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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-[micro]m interelectrode spacing. These devices were operated in nitrogen over a range of 10-2000 torr, at temperatures as high as 1000[degrees]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 [mm.sup.2]. 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. [2008-0262] Index Terms--Plasma applications, plasma confinement, plasma measurements, plasma properties, pressure effects, sensitivity.

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-ram-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-[micro]m-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. [2008-(1154] Index Terms--Elgiloy, magnetoelasticity, Metglas, microsensors, photochemical machining, resonant sensors.

This paper describes two stainless steel microstructures that are microelectrodischarge machined from 50-[micro]m-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 400 x 750-[micro][m.sup.2] 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 [micro]V per cm/s of flow (of saline) over a 180 cm/s dynamic range, with a magnetic field of about 0.25 T. [1733] Index Terms--Bloodflow, cardiac, microelectrodischarge machining, sensor network, wireless.

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 ([micro]EDM) and batch mode micro ultrasonic machining ([micro]USM). An electroplating mold is first created on a silicon of metal wafer using standard lithography, then using the electroplated pattern as an electrode to [micro]EDM a hard metal (stainless steel or WC/Co) tool, which is finally used in the [micro]USM of the ceramic substrate. A related process (SEDUS) uses serial [micro]EDM and omits lithography for rapid prototyping of simple patterns. Feature sizes of 25 [micro]m within a 4.5 x 4.5 [mm.sup.2] die have been micromachined on glass-mica (Macor) ceramic plates with 34 [micro]m depth. The ultrasonic step achieves 18 [micro]m/min. machining rate, with a tool wear ratio of less than 6% for the staiuless 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/[micro]m thickness and 450 [micro]m x 420 [micro]m footprint produces a displacement of [approximately equal to] 2[micro]m at 40 V. [1652] Index Terms--Ceramic micromachining, microelectro-discharge machining (EDM), piezoelectric micro actuator, ultrasonic micromachining.

Microsystems using electrothermal bent-beam microactuators have been demonstrated for a variety of applications including optical attenuators, RF switches, and micro positioners, thus creating a need for information on the longevity of these devices. This paper reports on the dc and pulse mode lifetime testing of this class of actuators constructed using polysilicon and p++ doped single crystal silicon. The relative temperature profile along the top surface of an actuator is experimentally verified by scanning probe microscopy. Displacement measurements are used to explore links between aging behavior and the design variables and operating conditions. At low power levels (which result in average operating temperatures of 300-400 [degrees]C) both polysilicon and p++ Si devices provide continuous dc operation for >1400 min. in air without change in amplitude. While some types of p++ Si devices show monotonic loss of amplitude in pulse tests, others have been operated up to 30 million cycles without degradation. The displacement for polysilicon actuators can either increase of decrease depending on the geometry of the device and operating conditions, both of which are related to temperature and stress of the structural members. Polysilicon grain transformations are observed over extended operation at high temperatures. Performance changes are correlated to material properties using SEM and TEM images. [1682] Index Terms--Actuator, electrothermal, lifetime, micromachining, polysilicon, in situ annealing.

This paper investigates the dynamics of bent-beam electrothermal actuators and their use in impact actuation of other micromechanical elements, and in particular the issue of energy efficiency achieved by temporal variations in electrical drive signals. A transient thermal model of an actuator beam shows that the uniformity of temperature profile is greater when activating with short electrical pulses, which results in larger achievable displacements and forces. A dynamic force analysis reveals that using a train of pulses, referred to as a burst pulse, for activation achieves significant impact forces due to high velocities at the point of impact. The analytical trends are confirmed through experimental observations of microfabricated metal test structures in which actuators work against bistable mechanisms. Measurements of 2 mm and 3mm long actuators show that pulsed activation results in > 5 x reduction in energy consumption, with the activation energy falling from over 1000 [mciro]J at dc activation, to less than 200 [micro]J using a 0.2-ms voltage pulse. The actuators however consume higher instantaneous power levels at shorter pulses, which may inhibit the use of pulses less than 1 ms in width. Further, the energy consumption through burst activation is 70% that of a single pulse, if sufficient impact forces are generated. [1566] Index Terms--Bent-beam electrothermal actuator, bistable structure, burst pulse drive, single pulse drive.

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 x 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 x [10.sup.-6] cc/min. High thermal isolation is obtained between the polysilicon heater and the rest of the device. [1073] Index Terms--High temperature, thermal isolation, thermal transpiration, thermomolecular, vacuum pump.

This paper reports on a micromachined Kelvin probe structure with an integrated scanning tip and an integrated electrothermal actuator that provides axial dithering motion. The device is fabricated from metal foil by a modified microelectrodischarge machining process that allows electrical isolation within the device. In particular, it permits the incorporation of a wide epoxy plug that creates an insulating gap with low parasitic capacitance between the probe and the actuator. The epoxy structures are found to withstand the thermal and mechanical conditions encountered during device operation. The device is used to measure changes in the external surface potential of a parylene microfluidic channel as a function of varying pH of liquid inside the channel. A contact potential difference of [approximately equal to] 6V is measured for a change in pH from 4 to 8 within the channel. The device is also used to map embedded charge in a thin Si[O.sub.2] layer on a Si substrate, showing it to be suitable for monitoring microelectronics manufacturing processes. [1072] Index Terms--Contact potential, oxide charge, pH, surface potential.

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 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 < 3 pW/K. [1125] Index Terms--Polyimide probe, scanning probe, thermal imaging.

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-[micro]m-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 Index Terms--Angioplasty, arc, electrodischarge, micromachining, stent.

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.

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 [micro]m structural thickness and 10 [micro]m 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 Index Terms--Dissolved wafer process, liquid encapsulation, pressure sensor, servo-controller.

This paper describes a laterally deflecting micromachined device that offers high sensitivity and wide dynamic range to electronically monitor the thermal expansion coefficient, tensile and compressive residual strain and Young's modulus of microstructural materials, as well as the temperature dependence of these properties. The device uses sidewall capacitance between interdigitated tines to sense displacement caused by the release of residual stress in bent-beam suspension. Electrostatic force is used to obtain load-deflection profiles. The suspensions and tines are arranged such that output is a differential readout, immune to common mode parasitic capacitance. Analytical and numerical modeling results are presented and the device concept is verified by three different fabrication approaches using polysilicon and nickel as structural materials. Measured values of residual strain, thermal expansion and Young's modulus are very consistent with measurements taken by other approaches and those reported previously. For example, the residual strain in certain electrodeposited Ni structures was tracked from 68.5 microstrain at 23[degrees]C to -420 microstrain at 130[degrees]C, providing an expansion coefficient of 8.2 ppm/K; the best fit Young's modulus provided by the device was 115 GPa. [737] Index Terms--Capacitive measurement, strain, temperature coefficient, Young's modulus.

A novel heating technique, electromagnetic induction heating (EMIH), uses electromagnetic radiation, ranging in frequency from a few megahertz to tens of gigahertz, to volumetrically heat silicon above 1000 [degrees]C in only a few seconds. Typical power requirements fall between 900 to 1300 W for silicon wafers 75 to 100 mm in diameter. This technique has successfully produced direct silicon wafer-to-wafer bonds without the use of an intermediate glue layer. Infrared images indicate void free bonds that could not be delaminated with knife-edge tests. In addition, four pairs of stacked wafers were bonded simultaneously in 5 min, demonstrating the potential for multiwafer bonds and high-throughput batch processing. [690] Index Terms--Bonding, electromagnetic, radiation, silicon.

This paper describes a micro-electro-discharge machining (micro-EDM) technique that uses electrode arrays to achieve high parallelism and throughput in the machining. It explores constraints in the fabrication and usage of high aspect ratio LIGA-fabricated electrode arrays, as well as the limits imposed by the pulse discharge circuits on machining rates. An array of 400 Cu electrodes with 20 [micro]m diameter was used to machine perforations in 50-[micro]m-thick stainless steel. To increase the spatial and temporal multiplicity of discharge pulses, arrays of electrodes with lithographically fabricated interconnect and block-wise independent pulse control resistance-capacitance (RC) circuits are used, resulting in >100x improvement in throughput compared to single electrodes. However, it was found to compromise surface smoothness. A modified pulse generation scheme that exploits the parasitic capacitance of the interconnect offers similarly high machining rates and is more amenable to integration. Stainless steel workpieces of 100 [micro]m thickness were machined by 100 [micro]m x 100 [micro]m square cross-section electrodes using in 85 s using an 80-V power supply. Surface smoothness was unaffected by electrode multiplicity. Using electrode arrays with four circuits, batch production of 36 WC-Co gears with 300 [micro]m outside diameter and 70 [micro]m thickness in 15 min is demonstrated. [692] Index Terms--Electro-discharge machining (EDM), high aspect ratio, LIGA, metal microstructures.

Parametric modeling of a microaccelerometer is used to compare two optimization criteria in the design of experiments for finite-element analysis (FEA). I- and D-optimality criteria are used to specify a near-minimal set of 38 input points in multidimensional input space at which FEA is performed. The accelerometer is comprised of a rigid proof mass and four suspension beams. Its response is determined as a function of acceleration along the input and cross axes, temperature, and two structural variables, and the related performance compromises are identified. It is shown that both I- and D-optimality criteria provide good results, with displacement residuals spread over ranges of magnitude 1.6 and 2.3 [[micro]meter], respectively, in a large input domain over which the range of displacement has a magnitude exceeding 13 [[micro]meter]. Additionally, the results suggest that for the particular device that was considered, the temperature coefficients of offset and sensitivity have smaller magnitudes when the suspension beams are attached near the center of each side of the proof mass. Index Terms - Inertial sensors, microsensors, microstructures.

We examine a new class of sensitive and compact passive strain sensors that utilize a pair of narrow bent beams with an apex at their mid-points. The narrow beams amplify and transform deformations caused by residual stress into opposing displacements of the apices, where vernier scales are positioned to quantify the deformation. An analytical method to correlate vernier readings to residual stress is outlined, and its results are corroborated by finite-element modeling. It is shown that tensile and compressive residual stress levels below 10 MPa, corresponding to strains below 6 x [10.sup.-5], can be measured in a 1.5-[[micro]meter]-thick layer of polysilicon using a pair of beams that are 2 [[micro]meter] wide, 200 [[micro]meter] long, and bent 0.05 radians (2.86 [degrees]) to the long axis of the device. Experimental data is presented from bent-beam strain sensors that were fabricated from boron-doped single crystal silicon using the dissolved wafer process and from polycrystalline silicon using surface micromachining. Measurements from these devices agree well with those obtained by other methods.

An improved bulk silicon micromachining process is presented. The simple method, which yields microelectromechanical devices from boron-doped bulk silicon, necessitates only three masking steps and overcomes limitations on the thickness-to-width aspect ratio with an improved reactive ion etching scheme. The technology is used in the fabrication of laterally driven comb structures, some of which are analysed in the study.

This paper reports on the use of bent-beam electrothermal actuators for the purpose of generating rotary and long-throw rectilinear displacements. The rotary displacements are achieved by orthogonally arranged pairs of cascaded actuators that are used to rotate a gear. Devices were fabricated using electroplated Ni, [p.sup.++] Si, and polysilicon as structural materials. Displacements of 20-30 [micro]m with loading forces [is greater than] 150 [micro]N at actuation voltages [is less than] 12 V and power dissipation [is less than] 300 mW could be achieved in the orthogonally arranged actuator pairs. A design that occupies [is less than] 1 [mm.sup.2] area is presented. Long-throw rectilinear displacements were achieved by inchworm mechanisms in which pairs of opposing actuators grip and shift a central shank that is cantilevered on a flexible suspension. A passive lock holds the displaced shank between pushes and when the power is off. This arrangement permits large output forces to be developed at large displacements, and requires zero standby power. Several designs were fabricated using electroplated Ni as the structural material. Forces [is greater than] 200 [micro]N at displacements [is greater than] 100 [micro]m were measured. [624] Index Terms--Inchworm, micromachining, micromotor, positioner, scanner, thermal actuator.

This paper describes electrothermal microactuators that generate rectilinear displacements and forces by leveraging deformations caused by localized thermal stresses. In one manifestation, an electric current is passed through a V-shaped beam anchored at both ends, and thermal expansion caused by joule heating pushes the apex outward. Analytical and finite element models of device performance are presented along with measured results of devices fabricated using electroplated Ni and [p.sup.++] Si as structural materials. A maskless process extension for incorporating thermal and electrical isolation is described. Nickel devices with 410-[micro]m-long, 6-[micro]m-wide, and 3-[micro]m-thick beams demonstrate 10 [micro]m static displacements at 79 mW input power; silicon devices with 800-[micro]m-long, 13.9-[micro]m-wide, and 3.7-[micro]m-thick beams demonstrate 5 [micro]m displacement at 180 mW input power. Cascaded silicon devices using three beams of similar dimensions offer comparable displacement with 50-60% savings in power consumption. The peak output forces generated are estimated to be in the range from 1 to 10 mN for the single beam devices and from 0.1 to 1 mN for the cascaded devices. Measured bandwidths are [approximately equal] 700 Hz for both. The typical drive voltages used are [is less than or equal to] 12 V, permitting the use of standard electronic interfaces that are generally inadequate for electrostatic actuators. [592] Index Terms--Micromachining, micromotors, positioners, thermal actuators.

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.

This paper describes micromachined scanning thermocouple probes that exploit the low thermal conductivity and the high mechanical flexibility of polyimide as a structural material. They are surface micromachined using a low-temperature six-mask process suitable for appending to a CMOS fabrication sequence. The probes are 200-1000-[micro]m long, 40-120-[micro]m wide, and of varying thickness. They are assembled by a flip-over approach that eliminates the need for dissolving the substrate wafer or removing the probe from it. Temperature sensing is provided by thin-film Ni/W or chromel/alumel thermopiles embedded in the polyimide, which provide Seebeck coefficients of 22.5 and 37.5 [micro]V/K per junction, respectively. Modeling results indicate that the low thermal conductivity of polyimide, causes the temperature drop along the probe length to be much higher than with other candidate materials such as Si or Si[O.sub.2], which contributes to improved thermal isolation of the sample and higher temperature sensitivity of the probe. However, the response time of the probe is compromised, and the measured -3 dB bandwidth of the probes is [approximately equals] 500 Hz. A sample scan is presented. [561] Index Terms--Polymide, scanning microscopy, surface micromachining, thermocouple.

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 on amicromachined Si/glass stack recuperative heat exchanger with in situ temperature sensors. Numerous high-conductivity silicon plates with integrated platinum resistance temperature detectors (Pt RTDs) are stacked, alternating with low-conductivity Pyrex spacers. The device has a 1 × 1-cm2 footprint and a length of up to 3.5 cm. It is intended for use in Joule-Thomson (J-T) coolers and can sustain pressure exceeding 1 MPa. Tests at cold-end inlet temperatures of 237 K-252 K show that the heat exchanger effectiveness is 0.9 with 0.039-g/s helium mass flow rate. The integrated Pt RTDs present a linear response of 0.26%-0.30%/K over an operational range of 205 K-296 K but remain usable at lower temperatures. In self-cooling tests with ethane as the working fluid, a J-T system with the heat exchanger drops 76.1 K below the inlet temperature, achieving 218.7 K for a pressure of 835.8 kPa. The system reaches 200 K in transient state; further cooling is limited by impurities that freeze within the flow stream. In J-T self-cooling tests with an external heat load, the system reaches 239 K while providing 1 W of cooling. In all cases, there is an additional parasitic heat load estimated at 300-500 mW. [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]

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 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]