Showing papers in "Journal of Micromechanics and Microengineering in 2002"

Characterization of the mechanical behavior of an electrically actuated microbeam

Abstract: We present a nonlinear model of electrically actuated microbeams accounting for the electrostatic forcing of the air gap capacitor, the restoring force of the microbeam and the axial load applied to the microbeam The boundary-value problem describing the static deflection of the microbeam under the electrostatic force due to a dc polarization voltage is solved numerically The eigenvalue problem describing the vibration of the microbeam around its statically deflected position is solved numerically for the natural frequencies and mode shapes Comparison of results generated by our model to the experimental results shows excellent agreement, thus verifying the model Our results show that failure to account for mid-plane stretching in the microbeam restoring force leads to an underestimation of the stability limits It also shows that the ratio of the width of the air gap to the microbeam thickness can be tuned to extend the domain of the linear relationship between the dc polarization voltage and the fundamental natural frequency This fact and the ability of the nonlinear model to accurately predict the natural frequencies for any dc polarization voltage allow designers to use a wider range of dc polarization voltages in resonators

Pull-in voltage analysis of electrostatically actuated beam structures with fixed–fixed and fixed–free end conditions

Abstract: In this paper, a closed-form expression for the pull-in voltage of fixed–fixed beams and fixed–free beams is derived starting from the known expression of a simple lumped spring-mass system. The effects of partial electrode configuration, of axial stress, non-linear stiffening, charge re-distribution and fringing fields are all included in the final expression. Further, the results obtained are summarized and validated with other existing empirical and analytical models as well as with finite element simulation results. The model agrees well with finite element simulation results obtained with COVENTORWARE software.

Development of a microfluidic device for fluorescence activated cell sorting

Abstract: This paper describes the development towards a miniaturized analytical system that can perform the major key functions of a flow cytometer. The development aims at diagnostic applications for cell counting and sorting with the ultimate goal of a low-cost portable instrument for point of care diagnosis. The present systems configuration consists of a disposable microfluidic device, that enables injection, single file cell flow through a miniaturized laser induced fluorescence detection system as well as sorting of identified samples. The microfluidic devices were fabricated by means of rapid prototyping technologies based on thick film photo-polymers. This paper reports various approaches on cell sorting and demonstrates sorting of single cells by means of an off-chip valve switching technique. The miniaturized fluorescence detection system employs active and passive micro-optical components, including semiconductor laser and ultra bright LED sources, highly sensitive avalanche photodiodes as well as micro-prism, holographic diffraction gratings and fibre optics for transmission and collection of light. Furthermore we demonstrate the feasibility of integrating solid-state components as part of an on-chip detection system.

A new fabrication process for ultra-thick microfluidic microstructures utilizing SU-8 photoresist

Abstract: In this paper we describe a new process for fabricating ultra-thick microfluidic devices utilizing SU-8 50 negative photoresist (PR) by standard UV lithography. Instead of using a conventional spin coater, a simple 'constant-volume-injection' method is used to create a thick SU-8 PR film up to 1.5 mm with a single coating. The SU-8 PR is self-planarized during the modified soft-baking process and forms a highly-uniform surface without any edge bead effect, which commonly occurs while using a spin coater. Photomasks can be in close contact with the PR and a better lithographic image can be generated. Experimental data show that the average thickness is 494.32 ± 17.13 μm for a 500 μm thick film (n = 7) and the uniformity is less than 3.1% over a 10 × 10 cm2 area. In this study, the temperatures for the soft-baking process and post-exposure baking are 120 °C and 60 °C, respectively. These proved to be capable of reducing the processing time and of obtaining a better pattern definition of the SU-8 structures. We also report on an innovative photomask design for fabricating ultra-deep trenches, which prevents the structures from cracking and distorting during developing and hard-baking processes. In this paper, two microfluidic structures have been demonstrated using the developed novel methods, including a micronozzle for thruster applications and a microfluidic device with micropost arrays for bioanalytical applications.

Design and fabrication of artificial lateral line flow sensors

Abstract: Underwater flow sensing is important for many robotics and military applications, including underwater robots and vessels. We report the development of micromachined, distributed flow sensors based on a biological inspiration, the fish lateral line sensors. Design and fabrication processes for realizing individual lateral line sensor nodes are discussed in this paper, along with preliminary characterization results.

SU-8 thick photoresist processing as a functional material for MEMS applications

Abstract: The use of SU-8 high aspect ratio, thick, photoresist as a functional material for MEMS applications is described in this paper. SU-8 processing is developed to implement low-stress SU-8 structures as permanent and functional material incorporated with silicon-on-insulator technologies. Silicon micromachined cantilevers were fabricated with SU-8 structures on the cantilevers as added masses. Separation of material function can be achieved in this way. Silicon provides excellent mechanical properties, while SU-8 is used as extra mass to adjust the mechanical behaviour. The resonance behaviour of the cantilever structure with SU-8 is characterized through measurement, simulation and calculation, and the strength of the SU-8 material for this purpose is evaluated. The results show that SU-8 is well suited as a permanent material in mechanically active MEMS devices, and several applications are suggested. 3D MEMS architectures can also be achieved in this manner.

Energy transfer model for squeeze-film air damping in low vacuum

Abstract: High quality factors are essential for vibratory microsensors. Therefore, the vibrating structure of the sensors is often encapsulated in a housing where the air is evacuated for reduced air damping. However, the vacuum is usually low and the quality factor is still mainly determined by the energy losses to the surrounding air molecules. Air damping in low vacuum is usually estimated using the free molecular model proposed by Christian (Christian R 1966 Vacuum 16 175–8). The major drawback of the model is that the effect of the nearby objects (e.g. the electrodes for electrostatic driving) and the dimensions of the plate cannot be considered. Therefore, the damping effect is often significantly underestimated for real structures. This paper proposes a new model for air damping of microstructures in low vacuum. In this model, the damping effect is calculated by using an energy transfer mechanism instead of the momentum transfer mechanism in Christian's model. For an isolated oscillating plate, the calculated quality factor by the model is the same as that by Christian's model. However, for an oscillating plate with a neighboring object, the damping effect by the new model is related to the dimensions of the vibrating plate and the gap between the plate and the nearby object. The quality factors calculated agree with experimental data better than with Christian's model by about an order of magnitude.

A 32-site neural recording probe fabricated by DRIE of SOI substrates

Abstract: An all-dry silicon-etch based micromachining process for neural probes was demonstrated in the manufacture of a probe with a 32-site recording electrode array. The fork-like probe shafts were formed by double-sided deep reactive ion etching (DRIE) of a silicon-on-insulator (SOI) substrate, with the buried SiO2 layer acting as an etch stop. The shafts typically had the dimensions 5 mm × 25 μm × 20 μm and ended in chisel-shaped tips with lateral taper angles of 4°. An array of Ir electrodes, each 100 μm2, and Au conductor traces were formed on top of the shafts by e-beam evaporation. An accompanying interconnect solution based on flexible printed circuitry was designed, enabling precise and flexible positioning of the probes in neural tissue. SEM studies showed sharply defined probes and probe tips. The electrical yield and function were verified in bench-top measurements in saline. The magnitude of the electrode impedance was in the 1 MΩ range at 1 kHz, which is consistent with neurophysiological recordings.

A bulk microfabricated multi-axis capacitive cellular force sensor using transverse comb drives

Abstract: This paper presents design, fabrication and calibration results for a novel 2-DOF capacitive force sensor capable of resolving forces up to 490 µN with a resolution of 0.01 µN in x, and up to 900 µN with a resolution of 0.24 µN in y. A simple fabrication process using deep reactive ion etching (DRIE) on silicon-on-insulator (SOI) wafers forms the 3D high aspect ratio structure. A transverse mode comb drive movement is used to greatly improve device sensitivity. Among other advantages of the developed process is a dice-free release of wafer structures, allowing fragile structures to be individually packaged. Notching or footing effects and bowing effects are well-known problems in DRIE on SOI wafers. Techniques to overcome notching and bowing effects using a PlasmaTherm SLR-770 etcher are presented that do not require hardware modifications. The application of the force sensor is for providing real-time force feedback during individual cell manipulation tasks.

Simulation of the filling process in micro channels for polymeric materials

Abstract: There is some evidence indicating that polymeric flows in micro channels differ significantly from those in macro geometries. As micro molding is attracting more attention these days, efforts need to be made to identify the significant factors that influence microscale polymeric flow behaviors and to develop new simulation schemes for micro molding. In this study, we have investigated the consequences of microscale phenomena, particularly size-dependent viscosity, wall slip and surface tension, on the filling process of polymeric materials into micro channels. The standard scheme of two and half dimensions for injection molding simulation was modified to include these microscale effects. With data currently available for polystyrene, the simulation results indicate the importance of employing size-dependent viscosity and wall slip to predict micro filling behaviors. It appears that wall slip should always occur in channels downsized to several micrometers or less, because the wall stress would otherwise be enormous. The surface tension effects turn out to be less important and can be neglected in micro injection molding in which high injection pressure is employed.

Precise temperature control and rapid thermal cycling in a micromachined DNA polymerase chain reaction chip

Abstract: We have fabricated Si-based micromachined DNA polymerase chain reaction (PCR) chips with different groove depths. The platinum thin-film micro heater and the temperature sensor have been integrated on the chip. The volume of the PCR chamber in the chip is about 3.6 ?l and the chip size is 17 ? 40 mm2. The effects of groove geometry, including width, depth and position, on the thermal characteristics of the PCR chip have been investigated by numerical analysis and experimental measurement. From the results, the power consumption required for the PCR chip is reduced with the increase of groove depth. Compared with results for the case of no groove, the power consumption of the chip with a groove of 280 ?m is reduced by 24.0%, 23.3% and 25.6% with annealing, extension and denaturation, respectively. The heating rate is increased rapidly with the increase of the groove depth. In particular, it is revealed that this effect is predominant for depths in the region above 280 ?m. For a more precise control of chip temperature, the nonlinear feedback proportional-integral control scheme is used. The obtained heating and cooling rates are about 36 ?C s?1 and 22 ?C s?1, respectively. The overshoot and the steady state error are less than 0.7 ?C and ?0.1 ?C, respectively. In the experiment, the effects of the PCR buffer and the bubbles in the chamber on the temperature uniformity have also been studied. From the temperature measurement, it is revealed that the temperature difference between the thin-film sensor (on the lower plate) and the PCR buffer can be neglected if there is no air bubble in the PCR buffer. With such a high performance control scheme, we could implement a remarkable thermal cycling of conducting 30 cycles for 3 min. Finally, the chip PCR of plasmid DNA was successfully performed with no additives using the temperature control system.

A low-temperature wafer bonding technique using patternable materials

Abstract: In this paper we present a silicon wafer bonding technique for 3D microstructures using MEMS process technology. Photo-definable material with patternable characteristics served as the bonding layer between the silicon wafers. A bonding process was developed and several types of photo-definable material were tested for bonding strength and pattern spatial resolution. The results indicated that SU-8 is the best material with a bonding strength of up to 213 kg cm−2 (20.6 MPa), and a spatial resolution of 10 μm, at a layer thickness of up to 100 μm. The low-temperature bonding technique that is presented is particularly suitable for microstructure and microelectronics integration involved in MEMS packaging.

A polydimethylsiloxane (PDMS) deformable diffraction grating for monitoring of local pressure in microfluidic devices

Abstract: In this paper, a novel optical method for monitoring of local pressure in microfluidic devices using a deformable diffraction grating is presented. A test device was fabricated with transparent silicone elastomer - polydimethylsiloxane (PDMS) - using the replica moulding technique. The moulded PDMS chip and a flat glass plate have a bonding interface, which defines a 2 mm×2 mm diffraction grating and a 200 µm wide, 20 µm deep microchannel. The grating consists of 5 µm wide, 2 µm deep rectangular grooves arrayed with a period of 10 µm. All the grooves are connected to the microchannel, and deformed by internal pressure. The optical response of the device to pressure ranging from -80 to 100 kPa is presented and compared with the theoretical prediction. It is also demonstrated that the test device can be used for measurement of air flow rates ranging from 0 to 0.3 ml min-1. The major advantages of this method are simple design and inexpensive fabrication. This method is not only desirable for flow characterization of microfluidic devices, but also opens up the possibility of producing new types of fibre-optic pressure sensor and pressure-driven optical modulator.

Through-wafer copper electroplating for three-dimensional interconnects

Abstract: Through-wafer electrical connections are becoming increasingly important for three-dimensional integrated circuits, microelectromechanical systems packaging and radio-frequency components In this paper, we report our current results on the formation of through-wafer metal plugs using the copper electroplating technique Several approaches for via filling are investigated, such as filling before or after wafer thinning Among the methods experimented, the one-side Cu plating and bottom-up filling appears to be the most suitable technique for copper filling into high aspect ratio vias Using this method, we demonstrate the successful filling of vias with an aspect ratio of up to 7 Copper plugs as small as 20 × 20 μm2 are obtained uniformly over 4 inch Si wafers

Polyimide sacrificial layer and novel materials for post-processing surface micromachining

Abstract: We present a low-temperature post-processing module, utilizing polyimide as a sacrificial layer and novel materials such as PECVD SiC and metals (sputtered aluminium and titanium) as structural layers. The use of spin-on polyimide allows an all-dry final release step overcoming stiction problems often encountered in wet sacrificial etching processes. The spinning and curing procedure has been tailored to the specific needs of the IC-compatible post-process module. For the patterning of the polyimide, thin films of aluminium, PECVD silicon oxide or silicon carbide are employed as a mask layer. Anisotropic etching of the mask film and of the polyimide layer is accomplished by RIE. After patterning the structural layer, sacrificial etching of the polyimide is done using an isotropic dry etch process in high-density oxygen plasma. An underetch rate of 4 μm min−1 is achieved. Compatibility with different structural materials is tested and test structures are designed and realized in a fully post-processing surface micromachining module.

Micro-channel filling flow considering surface tension effect

Abstract: Understanding filling flow into micro-channels is important in designing micro-injection molding, micro-fluidic devices and an MIMIC (micromolding in capillaries) process. In this paper, we investigated, both experimentally and numerically, 'transient filling' flow into micro-channels, which differs from steady-state completely 'filled' flow in micro-channels. An experimental flow visualization system was devised to facilitate observation of flow characteristics in filling into micro-channels. Three sets of micro-channels of various widths of different thicknesses (20, 30, and 40 μm) were fabricated using SU-8 on the silicon substrate to find a geometric effect with regard to pressure gradient, viscous force and, in particular, surface tension. A numerical analysis system has also been developed taking into account the surface tension effect with a contact angle concept. Experimental observations indicate that surface tension significantly affects the filling flow to such an extent that even a flow blockage phenomenon was observed at channels of small width and thickness. A numerical analysis system also confirms that the flow blockage phenomenon could take place due to the flow hindrance effect of surface tension, which is consistent with experimental observation. For proper numerical simulations, two correction factors have also been proposed to correct the conventional hydraulic radius for the filling flow in rectangular cross-sectioned channels.

Fabrication and testing of all solid-state microscale lithium batteries for microspacecraft applications

Abstract: A microfabrication process has been developed to prepare thin film solid-state lithium batteries as small as 50 μm × 50 μm. Individual cells operate nominally at 3.9 V with 10 μA h cm−2 for a 0.25 μm thick cathode film. The cells are easily fabricated in series and parallel arrangement to yield batteries with higher voltage and/or capacity. Multiple charge/ discharge cycles are possible, though an apparent reaction of the in situ plated Li film with water or oxygen decreases cycle life several orders of magnitude from expected results. Further optimization of an encapsulating film will likely extend the cell cyclability. These microbattery arrays will be useful for providing on-chip power for low current, high voltage applications for microspacecraft and other miniaturized systems.

Development of micromachine tool prototypes for microfactories

Abstract: At present, many areas of industry have strong tendencies towards miniaturization of products. Mechanical components of these products as a rule are manufactured using conventional large-scale equipment or micromechanical equipment based on microelectronic technology (MEMS). The first method has some drawbacks because conventional large-scale equipment consumes much energy, space and material. The second method seems to be more advanced but has some limitations, for example, two-dimensional (2D) or 2.5-dimensional shapes of components and materials compatible with silicon technology. In this paper, we consider an alternative technology of micromechanical device production. This technology is based on micromachine tools (MMT) and microassembly devices, which can be produced as sequential generations of microequipment. The first generation can be produced by conventional large-scale equipment. The machine tools of this generation can have overall sizes of 100–200 mm. Using microequipment of this generation, second generation microequipment having smaller overall sizes can be produced. This process can be repeated to produce generations of micromachine tools having overall sizes of some millimetres. In this paper we describe the efforts and some results of first generation microequipment prototyping. A micromachining centre having an overall size of 130 × 160 × 85 mm3 was produced and characterized. This centre has allowed us to manufacture micromechanical details having sizes from 50 µm to 5 mm. These details have complex three-dimensional shapes (for example, screw, gear, graduated shaft, conic details, etc), and are made from different materials, such as brass, steel, different plastics etc. We have started to investigate and to make prototypes of the assembly microdevices controlled by a computer vision system. In this paper we also describe an example of the applications (microfilters) for the proposed technology.

Self-aligning gas/liquid micropump

Abstract: In this paper a piezoelectrically driven silicon membrane pump with passive dynamic valves is described. It is designed to pump gases and liquids and to be tolerant to gas bubbles. Reducing the dead volume within the pump, and thus increasing the compression ratio, one achieves the gas pumping. The main advantages and novel features of the pump described in the paper are the self-aligning of the membrane unit to the valve unit and the possibility of using screen-printed PZT as actuator, which enables mass production and thus low-cost micropumps. A liquid pump rate of 1500 μl min−1 and a gas pump rate of 690 μl min−1 were achieved.

Self-aligning microfluidic interconnects for glass- and plastic-based microfluidic systems

Abstract: In this work, we present novel self-aligning fluidic interconnection techniques with low dead volume and pressure drop for generic microfluidic systems and capillary electrophoresis chips. We have successfully designed, fabricated and characterized two self-aligning fluidic interconnection techniques in this work, both resulting in low dead volume and low pressure drop across the interconnects. The first technique is a serial assembly technique, in which each fluidic interconnect is assembled individually, exhibiting a pressure drop of 977 Pa (0.14 psi) at a flow rate of 100 µl min-1. The second technique is a parallel assembly technique that is suitable for high-density interconnects with multi-stacked generic microfluidic systems, which has a pressure drop of 1024 Pa (0.15 psi) at a flow rate of 100 µl min-1. Furthermore, the parallel assembly technique is ideally suited for plastic-based microfluidic systems. We have simulated the flow characteristics of these interconnection schemes and, based in part on the simulation results, we have designed the above interconnection schemes. We have also characterized these interconnects in terms of the physical robustness of the interconnection scheme. The serial interconnection scheme can theoretically withstand 2.6 MPa and the parallel interconnection scheme can withstand a theoretical maximum pressure of 6.6 MPa.

A low-temperature bonding technique using spin-on fluorocarbon polymers to assemble microsystems

Abstract: A new low-temperature biochemically compatible polymer bonding process has been successfully developed. The bonding has been characterized for bond strength and chemical resistance. This technique has successfully addressed a major challenge in the development of microfluidic systems from discrete components by enabling the bonding of the components to the microfluidic motherboards at low temperatures and ensuring reliable, leak-proof and chemically inert bonding. This bonding technique uses a spin-on Teflon-like amorphous fluorocarbon polymer. The bonding technique lowers the bonding temperature (~160 °C), shows a good bond strength of 4.3 MPa in silicon-to-silicon, and has excellent chemical resistance to various chemicals used in microelectromechanical systems processing.

Fabrication of two-dimensional arrays of microlenses and their applications in photolithography

Abstract: This paper describes several methods for the fabrication of microlenses, and demonstrates a lithographic technique that uses a microlens array to pattern the intensity of light incident on photoresist. Three different methods were used to fabricate microlenses: (i) self-assembly of transparent microspheres, (ii) melting and reflow of photoresist on glass substrates and (iii) self-assembly of liquid polymers on functionalized surfaces. These methods provide different advantages and convenience for the fabrication of microlenses. Microlens arrays produced by these techniques were used in photolithography to produce arrays of micropatterns in photoresist. The distribution of these micropatterns replicates the distribution of the microlenses in the array. Two types of illumination are used for exposure in this technique: collimated flood illumination and illumination through a mask. Depending on which type of exposure is used, a single microlens array can produce different patterns on its image plane: (i) an array of circular or noncircular microlenses under collimated illumination produces an array of optical micropatterns on an image plane positioned within micrometer distances from the lens array. The array of optical micropatterns corresponds to the distribution of spatial irradiance generated by simple lensing of the microlens array. The shapes of these micropatterns depend on the shapes and profiles of the microlenses. (ii) Under illumination patterned by a mask, each microlens approximately replicates the image of the patterned light source and produces a micro-scale image of this source on its image plane. The array of microlenses generates an array of repetitive micropatterns on the common image plane of the lens array. The shapes of the micropatterns depend on the patterns of the masks. Gray-scale masks can be used to produce repetitive microstructures with controlled profiles. Both techniques can generate microstructures with submicron resolution. We demonstrate that both methods produce arrays of uniform micropatterns over an area larger than 10 cm2.

Optical particle detection integrated in a dielectrophoretic lab-on-a-chip

Abstract: The design and fabrication of a dielectrophoretic "lab-on-a-chip" device for bioparticle processing and counting is presented. The device consists of a multi-layer travelling wave dielectrophoretic electrode array for manipulating particles and/or fluids, micro channels for delivering samples, and optical fibres for counting particles and/or measuring their velocities. Single particles were detected optically using either light scattering or fluorescence emission. The technology described in this work is potentially applicable to a range of particulate diagnostic systems.

A simple method for microlens fabrication by the modified LIGA process

Abstract: Microlenses and microlens arrays were fabricated using a novel fabrication technology based on the exposure of a resist (usually PMMA) to deep x-rays and subsequent thermal treatment. The fabrication technology is very simple and produces microlenses and microlens arrays with good surface roughness (less than 1 nm). The molecular weight and glass transition temperature of PMMA is reduced when it is irradiated with deep x-rays. The microlenses were produced through the effects of volume change, surface tension, and reflow during thermal treatment of irradiated PMMA. The geometry of the microlens was determined by parameters such as the x-ray dose applied to the PMMA, the diameter of the microlens, along with the heating temperature, heating time and cooling rate in the thermal treatment. Microlenses were produced with diameters ranging from 30 to 1500 μm. The modified LIGA process was used to construct not only hemispherical microlenses, but also structures that were rectangular-shaped, star-shaped, etc.

Fabrication of MEMS devices by using anhydrous HF gas-phase etching with alcoholic vapor

Abstract: In silicon surface micromachining, anhydrous HF GPE process was verified as a very effective method for the dry release of microstructures. The developed gas-phase etching (GPE) process with anhydrous hydrogen fluoride (HF) gas and alcoholic vapor such as methanol, isopropyl alcohol (IPA) was characterized and its selective etching properties were discussed. The structural layers are P-doped multi-stacked polysilicon and silicon-on-insulator (SOI) substrates and sacrificial layers are tetraethylorthosilicate (TEOS), low-temperature oxide (LTO), plasma enhanced chemical vapor deposition (PECVD) oxide, phosphosilicate glass (PSG) and thermal oxides on silicon nitride or polysilicon substrates. We successfully fabricated and characterized micro electro mechanical system (MEMS) devices with no virtually process-induced stiction and no residues. The characteristics of the MEMS devices for microsensor and microactuator, microfluidic elements and optical MEMS application were evaluated by experiment.

Characterization of a highly sensitive ultra-thin piezoresistive silicon cantilever probe and its application in gas flow velocity sensing

Abstract: We present a highly sensitive ultra-thin micromachined silicon cantilever beam with an integrated strain gauge on its root for optimizing piezoresistive readout. The mechanical characteristics and electrical readout of the cantilever beam, such as spring constant, resonant frequencies and piezoresistive sensitivity, are theoretically given from the derived formulae or from finite element modeling. The results of characterization show reasonably good agreement between the experimental results and the theoretical values. As one of the applications, for the first time the fabricated silicon cantilever beams have been applied to measure airflow velocity distribution in a steel pipe with an inner diameter of 7.0 mm. The experimental piezoresistive sensitivity (ΔR/R)/y(0) is in the range of 0.23–2.89 × 10−6 nm−1 in the beam bending tests, and the experimental flow sensitivity (ΔR/R)/Vgas2 is in the range of 0.652–4.489 × 10−5 (m s−1)−2 in the airflow velocity tests. The experimental detectable minimum airflow velocity is 7.0 cm s−1, which is comparable to that of a hot wire anemometer.

Bulk silicon micromachining for MEMS in optical communication systems

Abstract: Crystalline silicon has become more and more important for optical MEMS. The increased need of bandwidth in optical communication networks has led to a number of new optical MEMS devices such as moving-fibre and moving-waveguide switches, optical cross-connects, mirrors, resonators, optical benches and fibre alignment structures which are based on wet anisotropic micromachining techniques and deep reactive ion etching of single-crystal silicon. The excellent mechanical properties as well as the optical properties and orientation-dependent etching behaviour of crystalline silicon attract attention for reliable optical components based on surface micromachining, silicon-on-insulator, integrated optics and bulk micromachining. Anisotropic etching is especially useful for the batch fabrication of large opto-mechanical devices with sub-μm precision.

Low-cost thermoforming of micro fluidic analysis chips

Abstract: We present a new method for the low-cost manufacture of micro fluidic devices from polymers for single use. Within a one-step or two-step process inside a hot embossing press, micro channels are thermoformed into a thin plastic film and welded on to a thicker plastic film or sheet. Sterile, hermetically sealed micro fluidic structures were fabricated from polystyrene for easy opening immediately before use. It even appears to be possible to produce micro fluidic analysis chips from polymers on a coil from which single devices are cut off for use.

PIV measurements in a microfluidic 3D-sheathing structure with three-dimensional flow behaviour

Abstract: The design and production time for complex microfluidic systems is considerable, often up to several months. It is therefore important to be able to understand and predict the flow phenomena prior to design and fabrication of the microdevice in order to save costly fabrication resources. The structures are often of complex geometry and include strongly three-dimensional flow behaviour, which poses a challenge for the micro particle image velocimetry (micro-PIV) technique. The flow in a microfluidic 3D-sheathing structure has been measured throughout the volume using micro-PIV. In addition, a stereoscopic principle was applied to obtain all three velocity components, showing the feasibility of obtaining full volume mapping (x, y, z, U, V, W) from micro-PIV measurements. The results are compared with computational fluid dynamics (CFD) simulations.

In-plane linear displacement bistable microrelay

Abstract: In this paper we investigate the linear displacement bistable mechanism (LDBM) for use in microrelays. The LDBM, thermal actuators and contacts are integrated to demonstrate a relay design. The performance of the relay is characterized using relay performance metrics, including size (1.92 mm2), contact force (23.4 μN), switching time (340 μs), breakdown voltage (>475 V) and isolation (>235 V). The actuation voltage and current are 11 V and 85 mA, respectively. The ac characteristics, including contact-to-contact crosstalk and ac isolation are also measured. The testing results demonstrate that it is feasible to use the LDBM as a microrelay and that it has potential for use in future applications.