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Microelectromechanical Systems, Journal of

Popular Articles (February 2015)

Includes the top 50 most frequently downloaded documents for this publication according to the most recent monthly usage statistics.
  • 1. Optical MEMS: From Micromirrors to Complex Systems

    Publication Year: 2014 , Page(s): 517 - 538
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (7448 KB) |  | HTML iconHTML  

    Microelectromechanical system (MEMS) technology, and surface micromachining in particular, have led to the development of miniaturized optical devices with a substantial impact in a large number of application areas. The reason is the unique MEMS characteristics that are advantageous in fabrication, systems integration, and operation of micro-optical systems. The precision mechanics of MEMS, microfabrication techniques, and optical functionality all make possible a wide variety of movable and tunable mirrors, lenses, filters, and other optical structures. In these systems, electrostatic, magnetic, thermal, and pneumatic actuators provide mechanical precision and control. The large number of electromagnetic modes that can be accommodated by beam-steering micromirrors and diffractive optical MEMS, combined with the precision of these types of elements, is utilized in fiber-optical switches and filters, including dispersion compensators. The potential to integrate optics with electronics and mechanics is a great advantage in biomedical instrumentation, where the integration of miniaturized optical detection systems with microfluidics enables smaller, faster, more-functional, and cheaper systems. The precise dimensions and alignment of MEMS devices, combined with the mechanical stability that comes with miniaturization, make optical MEMS sensors well suited to a variety of challenging measurements. Micro-optical systems also benefit from the addition of nanostructures to the MEMS toolbox. Photonic crystals and microcavities, which represent the ultimate in miniaturized optical components, enable further scaling of optical MEMS. View full abstract»

    Open Access
  • 2. Etch rates for micromachining processing

    Publication Year: 1996 , Page(s): 256 - 269
    Cited by:  Papers (152)  |  Patents (198)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1532 KB)  

    The etch rates for 317 combinations of 16 materials (single-crystal silicon, doped, and undoped polysilicon, several types of silicon dioxide, stoichiometric and silicon-rich silicon nitride, aluminum, tungsten, titanium, Ti/W alloy, and two brands of positive photoresist) used in the fabrication of microelectromechanical systems and integrated circuits in 28 wet, plasma, and plasmaless-gas-phase etches (several HF solutions, H3PO4, HNO3 +H2O+NH4F, KOH, Type A aluminum etchant, H 2O+H2O2+HF, H2O2, piranha, acetone, HF vapor, XeF2, and various combinations of SF6, CF4, CHF3, Cl2, O2 , N2, and He in plasmas) were measured and are tabulated. Etch preparation, use, and chemical reactions (from the technical literature) are given. Sample preparation and MEMS applications are described for the materials View full abstract»

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  • 3. What is the Young's Modulus of Silicon?

    Publication Year: 2010 , Page(s): 229 - 238
    Cited by:  Papers (162)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (577 KB) |  | HTML iconHTML  

    The Young's modulus (E) of a material is a key parameter for mechanical engineering design. Silicon, the most common single material used in microelectromechanical systems (MEMS), is an anisotropic crystalline material whose material properties depend on orientation relative to the crystal lattice. This fact means that the correct value of E for analyzing two different designs in silicon may differ by up to 45%. However, perhaps, because of the perceived complexity of the subject, many researchers oversimplify silicon elastic behavior and use inaccurate values for design and analysis. This paper presents the best known elasticity data for silicon, both in depth and in a summary form, so that it may be readily accessible to MEMS designers. View full abstract»

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  • 4. Etch rates for micromachining processing-Part II

    Publication Year: 2003 , Page(s): 761 - 778
    Cited by:  Papers (192)  |  Patents (71)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1047 KB) |  | HTML iconHTML  

    Samples of 53 materials that are used or potentially can be used or in the fabrication of microelectromechanical systems and integrated circuits were prepared: single-crystal silicon with two doping levels, polycrystalline silicon with two doping levels, polycrystalline germanium, polycrystalline SiGe, graphite, fused quartz, Pyrex 7740, nine other preparations of silicon dioxide, four preparations of silicon nitride, sapphire, two preparations of aluminum oxide, aluminum, Al/2%Si, titanium, vanadium, niobium, two preparations of tantalum, two preparations of chromium, Cr on Au, molybdenum, tungsten, nickel, palladium, platinum, copper, silver, gold, 10 Ti/90 W, 80 Ni/20 Cr, TiN, four types of photoresist, resist pen, Parylene-C, and spin-on polyimide. Selected samples were etched in 35 different etches: isotropic silicon etchant, potassium hydroxide, 10:1 HF, 5:1 BHF, Pad Etch 4, hot phosphoric acid, Aluminum Etchant Type A, titanium wet etchant, CR-7 chromium etchant, CR-14 chromium etchant, molybdenum etchant, warm hydrogen peroxide, Copper Etchant Type CE-200, Copper Etchant APS 100, dilute aqua regia, AU-5 gold etchant, Nichrome Etchant TFN, hot sulfuric+phosphoric acids, Piranha, Microstrip 2001, acetone, methanol, isopropanol, xenon difluoride, HF+H2O vapor, oxygen plasma, two deep reactive ion etch recipes with two different types of wafer clamping, SF6 plasma, SF6+O2 plasma, CF4 plasma, CF4+O2 plasma, and argon ion milling. The etch rates of 620 combinations of these were measured. The etch rates of thermal oxide in different dilutions of HF and BHF are also reported. Sample preparation and information about the etches is given. View full abstract»

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  • 5. Fabrication and Characterization of Microstacked PZT Actuator for MEMS Applications

    Publication Year: 2015 , Page(s): 80 - 90
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3357 KB) |  | HTML iconHTML  

    A microstacked PZT actuator of dimensions 8 mm × 0.8 mm × 0.4 mm and capable of 2.3-μm actuation under a voltage of 100 V was fabricated and characterized. This actuator was then integrated into a silicon microstage with dimensions of 20 mm × 20 mm × 0.4 mm requiring actuation by a miniaturized actuator. The microstage was designed containing a Moonie amplification mechanism in order to further amplify the actuation of the stacked PZT actuator. Experimental characterization of the microstage performance indicated that the combination of a stacked PZT actuator with the Moonie amplification mechanism was successful in enabling high amplification of the microstage to ~15 times the original displacement of the PZT actuator. A displacement of 16.5 μm at an applied voltage of 60 V and a resonant frequency of 456 Hz in the lateral vibration mode was observed. The relationship between the actuator parameters and the microstage design and performance was also discussed in order to show that the customized fabrication of a miniature actuator was imperative for the successful design of a high area-efficiency microstage. Analytical derivation of the displacement of the stacked PZT actuator was also carried out in order to evaluate the effectiveness of the fabricated actuator compared with the ideal stacked PZT structure. View full abstract»

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  • 6. Gallium Nitride as an Electromechanical Material

    Publication Year: 2014 , Page(s): 1252 - 1271
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (5181 KB) |  | HTML iconHTML  

    Gallium nitride (GaN) is a wide bandgap semiconductor material and is the most popular material after silicon in the semiconductor industry. The prime movers behind this trend are LEDs, microwave, and more recently, power electronics. New areas of research also include spintronics and nanoribbon transistors, which leverage some of the unique properties of GaN. GaN has electron mobility comparable with silicon, but with a bandgap that is three times larger, making it an excellent candidate for high-power applications and high-temperature operation. The ability to form thin-AlGaN/GaN heterostructures, which exhibit the 2-D electron gas phenomenon leads to high-electron mobility transistors, which exhibit high Johnson's figure of merit. Another interesting direction for GaN research, which is largely unexplored, is GaN-based micromechanical devices or GaN microelectromechanical systems (MEMS). To fully unlock the potential of GaN and realize new advanced all-GaN integrated circuits, it is essential to cointegrate passive devices (such as resonators and filters), sensors (such as temperature and gas sensors), and other more than Moore functional devices with GaN active electronics. Therefore, there is a growing interest in the use of GaN as a mechanical material. This paper reviews the electromechanical, thermal, acoustic, and piezoelectric properties of GaN, and describes the working principle of some of the reported high-performance GaN-based microelectromechanical components. It also provides an outlook for possible research directions in GaN MEMS. View full abstract»

    Open Access
  • 7. Studies on surface wettability of poly(dimethyl) siloxane (PDMS) and glass under oxygen-plasma treatment and correlation with bond strength

    Publication Year: 2005 , Page(s): 590 - 597
    Cited by:  Papers (165)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (432 KB)  

    An issue in microfabrication of the fluidic channels in glass/poly (dimethyl siloxane) (PDMS) is the absence of a well-defined study of the bonding strength between the surfaces making up these channels. Although most of the research papers mention the use of oxygen plasma for developing chemical (siloxane) bonds between the participating surfaces, yet they only define a certain set of parameters, tailored to a specific setup. An important requirement of all the microfluidics/biosensors industry is the development of a general regime, which defines a systematic method of gauging the bond strength between the participating surfaces in advance by correlation to a common parameter. This enhances the reliability of the devices and also gives a structured approach to its future large-scale manufacturing. In this paper, we explore the possibility of the existence of a common scale, which can be used to gauge bond strength between various surfaces. We find that the changes in wettability of surfaces owing to various levels of plasma exposure can be a useful parameter to gauge the bond strength. We obtained a good correlation between contact angle of deionized water (a direct measure of wettability) on the PDMS and glass surfaces based on various dosages or oxygen plasma treatment. The exposure was done first in an inductively coupled high-density (ICP) plasma system and then in plasma enhanced chemical vapor deposition (PECVD) system. This was followed by the measurement of bond strength by use or the standardized blister test. View full abstract»

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  • 8. Microfabrication Methods for Biodegradable Polymeric Carriers for Drug Delivery System Applications: A Review

    Publication Year: 2015 , Page(s): 10 - 18
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2571 KB) |  | HTML iconHTML  

    A drug delivery system is used for targeting drugs to specific cells. Various drug carriers, that also reduce the side effects of unbound drugs, have been introduced and commercialized in the pharmaceutical field. Among them, synthetic biodegradable polymers have received much attention attributed to their low toxicity, controllable biodegradation rates, manufacturability, and low costs. This paper reviews the salient characteristics of biodegradable polymers as drug carriers and their microfabrication methods. The reviewed microfabrication methods include laser micromachining, rapid prototyping, replication, emulsification, microfluidic fabrication, and X-ray-lithography-based methods. For these microfabrication methods, critical dimensions, feature variety, solvent compatibility, production throughput, and tooling requirements are also summarized. View full abstract»

    Open Access
  • 9. Silk-Backed Structural Optimization of High-Density Flexible Intracortical Neural Probes

    Publication Year: 2015 , Page(s): 62 - 69
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3541 KB) |  | HTML iconHTML  

    Many chronic neuroscience studies require neural probes that can reliably record with a large number of electrodes in a densely configured array. Previous works have shown that adverse tissue reaction can be significantly reduced as probe shanks are scaled down toward subcellular dimensions. In addition, flexible probes can mitigate shear stress-induced tissue damage due to micromotion. However, both size reduction and flexibility compromise probe's ability to penetrate the pia mater, especially when many electrodes are distributed across multiple probe shanks. In this paper, we present a method to lithographically pattern a biodegradable silk coating that provides temporary mechanical stiffness for the surgical insertion of flexible probes without any conventional design constraints on the probe size, shape, or material. After insertion, the silk is completely dissolved in the tissue, only leaving the flexible minimum-geometry probes inside the brain. We validated the design by successfully inserting silk-backed 64-channel parylene probes into the motor cortex of Long-Evans rats (n = 6) and recorded in vivo neural activity for six weeks. View full abstract»

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  • 10. Three-dimensional micro-channel fabrication in polydimethylsiloxane (PDMS) elastomer

    Publication Year: 2000 , Page(s): 76 - 81
    Cited by:  Papers (367)  |  Patents (123)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    This paper describes a fabrication technique for building three-dimensional (3-D) micro-channels in polydimethylsiloxane (PDMS) elastomer. The process allows for the stacking of many thin (less than 100-/spl mu/m thick) patterned PDMS layers to realize complex 3-D channel paths. The master for each layer is formed on a silicon wafer using an epoxy-based photoresist (SU 8). PDMS is cast against the master producing molded layers containing channels and openings. To realize thin layers with openings, a sandwich molding configuration was developed that allows precise control of the PDMS thickness. The master wafer is clamped within a sandwich that includes flat aluminum plates, a flexible polyester film layer, a rigid Pyrex wafer, and a rubber sheet. A parametric study is performed on PDMS surface activation in a reactive-ion-etching system and the subsequent methanol treatment for bonding and aligning very thin individual components to a substrate. Low RF power and short treatment times are better than high RF power and long treatment times, respectively, for instant bonding. Layer-to-layer alignment of less then 15 /spl mu/m is achieved with manual alignment techniques that utilize surface tension driven self-alignment methods. A coring procedure is used to realize off-chip fluidic connections via the bottom PDMS layer, allowing the top layer to remain smooth and flat for complete optical access. View full abstract»

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  • 11. There's plenty of room at the bottom [data storage]

    Publication Year: 1992 , Page(s): 60 - 66
    Cited by:  Papers (36)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (707 KB)  

    The problem of manipulating and controlling things on a small scale is discussed. The question of how to write the entire 24 volumes of the Encyclopaedia Britannica on the head of a pin is examined. The question of how to read it is also discussed, focusing on the need to make the electron microscope more powerful. Other aspects of miniaturization and of making things on a small scale are discussed, including miniaturizing the computer, miniaturization by evaporation, problems of lubrication, and rearranging atoms.<> View full abstract»

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  • 12. Optical Power Delivery and Data Transmission in a Wireless and Batteryless Microsystem Using a Single Light Emitting Diode

    Publication Year: 2015 , Page(s): 155 - 165
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2141 KB) |  | HTML iconHTML  

    In this paper, a light emitting diode (LED) is used both to harvest energy and to transmit data in a wireless and batteryless microsystem. The microsystem consists of an LED die (350 μm × 350 μm), an application specific integrated circuit (230 μm × 210 μm) and a storage capacitor (0.5 mm × 1 mm) forming a small footprint. A modular optical energy management and data transmission framework is presented. A proof of concept design that transmits a 16-bit identification number serially at a data rate depending on the amount of received optical power is described. The LED has a power efficiency of 22%; better than silicon photodiodes under monochromatic light of 680-nm wavelength. The higher voltage supplied by the LED compared with a silicon photodiode allows circuitry to be powered directly from it without requiring the elevation of the photovoltaic potential, as in the case of using on-chip silicon photodiodes. Data transmission task of the LED requires a charge pump circuit to elevate the photovoltaic voltage. The 0.8 V generated by the LED under a 680-nm laser beam of 4-mW/mm2 optical power density is elevated to 1.4 V for optical transmission at a rate of 4 kbit/s. Under 70-mW/mm2 optical power density, 1.3 V is elevated to 2.4 V, achieving a data rate of 26 kbit/s. View full abstract»

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  • 13. Development of a Broadband Triboelectric Energy Harvester With SU-8 Micropillars

    Publication Year: 2015 , Page(s): 91 - 99
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2732 KB) |  | HTML iconHTML  

    This paper describes a broadband energy harvester working on the principle of contact electrification or triboelectric charging. Design and fabrication of the device have been discussed. The device uses contact and separation mechanism using a cantilever to generate triboelectric charges. This mechanism introduces nonlinearity in the cantilever, which results in broadband behavior of triboelectric energy harvester. The device uses SU-8 micropillar arrays to enhance the triboelectric charging. A study is conducted to study the effect of the micropillar sizes on the power output of devices. The devices were tested at different acceleration levels. The peak power output achieved is 0.91 μW at an acceleration of 1g. The amplitude limiter based design of the energy harvester enables broadening of operating bandwidth as the acceleration level increases. A maximum operating bandwidth of 22.05 Hz was observed at 1.4g increasing from an operating bandwidth of 9.43 Hz at 0.4g. View full abstract»

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  • 14. High Resolution Magnetometer Based on a High Frequency Magnetoelectric MEMS-CMOS Oscillator

    Publication Year: 2015 , Page(s): 134 - 143
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3772 KB) |  | HTML iconHTML  

    This paper demonstrates a miniaturized and high resolution (16 nT/Hz1/2) magnetometer based on a high frequency (168.1 MHz) magnetoelectric Microelectromechanical Systems-Complementary metal-oxidesemiconductor (MEMSCMOS) oscillator. For the first time, a high frequency and high electromechanical performance (quality factor, Q ~ 1084 and electromechanical coupling coefficient, kt2 ~ 1.18%) magnetoelectric micromechanical resonator based on a self-biased aluminum nitride/iron-gallium-boron (AlN/FeGaB) bilayer nanoplate (250/250 nm) is implemented and used to synthesize a low noise frequency source (2.7 Hz/Hz1/2) whose output frequency is highly sensitive to external magnetic field (169 Hz/μT at zero magnetic field bias). The angular sensitivity of the magnetometer for electronic compass applications is also investigated showing an ultrahigh angular resolution of 0.34° for a 10-μT conservative estimate of the earth's magnetic field, due to the strongly anisotropic sensitivity of the self-biased AlN/FeGaB magnetoelectric resonator. This paper represents the first demonstration of a high resolution self-biased MEMS magnetoelectric resonant sensor interfaced to a compact and low power self-sustained CMOS oscillator as direct frequency readout for the implementation of miniaturized and low power magnetometers with detection limit pushed in ~10s nT/Hz1/2 range. View full abstract»

    Freely Available from IEEE
  • 15. A MEMS Low-Noise Sound Pressure Gradient Microphone With Capacitive Sensing

    Publication Year: 2015 , Page(s): 241 - 248
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (5258 KB) |  | HTML iconHTML  

    A silicon microelectromechanical systems microphone is described that detects sound pressure gradients. The diaphragm consists of a stiffened plate that rotates around a central axis in response to sound pressure gradients. The motion of the diaphragm is converted into an electronic signal through the use of interdigitated comb fins that enable capacitive sensing. Measured results show that the microphone achieves a substantially lower low-frequency sound pressure-referred noise floor than can be achieved using existing dual miniature microphone systems. Measured directivity patterns are shown to be very close to what is expected for sound pressure gradient receivers over a broad range of frequencies. View full abstract»

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  • 16. Temperature Dependence of the Elastic Constants of Doped Silicon

    Publication Year: 2014 , Page(s): 1
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (5438 KB)  

    Resonators fabricated in heavily doped silicon have been noted to have a reduced frequency-temperature dependence compared with lightly doped silicon. The resonant frequency of silicon microelectromechanical systems (MEMS) resonators is largely governed by the material’s elastic properties, which are known to depend on doping. In this paper, a suite of different types and orientations of resonators were used to extract the first- and second-order temperature dependences of the elastic constants of p-doped silicon up to 1.7e20 cm (^{math\rm {math\bf {-3}}}) , and n-doped up to 6.6e19 cm (^{math\rm {math\bf {-3}}}) . It is shown that these temperature-dependent elastic constants may be used in finite element analysis to predict the frequency-temperature dependence of similarly doped silicon resonators.[2013-0331] View full abstract»

    Open Access
  • 17. Demonstration of 1 Million $Q$ -Factor on Microglassblown Wineglass Resonators With Out-of-Plane Electrostatic Transduction

    Publication Year: 2015 , Page(s): 29 - 37
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (5059 KB) |  | HTML iconHTML  

    In this paper, we report Q-factor over 1 million on both n = 2 wineglass modes, and high-frequency symmetry (Af/f ) of 132 ppm on wafer-level microglassblown 3-D fused silica wineglass resonators at a compact size of 7-mm diameter and center frequency of 105 kHz. In addition, we demonstrate for the first time, out-of-plane capacitive transduction on microelectromechanical systems wineglass resonators. High Q-factor is enabled by a high aspect ratio, self-aligned glassblown stem structure, careful surface treatment of the perimeter area, and low internal loss fused silica material. Electrostatic transduction is enabled by detecting the spatial deformation of the 3-D wineglass structure using a new out-of-plane electrode architecture. Out-of-plane electrode architecture enables the use of sacrificial layers to define the capacitive gaps and 10 μm capacitive gaps have been demonstrated on a 7-mm shell, resulting in over 9 pF of active capacitance within the device. Microglassblowing may enable batch-fabrication of high-performance fused silica wineglass gyroscopes at a significantly lower cost than their precision-machined macroscale counterparts. View full abstract»

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  • 18. Metallic Glass Hemispherical Shell Resonators

    Publication Year: 2015 , Page(s): 19 - 28
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3285 KB) |  | HTML iconHTML  

    By utilizing bulk metallic glasses' (BMGs) unique combination of amorphous structure, material properties, and fabrication opportunities, ultrasmooth and symmetric 3-D metallic glass resonators that are complimentary metal oxide semiconductor (CMOS) post-processing compatible are fabricated. Surface roughness to size ratio fabrication precision in the order of 100 parts per billion is demonstrated with a 3-mm diameter Pt57.5Cu14.7Ni5.3P22.5 BMG hemispherical shell with a thickness variation <;100 nm and a surface roughness of <;1 nm Ra. The resonator exhibits a resonant frequency of 13.9440 kHz ± 0.1 Hz with 0.035% frequency mismatch between degenerate N = 2 wineglass modes with a quality factor of 6200. This performance was obtained in the asmolded state without any device tuning or trimming. Another resonator with N = 2 resonant modes at 9.393 and 9.401 kHz, and quality factors of 7800 and 6500 was mounted into an integrated electrode system. Electrical readout by capacitive sensing in both time and frequency domains showed a resonance shift to 9.461 and 9.483 kHz, respectively. The quality factor was reduced to 5400 and 5300, respectively. This investigation demonstrates that BMG resonators may serve as a basis for robust microelectromechanical systems resonator devices with increased performance and low-cost fabrication techniques that exploits the atomic structure, unique softening behavior, strength, formability, and toughness of metallic glasses. View full abstract»

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  • 19. Piezoelectric MEMS Energy Harvester for Low-Frequency Vibrations With Wideband Operation Range and Steadily Increased Output Power

    Publication Year: 2011 , Page(s): 1131 - 1142
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1638 KB) |  | HTML iconHTML  

    A piezoelectric MEMS energy harvester (EH) with low resonant frequency and wide operation bandwidth was designed, microfabricated, and characterized. The MEMS piezoelectric energy harvesting cantilever consists of a silicon beam integrated with piezoelectric thin film (PZT) elements parallel-arranged on top and a silicon proof mass resulting in a low resonant frequency of 36 Hz. The whole chip was assembled onto a metal carrier with a limited spacer such that the operation frequency bandwidth can be widened to 17 Hz at the input acceleration of 1.0 g during frequency up-sweep. Load voltage and power generation for different numbers of PZT elements in series and in parallel connections were compared and discussed based on experimental and simulation results. Moreover, the EH device has a wideband and steadily increased power generation from 19.4 nW to 51.3 nW within the operation frequency bandwidth ranging from 30 Hz to 47 Hz at 1.0 g. Based on theoretical estimation, a potential output power of 0.53 μW could be harvested from low and irregular frequency vibrations by adjusting the PZT pattern and spacer thickness to achieve an optimal design. View full abstract»

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  • 20. Analytical Modeling of a Novel High- $Q$ Disk Resonator for Liquid-Phase Applications

    Publication Year: 2015 , Page(s): 38 - 49
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2217 KB) |  | HTML iconHTML  

    To overcome the detrimental effects of liquid environments on microelectromechanical systems resonator performance, the in-fluid vibration of a novel disk resonator supported by two electrothermally driven legs is investigated through analytical modeling and the effects of the system's geometric/material parameters on the dynamic response are explored. The all-shear interaction device (ASID) is based on engaging the surrounding fluid primarily through shearing action. The theory comprises a continuous-system, multimodal model, and a single-degree-of-freedom model, the latter yielding simple formulas for the fundamental-mode resonant characteristics that often furnish excellent estimates to the results based on the more general model. Comparisons between theoretical predictions and previously published liquid-phase quality factor (Q) data (silicon devices in heptane) show that the theoretical results capture the observed trends and also give very good quantitative estimates, particularly for the highest Q devices. Moreover, the highest Q value measured in the earlier study (304) corresponded to a specimen whose disk radius-to-thickness ratio was 2.5, a value that compares well with the optimal value of 2.3 predicted by the present model. The insight furnished by the proposed theory is expected to lead to further improvements in ASID design to achieve unprecedented levels of performance for a wide variety of liquid-phase resonator applications. View full abstract»

    Freely Available from IEEE
  • 21. Comparison of MEMS PZT Cantilevers Based on d_{31} and d_{33} Modes for Vibration Energy Harvesting

    Publication Year: 2013 , Page(s): 26 - 33
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (644 KB) |  | HTML iconHTML  

    d 31 and d33 mode microelectromechanical systems piezoelectric energy harvesters (PEHs) were fabricated and compared to investigate their output powers converted from vibration. Both types of devices have the same dimensions in a cantilever structure and aim to effectively couple vibration from ambient conditions. The resonant frequencies of the cantilevers are 243 Hz. Two types of devices were compared using mathematical equations based on an equivalent circuit model. The output power of the d31 mode PEH was 2.15 μW and 2.33 μW in experiment and modeling, respectively. The d33 mode PEHs generated output power ranging between 0.62 and 1.71 μW when the width of the interdigital electrode (IDE) is ranging from 8 to 16 μm and finger spacing is varied from 4 to 16 μm. The output power of the d33 mode device strongly depends on the dimensions of IDE. The analysis of material constant and electrode design was conducted in conjunction with developing a mathematical equation. The result predicts that the output power of d33 mode PEH can be higher than that of d31 mode PEH when the finger width is reduced to 2 μm and finger spacing is between 8 and 20 μm. View full abstract»

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  • 22. What is MEMS Gyrocompassing? Comparative Analysis of Maytagging and Carouseling

    Publication Year: 2013 , Page(s): 1257 - 1266
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2727 KB) |  | HTML iconHTML  

    North-finding based on micromachined gyroscopes is an attractive possibility. This paper analyzes north-finding methods and demonstrates a measured 4 mrad standard deviation azimuth uncertainty using an in-house developed vibratory silicon MEMS quadruple mass gyroscope (QMG). We instrumented a vacuum packaged QMG with isotropic Q-factor of 1.2 million and Allan deviation bias instability of 0.2 °/hr for azimuth detection by measuring the earth's rotation. Continuous rotation (“carouseling”) produced azimuth datapoints with uncertainty diminishing as the square root of the number of turns. Integration of 100 datapoints with normally distributed errors reduced uncertainty to 4 mrad, beyond the noise of current QMG instrumentation. We also implemented self-calibration methods, including in-situ temperature sensing and discrete ±180° turning (“maytagging” or two-point gyrocompassing) as potential alternatives to carouseling. While both mechanizations produced similar azimuth uncertainty, we conclude that carouseling is more advantageous as it is robust to bias, scale-factor, and temperature drifts, although it requires a rotary platform providing continuous rotation. Maytagging, on the other hand, can be implemented using a simple turn table, but requires calibration due to temperature-induced drifts. View full abstract»

    Freely Available from IEEE
  • 23. Piezoelectric Aluminum Nitride Vibrating Contour-Mode MEMS Resonators

    Publication Year: 2006 , Page(s): 1406 - 1418
    Cited by:  Papers (102)  |  Patents (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2126 KB)  

    This paper reports theoretical analysis and experimental results on a new class of rectangular plate and ring-shaped contour-mode piezoelectric aluminum nitride radio-frequency microelectromechanical systems resonators that span a frequency range from 19 to 656 MHz showing high-quality factors in air (Qmax=4300 at 229.9 MHz), low motional resistance (ranging from 50 to 700 Omega), and center frequencies that are lithographically defined. These resonators achieve the lowest value of motional resistance ever reported for contour-mode resonators and combine it with high Q factors, therefore enabling the fabrication of arrays of high-performance microresonators with different frequencies on a single chip. Uncompensated temperature coefficients of frequency of approximately -25 ppm/degC were also recorded for these resonators. Initial discussions on mass loading mechanisms induced by metal electrodes and energy loss phenomenon are provided View full abstract»

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  • 24. Simulation, Design, Fabrication, and Testing of a MEMS Resettable Circuit Breaker

    Publication Year: 2015 , Page(s): 232 - 240
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2907 KB) |  | HTML iconHTML  

    We describe a novel concept for a microelectromechanical systems (MEMS) resettable circuit breaker. The concept involves fabricating the circuit breaker and the reset switch using a single microcantilever. The MEMS resettable circuit breaker consists of a microcantilever that is pulled toward the bottom electrode by electrostatic actuation. The MEMS cantilever also has a thermal heater, and when a current passes through the heater, it overcomes the electrostatic actuation force thereby disconnecting the circuit. A detailed finite element analysis using thermal-electric-structural multiphysics phenomena was studied. Electrostatic-structural coupled-field analysis shows the circuit breaker switch has a pull-in voltage of about 31 V for a singlecrystal Si cantilever with a thickness of 2 μm, a length of 1000 μm, and a width of 500 μm. Thermal-electric coupledfield analysis shows the switch maximum temperature is 80.5 °C at a 50-mA current flow. Thermal-electric-structural sequential analysis shows the cantilever tip has a maximum upward displacement of 0.3 μm, which is just enough to open the switch. The impact of the initial film stress in the SiO2 insulation layer was also simulated, and the results show that the film stress has a significant impact on the initial cantilever position after release. Fabrication of the chips was done using two wafers, a silicon-on-insulator (SOI) wafer, and a double-side polished silicon wafer. The SOI wafer device silicon layer was selected as cantilever material. Platinum was selected as heater material and chrome-gold was selected for bonding, trace, and electrostatic electrodes. Electrical testing results confirmed the proposed and simulated operation principle of the MEMS resettable circuit breaker. The results showed that the switch achieved good contact at an electrostatic switch-ON voltage of about 55 V. The measured circuit breaker current threshold is in the range of 45-55 m- . View full abstract»

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  • 25. Ink-jet printed nanoparticle microelectromechanical systems

    Publication Year: 2002 , Page(s): 54 - 60
    Cited by:  Papers (190)  |  Patents (53)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (171 KB) |  | HTML iconHTML  

    Reports a method to additively build three-dimensional (3-D) microelectromechanical systems (MEMS) and electrical circuitry by ink-jet printing nanoparticle metal colloids. Fabricating metallic structures from nanoparticles avoids the extreme processing conditions required for standard lithographic fabrication and molten-metal-droplet deposition. Nanoparticles typically measure 1 to 100 nm in diameter and can be sintered at plastic-compatible temperatures as low as 300°C to form material nearly indistinguishable from the bulk material. Multiple ink-jet print heads mounted to a computer-controlled 3-axis gantry deposit the 10% by weight metal colloid ink layer-by-layer onto a heated substrate to make two-dimensional (2-D) and 3-D structures. We report a high-Q resonant inductive coil, linear and rotary electrostatic-drive motors, and in-plane and vertical electrothermal actuators. The devices, printed in minutes with a 100 μm feature size, were made out of silver and gold material with high conductivity,and feature as many as 400 layers, insulators, 10:1 vertical aspect ratios, and etch-released mechanical structure. These results suggest a route to a desktop or large-area MEMS fabrication system characterized by many layers, low cost, and data-driven fabrication for rapid turn-around time, and represent the first use of ink-jet printing to build active MEMS View full abstract»

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  • 26. Terahertz Photoacoustic Spectroscopy Using an MEMS Cantilever Sensor

    Publication Year: 2015 , Page(s): 216 - 223
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1675 KB) |  | HTML iconHTML  

    In this paper, a microelectromechanical systems cantilever sensor was designed, modeled, and fabricated to measure the photoacoustic (PA) response of gases under very low vacuum conditions. The micromachined devices were fabricated using silicon-on-insulator wafers and then tested in a custom-built, miniature, vacuum chamber during this first-ever demonstration. Terahertz radiation was amplitude modulated to excite the gas under test and perform PA molecular spectroscopy. Experimental data show a predominantly linear response that directly correlates measured cantilever deflection to PA signals. Excellent low pressure (i.e., 2-40 mTorr) methyl cyanide PA spectral data were collected resulting in a system sensitivity of 1.97 × 10-5 cm-1 and a normalized noise equivalent absorption coefficient of 1.39 × 10-9 cm-1 W Hz-1/2. View full abstract»

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  • 27. An Omnidirectional MEMS Ultrasonic Energy Harvester for Implanted Devices

    Publication Year: 2014 , Page(s): 1454 - 1462
    Multimedia
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    This paper presents the design and characterization of a microelectromechanical systems (MEMS)-based energy harvester with target applications, including implanted biomedical sensors and actuators. The harvester is designed to utilize ultrasonic waves from an external transmitter for mechanical excitation, with electrostatic transducers being used to convert the vibrations of a central mass structure into electrical energy. The device features a novel 3-degrees of freedom design, which enables energy to be produced by the harvester in any orientation. The harvester is fabricated using a conventional silicon-on-insulator MEMS process, with experimental testing showing that the system is able to generate 24.7, 19.8, and 14.5nW of electrical power, respectively, via the device's x-, y- and z-axis resonance modes over a 15-s period. View full abstract»

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  • 28. Evaluation of elastic properties and temperature effects in Si thin films using an electrostatic microresonator

    Publication Year: 2003 , Page(s): 524 - 530
    Cited by:  Papers (10)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (526 KB)  

    Laterally driven microresonators were used to estimate the temperature-dependent elastic modulus of single-crystalline Si for microelectromechanical systems (MEMS). The resonators were fabricated through surface micromachining from silicon-on-glass wafers. They were moved laterally by alternating electrostatic force at a series of frequencies, and then a resonance frequency was determined, under temperature cycling in the range of 25°C to 600°C, by detecting the maximum displacement. The elastic modulus was obtained in the temperature range by Rayleigh's energy method from the detected resonance frequency. At this time, the temperature dependency of elastic modulus was affected by surface oxidation as well as its intrinsic variation: a temperature cycle permanently reduces the resonance frequency. The effect of Si oxidation was analyzed for thermal cycling by applying a simple composite model to the measured frequency data; here the oxide thickness was estimated from the difference in the resonance frequency before and after the temperature cycle, and was confirmed by field-emission scanning electron microscopy. Finally, the temperature coefficient of the elastic modulus of Si in the <110> direction was determined as -64×10-6[°C-1]. This value was quite comparable to those reported in previous literatures, and much more so if the specimen temperature is calibrated more exactly. View full abstract»

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  • 29. Sidewall Nanotexturing for High Rupture Strength of Silicon Solar Cells

    Publication Year: 2015 , Page(s): 7 - 9
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    Photovoltaic, microelectromechanical systems, and integrated circuit industries are demanding a technology to enable the high rupture resistant silicon wafer production to improve the manufacturing yield. The presented silicon nanotexture patterning on the edges and sidewalls by wet chemical etching process can protect single-crystalline and multicrystalline silicon samples from rupture. Bending tests indicate a mechanical strength enhancement of ~ 72%-75% for sc-silicon and ~71%-73% for mc-silicon samples. In addition, the front and back surfaces of the samples remain intact and appropriate for any further semiconductor processes. This technology was implemented in solar cells that exhibited a strength improvement of nearly 73% without affecting their photovoltaic performances, anticipating an effective solution for the solar cell manufacturing industry. View full abstract»

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  • 30. Electromagnetic Energy Harvester With Flexible Coils and Magnetic Spring for 1-10 Hz Resonance

    Publication Year: 2015 , Page(s): 1
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    This paper presents an energy harvester with microfabricated flexible coils (rolled and aligned to a magnet array for maximum magnetic flux change) and magnetic spring to generate electrical power from human body motion. The magnet array is suspended by a magnetic spring for a resonant frequency of several hertz. An analytical model of vibration-driven energy harvester with magnetic spring through magnet and coil arrays is developed to explore the power generation with various magnet ranges and vibration amplitudes. Experimental results show that the electromagnetic energy harvester with six 7-turn microfabricated coils (occupying 3.8 cc and weighing 8.5 gram) generates an induced electromotive force (EMF) of Vrms = 6.7 mV with 0.53-μW power output (into 21-Ω load) from 0.27-g acceleration at 8 Hz (corresponding to 1.05-mm vibration amplitude). Its larger-scale version with sixteen 200-turn wire-wound coils (occupying 26 cc and weighing 98 gram) generates an EMF of Vrms = 1.3 V with 4.3-mW power output (into 100-Ω load) from 0.5-g acceleration at 5.5 Hz (corresponding to 4.1-mm vibration amplitude). When the larger-scale version of the energy harvester is placed in a backpack of a human walking at various speeds, the power output is increased as the walking speed is increased from 0.45 m/s (slow walking) to 2.68 m/s (slow running), and reaches 14.8 mW at 2.68 m/s. [2014-0323] View full abstract»

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  • 31. Nonlinear Dynamics of Spring Softening and Hardening in Folded-MEMS Comb Drive Resonators

    Publication Year: 2011 , Page(s): 943 - 958
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1653 KB) |  | HTML iconHTML  

    This paper studies analytically and numerically the spring softening and hardening phenomena that occur in electrostatically actuated microelectromechanical systems comb drive resonators utilizing folded suspension beams. An analytical expression for the electrostatic force generated between the combs of the rotor and the stator is derived and takes into account both the transverse and longitudinal capacitances present. After formulating the problem, the resulting stiff differential equations are solved analytically using the method of multiple scales, and a closed-form solution is obtained. Furthermore, the nonlinear boundary value problem that describes the dynamics of inextensional spring beams is solved using straightforward perturbation to obtain the linear and nonlinear spring constants of the beam. The analytical solution is verified numerically using a Matlab/Simulink environment, and the results from both analyses exhibit excellent agreement. Stability analysis based on phase plane trajectory is also presented and fully explains previously reported empirical results that lacked sufficient theoretical description. Finally, the proposed solutions are, once again, verified with previously published measurement results. The closed-form solutions provided are easy to apply and enable predicting the actual behavior of resonators and gyroscopes with similar structures. View full abstract»

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  • 32. Capacitive-Piezoelectric Transducers for High-Q Micromechanical AlN Resonators

    Publication Year: 2014 , Page(s): 1
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (3598 KB)  

    A capacitive-piezoelectric (also known as, capacitive-piezo) transducer that combines the strengths of capacitive and piezoelectric mechanisms to achieve a combination of electromechanical coupling and Q higher than otherwise attainable by either mechanism separately, has allowed demonstration of a 1.2-GHz contour-mode aluminum nitride (AlN) ring resonator with Q > 3000 on par with the highest measured d₃₁-transduced AlN-only piezoelectric resonators past 1 GHz, and a 50-MHz disk array with an even higher Q > 12,000. Here, the key innovation is to separate the piezoelectric resonator from its metal electrodes by tiny gaps to eliminate metal material and metal-to-piezoelectric interface losses thought to limit thin-film piezoelectric resonator Q, while also maintaining high electric field strength to preserve a strong piezoelectric effect. While Q increases, electromechanical coupling decreases, but the k²eff · Q product can still increase overall. More importantly, use of the capacitive-piezo transducer allows a designer to trade electromechanical coupling for Q, providing a very useful method to tailor Q and coupling for narrowband radio frequency (RF) channel-selecting filters for which Q trumps coupling. This capacitive-piezo transducer concept does not require dc-bias voltages and allows for much thicker electrodes that reduce series resistance without mass loading the resonant structure. The latter is especially important as resonators and their supports continue to scale toward even higher frequencies. [2013-0395] View full abstract»

    Open Access
  • 33. A microreactor for hydrogen production in micro fuel cell applications

    Publication Year: 2004 , Page(s): 7 - 18
    Cited by:  Papers (97)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1096 KB) |  | HTML iconHTML  

    A silicon-chip based microreactor has been successfully fabricated and tested for carrying out the reaction of methanol reforming for microscale hydrogen production. The developed microreactor in combination with a micro fuel cell is proposed as an alternative to conventional portable sources of electricity such as batteries due to its ability to provide an uninterrupted supply of electricity as long as a supply of methanol and water can be provided. The microreformer-fuel cell combination has the advantage of not requiring the tedious recharging cycles needed by conventional rechargeable lithium-ion batteries. It also offers significantly higher energy storage densities, which translates into less frequent "recharging" through the refilling of methanol fuel. The microreactor consists of a network of catalyst-packed parallel microchannels of depths ranging from 200 to 400 μm with a catalyst particle filter near the outlet fabricated using photolithography and deep-reactive ion etching (DRIE) on a silicon substrate. Issues related to microchannel and filter capping, on-chip heating and temperature sensing, introduction and trapping of catalyst particles in the microchannels, flow distribution, microfluidic interfacing, and thermal insulation have been addressed. Experimental runs have demonstrated a methanol to hydrogen molar conversion of at least 85% to 90% at flow rates enough to supply hydrogen to an 8- to 10-W fuel cell. View full abstract»

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

    Publication Year: 2004 , Page(s): 559 - 567
    Cited by:  Papers (51)  |  Patents (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1312 KB) |  | HTML iconHTML  

    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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  • 35. High Speed Focus Control MEMS Mirror With Controlled Air Damping for Vital Microscopy

    Publication Year: 2013 , Page(s): 938 - 948
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (9500 KB) |  | HTML iconHTML  

    A high speed focus control microelectromechanical systems (MEMS) mirror with a step response time of 100 μsec and small-displacement bandwidth of 25 kHz is reported for a 3 mm diameter, electrostatically actuated SU-8 membrane mirror. The dominant effect limiting the mirror bandwidth is viscous air damping, and the innovation we describe is the use of a perforated counter-electrode backplate that facilitates air flow underneath the membrane. We have adopted a model, originally developed for a MEMS microphone, to engineer the damping characteristics and design the air hole patterns. Cryogenic deep silicon etching creates through-wafer perforations in the backplate, and fabricated devices achieve wide-bandwidth actuation. The design approach, fabrication process, and dynamic characterization of the MEMS mirrors are shown. Finally, the focus control mirror is used in a confocal microscope for fast axial focus scanning to provide x-z cross-sectioned in vivo images. View full abstract»

    Freely Available from IEEE
  • 36. The Impact of Damping on the Frequency Stability of Nonlinear MEMS Oscillators

    Publication Year: 2015 , Page(s): 1
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    Linear models for oscillator noise predict an improvement in frequency stability with increasing quality factor. Although it is well known that this result does not apply to oscillators embedding nonlinear resonators, systematic experimental investigations of the impact of damping on frequency stability of nonlinear microelectromechanical system (MEMS) oscillators has not been previously reported. This paper studies the frequency stability of a nonlinear MEMS oscillator under variable damping conditions. Analytical and experimental investigation of a MEMS square-wave oscillator embedding a double-ended tuning fork resonator driven into the nonlinear regime is introduced. The experimental results indicate that for a preset drive level, the variation of air damping changes the onset of nonlinear behavior in the resonator, which not only impacts the output frequency, but also the phase/frequency noise of a nonlinear MEMS square wave oscillator. The random walk frequency noise and flicker frequency noise levels are strongly correlated with the nonlinear operating point of the resonator, whereas the white phase and white frequency noise levels are impacted both by the output power and by operative nonlinearities. [2014-0304] View full abstract»

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  • 37. Batch Mode Microultrasonic Machining ( $boldsymbol mu $ USM) Using Workpiece Vibration

    Publication Year: 2015 , Page(s): 1 - 3
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    This letter reports on the evaluation of an unconventional approach to microultrasonic machining in which the workpiece is vibrated while the tool remains static. The vibration of the workpiece, and not the tool, alleviates the accumulation and the agglomeration of the slurry particles and debris between the machined features. This approach is appealing for batch mode pattern transfer of closely packed features into ceramics and glass. However, the question of how the workpiece vibration will cause selective machining of features on the opposing tool surface has not been addressed. In this effort, fluidic modeling is performed to study slurry flow due to workpiece vibration. The modeling reveals a higher slurry velocity (2.20-2.46 m/s) in the target machining regions confined by the proximity of the tool tips and a lower velocity (0.16-0.50 m/s) elsewhere. To demonstrate and characterize the resulting machining ability, arrayed tools made from stainless steel #304 with feature sizes ranging from 5-50 μm were used on flat workpieces of fused silica. At 20-kHz vibration frequency and 12-μm tool-to-workpiece separation, the average machining rates ranged from 6-90 nm/s for workpiece vibration amplitudes ranging from 1-5 μm. The average surface roughness, Sa, was 40-65 nm. The tool wear, i.e., the ratio of the tool height worn to the machined depth, was <;4%. View full abstract»

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  • 38. Creating, transporting, cutting, and merging liquid droplets by electrowetting-based actuation for digital microfluidic circuits

    Publication Year: 2003 , Page(s): 70 - 80
    Cited by:  Papers (411)  |  Patents (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1323 KB) |  | HTML iconHTML  

    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 (μTAS): 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. View full abstract»

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  • 39. Simultaneous Remote Sensing of Temperature and Humidity by LC-Type Passive Wireless Sensors

    Publication Year: 2015 , Page(s): 1
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2322 KB)  

    This paper presents an integrated wireless passive sensor for remotely monitoring both temperature and relative humidity. The sensor consists of a coil and a capacitor to form an inductor-capacitor (LC) resonant circuit, which oscillates electrically at its resonant frequency. The inductor was a single-layer planar spiral copper inductor and the capacitor was fabricated by the silicon-on-glass process, which utilizes graphene oxide films as the sensing material. The change of the capacitance due to environmental humidity variation shifts the resonant frequency, while environmental temperature affects the resistance and capacitance of the LC circuit and changes the resonant frequency and quality factor. By monitoring the real portion magnitude maximum of the impedance and the resonant frequency for the sensor, it is possible to get the capacitance and resistance from which the temperature and humidity can be extracted. The results presented here show that the sensitivity of the passive wireless sensor is about -17.80 kHz/%RH and 7.32 Ω/%RH at 25 °C from 55%RH to 95%RH, and it is about -7.69 kHz/°C and 6.27 Ω/°C at 65%RH from 10 °C to 40 °C. [2014-0311] View full abstract»

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  • 40. A MEMS Dielectric Affinity Glucose Biosensor

    Publication Year: 2014 , Page(s): 14 - 20
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB) |  | HTML iconHTML  

    Continuous glucose monitoring (CGM) sensors based on affinity detection are desirable for long-term and stable glucose management. However, most affinity sensors contain mechanical moving structures and complex design in sensor actuation and signal readout, limiting their reliability in subcutaneously implantable glucose detection. We have previously demonstrated a proof-of-concept dielectric glucose sensor that measured pre-mixed glucose-sensitive polymer solutions at various glucose concentrations. This sensor features simplicity in sensor design, and possesses high specificity and accuracy in glucose detection. However, lack of glucose diffusion passage, this device is unable to fulfill real-time in-vivo monitoring. As a major improvement to this device, we present in this paper a fully implantable MEMS dielectric affinity glucose biosensor that contains a perforated electrode embedded in a suspended diaphragm. This capacitive-based sensor contains no moving parts, and enables glucose diffusion and real-time monitoring. The experimental results indicate that this sensor can detect glucose solutions at physiological concentrations and possesses good reversibility and reliability. This sensor has a time constant to glucose concentration change at approximately 3 min, which is comparable to commercial systems. The sensor has potential applications in fully implantable CGM that require excellent long-term stability and reliability. View full abstract»

    Freely Available from IEEE
  • 41. Parallel Averaging for Thermal Noise Mitigation in MEMS Electrothermal Displacement Sensors

    Publication Year: 2015 , Page(s): 4 - 6
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (887 KB) |  | HTML iconHTML  

    The sensitivity of an electrothermal displacement sensor increases with its temperature, whereas a higher temperature range leads to higher thermal noise level, which imposes a tradeoff on the sensor's achievable resolution. We have developed a multiple sensor displacement measurement technique on a 1-degree-of-freedom silicon-on-insulator microelectromechanical systems nanopositioner that mitigates the mentioned tradeoff. To obtain maximum improvement, it is necessary to supply equal power to all of the sensors to ensure equal sensitivity. By combining three identical sensors, we have successfully achieved a 4-dB improvement in signal-to-noise ratio, which is in a good agreement with the averaging theory. Experiments show that the displacement resolution is improved from 0.3 to 0.15 nm/√(Hz) in the prototype nanopositioner. Furthermore, improvement is possible by increasing the number of sensors around the stage. View full abstract»

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  • 42. Thermal Characterization of Microheated Microchannels With Spatially Resolved Two-Color Fluorescence Thermometry

    Publication Year: 2015 , Page(s): 115 - 125
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2061 KB) |  | HTML iconHTML  

    Two-color fluorescence thermometry is a well known, noninvasive, and accurate technique used to measure temperature in liquids. In this paper, we present an improved methodology that enhances the spatial accuracy of the technique by minimizing image-pair distortion errors and its subsequent use in the characterization of heated microchannels. In order to spatially calibrate the image-pair and to quantify the distortion of one image with respect to the other, particle image velocimetry was performed with sandpaper. Results show that the objective lens and the primary dichroic mirror does not significantly affect the beam path and that the main source of distortion is likely to occur between the secondary dichroic mirror and the reflective mirrors within the emission splitting system. This spatial calibration and correlation methodology was used to map the temperature distribution in microheated microchannels. The experimentally calculated advective efficiency results showed good agreement against their numerically computed counterparts. These results suggest that the power supplied to the microheaters should be varied accordingly to maintain fixed heat flux conditions through the microchannel walls as a function of flow rate. View full abstract»

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  • 43. Thin film shape memory alloy microactuators

    Publication Year: 1996 , Page(s): 270 - 282
    Cited by:  Papers (179)  |  Patents (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2308 KB)  

    Thin film shape memory alloys (SMAs) have the potential to become a primary actuating mechanism for mechanical devices with dimensions in the micron-to-millimeter range requiring large forces over long displacements. The work output per volume of thin film SMA microactuators exceeds that of other microactuation mechanisms such as electrostatic, magnetic, thermal bimorph, piezoelectric, and thermopneumatic, and it is possible to achieve cycling frequencies on the order of 100 Hz due to the rapid heat transfer rates associated with thin film devices. In this paper, a quantitative comparison of several microactuation schemes is made, techniques for depositing and characterizing Ni-Ti-based shape memory films are evaluated, and micromachining and design issues for SMA microactuators are discussed. The substrate curvature method is used to investigate the thermo-mechanical properties of Ni-Ti-Cu SMA films, revealing recoverable stresses up to 510 MPa, transformation temperatures above 32°C, and hysteresis widths between 5 and 13°C. Fatigue data shows that for small strains, applied loads up to 350 MPa can be sustained for thousands of cycles. Two micromachined shape memory-actuated devices-a microgripper and microvalve-also are presented View full abstract»

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  • 44. A Microfabricated Wireless RF Pressure Sensor Made Completely of Biodegradable Materials

    Publication Year: 2014 , Page(s): 4 - 13
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1840 KB) |  | HTML iconHTML  

    A wireless RF MEMS pressure sensor made entirely of biodegradable materials is presented. Such biodegradable sensors may be appropriate for short-term, acute medical implantation applications as they potentially eliminate the need for implant extraction when sensing is no longer required. The biodegradable sensors described here require structural materials for pressure sensing, dielectric materials for insulation, and conducting materials for formation of electrical elements and wireless links. Zinc/iron bilayers were used as the sensor conductor material, and known biodegradable polymers poly-L-lactide and polycaprolactone were used as dielectric and structural materials. Zinc, which otherwise degrades very slowly on its own under biological conditions, is galvanically activated when electrically connected to iron in saline, greatly increasing the total degradation rate of the conductors. To avoid contact of the biodegradable materials with the strong chemicals or solvents that are typically used in conventional MEMS fabrication, embossing, multilayer folding, and lamination were combined with traditional techniques during fabrication. The fabricated sensor was wirelessly tested in both air and 0.9% saline and demonstrated a linear frequency response with external applied pressure. A sensitivity of 39 kHz/kPa was measured in the 0-20 kPa pressure range in air and initially in saline. After immersion in saline for 20 h, the sensor stabilized, remaining stable and functional for 86 h with a sensitivity of -54±4 kHz/kPa. View full abstract»

    Freely Available from IEEE
  • 45. An Implantable X-Ray-Based Blood Pressure Microsensor for Coronary In-Stent Restenosis Surveillance and Prevention

    Publication Year: 2015 , Page(s): 50 - 61
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1515 KB) |  | HTML iconHTML  

    Coronary artery disease is a leading cause of mortality in the U.S. and percutaneous coronary intervention with stent placement is a common treatment. Stents often fail through coronary in-stent restenosis. Periodically monitoring restenosis could help alert the physician of any problems earlier, reduce myocardial reinfarctions, and improve outcomes. Currently, there are no inexpensive and noninvasive techniques to monitor stent patency. We describe an X-ray-addressable blood pressure (X-BP) microsensor. The X-BP has a column of radio-opaque liquid that changes its length with blood pressure. The X-BP allows for the noninvasive evaluation of the pressure drop across a stent and the fractional flow reserve (FFR) on radiographs. A FFR threshold of 0.75-0.8 is clinically established as the cutoff for the identification of hemodynamically significant stenosis that requires intervention. The X-BP membrane was modeled and the X-ray signal-to-noise ratio of different sensor dimensions was experimentally determined. Based on this data, optimal design parameters were selected. The sensor was prototyped and tested under microscope with radiographs and video fluoroscopy. The sensor has a potential dynamic range of 0-200 mmHg, and can reliably resolve the clinically important pressure drop of 20%-25% across the dynamic range for an FFR value of 0.8-0.75 or less. The X-BP also has a time constant <;32 ms with no appreciable hysteresis. We believe this sensor can be used for periodic screening of coronary in-stent restenosis. View full abstract»

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  • 46. An Integrated Electrostatic Peristaltic 18-Stage Gas Micropump With Active Microvalves

    Publication Year: 2015 , Page(s): 192 - 206
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (4823 KB) |  | HTML iconHTML  

    We report the development of fully integrated peristaltic multistage (18-, 4-, and 2-stage) electrostatic gas micropumps with integrated active microvalves. These micropumps uniquely combine a number of approaches to achieve highpressure, high flow rate, multimode, and low-power pumping of compressible gases: (1) multistage (up to 18-stage) configuration to generate high pressure accumulation across the pump, while allowing each stage to operate at low pressure burden; (2) gas resonance-based high-frequency (>10 kHz) operation of both the micropumps and the microvalves to achieve high mass flow rates despite the small volume displacement of microscale membranes; (3) active timing control of microvalves to regulate compressible gas pumping into multiple modes for either high flow rate or high pressure; and (4) electrostatic actuation to minimize power consumption despite multiple (up to 28) membrane operation. The multistage micropumps contain 18, 4, and 2 pumps connected in series sandwiched by 19, 5, and 3 microvalves, respectively. The fabricated 18-, 4-, and 2-stage pumps, respectively, produced high air flow rates of ~4.0, 3.0, and 2.7 sccm and maximum pressure differentials of ~17.5, 7.0, and 2.5 kPa with total power consumptions of only ~57, 15.1 and 9.1 mW, respectively. They have active areas of 15.5 × 12.7 and 18.3 × 7.1, 15.0 × 7.0 mm2, and total package volumes of 25.1 × 19.1 × 1, 27.8 × 11.6 × 1, and 23.0 × 12.4 × 1 mm3, respectively. They demonstrated two pumping modes using different microvalve timing (high flow rate timing and high pressure timing), resulting in notable changes in flow rates and pressure generation. One 4-stage micropump has been actuated for a total running time of more than 700 min over 32 months. View full abstract»

    Freely Available from IEEE
  • 47. A 3-D Stacked High- Q PI-Based MEMS Inductor for Wireless Power Transmission System in Bio-Implanted Applications

    Publication Year: 2014 , Page(s): 888 - 898
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2804 KB) |  | HTML iconHTML  

    This paper presents high-Q factor 3-D stacked MEMS inductors on polyimide substrate for wireless power transmission systems. The 3-D double layer stacked structure was designed, fabricated, and characterized, and self-planarization of polyimide was realized. The 3-D inductor achieves an inductance of 7.189 μH with a high-Q factor of 26.1 at 4.3 MHz. An inductively coupled wireless power transmission system was set up using the 3-D inductor in combination with a solenoid transmitting coil. At the resonant frequency of 1.6 MHz, the peak-to-peak output open circuit voltage could reach 5.2 V with a maximum power transmission efficiency of 11.74% and an output power of 35.5 mW. Effects of the load impedance and transmission distance on the output power were also investigated. Using this wireless transmission system, the driving of an implanted 3-D microelectrode array for neural prosthesis was demonstrated successfully, indicating that this 3-D stacked MEMS inductor design shows promise for applications in supplying power for implanted medical devices. View full abstract»

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  • 48. A CMOS-MEMS mirror with curled-hinge comb drives

    Publication Year: 2003 , Page(s): 450 - 457
    Cited by:  Papers (40)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2411 KB) |  | HTML iconHTML  

    A micromirror achieves up to ±4.7° angular displacement with 18 Vdc by a comb-drive design that uses vertical angled offset of the comb fingers. Structures are made from a combination of CMOS interconnect layers and a thick underlying silicon layer. Electrical isolation of the silicon fingers is realized with a slight silicon undercut etch, which disconnects sufficiently narrow pieces of silicon under the CMOS microstructures. The 1 mm by 1 mm micromirror is made of an approximately 40 μm-thick single-crystal silicon plate coated with aluminum from the CMOS interconnect stack. The mirror has a peak-to-peak curling of 0.5 μm. Fabrication starts with a conventional CMOS process followed by dry-etch micromachining steps. There is no need for wafer bonding and accurate front-to-backside alignment. Such capability has potential applications in biomedical imaging, optical switches, optical scanners, interferometric systems, and vibratory gyroscopes. View full abstract»

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  • 49. Accurate Modeling of Quality Factor Behavior of Complex Silicon MEMS Resonators

    Publication Year: 2014 , Page(s): 1
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (2439 KB)  

    The quality factor of a resonator represents the decay of vibrational energy over time, and is directly related to the frequency response and other key parameters that determine performance of inertial sensors and oscillators. Accurate prediction of the quality factor is essential for designing high-performance microelectromechanical (MEMS) devices. Several energy dissipation mechanisms contribute to the quality factor. Due to computational complexity, highly simplified models for the dominant dissipation mechanism, such as Zener's model for thermoelastic dissipation (TED), are often employed. However, the intuition provided by these models is inadequate to predict the quality factor of more complex designs and can be highly misleading. In this paper, we construct complete, quantitative, and predictive models with finite-element methods for the intrinsic energy dissipation mechanisms in MEMS resonators using full anisotropic representation of crystalline silicon and the temperature dependence of all parameters. We find that TED is often a more significant source of damping than has been assumed, because of the previously neglected role of crystalline anisotropy and small geometric features, such as etch release holes-all of which can now be included in practical models. We show that these models, along with simpler scaling models for extrinsic dissipation mechanisms, explain measurements of quality factor in diverse sets of MEMS resonators with unprecedented accuracy. [2014-0106] View full abstract»

    Open Access
  • 50. An Electrothermally Actuated VO2-Based MEMS Using Self-Sensing Feedback Control

    Publication Year: 2015 , Page(s): 100 - 107
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3141 KB) |  | HTML iconHTML  

    A self-sensing approach is used to accurately control the large displacements observed in VO2-based microelectromechanical systems actuators. The device is operated electrothermally using integrated resistive heaters. The coupling of the abrupt electrical and mechanical changes in VO2 films across its phase transition allow for the estimation of the device's deflection by monitoring the film's resistance. Furthermore, the typical hysteretic behavior observed in VO2 films is significantly reduced in the present device and the need for optical testing equipment is eliminated. The displacement-resistance relationship is modeled by a memoryless Boltzmann function consisting of four parameters, which are optimized to fit the experimental data with an average error of 1.1 μm throughout the complete actuation range of 95 μm. The estimated deflection is used as feedback to achieve closed-loop micropositioning control of the device, which is designed from the system dynamics obtained experimentally. Closed-loop sinusoidal and step reference response experiments are performed in order to show the effectiveness of the self-sensing feedback technique used. In the closed-loop sinusoidal frequency response, a cutoff frequency of 43 Hz is observed with a maximum actual deflection error of 0.19 dB up to the phase margin frequency of 30 Hz. In the step response, an average actual displacement steady-state error of ±1.15 μm is obtained with response times ranging from 5 to 12 ms. 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