Nanoporous alumina as a dielectric for microcavity plasma devices: Multilayer Al/ Al2O3 structures

Nanostructured Al2O3 films with mean pore diameters of 20 nm, 5-30 μm in thickness, and grown onto Al foil by a multiple step electrochemical process, provide a dielectric having superior properties for microplasma devices and arrays. Multilayer Al/nanoporous Al2O3 structures with a 100-300 μm diameter (dia.) cylindrical microcavity and an overall thickness of ~200 μm are robust and operate in the abnormal glow mode for Ne or Ar/2-5% N2 mixture gas pressures (300 K) of 500-700 Torr. When driven with a sinusoidal ac waveform at frequencies of 5-20 kHz, small arrays (3×3→10×10) of 100 μm dia. devices operate in Ne at rms voltages and currents of ~160-270 V and 0.4-4.5 mA, respectively. Arrays as large as 10×10 have been fabricated to date and generate azimuthally uniform discharges in each pixel without the need for external ballast. For an rms voltage of ~275 V, 5×5 arrays of 100 μm dia. devices produce a luminance of 2700 cd m-2 in 600 Torr of Ne for a sinusoidal ac excitation frequency of 20 kHz.