Showing papers in "IEEE\/ASME Journal of Microelectromechanical Systems in 2006"

Piezoelectric Aluminum Nitride Vibrating Contour-Mode MEMS Resonators

Abstract: 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

A Flexible Polymer Tactile Sensor: Fabrication and Modular Expandability for Large Area Deployment

Abstract: In this paper, we propose and demonstrate a modular expandable capacitive tactile sensor using polydimethylsiloxsane (PDMS) elastomer. A sensor module consists of 16times16 tactile cells with 1 mm spatial resolution, similar to that of human skin, and interconnection lines for expandability. The sensor has been fabricated by using five PDMS layers bonded together. In order to customize the sensitivity of a sensor, we cast PDMS by spin coating and cured it on a highly planarized stage for uniform thickness. The cell size is 600times600 mum2 and initial capacitance of each cell is about 180 fF. Tactile response of a cell has been measured using a commercial force gauge having 1 mN resolution and a motorized z-axis precision stage with 100 nm resolution. The fabricated cell shows a sensitivity of 3%/mN within the full scale range of 40 mN (250 kPa). Four tactile modules have been successfully attached by using anisotropic conductive paste to demonstrate expandability of the proposed sensors. Various tactile images have been successfully captured by single sensor module as well as the expanded 32times32 array sensors

Two-axis electromagnetic microscanner for high resolution displays

Abstract: A novel microelectromechanical systems (MEMS) actuation technique is developed for retinal scanning display and imaging applications allowing effective drive of a two-axes scanning mirror to wide angles at high frequency. Modeling of the device in mechanical and electrical domains, as well as the experimental characterization is described. Full optical scan angles of 65deg and 53deg are achieved for slow (60 Hz sawtooth) and fast (21.3 kHz sinusoid) scan directions, respectively. In combination with a mirror size of 1.5 mm, a resulting thetasopt D product of 79.5 degmiddotmm for fast axis is obtained. This two-dimensional (2-D) magnetic actuation technique delivers sufficient torque to allow non-resonant operation as low as dc in the slow-scan axis while at the same time allowing one-atmosphere operation even at fast-scan axis frequencies large enough to support SXGA (1280 times 1024) resolution scanned beam displays

An untethered, electrostatic, globally controllable MEMS micro-robot

Abstract: We present an untethered, electrostatic, MEMS micro-robot, with dimensions of 60 /spl mu/m by 250 /spl mu/m by 10 /spl mu/m. The device consists of a curved, cantilevered steering arm, mounted on an untethered scratch drive actuator (USDA). These two components are fabricated monolithically from the same sheet of conductive polysilicon, and receive a common power and control signal through a capacitive coupling with an underlying electrical grid. All locations on the grid receive the same power and control signal, so that the devices can be operated without knowledge of their position on the substrate. Individual control of the component actuators provides two distinct motion gaits (forward motion and turning), which together allow full coverage of a planar workspace. These MEMS micro-robots demonstrate turning error of less than 3.7/spl deg//mm during forward motion, turn with radii as small as 176 /spl mu/m, and achieve speeds of over 200 /spl mu/m/sec with an average step size as small as 12 nm. They have been shown to operate open-loop for distances exceeding 35 cm without failure, and can be controlled through teleoperation to navigate complex paths. The devices were fabricated through a multiuser surface micromachining process, and were postprocessed to add a patterned layer of tensile chromium, which curls the steering arms upward. After sacrificial release, the devices were transferred with a vacuum microprobe to the electrical grid for testing. This grid consists of a silicon substrate coated with 13-/spl mu/m microfabricated electrodes, arranged in an interdigitated fashion with 2-/spl mu/m spaces. The electrodes are insulated by a layer of electron-beam-evaporated zirconium dioxide, so that devices placed on top of the electrodes will experience an electrostatic force in response to an applied voltage. Control waveforms are broadcast to the device through the capacitive power coupling, and are decoded by the electromechanical response of the device body. Hysteresis in the system allows on-board storage of n=2 bits of state information in response to these electrical signals. The presence of on-board state information within the device itself allows each of the two device subsystems (USDA and steering arm) to be individually addressed and controlled. We describe this communication and control strategy and show necessary and sufficient conditions for voltage-selective actuation of all 2/sup n/ system states, both for our devices (n=2), and for the more general case (where n is larger.).

Error sources in in-plane silicon tuning-fork MEMS gyroscopes

Abstract: This paper analyzes the error sources defining tactical-grade performance in silicon, in-plane tuning-fork gyroscopes such as the Honeywell-Draper units being delivered for military applications. These analyses have not yet appeared in the literature. These units incorporate crystalline silicon anodically bonded to a glass substrate. After general descriptions of the tuning-fork gyroscope, ordering modal frequencies, fundamental dynamics, force, and fluid coupling, which dictate the need for vacuum packaging, mechanical quadrature, and electrical coupling are analyzed. Alternative strategies for handling these engineering issues are discussed by introducing the Systron Donner/BEI quartz rate sensor, a successful commercial product, and the Analog Device (ADXRS), which is designed for automotive applications.

Electrical, Thermal, and Mechanical Characterization of Silicon Microcantilever Heaters

Abstract: Silicon atomic force microscope (AFM) cantilevers having integrated solid-state heaters were originally developed for application to data storage, but have since been applied to metrology, thermophysical property measurements, and nanoscale manufacturing. These applications beyond data storage have strict requirements for mechanical characterization and precise temperature calibration of the cantilever. This paper describes detailed mechanical, electrical, and thermal characterization and calibration of AFM cantilevers having integrated solid-state heaters. Analysis of the cantilever response to electrical excitation in both time and frequency domains aids in resolving heat transfer mechanisms in the cantilever. Raman spectroscopy provides local temperature measurement along the cantilever with resolution near 1 mum and 5degC and also provides local surface stress measurements. Observation of the cantilever mechanical thermal noise spectrum at room temperature and while heated provides insight into cantilever mechanical behavior and compares well with finite-element analysis. The characterization and calibration methodology reported here expands the use of heated AFM cantilevers, particularly the uses for nanomanufacturing and sensing

Engineering MEMS Resonators With Low Thermoelastic Damping

Abstract: This paper presents two approaches to analyzing and calculating thermoelastic damping in micromechanical resonators. The first approach solves the fully coupled thermomechanical equations that capture the physics of thermoelastic damping in both two and three dimensions for arbitrary structures. The second approach uses the eigenvalues and eigenvectors of the uncoupled thermal and mechanical dynamics equations to calculate damping. We demonstrate the use of the latter approach to identify the thermal modes that contribute most to damping, and present an example that illustrates how this information may be used to design devices with higher quality factors. Both approaches are numerically implemented using a finite-element solver (Comsol Multiphysics). We calculate damping in typical micromechanical resonator structures using Comsol Multiphysics and compare the results with experimental data reported in literature for these devices

Long-Term and Accelerated Life Testing of a Novel Single-Wafer Vacuum Encapsulation for MEMS Resonators

Abstract: We have developed a single-wafer vacuum encapsulation for microelectromechanical systems (MEMS), using a thick (20-mum) polysilicon encapsulation to package micromechanical resonators in a pressure 600 cycles of -50 to 80degC, and no measurable change in cavity pressure was seen. We have also performed accelerated leakage tests by driving hydrogen gas in and out of the encapsulation at elevated temperature. Two results have come from these hydrogen diffusion tests. First, hydrogen diffusion rates through the encapsulation at temperatures 300-400degC have been determined. Second, the package was shown to withstand multiple temperature cycles between room and 300-400degC without showing any adverse affects. The high robustness and stability of the encapsulation can be attributed to the clean, high-temperature environment during the sealing process

Thermal annealing in hydrogen for 3-D profile transformation on silicon-on-insulator and sidewall roughness reduction

Abstract: A fast, effective process using hydrogen annealing is introduced to perform profile transformation on silicon-on-insulator (SOI) and to reduce sidewall roughness on silicon surfaces. By controlling the dimensions of as-etched structures, microspheres with 1 /spl mu/m radii, submicron wires with 0.5 /spl mu/m radii, and a microdisk toroid with 0.2 /spl mu/m toroidal radius have been successfully demonstrated on SOI substrates. Utilizing this technique, we also observe the root-mean-square (rms) sidewall roughness dramatically reduced from 20 to 0.26 nm. A theoretical model is presented to analyze the profile transformation, and experimental results show this process can be engineered by several parameters including temperature, pressure, and time.

Electromechanical Model of Electrically Actuated Narrow Microbeams

Abstract: A consistent one-dimensional distributed electromechanical model of an electrically actuated narrow microbeam with width/height between 0.5–2.0 is derived, and the needed pull-in parameters are extracted with different methods. The model accounts for the position-dependent electrostatic loading, the fringing field effects due to both the finite width and the finite thickness of a microbeam, the mid-plane stretching, the mechanical distributed stiffness, and the residual axial load. Both clamped–clamped and clamped-free (cantilever) microbeams are considered. The method of moments is used to estimate the electrostatic load. The resulting nonlinear fourth-order differential equation under appropriate boundary conditions is solved by two methods. Initially, a one-degree-of-freedom model is proposed to find an approximate solution of the problem. Subsequently, the meshless local Petrov–Galerkin (MLPG) and the finite-element (FE) methods are used, and results from the three methods are compared. For the MLPG method, the kinematic boundary conditions are enforced by introducing a set of Lagrange multipliers, and the trial and the test functions are constructed using the generalized moving least-squares approximation. The nonlinear system of algebraic equations arising from the MLPG and the FE methods are solved by using the displacement iteration pull-in extraction (DIPIE) algorithm. Three-dimensional FE simulations of narrow cantilever and clamped–clamped microbeams are also performed with the commercial code ANSYS. Furthermore, computed results are compared with those arising from other distributed models available in the literature, and it is shown that improper fringing fields give inaccurate estimations of the pull-in voltages and of the pull-in deflections. 1641

Single-Pole Eight-Throw RF MEMS Rotary Switch

Abstract: The design, fabrication, and measured performance of a novel single-pole eight-throw radio-frequency (RF) microelectromechanical systems (MEMS) rotary switch are described. The concept of this rotary switch is based on the adaptation of the axial gap wobble motor. A prototype switch has been made using separately fabricated stator, rotor, and cap components that are then assembled. A rigorous procedure was setup to investigate the direct current (dc) contact resistance over a total of four million rotor contact closures, with half a million closures made on each of the eight stator contacts. It was found that there was no obvious systematic trend in contact resistance over time. An average contact resistance of 2.5 Omega was recorded; however, values as low as 1.0 Omega were also found. The assembled rotary switch demonstrated an excellent RF performance. With the inclusion of feed lines, the insertion loss was 2.65 dB at 20 GHz, after renormalizing the measurement reference impedance. When the loss of the feed lines is subtracted, the worst-case on-state intrinsic insertion loss of the rotary switch is only 2.16 dB at 20 GHz. A worst-case off-state isolation of 31 dB was also measured over the 20-GHz bandwidth. The effective performance figure-of-merit for this switch in an arbitrary position was calculated to be 10.7 THz. To the authors' knowledge, this is the first example of a true single-pole multiple-throw RF MEMS rotary switch

Vacuum-Packaged Suspended Microchannel Resonant Mass Sensor for Biomolecular Detection

Abstract: There is a great need in experimental biology for tools to study interactions between biological molecules and to profile expression levels of large numbers of proteins. This paper describes the fabrication, packaging and testing of a resonant mass sensor for the detection of biomolecules in a microfluidic format. The transducer employs a suspended microchannel as the resonating element, thereby avoiding the problems of damping and viscous drag that normally degrade the sensitivity of resonant sensors in liquid. Our device differs from a vibrating tube densitometer in that the channel is very thin, which enables the detection of molecules that bind to the channel walls; this provides a path to specificity via molecular recognition by immobilized receptors. The fabrication is based on a sacrificial polysilicon process with low-stress low-pressure chemical-vapor deposited (LPCVD) silicon nitride as the structural material, and the resonator is vacuum packaged on the wafer scale using glass frit bonding. Packaged resonators exhibit a sensitivity of 0.8 ppm/(ngmiddotcm2) and a mechanical quality factor of up to 700. To the best of our knowledge, this quality factor is among the highest so far reported for resonant sensors with comparable surface mass sensitivity in liquid

Multidirectional UV Lithography for Complex 3-D MEMS Structures

Abstract: Various three-dimensionally (3-D) complex MEMS structures are fabricated using multidirectional ultraviolet (UV) lithography, which includes reverse-side exposure through a UV-transparent substrate, inclined exposure with or without simultaneous substrate rotation, and the combination of these processes. A reverse-side exposure scheme through UV-transparent substrates (e.g., glass, sapphire, or quartz) has been exploited for implementing high-aspect-ratio structures (greater than 20:1), repeatable self-alignment photoresist patterning with subsequent metallization on a BST/sapphire substrate, and unconventional patterning using substrate optics such as proximity patterning or integrated lens techniques. Inclined exposure has been applied to a SU-8 substrate with differing inclination angles and incidence directions. The refractive index of SU-8 is experimentally determined to be 1.68 by means of test structures fabricated using this approach. Implemented structures using the inclined exposure include vertical screen structures, inclined tubes, and conical shape structures. Dynamic mode operation, in which the substrate is continuously rotated and tilted during exposure is also discussed. Examples of achievable 3-D structures using dynamic mode operation are presented

Modeling the fluid dynamics of electrowetting on dielectric (EWOD)

Abstract: This paper discusses the modeling and simulation of a parallel-plate Electrowetting On Dielectric (EWOD) device that moves fluid droplets through surface tension effects. We model the fluid dynamics by using Hele-Shaw type equations with a focus on including the relevant boundary phenomena. Specifically, we show that contact angle saturation and hysteresis are needed to predict the correct shape and time scale of droplet motion. We demonstrate this by comparing our simulation to experimental data for a splitting droplet. Without these boundary effects, the simulation shows the droplet splitting into three pieces instead of two and the motion is over 15 times faster than the experiment. We then show how including the saturation characteristics of the device, and a simple model of contact angle hysteresis, allows the simulation to better predict the splitting experiment. The match is not perfect and suffers mainly because contact line pinning is not included. This is followed by a comparison between our simulation, whose parameters are now frozen, and a new experiment involving bulk droplet motion. Our numerical implementation uses the level set method, is fast, and is being used to design algorithms for the precise control of microdroplet motion, mixing, and splitting

Mechanically Corner-Coupled Square Microresonator Array for Reduced Series Motional Resistance

Abstract: Substantial reductions in vibrating micromechanical resonator series motional resistance Rx have been attained by mechanically coupling and exciting a parallel array of corner-coupled polysilicon square plate resonators. Using this technique with seven resonators, an effective Rx of 480 Omega has been attained at 70 MHz, which is more than 5.9X smaller than the 2.82 kOmega exhibited by a stand-alone transverse-mode corner-supported square resonator, and all this achieved while still maintaining an effective Q>9000. This method for Rx-reduction is superior to methods based on brute force scaling of electrode-to-resonator gaps or dc-bias increases, because it allows a reduction in Rx without sacrificing linearity, and thereby breaks the Rx versus dynamic range tradeoff often seen when scaling. This paper also compares two types of anchoring schemes for transverse-mode square micromechanical resonators and models the effect of support beam parameters on resonance frequency

A Planar Array of Micro-Fabricated Electrospray Emitters for Thruster Applications

Abstract: This paper reports the design, fabrication, and experimental characterization of a planar array of micro-fabricated electrospray emitters intended for space propulsion applications in micro-satellites. The engine uses the ionic liquid EMI-BF4 as propellant. Electrospray engines take advantage of the electrohydrodynamic effect known as Taylor cone to produce thrust. The array is designed with an open architecture and it is composed of a set of spikes, i.e., emitters, coming out from a propellant pool. There are two configurations for the emitters: fully sharpened slender emitters, i.e., pencils, and truncated pyramidal emitters, i.e., volcanoes. The arrays have between 4 and 1024 emitters in an active area of 0.64 cm2. The surface of the engine (tank and emitters) is covered with "black silicon" that acts as wicking material. The micro-fabrication of the engine is described. The paper reports experimental characterization of the hydraulics system including wettability tests, current/emitter-voltage characteristics, and imprints of the exit stream on a collector. Preliminary results demonstrating the feasibility of obtaining substantially larger emission currents at the same extraction voltage by controlling the temperature are also reported. The paper compares the experimental current/emitter-voltage characteristics with relevant theories of field emission of electrons

Dynamic pull-in of parallel-plate and torsional electrostatic MEMS actuators

Abstract: An analysis of the dynamic characteristics of pull-in for parallel-plate and torsional electrostatic actuators is presented. Traditionally, the analysis for pull-in has been done using quasi-static assumptions. However, it was recently shown experimentally that a step input can cause a decrease in the voltage required for pull-in to occur. We propose an energy-based solution for the step voltage required for pull-in that predicts the experimentally observed decrease in the pull-in voltage. We then use similar energy techniques to explore pull-in due to an actuation signal that is modulated depending on the sign of the velocity of the plate (i.e., modulated at the instantaneous mechanical resonant frequency). For this type of actuation signal, significant reductions in the pull-in voltage can theoretically be achieved without changing the stiffness of the structure. This analysis is significant to both parallel-plate and torsional electrostatic microelectromechanical systems (MEMS) switching structures where a reduced operating voltage without sacrificing stiffness is desired, as well as electrostatic MEMS oscillators where pull-in due to dynamic effects needs to be avoided

Impact of geometry on thermoelastic dissipation in micromechanical resonant beams

Abstract: Thermoelastic dissipation (TED) is analyzed for complex geometries of micromechanical resonators, demonstrating the impact of resonator design (i.e., slots machined into flexural beams) on TED-limited quality factor. Zener first described TED for simple beams in 1937. This work extends beyond simple beams into arbitrary geometries, verifying simulations that completely capture the coupled physics that occur. Novel geometries of slots engineered at specific locations within the flexural resonator beams are utilized. These slots drastically affect the thermal-mechanical coupling and have an impact on the quality factor, providing resonators with quality factors higher than those predicted by simple Zener theory. The ideal location for maximum impact of slots is determined to be in regions of high strain. We have demonstrated the ability to predict and control the quality factor of micromechanical resonators limited by thermoelastic dissipation. This enables tuning of the quality factor by structure design without the need to scale its size, thus allowing for enhanced design optimization

Micromachined Antenna Stents and Cuffs for Monitoring Intraluminal Pressure and Flow

Abstract: This paper describes two stainless steel microstructures that are microelectrodischarge machined from 50-mum-thick planar foil for intraluminal measurements of pressure and flow (with potential for applications ranging from blood vessels to bile ducts). The first structure is an inductive antenna stent (stentenna) with 20-mm length and 3.5-mm expanded diameter. It is coupled with capacitive elements to form resonant LC tanks that can be telemetrically queried. The resulting LC tanks are deployed inside silicone mock arteries using standard angioplasty balloons and used in a passive telemetry scheme to sense changes in pressure and flow. Using water as the test fluid, the resonant peaks shift from about 215 to 208 MHz as the flow is increased from 0 to 370 mL/min. The second structure is a ring-shaped intraluminal cuff with two 400times750-mum2 electrodes that are used to provide a direct transduction of flow velocity in the presence of a magnetic field. It is fabricated in a manner similar to the stentenna, but with an insulating segment. The voltage has a linear dependence on flow rate, changing by 3.1-4.3 muV per cm/s of flow (of saline) over a 180 cm/s dynamic range, with a magnetic field of about 0.25 T

Using feedback control of microflows to independently steer multiple particles

Abstract: In this paper, we show how to combine microfluidics and feedback control to independently steer multiple particles with micrometer accuracy in two spatial dimensions. The particles are steered by creating a fluid flow that carries all the particles from where they are to where they should be at each time step. Our control loop comprises sensing, computation, and actuation to steer particles along user-input trajectories. Particle locations are identified in real-time by an optical system and transferred to a control algorithm that then determines the electrode voltages necessary to create a flow field to carry all the particles to their next desired locations. The process repeats at the next time instant. Our method achieves inexpensive steering of particles by using conventional electroosmotic actuation in microfluidic channels. This type of particle steering does not require optical traps and can noninvasively steer neutral or charged particles and objects that cannot be captured by laser tweezers. (Laser tweezers cannot steer reflective particles, or particles where the index of refraction is lower than (or for more sophisticated optical vortex holographic tweezers does not differ substantially from) that of the surrounding medium.) We show proof-of-concept PDMS devices, having four and eight electrodes, with control algorithms that can steer one and three particles, respectively. In particular, we demonstrate experimentally that it is possible to use electroosmotic flow to accurately steer and trap multiple particles at once

Fabrication of Flexible Neural Probes With Built-In Microfluidic Channels by Thermal Bonding of Parylene

Abstract: This paper describes the fabrication technology and characterization of Parylene neural probes containing fluidic channels for delivery of small amounts of drugs into biological tissue as well as neural recording. We present a first attempt to realize such neural probes by micromolding and thermal bonding of Parylene. Compared to the common fabrication method, where a sacrificial photoresist layer is sandwiched between two Parylene layers, the major advantages of this process are, that the time consuming photoresist dissolution is omitted, and that the adhesion between the Parylene layers could be improved. The electrodes were characterized by impedance measurements, in which an impedance sufficiently low for neural recording was observed. Fluidic injection experiments with the microchannel have shown that nanoliter volumes can be injected

High-Speed MEMS-Based Gas Chromatography

Abstract: This paper reports microfabricated silicon-glass separation columns for high-speed micro gas chromatography (muGC) systems. The microfabricated columns are integrated with resistive heaters and temperatures sensors and capacitive pressure sensors to allow temperature and pressure programming and flow control and to achieve reproducible separations in a muGC system. These 25-cm-long, 150-mum-wide, and 250-mum-deep columns are fabricated on a 1.2-cm square die using a silicon-on-glass dissolved wafer process. Programmed with temperature ramps of 10 degC/s, the low-mass columns separate eleven-component gaseous mixtures in less than 10 s, including alkanes from C5 to C16 and simulants for C-4, TNT, sarin, and mustard gas. When used in arrayed architectures, these MEMS columns should allow high-speed analysis without sacrificing separation efficiency

Polyurethane rubber all-polymer artificial hair cell sensor

Abstract: In this paper, we present the design, fabrication process, and preliminary testing results of an artificial hair cell (AHC) sensor made entirely of polymer materials from the substrate level up. The new AHC sensor utilizes polyurethane elastomers for sensing and structures. The AHC can detect two-axis deflection of a vertical polyurethane hair using carbon-impregnated polyurethane force sensitive resistors (FSRs). AHC with cylindrical hair cross-section exhibit sensitivity of 245 ppm resistance change for every micron (ppm/mum) of tip deflection. The AHC threshold detection level of 3 mum compares favorably with insect tactile hair cells having thresholds on the order of 30-50 mum. Furthermore, we have characterized the mechanical and chemical properties of two-part room-temperature-curing polyurethane elastomers in the context of microfabrication. Elastic properties, chemical resistance, thermal oxidative decomposition, and adhesion properties are tested and compared to the performance of polydimethylsiloxane (PDMS), a widely used elastomeric material. Polyurethane elastomer exhibit superior mechanical tear resistance and ability to adhere to substrates compared to PDMS

All PDMS pneumatic microfinger with bidirectional motion and its application

Abstract: This paper describes the experimental results on static and dynamic bending motions of all polydimethylsiloxane (PDMS) pneumatic microfinger. The proposed pneumatic microfinger consists of two PDMS diaphragms with different thicknesses or material properties. The microfinger is fabricated through PDMS molding process and the PDMS-to-PDMS bonding process. The out-of-plane motion of the microfinger is achieved by using the pulling force of the inflated actuator diaphragms while the square wave pneumatic force is supplied to the balloon actuators. In the case of the microfinger with different thickness of two diaphragms, the pressure-dependent dual-bending motion of the microfinger is available. The proposed working principle is confirmed from the steady-state bending angle measurement of the two types of the microfingers with different thicknesses of the bottom PDMS layers. While the pneumatic force is less than 20 kPa, the top diaphragm of Type A microfinger is fully inflated and the microfinger moves downward. Around 20 kPa, the bending direction of the microfinger starts to be changed from downward to upward. The microfinger with two types of PDMS films with different mixing ratio of base polymer and curing agent is also proposed for the improvement of the PDMS-to-PDMS bonding strength, the material property change, and the rapid manufacturing process. The microfinger moves only upward because the top PDMS diaphragm with excess of silicon hydride group is relatively stiffer than the bottom PDMS diaphragm with excess of vinyl group. The dynamic bending motion of the single microfinger and the object-lifting motion of the microfinger array are observed to evaluate their performance. The dynamic bending angle of the microfinger with golden air bone length is about 179deg at 1 Hz, while the square wave input pressure of 250 kPa is supplied to finger structure

Complex nonlinear oscillations in electrostatically actuated microstructures

Abstract: In this paper, new nonlinear dynamic properties of electrostatically actuated microstructures [referred to as electrostatic microelectromechanical systems (MEMS)] observed under superharmonic excitations are presented using numerical simulations. Application of a large dc bias (close to the pull-in voltage of the device) is found to bring the device to a nonlinear state. This nonlinear state (referred to as "dc-symmetry breaking") can be clearly observed from the characteristic change in the phase-plot of the device. Once a steady nonlinear state is reached, application of an ac signal at the Mth superharmonic frequency with an amplitude around "ac-symmetry breaking" gives rise to M oscillations per period or M-cycles in the MEM device. "ac-symmetry breaking" can also be observed by a characteristic change in the phase-plot of the device. On further increasing the ac voltage, a period doubling sequence takes place resulting in the formation of 2/sup n/M-cycles in the system at the Mth superharmonic frequency. An interesting chaotic transition (banded chaos) is observed during the period doubling bifurcations. The nonlinear nature of the electrostatic force acting on the MEM device is found to be responsible for the reported observations. The significance of the mechanical and the fluidic nonlinearities is also studied.

On the dynamic pull-in of electrostatic actuators with multiple degrees of freedom and multiple voltage sources

Abstract: This study considers the dynamic response of electrostatic actuators with multiple degrees of freedom that are driven by multiple voltage sources. The critical values of the applied voltages beyond which the dynamic response becomes unstable are investigated. A methodology for extracting a lower bound for this dynamic pull-in voltage is proposed. This lower bound is based on the stable and unstable static response of the system, and can be rapidly extracted because it does not require time integration of momentum equations. As example problems, the dynamic pull-in of two prevalent electrostatic actuators is analyzed.

High-energy density miniature thermoelectric generator using catalytic combustion

Abstract: This paper describes the components and system of a thermoelectric (TE) generator with a catalytic butane combustor. The combustion chamber with a size of 8 mm/spl times/8 mm/spl times/0.4 mm is etched in a 0.65-mm-thick silicon substrate, and bonded to both sides of a 0.77-mm-thick glass substrate with a thin-film ignition heater. A set of 34 couples of BiTe TE elements, each with a size of 0.65 mm/spl times/0.65 mm/spl times/2 mm, are directly bonded to both sides of the combustor. The combustor without the TE modules was tested using butane as fuel, and self-sustaining combustion and electrical ignition were achieved. Also, nearly 100% combustion efficiency and a uniform temperature distribution were confirmed by gas chromatography and infrared thermoimaging, respectively. When the TE modules were attached to the combustor, however, butane combustion was impossible. The characteristics of TE generation were measured using hydrogen as fuel. When a theoretical combustion power was 6.6 W, the maximum output power of 184 mW was obtained with a load of 5.68 /spl Omega/. The total efficiency in this experiment was 2.8% (184 mW/6.6 W).

Design and fabrication of a micromachined planar patch-clamp substrate with integrated microfluidics for single-cell measurements

Abstract: We have designed, fabricated, tested, and integrated microfabricated planar patch-clamp substrates and poly(dimethylsiloxane) (PDMS) microfluidic components. Substrates with cell-patch-site aperture diameters ranging from 300nm to 12 /spl mu/m were produced using standard MEMS-fabrication techniques. The resistance of the cell-patch sites and substrate capacitance were measured using impedance spectroscopy. The resistance of the microfabricated apertures ranged from 200 k/spl Omega/ to 47 M/spl Omega/ for apertures ranging from 12 /spl mu/m to 750 nm, respectively. The substrate capacitance was 17.2 pF per mm/sup 2/ of fluid contact area for substrates with a 2-/spl mu/m-thick layer of silicon dioxide. In addition, the ability of the planar patch-clamp substrates to form high-resistance seals in excess of 1 G/spl Omega/ has been confirmed using Chinese hamster ovary cells (CHO-K1). Testing shows that the microfluidic components are appropriate for driving human embryonic kidney cells (HEK 293) to patch apertures, for trapping cells on patch apertures, and for exchanging the extracellular fluid environment.

Micromachined High-Aspect-Ratio Parylene Spring and Its Application to Low-Frequency Accelerometers

Abstract: A new microfabrication technology for high-aspect- ratio parylene structure has been developed for soft spring applications. Free-standing parylene beams with widths of 10–40 $mu m$ and aspect ratios of 10–20 have been successfully fabricated. Since parylene has a small Young's modulus, a high-aspect-ratio beam with a spring constant of the order of $1,times, 10 ^-3~ N/ m$ has been realized. The large yield strain of parylene enables a test structure to have a large-amplitude oscillation of 600 $mu m _ pmathchar"702D p$ , without any failure of the high-aspect-ratio springs. An early prototype of in-plane capacitive accelerometer was also developed. It was found that its resonant frequency is as low as 37 Hz, and the noise spectral density is 64 $mu g/( Hz)^0.5$ .1606

Resonant Magnetic Field Sensor With Frequency Output

Abstract: This paper presents a novel type of resonant magnetic field sensor exploiting the Lorentz force and providing a frequency output. The mechanical resonator, a cantilever structure, is embedded as the frequency-determining element in an electrical oscillator. By generating an electrical current proportional to the position of the cantilever, a Lorentz force acting like an additional equivalent spring is exerted on the cantilever in the presence of a magnetic field. Thus, the oscillation frequency of the system, which is a function of the resonator's equivalent spring constant, is modulated by the magnetic field to be measured. The resonant magnetic field sensor is fabricated using an industrial CMOS process, followed by a two-mask micromachining sequence to release the cantilever structure. The characterized devices show a sensitivity of 60 kHz/Tesla at their resonance frequency f0 =175 kHz and a short-term frequency stability of 0.025 Hz, which corresponds to a resolution below 1 muT. The devices can thus be used for Earth magnetic field applications, such as an electronic compass. The novel resonant magnetic field sensor benefits from an efficient continuous offset cancellation technique, which consist in evaluating the frequency difference measured with and without excitation current as output signal