Showing papers in "Sensors and Actuators A-physical in 2001"

Design and fabrication of a new vibration-based electromechanical power generator

Abstract: A device is described for generating electrical power from mechanical energy in a vibrating environment. The design utilises an electromagnetic transducer and its operating principle is based on the relative movement of a magnet pole with respect to a coil. The approach is suitable for embedded remote microsystems structures with no physical links to the outside world. Simulation, modelling and test results following fabrication of a first prototype have demonstrated that generation of practical amounts of power within a reasonable space is possible. Power generation of more than 1 mW within a volume of 240 mm3 at a vibration frequency of 320 Hz has been obtained.

Overview of low temperature co-fired ceramics tape technology for meso-system technology (MsST)

Abstract: For certain applications low temperature co-fired ceramic (LTCC) tape materials used in multi-layer packages offers the potential of emulating a great deal of silicon sensor/actuator technology at the meso scale level. The goal of this review is to describe meso-system technology (MsST) using LTCC, thick film and silicon technologies. A mayor MST application being addressed today is fluid handling for miniaturized chemical analytical systems. For larger MST-3D applications, in the meso-size (from 10 to several hundred microns), it would be desirable to have a material compatible with hybrid microelectronics, with suitable thermal, mechanical and electrical properties, easy to fabricate and inexpensive to process. Such a material is the LTCC tape multilayer system. One of the important features of LTCC technology is the possibility of fabricating 3D structures using multiple layers. In this review, we want to emphasize sensors and actuators for meso-systems exploring LTCC Tape possibilities in the following ways: Sensors for proximity measurement; Fluid media realization of vias, holes, cavities, channels and manifolds; Sensors for flow measurement; Actuators for hybrid microvalves & micropumps. # 2001 Elsevier Science B.V. All rights reserved.

Ultrasonic micromixer for microfluidic systems

Abstract: This paper describes the design, fabrication and evaluation of an active micromixer for continuous flow. Mixing occurs directly from ultrasonic vibration. The intended use of the device is for integrated microchemical synthesis systems or for micro total analysis systems. The patterns of inlets, outlet and mixing chamber were formed in glass. The entire flow path was encapsulated by anodic bonding of a Si wafer to the glass. A diaphragm ( 6 mm ×6 mm ×0.15 mm ) was etched on the Si side to prevent ultrasonic radiation from escaping to the other parts of the device. The ultrasonic vibration originated from a bulk piezoelectric lead–zirconate–titanate (PZT) ceramic ( 5 mm ×4 mm ×0.15 mm ). The PZT was adhered on the diaphragm and was excited by a 60 kHz square wave at 50 V (peak-to-peak). Liquids were mixed in a chamber ( 6 mm ×6 mm ×0.06 mm ) with the Si oscillating diaphragm driven by the PZT. A solution of uranine and water was used to evaluate the effectiveness of mixing. The entire process was recorded using a fluorescent microscope equipped with a digital camera. The laminar flows of the uranine solution (5 ml/min) and water (5 ml/min) were mixed continuously and effectively when the PZT was excited. The temperature rise of our device was 15°C due to the ultrasonic irradiation.

Electrochemical deposition and characterization of conducting polymer polypyrrole/PSS on multichannel neural probes

Abstract: The conducting polymer polypyrrole (PPy) doped with polystyrene sulfonate (PSS) was electrochemically deposited onto the electrode sites of micromachined neural probes. The surface morphology of the films was found to vary with coating thickness. Examinations of atomic force microscope (AFM) images of the coatings using the power spectral density (PSD) method revealed the spatial frequency dependence of surface roughness. The magnitude of the impedance of the PPy/PSS coated electrode at the biologically relevant frequency of 1 kHz decreased with increasing thickness as the film roughens. The lowest impedance was observed at a thickness of ∼13 μm. This decrease in impedance was correlated to the increase in effective surface area. The power-law behavior of the impedance spectra was quantitatively correlated with the fractal characteristics of the polymer-coated electrode surface morphology. High quality neural signals were recorded acutely from cerebellum of guinea pig through the PPy/PSS coated electrodes.

A wireless batch sealed absolute capacitive pressure sensor

Abstract: This paper reports the development of an absolute wireless pressure sensor that consists of a capacitive sensor and a gold-electroplated planar coil. Applied pressure deflects a 6 μm-thin silicon diaphragm, changing the capacitance formed between it and a metal electrode supported on a glass substrate. The resonant frequency of the LC circuit formed by the capacitor and the inductor changes as the capacitance changes; this change is sensed remotely through inductive coupling, eliminating the need for wire connection or implanted telemetry circuits. The sensor is fabricated using the dissolved-wafer process and utilizes a boron-doped silicon diaphragm supported on an insulating glass substrate. The complete sensor measures 2.6 mm ×1.6 mm in size and incorporates a 24-turns gold-electroplated coil that has a measured inductance of 1.2 μH. The sensor is designed to provide a resonant frequency change in the range 95–103 MHz for a pressure change in the range 0–50 mmHg with respect to ambient pressure, providing a pressure responsivity and sensitivity of 160 kHz/mmHg and 1553 ppm/mmHg, respectively. The measured pressure responsivity and sensitivity of the fabricated device are 120 kHz/mmHg and 1579 ppm/mmHg, respectively.

Wireless energy transfer for stand-alone systems: a comparison between low and high power applicability

Abstract: The applicability of micro-systems, designed to contain monitoring or actuating devices is often hampered by accessibility. For systems with low power demands, the use of inductive links for wireless energy and data transfer to the remote system is a widely acknowledged solution. Design strategies that optimise towards power transfer efficiency for given geometric constraints, have been proposed. With the introduction of more power consuming components, such as small dc motors, in micro-systems, a demand was created for inductive links with high power transfer possibilities combined with a high overall efficiency. This paper describes the design considerations for such high energy inductive links. An inductive link is presented, capable of transferring 20 W of power over a distance of 1 cm with an overall efficiency of 80%. In addition, ongoing developments will be outlined, such as data-transmission and external voltage regulation.

Design and application of a wireless, passive, resonant-circuit environmental monitoring sensor

Abstract: A wireless, passive, remote query sensor platform is presented capable of monitoring the complex permittivity of a surrounding medium, temperature, humidity, and pressure. The sensor is a planar two-dimensional inductor–capacitor circuit, of scaleable-size, that resonates at a characteristic frequency the value of which is dependent upon the parameters of interest. The resonant frequency of the sensor is detected remotely with one or a pair of loop antennas by measuring the impedance or voltage spectrum of the antenna(s), with the environmental parameters of interest then calculated from the measured resonant frequency. The wireless, remote query nature of the platform enables the LC sensor to monitor the environmental conditions from within sealed opaque containers. The paper describes the operational principles, design criteria, illustrative applications, and performance limitations of the sensor platform.

Study of contacts in an electrostatically actuated microswitch

Abstract: Surface micromachined, electrostatically actuated microswitches have been developed at Northeastern University. Microswitches with gold contacts typically have an initial contact resistance of the order of 0.1 Ω over the first 10 5 cycles of lifetime while cold-switching 4 mA, and have a current handling capability of about 20 mA. In general, the contact resistance decreases over the first few thousand switch cycles, and degrades progressively when the switches are cycled beyond approximately 10 6 cycles. In this work, the microswitch contact resistance is studied on the basis of a clean metal contact resistance model. Comparison of the measured contact resistance (measured as a function of contact force) with the characteristics predicted by the model shows approximate agreement. The discrepancies between the model characteristics and measurements are discussed briefly.

Deep reactive ion etching of Pyrex glass using SF6 plasma

Abstract: Deep reactive ion etching of Pyrex glass has been characterized in sulfur hexafluoride plasma (SF6). High etch rate (∼0.6 μm/min) was demonstrated under a condition of low pressure (0.2 Pa) and high self-bias (−390 V) by using a magnetically enhanced inductively coupled plasma reactive ion etching. Vertical etch profile (taper angle ∼88°), high aspect ratio (>10) and through-wafer etching of Pyrex glass (200 μm in thickness) were achieved under the condition by using thick (20 μm) and vertical electroplated nickel film as mask. The vertical etch profile was achieved when the mask opening is narrower than 20 μm because the deposition of nonvolatile product on the sidewall is reduced. A novel etching technique “scoop-out etching” was demonstrated by using the present etching characteristics.

Mechanical design and optimization of capacitive micromachined switch

Abstract: Design and optimization of a shunt capacitive micromachined switch is presented. The micromachined switch consists of a thin metal membrane called the “bridge” suspended over a center conductor, and fixed at both ends to the ground conductors of a coplanar waveguide (CPW) line. A static electromechanical model considering the residual stress effects is developed to predict the effective stiffness constant and the critical collapse voltage of the bridge for several typical bridge geometries. The deformation of the bridge and its contact behavior with the dielectric layer are analyzed using the finite element method (FEM) in order to explore a good contact field with different bridge geometries. Furthermore, a nonlinear dynamic model that captures the effects of electrostatic forces, elastic deformation, residual stress, inertia, and squeeze film damping is developed, and is used for predicting the switching speed (including the switching-down and the switching-up time) and the Q -factor. The effects of variation of important parameters on the mechanical performance have been studied in detail, and the results are expected to be useful in the design of optimum shunt capacitive micromachined switch. The results may also be useful in the design of actuators with membranes or bridges.

Piezoelectric thin film micromechanical beam resonators

Abstract: Piezoelectric micromechanical beam resonators are investigated for application to electromechanical filters. The derivation of a dynamic admittance model describing the electromechanical behavior of the resonators is presented. Predictions from this model indicate that piezoelectric beam resonators offer significant potential for high-frequency applications. Using a simple three-mask fabrication process based on zinc oxide active films, doubly-clamped piezoelectric beam resonators with center frequencies ranging from 158 kHz to 1.18 MHz are reported. Resonators with both ZnO and SiO 2 substrates have been realized, and triple-beam configurations investigated for reducing mechanical anchor losses. Measured quality factors range from Q =3700 at 158 kHz to Q =930 at 1.18 MHz.

The effect of isopropyl alcohol on etching rate and roughness of (1 0 0) Si surface etched in KOH and TMAH solutions

Abstract: The etching process of (1 0 0) silicon wafers in KOH and TMAH solutions with isopropyl alcohol (IPA) has been studied. The etching rates of different crystallographic planes in the wide range of solutions concentration have been estimated. The mutual relations of the etching rates of these planes have been analysed. Special emphasis was put on the roughness of silicon surface obtained in effect of etching. It was proved that IPA added to the solution improves the morphology of resulted surface. Detailed indications about the solution composition, ensuring satisfactory surface quality have been given. On the basis of experimental results and theoretical considerations, some attempts were made to explain the etching behaviour of silicon in KOH and TMAH solutions with IPA addition. It was suggested that TMA+ ions play similar role in the solution to IPA particles and participate in smoothening of the etched surface.

A study of the static characteristics of a torsional micromirror

Abstract: Torsional micromirror has been widely used in many applications as diverse as optical communication, laser scanning related and spatial light modulator related applications. In different applications the torsional micromirror may have different arrangements. A general analysis of the static characteristics of the torsional micromirror, especially its snap-down effect, is able to simplify the design of torsional micromirror. This paper describes the static characteristics of an electrostatically-actuated torsional micromirror based on the parallel-plate capacitor model. First, a normalized equation that governs the static actuation property of the torsional micromirror device is derived, and the relationship between rotation angle and driving voltage are also determined. Thereafter, the snap-down effect is specially investigated, leading to the revealment of the direct relationships of the electrode size with the snap-down angle and the maximum driving voltage. Based on the model, a 100 μm ×100 μm torsional micromirror and a array of torsional micromirrors are fabricated using the three-layer-polysilicon micromachining process to verify the static actuation relation and the snap-down effect, respectively. The rotation angle of the micromirror is measured using an optical projection method. The experimental set-up and data are processed and analyzed in accordance with ISO guideline. It is shown that the experimental results are in good agreement with the theoretical analysis.

A MEMS radio-frequency ion mobility spectrometer for chemical vapor detection

Abstract: A first-of-a-kind micro-electro-mechanical systems (MEMS) radio-frequency ion mobility spectrometer (rf-IMS) with a miniature drift tube of total volume 0.6 cm 3 has been fabricated and tested. The spectrometer has detection limits in the parts per billion (ppb) and the ability to identify chemicals such as isomers of xylene not resolved in conventional time-of-flight ion mobility spectrometry. Spectrometer operation with a miniature 10.6 eV (l ¼ 116:5 nm) UV photodischarge lamp and a 1 mCi radioactive ionization source has been demonstrated. The resultant spectra with both these ionization sources are similar, with several additional peaks evident for the radioactive source. The effect of varying the carrier gas flow rate on the resultant spectra has been investigated and optimal flow conditions are found at flow rates between 2 and 3 l/min. The rf-IMS has been interfaced to a mass spectrometer (MS) and rf-IMS spectral peaks have been confirmed. The rf-IMS/MS configuration illustrates another use for the rf-IMS as a pre-filter for atmospheric pressure chemical ionization (APCI) mass spectrometry applications. # 2001 Elsevier Science B.V. All rights reserved.

Anemometer with hot platinum thin film

Abstract: The techniques of micromachining silicon are used for the manufacture of an anemometer with low electric consumption and great sensitivity. To reduce the energy consumption, a suspended membrane of silicon rich silicon nitride SiNx makes it possible to carry out the heat insulation between the heater and the substrate. Platinum (Pt) thin film (3000 A) with titanium (300 A) adhesion layer on SiNx/Si substrate is used for the hot resistor. Among the methods of Pt deposition tested, electron beam evaporation gives the best results for the temperature coefficient of resistance (TCR) of Pt. Its response time is about 6 ms. Sensitivity in laminar and turbulent flow range are respectively 4.80 mV/(m/s)0.45/mW and of 0.705 mV/(m/s)0.8/mW for about 20 mW power supplied. The experiments show that the temperature rise of the sensor is not sensitive to the ambient temperature. Moreover, sensor response shows no significant changes according to parallel or perpendicular orientation of the gas flow.

Micro magnetic silicone elastomer membrane actuator

Abstract: We present results of the design, fabrication, and testing of a microfabricated, membrane-type magnetic actuator. Magnetic pieces made of electroplated Permalloy (Ni80Fe20) are embedded in a thin flexible membrane made of silicone elastomer. When an external magnetic field is applied, a torque generated on the magnetic pieces produces membrane displacement. Permalloy pieces that are 100-mm-wide, 870mm-long, and 22-mm-thick are strategically positioned in a 2-mm-square, 40-mm-thick polydimethylsiloxane (PDMS) membrane (Sylgard 184). This design, produced through numerical simulations, is optimized to realize large membrane displacements. Tests performed on this membrane actuator showed displacements >80 mm in the presence of a 2:85 10 5 A/m external magnetic field. Larger displacements are possible with greater magnetization fields. This type of membrane actuator can be applied to the fabrication of tetherless micropumps for use in microfluidic systems. # 2001 Elsevier Science B.V. All rights reserved.

Microfabricated electroporation chip for single cell membrane permeabilization

Abstract: Silicon microfabrication technology was used to develop a chip that can incorporate a live biological cell in its electrical circuit and thereby induce controlled electroporation in the cell. Electroporation employs electrical pulses applied across a cell for cell membrane permeabilization. Commonly used in biotechnology for genetic engineering of cells in a batch, this chip is the first microfabricated device in which cells can be individually electroporated. This paper describes the design and fabrication of the chip in detail. To characterize the performance of the microelectroporation chip, an electrical model of the device is developed together with typical experimental results.

Characterizations of VO2-based uncooled microbolometer linear array

Abstract: Vanadium dioxide (VO 2 ) thin films are materials for uncooled microbolometer due to their high temperature coefficient of resistance (TCR) at room temperature. This paper describes the design and fabrication of eight-element uncooled microbolometer linear array using the films and micromachining technology. The characteristics of the array is investigated in the spectral region of 8–12 μm. The fabricated detectors exhibit responsivity of over 10 kV/W, detectivity of approximate 1.94×10 8 cm Hz 1/2 /W, and thermal time constant of 11 ms, at 300 K and at a frequency of 30 Hz. Furthermore, the uncorrected response uniformity of the linear array bolometers is less than 20%.

Design and simulation of an implantable medical drug delivery system using microelectromechanical systems technology

Abstract: A unique design of an implantable micropump for medical drug delivery systems was proposed The peristaltic pumping principle was selected Three pump chambers are individually actuated by each bulk PZT (lead zirconate titanate) disk in a peristaltic motion It is this peristaltic motion that propels the fluid The design of the micropump includes inlet, three pump chambers, three silicon membranes, three normally closed active valves, three bulk PZT actuators, three actuation reservoirs, flow microchannels, and outlet To prohibit flow when no power is applied, the micropump was designed to be normally closed The pump features an integral valve/membrane design such that the pump chambers not only pump the liquid, but also function as the inlet and outlet valves To determine the dimensions of the proposed micropump, analytical modeling of the micropump chamber was conducted The design tradeoffs between maximizing the pumped volume and reducing the overall size of the proposed micropump were analyzed An electromechanical coupled field simulation using the FEA method was employed Based upon the simulation results, 6 and 12 mm diameter silicon membranes with different thickness of 40 and 80 μm were fabricated using microelectromechanical systems (MEMS) technology The deflection of these silicon membranes was tested The PZT actuator was manually glued onto the micropump chamber The testing data agreed well with the FEA simulation of the deflection The conductive adhesive layer dramatically reduces the deflection A 12 mm in diameter and 40 μm thick silicon membrane in each pump chamber is needed to meet the micropump design requirements The fabrication and experiments of these silicon membranes reported in this paper determine the dimensions and fabrication processes for the complete micropump A 70 mm ×35 mm ×10 mm micropump will be fabricated using MEMS fabrication technology The complete micropump will be characterized to verify our design

Fabrication of TiNi shape memory micropump

Abstract: We have developed a shape memory alloy (SMA) actuated micropump as a component for use in micro analysis or micro dosage systems. In this paper, we will discuss the fabrication process and dynamic actuation properties of an SMA actuator, as well as the first result of pumping properties of a completed SMA micropump. TiNi thin film of about 6 μm in thickness was deposited onto a Si wafer with a square recess on its reverse side, and memorized an initial flat shape. The TiNi thin film and a Pyrex glass cap with a square recess were then anodically bonded together in a vacuum to form a chamber to which a bias pressure was to be applied to deform the TiNi thin film. After removing the remaining Si layer beneath the TiNi thin film by RIE in SF6 plasma, a shape memory actuator of 5 mm square in size was completed. A Si check valve structure was also fabricated through a process of anisotropic etching and fusion bonding and was assembled with the actuator. The fabricated micropump with a size of 10 mm ×20 mm ×1.4 mm was driven by thermal cycles of resistive heating and air-cooling under bias pressure which was applied by a nitrogen gas flow. The completed SMA micropump proved to give a flow rate of 0.4 μl per cycle at a bias pressure of 100 kPa.

Alkene Based Monolayer Films As Anti Stiction Coatings For Polysilicon MEMS

Abstract: This paper describes a new class of anti-stiction coatings for polysilicon MEMS. This class of molecular film is based on the free radical reaction of a primary alkene (e.g. 1-octadecene C16H33CHCH2) with hydrogen terminated silicon [1] , [2] . The new coating has several key advantages over the previously reported octadecyltrichlorosilane (OTS) and perfluorodecyltrichlorosilane (FDTS) based self-assembled monolayers (SAM) [3] , [4] : (1) the coating does not produce HCl at any stage in the monolayer formation whereas chlorosilane based chemistry does. (2) The coating does not require the formation of an intervening charge-trapping oxide layer. (3) The film formation procedure for alkene based monolayers is simpler than for chlorosilane based SAMs for two main reasons. First, the surface re-oxidation step is entirely eliminated. Second, the coating solution does not need to be conditioned before use, since water is not a reagent in this process. (4) The coating process is much more robust since it is essentially insensitive to relative humidity. (5) The coated structures have many fewer particulates in comparison to those coated with OTS. (6) The coating process can be made selective to coat only exposed silicon by generating radicals using a radical initiator. The coating has been evaluated in several ways, including X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), contact angle analysis, work of adhesion by cantilever beam array technique and coefficient of static friction using a sidewall testing device. The octadecene film is compared to the OTS SAM with respect to anti-stiction properties. XPS data confirm the absence of oxygen in both freshly prepared samples and in samples aged for more than 4 months in laboratory ambient. Water and hexadecane contact angles, and work of adhesion data are similar to those of OTS. AFM shows that the samples, which receive 1-octadecene films, accumulate far fewer particles during processing than those which receive the OTS SAM treatment. Based upon the data presented here, we find that the anti-stiction properties of films produced with the alkene chemistry are indeed comparable to those produced with the chlorosilane SAMs, but without many of the limitations imposed by the chlorosilane chemistry.

Tracking system with five degrees of freedom using a 2D-array of Hall sensors and a permanent magnet

Abstract: Based on a 2D-array of 16 cylindrical Hall sensors and a permanent magnet, a tracking system with five degrees of freedom is analysed in this paper. The system accuracy is studied, including offset drifts, sensitivity mismatches and the number of sensors. A detection distance as large as 14 cm (during 1 h without calibration) is achieved using a magnet of 0.2 cm3. The position and orientation of the marker is displayed in real time with a sampling frequency up to 50 Hz. The sensing system is small enough to be hand-held and can be used in a normal environment.

High-cycle fatigue and durability of polycrystalline silicon thin films in ambient air

Abstract: To evaluate the long-term durability properties of materials for microelectromechanical systems (MEMS), the stress-life ( S / N ) cyclic fatigue behavior of a 2-μm thick polycrystalline silicon film was evaluated in laboratory air using an electrostatically actuated notched cantilever beam resonator. A total of 28 specimens were tested for failure under high frequency (∼40 kHz) cyclic loads with lives ranging from about 10 s to 34 days (3×10 5 to 1.2×10 11 cycles) over fully reversed, sinusoidal stress amplitudes varying from ∼2.0 to 4.0 GPa. The thin-film polycrystalline silicon cantilever beams exhibited a time-delayed failure that was accompanied by a continuous increase in the compliance of the specimen. This apparent cyclic fatigue effect resulted in an endurance strength, at greater than 10 9 cycles, of ∼2 GPa, i.e. roughly one-half of the (single cycle) fracture strength. Based on experimental and numerical results, the fatigue process is attributed to a novel mechanism involving the environmentally-assisted cracking of the surface oxide film (termed reaction-layer fatigue). These results provide the most comprehensive, high-cycle, endurance data for designers of polysilicon micromechanical components available to date.

Electrostrictive poly(vinylidene fluoride-trifluoroethylene) copolymers

Abstract: High energy electron (1.0–2.55 MeV) irradiation was used to modify the phase transitional behavior of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) copolymers in an attempt to significantly improve the electromechanical properties of the copolymers. It is found that the copolymers under a proper irradiation treatment exhibit very little room temperature polarization hysteresis and very large electrostrictive strain (the longitudinal strain of −5% can be achieved). Because of the large anisotropy in the strain responses along and perpendicular to the polymer chain, the transverse strain can be tuned over a broad range by varying the film stretching condition. For unstretched films, the magnitude of transverse strain is approximately about/less than 1/3 of that of the longitudinal strain, and for stretched films, the transverse strain along the stretching direction is comparable to the longitudinal strain. In addition to the high strain response, the irradiated copolymers also possess high elastic energy density and mechanical load capability as indicated by the relatively high elastic modulus of the copolymer and the high strain response of the transverse strain even under 40 MPa tensile stress. The high strain and high elastic modulus of the irradiated copolymer also result in an improved electromechanical coupling factor where the transverse coupling factor of 0.45 has been observed. The frequency dependence of the strain response was also characterized up to near 100 kHz and the results show that the high electromechanical response can be maintained to high frequencies. Several unimorph actuators were fabricated using the modified copolymer and the test results demonstrate high performance of the devices due to the high strain and high load capability of the material.

Integrated Hall-effect magnetic sensors

Abstract: Integrated Hall magnetic sensors are used in automotive and computer industry. Their farther penetration into other applications is mainly hampered by the problems of switching noise and of offset and drift related to the packaging stress. The equivalent magnetic noise and offset can be dramatically reduced by integrating magnetic flux concentrators on the sensor chip. A promising way to eliminate the influences of packaging stress and temperature variations is to apply the self-calibration using an integrated coil.

Magnetic sensors for automotive applications

Abstract: Magnetic sensors offer several key advantages: they allow contactless and, consequently, wear-free measurement of mechanical quantities like angle of rotation and angular speed. They are robust and inexpensive to manufacture. As one example of magnetic sensors in production at Robert Bosch GmbH, the steering wheel sensor LWS3 is shown, developed for the electronic stability program (ESP), which prevents vehicles from spinning. We recently demonstrated, that the inherent limitation of the AMR-effect to an 180° angular range can be overcome by using a switchable magnetic field generated inside the sensor element. For a new generation of magnetic sensors, the technology of giant magneto-resistance (GMR) thin film systems promises several advantages like larger working distances, more precise angular position measurement in a wider range (up to 360°), smaller and therefore cheaper sensor chips and economic system solutions due to the higher signal output. A GMR multilayer system of CoCu/Cu was developed, which fulfills the requirement of having no hysteresis in the magneto-resistive characteristics. On the other hand, research is still going on for sensitive GMR layers, which are stable at temperatures of 200°C (or more) for long time periods of at least 500 h. Thin film systems of spin valve type, used in read heads for disc drives, have been thoroughly evaluated about whether they can be used in sensors for automotive applications. The great challenge is to generate GMR thin film systems which cover a much wider range of features than the existing technologies of Hall and AMR and which can be produced at lower cost. Only versatile GMR sensors will lead to high production volumes, which are needed for a cost efficient fabrication as in other modern micro technologies.

Micromechanical devices with embedded electro-thermal-compliant actuation

Abstract: At the micro-scale, thermal actuation provides larger forces compared to the widely-used electrostatic actuation. In this paper, we highlight another advantage of thermal actuation, viz. the ease with which it can be utilized to achieve a novel embedded electro-thermal-compliant (ETC) actuation for MEMS. The principle of ETC actuation is based on the selective non-uniform Joule heating and the accompanying constrained thermal expansion. It is shown here that appropriate topology and shape of the structures give rise to many types of actuators and devices. Additionally, selective doping of silicon ETC devices is used to enhance the non-uniform heating and thus the deformation. A number of novel ETC building blocks and devices are described, and their analysis and design issues are discussed. The devices were microfabricated using MCNC’s MUMPs foundry process as well as a bulk-micromachining process called PennSOIL (Penn silicon-on-insulator layer). The designs are validated with the simulations and the experimental observations. The experimental measurements are quantitatively compared with the theoretical predictions for a novel ETC microactuator with selective doping.

Miniature valveless pumps based on printed circuit board technique

Abstract: This paper presents a new concept of designing microfluidic devices. By using printed circuit board (PCB) as the substrate material, miniature valveless pumps have been successfully developed. The pump can be operated as a single diffuser/nozzle pump or a peristaltic pump, and can delivery a maximum flow rate of 3 ml/min. The detailed design, fabrication, and characterization of the pumps are described in the paper. The PCB technique presents a low-cost and flexible alternative for small-scale production of microfludic devices.

Characteristics and fabrication of NiTi/Si diaphragm micropump

Abstract: A novel micropump actuated by NiTi/Si composite diaphragm was described in this paper. The driving principle, microfabrication processes and characteristics of the pump were reported. The pump is composed of a deformable chamber and two silicon flap check valves. The outer dimension of the pump is 6 mm ×6 mm ×1.5 mm , with the diaphragm size of 3 mm ×3 mm ×20 μm. The fabrication processes include silicon micromachining and AuSi eutectic bonding. By using the recoverable force of NiTi thin-film and biasing force of silicon membrane, the actuation diaphragm realized reciprocating motion effectively. Experimental results show that the pump has superior performance, such as high pumping yield (up to 340 μl/min), high working frequency (up to 100 Hz), and long fatigue life time (more than 4×107 working cycles).

Swimming micro-machine driven by magnetic torque

Abstract: Magnetic micro-machines capable of swimming through liquid or gel were fabricated. The micro-machines were driven by an external rotating magnetic field and featured a screw-shaped structure and permanent magnet. The machines could swim under condition of a Reynolds number ( Re ) of 10 −7 , and were able to run through agar or a bovine tissue sample using the same principle. Their running behavior was dependent on the frequency and strength of the external field, and on the surrounding media. These machines have great potential for medical applications in the human body.