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Showing papers in "Journal of Micromechanics and Microengineering in 2012"


Journal ArticleDOI
TL;DR: In this article, a description of the key properties of a MEMS resonator that determine the overall performance of the MEMS oscillator is given and an overview is given of methods that have been demonstrated to improve the frequency stability.
Abstract: MEMS-based oscillators are an emerging class of highly miniaturized, batch manufacturable timing devices that can rival the electrical performance of well-established quartz-based oscillators. In this review, a description is given of the key properties of a MEMS resonator that determine the overall performance of a MEMS oscillator. Piezoelectric, capacitive and active resonator transduction methods are compared and their impact on oscillator noise and power dissipation is explained. An overview is given of the performance of MEMS resonators and MEMS-based oscillators that have been demonstrated to date. Mechanisms that affect the frequency stability of the resonator, such as temperature-induced frequency drift, are explained and an overview is given of methods that have been demonstrated to improve the frequency stability. The aforementioned performance indicators of MEMS-based oscillators are benchmarked against established quartz and CMOS technologies.

399 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used thermoplastic biomaterial polycaprolactone (PCL) as a framework for enhancing the mechanical stability of a 3D bioprinted construct.
Abstract: The aim of this study was to build a mechanically enhanced three-dimensional (3D) bioprinted construct containing two different cell types for osteochondral tissue regeneration. Recently, the production of 3D cell-laden structures using various scaffold-free cell printing technologies has opened up new possibilities. However, ideal 3D complex tissues or organs have not yet been printed because gel-state hydrogels have been used as the principal material and are unable to maintain the desired 3D structure due to their poor mechanical strength. In this study, thermoplastic biomaterial polycaprolactone (PCL), which shows relatively high mechanical properties as compared with hydrogel, was used as a framework for enhancing the mechanical stability of the bioprinted construct. Two different alginate solutions were then infused into the previously prepared framework consisting of PCL to create the 3D construct for osteochondral printing. For this work, a multi-head tissue/organ building system (MtoBS), which was particularly designed to dispense thermoplastic biomaterial and hydrogel having completely different rheology properties, was newly developed and used to bioprint osteochondral tissue. It was confirmed that the line width, position and volume control of PCL and alginate solutions were adjustable in the MtoBS. Most importantly, dual cell-laden 3D constructs consisting of osteoblasts and chondrocytes were successfully fabricated. Further, the separately dispensed osteoblasts and chondrocytes not only retained their initial position and viability, but also proliferated up to 7?days after being dispensed.

354 citations


Journal ArticleDOI
TL;DR: An integrated functional contact lens, composed of a differential glucose sensor module, metal interconnects, sensor read-out circuit, antenna and telecommunication circuit, to monitor tear glucose levels wirelessly, continuously and non-invasively is presented.
Abstract: We present an integrated functional contact lens, composed of a differential glucose sensor module, metal interconnects, sensor read-out circuit, antenna and telecommunication circuit, to monitor tear glucose levels wirelessly, continuously and non-invasively. The electrochemical differential sensor module is based on immobilization of activated and de-activated glucose oxidase. We characterized the sensor on a model polymer eye and determined that it showed good repeatability, molecular interference rejection and linearity in the range of 0–2 mM glucose, covering normal tear glucose concentrations (0.1–0.6 mM). We also report the temperature, ageing and protein-fouling sensitivity of the sensor. We report the design and implementation of a low-power (3 µW) sensor read-out and telecommunication circuit to deliver wireless power and transmit data for the sensor module. Using this small chip (0.36 mm2), we produced an integrated contact lens with sensors and demonstrated wireless operation of the system and glucose read-out over the distance of several centimeters.

192 citations


Journal ArticleDOI
TL;DR: In this paper, the authors presented a fabrication process based on printed circuit board manufacturing techniques for creating monolithic, topologically complex, three-dimensional machines in parallel at the millimeter to centimeter scales.
Abstract: Silicon-based MEMS techniques dominate sub-millimeter scale manufacturing, while a myriad of conventional methods exist to produce larger machines measured in centimeters and beyond. So-called mesoscale devices, existing between these length scales, remain difficult to manufacture. We present a versatile fabrication process, loosely based on printed circuit board manufacturing techniques, for creating monolithic, topologically complex, three-dimensional machines in parallel at the millimeter to centimeter scales. The fabrication of a 90?mg flapping wing robotic insect demonstrates the sophistication attainable by these techniques, which are expected to support device manufacturing on an industrial scale.

179 citations


Journal ArticleDOI
TL;DR: In this article, a magnetoelectric (ME) composite was used for the measurement of biomagnetic signals in the pico-and femtotesla regime superconducting interference devices (SQUIDs).
Abstract: For the measurement of biomagnetic signals in the pico- and femtotesla regime superconducting interference devices (SQUIDs) are commonly used. Their major limitation comes from helium cooling which makes these sensors bulky and expensive. We show that MEMS sensors based on magnetoelectric (ME) composites could be capable as a replacement for biomagnetic measurements. Using surface micromachining processes a cantilever beam with a stack composed of SiO2/Ti/Pt/AlN/Cr/FeCoSiB was fabricated on a 150 mm Si (1 0 0) wafer. First measurements of a rectangular micro cantilever with a thickness of 4 µm and lateral dimensions of 0.2 mm × 1.12 mm showed a giant ME coefficient αME = 1000 (V m−1)/(A m−1) in resonance at 2.4 kHz. The resulting static ME coefficient is αME = 14 (V m−1)/(A m−1). In resonance operation a sensitivity of 780 V T−1 and noise levels as low as 100 pT Hz−1/2 have been reached.

131 citations


Journal ArticleDOI
TL;DR: In this article, the fabrication of nanostructured substrates with precisely controlled geometries and arrangements plays an important role in studies of surface-enhanced Raman scattering (SERS).
Abstract: The fabrication of nanostructured substrates with precisely controlled geometries and arrangements plays an important role in studies of surface-enhanced Raman scattering (SERS). Here, we present two processes based on electron-beam lithography to fabricate gold nanostructures for SERS. One process involves making use of metal lift-off and the other involves the use of the plasma etching. These two processes allow the successful fabrication of gold nanostructures with various kinds of geometrical shapes and different periodic arrangements. 4-mercaptopyridine (4-MPy) and Rhodamine 6G (R6G) molecules are used to probe SERS signals on the nanostructures. The SERS investigations on the nanostructured substrates demonstrate that the gold nanostructured substrates have resulted in large SERS enhancement, which is highly dependent on the geometrical shapes and arrangements of the gold nanostructures.

128 citations


Journal ArticleDOI
TL;DR: In this paper, a differential pressure sensor using a piezoresistive cantilever with the dimensions of 125?m?100?m?0.3?m was presented.
Abstract: This paper reports on a differential pressure sensor using a piezoresistive cantilever with the dimensions of 125 ?m?100 ?m?0.3 ?m. The sensor has a higher sensitivity than a traditional diaphragm sensor because of the three free edges of the cantilever. The measured results indicated that the fabricated cantilever bent according to theory when differential pressure was applied. The sensitivity and resolution of the differential pressure were 3.2?10?4?Pa?1?and 0.02 Pa from??20 Pa to 20 Pa, respectively.

123 citations


Journal ArticleDOI
TL;DR: In this article, a simple and effective method without vacuum to control the wetting properties of AISI 316L stainless steel using femtosecond laser pulses at high repetition rate has been developed.
Abstract: A simple and effective method without vacuum to control the wetting properties of AISI 316L stainless steel using femtosecond laser pulses at high repetition rate has been developed. Both hydrophilic and hydrophobic surfaces were formed by creating micro-conical structures on the surface with femtosecond laser irradiation in air. The scan speed was found to be an effective parameter in controlling micro-cone morphology, size and number densities and contact angles during surface wettability experiments. It was found during surface wettability experiments that the contact angle of water varied from 0? (superhydrophilic) to 113? on laser micro-cone textured surfaces depending on processing conditions. Additionally, a superhydrophobic AISI 316L stainless steel surface was created (contact angle ?150?) with a functionalized silane coating on already hydrophobic surface geometry.

121 citations



Journal ArticleDOI
TL;DR: In this paper, a comprehensive review of the reliability issues hampering capacitive RF MEMS switches in their development toward commercialization is presented, and a recipe for a conceptual 'ideal' switch from a reliability point of view, based on the lessons learned.
Abstract: This paper presents a comprehensive review of the reliability issues hampering capacitive RF MEMS switches in their development toward commercialization. Dielectric charging and its effects on device behavior are extensively addressed, as well as the application of different dielectric materials, improvements in the mechanical design and the use of advanced actuation waveforms. It is concluded that viable capacitive RF MEMS switches with a great chance of market acceptance preferably have no actuation voltage across a dielectric at all, contrary to the ‘standard’ geometry. This is substantiated by the reliability data of a number of dielectric-less MEMS switch designs. However, a dielectric can be used for the signal itself, resulting in a higher Con/Coff ratio than that one would be able to achieve in a switch without any dielectric. The other reliability issues of these devices are also covered, such as creep, RF-power-related failures and packaging reliability. This paper concludes with a recipe for a conceptual ‘ideal’ switch from a reliability point of view, based on the lessons learned.

103 citations


Journal ArticleDOI
TL;DR: In this article, a stretchable electrical interconnections are realized by patterning a 200 nm thick sputter-deposited gold film into meandering horseshoe shapes, functioning as "two-dimensional springs" when embedded in a silicone elastomer.
Abstract: A new fabrication technology for stretchable electrical interconnections is presented. This technology can be used to connect various non-stretchable polyimide islands hosting conventional electronic components. The interconnections are realized by patterning a 200 nm thick sputter-deposited gold film into meandering horseshoe shapes, functioning as 'two-dimensional springs' when embedded in a silicone elastomer. Polyimide support is introduced around the meandering conductors as a means to improve the mechanical performance. Processing is done on a temporary carrier; the islands and interconnections are embedded in polydimethylsiloxane in a final stage. To this end, a release technique compatible with high temperatures up to 350 based on the evaporation of a 400 nm thick layer of potassium chloride is developed. Test structures consisting of stretchable interconnections with a varying polyimide support width were fabricated. These were strained up to twice their original length without compromising their functionality. Also cyclic mechanical loading at various strains was performed, indicating the influence of the polyimide support width on the lifetime. At strains of 10%, a minimum lifetime of 500 000 cycles is demonstrated. The presented technology thus provides a promising route towards the fabrication of stretchable electronic circuits with enhanced reliability.

Journal ArticleDOI
TL;DR: In this paper, the authors used the micro injection molding process to replicate micro/nano-scale channels and ridges from a bulk metallic glass (BMG) cavity insert.
Abstract: The development of MEMS and microsystems needs a reliable mass production process to fabricate micro components with micro/nano-scale features. In our study, we used the micro injection molding process to replicate micro/nano-scale channels and ridges from a bulk metallic glass (BMG) cavity insert. High-density polyethylene was used as the molding material and the design of experiment approach was adopted to systematically and statistically investigate the relationship between machine parameters, real process conditions and replication quality. The peak cavity pressure and temperature were selected as process characteristic values to describe the real process conditions that the material experienced during the filling process. The experiments revealed that the replication of ridges, including feature edge, profile and filling height, was sensitive to the flow direction; cavity pressure and temperature both increased with holding pressure and mold temperature; replication quality can be improved by increasing cavity pressure and temperature within a certain range. The replication quality of micro/nano features is tightly related to the thermomechanical history of material experienced during the molding process. In addition, the longevity and roughness of the BMG insert were also evaluated based on the number of injection molding cycles.

Journal ArticleDOI
TL;DR: In this paper, a Hertz contact model of the impact force between the proof mass and the end-stops is analyzed and compared to a linear stiffness model, and the resulting impact force model is then included into a SPICE model of an electrostatic harvester.
Abstract: In micro scale energy harvesting devices, end-stops that limit the proof mass motion are inevitable from reliability concerns and can even be exploited as a functional element to achieve a broadband response. To investigate how these can be modelled, both characterization and modelling of vibration energy harvesters with end-stop effects are presented in this paper. A Hertz contact model of the impact force between the proof mass and the end-stops is analysed and compared to a linear stiffness model. The resulting impact force model is then included into a SPICE model of an electrostatic harvester. The performance prediction of the model is validated by comparing simulations and measurements on two different prototypes, one with mechanical quality factor Qm = 5.7 and one with Qm = 203.5. The electromechanical coupling factors of the two devices are respectively k2 = 1.44% and 2.52%. Both devices display the well-known jump phenomenon and output voltage saturation during, respectively, frequency and amplitude sweeps. Under low-level broadband excitations, the high-Qm device performs in agreement with linear theory at an efficiency of 71.8%. For sufficiently high acceleration power spectral density (PSD), it displays a soft limit on the output power and a bandwidth increase, e.g. a factor 3.7 increase of 3 dB bandwidth when increasing the acceleration PSD from 0.34 × 10−3 to 0.55 × 10−3 g2 Hz−1. The end-stop effects reduce the device efficiency down to 35.4% at 1.69 × 10−3 g2 Hz−1. A comparison between model and experiment shows that a model with end-stop stiffness extracted from the contact analysis can adequately model the nonlinear end-stop effects both for narrow- and broadband accelerations.

Journal ArticleDOI
TL;DR: In this paper, the design, integration and operation of a unique E-jet printing platform is discussed, where the uniqueness lies in the ability to utilize multiple materials in the same overall printhead, enabling increased degrees of heterogeneous integration of different functionalities on a single substrate.
Abstract: Electrohydrodynamic jet (E-jet) printing has emerged as a high-resolution alternative to other forms of direct solution-based fabrication approaches, such as ink-jet printing This paper discusses the design, integration and operation of a unique E-jet printing platform The uniqueness lies in the ability to utilize multiple materials in the same overall print-head, thereby enabling increased degrees of heterogeneous integration of different functionalities on a single substrate By utilizing multiple individual print-heads, with a carrousel indexing among them, increased material flexibility is achieved The hardware design and system operation for a relatively inexpensive system are developed and presented Crossover interconnects and multiple fluorescent tagged proteins, demonstrating printed electronics and biological sensing applications, respectively

Journal ArticleDOI
TL;DR: In this article, 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.
Abstract: 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.

Journal ArticleDOI
TL;DR: In this article, a novel electromagnetic energy harvester (EH) with multiple vibration modes has been developed and characterized using three-dimensional (3D) excitation at different frequencies.
Abstract: A novel electromagnetic energy harvester (EH) with multiple vibration modes has been developed and characterized using three-dimensional (3D) excitation at different frequencies. The device consists of a movable circular-mass patterned with three sets of double-layer aluminum (Al) coils, a circular-ring system incorporating a magnet and a supporting beam. The 3D dynamic behavior and performance analysis of the device shows that the first vibration mode of 1285 Hz is an out-of-plane motion, while the second and third modes of 1470 and 1550 Hz, respectively, are in-plane at angles of 60 ◦ (240 ◦ ) and 150 ◦ (330 ◦ ) to the horizontal (x-) axis. For an excitation acceleration of 1 g, the maximum power density achieved are 0.444, 0.242 and 0.125 μ Wc m −3 at vibration modes of I, II and III, respectively. The experimental results are in good agreement with the simulation and indicate a good potential in the development of a 3D EH device. (Some figures may appear in colour only in the online journal)

Journal ArticleDOI
TL;DR: In this article, the poly(dimethylsiloxane-ethylene oxide polymeric) (PDMS-b-PEO) is used in this project as a surfactant additive to be added into the PDMS base and the curing agent mixture during polymerization and to create hydrophilic PEO-PDMS.
Abstract: Polydimethylsiloxane (PDMS) is a popularly used nontoxic and biocompatible material in microfluidic systems, which is relatively cheap and does not break easily like glass. The simple fabrication, optical transparency and elastomeric property make PDMS a handy material to work with. In order to develop different applications of PDMS in microfluidics and bioengineering, it is necessary to modify the PDMS surface nature to improve wetting characteristics, and to have a better control in nonspecific binding of proteins and cells, as well as to increase adhesion. At the moment, the hydrophilic surface modification performance of PDMS is known to recover its hydrophobicity shortly after oxidation modification, which is not stable in the long term (Owen and Smith 1994 J. Adhes. Sci. Technol. 8 1063–75). This paper presents a long-term stable hydrophilic surface modification processing of PDMS. The poly(dimethylsiloxane-ethylene oxide polymeric) (PDMS-b-PEO) is used in this project as a surfactant additive to be added into the PDMS base and the curing agent mixture during polymerization and to create hydrophilic PEO-PDMS. The contact angle can be controlled at 21.5–80.9° with the different mixing ratios and the hydrophilicity will remain stable for two months and then slightly varied later. We also investigate the bonding conditions of the modified PDMS to a silicon wafer and a glass wafer. To demonstrate its applications, we designed a device which consists of microchannels on a silicon wafer, and PEO-PDMS is utilized as a cover sheet. The capillary function was investigated under the different contact angles of PED-PDMS and with different aspect ratios of microchannels. All of the processes and testing data are presented in detail. This easy and cost-effective modified PDMS with a good bonding property can be widely used in the capillary device and systems, and microfluidic devices for fluid flow control of the microchannels in biological, chemical, medical applications.

Journal ArticleDOI
TL;DR: In this article, a microelectro-mechanical system-based experimental technique was used to measure thermal conductivity of freestanding ultra-thin films of amorphous silicon nitride (Si3N4) as a function of mechanical strain.
Abstract: We present a micro-electro-mechanical system-based experimental technique to measure thermal conductivity of freestanding ultra-thin films of amorphous silicon nitride (Si3N4) as a function of mechanical strain. Using a combination of infrared thermal micrography and multi-physics simulation, we measured thermal conductivity of 50 nm thick silicon nitride films to observe it decrease from 2.7 W (m K)?1?at zero strain to 0.34 W (m K)?1?at about 2.4% tensile strain. We propose that such strong strain?thermal conductivity coupling is due to strain effects on fraction?phonon interaction that decreases the dominant hopping mode conduction in the amorphous silicon nitride specimens.

Journal ArticleDOI
TL;DR: In this article, the design and fabrication of batch-processed cantilever probes with electrical shielding for scanning microwave impedance microscopy is presented, and the diameter of the tip apex, which defines the electrical resolution, is less than 50 nm.
Abstract: 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

Journal ArticleDOI
TL;DR: In this paper, an array of dielectric elastomer microactuators is used to study mechanotransduction of individual cells, and the position of each dot is tracked to measure displacement and strain profiles as a function of voltage.
Abstract: Cells regulate their behavior in response to mechanical strains. Cell cultures to study mechanotransuction are typically cm2 in area, far too large to monitor single cell response. We have developed an array of dielectric elastomer microactuators as a tool to study mechanotransduction of individual cells. The array consists of 72 100 μm × 200 μm electroactive polymer actuators which expand uniaxially when a voltage is applied. Single cells will be attached on each actuator to study their response to periodic mechanical strains. The device is fabricated by patterning compliant microelectrodes on both sides of a 30 μm thick polydimethylsiloxane membrane, which is bonded to a Pyrex chip with 200 μm wide trenches. Low-energy metal ion implantation is used to make stretchable electrodes and we demonstrate here the successful miniaturization of such ion-implanted electrodes. The top electrode covers the full membrane area, while the bottom electrodes are 100 μm wide parallel lines, perpendicular to the trenches. Applying a voltage between the top and bottom electrodes leads to uniaxial expansion of the membrane at the intersection of the bottom electrodes and the trenches. To characterize the in-plane strain, an array of 4 μm diameter aluminum dots is deposited on each actuator. The position of each dot is tracked, allowing displacement and strain profiles to be measured as a function of voltage. The uniaxial strain reaches 4.7% at 2.9 kV with a 0.2 s response time, sufficient to stimulate most cells with relevant biological strains and frequencies.

Journal ArticleDOI
TL;DR: In this paper, an opto-actuable device fabricated using micro-machined silicon molds is presented, which is made from a composite material containing carbon nanotubes (CNTs) embedded in a liquid crystal elastomer (LCE) matrix.
Abstract: This paper reports an opto-actuable device fabricated using micro-machined silicon moulds. The actuating component of the device is made from a composite material containing carbon nanotubes (CNTs) embedded in a liquid crystal elastomer (LCE) matrix. We demonstrate the fabrication of a patterned LCE-CNT film by a combination of mechanical stretching and thermal cross-linking. The resulting poly-domain LCE-CNT film contains ‘blister-shaped’ mono-domain regions, which reversibly change their shape under light irradiation and hence can be used as dynamic Braille dots. We demonstrate that blisters with diameters of 1.0 and 1.5 mm, and wall thickness 300 µm, will mechanically contract under irradiation by a laser diode with optical power up to 60 mW. The magnitude of this contraction was up to 40 µm, which is more than 10% of their height in the ‘rest’ state. The stabilization time of the material is less than 6 s for both actuation and recovery. We also carried out preliminary tests on the repeatability of this photo-actuation process, observing no material or performance degradation. This manufacturing approach establishes a starting point for the design and fabrication of wide-area tactile actuators, which are promising candidates for the development of new Braille reading applications for the visually impaired.

Journal ArticleDOI
TL;DR: In this paper, lifetime limitations and failure analysis of many packaged RF MEMS ohmic contacting switches with Au-Au, Au-Ir, and Au-Pt contact materials operating with 100 μN of contact force per contact in hermetically sealed glass wall packages.
Abstract: We present lifetime limitations and failure analysis of many packaged RF MEMS ohmic contacting switches with Au–Au, Au–Ir, and Au–Pt contact materials operating with 100 μN of contact force per contact in hermetically sealed glass wall packages. All metals were tested using the same switch design in a controlled environment to provide a comparison between the performance of the different materials and their corresponding failure mechanisms. The switch lifetimes of the different contact materials varied from several hundred cycles to 200 million cycles with different mechanisms causing failures for different contact materials. Switches with Au–Au contacts failed due to adhesion when thoroughly cleaned while switches with dissimilar metal contacts (Au–Ir and Au–Pt) operated without adhesion failures but failed due to carbon accumulation on the contacts even in a clean, packaged environment as a result of the catalytic behavior of the contact materials. Switch lifetimes correlated inversely with catalytic behavior of the contact metals. The data suggests the path to increase switch lifetime is to use favorable catalytic materials as contacts, design switches with higher contact forces to break through any residual contamination, and use cleaner, probably smaller, packages. (Some figures may appear in colour only in the online journal)

Journal ArticleDOI
TL;DR: A temperature-controlled microfluidic acoustophoresis device capable of separating particles and transferring blood cells from undiluted whole human blood at a volume throughput greater than 1 L h −1 is reported.
Abstract: We report a temperature-controlled microfluidic acoustophoresis device capable of separating particles and transferring blood cells from undiluted whole human blood at a volume throughput greater than 1 L h −1 . The device is fabricated from glass substrates and polymer sheets in microscope-slide format using low-cost, rapid-prototyping techniques. This high-throughput acoustophoresis chip (HTAC) utilizes a temperature-stabilized, standing ultrasonic wave, which imposes differential acoustic radiation forces that can separate particles according to size, density and compressibility. The device proved capable of separating a mixture of 10- and 2-μm-diameter polystyrene beads with a sorting efficiency of 0.8 at a flow rate of 1 Lh −1 . As a first step toward biological applications, the HTAC was also tested in processing whole human blood and proved capable of transferring blood cells from undiluted whole human blood with an efficiency of 0.95 at 1 Lh −1 and 0.82 at 2 Lh −1 . (Some figures may appear in colour only in the online journal)

Journal ArticleDOI
TL;DR: In this article, a method of producing sharp tipped plastic hollow microneedle arrays using microinjection molding is presented, where three mould inserts are used to create the sharp tips of the micronedles.
Abstract: A method of producing sharp tipped plastic hollow microneedle arrays using microinjection moulding is presented in this paper. Unlike traditional approaches, three mould inserts were used to create the sharp tips of the microneedles. Mould inserts with low surface roughness were fabricated using a picosecond laser machine. Sharp tipped plastic hollow microneedles 500 µm in height were fabricated using a microinjection moulding machine developed by the authors’ group. In addition, the strength of the microneedle was studied by simulation and penetration experiments. Results show that the microneedles can penetrate into skin, delivering liquid successfully without any breakage or severe deformation. Techniques presented in this paper can be used to fabricate sharp tipped plastic hollow microneedle arrays massively with low cost.

Journal ArticleDOI
TL;DR: In this article, the results of 3D printing depend on the piezoelectric voltage pulse, the substrate heating temperature and the structure height, resulting in the identification of thermal regions of optimal printing for best printing results.
Abstract: 3D solid and pocketed micro-wires and micro-walls are needed for emerging applications that require fine-scale functional structures in three dimensions, including micro-heaters, micro-reactors and solar cells. To fulfill this demand, 3D micro-structures with high aspect ratios (>50:1) are developed on a low-cost basis that is applicable for mass production with high throughput, also enabling the printing of structures that cannot be manufactured by conventional techniques. Additively patterned 3D gold micro-walls and -wires are grown by piezoelectric inkjet printing of nanofluids, selectively combined with in situ simultaneous laser annealing that can be applied to large-scale bulk production. It is demonstrated how the results of 3D printing depend on the piezoelectric voltage pulse, the substrate heating temperature and the structure height, resulting in the identification of thermal regions of optimal printing for best printing results. Furthermore a parametric analysis of the applied substrate temperature during printing leads to proposed temperature ranges for solid and pocketed micro-wire and micro-wall growth for selected frequency and voltages.

Journal ArticleDOI
TL;DR: A micropillar-based on-chip system which is capable of quantifying multi-point locomotive forces of a moving C. elegans and worm muscle development can be an enabling technology that allows biologist to gain a better understanding of subtle force patterns of C. elegans.
Abstract: 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.

Journal ArticleDOI
TL;DR: In this paper, anodic bonding of silicon and relatively thick glass wafers was used for the fabrication of atomic reference cells with dimensions larger than standard micromachined cells for use in compact atomic devices such as vapour-cell atomic clocks or magnetometers.
Abstract: This paper presents a new fabrication method to manufacture alkali reference cells having dimensions larger than standard micromachined cells and smaller than glass-blown ones, for use in compact atomic devices such as vapour-cell atomic clocks or magnetometers. The technology is based on anodic bonding of silicon and relatively thick glass wafers and fills a gap in cell sizes and technologies available up to now: on one side, microfabrication technologies with typical dimensions <= 2 mm and on the other side, classical glass-blowing technologies for typical dimensions of about 6-10 mm or larger. The fabrication process is described for cells containing atomic Rb and spectroscopic measurements (optical absorption spectrum and double resonance) are reported. The analysis of the bonding strength of our cells was performed and shows that the first anodic bonding steps exhibit higher bonding strengths than the later ones. The spectroscopic results show a good quality of the cells. From the double-resonance signals, we predict a clock stability of approximate to 3 x 10(-11) at 1 s of integration time, which compares well to the performance of compact commercial Rb atomic clocks.

Journal ArticleDOI
TL;DR: In this article, the effect of laser pulse duration and photon energy on the surface chemistry and morphology and subsequent wetting properties of polymeric surfaces treated with UV laser pulses was investigated.
Abstract: This paper demonstrates the application of ultrashort-pulsed lasers as a unique tool for controllable modification of the surface wettability of polymers from high hydrophilicity to superhydrophobicity. This is achieved by exploiting the effect of laser pulse duration and photon energy on the surface chemistry and morphology and subsequent wetting properties of polymeric surfaces treated with UV laser pulses. In three different pulse duration regimes, ranging from femtosecond to nanosecond and two different photon wavelengths, we have systematically altered the wettability of polyethersulfone surfaces from highly hydrophilic to superhydrophobic. Our results indicate that, despite the remarkable changes in the surface morphology attained, the surface wettability variations are dominantly caused by laser-induced chemical modifications, which are highly dependent on the pulse energy and duration. The ability of tuning the wetting properties and thus the surface energy of laser-treated polymer surfaces within a broad range makes them excellent candidates for liquid flow control in microfluidics and biological adhesion applications.

Journal ArticleDOI
TL;DR: In this paper, the energy conversion of quasi-static magnetic field variations into electricity was investigated for harvesters coupling magnetostrictive and piezoelectric materials, and experimental results were exposed for two macroscopic demonstrators based on the rotation of a permanent magnet.
Abstract: 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.

Journal ArticleDOI
TL;DR: In this article, the authors demonstrate femtosecond laser fabrication of micro-tubes with a height of several tens of micrometers in the photopolymer SZ2080 by three different methods: direct laser writing, using the optical vortex beam and holographic lithography.
Abstract: In this paper we demonstrate femtosecond laser fabrication of micro-tubes with a height of several tens of micrometers in the photopolymer SZ2080 by three different methods: direct laser writing, using the optical vortex beam and holographic lithography. The flexibility of direct laser writing and dramatic increase of production efficiency by applying the vortex-shaped beam and four-beam interference approaches are presented. Sample arrays of micro-tubes were successfully manufactured applying all three methods and the fabrication quality as well as efficiency of the methods is compared. The processing time of a single micro-tube with 60 ?m height and 3 ?m inner radius is reduced 400 times for the holographic lithography technique and 500 times for the optical vortex method compared with the direct laser writing technique. The processing time of a micro-tube array containing 400?micro-tubes is the shortest for the holographic lithography method but not for the optical vortex method as in the case of a single micro-tube, because the holographic lithography method does not require time for sample translation. Additionally, the holographic lithography enables manufacturing of the whole micro-tube array by a single exposure. Although point-by-point photo-structuring ensures unmatched complexity of manufactured microstructures, employing nowadays high repetition rate amplified femtosecond lasers combined with beam shaping or several beam interference can envisage industrial applications for practical demands.