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This paper reports on dc pulse-powered microdischarges in air at atmospheric pressure and their potential utility in chemical sensing. For electrode gaps of 50-100 [micro]m, microdischarges take the form of a glow discharge, an arc discharge, or a hybrid of the two. Arc microdischarges have high optical intensity but suffer from high background emission. Glow microdischarges have low background emission, but the prominent emission is confined in the UV-blue region of the spectrum. The arc--glow hybrid has characteristics that are intermediate between the two and can be tuned by circuitry to suit the chemical sensing application. A handheld system for chemical analysis using synchronized emission spectroscopy of these pulsed microdischarges is demonstrated. The system employs an exchangeable sensor chip (different for gas and liquid samples), a control circuit, and a commercially available portable spectrum analyzer coupled to a handheld computer. A pump and inert carrier gases are not utilized. The system can generate one or a series of single-shot microdischarges per chemical analysis. The gas discharge microchip, which utilizes electroplated copper electrodes on a glass substrate, has an electrode separation of 75 [micro]m and an active area of 300 x 300 [micro][m.sup.2]. The handheld system has been used to detect 17 ppm of acetone vapor in air. The liquid discharge microchip also has an electrode gap of 75 [micro]m and an active area of 1 x 1 [mm.sup.2]. It uses a porous cathode fabricated by micromolding and sintering glass frit slurry in a microchannel. When a microdischarge is initiated between the metal anode and the wet cathode, the liquid is sputtered into the microdischarge and emits characteristic line spectra. In this configuration, the system can detect 2 ppm of aqueous Cr without preconcentration. Index Terms--Chemical sensing systems, gas detectors, gas discharge devices, microarc, microdischarge, microplasma, water chemistry.

This paper reports deposition of silicon at elevated and room temperatures in spatially localized areas of a microchip by plasma-enhanced chemical vapor deposition using microplasmas. The microplasmas are generated by providing dc power to thin-film Ti electrodes patterned on the microchip. Electrode arrangements include configurations in which multiple cathode elements share a single anode. At the operating pressures used, the plasma glow is confined to the region directly over the energized cathodes only, and the deposition is localized to these regions. A silane ambient allows Si to be deposited at 6.7-15.9 nm/min using cathode power densities of 3.65-9.35 W/[cm.sup.2], with the substrate heated to 300 [degrees]C. At room temperature, deposition rates up to 4.2 nm/min are realized. Also described is a plasma-coupling technique that permits isolated metal pads to be powered by plasma spreading from a proximate cathode at certain levels of power and pressure. This permits controlled variations of silicon thickness in a subarray of unbiased electrodes, simplifying the powering scheme. Index Terms--Plasma-enhanced chemical vapor deposition (PECVD), polysilicon, thin-film deposition.

This paper explores the use of miniaturized magnets to enhance the parameters of dc microplasmas. The microplasmas are powered by thin coaxial electrodes and are enhanced by a coaxial magnetron configuration machined from niobium composite magnets. At operating pressures of 1-4 torr, a glow region that is confined to the volume directly over the cathode, forms a traditional magnetron-type annular ring. Three coaxial magnets, ranging in total size from 3.2 to 7.2 mm in outside diameter generate measured magnetic fields up to 3030 G. The magnetic field structure is profiled with a small Hall probe and is modeled by finite-element analysis. The plasma currents for various applied voltages are measured, and the plasma breakdown/termination voltages are determined. In nitrogen ambients at 1.2 torr and 370-V bias, the current changes from 9.3 mA in the absence of a magnetic field to 17.6 mA with the addition of the largest magnet. The sheath region decreases with the addition of the magnetic structures, illustrating an effect on the Debye length and, therefore, the local plasma density. The dimensions of the sheath are found to vary radially within the annular microplasma. The smallest sheath corresponds to the region of highest magnetic field over the south pole for the largest magnetic configuration. This effect is used to generate a microplasma in SF8 on a silicon wafer producing a localized etch. The etch rate in the region of the brightest glow is three times greater than the weakest etch rate, allowing spatially localized etch selectivity without masking. Index Terms--Magnetic confinement, manufacturing, microdischarge, microplasma, sensing.