Table of contents

This special section of Journal of Micromechanics and Microengineering features papers selected from the 11th International Workshop on Micro and Nanotechnology for Power Generation and Energy Conversion Applications (PowerMEMS 2011), held at Sejong Hotel in Seoul, Korea during 15–18 November 2011. Since the first PowerMEMS workshop held in Sendai, Japan in 2000, the workshop has developed as the premier forum for reporting research results in micro and nanotechnology for power generation, energy conversion, harvesting and processing applications, including in-depth technical issues on nanostructures and materials for small-scale high-density energy and thermal management. Potential PowerMEMS applications cover not only portable power devices for consumer electronics and remote sensors, but also micro engines, impulsive thrusters and fuel cells for systems ranging from the nanometer to the millimeter scale. The 2011 technical program consists of 1 plenary talk, 4 invited talks and 118 contributed presentations. The 48 oral and 70 poster presentations, selected by 27 Technical Program Committee Members from 131 submitted abstracts, have stimulated lively discussion maximizing the interaction between participants. Among them, this special section includes 9 papers covering micro-scale power generators, energy converters, harvesters, thrusters and thermal coolers. Finally, we are grateful to the members of the International Steering Committee, the Technical Program Committee, and the Local Organizing Committee for their efforts and contributions to PowerMEMS 2011. We also thank the two companies Samsung Electro-Mechanics and LG Elite for technical tour arrangements. Special thanks go to Dr Ian Forbes, the editorial staff of the Journal of Micromechanics and Microengineering, as well as to the staff of IOP Publishing for making this special section possible.

This paper reports on an integrated energy harvesting prototype that consists of dispenser-printed thermoelectric energy harvesting and electrochemical energy storage devices. Parallel-connected thermoelectric devices with low internal resistances were designed, fabricated and characterized. The use of a commercially available dc-to-dc converter was explored to step-up a 27.1 mV input voltage from a printed thermoelectric device to a regulated 2.34 V output at a maximum of 34% conversion efficiency. The regulated power succeeds in charging dispenser-printed, zinc-based micro-batteries with charging efficiencies of up to 67%. The prototype presented in this work demonstrates the feasibility of deploying a printable, cost-effective and perpetual power solution for practical wireless sensor network applications.

In previous research we have demonstrated a micro thermomechanical pyroelectric generator (µTMPG) as an alternative to thermoelectric generators to harvest ambient heat energy. In such a device, a thermal mass oscillates between a hot and a cold side by virtue of the bistability of its mechanical mount, thus generating a temporal thermal gradient over a pyroelectric material in between. The operational frequency as a major factor deciding the power output of the µTMPG is in turn dependent on the thermal contact resistance (TCR) present at the mating regions of thermal mass, hot and cold sides. Hence, we have investigated the incorporation of an array of Galinstan droplets at the mating interfaces to reduce the TCR. These arrays are fabricated by selective deposition of Galinstan on a laser-micromachined silicon substrate. After incorporating such an array the operational frequency of the µTMPG increases by at least 50%.

This paper reports the fabrication, characterization and modeling of microelectromechanical inductor (MEMI) devices, which employ electrodynamic coupling and mechanical energy storage to boost the apparent electrical inductance of electrical conductors. The microfabricated MEMI devices comprise an electrically conducting, mechanically suspended clamped–clamped copper beam that is placed in a transverse static magnetic field. Under an ac current excitation, the beam is forced to vibrate via the electrodynamic interactions between the electrical current and the static magnetic field. This electromechanical coupling results in a large apparent electrical inductance. The microfabrication and subsequent characterization of a variety of test structures is presented. The devices exhibit a peak quality factor up to 5.6 and net areal inductance densities of up to 3.5 µH mm⁻². The experimentally observed behavior is compared against theoretical models using extracted system parameters.

This paper presents the development of a micro-solid propellant thruster array with improved repeatability. The repeatability and low performance variation of each thruster unit with a high ignition success rate is essential in micro-solid propellant thruster array. To date, the study on the improvement of the repeatability has not yet been reported. As the first step for this study, we propose a new type of micro igniter, using a glass wafer called the heater-contact micro igniter. This igniter is also designed to improve the ignition characteristics of a glass-based micro igniter. The prototype of the igniter array is designed and fabricated to establish its fabrication process and to conduct its performance evaluation. Through the firing test, the performance of the heater-contact micro igniter is verified. The 5 × 5 sized micro-solid propellant thruster array is designed and fabricated applying the developed heater-contact igniter. The measured average thrust of each thruster unit is 2.542 N, and calculated standard deviation is 0.369 N. The calculated average total impulse and its standard deviation are 0.182 and 0.04 mNs, respectively. Based on these results, the improvement of repeatability is verified. Finally, the ignition control system of the micro-thruster array is developed.

This work gives experimental evidence of a promising method of thermal-to-electric energy conversion by coupling shape memory effect (SME) and direct piezoelectric effect (DPE) for harvesting quasi-static ambient temperature variations. Two original prototypes of thermal energy harvesters have been fabricated and tested experimentally. The first is a hybrid laminated composite consisting of TiNiCu shape memory alloy (SMA) and macro fiber composite piezoelectric. This composite comprises 0.1 cm³ of active materials and harvests 75 µJ of energy for each temperature variation of 60 °C. The second prototype is a SME/DPE 'machine' which uses the thermally induced linear strains of the SMA to bend a bulk PZT ceramic plate through a specially designed mechanical structure. The SME/DPE 'machine' with 0.2 cm³ of active material harvests 90 µJ over a temperature increase of 35 °C (60 µJ when cooling). In contrast to pyroelectric materials, such harvesters are also compatible with both small and slow temperature variations.

We have integrated carbon felt, a traditional fuel cell gas diffusion layer, with silicon micro fuel cells. To this end we used two silicon microfabrication procedures using reactive ion etching: formation of black silicon and sinking of flowfield. The former decreases electrical contact resistance to the diffusion layer, the latter serves to contain the reactant gases. The micro fuel cells, where the flowfield was covered by black silicon nano-needles, showed better performance (127 mW cm⁻²) compared to the same cells without black silicon (114 mW cm⁻²). The black silicon fuel cells were also more stable during an overnight chronoamperometric measurement.

We describe the fabrication and characterization of a significantly improved version of a microelectromechanical system-based PZT/PZT thick film bimorph vibration energy harvester with an integrated silicon proof mass; the harvester is fabricated in a fully monolithic process. The main advantage of bimorph vibration energy harvesters is that strain energy is not lost in mechanical support materials since only Pb(Zr_xTi_1-x)O₃ (PZT) is strained; as a result, the effective system coupling coefficient is increased, and thus a potential for significantly higher output power is released. In addition, when the two layers are connected in series, the output voltage is increased, and as a result the relative power loss in the necessary rectifying circuit is reduced. We describe an improved process scheme for the energy harvester, which resulted in a robust fabrication process with a record high fabrication yield of 98%. The robust fabrication process allowed a high pressure treatment of the screen printed PZT thick films prior to sintering. The high pressure treatment improved the PZT thick film performance and increased the harvester power output to 37.1 μW at 1 g root mean square acceleration. We also characterize the harvester performance when only one of the PZT layers is used while the other is left open or short circuit.

A solid-state micro magnetic refrigerator (SSMMR) has some advantages to cool microdevices because of its high efficiency and simple structure. In this study, we demonstrated the actual cooling of a thermally-isolated microstructure, which is a main component of the SSMMR, by the magnetocaloric effect. The thermal isolation structure is composed of parylene high-aspect-ratio beams for both high thermal isolation and high stiffness. A magnetic field switch was designed and fabricated to control the magnetic flux density from 0 T to about 1 T. Under this magnetic flux density change, the maximum temperature change of 1.0 °C was confirmed.

In this paper, harvesters coupling magnetostrictive and piezoelectric materials are investigated. The energy conversion of quasi-static magnetic field variations into electricity is detailed. Experimental results are exposed for two macroscopic demonstrators based on the rotation of a permanent magnet. These composite/hybrid devices use both piezoelectric and magnetostrictive (amorphous FeSiB ribbon or bulk Terfenol-D) materials. A quasi-static (or ultra-low frequency) harvester is constructed with exploitable output voltage, even in quasi-static mode. Integrated micro-harvesters using sub-micron multilayers of active materials on Si have been built and are currently being characterized.

We present a waved microchannel for continuous focusing of microparticles and cells using negative direct current (dc) dielectrophoresis. The waved channel is composed of consecutive s-shaped curved channels in series to generate an electric field gradient required for the dielectrophoretic effect. When particles move electrokinetically through the channel, the experienced negative dielectrophoretic forces alternate directions within two adjacent semicircular microchannels, leading to a focused continuous-flow stream along the channel centerline. Both the experimentally observed and numerically simulated results of the focusing performance are reported, which coincide acceptably in proportion to the specified dimensions (i.e. inlet and outlet of the waved channel). How the applied electric field, particle size and medium concentration affect the performance was studied by focusing polystyrene microparticles of varying sizes. As an application in the field of biology, the focusing of yeast cells in the waved mcirochannel was tested. This waved microchannel shows a great potential for microflow cytometry applications and is expected to be widely used before different processing steps in lab-on-a-chip devices with integrated functions.

Determining the interfacial adhesion of ultrathin functional films in micro-electro-mechanical systems (MEMS) and nano-electro-mechanical systems (NEMS) becomes increasingly crucial for optimal design of MEMS/NEMS devices. However, direct measurement of adhesion properties of ultrathin films can be challenging, as the traditional metrology of adhesion at macroscopic scales becomes unsuitable in dealing with samples of extremely small dimension. In this paper, we present a feasible and robust approach combining nano-transfer printing (nTP) experiments and mechanics modeling to quantitatively determine the interfacial adhesion of submicron thin films. We show that the measurements of the interfacial adhesion of a submicron polycarbonate (PC) thin film on a PC substrate at multiple locations in multiple samples agree within 7.3%, demonstrating the accuracy and robustness of our approach. Given the versatility of the nTP process, the approach demonstrated in this paper is expected to be generally applicable to measure the adhesion of interfaces of other material combinations. In this sense, this study sheds light on better understanding of the adhesive properties of functional interfaces in MEMS and NEMS.

In this paper, we present a theoretical and experimental investigation into the dynamic response of an electrostatically actuated microbeam when subjected to drop-table test. For the theoretical part, a reduced-order model based on an Euler–Bernoulli beam model is utilized. The model accounts for the electrostatic bias on the microbeam and the shock pulse of the drop-table test. Simulation results are presented showing the combined effect of electrostatic force and mechanical shock in triggering early pull-in instability of the cantilever microbeams. The analytical simulation results are validated by finite-element results for the static response. Dynamic pull-in threshold as a function of the mechanical shock amplitude is shown over a wide range of shock spanning hundreds of thousands of g up to zero g. For the experimental part, a micromachined cantilever beam made of gold of length 50 µm is subjected to drop-table tests while being biased by electrostatic loads. Several experimental data are shown demonstrating the phenomenon of collapse due to the combined shock and electrostatic forces. It is also demonstrated that by biasing short and too stiff microbeams with electrostatic voltages, their stiffness is weakened. This lowers their threshold of collapse considerably to the range of acceleration that enables testing them with in-house shock testing equipments, such as drop-table tests.

This paper presents the design, fabrication and measurement of the first pull-in free tunable evanescent-mode microwave resonator based on arrays of electrostatically actuated fringing-field RF-MEMS tuners. Electrostatic fringing-field actuation (EFFA) is the key on achieving a wide tunable frequency range that is not limited by the conventional pull-in instability. Furthermore, total lack of dielectric layers and no overlap between the pull-down electrode and movable beams significantly enhance the robustness of our proposed tuning mechanism by making it devoid of dielectric charging and stiction and amenable to high-yield manufacturing. The proposed electrostatic fringing-field tuners are demonstrated in a highly loaded evanescent-mode cavity-based resonator. The measured unloaded quality factor is 280–515 from 12.5 to 15.5 GHz. In addition, a 10× improvement in switching time is demonstrated for the first time for EFFA tuners in a tunable microwave component by employing dc-dynamic biasing waveforms. With dynamic biasing, the measured up-to-down and down-to-up switching times of the resonator are 190 and 148 μs, respectively. On the other hand, conventional step biasing results in switching times of 5.2 and 8 ms for up-to-down and down-to-up states, respectively.

The principal aim of this work was to characterize deep silicon etching at sample temperatures well below room temperature, using an SF₆/O₂ inductively coupled plasma for micro-electro-mechanical systems applications. In this paper, a study of the etch rates and etch profiles of deep silicon trenches has been undertaken for a series of etching parameters, including RF power, sample stage temperature and O₂ gas flow rate. Based on the experimental observations, the formation of an SiO_xF_y passivation layer, the rate of ion collision through the sheath field and the silicon crystallographic orientation are found to be the three main parameters that affect the etching process. In addition, the formation mechanism of 'black silicon' (nanopillar-based Si structures) has also been proposed based on the experimental data and a simple physical model. For the purpose of silicon bulk micromachining, an optimized recipe has been developed that is suitable for the fabrication of high aspect ratio Si cantilevers on silicon-on-insulator-based waveguide wafers.

A single-sheet backlight unit (BLU) for a liquid crystal display (LCD) with improved light extraction efficiency was developed. A new microstructure on the light-guide plate (LGP), namely a merged-dot pattern, is proposed. The effective emission area was significantly increased by using the proposed light-extracting structure, resulting in high light extraction efficiency. Through optical simulation, we investigated the effect of the enlarged emission area on the luminance and vertical light emitting performance of the single-sheet LGP. Then, in order to verify the simulation result, we fabricated a polydimethylsiloxane (PDMS) LGP containing the proposed light-extracting microstructure by using backside 3D diffuser lithography and the PDMS replication processes. The fabricated single-sheet BLU showed an average luminance of 4197 cd m⁻² with four 0.97 cd LEDs, corresponding to 27.8% enhancement over the LGP without the merged-dot patterns.

We report on the fabrication and characterization of electrostatic gas micro-pumps integrated with polyimide check valves. Touch-mode capacitance actuation, enabled by a fixed silicon electrode and a metal/polyimide diaphragm, creates the suction and push-out of the ambient gas; the gas flow is rectified by the check valves located at the inlet and outlet of the pump. The fabricated pumps were tested with various actuation voltages at different frequencies and duty cycles; an emphasis was placed on investigating the effect of valve flow conductance on the gas pumping characteristics. The pump with higher valve conductance could increase the operating frequency of the pump and affect the pumping characteristics from a pulsating flow to a continuous flow, leading to a higher gas flow rate. This electrostatic pump has a flow control resolution of 1 µL min⁻¹; it could generate a gas flow up to 106 µL min⁻¹.

Silicon nanowire (SiNW)-based cantilever flow sensors with three different cantilever sizes (10 × 50, 20 × 90 and 40 × 100 µm²) and various SiNW lengths (2, 5 and 10 µm) have been designed for air velocity sensing. The total device thickness is around 3 µm, which consists of the bottom SiO₂ layer (0.5 µm) and the top SiN_x layer (2.5 µm). In addition, the SiN_x layer is used to compensate the initial stress and also enhance the device immunity to air-flow-induced vibrations significantly. To experience the maximum strain induced by the air flow, SiNWs are embedded at the clamp point where the cantilever is anchored to the substrate. Taking advantage of the superior properties of SiNWs, the reported flow sensor shows outstanding air-flow-sensing capability in terms of sensitivity, linearity and hysteresis. With only a supply voltage of 0.1 V and the high initial resistance of the piezoresistive SiNWs, significant energy saving is reached in contrast to the thermal-based flow sensors as well as other recently reported piezoresistive designs. Last but not least, the significant size reduction of our device demonstrates the great scalability of SiNW-based flow sensors.

Caenorhabditis elegans is a well-established model organism and has been gaining interest particularly related to worm locomotion and the investigation of the relationship between muscle arms and the motion pattern of the nematode. In this paper, we report on a micropillar-based on-chip system which is capable of quantifying multi-point locomotive forces of a moving C. elegans. A Polydimethylsiloxane (PDMS) device was microfabricated to allow C. elegans to move in a matrix of micropillars in a channel, and an image processing method was developed to resolve the worm force from the bending pillars. The current micropillar-based system is able to measure force with a resolution of 2.07 µN for body width of 80 µm. Initial experiments have been conducted to collect a maximum force level for thirteen wild type worm samples. A maximum force level of 61.94 µN was observed from 1571 data points, based on which an average maximum force level was 32.61 µN for multi-point measurements. The demonstrated capabilities of the system can be an enabling technology that allows biologist to gain a better understanding of subtle force patterns of C. elegans and worm muscle development.

The glass-based low-temperature polycrystalline-silicon (LTPS) thin-film transistor (TFT) process, widely known for making liquid crystal displays, is utilized in this work to realize a fully integrated, microbead-based micro-manipulation and biosensing platform. The operation utilizes arrays of microelectrodes made of transparent iridium tin oxide (ITO) to move the immobilized polystyrene microbeads to the sensor surface by dielectrophoresis (DEP). Detection of remaining microbeads after a specific antigen/antibody reaction is accomplished by photo-detectors under the transparent electrodes. It was found that microbeads can be driven successfully by the 30 × 30 µm² microelectrodes separated by 10 µm with no more than 6 V_p–p, which is compatible with the operating range of thin-film transistors. Microbeads immobilized with antimouse immunoglobulin (IgG) and prostate-specific antigen (PSA) antibody were successfully detected after specific binding, illustrating the potential of LTPS TFT microarrays for more versatile biosensing applications.

This paper describes the study of the conventional silicon/glass anodic bonding with plasma enhanced chemical vapor deposited silicon carbide (PE-SiC) as the intermediate layer, in order to evaluate the feasibilities of applying PE-SiC as the device's passivation layer prior to the packaging bonding and construction layer based on the bond-and-transfer technique. It is found that the mechanism of this bonding is similar to the traditional anodic bonding. As the PE-SiC thickened, the bond strength declined; meanwhile, the leak rate remained at the same level with the silicon/glass bonding. Further experiments revealed that the bonding increased the interlayer's tensile stress by 70.7 MPa and diminished the stress gradient by 24.6 MPa µm⁻¹.

We present high-speed force probes with on-chip actuation and sensing for the measurement of pN-scale forces at the microsecond timescale. We achieve a high resonant frequency in water (1–100 kHz) with requisite low spring constants (0.3–40 pN nm⁻¹) and low integrated force noise (1–100 pN) by targeting probe dimensions on the order of 300 nm thick, 1–2 μm wide and 30–200 μm long. Forces are measured using silicon piezoresistors, while the probes are actuated thermally with an aluminum unimorph and silicon heater. The piezoresistive sensors are designed using the open-source numerical optimization code that incorporates constraints on operating temperature. Parylene passivation enables operation in ionic media and we demonstrate simultaneous actuation and sensing. The improved design and fabrication techniques that we describe enable a 10–20-fold improvement in force resolution or measurement bandwidth over prior piezoresistive cantilevers of comparable thickness.

A zirconia microelectromechanical-system-based microthruster was fabricated through a newly developed fabrication route. Gel casting of homogenously dispersed zirconia suspension on polydimethylsiloxane soft mold was utilized to replicate the geometries of microthruster design onto a ceramic layer of about 1.2 mm thick. Lamination of the patterned ceramic layer to another flat ceramic layer and subsequent sintering produced the microthruster. Characterizations on the fabricated prototype showed good shape retention on the replicated geometries and good quality of lamination. Shrinkage of about 10–15% was noted after sintering. The current fabrication route is particularly promising for the development of high-performance micropropulsion systems which require their structural material to survive in an extreme environment which is corrosive, of high temperature and highly oxidative.

A double-sided wet etch process has been proposed to fabricate vertical structures in 〈1 0 0〉 oriented silicon substrate. Both sides of a {1 0 0} silicon wafer have been patterned identically along the 〈1 1 0〉 direction, and etched using potassium hydroxide (KOH) solution. By precisly controlling the etch time, using etch-timer structure and additive control, structures with smooth and vertical {1 1 0} sidewalls have been fabricated at the edges of a rectangular opening without undercut. Rectangular through-holes, bridges and cantilevers have been constructed using the proposed process. The measured average surface roughness of the vertical sidewall was 481 nm, which has been further reduced to 217 nm and 218 nm by postetching using a KOH–IPA and TMAH–Triton mixture, respectively. Slanted {4 1 1} planes exposed at the concave corners during the vertical etch process have been successfully removed or diminished by the postetching process. A bridge structure with a high aspect ratio of 39:1 has been fabricated, and cantilevers without undercutting were successfully constructed by applying the compensation technique. The proposed process can potentially be utilized in place of the deep reactive ion etching process for the fabrication of structures having vertical through-holes, such as through-silicon vias, high aspect ratio springs and filters for microfluidic applications.

In this paper, a particle counting system using a CMOS image sensor is demonstrated. The system utilizes a linear photodetector array as a detection element. Therefore, the particles are detected by multiple detectors simultaneously, in contrast to a single detector in conventional particle counting devices, while maintaining the sensitivity. Another advantage of the proposed system is that particles are detected across the full-channel width which removes the need for a particle-focusing method. Also, the proposed system can easily be integrated with a microfluidic chip fabricated on a transparent substrate, as the counting system is attached under the microchannel and counts the particles optically. Detection of polystyrene microbeads has been tested at a flow rate of 5.15 mm s⁻¹. For 21 measurements, the proposed system showed an average count error of 4.56% and a standard deviation of 3.06% using a proposed compensation algorithm. Potentially, the proposed system can detect even smaller particles simply by utilizing a higher resolution CMOS image sensor.

Differential vibrating accelerometer (DVA) is a resonant-type sensor which detects the change in the resonant frequency in the presence of acceleration input, i.e. inertial loading. However, the resonant frequency of micromachined silicon resonators is sensitive to the temperature change as well as the input acceleration. Therefore, to design a high-precision vibrating accelerometer, the temperature sensitivity of the resonant frequency has to be predicted and compensated accurately. In this study, a temperature compensation method for resonant frequency is proposed which controls the electrostatic stiffness of the dual-ended tuning fork (DETF) using the temperature-dependent dc voltage between the parallel plate electrodes. To do this, the electromechanical model is derived first to predict the change in the electrostatic stiffness and the resonant frequency resulting from the dc voltage between the resonator and the electrodes. Next, the temperature sensitivity of the resonant frequency is modeled, estimated and compared with the measured values. Then it is shown that the resonant frequency of the DETF can be kept constant in the operating temperature range by applying the temperature-dependent driving voltage to the parallel plate electrodes. The proposed method is validated through experiment.

High aspect ratio solid silicon microneedles with a concave conic shape were fabricated. Hydrofluoric acid–nitric acid–acetic acid (HNA) etching parameters were characterized and optimized to produce microneedles that have long and narrow bodies with smooth surfaces, suitable for transdermal drug delivery applications. The etching parameters were characterized by varying the HNA composition, the optical mask's window size, the etching temperature and bath agitation. An L9 orthogonal Taguchi experiment with three factors, each having three levels, was utilized to determine the optimal fabrication parameters. Isoetch contours for HNA composition with 0% and 10% acetic acid concentrations were presented and a high nitric acid region was identified to produce microneedles with smooth surfaces. It is observed that an increase in window size indiscriminately increases the etch rate in both the vertical and lateral directions, while an increase in etching temperature beyond 35 °C causes the etching to become rapid and uncontrollable. Bath agitation and sample placement could be manipulated to achieve a higher vertical etch rate compared to its lateral counterpart in order to construct high aspect ratio microneedles. The Taguchi experiment performed suggests that a HNA composition of 2:7:1 (HF:HNO₃:CH₃COOH), window size of 500 µm and agitation rate of 450 RPM are optimal. Solid silicon microneedles with an average height of 159.4 µm, an average base width of 110.9 µm, an aspect ratio of 1.44, and a tip angle and diameter of 19.2° and 0.38 µm respectively were successfully fabricated.

Optical filters for blocking ultraviolet (UV) light were fabricated by doping various polymer hosts with a UV absorbing chromophore. The polymers were polydimethylsiloxane (PDMS), a silicone elastomer frequently used in microfluidics, SU-8, a photopatternable epoxy, and Humiseal 1B66, an acrylic coating used for moisture protection of integrated circuits. The chromophore was 2-(2'-hydroxy-5'-methylphenyl) benzotriazole (BTA), which has a high extinction coefficient between 300 nm and 400 nm. We demonstrate filters 5 µm thick that exhibit high ultraviolet rejection (nearly −40 dB at 342 nm) yet pass visible light (near 0 dB above 400 nm), making them ideal for ultraviolet-excited fluorescence sensing within microsystems. The absorbance of the BTA depended on the host polymer. These filters are promising for integrated fluorescence spectroscopy in bioanalytical platforms because they can be patterned by dry etching, molding or exposure to ultraviolet light.

Novel cost-effective methods for polymeric and metallic nanochannel fabrication have been demonstrated using an electrospun nanofiber array. Like other electrospun nanofiber-based nanofabrication methods, our system also showed high throughput as well as cost-effective performances. Unlike other systems, however, our fabrication scheme provides a pseudo-parallel nanofiber array a few centimeters long at a speed of several tens of fibers per second based on our unique inclined-gap fiber collecting system. Pseudo-parallel nanofiber arrays were used either directly for the PDMS molding process or for the metal lift-off process followed by the SiO₂ deposition process to produce the nanochannel array. While the PDMS molding process was a simple fabrication based on one-step casting, the metal lift-off process followed by SiO₂ deposition allowed finetuning on height and width of nanogrooves down to subhundred nanometers from a few micrometers. Nanogrooves were covered either with cover glass or with PDMS slab and nanochannel connectivity was investigated with a fluorescent dye. Also, nanochannel arrays were used to investigate mobility and conformations of λ-DNA.

An array of pulse-driven magnetostatic micro-actuators with 2 mm pitch is proposed for highly deformable active surfaces. A wide range of applications can benefit from such devices, from droplet manipulation and active flow control to tactile display, for which this device was initially designed. This design ensures robustness, ease of fabrication and mass production compatibility. The device is composed of an array of 4 × 4 highly resistant elastomeric membranes achieved using microfabrication techniques. The magnetostatic actuation system is based on the interaction between a miniature coil and a SmCo micro-magnet. This mechanism was optimized by the finite-element method, leading to the introduction of different ferromagnetic circuits. Mechanical characterizations were achieved by laser interferometry. The micro-actuators can be used either in continuous mode or in pulse mode, allowing wide bandwidth, from dc to 1.5 kHz, and vibration amplitudes up to 150 μm for instantaneous forces of 30 mN. The device has good actuation homogeneity with ±20% amplitude variations between its actuators; low crosstalk (<5%) was also demonstrated. Finally, an improved actuation design benefiting from electroplated NiFe thin films is proposed and characterized, increasing performances (forces and displacements) by 50%.

A mold used in creating diffractive optical elements significantly affects the quality of these devices. In this study, we improved traditional microlens fabrication processes, which have shortcomings, mainly by combining gas-assisted imprint technology and the lithographie galvanoformung abformung (LIGA)-like process. This combination resulted in the production of high-quality optical components with high replication rates, high uniformity, large areas and high flexibility. Given the pixel size of the panel used, the optimal viewing distance, the film thickness and the glass thickness in the formula, we could determine the radius of curvature and the thickness of the lens. By the use of U-groove machining, precise electroforming and embossing to produce polydimethylsiloxane (PDMS) molds, lens film elements can be produced via an ultraviolet (UV)-cured molding process that converts microlenses into flexible polyethylene terephthalate films. In this study, the microlenticular lens mold is fabricated by U-groove machining, Ni electroforming and PDMS casting. Then, the PDMS mold with microlenticular lens structure is used in the gas-assisted UV imprint process and the PET film with microlenticular lens array is obtained. The lenticular lens had a radius of curvature and height of 228 and 18 µm, respectively. A 3D confocal laser microscope was used to measure the radius of curvature and the spacing of the metal molds, nickel (Ni) molds, PDMS molds and the finished thin-film products. The geometry of the final microlenticular lens was very close to the design values. All geometric errors were below 5%, the surface roughness reached the optical level (with all Ra values less than 10 nm) and the replication rate was 95%. The results demonstrate that this process can be used to fabricate gapless, lenticular-shaped, high-precision microlens arrays with a unitary curvature.

The standard lithographic techniques to fabricate electronic components involve the use of polymers, baking steps and chemicals. This typically restricts their application to flat substrates made up of standard materials. Stencil lithography has been proposed as a stable alternative to the standard lithographic techniques. In this paper, we demonstrate the completely resistless all-through-stencil fabrication of electronic components, by performing all essential fabrication steps—implantation, etching and metallization—using stencil lithography. This is performed on a planar substrate as well as on pre-patterned 3D substrates, thus showing the potential of this technique for applications in the field of accelerometers, pressure, gas and radiation sensors.

This paper presents a multi-electrode and pre-deformed bilayer spring structure electrostatic attractive microelectromechanical systems (MEMS) actuator; it has large stroke at relatively low actuation voltage. Generally, electrostatic-attractive-force-based actuators have small stroke due to the instability resulted from the electrostatic 'pull-in' phenomenon. However, in many applications, the electrostatic micro-actuator with large stroke at low voltage is more preferred. By introducing a multi-electrode and a pre-deformed bilayer spring structure, an electrostatic attractive MEMS actuator with large stroke at very low actuation voltage has been successfully demonstrated in this paper. The actuator contains a central plate with a size of 300 µm × 300 µm × 1.5 µm and it is supported by four L-shaped bilayer springs which are pre-deformed due to residual stresses. Each bilayer spring is simultaneously attracted by three adjacent fixed electrodes, and the factors affecting the electrostatic attractive force are analyzed by a finite element analysis method. The prototype of the actuator is fabricated by poly-multi-user-MEMS-process (PolyMUMP) and the static performance is tested using a white light interferometer. The measured stroke of the actuator reaches 2 µm at 13 V dc, and it shows a good agreement with the simulation.

We describe a new class of electrostatic actuators with a compliant electrode made of liquid metal alloy contained by a thin elastomeric membrane. We illustrate the use of such actuators as on-chip microvalves for gas flow control. The microvalve comprises of one fixed electrode spanning the floor and sidewalls of the trapezoidal gas channel and one corresponding flexible electrode suspended across the channel. Details of fabrication and preliminary characterization of on/off and proportional valving are presented.

In this paper, the adhesion of SU-8 and Epoclad polymers to silicon substrates is quantified as an energy release rate, and the effect of a chromium coating as an adhesion promoter is studied. The intention is to quantify the adhesion strength for processing parameters that were previously optimized to yield good adhesion for various patterns and layer thicknesses. To do so, a custom tool is built to measure the force to shear off a square button of the epoxy from the substrate. Silicon and the silicon wafers coated with chromium were used as a substrate. Fracture mechanics is used to model this test and an energy release rate for different combinations of epoxies and substrates is determined. The energy release rates between SU-8 and Si and between SU-8 and Cr are measured to be 1.7×10² ± 0.3×10² J m⁻² and 2.6×10² ± 0.5×10² J m⁻², respectively. The energy release rates between Epoclad and Si and between Epoclad and Cr were determined to be 2.8×10² ± 0.4×10² J m⁻² and 35 ± 6 J m⁻², respectively.