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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1979

Trends and Techniques for Space Base Electronics

Simulations of various phosphorus and boron diffusions in SOS were completed and a sputtering system, furnaces, and photolithography related equipment were set up. Double layer metal experiments initially utilized wet chemistry techniques. By incorporating ultrasonic etching of the vias, premetal cleaning a modified buffered HF, phosphorus doped vapox, and extended sintering, yields of 98% were obtained using the standard test pattern. A two dimensional modeling program was written for simulating short channel MOSFETs with nonuniform substrate doping. A key simplifying assumption used is that the majority carriers can be represented by a sheet charge at the silicon dioxide silicon interface. Although the program is incomplete, the two dimensional Poisson equation for the potential distribution was achieved. The status of other Z-D MOSFET simulation programs is summarized.

Trotter, J. D.↗
NASA NTRS2010

Method for selective CMP of polysilicon

A method of removing polysilicon in preference to silicon dioxide and/or silicon nitride by chemical mechanical polishing. The method removes polysilicon from a surface at a high removal rate while maintaining a high selectivity of polysilicon to silicon dioxide and/or a polysilicon to silicon nitride. The method is particularly suitable for use in the fabrication of MEMS devices.

Babu, Suryadevara V.↗
NASA NTRS1983

Surface acoustic wave/silicon monolithic sensor/processor

A new technique for sputter deposition of piezoelectric zinc oxide (ZnO) is described. An argon-ion milling system was converted to sputter zinc oxide films in an oxygen atmosphere using a pure zinc oxide target. Piezoelectric films were grown on silicon dioxide and silicon dioxide overlayed with gold. The sputtered films were evaluated using surface acoustic wave measurements, X-ray diffraction, scanning electron microscopy, Auger electron spectroscopy, and resistivity measurements. The effect of the sputtering conditions on the film quality and the result of post-deposition annealing are discussed. The application of these films to the generation of surface acoustic waves is also discussed.

Kowel, S. T.↗
NASA NTRS2006

Stability Enhancement of Polymeric Sensing Films Using Fillers

Experiments have shown the stability enhancement of polymeric sensing films on mixing the polymer with colloidal filler particles (submicron-sized) of carbon black, silver, titanium dioxide, and fumed silicon dioxide. The polymer films are candidates for potential use as sensing media in micro/nano chemical sensor devices. The need for stability enhancement of polymer sensing films arises because such films have been found to exhibit unpredictable changes in sensing activity over time, which could result in a possible failure of the sensor device. The changes in the physical properties of a polymer sensing film caused by the sorption of a target molecule can be measured by any of several established transduction techniques: electrochemical, optical, calorimetric, or piezoelectric, for example. The transduction technique used in the current polymer stability experiments is based on piezoelectric principles using a quartz-crystal microbalance (QCM). The surface of the QCM is coated with the polymer, and the mass uptake by the polymer film causes a change in the oscillating frequency of the quartz crystal. The polymer used for the current study is ethyl cellulose. The polymer/ polymer composite solutions were prepared in 1,3 dioxolane solvent. The filler concentration was fixed at 10 weight percent for the composites. The polymer or polymer composite solutions were cast on the quartz crystal having a fundamental frequency of about 6 MHz. The coated crystal was subjected to a multistage drying process to remove all measurable traces of the solvent. In each experiment, the frequency of oscillation was measured while the QCM was exposed to clean, dry, flowing air for about 30 minutes, then to air containing a known concentration of isopropanol for about 30 minutes, then again to clean dry air for about 30 minutes, and so forth. This cycle of measurements for varying isopropanol concentrations was repeated at intervals for several months. The figure depicts some of the sensing film stability results for ethyl cellulose polymer, ethyl cellulose-carbon black, and ethyl cellulose-silicon dioxide composite systems. An ethyl cellulose film exhibited a marked decline in response in the first few months of study and settled to a steady average response after about four months. However, response varied widely around the average response for ethyl cellulose film. In contrast, ethyl cellulose- carbon black and ethyl cellulose-silicon dioxide composites also declined in the early months, but showed more repeatable sensing film activity after the initial decline. Similar trends were observed in experiments for ethyl cellulose-titanium dioxide and ethyl cellulose-silver composites.

Lin, Brian↗
NASA NTRS2010

Efficient thermoelectric device

A high efficiency thermo electric device comprising a multi nanolayer structure of alternating insulator and insulator/metal material that is irradiated across the plane of the layer structure with ionizing radiation. The ionizing radiation produces nanocrystals in the layered structure that increase the electrical conductivity and decrease the thermal conductivity thereby increasing the thermoelectric figure of merit. Figures of merit as high as 2.5 have been achieved using layers of co-deposited gold and silicon dioxide interspersed with layers of silicon dioxide. The gold to silicon dioxide ratio was 0.04. 5 MeV silicon ions were used to irradiate the structure. Other metals and insulators may be substituted. Other ionizing radiation sources may be used. The structure tolerates a wide range of metal to insulator ratio.

Ila, Daryush↗
NASA NTRS1985

Protection of solar array blankets from attack by low earth orbital atomic oxygen

The ram impact of low earth orbital atomic oxygen causes oxidation of spacecraft materials including polymers such as polyimides. The rate of oxidation is sufficiently high to potentially compromise the long term durability of Kapton solar array blankets. Ion beam sputter deposited atomic oxygen protective coatings of aluminum oxide, silicon dioxide, and codeposited silicon dioxide with small amounts of polytetrafluoroethylene were evaluated both in RF plasma asher tests and in low earth orbit. Deposition techniques, mechanical properties, and atomic oxygen protection performance are presented.

Banks, Bruce A.↗
NASA NTRS1990

Electron beam induced damage in PECVD Si3N4 and SiO2 films on InP

Phosphorus rich plasma enhanced chemical vapor deposition (PECVD) of silicon nitride and silicon dioxide films on n-type indium phosphide (InP) substrates were exposed to electron beam irradiation in the 5 to 40 keV range for the purpose of characterizing the damage induced in the dielectic. The electron beam exposure was on the range of 10(exp -7) to 10(exp -3) C/sq cm. The damage to the devices was characterized by capacitance-voltage (C-V) measurements of the metal insulator semiconductor (MIS) capacitors. These results were compared to results obtained for radiation damage of thermal silicon dioxide on silicon (Si) MOS capacitors with similar exposures. The radiation induced damage in the PECVD silicon nitride films on InP was successfully annealed out in an hydrogen/nitrogen (H2/N2) ambient at 400 C for 15 min. The PECVD silicon dioxide films on InP had the least radiation damage, while the thermal silicon dioxide films on Si had the most radiation damage.

Pantic, Dragan M.↗
NASA NTRS1989

Electron-beam induced damage in thin insulating films on compound semiconductors

Phosphorus rich plasma enhanced chemical vapor deposition (PECVD) of silicon nitride and silicon dioxide films on n-type indium phosphide (InP) substrates were exposed to electron-beam irradiation in the 5 to 40 keV range for the purpose of characterizing the damage induced in the dielectric. The electron-beam exposure was on the range of 10(exp -7) to 10(exp -3) C/sq cm. The damage to the devices was characterized by capacitance-voltage (C-V) measurements of the metal insulator semiconductor (MIS) capacitors. These results were compared to results obtained for radiation damage of thermal silicon dioxide on silicon (Si) MOS capacitors with similar exposures. The radiation induced damage in the PECVD silicon nitride films on InP was successfully annealed out in an hydrogen/nitrogen (H2/N2) ambient at 400 C for 15 min. The PECVD silicon dioxide films on InP had the least radiation damage, while the thermal silicon dioxide films on Si had the most radiation damage.

Pantic, Dragan M.↗
NASA NTRS1990

Method of fabricating germanium and gallium arsenide devices

A method of semiconductor diode fabrication is disclosed which relies on the epitaxial growth of a precisely doped thickness layer of gallium arsenide or germanium on a semi-insulating or intrinsic substrate, respectively, of gallium arsenide or germanium by either molecular beam epitaxy (MBE) or by metal-organic chemical vapor deposition (MOCVD). The method involves: depositing a layer of doped or undoped silicon dioxide on a germanium or gallium arsenide wafer or substrate, selectively removing the silicon dioxide layer to define one or more surface regions for a device to be fabricated thereon, growing a matched epitaxial layer of doped germanium or gallium arsenide of an appropriate thickness using MBE or MOCVD techniques on both the silicon dioxide layer and the defined one or more regions; and etching the silicon dioxide and the epitaxial material on top of the silicon dioxide to leave a matched epitaxial layer of germanium or gallium arsenide on the germanium or gallium arsenide substrate, respectively, and upon which a field effect device can thereafter be formed.

Jhabvala, Murzban↗
NASA NTRS2006

Silicon-Based Optical Modulator with Ferroelectric Layer

According to a proposal, a silicon dioxide layer in a high-speed, low-power, silicon- based electro-optical modulator would be replaced by a layer of lead zirconate titanate or other ferroelectric oxide material. The purpose of this modification is to enhance the power performance and functionality of the modulator. In its unmodified form, the particular silicon- based electro-optical modulator is of an advanced design that overcomes the speed limitation of prior silicon-based electro- optical modulators. Whereas modulation frequencies of such devices had been limited to about 20 MHz, this modulator can operate at modulation frequencies as high as 1 GHz. This modulator can be characterized as a silicon-waveguide-based metal oxide/semiconductor (MOS) capacitor phase shifter in which modulation of the index of refraction in silicon is obtained by exploiting the free-charge-carrier-plasma dispersion effect. As shown in the figure, the modulator includes an n-doped crystalline silicon slab (the silicon layer of a silicon- on-insulator wafer) and a p-doped polycrystalline silicon rib with a gate oxide layer (the aforementioned silicon dioxide layer) sandwiched between them. Under accumulation conditions, the majority charge carriers in the silicon waveguide modify the index of refraction so that a phase shift is induced in the optical mode propagating in the waveguide. The advantage of using an MOS capacitor phase shifter is that it is possible to achieve high modulation speed because there are no slow carrier-generation or -recombination processes involved in the accumulation operation. The main advantage of the proposed substitution of a ferroelectric oxide layer for the silicon dioxide layer would arise from the spontaneous polarization effect of the ferroelectric layer: This spontaneous polarization would maintain accumulation conditions in the absence of applied voltage. Consequently, once the device had been switched to a given optical state, it would remain in that state, even in the absence of applied voltage (in other words, even with power turned off). A secondary advantage is that because the ferroelectric layer would have an index of refraction larger than that of silicon dioxide, there could be some reduction of optical losses attributable to fabrication of the modulator

Sheldon, Douglas↗
NASA NTRS1982

Tribological properties of sintered polycrystalline and single crystal silicon carbide

Tribological studies and X-ray photoelectron spectroscopy analyses were conducted with sintered polycrystalline and single crystal silicon carbide surfaces in sliding contact with iron at various temperatures to 1500 C in a vacuum of 30 nPa. The results indicate that there is a significant temperature influence on both the friction properties and the surface chemistry of silicon carbide. The main contaminants on the as received sintered polycrystalline silicon carbide surfaces are adsorbed carbon, oxygen, graphite, and silicon dioxide. The surface revealed a low coefficient of friction. This is due to the presence of the graphite on the surface. At temperatures of 400 to 600 C graphite and copious amount of silicon dioxide were observed on the polycrystalline silicon carbide surface in addition to silicon carbide. At 800 C, the amount of the silicon dioxide decreased rapidly and the silicon carbide type silicon and carbon peaks were at a maximum intensity in the XPS spectra. The coefficients of friction were high in the temperature range 400 to 800 C. Small amounts of carbon and oxygen contaminants were observed on the as received single crystal silicon carbide surface below 250 C. Silicon carbide type silicon and carbon peaks were seen on the silicon carbide in addition to very small amount of graphite and silicon dioxide at temperatures of 450 to 800 C.

Miyoshi, K.↗
NASA NTRS1991

Whiskerless Schottky diode

A Schottky diode for millimeter and submillimeter wave applications is comprised of a multi-layered structure including active layers of gallium arsenide on a semi-insulating gallium arsenide substrate with first and second insulating layers of silicon dioxide on the active layers of gallium arsenide. An ohmic contact pad lays on the silicon dioxide layers. An anode is formed in a window which is in and through the silicon dioxide layers. An elongated contact finger extends from the pad to the anode and a trench, preferably a transverse channel or trench of predetermined width, is formed in the active layers of the diode structure under the contact finger. The channel extends through the active layers to or substantially to the interface of the semi-insulating gallium arsenide substrate and the adjacent gallium arsenide layer which constitutes a buffer layer. Such a structure minimizes the effect of the major source of shunt capacitance by interrupting the current path between the conductive layers beneath the anode contact pad and the ohmic contact. Other embodiments of the diode may substitute various insulating or semi-insulating materials for the silicon dioxide, various semi-conductors for the active layers of gallium arsenide, and other materials for the substrate, which may be insulating or semi-insulating.

Bishop, William L.↗
NASA NTRS1994

Protective coating for ceramic materials

A protective coating for ceramic materials such as those made of silicon carbide, aluminum oxide, zirconium oxide, aluminoborosilicate and silicon dioxide, and a thermal control structure comprising a ceramic material having coated thereon the protective coating. The protective coating contains, in admixture, silicon dioxide powder, colloidal silicon dioxide, water, and one or more emittance agents selected from silicon tetraboride, silicon hexaboride, silicon carbide, molybdenum disilicide, tungsten disilicide and zirconium diboride. In another aspect, the protective coating is coated on a flexible ceramic fabric which is the outer cover of a composite insulation. In yet another aspect, a metallic foil is bonded to the outer surface of a ceramic fabric outer cover of a composite insulation via the protective coating. A primary application of this invention is as a protective coating for ceramic materials used in a heat shield for space vehicles subjected to very high aero-convective heating environments.

Kourtides, Demetrius A.↗
NASA NTRS1979

A study of trends and techniques for space base electronics

The use of dry processing and alternate dielectrics for processing wafers is reported. A two dimensional modeling program was written for the simulation of short channel MOSFETs with nonuniform substrate doping. A key simplifying assumption used is that the majority carriers can be represented by a sheet charge at the silicon dioxide-silicon interface. In solving current continuity equation, the program does not converge. However, solving the two dimensional Poisson equation for the potential distribution was achieved. The status of other 2D MOSFET simulation programs are summarized.

Trotter, J. D.↗
NASA NTRS1983

Sputtering of silicon and its compounds in the electronic stopping region

Silicon, silicon dioxide, and silicon nitride have been sputtered with chlorine ions at 5 MeV and 20 MeV. While the yield from the silicon target was unmeasurably low, the insulating compounds exhibited the enhanced yields observed in other insulating targets. The yield follows the electronic stopping power and seems to be independent of the target's thermal properties. Some of the data suggest that the enhanced sputtering mechanism may be active in extremely thin films (not less than 3 monolayers).

Qiu, Y.↗
NASA NTRS1989

Variable-Energy Ion Beams For Modification Of Surfaces

Beam of low-energy negative oxygen ions used to grow layer of silicon dioxide on silicon. Beam unique both in purity, contains no molecular oxygen or other charged species, and in low energy, which is insufficient to damage silicon by physically displacing atoms. Low-energy growth accomplished with help of ion-beam apparatus. Directs electrons into crosswise stream of gas, generating stream of negative ions. Pair of charged plates separates ions from accompanying electrons and diverts ion beam to target - silicon substrate. Diameter of beam at target 0.5 to 0.75 cm. Promises useful device to study oxidation of semiconductors and, in certain applications, to replace conventional oxidation processes.

Chutjian, Ara↗
NASA NTRS1999

Monte Carlo Simulation of Nanoparticle Encapsulation in Flames

Gas-phase combustion (flame) synthesis has been an essential industrial process for producing large quantities of powder materials such as carbon black, titanium dioxide, and silicon dioxide. Flames typically produce simple oxides, with carbon black being the noted exception because the oxides of carbon are gaseous and are easily separated from the particulate matter that is formed during fuel pyrolysis. Furthermore, the powders produced in flames are usually agglomerated, nanometer-sized particles (nanoparticles). This composition and morphology is acceptable for many applications. However, the present interest in nanoparticles for advanced materials application has led to efforts to employ flames for the synthesis of unagglomerated nanoparticles (2 to 100 nm) of metals and non-oxide ceramics. Sodium-halide chemistry has proven to be viable for producing metals and non-oxide ceramics in flames. Materials that have been produced to date include Si (Calcote and Felder, 1993), TiN, TiB2, TiC, TiSi2, SiC, B4C (Glassman et al, 1993) Al, W, Ti, TiB2, AlN, and W-Ti and Al-AlN composites (DuFaux and Axelbaum, 1995, Axelbaum et al 1996,1997). Many more materials are possible. The main challenge that faces application of flame synthesis for advanced materials is overcoming formation of agglomerates in flames (Brezinsky, 1997). The high temperatures and high number densities in the flame environment favor the formation of agglomerates. Agglomerates must be avoided for many reasons. For example, when nanopowders are consolidated, agglomerates have a deleterious effect on compaction density, leading to voids in the final part. Efforts to avoid agglomeration in flames without substantially reducing particle number density and, consequently, production rate, have had limited success. Another critical challenge that faces all synthesis routes for nanopowders is ensuring that the powders are high purity and that the process is scaleable. Though the containerless, high temperature environment of a flame is excellent for producing high-purity simple compounds, ultrafine metals and non-oxide ceramic powders are inherently reactive in the presence of oxygen and/or moisture. Thus, the handling of these powders after synthesis poses a challenging problem. Impurities acquired during handling of nanoparticles have plagued the advancement of nanostructured materials technology.

Sun, Z.↗