Sensors and Actuators A Physical

Published by Elsevier
Print ISSN: 0924-4247
Publications
This paper presents a method to provide electrical connection to a 2D capacitive micromachined ultrasonic transducer (CMUT) array. The interconnects are processed after the CMUTs are fabricated on the front side of a silicon wafer. Connections to array elements are made from the back side of the substrate via highly conductive silicon pillars that result from a deep reactive ion etching (DRIE) process. Flip-chip bonding is used to integrate the CMUT array with an integrated circuit (IC) that comprises the front-end circuits for the transducer and provides mechanical support for the trench-isolated array elements. Design, fabrication process and characterization results are presented. The advantages when compared to other through-wafer interconnect techniques are discussed.
 
High sensing resolution is required in sensing of surgical instrument motion in micromanipulation tasks. Accelerometers can be employed to sense physiological motion of the instrument during micromanipulation. Various configurations of accelerometer placement had been introduced in the past to sense motion of a rigid-body such as a surgical instrument. Placement (location and orientation) of accelerometers fixed in the instrument plays a significant role in achieving high sensing resolution. However, there is no literature or work on the effect of placement of accelerometers on sensing resolution. In this paper, an approach of placement of accelerometers within an available space to obtain highest possible sensing resolution in sensing of rigid-body motion in micromanipulation tasks is proposed. Superiority of the proposed placement approach is shown in sensing of a microsurgical instrument angular motion by comparing sensing resolutions achieved as a result of employing the configuration following the proposed approach and the existing configurations. Apart from achieving high sensing resolution, and design simplicity, the proposed placement approach also provides flexibility in placing accelerometers; hence it is especially useful in applications with limited available space to mount accelerometers.
 
Ultrasonic sensors can be used to determine physical fluid parameters like viscosity, density, and speed of sound. In this contribution, we present the concept for an integrated sensor utilizing pressure waves to sense the characteristic acoustic impedance of a fluid. We note that the basic setup generally allows to determine the longitudinal viscosity and the speed of sound if it is operated in a resonant mode as will be discussed elsewhere. In this contribution, we particularly focus on a modified setup where interferences are suppressed by introducing a wedge reflector. This enables sensing of the liquid's characteristic acoustic impedance, which can serve as parameter in condition monitoring applications. We present a device model, experimental results and their evaluation.
 
With the increasing popularity of actuators involving smart materials like piezoelectric, control of such materials becomes important. The existence of the inherent hysteretic behavior hinders the tracking accuracy of the actuators. To make matters worse, the hysteretic behavior changes with rate. One of the suggested ways is to have a feedforward controller to linearize the relationship between the input and output. Thus, the hysteretic behavior of the actuator must first be modeled by sensing the relationship between the input voltage and output displacement. Unfortunately, the hysteretic behavior is dependent on individual actuator and also environmental conditions like temperature. It is troublesome and costly to model the hysteresis regularly. In addition, the hysteretic behavior of the actuators also changes with age. Most literature model the actuator using a cascade of rate-independent hysteresis operators and a dynamical system. However, the inertial dynamics of the structure is not the only contributing factor. A complete model will be complex. Thus, based on the studies done on the phenomenological hysteretic behavior with rate, this paper proposes an adaptive rate-dependent feedforward controller with Prandtl-Ishlinskii (PI) hysteresis operators for piezoelectric actuators. This adaptive controller is achieved by adapting the coefficients to manipulate the weights of the play operators. Actual experiments are conducted to demonstrate the effectiveness of the adaptive controller. The main contribution of this paper is its ability to perform tracking control of non-periodic motion and is illustrated with the tracking control ability of a couple of different non-periodic waveforms which were created by passing random numbers through a low pass filter with a cutoff frequency of 20Hz.
 
A tetrode is a bundle of four microwires that can record from multiple neurons simultaneously in the brain of a freely moving animal. Tetrodes are usually electroplated to reduce impedances from 2-3 MΩ to 200-500 kΩ (measured at 1 kHz), which increases the signal-to-noise ratio and allows for the recording of small amplitude signals. Tetrodes with even lower impedances could improve neural recordings but cannot be made using standard electroplating methods without shorting. We were able to electroplate tetrodes to 30-70 kΩ by adding polyethylene glycol (PEG) or multi-walled carbon nanotube (MWCNT) solutions to a commercial gold-plating solution. The MWCNTs and PEG acted as inhibitors in the electroplating process and created large-surface-area, low-impedance coatings on the tetrode tips.
 
Current methods of optimizing electroosmotic (EO) pump performance include reducing pore diameter and reducing ionic strength of the pumped electrolyte. However, these approaches each increase the fraction of total ionic current carried by diffuse electric double layer (EDL) counterions. When this fraction becomes significant, concentration polarization (CP) effects become important, and traditional EO pump models are no longer valid. We here report on the first simultaneous concentration field measurements, pH visualizations, flow rate, and voltage measurements on such systems. Together, these measurements elucidate key parameters affecting EO pump performance in the CP dominated regime. Concentration field visualizations show propagating CP enrichment and depletion fronts sourced by our pump substrate and traveling at order mm/min velocities through millimeter-scale channels connected serially to our pump. The observed propagation in millimeter-scale channels is not explained by current propagating CP models. Additionally, visualizations show that CP fronts are sourced by and propagate from the electrodes of our system, and then interact with the EO pump-generated CP zones. With pH visualizations, we directly detect that electrolyte properties vary sharply across the anode enrichment front interface. Our observations lead us to hypothesize possible mechanisms for the propagation of both pump- and electrode-sourced CP zones. Lastly, our experiments show the dynamics associated with the interaction of electrode and membrane CP fronts, and we describe the effect of these phenomena on EO pump flow rates and applied voltages under galvanostatic conditions.
 
This paper describes the design, microfabrication and testing of a pre-aligned array of fiber couplers using direct UV-lithography of SU-8. The fiber coupler array includes an out-of-plane refractive microlens array and two fiberport collimator arrays. With the optical axis of the pixels parallel to the substrate, each pixel of the microlens array can be pre-aligned with the corresponding pixels of the fiberport collimator array as defined by the lithography mask design. This out-of-plane polymer 3D microlens array is pre-aligned with the fiber collimator arrays with no additional adjustment and assembly required, therefore, it helps to dramatically reduce the running cost and improve the alignment quality and coupling efficiency. In addition, the experimental results for the fiber couplers are also presented and analyzed.
 
Magnetoelastic sensors are used in a wide field of wireless sensing applications. The sensing element is a low-cost magnetostrictive ribbon whose resonant frequency depends on the measured quantity. The accuracy of magnetoelastic sensors is limited by the fact that the resonant frequency is also affected by the earth's magnetic field. In this paper we present a technique to minimize this effect by applying an antisymmetric magnetic bias field to the ribbon. The ribbon's response to external perturbation fields was measured and compared to a conventional sensor design. Our results show that the influence of the earth's magnetic field could be reduced by 77%.
 
There are a number of applications for microstructure devices consisting of a regular pattern of perforations, and many of these utilize fluid damping. For the analysis of viscous damping and for calculating the spring force in some cases, it is possible to take advantage of the regular hole pattern by assuming periodicity. Here a model is developed to determine these quantities based on the solution of the Stokes' equations for the air flow. Viscous damping is directly related to thermal-mechanical noise. As a result, the design of perforated microstructures with minimal viscous damping is of real practical importance. A method is developed to calculate the damping coefficient in microstructures with periodic perforations. The result can be used to minimize squeeze film damping. Since micromachined devices have finite dimensions, the periodic model for the perforated microstructure has to be associated with the calculation of some frame (edge) corrections. Analysis of the edge corrections has also been performed. Results from analytical formulas and numerical simulations match very well with published measured data.
 
Microcantilevers are used in a number of applications including atomic-force microscopy (AFM). In this work, deflection-sensing elements along with heating elements are integrated onto micromachined cantilever arrays to increase sensitivity, and reduce complexity and cost. An array of probes with 5-10 nm gold ultrathin film sensors on silicon substrates for high throughput scanning probe microscopy is developed. The deflection sensitivity is 0.2 ppm/nm. Plots of the change in resistance of the sensing element with displacement are used to calibrate the probes and determine probe contact with the substrate. Topographical scans demonstrate high throughput and nanometer resolution. The heating elements are calibrated and the thermal coefficient of resistance (TCR) is 655 ppm/K. The melting temperature of a material is measured by locally heating the material with the heating element of the cantilever while monitoring the bending with the deflection sensing element. The melting point value measured with this method is in close agreement with the reported value in literature.
 
The encapsulation and packaging reliability in fully integrated, fully wireless 100 channel Utah Slant Electrode Array (USEA)/integrated neural interface-recording version 5 (INI-R5) has been evaluated by monitoring the extended long term in-vitro functional stability and recording longevity. The INI encapsulated with 6-μm Parylene-C was immersed in phosphate buffer saline (PBS) at room temperature for a period of over 12 months. The USEA/INI-R5, while being soaked was powered and configured wirelessly through 2.765 MHz inductive link and the transmitted frequency shift keying (FSK) modulated radio-frequency (RF) (900 MHz Industrial, scientific, medical-ISM band) signal was also recorded wirelessly as a function of soak time. In order to test the long term recording ability, in-vitro wireless recording was performed in agarose for few channels. The full functionality and the ability of the electrodes to record artificial neural signals even after 12 months of PBS soak provides a measure of encapsulation reliability, the functional and recording stability in fully integrated wireless neural interface and potential usefulness for future chronic implants.
 
A novel fabrication technique has been developed for creating high density (6.25 electrodes/mm(2)), out of plane, high aspect ratio silicon-based convoluted microelectrode arrays for neural and retinal prostheses. The convoluted shape of the surface defined by the tips of the electrodes could compliment the curved surfaces of peripheral nerves and the cortex, and in the case of retina, its spherical geometry. The geometry of these electrode arrays has the potential to facilitate implantation in the nerve fascicles and to physically stabilize it against displacement after insertion. This report presents a unique combination of variable depth dicing and wet isotropic etching for the fabrication of a variety of convoluted neural array geometries. Also, a method of deinsulating the electrode tips using photoresist as a mask and the limitations of this technique on uniformity are discussed.
 
Microsystem technology is well suited to batch fabricate microelectrode arrays, such as the Utah electrode array (UEA), intended for recording and stimulating neural tissue. Fabrication of the UEA is primarily based on the use of dicing and wet etching to achieve high aspect ratio (15:1) penetrating electrodes. An important step in the array fabrication is the etching of electrodes to produce needle-shape electrodes with sharp tips. Traditional etching processes are performed on a single array, and the etching conditions are not optimized. As a result, the process leads to variable geometries of electrodes within an array. Furthermore, the process is not only time consuming but also labor-intensive. This report presents a wafer-scale etching method for the UEA. The method offers several advantages, such as substantial reduction in the processing time, higher throughput and lower cost. More importantly, the method increases the geometrical uniformity from electrode to electrode within an array (1.5 ± 0.5 % non-uniformity), and from array to array within a wafer (2 ± 0.3 % non-uniformity). Also, the etching rate of silicon columns, produced by dicing, are studied as a function of temperature, etching time and stirring rate in a nitric acid rich HF-HNO(3) solution. These parameters were found to be related to the etching rates over the ranges studied and more-importantly affect the uniformity of the etched silicon columns. An optimum etching condition was established to achieve uniform shape electrode arrays on wafer-scale.
 
Megavoltage x-ray imaging performed during radiotherapy is the method of choice for geometric verification of patient localization and dose delivery. Presently, such imaging is increasingly performed using electronic portal imaging devices (EPIDs) based on indirect detection active matrix flat panel imagers (AMFPIs). These devices use a scintillating phosphor screen in order to convert incident x-rays into optical photons, which are then detected by the underlying active matrix photodiode array. The use of a continuous phosphor introduces a trade-off between x-ray quantum efficiency and spatial resolution, which limits current devices to use only ∼2% of the incident x-rays. This trade-off can be circumvented by "segmented phosphor screens", comprising a two-dimensional matrix of optically-isolated cell structures filled with scintillating phosphor. In this work we describe the fabrication of millimeter-thick segmented phosphor screens using the MEMS (micro-electro-mechanical-system) polymer SU-8. This method is capable of being extended to large-area substrates.
 
This study describes the functioning of a novel sensor to measure cortisol concentration in the interstitial fluid (ISF) of a human subject. ISF is extracted by means of vacuum pressure from micropores created on the stratum corneum layer of the skin. The pores are produced by focusing a near infrared laser on a layer of black dye material attached to the skin. The pores are viable for approximately three days after skin poration. Cortisol measurements are based on electrochemical impedance (EIS) technique. Gold microelectrode arrays functionalized with Dithiobis (succinimidyl propionate) self-assembled monolayer (SAM) have been used to fabricate an ultrasensitive, disposable, electrochemical cortisol immunosensor. The biosensor was successfully used for in-vitro measurement of cortisol in ISF. Tests in a laboratory setup show that the sensor exhibits a linear response to cortisol concentrations in the range 1 pm to 100 nM. A small pilot clinical study showed that in-vitro immunosensor readings, when compared with commercial evaluation using enzyme-linked immunoassay (ELISA) method, correlated well with cortisol levels in saliva and ISF. Further, circadian rhythm could be established between the subject's ISF and the saliva samples collected over 24 hours time-period. Cortisol levels in ISF were found reliably higher than in saliva. This Research establishes the feasibility of using impedance based biosensor architecture for a disposable, wearable cortisol detector. The projected commercial in-vivo real-time cortisol sensor device, besides being minimally invasive, will allow continuous ISF harvesting and cortisol monitoring over 24 hours even when the subject is asleep. Forthcoming, this sensor could be interfaced to a wireless health monitoring system that could transfer sensor data over existing wide-area networks such as the internet and a cellular phone network to enable real-time remote monitoring of subjects.
 
In this paper, we present the design and fabrication of a 1D beam steering device based on planar electro-optic thermal-plastic prisms and a collimator lens array. With the elimination of moving parts, the proposed device is able to overcome the mechanical limitations of present scanning devices, such as fatigue and low operating frequency, while maintaining a small system footprint (~0.5mm×0.5mm). From experimental data, our prototype device is able to achieve a maximum deflection angle of 5.6° for a single stage prism design and 29.2° for a cascaded three prisms stage design. The lens array shows a 4µm collimated beam diameter.
 
The static and dynamic characteristics of a bimorph deformable mirror (DM) for use in an adaptive optics system are described. The DM is a 35-actuator device composed of two disks of lead magnesium niobate (PMN), an electrostrictive ceramic that produces a mechanical strain in response to an imposed electric field. A custom stroboscopic phase-shifting interferometer was developed to measure the deformation of the mirror in response to applied voltage. The ability of the mirror to replicate optical aberrations described by the Zernike polynomials was tested as a measure of the mirror's static performance. The natural frequencies of the DM were measured up to 20 kHz using both stroboscopic interferometry as well as a commercial laser Doppler vibrometer (LDV). Interferometric measurements of the DM surface profile were analyzed by fitting the surface with mode-shapes predicted using classical plate theory for an elastically supported disk. The measured natural frequencies were found to be in good agreement with the predictions of the theoretical model.
 
We present giant magnetoresistance (GMR) spin valve sensors designed for detection of superparamagnetic nanoparticles as potential biomolecular labels in magnetic biodetection technology. We discuss the sensor design and experimentally demonstrate that as few as approximately 23 monodisperse 16-nm superparamagnetic Fe(3)O(4) nanoparticles can be detected by submicron spin valve sensors at room temperature without resorting to lock-in detection. A patterned self-assembly method of nanoparticles, based on a polymer-mediated process and fine lithography, is developed for the detection. It is found that sensor signal increases linearly with the number of nanoparticles.
 
We demonstrate the operation of a digital microfluidic lab-on-a-chip system utilizing Electro Wetting on Dielectrics (EWOD) as the actuation principle and a High Fundamental Frequency (HFF; 50 MHz) quartz crystal microbalance (QCM) resonator as a mass-sensitive sensor. In a first experiment we have tested the reversible formation of a phosphor-lipid monolayer of phospholipid vesicles out of an aqueous buffer suspension onto a bio-functionalized integrated QCM sensor. A binding of bio-molecules results in an altered mass load of the resonant sensor and a shift of the resonance frequency can be measured. In the second part of the experiment, the formation of a protein multilayer composed of the biomolecule streptavidin and biotinylated immunoglobulin G was monitored. Additionally, the macroscopic contact angle was optically measured in order to verify the bio-specific binding and to test the implications onto the balance of the surface tensions. Using these sample applications, we were able to demonstrate and to verify the feasibility of integrating a mass-sensitive QCM sensor into a digital microfluidic chip.
 
Hydrogels have been demonstrated to swell in response to a number of external stimuli including pH, CO2, glucose, and ionic strength making them useful for detection of metabolic analytes. To measure hydrogel swelling pressure, we have fabricated and tested novel perforated diaphragm piezoresistive pressure sensor arrays that couple the pressure sensing diaphragm with a perforated semi-permeable membrane. The 2 × 2 arrays measure approximately 3 × 5 mm² and consist of four square sensing diaphragms with widths of 1.0, 1.25, and 1.5 mm used to measure full scale pressures of 50, 25, and 5 kPa, respectively. An optimized geometry of micro pores was etched in silicon diaphragm to allow analyte diffusion into the sensor cavity where the hydrogel material is located. The 14-step front side wafer process was carried out by a commercial foundry service (MSF, Frankfurt (Oder), Germany) and diaphragm pores were created using combination of potassium hydroxide (KOH) etching and deep reactive ion etching (DRIE).
 
Application of magnetoelastic thick-film sensors to the measurement of thin-film elastic moduli is described in this study. An analytical model is derived, that relates the resonant frequency of a magnetoelastic sensor to the elasticity and density of an applied thin-film. Limits of the model are analyzed, and related to experimental measurements using thin-films of silver and aluminum. For 500 nm thick-films, the measured Young's modulus of elasticity for Al and Ag is found to be within 1.6% of standard data. Using commercially available magnetoelastic sensors, the elasticity of coatings, approximately 30 nm thick, can readily be measured.
 
We present a passive, miniature check valve which can be manufactured using standard techniques ideal for low-cost, disposable systems used in medical devices and other applications. The body of the valve consists of a hollow cylindrical core, closed at one end, with a side port and a cylindrical elastomeric sleeve placed over the core body, covering the side port. The pressure required for initial opening of the valve, referred to as cracking pressure, can be adjusted, and depends predominantly on the valve core outer diameter, the sleeve inner diameter, the sleeve wall thickness, and the sleeve material's modulus of elasticity. These parameters can be controlled to tight tolerances, while the tolerances on other features can be relaxed, which simplifies valve manufacturing and assembly. Valve embodiments produced from different materials, and with varying critical dimensions, exhibited distinct and reproducible cracking pressures in the range of 2 to 20 PSI. The cracking pressure did not vary significantly as a function of flow rate. No back flow leakage was encountered up to 30 PSI, the pressure limit of the sensor used in this experiment. Most of the valves tested had small internal volumes of 3-4 μL. The internal volume can be further reduced by selecting a core of smaller inner diameter. In contrast to lithography-based microvalves that generally must be manufactured in-situ within the fluidic device, the herein presented valve can be manufactured independently of, and can be readily integrated into fluidic systems manufactured via a wide selection of fabrication methods.
 
Reliable chronic operation of implantable medical devices such as the Utah Electrode Array (UEA) for neural interface requires elimination of transcutaneous wire connections for signal processing, powering and communication of the device. A wireless power source that allows integration with the UEA is therefore necessary. While (rechargeable) micro batteries as well as biological micro fuel cells are yet far from meeting the power density and lifetime requirements of an implantable neural interface device, inductive coupling between two coils is a promising approach to power such a device with highly restricted dimensions. The power receiving coils presented in this paper were designed to maximize the inductance and quality factor of the coils and microfabricated using polymer based thin film technologies. A flexible configuration of stacked thin film coils allows parallel and serial switching, thereby allowing to tune the coil's resonance frequency. The electrical properties of the fabricated coils were characterized and their power transmission performance was investigated in laboratory condition.
 
We have successfully fabricated x(0.65PMN-0.35PT)-(1 - x)PZT (xPMN-PT-(1 - x)PZT), where x is 0.1, 0.3, 0.5, 0.7 and 0.9, thick films with a thickness of approximately 9 µm on platinized silicon substrate by employing a composite sol-gel technique. X-ray diffraction analysis and scanning electron microscopy revealed that these films are dense and creak-free with well-crystallized perovskite phase in the whole composition range. The dielectric constant can be controllably adjusted by using different compositions. Higher PZT content of xPMN-PT-(1 - x)PZT films show better ferroelectric properties. A representative 0.9PMN-PT-0.1PZT thick film transducer is built. It has 200 MHz center frequency with a -6 dB bandwidth of 38% (76 MHz). The measured two-way insertion loss is 65 dB.
 
This paper describes the application of magnetically-soft ribbon-like sensors for measurement of temperature and stress, as well as corrosive monitoring, based upon changes in the amplitudes of the higher-order harmonics generated by the sensors in response to a magnetic interrogation signal. The sensors operate independently of mass loading, and so can be placed or rigidly embedded inside nonmetallic, opaque structures such as concrete or plastic. The passive harmonic-based sensor is remotely monitored through a single coplanar interrogation and detection coil. Effects due to the relative location of the sensor are eliminated by tracking harmonic amplitude ratios, thereby, enabling wide area monitoring. The wireless, passive, mass loading independent nature of the described sensor platform makes it ideally suited for long-term structural monitoring applications, such as measurement of temperature and stress inside concrete structures. A theoretical model is presented to explain the origin and behavior of the higher-order harmonics in response to temperature and stress.
 
The paper gives an analytical approximation to the viscous damping coefficient due to the motion of a gas between a pair of closely spaced fluctuating plates in which one of the plates contains a regular system of circular holes. These types of structures are important parts of many microelectromechanical devices realized in MEMS technology as microphones, microaccelerometers, resonators, etc.The pressure satisfies a Reynolds' type equation with coefficients accounting for all the important effects: compressibility of the gas, inertia and possibly slip of the gas on the plates. An analytical expression for the optimum number of circular holes which assure a minimum value of the total damping coefficient is given. This value realizes an equilibrium between the squeeze-film damping and the viscous resistance of the holes.The paper also provides analytical design formulas to be used in the case of regular circular perforated plates.
 
The electromechanical performance of piezoelectric scanning mirrors for endoscopy imaging is presented. The devices are supported by a single actuating cantilever to achieve a high fill factor, the ratio of mirror area to the combined mirror and actuator area. The largest fill factor devices (74%) achieved 10° mechanical scan range at +/-10V with a 300 μm long cantilever. The largest angular displacement of 30° mechanical scan range was obtained with a 500 μm long cantilever device with a 63% fill factor driven at 40 Vpp. A systematic investigation of device performance (displacement and speed) as a function of fabrication and operational parameters including the stress balance in the cantilever revealed unexpectedly large displacements with lack of inversion at the coercive field. An interpretation of the results is presented based on piezoelectric film domain orientation and clamping with supporting piezoelectric film characterization measurements.
 
Free-standing magnetoelastic thick-film sensors have a characteristic resonant frequency that can be determined by monitoring the magnetic flux emitted from the sensor in response to a time varying magnetic field. This property allows the sensors to be monitored remotely without the use of direct physical connections, such as wires, enabling measurement of environmental parameters from within sealed, opaque containers. In this work, we report on application of magnetoelastic sensors to measurement of atmospheric pressure, fluid-flow velocity, temperature, and mass load. Mass loading effects are demonstrated by fabrication of a remote query humidity sensor, made by coating the magnetoelastic thick film with a thin layer of solgel deposited Al2O3 that reversibly changes mass in response to humidity.
 
A common micromixer design strategy is to generate interleaved flow topologies to enhance diffusion. However, problems with these designs include complicated structures and dead volumes within the flow fields. We present an active micromixer using a resonating piezoceramic/silicon composite diaphragm to generate acoustic streaming flow topologies. Circulation patterns are observed experimentally and correlate to the resonant mode shapes of the diaphragm. The dead volumes in the flow field are eliminated by rapidly switching from one discrete resonant mode to another (i.e., resonant mode-hop). Mixer performance is characterized by mixing buffer with a fluorescence tracer containing fluorescein. Movies of the mixing process are analyzed by converting fluorescent images to two-dimensional fluorescein concentration distributions. The results demonstrate that mode-hopping operation rapidly homogenized chamber contents, circumventing diffusion-isolated zones.
 
The resonant frequency and quality factor Q of a liquid immersed magnetoelastic sensor are shown to shift linearly with the liquid viscosity and density product. Measurements using different grade oils, organic chemicals, and glycerol-water mixtures show that the surface roughness of the sensor in combination with the molecular size of the liquid play important roles in determining measurement sensitivity, which can be controlled through adjusting the surface roughness of the sensor surface. A theoretical model describing the sensor resonant frequency and quality factor Q as a function of liquid properties is developed using a novel equivalent circuit approach. Experimental results are in agreement with theory when the liquid molecule size is larger than the average surface roughness. However, when the molecular size of the liquid is small relative to the surface roughness features molecules are trapped, and the trapped molecules act both as a mass load and viscous load; the result is higher viscous damping of the sensor than expected.
 
Magnetically soft, magnetostrictive metallic glass ribbons are used as in-situ remote query viscosity sensors. When immersed in a liquid, changes in the resonant frequency of the ribbon-like sensors are shown to correlate with the square root of the liquid viscosity and density product. An elastic wave model is presented that describes the sensor response as a function of the frictional forces acting upon the sensor surface.
 
An optical-based motion sensing system has been developed for real-time sensing of instrument motion in micromanipulation. The main components of the system consist of a pair of position sensitive detectors (PSD), lenses, an infrared (IR) diode that illuminates the workspace of the system, a non-reflective intraocular shaft, and a white reflective ball attached at the end of the shaft. The system calculates 3D displacement of the ball inside the workspace using the centroid position of the IR rays that are reflected from the ball and strike the PSDs. In order to eliminate inherent nonlinearity of the system, calibration using a feedforward neural network is proposed and presented. Handling of different ambient light and environment light conditions not to affect the system accuracy is described. Analyses of the whole optical system and effect of instrument orientation on the system accuracy are presented. Sensing resolution, dynamic accuracies at a few different frequencies, and static accuracies at a few different orientations of the instrument are reported. The system and the analyses are useful in assessing performance of hand-held microsurgical instruments and operator performance in micromanipulation tasks.
 
This work presents a concave corner compensation technique, to substantially reduce the residual (111) flanges between two vertical (010)-(001) planes, underetched on a (100) silicon wafer. A carefully-planned set of rectangles is used, oriented parallel or perpendicular to the wafer flat, at 45° to the desired underetched vertical (010) and (001) planes. The set of rectangles are designed based on several principles, and the behavior during etching is graphically and numerically simulated. The predicted behavior is confirmed by experiment. The technique is used to fabricate a square-cross-section beam for an angular rate measurement sensor. Natural frequencies in horizontal and vertical directions are simulated and compared to measurement
 
Polycrystalline and single-crystalline 3C silicon carbide films hetero-epitaxially grown on 3 '' or 4 '' Si wafers have been obtained by a hot-wall type low-pressure chemical-vapour depositon (LPCVD). The internal stress of the polycrystalline film can be adjusted from 30 to 250 MPa (tensile) by changing the growth parameters, while that of the single crystal ranges from 100 to 200 MPa (tensile), The stress uniformity of the 46 mm(2) polycrystalline membrane is measured to be +/- 9.7%, while that of the single one is +/- 3.0%. The biaxial Young's modulus is around 450 GPa for both the films and the burst strength for a 2.0 mu m thick 20 mm(2) polycrystalline membrane is about 0.4 kgf cm(-2). Optical transparencies of 1.0 mu m thick membranes are 70 and 80% at 633 nm for the polycrystal and the single crystal, respectively, The single crystal always shows higher transmission over the wavelength range studied and an extended absorption edge to the shorter wavelengths. The current values of mobility, carrier density and resistivity of the single crystal are roughly 180 cm(2) V-1 s(-1), 2 x 10(18) cm(-3) and 0.02 Omega cm, respectively.
 
In the present paper, we describe the results of the 3D FEM modelling performed by the University of Bordeaux on the micro-shutter devices developed by Centro Ricerche Fiat. After a brief introduction on recent works about shutters in the Fiat Research Center, the authors describe the FEM modelling of a micro-shutter device. The next section presents the numerical methodology used for this electro-mechanical coupled study. The coupled study is made in two steps: first, an electrostatic analysis is computed to determine the force acting on the flexible conductor; then a structural analysis is performed to obtain the deformation which is used to remesh the electrostatic model. The next section shows results of computations and different threshold voltages obtained in functions of the petal and dielectric layer thickness. These results indicate how threshold voltages are very dependant on these geometrical parameters. In conclusion, the authors explain the interest of this numerical tool for the prediction of optimum parameters before designing a micro-shutter device.
 
6H-SiC piezoresistive pressure sensors operational at 500°C, were batch fabricated and tested. The full scale output (FSO at 1000 psi) was 40.66 mV and 20.03 mV at 23°C and 500°C, respectively, The full-scale linearity of -0.17% and hysteresis of 0.17% compared favorably with current technology. No serious degradation was observed when operated for ten hours at 500°C, The temperature coefficient of resistance (TCR), was -0.25%/°C and -0.05%/°C at 100°C and 500°C, respectively, The temperature coefficient of gauge factor (TCGF) exhibited negative values of 0.19%/°C and -0.11%°C at 100°C and 500°C, respectively, This work demonstrated batch manufacturing and operation of pressure sensors for temperatures beyond silicon technology
 
A novel, media-isolated, temperature-compensated, bulk-micromachined integrated absolute pressure sensor has successfully been developed. The sensor is usable for most applications involving exposure to harsh media, such as fuel vapor seen by manifold absolute pressure (MAP) sensors. The device consists of two dice bonded together. Devices are batch fabricated by bonding two wafers together prior to sawing. The bottom wafer contains bulk-micromachined piezoresistive pressure sensors and the top wafer contains signal-conditioning integrated circuitry. The pressure sensors and the integrated circuits are coupled together by wirebonding from the top die down to the bottom die through via holes anisotropically etched in the top wafer. Characterization of the device indicates that the devices fabricated meet the specifications of a MAP sensor.
 
The pervasiveness of automotive passive restraint systems has emphasized the need for improving system reliability while simultaneously reducing the cost and size of the system. This paper describes the integrated silicon automotive accelerometer (ISAAC), which consists of a silicon micromachined die fabricated in a dissolved-wafer process and a CMOS ASIC that are combined in a standard plastic package. The resultant device meets the functional, cost, and reliability requirements of the next generation of automotive passive restraint systems.
 
Prototype low-noise miniature accelerometers have been fabricated with electron-tunneling transducers. The electron-tunneling transducer permits detection of small displacements of the proof mass with high electrical response; such a transducer is essential for a high-performance miniature accelerometer. Prototype accelerometers have shown self-noise of approximately 10-7 g (Hz)-1/2 or less between 10 and 200 Hz, and close to 10-8 g (Hz)-1/2 near the resonance frequency of 100 Hz. Directivity measurements give nulls at least 50 dB below the maximum. A dual-axis prototype designed for underwater acoustic applications is packaged in an 8 cm3 volume with a mass of 8 g.
 
A new structure for a piezoresistive triaxial accelerometer has been designed and fabricated. The FEM simulations shows a null cross sensitivity for the x and y detection and a very low level one for the z direction, <1.6%. The metal lines and the thickness of the passivation silicon oxide layers have been reduced to decrease stresses in the devices. The technology for the devices is a combination of bulk and surface micromachining based on commercial BESOI wafers
 
A pure CMOS integrated accelerometer was realised using surface micromachining as structural technique. The samples were fabricated by a 14 mask 0.8 μm CMOS standard process in a Siemens production line. Only the standard layers of the process (350 nm polysilicon and 600 nm oxide as sacrificial layer) are used to build up the surface micromachined device. Sensor release and antisticking are also CMOS-compatible. The movement of a seismic mass normal to the chip surface is capacitively detected (open loop) and transformed on chip into a digital output signal by a robust circuit for measuring sub-fF capacitance differences. Parasitics are suppressed on chip. The sensor was designed to measure accelerations up to 50 g. A resolution of ±0.6 g corresponding to a capacitance change of ±0.1 fF was observed
 
A capacitive accelerometer using SDB-SOI (silicon direct bonding -silicon on insulator) structure has been developed. The mass and beams of the accelerometer are fabricated with a single-crystal silicon layer 10 mu m thick. The beam is formed in a spiral shape to the obtain longest beam in the minimum area. The silicon dioxide layer is etched sacrificially, which determines the capacitance gap as 1 mu m. Seven kinds of accelerometers for different measurement ranges have been integrated in the same chip. The capacitance changes of the accelerometers are detected by a capacitance to voltage converter IC (TI28882D), and the output characteristics evaluated. As a result, a high sensitivity of 200 mV G(-1) and wide frequency response of 200 Hz have been achieved.
 
A novel micromachined accelerometer based on thermal-bubble technology is proposed and demonstrated. The only moving element in the accelerometer is a small thermal-bubble created by using a high flux heater to vaporize the liquid contained in the micro-chamber. The basic physical characteristics, including the heat transfer and fluid flow behavior of this sensor, are analyzed and discussed. The feasibility and performance of the proposed accelerometer are verified using numerical simulations and demonstrated experimentally using a designed test setup. The results conclude that the presented design has better response and higher sensitivity comparing to its counterparts.
 
A beam-mass piezoresistive micro-accelerometer sensitive to acceleration components in the chip plane and vertical to the beam direction has been developed. The beam is in the 〈100〉 direction with sidewalls vertical to the (001) wafer surface. The top side of the beam is widened slightly to make enough room to accommodate the piezoresistors. Therefore, the beam has a T-shaped cross-section. Two n-type piezoresistors on the top side of the beam, forming a half bridge, serve as sensing elements. The sensitivity of the device is about 0.5 mv/g/5v and the resonant frequency is about 1.2 kHz
 
In the project “IRMA-EU” (IRMA: Integrated Resonant Accelerometer Microsystem for Automotive Applications), a project sponsored by the European Commision under ESPRIT, SensoNor and project partners Autoliv and SINTEF are developing a resonant structure two-chip accelerometer silicon microsystem for automotive applications, the SA30: Crash Sensor for front impacts, with range ±50 g. The project is focusing on the development of key process technologies, product designs and manufacture of functional prototypes. The IRMA project is coordinated with other activities performed by the partners to cover all aspects of research and technology development as well establishment of high volume production capabilities needed for successful product innovation of this new generation of crash sensors. The sensing principle is an acceleration sensitive resonant structure, with an ASIC for resonance control and signal conditioning. Prototypes in silicon of both the sensor chip and the ASIC chip have confirmed the feasibility of the concept, and ramp up to high volume production has now started
 
Fiber Bragg grating (FBG) sensors are promising candidates for strain measurements in smart structures. The wavelength-encoded nature of the reflected signals from FBGs allows for absolute strain measurement and for multi-point operation based on wavelength division multiplexing (WDM). To measure strain variation with good accuracy, detection of the small shift in the Bragg wavelength is essential. In this paper, we report the use of a digital matched filter (DMF) for improving the wavelength detection accuracy. The DMF technique has been used extensively in image processing and pattern recognition for the detection of weak signals in a noisy environment. We apply it here for the detection of Bragg wavelength in FBG sensors when the SNR is low.
 
The authors have proposed a kind of non-contact linear motors driven by SAWs, in which the fluid is introduced between the stator and the slider. As the SAWs are excited in the stators, the sliders will be driven by SAW streaming in linear motion. The experiments results show that the the slider displacement increases exponentially as time increase, at the same time, the slider velocity is proportional to the driving voltage, and decreases exponentially approximately with the thickness of the aqueous solution of glycerin increase.
 
Surface micromachined, electrostatically actuated microswitches have been developed at Northeastern University. Microswitches have an initial contact resistance of 0.5-1 Ω, and current handling capability of about 20 mA. Typically, contact resistance degrades progressively when the switches are cycled beyond approximately 10<sup>6 </sup> cycles. In this work, the microswitch contact resistance is studied on the basis of a simple, clean metal contact resistance model. Comparison of measured contact resistance (measured as a function of contact force) with the characteristics predicted by the model shows the measured resistance to be higher than the prediction, approximately by an order of magnitude, suggesting that insulating films at the contact interface need to be taken into account. Microswitches with a large number of parallel contacts have also been developed, and measurement data is presented showing that these devices have a current handling capability greater than 150 mA
 
Micromachined silicon cantilever beams actuated by the converse piezoelectric effect are of great interest for actuator applications [1], and for the characterization of piezoelectric thin films [2]. In this work a study of the mechanical response of piezoelectrically operated heterogeneous bimorph structures is given and compared with finite elements simulations. Determination of the piezoelectric parameter d31 using interferometric displacement measurements, electrical impedance measurements, and finite element calculation will be discussed.
 
Top-cited authors
Robert Puers
  • KU Leuven
P.M. Sarro
  • Delft University of Technology
Göran Stemme
  • KTH Royal Institute of Technology
Stephen P Beeby
  • University of Southampton
M. C. Elwenspoek
  • University of Twente