Table of contents

We demonstrate a MEMS micromirror enabled handheld confocal imaging probe for portable oral cancer detection, where a comparatively large field of view (FOV) was generated through the programmable Lissajous scanning pattern of the MEMS micromirror. Miniaturized handheld MEMS confocal imaging probe was developed, and further compared with the desktop confocal prototype under clinical setting. For the handheld confocal imaging system, optical design simulations using CODE V^R® shows the lateral and axial resolution to be 0.98 µm and 4.2 µm, where experimental values were determined to be 3 µm and 5.8 µm, respectively, with a FOV of 280 µm×300 µm. Fast Lissajous imaging speed up to 2 fps was realized with improved Labview and Java based real-time imaging software. Properties such as 3D imaging through autofocusing and mosaic imaging for extended lateral view (6 mm × 8 mm) were examined for carcinoma real-time pathology. Neoplastic lesion tissues of giant cell fibroma and peripheral ossifying fibroma, the fibroma inside the paraffin box and ex vivo gross tissues were imaged by the bench-top and handheld imaging modalities, and further compared with commercial microscope imaging results. The MEMS scanner-based handheld confocal imaging probe shows great promise as a potential clinical tool for oral cancer diagnosis and treatment.

Micromachined force/tactile sensors using nickel–chromium piezoresistors have been investigated experimentally and through finite-element analysis. The force sensors were designed with a suspended aluminum oxide (Al₂O₃) membrane and optimally placed piezoresistors to measure the strain in the membrane when deflected with an applied force. Different devices, each with varying size and shape of both the membrane and the piezoresistors, were designed, fabricated and characterized. The piezoresistors were placed into a half-Wheatstone bridge configuration with two active and two passive nickel–chromium resistors to provide temperature drift compensation. The force sensors were characterized using a load cell and a nanopositioner to measure the sensor response with applied load. Piezoresistive gauge factors in the range of 1–5.2 have been calculated for the thin film nichrome (NiCr 80/20 wt%) from the measured results. The force sensors were calculated to have a noise equivalent force of 65–245 nN.

Novel 2 × 2 mm² MEMS capacitive plates with two cavities (two capacitors) have been designed, modeled and fabricated for power harvesting by utilizing residual mechanical vibration in the environment using the electrostatic mechanism. The device is unique in the use of an innovative two-cavity design and electroplated nickel as the main structural material. When the capacitance increases for one capacitor, it will decrease for the other. This allows us to use both up and down directions to generate energy. The two-cavity design has achieved higher average power than conventional single-cavity devices under a wide range of vibration frequencies and amplitudes based on the time-domain simulations using Matlab. The movable plate was designed to vibrate without deformation and with resonance frequencies of around 900 Hz and lower using COMSOL finite element tool. The prototype two-cavity MEMS variable capacitor has been successfully fabricated using surface micromachining. The initial testing to investigate the electrical dynamic behavior and power generation from the fabricated devices was also implemented.

We studied a technique for fabricating metallic nanostamps with void-free, high-aspect-ratio nanostructures, using a pulse reverse current (PRC) electroforming process. During conventional electroforming of high-aspect-ratio nanostructures, a high current distribution is concentrated at the top and bottom corners, resulting in relatively fast growth of the nickel electroformed layer. This phenomenon leads to the formation of nanovoids in a metallic nanostamp, causing degradation of the stamp performance. To prevent the formation of nanovoids, we controlled the current waveform during the electroforming process. In this way, the process suppressed the formation of nanovoids, while effectively achieving a uniform current distribution. As practical examples, two types of metallic nanostamps were fabricated via direct current and PRC electroforming processes, one with a pitch of 0.8 µm and a height of 1.8 µm, and another with a pitch of 350 nm and a height of 525 nm. The internal nanovoids developed during the electroforming process were measured and analyzed.

Considering the buffer layer and electrodes, we set up a piezoelectric multilayered cantilever model to evaluate the dynamic performance of the micro-cantilevered piezo-actuator (MCPA) based on Euler–Bernoulli beam theory without considering the residual stresses on the MCPA. Adopting the material and geometric parameters of the previous MCPAs with the different lengths, the first-mode resonance frequency–beam length, the tip deflection–voltage and harmonic response curves are simulated by using the traditional and proposed models, and the results based on the proposed model are much closer to the experimental and finite element simulation results than those based on the traditional model, indicating that the proposed model is valid for evaluating the actuation performances of the MCPA. The effect of the mechanical damping and bending stiffness on the actuation performance of the MCPA is also discussed. Using the proposed model, the dependences of the first-mode resonance frequency and tip deflection of the MCPA on non-piezoelectric layer thicknesses are analyzed at the certain driving voltage. The above-mentioned methods and conclusions can be used for the structure optimized design and performance improvement of MCPAs.

We present a low-cost fabrication technique of a polymer-based micro-optical-electrical-mechanical systems (MOEMS) suited for the dynamic focusing of VCSELs (vertical-cavity surface-emitting lasers). A simple method based on an SU(8) double exposure is proposed for the collective integration of small footprint transparent suspended membrane arrays on vertical laser diodes. We demonstrate that this kind of MOEMS can provide under thermal actuation a vertical displacement of around 0.2 µm W⁻¹ over a maximal range of 8 µm. As a wide range of initial gaps between the membrane and the laser source can be chosen, this approach opens new insights into the dynamic control of the VCSEL beam waist position as well as for tunable VCSEL fabrication.

We demonstrate embedding of chiplets into wafers to bypass the monolithic integration challenges of combining micro-mechanical devices with active circuitry. Dry alignment is provided by passive guide tabs, which are created through polysilicon refill of frontside etched trenches. The guide tabs are compatible with further processing on the wafer. Precision chiplets are created by through-wafer etching. After chiplet drop-in, optical detection provides feedback of chiplet jamming, and horizontal driving of the chiplets finishes the zero insertion force assembly process. We demonstrate less than 2.5 µm of chiplet to substrate alignment error. Theoretical scaling of alignment accuracy reaches numbers comparable to photolithography, allowing high density interconnects for heterogeneous integration without precision manipulators.

A multilayer polydimethylsiloxane microdevice for cell-based high-throughput drug screening is described in this paper. This established microdevice was based on a modularization method and it integrated a drug/medium concentration gradient generator (CGG), pneumatic microvalves and a cell culture microchamber array. The CGG was able to generate five steps of linear concentrations with the same outlet flow rate. The medium/drug flowed through CGG and then into the pear-shaped cell culture microchambers vertically. This vertical perfusion mode was used to reduce the impact of the shear stress on the physiology of cells induced by the fluid flow in the microchambers. Pear-shaped microchambers with two arrays of miropillars at each outlet were adopted in this microdevice, which were beneficial to cell distribution. The chemotherapeutics Cisplatin (DDP)-induced Cisplatin-resistant cell line A549/DDP apoptotic experiments were performed well on this platform. The results showed that this novel microdevice could not only provide well-defined and stable conditions for cell culture, but was also useful for cell-based high-throughput drug screening with less reagents and time consumption.

A compact packaging solution for microelectromechanical systems (MEMS) devices is presented. The 3D-integrated packaging solution was designed for the instrumentation of a spinal screw with a wireless sensor array, but may be adapted for a variety of applications. To achieve the compact package size, an unobtrusive through-silicon via (TSV) design was added to the microfabrication process flow for the MEMS sensor. These TSVs allowed vertical integration of the MEMS devices onto flexible printed circuit boards (FPCBs) using a flip–chip system. Ohmic connections with resistance values below 1 Ω have been achieved for 100 µm TSVs in 300 and 500 µm substrates. This paper describes the design and microfabrication process flow for the TSVs, and provides details on the flip–chip techniques used to electrically and structurally connect the MEMS devices to the FPCBs.

We consider squeeze-film gas damping during microbeam motion away and toward a substrate as it occurs during opening and closing of RF switches and other MEMS devices with moving components. The numerical solution of the gas-damping problem in two-dimensional geometries is obtained based on the Boltzmann–ES-BGK equation. The difference in damping force between a downward- and upward-moving beam with a gap-to-width ratio of 34 is shown to vary from as little as from 5% for low beam velocities of 0.1 m s⁻¹ to more than 200% at 2.4 m s⁻¹. For a constant velocity magnitude of 0.8 m s⁻¹, this difference increases from 60% to almost 90% when the pressure is reduced by an order of magnitude. The numerical simulations are consistent with earlier observations of a significantly higher damping force during the closing of a capacitive RF MEMS switch reported by Steeneken et al (2005 J. Micromech. Microeng.15 176–84). The physical mechanism leading to this nonlinear dependence of the damping force on velocity has been attributed to the differences in the flow rarefaction regime for the gas in the microgap.

The stability of flow focusing taking place in a converging–diverging nozzle, as well as the size of the resulting microjets, is examined experimentally in this paper. The results obtained in most aspects of the problem are similar to those of the classical plate-orifice configuration. There is, however, a notable difference between flow focusing in nozzles and in the plate-orifice configuration. In the former case, the liquid meniscus oscillates laterally (global whipping) for a significant area of the control parameter plane, a phenomenon never observed when focusing with the plate-orifice configuration. Global whipping may constitute an important drawback of flow focusing with nozzles because it reduces the robustness of the technique.

This paper presents the low-cost, fine-resolution printing of conductive copper patterns on silicon substrate. The colloidal solution containing copper nanoparticles is deposited through electrohydrodynamic printing technology. Conductive copper tracks of different width are printed by varying the operating conditions (applied voltage and flow rate) and controlling the jet diameter. The minimum pattern width achieved was approximately 12 µm with the average thickness of 82 nm across the width after the sintering process. The achieved pattern width is five times smaller than the capillary used for patterning. The morphology and purity of the printed copper tracks were analyzed through scanning electron microscopy (SEM), atomic force microscopy (AFM) and x-ray diffraction (XRD). The current–voltage (I–V) characteristic of the printed copper tracks showed linear Ohmic behavior and exhibited resistivity ranging from 5.98 × 10⁻⁸ Ω m⁻¹ to 2.42 × 10⁻⁷ Ω m⁻¹.

The adverse effect of mechanical agitation (magnetic bead stirring) as well as galvanic interaction between the evolving facets of the etch front on the amount of undercutting during anisotropic etching of Si{1 0 0} wafers in surfactant-added tetramethylammonium hydroxide (TMAH) is studied by etching different mask patterns in magnetically stirred and nonstirred solutions. Triton X-100, with formula C₁₄H₂₂O(C₂H₄O)_n, where n = 9–10, is used as the surfactant. The stirring results conclude that the adsorption of the surfactant on the etched silicon surfaces is predominantly physical in nature rather than chemical (physisorption versus chemisorption). The proposed model to account for the galvanic interaction between the evolving facets indicates that the underlying chemical etching process can be significantly surpassed by the onset of an electrochemical etching contribution when the relative area of the exposed {1 0 0} surface becomes relatively small in comparison to that of the developed {1 1 1} sidewalls. This study is useful for engineering applications where surfactant-added TMAH is used for the fabrication of silicon MEMS structures that should contain negligible undercutting.

A simple micromachined process based on one photomask is developed for a novel micropreconcentrator (µPCT) used in a micro gas chromatograph (µGC). Unique thick silver heating microstructures with a high surface area for microheater of µPCT are fabricated by combining the microfluidic laminar flow technique and the Tollens' reaction within a microchannel. Silver deposition using this laminar flow patterning technique provides a higher deposition rate and easier microfabrication compared to conventional micromachined technologies for thick metal microstructures (>200 µm). An amorphous and porous carbon film that functions as an adsorbent is grown on microheaters inside the microchannel. The µPCT can be heated to >300 °C rapidly by applying a constant electrical power of ∼1 W with a heating rate of 10 °C s⁻¹. Four volatile organic compounds, acetone, benzene, toluene and xylene, are collected through the proposed novel µPCTs and separated successfully using a 17 m long gas chromatography column. The peak widths at half height (PWHHs) of the four compounds are relatively narrow (<6 s), and the minimum PWHH of 3.75 s is obtained for acetone. The preconcentration factors are >38 000 for benzene and toluene.

Thermal flow sensors have been designed, fabricated, and characterized. All bulk material in these devices is silicon so that they are integratable in silicon-based microsystems. To mitigate heat losses and to allow for use of corrosive gases, the heating and sensing thin film titanium/platinum elements, injecting and extracting heat, respectively, from the flow, are placed outside the channel on top of a membrane consisting of alternating layers of stress-balancing silicon dioxide and silicon nitride. For the fabrication, an unconventional bond surface protection method using sputter-deposited aluminum instead of thermal silicon dioxide is used in the process steps prior to silicon fusion bonding. A method for performing lift-off on top of the transparent membrane was also developed. The sensors, measuring 9.5 × 9.5 mm², are characterized in calorimetric and time-of-flight modes with nitrogen flow rates between 0 sccm and 300 sccm. The maximum calorimetric sensor flow signal and sensitivity are 0.95 mV and 29 µV sccm⁻¹, respectively, with power consumption less than 40 mW. The time-of-flight mode is found to have a wider detectable flow range compared with calorimetric mode, and the time of flight measured indicates a response time of the sensor in the millisecond range. The design and operation of a sensor with high sensitivity and large flow range are discussed. A key element of this discussion is the configuration of the array of heaters and gauges along the channel to obtain different sensitivities and extend the operational range. This means that the sensor can be tailored to different flow ranges.

In this paper we investigate a flexible method for the fabrication of complex microstructures using binding microparticles. Utilizing optical forces, micro-objects are caught, positioned and used as building blocks to form defined structures, analogous to assembling processes in the macroscopic world. Durable linkage between the individual particles is realized using biomolecules with high affinities applied as particle coatings. Planar structures can be assembled employing optical manipulation as well as three-dimensional patterns by stacking the generated layers. Even the properties of the generated structures can be locally designed as desired by using building blocks from diverse materials exhibiting different properties. This method benefits from its simplicity and the potential extensibility of the fabricated structure at any time of the experiment.

In this paper, we have designed a fabrication process for microgenerators by bonding a piezoelectric ceramic Pb(Zr,Ti)O₃ (PZT) plate to a silicon on insulator (SOI) wafer. The key techniques of the process include the low-temperature bonding technique using conductive epoxy resin, thinning of the bulk PZT using mechanical lapping and wet-etching combined method, and the micromachining of bulk ceramics by dicing. Through the development and optimization of the process, a piezoelectric MEMS power generator array was successfully fabricated. The typical device is selected to characterize the output performance of the microgenerators, while the composite beam dimension of PZT and silicon layer is about 3080 µm × 800 µm × 31 µm and the dimension of Ni proof mass is about 900 µm × 800 µm × 450 µm. The experimental results show that the output voltage, output power and power density of this device are 2.72 V_P-P, 11.56 µW and 28 856.7 µW cm⁻³ at the resonant frequency of 514.1 Hz when it matches an optimal resistive load of 70 kΩ under the excitation of 1g acceleration. The output performance of this device is higher, compared with that of other reported MEMS power generators, which demonstrates that this novel technique has great potential to fabricate high-performance piezoelectric MEMS energy harvester.

A stop grating concept is proposed to improve polymer filling in the thermal imprinting of a micro Fresnel lens structure. The stop grating consists of line and space structures outside the Fresnel lens pattern zone area. The experimental results have proved that the stop grating can help to achieve the complete filling of a mold, at the same time acting as a stop to prevent possible damage to the mold surface relief structures during imprinting press. A computer simulation was carried out to identify the phenomena of micro-holes at the edge of imprinted pattern. By removing the cavity between the pattern area and stop grating, perfect imprinting results have been achieved.

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

The NeuroMedicator is a micropump integrated with application-specific silicon microprobes aimed for drug delivery in neural research with small animals. The micropump has outer dimensions of 11 × 15 × 3 mm³ and contains 16 reservoirs each having a capacity of 0.25 µL. Thereby, the reservoirs are interconnected in a pearl-chain-like manner and are connected to two 8 mm long silicon microprobes. Each microprobe has a cross-sectional area of 250 × 250 µm² and features an integrated drug delivery channel of 50 × 50 µm² with an outlet of 25 µm in diameter. The drug is loaded to the micropump prior to implantation. After implantation, individual 0.25 µL portions of drug can be sequentially released by short heating pulses applied to a polydimethylsiloxane (PDMS) layer containing Expancel® microspheres. Due to local, irreversible thermal expansion of the elastic composite material, the drug is displaced from the reservoirs and released through the microprobe outlet directly to the neural tissue. While implanted, leakage of drug by diffusion occurs due to the open microprobe outlets. The maximum leakage within the first three days after implantation is calculated to be equivalent to 0.06 µL of drug solution.

This paper presents the validation of molecule-based pressure sensors in straight PDMS microchannel and further applications on acquiring the detailed pressure profiles in constricted PDMS microchannel. The experimental technique using molecule-based pressure sensor has been applied in various microscale measurements; however, deviations between theoretical and experimental results were also reported. The inconsistency is most likely due to the rough and heterogeneous channel surfaces. To validate the experimental technique with classic straight microchannel flow, the pressure distributions were measured at Reynolds numbers ranging from 10 to 86, and Knudsen numbers ranging from 0.0015 to 0.014. The experimental results acquired in the straight microchannel show excellent agreements with analytical solutions obtained from Navier–Stokes equations and first-order slip boundary condition. The pressure profiles acquired in the constricted microchannel show an apparent pressure drop, which indicates the flow recirculation, near the constriction area. The pressure recovery after the constriction structure was delayed further with increasing flow rate. There were more than 3000 data points acquired inside the 1 cm long PDMS microchannel from the entrance to the exit and 33 data points were acquired across the microchannel width 100 µm. Detailed resolution up to 3 µm per pixel in the local pressure evolution has been realized in the current experimental setup using a standard camera lens and extension tubes.

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

The evaluation technique of gas permeable characterization has been developed for an increased efficiency of gas–liquid chemical reactions and high accuracy of environmental diagnosis. This technique enables us to measure spatial distributions of velocity and dissolved gas concentration by utilizing confocal micron-resolution particle image velocimetry combined with a laser-induced fluorescence technique. Microfluidic devices with gas permeability through polymer membranes are composed of a cover glass and a polydimethylsiloxane (PDMS) chip with the ability to permeate various gases, since PDMS is an elastomeric material. In the chip, microchannels are manufactured using a cryogenic micromachining system. The gas permeation is dominated by several factors, such as the gas and liquid flow rates, the membrane thickness between the gas and liquid flow, and the surface area of the membranes. The advantage of the present device is to realize the control of gas permeability by changing the surface roughness of PDMS, because the cryogenic micromachining enables us to control the surface roughness of microchannels and an increase in roughness yields an increase in the surface area of membranes. The experiments were performed under several conditions with a change in the gas flow rate, the PDMS membrane thickness and the surface roughness, which affect the gas permeation phenomena. The spatial distributions of velocity and dissolved gas concentration were measured in the liquid flow fields. The results indicate that the velocity-vector distributions have similar patterns under all experimental conditions, while the dissolved gas concentration distributions have different patterns. It was observed that the gas permeability through PDMS membranes increased with an increase in gas flow rates and surface roughness and with a decrease in membrane thicknesses, which is in qualitative agreement with membrane theory. The important conclusion is that the proposed technique is suggested to have the possibility of evaluating the characterization of gas permeable microfluidic device through membranes.

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

A novel MEMS wireless millimeter-wave power sensor based on GaAs MMIC technology is presented in this paper. The principle of this wireless millimeter-wave power sensor is explained. It is designed and fabricated using MEMS technology and the GaAs MMIC process. With the millimeter-wave power range from 0.1 to 80 mW, the sensitivity of the wireless millimeter-wave power sensor is about 0.246 mV mW⁻¹ at 35 GHz. In order to verify the power detection capability, this wireless power sensor is mounted on a PCB which influences the microwave performance of the CPW-fed antenna including the return loss and the radiation pattern. The frequency-dependent characteristic and the degree-dependent characteristic of this wireless power sensor are researched. Furthermore, in addition to the combination of the advantages of CPW-fed antenna with the advantages of the thermoelectric power sensor, another significant advantage of this wireless millimeter-wave power sensor is that it can be integrated with MMICs and other planar connecting circuit structures with zero dc power consumption. These features make it suitable for various applications ranging from the environment or space radiation detection systems to radar receiver and transmitter systems.

We report improvements in the detection limit and responsivity of biomimetic hair-flow sensors by electrostatic spring softening. Applying a dc-bias voltage to our capacitive flow sensors results in a reduced sensory threshold, improving the mechanical transfer and flow detection limit by more than 6 dB. We further show that the sensor's responsivity for airflows is also improved on application of high-frequency ac-bias voltages to the sensor's capacitive structures with little sensitivity to the bias frequency.

In this paper, the concept, fabrication, activation and testing of a novel synchronous micropump based on microfabricated copper coils and polymer magnets are presented. The pump works by the synchronized rotation of two polymer magnets in an annular SU-8 microfluidic channel. Magnet rotation is achieved by sequentially activating a set of planar coils to repel or attract the first magnet (traveling magnet) through the channel, while the second one is anchored between the inlet and the outlet ports. At the end of each pumping cycle, the magnets exchange their anchored and traveling functions. The synchronization of magnet rotation has been achieved through programming two activation schemes that proved the high dependence of the pump operation and performance on employed activation scheme parameters. The magnetic forces exerted from electroplated coils on the polymer magnet were tested experimentally using a three-dimensional force sensor. Different coil dimensions have been investigated. A maximum force of 658 µN at an applied current of 138 mA was achieved. The micropump has successfully pumped water with rotational speeds up to 83.33 rpm. Water flow rates in the range of 17.3 µL min⁻¹ at 31.25 rpm to 158.7 µL min⁻¹ at 83.33 rpm were achieved.

In this paper we describe a general method to avoid stress-induced buckling of thin and large freestanding membranes. We show that using properly designed supports, in the form of microbeams, we can reduce the out-of-plane deflection of the membrane while maintaining its stiffness. As a proof of principle, we used a silicon-on-insulator (SOI) platform to fabricate 30 µm wide, 220 nm thick, free-standing Si membranes, supported by four 15 µm long and 3 µm wide microbeams. Using our approach, we are able to achieve an out-of-plane deformation of the membrane smaller than 50 nm in spite of 39 MPa of compressive internal stress. Our method is general, and can be applied to different material systems with compressive or tensile internal stress.

This paper reports the simulation, design, fabrication and characterization of thermal sensors integrated into an ultrathin active MEMS membrane. Temperature detection is combined without any additional fabrication steps to thermal actuation. Mixing the actuation with a thermal measurement within the membrane allows us to monitor temperature during membrane deflection. Prototypes are fabricated using standard CMOS processes and a deep reactive ion etching process to release the membrane. Inner and outer actuation lead to large membrane deflection. Using such sensors, we extract the temperature profile of the thermally actuated membrane. A good fitting between finite element method simulation and characterization results validates the sensors. Finally, the optimal position of thermal sensors is extracted from this study.

The stability of the resonance frequency (f_res) characteristics of MEMS resonators upon long-term cycling is crucial for many applications. Thin-film silicon MEMS have been developed to take advantage of their low-temperature processing and large area deposition characteristics. A reliability and stability study of thin-film-doped hydrogenated amorphous silicon (n⁺-a-Si:H)-aluminum MEMS resonators fabricated on glass substrates at a maximum processing temperature of 110 °C is presented. Long-term cycling of thin-film silicon microbridge resonators with different top electrode configurations was performed in vacuum and in air using electrostatic actuation. The number of cycles to failure, the f_res stability, the quality factor (Q) stability and the effect of measurement temperature are studied. The resonant bridges withstand the industry standard of 10¹¹ continuous cycles at high load with no failure reported both in vacuum and air with f_res shifts which depend on the resonator top electrode configuration. No Q degradation was observed. Frequency stability better than ±20 ppm was observed in vacuum after long-term cycling.

The charging and discharging behavior of silicon dioxide, silicon nitride and aluminum nitride dielectric coatings on microfabricated aluminum electrodes in response to an applied voltage, thermal treatment, operating environment and monolayer coating have been investigated through Kelvin probe force microscopy (KPFM) techniques. Correlated results from surface potential measurements and finite element simulations demonstrate the existence of capacitive coupling between the KPFM probe tip assembly and the device sample which give rise to as much as 20–40% difference between the applied bias and the measured surface potential. Surface charge mobility on the three material systems has been differentiated focusing on the influence of bulk and surface water and the relevant physicochemical properties. The merits and limitations of proposed schemes for mitigating the effects of dielectric charging, including thermal treatment and monolayer coating, are presented.

This paper presents a low-temperature zero-level packaging technique using a dry film type of PerMX polymer for RF devices. Silicon cap packaging with PerMX sealing ring and PerMX cap packaging through multilayer lamination have been implemented. All of the fabrication process has been performed at temperature less than 150 °C. The influence of each packaging cap on the packaged coplanar waveguide was first investigated using the HFSS electromagnetic simulation. The RF measurement results showed that both packaging caps did not have significant influence on the performance of transmission lines. The insertion loss changes before and after packaging were almost negligible up to 30 GHz, and the return losses were better than 20 dB. Also, the deformation of PerMX structures concerning the packaging processes has been studied. For silicon capping, the volumetric compression of PerMX sealing ring by the bonding process has been observed. For PerMX cap packaging, the deflection of the polymer cap has been investigated as a function of sealing ring width for the different cap size. Measured results had good agreement with the ANSYS simulated ones.

Advances in fluorescent live cell imaging provide high-content information that relates a cell's life events to its ancestors. An important requirement to track clonal growth and development is the retention of motile cells derived from an ancestor within the same microscopic field of view for days to weeks, while recording fluorescence images and controlling the mechanical and biochemical microenvironments that regulate cell growth and differentiation. The aim of this study was to design a microwell device for long-term, time-lapse imaging of motile cells with the specific requirements of (a) inoculating devices with an average of one cell per well and (b) retaining progeny of cells within a single microscopic field of view for extended growth periods. A two-layer PDMS microwell culture device consisting of a parallel-plate flow cell bonded on top of a microwell array was developed for cell capture and clonal culture. Cell deposition statistics were related to microwell geometry (plate separation and well depth) and the Reynolds number. Computational fluid dynamics was used to simulate flow in the microdevices as well as cell–fluid interactions. Analysis of the forces acting upon a cell was used to predict cell docking zones, which were confirmed by experimental observations. Cell–fluid dynamic interactions are important considerations for design of microdevices for long-term, live cell imaging. The analysis of force and torque balance provides a reasonable approximation for cell displacement forces. It is computationally less intensive compared to simulation of cell trajectories, and can be applied to a wide range of microdevice geometries to predict the cell docking behavior.

The chemical and physical properties of platinum (Pt) make it a useful material for microelectromechanical systems and microfluidic applications such as lab-on-a-chip devices. Platinum thin-films are frequently employed in applications where electrodes with high chemical stability, low electrical resistance or a high melting point are needed. Due to its chemical inertness it is however also one of the most difficult metals to pattern. The gold standard for patterning is chlorine RIE etching, a capital-intensive process not available in all labs. Here we present simple fabrication protocols for wet etching Pt thin-films in hot Aqua Regia based on sputtered Ti/Pt/Cr and Cr/Pt/Cr metal multilayers. Chromium (Cr) or titanium (Ti) is used as an adhesion layer for the Pt. Cr is used as a hard masking layer during the Pt etch as it can be easily and accurately patterned with photoresist and withstands the Aqua Regia. The Cr pattern is transferred into the Pt and the Cr mask later removed. Only standard chemicals and cleanroom equipment/tools are required. Prior to the Aqua Regia etch any surface passivation on the Pt is needs to be removed. This is usually achieved by a quick dip in dilute hydrofluoric acid (HF). HF is usually also used for wet-etching the Ti adhesion layer. We avoid the use of HF for both steps by replacing the HF-dip with an argon (Ar) plasma treatment and etching the Ti layer with a hydrogen peroxide (H₂O₂) based etchant.

Nanopores were fabricated using a transmission electron microscope (TEM). By manipulating TEM parameters, such as relative stage settings, electron beam shape and dwell time, it was possible to fabricate both single and ordered arrangements of nanopores with controlled geometries in silicon nitride membranes supported on a silicon window. Three distinct nanopore geometries with circular, elliptical and triangular cross-sections were fabricated. The smallest critical dimension reported here is on the order of 3 nm for the elliptical pore.