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Pad printer for electronics. Final report

Description: This is the Final report on DARPA-sponsored development Program Pad Printer for Electronics DE-FC04-95AL87486 which was initiated in February, 1995 and intended to run 24 months to February 1997. The Program has significant value to the Thick Film processing industry, an electronic manufacturing alternative for producing functional modules integrated at the multichip level. The result is highly reliable, high volumetric efficiency, subassemblies for military applications and for commercial applications in severe environments, such as automotive, portable communications, and bio-implantable devices. The program progressed quite satisfactorily through 19 months, when it encountered severe, non-technical, difficulties. Resolving these difficulties resulted in several months of delay in completing the Program, but resulted in only a trivial increase in total program cost and no increase in cost to the sponsor. The principle Objective of the Program was the development of a printing system -- machine and appropriate inks -- compatible with existing thick-film processing but offering a 5x improvement in line density. This objective has been met. The Pad Printer is capable of printing suitable inks in traces 25 g wide on 50g centers to a fired thickness of 3 {mu}; each of these parameters is roughly 1/5 the value of the current alternative, silk-screen printing. The available inks represent an assortment of conductor, dielectric, and insulator formulations and the knowledge developed permits extending this family of inks to new and diverse functional materials. An important secondary objective was maximum compatibility with existing Thick Film processing; the printer and ink systems may be substituted directly for the silk screen printers in existing processes. The Program reached or exceeded its other Technical Objectives in almost every case and, in those few instances where the objective was only partially met, work continues under private funding.
Date: May 1, 1998
Partner: UNT Libraries Government Documents Department

Evolutionary dynamics on random structures

Description: In this paper the authors consider the evolutionary dynamics of populations of sequences, under a process of selection at the phenotypic level of structures. They use a simple graph-theoretic representation of structures which captures well the properties of the mapping between RNA sequences and their molecular structure. Each sequence is assigned to a structure by means of a sequence-to-structure mapping. The authors make the basic assumption that every fitness landscape can be factorized through the structures. The set of all sequences that map into a particular random structure can then be modeled as a random graph in sequence space, the so-called neutral network. They analyze in detail how an evolving population searches for new structures, in particular how they switch from one neutral network to another. They verify that transitions occur directly between neutral networks, and study the effects of different population sizes and the influence of the relatedness of the structures on these transitions. In fitness landscapes where several structures exhibit high fitness, the authors then study evolutionary paths on the structural level taken by the population during its search. They present a new way of expressing structural similarities which are shown to have relevant implications for the time evolution of the population.
Date: April 1, 1997
Creator: Fraser, S.M. & Reidys, C.M.
Partner: UNT Libraries Government Documents Department

Uncooled IR photon detection using MEMS micro-structures

Description: Generation of free carriers in a semiconductor gives rise to mechanical stress. Photo-induced stress phenomena in MEMS micro-structures can be used in the room temperature detection of infrared photons. Choice of the appropriate semiconductor material for the MEMS micro-structures determines the cutoff wavelength of the uncooled infrared photon detector. The authors have measured the deflection of silicon and indium antimonide micro-structures resulting from a photo-induced stress. The excess charge carriers responsible for the photo-induced stress were produced via photon irradiation from both a diode laser and a black body source. In the case of Si, the photo-induced stress is of opposite direction and about four times larger than the thermal stress. For indium antimonide the direction of stress is the same as due to thermal effects. The photo-induced stress can be distinguished from the thermal stress based on the cut-off wavelength, response speed, and perhaps the direction of the microstructure deflection.
Date: August 1, 1998
Creator: Datskos, P.G. & Rajic, S.
Partner: UNT Libraries Government Documents Department

Systems thinking for manufacturing: Distributed, multi-disciplinary simulations for graduate education

Description: This project summary first discusses the methodology employed, distributed interactive simulation, then describes the architecture and some of the features of the project, and finally examines potential applications in graduate education. A distributed simulation is one composed of different modules that are resident on different computers. The top-level model consists of a number of integrated sub-models which exchange data. The sub-models are part of a functional whole; they are linked to each other by input and output parameters. A variable output by one sub-model is the input to one or more of the other sub-models, and vice-versa. Each sub-model depicts a separate facet of a complex system. This approach borrows conceptually from object-oriented programming, where each component is independent and encapsulated from the others, while exchanging data through a prescribed interface. The example used is a battery factory producing an advanced fuel cell for replacement of batteries in cellular phones.
Date: October 1, 1997
Creator: Hahn, H. & Kunsberg, P.
Partner: UNT Libraries Government Documents Department

Humanitarian mine detection by acoustic resonance

Description: The JASON Committee at MITRE Corp. was tasked by DARPA to inquire into suitable technologies for humanitarian mine detection. Acoustic resonance was one of the very few technologies that the JASONs determined might be promising for the task, but was as yet unexplored at the time that they conducted their inquiry. The objective of this Seed Money investigation into acoustic resonance was to determine if it would be feasible to use acoustic resonance to provide an improvement to present methods for humanitarian mine detection. As detailed in this report, acoustic resonance methods do not appear to be feasible for this task. Although acoustic resonant responses are relatively easy to detect when they exist, they are very difficult to excite by the non-contact means that must be used for buried objects. Despite many different attempts, this research did not discover any practical means of using sound to excite resonant responses in objects known to have strong resonances. The shaker table experiments did see an effect that might be attributable to the resonance of the object under test, but the effect was weak, and exploited the a priori knowledge of the resonant frequency of the object under test to distinguish it from the background. If experiments that used objects known to have strong acoustic resonances produced such marginal results, this does not seem to be a practical method to detect objects with weak resonances or non-existent resonances. The results of this work contribute to the ORNL countermine initiative. ORNL is exploring several unconventional mine detection technologies, and is proposed to explore others. Since this research has discovered some major pitfalls in non-metallic mine detection, this experience will add realism to other strategies proposed for mine detection technologies. The experiment provided hands-on experience with inert plastic mines under field conditions, and gives ORNL ...
Date: March 1, 1998
Creator: Kercel, S.W.
Partner: UNT Libraries Government Documents Department

Unique interactive projection display screen

Description: Projection systems continue to be the best method to produce large (1 meter and larger) displays. However, in order to produce a large display, considerable volume is typically required. The Polyplanar Optic Display (POD) is a novel type of projection display screen, which for the first time, makes it possible to produce a large projection system that is self-contained and only inches thick. In addition, this display screen is matte black in appearance allowing it to be used in high ambient light conditions. This screen is also interactive and can be remotely controlled via an infrared optical pointer resulting in mouse-like control of the display. Furthermore, this display need not be flat since it can be made curved to wrap around a viewer as well as being flexible.
Date: November 1, 1997
Creator: Veligdan, J.T.
Partner: UNT Libraries Government Documents Department

Effects of thermomechanical processing on the resulting mechanical properties of 6101 aluminum foam

Description: Porous materials represent a tremendous weight savings for light-weight structural applications. The fabrication path can play a critical role in the resulting properties. High porosity aluminum was fabricated in a number of ways. The starting material was a cast 6101 aluminum that had a relative density of 9.8%. The cast aluminum block was compressed by uniaxial, biaxial, and triaxial densification. Uniaxial compression was done at room temperature and 200 C. Biaxial compression was achieved by unidirectional rolling at room temperature and 200 C. Triaxial compression was done by cold isostatic pressing at 3.4, 6.7, and 34 MPa (0.5, 1.0, and 5.0 ksi). Metallography and mechanical test specimens were machines from the processed bars. The mechanical properties showed that the relative yield strength depended both on relative density and processing temperature.
Date: December 1, 1998
Creator: Margevicius, R.W.; Stanek, P.W. & Jacobson, L.A.
Partner: UNT Libraries Government Documents Department

Extreme ultraviolet interferometry

Description: EUV lithography is a promising and viable candidate for circuit fabrication with 0.1-micron critical dimension and smaller. In order to achieve diffraction-limited performance, all-reflective multilayer-coated lithographic imaging systems operating near 13-nm wavelength and 0.1 NA have system wavefront tolerances of 0.27 nm, or 0.02 waves RMS. Owing to the highly-sensitive resonant reflective properties of multilayer mirrors and extraordinarily tight tolerances set forth for their fabrication, EUV optical systems require at-wavelength EUV interferometry for final alignment and qualification. This dissertation discusses the development and successful implementation of high-accuracy EUV interferometric techniques. Proof-of-principle experiments with a prototype EUV point-diffraction interferometer for the measurement of Fresnel zoneplate lenses first demonstrated sub-wavelength EUV interferometric capability. These experiments spurred the development of the superior phase-shifting point-diffraction interferometer (PS/PDI), which has been implemented for the testing of an all-reflective lithographic-quality EUV optical system. Both systems rely on pinhole diffraction to produce spherical reference wavefronts in a common-path geometry. Extensive experiments demonstrate EUV wavefront-measuring precision beyond 0.02 waves RMS. EUV imaging experiments provide verification of the high-accuracy of the point-diffraction principle, and demonstrate the utility of the measurements in successfully predicting imaging performance. Complementary to the experimental research, several areas of theoretical investigation related to the novel PS/PDI system are presented. First-principles electromagnetic field simulations of pinhole diffraction are conducted to ascertain the upper limits of measurement accuracy and to guide selection of the pinhole diameter. Investigations of the relative merits of different PS/PDI configurations accompany a general study of the most significant sources of systematic measurement errors. To overcome a variety of experimental difficulties, several new methods in interferogram analysis and phase-retrieval were developed: the Fourier-Transform Method of Phase-Shift Determination, which uses Fourier-domain analysis to improve the accuracy of phase-shifting interferometry; the Fourier-Transform Guided Unwrap Method, which was developed to overcome difficulties associated with a high ...
Date: December 1, 1997
Creator: Goldberg, K.A.
Partner: UNT Libraries Government Documents Department

Active chatter control in a milling machine

Description: The use of active feedback compensation to mitigate cutting instabilities in an advanced milling machine is discussed in this paper. A linear structural model delineating dynamics significant to the onset of cutting instabilities was combined with a nonlinear cutting model to form a dynamic depiction of an existing milling machine. The model was validated with experimental data. Modifications made to an existing machine model were used to predict alterations in dynamics due to the integration of active feedback compensation. From simulations, subcomponent requirements were evaluated and cutting enhancements were predicted. Active compensation was shown to enable more than double the metal removal rate over conventional milling machines. 25 refs., 10 figs., 1 tab.
Date: August 1, 1997
Creator: Dohner, J.L.; Hinnerichs, T.D. & Lauffer, J.P.
Partner: UNT Libraries Government Documents Department

Techniques for evaluation of E-beam evaporative processes

Description: High dynamic range video imaging of the molten pool surface has provided insight regarding process responses at the melt pool liquid-vapor interface. A water-cooled video camera provides continuous high resolution imaging of the pool surface from a low angle position within 20 cm of the liquid-vapor interface. From the vantage point, the e-beam footprint is clearly defined and melt pool free surface shape can be observed. Effects of changes in a beam footprint, power distribution, and sweep frequency on pool surface shape and stability of vaporization are immediately shown. Other events observed and recorded include: formation of the pool and dissipation of ``rafts`` on the pool surface during startup, behavior of feed material as it enters the pool, effects of feed configuration changes on mixing of feed entering the pool volume and behaviors of co-evaporated materials of different vapor pressures at the feed/pool boundary. When used in conjunction with laser vapor monitoring, correlation between pool surface phenomena and vaporizer performance has been identified. This video capability was used in verifying the titanium evaporation model results presented at this conference by confirming the calculated melt pool surface deformations caused by vapor pressure of the departing evaporant at the liquid-vapor interface.
Date: October 1, 1996
Creator: Meier, T.C. & Nelson, C.M.
Partner: UNT Libraries Government Documents Department

Investigation of Wavelet-Based Enhancements to Nuclear Quadrupole Resonance Explosives Detectors

Description: Nuclear Quadrupole Resonance (NQR) is effective for the detection and identification of certain types of explosives such as RDX, PETN and TNT. In explosive detection, the NQR response of certain 14N nuclei present in the crystalline material is probed. The 14N nuclei possess a nuclear quadrupole moment which in the presence of an electric field gradient produces an energy level splitting which may be excited by radio-frequency magnetic fields. Pulsing on the sample with a radio signal of the appropriate frequency produces a transient NQR response which may then be detected. Since the resonant frequency is dependent upon both the quadrupole moment of the 14N nucleus and the nature of the local electric field gradients, it is very compound specific. Under DARPA sponsorship, the authors are using multiresolution methods to investigate the enhancement of operation of NQR explosives detectors used for land mine detection. For this application, NQR processing time must be reduced to less than one second. False alarm responses due to acoustic and piezoelectric ringing must be suppressed. Also, as TNT is the most prevalent explosive found in land mines, NQR detection of TNT must be made practical despite unfavorable relaxation tunes. All three issues require improvement in signal-to-noise ratio, and all would benefit from improved feature extraction. This paper reports some of the insights provided by multiresolution methods that can be used to obtain these improvements. It includes results of multiresolution analysis of experimentally observed NQR signatures for RDX responses and various false alarm signatures in the absence of explosive compounds.
Date: June 1, 1998
Creator: Kercel, Stephen W.; Dress, William B.; Hibbs, Andrew D. & Barrall, Geoffrey A.
Partner: UNT Libraries Government Documents Department

A directory service for configuring high-performance distributed computations

Description: High-performance execution in distributed computing environments often requires careful selection and configuration not only of computers, networks, and other resources but also of the protocols and algorithms used by applications. Selection and configuration in turn require access to accurate, up-to-date information on the structure and state of available resources. Unfortunately, no standard mechanism exists for organizing or accessing such information. Consequently, different tools and applications adopt ad hoc mechanisms, or they compromise their portability and performance by using default configurations. We propose a Metacomputing Directory Service that provides efficient and scalable access to diverse, dynamic, and distributed information about resource structure and state. We define an extensible data model to represent required information and present a scalable, high-performance, distributed implementation. The data representation and application programming interface are adopted from the Lightweight Directory Access Protocol; the data model and implementation are new. We use the Globus distributed computing toolkit to illustrate how this directory service enables the development of more flexible and efficient distributed computing services and applications.
Date: August 1, 1997
Creator: Fitzgerald, S.; Kesselman, C. & Foster, I.
Partner: UNT Libraries Government Documents Department

Processing challenges for GaN-based photonic and electronic devices

Description: The wide gap materials SiC, GaN and to a lesser extent diamond are attracting great interest for high power/high temperature electronics. There are a host of device processing challenges presented by these materials because of their physical and chemical stability, including difficulty in achieving stable, low contact resistances, especially for one conductivity type, absence of convenient wet etch recipes, generally slow dry etch rates, the high temperatures needed for implant activation, control of suitable gate dielectrics and the lack of cheap, large diameter conducting and semi-insulating substrates. The relatively deep ionization levels of some of the common dopants (Mg in GaN; B, Al in SiC; P in diamond) means that carrier densities may be low at room temperature, and thus contact resistances will be greatly improved provided the metallization is stable and reliable. Some recent work with CoSi{sub x} on SiC and W-alloys on GaN show promise for improved ohmic contacts. The issue of unintentional hydrogen passivation of dopants will also be covered - this leads to strong increases in resistivity of p-SiC and GaN, but to large decreases in resistivity of diamond. Recent work on development of wet etches has found recipes for AlN (KOH), while photochemical etching of SiC and GaN has been reported. In the latter cases p-type materials is not etched, which can be a major liability in some devices. The dry etch results obtained with various novel reactors, including ICP, ECR and LE4 will be compared - the high ion densities in the former techniques produce the highest etch rates for strongly-bonded materials, but can lead to preferential loss of N from the nitrides and therefore to a highly conducting surface. This is potentially a major problem for fabrication of dry etched, recessed gate FET structures.
Date: September 1, 1997
Creator: Pearton, S.J.; Ren, F. & Shul, R.J.
Partner: UNT Libraries Government Documents Department

A human supervisory approach to rapid world modeling through the use of geometric primitives

Description: A three-dimensional world model is crucial for many robot-oriented tasks. The most efficient mapping configuration use geometric primitives to model environments, and are easy to store and process. In the past, modeling techniques have been either fully manual or autonomous. Manual methods are extremely time consuming but also highly accurate and flexible. On the other hand autonomous techniques are fast but inflexible and often inaccurate. The method presented in this paper combines the two thereby yielding a highly efficient, flexible, and accurate tool. Our methods enable a human supervisor to quickly construct a fully defined world model from unfiltered and unsegmented real-world range data.
Date: August 11, 1997
Creator: Luck, J. & Roberts, R.
Partner: UNT Libraries Government Documents Department

Hydrogen diffusion and chemistry during the annealing-induced generation of mobile protons in the oxide layer of Si/SiO{sub 2}/Si capacitors

Description: In a number of recent studies the generation of mobile protons in the buried oxide of SOI materials and in thermal oxide buried underneath a poly-Si layer has been discussed. The protons are found to be stable and can be easily rearranged by applying an electric field. The details of the hydrogen reactions leading to the generation of the mobile H{sup +} are still under investigation. In a recent work a dynamic equilibrium model was presented. The forward reaction dominates above {approximately} 500 C and the resulting H{sup +} is mobile and entrapped inside the SiO{sub 2}. The electron is donated to the Si. The H{sup 0} is likely to be formed through H{sub 2} + K {Leftrightarrow} HK + H{sup 0}, where K is a cracking site. In the same work it was shown that the reactive hydrogen species enter the oxide from the device edges. Hence, the amount of the reactive species reaching the oxide by diffusion through the Si overlayer is negligible. These results seem to contradict earlier studies where it is shown that hydrogen can easily diffuse through the top Si layer under the given experimental conditions. The authors present here new details on hydrogen diffusion and chemistry during the protonation anneal that may offer an explanation for the hydrogen diffusion paradox. The new findings suggest that reactions at the ambient/SiO{sub 2} interface play a key role.
Date: September 1, 1998
Creator: Vanhuesden, K.; Devine, R.A.B.; Fleetwood, D.M. & Warren, W.L.
Partner: UNT Libraries Government Documents Department

RF magnetron sputter-deposition of La{sub 0.5}CoO{sub 3}//Pt composite electrodes for Pb(Zr,Ti)O{sub 3} thin film capacitors

Description: La{sub 0.5}Sr{sub 0.5}CoO{sub 3} (LSCO) thin films have been deposited using RF magnetron sputter-deposition for use as an electrode material for PZT (PbZrTiO{sub 3}) thin film capacitors. Effect of O{sub 2}:Ar sputter gas ratio during deposition, on LSCO film properties was studied. It was found that the resistivity of the LSCO films deposited at ambient temperature decreases as the O{sub 2}: Ar ratio was increased for both as-deposited and annealed films. It was also found that thin overlayers of LSCO tend to stabilize the underlying Pt//Ti electrode structure during subsequent thermal processing. The LSCO//Pt//Ti composite electrode stack has a low resistivity and provides excellent fatigue performance for PZT capacitors. Furthermore, the LSCO//Pt//Ti electrode sheet resistance does not degrade with annealing temperature and the electrode does not display hillock formation. Possible mechanisms for the stabilization of the Pt//Ti electrode with LSCO overlayers are discussed.
Date: July 1, 1996
Creator: Raymond, M.V.; Al-Shareef, H.N.; Tuttle, B.A.; DiMos, D. & Evans, J.T.
Partner: UNT Libraries Government Documents Department

Ultra-thin overcoats for the head/disk interface tribology

Description: Areal density in magnetic storage is increasing at a blistering pace of 60% annually. Recently IBM announced its mobile product with the industry highest areal density of 2.64 Gb/In{sup 2}. The areal density demonstrations have shown up to 5 Gb/In{sup 2} possible. Reaching higher areal density targets dictate that magnetic spacing between heads and disks be reduced. For the example of a 10 Gb/In{sup 2} areal density goal, the magnetic spacing should be {approx}25 nm. In budgeting this magnetic spacing, it is required that disk and slider air bearing surface overcoats thickness be reduced to 5 nm range. Present choice of carbon overcoat in the magnetic storage hard disk drive industry is sputter deposited, hydrogenated carbon (CH{sub x}) with thickness in the range of 12-15 nm on heads and disks. Novel overcoats such as nitrogenated carbon (CN{sub x}) and cathodic arc carbon films are being developed for future applications. Cathodic arc deposition forms ultra-thin amorphous hard carbon films of high sp{sup 3} content, high hardness, and low coefficient of friction. These properties make it of great interest for head/disk interface application, in particular for contact recording. In many cases, the tribological properties of the head disk interface could be improved by factors up to ten applying cathodic arc overcoats to the slider or disk surface. This paper reviews the results of cathodic arc ultra-thin (2-10 nm) carbon overcoats for head/disk interface tribological applications.
Date: May 1997
Creator: Bhatia, C. S.; Anders, S. & Brown, I. G.
Partner: UNT Libraries Government Documents Department

Voltage shifts and defect-dipoles in ferroelectric capacitors

Description: We review the processes and mechanisms by which voltage offsets occur in the hysteresis loop of ferroelectric materials. Simply stated, voltage shifts arise from near-interfacial charge trapping in the ferroelectric. We show that the impetus behind voltage shifts in ferroelectric capacitors is the net polarization, with the net polarization being determined by the perovskite and the aligned defect-dipole components. Some common defect-dipoles in the PZT system are lead vacancy-oxygen vacancy complexes. One way to change the net polarization in the ferroelectric is to subject the PZT capacitor to a dc bias at elevated temperature; this process is spectroscopically shown to align defect-dipoles along the direction of the applied electric field. The alignment of defect-dipoles can strongly impact several material properties. One such impact is that it can lead to enhanced voltage shifts (imprint). It is proposed that the net polarization determines the spatial location of the asymmetrically trapped charge that are the cause for the voltage shifts. An enhanced polarization at one electrode interface can lead to larger voltage shifts since it lowers the electrostatic potential well for electron trapping, i.e., more electron trapping can occur. Defect-dipole alignment is also shown to increase the UV sensitivity of the ferroelectric.
Date: December 1, 1996
Creator: Warren, W.L.; Pike, G.E. & Dimos, D.
Partner: UNT Libraries Government Documents Department

Parallel matrix transpose algorithms on distributed memory concurrent computers

Description: This paper describes parallel matrix transpose algorithms on distributed memory concurrent processors. We assume that the matrix is distributed over a P {times} Q processor template with a block scattered data distribution. P, Q, and the block size can be arbitrary, so the algorithms have wide applicability. The algorithms make use of non-blocking, point-to-point communication between processors. The use of nonblocking communication allows a processor to overlap the messages that it sends to different processors, thereby avoiding unnecessary synchronization. Combined with the matrix multiplication routine, C = A {center_dot} B, the algorithms are used to compute parallel multiplications of transposed matrices, C = A{sup T} {center_dot} B{sup T}, in the PUMMA package. Details of the parallel implementation of the algorithms are given, and results are presented for runs on the Intel Touchstone Delta computer.
Date: December 31, 1994
Creator: Choi, Jaeyoung; Dongarra, J. & Walker, D.W.
Partner: UNT Libraries Government Documents Department

Hydrothermal oxidation of Navy shipboard excess hazardous materials

Description: This study demonstrated effective destruction, using a novel supercritical water oxidation reactor, of oil, jet fuel, and hydraulic fluid, common excess hazardous materials found on-board Navy vessels. This reactor uses an advanced injector design to mix the hazardous compounds with water, oxidizer, and a supplementary fuel and it uses a transpiring wall to protect the surface of the reactor from corrosion and salt deposition. Our program was divided into four parts. First, basic chemical kinetic data were generated in a simple, tubular-configured reactor for short reaction times (<1 second) and long reaction times (>5 seconds) as a function of temperature. Second, using the data, an engineering model was developed for the more complicated industrial reactor mentioned above. Third, the three hazardous materials were destroyed in a quarter-scale version of the industrial reactor. Finally, the test data were compared with the model. The model and the experimental results for the quarter-scale reactor are described and compared in this report. A companion report discusses the first part of the program to generate basic chemical kinetic data. The injector and reactor worked as expected. The oxidation reaction with the supplementary fuel was initiated between 400 {degrees}C and 450 {degrees}C. The released energy raised the reactor temperature to greater than 600 {degrees}C. At that temperature, the hazardous materials were efficiently destroyed in less than five seconds. The model shows good agreement with the test data and has proven to be a useful tool in designing the system and understanding the test results. 16 refs., 17 figs., 11 tabs.
Date: March 1, 1997
Creator: LaJeunesse, C.A.; Haroldsen, B.L.; Rice, S.F. & Brown, B.G.
Partner: UNT Libraries Government Documents Department

Current transport in W and WSI{sub x} ohmic contacts to InGaN and InN

Description: The temperature dependence of the specific contact resistance of W and WSi{sub 0.44} contacts on n{sup +} In{sub 0.65}Ga{sub 0.35}N and InN was measured in the range -50 {degrees}C to 125 {degrees}C. The results were compared to theoretical values for different conduction mechanisms, to further elucidate the conduction mechanism in these contact schemes for all but as-deposited metal to InN where thermionic emission appears to be the dominant mechanism. The contacts were found to produce low specific resistance ohmic contacts to InGaN at room temperature, e{sup c} {approximately} 10{sup -7} {Omega} {center_dot} cm{sup 2} for W and e{sub c} of 4x 10{sup -7} {Omega} {center_dot} cm{sup 2} for WSi{sub x}. InN metallized with W produced ohmic contacts with e{sub c} {approximately} 10{sup -7} {Omega} {center_dot} cm{sup 2} and e{sub c} {approximately} 10{sup -6} {Omega} {center_dot} cm{sup 2} for WSi{sub x} at room temperature.
Date: October 1, 1997
Creator: Vartuli, C.B.; Pearton, S.J. & Abernathy, C.R.
Partner: UNT Libraries Government Documents Department

The effect of aspect ratio and sp2/sp3 content on the field emission properties of carbon films grown by Ns-spiked PECVD

Description: The authors have deposited carbon films from mixtures of methane and N{sub 2} using Plasma Enhanced Chemical Vapor Deposition. By changing the percentage of N{sub 2} in the feed gas, they were able to produce films that have various aspect ratios and sp{sup 2}/sp{sup 3} contents. The film with the highest field emission contains spears of aspect ratio of 10:1. They also found that in their sp{sup 3}-rich films, higher sp{sup 2} content enhanced field emission. This is ascribed to improved charge transport to the field emission sites.
Date: April 1998
Creator: Tong, W.; Felter, T. E.; Pan, L. S.; Anders, S.; Cossy-Facre, A. & Stammler, T.
Partner: UNT Libraries Government Documents Department

On properties of boundaries and electron conductivity in mesoscopic polycrystalline silicon films for memory devices

Description: The authors present the results of MD modeling on the structural properties of grain boundaries (GB) in thin polycrystalline films. The transition from crystalline boundaries with low mismatch angle to amorphous boundaries is investigated. It is shown that the structures of the GBs satisfy a thermodynamical criterion suggested in a cited reference. The potential energy of silicon atoms is closely related with a geometrical quantity -- tetragonality of their coordination with their nearest neighbors. A crossover of the length of localization is observed to analyze the crossover of the length of localization of the single electron states and properties of conductance of the thin polycrystalline film at low temperature. They use a two-dimensional Anderson localization model, with the random one site electron charging energy for a single grain (dot), random non-diagonal matrix elements, and random number of connections between the neighboring grains. The results on the crossover behavior of localization length of the single electron states and characteristic properties of conductance are presented in the region of parameters where the transition from an insulator to a conductor regimes takes place.
Date: February 1, 1998
Creator: Berman, G.P.; Doolen, G.D.; Mainieri, R.; Rehacek, J.; Campbell, D.K.; Luchnikov, V.A. et al.
Partner: UNT Libraries Government Documents Department

Characterization of novel powder and thin film RGB phosphors for field emissions display application

Description: The spectral response, brightness and outgassing characteristics of new, low-voltage phosphors for application in field-emission flat-panel displays, are presented. The tested phosphor materials include combustion synthesized powders and thin films prepared by RF-diode or magnetron sputtering, laser ablation and molecular beam epitaxy. These cathodoluminescent materials are tested with e-beam excitation at currents up to 50 {mu}A within the 200-2000V (e.g. {open_quotes}low-voltage{close_quotes}) and 3-8 kV (e.g. {open_quotes}medium voltage{close_quotes}) ranges. The spectral coordinates are compared to commercial low-voltage P22 phosphors. Phosphor outgassing, as a function of time is measured with a residual gas analyzer at fixed 50 {mu}A beam current in the low-voltage range. We find that levels of outgassing stabilize to low values after the first few hours of excitation. The desorption rates measured for powder phosphor layers with different thickness are compared to desorption from thin films.
Date: December 31, 1996
Creator: Chakhovskoi, A.G.; Hunt, C.E.; Malinowski, M.E.; Felter, T.E. & Talin, A.A.
Partner: UNT Libraries Government Documents Department