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Multilayer interconnections are needed for microdevices with a large number of independent electrodes. A multi-level photolithographic process is commonly employed to provide multilayer interconnections in integrated circuit (IC) devices, but it is often too expensive for large-area or disposable devices frequently needed for microfluidics. The printed circuit board (PCB) can provide multilayer interconnection at low cost, but its rough topography poses a challenge for small droplets to slide over. Here we report a low-cost fabrication of low-topography multilayer interconnects by selective and controlled anodization of thin-film metal layers. The process utilizes anodization of metal (tantalum in this paper) or, more specifically, repetitions of a partial anodization to form insulation layers between conductive layers and a full anodization to form isolating regions between electrodes, replacing the usual process of depositing, planarizing, and etching insulation layers. After verifying the electric connections and insulations as intended, the developed method is applied to electrowetting-on-dielectric (EWOD), whose complex microfluidic products are currently built on PCB or thin-film transistor (TFT) substrates. To demonstrate the utility, we fabricated a 3 metal-layer EWOD device with steps (surface topography) less than 1 micrometer (vs. > 10 micrometers of PCB EWOD devices) and confirmed basic digital microfluidic operations.

Thermal conductance switches enable active and reconfigurable thermal control and management for a wide variety of applications. We demonstrate a thermal conductance switch based on the actuation of liquid droplets in a co-planar electro-wetting-on-dielectric (EWOD) configuration. By eliminating the need for relative motions of two heat transfer surfaces, the device provides a significant advantage in the mechanical design of adaptive thermal control systems. Proof-of-concept devices are constructed and characterized to confirm the mechanism of droplet detachment and attachment for thermal switching. Numerical simulation is performed to elucidate the experimentally measured thermal performance and identify thermocapillary flows as an important contributor to heat transfer for certain dielectric liquids. The present work provides a proof-of-concept demonstration of novel thermal conductance switches and offers physical insights to help systematically design the switches for practical applications.

We propose a convenient method to detect the detailed wetting states of grating-type superhydrophobic (SHPo) surfaces under water. Although the silvery plastron makes the nonwetted state easily discernable from the wetted, which appears black, various sub-states of the nonwetted state have so far been indistinguishable without special techniques such as confocal microscopy. For certain applications, however, different sub-states within the nonwetted state may have dramatically different effects. Applied for drag reduction experiments, here we develop an observation strategy that reveals the sub-states of plastron on grating SHPo surface to naked eyes for the first time. The results are confirmed by visualizing the liquid-air interfaces on the submerged surface with optical microscope.

Owing to advances in micro- and nanofabrication methods over the last two decades, the degree of sophistication with which solid surfaces can be engineered today has caused a resurgence of interest in the topic of engineering surfaces for phase change heat transfer. This review aims at bridging the gap between the material sciences and heat transfer communities. It makes the argument that optimum surfaces need to address the specificities of phase change heat transfer in the way that a key matches its lock. This calls for the design and fabrication of adaptive surfaces with multiscale textures and non-uniform wettability. Among numerous challenges to meet the rising global energy demand in a sustainable manner, improving phase change heat transfer has been at the forefront of engineering research for decades. The high heat transfer rates associated with phase change heat transfer are essential to energy and industry applications; but phase change is also inherently associated with poor thermodynamic efficiency at low heat flux, and violent instabilities at high heat flux. Engineers have tried since the 1930s to fabricate solid surfaces that improve phase change heat transfer. The development of micro and nanotechnologies has made feasible the high-resolution control of surface texture and chemistry over length scales ranging from molecular levels to centimeters. This paper reviews the fabrication techniques available for metallic and silicon-based surfaces, considering sintered and polymeric coatings. The influence of such surfaces in multiphase processes of high practical interest, e.g., boiling, condensation, freezing, and the associated physical phenomena are reviewed. The case is made that while engineers are in principle able to manufacture surfaces with optimum nucleation or thermofluid transport characteristics, more theoretical and experimental efforts are needed to guide the design and cost-effective fabrication of surfaces that not only satisfy the existing technological needs, but also catalyze new discoveries

Superhydrophobic and superoleophobic surfaces have so far been made by roughening a hydrophobic material. However, no surfaces were able to repel extremely-low-energy liquids such as fluorinated solvents, which completely wet even the most hydrophobic material. We show how roughness alone, if made of a specific doubly reentrant structure that enables very low liquid-solid contact fraction, can render the surface of any material superrepellent. Starting from a completely wettable material (silica), we micro- and nanostructure its surface to make it superomniphobic and bounce off all available liquids, including perfluorohexane. The same superomniphobicity is further confirmed with identical surfaces of a metal and a polymer. Free of any hydrophobic coating, the superomniphobic silica surface also withstands temperatures over 1000°C and resists biofouling.

Progress in the miniaturization of batteries has lagged well behind that of microelectronics. Although lithium-ion (Li-ion) battery technology has been vital in advancing portable consumer electronics, it is not clear whether future generations of microscale devices can be powered using traditional battery designs. In this paper, we report on the fabrication and properties of battery electrodes comprised of arrays of vertically aligned carbon rods. The electrodes exhibit good reversibility and represent the first carbon arrays to achieve areal capacities greater than 5 mAh cm−2 at relatively large current densities, although the capacity does fade with cycling. The 3D battery designs based on these architectures offer the promise of achieving high energy densities within small footprint areas.

We present an electrostatically actuated rotary stage featuring liquid rings, which serve as both mechanical bearings and electric connections between the rotor and the substrate. The liquid rings are formed by confining a liquid inside hydrophilic grooves and repelling it from the superhydrophobic surfaces outside the grooves. Made of a fluid, the liquid-ring bearing avoids the dry friction of the solid bearings, significantly improving the reliability. Formed as rings, it avoids the resistance of contactangle hysteresis sliding over droplets, and hence dramatically reducing the static friction. Furthermore, surface tension facilitates the self-alignment of the rotor to the substrate and stator during the assembly and provides the stability against drift and shock during operation. Electrically, each liquid ring passes an independent electric signal, allowing a direct electrical path between the substrate and potential components on the rotor. A three-phase electrostatic rotary stage has been design, fabricated, and tested. The minimum torque to initiate the rotation is ∼2.5nṄm - hundreds of times smaller than droplet-based counterparts. The device has operated successfully by applying sequential voltages of 50V DC between the rotor and the stators. The electric transmission has been verified by powering an LED on a rotating rotor. This is the first report of an electrostatically actuated rotating microdevice with a liquid bearing and a direct power transmission. © 2013 IEEE.

A gas in between micro- or nanostructures on a submerged superhydrophobic (SHPo) surface allows the liquid on the structures to flow with an effective slip. If large enough, this slippage may entail a drag reduction appreciable for many flow systems. However, the large discrepancies among the slippage levels reported in the literature have led to a widespread misunderstanding on the drag-reducing ability of SHPo surfaces. Today we know that the amount of slip, generally quantified with a slip length, is mainly determined by the structural features of SHPo surfaces, such as the pitch, solid fraction, and pattern type, and further affected by secondary factors, such as the state of the liquid–gas interface. Reviewing the experimental data of laminar flows in the literature comprehensively and comparing them with the theoretical predictions, we provide a global picture of the liquid slip on structured surfaces to assist in rational design of SHPo surfaces for drag reduction. Because the trapped gas, called plastron, vanishes along with its slippage effect in most application conditions, lastly we discuss the recent efforts to prevent its loss. This review is limited to laminar flows, for which the SHPo drag reduction is reasonably well understood.

Finding the size and distance of objects viewed through a single optical path-a typical endoscopic condition-is a challenge. Stereo imaging, which would provide the size and distance information, typically requires multiple optical channels or other elaborate techniques, increasing the endoscope diameter and system complexity. This paper reports the development of a miniature flipping disk device that enables stereo measurement, and demonstrates the operation of the device installed in an endoscope. The fabricated Pyrex disk (1.2 mm in diameter and 485 μm in thickness), anodically bonded to a 50-μm-thick silicon vertical comb-drive actuator, is flipped to ±10.7° at a resonant frequency of 414 Hz by 10 VAC of electrostatic actuation. The image shift made by such glass flipping provides a reference dimension, against which the real size and distance of objects seen through a standard single-channel endoscope can be estimated.

We report monolithic fabrication of parallel-plate electrowetting-on-dielectric (EWOD) chips for digital micro-fluidics of picoliter droplets. Instead of assembling a second substrate to form a top plate-the common practice with all previous parallel-plate EWOD chips-the top plate is surface micromachined as a transparent thin-film membrane that forms a monolithic cavity having a gap height on the order of micrometers with excellent accuracy and uniformity. The membrane is embedded with EWOD driving electrodes and confines droplets against the device substrate to perform digital microfluidic operations. Two main attributes of the monolithic architecture that distinguish it from tradition methods are: (i) it enables excellent control of droplet dimensions down to the micrometer scale, and (ii) it does not require the typical alignment and assembly steps. Basic device functions such as creation and splitting are verified by EWOD actuation of ~100 picoliter droplets surrounded by air or oil inside a 10 μm-high cavity. Additionally, flow focusing of droplets containing 5.3 μm beads demonstrates one example of the utilities afforded by monolithic fabrication.

A high-yield fabrication process for dense arrays of very-high-aspect-ratio (VHAR) freestanding metal posts and gratings is developed. Silicon molds of regularly arranged through-holes or trenches are first fabricated by photoelectrochemical etching. By studying the etching parameters, including geometry constraint, current density and potential, electrolyte concentration, and etching time, we succeed to produce dense arrays of VHAR holes ( depth = 610 μm; diameter = 5 μm; pitch = 14 μm) and trenches (depth = 320 μm ; width = 4 μm; pitch = 8 μm) with yields higher than 99% on 2-cm2 processing areas. The VHAR molds are then filled with metals using a new bottom-up electroplating technique, which features an intermittent vacuum degassing to remove the air and hydrogen bubbles from such deep and narrow voids during the plating. Zinc and nickel are successfully electroplated in high quality, and the freestanding metal structures are obtained by removing the silicon molds by XeF2 etching. Obtained are maximum aspect ratios of 120 : 1 for posts (height = 600 μm; diameter = 5 μm; pitch = 14 μm) and over 60 : 1 for gratings (height = 250 μm; width = 4 μm; pitch = 8 μm) with yields higher than 99% on ~ 0.5-1-cm2 samples.

Thin-film thermoelectric devices have potentially greater efficiency than bulk devices because of quantum and classical size effects involving electrons and phonons. We discuss criteria for the design of thin-film thermoelectric microcoolers to achieve high performance. The devices considered are membrane structures based on electron transport along the film plane. A model is developed to include the effects of heat loss and leg shape. The design is optimized based on the modeling results and used to guide microcooler fabrication.

This paper reports the design, fabrication, and testing of a liquid-metal (LM) droplet-based radio-frequency microelectromechanical systems (RF MEMS) shunt switch with dc-40 GHz performance. The switch demonstrates better than 0.3 dB insertion loss and 20 dB isolation up to 40 GHz, achieving significant improvements over previous LM-based RF MEMS switches. The improvement is attributed to use of electrowetting on dielectric (EWOD) as a new actuation mechanism, which allows design optimized for RF switching. A two-droplet design is devised to solve the biasing problem of the actuation electrode that would otherwise limit the performance of a single-droplet design. The switch design uses a microframe structure to accurately position the liquid-solid contact line while also absorbing variations in deposited LM volumes. By sliding the liquid-solid contact line electrostatically through EWOD, the switch demonstrates bounceless switching, low switch-on time (60 mus), and low power consumption (10 nJ per cycle).

A thin-film encapsulation process, featuring low-temperature steps, hermetic sealing (preliminary), and RF-compatible shell, is reported. Uniquely attractive as compared with the existing MEMS packaging approaches is its capability to monolithically package metal microstructures inside a microcavity on chip in one continuous surface-micromachining process. The key for this process is a technique to fabricate a large freestanding porous membrane on chip by postdeposition anodization of thin-film aluminum at room temperature. The porous-alumina membrane allows for the diffusion of gas or liquid etchants through the nanopores to etch away the sacrificial material underneath, freeing the movable microstructures encapsulated inside the cavity. To seal the package, a thin film is deposited over the alumina shell whose nanoscale pores of a high aspect ratio (> 30) do not allow any detectable penetration of the sealing material. The low-temperature (

This paper describes a technique to increase the efficiency of magnetic concentration on an electrowetting-on-dielectric (EWOD)-based droplet (digital) microfluidic platform operated in air, i.e., on dry surface. Key differences in the force scenario for droplet microfluidics vis-a-vis the conventional continuous microfluidic systems are identified to explain the rationale behind the proposed idea. In particular, the weakness of the magnetic force relative to the bead-substrate adhesion and the liquid-air interfacial tension is highlighted, and a new technique to achieve high-efficiency magnetic collection with the assistance of the interfacial force is proposed. An improvement in collection efficiency (e.g., from ~ 73% to ~ 99%) is observed with the new technique of ldquomeniscus-assisted magnetic bead collectionrdquo. In addition, isolation of the magnetic species from a mixed sample of magnetic and nonmagnetic beads is demonstrated. Comparison with other related reports is also presented.

We report the contact line dynamics of sessile water droplets, 1.1-1.6 mm in radius, spread by electrowetting in air. Coplanar electrodes patterned on the substrate allow a true sessile condition with no wire into the droplet. The frequency response of the droplets is studied using 25 VAC ranging from 10 to 205 Hz. The effect of contact angle hysteresis is seen in form of stick-slip motion. A model developed provides a good match to the experimental result. Step response is studied with voltages in the range of 20-80 VDC. Two regimes of motion are observed. In the first regime, local flows cause the contact line speed to increase and reach a maximum while the contact angle is still changing. Global flows in the second regime cause the contact line to move with a reduced speed and attain the spherical shape pertaining to the new equilibrium contact angle. A model is used to describe the motion.

Liquid-metal (LM) droplet-based MEMS switches have mostly been restricted to slow applications until now due to the following reasons: (1) a relatively large switching gap (distance) needed to accommodate imprecise volumes and locations of droplets on the device and (2) lack of high-speed actuation to move the droplets quickly across the switching gap. To combat these problems, we explore switching by sliding the solid-LM-gas triple contact line rather than the entire droplet. This new approach allows us to use a microframe, which not only consistently positions the LM droplet but also makes the switching gap less sensitive to the errors in the deposited-droplet volume, allowing us to design microswitches with very small switching gaps (e.g., 10 mum for 600 mum-diameter droplets). Furthermore, a study of electrowetting-on-dielectric identifies a regime of fast contact-line sliding at the onset of droplet spreading. By moving the contact line fast across a small switching distance, we demonstrate a low-latency LM switch with 60 mus switch-on latency ( ~ 20 times better than other LM-switch technologies) and better than 5 mus signal rise/fall time, while boasting no contact bounce, as expected from an LM switch. High power-handling capability and long-term reliability are also discussed.

A tilt sensor has been realized based on electrolytic solution, which is filled in a micromachined 400 μm-deep cavity and responded relative to tilt angle due to the gravity. The device consists of anisotropically etched deep cavity to contain electrolytic solution and Au/NiCr metal electrodes to detect the electrical signal formed on non-planar surfaces from the substrate surface to the bottom of the cavity. The tilting motion of the device changes the immersed area of the electrodes in the electrolytic solution and the unbalanced ratio of the elecrical siganal is monitored by the change in its resistance. Injected electrolyte solution should be carefully determined because it must have not only small resistance but also small viscosity. Potassium hydroxide (KOH) solution is chosen as the electrolyte due to the relatively high ionic conductance and it is diluted with methanol for an optimized concentration considering the viscosity. The fabricated electrolytic tilt sensor is excited by an alternating current to prevent electrolysis in the electrolyte-filled cavity and measured by Wheatstone bridge circuit to read the variation of resistance with respect to an incoming inclination. Experiments reveal that the resistance of KOH electrolyte is smallest at 5 wt% in its concentration and 800 Hz in the driving frequency. The tested Micro Electro Mechanical Systems (MEMS)-based electrolytic tilt sensor with KOH solution shows a resolution of approximately 50 mV per 1° of inclination angle change and operating angle range of ±60°. The measured output characteristic of the fabricated MEMS-based electrolytic tilt sensor sustains comparison with other conventional electrolytic tilt sensors. Moreover, MEMS-based sensor prevails in its small size, low cost and possible mass production.

Silicon-micromachining techniques have been combined with conventional material-synthesis methods to develop microelectrodes for 3-D microbatteries. The resulting electrodes feature an organized array of high-aspect-ratio microscale posts fabricated on the current collector to increase their surface area and volume for a given footprint area of the device. The diameter of the posts ranges from a few micrometers to a few hundred micrometers, with aspect ratios as high as 50. The fabrication approach is based on micromolding of the electrode materials and subsequent etching of the mold to release the electrode structures. Deep reactive-ion-etching or photo-assisted anodic etching has been used to form an array of deep holes in the silicon mold. Electroplating or colloidal-processing method has been used to fill the mold with battery-electrode materials. Measurements on electrochemical half-cells indicated that the 3-D electrode arrays, which are composed of vanadium oxide nanorolls or carbon, exhibited much greater energy densities (per-footprint area) than that of the traditional 2-D electrode geometries. The use of electroplating enabled us to fabricate 3-D interdigitated arrays of nickel and zinc; and battery operation was demonstrated. [2006-0293].

In this paper, we present a novel microfabrication technique that solves the main problems of existing monolithic on-chip encapsulation methods for polysilicon surface micromachining. The encapsulation technique includes the formation of a nanoporous polysilicon shell, creation of a cavity by removing the sacrificial layer through the pores in the shell, and sealing the cavity at a low pressure. Formed porous by postdeposition electrochemical etching on top of a sacrificial layer, the porous polysilicon is thick enough to free-stand when released, unlike the previously reported as-deposited permeable polysilicon. Benefiting from the dense pores through the polysilicon layer, the sacrificial material was removed in just one minute, and the vacuum sealing was achieved by a low-pressure chemical vapor deposition polysilicon as thin as 1000 Aring with no sealing material detected inside the cavity. The pressure inside the sealed cavity, measured by an encapsulated polysilicon Pirani gauge, was around 130 mTorr and showed no noticeable leak (

This study was conducted to find out effects of abnormal kernels of 0 to 30% in brown rice on quality characteristics during milling using friction type test mill. The average hardness values of abnormal and normal brown rice kernels were 6.52 kg, 8.48 kg, respectively. According to the increase of abnormal kernels in brown rice, grain temperature, required electrical energy, the broken kernels ratio, and the weight of solid matter on the surface of milled rice were increased due to crush of the abnormal kernels during milling, which proves that abnormal kernels in brown rice should be removed before milling to improve milling characteristics.

We develop a transparent superhydrophobic (SHPo) surface with an imbedded electrode to investigate the selflimiting gas recovery mechanism reported for a long-term SHPo state underwater [1]. The surface is made from two Teflon sheets by two hot-embossing steps that embed a metal strip in between. The self-initiation of electrochemical gas generation at liquid impalement and self-termination at full gas recovery of a microtrench is directly visualized. Furthermore, we develop a high-pressure chamber to study the mechanism at elevated hydrostatic pressures (up to 4 atm tested).

We report a new method to fabricate multilayer interconnections without requiring wet or dry etching or deposition of insulating layers. Three levels of electrical connections are obtained by merely repeating deposition, photolithography, and anodization of a metal layer. Without the need to etch metal layers or deposit and etch insulation layers, the overall process is simple, cheap, safe, and of low temperature. While the utility is general for a wide variety of microdevices and electronics, in this paper we demonstrate one application by developing a low-cost fabrication of a large-array electrowetting-on-dielectric (EWOD) chip that requires three metal layers.

We report a micro- and nano-machined surface cavity on which boiling nucleation resumes after ceasing in perfluorohexane (i.e., FC-72, a Fluorinert™ from 3M™) for a short time. To the best of our knowledge, this is the first such success with FC-72, which has the lowest surface tension of all available liquids and completely wets any existing material including Teflon® so that all surface cavities get flooded once nucleation stops. Despite the wide usage in electronics cooling, FC-72 was never considered for boiling heat transfer because once cooled boiling would not restart without an excessive heating. Our result experimentally supports the half-century-old idea of doubly re-entrant cavities envisioned to facilitate more stable nucleation, encouraging further development.

We report that superhydrophobic (SHPo) surfaces based purely on surface structuring shows a robust super-repellency under a prolonged contact with serum droplet as an example of protein-rich biological fluids. In contrast, normal SHPo surfaces, which are based on surface chemistry and surface structuring, lose repellency and eventually get wetted in the same tests. This is the first report of a SHPo surface maintaining super-repellency to a biological fluid.

© The Royal Society of Chemistry 2015. Despite the fact that superhydrophobic surfaces possess useful and unique properties, their practical application has remained limited by durability issues. Among those, the wetting transition, whereby a surface gets impregnated by the liquid and permanently loses its superhydrophobicity, certainly constitutes the most limiting aspect under many realistic conditions. In this study, we revisit this so-called Cassie-to-Wenzel transition (CWT) under the broadly encountered situation of liquid drop impact. Using model hydrophobic micropillar surfaces of various geometrical characteristics and high speed imaging, we identify that CWT can occur through different mechanisms, and at different impact stages. At early impact stages, right after contact, CWT occurs through the well established dynamic pressure scenario of which we provide here a fully quantitative description. Comparing the critical wetting pressure of surfaces and the theoretical pressure distribution inside the liquid drop, we provide not only the CWT threshold but also the hardly reported wetted area which directly affects the surface spoiling. At a later stage, we report for the first time to our knowledge, a new CWT which occurs during the drop recoil toward bouncing. With the help of numerical simulations, we discuss the mechanism underlying this new transition and provide a simple model based on impulse conservation which successfully captures the transition threshold. By shedding light on the complex interaction between impacting water drops and surface structures, the present study will facilitate designing superhydrophobic surfaces with a desirable wetting state during drop impact.

We report a simple but efficient nanofabrication method to create a dense (nanoscale pitch) array of silicon nanostructures (post and grate) of varying height and shape over a large sample area. By coupling interference lithography with deep reactive ion etching (DRIE) in one process flow, we?achieved silicon nanostructures of excellent regularity, currently with a pitch (i.e., period) of 230?nm, and uniform coverage, currently over 2 ? 2?cm2. The new nanofabrication practice of coupling interference lithography with DRIE not only simplified the nanofabrication process but also produced high-aspect-ratio (higher than 10) nanostructures. By regulating etching parameters, the nanoscopic scalloping problem typical in Bosch DRIE was not only controlled but also utilized to realize sophisticated sidewall profiles, such as tips with a pointed or a re-entrant profile. We showed the tips could be further sharpened by thermal oxidation and subsequent removal of the oxide. Well-defined nanostructures over a large area with controllable sidewall profiles and tip shapes open new application possibilities in areas beyond nanoelectronics, such as microfluidics and tissue engineering.

This paper studies and characterizes electrowetting-on-dielectric (EWOD) actuations on coplanar electrodes with an electrode-free cover plate or no cover plate. By arranging driving and reference electrodes on one plate, such an EWOD configuration can accommodate more sensing mechanisms from above and thus allows increased flexibility for system development. Various coplanar electrodes are tested for contact angle changes by EWOD with a focus on the effect of the percentage gap between electrodes and are found to be in good agreement with a simple analytical model. The droplet-moving devices demonstrate the successful moving, cutting and merging of droplets (~0.1 µl) in a parallel-plate configuration, i.e., between the driving plate with coplanar electrodes and the passive plate with no electrode. EWOD actuation in single plate configuration, i.e. no cover plate, is also demonstrated, adding additional flexibility for the system design.

The dominance of surface tension over inertia in microscale and favorable scale effect for electrostatic actuation allow electrostatically driven metal-droplet systems practical. Because of such potential advantages as low contact resistance, naturally bistable operation, and high switch density, the liquid-metal droplet switch is an excellent candidate for reconfigurable circuit interconnections. Following earlier droplet microswitch examples and related studies of metal-droplet behavior, we report the first functioning droplet switch directly integrated on top of a functional CMOS circuit. While the surface tension dominance makes the droplet switches practical as a mechanical system and also brings bistability, it also requires a high electric field to move the droplet. We implement the concept of physical surface modification to lower the driving voltage to a value that a commercial CMOS process can provide. Unlike previous droplet switches, the reported device is planar-processed to allow the integration with the underlying CMOS circuits. The integrated switch is made functional by such provisions as self-limiting actuation and by optimizing the electrostatic force in the planar configuration and avoiding liquid-metal "flooding" into surface patterns. A fabrication process for low driving voltage and high compatibility is developed to integrate the droplet switch on the custom-developed CMOS chip. A packaging method adapted from well-established microelectronic packaging isolates the active switch space from the surrounding environment. Low driving voltage (as low as 15 V) and millisecond switching speed are achieved by the current on-chip device. While the current device uses ~150 mum droplets for demonstration, additional theoretical and experimental results indicate that further miniaturization would lead to smaller devices and lower operation voltage

An electrolytic tilt sensor has been designed and fabricated using micro electro mechanical systems (MEMS) technique. The anisotropic KOH etching is used to form a deep Si cavity where conductive electrolyte solution is filled in. Au/NiCr electrodes are simultaneously deposited and patterned using e-beam evaporator with an aligned shadow mask, which is fabricated by through-wafer via etching on a 400-µm-thick Si wafer. A composite electrolyte of 4.8 µL in the volume is filled in the anisotropically-etched cavity that has a volume of 7.3 µL. The electrolyte solution is comprised of variable amount of KCl and a mixture of deionized (DI) water, ethanol and methanol (50, 25, and 25 vol %, respectively). When the electrolyte is injected into the cavity, a cover glass is bonded to seal the electrolyte solution. The fabricated electrolytic tilt sensor is excited by an alternating current to prevent electrolysis in the electrolyte-filled cavity and measured by Wheatstone bridge setup that reads the variation of resistance with respect to an incoming inclination. The measured output characteristic of the MEMS-based electrolytic tilt sensor is as good as that of a conventional electrolytic tilt sensor. Moreover, MEMS-based sensor prevails in its small size, low cost and possible mass production.

The effect of medium components such as wheat bran, rice bran, oat meal, and soybean meal as basic ingredients and KH2PO4, glucose, and molasses as additives on mass production and anti-potato common scab activ ity of a streptomycete A020645 strain as a biocontrol agent (BCA) candidate was investigated. Of basicingredients, oat meal was the best one for mass poduction and enhancement of anti-potato common scabactivity. The biomass production of the active strain was more enhanced when 0.1-0.01.% glucose or molassesas additive were added into the basic medium. These information may have important implications in applying for effective formulation of BCA.

Evaluating the anodized tantalum pentoxide (Ta2O5) that has been recently reported as a dielectric for low-voltage electrowetting-on-dielectric (EWOD) devices, we find a severe deterioration in performance if the working liquid is actuated with positive dc voltage. In an effort to reduce the limitation of this otherwise attractive dielectric material for EWOD, proposed herein is a Ta2O5 layer prepared by anodizing a sputtered Ta2O5 film. This sputtered-anodized Ta2O5 allows the use of positive dc signals, while maintaining the low-voltage actuation for which the anodized Ta 2O5 was originally introduced. All the EWOD tests were performed with a conductive liquid droplet in an air environment. © 1992-2012 IEEE.

Mesoporous materials offer several unique properties when incorporated in microelectromechanical systems (MEMS) including low density, thermal insulation and the ability to carry out rapid etching. This paper describes the development of two mesoporous thin film materials for MEMS structures, an organically modified silicate and crystalline TiO2. The morphologies of the mesoporous thin films are similar in that they have approximately 50% volume porosity, an average pore diameter of ∼5 nm, and a narrow pore size distribution. However, the chemistries of the two materials are very different as are their properties for MEMS applications. The organically modified silicate film is designed to have controlled hydrophobicity. CH3 groups which are present in the sol precursor are retained in the final material despite the 400∘C calcination temperature used for producing the porous mesostructure. Contact angles as high as 80 degrees have been achieved. The mesoporous TiO2 is designed to have resistance to HF etching. Heat treatments of the mesoporous material are carefully controlled enabling the TiO2 pore walls to crystallize without collapsing the pore network structure. A combination of anatase and rutile phases are produced in the solid phase and exhibit excellent resistance to HF.

A fiber optic pH sensor has been fabricated using nile blue entrapped in an ammonia catalyzed silica sol-gel film coated on glass substrate by dip-coating. The sensor was fixed on the end of an optical fiber. The sensor showed pH sensitivity when dipped into liquids at different pHs. Linear and reproducible responses were obtained in standard buffer solutions in the pH range , which encompasses the clinically-relevant range. The effects of interferences on the determination of pH were also investigated. The sensors were successfully applied to the determination of pH in different commercial ionic drinks.

We have investigated a novel material, thin-film aerogel, for use in microelectromechanical systems (MEMS) and determined its mechanical properties on the microscale. Fabrication processes, including photolithography and etching, have been developed to build the overhanging cantilevers and bridges used for the measurement. Young's modulus for the deposited aerogel material has been measured from the resonant frequencies of those microstructures. A nanoindentation test allows us to estimate not only Young's modulus but also the hardness of the thin-film aerogel deposited on a silicon wafer. These results show that the aerogel has unique properties in a MEMS not found with other materials.

Electrowetting and dielectrophoretic actuation are potentially important microfluidic mechanisms for the transport, dispensing, and manipulation of liquid using simple electrode structures patterned on a substrate. These two mechanisms are, respectively, the low- and high-frequency limits of the electromechanical response of an aqueous liquid to an electric field. The Maxwell stress tensor and an RC circuit model are used to develop a simple predictive model for these electromechanics. The model is tested by measuring electric-field-induced pressure changes within an aqueous droplet trapped between two parallel, disk-shaped electrodes immersed in a bath of immiscible, insulating oil. The experiment is an adaptation of Quincke's original bubble method for measuring the dielectric constant of a liquid. For AC voltages lower than ∼100 V-rms, the pressure data largely conform to the square-law predictions of the model. At higher voltages, this square-law behavior is no longer evident, a result consistent with...

Optical actuation of liquid droplets has been experimentally demonstrated for the first time using a novel optoelectrowetting (OEW) principle. The optoelectrowetting surface is realized by integrating a photoconductive material underneath a two-dimensional array of electrowetting electrodes. Contact angle change as large as 308 has been achieved when illuminated by a light beam with an intensity of 65 mW/cm 2 . A micro-liter droplet of deionized water has been successfully transported by a 4 mW laser beam across a 1 cm � 1 cm OEW surface. The droplet speed is measured to be 7 mm/s. Light actuation enables complex microfluidic functions to be performed on a single chip without encountering the wiring bottleneck of two-dimensional array of electrowetting electrodes. Published by Elsevier Science B.V.

Reports the completion of four fundamental fluidic operations considered essential to build digital microfluidic circuits, which can be used for lab-on-a-chip or micro total analysis system (/spl mu/TAS): 1) creating, 2) transporting, 3) cutting, and 4) merging liquid droplets, all by electrowetting, i.e., controlling the wetting property of the surface through electric potential. The surface used in this report is, more specifically, an electrode covered with dielectrics, hence, called electrowetting-on-dielectric (EWOD). All the fluidic movement is confined between two plates, which we call parallel-plate channel, rather than through closed channels or on open surfaces. While transporting and merging droplets are easily verified, we discover that there exists a design criterion for a given set of materials beyond which the droplet simply cannot be cut by EWOD mechanism. The condition for successful cutting is theoretically analyzed by examining the channel gap, the droplet size and the degree of contact angle change by electrowetting on dielectric (EWOD). A series of experiments is run and verifies the criterion.

In this paper, we first report a micropump actuated by surface tension based on continuous electrowetting (CEW). We have used the surface-tension-induced motion of a mercury drop in a microchannel filled with an electrolyte as actuation energy for the micropump. This allows low voltage operation as well as low-power consumption. The micropump is composed of a stack of three wafers bonded together. The microchannel is formed on a glass wafer using SU-8 and is filled with electrolyte where the mercury drop is inserted. The movement of the mercury pushes or drags the electrolyte, resulting in the deflection of a membrane that is formed on the second silicon wafer. Another silicon wafer, which has passive check valves and holes, is stacked on the membrane wafer, forming inlet and outlet chambers. Finally, these two chambers are connected through a silicone tube forming the complete micropump. The performance of the fabricated micropump has been tested for various operation voltages and frequencies. We have demonstrated actual liquid pumping up to 70 /spl mu/l/min with a driving voltage of 2.3 V and a power consumption of 170 /spl mu/W. The maximum pump pressure is about 800 Pa at the applied voltage of 2.3 V with an operation frequency of 25 Hz.

This paper reports sliding of micro liquid-metal droplets by electrostatic actuation for MEMS applications, bi-stable switching in particular. Basic theory concerning droplets on a plane solid surface is exposed followed by experimental study. Being a major parameter in the modeling of sliding droplets, the contact angle has been characterized in the case of mercury on an oxidized silicon wafer. The method used involves both traditional optical microscope and confocal laser imaging. The contact angle is found to be around 137/spl deg/ with an associated standard deviation of 8/spl deg/. The sample preparation is detailed. The droplets deposition method is based on selective condensation of mercury vapor on gold dots acting as preferred nucleation sites. This technique provides control of droplet dimensions and locations and is suitable for batch fabrication. Experimental study of electrostatic actuation coupled with finite-element method (FEM) analysis is described, leading to the determination of the sliding condition parameter, which represents a contact angle hysteresis of about 6/spl deg/. Experimental results also confirm the proportionality between minimum driving force and droplet dimension. Finally, a design optimization methodology is proposed, based on the use of finite-element model simulations.

This paper deals with electrowetting (EW) and electrowetting-on-dielectric (EWOD) principles applied to microfluidic devices. EW and EWOD are principles that can control wettability of liquids on solid surfaces using electric potential. While EW is controlling wettability of a certain electrolyte on a metal electrode by varying electric energy across the electrical double layer (EDL), EWOD applies to virtually any aqueous liquid by varying electric energy across the thin dielectric film between the liquid and conducting substrate. These driving mechanisms have many advantages. By electrically changing the wettability of each of the electrode patterns on a surface, a liquid on these electrodes can be shaped and driven along the active electrodes, making microfluidics extremely simple both for device fabrication and operation. It is also worth noting that, driven by surface tension, the mechanism becomes more effective as the size of the device becomes smaller. This paper describes fundamental concepts and the proof-of-concept experiments, modeling and design, microfabrication processes, and initial testing results for the microfluidic devices based on the EW and EWOD principles.

Solid phase extraction was incorporated into an electrowetting-on-dielectric chip for radiochemical purification of a positron emission tomography tracer that was radiolabeled on the same chip. The radiotracer droplet was mixed with alumina particles, and the alumina particles were filtered out from the droplet through a line of pillars, all by electrowetting droplet movement. Fluorination reaction and on-chip purification were analyzed with both Cerenkov imaging and off-chip radio-thin layer chromatography measurements. The measurements were compared to test the validity of the combined use of filtration on-chip and Cerenkov imaging as an alternative approach for monitoring reaction yield without the need to extract sample from the chip.

This paper describes the first microelectromechanical systems (MEMS) demonstration device that adopts surface tension as the driving force. A liquid-metal droplet can be driven in an electrolyte-filled capillary by locally modifying the surface tension with electric potential. We explore this so-called continuous electrowetting phenomenon for MEMS and present crucial design and fabrication technology that reduce the surface-tension-driving principle, inherently powerful in microscale, into practice. The key issues that are identified and investigated include the problem of material compatibility, electrode polarization, and electrolysis, as well as the micromachining process. Based on the results from the initial test devices and the design concept for a long-range movement of the liquid-metal droplet, we demonstrate a liquid micromotor, an electrolyte and liquid-metal droplets rotating along a microchannel loop. Smooth and wear-free rotation of the liquid system is shown at a speed of /spl sim/40 mm/s (or 420 r/min along a 2-mm loop) with a driving voltage of only 2.8 V and little power consumption (10-100 /spl mu/W).

The mechanical properties of single-crystalline silicon are measured by uniaxial tension tests from microscale beam specimens patterned by four different common silicon etchants — KOH, EDP, TMAH and XeF2. SOI wafers are used to prepare test samples, which are 3–5 μm thick, 20–100 μm wide, and 6 mm long beam specimens; these are monolithically mounted on a temporary frame. A uniaxial tension test has been designed to accommodate microscale test requirements such as sample handling, sample alignment, and friction elimination. Stress and strain are measured using a commercial load cell and a laser interferometry system, respectively. Young's modulus of silicon in the 〈110〉 direction is measured to be 169.2±3.5 GPa, very close to the widely accepted value of 168.9 GPa obtained from a macroscale sample by an ultrasonic method. The fracture strength in the 〈110〉 direction is measured to vary from 0.6 to 1.2 GPa, and is apparently affected by the etching process employed to make the microscale specimen. As surface defects are expected to be the main factor determining the strength of the specimen, surface morphology is examined not only as a function of etchants but also as a function of mask-to-crystal direction misalignment after KOH etching. In the case of samples prepared by KOH etching, measured fracture strengths are 0.94 and 0.72 GPa from samples with 0° and 2° misalignments, respectively.

A summary of the influence of microfabrication processes (wet and dry etching) and crystal orientation on the effective shear strength of microridges is addressed in this paper. Test results indicate that both crystal orientation and geometry plays an important role in determining the strength. The largest shear strengths obtained were for triangular and rectangular ridges fabricated with wet etching and deep RIE respectively. Both of these structures had similar crystal orientations. These strength values were approximately 3.5 times larger than the lowest strengths measured for wet etching structures. Using Chlorine RIE, we were able to demonstrate the influence of crystal orientation on strength, with microridges of {110} sidewall made on a (100) wafer the largest. For wet etching, we found that the strength was concentration dependent. For example, a 45% KOH fabricated structure produced strength values 65% higher than 30% KOH fabricated ones (note crystal orientation the same). This was attributed to a geometric effect, that is the 45% KOH solution had a “V” shaped bottom while the 30% KOH had a flat bottom. EDP and TMAH values had similar strengths to the 30% KOH solution (note similar crystal orientation). Therefore, microcomponent strength is strongly dependent upon fabrication process as well as crystal orientation.

The microscopic mechanical devices in microelectromechanical systems (MEMS) use materials such as silicon and many other thin films, which had not previously been considered mechanical materials and thus are not well characterized regarding their mechanical properties. However, as the field matures, sustained research and commercial development in the coming years will demand better understanding of mechanical properties such as Young's modulus and the fracture strength. Uniaxial tension testing is generally considered the most reliable way to measure the mechanical properties. However, the problems associated with the microscopic size of the test specimen for MEMS, such as sample handling and sample alignment, led to such alternative ways as membrane-bulge testing and natural frequency testing at the beginning of MEMS. In this paper, recent methods for testing microscale mechanical properties and their results are summarized. Many reports, based on two distinct types of test, beam bending and direct tension, are introduced. The efforts to integrate the sample and loading system on the microscopic scale are also explained. Studies of fatigue, the most recent development in microscale measurement of mechanical properties, are discussed. The results from the testing methods described are listed for comparison.

A Pd-SiC Schottky diode for detection of hydrogen gas operating at high temperature was fabricated. Hydrogen-sensing behaviors of Pd-SiC Schottky diode have been analyzed as a function of hydrogen concentration and temperature by current-voltage (I-V) and ΔI-t methods under steady-state and transient conditions. The effect of hydrogen adsorption on the barrier height was investigated. Analysis of the steady-state kinetics using I-V method confirmed that the atomistic hydrogen adsorption process is responsible for the barrier height change in the diode.