Francis P. Fehlner

Electrical Behavior of Composite Discontinuous Films

Composite discontinuous films of gold‐rich islands grown on palladium nucleii exhibit two distinctly different regions of temperature‐dependent conductivity. At low temperatures, film properties are dominated by a process characteristic of large gold‐rich islands which are closely spaced. This results in a film with a high resistivity and a low activation energy. At higher temperatures, the process abruptly changes and the conductivity of the film begins to increase rapidly with temperature. The dominant transport process in this conductivity region is attributed to activated tunneling between the small palladium‐rich islands.

Cusp mirror—Heat pipe evacuated tubular solar thermal collector

Abstract A solar thermal collector was constructed based on an internal 1.15X cusp concentrator, thermal insulation involving a vacuum and selective absorber, and thermal transfer to a manifold via heat-pipe action. Performance of the collector was compared with that of an evacuated, selectively coated, flat-plate absorber equipped with flow-through heat transfer. It was shown that with single collector tubes, mirror losses lowered the optical efficiency of the cusp, heat-pipe collector below that of the flat plate, while the smaller absorber area of the heat pipe reduced thermal losses at absorber temperatures above ambient. Thus, a crossover in efficiency occurred such that the flat plate was more efficient at low ΔT H while the cusp-heat pipe was more efficient at high ΔT H . Testing of modules showed that manifold losses and gains could dominate these collector effects when the collector area approximately equaled the manifold area.

BEHAVIOR OF ULTRATHIN ZIRCONIUM FILMS UPON EXPOSURE TO OXYGEN.

Discontinuous films of zirconium, having surface resistivities between 104 and 106 Ω sq−1, were deposited on glass substrates in ultrahigh vacuum and then exposed to oxygen pressures in the range of 5×10−7 to 4×10−8 Torr at temperatures of 25° and −196°C. The change in film resistance with time was monitored and a plot of logR vs logt was constructed. This graph was initially concave upwards, but became linear after a time which was characteristic of monolayer formation.An interpretation of the film behavior was based on the transport of electrons by tunneling through gaps separating the metal islands. The initial change in film resistance was caused by an increase in the zirconium work function. This increase was due to oxygen monolayer formation. The subsequent linear log‐log behavior was caused by an increase in the tunneling distance which resulted from oxidation of the metal islands.Values for both the interisland spacing and the room‐temperature oxidation rate constant have been calculated from the ...

Thin films on glass for liquid crystal displays

Abstract Liquid crystal displays have become the major flat panel display technology for use in portable computers. They consist of two coated glass plates with the liquid crystal sandwiched between them. Operation of this electro-optic device depends on a combination of transparent conductors, semiconductors, insulators and metals along with polymer alignment layers, liquid crystals and polarizers. Properties and applications of the inorganic films are reviewed in the present paper.

Chemical treatment of glass substrates

Abstract The effects of cleaning on the near-surface composition of Corning Code 1737 glass was studied. Cleaned glass substrates were found to develop a thin silica-rich surface layer approximately 6 nm thick formed by chemical leaching. The presence of this layer was verified by X-ray photoelectron spectroscopy, scanning transmission electron microscopy and X-ray scattering. Atomic force microscopy measurements of the glass before and after cleaning showed no increase in the surface roughness. Top-gated polycrystalline silicon thin film transistors fabricated on cleaned substrates had leakage currents, similar to those on substrates with deposited SiO2 layers.

Sodium redistribution between oxide phases

Alkali transport between a glass substrate and an oxide over layer occurs by a mechanism of ion exchange between the alkali and protons. Thermodynamics requires that the difference in chemical potential of the alkali and the proton be the same in both phases at equilibrium. The influence of chemical composition of the glass on the chemical potential of alkali ions is discussed. Good agreement between predictions of the direction of alkali transport and observed transport is obtained.

Oxidation at low temperatures

Abstract The growth of oxide films on metals and semiconductors at low temperatures was not adequately explained until Mott proposed electron tunnelling as the mechanism of charge neutralization. This led to the Cabrera-Mott model of oxidation in which a self-induced field reduces the activation energy for ion movement. The resulting equation was shown by Fehlner to fit the oxidation kinetics when network-forming oxides can grow. The present work examines kinetic data for network modifiers and attempts to fit them to a direct logarithmic expression of Uhlig. Trapped charge is assumed to limit electron transfer. Charge densities in the 1018−1020cm−3 range are found for Cu, Na, Be, Zn, and Fe.

Glass: A critical material in the development of electronic displays

— Electronic displays may be grouped into two categories, vacuum based and solid state. In both cases, glass has served as the package for the active components making up the display. Thus, glass has often been the limiting factor in the development of these technologies. This paper discusses the interrelationships between the two.

Alumina barrier layers on LCD glass

Abstract Effective diffusion coefficients, D e , for the movement of sodium from an LCD glass into a sputtered alumina barrier layer have been determined. Secondary ion mass spectrometry analysis was used to measure sodium concentrations in 100 nm thick alumina films on soda lime glass at 520°C and for similar films on alkaline earth boroaluminosilicate glass at 650°C. Calculated values of D e are compared with extrapolated values of the diffusion coefficient, D , for sodium in polycrystalline alumina. The agreement is inconsistent. This is explained in terms of the countercurrent of hydrogen ions needed to maintain charge neutrality when a sodium ion moves out of the glass into the alumina film.

Effect of barrier layer thickness on the performance of thin film transistors on glass substrates

Top-gated poly-Si thin film transistors (TFTs) were fabricated on Corning COde 1737 glass substrates coated with SiO2 barrier layers of varying thickness. The leakage current, or minimum current in the off state of the transistor, was measured and analyzed to evaluate the influence of barrier layer thickness on the TFT characteristics. Our results indicate that using a thick barrier layer may results in higher TFT leakage currents. Control devices on oxidized silicon have higher leakage currents than TFTs on barrier coated Code 1737 glass. Those on glass substrates show the effect of barrier layer thickness. As the barrier layer thickness increases the leakage current also increase. One possible explanation for this is the nature of the glass substrate. Even a thin SiO2 layer can suppress diffusion of electrically active impurities from the substrate to the device. However, aluminoborosilicate glasses such as Corning Code 1737 are also known to act as sinks for sodium and other process impurities. Thick barrier layers separate the TFT from the gettering effects of the substrate and limit the removal of impurities from the device region.