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NASA NTRS1991

Improving the Reliability and Modal Stability of High Power 870 nm AlGaAs CSP Laser Diodes for Applications to Free Space Communication Systems

The operating characteristics (power-current, beam divergence, etc.) and reliability assessment of high-power CSP lasers is discussed. The emission wavelength of these lasers was optimized at 860 to 880 nm. The operational characteristics of a new laser, the inverse channel substrate planar (ICSP) laser, grown by metalorganic chemical vapor deposition (MOCVD), is discussed and the reliability assessment of this laser is reported. The highlights of this study include a reduction in the threshold current value for the laser to 15 mA and a degradation rate of less than 2 kW/hr for the lasers operating at 60 mW of peak output power.

Connolly, J. C.↗

NASA NTRS1992

Double-Current-Confined CSP Laser

Improved channeled-substrate-planar (CSP) lasers that emit at wavelengths between 860 and 880 nm grown by liquid-phase epitaxy (LPE). Exhibit record high output powers and efficiencies, attained without sacrifice of desirable characteristics of lasers. In fabrication, second reverse-bias p/n junction incorporated to reduce required current. By incorporating two reverse-bias junctions in CSP structure, one doubly confines current. Lasers used eventually as sources of light in intersatellite communications systems and, specifically, NASA Advanced Communications Technology Satellite (ACTS) System.

Connolly, John C.↗

NASA NTRS2005

Thermal Catalytic Oxidation of Airborne Contaminants by a Reactor Using Ultra-Short Channel Length, Monolithic Catalyst Substrates

Contaminated air, whether in a crewed spacecraft cabin or terrestrial work and living spaces, is a pervasive problem affecting human health, performance, and well being. The need for highly effective, economical air quality processes spans a wide range of terrestrial and space flight applications. Typically, air quality control processes rely on absorption-based processes. Most industrial packed-bed adsorption processes use activated carbon. Once saturated, the carbon is either dumped or regenerated. In either case, the dumped carbon and concentrated waste streams constitute a hazardous waste that must be handled safely while minimizing environmental impact. Thermal catalytic oxidation processes designed to address waste handling issues are moving to the forefront of cleaner air quality control and process gas decontamination processes. Careful consideration in designing the catalyst substrate and reactor can lead to more complete contaminant destruction and poisoning resistance. Maintenance improvements leading to reduced waste handling and process downtime can also be realized. Performance of a prototype thermal catalytic reaction based on ultra-short waste channel, monolith catalyst substrate design, under a variety of process flow and contaminant loading conditions, is discussed.

Perry, J. L.↗

NASA NTRS1987

Semiconductor structure and devices

Semiconductor devices such as lasers which include a substrate with a channel therein with a clad layer overlying the substrate and filling the channel exhibit irregularities such as terraces in the surface of the clad layer which are detrimental to device performance. These irregularities are substantially eliminated by forming the channel in a surface of a buffer layer greater than about 4 micrometers thick on the substrate and forming the clad layer over the buffer layer and the channel. CW lasers incorporating the principles of the invention exhibit the highest output power in a single spatial mode and maximum output power which have been observed to date.

Dinkel, Nancy A.↗

NASA NTRS2007

Fabrication of Buried Nanochannels From Nanowire Patterns

A method of fabricating channels having widths of tens of nanometers in silicon substrates and burying the channels under overlying layers of dielectric materials has been demonstrated. With further refinement, the method might be useful for fabricating nanochannels for manipulation and analysis of large biomolecules at single-molecule resolution. Unlike in prior methods, burying the channels does not involve bonding of flat wafers to the silicon substrates to cover exposed channels in the substrates. Instead, the formation and burying of the channels are accomplished in a more sophisticated process that is less vulnerable to defects in the substrates and less likely to result in clogging of, or leakage from, the channels. In this method, the first step is to establish the channel pattern by forming an array of sacrificial metal nanowires on an SiO2-on-Si substrate. In particular, the wire pattern is made by use of focused-ion-beam (FIB) lithography and a subsequent metallization/lift-off process. The pattern of metal nanowires is then transferred onto the SiO2 layer by reactive-ion etching, which yields sacrificial SiO2 nanowires covered by metal. After removal of the metal covering the SiO2 nanowires, what remains are SiO2 nanowires on an Si substrate. Plasma-enhanced chemical vapor deposition (PECVD) is used to form a layer of a dielectric material over the Si substrate and over the SiO2 wires on the surface of the substrate. FIB milling is then performed to form trenches at both ends of each SiO2 wire. The trenches serve as openings for the entry of chemicals that etch SiO2 much faster than they etch Si. Provided that the nanowires are not so long that the diffusion of the etching chemicals is blocked, the sacrificial SiO2 nanowires become etched out from between the dielectric material and the Si substrate, leaving buried channels. At the time of reporting the information for this article, channels 3 m long, 20 nm deep, and 80 nm wide (see figure) had been fabricated by this method.

Choi, Daniel↗

NASA NTRS2003

Structure, Function, Self-Assembly and Origin of Simple Membrane Proteins

Integral membrane proteins perform such essential cellular functions as transport of ions, nutrients and waste products across cell walls, transduction of environmental signals, regulation of cell fusion, recognition of other cells, energy capture and its conversion into high-energy compounds. In fact, 30-40% of genes in modem organisms codes for membrane proteins. Although contemporary membrane proteins or their functional assemblies can be quite complex, their transmembrane fragments are usually remarkably simple. The most common structural motif for these fragments is a bundle of alpha-helices, but occasionally it could be a beta-barrel. In a series of molecular dynamics computer simulations we investigated self-organizing properties of simple membrane proteins based on these structural motifs. Specifically, we studied folding and insertion into membranes of short, nonpolar or amphiphatic peptides. We also investigated glycophorin A, a peptide that forms sequence-specific dimers, and a transmembrane aggregate of four identical alpha-helices that forms an efficient and selective voltage-gated proton channel was investigated. Many peptides are attracted to water-membrane interfaces. Once at the interface, nonpolar peptides spontaneously fold to a-helices. Whenever the sequence permits, peptides that contain both polar and nonpolar amino also adopt helical structures, in which polar and nonpolar amino acid side chains are immersed in water and membrane, respectively. Specific identity of side chains is less important. Helical peptides at the interface could insert into the membrane and adopt a transmembrane conformation. However, insertion of a single helix is unfavorable because polar groups in the peptide become completely dehydrated upon insertion. The unfavorable free energy of insertion can be regained by spontaneous association of peptides in the membrane. The first step in this process is the formation of dimers, although the most common are aggregates of 4-7 helices. The helices could arrange themselves such that they formed pores capable of transporting ions and small molecules across membranes. Stability of transmembrane aggregates of simple proteins is often only marginal and, therefore, it can be regulated by environmental signals or small sequence modifications in the region of interhelical interactions. A key step in the earliest evolution of membrane proteins was the emergence of selectivity for specific substrates. Many channels could become selective if one or only a few properly chosen amino acids are properly placed along the channel, acting as filters or gates. This is a convenient evolutionary solution because it does not require imposing conditions on the whole sequence.

Pohorille, Andrew↗

NASA NTRS1998

Micromachined peristaltic pump

A micromachined pump including a channel formed in a semiconductor substrate by conventional processes such as chemical etching. A number of insulating barriers are established in the substrate parallel to one another and transverse to the channel. The barriers separate a series of electrically conductive strips. An overlying flexible conductive membrane is applied over the channel and conductive strips with an insulating layer separating the conductive strips from the conductive membrane. Application of a sequential voltage to the series of strips pulls the membrane into the channel portion of each successive strip to achieve a pumping action. A particularly desirable arrangement employs a micromachined push-pull dual channel cavity employing two substrates with a single membrane sandwiched between them.

Hartley, Frank T.↗

NASA NTRS1978

High resolution masks for ion milling pores through substrates of biological interest

The feasibility was investigated of electrochemically oxidizing vapor deposited aluminum coatings to produce porous aluminum oxide coatings with submicron pore diameters and with straight channels normal to the substrate surface. Porous aluminum oxide coatings were produced from vapor deposited aluminum coatings on thin stainless steel (304), copper, Teflon (FEP) and Kapton substrates and also on pure aluminum substrates. Scanning electron microscope examination indicated that porous oxide coatings can be produced with straight channels, appropriate pore diameters and none or minimal intervening residual aluminum. The oxide coatings on the copper and Kapton substrates had the straightest channels and in general were superior to those fabricated on the other substrate materials. For oxide coatings fabricated at 600 V and 300 V, pore diameters were 0.4-0.6, and 0.3 micron with center-to-center spacing of 0.7-0.8, and 0.4 micron, respectively. Estimated direct labor and materials costs to prepare an oxide mask is anticipated to be about $4-$6 per square foot.

Donovan, S. S.↗

NASA NTRS2004

Microsensor Technologies for Plant Growth System Monitoring

This document covered the following: a) demonstration of feasibility of microsensor for tube and particulate growth systems; b) Dissolved oxygen; c)Wetness; d) Flexible microfluidic substrate with microfluidic channels and microsensor arrays; e)Dynamic root zone control/monitoring in microgravity; f)Rapid prototyping of phytoremediation; and g) A new tool for root physiology and pathology.

Kim, Chang-Soo↗

NASA NTRS1991

Epitaxial yttria-stabilized zirconia on (1 -1 0 2) sapphire for YBa2Cu3O(7-delta) thin films

Epitaxial yttria-stabilized zirconia (YSZ) films were deposited on (1 -1 0 2) sapphire by pulsed laser deposition. The films are formed in a cubic phase with the a axis normal to the substrate surface. Ion beam channeling measurements show that the YSZ films are highly crystalline with a channeling minimum yield of 8 percent. The epitaxial relationship between the film and substrate is further confirmed by a cross-section TEM study. Epitaxial YBa2Cu3O(7-delta) thin films deposited on YSZ/sapphire have Tc and Jc of up to 89 K and 10 to the 6th A/sq cm at 77 K, respectively.

Wu, X. D.↗

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 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 NTRS1990

Low-temperature microwave characteristics of pseudomorphic In(x)Ga(1-x) As/In(0.52)Al(0.48)As modulation-doped field-effect transistors

Low-temperature microwave measurements of both lattice-matched and pseudomorphic In(x)Ga(1-x)As/In(0.48)As (x = 0.53, 0.60, and 0.70) channel MODFETs on InP substrates were carried out in a cryogenic measurement system. The measurements were done in the temperature range of 77 to 300 K and in the frequency range of 0.5 to 11.0 GHz at different bias conditions. The cutoff frequency (fT) for the In(x)Ga(1-x)As/In(0.52)Al(0.48)As MODFETs improved from 22 to 29 GHz, 29 to 38 GHz, and 39 to 51 GHz, for x = 0.53, 0.60, and 0.70, respectively, as the temperature was lowered from 300 to 77 K, which is approximately a 31 percent increase at each composition. No degradations were observed in device performance. These results indicate an excellent potential of the pseudomorphic devices at low temperatures.

Lai, R.↗

NASA NTRS2005

Performance Characterization of a Prototype Ultra-Short Channel Monolith Catalytic Reactor for Air Quality Control Applications

Contaminated air and process gases, whether in a crewed spacecraft cabin atmosphere, the working volume of a microgravity science or ground-based laboratory experiment facility, or the exhaust from an automobile, are pervasive problems that ultimately effect human health, performance, and well-being. The need for highly-effective, economical decontamination processes spans a wide range of terrestrial and space flight applications. Adsorption processes are used widely for process gas decontamination. Most industrial packed bed adsorption processes use activated carbon because it is cheap and highly effective. Once saturated, however, the adsorbent is a concentrated source of contaminants. Industrial applications either dump or regenerate the activated carbon. Regeneration may be accomplished in-situ or at an off-site location. In either case, concentrated contaminated waste streams must be handled appropriately to minimize environmental impact. As economic and regulatory forces drive toward minimizing waste and environmental impact, thermal catalytic oxidation is becoming more attractive. Through novel reactor and catalyst design, more complete contaminant destruction and greater resistance to poisoning can achieved leading to less waste handling, process down-time, and maintenance. Performance of a prototype thermal catalytic reactor, based on ultra-short channel monolith (USCM) catalyst substrate design, under a variety of process flow and contaminant loading conditions is discussed. The experimental results are evaluated against present and future air quality control and process gas purification processes used on board crewed spacecraft.

Perry, J. L.↗

NASA NTRS2009

G(sup 4)FET Implementations of Some Logic Circuits

Some logic circuits have been built and demonstrated to work substantially as intended, all as part of a continuing effort to exploit the high degrees of design flexibility and functionality of the electronic devices known as G(sup 4)FETs and described below. These logic circuits are intended to serve as prototypes of more complex advanced programmable-logicdevice-type integrated circuits, including field-programmable gate arrays (FPGAs). In comparison with prior FPGAs, these advanced FPGAs could be much more efficient because the functionality of G(sup 4)FETs is such that fewer discrete components are needed to perform a given logic function in G(sup 4)FET circuitry than are needed perform the same logic function in conventional transistor-based circuitry. The underlying concept of using G(sup 4)FETs as building blocks of programmable logic circuitry was also described, from a different perspective, in G(sup 4)FETs as Universal and Programmable Logic Gates (NPO-41698), NASA Tech Briefs, Vol. 31, No. 7 (July 2007), page 44. A G(sup 4)FET can be characterized as an accumulation-mode silicon-on-insulator (SOI) metal oxide/semiconductor field-effect transistor (MOSFET) featuring two junction field-effect transistor (JFET) gates. The structure of a G(sup 4)FET (see Figure 1) is the same as that of a p-channel inversion-mode SOI MOSFET with two body contacts on each side of the channel. The top gate (G1), the substrate emulating a back gate (G2), and the junction gates (JG1 and JG2) can be biased independently of each other and, hence, each can be used to independently control some aspects of the conduction characteristics of the transistor. The independence of the actions of the four gates is what affords the enhanced functionality and design flexibility of G(sup 4)FETs. The present G(sup 4)FET logic circuits include an adjustable-threshold inverter, a real-time-reconfigurable logic gate, and a dynamic random-access memory (DRAM) cell (see Figure 2). The configuration of the adjustable-threshold inverter is similar to that of an ordinary complementary metal oxide semiconductor (CMOS) inverter except that an NMOSFET (a MOSFET having an n-doped channel and a p-doped Si substrate) is replaced by an n-channel G(sup 4)FET

Mojarradi, Mohammad↗

NASA NTRS1981

Transient catalytic combustor model

A quasi-steady gas phase and thermally thin substrate model is used to analyze the transient behavior of catalytic monolith combustors in fuel lean operation. The combustor response delay is due to the substrate thermal inertia. Fast response is favored by thin substrate, short catalytic bed length, high combustor inlet and final temperatures, and small gas channel diameters. The calculated gas and substrate temperature time history at different axial positions provides an understanding of how the catalytic combustor responds to an upstream condition change. The computed results also suggest that the gas residence times in the catalytic bed in the after bed space are correlatable with the nondimensional combustor response time. The model also performs steady state combustion calculations; and the computed steady state emission characteristics show agreement with available experimental data in the range of parameters covered. A catalytic combustor design for automotive gas turbine engine which has reasonably fast response ( 1 second) and can satisfy the emission goals in an acceptable total combustor length is possible.

Tien, J. S.↗

NASA NTRS1978

Solar cell collector and method for producing same

A transparent, conductive collector layer containing conductive metal channels is formed as a layer on a photovoltaic substrate by coating a photovoltaic substract with a conductive mixed metal layer. A heat sink having portions protruding from one of its surfaces is attached. These protruding portions define a continuous pattern in combination with recessed regions among them such that they are in contact with the conductive layer of the photovoltaic substrate. Heating the substrate while simultaneously oxidizing the portions of the conductive layer exposed to a gaseous oxidizing substance forced into the recessed regions of the heat sink, creates a transparent metal oxide layer on the substrate. A continous pattern of highly conductive metal channels is contained in the metal oxide layer.

Evans, J. C., Jr.↗

NASA NTRS1977

Optically activated switch/modulator using a photoconductor and two channel waveguides

An optically activated switch was fabricated on LiNbO3 substrate by deposition of photoconductor-metal electrode structure on two channel waveguides obtained by the outdiffusion process. One waveguide was overcoated with a CdS film, and served as a light detector which converted the optical signal in that waveguide into an electric signal. Utilizing the electrooptic effect, this electric signal modulated the light propagating in the second waveguide by changing the refractive index, and the cutoff condition, of the waveguiding channel between two metal electrodes. The waveguides in the optically controlled switch can be either single or multimode. The length of the device can be short in comparison with other switching schemes. When binary optical signals are applied to the two waveguides, the switch can perform logic AND, NEGATION, OR and pseudo-amplification operations.

Goldberg, L.↗