Low-Temperature CVD Carbon Coatings on Glass Plates for Flat Panel Display Applications
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LOW-TEMPERATURE CVD CARBON COATINGS ON GLASS PLATES FOR FLAT PANEL DISPLAY APPLICATIONS YONHUA TZENG*, CHAO LIU*, CALVIN CUTSHAW *, AND ZHENG CHEN** * Alabama Microelectronics Science and Technology Center, Department of Electrical and Computer Engineering, Auburn University, AL 36849 ** Space Power Institute, Auburn University, AL 36849 ABSTRACT Low-temperature chemical vapor deposition processes were studied for coating carbon films on metal-coated glass plates. Thermal CVD in hydrocarbon mixtures was used for carbon deposition at temperatures between 300°C and 550°C. Carbon deposited on metal coated glass plates were examined by SEM and analyzed using a pin to disk setup in an ultra high vacuum chamber for measuring the electron emission characteristics. Using a one-millimeter diameter tungsten rod with a hemispherical tip as the anode while the carbon coatings as the cathode, current-voltage characteristics of the carbon coatings were measured and used for calculating the electric field at which electron emission started as well as calculating the field enhancement factor of the carbon coatings. Field emission of electrons from carbon coatings starting from an electric field as low as 1.4 volts per micrometer has been achieved. INTRODUCTION In order to use carbon coatings as the electron field emitters for large-area plasma displays it is desirable that an inexpensive substrate such as a glass plate is used for carbon deposition. A conductive layer needs to be deposited on a glass plate before carbon is coated onto the substrate and used as a cold cathode. Because of the low melting point of glass and the large mismatch in the coefficient of thermal expansion between metal and glass, carbon deposition cannot be performed at too high a temperature that is usually considered optimal for carbon nanotube coating on metal substrates. The mismatch in coefficients of thermal expansion for metal coatings and glass makes the adhesion of carbon coatings on glass more difficult when the glass plate has to be heated to a high temperature and then cooled down to the room temperature. Various low temperature CVD techniques are being studied to achieve low threshold field emission of electrons at a high emission current density. In this paper, the results based on thermal CVD techniques are presented. EXPERIMENTS Shown in Figure 1 is the schematic diagram for the thermal CVD reactor that was used for this study. Mixtures of acetylene and argon or nitrogen [1] were fed into a quartz tubing chamber that was evacuated by a mechanical pump. Gas pressure was controlled by a throttle valve and monitored by a manometer pressure gauge. A resistive heater was used to heat the
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quartz tubing and the substrate inside the tubing to a preset temperature. Copper, nickel, and Cobalt were used as the catalysts for the carbon coatings.
Figure 1. Schematic diagram for the thermal CVD reactor. Carbon coated substrates were then loaded into a high vacuum chamber shown in figure 2 that was pumped down by a turbomolecular pump and an ion p
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