Arrays of Al∕Al2O3/glass microplasma devices with microcavities having diamond or circular cross-sectional geometries and radiating (active) areas >20cm2 have been operated sealed-off in Ne, Ar, and Ar∕D2 gas mixtures. Microcavities are fabricated in only one of the two electrodes, and the thickness of the completed package is ∼170μm (excluding the quartz output window). Excited by a sinusoidal 20kHz voltage wave form, arrays with active areas of 4.5×3cm2 exhibit ignition voltages as low as 110±5V rms for Ne pressures of 400–700Torr. Mixtures of 1% D2 in Ar at a total pressure of 300Torr produce wavelength-integrated (λ∼250–400nm) intensities of ∼1mWcm−2 over a 25cm2 area. Optical micrographs show the operation of the microplasmas in two well-defined modes. For current densities below a threshold value (∼53mAcm−2 for 250μm dia. cavities and pNe=400Torr), diffuse uniform plasma is produced in each cavity but, with higher currents, a positive column having near-cylindrical geometry appears, as evidenced by the generation of intense emission localized in the region of weak electric field gradient near the axis of symmetry.
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