Showing papers on "Power density published in 2004"

High power density thermoelectric systems

Abstract: A number of compact, high-efficiency and high-power density thermoelectric systems utilizing the advantages of thermal isolation are described. Such configurations exhibit high system efficiency and power density. Some configurations exhibit a substantial reduction in the amount of thermoelectric material required.

Power and linearity characteristics of field-plated recessed-gate AlGaN-GaN HEMTs

Abstract: Record power density and high-efficiency operation with AlGaN-GaN high-electron mobility transistor (HEMT) devices have been achieved by adopting a field-plated gate-recessed structure. Devices grown on SiC substrate yielded very high power density (18.8 W/mm with 43% power-added efficiency (PAE) as well as high efficiency (74% with 6 W/mm) under single-tone continuous-wave testing at 4 GHz. Devices also showed excellent linearity characteristics when measured under two-tone continuous-wave signals at 4 GHz. When biased in deep-class AB (33 mA/mm, 3% I/sub max/) device maintained a carrier to third-order intermodulation ratio of 30 dBc up to a power level of 2.4 W/mm with 53% PAE; increasing bias current to 66 mA/mm (6% I/sub max/) allowed high linear operation (45 dBc) up to a power level of 1.4 W/mm with 38% PAE.

Apparatus and methods for microchannel cooling of semiconductor integrated circuit packages

Abstract: Apparatus and methods are provided for microchannel cooling of electronic devices such as IC chips, which enable efficient and low operating pressure microchannel cooling of high power density electronic devices having a non-uniform power density distribution, which are mounted face down on a package substrate. For example, integrated microchannel cooler devices (or microchannel heat sink devices) for cooling IC chips are designed to provide uniform flow and distribution of coolant fluid and minimize pressure drops along coolant flow paths, as well as provide variable localized cooling capabilities for high power density regions (or “hot spots”) of IC chips with higher than average power densities.

12 W/mm power density AlGaN/GaN HEMTs on sapphire substrate

Abstract: Record power performance at 4 GHz has been obtained using field-plated AlGaN/GaN HEMTs on sapphire substrate. High power density (12 W/mm) as well as high efficiency (58%) have been measured. A comparison between devices with and without field plate on the same sample showed a significant reduction in knee-voltage walk-out for the field-plated device, thus enabling high power and efficiency operation.

Microfluidic Devices for Energy Conversion: Planar Integration and Performance of a Passive, Fully Immersed H2−O2 Fuel Cell

Abstract: We describe the fabrication and performance of a passive, microfluidics-based H2-O2 microfluidic fuel cell using thin film Pt electrodes embedded in a poly(dimethylsiloxane) (PDMS) device. The electrode array is fully immersed in a liquid electrolyte confined inside the microchannel network, which serves also as a thin gas-permeable membrane through which the reactants are fed to the electrodes. The cell operates at room temperature with a maximum power density of around 700 microW/cm(2), while its performance, as recorded by monitoring the corresponding polarization curves and the power density plots, is affected by the pH of the electrolyte, its concentration, the surface area of the Pt electrodes, and the thickness of the PDMS membrane. The best results were obtained in basic solutions using electrochemically roughened Pt electrodes, the roughness factor, R(f), of which was around 90 relative to a smooth Pt film. In addition, the operating lifetime of the fuel cell was found to be longer for the one using higher surface area electrodes.

Analysis, design and experimentation of a high voltage power supply for ozone generation based on the current-fed parallel-resonant push-pull inverter

Abstract: The use of supply frequencies above 50-60 Hz allows for an increase in the power density applied to the ozonizer electrode surface and an increase in ozone production for a given surface area, while decreasing the necessary peak voltage. Parallel-resonant converters are well suited for supplying the high capacitive load of ozonizers. Therefore, in this paper the current-fed parallel-resonant push-pull inverter is proposed as a good option to implement high-voltage high-frequency power supplies for ozone generators. The proposed converter is analyzed and some important characteristics are obtained. The design and implementation of the complete power supply are also shown. The UC3872 integrated circuit is proposed in order to operate the converter at resonance, allowing us to maintain a good response disregarding the changes in electric parameters of the transformer-ozonizer pair. Experimental results for a 50-W prototype are also provided.

Power performance of AlGaN-GaN HEMTs grown on SiC by plasma-assisted MBE

Abstract: We report AlGaN-GaN high electron mobility transistors (HEMTs) grown by molecular beam epitaxy (MBE) on SiC substrates with excellent microwave power and efficiency performance. The GaN buffers in these samples were doped with carbon to make them insulating. To reduce gate leakage, a thin silicon nitride film was deposited on the AlGaN surface by chemical vapor deposition. At 4 GHz, an output power density of 6.6 W/mm was obtained with 57% power-added efficiency (PAE) and a gain of 10 dB at a drain bias of 35 V. This is the highest PAE reported until now at 4 GHz in AlGaN-GaN HEMTs grown by MBE. At 10 GHz, we measured an output power density of 7.3 W/mm with a PAE of 36% and gain of 7.6 dB at 40-V drain bias.

Ca2.7Bi0.3Co4O9∕La0.9Bi0.1NiO3 thermoelectric deviceswith high output power density

Abstract: Different versions of a thermoelectric unicouple composed of p-type Ca2.7Bi0.3Co4O9 (Co-349) and n-type La0.9Bi0.1NiO3 (Ni-113) bulks were constructed using Ag paste containing p- and n-type oxide powders, prepared from the same bulks, for connection of the p and n legs, respectively. Internal resistance (RI) of the unicouple corrected using Ag paste containing 6 wt. % of the oxide powders is 26.2mΩ at 1073K in air and decreases with increasing temperature. Maximum output power (Pmax), evaluated using the formula Pmax=VO2∕4RI, (VO is open-circuit voltage), is 94mW at 1073K (ΔT=500K) and increases with temperature. This value corresponds to a volume power density of 0.66W∕cm3.

9.4-W/mm power density AlGaN-GaN HEMTs on free-standing GaN substrates

Abstract: High power microwave AlGaN-GaN high electron-mobility transistors (HEMTs) on free-standing GaN substrates are demonstrated for the first time. Measured gate leakage was -2.2 /spl mu/A/mm at -20 V and -10 /spl mu/A/mm at -45 V gate bias. When operated at a drain bias of 50 V, devices showed a record continuous-wave output power density of 9.4 W/mm at 10 GHz with an associated power-added efficiency of 40%. Long-term stability of device RF operation was also examined. Under room conditions, devices driven at 25 V and 3-dB gain compression remained stable in 200 h, degrading only by 0.18 dB in output power. Such results illustrate the potential of GaN substrate technology in supporting reliable, high performance AlGaN-GaN HEMTs for microwave power applications.

AlGaN-based ultraviolet light-emitting diodes grown on AlN epilayers

Abstract: AlGaN-based deep-ultraviolet light-emitting diode (LED) structures, which radiate light at 305 and 290nm, have been grown on sapphire substrates using an AlN epilayer template. The fabricated devices have a circular geometry to enhance current spreading and light extraction. Circular UV LEDs of different sizes have been characterized. It was found that smaller disk LEDs had higher saturation optical power densities but lower optical powers than the larger devices. This trade-off between power and power density is a result of a compromise between electrical and thermal resistance, as well as the current crowding effect (which is due to the low electrical conductivity of high aluminum composition n- and p‐AlGaN layers). Disk UV LEDs should thus have a moderate size to best utilize both total optical power and power density. For 0.85mm×0.85mm interdigitated LEDs, a saturation optical power of 2.9mW (1.8mW) at 305nm (290nm) was also obtained under dc operation.

Multimode pumped continuous-wave solid-state Raman laser.

Abstract: We demonstrate the continuous-wave operation of a solid-state Raman laser containing a barium nitrate crystal as the Raman medium. The Raman laser, which has a singly resonant cavity, is pumped by multimode radiation. The Raman oscillation threshold is reached at ∼2 W of pump power. As much as 500 kW/cm2 of Stokes power density at 60‐kW/cm2 pump power density is obtained in the cavity.

Higher power density downstream plasma

Abstract: A method and system to obtain a high power density plasma to efficiently generate high concentrations of plasma downstream from one or more plasma sources. A first embodiment of the invention involves a method to provide an improved power density for dissociating one or more gases to create plasma. A second embodiment of the invention involves a method to provide multiple chambers for dissociating one or more gases to create plasma. A third embodiment involves an apparatus using a constriction in a discharge chamber containing one or more gases, to provide an improved power density for dissociating one or more gases to create plasma. A fourth embodiment involves an apparatus using a constriction in multiple discharge chambers containing one or more gases, to provide an improved power density for dissociating one or more gases to create plasma.

Stable High-Power Green Light Generation with Thermally Conductive Periodically Poled Stoichiometric Lithium Tantalate

Abstract: Periodically poled stoichiometric lithium tantalate was used for an efficient green light generation based on frequency doubling of a pulsed Nd:YVO4 laser. The achieved average peak power density of 9.2 MW/cm2 was sufficiently stable without spatial distortion of green light at 532 nm at room temperature (33°C). A small phase matching temperature adjustment (0.5°C) was required at the maximum average output power of 4.4 W owing to its high thermal conductivity.

A modeling approach for addressing power supply switching noise related failures of integrated circuits

Abstract: Power density of high-end microprocessors has been increasing by approximately 80% per technology generation, while the voltage is scaling by a factor of 0.8. This leads to 225% increase in current per unit area in successive generation of technologies. The cost of maintaining the same IR drop becomes too high. This leads to compromise in power delivery and power grid becomes a performance limiter. Traditional performance related test techniques with transition and path delay fault models focus on testing the logic but not the power delivery. In this paper we view power grid as performance limiter and develop a fault model to address the problem of vector generation for delay faults arising out of power delivery problems. A fault extraction methodology applied to a microprocessor design block is explained.

AlGaN/GaN HEMTs on Si substrate with 7 W/mm output power density at 10 GHz

Abstract: The first 10 GHz power performance of AlGaN/GaN HEMTs on silicon substrate is reported. Molecular beam epitaxy grown AlGaN/GaN heterostructure and field-plate gates with 0.3 µm length are employed to fabricate the devices on 2-inch Si (111) substrates. A maximum current density of 850 mA/mm and an extrinsic transconductance of 220 mS/mm are achieved. Load pull measurements at 10 GHz demonstrate a continuous-wave output power density of 7 W/mm, which is the highest power density reported to date for an Si-based transistor. A peak power added efficiency of 52% is achieved for these devices at 10 GHz.

High power density and/or linearity transistors

Abstract: Field effect transistors having a power density of greater than 25 W/mm when operated at a frequency of at least 4 GHz are provided. The power density may be at least 30 W/mm when operated at 4 GHz. The power density of at least 30 W/mm may be provided at a drain voltage of 120 V. Transistors with a power density of at least 30 W/mm when operated at 8 GHz are also provided. The power density of at least 30 W/mm may be provided at a drain voltage of 120 V. Field effect transistors having a power density of greater than 20 W/mm when operated at a frequency of at least 10 GHz are also provided. Field effect transistors having a power density of at least 2.5 W/mm and a two tone linearity of at least −30 dBc of third order intermodulation distortion at a center frequency of at least 4 GHz and a power added efficiency (PAE) of at least 40% are also provided.

Achievement of the highest performance of a CCMHD generator: an isentropic efficiency of 63% and an enthalpy extraction ratio of 31%

Abstract: In this paper we describe the highest-performance closed-cycle magnetohydrodynamic (CCMHD) power generator driven by a shock-tube. Despite the use of a small-scale device having a power-generating volume of approximately 4 liters, outstanding performance, namely, the isentropic efficiency of 63%, the enthalpy extraction ratio of 30.8%, the electrical power output of 1.23 MW, and the power density of 297 MW/m/sup 3/, is achieved at the stagnation temperature of 2250 K and the applied magnetic flux density of 3.0 T. The following facts contribute to the world's highest performance of the CCMHD power generator: a less-divergent generator shape; the employment of cesium-seeded helium gas; the introduction of an inlet swirl; and the production of homogeneous plasma.

Tunneling hot spots and heating in magnetic tunnel junctions

Abstract: In this work the thermal heating of tunnel junctions is investigated doing one-dimensional numerical simulations by solving the heat equation. The temperature increase is proportional to the power density jV, which is confirmed by transport measurements on patterned μm size junctions. The observed temperature increase was 2.3 K/(mW μm−2) compared to a simulation result of 0.9 K/(mW μm−2). Tunneling AFM measurements on 4, 5.4, and 6.7 A barrier half-junctions, show hot spots with current densities up to 13 times the average density value. The current concentration could explain the higher heating observed experimentally compared to the simulated value. The hot spot density is 600–900/μm2 occupying roughly 5% of the barrier surface.

The Influence of Various Hybrid Welding Parameters on Bead Geometry Arc power and transfer mode greatly affect bead width, penetration, and reinforcement

Abstract: A series of hybrid welding (gas metal arc welding-CO 2 laser beam welding) experiments was conducted in which the two energy sources were cou- pled in one process zone on the surface of a 316L austenitic stainless steel work- piece. Arc and laser power were varied in order to study their influence on various bead dimensions. Arc power and, conse- quently, the mode of metal transfer have a great influence on bead width W, arc and laser penetration M and L, and bead rein- forcement R. Increasing arc power in- creases W and L, whereas it reduces M and R. Laser power and hence the laser- induced metal vapor significantly influ- ences the features of the metal transfer mode in the arc process. Higher laser pow- ers prolong the arc burning time T a at the expense of the short circuit frequency Nsc , which assists in increasing M and L. At constant laser power, the contribution of the M solely into the total penetration M + L is always bigger than that of the L. interaction between the two energy sources is optimized. The arc welding process, characterized by relatively lower power density and wider process zone, gives a wide bead, thus enhancing the joint's root bridging ability and enlarging the manufacturing tolerances for joint preparation. Simultaneously, the laser beam process, characterized by higher lo- calized power density, leads to a deeper penetration. Thus in hybrid GMA-laser beam welding, a wide and deep bead is achieved at higher welding speeds when compared with the GMAW process by its own (Ref. 8). This accordingly leads to less heat input per unit length, less thermal distortion, and therefore, less residual stresses, narrower heat-affected zone (HAZ), and more important, increased