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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 reports a microfluidic device that integrates electrical and optical features required for field-portable water-chemistry testing by discharge spectroscopy. The device utilizes a dc-powered spark between a metal anode and a liquid cathode as the spectral source. Impurities are sputtered from the water sample into the microdischarge and characteristic atomic transitions due to them are detected optically. A blazed grating is used as the dispersion element. The device is fabricated from stacked glass layers, and is assembled and used with a charge-coupled device (CCD) sensing element to distinguish atomic spectra. Two structural variations and optical arrangements are reported. Detection of Cr and other chemicals in water samples has been successfully demonstrated with both devices. The angular resolution in terms of angular change per unit variation in wavelength ([??][theta]/[??][lambda]) is experimentally determined to be approximately 0.10 rad/[micro]m, as opposed to the idealized theoretical estimate of 0.22 rad/[micro]m. This is because the microdischarge is uncollimated and not a point source. However, this is sufficient angular resolution to allow critical spectra of metal impurities to be distinguished. Index Terms--Chemical sensing, dispersion optics, microdischarge, sample delivery, water chemistry.

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.

In order to understand the details of high-field breakdown in microstructures that are vacuum packaged, a series of experiments are used to determine characteristics of microdischarges. The results support a reinterpretation of conventional assumptions based upon large scale discharges. When planar microelectrodes are used, Paschen's curve is not applicable in the traditional sense: the breakdown voltage is relatively insensitive to pressure in the 1-20 torr range, and remains at ~400 V for air ambient. However, the spatial distribution of discharge current does vary with the pressure and the power. Large voltage gradients are supported in the glow region which is confined to a few millimeters directly above the cathode, and within a few hundred microns of its lateral edge. Their magnitudes range from 100 000-500 000 V/m for operating pressures ranging from 1.2-6 torr. Based on these results, guidelines are provided for the design of high-voltage microsystems. [916] Index Terms--Electric breakdown, electrostatic devices, microdischarge, microplasma.

The detection of trace contaminants in water by spectroscopy of micro glow discharges operating in air or at moderate vacuum using liquid electrodes is discussed. The development of a liquid electrode spectral emission chip (LEd-SpEC) is described.

This article explores electric current and field distributions in dc microplasmas, which have distinctive characteristics that are not evident at larger dimensions. These microplasmas, which are powered by coplanar thin-film metal electrodes with 400-μm minimum separations on a glass substrate, are potentially useful for microsystems in both sensing and microfabrication contexts. Experiments in N[sub 2] ambient show that electron current favors electrode separations of 4 mm at 1.2 Torr, reducing to 0.4 mm at 10 Torr. The glow region is confined directly above the cathode, and within 200–500 μm of its lateral edge. Voltage gradients of 100 kV/m exist in this glow region at 1.2 Torr, increasing to 500 kV/m at 6 Torr, far in excess of those observed in larger plasmas. Numerical simulations indicate that the microplasmas are highly nonquasineutral, with a large ion density proximate to the cathode, responsible for a dense space-charge region, and the strong electric fields in the glow region. It is responsible for the bulk of the ionization and has a bimodal electron energy distribution function, with a local peak at 420 eV. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This paper reports on the generation of spatially confined plasmas and their application to silicon etching. The etching is performed using [SF.sub.6] gas and dc power applied between thin-film electrodes patterned on the silicon wafer to be etched. The electrodes also serve as a mask for the etching. The typical operating pressure and power density are in the range of 1-20 Torr and 1-10 W/[cm.sup.2], respectively. The plasma confinement can be varied from [is less than] 100[micro]m to [is greater than] 1 cm by varying the electrode area, operating pressure, and power. High power densities can be achieved at moderate currents because the electrode areas are small. Etch rates of 4-17 [micro]m/min., which enable through-wafer etching and varying degrees of anisotropy, have been achieved. The etch rate increases with power density, whereas the etch rate per unit power density increases with operating pressure. Scaling effects are explored for varying sized mask openings. Plasma resistance measurements and electric field modeling are used to provide an initial assessment of the microplasmas. [570] Index Terms--dc plasma, dry etching, microplasma, micromachining, semiconductor plasma.

On-chip microplasmas have previously been used in designing a compact and portable device for identifying pollutants in a water sample. By exciting a liquid sample with a high energy microdischarge and recording the spectral wavelengths emitted, the individual elements in the liquid are distinguishable. In particular, this study focuses on cesium, a contaminant from nuclear incidents such as the collapse of the nuclear power plant in Fukushima, Japan. This article shows that not only can the presence of cesium be clearly determined at concentrations as low as 10 ppb, but the relative concentration contained in the sample can be determined through the discharges' relative spectral intensity. [ABSTRACT FROM AUTHOR]

Halloysite nanotubes (HNTs) are a naturally-occurring aluminosilicate whose dimensions measure microns in length and tens of nanometers in diameter. Bonding defects between the alumina and silica lead to net negative and positive charges on the exterior and interior lumen, respectively. HNTs have been shown to enhance the material properties of polymer matrices and enable the sustained release of loaded chemicals, drugs, and growth factors. Due to the net charges, these nanotubes can also be readily coated in layered-depositions using the HNT exterior lumen's net negative charge as the basis for assembly. These coatings are primarily done through wet chemical processes, the majority of which are limited in their use of desired chemicals, due to the polarity of the halloysite. Furthermore, this restriction in the type of chemicals used often requires the use of more toxic chemicals in place of greener options, and typically necessitates the use of a significantly longer chemical process to achieve the desired coating. In this study, we show that HNTs can be coated with metal acetylacetonates--compounds primarily employed in the synthesis of nanoparticles, as metal catalysts, and as NMR shift reagents--through a dry sintering process. This method was capable of thermally decaying the metal acetylacetonate, resulting in a free positively-charged metal ion that readily bonded to the negatively-charged HNT exterior, resulting in metallic coatings forming on the HNT surface. Our coating method may enable greater deposition of coated material onto these nanotubes as required for a desired application. Furthermore, the use of chemical processes using toxic chemicals is not required, thus eliminating exposure to toxic chemicals and costs associated with the disposal of the resultant chemical waste. [ABSTRACT FROM AUTHOR]

This paper reports a microfluidic device that integrates electrical and optical features required for field-portable water-chemistry testing by discharge spectroscopy. The device utilizes a dc-powered spark between a metal anode and a liquid cathode as the spectral source. Impurities are sputtered from the water sample into the microdischarge and characteristic atomic transitions due to them are detected optically. A blazed grating is used as the dispersion element. The device is fabricated from stacked glass layers, and is assembled and used with a charge-coupled device (CCD) sensing element to distinguish atomic spectra. Two structural variations and optical arrangements are reported. Detection of Cr and other chemicals in water samples has been successfully demonstrated with both devices. The angular resolution in terms of angular change per unit variation in wavelength (∂θ/∂λ) is experimentally determined to be approximately 0.10 rad/µm, as opposed to the idealized theoretical estimate of 0.22 rad/µm. This is because the microdischarge is uncollimated and not a point source. However, this is sufficient angular resolution to allow critical spectra of metal impurities to be distinguished. [ABSTRACT FROM AUTHOR]