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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Advanced detectors and signal processing for bubble memories

The feasibility of combining silicon and magnetic bubble technologies is demonstrated. Results of bubble film annealing indicate that a low temperature silicon on garnet technology is the most likely one to succeed commercially. Annealing ambients are also shown to have a major effect on the magnetic properties of bubble films. Functional MOSFETs were fabricated on bubble films coated with thick (approximately 1 micron) SiO2 layers. The two main problems with these silicon on garnet MOSFETs are low electron mobilities and large gate leakage currents. Results indicate that the laser recrystallized silicon and gate oxide (SiO2) layers are contaminated. The data suggest that part of the contaminating ions originate in the sputtered oxide spacer layer and part originates in the bubble film itself. A diffusion barrier, such as silicon nitride, placed between the bubble film and the silicon layer should eliminate the contamination induced problem.

Kryder, M. H.↗
NASA NTRS1986

Fabrication of an X-Ray Imaging Detector

X-ray detector array yields mosaic image of object emitting 1- to 30-keV range fabricated from n-doped silicon wafer. In proposed fabrication technique, thin walls of diffused n+ dopant divide wafer into pixels of rectangular cross section, each containing central electrode of thermally migrated p-type metal. This pnn+ arrangement reduces leakage current by preventing transistor action caused by pnp structure of earlier version.

Alcorn, G. E.↗
NASA NTRS1986

The aging correlation (RH + t): Relative humidity (%) + temperature (deg C)

An aging correlation between corrosion lifetime, and relative humidity RH (%) and temperature t (C) has been reported in the literature. This aging correlation is a semi-log plot of corrosion lifetime on the log scale versus the interesting summation term RH(%) + t(C) on the linear scale. This empirical correlation was derived from observation of experimental data trends and has been referred to as an experimental law. Using electrical resistivity data of polyvinyl butyral (PVB) measured as a function of relative humidity and temperature, it was found that the electrical resistivity could be expressed as a function of the term RH(%) t(C). Thus, if corrosion is related to leakage current through an organic insulator, which, in turn, is a function of RH and t, then some partial theoretical validity for the correlation is indicated. This article describes the derivation of the term RH(%) t(C) from PVB electrical resistivity data.

Cuddihy, E. F.↗
NASA NTRS1985

Moisture-temperature degradation in module encapsulants: The general problem of moisture in photovoltaic encapsulants

A general research approach was outlined toward understanding water-module interactions and the influence of temperature involving the need to: quantify module performance loss versus level of accumulated degradation, establish the dependence of the degradation reaction rate on module moisture and temperature levels, and determine module moisture and temperature levels in field environments. These elements were illustrated with examples drawn from studies of the now relatively well understood module electrochemical degradation process. Research data presented include temperature and humidity-dependent equilibrium leakage current values for multiparameter module material and design configurations. The contributions of surface, volume, and interfacial conductivities was demonstrated. Research directions were suggested to more fully understand the contributions to overall module conductivity of surface, volume, and interfacial conductivities over ranges of temperature and relative humidity characteristic of field environments.

Mon, G. R.↗
NASA NTRS1985

Preliminary study: Moisture-polymer interaction. Stuby objectives

The problems associated with mathematically modeling water-module interaction phenomena, including sorption and desorption, diffusion, and permeation are discussed. With reliable analytical models, an extensive materials data base, and solar radiation surface meteorological observations (SOLMET) weather data, predicting module lifetimes in realistic environments can become a practical reality. The status of the present techniques of simulating the various transport mechanisms was reported. The Dent model (a modified Brunauer-Emmet-Teller) approach represented polyvinyl butyral (PVB) sorption data. A 100-layer material model and Fick's diffusion model gave diffusivity values exhibiting adequate agreement with those measured for PVB. Diffusivity of PVB is concentration dependent, decreasing as the water content in PVB increases. The temperature dependence of diffusion in PVB is well modeled by the Arrhenius rate equation. Equilibrium conductivity and leakage current data are well represented by Hearle's model for bulk ionic conductivity. A nodal network analysis using the Systems Improved Numerical Differencing Analyzer (SINDA) Thermal Analyzer gave reasonable correlation with measurable data. It is concluded that realistic lifetime predictions seem to be feasible.

Wen, L. C.↗
NASA NTRS1987

LEO high voltage solar array arcing response model

A series of mathematical models were developed that describe the electrical behavior of a large solar cell array floating electrically in the low Earth orbit (LEO) space plasma and struck by an arc at a point of negative bias. There are now three models in this series: ARCII, which is a fully analytical, linearized model; ARCIII, which is an extension of ARCIII that includes solar cell inductance as well as load reactance; Nonlinear ARC, which is a numerical model able to treat effects such as non-linearized, i.e., logarithmic solar cell I/V characteristics, conductance switching as a solar cell crosses plasma ground on a voltage excursion and non-ohmic plasma leakage current collection.

Metz, Roger N.↗
NASA NTRS1987

Water-absorbing capacitor system for measuring relative humidity

A method and apparatus using a known water-absorbent polymer as a capacitor which is operated at a dc voltage for measuring relative humidity is presented. When formed as a layer between porous electrically-conductive electrodes and operated in an RC oscillator circuit, the oscillator frequency varies inversely with the partial pressure of the moisture to be measured. In a preferred embodiment, the capacitor is formed from Nafion and is operated at a low dc voltage with a resistor as an RC circuit in an RC oscillator. At the low voltage, the leakage current is proper for oscillation over a satisfactory range. The frequency of oscillation varies in an essentially linear fashion with relative humidity which is represented by the moisture being absorbed into the Nafion. The oscillation frequency is detected by a frequency detector.

Laue, Eric G.↗
NASA NTRS1987

Optical communication with semiconductor laser diodes

A 25 megabit/sec direct detection optical communication system that used Q=4 PPM signalling was constructed and its performance measured under laboratory conditions. The system used a single-mode AlGaAs laser diode transmitter and low noise silicon avalanche photodiode (APD) photodetector. Comparison of measured performance with the theoretical revealed that modeling the APD output as a Gaussian process under conditions of negligible background radiation and low (less than 10 to the -12 power A) APD bulk leakage currents leads to substantial underestimates of optimal APD gain to use and overestimates of system bit error probability. A procedure is given to numerically compute system performance which uses the more accurate Webb's Approximation of the exact Conradi distribution for the APD ouput signal that does not require excessive amounts of computer time (a few minutes of VAX 8600 CPU time per system operating point). Examples are given which illustrate the breakdown of the Gaussian approximation in assessing system performance. This system achieved a bit error probability of 10 to the -6 power at a received signal energy corresponding to an average of 60 absorbed photons/bit and optimal APD gain of 700.

Davidson, F.↗
NASA NTRS1988

Space station induced electromagnetic effects

Several mechanisms which can cause electric (E) and magnetic (B) field contaminations of the Space Station environment are identified. The level of E and B fields generated by some of them such as the motion of the vehicle across the ambient magnetic field B(0) and the 20-kHz leakage currents and charges can be controlled by proper design considerations. On the other hand, there are some mechanisms which are inherent to the interaction of large vehicles with the plasma and probably their contributions to E and B fields cannot be controlled; these include plasma waves in the wake and ram directions and the effects of the volume current generated by the ionization of neutrals. The interaction of high-voltage solar arrays with plasma is yet another rich source of E and B fields and it is probably uncontrollable. Wherever possible, quantitative estimates of E and B are given. A set of recommendations is included for further study in areas where indepth knowledge is seriously lacking.

Singh, N.↗
NASA NTRS1987

Encapsulant free-surfaces and interfaces: Critical parameters in controlling cell corrosion

Results are reported of studying the interaction of moisture with photovoltaic (PV) modules and custom-built test coupons in both laboratory and outdoor ambient environments. Characteristics measured included module cell-to-frame leakage currents, encapsulant bulk and surface currents, glass surface currents, and encapsulant/glass interface currents as functions of temperature and humidity. Using a computer model of interelectrode conduction, preferential conduction paths in PVB- and EVA-encapsulated modules are identified. In comparing the results of field and laboratory test environments on identical samples, comments are made about the greater severity of the outdoor environment. Several aspects of water-module interaction, including design strategies and continuing research, are discussed.

Mon, G.↗
NASA NTRS1988

Barrier height enhancement of InP-based n-Ga(0.47)In(0.53)As Schottky-barrier diodes grown by molecular beam epitaxy

Barrier height enhancement of an InP-based p(+)n-Ga(0.47)In(0.53)As Schottky diode grown by MBE has been demonstrated for infra-red photodetector applications. A barrier height of 0.35 eV for n-Ga(0.47)In(0.53)As Schottky barrier diodes, was increased to the effective barrier height of 0.55 eV, with a p(+)-Ga(0.47)In(0.53)As surface layer of 30 nm thick. The results show a reverse leakage current density of 0.0015 A/sq cm and a junction capacitance of 0.3 pF, which are comparable to those of p-Ga(0.47)In(0.53)As Schottky-barrier diodes at a reverse bias voltage of 5 V.

Kim, J. H.↗
NASA NTRS1988

Gaussian approximation versus nearly exact performance analysis of optical communication systems with PPM signaling and APD receivers

A 25-Mb/s direct-detection optical communication system that used Q = 4 PPM (pulse-position modulation) signaling was constructed and its performance measured under laboratory conditions. The system used a single-mode AlGaAs laser diode (lambda = 834 nm) and low-noise silicon avalanche photodiode (APD). A procedure for numerically computing system performance is given that uses the nearly exact Webb approximation of the true Conradi distribution for the APD output and does not require excessive amounts of computer time. Comparison revealed that modeling the APD ouptut as a Gaussian process under conditions of negligible background radiation and low (less than 10 to the -12 A) APD bulk leakage currents leads to substantial underestimates of optimal APD gain and overestimates of system bit error probability. Examples illustrate the breakdown of the Gaussian approximation in assessing system performance. The measured performance was in excellent agreement with that predicted by the computational procedure. The system achieved a bit error probability of 10 to the -6 at a received signal energy, corresponding to an average of 60 absorbed photons/bit and optimal APD gain of 700.

Davidson, Frederic M.↗
NASA NTRS1989

Computer analysis of the negative differential resistance switching phenomenon of double-injection devices

By directly solving the semiconductor differential equations for the double-injection (DI) devices involving two interacting deep levels, the authors studied the negative differential resistance switching characteristic and its relationship with the device dimension, doping level, and dependence on the deep impurity profile. Computer simulation showed that although one can increase the threshold voltage by increasing the device length, the excessive holding voltage that would follow would put this device in a very limited application such as pulse power source. The excessive leakage current in the low conductance state also jeopardizes the attempt to use the device for any practical purpose. Unless there are new materials and deep impurities found that have a great differential hole and electron capture cross sections and a reasonable energy bandgap for low intrinsic carrier concentration, no big improvement in the fate of DI devices is expected in the near future.

Shieh, Tsay-Jiu↗
NASA NTRS1991

Alternative AlxGa1-xAs/GaAs Transistors For Neural Networks

Further development efforts yield alternative version of transistors described in "High-Gain AlxGa1-xAs/GaAs Transistors For Neural Networks" (NPO-18101). Efforts focused on determining effects of various aspects of design and of fabrication processes upon leakage currents and on current gain.

Kim, Jae-Hoon↗
NASA NTRS1991

Electrical characterization of glass, teflon, and tantalum capacitors at high temperatures

Dielectric materials and electrical components and devices employed in radiation fields and the space environment are often exposed to elevated temperatures among other things. Therefore, these systems must withstand the high temperature exposure while still providing good electrical and other functional properties. Experiments were carried out to evaluate glass, teflon, and tantalum capacitors for potential use in high temperature applications. The capacitors were characterized in terms of their capacitance and dielectric loss as a function of temperature up to 200 C. At a given temperature, these properties were obtained in a frequency range of 50 Hz to 100 kHz. The DC leakage current measurements were also performed in a temperature range from 20 to 200 C. The obtained results are discussed and conclusions are made concerning the suitability of the capacitors investigated for high temperature applications.

Hammoud, A. N.↗
NASA NTRS1991

Squeezed photon-number noise and sub-Poissonian electrical partition noise in a semiconductor laser

Amplitude noise on the light from a semiconductor laser produced a photocurrent fluctuation spectrum that was a maximum of 85 percent (-8.3 dB) below the shot-noise limit. Squeezing in semiconductor lasers is not limited by the overall quantum, or current transfer, efficiency from the laser injection current to the detector photocurrent. Current leakage away from the lasing junction does not introduce Poissonian partition noise.

Richardson, W. H.↗
NASA NTRS1992

Electrical properties of teflon and ceramic capacitors at high temperatures

Space power systems and components are often required to operate efficiently and reliably in harsh environments where stresses, such as high temperature, are encountered. These systems must, therefore, withstand exposure to high temperature while still providing good electrical and other functional properties. Experiments were carried out to evaluate Teflon and ceramic capacitors for potential use in high temperature applications. The capacitors were characterized in terms of their capacitance and dielectric loss as a function of temperature, up to 200 C. At a given temperature, these properties were obtained in a frequency range of 50 Hz to 100 kHz. DC leakage current measurements were also performed in a temperature range from 25 to 200 C. The results obtained are discussed and conclusions are made concerning the suitability of the capacitors studied for high temperature applications.

Hammoud, A. N.↗
NASA NTRS1992

PASP Plus: An experiment to measure space-environment effects on photovoltaic power subsystems

The Photovoltaic Array Space Power Plus Diagnostic experiment (PASP Plus) was accepted as part of the APEX Mission payload aboard a Pegastar satellite to be orbited by a Pegasus launch vehicle in late 1992. The mission's elliptical orbit will allow us to investigate both space plasma and space radiation effects. PASP Plus will have eleven types of solar arrays and a full complement of environmental and interactions diagnostic sensors. Measurements of space-plasma interactions on the various solar arrays will be made at large negative voltages (to investigate arcing parameters) and at large positive voltages (to investigate leakage currents) by biasing the arrays to various levels up to -500 and +500 volts. The long-term deterioration in solar array performance caused by exposure to space radiation will also be investigated; radiation dosage will be measured by an electron/proton dosimeter included in the environmental sensor complement. Experimental results from PASP Plus will help establish cause-and-effect relationships and lead to improved design guidelines and test standards for new-technology solar arrays.

Guidice, Donald A.↗