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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]

A chemical recognition algorithm is an integral part of any autonomous microscale gas chromatography (µGC) system for automated chemical analysis. For a multi-detector µGC system, the chemical analysis must account for the retention time of each chemical analyte as well as the relative response of each detector to each analyte, i.e., the detector response pattern (DRP). In contrast to the common approaches of heuristically using principal component analysis and machine learning, this paper reports a rule-based automated chemical recognition algorithm for a multi-cell, multi-detector µGC system, in which the DRP is related to theoretical principles; consequently, this algorithm only requires a small amount of calibration data but not extensive training data. For processing both the retention time and the raw DRP, the algorithm applies rules based on expert knowledge to compare the detected peaks; these rules are located in a customized software library. Additionally, the algorithm provides special handling for chromatogram peaks with a small signal-to-noise ratio. It also provides separate special handling for asymmetrical peaks that may result from surface adsorptive analytes. This work also describes an experimental evaluation in which the algorithm used the relative response of two complementary types of capacitive detectors as well as a photoionization detector that were incorporated into the µGC system of interest. In these tests, which were performed on chromatograms with 21–31 peaks for each detector, the true positive rate was 96.3%, the true negative rate was 94.1%, the false positive rate was 5.9%, and the false negative rate was 3.7%. The results demonstrated that the algorithm can support µGC systems for automated chemical screening and early warning applications. [ABSTRACT FROM AUTHOR]

This paper presents a microfabricated sensor that uses electrical microdischarges to sense the deflection of a diaphragm under applied pressure. The sensor responds by redistributing electron current of pulsed microdischarges between one cathode ( $K$ ), a reference anode (A1), and a deflecting anode (A2), all of which are located in a cavity under the diaphragm; the differential anode current indicates the applied pressure. In this paper, the sensor is monolithically fabricated from a single silicon wafer, using a combination of surface micromachining and through-wafer isolated bulk-silicon lead transfer (TWIST) technology. The TWIST technology provides lead transfer into the sealed cavity as well as backside contacts, allowing miniaturization of the device footprint and surface mount assembly within systems. The active footprint of the complete sensor measures 300\times 300 \,\,\mu \text {m}^{2} in size, making it the smallest sealed microdischarge-based pressure sensor reported to date. The normalized differential current from the anodes monotonically increases from −0.7 to 0.2 as the external pressure increases from 1 to 8 atm. [2017–0274] [ABSTRACT FROM PUBLISHER]

Microfabricated radiation detectors can be used to provide first alert information about presence of harmful radiation. This paper describes a micromachined gamma detector that operates in the Geiger–Muller (G–M) regime. Gamma rays eject photoelectrons from the cathode material through the photoelectric effect and/or Compton scattering, which in turn ionize the Ar fill-gas providing a current pulse. The detector utilizes cathode stacks that are micromachined from stainless steel #304 foil. Micromachined glass fingers with thin-film anode metal traces are positioned transversely through aligned perforations in the stacked cathodes. This orthogonal array of anodes and cathodes effectively distinguishes electron avalanche regions from drift regions despite the miniaturization, thereby reducing the likelihood of spurious discharges. Overall, the detector diameter and height are 9 and 2.5 mm, respectively. Detector performance is characterized using a 99- $\mu $ Ci 137Cs source placed at a distance of 3 cm from the detector. In an integration time of 10 min at an applied voltage of 630 V, a source:background ratio of 89:1 is achieved—a fivefold improvement over the previously reported micromachined devices operating in the G–M regime. This architecture also reduces the typical charge per discharge to 6.6 pC, allowing the estimated dead time between detection events to be $\sim 1 \mu $ s. [2014-0333] [ABSTRACT FROM PUBLISHER]

This paper describes in situ dynamic calibration of microfabricated Pirani gauges, which are commonly used to measure vacuum levels in microsystems that may include pumps, valves, and other pressure modulation elements. Calibration is accomplished with a configuration where two sides of the supporting membrane of a Pirani gauge are at different pressures: an interior pressure within the microsystems and an exterior ambient pressure that can be directly controlled. This particular configuration is increasingly common as Pirani gauges are embedded in complex fluidic pathways such as those found in micro-gas chromatographs and multistage gas pumps. In the dynamic calibration the ambient pressure is rapidly modulated, while the interior pressure in the sense gap of the Pirani gauge remains relatively unchanged. The exterior pressure that is equal to the interior pressure is determined by a regression model. The dynamic calibration procedure and subsequent error analysis are illustrated by application to a 162-stage monolithic Knudsen vacuum pump. For this device, dynamic calibration improves the estimated upstream pressure from 30 (as suggested by uncorrected static calibration) to 0.9 Torr, with a 95.4% confidence interval from 0.7 to 1.1 Torr, assuming normal (Gaussian) distribution. These results demonstrate that dynamic calibration can be significantly more accurate than conventional static calibration for certain types of devices. [ABSTRACT FROM AUTHOR]

In this paper, we describe the rotary motion, by Marangoni flow, of a millimeter-scale rotary structure immersed in a thin layer of liquid. A 16 × 8 array of 1 × 0.8 × 0.3 mm3 surface-mount resistors is suspended ≈ 500 μm above the liquid to serve as a programmable heat source. The continuous operation of resistor elements is used to impose a spatially-defined temperature gradient on the surface of the liquid. With a maximum temperature gradient of 36.6 K/mm at the surface of a 2 mm-thick film of liquid with viscosity 5 cSt, a stainless steel rotary structure with a weight of ≈ 10 mg, a diameter of 4.1 mm, and blade angle of 34° takes 28 s to make a 360° rotation. In general, the angular velocity of the rotary structure is affected by the temperature gradient of the liquid surface and liquid viscosity among several factors. [ABSTRACT FROM AUTHOR]

This paper presents a monolithic pulsed high-voltage (HV) generator utilizing a single piezoelectric element (PZT51 disk, 5 mm in diameter and 740 \mum thick) with electrodes series-connected via a flexible polyimide cable. The design, fabrication, assembly, and testing of the HV generator are described. In response to transient mechanical load, the HV generator is evaluated within the stress range from 1 to 5 MPa, and the corresponding peak output voltages vary from 100 to 900 V. Performance comparison between single-electrode pair HV generator and three-electrode pair device indicates series-connected electrodes on a monolithic PZT element greatly boost the output voltage under the same mechanical load conditions. In further tests, the generated high-voltage pulses exceed 1.35 kV and are successfully used to initiate microdischarges on monolithically patterned electrodes across a 75 \mum air gap. The measured capacitance of the test HV generator is 25 pF and the calculated charge delivered to the terminal electrodes in each discharge is 34 nC. The nonlinear piezoelectric property of the PZT51 in transient mode is studied. We experimentally obtain a linear increase of the effective piezoelectric coefficient as the applied pressure increases within the range from 1 to 5 MPa. [2012-0356] [ABSTRACT FROM PUBLISHER]

The high throughput size sorting of particles in liquid suspensions is of interest for a variety of microanalytical and micromanufacturing applications. Hollow glass cenospheres of various diameters ranging from 5 to 200 μm are sorted according to size by evaporation of isopropyl alcohol droplets on an unpatterned glass substrate. By raising the temperature of the glass substrate, a stable Marangoni convection is developed inside the droplet. At a substrate temperature of 55 °C, more of the larger spheres (150-200 μm) are deposited near the droplet center, but smaller spheres <50 μm are found everywhere throughout the dried region. Better sorting is observed when the temperature of the substrate is above the boiling point of the liquid. When the substrate temperature is 85 °C, higher than the boiling point of IPA, most of the spheres <50 μm are transported close to the droplet edge. In the center of the dried pattern obtained from a 0.5 μl droplet, the spheres with >150 μm diameter outnumber those with <50 μm diameter by 6 x. The deposited spheres remain attached to the substrate surface when dry. The self-assembled nature of this drying pattern results in size sorting. [ABSTRACT FROM AUTHOR]

Digitally dependent firms, which are linked to a large number of other firms with varying capabilities, are challenged on evaluating networks with which to engage. Empirically supported heuristic guidance can aid firms in identifying alliances to strengthen capability. We report a case study of firms linked to the Internet of Things (IoT) with a broad view of firms that leverage digital technologies to offer a diverse range of next generation consumer and industrial products and services. This article includes a network analysis of their publicly declared deals to reveal clusters of high volume deals-making activity and their respective hub firms. Based on the rationale of deals of the hub firms, the firms are categorized in a perceptual framework of market-oriented versus technology-seeking inclination. The inclinations of these hub firms were found to vary between technology-seeking, market-oriented, and ambidextrous. The results of this article can inform hub firms in assessing investment portfolios, nonhub firms in evaluating networks governed by hub firms, and policy makers to design incentives for digital adoption. [ABSTRACT FROM AUTHOR]

Abstract: This paper explores the viability of bulk metal foils, in particular platinum–rhodium (Pt–Rh), for use in high power micromechanical relays. The electrical and thermal response of electrostatically actuated three-terminal micro-relays is evaluated. The micro-relays have a footprint of 6.5mm2 and an actuation area of 1.32mm2. A stacked double cantilever structure isolates the actuation electrode from the current path. A micromachined heat sink is located on the upper cantilever. The devices are fabricated by micro-electrodischarge machining and directly assembled on power rated printed circuit boards. The impact of contact materials, and forced cooling is addressed. Preliminary results suggest that the Pt–Rh devices have total on-state resistances of 1.25Ω and can handle currents substantially in excess of 1A, and potentially in excess of 2.6A. [Copyright &y& Elsevier]

Abstract: In this paper, we introduce the use of thin mesoporous mixed cellulose ester (polymer) membranes as the enabling element of miniature, motionless gas pumps. The pores within these membranes serve as channels that constrain gas molecules to the free molecular or transitional gas flow regimes. A temperature gradient across the membranes causes a transpiration based gas flow from the cold side to the hot side; this type of flow is the basis of Knudsen pumps. Gas flow characteristics and vacuum generation capabilities of polymer membranes with three different pore-sizes are reported. In this group, membranes with 25nm pore-size provide superior functionality. For an input power of 1.4W/cm2, Knudsen pump test structures based on this membrane material provide a typical gas flow rate of ≈0.93sccm/cm2 in the absence of pressure load. The transient pressure response is used to quantify various non-idealities. Experiments suggest that these polymer membranes are relatively defect-free as compared to bulk microporous ceramics that were previously evaluated for similar applications. In longevity tests performed to date, a polymer pump has operated continuously for ≈6000h without significant deterioration in its performance. [Copyright &y& Elsevier]

Abstract: This paper describes an investigation of microfluidic actuation of doublet patterns in samples of water on blank substrates, using singular and arrayed microfabricated thermal probes. A doublet is a two-dimensional flow pattern consisting of adjacent, opposing vortices with linear streamlines between them. In this work, each probe consists of a polyimide thin film cantilever with a metal heater near the tip which generates a temperature gradient up to 1°C/μm along its length. The probes are 360μm long, 42–120μm wide, and 3.5μm thick, and the tips are typically <1mm away from the liquid surface. The velocity of the doublet flow can be controlled by adjusting the temperature of the heat source or by controlling the gap or attack angle between the heat source and the liquid surface. Linear flow velocities exceeding 5mm/s and rotational velocities exceeding 1200rpm are reported. [Copyright &y& Elsevier]

Wireless signals are inherently generated with each discharge in micro-electro-discharge machining (μEDM), allowing direct observation of discharge quality. While traditional methods of monitoring machining quality rely on electrical characteristics at the discharge supply terminals, the wireless method provides more accurate information because it is less affected by electrical parasitics in the supply loop and by spatial averaging. The depth location of a metal-metal interface can be distinguished in the wireless signal. This is useful for determining the stop depth in certain processes. For example, in machining through samples of stainless steel into an electroplated copper backing layer, the metal transition is identified by a 10-dBm change in wireless-signal strength for the 300-350-MHz band and a 5-dBm average change across the full 1-GHz bandwidth. As debris accumulate in the discharge gaps, shifts in the wireless spectra can also indicate spurious discharges that could damage the workpiece and tool. For example, when copper micromachining becomes debris dominated, the 800-850-MHz band drops 4 dBm in signal strength, with a 2.2-dBm average drop across the full 1-GHz bandwidth. [ABSTRACT FROM AUTHOR]

This paper presents a contactless droplet manipulation system that relies on thermally generated Marangoni flows. Programmable 2-D control of aqueous microdroplets suspended in an oil film on a plain featureless glass substrate is achieved using a 128-pixel heater array suspended 100-500 μm above the oil layer. The heaters generate surface temperature perturbations (< 25 °C), resulting in local Marangoni flows that can move droplets in either a push or a pull mode. Programmed movement is achieved by the sequential activation of the heaters, with digital control circuitry and a graphical interface providing addressable control of each heater. Droplets with diameters of 300-1000 μm are manipulated and merged at speeds up to 140 μm/s. Evaporation rates can be reduced by almost two orders of magnitude by using a two-layer-oil medium, and the choice of an optimum carrier fluid can achieve fluid velocities over 17000 μm/s. The system provides a contactless platform for parallel droplet-based assays. As such, it circumvents the challenges of sample contamination and loss that occur when a droplet interacts with a solid surface [ABSTRACT FROM AUTHOR]

Two versions of microdischarge-based pressure sensors, which operate by measuring the change, with pressure, in the spatial current distribution of pulsed dc microdischarges, are reported. The inherently high temperatures of the ions and electrons in the microdischarges make these devices amenable to high-temperature operation. The first sensor type uses 3-D arrays of horizontal bulk metal electrodes embedded in quartz substrates with electrode diameters of 1-2 mm and 50-100-μm interelectrode spacing. These devices were operated in nitrogen over a range of 10-2000 torr, at temperatures as high as 1000 °C. The maximum measured sensitivity was 5420 ppm/torr at the low end of the dynamic range and 500 ppm/torr at the high end, while the temperature coefficient of sensitivity ranged from -925 to -550 ppm/K. Sensors of the second type use planar electrodes and have active areas as small as 0.13 mm². These devices, when tested in a chemical sensing system flowing helium as a carrier gas, had a maximum sensitivity of 9800 ppm/torr, a dynamic range of 25- 200 torr, and a temperature coefficient of sensitivity of approximately -1412 ppm/K. [ABSTRACT FROM AUTHOR]

This paper presents a system for wirelessly monitoring the accumulation of sludge in a biliary stent. Two generations of the system are detailed. The first-generation system utilizes a 2 x 37.5-mm ribbon sensor with a mass of 18 mg, along with 0.8-mm-thick x 1.6-mm-diameter neodymium magnets to bias the sensor. Both components are integrated with a 4-mm-diameter stainless steel stent. The second-generation system comprises a sensor and a magnetic layer [consisting of strontium ferrite particles suspended in polydimethylsiloxane (PDMS)] that conform to the meshed topology and tubular curvature of a 5-mm-diameter Elgiloy stent. The second-generation sensors have an active area of 7.5 x 29 mm and a mass of 9.1 mg. The sensors in both generations are fabricated from 28-μm-thick foils of magneto- elastic 2826MB Metglas, an amorphous Ni-Fe alloy. Analytical and finite-element models that predict sensor response in the dynamic biological environment are presented. The response of each system to viscosity changes that precede and accompany biliary sludge accumulation is tested, with resonant frequency changes of 2.8% and 6.5% over a 10-cP range for each respective generation. Sludge accumulation is simulated with successive coatings of either paraffin or an acrylate terpolymer. Resonant frequency response to this mass loading effect is similar for both generations of the system, showing a 40% decrease after applying a mass load of 2.5 x the mass of the sensor. [ABSTRACT FROM AUTHOR]

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/cm², with the substrate heated to 300 °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. [ABSTRACT FROM AUTHOR]

This paper describes two stainless steel microstructures that are microelectrodischarge machined from 50-µm-thick planar foil for intraluminal measurements of pressure and flow (with potential for applications ranging from blood vessels to bile ducts). The first structure is an inductive antenna stent (stentenna) with 20-mm length and 3.5-mm expanded diameter. It is coupled with capacitive elements to form resonant LC tanks that can be telemetrically queried. The resulting LC tanks are deployed inside silicone mock arteries using standard angioplasty balloons and used in a passive telemetry scheme to sense changes in pressure and flow. Using water as the test fluid, the resonant peaks shift from about 215 to 208 MHz as the flow is increased from 0 to 370 mL/min. The second structure is a ring-shaped intraluminal cuff with two 100 × 750-µm² electrodes that are used to provide a direct transduction of flow velocity in the presence of a magnetic field. It is fabricated in a manner similar to the stentenna, but with an insulating segment. The voltage has a linear dependence on flow rate, changing by 3.1-4.3 µV per cm/s of flow (of saline) over a 180 cm/s dynamic range, with a magnetic field of about 0.25 T. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a preliminary exploration of high-speed contact mode performed with a polyimide probe. The probe is batch micromachined by a lithographic manufacturing process. It offers a spring constant of <0.1N/m, a resonance frequency of about 50kHz, and a tip diameter of 50–100nm. The probe is particularly suitable for scanning soft specimens such as biological and polymeric samples. Topographical contact mode imaging at high scanning rates of 48Hz (1.47mm/s) has been demonstrated, detecting features <100nm over a 15μm scan, yielding >7 bit resolution at 48Hz. Scanning rates of 16Hz (0.5mm/s) have been demonstrated for lateral force imaging with spatial resolution of 100nm over a 15μm scan, which translates into >7 bit resolution at 16Hz. These results suggest that the probe can be used in high throughput applications. [Copyright &y& Elsevier]

This paper reports on a batch mode planar pattern transfer process for bulk ceramics, glass, and other hard, brittle, nonconductive materials suitable for micromachined transducers and packages. The process is named LEEDUS, as it combines lithography, electroplating, batch mode micro electro-discharge machining (μEDM) and batch mode micro ultrasonic machining (μUSM). An electroplating mold is first created on a silicon or metal wafer using standard lithography, then using the electroplated pattern as an electrode to μEDM a hard metal (stainless steel or WC/Co) tool, which is finally used in the μUSM of the ceramic substrate. A related process (SEDUS) uses serial μEDM and omits lithography for rapid prototyping of simple patterns. Feature sizes of 25 μm within a 4.5 × 4.5 mm² die have been micromachined on glass-mica (Macor) ceramic plates with 34 μm depth. The ultrasonic step achieves 18 μm/min. machining rate, with a tool wear ratio of less than 6% for the stainless steel microtool. Other process characteristics are also described. As a demonstration, octagonal and circular spiral shaped in-plane actuators were fabricated from bulk lead zirconate titanate (PZT) plate using the LEEDUS/SEDUS process. A device of 20 μm thickness and 450 μm × 420 μm footprint produces a displacement of ≈2μm at 40 V. [ABSTRACT FROM AUTHOR]

This paper describes the design, fabrication, and testing of a single-chip micromachined implementation of a Knudsen pump, which uses the principle of thermal transpiration, and has no moving parts. A six-mask microfabrication process was used to fabricate the pump using a glass substrate and silicon wafer. The Knudsen pump and two integrated pressure sensors occupy an area of 1.5 mm × 2 mm. Measurements show that while operating in standard laboratory conditions this device can evacuate a cavity to 0.46 atm using 80 mW input power. The pumpdown time of an on-chip chamber and pressure sensor cavity with a total volume of 80 000 cubic micrometers is only 2 s, with a peak pump speed of 1 × 10-6 cc/min. High thermal isolation is obtained between the polysilicon heater and the rest of the device. [ABSTRACT FROM AUTHOR]

This paper presents an interface circuit for low-frequency dithering measurements of resistor-based transducers. It is demonstrated in the context of a polyimide-shank scanning thermal microscopy probe which provides high thermal sensitivity and spatial resolution, but has a low bandwidth from both mechanical and thermal perspectives. These pose challenges in temperature dithering and control, as well as noise immunity. The circuit includes a proportional-integral controller and a demodulator, along with appropriate amplifier and filter blocks. It keeps the average temperature of the probe tip constant while synchronously detecting variations in the second harmonic of the modulated signal as the tip is scanned across the sample surface. Strategic choices in the circuit architecture and topology are evaluated, and the overall system including the sensor and the circuit is simulated. Measurements of the implemented system show that a signal-to-noise ratio (SNR) of 15.7 is achieved while scanning a photoresist sample of 218 nm thickness on a silicon substrate, and that the detection limit for variations in thermal conductance is C 3 pW/K. [1125] [ABSTRACT FROM AUTHOR]

A new approach that uses planar batch manufacturing technologies is presented for the design and fabrication of coronary artery stents. Stent samples with different wall patterns have been fabricated from 50-µm-thick stainless steel foil using microelectrodischarge machining. Stents have been expanded to tubular shapes by using angioplasty balloons, both inside mock arteries and without external confinement (i.e., free-standing). Free-standing stents exhibit diameter variations of <±4%, almost zero radial recoil after deflation of the balloon, and longitudinal shrinkage of <3% upon expansion. A variation that uses breakable links to provide additional customization in electrical and mechanical properties is also presented. Loading tests reveal that the radial stiffness of some patterns is comparable to that of commercially available stents with greater wall thickness, while bending compliance, at 0.02 m/N for a 4-mm-long section of the stent, is also favorably large. [ABSTRACT FROM AUTHOR]

This paper reports the design, fabrication, packaging, and testing of a relay-type threshold accelerometer array. The array includes 15 different sense elements ranging from 10 to 150 g in 10 g increments, and triply redundant 20 and 100 g sense elements for a total of 19 elements. The devices were fabricated using a modified sacrificial LIGA technique that creates a 100–300 μm thick nickel structure with gold plated contacts. The threshold accelerometer array was evaluated by measuring its response to an applied acceleration (using a centrifuge) and by using two built-in testing methods: a pull-in voltage test, and a transit time test. Unlike the pull-in voltage test, the transit time test is sensitive to variations in the proof mass and spring constant. The average results from the centrifuge test, pull-in voltage test, and transit time test are all within approximately 20% of the expected values that are analytically calculated. In addition to the relay-type threshold sensing, the devices permit non-discretized readout of the acceleration using an alternative sense mode, in which the capacitance between the test electrode and proof mass was measured. This measurement shows a sensitivity of 670 aF/g for a 50 g threshold accelerometer, which is also within 20% of theoretical estimates. [Copyright &y& Elsevier]

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 break- down/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 SF6 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. [ABSTRACT FROM AUTHOR]

Reports that a series of experiments are used to determine characteristics of microdischarges, in order to understand the details of high-field breakdown in microstructures that are vacuum packaged. Non-applicability of Paschen's curve when planar microelectrodes are used; Breakdown voltage that is insensitive to pressure in the 1-20 torr range; Variation of spatial distribution of discharge current with the pressure and the power.

A silicon-micromachined servo-controlled capacitive pressure sensor is described. The use of a capped-cylinder shape with pick-off electrodes external to a sealed cavity permits this device to be fabricated in only three masking steps. Device behavior is evaluated experimentally and by finite element analysis. A fabricated device with 2 mm diameter, 9.7 µm structural thickness and 10 µm cavity height provides a measured sensitivity of 0.516 V/kPa over a dynamic range of 20-100 kPa gauge pressure, with a nonlinearity of <3.22% of full scale. The open-loop sensitivity of this device averaged over a dynamic range of 0-250 kPa is -408 ppm/kPa. A voltage bias applied to the servo-electrode can be used to tune both the open-loop and servo-controlled sensitivity by more than 30%. An alternative design in which the Si electrode is segmented to relieve residual stress provides 10-20% more open-loop sensitivity with similar structural dimensions. Fabricated devices are sealed within a metal package filled with an inert dielectric liquid. This enhanced open-loop sensitivity by a factor of about 1.7, and in servo-controlled operation, reduced restoring voltage by a similar factor. Measurements and analysis of temperature responses of these devices are presented. [ABSTRACT FROM AUTHOR]

This paper reports on the detection of trace contaminants in water by spectroscopy of micro glow discharges that operate in air or at moderate vacuum using liquid electrodes. A liquid electrode spectral emission chip (LEd-SpEC) has been developed to perform this function. The device is fabricated by a four mask process, and provides a reservoir and channels in a glass substrate, along with electrodes that bias the water sample. Liquid from the cathode is sputtered into the discharge, for spectroscopic detection of impurities. Using a commercial spectrometer, Na concentrations <10 ppm, and Pb concentrations of 5 ppm, and Al and Cr concentrations of 10 ppm have been measured. The ratio of Na spectral intensity to that of ambient N[sub 2] is shown to be a suitable measure of Na impurity concentration over several orders of magnitude. The addition of HNO[sub 3] to lower the pH of the liquid solution increases this ratio by almost an order of magnitude. By selectively doping the solution, the device can also he used as a customizable optical source for UV and visible wavelengths. [ABSTRACT FROM AUTHOR]

Investigates the silicon-silicon bonding by electromagnetic induction heating. Level of conductivity; Temperature distribution; Volumetric heating rates; Strength of the microwave-heated bonds; Infrared images of the bonded wafers.

Describes the micro-electro-discharge machining technique. Use of electrode arrays to achieved high parallelism; Usage of high aspect ratio LIGA-fabricated electrode arrays; Limitation imposed by pulse discharge circuits on machining rates.

Presents the generation of spatially confined plasmas. Application of plasmas to silicon etching; Use of the etching SF(sub 6) gas and direct current power; Variation of plasma confinement; Determination of power densities at moderate currents.

Describes the silicon micromachined thermal profilers (SMTP's) which are structurally comprised of a probe that can be longitudinally actuated by an integrated electrostatically driven suspension. Structure and theoretical analysis of the SMTP; Silicon micromachining technique used in fabricating SMTP; Discussion on mechanical characterization of dissolved wafer process comb drive suspensions; Conclusion.

Focuses on the use of the parametric modeling of a microaccelerometer for the purpose of comparing two optimization criteria in the design of experiments for finite-element analysis (FEA). What the accelerometer is comprised of; Information on the role of the FEA.

Presents a study to evaluate the impact of high-thermal budget anneals on polysilicon under a variety of processing conditions. Details on experiments done during study; Findings of study; Discussion on findings.

We report a method for addressing gas leakage in micromachined valves. The valves used for evaluating the proposed concept utilize a silicon valve seat that is bonded to a glass substrate and actuated by a piezoelectric stack, all of which are assembled within a ceramic package. The sealing method uses the capillary forces of a liquid sealant on the valve seat to reduce gas leakage below measurable limits. The gas leak rates are compared in valves with and without the seal enhancement. For example, a valve closes against 13.5 kPa with 10 V actuation, compared to 40 V required without the enhancement. Leakage is also evaluated for liquid flow. [ABSTRACT FROM AUTHOR]

We report a method for the selective chemisorption of oxygen and nitrogen in sealed cavities utilizing microdischarges between thin-film Ti electrodes. The method is used to remove contaminating air from both inert and organic gas environments, reducing the nitrogen and oxygen concentrations by factors of 50 and 16, respectively. A microchip-based optical emission spectroscopic sensor is used to monitor the purification. The purification improves the ability of the optical emission sensor to detect carbon by a factor of 8. The method has been tested at temperatures between 23 and 200 °C. [ABSTRACT FROM AUTHOR]

We explore the use of a naturally occurring zeolite, clinoptilolite, for a chip-scale, thermal transpiration-based gas pump. The nanopores in clinoptilolite enable the required free-molecular flow, even at atmospheric pressure. The pump utilizes a foil heater located between zeolite disks in a plastic package. A 2.3 mm thick zeolite disk generates a typical gas flow rate of 6.6×10-3 cc/min-cm2 with an input power of <300 mW/cm2. The performance is constrained by imperfections in clinoptilolite, which provide estimated leakage apertures of 10.2–13.5 μm/cm2 of flow cross section. The transient response of the pump is studied to quantify nonidealities. [ABSTRACT FROM AUTHOR]

The authors show that a variety of controlled flow patterns, including toroidal cells and surface doublets, can be generated in 80–400 μm thick liquid films by placing scanning microscopy probes with integrated heaters just above the surface (<400 μm separation). The probes project sharp temperature gradients on the liquid surface which drive Marangoni flow. Flow velocities approaching 3000 μm/s are experimentally demonstrated on length scales of 20–200 μm with <20 mW input power. For liquids such as water and oil, in which the surface tension coefficient is ≈0.2 mN/m K, flows >1000 μm/s can be accomplished with surface temperature perturbations <1 °C. This technique enables microfluidic manipulation on unpatterned substrates. [ABSTRACT FROM AUTHOR]

Abstract Miniaturized magnetron gauges are necessary for monitoring vacuum level in miniature vacuum chambers. This paper addresses the challenges of designing the magnetron cavity and configuring the electric and magnetic fields within it while meeting the contradictory constraints of small size and high vacuum level that make electron confinement and accumulation difficult. The resulting gauge has an internal volume of 0.3 cm3 and is designed for and fabricated by advanced 3D printing – including direct metal laser sintering of 316 L stainless steel. Additionally, it is capable of directly attaching to a standard vacuum electrical feedthrough. A particle tracing simulation is used to assess the electron confinement for a range of operating conditions. Experimental characterization shows that the operating pressures extend from 10 nTorr (1.33 μPa) to 1 mTorr (133 mPa). The gauge current is repeatable over the characterized pressures at various values of supply source voltage, V S , from −1000 V to −2500 V, and ranges from ≈1 nA to ≈100 μA over these pressures and voltages. The effects of V S and pressure are examined and compared to prior work. This gauge is at least 30× smaller than commercially available magnetron gauges (e.g., a typical inverted magnetron transducer has an internal volume of 15 cm3). Highlights • A 3D-Printed Miniature Magnetron Gauge for Ultra-High Vacuum Environments. • A 0.3 cm3 magnetron gauge is presented, ∼30× smaller than commercial gauges. • 3D-printing of gauge from 316 L stainless steel facilitates miniaturization. • The gauge is capable of measuring from 10 nTorr (1.33 μPa) to 1 mTorr (133 mPa). • The gauge sensitivity is linear over a wide range, at 0.416 A/Torr (3.13 mA/Pa). [ABSTRACT FROM AUTHOR]

The authors comment on a study which investigated the use of thermochemical lithography to pattern an electroluminescent polymer with nanoscale resolution, conducted by Franco Cacialli and colleagues at the London Centre for Nanotechnology in England. They also note that the study highlights the potential for high resolution and the ability to pattern a wide range of materials, two of the most promising aspects of thermochemical lithography.

This paper reports a magnet-less enhanced-efficiency electron trapping module (E3TM) that uses micromachined components to provide electron trapping using only RF electric fields. The structure of the E3TM is comprised of five microfabricated elements that include two perforated electrodes. Importantly, the electrode perforations are only 130 $\mu \text{m}$ in diameter in order to control the fringing electric field near the electrodes. The microfabricated elements enable a large volume efficiency, with the device occupying a volume of 1.63 cm3, of which 75.7% is available for the trap. The electron density as measured by proxy with a small probe near the center of the RF electron trap is approximated as $2.24 \times 10^{6}$ cm−3 when the E3TM is tuned to and operated at 96.9 MHz, and is approximated as $2.16 \times 10^{6}$ cm−3 when tuned to and operated at 141.3 MHz. This trap could potentially be used to enable a magnet-less ion pump for maintaining ultra-high vacuum in chip-scale atomic clocks or other atomic microsystems that are sensitive to magnetic fields. [2017–0296] [ABSTRACT FROM AUTHOR]

This paper reports an integrated micro gas chromatography (µGC) architecture which utilizes a bi-directional micropump. Four integral components-–the bi-directional Knudsen pump (KP2), a two-stage preconcentrator-focuser (PCF2), a separation column, and a gas detector-–are integrated in a 4.3 cm3 stack, forming a serial flow path. All four components are fabricated using the same three-mask process. Compared to the conventional approach used with multi-stage preconcentrators, in which valves are used to reverse flow between the sampling phase and the separation phase, this µGC architecture reduces the overall complexity. In this architecture, the vapors being sampled are drawn through the detector and column before reaching the PCF2. The microsystem operation is experimentally validated by quantitative analyses of benzene, toluene, and xylene vapors ranging in concentration from 43–1167 mg m−3. [ABSTRACT FROM AUTHOR]

Using distributed MEMS pressure sensors to measure small flow rates in high resistance fluidic channels is fraught with challenges far beyond the performance of the pressure sensing element. In a typical core-flood experiment, which may last several months, flow-induced pressure gradients are generated in porous rock core samples wrapped in a polymer sheath. Measuring these pressure gradients along the flow path requires high resolution pressure measurement while contending with difficult test conditions such as large bias pressures (up to 20 bar) and temperatures (up to 125 °C), as well as the presence of corrosive fluids. This work is directed at a system for using passive wireless inductive-capacitive (LC) pressure sensors that are distributed along the flow path to measure the pressure gradient. The sensors are wirelessly interrogated with readout electronics placed exterior to the polymer sheath for continuous monitoring of experiments. Using microfabricated pressure sensors that are smaller than ø15 × 3.0 mm3, an LC sensor design model for minimizing pressure resolution, accounting for sensor packaging and environmental artifacts is investigated and experimentally validated. A test setup, built to provide fluid-flow pressure differentials to LC sensors with conditions that mimic placement of the sensors within the wall of the sheath, is used to test the system. Experimental results show the microsystem operating over full-scale pressure range of 20,700 mbar and temperatures up to 125 °C, while achieving pressure resolution of <1 mbar, and resolving gradients of 10–30 mL/min, which are typical in core-flood experiments. [ABSTRACT FROM AUTHOR]

This paper presents a low-temperature batch mode packaging process for microsystems that are intended for harsh environments, in particular those with high pressure and high salinity, such as encountered in downhole data logging for oil exploration and production. The package consists of a shell made from a high-strength material, such as stainless steel (SS), and an insert made from a deformable material, such as aluminum (Al). The process includes a batch mode method for chip integration and a batch mode microcrimping method for package assembly. In a process demonstration, a $5 \times 5$ array of packages was made from SS 316 and Al alloy 3003, with dummy silicon chips encapsulated inside. Each package had an outer dimension of 0.5 mm along each axis. Two layers of coatings were deposited on the packages, including 50-nm-thick Al2O3 deposited by atomic layer deposition and 5- \mu \text{m} -thick Parylene C made by vapor phase deposition to protect against corrosion. The packages survive at least 72 h in the standard American Petroleum Institute hot brine at 80 °C. The packages also survive pressure >200 MPa. [ABSTRACT FROM AUTHOR]

This paper describes the analysis, design, and microfabrication of a Knudsen pump for high flow generation. The Knudsen pump generates gas streams from the cold end to the hot end using free-molecular flow without moving parts. The designed Knudsen pump has densely arrayed vertically oriented 2- \mu \textm wide rectangular channels for providing high flow. The temperature gradient is provided between a thin-film metal heater and a gridded Si heat sink in the Knudsen pump structure. The Knudsen pump is fabricated on a single silicon-on-insulator wafer using a four-mask lithographic process. The sidewalls of the rectangular channels are constructed by atomic layer deposition of Al2O3 on sacrificial Si channels and subsequent Si etching. The fabricated Knudsen pumps have designed footprints ranging from 0.4–3.2 cm ^2 . At atmospheric pressure, the fabricated Knudsen pumps provide a maximum measured air flow rate of >200 sccm with response time of <0.5 s. Experimental results have also shown that these Knudsen pumps are most suitable for pumping at moderate vacuum pressure of $\approx 200$ Torr (27 kPa). [2014-0367] [ABSTRACT FROM PUBLISHER]

A dynamic model is presented for a novel magnetoelastic rotary micro-motor. Magnetoelastic excitation results in a rotary motor with comparatively large payload even under direct wireless actuation, but the resulting stator behavior is significantly different from that of prior micro-scale rotary motors. A parametric modal model is developed from conservation of momentum, a second order linear distributed stator and ballistic rotor motion. The modes and a pre-stressed finite element model are also described to support the parametric modal model. The typical simulated model output and parametric analyses are presented with important trends and behaviors of the micro-motor motion, including stochastic features of rotary and vertical motion, and experimental validation. The dynamics of the micro-motor under certain inputs and design parameters are also estimated by the model. [ABSTRACT FROM AUTHOR]

This paper describes resonant wireless strain sensors fabricated from magnetoelastic alloys. The transduction mechanism is the ΔE effect-the change in stiffness of magnetoelastic materials with applied strain or magnetic field. This is measured as a shift in the resonant frequency and is detected wirelessly using pick-up coils utilizing the magnetoelastic coupling of these materials. The sensors are fabricated from a 28-μm-thick foil of Metglas 2826 MB (Fe40Ni38Mo4B18), a ferromagnetic magnetoelastic alloy, using microelectrodischarge machining. Two sensor types are described-single and differential. The single sensor has an active area of 7 × 2 mm2, excluding the anchors. At 23°C, it operates at a resonant frequency of 230.8 kHz and has a sensitivity of 13 × 103 ppm/mstrain; the dynamic range is 0.05-1.05 mstrain. The differential sensor includes a strain independent reference resonator of area 2 × 0.5 mm2 in addition to a sensing element of area 2.5 × 0.5 mm2 that is divided into two segments. The sensor resonance is at 266.4 kHz and reference resonance is at 492.75 kHz. The differential sensor provides a dynamic range for 0-1.85 mstrain with a sensitivity of 12.5 × 103 ppm/mstrain at 23°C. The reference resonator of the differential sensor is used to compensate for the temperature dependence of the Young's modulus of Metglas 2826 MB, which is experimentally estimated to be -524 ppm/°C. For an increment of 35°C, uncompensated sensors exhibit a resonant frequency shift of up to 42% of the dynamic range for the single sensor and 30% of the dynamic range of the differential sensor, underscoring the necessity of temperature compensation. The geometry of both types of sensors can be modified to accommodate a variety of sensitivity and dynamic range requirements. [ABSTRACT FROM AUTHOR]

This paper investigates a two-part architecture for a Knudsen vacuum pump with no moving parts. This type of pump exploits the thermal transpiration that results from the free-molecular flow in nonisothermal channels. For a high compression ratio, 162 stages are serially cascaded. The two-part architecture uses 54 stages designed for the pressure range from 760 to ≈ 50 Torr, and 108 stages designed for lower pressures. This approach provides greater compression ratio and speed than using a uniform design for each stage. Finite element simulations and analytical design analysis are presented. A five-mask single-wafer fabrication process is used for monolithic integration of the Knudsen pump that has a footprint of 12 × 15 mm2. The pressure levels of each stage are measured by integrated Pirani gauges. Experimental evaluation shows that, using an input power of ≈ 0.39 W, the evacuated chamber is reduced from 760 to ≈ 0.9 Torr, resulting in a compression ratio of ≈ 844. The vacuum levels are sustained during 37 days of continuous operation. [ABSTRACT FROM AUTHOR]

This paper reports a self-aligned three-dimensional process (3D-SOULE) that incorporates batch-mode micro ultrasonic machining (µUSM), lapping and micro electro-discharge machining (µEDM) for fabrication of concave and mushroom-shaped spherical structures from hard and brittle materials. To demonstrate the process, 1 mm structures are fabricated from glass and ruby spheres. The µEDM technique is used to create the tool for μUSM from stainless steel spheres. Stainless steel 440, which provides a tool wear ratio <5%, is chosen as the tool material. A 2 × 2 array is used for batch processing. For an ultrasound generator frequency of 20 kHz and a vibration amplitude of 15 µm, machining rates of 24 and 12 µm min−1 are obtained for glass and ruby spheres, respectively. An approximate linear relationship is observed between the measured roughness (Ra) of the machined surface and the product of the fracture toughness (KIC) and the hardness (H) of the workpiece material (KIC3/2H1/2). [ABSTRACT FROM AUTHOR]

This paper reports recent advances in batch mode micro-electro-discharge machining (μEDM) for high precision micromachining of metal alloys such as stainless steel. High-aspect-ratio silicon microstructures with fine feature sizes formed by deep reactive ion etching are used as cutting tools. To machine workpiece features with widths ≤10 μm, a silicon dioxide coating is necessary to passivate the sidewalls of the silicon tools from spurious discharges. In the machined workpieces, a minimum feature size of ≈7 im and an aspect ratio up to 3.2 are demonstrated by the batch mode iEDM of stainless steel 304 and titanium (Grade 1) substrates. Machining rates up to ≈5 μm min-1 in feature depth are achieved in batch mode micromachining of typical microfluidic structures, including arrays of channels and cavities of different sizes. The machined features are uniform across a die-scale area of 5 x 5 mm2. Other machining characteristics are also discussed. [ABSTRACT FROM AUTHOR]