Direct current cathode boundary layer discharges in xenon for excimer lamps

Abstract

Summary form only given. Cathode boundary layer (CBL) discharges are high-pressure, nonequilibrium gas discharges between a planar cathode and a ring-shape anode separated by a dielectric with an opening. The large concentration of high-energy electrons in these discharge plasmas, and the high gas density make them favorable for excimer formation when operated in rare gases. The openings on the dielectrics and the anode are of the same size (sub-mm to several mm) and aligned. The structures were manually assembled by attaching, using Torr Sealreg, a perforated molybdenum foil on a 100 to 250 mum thick, perforated alumina wafer. A second molybdenum foil was then placed on top of the alumina to serve as the cathode. However, industrial applications (e.g. the use of arrays of these microdischarges in flat panel excimer lamps), require a simpler method of fabrication for the electrode structures. We have used plasma spraying as a method and successfully generated large area sandwich structures with zirconia as the dielectric between the molybdenum electrodes. We have studied the excimer emission of xenon CBL discharges at a wavelength of 172 nm in a wide range of pressure (75 to 760 torr) and current (muA to ~10 mA). With increase of pressure, the excimer intensity was found to increase. However, the discharge also tended to become more unstable. We have therefore focused on a pressure range of 250 to 300 torr for optimum operation. The excimer intensity peaks at a certain current, which for 250 torr and a cathode diameter of 0.75 mm is approximately 0.9 mA, corresponding to a current density of about 0.2 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . This maximum emission coincides with the development of self-organized patterns of the discharge plasma. The excimer radiant emittance was measured as 0.5-1.5 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The resistive current-voltage characteristic in the self-organization range allows operating multiple discharges in parallel without individual ballast, and consequently the fabrication of large area flat panel excimer lamps