120 V AC, 3-phase, at 60 Hz. The generator is designed to meet both requirements. The diesel engine provides the prime power to the generator at 1800 RPM. The generator is a four-pole two stator winding machine supplying power at 50 V AC, 60 Hz, 12-phase to the power electronics, and 120 V AC, 60 Hz, 3-phase to the auxiliaries of the system. The field winding of the generator consists of HTS coils; the stator has two ambient temperature air gap windings. The cooling of the field winding is provided by heat exchange with helium gas cooled by a Gifford McMahon cryocooler.

Semiconductor strained layers

During the past 25 years (after the growth of the first pseudomorphic GeSi strained layers on Si) we have seen a steady accumulation of new materials and devices with enhanced performance made possible by strain. The past year has been good for strained layers. Until recently, short wavelength (violet to green) and mid-infrared (2–5 μm) regions of the spectrum were not accessible to photonic devices. Short wavelength light emitting diodes and laser diodes have been developed using III—Nitride and II–VI strained layers. Improved mid-infrared lasers, using Sb-based III–V semiconductor strained layers, have also been fabricated. These advances have been possible due to improvements in growth techniques as well as in the modelling and computer simulations of layers compositions and device structures. Full band Monte Carlo simulations of electron transport in strained Si predict very high electron mobilities. Computer simulations show that complementary metal oxide silicon circuits, fabricated with strained layer GeSi transistors will have considerably improved performance. Electronic devices based on GeSi strained layers have shown further improvements in high frequency and high power performance. Many devices based on strained layers are being used in commercial equipment. Advances have been made both in modelling and determining the nonuniform strain, using a Raman technique.

High-linearity and small-chip AlGaAs/GaAs power HBTs for L-band personal digital cellular applications

A high-linearity AlGaAs/GaAs power heterojunction bipolar transistor (HBT) is developed for personal digital cellular phones. For compact chip layout, thermal design was considered. To improve power performance, proton implantation, optimum alloy condition for collector electrodes, and multiple via holes were used. A 2400-μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -emitter-area HBT fabricated on a 0.5×0.67 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> substrate exhibits adjacent channel leakage powers below -53 dBc for 0.95- and 1.5-GHz /spl pi//4-shifted QPSK modulated input signals at a low collector-emitter voltage of 3.4 V. The HBT produces a 31.7-dBm output power, 50% power-added efficiency, and 15-dB linear power gain at 0.95 GHz, and produced a 31.3-dBm output power, 52% power-added efficiency, and 11.5-dB linear power gain at 1.5 GHz. These results were achieved on about one-fifth of the substrate area of conventional GaAs FETs.

FLEXIBLE AC TRANSMISSION SYSTEMS (FACTS)

ABSTRACT The paper reviews literature which addresses the application of Flexible AC Transmission System (FACTS) concepts to the improvement of Power System utilisation and performance. It summarises literature on using high speed thyristor based control of HVAC power system elements to enhance the power carrying capacity of existing transmission circuits without compromising reliability. It describes a study system representative of existing power systems that has been developed to evaluate the economic and technical issues of loading transmission lines to their thermal limits. Considered are two scenarios, a multi-line corridor and a long radial interconnection, where the issues addressed are transient and dynamic stability, power flow control, reactive support and voltage stability. A benchmark system is developed to validate performance of die more simple devices. It is concluded that FACTS devices have the potential to significantly increase system stability margins thereby increasing loading capability of existing transmission corridors such as between Scotland and England. Economic evaluations of the applications reviewed in the literature show that FACTS devices are attractive when compared with the other methods of achieving similar performance objectives.

High gain, pulsed power [formula omitted] HBTs

A layout to minimize parasitic elements which reduce the common emitter Heterojunction Bipolar Transistor (HBT) gain and efficiency is described. Layout modifications are based upon consideration of the HBT device model that predicts better performance by reducing feedback elements. Reducing the base contacts size to minimize extrinsic base-collector capacitance, and reducing inductance in the ground connection are the primary paths to better performance. The improvements in small signal and power performance for several HBT variations are described. The changes result in a 320 μm 2 emitter area HBT which operating pulsed at 10 GHz delivers 1.25 W output power with 10.5 dB associated gain and 56% power-added efficiency.

Power dissipation models and performance improvement techniques for CMOS inverters with RC line and tree interconnections

Physical power dissipation models of CMOS inverters with RC line and tree interconnection networks are presented. Compared to SPICE simulation results, the maximum error in the model calculated results using the models is 12% for power dissipation in CMOS inverters with different RC values in each branch of the tree networks, different gate sizes, device parameters, and even input excitation waveforms not deviating much from the characteristic waveforms. Based upon the mathematical optimisation method, as well as on the developed power dissipation models and the delay models, an experimental sizing program is also constructed for improving various circuit performances such as delay time, power-delay product, and delay time with fixed power dissipation specifications. In this program, given the size of the input logic gate and its driving interconnection resistances, capacitances, and structures, users can choose one improvement technique and determine the suitable sizes and/or number of drivers/repeaters for optimal circuit performance. It is found from the sizing results of the experimental CAD program that the required tapering factor for minimum power-delay product in cascaded drivers of interconnection lines or trees is in the range 2–6 instead of 4–8 for a minimum delay. It is also shown that the technique of optimal-size repeaters with cascaded input drivers can lead to the lowest delay time and power-delay product.

VARCOV II: a computer program for the multivariate analysis of growth and response curves

A FORTRAN computer program written to perform a multivariate analysis of growth and response curves is described. The underlying statistical methodology is particularly applicable with incomplete observations, and may offer improved power performance to the distribution-free methods described previously.