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Microelectromechanical Systems, Journal of

Issue 4 • Date Aug. 2004

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Displaying Results 1 - 25 of 25
  • Table of contents

    Page(s): c1 - c4
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  • Journal of Microelectromechanical Systems publication information

    Page(s): c2
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  • Surface tension driven formation of microstructures

    Page(s): 553 - 558
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    The controlled formation of curved, three-dimensional (3-D) microstructures can be accomplished through solidification from a liquid phase. As a demonstration, we have placed objects in contact with the interface of a photopolymerizable liquid and air to create various liquid menisci that were subsequently solidified with ultraviolet radiation. Geometric control is achieved through variation of physical and environmental parameters; for example, solidified menisci formed at 25°C were 300 μm taller than those formed at 7°C. Comparisons between the polymerized structures and theoretical predictions for liquid menisci indicate that the polymerization process results in repeatable changes in contact angle and meniscus size. View full abstract»

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  • Three-dimensional hydrodynamic focusing in polydimethylsiloxane (PDMS) microchannels

    Page(s): 559 - 567
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    This paper presents a generalization of the hydrodynamic focusing technique to three-dimensions. Three-dimensional (3-D) hydrodynamic focusing offers the advantages of precision positioning of molecules in both vertical and lateral dimensions and minimizing the interaction of the sample fluid with the surfaces of the channel walls. In an ideal approach, 3-D hydrodynamic focusing could be achieved by completely surrounding the sample flow by a cylindrical sheath flow that constrains the sample flow to the center of the channel in both the lateral and the vertical dimensions. We present here design and simulation, 3-D fabrication, and experimental results from a piecewise approximation to such a cylindrical flow. Two-dimensional (2-D) and 3-D hydrodynamic focusing chips were fabricated using micromolding methods with polydimethylsiloxane (PDMS). Three-dimensional hydrodynamic focusing chips were fabricated using the "membrane sandwich" method. Laser scanning confocal microscopy was used to study the hydrodynamic focusing experiments performed in the 2-D and 3-D chips with Rhodamine 6G solution as the sample fluid and water as the sheath fluid. View full abstract»

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  • A method for precision patterning of silicone elastomer and its applications

    Page(s): 568 - 575
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    This paper presents a general microfabrication method for precision patterning of thin-film poly(dimethylsiloxane) (PDMS). The method enables PDMS microstructures with controlled lateral dimensions and thickness on a silicon or glass substrate. Two applications based on this new method are discussed. First, a scanning probe microscopy (SPM) probe with PDMS tip is developed and used for scanning probe contact printing (SPCP). Second, this paper demonstrates surface micromachined membranes with integrated silicone gaskets. View full abstract»

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  • A micromechanical flow sensor for microfluidic applications

    Page(s): 576 - 585
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    We fabricated a microfluidic flow meter and measured its response to fluid flow in a microfluidic channel. The flow meter consisted of a micromechanical plate, coupled to a laser deflection system to measure the deflection of the plate during fluid flow. The 100 μm square plate was clamped on three sides and elevated 3 μm above the bottom surface of the channel. The response of the flow meter was measured for flow rates, ranging from 2.1 to 41.7 μL/min. Several fluids, with dynamic viscosities ranging from 0.8 to 4.5×10-3 N/m, were flowed through the channels. Flow was established in the microfluidic channel by means of a syringe pump, and the angular deflection of the plate monitored. The response of the plate to flow of a fluid with a viscosity of 4.5×10-3 N/m was linear for all flow rates, while the plate responded linearly to flow rates less than 4.2 μL/min of solutions with lower dynamic viscosities. The sensitivity of the deflection of the plate to fluid flow was 12.5±0.2 μrad/(μL/min), for a fluid with a viscosity of 4.5×10-3 N/m. The encapsulated plate provided local flow information along the length of a microfluidic channel. View full abstract»

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  • A valved responsive hydrogel microdispensing device with integrated pressure source

    Page(s): 586 - 593
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    Stimulus responsive hydrogels provide the actuation pressure required for both valving and dispensing functions in the device presented. The microdispensing device uses an array of responsive hydrogels to deform a flexible membrane above a fluid reservoir chamber. When the microvalve is open, the deformation of the membrane reduces the volume of the reservoir chamber and pushes fluid through the microvalve. When the microvalve is closed, the expanding hydrogel array generates a storable pressure source that will result in fluid dispensing once the microvalve is opened. Experiments determined the pressure generated by this device to be 35 kPa. The device has a stroke volume of 45 μL, and is able to hold the pressure for over 24 h. View full abstract»

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  • Design, fabrication, and characterization of thermally actuated probe arrays for dip pen nanolithography

    Page(s): 594 - 602
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    In Dip Pen Nanolithography (DPN), arbitrary nanoscale chemical patterns can be created by the diffusion of chemicals from the tip of an atomic force microscope (AFM) probe to a surface. This paper describes the design, optimization, fabrication, and testing of an actuated multi-probe DPN array. The probe array consists of 10 thermal bimorph active probes made of silicon nitride and gold. The probes are 300 μm long and the tips are spaced 100 μm apart. An actuation current of 10 mA produces a tip deflection of 8 μm, which is enough to remove individual tips from the surface independent of the adjacent probes. An analytical probe model is presented and used to optimize the design against several possible failure modes. The array is demonstrated by using it to simultaneously write 10 unique octadecanethiol patterns on a gold surface. Pattern linewidth as small as 80 nm has been created at a maximum write speed of 20 μm/sec. By writing multiple, distinctly different patterns in parallel, this device provides a significant improvement in throughput and flexibility over conventional AFM probes in the DPN process. View full abstract»

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  • Three-dimensional micro-self-assembly using hydrophobic interaction controlled by self-assembled monolayers

    Page(s): 603 - 611
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    This paper describes three-dimensional micro-self-assembly using hydrophobic interaction. The interaction between microparticles was controlled using self-assembled monolayers formed on the particles. The particles were stirred in a dispersion liquid to create a binding for connecting their surfaces directly. The interaction between the particles was described by the thermodynamic free energy of adhesion, which was calculated using the surface free energies of the solids and the liquid. The calculated free energy was then used to predict the bindings between particles. The binding probability was estimated by counting the number of microparticles that became bound to hydrophobic and to hydrophilic areas patterned on a substrate. The ratio of the bound particles was correlated to the difference between the free energies of the two areas, as predicted using the free energy calculation. This means that microparticle binding is controlled by the surface properties. Structures composed of several microparticles were successfully self-assembled using this principle. Hydrophobic interaction can thus be applied to micro-scale self-assembly. View full abstract»

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  • Hybrid nanotransport system by biomolecular linear motors

    Page(s): 612 - 619
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    We have demonstrated a novel micro/nanotransport system using biomolecular motors driven by adenosine triphosphate (ATP). For the driving mechanism, microtubule-kinesin system, which is one of the linear biomolecular motor systems was investigated. ATP dissolved in an aqueous condition is hydrolyzed to adenosine diphosphate (ADP) to energize the bionanoactuators in this mechanism. This means the system does not require an external electrical or mechanical energy source. Therefore, a purely chemical system which is similar to the in vivo transport will be realized. This paper reports some fundamental studies to integrate biomaterials and MEMS. The microtubules, or rail molecules, were patterned on a glass substrate with poly(dimethyl siloxane) (PDMS) using a regular soft lithography technique. Microbeads (320 nm in diameter) and a micromachined structure (2×3 μm, 2 μm in thickness) coated with kinesin molecules were transported along the microtubules at an average speed of 476±56 and 308 nm/s, respectively. While ATP injection activated the transport system we have also managed to provide repetitive on/off control using hexokinase as an inhibitor. For the minimum response time in the repetitive control, the optimized concentration for ATP was 102 μM and 103 U/L for hexokinase. View full abstract»

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  • Electrocapillary piston motion and a prototype of phase-manipulating micromirror

    Page(s): 620 - 627
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    In this paper, we study the piston motion of a mercury droplet that is confined in a metal-plated microhole. This droplet is actuated by the electrocapillary effect and large displacements of up to 210 μm are achieved with very low voltages (∼2 V). We use a high-speed camera (10,000 frames/s) to capture the piston motion and we find the resonance frequency is ∼50 Hz. The mercury droplet geometry in equilibrium state is analyzed based on Laplace equation and volume conservation. A mathematical model is developed; it predicts that the resonant frequency of mercury droplet is 150 Hz. A prototype of piston-motion micromirror is also demonstrated in the experiment, with a frequency of 400 Hz and amplitude of ∼8 μm at 2 V. View full abstract»

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  • An in-plane high-sensitivity, low-noise micro-g silicon accelerometer with CMOS readout circuitry

    Page(s): 628 - 635
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    A high-sensitivity, low-noise in-plane (lateral) capacitive silicon microaccelerometer utilizing a combined surface and bulk micromachining technology is reported. The accelerometer utilizes a 0.5-mm-thick, 2.4×1.0 mm2 proof-mass and high aspect-ratio vertical polysilicon sensing electrodes fabricated using a trench refill process. The electrodes are separated from the proof-mass by a 1.1-μm sensing gap formed using a sacrificial oxide layer. The measured device sensitivity is 5.6 pF/g. A CMOS readout circuit utilizing a switched-capacitor front-end Σ-Δ modulator operating at 1 MHz with chopper stabilization and correlated double sampling technique, can resolve a capacitance of 10 aF over a dynamic range of 120 dB in a 1 Hz BW. The measured input referred noise floor of the accelerometer-CMOS interface circuit is 1.6μg/√Hz in atmosphere. View full abstract»

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  • A sweeping mode integrated fingerprint sensor with 256 tactile microbeams

    Page(s): 636 - 644
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    This paper reports recent advances in the development of a tactile fingerprint sensor made by a CMOS compatible front side bulk micromachining technology. This device enables the measurement of a fingerprint by the way of a mechanical scanning principle of the finger roughness. While this sensing principle has shown good results on a first prototype of reduced width, we present here the design, fabrication and test of a new sensor. This sensor contains 256 pressure sensitive microbeams for a total length of 1.28 cm and is fully integrated with analog and mixed signal electronics. In this paper we will detail the general working principle of the tactile fingerprint sensor and the two prototypes that have been manufactured and tested with a special focus on the electronic architecture and the test results of the second prototype. View full abstract»

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  • Nonlinear dynamic characteristics of piezoelectric bending actuators under strong applied electric field

    Page(s): 645 - 652
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    Dynamic characteristics of piezoelectric bending actuators under low and high electric fields are studied using the asymptotic theory of nonstationary vibrations. The proposed nonlinear model predicts the changes in fundamental resonant frequencies of the piezoelectric cantilever. The predicted resonance amplitude of the tip deflections of the piezoelectric actuators, which increases with the increase in the magnitude of the electric field, well agrees with the experimental results. Additionally, the decrease in the mechanical quality factor with the increase in the electric field, the tip deflection of piezoelectric actuators near resonance frequency,and the amplitude of the tip deflection at the fundamental vibration tone under an applied electric field varying with time have also been obtained using the present model. View full abstract»

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  • An improved Reynolds-equation model for gas damping of microbeam motion

    Page(s): 653 - 659
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    An improved gas-damping model for the out-of-plane motion of a near-substrate microbeam is developed based on the Reynolds equation (RE). A boundary condition for the RE is developed that relates the pressure at the beam edge to the beam motion. The coefficients in this boundary condition are determined from Navier-Stokes slip-jump (NSSJ) simulations for small slip lengths (relative to the gap height) and from direct simulation Monte Carlo (DSMC) molecular gas dynamics simulations for larger slip lengths. This boundary condition significantly improves the accuracy of the RE when the microbeam width is only slightly greater than the gap height between the microbeam and the substrate. The improved RE model is applied to microbeams fabricated using the SUMMiT V process. View full abstract»

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  • An electrostatic, on/off microvalve designed for gas fuel delivery for the MIT microengine

    Page(s): 660 - 668
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    The MIT micro-gas turbine engine requires an integrated fuel-metering device in order to implement on-board engine control. Graded fuel control can be achieved with an array of on/off valves. Each valve in the array must withstand an annealing temperature of 1100°C during fabrication and open against 1 MPa of supply pressure at 400°C operating temperature. This paper presents the design, fabrication and testing of an electrostatic, on/off silicon prototype valve. Tested with nitrogen at room temperature, the valve opened against a differential pressure of 0.9 MPa with 136 V and delivered a mass flow rate of 45 sccm (3.38 g/h). At 0.1y MPa upstream pressure, the helium leak-rate was measured to be 6×10-3 sccm. The valve showed no sign of failure after being continuously actuated for more than 105 cycles. The prototype valve will serve as the base-line design for the engine fuel valve array. View full abstract»

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  • Pulsed-laser annealing, a low-thermal-budget technique for eliminating stress gradient in poly-SiGe MEMS structures

    Page(s): 669 - 675
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    In this paper, we demonstrate eliminating the stress gradient in polycrystalline silicon germanium films at temperatures compatible with standard CMOS (Al interconnects) backend processing. First, we study the effect of varying the germanium concentration from 40% to 90%, layer thickness, deposition pressure from 650 to 800 mtorr and deposition temperature from 400 to 450°C, on the mechanical properties of SiGe films. Then the effect of excimer laser annealing (248 nm, 38 ns, 780 mJ/cm2) on stress gradient is analyzed. It is demonstrated that stress gradient can be eliminated completely by depositing SixGe1-x(10% View full abstract»

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  • Development of Si-SiC hybrid structures for elevated temperature micro-turbomachinery

    Page(s): 676 - 687
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    The design of the Massachusetts Institute of Technology (MIT) microengine is limited in part by the material capability of Si primarily due to the pronounced thermal-softening and strain-softening at temperatures higher than the brittle-to-ductile transition temperature (BDT), approximately 550°C. In order to circumvent this limitation, it has been proposed to reinforce the Si with chemical vapor deposited (CVD) SiC in strategic locations to create a Si-SiC hybrid microengine turbine spool. Detailed design of Si-SiC hybrid structures for high temperature micro-turbomachinery, however, has been hampered by the lack of understanding of the mechanical behavior of Si and SiC hybrid structures at elevated temperatures and by the unavailability of accurate material properties data for both Si and SiC at the temperatures of interest. In this work, a series of initial thermomechanical FE analyzes have been performed to assess the advantage of the hybrid structures, and to provide structural design criteria and fabrication requirements. Then, the feasibility of the Si-SiC hybrid structures concept for elevated temperature micro-turbomachinery was verified based on more rigorous mechanical testing at high temperatures. Finally, the Si-SiC hybrid spool design was critically reevaluated with regard to creep using a Si constitutive model developed as a separate effort. View full abstract»

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  • Zirconium tungstate (ZrW2O8)-based micromachined negative thermal-expansion thin films

    Page(s): 688 - 695
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    Negative expansion materials are relatively rare but promise to be particularly useful in designing thermally sensitive mechanical devices. Although negative thermal expansion (NTE) in bulk materials such as ZrW2O8 has been extensively studied, this paper reports the first deposition of a NTE material thin film. ZrWxOy films were deposited by electron beam evaporation and reactive cosputtering. The films were processed and patterned for various microstructures. The coefficients of thermal expansion of the deposited thin films were determined by measuring the change in curvature with temperature. It was found that evaporated films but not sputtered films, which were denser than the evaporated films, exhibited NTE. It was also found that NTE behavior occurred across a variety of stoichiometries. Since crystalline ZrW2O8 and thin film ZrWxOy both have low densities and show negative expansion, it is speculated that similar physical mechanisms, as discussed in the text, are at work. Further, since the deposition conditions of a thin film can often be changed to control density, it is speculated that a wider variety of thin films than bulk crystals might be made to have NTE. View full abstract»

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  • Recovery of stiction-failed MEMS structures using laser-induced stress waves

    Page(s): 696 - 700
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    Stiction, or adhesion between suspended structures and the underlying surface, is a hurdle in batch fabricating long, freestanding MEMS structures. A novel technique is presented in this paper to release stiction. In this technique, a nanosecond rise time stress wave is launched on the backside of the Si substrate by impinging a 2.5 ns-duration Nd:YAG laser pulse onto a 3-mm-dia area. The compressive stress wave propagates through the Si substrate and arrives at the site of several stiction-failed cantilevers on the front Si surface. The compressive stress wave propagates through the cantilevered structures and is reflected into a tensile wave from their free surfaces. The returning tensile wave pries off the interface, releasing the cantilevers. The procedure is demonstrated on a MEMS chip with stiction-failed cantilevers with varying lengths from 100 μm to 1000 μm. The threshold laser energy to release stiction increased linearly with cantilever lengths. Beam recovery began at a laser fluence of 11 kJ/m2 laser energy. 70% of the tested beams had been recovered after impingement with a fluence of 26 kJ/m2. After the highest applied laser fluence of 40 kJ/m2, 90% of the tested beams had been recovered. No damage to the structures or surrounding features was observed below 40 kJ/m2. Because of rather low laser fluence, no thermal damage to the back surface of Si was noted. Since it literally takes few seconds to release stiction, the proposed technique can be implemented in MEMS foundry, and for repair of in-use stiction failed MEMS devices. View full abstract»

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  • 18th IEEE International Conference on Micro Electro Mechanical Systems

    Page(s): 701
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  • Call for Papers—Transducers'05

    Page(s): 702
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    Freely Available from IEEE
  • 2004 IEEE International Electron Devices Meeting

    Page(s): 703
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    Freely Available from IEEE
  • IEEE International Conference on Microelectronic Test Structures

    Page(s): 704
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    Freely Available from IEEE
  • Journal of Microelectromechanical Systems Information for authors

    Page(s): c3
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Aims & Scope

The topics of interest include, but are not limited to: devices ranging in size from microns to millimeters, IC-compatible fabrication techniques, other fabrication techniques, measurement of micro phenomena, theoretical results, new materials and designs, micro actuators, micro robots, micro batteries, bearings, wear, reliability, electrical interconnections, micro telemanipulation, and standards appropriate to MEMS. Application examples and application oriented devices in fluidics, optics, bio-medical engineering, etc., are also of central interest.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Christofer Hierold
ETH Zürich, Micro and Nanosystems