Showing papers on "Power density published in 1994"

Method of producing VDMOS device of increased power density

Abstract: A vertical double diffused metal-on-semiconductor device is produced by a method involving the formation of horizontally separated bodies of heavily doped Si and sources by a self-aligned process and a lift-off process along with the formation of trenches having negatively-sloped side-walls.

Utility of extracting alpha particle energy by waves

Abstract: The utility of extracting CY particle power, and then diverting this power to fast fuel ions, is investigated. As power is diverted to fast ions and then to ions, a number of effects come into play, as the relative amounts of pressure taken up by electrons, fuel ions and fast CY particles shift. In addition, if the CY particle power is diverted to fast fuel ions, there is an enhanced fusion reactivity because of the non-thermal component of the ion distribution. Some useful expressions for describing these effects are derived, and it is shown that fusion reactors with power density about twice what otherwise might be obtained can be contemplated, so long as a substantial amount of the 01 particle power can be diverted. Interestingly, in this mode of operation, once the electron heat is sufficiently confined, further improvement in confinement is actually not desirable. A similar improvement in fusion power density can be obtained for advanced fuel mixtures such as D-3He, where the power of both the energetic CY particles and the energetic protons might be diverted advantageously.

Optical gain of optically pumped Al0.1Ga0.9N/GaN double heterostructure at room temperature

Abstract: In this letter, we report the measurement of the gain of an optically pumped Al0.1Ga0.9N/GaN double heterostructure (DH) which was prepared on a sapphire substrate by metalorganic vapor phase epitaxy using an AlN buffer layer. At room temperature, the optical gain of stimulated emission from Al0.1Ga0.9N/GaN DH was measured to be 160 cm−1 at pumping power density of 200 kW/cm2.

High efficiency DC-DC converter

Abstract: A family of power converter topologies employing two complementary switches in the primary and two MOSFET synchronous rectifiers in the secondary is presented. The use of two complementary switches in the primary leads to soft transitions across the switching elements, and the complementary square waveforms reflected in the secondary offers a simple and efficient driving waveform for the synchronous rectifiers. Employing one of these topological configurations, a very high efficiency and high power density 150 W converter was implemented. The power converter operates from an input voltage of 35 V to 72 V providing 5 V at 30 A, with an efficiency above 90% at full load. High efficiency combined with the use of a full integrated multilayer PCB magnetic technology has allowed a power density of 51 W/in/sup 3/. >

Semiconductor Raman lasers

Abstract: The semiconductor Raman laser using the longitudinal optical phonon mode of GaP has a very low threshold value of optical input power. To reduce the threshold optical input power and power density further, a crystal as thin as 160 µm with a wave-guiding structure is used. Epitaxial layers of GaP with a thickness of 280 µm are demonstrated as the low-threshold semiconductor Raman laser, for which the threshold input power density is as low as 1.7 × 106 W/cm2.

High Power and High Frequency Silicon Carbide Devices

Abstract: The breakdown electric field of 4H-SiC as a function of doping was measured using pn junction rectifiers, with maximum voltages of 1130 V being achieved. 4H-SiC vertical power MOSFET structures have shown specific on-resistances of 33 mΩ-cm2 for devices capable of blocking 150 V. A current density of 100 A/cm2 was achieved at a drain voltage of 3.3 V. Thyristors fabricated in SiC have also shown blocking voltages of 160 V and 100 A/cm2 at 3.0 V. High temperature operation was measured, with the power MOSFETs operating to 300°C, and the thyristors operating to 500°C. Submicron 6H- and 4H-SiC MESFETs have shown good I-V characteristics to Vd= 40 V, with an Idss of 200-300 mA/mm. The maximum operating frequencies (fmax) achieved for 6H-SiC MESFETs is 13.8 GHz, with small-signal power gains of 9.8 dB and 2.9 dB at 5 GHz and 10 GHz, respectively. 4H-SiC MESFETs have demonstrated an RF output power density of 2.8 W/mm at 1.8 GHz. This is the highest power density ever reported for SiC and is 2-3 times higher than reported for comparable GaAs devices.

Non-equilibrium synthesis of Fe-Cr-C-W alloy by laser cladding

Abstract: Synthesis of Fe-Cr-C-W alloy using the laser cladding technique offered an opportunity to produce a novel wear-resistant material with fine and uniform microstructure. Use of preheating during laser cladding Fe-Cr-C-W provided crack-free clads. The preheating temperature was very critical to eliminate cracks in the clad. Different complex types of carbide were observed in this research. Overall laser process parameters such as power density or specific energy as well as preheating temperature affected the characteristics of the carbide precipitates in the matrix. The increase of solid solubility and high cooling rate resulted in good metallurgical characteristics. Mostly M6C or M23C6 type carbides were observed. Usually diamond-shaped M6C carbides showed good tribological characteristics. In general, increasing the power density brought an increase of average hardness, while decreasing the power density brought a decrease of wear scar width. The laser-clad Fe-Cr-C-W alloy showed better wear properties than laser-clad Fe-Cr-Mn-C and several times smaller scar width as compared to Stellite 6 hard-facing during line-contact wear testing.

Characteristics of Ablation Plasma Produced by Intense, Pulsed, Ion Beam

Abstract: Characteristics of ablation plasma produced by the irradiation of an intense, pulsed, ion beam on targets, which has been known to be very effective in preparing thin films and is known as ion-beam evaporation (IBE), have been investigated experimentally by time-of-flight of ion-flux density measured by biased ion collector (BIC). With ion-beam power density of ~109 W/cm2, the velocity and the kinetic energy of the ablation plasma were measured at various positions from the substrate using a titanium or aluminum target. An analytic solution derived from one-dimensional hydrodynamic expansion into a vacuum has been developed for the IBE process. Using such a model, it is possible to deduce the temperature in IBE from the signals of BICs. This method is also applicable to other intense pulsed energy sources such as lasers or electron beams.

The influence of surface heating on the birefringence distribution in injection molded parts

Abstract: In order to reduce the frozen-in orientation. which is usually present in injection molded products, the effect of high-performance mold surface heaters was investigated. The heaters are capable of changing their surface temperature by 70°C within a few tenths of a second typically, which minimizes their effect on the cooling time. The effects of the heating time, the instant of heating, and the heating power on the birefringence distribution of a polystyrene resin were studied. Reductions of the birefringence peak by a factor 4 to 7 were observed. The birefringence is removed most effectively by heating briefly before and during the injection stage. A heating pulse of about one second and with a power density of 20 W/cm2 then seems to be sufficient. A minimum power density of 10 W/cm2 is needed for the relaxation to occur in this specific system.

Measurement of free-carrier nonlinearities in ZnSe based on the Z-scan technique with a nanosecond laser.

Abstract: Self-defocusing and nonlinear absorption resulting from two-photon-excited free charge carriers were observed in polycrystalline ZnSe at the low power density of ~ 30 MW/cm2 by use of the Z-scan technique with nanosecond laser pulses. The total carrier absorption cross section and the variation of refractive index per unit of photoexcited carrier density were estimated to be 0.80 ± 0.10 × 10−18 cm2 and 0.60 ± 0.15 × 10−21 cm3, respectively.

Observation of stimulated emission in the near ultraviolet from a molecular beam epitaxy grown GaN film on sapphire in a vertical‐cavity, single pass configuration

Abstract: We report the first observation of stimulated emission from a GaN film grown by ion‐assisted molecular beam epitaxy. The observed near‐UV optical emission power was a nonlinear function of the pump power density. The characteristics of the observed stimulated emission are similar to those observed recently from films grown with low‐pressure metalorganic chemical vapor deposition techniques.

Les piles à combustible : application au véhicule électrique

Abstract: After a short historical survey, the principles of fuel cells are discussed, underlining electrocatalytic problems to be overcome to increase their energy efficiency, and power density. The different kinds of fuel cells are then presented, with their advantages and disadvantages, and their possible uses, particularly as power sources for electric vehicles. Different means of fuel and hydrogen storage are also discussed. Finally the two types of fuel cells, which appear the best candidates for an electric vehicle, are presented in details, i.e. the H 2 /air Proton Exchange Membrane Fuel Cell, and the Direct Methanol/air Fuel Cell

Optimum design of distributed power-FET amplifiers. Application to a 2-18 GHz MMIC module exhibiting improved power performances

Abstract: A suitable and effective design method of distributed power amplifiers, based on the optimum FET load requirement for power operation, is proposed in this paper. An analytical determination of the gate and drain line characteristic admittances provides both the initial values and right directions for an optimum design. The best trade-offs between wide band and high power operation have been investigated. To validate the method, a FET amplifier demonstrator with a gate periphery of 1.2 mm has been manufactured at the Texas Instruments foundry. The MMIC amplifier demonstrated state of the art power density performance of 340 mW/mm over the 2-18 GHz band associated with 14.2% power added efficiency, 26.5% drain efficiency and 26.1 dBm output power at 1 dB compression in CW operation. >

Jet O2(1Δ) generator with oxygen pressures up to 13.3 kPa

Abstract: The output parameters of a jet-type singlet oxygen generator were investigated. An increase in the jet and gas flow velocities through a reactor to 20 and 30 m s-1, respectively, made it possible to generate O2 at pressures up to 13.3 kPa and with the O2(1Δ) fraction of about 60%. The power density of the electron energy coupled out across the generator cross section was 0.77 kW cm-2, which was over one order of magnitude higher than the corresponding power density obtained for other types of singlet oxygen generator. The high efficiency was due to the large specific area of the contact between the phases as a result of breakup of the jets and due to a fast rate of mass transfer in the liquid phase (exceeding the diffusion rate). The capture of the gas by the jets had to be allowed for in the calculations.

A High Power Density, High Voltage Power Supply For A Pulsed Radar System

Abstract: waveform oscillating at the L-C resonant frequency [ 11. Figure 1 shows an equivalent circuit of the resonant tank . A 37 kW, 30 kV DC-DC converter has been built and tested for a pulsed microwave radar tube application. The converter utilizes IGBT transistors in a series resonant DISCRETE DISCRETE LEAKAGE PARASITIC topology to achieve a power density of 4 kWkg pulsed, and 2.6 kWkg average. The converter operates from an input voltage of 30 kV. A resonant frequency of 70 kHz was selected to minimize transformer mass while maintaining a converter efficiency in excess of 92%. A voltage regulation of _. +0.25% has been achieved through the use of an offset comparator and a pulse modulation control system. The theory of operation, circuit topology and test results are given in this paper. TRANSFORMER TRANSFORMER

A high-power GaAs FET having buried plated heat sink for high-performance MMIC's

Abstract: This paper reports an FET structure, named "Advanced SIV FET" (advanced source island via-hole FET). The developed structure contains a selectively formed buried PHS (plated heat sink) instead of having thick backside gold metal. In this FET, the thickness of the substrate under the active layer, which produces heat during operation, is set to be 30 /spl mu/m with a buried 70 /spl mu/m thick gold plated heat sink for achieving low thermal resistance, and the thickness of other portion of the chip is set to be 100 /spl mu/m for low loss in microstrip lines and sufficient mechanical strength. This FET structure has provided higher power output and power added efficiency with great simplicity of wafer and chip handling. The experimental results have shown that an FET, of 1350 /spl mu/m gate width, has achieved a superior low thermal resistance of 16/spl deg/C/W corresponding to a maximum channel temperature of 42.1/spl deg/C. RF performances, at V/sub ds/=7 V, show a power output as high as 27.9 dBm with a power added efficiency of 32% at the 1 dB power compression point and a linear gain of 8.3 dB all at 18 GHz. It also has achieved an excellent power density of 0.54 W/mm at V/sub ds/=8 V. This structure has shown mechanical reliability which conforms to MIL-STD-883. >

Operational characteristics of a pulse-sustained dc-excited transverse-flow cw CO2 laser of 5-kW output power

Abstract: Performance characteristics of a transverse-gas-flow cw CO2 laser in which dc discharge was sustained by simultaneous application of high-repetition-rate, high-voltage, short-duration electrical pulses are presented. This excitation scheme enabled maintaining a stable and uniform discharge with electrical input power density more than 15 W/cm3 in a typical laser gas mixture of 2 mbar CO2, 14 mbar N2, and 30 mbar He. Maximum laser power of 5.2 kW was obtained with 15% electro-optic efficiency from a pair of active regions each of 1-rn length incorporated with a folded stable optical resonator. The effect of water vapor on laser performance is also discussed.

High-power twin-beam gyrotrons operating at the second gyrofrequency harmonic

Abstract: The results of two experiments with a gyrotron operating at the second gyrofrequency harmonic, using two active electron beams, are reported. The internal (additional) beam is coupled weakly to the field by a spurious mode. The currents of the two beams can be controlled independently. The output characteristics of the gyrotons are plotted for various beam currents. The additional beam substantially enhances the operating mode stability and makes an appreciable contribution to the output power. The maximum output power was 0.87 MW at 25% efficiency, beam currents of 57 A and 13 A, and voltage 60 kV. The highest efficiency was 40%. The results suggest that electron-optical systems with two active beams, regardless of some complications of gun design, are promising for short-wave gyrotrons to operate at the fundamental cyclotron resonance. The specific power dissipation in the collector is observed to decrease (in comparison with a single-beam analog).

Solid material evaporation into an electron cyclotron resonance source by laser ablation

Abstract: In an effort to explore new methods of producing ion beams from solid materials, a laser‐ablation technique for evaporating materials directly into an electron cyclotron resonance (ECR) ion source plasma was developed. A pulsed NdYaG laser with approximately 25 W average power and peak power density on the order of 107 W/cm2 has been used off‐line to measure ablation rates of various materials as a function of peak laser power. The benefits anticipated from the successful demonstration of this technique include the ability to use very small quantities of materials efficiently, improved material efficiency of incorporation into the ECR plasma, and decoupling of the material evaporation process from the ECR source tuning operation. The results of these tests are reported herein and the design is described for incorporating such a system directly with the Argonne Tandem Linac Accelerator System Positive Ion Injector ECR (ATLAS PII‐ECR) ion source.

First ohmic H modes in ALCATOR C-MOD

Abstract: Ohmic H modes have been achieved in ALCATOR C-MOD with toroidal fields up to BT ≈ 5.25 T and line averaged densities up to ne ≈ 1.4 × 1020 m-3 with less than 1 MW of input power. In ELM-free cases at lower toroidal fields, the energy confinement increases by at least 60% and the particle confinement increases by more than a factor of two. The ELM-free H modes appear to fit the threshold power scaling observed on other tokamaks, P/S (MW/m2)=4.4 × 10-3 neBT (1019 m-3.T), up to power densities of about 0.15 MW/m2. At higher toroidal fields, ELMy H modes were observed after the injection of lithium pellets at about half of the scaled threshold power density. All of these results were obtained with molybdenum plasma facing components and the ELM-free H modes were obtained without boronization or other wall coatings

Magnetic and electromagnetic circuit components having embedded magnetic material in a high density interconnect structure

Abstract: A magnetic or electromagnetic circuit component includes an embedded magnetic material (e.g., ferromagnetic) in an HDI structure with alternating dielectric and metal or winding layers. In one embodiment, the ferromagnetic material is situated in a substrate well, or cavity, with or without an adhesive. Alternatively, the ferromagnetic material is co-fired with the ceramic substrate and then machined to achieve a required core shape. An electroplating process is employed to construct the metal layers, such process including differential plating for varying the thickness of metal layers and/or other portions of the circuit. Laser ablation or any other suitable technique is employed to make through-holes for insertion of the posts of a ferromagnetic core plate used to complete a magnetic circuit, if required. Advantageously, a magnetic or electromagnetic component may have a height of less than about 0.1 inch. Furthermore, such magnetic or electromagnetic circuit components allow for very low inductance interconnections between these components and other circuit elements. Moreover, in a power supply, for example, not only can the complete power supply be built using HDI technology, but power density is increased at relatively low cost and at a high level of reproducibility.

Emittance theory for thin film selective emitter

Abstract: Thin films of high temperature garnet materials such as yttrium aluminum garnet (YAG) doped with rare earths are currently being investigated as selective emitters. This paper presents a radiative transfer analysis of the thin film emitter. From this analysis the emitter efficiency and power density are calculated. Results based on measured extinction coefficients for erbium-YAG and holmium-YAG are presented. These results indicated that emitter efficiencies of 50 percent and power densities of several watts/sq cm are attainable at moderate temperatures (less than 1750 K).

Aluminum fuel cell power sources for long range unmanned underwater vehicles

Abstract: Two aluminum fuel cell power sources have been developed by Alupower for unmanned underwater vehicle propulsion based on solids management and solids free variants of the technology. The solids managed aluminum fuel cell power source will exceed the ARPA defined requirements in terms of energy and power density if liquid oxygen is used as the oxidant supply. For higher power density applications, the solids free aluminum fuel cell power source can provide 60 kWh at 3 kW from a 4-foot long section of a 21-inch diameter vehicle. Higher power density and energy density versions of both the solids managed and solids free aluminum fuel cell power source requires the development of open cycle systems. The life cycle costs of an aluminum fuel cell power source are lower than those of a silver-zinc battery averaged over 100 vehicle missions.

Target ablation characteristics during pulsed laser deposition of thin films

Abstract: A theoretical study into the target ablation characteristics during pulsed laser deposition of thin films was performed. The optical properties (absorption coefficient, reflectivity), power density of the laser pulse and thermophysical properties of the material including thermal conductivity, heat capacity, etc., control the nature of the evaporation process. Based on the laser target interactions, two separate heating regimes, depending on the thermal diffusion distance and the absorption coefficient of the target, have been identified: (i) the surface heating regime in which the laser energy is deposited near the target surface, and (ii) the volume heating regime in which a volume of the solid material is heated by the laser pulse. In both these regimes, vaporization of the target can proceed either by planar surface etching or by volume etching in which solid material may be ejected from the target surface. The thermophysical and the optical properties of the target, and the laser parameters determine the specific nature of the ablation regime. Volume ablation is more likely to occur in the volume heating regime where target absorption coefficients for the incident laser beam are relatively small. The theoretical aspects of both these heating regimes are investigated in detail. The effect of plasma absorption in controlling the ablation characteristics is also theoretically investigated.

Radiative performance of rare earth garnet thin film selective emitters

Abstract: In this paper we present the first emitter efficiency results for the thin film 40 percent Er-1.5 percent Ho YAG (Yttrium Aluminum Garnet, Y3Al5O12) and 25 percent Ho YAG selective emitter at 1500 K with a platinum substrate. Spectral emittance and emissive power measurements were made (1.2 less than lambda less than 3.2 microns). Emitter efficiency and power density are significantly improved with the addition of multiple rare earth dopants. Predicted efficiency results are presented for an optimized (equal power density in the Er, (4)I(sub 15/2)-(4)I(sub 13/2) at 1.5 microns, and Ho, (5)I(sub 7)-(5)I(sub 8) at 2.0 micron emission bands) Er-Ho YAG thin film selective emitter.

Microwave power performance of InP-based double heterojunction bipolar transistors for C- and X-band applications

Abstract: We report on the microwave performance of InP-based double heterojunction bipolar transistors (DHBT) for X-band and C-band applications with power cells operating at an output power greater than 2 W. Our power performance characterization indicated a combination of high power density and high efficiency at both 4.5 and 9 GHz. At 4.5 GHz we measured over 2 W output power (4.3 W/mm power density) and a peak power-added-efficiency (PAE) of 60%. AT 9 GHz the peak measured power was over 1 W (5 W/mm) and the peak PAE was 60%. These are the first reports of substantial microwave power performance in this new device technology based on the InP material system. >

1 W Ku-band AlGaAs/GaAs power HBTs with 72% peak power-added efficiency

Abstract: High power and high-efficiency multi-finger HBTs (heterojunction bipolar transistors) have been successfully realized at Ku-band by using emitter ballasting resistors and a PHS (plated heat sink) structure. An output power of 1 W with power added efficiency (PAE) of 72% at 12 GHz has been achieved from a ten-finger HBT with the total emitter size of 300 /spl mu/m/sup 2/. 72% PAE with the output power density of 5.0 W/mm is the best performance in the HBTs of which the output powers are more than 1 W at Ku-band. >