Table of contents

A process for fabricating arbitrary-shaped, two- and three-dimensional silicon and porous silicon components has been developed, based on high-energy ion irradiation, such as 250 keV to 1 MeV protons and helium. Irradiation alters the hole current flow during subsequent electrochemical anodization, allowing the anodization rate to be slowed or stopped for low/high fluences. For moderate fluences the anodization rate is selectively stopped only at depths corresponding to the high defect density at the end of ion range, allowing true three-dimensional silicon machining. The use of this process in fields including optics, photonics, holography and nanoscale depth machining is reviewed.

In this paper an active 3D mixer for lab-on-chip applications is presented. The micrometer size cone shape holes are ablated on a PMMA sheet utilizing a CO₂ laser. The holes are filled with Fe micro-particles and the whole structure is molded with PDMS which cause the Fe micro-particles to be trapped in a PDMS cone structure. These Fe-doped PDMS cones are placed in a PMMA micro-channel structure fabricated by CO₂ laser machining. By applying an external periodic magnetic field, the cones periodically bend in the micro-channel and stir the fluid. The fabrication method and the effect of the magnetic field on the bending of the cones with different aspect ratios is also discussed utilizing computer simulation. Doping the polymers with micro- and nano-metallic particles has been carried out by different research groups before, but according to our knowledge, application of such structures for the fabrication of a 3D active mixer has not been presented before.

A parameterized model for the impact dynamics of a piezoelectric microactuator is proposed, and a system-identification procedure for quantifying model parameters is presented. The proposed model incorporates squeeze-film damping, adhesion and coefficient-of-restitution effects. Following parameter quantification from sample data of bouncing impacts and progressive ramped-square-wave inputs, the model is found to be effective in predicting the time response of the actuator to a range of square-wave and sinusoidal inputs. The main contributions of this paper are to show that the dynamic response to micro-scale contact can be predicted using simple lumped-parameter modeling after a proposed system-identification procedure is performed and that certain small-scale forces can be quantified. For example, for motions where bounce of the cantilever tip may occur, the range of adhesion is found to be time dependent and vary between approximately 20 and 520 nN, while the range of squeeze-film damping is estimated to be between 50 and 130 nN, depending on the input signal frequency and amplitude. The presence, absence and quantity of bounces upon impact are predicted very accurately, while oscillation amplitudes and contact durations are predicted to be between 1% and 30% error for the majority of many test cases of periodic inputs between 5 and 100 Hz.

The accurate and rapid replication of micro-/nano-features with a high aspect ratio (AR) is one of the main challenges in micro-molding. In this work, the micro-injection–compression molding (µ-ICM) process and a new monitoring technique were combined to replicate micro-features with controllable and detectable ARs. Using a surface strain sensor mounted on the external surface of the mold, indirect acquisition of accurate cavity pressure during post-filling was realized, based on the specific pressure distribution on the mold predicted by the Hele–Shaw flow simulation. The feasibility of the proposed measuring technique was verified both numerically via finite-element analysis for the mold strain and experimentally by comparing cavity pressure profiles acquired directly and indirectly. Furthermore, primarily dominated by the maximum cavity pressure appearing during post-filling, the AR of molded polystyrene micro-feature in the downstream of cavity could be monitored via this technique with certain accuracy, and controlled by manipulating the compression force. Also the qualitative AR results of the other upstream micro-features were detectable in µ-ICM. Within a cycle time of 26 s, a maximum AR of about 12.1 was achieved on micro-features, indicating the potential for the mass production of complex micro parts applying µ-ICM.

We developed a surface-micromachined tunable Fabry–Pérot interferometer for the thermal infrared spectral range of wavelengths 7–12 µm. In this paper, we present the device performance in terms of the optical transmission and the tunability. The device represents the first layout that proved successful in terms of the manufacturing process yield (about 80%). The optical transmission over the wavelengths from 3 to 20 µm is presented with the emphasis on analysing the first-order transmission peak. The transmission band width and the peak height are compared using the existing theory for this type of an interferometer. The deviation from an ideal performance is resolved and partly explained through the known structural unidealities.

A novel microfabrication technique was developed to create silicon nanowires (SiNWs) on orthogonal surfaces of microchannels machined on top of a silicon wafer. Using a two-step metal-assisted etching process, the SiNW for the first time could be selectively fabricated on two different crystalline directions—the channel top and bottom surfaces oriented in the (1 0 0) direction while the sidewall surfaces in the (1 1 0) direction. Different SiNW etching conditions were investigated to get the optimal height, density, morphology and orientation for the SiNWs on the microchannels. The resulting samples were tested as heat sinks with water for their pool boiling applications. The sidewall SiNWs affected bubble behaviors and played important roles during the boiling process. The critical heat flux and the heat transfer coefficient both were thus improved compared to a plain silicon surface and a silicon chip with only microchannels.

The influence of perforation on the electrostatic force for thick micro-electromechanical (MEMS) structures is analyzed theoretically and experimentally. A three-dimensional numerical model is provided in order to evaluate the influence of the fringe capacitive field on the electrostatic force. Several configurations of perforated MEMS structures were characterized under ambient air conditions and experimental results demonstrate good consistency with the model prediction. Moreover, a comparative study on the effect of perforation on damping (quality factor) was performed. A quality factor was experimentally determined by analyzing frequency response under electrostatic excitation and time response under pulse loading, and was compared to a few analytical models, which demonstrate reasonable agreement with the measured results. Our study demonstrates that perforation has a significant effect on the quality factor, while its contribution of the electrostatic fringe capacitive field ranges between additional few to few tens of per cents.

In this study, the direct ink-jet metallization of finger electrodes on a multi-crystalline silicon solar cell is attempted and the impact of the silver particle size on solar cell efficiency is investigated using silver nano-inks with two different silver particle sizes. When the silver particle size approaches the nano-metric regime of around 18.1 nm, the solar cell efficiency is as low as 8.6%. On the other hand, the solar cell efficiency increases up to a maximum of 12.1% using silver particles that are around 180 nm in size. It is found that the dependence of the solar cell efficiency on the silver particle size is related to the effective volume ratio of a dispersant to silver. As the effective volume ratio increases, detrimental effects, such as an explosive decomposition of the dispersant and high residual stress due to the high volumetric shrinkage of a direct ink-jet printed finger electrode, result in poor contact formation which eventually leads to poor solar cell efficiency. With these experimental results, potential development directions for an ink-jet printer for the direct metallization of a silicon solar cell are comprehensively discussed.

Microfabricated single-cell capture and DNA stretching devices have been produced by injection molding. The fabrication scheme employed deep reactive ion etching in a silicon substrate, electroplating in nickel and molding in cyclic olefin polymer. This work proposes technical solutions to fabrication challenges associated with chip sealing and demolding of polymer high-volume replication methods. UV-assisted thermal bonding was found to ensure a strong seal of the microstructures in the molded part without altering the geometry of the channels. In the DNA stretching device, a low aspect ratio nanoslit (1/200) connecting two larger micro-channels was used to stretch a 168.5 kbp DNA molecule, while in the other device single-HeLa cells were captured against a micro-aperture connecting two larger microfluidic channels. Different dry etching processes have been investigated for the master origination of the cell-capture device. The combination of a modified Bosch process and an isotropic polysilicon etch was found to ensure the ease of demolding by resulting in slightly positively tapered sidewalls with negligible undercut at the mask interface.

Pollen tubes are an excellent model for the investigation of plant cell growth: they elongate at very high rates and are easily cultured in vitro. One major constraint in the study of pollen tube growth has been the difficulty in providing an in vitro testing environment that physically resembles the in vivo conditions. This work presents the development of a microfluidic platform for the study and manipulation of individual pollen tubes. The platform is fabricated from polydimethylsiloxane using a Silicon/SU-8 mold and makes use of microfluidics to distribute pollen grains to serially arranged microchannels into which the tubes grow to allow for individual testing. A 2D finite element fluid analysis is done to assist optimization of the architectural design. Validation of the device is carried out by growing Camellia japonica pollen. Results show that pollen tube germination and growth rate within the microfluidic network are similar to those obtained in conventional plate or batch assays. The microfluidic network allows for specific testing of a variety of structural features as demonstrated with a simple collision test, and it permits the straightforward integration of further single-cell test assays.

We have investigated the electromechanical properties of single-walled carbon nanotubes (SWNTs) by constructing carbon nanotube transistors on micro-cantilevers. SWNTs and ultra-long carbon nanotubes (UNTs) were grown on free-standing Si₃N₄ membranes by using chemical vapor deposition, and electrical contacts were generated with electron beam lithography and lift-off. The cantilevers bearing SWNT devices were micromachined so that hybrid cantilevers with various spring constants were fabricated. To measure the electromechanical properties of the SWNTs, precisely controlled forces were generated by a microbalance and applied to the hybrid cantilever devices. Upon bending, the conductances of the metallic and large-gap semiconducting UNTs showed no notable change, whereas the conductances of the small-gap semiconducting UNTs and networks of SWNTs increased. Numerical simulations of bended SWNT made using a multiscale simulator supported the hypothesis that the small-gap semiconducting SWNTs undergo a metallic transformation upon bending.

A maskless convex corner compensation technique in a 25 wt% TMAH water solution at the temperature of 80 °C is presented and analyzed. The maskless convex corner compensation technique is defined as a combination of masked and maskless anisotropic etching with convex corner compensation in the form of a 〈1 0 0〉 oriented beam. This technique enables the fabrication of three-level micromachined silicon structures with compensated convex corner at the bottom of the etched structure. All the planes that appear during the etching of (1 0 0) silicon in the 25 wt% TMAH water solution at the temperature of 80 °C are determined. Analytical relations have been found to explain the etching of all exposed planes and to calculate their etch rates. Analytical relations are determined and empirically verified in order to obtain regular shapes of the three-level silicon mesa structures. A boss for a low-pressure piezoresistive sensor has been fabricated as an example of the maskless convex corner compensation technique.

This paper describes the design and demonstration of a novel, easily fabricated micro-Coulter counter utilizing liquid metal electrodes. Fluid and electrode channels were fabricated simultaneously in a single lithographic patterning step. Eutectic gallium–indium (EGaIn) was injected into the device to form functional electrodes in a cross-channel parallel configuration. Functionality of the device was demonstrated at an ac excitation frequency of 5 kHz using a polymer microsphere suspension and simple post-processing techniques. The device successfully detected particles, exhibiting an output response proportional to particle size. EGaIn was demonstrated to be an effective micro-fluidic electrode material and provided a novel approach for the fabrication of a functional micro-Coulter counter.

This work introduces microscale dual roller casting (MDRC), a novel high-throughput fabrication method for creating continuous micropatterned surfaces using thermosetting polymers. MDRC utilizes a pair of rotating, heated cylindrical molds with microscale surface patterns to cure a continuous microstructured film. Using unmodified polydimethylsiloxane as the thermosetting polymer, we were able to create optically transparent, biocompatible surfaces with submicron patterning fidelity. Compared to other roll-to-roll fabrication processes, this method offers increased flexibility in the types of materials and topography that can be generated, including dual-sided patterning, embedded materials and tunable film thickness.

Periodic nanostructures have been widely used on emerging nano-products such as plasmonic solar cell and nano-optics. However, lack of cost-effective fabrication techniques has become the bottleneck for commercialization of these nano-products. In this work, we develop a scale up approach to fabricate high-precision nanostructures in large area. In this method, a nano-scale single crystal diamond (SCD) tool is produced by focused ion beam (FIB) machining. The nano SCD tool is then further applied to cut periodic nanostructures using single-point diamond turning (SPDT). A divergence compensation method and surface topography generation model forms a deterministic FIB fabrication approach. It has been used to generate four periods of the required periodic nano-grating structures (with a minimal dimension of 150 nm) on a normal SCD tool tip and achieves 10 nm form accuracy. The contribution of the beam tail effect has also been evaluated by using the surface topography simulation method. The fabricated diamond tool is then applied to obtain nano-grating on an electroless nickel substrate in a total area of 5 × 2 mm² through SPDT. The whole SPDT machine process only takes 2 min (with a material removal rate up to 1.8 × 10⁴ μm³ s⁻¹). Due to the elastic recovery that occurred upon the workpiece material, the practical cutting width is 13 nm smaller than the tool tip. The machining trial shows it is very promising to apply this scale up nanofabrication approach for commercialization of nano-products which possess period nanostructures.

A novel approach based on three-dimensional (3D) architecture for polymeric photovoltaic cells made up of an array of sub-micron and nano-pillars which not only increase the area of the light absorbing surface, but also improve the carrier collection efficiency of bulk-heterojunction organic solar cells is presented. The approach also introduces coating of 3D anodes with a new solution-processable highly conductive transparent polymer (Orgacon™) that replaces expensive vacuum-deposited ITO (indium tin oxide) as well as the additional hole-collecting layer of conventional PEDOT:PSS (poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate)). In addition, the described procedure is well suited to roll-to-roll high-throughput manufacturing. The high aspect-ratio 3D pillars which form the basis for this new architecture are patterned through micro-electromechanical-system- and nano-electromechanical-system-based processes. For the particular case of P3HT (poly(3-hexylthiophene)) and PCBM (phenyl-C61-butyric acid methyl ester) active material, efficiencies in excess of 6% have been achieved for these photovoltaic cells of 3D architecture using ITO-less flexible PET (polyethylene terephthalate) substrates. This increase in efficiency turns out to be more than twice higher than those achieved for their 2D counterparts.

Traditional scaffold fabrication methods used in tissue engineering enable only limited control over essential parameters such as porosity, pore size and pore interconnectivity. In this study, we designed and fabricated five different types of three-dimensionally interconnected, highly porous scaffolds with precise control over the scaffold characteristics. We used two-photon polymerization (2PP) with a commercial polymer–ceramic material (Ormocomp®) for scaffold fabrication. Also for the first time, we analyzed the 2PP fabrication accuracy with respect to scaffold design parameters. Our results showed that the porosity values decreased up to 13% compared to the design specifications due to the fabrication process and the shrinkage of the material. Finally, we showed that our scaffolds supported human adipose stem cell adhesion and proliferation in a six day culture. By precise tuning of scaffold parameters, our design and fabrication method provides a novel approach for studying the effect of scaffold architecture on cell behavior in vitro.

We propose a novel packaging method for preparing thin polyimide (PI) multichannel microelectrodes. The electrodes were connected simply by making a via-hole at the interconnection pad of a thin PI electrode, and a nickel (Ni) ring was constructed by electroplating through the via-hole to permit stable soldering with strong adhesion to the electrode and the printed circuit board. The electroplating conditions were optimized for the construction of a well-organized Ni ring. The electrical properties of the packaged electrode were evaluated by fabricating and packaging a 40-channel thin PI electrode. Animal experiments were performed using the packaged electrode for high-resolution recording of somatosensory evoked potential from the skull of a rat. The in vivo and in vitro tests demonstrated that the packaged PI electrode may be used broadly for the continuous measurement of bio-signals or for neural prosthetics.

Vitrification can be achieved by flash freezing and thawing (i.e. quenching) when ice crystal formation is inhibited in a cryogenic environment. Such ultra-rapid cooling and rewarming occurs due to the large temperature difference between the liquid and its surrounding medium. Here, we analyze the crystallization behavior of a droplet (i.e. vitrification and devitrification) by using a numerical model. The numerical results were found to explain the experimental observations successfully. The findings showed that for successful cryopreservation not only sufficiently fast cooling, but also rewarming processes should be designed and controlled to avoid devitrification of a droplet.

Biomimetic fabrication of nanostructured materials has recently attracted the attention of researchers as a cost-effective and easily applicable method of nanotexturing. Different techniques and materials have been used in order to replicate natural patterns, among which polydimethylsiloxane (PDMS Sylgard 184®) was recently used to replicate the micro- and nanoscale patterns from centric diatoms. In this paper, we test the reproducibility and precision of this approach using various morphologically different diatom species trying to optimize the molding parameters. The optimization process is focused on immobilization of diatoms on the glass support, which serves as a master for templating, as well as on the parameters of PDMS fabrication such as the ratio of the curing agent and elastomer, use of vacuum, curing time and temperature. The results indicate that higher ratios of curing agent and elastomer, longer curing time and lower temperature are the most favorable conditions to obtain negative diatom replicas of good quality with features of 50 nm. Although this method can give very precise results producing high-resolution molds with all micro- and nanostructures replicated, we revealed some limitations regarding the size and morphology of the species used. These results indicate that large round and flat diatom species seem to be more suitable for the cast molding.

This paper presents a Si/SU-8 composite electro-thermal microactuator that can generate a precisely rectilinear in-plane stroke. The microactuator consists of a pair of electro-thermally activated composite bimorphs which are joined at their tips through a central Si beam. When activated, the central beam deflects and outputs an in-plane rectilinear stroke at its center. The central stroke is precisely rectilinear along the plane of symmetry due to very high stiffness in the orthogonal directions to the stroke. This composite thermal microactuator produces a much larger rectilinear stroke and blocked force per unit temperature rise compared to an all-silicon one. At a temperature rise below 87 °C (driven below 8.0 V), the stroke increases linearly with the temperature rise up to 8.0 µm. Analytical and finite element models are developed for this range of actuation. Beyond an 87 °C temperature rise, the stroke was further enhanced by Poisson's ratio effect on SU-8 which increases the effective coefficient of thermal expansion of the composite. The microactuator could produce a maximum rectilinear stroke of 42 µm and a maximum estimated blocked force of 60 mN at a driving voltage of 14.5 V which causes a SU-8 average temperature rise of 266 °C.

In this paper, a compact micro-stereolithography (MSTL) apparatus of tabletop size was designed and constructed using a Blu-ray optical pickup unit (OPU), which came from a commercial Blu-ray optical disk driver. This is the very first application of a Blu-ray OPU to a light source of a MSTL system. A three-axis stage was adopted to obtain 3D motions, and a simple optic system was added to extend the focal length of a Blu-ray OPU for avoiding the physical interference. A liquid photo-curable resin suitable for the system was recomposed by modifying previously reported one. Then, the fabrication characteristics were investigated by constructing single-line structures at varying parameters such as laser power, scan speed and aperture diameter. The cured depth and width of the single-line structures decreased as the irradiated energy, which is determined by laser power and scan speed, decreased. Interestingly, the result also showed that the aperture diameter can effectively control the aspect ratio of cured depth and width. The increase of aperture diameter brings about the decrease of cured depth and increase of cured width. Based on the results of single-line exposure experiment, various 3D micro-structures were successfully fabricated. From this study, it can be shown that the Blu-ray-based MSTL system and the resin are suitable for fabricating complicated 3D micro-structures with reproducibility.

This paper reports on the effective use of capillary self-alignment for low-cost and time-efficient assembly of heterogeneous foil components into a smart electronic identification label. Particularly, we demonstrate the accurate (better than 50 µm) alignment of cm-sized functional foil dies. We investigated the role played by the assembly liquid, by the size and the weight of assembling dies and by their initial offsets in the self-alignment performance. It was shown that there is a definite range of initial offsets allowing dies to align with high accuracy and within approximately the same time window, irrespective of their initial offset.

Understanding the contact behavior of a microelectromechanical system (MEMS) switch is of great importance to reach a high-reliability level for micro-switch applications. The deformation occurring at the many a-spots produced by the mechanical contact of asperities can be elastic, elastic–plastic, fully plastic or any combination of the three types of deformation and has a strong effect on the contact resistance. This work presents an electrical contact resistance model for a rough MEMS switch. A dimensionless parameter k, which is a function of the electron mean free path and the roughness parameters of contacting surfaces, is introduced to identify the contact resistance. The results show that the dimensionless contact resistance is a strong function of the dimensionless contact load, the plasticity index ψ and the parameter k. The theoretical results are in good agreement with some of the experimental results.

We report development and application of 3D structured nano-microfluidic devices that were produced via soft lithography with poly(dimethylsiloxane). The procedure does not rely on hazardous or time-consuming production steps. Here, the nanochannels were created by channel-spanning ridges that reduce the flow height of the microchannel. Several realizations of the ridge layout and nanochannel height are demonstrated, depicting the high potential of this technique. The nanochannels proved to be stable even for width-to-height aspect ratios of 873:1. Additionally, an application of these submicrometer structures is presented with a new technique of a dielectrophoretic mobility shift assay (DEMSA). The DEMSA was used to detect different DNA variants, e.g. protein–DNA-complexes, via a shift in (dielectrophoretically retarded) migration velocities within an array of nanoslits.

We propose a flexible tactile sensor using sub-µm-thick Si piezoresistive cantilevers for shear stress detection. The thin Si piezoresistive cantilevers were fabricated on the device layer of a silicon on insulator (SOI) wafer. By using an adhesion-based transfer method, only these thin and fragile cantilevers were transferred from the rigid handling layer of the SOI wafer to the polydimethylsiloxane layer without damage. Because the thin Si cantilevers have high durability of bending, the proposed sensor can be attached to a thin rod-type structure serving as the finger of a robotic hand. The cantilevers were arrayed in orthogonal directions to measure the X and Y directional components of applied shear stresses independently. We evaluated the bending durability of our flexible tactile sensor and confirmed that the sensor can be attached to a rod with a radius of 10 mm. The sensitivity of the flexible tactile sensor attached to a curved surface was 1.7 × 10⁻⁶ Pa⁻¹ on average for a range of shear stresses from −1.8 × 10³ to 1.8 × 10³ Pa applied along its surface. It independently detected the X and Y directional components of the applied shear stresses.

This work presents a facile method to fabricate concave microlens arrays (MLAs) with controllable shape and high fill factor on cylindrical silica glass by a femtosecond laser-enhanced chemical wet etching process. The hexagonal and rectangular MLAs are flexibly fabricated on the silica glass cylinder with a diameter of 3 mm. The morphological characteristics of MLAs are measured by a scanning electron microscope and a laser scanning confocal microscope. The measurements show that the good uniformity and high packing density MLA structures are generated. It has also been demonstrated that the shape and size of the concave structures could be easily tuned by changing laser power and the arrangement of laser exposure spots. The convex MLAs replicated by the polymer casting method experience excellent image quality.

Three-dimensional (3D) molding is a simple and effective technique using a modified hot embossing process to produce large area, hierarchical 3D micro/nanostructures in polymer substrates. However, the use of a thin intermediate polydimethylsiloxane (PDMS) stamp inevitably causes dimensional changes in the 3D molded channel, with respect to those in the brass mold protrusion and the intermediate PDMS stamp structures. Here we investigate the deformation behavior of the 3D molded poly(methyl methacrylate) (PMMA) substrate and the intermediate PDMS stamp in 3D molding through both experimentation and numerical simulation. Depending on the height, period and aspect ratio of the brass mold protrusions and the thickness of the intermediate PDMS stamp, strain contours of the intermediate PDMS stamp layer along the periphery of the 3D molded channels are varying, which leads to a nonuniform elongation of the imprinted structures in the 3D molded channel. Increasing the height and decreasing the period of brass mold protrusions leads to higher total strain of the intermediate PDMS stamp. It was found that for high aspect ratio brass mold protrusions the maximum strain of the intermediate layer occurs in the bottom center of the 3D channels. However, with decreasing aspect ratio of the brass mold protrusion the highest elongation occurs at the bottom corners of the channel causing less elongation of the intermediate PDMS stamp and imprinted structures on the bottom surface of the 3D channel. These experimental results are in good agreement with the results obtained from the numerical simulation performed with a simple 2D model.

The fabrication of a poly(methyl methacrylate) (PMMA)-micromachined fluid lens with an optimally designed built-in electromagnetic actuator was demonstrated in this study. Through a finite element method, the number of winding turns and the distance between magnetic moments were estimated to design an effective and miniaturized electromagnetic actuator. The lens body composed of PMMA structures was simply and rapidly micromachined using computer numerical control micro-milling. The poly(dimethylsiloxane) (PDMS) membranes for electromagnetic actuation were bonded to the PMMA structures by using the proposed PMMA–PDMS bonding technique, which uses an SiO₂ intermediate layer. A physical repulsive force produced by the electromagnetic actuator applies a controllable fluidic pressure to a fluidic chamber that is sealed with the PDMS membrane, thus allowing dynamic focusing. The focus tunability of the fabricated lens was 67 diopters with a focus hysteresis of less than 1 mm and a response time of 2 ms. The solenoid of the built-in actuator showed negligible thermal crosstalk to the lens.

This work develops an image stabilizer (IS) that is fabricated using micro-electro-mechanical system (MEMS) technology and is designed to counteract the vibrations when human using cellular phone cameras. The proposed IS has dimensions of 8.8 × 8.8 × 0.3 mm³ and is strong enough to suspend an image sensor. The processes that is utilized to fabricate the IS includes inductive coupled plasma (ICP) processes, reactive ion etching (RIE) processes and the flip-chip bonding method. The IS is designed to enable the electrical signals from the suspended image sensor to be successfully emitted out using signal output beams, and the maximum actuating distance of the stage exceeds 24.835 µm when the driving current is 155 mA. Depending on integration of MEMS device and designed controller, the proposed IS can decrease the hand tremor by 72.5%.

In this paper we present a novel fabrication technique that utilizes polycaprolactone (PCL) as a bonding medium due to its low melting temperature property. PCL is biodegradable polyester with a melting point of 60 °C, and a glass transition temperature of −60 °C [1–10]. It is used as a rapid bonding medium in the fabrication process that readily produces complete microfluidic chips. The microchannels are produced via laser ablation micromachining and thermal embossing, followed by bonding with PCL. The PCL is uniformly coated on a piece of polymer sheet to produce a thin film on its surface. A complete microfluidic channel is formed by enclosing the open channel with the PCL-coated polymer piece. This fabrication technique lends itself readily to various polymers, such as (poly)methylmethacrylate (PMMA), polycarbonate (PC), polyetherimide (PEI) and poly(ethylene terephthalate) (PETE), facilitating device production for a variety of application, even permitting hybrid polymer chips. The bonding was performed rapidly at 60 °C. This approach provides a more direct method to generate hard polymer microfluidic chips than classical techniques and is therefore highly amendable to rapid prototyping. This work also explores the use of PCL as an alternative approach to making simple, cost-effective universal adhesive for bonding interconnects. Bonding is performed at 60 °C, by placing the adhesive layer in between an interconnect port and a microchip. This method allows for connections to be made easily and quickly.

We present a rapid, high-yield fabrication process for Parylene C microbellows for large deflection applications and their characterization. Bellows having different convolution number, wall thickness, inner diameter and outer diameter and layer height were fabricated using a lost wax-like process. The effect of design parameters on overall bellows performance was evaluated through load–deflection testing and finite element modeling (FEM) simulations. Large deflection (∼mm) was achieved under relatively low applied pressure (∼kPa). The onset of bellows hysteresis (4.19 kPa or 0.60 psi) was determined in mechanical testing and approximated by FEM. For the bellows tested, convolution number, wall thickness and outer diameter had the greatest impact on load–deflection (axial extension) performance. Demonstration of bellows for fluid pumping was achieved through integration with electrochemical actuators operated under low power (∼3 mW). Combined with the biocompatibility, chemical inertness and low permeability of Parylene C, microelectromechanical systems (MEMS) bellows have the potential to enable novel applications in MEMS actuators and microfluidic systems.

This work reports on the development of a lab demonstrated resonant mass sensor towards mid-size production. The issues associated with scaling-up production of the microfabricated chip are discussed with particular focus on yield and device reproducibility, as well as the constraints imposed on the design and manufacturing of the device when packaging and integration must be taken into account. Issues of modal alignment and ambient operational pressure are discussed. Fabricated devices show a 4.81 Hz pg⁻¹ mass sensitivity with a temperature sensitivity of typically 10 Hz °C⁻¹.

This paper presents a novel force sensitive structure exploiting a dynamic mode for probing the elastic properties of living cells. A key feature of this structure is the possibility of conducting measurements in liquid environments while keeping high dynamic performances. The structure indeed provides a steady area that can be adapted so that suspension or adherent cells can be placed in a culture medium. The steady area is also connected to two adjacent beam resonators. Because these resonators never need to be immersed into the culture medium during measurements, forces applied to cells can be estimated with a high sensitivity via frequency shifts. In this paper, we conduct an extensive theoretical analysis to investigate the nonlinear effects of large static pre-deflections on the dynamic behavior of the structure. As a proof of concept, we also report the fabrication, characterization and calibration of the first prototype intended to deal with suspension cells with a diameter ranging from 100 to 500 μm. This prototype currently offers a quality factor of 700 and a force sensitivity of ∼2.6 Hz mN⁻¹. We also demonstrate that the prototype is capable of measuring the elastic modulus of biological samples in a rapid and sufficiently accurate manner without the need of a descriptive model.

Recently, ac electro-osmosis (ACEO) has attracted intensive attention due to its capabilities of pumping and mixing enhancement with relatively low voltages. In this paper, we report the effects of electrode arrangement on the performance of a micromixer using dc-biased ACEO with respect to flow rate and ac frequency. The mixer consists of two inlet channels and a straight main microchannel with gold electrode pairs deposited on its bottom, and utilizes asymmetric vortex flows generated by dc-biased ACEO for mixing. The results indicate that there is significant dependence of mixing performance on the number of electrode pairs, especially for different flow rates. For example, the single electrode pair resulted in the best mixing performance at the highest flow rate of 9 µL min⁻¹ (average velocity of 2.5 cm s⁻¹) while three or four electrode pairs provided the maximum mixing performance for the flow rate lower than 4 µL min⁻¹ (4.11 cm s⁻¹). Also, we found that a mixing index of 95% can be achieved by using three electrode pairs while a single electrode pair leads to a mixing index of 85% for a given condition.

The printing quality delivered by a drop-on-demand inkjet printhead is severely affected by the residual oscillations in an ink channel and the cross-talk between neighboring ink channels. For a single ink channel, our earlier contribution shows that the actuation pulse can be designed, using a physical model, to effectively damp the residual oscillations. It is not always possible to obtain a good physical model for a single ink channel. A physical model for a multi-input multi-output (MIMO) inkjet printhead is made even more sophisticated by the presence of the cross-talk effect. This paper proposes a system identification-based approach to build a MIMO model for an inkjet printhead. Additionally, the identified MIMO model is used to design new actuation pulses to effectively minimize the residual oscillations and the cross-talk. Using simulation and experimental results, we demonstrate the efficacy of the proposed method.

We report a novel fabrication process for bimorph based electrothermal devices that involves surface and bulk micromachining on an SOI (silicon-on-insulator) wafer. The bimorph transducers consist of aluminum (Al)-–tungsten (W) beams with a thin layer of SiO₂ encapsulating the W-layer and electrically isolating it from the Al-layer. The widely different coefficients of thermal expansion (CTE) of Al and W ensure high bimorph sensitivity. The W-layer acts as an active layer of the bimorph and also as a resistive heater for actuation by Joule heating. Proof mass and rigid beams can be incorporated into the design by utilizing the device layer of the wafer. Thermal isolation between the bimorphs and the substrate; and between bimorphs and the proof mass or rigid beams is achieved by a spin-coated polyimide layer. The process ensures improved robustness compared to comparable designs that typically utilize SiO₂ thin-film for thermal isolation. The process can be adapted to a wide range of electrothermal devices, and enables design and layout engineers to trade off speed for achieving lower power consumption and vice versa. We report fabrication and test results on 1D (one-dimensional) electrothermal scanning micromirrors. The fabricated devices have significantly better robustness compared to previously reported mirrors with Al-SiO₂ bimorphs and SiO₂ thermal isolation.

This paper reports the process of creating bumps on the surface of polystyrene (PS) induced by a CO₂ laser at low powers. The paper also outlines the procedure for growing bumps induced by multiple laser scans on the aforementioned bumps. These bumps result from the net volume gain of the laser heat-affected zone on the PS rather than from a deposition process, and the expansion of the heat-affected zone on PS was verified by measuring the hardness change using nanoindentation. The bumps have a much smoother surface than microchannels fabricated with laser cutting; depending on the laser power, they have heights ranging from hundreds of nanometers to 42 µm. The laser scanning speed and scan times along with this technique offer a fast and low-cost alternative for fabricating molds for multi-depth PDMS microfluidic devices.

This research investigates the design, fabrication and testing of an easy-to-use and disposable microfluidic system for DNA amplification detection. This is suitable for point-of-care testing (POCT) applications. The microfluidic system utilizes biotin-labelled DNA to agglutinate streptavidin-coated microspheres. The microfluidic system is designed to retain aggregates of cross-linked microspheres as opposed to single microspheres, indicating the detection of biotin-labelled DNA. The microfluidic platform is composed of a filter design and inlet/outlet reservoirs, which was fabricated using microfabrication techniques. This research demonstrates that the microfluidic system is an improvement on the current DNA detection technique that uses particle agglutination. Such a system may, in turn, form the basis of future hand-held, compact, point-of-care biosensors for disease screening and identification.

We propose a modified flow focusing configuration to produce low-viscosity microjets at much smaller flow rates than those reached by the standard configuration. In the modified flow focusing device, a sharpened rod blocks the recirculation cell appearing in the tapering liquid meniscus for low flow rates, which considerably improves its stability. We measured the minimum flow rates attainable with the modified configuration and compared the results with the corresponding values for the standard technique. For moderate and large applied pressure drops, the minimum flow rate reached with the modified configuration was about five times smaller than its counterpart in the standard configuration. The Weber numbers of the jets produced with the modified flow focusing configuration were considerably smaller than those with the standard technique. Numerical simulations were conducted to show how the presence of the inner rod substantially changes the flow pattern in the liquid meniscus.

This paper presents the design and fabrication of batch-processed cantilever probes with electrical shielding for scanning microwave impedance microscopy. The diameter of the tip apex, which defines the electrical resolution, is less than 50 nm. The width of the stripline and the thicknesses of the insulation dielectrics are optimized for a small series resistance (<5 Ω) and a small background capacitance (∼1 pF), both critical for high sensitivity imaging on various samples. The coaxial shielding ensures that only the probe tip interacts with the sample. The structure of the cantilever is designed to be symmetric to balance the stresses and thermal expansions of different layers so that the cantilever remains straight under variable temperatures. Such shielded cantilever probes produced in the wafer scale will facilitate enormous applications on nanoscale dielectric and conductivity imaging.

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