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Microelectromechanical Systems, Journal of

Issue 2 • Date April 2013

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Displaying Results 1 - 25 of 35
  • Table of contents

    Page(s): C1 - C2
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  • Journal of Microelectromechanical Systems publication information

    Page(s): C2
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  • Sputtered–Anodized \hbox {Ta}_{2}\hbox {O}_{5} as the Dielectric Layer for Electrowetting-on-Dielectric

    Page(s): 253 - 255
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    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 Ta2O5 was originally introduced. All the EWOD tests were performed with a conductive liquid droplet in an air environment. View full abstract»

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  • A Flexible Paper-Based Microdischarge Array Device for Maskless Patterning on Nonflat Surfaces

    Page(s): 256 - 258
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    This letter presents a simple and economical paper-based device that is able to generate an array of stable Ar microdischarges. This is a dielectric-barrier-discharge device that exhibits filamentary-type features. The device is sustained by an ac voltage with a 550-V amplitude and 10-kHz frequency. Optical emission spectra show that Ar lines dominate the emission, with a trace amount of CH and C2 emissions. Despite slight damage, the electrode lifetime exceeds 20 min. Results demonstrate that this device is flexible and is able to achieve maskless patterning of hydrophilic patterns on flat and curved glass surfaces. View full abstract»

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  • Effect of Galvanic Corrosion-Induced Roughness on Sidewall Adhesion in Polycrystalline Silicon Microelectromechanical Systems

    Page(s): 259 - 261
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    A custom microdevice was used to study the effect of hydrofluoric acid processing on the force of adhesion at a silicon sidewall contact interface. Devices exposed to acidic etchant solution for a longer period of time were found to have a significantly higher surface roughness and a lower adhesion force. These results are attributed to an accelerated formation of porous silicon caused by a release etch-induced galvanic couple between the structural silicon and the gold electrical contact pads. Experiments are interpreted in light of galvanic corrosion mechanisms and the effect on the principal components in nanoscale adhesion. View full abstract»

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  • Crystallographic Effects on Energy Dissipation in High- Q Silicon Bulk-Mode Resonators

    Page(s): 262 - 264
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    This letter reports measured results of quality factor (Q ) for single-crystal silicon square-plate resonators in relation to their crystal orientation within the (100) plane. Results from both the Lamé and extensional modes oriented in the 〈110〉 and 〈100〉 axes are presented. Q appears to be dependent on orientation for the Lamé mode. In the extensional mode, there is no significant difference in Q between the two axes due to the dominance of anchor loss. These trends agree well with the brief theoretical analysis that we have described here to provide a quantitative basis for interpreting the trends between Q and orientation observed in our measurements. View full abstract»

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  • Oven-Based Thermally Tunable Aluminum Nitride Microresonators

    Page(s): 265 - 275
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    Frequency tuning of aluminum nitride (AlN) microresonators has been demonstrated via localized heating (ovenization) of the resonator. Specifically, piezoelectrically driven ~ 100 MHz microresonators were heated by embedded joule heaters in vacuum. Three different designs with three different film stacks were tested, and among the tested devices, thermal resistances as large as 92 K/mW have been demonstrated, which corresponds to 1-mW power consumption to yield a temperature increase of 92°C. To minimize heat loss, the devices were suspended from the substrate by high thermal isolation beam-type supports. The beams exhibit very high thermal resistance not only due to their high length to cross-sectional area ratio but also because they are made of thin-film-deposited polycrystalline aluminum nitride. Film-deposited AlN has been shown to have thermal conductivity much lower than that measured in bulk materials. Thermal time constants for these devices were measured ranging from submilliseconds to 10 ms depending on the design and film stacks, and frequency tunability was measured as high as 2548 parts per million/mW. The availability of a power-efficient frequency tuning method, coupled with all other performance benefits, makes AlN microresonators a promising candidate for the next-generation timing devices and tunable filters for multiband communication systems. View full abstract»

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  • Electronic Detection Strategies for a MEMS-Based Biosensor

    Page(s): 276 - 284
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    This work reports on the development of control electronics for a resonant mode biosensor. The laboratory demonstrated sensor initially showed a signal-to-noise ratio of -100 dB. With the application of half-frequency drive, frequency down conversion, appropriate filtering, and digital signal processing, a cost-effective electronic solution demonstrated a signal-to-noise ratio of +30 dB. This paper highlights important aspects in the design of integrated solutions to microelectromechanical systems-based sensors. View full abstract»

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  • Design, Simulation, and Characterization of a Bimorph Varifocal Micromirror and Its Application in an Optical Imaging System

    Page(s): 285 - 294
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    A 1.2-mm-diameter gold-silicon bimorph varifocal micromirror (VFM) has been designed and investigated for imaging applications. Several prototypes have been fabricated in a 10-μm-thick single-crystal silicon-on-insulator material. Controlled variation of the radius of curvature using electrothermal and optothermal actuation has been demonstrated. A finite-element-based simulation of the device behavior has been undertaken. Experimental characterization has shown that the device focusing power varied from an initial 87 dioptre to 69 dioptre by applying dc electrical power of 33 mW and produced a focusing power value of 59 dioptre when optothermally actuated with a normally incident laser beam of 488-nm wavelength and 43 mW. When electrothermally driven, the mechanical rise and fall times of the device were measured as 130 and 120 ms, respectively. Experimental and theoretical analyses using Zernike coefficients show that, throughout the actuation range, the aberration of the VFM is mainly a small defocus term, with negligible higher order aberrations. A compact active imaging system incorporating the VFM has been also demonstrated. This system was capable of focusing several objects located along the optical axis with a maximum tracking range of 134 mm. View full abstract»

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  • Electrical Admittance Spectroscopy for Piezoelectric MEMS

    Page(s): 295 - 302
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    A simple measurement architecture based on a transimpedance amplifier is demonstrated for the electrical admittance spectroscopy of small-scale transducers. The simplicity and low cost of the measurement system as compared to dedicated network analyzers may make spectroscopy measurements more widely accessible. The approach is adaptable to cover a broad frequency range and can be used for transducers with very small capacitance and high impedance. Measurements are demonstrated on piezoelectric micromachined transducers fabricated on silicon-on-insulator wafers and composed of 20-μm -thick epitaxial beams with 800-nm-thick lead zirconate titanate films along the surface. A complete system identification (ID) procedure based purely on measured phase spectra is also summarized. A unique perspective to the system ID procedure is provided based on poles and zeros of the admittance transfer function and geometry in the complex plane. A rigorous procedure for simultaneously extracting the transducer coupling ratio, undamped natural frequency, and damping ratio is summarized which is particularly useful for lightly coupled sensors, in which case fitting parameters by inspection is challenging and can lead to errors. This system identification approach is summarized on beams with coupling coefficients as small as 0.35%. The system ID procedure further consists of extracting effective e31 coefficients, which, for the sensors in this work, are in the range 8.7-9.3 C/m2. View full abstract»

    Freely Available from IEEE
  • Bias Contributions in a MEMS Tuning Fork Gyroscope

    Page(s): 303 - 308
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    This paper analyzes the bias sources of mechanical and electrostatic origin in a tuning fork microelectromechanical systems (MEMS) gyroscope. In a gyroscope which is symmetrical and has no defect, there would be no bias; technological defects should be investigated in order to identify and quantify bias sources, which arise from quadrature and in-phase errors. Technological dispersions within the etching step of the mechanical structure are a major source of errors. Dispersions at the scale of a single MEMS particularly matter by impacting springs and electrodes. Design rules are defined for a z-axis gyroscope in order to curb these errors: In particular, specific drive springs, which are very stiff in the sense direction, and a mechanical decoupling between drive and sense are indicated to decrease errors. Local dispersion of the width of beams has been assessed with a network of electrical test structures and leads to a local standard deviation of 3-6 nm at the scale of a MEMS gyroscope device. The optimized design enables to obtain a total error of less than 300°/s on very compact z-axis gyroscopes with an area of mechanical part of 0.5 mm2. View full abstract»

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  • Sub-Torr Chip-Scale Sputter-Ion Pump Based on a Penning Cell Array Architecture

    Page(s): 309 - 317
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    This paper investigates a miniaturized, chip-scale Penning cell array for sputter-ion pumping. In a 2.5 cm3 package, a 0.2 cm3 pump architecture with 1.5 mm diameter cells in a 4 × 2 array reduces pressure from 1 Torr (133.3 Pa) to <; 200 mTorr (26.6 Pa) in about 10 h, and from 115 mTorr (15.3 Pa) to <; 10 mTorr (1.33 Pa) in 4 h. The rate of molecular removal in this range of pressures is 0.09 ×1013 to 1.17 ×1013 molecules/s. Experiments show that the architecture is capable of igniting and sustaining the plasma required for operating at a pressure at least as low as 1.5 μTorr (200 nPa). The advantage of the Penning cell architecture reported here in comparison to other chip-scale ion pump architectures is the drastically reduced operating pressures that can be achieved and maintained. The microdischarge requires 450-600 V applied across the device and consumes 100-250 mW. The Penning cell array architecture shows significant promise for power efficient high-vacuum pumping in chip-scale and smaller systems. View full abstract»

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  • Parametric Excitation, Amplification, and Tuning of MEMS Folded-Beam Comb Drive Oscillator

    Page(s): 318 - 330
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    This paper proposes a new approach for parametric excitation, parametric amplification, and linear and nonlinear tuning of the folded-beam interdigitated comb drive oscillator. The approach is based on adding a new electrode that generates electrostatic force on the truss and accordingly generates axial stress on the folded beams. Depending on the application, this force can be dc force for resonance frequency tuning or ac force that is used for parametric excitation or amplification. Parametric excitation and amplification are utilized to enhance the effective quality factor of the system; therefore, they are used in sensors where the quality factor is a key parameter in determining their performance. The major advantages of this oscillator over traditional types of parametrically excited microelectromechanical systems (MEMS) oscillators are its ability to suppress nonlinearity and achieve high amplitude of oscillation. Here, the extended Hamilton principle is used to derive the equation of motion of the resonator. Then, an approximate solution is introduced using perturbation method of multiple scales. Finally, the frequency response of the oscillator in four different excitation conditions which are resonance frequency tuning, parametric amplification, parametric resonance, and parametric and forced resonance are presented. The approach presented here has the potential to enhance the performance of several MEMS sensor and actuator devices. View full abstract»

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  • Radio-Controlled Microactuator Based on Shape-Memory-Alloy Spiral-Coil Inductor

    Page(s): 331 - 338
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    This paper reports a bulk-micromachined shape-memory-alloy (SMA) actuator in the form of a spiral coil that constitutes an inductor-capacitor resonant circuit. The out-of-plane actuation of the SMA spiral-coil inductor is wirelessly controlled using external radio frequency (RF) magnetic fields. The resonant circuit is used as a frequency-selective wireless heater in which the SMA inductor produces heat to activate its own actuation when resonated with the RF magnetic field. The direct integration of bulk-micromachined nitinol SMA with a threshold temperature of 65 °C into a planar microfabrication process is enabled to build the 3-D spiral-coil SMA actuator in a self-assembled manner using a SiO2 reset layer patterned on the SMA coil. The fabricated SMA structure yields an out-of-plane displacement of 466 μm in the cold state. The full actuation to the flat state is reached at 70°C upon tuning the field frequency to ~ 230 MHz with an RF output power of 0.7 W. The developed actuator is demonstrated to provide a maximum force of 30 mN. The temporal response of the actuator is revealed to be two to three times faster than that of previously reported wireless SMA actuators with separate heat sources. View full abstract»

    Freely Available from IEEE
  • Photopatterning of Thiol-ene-Acrylate Copolymers

    Page(s): 339 - 348
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    Thiol-ene-acrylate copolymers exhibit a unique blend of characteristics which make them suitable for both photolithographic patterning and material property tuning. Five thiol-ene-acrylate monomer blends are found to exhibit similar reaction rates via photo-differential scanning calorimetry, while dynamic mechanical analysis shows the trend in the thermomechanical properties of three of the systems. Two selected thiol-ene-acrylate systems showed rapid polymerization with low apparent shrinkage and relatively low heat evolution (when compared to acrylates) with excellent patternability, while a binary acrylate system shows extreme apparent shrinkage, greater heat evolution, and does not replicate the mask pattern in a controllable fashion. The apparent shrinkage is a measure of patternability, since this quantity represents the actual polymer dimensions when compared to the desired dimension (i.e., photomask pattern). View full abstract»

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  • NiCr MEMS Tactile Sensors Embedded in Polyimide Toward Smart Skin

    Page(s): 349 - 355
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    Piezoresistive NiCr tactile sensors have been developed on surface micromachined aluminum oxide membranes, embedded between two polyimide layers, i.e., one serving as a substrate, another as a superstrate. A novel method to bond a flexible superstrate polyimide layer onto a microelectromechanical system tactile sensor array is presented. The piezoresistors were connected in a half-Wheatstone bridge configuration to minimize the effects of thermal drift. Three different types of sensor designs were fabricated and characterized to obtain the nichrome thin-film gauge factor. The experimental results were compared with those simulated for the same conditions of membrane deflection. The gauge factors range between 2.2 and 7.9 for sensors with a superstrate and between 1.5 and 3.2 without a superstrate. View full abstract»

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  • A Single-Mask Process for 3-D Microstructure Fabrication in PDMS

    Page(s): 356 - 362
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    This paper reports a single-mask process technique to develop 3-D structures in polydimethylsiloxane (PDMS) finding a wide variety of applications in microfluidics. This technique enables the fabrication of channels and cavities having round corners and many other customized shapes in PDMS in a predictable manner. The process relies on reactive-ion-etching lag to form 3-D channels and cavities in silicon in a single-etch process. The negative replica of patterns is then transferred from the silicon substrate to a glass master by using anodic bonding under vacuum, glass reflowing at temperatures above 700 °C for about 5 h, and complete removal of silicon in KOH. Finally, soft lithography is exploited to transfer the structures to PDMS maintaining the same aspect ratio and feature sizes of the original patterns in silicon. As a case example, an insulator-based dielectrophoresis (iDEP) device with 3-D constrictions has been developed that can operate at lower applied potentials compared with previously reported 2-D iDEP designs. Using the 3-D iDEP device, trapping of 2-μm and 500-nm polystyrene beads was achieved with an applied potential of 150 and 350 V, respectively, with more than 80% trapping efficiency. View full abstract»

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  • Interdigitated 3-D Silicon Ring Microelectrodes for DEP-Based Particle Manipulation

    Page(s): 363 - 371
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    This paper describes the design, the fabrication, and the characterization of an interdigitated 3-D silicon (Si) ring microelectrodes for dielectrophoretic (DEP) manipulation of particles. The 3-D microelectrodes are derived from a high-aspect-ratio comb structure etched in a doped single crystal Si on an insulating dielectric (silicon-on-insulator). Fingers of the comb are evolved into ring microelectrodes once perforated with a linear array of well-defined round lateral constrictions. This is achieved by the segmented finger layout and the Si dry release strategy borrowed from inertial microelectromechanical systems. The fingers and their interspaces are sealed with a cover layer forming a microfluidic flow chamber surrounded by 3-D microelectrodes and accessible via single inlet/outlet. The functionality of the device has been verified on 2- and 10-μm polystyrene microspheres in pressure-driven flow through the ring microelectrodes at 3.3 μL/min effectively focusing them into streams or trapping them around the fingers at moderate voltage levels (20-40 Vpp). View full abstract»

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  • Electroosmotic Augmentation in Flexural Plate Wave Micropumps

    Page(s): 372 - 385
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    We investigate the effectiveness and applicability of electroosmotic augmentation in flexural plate wave (FPW) micropumps for enhanced capabilities. Flow rates generated in FPW micro-scale flow systems are restricted particularly when the channel height is greater than the acoustic wave length. The proposed concept can be exploited to integrate micropumps into complex microfluidic chips improving the portability of micro-total-analysis systems along with the capabilities of actively controlling acoustics and electrokinetics for micro-mixer applications. A computational study of electroosmotic augmentation in FPW micropumps is presented where FPWs are considered by a moving wall model. A transient analysis of compressible flows of water is performed for microchannels. An isothermal equation of state for water is employed. The nonlinear Poisson-Boltzmann and Laplace equations are used to model the induced electric double layer (EDL) potential and the applied electric potential. Coupled electroosmotic and acoustics cases are investigated for two channel heights while the electric field intensity of the electrokinetic body forces and actuation frequency of acoustic excitations are varied. For deeper microchannels, increasing the actuation frequency of the wall motion does not improve the generated flow rate significantly. Inclusion of electroosmotic effects is more efficient than increasing the intensity of acoustic perturbations whenever high flow rates are required in micro-mixer applications. View full abstract»

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  • Stress Relaxation Mechanism With a Ring-Shaped Beam for a Piezoresistive Three-Axis Accelerometer

    Page(s): 386 - 394
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    A novel stress-relaxation structure with a ring-shaped beam for ensuring stability in a piezoresistive three-axis accelerometer assembled using wafer-level encapsulation and resin-mold packaging is proposed and evaluated in this paper. The reduction of the unstable increase in sensitivity due to buckling against three stress sources, i.e., the thermal stress in device fabrication, wafer bonding, and resin molding, was evaluated by both computer simulation and experiments on test samples. The measured increase in sensitivity due to stress during wafer bonding and resin molding was kept at 1.26 times using the ring-shaped beam, compared with 7.64 times when using a conventional straight beam. In addition, the standard deviation in the sensitivity of resin-molded samples was kept at 0.04 mV/G using the ring-shaped beam, compared with 2.19 mV/G using the straight beam. The sensitivity variation against the temperature change was also kept small and linear; thus, the effect of the ring-shaped beam was confirmed. View full abstract»

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  • A Tunable Miniaturized RF MEMS Resonator With Simultaneous High Q (500–735) and Fast Response Speed (< \hbox {10}-\hbox {60} \mu\hbox {s})

    Page(s): 395 - 405
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    This paper reports on the design, fabrication, and measurement of a novel radio frequency (RF) microelectromechanical systems (MEMS) tunable all-silicon evanescent-mode cavity-based resonator that simultaneously achieves high quality factor and fast response speed. The resonator is based on a 1.5-mm-deep silicon-etched cavity attached to a gold-coated silicon substrate with an array of 75 185-μm-long 20-μm-wide 1- μm-thick gold beams. The 54- mm3 resonator is tunable from 15.2 GHz up to 16.5 GHz (analog tuning range) and up to 17.8-GHz range (digital tuning range) with an array of 75 MEMS fixed-fixed beams. The MEMS beams are biased against their own silicon substrate. This helps keep RF leakage at a minimum and permits high quality factors of 500-735 for the all-silicon configuration. By applying dynamic biasing waveforms, the MEMS tuners respond within 9 μs (actuation time) and 60 μs (release including settling time). To the best of the authors' knowledge, the presented resonator is more than 3 × smaller, achieves nearly 30% higher average quality factor, and is at least 10-100 × faster than state-of-the-art resonators based on similar technology, implemented in similar frequency ranges. View full abstract»

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  • \hbox {MnO}_{2} Nanowire Embedded Hydrogen Peroxide Monopropellant MEMS Thruster

    Page(s): 406 - 417
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    Feasibility of chemically synthesized MnO2 nanowire catalyst embedded silicon microelectromechanical systems (MEMS) H2O2 monopropellant microthruster has been demonstrated. Due to exothermic reaction process, sustenance of thrust generation does not require any heating of propellant thus minimizing electrical power requirement. The thruster device integrates inlet nozzle, microchannel, MnO2 nanowire embedded reaction chamber, in-plane exit nozzle and a microheater in the silicon layer. Nozzle configuration and catalyst bed was designed using simple analytical equations to achieve complete decomposition of H2 O2 and maximum thrust force by controlling the propellant flow. Simulation of hydrogen peroxide decomposition process was carried out to evaluate the thermo-chemical characteristics. The MnO2 nanowire has been obtained using a low-cost synthesis process and characterized using field emission scanning electron microscopy, Energy-dispersive X-ray spectroscopy, transmission electron microscopy, and X-ray diffraction studies. Thruster fabrication using micromachining process and its testing have been briefly described. The device is capable to produce 1 mN thrust and specific impulse of 180 s using 50 wt.% concentrated H2O2 of flow rate 1.25 mg/s with total ignition energy of 44 J required for preheating the catalyst bed. Detailed thrust measurement was carried out with propellant mass flow rate for different throat area of exit nozzle, and the results were interpreted with theoretical model. View full abstract»

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  • Comparison of the Stress Distribution and Fatigue Behavior of 10- and 25- \mu\hbox {m} -Thick Deep-Reactive-Ion-Etched Si Kilohertz Resonators

    Page(s): 418 - 429
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    The stress distribution and fatigue behavior of nominally identical kilohertz fatigue resonators with two different thicknesses, 10 and 25 μm, was compared in this study. The results highlight the non-uniform 3-D stress distribution of the micron-scale notched cantilever beams that depends on the thickness. The areas corresponding to the first principal stress being within 2% of the maximum value are much smaller than the overall notch area and are a function of device thickness. It is also shown that the non-negligible influence of small, nanometer-scale geometrical variations in the dimensions of nominally identical devices on the maximum stress values can be accounted for by measuring the device's resonant frequency (f0). The observed scatter in the fatigue results of these microresonators is in part associated with the challenge in accurately calculating the local stress amplitudes. Despite that large scatter, the fatigue behavior of the 10 and 25 μm thick devices is similar. Particularly, the overall relative decrease rates in f0 are well related to fatigue life (Nf) and can be used to predict Nf within a factor of 5, for Nf ranging from 104 to 1010 cycles. View full abstract»

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  • Optomechanical Cavity With a Buckled Mirror

    Page(s): 430 - 437
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    We study an optomechanical cavity, in which a buckled suspended beam serves as a mirror. The mechanical resonance frequency of the beam obtains a minimum value near the buckling temperature. Contrary to the common case, in which self-excited oscillations of the suspended mirror are optically induced by injecting blue detuned laser light, in our case, self-excited oscillations are observed with red detuned light. These observations are attributed to a retarded thermal (i.e., bolometric) force acting on the buckled mirror in the inward direction (i.e., toward the other mirror). With relatively high laser power, other interesting effects are observed, including period doubling of self-excited oscillations and intermode coupling. View full abstract»

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  • Nondestructive Inspection of Buried Channels and Cavities in Silicon

    Page(s): 438 - 442
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    Microelectromechanical systems and microfluidic devices feature buried channels, cavities, and other embedded microstructures. These features are usually examined by breaking the wafer and by imaging the revealed cross section. We propose a nondestructive technique to evaluate the shape and surface quality of buried microchannels with submicrometer resolution. The technique relies on infrared light interferometry. We employed the technique to nondestructively examine channels and cavities through a silicon roof. With the proposed technique, we can quantitatively examine the size and shape of microchannels that are hidden to visible light. 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