Table of contents

Stents are artificial implants that provide scaffolding to a cavity inside the body. This paper presents a new luminal device for reducing the mechanical failure of stents due to recoil, which is one of the most important issues in stenting. This device, which we call a recoil-resilient ring (RRR), is utilized standalone or potentially integrated with existing stents to address the problem of recoil. The proposed structure aims to minimize the need for high-pressure overexpansion that can induce intra-luminal trauma and excess growth of vascular tissue causing later restenosis. The RRR is an overlapped open ring with asymmetrical sawtooth structures that are intermeshed. These teeth can slide on top of each other, while the ring is radially expanded, but interlock step-by-step so as to keep the final expanded state against compressional forces that normally cause recoil. The RRRs thus deliver balloon expandability and, when integrated with a stent, bring both radial rigidity and longitudinal flexibility to the stent. The design of the RRR is investigated through finite element analysis (FEA), and then the devices are fabricated using micro-electro-discharge machining of 200-µm-thick Nitinol sheet. The standalone RRR is balloon expandable in vitro by 5–7 Atm in pressure, which is well within the recommended in vivo pressure ranges for stenting procedures. FEA compression tests indicate 13× less reduction of the cross-sectional area of the RRR compared with a typical stainless steel stent. These results also show perfect elastic recovery of the RRR after removal of the pressure compared to the remaining plastic deformations of the stainless steel stent. On the other hand, experimental loading tests show that the fabricated RRRs have 2.8× radial stiffness compared to a two-column section of a commercial stent while exhibiting comparable elastic recovery. Furthermore, testing of in vitro expansion in a mock artery tube shows around 2.9% recoil, approximately 5–11× smaller than the recoil reported for commercial stents. These experimental results demonstrate the effectiveness of the device design for the targeted luminal support and stenting applications.

Microscale sensors and transducers based on magnetic forces can be used to provide wireless, contamination-free interaction with micro- and nanoenvironments. However, integration of magnetic components with typical microfabrication processes can be challenging. Here we show the creation and characterization of polymer micromagnets that can be utilized in microelectromechanical systems (MEMS), microfluidics, microassembly and microrobotics applications. These magnets can be patterned using standard UV lithography, are inexpensive to manufacture, and require limited equipment to produce. We demonstrate the creation of polymer micromagnets with 3 µm feature resolution and greater than 10:1 aspect ratio, the controlled movement of freestanding structures using contact-free applied magnetic fields, and the fabrication of novel 'hybrid' magnetic microstructures with controlled heterogeneity of magnetic properties.

The performance and long-term reliability of a silicon vapor chamber (SVC) developed for thermal management of high-power electronics critically depend on compatibility of the component materials. A hermetically sealed SVC presented in this paper is composed of bulk silicon, glass-frit as a bonding agent, lead/tin solder as an interface sealant and a copper charging tube. These materials, in the presence of a water/vapor environment, may chemically react and release noncondensable gas (NCG), which can weaken structural strength and degrade the heat transfer performance with time. The present work reports detailed studies on chemical compatibility of the components and potential solutions to avoid the resulting thermal performance degradation. Silicon surface oxidation and purification of operating liquid are necessary steps to reduce performance degradation in the transient period. A lead-based solder with its low reflow temperature is found to be electrochemically stable in water/vapor environment. High glazing temperature solidifies molecular bonding in glass-frit and mitigates PbO precipitation. Numerous liquid flushes guarantee removal of chemical residual after the charging tube is soldered to SVC. With these improvements on the SVC material and process compatibility, high effective thermal conductivity and steady heat transfer performance are obtained.

A new concept for uncooled infrared (IR) imaging with a high fill-factor SOI diode structure has been proposed. This approach has the potential of reaching a noise equivalent temperature difference (NETD) in the milli-Kelvin range. This detector makes the IR absorbing structure cover almost the entire pixel area, in which the fill factor can reach 80%. Using the multilever structure, thermal isolation can be independently optimized without sacrificing the IR absorption area. The analysis shows that this high fill-factor SOI diode uncooled IR focal plane array can be made without failure of structure breakdown or buckling. The design shows that the sensitivity is of 7.75 × 10⁻³ V K⁻¹, and the NETD is of 42 mK (f/1.0, 30Hz) which can be achieved in a 35 µm × 35 µm micromachined structure.

In this paper we report three mechanisms causing surface defects on Si sidewalls during Si etching for TSV. The first mechanism causing surface defects was a downward surface-defect formation due to the participation of the residual polymerizing gas in the transition periods between passivation steps and etch steps. The second mechanism was an upward surface-defect formation due to etchant attacking the interface between the Si and the sidewall polymer. Although the sidewall polymer was thick enough to protect the Si surface, it was not possible to avoid surface defects if the etch step was not switched to the following passivation step in time. The third mechanism was a sponge-like surface-defect formation caused by either poor polymer depositions or voids inside the sidewall polymer. The sponge-like surface defects were formed by Si isotropic etching through the weak points of the sidewall polymer. All three surface defects were considered as the major factors on TSV integration and packaging reliability issues.

A silicon free molecule micro-resistojet (FMMR) with a thermally insulating suspension frame composed of silicon dioxide has been designed, fabricated and tested. The concept was developed to increase the efficiency of FMMRs, especially in silicon-based integrated systems. Fabrication of the thick insulating frame was performed through oxidation of high-aspect ratio silicon trenches. The thermal properties of the 1 cm² thruster were evaluated using an IR camera, and it was found that when the volume inside the frame is heated more than 200 °C using integrated nickel heaters, the temperature increase in the volume outside the frame is less than 50 °C. During operation in vacuum, the thrust range was calculated to be about 13–1070 µN and the maximum specific impulse 54 s. At maximum thrust, and a power consumption of 1.6 W, the total efficiency of the thruster was 17%. Designs of more efficient and versatile systems are discussed.

In this paper, we present a proton exchange membrane fuel cell (PEMFC) integrated with an electromagnetic (EM) air pump. The EM air pump provides the PEMFC with air by reciprocating motions of the permanent magnet attached to a flexible membrane. We performed a parametric study to decide the optimal dimensions of the reciprocating EM air pump. The effects of various operating parameters on the EM air pump were investigated with the root-mean-square (RMS) flow rate and current. A core with a higher relative permeability shows better performance. The RMS current linearly increases with the applied voltage and shows no dependence on the frequency. The RMS flow rate also increases with the voltage. The RMS flow rate per power consumption is highest at the frequency around 20 Hz and decreases as the applied voltage increases. When the reciprocating EM air pump was used to supply air to the portable PEMFC, it was found that the power density of the PEMFC increases with the applied voltage and shows the highest performance at the frequency of 10 Hz. We compared the performance of the PEMFC between the flow meter and the EM air pump used as an air supplier. About 81% of the output power using the flow meter was obtained when the EM air pump is operated at the applied voltage of 5 V. The parasitic power ratio reaches at its minimum value about 0.1 with an EM applied voltage of 0.25V.

Inkjet-printed microlens arrays (MLAs) were fabricated using hydrophilic confinement by UV/ozone treatment. The MLAs were made from negative photoresist SU-8 (n = 1.63 at 530 nm). A film of 10 µm thick SU-8 shadow mask was used to define UV/ozone-treated hydrophilic zones on an SU-8 photoresist base layer. An inkjet print head was used to jet SU-8 photoresist drops onto these zones. After UV-curing, MLAs with diameters of 150, 200, 400, 800 and 1000 µm were successfully fabricated. Contact angles of MLAs increased from 22° (on MLAs fabricated using an SU-8 photoresist base layer without any surface treatment) to 45.5°, 47.7°, 52.4°, 51.3° and 54.2°, for 150, 200, 400, 800 and 1000 µm lens diameters, respectively. Using hydrophilic confinement, MLAs with a wide range of contact angles can be fabricated with diameters from 150 µm to 1 mm. This method provides a simple, cost-effective fabrication process without need for etch-transfer.

A new technique is proposed in this paper to produce jets, droplets, and emulsions with sizes ranging from tens of microns down to the submicrometer scale. Liquid is injected at a constant flow rate through a hypodermic needle to form a film over the needle's outer surface. This film flows toward the needle tip until a liquid ligament is steadily ejected. Both the film motion and the liquid ejection are driven by the viscous and pressure forces exerted by a coflowing fluid stream. If this stream is a high-speed gas current, the outcome is a capillary jet which breaks up into droplets due to the Rayleigh instability. Micrometer emulsions are also produced by this instability mechanism when the injected liquid is focused by a viscous liquid stream. The minimum flow rates reached with the proposed technique are two orders of magnitude lower than those of the standard flow focusing configuration. This sharp reduction of the minimum flow rate allows one to form steady jets with radii down to the submicrometer scale. The stability of this new configuration is analyzed experimentally for both gas–liquid and liquid–liquid systems. In most of the cases, the loss of stability must be attributed to the liquid source because the critical Weber (capillary) number for the gas–liquid (liquid–liquid) case was significantly greater than the value corresponding to the convective/absolute instability transition in the jet.

The assembly of micrometer-sized parts is an important manufacturing process; any development in it could potentially change the current manufacturing practices for micrometer-scale devices. Due to the lack of reliable microassembly techniques, these devices are often manufactured using silicon, which includes etching and depositions with little use of assembly processes. The result is the requirement of specialized manufacturing conditions with hazardous byproducts and limited applications where only simple mechanisms are allowed. Optical tweezers are non-contact type manipulators that are very suitable for assembling microparts and solve one of the most difficult problems for microassembly, which is the sticking of the physical manipulator to the micropart. Although contact type manipulators can be surface modified to be non-sticky, this involves extra preprocessing—optical tweezers do not require such additional efforts. The weakness of using optical tweezers is that the permanent assembly of parts is not possible as only very small forces can be applied. We introduce an advanced microassembly environment with the combined use of optical tweezers and a motorized microtip, where the former is used to position two parts and the latter is used to introduce deformation in the parts so that they form a strongly fitted assembly.

In this paper, electrohydrodynamic jetting is investigated in order to print ultra-fine dots and lines in drop-on-demand (DOD) mode, using micro-electromechanical system-based printhead with a piezoelectric actuator. In such hybrid system, jetting ultra-fine droplets in DOD mode, without applying an extremely high-voltage pulse, is possible as the meniscus is first disturbed by a piezoelectric actuator and the droplet is ejected by the applied electric field. As the amplitude of the drive waveform of the piezoelectric actuator is varied, droplets with volumes of 3.4 to 46.8 pL are realized. As the amplitude of the electric field is increased, the ejected droplets lengthen and at 8 kV, thin elliptical dots are printed. Although changing the jetting frequency from 0.1 to 2.0 kHz resulted in volume reduction from 9.4 pL down to 2.9 pL, the DOD characteristic is well maintained throughout. Such hybrid jetting characteristics enable the generation of diverse patterns in the printed electronics area.

A monolithically integrated glass microlens optical scanner is presented. A new wafer-level fabrication approach addresses the issue of microlens integration and alignment in conventional microlens integrated devices. A through-silicon plano-convex glass microlens has been fabricated on a silicon substrate prior to the formation of an integrated microlens actuator, realized through two thermal reflow processes at 850 °C. A lateral comb drive is adapted to demonstrate the glass microlens scanner. The 800 µm diameter microlens was laterally shifted up to ±51.6 µm when an ac voltage of 28.5 V in amplitude was applied at a resonant frequency of 1.749 kHz at atmospheric pressure. The optical scanning angle of ±2.0° has been obtained with the fabricated device.

This work presents a convenient and versatile prototyping method for integrating surface-micromachined microelectromechanical systems (MEMS) directly above IC electronics, at the die level. Such localized implementation helps reduce development costs associated with the acquisition of full-sized semiconductor wafers. To demonstrate the validity of this method, variants of an IC-compatible surface-micromachining MEMS process are used to build different MEMS devices above a commercial transimpedance amplifier chip. Subsequent functional assessments for both the electronics and the MEMS indicate that the integration is successful, validating the prototyping methodology presented in this work, as well as the suitability of the selected MEMS technology for above-IC integration.

This paper reports on the fabrication and characterization of a novel laterally-driven piezoelectric bimorph micro electro mechanical systems actuator with high aspect-ratio (AR) lead–zirconate–titanate (PZT) structures. The PZT structures (AR=8) sandwiched with Pt sidewall electrodes were fabricated by a nanocomposite sol–gel process with micromachined silicon templates. A single-cantilever-type lateral bimorph actuator was successfully fabricated, and no initial vertical bending was observed, even on a 500 µm long actuator. A lateral displacement of 10 µm was obtained in bimorph actuation at driving voltages of +25 V/−5 V. Then the piezoelectric property of the PZT structure was characterized from the actuator's performance. The lateral piezoelectric actuator has a variety of potential applications as a replacement for electrostatic comb drive actuators occupying a large area.

A new through-silicon via (TSV) build-up stacking method using oxide bonding is proposed and implemented in this work. The proposed method can be applied to the fabrication of a TSV stack chip. Thermal stress analysis was carried out to compare the structural reliability between conventional TSV and the proposed TSV model. The simulation results indicate that the proposed TSV model is more reliable than the conventional model with respect to stress in the stack chip. Experiments were conducted by oxide bonding of chips and the oxide bonding energy was acquired by a four point bending test. The obtained bonding energy sufficiently exceeds the energy criteria of 3D stacking. Thus, two oxide wafers with an 8 inch diameter were bonded by oxide bonding at the wafer level. The 0.6 µm thick oxide layers were located between bonded wafers and the top wafer was thinned down to fabricate blind via at the top of bonded wafer. The thickness of the top and bottom wafer is to 70 and 725 µm, respectively, after the top chemical mechanical polishing (CMP) process. Then blind vias were fabricated by deep reactive ion etching; the diameter and depth of the via is 20 µm and 150 µm, respectively. A through hole was formed by bottom CMP; total thickness of the oxide bonded wafer is 140 µm. The dielectric layer (SiO2), adhesion and diffusion barrier (TiN, Ti) and wetting layer (Cu) were deposited sequentially to improve the wettability of the via wall. Since the molten solder cannot be filled in the via if there is no wetting layer at the via wall. Finally, the vias were successfully filled with molten solder within 10 s.

A silicon micro-machined thermal gas flow sensor operating in anemometric mode has been designed, fabricated and investigated for continuous and pulsatile flows. The sensor is specifically designed to achieve high sensitivity, fast response time and high robustness. It is composed of four metallic resistors interconnected to form a Wheatstone bridge. Two of them act simultaneously as the heating and sensing elements and the two others are used as a temperature reference. The heating element consists of a metallic wire of platinum Pt (2 µm width, 2 mm length) maintained on each lateral side by periodic silicon oxide SiO₂ micro-bridges. Finite element simulations show that this structure achieves a fast thermal response time of 200 µs in constant current operating mode and a coefficient of temperature rise close to 25 °C/120 µW based on bulk electrical resistivity and when the Pt wire and SiO₂ thicknesses are close to 100 nm and 500 nm, respectively. This design allows the fabrication of a robust thermal flow sensor with heating elements as long as possible, which enables accurate measurements with high signal to noise ratio. The sensor is then characterised experimentally; its electrical and thermal properties are obtained in the absence of fluid flow. These results confirm the effectiveness of the thermal insulation as predicted by the simulations. In a second step, the fluidic characterizations are reported and discussed for both continuous and pulsatile flows. In continuous mode, the sensor response was studied for gas flow rate ranging from 0 L min⁻¹ to 10 L min⁻¹. In pulsatile mode, the sensor is integrated inside a channel of a micro-valve actuated at 200 Hz. The measurements are compared with those obtained by a classical commercial hot wire.

Copper forms a porous oxide, allowing the formation of oxide layers up to tens of microns thick to be created at modest processing temperatures. In this work, the controlled oxidation of copper is employed within an all-metal electroplating process to create electrically insulating, structural posts and beams. This capability could eliminate the additional dielectric deposition and patterning steps that are often needed during the construction of sensors, waveguides, and other microfabricated devices. In this paper, copper oxidation rates for thermal and plasma-assisted growth methods are characterized. Time control of the oxide growth enables larger copper structures to remain conductive while smaller copper posts are fully oxidized. The concept is demonstrated using the controlled oxidation of a copper layer between two nickel layers to fabricate nickel inductors having both copper electrical vias and copper oxide support pillars. Nickel was utilized in this demonstration for its resistance against low temperature oxidation and interdiffusion with copper.

In this paper, we present a vision measurement technique to evaluate electrohydrodynamic (EHD) inkjet behavior, and discuss the effects of the pulse voltage shape on the EHD jets for drop-on-demand printing, including the falling and rising time in the pulse voltage. Sequential images acquired by a charge-coupled device (CCD) camera with a strobe light-emitting diode (LED) were used to visualize EHD jet behavior with respect to time. A vision algorithm was implemented in an EHD jet system to enable in situ measurement and analysis of EHD jets. A guideline for selecting pulse shape parameters is also presented, to enable the achievement of high-frequency reliable jets for drop-on-demand printing. Printing results are presented to demonstrate the drop consistency of jets.

This study presents a ring-type micro-structure design on the substrate and its corresponding micro fabrication processes for a lens-type light-emitting diode (LED) package. The dome-type or crater-type silicone lenses are achieved by a dispensing and embossing process rather than a molding process. Silicone with a high viscosity and thixotropy index is used as the encapsulant material. The ring-type micro structure is adopted to confine the dispensed silicone encapsulant so as to form the packaged lens. With the architecture and process described, this LED package technology herein has three merits: (1) the flexibility of lens-type LED package designs is enhanced; (2) a dome-type package design is used to enhance the intensity; (3) a crater-type package design is used to enhance the view angle. Measurement results show the ratio between the lens height and lens radius can vary from 0.4 to 1 by changing the volume of dispensed silicone. The view angles of dome-type and crater-type packages can reach 155° ± 5° and 175° ± 5°, respectively. As compared with the commercial plastic leaded chip carrier-type package, the luminous flux of a monochromatic blue light LED is improved by 15% by the dome-type package (improved by 7% by the crater-type package) and the luminous flux of a white light LED is improved by 25% by the dome-type package (improved by 13% by the crater-type package). The luminous flux of monochromatic blue light LED and white light LED are respectively improved by 8% and 12% by the dome-type package as compare with the crater-type package.

The mechanism behind the degradation of the mechanical properties of silicon (Si) microcantilevers caused by plasma-induced surface defects was investigated. The resonant frequency (f) and quality factor (Q factor) were deteriorated by defects generated after irradiating Ar plasma. We found that Young's modulus in the surface region was decreased after the plasma irradiation, but this does not explain the drastic change to the resonant frequency. The decrease could be explained by using a model in which a surface defect layer causes energy dissipation. Hydrogen annealing at 450 °C and rapid thermal annealing at 1000 °C could not repair the mechanical properties degraded by the plasma irradiation. After annealing, Young's modulus was not recovered while the dangling bonds were diminished, because the annealing could not restore the crystalline structure of the silicon. These results indicate that extensive defects such as dislocations or amorphous phases may be generated during plasma irradiation, causing energy dissipation. Since the degraded mechanical property in the plasma processes cannot be restored by annealing, it is important to prevent any damage from occurring at any stage of the processes.

This paper presents a comb-drive actuator integrated with parylene-based flexible beams for large displacements at a low driving force. Single-crystal silicon and polysilicon are the traditional materials used for comb-drive actuators in the microeletromechanical systems industry. However, the larger Young's modulus limits the displacement at a low applied voltage. This study uses the parylene beams with the characteristic of a low modulus of the elastic comb-drive actuator as a compliant suspension to create a larger displacement (>50 µm) with smaller driving forces than that of silicon. High-aspect-ratio parylene beams can be fabricated through the deposition and removal of parylene in multiple stages on a silicon micro-trench. The proposed process uses a silicon-on-insulator wafer as the substrate to fabricate suspended silicon and parylene beams as rigid and compliant structures, respectively. The test devices of parylene- and silicon-based comb-drive actuators were fabricated with 100 pairs of comb fingers with gaps of 5 µm, and compliant beams of 15 µm in width, 2000 µm in span and 50 µm in thickness. When a driving voltage of 40 V dc was applied, the parylene-based comb-drive actuator generated a displacement of up to 55 µm, whereas the silicon-based comb-drive actuator generated a displacement of 2 µm. The parylene-based comb-drive actuator can generate about 27 times of displacement than that of silicon. This design is suitable for application in devices with large in-plane displacement and low switching speed.

Micromachined cryocoolers are attractive tools for cooling electronic chips and devices to cryogenic temperatures. A two-stage 30 K microcooler operating with nitrogen and hydrogen gas is fabricated using micromachining technology. The nitrogen and hydrogen stages cool down to about 94 and 30 K, respectively, using Joule–Thomson expansion in a restriction with a height of 1.10 μm. The nitrogen stage is typically operated between 1.1 bar at the low-pressure side and 85.1 bar at the high-pressure side. The hydrogen stage has a low pressure of 5.7 bar, whereas the high pressure is varied between 45.5 and 60.4 bar. In changing the pressure settings, the cooling power can more or less be exchanged between the two stages. These typically range from 21 to 84 mW at 95 K at the nitrogen stage, corresponding to 30 to 5 mW at 31–32 K at the hydrogen stage. This paper discusses the characterization of this two-stage microcooler. Experimental results on cool down and cooling power are compared to dynamic modeling predictions.

The application of fine line micro-circuitry onto ceramic substrates currently requires a multi step process including printing, baking and sintering. A new, one-step, process utilizing particle impact deposition is presented. This process directs a high velocity stream of copper particles within a helium carrier onto a ceramic substrate. Upon impact the particles deform and adhere to the substrate and to previously deposited particles. The use of a capillary tube as the flow nozzle restricts the jet and the resulting deposited copper to micron scale dimensions. The deposited copper is dense, with near zero porosity. Robot control of the jet position can yield precise conduction lines and component connections.

We report on the sensitivity of thin-film bulk acoustic resonators (FBARs) to localized contact mechanical forces, their design for high sensitivity and the performance under different forcing conditions and mechanisms. Cantilever and membrane structures are the examples chosen for structure and process flow design, finite element modeling and experimental characterization. To leverage on the high sensitivity of FBAR devices at the 2 GHz radio frequency, we carried out electrical bulk acoustic wave excitation and readout of the first longitudinal acoustic mode. Experiments to extract actual sensitivities included atomic force microscopy-driven force excitation, nanoindentation and manual force loading. A force sensitivity function with extracted values S (MHz N⁻¹) from 50 to 270 MHz N⁻¹ shows its dependence on the thin-film stack configuration, the extent of force which determines the linear regime and the spatial location of the force loading source. The discussion provides a force range and sensitivity benchmarking, possible manufacturing and application scenarios, and design guidelines for future integrated devices.

This paper presents results on the design and fabrication of an AT-cut quartz Lamb wave resonator with phononic crystal (PC) reflective gratings. The deep reactive ion etching process with a laboratory-made etcher was utilized to fabricate PC structures of the AT-cut quartz Lamb wave resonator. The finite element method was adopted to calculate the PC band structure, effective reflective distance from the PC boundary and further the resonant modes and admittance of the phononic Lamb wave resonant cavity. Through the comparison studies between the experimental and simulated results, a design process for the AT-cut quartz phononic Lamb wave resonator was proposed. It is noted that by using the phononic reflectors, the size of the Lamb wave resonator can be reduced significantly.

A stacked double-layer (SDL) thermopile-based infrared sensor, which comprised of 96 thermocouples on a suspended membrane, has been designed and fabricated with a CMOS-compatible process. The thermoelectric properties were characterized, and responsivity (R_s) of 202.8 V W⁻¹ and detectivity (D*) of 2.85*10⁸ cm Hz^1/2 W⁻¹ for a SDL thermopile were derived.

An all-carbon-based field effect transistor (FET) was fabricated on flexible polyethylene terephthalate substrates by the aerosol jet printing method described in this paper. Three different types of homogeneous conductive inks were made and then printed layer-by-layer to form the FET chips. The conducting-reduced graphene oxide was used as electrodes (source and drain) and channel, respectively. Graphene oxide was used as dielectrics while multi-walled carbon nanotubes acted as the gate electrode. The all-carbon-based FET shows a good mobility of 350 cm² (V s)^–1 at a drain bias of −1 V. This simple and novel method explores a promising way to fabricate all-carbon-based, flexible and low-cost electronic devices.

We describe multi-optical probe confocal microscopy using a micro-objective lens array for large areal inspection. A microlens array with 100 µm focal length, 80 µm diameter and 90 µm pitch was designed and fabricated with an array size of 10 × 10. In order to produce the high-fidelity microlens array, a UV imprinting process was employed, and a UV transparent mold for the imprinting process was manufactured by replicating a reflow lens master. A blocking filter between the microlenses was introduced to minimize crosstalk and stray light noise for high resolution and high contrast imaging. The developed system is characterized by a 1 mm × 1 mm field of view with a nano-stage with 100 µm travel length. The lateral resolution was measured to be 0.79 µm. The method can be used for various applications such as the inspection of electric devices including display panels and large-area printed circuits with a high resolution.

In this article, a novel hybrid fabrication technology is presented that uses both a flexible polymer (polydimethylsiloxane-–PDMS) and a rigid polymer (SU-8). A covalent bond between the flexible and rigid polymer layers is achieved using an oxygen plasma treatment during a layer-by-layer direct spin-on process. Precise alignment of the features in each layer and a highly repeatable method are achieved by this new process. As a proof-of-concept, we successfully fabricated PDMS-based flexible microfluidic devices with SU-8-based rigid world-to-chip/chip-to-world interconnects. The bond strength between the PDMS and SU-8 layers is measured by three methods: (1) Instron® microtester to pull apart the layers; (2) voice coil actuator to test the bond between interconnects and the substrate; and (3) microfluidic pressurization test to evaluate the bond strength along the channels. The bond strength between the flexible PDMS layer and the rigid SU-8 features is very strong; the bond between these two polymers does not fail during these evaluations although the integrity of the PDMS layer itself fails during the microtester evaluation. Additionally, the layer-by-layer direct spin-on process resulted in a repeatable process and precise alignment of the features in each layer, which are necessary in order to achieve consistent performance from the fabricated devices. The rigid SU-8 interconnects fabricated onto a flexible PDMS device serve as a world-to-chip/chip-to-world interconnects for the direct connection with Tygon® tubing. Three different designs of hybrid (PDMS and SU-8 based) microfluidic devices are designed, fabricated and tested. Each variation differed in the microchannel design in order to demonstrate the versatility of the process to make devices on multiple scales and patterns. These hybrid microfluidic devices are capable of functioning without leakage up to pressures of 85.85 ±3.56 kPa. Although microfluidic channels with interconnects are shown as a proof-of-concept, the fabrication process demonstrated herein could be utilized to develop a number of more sophisticated microfluidic and biomedical devices.

In this paper, we report the numerical and experimental study on micromechanical resonators which are made by introducing defects on an otherwise perfect two-dimensional (2D) silicon phononic crystal (PnC) slab. The 2D PnC slab is made by etching a square array of cylindrical air holes in a free-standing silicon plate with a thickness of 10 µm, while the defects are created by reducing the radii of three rows of air holes at the centre of the 2D PnC slab. Three resonators with different values of reduced radii, i.e., 2 µm, 4 µm and 6 µm, are included in this study. The finite-element-modelling method is used to calculate the band structure of the perfect 2D PnC slab and to analyse the different mode shapes of the structure. The design, numerical modelling, fabrication process, as well as characterization results and discussions of the three PnC resonators are also included. Due to its CMOS-compatibility, aluminium nitride is chosen to be the piezoelectric material of the inter-digital transducers, which are used to generate and detect acoustic waves. Testing is done to characterize the resonant frequency (f), quality factor (Q), as well as insertion loss of each of the three microfabricated PnC resonators and the results are discussed by analysing the simulated transmission spectra, the defected band structures, and the steady-state displacement profiles of the structures at their respective resonant frequencies. The experimental results show that the designed PnC resonators with reduced central-hole radii have higher resonant frequency and higher quality factors as compared to their normal Fabry–Perot counterpart, thanks to the higher-frequency modes supported within the cavity and slow sound effect in the lateral direction introduced by the central holes with reduced radii, respectively. As a result, the achieved (f-Q) product can be as high as 2.96 × 10¹¹, which is among the highest for silicon resonators operating in air.

High efficiency heat exchangers, such as intercoolers and recuperators, are composed of complex and compact structures to enhance heat transfer. This limits the installation of conventional temperature sensors to measure the temperature inside the heat exchanger without flow disturbance. To overcome this limitation, we have developed a direct patterning method in which metal is sputtered onto a curved surface using film photoresist and the fabrication of thin film Au resistance temperature detection (RTD) temperature sensors. A photosensitive film resist has been used to overcome the difficulty of 3-dimensional photolithography on a curved surface. The film resist after 2-dimensional photolithography is laminated over an alumina rod which is deposited with Au as an RTD sensing material. The Au metal is etched chemically, and the film resist is removed to form the thin film Au-RTD temperature sensors. They are calibrated by measuring the resistance change against temperature in a thermally controlled furnace. The second order polynomial fit shows good agreement with the measured temperatures with a standard deviation of 0.02 for the temperature range of 20–450 °C. Finally, the performance of the Au-RTD temperature sensors was evaluated.

Recent developments in consumer electronics, e.g. smartphones, tablet PCs or compact cameras, demand the development of very compact, active, optical microsystems. Because of their low power consumption, low operation voltage and cheap fabrication, voltage-controlled electrochromic devices (ECDs) based on polymer materials are promising candidates. However, the broad application of ECDs is still hindered by crucial technological obstacles. In this paper, we address two main issues: the structuring of the electrochromic material (ECM) and its underlying transparent conductive electrode on a microscale and additionally, the assembly of the ECD as an electrochemical cell with the challenges of airtight sealing, appropriate chemical stability, electrical insulation and the necessity of defining a compartment to hold the liquid electrolyte inside the cell. We first introduce a technological sequence consisting of batch processes (UV lithography and dry and wet etching) to render the microscale structuring of the ECM possible. Furthermore, we exploit the outstanding properties of the thick film dry photoresist Ordyl SY 300 to complete the assembly of ECDs with single-layer technology. As a proof of principle, we present the first results of an ECD device based on a poly(3,4-ethylenedioxythiophene) (PEDOT) material that works as an aperture stop with three coaxial segments, each individually controlled by an external voltage.

This work explores the performance of different silicon retainer ring designs when integrated into silicon micro-turbines (SMTs) incorporating thrust style bearings supported on 500 µm diameter steel balls. Experimental performance curves are presented for SMTs with rotor diameters of 5 mm and 10 mm, each with five different retainer designs varying in mechanical rigidity, ball pocket shape and ball complement. It was found that the different retainer designs yielded different performance curves, with the closed pocket designs consistently requiring lower input power for a given rotation speed, and the most rigid retainers giving the best performance overall. Both 5 mm and 10 mm diameter devices have shown repeatable performance at rotation speeds up to and exceeding 20 000 RPM with input power levels below 2 W, and devices were tested for over 2.5 million revolutions without failure. Retainer rings are commonly used in macro-scale bearings to ensure uniform spacing between the rolling elements. The integration of retainers into micro-bearings could lower costs by reducing the number of balls required for stable operation, and also open up the possibility of 'smart' bearings with integrated sensors to monitor the bearing status.

This note presents the data on the dielectric breakdown of polydimethylsiloxane (PDMS) thin films with thicknesses from 2 to 14 μm between the silicon electrodes. The results demonstrate that there is a strong dependence of the breakdown field on both the electrode gap and shape. The breakdown fields range from 250 to 635 V μm⁻¹, depending on the electrode geometry and gap, approaching 10× the breakdown fields for air gaps of the same size. The results are critical for understanding the performance limits of PDMS thin films used in the electromechanical microsystems.

Degradation of the electrowetting effect by a repeated actuation is evaluated over an extended period (200 min) on electrowetting-on-dielectric samples for three popular fluoropolymer top coatings: Teflon, FluoroPel and Cytop. A conductive liquid droplet is tested in an air environment at electrowetting number Ew ≅ 0.34. A pulse train (6 s period and 50% duty cycle) of three different voltage types is used for the actuation: positive dc, negative dc and 1 kHz ac. For the dc actuations, electrowetting degrades gradually on Cytop but significantly faster on Teflon and FluoroPel under the tested conditions. For the ac actuation, electrowetting degrades gradually on all three materials in a similar fashion.

We describe a method for fabricating paper-based microfluidic devices using a commercially available CO₂ laser system. The method is versatile and allows for controlled through-cutting and ablative etching of nitrocellulose substrates. In addition, the laser system can cut a variety of components that are useful in the fabrication of paper-based devices, including cellulose wicking pads, glass fiber source pads and Mylar-based substrates for the device housing.

This is a Retraction for the article 2013 J. Micromech. Microeng. 23 035036.

The science reported in this article is not incorrect. This article does not include all co-authors who contributed to the work. The article incorrectly attributes work performed at the University of California to the University of Jordan, and fails to acknowledge contributions from Georgia Institute of Technology. This article does not acknowledge the sources of funding for the work and the reference list is incomplete. This article was submitted by Hamzeh K Bardaweel without the knowledge of the other authors.