Showing papers by "Warren B. Jackson published in 1996"

Position sensitive detector based image conversion system capable of preserving subpixel information

Abstract: An image detection and pixel processing system includes a plurality of position sensitive detector elements arranged to receive an image. Each position sensitive detector element provides information for determining both a total light intensity value within the position sensitive detector element and a centroid of light intensity indicative of light intensity position within the position sensitive detector element. An image processing assembly receives information from the plurality of position detector elements with the image processing assembly relating a pixel and its encompassed subpixel area to each corresponding position detector element. The total light intensity within the pixel and the centroid of light intensity within the subpixel is determined, with the image processing assembly rendering each subpixel area as an edge when magnitude of the centroid of light intensity is large.

Comment on ‘‘Reduction of hot electron degradation in metal oxide semiconductor transistors by deuterium processing’’ [Appl. Phys. Lett. 68, 2526 (1996)]

Abstract: Lyding et al. have recently reported significant improvements in the lifetime of metal oxide semiconductor ~MOS! transistors due to incorporation of deuterium ~D!, rather than hydrogen ~H!, at the Si/SiO2 interface. This remarkable achievement indicates that the Si–D bond is more resistant to hot-electron excitation than the Si–H bond. Lyding et al. pointed out that the phenomenon is probably analogous to the observed reduction in desorption of deuterium versus hydrogen from hydrogenated Si~100!:H surfaces using the scanning tunneling microscope ~STM!. In this comment, we propose a specific pathway for the dissociation of Si–H and Si–D bonds, providing a natural explanation for the difference in dissociation rates. Shen et al. have proposed that the low-voltage STMinduced desorption of Si–H bonds from Si~100! proceeds via a multiple-vibrational excitation by tunneling electrons. Electrons excite Si–H vibrational transitions with a rate proportional to the tunneling current. The extent to which vibrational energy can be stored in the bond depends on the lifetime, i.e., on the rate at which energy is lost by coupling to phonons. Because the lifetime of H on Si is long, efficient vibrational excitation is expected. In the quantitative analysis of Ref. 3, it was assumed that the vibrational energy is deposited in the stretch mode of the Si–H bond, which has a frequency around 2100 cm. The same assumption is usually implicitly made in discussions of dissociation of Si–H bonds. Our main purpose here is to point out that both the vibrational lifetime and carrier-enhanced dissociation mechanisms are most likely controlled by the Si–H bending modes. The vibrational frequency of the bending mode for Si–H is around 650 cm, and the estimated frequency for Si–D is around 460 cm. This value is close to the frequency of bulk TO phonon states at the X point ~463 cm21). We therefore expect the coupling of the Si–D bending mode to the Si bulk phonons to result in an efficient channel for deexcitation. While it is quite possible to reach a highly excited vibrational state in the case of Si–H, this will be more difficult for Si–D. Deuterium should therefore be much more resistant to STM-induced desorption and hot-electron induced dissociation, due to the relaxation of energy through the bending mode.

Hydrogen migration in polycrystalline silicon.

Abstract: Hydrogen migration in solid-state crystallized and low-pressure chemical-vapor-deposited (LPCVD) polycrystalline silicon (poly-Si) was investigated by deuterium diffusion experiments. The concentration profiles of deuterium, introduced into the poly-Si samples either from a remote D plasma or from a deuterated amorphous-silicon layer, were measured as a function of time and temperature. At high deuterium concentrations the diffusion was dispersive depending on exposure time. The dispersion is consistent with multiple trapping within a distribution of hopping barriers. The data can be explained by a two-level model used to explain diffusion in hydrogenated amorphous silicon. The energy difference between the transport level and the deuterium chemical potential was found to be about 1.2--1.3 eV. The shallow levels for hydrogen trapping are about 0.5 eV below the transport level, while the deep levels are about 1.5--1.7 eV below. The hydrogen chemical potential ${\mathrm{\ensuremath{\mu}}}_{\mathrm{H}}$ decreases as the temperature increases. At lower concentrations, ${\mathrm{\ensuremath{\mu}}}_{\mathrm{H}}$ was found to depend markedly on the method used to prepare the poly-Si, a result due in part to the dependence of crystallite size on the deposition process. Clear evidence for deuterium deep traps was found only in the solid-state crystallized material. The LPCVD-grown poly-Si, with columnar grains extending through the film thickness, displayed little evidence of deep trapping, and exhibited enhanced D diffusion. Many concentration profiles in the columnar LPCVD material indicated complex diffusion behavior, perhaps reflecting spatial variations of trap densities, complex formation, and/or multiple transport paths. Many aspects of the diffusion in poly-Si are consistent with diffusion data obtained in amorphous silicon. \textcopyright{} 1996 The American Physical Society.

Two-dimensional amorphous silicon image sensor arrays

Abstract: Large two-dimensional amorphous silicon image sensor arrays offer an advantage for high speed document scanning and medical X-ray imaging. We describe our page sized 200 spot per inch imager and the accompanying high speed readout electronics. The spatial resolution performance for white light and X-ray imaging is illustrated. We discuss how the important issues of noise and resolution depend on the properties of a-Si:H, and show how the material can be used to give improved performance of the imagers.

Image processing method and Image detection and pixel processing system

Abstract: of EP0771102An image detection and pixel processing system (10) includes a plurality of detector elements (22) for receiving an image. The detector elements are subdivided into a plurality of macrodetectors, with each macrodetector constituting four or more detector elements, and with each macrodetector providing information for determining both a total light intensity value within the macrodetector and a centroid of light intensity indicative of light intensity position within the macrodetector. An image processing assembly (30) receives information from the plurality of macrodetectors, with the image processing assembly relating a pixel and its encompassed subpixel area to each corresponding macrodetector, and further determining the total light intensity within the pixel and the centroid of light intensity within the subpixel. The image processing assembly is capable of rendering each subpixel area as an edge when magnitude of the centroid of light intensity is greater than a predetermined threshold.

Passively addressable fluid valves having S-shaped blocking films

Abstract: A bistable valve useful for paper handling applications is disclosed. The valve can be batch fabricated in two dimensional valve arrays, with each valve in the array being controlled by passive matrix addressing. Typically, each valve includes a valve housing having an aperture plate defining an aperture therethrough, and an opposing plate positioned in spaced apart relationship to the aperture plate. A flexible film or strip is attached at its first end to the aperture plate and at its second end to the opposing plate. Valve action is provided by use of at least two switching electrodes for moving the flexible film between an aperture blocking position and an aperture open position, with at least one of the switching electrodes positioned adjacent to the aperture plate and at least one of the switching electrodes positioned adjacent to the opposing plate. To reduce unswitched movement when the switching electrode bias is reduced or not present, at least two electrostatic or mechanical catches are used.

X-ray image system design using a human visual model

Abstract: Because of the complex response of the human visual system, typical measurements of image system quality such as the detective quantum efficiency, mean transfer function, and signal-to- noise ratio cannot always be used to determine conditions for optimal perceptual image quality. Using a model of the human vision system, the ViDEOS/Sarnoff Human Vision Discrimination Model (HVM), this work demonstrates that human vision models provide a promising quantitative measure of image perceptual quality. The model requires an image and a matching reference image in order to determine the perceptual difference between the images at each point. A simple model of a digital amorphous silicon medical x-ray system is used to create the necessary images as a function of various design parameters. The image pairs are then analyzed by the HVM. In all cases the dependence of perceived image quality closely follows measures of image quality as determined by the HVM for many image system design variations. Increasing the detector size actually increases the image quality in the presence of either readout or input noise. The model was also used to optimize the image system for a specific task optimization. As an example, the effect of system design parameters on tumor identification in mammographic images is determined.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Hydrogen in amorphous silicon

Abstract: Recently, significant progress has been made in understanding the energetics, transport, and kinetic behavior of hydrogen in silicon, particularly in hydrogenated amorphous silicon. Many of the basic features of the hydrogen density of states are understood. New experimental results on exchange, solubility, and local motion can be understood in terms of the density of states and are consistent with the kinetics of metastability.

Origin of the anomalous pulse-width dependence in capacitance transient measurements on n-type a-Si:H

Abstract: The dependence of capacitance transients on filling pulse width for n-type a-Si:H has been compared for devices with identical bulk n-type a-Si:H but different back contacts. The capacitance transients for devices with Ohmic Cr/n + back contacts do not exhibit any significant dependence on filling pulse width while the devices with non-Ohmic p + c-Si display the anomalous dependence previously attributed to defect relaxation. Measurements of current injection during the filling pulse indicates that charge injection is impeded by the non-Ohmic p + c-Si contacts. Variation of the filling pulse height is shown to yield apparent scaling in time, an effect previously thought to be unique to defect relaxation.

Trap Dominated Hydrogen Transport in Disordered Silicon

Abstract: Polycrystalline silicon (poly-Si) is receiving attention as an electronic material to replace hydrogenated amorphous silicon (a-Si:H) as active layer in device structures such as thin-film transistors and solar cells. Hydrogen transport in polycrystalline silicon was investigated by deuterium diffusion experiments. D was introduced either from a remote plasma or a solid-state source. The data can be explained by a two-level model used to explain diffusion in amorphous silicon. The energy difference between transport level and deuterium chemical potential was found to be 1.3 eV. A band of shallow levels for hydrogen trapping is located about 0.6 eV below the transport level, while deep levels are about 1.7 eV below.