Recent advances in the development of microplasma devices fabricated in a variety of materials systems (Si, ceramic multilayers, and metal/polymer structures) and configurations are reviewed. Arrays of microplasma emitters, having inverted pyramidal Si electrodes or produced in ceramic multilayer sandwiches with integrated ballasting for each pixel, have been demonstrated and arrays as large as 30×30 pixels are described. A new class of photodetectors, hybrid semiconductor/microplasma devices, is shown to exhibit photoresponsivities in the visible and near-infrared that are more than an order of magnitude larger than those typical of semiconductor avalanche photodiodes. Microdischarge devices having refractory or piezoelectric dielectric films such as Al 2 O 3 or BN have extended lifetimes (∼86% of initial radiant output after 100 h with an Al 2 O 3 dielectric) and controllable electrical characteristics. A segmented, linear array of microdischarges, fabricated in a ceramic multilayer structure and having an active length of ∼1 cm and a clear aperture of 80 × 360 µm 2 , exhibits evidence of gain on the 460.3 nm transition of Xe + , making it the first example of a microdischarge-driven optical amplifier.

The confinement of low temperature, non-equilibrium plasmas to cavities having characteristic spatial dimensions <1 mm is providing new avenues of inquiry for plasma science. Not only is a previously unexplored region of parameter space now accessible, but the interaction of the plasma with its material boundaries raises fascinating questions and opportunities. Other scientific issues that come to the fore include scaling relationships and the collisional processes that become prevalent in a high pressure environment. The general characteristics of microplasmas, as well as several emerging applications, are briefly described here. With regard to the latter, emphasis will be placed on photonics and, specifically, the demonstration of large (500 ×500) arrays of microcavity plasma devices in Si, the observation of photodetection in the visible, near-infrared and ultraviolet by a microplasma, and the measurement of optical gain in the blue (λ ∼ 460 nm) from a linear array of microplasmas in a ceramic structure.

Microdischarge devices having inverted, square pyramidal cathodes as small as 50 mϫ50 m at the base and 35 m in depth, have been fabricated in silicon and operated at gas pressures up to 1200 Torr. For the polyimide dielectric incorporated into these devices (r ϭ2.9), the discharges produced exhibit high differential resistance (ϳ2ϫ10 8 ⍀ in Ne͒, ignition voltages for a single device of ϳ260-290 V, and currents typically in the A range. Arrays as large as 10ϫ10 have been fabricated. For an 8 m thick polyimide dielectric layer, operating voltages as low as 200 V for a 5ϫ5 array have been measured for 700 Torr of Ne. Array lifetimes are presently limited to several hours by the thin ͑1200-2000 Å͒ Ni anode.

Selected highlights in the recent development of microplasma devices are reviewed with emphasis on large arrays of Si-based hybrid plasma/semiconductor pixels. Arrays of 40 000 (200 × 200) pixels, excited by sinusoidal ac waveforms at frequencies of 5-20 kHz, have now been realized. The fabrication of these arrays and their electrical and optical performance with rare gases and Ar/N 2 mixtures are briefly described. Metal/dielectric/metal devices having a piezoelectric dielectric (BaTiO 3 ), a cylindrical microcavity 50 µm in diameter, and a total thickness of ∼110 µm are also discussed. Finally, the introduction of multiwall carbon nanotubes into microdischarge devices as an auxiliary source of current is presented as being exemplary of the opportunities afforded by the integration of nanotechnology into microcavity plasma structures.

The spatial dynamics of the optical emission from an array of 50×50 individual microplasma devices is reported. The array is operated in noble gas at atmospheric pressure with an ac voltage. The optical emission is analyzed with phase and space resolution. It has been found that the emission is not continuous over the entire ac period, it occurs only twice in each cycle. Each of the observed emission phases shows a self-pulsing of the discharge, with several bursts of emission of a fixed width and repetition rate. Cross-talk between the individual devices can be observed through spatially resolved measurements.