J. G. Eden

Microdischarge devices fabricated in silicon

Cylindrical microdischarge cavities 200–400 μm in diameter and 0.5–5 mm in depth have been fabricated in silicon and operated at room temperature with neon or nitrogen at specific power loadings beyond 10 kW/cm3. The discharges are azimuthally uniform and stable operation at N2 and Ne pressures exceeding 1 atm and ∼600 Torr, respectively, has been realized for 400 μm diameter devices. Spectroscopic measurements on neon discharges demonstrate that the device behaves as a hollow cathode discharge for pressures >50 Torr. As evidenced by emission from Ne and Ne+ (2P,2F) states as well as N2 (C→B) fluorescence (316–492 nm), these discharge devices are intense sources of ultraviolet and visible radiation and are suitable for fabrication as arrays.

Microplasma devices fabricated in silicon, ceramic, and metal/polymer structures: arrays, emitters and photodetectors

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 Al2O3 or BN have extended lifetimes (~86% of initial radiant output after 100?h with an Al2O3 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??m2, exhibits evidence of gain on the 460.3 nm transition of Xe+, making it the first example of a microdischarge-driven optical amplifier.

Silicon microdischarge devices having inverted pyramidal cathodes: Fabrication and performance of arrays

Microdischarge devices having inverted, square pyramidal cathodes as small as 50 μm×50 μm at the base and 35 μm in depth, have been fabricated in silicon and operated at gas pressures up to 1200 Torr. For the polyimide dielectric incorporated into these devices (er=2.9), the discharges produced exhibit high differential resistance (∼2×108 Ω in Ne), ignition voltages for a single device of ∼260–290 V, and currents typically in the μA range. Arrays as large as 10×10 have been fabricated. For an 8 μm thick polyimide dielectric layer, operating voltages as low as 200 V for a 5×5 array have been measured for 700 Torr of Ne. Array lifetimes are presently limited to several hours by the thin (1200–2000 A) Ni anode.

Flexible microdischarge arrays: Metal/polymer devices

Flexible microdischarge arrays have been fabricated in metal–polymer–metal structures having a total thickness of ∼30 μm (∼1.2 mils). Composed of individual cylindrical devices having a diameter of 150 μm, positive differential resistance (30–120 kΩ), and operating voltages as low as 114 V for a 5 μm thick dielectric layer, the arrays operate at pressures beyond 700 Torr of Ne and in 1 atm of air. For Ne pressures ⩽ 200 Torr, emission is produced from Ne ion excited states lying more than 55 eV above the neutral ground state (2p6). The structures reported here are inexpensive to fabricate and have lifetimes beyond 50 h. Arrays that have been sealed by conventional lamination have also been operated successfully.

Label free biosensor incorporating a replica-molded, vertically emitting distributed feedback laser

A label free biosensor based upon a vertically emitting distributed feedback (DFB) laser has been demonstrated. The DFB laser comprises a replica-molded, one-dimensional dielectric grating coated with laser dye-doped polymer as the gain medium. Adsorption of biomolecules onto the laser surface alters the DFB laser emission wavelength, thereby permitting the kinetic adsorption of a protein polymer monolayer or the specific binding of small molecules to be quantified. A bulk sensitivity of 16.6nm per refractive index unit and the detection of a monolayer of the protein polymer poly(Lys, Phe) have been observed with this biosensor. The sensor represents a departure from conventional passive resonant optical sensors from the standpoint that the device actively generates its own narrowband high intensity output without stringent requirements on the coupling alignments, resulting in a simple, robust illumination and detection configuration.

Recent advances in microcavity plasma devices and arrays: a versatile photonic platform

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 x 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.

Microcavity plasma devices and arrays: A new realm of plasma physics and photonic applications

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 arrays: a new family of photonic devices

The optical and electrical characteristics of microdischarge devices and arrays fabricated in semiconductors and metal/polymer structures are described. Devices as small as (10 /spl mu/m)/sup 2/ in emitting area (nanoliters in volume) and arrays as large as 30 /spl times/ 30 have been demonstrated and operated at gas pressures up to and exceeding one atmosphere. This new generation of microoptical sources is capable of producing photons from the infrared to the vacuum ultraviolet and beyond and is well suited for integration with microoptoelectronic, fluidic, and mechanical systems.

Microdischarge arrays: a new family of photonic devices (revised*)

The optical and electrical characteristics of microdischarge devices and arrays fabricated in semiconductors and metal/polymer structures are described. Devices as small as (10 /spl mu/m)/sup 2/ in emitting area (nanoliters in volume) and arrays as large as 30 /spl times/ 30 have been demonstrated and operated at gas pressures up to and exceeding one atmosphere. This new generation of microoptical sources is capable of producing photons from the infrared to the vacuum ultraviolet and beyond and is well suited for integration with microoptoelectronic, fluidic, and mechanical systems.

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

Nanostructured Al2O3 films with mean pore diameters of 20 nm, 5–30μm 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 100–300μm diameter (dia.) cylindrical microcavity and an overall thickness of ∼200μm 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 100μm dia. devices operate in Ne at rms voltages and currents of ∼160–270V 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 ∼275V, 5×5 arrays of 100μm dia. devices produce a luminance of 2700cdm−2 in 600 Torr of Ne for a sinusoidal ac excitation frequency of 20 kHz.