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Micromachines, Volume 5, Issue 3 (September 2014), Pages 408-796

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Open AccessArticle Sequential Atmospheric Pressure Plasma-Assisted Laser Ablation of Photovoltaic Cover Glass for Improved Contour Accuracy
Micromachines 2014, 5(3), 408-419; doi:10.3390/mi5030408
Received: 28 May 2014 / Revised: 24 June 2014 / Accepted: 26 June 2014 / Published: 2 July 2014
Cited by 2 | PDF Full-text (1039 KB) | HTML Full-text | XML Full-text
Abstract
In this paper, we present sequential atmospheric pressure plasma-assisted laser ablation of photovoltaic cover glass. First, glass samples were plasma pre-treated using a hydrogenous plasma process gas in order to accomplish a modification of the near-surface glass network by a chemical reduction and
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In this paper, we present sequential atmospheric pressure plasma-assisted laser ablation of photovoltaic cover glass. First, glass samples were plasma pre-treated using a hydrogenous plasma process gas in order to accomplish a modification of the near-surface glass network by a chemical reduction and the implantation of hydrogen. As a result, the transmission at a wavelength of 355 nm was reduced by approximately 2% after plasma treatment duration of 60 min. Further, the surface polarity was increased by approximately 78%, indicating an increase of the near-surface index of refraction. Subsequently to the plasma pre-treatment, the samples were laser ablated applying the above-mentioned laser wavelength of a Nd:YAG nanosecond laser. Compared to untreated samples, a significant decrease of the form error by 45% without any mentionable change in the ablation rate was obtained in the case of pre-treated samples. For comparison, the results and findings are discussed with respect to previous work, where the presented plasma-assisted ablation procedure was applied to optical glasses. Full article
(This article belongs to the Special Issue Laser Micro- and Nano- Processing)
Open AccessArticle Design and Performance Analysis of Capacitive Micromachined Ultrasonic Transducer Linear Array
Micromachines 2014, 5(3), 420-431; doi:10.3390/mi5030420
Received: 2 May 2014 / Revised: 18 June 2014 / Accepted: 26 June 2014 / Published: 3 July 2014
Cited by 4 | PDF Full-text (864 KB) | HTML Full-text | XML Full-text
Abstract
An ultrasonic transducer is a key component to achieve ultrasonic imaging. This paper designs a new type of Microelectromechanical Systems (MEMS) based capacitive ultrasonic transducer and a linear array based on the transducer. Through directivity analysis, it can be found that its directivity
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An ultrasonic transducer is a key component to achieve ultrasonic imaging. This paper designs a new type of Microelectromechanical Systems (MEMS) based capacitive ultrasonic transducer and a linear array based on the transducer. Through directivity analysis, it can be found that its directivity is weak due to the small size of the designed transducer, but the directivity of the designed linear array is very strong. In order to further suppress the sidelobe interference and improve the resolution of the imaging system and imaging quality, the Dolph-Chebyshev weighting method and the Taylor weighting method are used to process −40dB sidelobe suppression, and satisfactory results are obtained, which can meet actual requirements. Full article
Open AccessArticle Fabrication and Characterization of Flexible Electrowetting on Dielectrics (EWOD) Microlens
Micromachines 2014, 5(3), 432-441; doi:10.3390/mi5030432
Received: 19 May 2014 / Revised: 16 June 2014 / Accepted: 16 June 2014 / Published: 4 July 2014
Cited by 6 | PDF Full-text (572 KB) | HTML Full-text | XML Full-text
Abstract
We present a flexible variable-focus converging microlens actuated by electrowetting on dielectric (EWOD). The microlens is made of two immiscible liquids and a soft polymer, polydimethylsiloxane (PDMS). Parylene intermediate layer is used to produce robust flexible electrode on PDMS. A low-temperature PDMS-compatible fabrication
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We present a flexible variable-focus converging microlens actuated by electrowetting on dielectric (EWOD). The microlens is made of two immiscible liquids and a soft polymer, polydimethylsiloxane (PDMS). Parylene intermediate layer is used to produce robust flexible electrode on PDMS. A low-temperature PDMS-compatible fabrication process has been developed to reduce the stress on the lens structure. The lens has been demonstrated to be able to conform to curved surfaces smoothly. The focal length of the microlens is 29–38 mm on a flat surface, and 31–41 mm on a curved surface, varying with the voltage applied. The resolving power of the microlens is 25.39 line pairs per mm by a 1951 United States Air Force (USAF) resolution chart and the lens aberrations are measured by a Shack-Hartmann wavefront sensor. The focal length behavior on a curved surface is discussed and for the current lens demonstrated the focal length is slightly longer on the curved surface as a result of the effect of the curved PDMS substrate. Full article
(This article belongs to the Special Issue Microlenses) Print Edition available
Open AccessArticle Implementation of Synchronous Micromotor in Developing Integrated Microfluidic Systems
Micromachines 2014, 5(3), 442-456; doi:10.3390/mi5030442
Received: 5 May 2014 / Revised: 8 June 2014 / Accepted: 7 July 2014 / Published: 18 July 2014
Cited by 9 | PDF Full-text (8098 KB) | HTML Full-text | XML Full-text
Abstract
This paper introduces the synchronous micromotor concept and presents new investigations on its application as an integrated driving mechanism in microfluidic systems. A spiral channel viscous micropump and a microstirrer are considered and tested as examples to verify the concept. The fabrication technology
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This paper introduces the synchronous micromotor concept and presents new investigations on its application as an integrated driving mechanism in microfluidic systems. A spiral channel viscous micropump and a microstirrer are considered and tested as examples to verify the concept. The fabrication technology of such integrated systems is based on UV depth lithography, electroplating and soft lithography. The synchronous micromotor consists of a stator including double layer coils, and a rotor disk containing alternate permanent magnets. The coils are distributed evenly around the stator and arranged in three phases. The phases are excited by sinusoidal currents with a corresponding phase shift resulting in a rotating magnetic field. Regarding the spiral channel viscous micropump, a spiral disk was fixed onto the rotor disk and run at different rotational speeds. Tests showed very promising results, with a flow rate up to 1023 µL·min−1 at a motor rotational speed of 4500 rpm. Furthermore, for the application of a microstirred-tank bioreactor, the rotor disk design was modified to work as a stirrer. The performance of the developed microbioreactor was tested over a time period of approximately 10 h under constant stirring. Tests demonstrated the successful cultivation of S. cerevisiae through the integration of the microstirrer in a microbioreactor system. These systems prove that synchronous micromotors are well suited to serve as integrated driving mechanisms of active microfluidic components. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
Open AccessArticle CO2 Laser Manufacturing of Miniaturised Lenses for Lab-on-a-Chip Systems
Micromachines 2014, 5(3), 457-471; doi:10.3390/mi5030457
Received: 30 May 2014 / Revised: 11 July 2014 / Accepted: 15 July 2014 / Published: 21 July 2014
Cited by 1 | PDF Full-text (2356 KB) | HTML Full-text | XML Full-text
Abstract
This article describes the manufacturing and characterisation of plano-convex miniaturised lenses using a CO2 laser engraving process in PMMA substrates. The technique allows for lenses to be fabricated rapidly and in a reproducible manner at depths of over 200 µm and for
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This article describes the manufacturing and characterisation of plano-convex miniaturised lenses using a CO2 laser engraving process in PMMA substrates. The technique allows for lenses to be fabricated rapidly and in a reproducible manner at depths of over 200 µm and for lens diameters of more than 3 mm. Experimental characterisation of the lens focal lengths shows good correlation with theory. The plano-convex lenses have been successfully embedded into capillary microfluidic systems alongside planar microlenses, allowing for a significant reduction of ancillary optics without a loss of detection sensitivity when performing fluorescence measurements. Such technology provides a significant step forward towards the portability of fluorescence- or luminescence-based systems for biological/chemical analysis. Full article
(This article belongs to the Special Issue Microlenses) Print Edition available
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Open AccessArticle Laser Direct Writing of Thick Hybrid Polymers for Microfluidic Chips
Micromachines 2014, 5(3), 472-485; doi:10.3390/mi5030472
Received: 10 June 2014 / Revised: 9 July 2014 / Accepted: 16 July 2014 / Published: 22 July 2014
Cited by 1 | PDF Full-text (1232 KB) | HTML Full-text | XML Full-text
Abstract
This work presents patterning of thick (10–50 µm) hybrid polymer structures of ORMOCER® by laser direct writing. ORMOCER® combine polymer-like fabrication processes with glass-like surface chemistry that is beneficial for many bio-microfluidic applications. ORMOCER® is liquid before exposure, so patterning
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This work presents patterning of thick (10–50 µm) hybrid polymer structures of ORMOCER® by laser direct writing. ORMOCER® combine polymer-like fabrication processes with glass-like surface chemistry that is beneficial for many bio-microfluidic applications. ORMOCER® is liquid before exposure, so patterning is done by contact-free lithography, such as proximity exposure. With laser direct writing, we obtained higher resolution patterns, with smaller radius of curvature (~2–4 µm), compared to proximity exposure (~10–20 µm). Process parameters were studied to find the optimal dose for different exposure conditions and ORMOCER® layer thicknesses. Two fluidic devices were successfully fabricated: a directional wetting device (fluidic diode) and an electrophoresis chip. The fluidic diode chip operation depends on the sharp corner geometry and water contact angle, and both have been successfully tailored to obtain diodicity. Electrophoresis chips were used to separate of two fluorescent dyes, rhodamine 123 and fluorescein. The electrophoresis chip also made use of ORMOCER® to ORMOCER® bonding. Full article
(This article belongs to the Special Issue Laser Micro- and Nano- Processing)
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Open AccessArticle Adaptive Liquid Lens Actuated by Droplet Movement
Micromachines 2014, 5(3), 496-504; doi:10.3390/mi5030496
Received: 5 June 2014 / Revised: 22 July 2014 / Accepted: 29 July 2014 / Published: 4 August 2014
Cited by 4 | PDF Full-text (16561 KB) | HTML Full-text | XML Full-text
Abstract
In this paper we report an adaptive liquid lens actuated by droplet movement. Four rectangular PMMA (Polymethyl Methacrylate) substrates are stacked to form the device structure. Two ITO (Indium Tin Oxide) sheets stick on the bottom substrate. One PMMA sheet with a light
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In this paper we report an adaptive liquid lens actuated by droplet movement. Four rectangular PMMA (Polymethyl Methacrylate) substrates are stacked to form the device structure. Two ITO (Indium Tin Oxide) sheets stick on the bottom substrate. One PMMA sheet with a light hole is inserted in the middle of the device. A conductive droplet is placed on the substrate and touches the PMMA sheet to form a small closed reservoir. The reservoir is filled with another immiscible non-conductive liquid. The non-conductive liquid can form a smooth concave interface with the light hole. When the device is applied with voltage, the droplet stretches towards the reservoir. The volume of the reservoir reduces, changing the curvature of the interface. The device can thus achieve the function of an adaptive lens. Our experiments show that the focal length can be varied from −10 to −159 mm as the applied voltage changes from 0 to 65 V. The response time of the liquid lens is ~75 ms. The proposed device has potential applications in many fields such as information displays, imaging systems, and laser scanning systems. Full article
(This article belongs to the Special Issue Microlenses) Print Edition available
Open AccessArticle Design, Fabrication and Computational Characterization of a 3D Micro-Valve Built by Multi-Photon Polymerization
Micromachines 2014, 5(3), 505-514; doi:10.3390/mi5030505
Received: 2 July 2014 / Revised: 24 July 2014 / Accepted: 25 July 2014 / Published: 6 August 2014
Cited by 5 | PDF Full-text (2370 KB) | HTML Full-text | XML Full-text
Abstract
We report on the design, modeling and fabrication by multi-photon polymerization of a complex medical fluidic device. The physical dimensions of the built micro-valve prototype are compared to those of its computer-designed model. Important fabrication issues such as achieving high dimensional resolution and
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We report on the design, modeling and fabrication by multi-photon polymerization of a complex medical fluidic device. The physical dimensions of the built micro-valve prototype are compared to those of its computer-designed model. Important fabrication issues such as achieving high dimensional resolution and ability to control distortion due to shrinkage are presented and discussed. The operational performance of both multi-photon and CAD-created models under steady blood flow conditions was evaluated and compared through computational fluid dynamics analysis. Full article
(This article belongs to the Special Issue Laser Micro- and Nano- Processing)
Open AccessArticle A Contact Angle Study of the Interaction between Embedded Amphiphilic Molecules and the PDMS Matrix in an Aqueous Environment
Micromachines 2014, 5(3), 515-527; doi:10.3390/mi5030515
Received: 16 April 2014 / Revised: 3 August 2014 / Accepted: 4 August 2014 / Published: 7 August 2014
PDF Full-text (1753 KB) | HTML Full-text | XML Full-text
Abstract
Poly(dimethylsiloxane) (PDMS) surface modification via gradient-induced transport of embedded amphiphilic molecules is a novel, easy, flexible, and environmentally friendly approach for reducing protein adsorption on PDMS in microfluidic applications. To better understand the processing and the potential use in the viability-sensitive applications such
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Poly(dimethylsiloxane) (PDMS) surface modification via gradient-induced transport of embedded amphiphilic molecules is a novel, easy, flexible, and environmentally friendly approach for reducing protein adsorption on PDMS in microfluidic applications. To better understand the processing and the potential use in the viability-sensitive applications such as manipulation and culturing of primary neural cells, we systematically investigate how embedded molecules interact with a PDMS matrix and its surface in aqueous environments by studying the wetting angle over time under various processing conditions, including water exposure time, water exposure temperature, curing master materials, in addition to comparing different embedded amphiphilic molecules. The results indicate that the water exposure time clearly plays an important role in the surface properties. Our interpretation is that molecular rearrangement of the surface-embedded molecules improves surface coverage in the short term; while over a longer period, the transport of molecules embedded in the bulk enhance its coverage. However, this improvement finally terminates when molecules transported from the bulk to the surface are not sufficient to replace the molecules leaching into the water. Full article
Open AccessArticle Deployable and Conformal Planar Micro-Devices: Design and Model Validation
Micromachines 2014, 5(3), 528-546; doi:10.3390/mi5030528
Received: 19 December 2013 / Revised: 22 July 2014 / Accepted: 31 July 2014 / Published: 11 August 2014
PDF Full-text (4375 KB) | HTML Full-text | XML Full-text
Abstract
We report a design concept for a deployable planar microdevice and the modeling and experimental validation of its mechanical behavior. The device consists of foldable membranes that are suspended between flexible stems and actuated by push-pull wires. Such a deployable device can be
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We report a design concept for a deployable planar microdevice and the modeling and experimental validation of its mechanical behavior. The device consists of foldable membranes that are suspended between flexible stems and actuated by push-pull wires. Such a deployable device can be introduced into a region of interest in its compact “collapsed” state and then deployed to conformally cover a large two-dimensional surface area for minimally invasive biomedical operations and other engineering applications. We develop and experimentally validate theoretical models based on the energy minimization approach to examine the conformality and figures of merit of the device. The experimental results obtained using model contact surfaces agree well with the prediction and quantitatively highlight the importance of the membrane bending modulus in controlling surface conformality. The present study establishes an early foundation for the mechanical design of this and related deployable planar microdevice concepts. Full article
Open AccessArticle Structural Design and Experimental Analysis of a Piezoelectric Vibration Feeder with a Magnetic Spring
Micromachines 2014, 5(3), 547-557; doi:10.3390/mi5030547
Received: 25 June 2014 / Revised: 2 August 2014 / Accepted: 5 August 2014 / Published: 19 August 2014
Cited by 1 | PDF Full-text (2461 KB) | HTML Full-text | XML Full-text
Abstract
A piezoelectric vibration feeder with a magnetic spring is discussed in this paper. The feeder can keep resonance frequency relatively stable under changing loading. Through the analysis on the working principle and magnetic spring stiffness characteristic of this feeder, the dynamic model was
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A piezoelectric vibration feeder with a magnetic spring is discussed in this paper. The feeder can keep resonance frequency relatively stable under changing loading. Through the analysis on the working principle and magnetic spring stiffness characteristic of this feeder, the dynamic model was established and the relationship among system resonance frequency, loading and magnetic spring stiffness was obtained. The analysis showed that, as the loading changed, the magnetic spring stiffness changed accordingly, which maintained a trend of stability in the system resonance frequency. A prototype was made for the experiment, and the relationship among the loading, magnetic spring axial clearance and system resonance frequency was obtained. The result showed that, when the loading changes, the resonance frequency and feeding speed tended to be stable, which matched the theoretical analysis. Through comparison with a traditional vibration feeder, within nominal loading, this new feeder has more stable resonance frequency and feeding speed. Full article
(This article belongs to the Special Issue Microactuators)
Open AccessArticle Simple Stacking Methods for Silicon Micro Fuel Cells
Micromachines 2014, 5(3), 558-569; doi:10.3390/mi5030558
Received: 3 July 2014 / Revised: 12 August 2014 / Accepted: 18 August 2014 / Published: 21 August 2014
PDF Full-text (3063 KB) | HTML Full-text | XML Full-text
Abstract
We present two simple methods, with parallel and serial gas flows, for the stacking of microfabricated silicon fuel cells with integrated current collectors, flow fields and gas diffusion layers. The gas diffusion layer is implemented using black silicon. In the two stacking methods
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We present two simple methods, with parallel and serial gas flows, for the stacking of microfabricated silicon fuel cells with integrated current collectors, flow fields and gas diffusion layers. The gas diffusion layer is implemented using black silicon. In the two stacking methods proposed in this work, the fluidic apertures and gas flow topology are rotationally symmetric and enable us to stack fuel cells without an increase in the number of electrical or fluidic ports or interconnects. Thanks to this simplicity and the structural compactness of each cell, the obtained stacks are very thin (~1.6 mm for a two-cell stack). We have fabricated two-cell stacks with two different gas flow topologies and obtained an open-circuit voltage (OCV) of 1.6 V and a power density of 63 mW·cm−2, proving the viability of the design. Full article
(This article belongs to the Special Issue Power MEMS)
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Open AccessArticle Reliability Investigation of GaN HEMTs for MMICs Applications
Micromachines 2014, 5(3), 570-582; doi:10.3390/mi5030570
Received: 30 May 2014 / Revised: 21 July 2014 / Accepted: 21 July 2014 / Published: 22 August 2014
PDF Full-text (2626 KB) | HTML Full-text | XML Full-text
Abstract
Results obtained during the evaluation of radio frequency (RF) reliability carried out on several devices fabricated with different epi-structure and field-plate geometries will be presented and discussed. Devices without a field-plate structure experienced a more severe degradation when compared to their counterparts while
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Results obtained during the evaluation of radio frequency (RF) reliability carried out on several devices fabricated with different epi-structure and field-plate geometries will be presented and discussed. Devices without a field-plate structure experienced a more severe degradation when compared to their counterparts while no significant correlation has been observed with respect of the different epi-structure tested. RF stress induced two main changes in the device electrical characteristics, i.e., an increase in drain current dispersion and a reduction in gate-leakage currents. Both of these phenomena can be explained by assuming a density increase of an acceptor trap located beneath the gate contact and in the device barrier layer. Numerical simulations carried out with the aim of supporting the proposed mechanism will also be presented. Full article
(This article belongs to the Special Issue Advances in MMICs)
Open AccessArticle Inkjet Printing of High Aspect Ratio Superparamagnetic SU-8 Microstructures with Preferential Magnetic Directions
Micromachines 2014, 5(3), 583-593; doi:10.3390/mi5030583
Received: 29 June 2014 / Revised: 2 August 2014 / Accepted: 18 August 2014 / Published: 25 August 2014
Cited by 3 | PDF Full-text (3832 KB) | HTML Full-text | XML Full-text
Abstract
Structuring SU-8 based superparamagnetic polymer composite (SPMPC) containing Fe3O4 nanoparticles by photolithography is limited in thickness due to light absorption by the nanoparticles. Hence, obtaining thicker structures requires alternative processing techniques. This paper presents a method based on inkjet printing
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Structuring SU-8 based superparamagnetic polymer composite (SPMPC) containing Fe3O4 nanoparticles by photolithography is limited in thickness due to light absorption by the nanoparticles. Hence, obtaining thicker structures requires alternative processing techniques. This paper presents a method based on inkjet printing and thermal curing for the fabrication of much thicker hemispherical microstructures of SPMPC. The microstructures are fabricated by inkjet printing the nanoparticle-doped SU-8 onto flat substrates functionalized to reduce the surface energy and thus the wetting. The thickness and the aspect ratio of the printed structures are further increased by printing the composite onto substrates with confinement pedestals. Fully crosslinked microstructures with a thickness up to 88.8 μm and edge angle of 112° ± 4° are obtained. Manipulation of the microstructures by an external field is enabled by creating lines of densely aggregated nanoparticles inside the composite. To this end, the printed microstructures are placed within an external magnetic field directly before crosslinking inducing the aggregation of dense Fe3O4 nanoparticle lines with in-plane and out-of-plane directions. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
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Open AccessArticle An Optofluidic Lens Array Microchip for High Resolution Stereo Microscopy
Micromachines 2014, 5(3), 607-621; doi:10.3390/mi5030607
Received: 9 June 2014 / Revised: 10 August 2014 / Accepted: 20 August 2014 / Published: 28 August 2014
Cited by 1 | PDF Full-text (11155 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We report the development of an add-on, chip-based, optical module—termed the Microfluidic-based Oil-immersion Lenses (μOIL) chip—which transforms any stereo microscope into a high-resolution, large field of view imaging platform. The μOIL chip consists of an array of ball mini-lenses that are assembled onto
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We report the development of an add-on, chip-based, optical module—termed the Microfluidic-based Oil-immersion Lenses (μOIL) chip—which transforms any stereo microscope into a high-resolution, large field of view imaging platform. The μOIL chip consists of an array of ball mini-lenses that are assembled onto a microfluidic silicon chip. The mini-lenses are made out of high refractive index material (sapphire) and they are half immersed in oil. Those two key features enable submicron resolution and a maximum numerical aperture of ~1.2. The μOIL chip is reusable and easy to operate as it can be placed directly on top of any biological sample. It improves the resolution of a stereo microscope by an order of magnitude without compromising the field of view; therefore, we believe it could become a versatile tool for use in various research studies and clinical applications. Full article
(This article belongs to the Special Issue Microlenses) Print Edition available
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Open AccessArticle Effect of β-PVDF Piezoelectric Transducers’ Positioning on the Acoustic Streaming Flows
Micromachines 2014, 5(3), 654-666; doi:10.3390/mi5030654
Received: 17 July 2014 / Revised: 24 July 2014 / Accepted: 6 August 2014 / Published: 1 September 2014
Cited by 2 | PDF Full-text (8134 KB) | HTML Full-text | XML Full-text
Abstract
This paper reports the numerical and experimental analysis of the acoustic streaming effect in a fluidic domain. The actuation of a piezoelectric transducer generates acoustic waves that propagate to the fluids, generating pressure gradients that induce the flow. The number and positioning of
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This paper reports the numerical and experimental analysis of the acoustic streaming effect in a fluidic domain. The actuation of a piezoelectric transducer generates acoustic waves that propagate to the fluids, generating pressure gradients that induce the flow. The number and positioning of the transducers affect the pressure gradients and, consequently, the resultant flow profile. Two actuation conditions were considered: (1) acoustic streaming generated by a 28 μm thick β-poly(vinylidene fluoride) (β-PVDF) piezoelectric transducer placed asymmetrically relative to the fluidic domain and (2) acoustic streaming generated by two 28 μm thick β-PVDF piezoelectric transducers placed perpendicularly to each other. The transducers were fixed to the lower left corner of a poly(methyl methacrylate) (PMMA)cuvette and were actuated with a 24 Vpp and 34.2 MHz sinusoidal voltage. The results show that the number of transducers and their positioning affects the shape and number of recirculation areas in the acoustic streaming flows. The obtained global flows show great potential for mixing and pumping, being an alternative to the previous geometries studied by the authors, namely, a single transducer placed symmetrically under a fluidic domain. Full article
(This article belongs to the Special Issue Micromixer & Micromixing)
Open AccessArticle Stop-flow Lithography to Continuously Fabricate Microlens Structures Utilizing an Adjustable Three-Dimensional Mask
Micromachines 2014, 5(3), 667-680; doi:10.3390/mi5030667
Received: 11 August 2014 / Revised: 1 September 2014 / Accepted: 3 September 2014 / Published: 10 September 2014
Cited by 2 | PDF Full-text (4769 KB) | HTML Full-text | XML Full-text
Abstract
Stop-flow lithography (SFL) is a microfluidic-based particle synthesis method, in which photolithography with a two dimensional (2D) photomask is performed in situ within a microfluidic environment to fabricate multifunctional microstructures. Here, we modified the SFL technique by utilizing an adjustable electrostatic-force-modulated 3D (EFM-3D)
[...] Read more.
Stop-flow lithography (SFL) is a microfluidic-based particle synthesis method, in which photolithography with a two dimensional (2D) photomask is performed in situ within a microfluidic environment to fabricate multifunctional microstructures. Here, we modified the SFL technique by utilizing an adjustable electrostatic-force-modulated 3D (EFM-3D) mask to continuously fabricate microlens structures for high-throughput production. The adjustable EFM-3D mask contains a layer filled with a UV-absorbing liquid and transparent elastomer structures in the shape of microlenses between two conductive glass substrates. An acrylate oligomer stream is photopolymerized via the microscope projection photolithography, where the EFM-3D mask was set at the field-stop plane of the microscope, thus forming the microlens structures. The produced microlens structures flow downstream without adhesion to the polydimethysiloxane (PDMS) microchannel surfaces due to the existence of an oxygen-aided inhibition layer. Microlens structures with variations in curvature and aperture can be produced by changing objective magnifications, controlling the morphology of the EFM-3D mask through electrostatic force, and varying the concentration of UV-light absorption dyes. We have successfully demonstrated to produce microlens structures with an aperture ranging from 50 μm to 2 mm and the smallest focus spot size of 0.59 μm. Our proposed method allows one to fabricate microlens structures in a fast, simple and high-throughput mode for application in micro-optical systems. Full article
Open AccessArticle A Single Cell Extraction Chip Using Vibration-Induced Whirling Flow and a Thermo-Responsive Gel Pattern
Micromachines 2014, 5(3), 681-696; doi:10.3390/mi5030681
Received: 17 July 2014 / Revised: 27 August 2014 / Accepted: 27 August 2014 / Published: 10 September 2014
Cited by 6 | PDF Full-text (22416 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
We propose a single cell extraction chip with an open structure, which utilizes vibration-induced whirling flow and a single cell catcher. By applying a circular vibration to a micropillar array spiral pattern, a whirling flow is induced around the micropillars, and target cells
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We propose a single cell extraction chip with an open structure, which utilizes vibration-induced whirling flow and a single cell catcher. By applying a circular vibration to a micropillar array spiral pattern, a whirling flow is induced around the micropillars, and target cells are transported towards the single cell catcher placed at the center of the spiral. The single cell catcher is composed of a single-cell-sized hole pattern of thermo-responsive gel. The gel swells at low temperatures (≲32 ◦C) and shrinks at high temperatures (≳32 ◦C), therefore, its volume expansion can be controlled by an integrated microheater. When the microheater is turned on, a single cell is trapped by the hole pattern of the single cell catcher. Then, when the microheater is turned off, the single cell catcher is cooled by the ambient temperature. The gel swells at this temperature, and the hole closes to catch the single cell. The caught cell can then be released into culture wells on a microtiter plate by heating the gel again. We conducted single cell extraction with the proposed chip and achieved a 60% success rate, of which 61% cells yielded live cells. Full article
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Open AccessArticle Three-Dimensional Glass Monolithic Micro-Flexure Fabricated by Femtosecond Laser Exposure and Chemical Etching
Micromachines 2014, 5(3), 697-710; doi:10.3390/mi5030697
Received: 18 August 2014 / Revised: 4 September 2014 / Accepted: 4 September 2014 / Published: 11 September 2014
Cited by 6 | PDF Full-text (6765 KB) | HTML Full-text | XML Full-text
Abstract
Flexures are components of micro-mechanisms efficiently replacing classical multi-part joints found at the macroscale. So far, flexures have been limited to two-dimensional planar designs due to the lack of a suitable three-dimensional micromanufacturing process. Here we demonstrate and characterize a high-strength transparent monolithic
[...] Read more.
Flexures are components of micro-mechanisms efficiently replacing classical multi-part joints found at the macroscale. So far, flexures have been limited to two-dimensional planar designs due to the lack of a suitable three-dimensional micromanufacturing process. Here we demonstrate and characterize a high-strength transparent monolithic three-dimensional flexural component fabricated out of fused silica using non-ablative femtosecond laser processing combined with chemical etching. As an illustration of the potential use of this flexure, we propose a design of a Hoecken linkage entirely made with three-dimensional cross-spring pivot hinges. Full article
(This article belongs to the Special Issue Laser Micro- and Nano- Processing)
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Open AccessArticle Evolution of Monolithic Technology for Wireless Communications: GaN MMIC Power Amplifiers For Microwave Radios
Micromachines 2014, 5(3), 711-721; doi:10.3390/mi5030711
Received: 5 June 2014 / Revised: 9 August 2014 / Accepted: 3 September 2014 / Published: 12 September 2014
PDF Full-text (867 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents the progress of monolithic technology for microwaveapplication, focusing on gallium nitride technology advances in the realization of integratedpower amplifiers. Three design examples, developed for microwave backhaul radios, areshown. The first design is a 7 GHz Doherty developed with a research
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This paper presents the progress of monolithic technology for microwaveapplication, focusing on gallium nitride technology advances in the realization of integratedpower amplifiers. Three design examples, developed for microwave backhaul radios, areshown. The first design is a 7 GHz Doherty developed with a research foundry, while thesecond and the third are a 7 GHz Doherty and a 7–15 GHz dual-band combined poweramplifiers, both based on a commercial foundry process. The employed architectures, themain design steps and the pros and cons of using gallium nitride technology are highlighted.The measured performance demonstrates the potentialities of the employed technology, andthe progress in the accuracy, reliability and performance of the process. Full article
(This article belongs to the Special Issue Advances in MMICs)
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Open AccessArticle Fabrication and Testing of an Osmotic Pressure Sensor for Glucose Sensing Application
Micromachines 2014, 5(3), 722-737; doi:10.3390/mi5030722
Received: 12 June 2014 / Revised: 18 August 2014 / Accepted: 5 September 2014 / Published: 18 September 2014
Cited by 2 | PDF Full-text (2251 KB) | HTML Full-text | XML Full-text
Abstract
This paper presents a chemical reaction-free sensor, based on the osmosis principle, fabricated to measure the change in glucose concentration levels. The sensor consists of a square cavity filled with a known concentration of glucose solution and sealed with a semi-permeable membrane. The
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This paper presents a chemical reaction-free sensor, based on the osmosis principle, fabricated to measure the change in glucose concentration levels. The sensor consists of a square cavity filled with a known concentration of glucose solution and sealed with a semi-permeable membrane. The volume inside the cavity changes in proportion to the glucose concentration outside the device and introduces the displacement in the silicon (Si) membrane on the top. The main considerations targeted for this sensor are better response time, chemical-free nature, improved lifetime and absence of any mechanical excitations. Moreover, as the size of a system plays a major role, efforts have been taken to reduce the dimension of the presented system. The designed glucose sensor is fabricated by employing a bulk micromachining technology on a SOI (silicon on insulator) substrate. This will allow batch fabrication, as well as the integration of the electronic circuit on the same substrate. The output voltage obtained is varied from Full article
(This article belongs to the Special Issue Micro/Nano Fabrication)
Open AccessArticle Optimized SU-8 Processing for Low-Cost Microstructures Fabrication without Cleanroom Facilities
Micromachines 2014, 5(3), 738-755; doi:10.3390/mi5030738
Received: 14 July 2014 / Revised: 9 September 2014 / Accepted: 12 September 2014 / Published: 22 September 2014
Cited by 17 | PDF Full-text (4715 KB) | HTML Full-text | XML Full-text
Abstract
The study and optimization of epoxy-based negative photoresist (SU-8) microstructures through a low-cost process and without the need for cleanroom facility is presented in this paper. It is demonstrated that the Ultraviolet Rays (UV) exposure equipment, commonly used in the Printed Circuit Board
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The study and optimization of epoxy-based negative photoresist (SU-8) microstructures through a low-cost process and without the need for cleanroom facility is presented in this paper. It is demonstrated that the Ultraviolet Rays (UV) exposure equipment, commonly used in the Printed Circuit Board (PCB) industry, can replace the more expensive and less available equipment, as the Mask Aligner that has been used in the last 15 years for SU-8 patterning. Moreover, high transparency masks, printed in a photomask, are used, instead of expensive chromium masks. The fabrication of well-defined SU-8 microstructures with aspect ratios more than 20 is successfully demonstrated with those facilities. The viability of using the gray-scale technology in the photomasks for the fabrication of 3D microstructures is also reported. Moreover, SU-8 microstructures for different applications are shown throughout the paper. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
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Open AccessArticle Multifunctional Material Structures Based on Laser-Etched Carbon Nanotube Arrays
Micromachines 2014, 5(3), 756-765; doi:10.3390/mi5030756
Received: 1 August 2014 / Revised: 10 September 2014 / Accepted: 12 September 2014 / Published: 22 September 2014
Cited by 1 | PDF Full-text (4824 KB) | HTML Full-text | XML Full-text
Abstract
High-power electronics in the transportation and aerospace sectors need size and weight reduction. Multifunctional and multistructured materials are currently being developed to couple electromagnetic (EM) and thermal properties, i.e., shielding against electromagnetic impulsions, and thermal management across the thermal interface material (TIM).
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High-power electronics in the transportation and aerospace sectors need size and weight reduction. Multifunctional and multistructured materials are currently being developed to couple electromagnetic (EM) and thermal properties, i.e., shielding against electromagnetic impulsions, and thermal management across the thermal interface material (TIM). In this work, we investigate laser-machined patterned carbon nanotube (CNT) micro-brushes as an alternative to metallic structures for driving simultaneously EM and heat propagation. The thermal and electromagnetic response of the CNT array is expected to be sensitive to the micro-structured pattern etched in the CNT brush. Full article
(This article belongs to the Special Issue Laser Micro- and Nano- Processing)
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Open AccessArticle SU-8 Photolithography as a Toolbox for Carbon MEMS
Micromachines 2014, 5(3), 766-782; doi:10.3390/mi5030766
Received: 26 June 2014 / Revised: 4 September 2014 / Accepted: 9 September 2014 / Published: 22 September 2014
Cited by 4 | PDF Full-text (2053 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The use of SU-8 as precursor for glass-like carbon, or glassy carbon, is presented here. SU-8 carbonizes when subject to high temperature under inert atmosphere. Although epoxy-based precursors can be patterned in a variety of ways, photolithography is chosen due to its resolution
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The use of SU-8 as precursor for glass-like carbon, or glassy carbon, is presented here. SU-8 carbonizes when subject to high temperature under inert atmosphere. Although epoxy-based precursors can be patterned in a variety of ways, photolithography is chosen due to its resolution and reproducibility. Here, a number of improvements to traditional photolithography are introduced to increase the versatility of the process. The shrinkage of SU-8 during carbonization is then detailed as one of the guidelines necessary to design carbon patterns. A couple of applications—(1) carbon-electrode dielectrophoresis for bioparticle manipulation; and (2) the use of carbon structures as micro-molds are also presented. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
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Open AccessArticle Stress-Free Bonding Technology with Pyrex for Highly Integrated 3D Fluidic Microsystems
Micromachines 2014, 5(3), 783-796; doi:10.3390/mi5030783
Received: 4 August 2014 / Revised: 5 September 2014 / Accepted: 11 September 2014 / Published: 23 September 2014
PDF Full-text (9615 KB) | HTML Full-text | XML Full-text
Abstract
In this article, a novel Pyrex reflow bonding technology is introduced which bonds two functional units made of silicon via a Pyrex reflow bonding process. The practical application demonstrated here is a precision dosing system that uses a mechanically actuated membrane micropump which
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In this article, a novel Pyrex reflow bonding technology is introduced which bonds two functional units made of silicon via a Pyrex reflow bonding process. The practical application demonstrated here is a precision dosing system that uses a mechanically actuated membrane micropump which includes passive membranes for fluid metering. To enable proper functioning after full integration, a technique for device assembly must be established which does not introduce additional stress into the system, but fulfills all other requirements, like pressure tolerance and chemical stability. This is achieved with a stress-free thermal bonding principle to bond Pyrex to silicon in a five-layer stack: after alignment, the silicon-Pyrex-silicon stack is heated to 730 °C. Above the glass transition temperature of 525 °C Pyrex exhibits viscoelastic behavior. This allows the glass layer to come into close mechanical contact with the upper and lower silicon layers. The high temperature and the close contact promotes the formation of a stable and reliable Si-O-Si bond, without introducing mechanical stress into the system, and without deformation upon cooling due to thermal mismatch. Full article
(This article belongs to the Special Issue Micropumps: Design, Fabrication and Applications)

Review

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Open AccessReview UV-LIGA: From Development to Commercialization
Micromachines 2014, 5(3), 486-495; doi:10.3390/mi5030486
Received: 17 June 2014 / Revised: 14 July 2014 / Accepted: 15 July 2014 / Published: 23 July 2014
Cited by 4 | PDF Full-text (10144 KB) | HTML Full-text | XML Full-text
Abstract
A major breakthrough in UV-LIGA (Lithographie, Galvanoformung and Abformung) started with the use of epoxy-based EPON® SU-8 photoresist in the mid-1990s. Using this photoresist has enabled the fabrication of tall and high aspect ratio structures without the use of a very expensive
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A major breakthrough in UV-LIGA (Lithographie, Galvanoformung and Abformung) started with the use of epoxy-based EPON® SU-8 photoresist in the mid-1990s. Using this photoresist has enabled the fabrication of tall and high aspect ratio structures without the use of a very expensive synchrotron source needed to expose the photoresist layer in X-ray LIGA. SU-8 photoresist appeared to be well-suited for LIGA templates, but also as a permanent material. Based on UV-LIGA and SU-8, Mimotec SA has developed processes to manufacture mold inserts and metallic components for various market fields. From one to three-level parts, from Ni to other materials, from simple to complicated parts with integrated functionalities, UV-LIGA has established itself as a manufacturing technology of importance for prototyping, as well as for mass-fabrication. This paper reviews some of the developments that led to commercial success in this field. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
Open AccessReview SU-8 as a Material for Microfabricated Particle Physics Detectors
Micromachines 2014, 5(3), 594-606; doi:10.3390/mi5030594
Received: 17 June 2014 / Revised: 1 August 2014 / Accepted: 4 August 2014 / Published: 26 August 2014
Cited by 1 | PDF Full-text (2132 KB) | HTML Full-text | XML Full-text
Abstract
Several recent detector technologies developed for particle physics applications are based on microfabricated structures. Detectors built with this approach generally exhibit the overall best performance in terms of spatial and time resolution. Many properties of the SU-8 photoepoxy make it suitable for the
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Several recent detector technologies developed for particle physics applications are based on microfabricated structures. Detectors built with this approach generally exhibit the overall best performance in terms of spatial and time resolution. Many properties of the SU-8 photoepoxy make it suitable for the manufacturing of microstructured particle detectors. This article aims to review some emerging detector technologies making use of SU-8 microstructuring, namely micropattern gaseous detectors and microfluidic scintillation detectors. The general working principle and main process steps for the fabrication of each device are reported, with a focus on the advantages brought to the device functionality by the use of SU-8. A novel process based on multiple bonding steps for the fabrication of thin multilayer microfluidic scintillation detectors developed by the authors is presented. Finally, a brief overview of the applications for the discussed devices is given. Full article
(This article belongs to the Special Issue 15 Years of SU8 as MEMS Material)
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Open AccessReview Integrated Magnetic MEMS Relays: Status of the Technology
Micromachines 2014, 5(3), 622-653; doi:10.3390/mi5030622
Received: 17 June 2014 / Revised: 24 July 2014 / Accepted: 19 August 2014 / Published: 29 August 2014
Cited by 7 | PDF Full-text (8363 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The development and application of magnetic technologies employing microfabricated magnetic structures for the production of switching components has generated enormous interest in the scientific and industrial communities over the last decade. Magnetic actuation offers many benefits when compared to other schemes for microelectromechanical
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The development and application of magnetic technologies employing microfabricated magnetic structures for the production of switching components has generated enormous interest in the scientific and industrial communities over the last decade. Magnetic actuation offers many benefits when compared to other schemes for microelectromechanical systems (MEMS), including the generation of forces that have higher magnitude and longer range. Magnetic actuation can be achieved using different excitation sources, which create challenges related to the integration with other technologies, such as CMOS (Complementary Metal Oxide Semiconductor), and the requirement to reduce power consumption. Novel designs and technologies are therefore sought to enable the use of magnetic switching architectures in integrated MEMS devices, without incurring excessive energy consumption. This article reviews the status of magnetic MEMS technology and presents devices recently developed by various research groups, with key focuses on integrability and effective power management, in addition to the ability to integrate the technology with other microelectronic fabrication processes. Full article
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