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Microelectromechanical Systems, Journal of

Issue 2 • Date April 2014

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Displaying Results 1 - 25 of 31
  • Table of contents

    Page(s): C1 - C4
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    Freely Available from IEEE
  • Journal of Microelectromechanical Systems publication information

    Page(s): C2
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    Freely Available from IEEE
  • Effects of Ambient Humidity on a Micromachined Silicon Thermal Wind Sensor

    Page(s): 253 - 255
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (398 KB) |  | HTML iconHTML  

    The effect of ambient humidity on a micromachined silicon 2-D thermal wind sensor has been investigated. The sensor includes a central heater and four temperature sensors. It measures the flow-induced temperature gradient on the heated surface. Properties of the ambient air, such as density, viscosity, heat conductivity, and specific heat capacity, are theoretically presented to explore their effects on the performance of the sensor at different relative humidity levels. The output of the sensor as a function of wind speed at different relative humidity levels has been measured. It shows that there is a measurable effect at both high relative humidity and temperature. The results presented here provide a valuable reference for the practical applications of the wind sensor. View full abstract»

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  • Large Stroke Vertical PZT Microactuator With High-Speed Rotational Scanning

    Page(s): 256 - 258
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    A thin-film piezoelectric microactuator using a novel combination of active vertical translational scanning and passive resonant rotational scanning is presented. Thin-film lead-zirconate-titanate unimorph bending beams surrounding a central platform provide nearly 200-μm displacement at 18 V with bandwidth greater than 200 Hz. Inside the platform, a mirror mount, or mirror surface, supported by silicon dioxide spring beams can be excited to resonance by low-voltage; high-frequency excitation of the outer PZT beams. Over ±5.5° mechanical resonance is obtained at 3.8 kHz and ±2 V. The combination of large translational vertical displacements and high-speed rotational scanning is intended to support real-time cross-sectional imaging in a dual axes confocal endomicroscope. View full abstract»

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  • MEMS Laser Scanners: A Review

    Page(s): 259 - 275
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    Laser scanners have been an integral part of MEMS research for more than three decades. During the last decade, miniaturized projection displays and various medical-imaging applications became the main driver for progress in MEMS laser scanners. Portable and truly miniaturized projectors became possible with the availability of red, green, and blue diode lasers during the past few years. Inherent traits of the laser scanning technology, such as the very large color gamut, scalability to higher resolutions within the same footprint, and capability of producing an always-in-focus image render it a very viable competitor in mobile projection. Here, we review the requirements on MEMS laser scanners for the demanding display applications, performance levels of the best scanners in the published literature, and the advantages and disadvantages of electrostatic, electromagnetic, piezoelectric, and mechanically coupled actuation principles. Resonant high-frequency scanners, low-frequency linear scanners, and 2-D scanners are included in this review. View full abstract»

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  • Liquid-Phase Capillary Etching of Poly(Dimethylsiloxane) Microchannels With Tetra-n-Butylammonium Fluoride

    Page(s): 276 - 283
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    Easy fabricability, along with other unique properties, has made poly(dimethylsiloxane) (PDMS) one of the most commonly used materials for microfluidics-based microdevices. However, unlike other polymer materials commonly used for microdevices, the PDMS cannot be easily etched or further changed upon polymerization, and therefore, fabrication method has been rather limited to replication molding. Here, we demonstrated liquid-phase capillary etching of the PDMS microchannels with tetra-n-butylammonium fluoride (TBAF) and characterized its etching profiles depending on the initial microchannel widths, TBAF flow rates, TBAF concentrations, and substrates used for the microfluidic channel sealing. The characterization showed that the microchannel circumference etch rate was linearly proportional to the TBAF flow rate and was faster at higher TBAF concentration. On the other hand, influence of the TBAF concentration on the horizontal and vertical etch rates was vastly different, with the vertical etch rate being much more affected by the concentration change. Potential applications of the liquid-phase capillary etching method were demonstrated by fabricating the PDMS microchannels with round-shaped cross sections, a microdevice with embedded 3-D metal electrodes with the electrodes directly exposed to the microfluidic channel, and a glass-PDMS-glass sandwich microchannel for high-clarity optical detection. We believe that the characterization of the liquid-phase capillary etching along with the applications demonstrated here will provide new capabilities for fabricating the PDMS-based microdevices that could not be easily fabricated by conventional replication molding processes. View full abstract»

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  • An Automatically Mode-Matched MEMS Gyroscope With Wide and Tunable Bandwidth

    Page(s): 284 - 297
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    This paper presents the architecture and experimental verification of the automatic mode-matching system that uses the phase relationship between the residual quadrature and drive signals in a gyroscope to achieve and maintain matched resonance mode frequencies. The system also allows adjusting the system bandwidth with the aid of the proportional-integral controller parameters of the sense-mode force-feedback controller, independently from the mechanical sensor bandwidth. This paper experimentally examines the bias instability and angle random walk (ARW) performances of the fully decoupled MEMS gyroscopes under mismatched (~ 100 Hz) and mode-matched conditions. In matched-mode operation, the system achieves mode matching with an error frequency separation between the drive and sense modes in this paper. In addition, it has been experimentally demonstrated that the bias instability and ARW performances of the studied MEMS gyroscope are improved up to 2.9 and 1.8 times, respectively, with the adjustable and already wide system bandwidth of 50 Hz under the mode-matched condition. Mode matching allows achieving an exceptional bias instability and ARW performances of 0.54 °/hr and 0.025 °/√hr, respectively. Furthermore, the drive and sense modes of the gyroscope show a different temperature coefficient of frequency (TCF) measured to be -14.1 ppm/°C and -23.2 ppm/°C, respectively, in a temperature range from 0 °C to 100 °C. Finally, the experimental data indicate and verify that the proposed system automatically maintains the frequency matching condition over a wide temperature range, even if TCF values of the drive and sense modes are quite different. View full abstract»

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  • Solvent Compatibility of Parylene C Film Layer

    Page(s): 298 - 307
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    Parylene C has been preferred in various microfluidic and packaging applications as a chemical barrier; therefore, its durability in chemicals is critical to maintain functionality of the devices. In this paper, we investigated solvent compatibility of Parylene C in a range of solvents with regard to swelling of it and the change in its surface roughness at room temperature. The results of Parylene C swelling were associated with solubility parameter, δ (cal/cm3)1/2, which is predicted from the parameters of dispersion, polar, and hydrogen-bonding forces. Solvents that swelled Parylene C film layer mostly were benzene, chloroform, trichloroethylene, and toluene, while methanol, 2-propanol, ethylene glycol, and water did not cause any swelling. Subsequently, the adverse effects of diffusion of solvents through a Parylene C film layer were demonstrated by stripping of the encapsulated photoresist. In addition, a comparison was made between Parylene C and poly(dimethyl)siloxane (PDMS) considering the data of swelling ratios obtained from the experimental findings and the literature, respectively. Experimental findings showed that Parylene C is much more compatible to solvents than PDMS in high-throughput microfluidic and packaging applications. These results will be of great value to scientists for understanding compatibility of any selected solvent on Parylene C in the applications of micro devices. View full abstract»

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  • Micro-Masonry of MEMS Sensors and Actuators

    Page(s): 308 - 314
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    Micro-masonry is a route to microassembly that involves elastomeric-stamp-based micromanipulation and direct bonding. This paper presents the assembly of MEMS mechanical sensors and actuators using micro-masonry, demonstrating its capability of constructing 3-D microdevices that are impossible or difficult to realize with monolithic microfabrication. Microfabrication processes for retrievable MEMS components (e.g., combs, spacers, and flexure beams) are developed. As micromanipulation tools, microtipped elastomeric stamps with reversible dry adhesion are also designed and fabricated to pick up and deterministically place those components. After the manipulation, the components are permanently bonded together via rapid thermal annealing without using any additional intermediate layers. The assembled MEMS device is modeled and analyzed in consideration of the microassembly misalignment. The sensing and actuating capabilities of the assembled MEMS devices are experimentally characterized. View full abstract»

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  • Electrostatic Energy Harvester Employing Conductive Droplet and Thin-Film Electret

    Page(s): 315 - 323
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    This paper presents detailed investigations on an electrostatic energy harvester using conductive droplet/marble rolling across a charged electret film. Both mercury droplets and ionic liquid marbles were used as the working medium. With a 1.2-mm mercury droplet rolling across the electret film of the prototype, a maximum output power was obtained at 0.18 μW and the peak value of the output voltage was 1.5 V. A semi-empirical model was developed to understand the output waveforms. Applied to the test data, it shows that the transducer short-circuit charge is mainly a function of droplet position in the pattern. Several factors influencing the output performance are discussed. Such droplet-based electrostatic energy harvesters are especially suitable for very low frequency vibration up to a few Hz. View full abstract»

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  • 3D Magnetic Field Sensor Concept for Use in Inertial Measurement Units (IMUs)

    Page(s): 324 - 333
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    We report on the design, fabrication, and characterization of a microfabricated 3D magnetic field sensor that is suitable for co-integration with inertial sensors to form single-chip inertial measurement units. In contrast to classical resonant MEMS magnetometers, which are based on Lorentz force measurement, our sensor uses permanent magnetic materials and piezoresistive detection with silicon strain gauges of nanometric section, leading to low power consumption and high sensitivity for small sensor size. Thin multilayers of CoFe and PtMn as ferro- and antiferromagnetic materials are integrated within the MEMS fabrication process. Sensitivities of 1.09 V/T for x- and y- components of the magnetic field and 0.124 V/T for z- component of the magnetic field were measured, respectively. To be sensitive to magnetic fields along all three spatial directions, two permanent magnetization directions on the same die are required. Implementation of the two magnetization directions was validated by a measured correlation of 99.7% between x- and y- sensitivity axes. Power consumption of the 3D sensor is for polarization with a 100 μA dc current. With resolutions of 100 nT/√Hz for x- and y-component of the magnetic field and 350 nT/√Hz for z- component, the sensor is suitable for precise measurement of earth magnetic field. View full abstract»

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  • Evaluation of Mode Dependent Fluid Damping in a High Frequency Drumhead Microresonator

    Page(s): 334 - 346
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    Design of high quality factor (Q) micromechanical resonators depends critically on our understanding of energy losses in their oscillations. The Q of such structures depends on process induced prestress in the structural geometry, interaction with the external environment, and the encapsulation method. We study the dominant fluid interaction related losses, namely, the squeeze film damping and acoustic radiation losses in a drumhead microresonator subjected to different prestress levels, operated in air, to predict its Q in various modes of oscillation. We present a detailed research of the acoustic radiation losses, associated with the 15 transverse vibration modes of the resonator using a hybrid analytical-computational approach. The prestressed squeeze film computation is based on the standard established numerical procedure. Our technique of computing acoustic damping based quality factor Qac includes calculation of the exact prestressed modes. We find that acoustic losses result in a non-monotonic variation of Qac in lower unstressed modes. Such non-monotonic variation disappears with the increase in the prestress levels. Although squeeze film damping dominates the net Q at lower frequencies, acoustic radiation losses dominate at higher frequencies. The combined computed losses correctly predict the experimentally measured Q of the resonator over a large range of resonant frequencies. View full abstract»

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  • Shock Impact Reliability and Failure Analysis of a Three-Axis MEMS Gyroscope

    Page(s): 347 - 355
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    This paper presents the reliability assessment of a three-axis microelectromechanical systems (MEMS) gyroscope subjected to various shock loading conditions. The reliability tests include three different impact orientations and several acceleration levels of shock impact, ranging from 1500 to 15 000 g. The package failure and functional failure of the MEMS devices are studied separately. The failure analysis shows package failures of the MEMS device at a shock level above 8000 g and the functional failures of the device caused by stiction or fractures in the comb structure at a moderate shock level around 4000 g. To have a comprehensive understanding of the failure modes and predict the failure modes, dynamic finite element analyzes with direct integration are employed to investigate the nonlinear responses of the MEMS device under shock impact loadings. Internal collisions between the movable elements and the stationary parts are modeled by contact definitions. The simulation results, such as the calculated structural deformation and stress distributions, can be used to predict potential failure sites and offer explanations to the observed package failures and comb structure fractures. Furthermore, the locations of possible stiction inside the MEMS structure are also predicted by the simulation results. View full abstract»

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  • Mechanical Response of Silicon MEMS Diaphragms to Applied Pressure

    Page(s): 356 - 363
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    The response of silicon-based MEMS diaphragms to applied pressure was studied to determine their ability to effectively measure the extent of blast overpressure. Different pressures (0-100 psi) were applied to silicon diaphragms of different diameters (1200, 1500, and 2200 μm) to study their mechanical response under both static and dynamic conditions using experimental and finite element analysis. A laser triangulation sensor was used to determine the diaphragm displacement as a function of blast pressure. High speed camera images were obtained to understand the response of the diaphragm at an applied blast pressure. Results show consistent behavior for deflections (10, 14, and 26 μm, respectively, at 40 psi) under dynamic conditions. Finite element analysis indicates that the dynamic deflection is larger than the corresponding static deflection for the same applied pressures. Burst strengths were not consistent, although the diaphragms fractured at their circumferential edges and showed a small degree of plastic deformation. It also appears that the diaphragm manifests a hemispherical as well as a conical deflection depending on applied blast pressures. View full abstract»

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  • Particle Swarm Optimization for Design of Slotted MEMS Resonators With Low Thermoelastic Dissipation

    Page(s): 364 - 371
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    The geometry of a slotted MEMS resonator was optimized using a binary particle swarm optimization technique to reduce energy dissipation from thermoelastic dissipation (TED). The optimization technique combines fundamental physics with bio-inspired algorithms to navigate the complicated design space that arises from multiphysical problems. Fully-coupled thermomechanical simulations were used for optimization of QTED, and a weakly-coupled approach was used for design analysis. Through this approach, a TED-limited Q of 56000 was simulated, showing a 40% improvement over previous designs that were generated from the conventional intuitive design approach. The discovery of non-intuitive designs with these techniques also leads to new insight about the behavior of TED. The design algorithm used in this paper can be readily adapted to a variety of MEMS design problems. View full abstract»

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  • Bulk-Aluminum Microfabrication for Micro Fuel Cells

    Page(s): 372 - 379
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    We present a simple method for microfabricating microfluidic devices by wet etching of bulk aluminum wafers. Aluminum wafers are identical to silicon wafers in terms of dimensions and can easily be processed in standard clean room processes like lithography, etching, and thin film deposition. Aluminum thin film wet etching in phosphoric acid-based etchants is well established. In this paper, it is extended to much greater depths than before. 80 μm deep structures have been fabricated. A hydrogen-fueled micro fuel cell has been microfabricated from bulk aluminum. These fuel cells achieved very high current densities of 1.1 A cm-2 and power density up to 228 mW cm-2. Considering the simplicity of bulk aluminum micromachining, these results are very encouraging. View full abstract»

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  • Uncertainty Quantification in Prediction of the In-Plane Young's Modulus of Thin Films With Fiber Texture

    Page(s): 380 - 390
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    Electrodeposited thin films in MEMS devices often show fiber texture resulting in transverse isotropic, effective elastic properties. It is of interest to predict these elastic properties since they play a role in device performance. In addition to predicting effective material properties of the devices, we quantify the uncertainty in our predictions of these material properties for use in downstream simulations aimed at studies of performance, lifetime, or reliability. In this paper, we estimate the numerical value of the effective in-plane Young's modulus of thin nickel polycrystalline films using numerical simulation. We also examine the variability and sensitivity of the in-plane Young's modulus due to uncertainties in microstructure geometry, crystallographic texture, and numerical values of single-crystal elastic constants. The importance of accurate characterization of the texture is shown, as is the sensitivity of the effective in-plane Young's modulus to single-crystal elastic moduli. View full abstract»

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  • Macro-to-Micro Interface for the Control of Cellular Organization

    Page(s): 391 - 397
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    The spatial organization of cellular communities plays a fundamental role in determining intercellular communication and emergent behavior. Few tools, however, exist to modulate tissue organization at the scale of individual cells, particularly in the case of dynamic manipulation. Micromechanical reconfigurable culture achieves dynamic control of tissue organization by culturing adherent cells on microfabricated plates that can be shifted to reorganize the arrangement of the cells. Although biological studies using this approach have been previously reported, this paper focuses on the engineering of the device, including the mechanism for translating manual manipulation to precise microscale position control, fault-tolerant design for manufacture, and the synthetic-to-living interface. View full abstract»

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  • Highly Integrable Pressurized Microvalve for Portable SU-8 Microfluidic Platforms

    Page(s): 398 - 405
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    In this paper, a highly integrable pressurized thermo-pneumatic microvalve for impulsion and handling of fluids in portable SU-8 microfluidic platforms is reported. The microvalve aims to overcome the dependence on external pressure sources for actuation in this kind of platforms by incorporating a pressurized chamber in the design. The microvalve consists of two modules. The first one is a pressurized SU-8 chamber which makes the microvalve portable and is used to store pneumatic energy, and the second one is a gold wire inserted in a thin SU-8 wall to make a thermo-pneumatic and single-use actuation. The gold wire heats the thin wall up, and the pneumatic energy stored in the chamber exerts pressure on the wall simultaneously. The wall breaks due to the combination of these effects, releasing the pressure stored in the chamber, and creating an unidirectional flow in an output channel. The microvalve has been fabricated and tested in the laboratory showing an activation time of 1 s and a required energy of 188 mJ, values which fit the theoretical model. The advantages of this microvalve as a microfluidic component lie in its independence of external pressure sources, its high integrability with electronics and microfluidics in the same substrate [printed circuit board(PCB)], and the low consumption with respect to other PCB/SU-8 microvalves. View full abstract»

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  • A Si-Micromachined 162-Stage Two-Part Knudsen Pump for On-Chip Vacuum

    Page(s): 406 - 416
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    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. View full abstract»

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  • Reduced Residual Stress Curvature and Branched Comb Fingers Increase Sensitivity of MEMS Acoustic Sensor

    Page(s): 417 - 423
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    We present an enhanced in-plane capacitive readout for sensing out-of-plane displacement in a MEMS acoustic sensor. The sensor is fabricated in a multi-user silicon-on-insulator process, using a thicker device layer to reduce misalignment between moving and fixed comb fingers. This misalignment is found to reduce the sensitivity and render the response nonlinear. In addition, incorporation of a branched comb design doubles the readout capacitor surface area for a given sensor size, to further increase the sensitivity. These two modifications restore linearity to the readout and increase its sensitivity to displacement by an order of magnitude. View full abstract»

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  • Multi-Height Precision Alignment With Selectively Developed Alignment Marks

    Page(s): 424 - 427
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    The alignment step in fabricating multi-height photoresist masters is a critical and time-consuming process. SU8 masters that combine very thin and thick layers can be difficult to align because of low contrast visibility. We increase visual contrast by selectively developing alignment marks to ease fabrication of masters with thick resist layers deposited on much thinner ones. In addition, we use a vernier calliper based alignment mark to achieve high precision alignment. View full abstract»

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  • An Active Thin-Film Cochlear Electrode Array With Monolithic Backing and Curl

    Page(s): 428 - 437
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    This paper reports the development of a robust, 32-site, four-channel, flexible cochlear implant as a prototype for a 128-site, eight-channel human prosthesis. The electrode array is comprised of metal layers embedded in Parylene C and includes parylene rings and self-curling parylene layers that can achieve a minimum radius of curvature . Finite element analysis simulations predict that the substrate stiffness of the arrays can be tailored from 0.2 to 1.4 kN·μm2 with parylene rings to increase the rigidity seven-fold over that of a flat parylene array. Guinea pig arrays have achieved insertion depths of up to 6.5 mm in the cochlea with no visible damage to the scala media. The application specific integrated circuit (ASIC) for the cochlear implant was realized in 0.5 μm technology to support a wide range of multisite multipolar stimulus configurations. The ASIC fits within the space of the otic bulla with a size of 2.2 mm by 2.5 mm and operates from a ±2.5 V supply at clock speeds up to 500 kHz. The maximum power consumption is 2.5 mW when outputting monopolar 500 μA biphasic pulses. View full abstract»

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  • High Stroke and High Deflection Bulk-PZT Diaphragm and Cantilever Micro Actuators and Effect of Pre-Stress on Device Performance

    Page(s): 438 - 451
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    This paper presents the design, simulation, fabrication, and experimental characterization of high-performance piezoelectric diaphragm and cantilever beam out-of-plane micro actuators that are fabricated from bulk lead zirconium titanate (PZT) films integrated on silicon. The utilized fabrication technology involves low-temperature diffusion solder bonding of a bulk piezoelectric ceramic on silicon, and subsequent lapping to achieve a desired PZT thickness. Different piezoelectric actuation modes (conventional longitudinal and transverse modes, and a novel shear mode) are explored and compared in terms of displacement range, and the diaphragm structures and electrodes are optimized via finite-element analysis (FEA). The effect of bonding prestress on the device performance is analytically characterized and verified through measurements. The close match between test data and simulation results suggests that the piezoelectric properties of integrated bulk-PZT5A films are mostly preserved without any necessity of re-polarization. Fabricated devices are tested for dynamic displacement range, power consumption, and temperature response, and FEA is used to evaluate the actuation forces. A 25- μm thick 1- mm2 sized diaphragm can provide 12 μmPP displacement at 111 kHz with power consumption, while 1-3.5 mm long cantilever beams of similar thickness provide 0.1-1 mmPP displacement at resonance frequencies of 0.7-7.4 kHz. The introduced devices can be leveraged in various ultrasonic and acoustic applications. View full abstract»

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  • Microdispenser With Continuous Flow and Selectable Target Volume for Microfluidic High-Pressure Applications

    Page(s): 452 - 458
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    This paper presents a reusable microdispenser intended for continuous flow dispensing of variable and controlled volumes of liquid against high back-pressures. The microdispenser consists of two active valves and a dispenser chamber, all actuated by the volume change associated with the solid-to-liquid phase transition of paraffin wax. It is fabricated using stainless steel sheets, a flexible printed circuit board, and a polyimide membrane. All are covered with Parylene C for insulation and fusion bonding at assembly. A finite element method (FEM) model of the paraffin actuator is used to predict the resulting flow characteristics. The results show dispensing of well-defined volumes of 350 and 540 nL, with a good repeatability between dispensing sequences, as well as reproducibility between devices. In addition, the flow characteristics show no back-pressure dependence of the dispensed flow in the interval 0.5-2.0 MPa. The FEM model can be used to predict the flow characteristics qualitatively. View full abstract»

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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.

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Meet Our Editors

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