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Embedding liquid metals (LMs) into an elastomer is emerging as a promising strategy for stretchable conductors. Existing manufacturing techniques are struggling between spatial resolution and process complexity and are limited to chemically resistant substrates. Here, we report on a hybrid process combining stencil lithography and centrifugal force-assisted patterning of liquid metal for the development of LM-based stretchable conductors. The selective wetting behavior of oxide-removed eutectic gallium–indium (EGaIn) on metal patterns defined by stencil lithography enables micrometer scale LM patterns on an elastomeric substrate. Stencil lithography allows for defining metal regions without harsh chemical treatments, making it suitable for a wide range of substrates. Microscale LM patterns are achieved by efficiently removing the excess material by the centrifugal forces experienced from spinning the substrate. The proposed approach allows for the creation of LM patterns with a line width as small as 2 μm on a stretchable poly(dimethylsiloxane) (PDMS) substrate. The electrical measurement results show that the fabricated EGaIn devices can endure 40% mechanical strain over several thousands of cycles. Furthermore, a stencil design using microbridges is proposed to address the mechanical stability issue in stencil lithography. An EGaIn conductor with a serpentine structure and an interdigitated capacitor are fabricated and characterized. The results demonstrate that the patterned serpentine conductors retain their functionality with applied mechanical strain up to 80%. The performance of the interdigitated capacitors upon applied strain is in good agreement with the theoretical estimation. Finally, we demonstrate our approach also on poly(octamethylene maleate (anhydride) citrate) (POMaC) substrates to broaden the use of the proposed method to not only flexible and stretchable but also biodegradable substrates, opening a way for in vivo transient microsystem engineering. The work presented here provides a versatile and reliable approach for manufacturing stretchable conductors.

Objective Colloid solutions are commonly used to maintain perioperative fluid homeostasis. In regard to perioperative infant-centered care, data about the impact of colloids are rare. New data suggest a possible positive effect of hydroxyethyl starch (HES) concerning blood brain barrier. Therefore we conduct a retrospective single center study of children scheduled for neurosurgery, age 10% of body blood volume, receiving either 6% HES 130/0.4 or 5% human albumin (HA). Results Out of 913 patients, 86 were included (HES = 30; HA = 56). Compared to HES [16.4 ± 9.2 ml/kg body weight (mean ± SD)] HA group received more colloid volume (25.7 ± 11.3), which had more blood loss [HA 54.8 ± 45.0; HES 30.5 ± 30.0 (%) estimated blood volume] and higher fluid balances. Fibrinogen was decreased and activated partial thromboplastin time was elevated in HA group. Urinary output, creatinine and urea levels did not differ between the two groups. Serum calcium, total protein levels were lower in HES group. HA treated infants tended to have shorter ICU and hospital stays. We conclude that none of the investigated colloid solutions were without leverage to infants. Consequently randomized controlled trials about perioperative goal-directed fluid replacement of children undergoing (neuro)-surgery with major blood loss are needed.

Local bandgap tuning in two-dimensional (2D) materials is of significant importance for electronic and optoelectronic devices but achieving controllable and reproducible strain engineering at the nanoscale remains a challenge. Here, we report on thermomechanical nanoindentation with a scanning probe to create strain nanopatterns in 2D transition metal dichalcogenides and graphene, enabling arbitrary patterns with a modulated bandgap at a spatial resolution down to 20 nm. The 2D material is in contact via van der Waals interactions with a thin polymer layer underneath that deforms due to the heat and indentation force from the heated probe. Specifically, we demonstrate that the local bandgap of molybdenum disulfide (MoS2) is spatially modulated up to 10% and is tunable up to 180 meV in magnitude at a linear rate of about −70 meV per percent of strain. The technique provides a versatile tool for investigating the localized strain engineering of 2D materials with nanometer-scale resolution., Nano Letters, 20 (11), ISSN:1530-6984, ISSN:1530-6992

The growth of MoS2 layers of desired dimensions at predefined locations is essential for fabricating opto-electronic devices based solely on MoS2 or on hetero-structures based on MoS2. Here we present a new route for patterned growth of MoS2 by combining radio frequency (RF) magnetron sputtering, stencil mask lithography and vapour phase sulfurization. The present method does not involve chemical etchants and organic photoresist and hence provides a simplified process of achieving MoS2 patterns. Here, the control over the number of layers (mono, few and bulk) of MoS2 is achieved by varying the thickness of Mo films. The statistical variation in thickness i.e., number of MoS2 layers within the individual patterns is investigated from Raman mappings which revealed the uniform growth of 3-4 MoS2 layers. From Kelvin probe force microscopy, the surface potential values of MoS2 patterns lie in the range -350 to -370 mV, which is consistent with 2D MoS2 layer with thickness of 3-4 layers. The surface potential analysis across individual patterns indicates weakly n-type doping of few layers MoS2 with Fermi level located ~0.83-0.85 eV below the conduction band edge.

We report on the design and characterization of single-chip electron spin resonance (ESR) detectors operating at 50 GHz, 92 GHz, and 146 GHz. The core of the single-chip ESR detectors is an integrated LC-oscillator, formed by a single turn aluminum planar coil, a metal-oxide-metal capacitor, and two metal-oxide semiconductor field effect transistors used as negative resistance network. On the same chip, a second, nominally identical, LC-oscillator together with a mixer and an output buffer are also integrated. Thanks to the slightly asymmetric capacitance of the mixer inputs, a signal at a few hundreds of MHz is obtained at the output of the mixer. The mixer is used for frequency down-conversion, with the aim to obtain an output signal at a frequency easily manageable off-chip. The coil diameters are 120 μm, 70 μm, and 45 μm for the U-band, W-band, and the D-band oscillators, respectively. The experimental frequency noises at 100 kHz offset from the carrier are 90 Hz/Hz1/2, 300 Hz/Hz1/2, and 700 Hz/Hz1/2 at 300 K, respectively. The ESR spectra are obtained by measuring the frequency variations of the single-chip oscillators as a function of the applied magnetic field. The experimental spin sensitivities, as measured with a sample of α,γ-bisdiphenylene-β-phenylallyl (BDPA)/benzene complex, are 1 × 108 spins/Hz1/2, 4 × 107 spins/Hz1/2, 2 × 107 spins/Hz1/2 at 300 K, respectively. We also show the possibility to perform experiments up to 360 GHz by means of the higher harmonics in the microwave field produced by the integrated single-chip LC-oscillators.

Triboelectric nanogenerator (TENG) has proven to be a robust power source to efficiently convert ambient mechanical energy into electricity. It experienced substantial growth in the past years owing to its appealing features that make it superior than other self-powering principles. In particular, it excels in high output performance, sustainability in powering capability, as well as the ability to work completely autonomously. However, in order for TENG to make a real impact for societal applications, further improvements towards cost-effective TENG are required, in particular by exploring new inexpensive electrification materials and by simplifying the manufacture procedure. In this work, we present a paper-TENG completely prepared using cost efficient, commercially available commodity materials, such as paper cards, Teflon tape, and graphite pencil. Here, paper was firstly utilized as both supporting structure and functionally triboelectric pair simultaneously, which is widely available at low cost, and in addition, to our advantage, it has a considerably high ability to lose electrons during triboelectrification. As scalable fabrication, we implemented a single step using sandpaper imprinting to increase effective friction area and simple electrode fabrication by means of a graphite pencil. These two technical innovations were systematically studied as to the micro/nano-textured surfaces and conductive electrodes. The electrical properties of fabricated paper TENGs were comprehensively investigated and proved to be a usable power source by using a well-designed vibration platform and practical body motion, respectively. The fabricated paper TENG was successfully utilized to move liquid droplets in designated directions via electro-wetting. This new implementation of controlled droplet manipulation shows an attractive potential of TENG's applications in multidisciplinary fields, such as inkjet printing and lab-on-chip biomedical micro/nano-systems.

The spatiotemporal architecture of the cell membrane and diffusion dynamics of its constituents (lipids and proteins) are critical for many cellular processes such as signaling, trafficking and cell adhesions. Sub-diffraction photonics based on plasmonics offer new opportunities to follow such events as they can confine electric fields in nanoscale hotspots with spatial dimensions comparable to single molecules (∼5 nm).

In recent years, a new electrification-based mechanism called triboelectric generator (TEG) has been demonstrated as a stable and renewable power source to convert ambient energy into remarkable electrical output. Various TEG configurations have been proposed to enhance the output performance focusing on improvements to its working principle and structural geometry. In order for TEG to make an impact in real life applications, further improvement is needed in particular in the choice of the pair of electrification materials beyond the choice of traditional materials that have been employed in the construction of TEGs. Here, we investigate silk fibroin as a novel material for TEG that occupies a top-tier position in the triboelectric series and possesses the outstanding ability of losing electrons easily. Several technical challenges have been successfully addressed and are shown herein. For instance, an oxygen plasma process is employed to improve the interfacial energy between silk fibroin film and substrate by chemical modification and nanoscale roughness increase, which allows for the reliable switching mechanism needed to generate the electric power. The comprehensive study and the systematical measurement were carried out to study the fabricated TEG, including electrical output test, stability and reliability, humidity effect, and performance comparison with traditional materials. The silk fibroin is proven to be a promising material to construct TEG, and the fabricated TEG exhibits stable high-output performance, with maximum voltage, current, and power density of 268 V, 5.78 μA, and 193.6 μW/cm2, respectively, to a load of 40 MΩ. Furthermore, this silk fibroin film has two advantageous potentials for the development of TEGs: higher than 90% transmittance in the visible spectrum region and controllable solubility in aqueous solutions. The former property preserves the intrinsic optical property of TEG and enables the realisation of an ultra-transparent device, while the latter moves us closer to the attractive future vision of realising TEG systems that biodegradable for environmental sensing or implantable for biomedical applications. Additionally, we demonstrate that his silk-fibroin-based TEG can directly produce energy to power two 4-bit liquid crystal displays (LCDs) and to actuate a microscale cantilever. As the first demonstration of TEG applied to power a mechanical micro-device,thisTEG-micro-cantilever microsystem shows an attractive potential to realize fully integrated smart transducers that are needed for autonomous sensor networks.

Nuclear magnetic resonance (NMR) experiments on subnanoliter (sub-nL) volumes are hindered by the limited sensitivity of the detector and the difficulties in positioning and holding such small samples in proximity of the detector. In this work, we report on NMR experiments on liquid and biological entities immersed in liquids having volumes down to 100 pL. These measurements are enabled by the fabrication of high spatial resolution 3D printed microfluidic structures, specifically conceived to guide and confine sub-nL samples in the sub-nL most sensitive volume of a single-chip integrated NMR probe. The microfluidic structures are fabricated using a two-photon polymerization 3D printing technique having a resolution better than 1 μm3. The high spatial resolution 3D printing approach adopted here allows to rapidly fabricate complex microfluidic structures tailored to position, hold, and feed biological samples, with a design that maximizes the NMR signals amplitude and minimizes the static magnetic field inhomogeneities. The layer separating the sample from the microcoil, crucial to exploit the volume of maximum sensitivity of the detector, has a thickness of 10 μm. To demonstrate the potential of this approach, we report NMR experiments on sub-nL intact biological entities in liquid media, specifically ova of the tardigrade Richtersius coronifer and sections of Caenorhabditis elegans nematodes. We show a sensitivity of 2.5x1013 spins/Hz1/2 on 1H nuclei at 7 T, sufficient to detect 6 pmol of 1H nuclei of endogenous compounds in active volumes down to 100 pL and in a measurement time of 3 hours. Spectral resolutions of 0.01 ppm in liquid samples and of 0.1 ppm in the investigated biological entities are also demonstrated. The obtained results may indicate a route for NMR studies at the single unit level of important biological entities having sub-nL volumes, such as living microscopic organisms and eggs of several mammalians, humans included.

Second harmonic generation (SHG) is an important tool for the study of plasmonic nanostructures and can open up important sensing applications since the second harmonic (SH) signal has an increased sensitivity to nanostructures shape and environment in comparison with the linear scattering [1,2]. SHG from plasmonic centrosymmetric nanostructures is controlled by two main properties. First, SHG is forbidden in the bulk of centrosymmetric structures in the dipolar approximation, meaning that nanostructures made of metals like gold and silver generate a SH signal coming mainly from their surfaces, where the symmetry is effectively broken. Second, because of the same symmetry reason, a dipolar excitation at the fundamental frequency induces SH modes with vanishing dipole moments [3]. In the case of plasmonic dimers, with the large intensity enhancement occurring in the gap, the SH emission is limited due to out-of-phase SH sources with destructive interferences in the far-field region. Consequently, new strategies must be developed to overcome this limitation.

While plasmonic antennas composed of building blocks made of the same material have been thoroughly studied, recent investigations have highlighted the unique opportunities enabled by making compositionally asymmetric plasmonic systems. So far, mainly heterostructures composed of nanospheres and nanodiscs have been investigated, revealing opportunities for the design of Fano resonant nanostructures, directional scattering, sensing and catalytic applications. In this article, an improved fabrication method is reported that enables precise tuning of the heterodimer geometry, with interparticle distances made down to a few nanometers between Au–Ag and Au–Al nanoparticles. A wide range of mode energy detuning and coupling conditions are observed by near field hyperspectral imaging performed with electron energy loss spectroscopy, supported by full wave analysis numerical simulations. These results provide direct insights into the mode hybridization of plasmonic heterodimers, pointing out the influence of each dimer constituent in the overall electromagnetic response. By relating the coupling of nondipolar modes and plasmon–interband interaction with the dimer geometry, this work facilitates the development of plasmonic heterostructures with tailored responses, beyond the possibilities offered by homodimers.

We fabricated amorphous silicon n-i-p solar cells with two types of nanopatterned back reflectors using stencil lithography. One reflector type has a plasmonic grating that is embedded in the ZnO layer; the other one has a metallic grating patterned on top of the Ag layer. From comparing the short-circuit current densities of the two device types, we conclude that light trapping through grating coupling is more efficient than coupling of light through the excitation of localized surface plasmons. The back reflectors were patterned with dot arrays by evaporation of Ag through millimeter-size stencil membranes. The stencils themselves were patterned by wafer-scale nanosphere lithography. The dot arrays have a periodicity of 428 nm and efficiently scatter light in the near-infrared wavelength range. Both back reflectors types lead to the same morphology for the silicon films. This allows us a fair comparison of the two light coupling mechanisms. We found a 14% and 19% short-circuit current density enhancement for the plasmonic and for the metallic grating, respectively. The external quantum efficiency gains between 550 and 650 nm show similar guided modes resonances for both device types, but the excitation is stronger for the device with the metallic grating.

The application of Au/Si3N4 stencil masks for the transfer of patterns using different MeV-ion beams with various substrates has been investigated. The techniques investigated were namely, conventional lithography with positive- and negative-tone resist polymers, oxygen ion-induced etching of PTFE and patterning using an etch-stop in silicon. We demonstrate that using different well-known microtechnology material-modification techniques, patterns can be transferred using stencil masks and broad ion beams to nanomachining scenarios. In the case of the etch-stop process; writing of 3D micropatterns with different height levels was achieved using a broad beam. The stencil masks were found to be durable with no obvious deterioration and well suited for exposure of large areas. (C) 2013 Elsevier B.V. All rights reserved.

Electron energy-loss spectroscopy (EELS) has become an experimental method of choice for the investigation of localized surface plasmon resonances, allowing the simultaneous mapping of the associated field distributions and their resonant energies with a nanoscale spatial resolution. The experimental observations have been well-supported by numerical models based on the computation of the Lorentz force acting on the impinging electrons by the scattered field. However, in this framework, the influence of the intrinsic properties of the plasmonic nanostructures studied with the electron energy-loss (EEL) measurements is somehow hidden in the global response. To overcome this limitation, we propose to go beyond this standard, and well-established, electron perspective and instead to interpret the EELS data using directly the intrinsic properties of the nanostructures, without regard to the force acting on the electron. The proposed method is particularly well-suited for the description of coupled plasmonic systems, because the role played by each individual nanoparticle in the observed EEL spectrum can be clearly disentangled, enabling a more subtle understanding of the underlying physical processes. As examples, we consider different plasmonic geometries in order to emphasize the benefits of this new conceptual approach for interpreting experimental EELS data. In particular, we use it to describe results from samples made by traditional thin film patterning and by arranging colloidal nanostructures.

We present a novel triboelectric nanogenerator (TENG) based on a paper-Teflon configuration fabricated by an easy and cost-efficient process. Carbon electrodes were hand-drawn by means of a graphite pencil on commercial paper cards, and the conductivity was confirmed by multimeter. In order to increase the effective triboelectric area, we used sandpaper imprinting to increase the surface roughness more than 2-fold compared to flat surfaces yielding a more than 6-fold enhancement of power density. The achieved output voltage, current and power density were ∼55 V, ∼2.5 μA and ∼17 μW/cm2, respectively. The arch-shaped TENG shows robust output power when pressed by fingers to power a 2-bit liquid crystal display (LCD) demonstrating its use as energy harvester based on low-cost, commodity materials such as paper, Teflon and graphite.

With the use of the stencil lithography, we fabricated pentacene thin-film transistors pre- pared directly on thermally oxidized silicon gates with channel lengths ranging from 2 to 600 lm. By performing 4-probe measurements or by using the transfer line method on these field-effect transistors, we were able to separate the respective contributions of the channel and the contacts to the transistor performance. The contact resistance depends strongly on the gate voltage and on the grain size and morphology; this behavior has been attributed to screening effects at the contact barriers. The low-field mobility in the channel is 0.5–0.6 cm2/Vs in long-channel transistors and reaches mobility in the order of 10 cm2/ Vs in short-channel transistors consisting essentially of a single grain.

A PDMS based tuneable microoptical system fabricated merging deep reactive ion etching, SU-8 and soft lithography, with a low-cost (mass-production), simple and highly repetitive technology, is presented. This system consists on a structure of two microlenses with uncoupled optical properties that can be mechanically actuated. This device was numerically simulated prior to its fabrication, to optimize its design and improve its behaviour. In addition, an optical characterization of the fabricated devices was carried out to provide a proof of concept of the presented devices and validate the proposed fabrication technology.

This brief presents a fully integrated nanoelectromechanical system (NEMS) resonator, operable at frequencies in the megahertz range, together with a compact built-in CMOS interfacing circuitry. The proposed low-power second-generation current conveyor circuit allows detailed read-out of the nanocantilever structure for either extraction of equivalent circuit models or comparative studies at different pressure and dc biasing conditions. In this sense, extensive experimental results are presented for a real mixed electromechanical system integrated through a combination of in-house standard CMOS technology and nanodevice post-processing by nanostencil lithography. The proposed read-out scheme can be easily adapted to operate the nanocantilever in closed loop operation as a stand-alone NEMS oscillator.

Plano-convex microlens arrays of organic-inorganic polymers with tailored optical properties are presented. The fine-tuning of each microlens within an array is achieved by confining inkjet printed drops of the polymeric ink onto pre-patterned substrates. The lens optical properties are thus freely specified, and high numerical apertures from 0.45 to 0.9 and focal lengths between 10 μm and 100 μm are demonstrated, confirming theoretical predictions. Combining nanoimprint lithography approaches and inkjet printing enables using the same material for the microlenses and their substrates, improving the optical performances. Microlens arrays with desired specifications are printed reaching yields up to 100% and high lens reproducibility with standard deviations of the apparent contact angle under 1° and of the numerical apertures and focal lengths under 6%. Microlens arrays involving lenses with different characteristics, e.g. multi focal length, and thus focal planes separated by only few microns are printed with the same reproducibility.

This paper reports on the design, fabrication and characterization of a novel micro-optical system for imaging that is based on a miniaturized reflective objective. The fabrication process innovatively combines two additive micro-fabrication techniques: inkjet printing, to create the smooth spherical mirror shape, and stencil lithography, for local metal deposition. The process is highly flexible and thus allows the fabrication of reflective micro-objectives of different optical properties, which can be tailored for targeted applications. The fabricated micro-objectives presented here are designed for endoscopic microscopy and exhibit a spot size of 1 micrometer, which represents a two-fold improvement over commercial spherical microlenses of comparable size.

Welcome to the 27th IEEE International Conference on Micro Electro Mechanical Systems (MEMS 2015) in Estoril, Portugal!

In this paper, the fabrication and use of stencils for full-wafer scale shadow mask (stencil) lithography is described. The stencils fabricated via microelectromechanical systems are mechanically stabilized and show clearly reduced stress-induced membrane deformation, which translates into a more accurate surface pattern definition. Solid-state SiN membranes 500 nm thick and up to 1 mm2 in size having a 20-mum-thick silicon support rim following the outline of the stencil apertures were fabricated in a 100-mm Si wafer. The minimum aperture size presented in this paper is 3 mum. The increase of membrane stability was confirmed by depositing a highly stressed 35-nm-thick chrome layer. The results demonstrate a stability increase of the Si-supported compared to nonsupported membrane with identical shape by up to 89% as measured by the reduced out-of-plane deflection of overhanging membrane sections. Comparison by scanning electron microscopy and atomic force microscopy of the resulting micropatterns obtained by Cr deposition through both unsupported and Si-rim supported stencils shows better edge sharpness and clearer spatial details for surface patterns deposited through the stabilized stencil compared to those deposited through the nonsupported stencil. The improved stabilized stencils allow for large-area high-density surface patterning while maintaining membrane stability and pattern definition during stencil lithography

We report on the fabrication and electrical characterization of functionalized solid-state nanopores in low stress silicon nitride membranes. First, a pore of approximately 50 nm diameter was drilled using a focused ion beam technique, followed by the local deposition of silicon dioxide. A low-energy electron beam induced the decomposition of adsorbed tetraethyl orthosilicate resulting in site-selective functionalization of the nanopore by the formation of highly insulating silicon oxide. The deposition occurs monolayer by monolayer, which allows for control of the final diameter with subnanometer accuracy. Changes in the pore diameter could be monitored in real time by scanning electron microscopy. Recorded ion currents flowing through a single nanopore revealed asymmetry in the ion conduction properties with the sign of the applied potential. The low-frequency excess noise observed at negative voltage originated from stepwise conductance fluctuations of the open pore.

An innovative release method of polymer cantilevers with embedded integrated metal electrodes is presented. The fabrication is based on the lithographic patterning of the electrode layout on a wafer surface, covered by two layers of SU-8 polymer: a 10-mum-thick photo-structured layer for the cantilever, and a 200-mum-thick layer for the chip body. The releasing method is based on dry etching of a 2-mum-thick sacrificial polysilicon layer. Devices with complex electrode layout embedded in free-standing 500-mum-long and 100-mum-wide SU-8 cantilever were fabricated and tested. We have optimized major fabrication steps such as the optimization of the SU-8 chip geometry for reduced residual stress and for enhanced underetching, and by defining multiple metal layers [titanium (Ti), aluminum (Al), bismuth (Bi)] for improved adhesion between metallic electrodes and polymer. The process was validated for a miniature 2times2 mum2 Hall-sensor integrated at the apex of a polymer microcantilever for scanning magnetic field sensing. The cantilever has a spring constant of cong1 N/m and a resonance frequency of cong17 kHz. Galvanometric characterization of the Hall sensor showed an input/output resistance of 200Omega, a device sensitivity of 0.05 V/AT and a minimum detectable magnetic flux density of 9 muT/Hz1/2 at frequencies above 1 kHz at room temperature. Quantitative magnetic field measurements of a microcoil were performed. The generic method allows for a stable integration of electrodes into polymers MEMS and it can readily be used for other types of microsensors where conducting metal electrodes are integrated in cantilevers for advanced scanning probe sensing applications

We have developed a new hybrid AFM probe combining an SU-8 polymer body with a full tungsten cantilever having a nanometric tip. The fabrication is based on surface micromachining a silicon wafer, where tungsten is sputter deposited in oxidation sharpened moulds to yield sharp tips with radius below 20 nm. The material properties of tungsten were measured, yielding a hardness of 14 GPa, a specific resistivity of 14.8 μohm cm and Young’s modulus of 380 GPa. Analyses of the probes show a mechanical quality factor of 90 in air, and a low contact resistance of 25 ohm on a gold sample is measured. AFM imaging is demonstrated. As a step in the development of a robust electrically conducting AFM probe, the results are very promising.

A rapid and simple method to fabricate tiny shadow-masks and their use in multi-layer surface patterning with in situ micromechanical alignment is presented. Instead of using silicon micromachining with through-wafer etching to define the thin membrane with etched apertures, we are using photoplastic SU-8-based resist as structural material of both membrane and support rim. Two layers, 5 and 150 μm thick, are structured by lithography and finally released from the surface. The free-standing SU-8 membranes have apertures ranging from 6 to 300 μm. They are placed and mechanically fixed to the surface, which needs to be patterned. Deposition by evaporation of Cr, Au, Al or other material through the membrane apertures results in an accurate 1:1 replication of the aperture pattern. In view of multi-layer patterning, we used in situ micromechanical alignment pins or jigs and achieved an overlay precision of

A process to fabricate functional polysilicon structures above large (4 x 4 mm(2)) thin (200 nm), very flat LPCVD silicon rich nitride membranes was developed. Key features of this fabrication process are the use of low-stress LPCVD silicon nitride, sacrificial layer etching, and minimization of membrane stress and deformation after fabrication, which was done by complete removal of the sacrificial layer, avoidance of sharp corners in the design of the functional polysilicon structures, and annealing of the polysilicon after doping. A polysilicon layer that was directly attached to the silicon nitride membrane was used. The polysilicon was doped locally to separate the rotors from the stators electrically, preventing short-circuiting. The layer was patterned with a hexagonal supporting structure that serves three main functions: membrane strengthening, electrical wiring and microactuation. As a demonstration of the technology a pseudo hexagonal polysilicon framework with embedded comb-drive actuated microshutter suspended above a similar to 150-nm thick membrane, was successfully fabricated.

Polymers have the ability to conform to surface contours down to a few nanometres. We studied the filling of transparent epoxy-type EPON SU-8 into nanoscale apertures made in a thin metal film as a new method for polymer/metal near-field optical structures. Mould replica processes combining silicon micromachining with the photo-curable SU-8 offer great potential for low-cost nanostructure fabrication. In addition to offering a route for mass production, the transparent pyramidal probes are expected to improve light transmission thanks to a wider geometry near the aperture. By combining silicon MEMS, mould geometry tuning by oxidation, anti-adhesion coating by self-assembled monolayer and mechanical release steps, we propose an advanced method for near-field optical probe fabrication. The major improvement is the possibility to fabricate nanoscale apertures directly o­n wafer scale during the microfabrication process and not o­n free-standing tips. Optical measurements were performed with the fabricated probes. The full width half maximum after a Gaussian fit of the intensity profile indicates a lateral optical resolution of approximate to 60 nm.

A high sensitivity field asymmetric ion mobility spectrometer (FAIMS) was designed, fabricated, and tested. The main components of the system are a 10.6 eV UV photoionization source, an ion filter driven by a high voltage/high frequency n-MOS inverter circuit, and a low noise ion detector. The ion filter electronics are capable to generate square waveforms with peak-to-peak voltages up to 1000 V at frequencies up to 1 MHz with adjustable duty cycles. The ion detector current amplifier has a gain up to 1012 V/A with an effective equivalent input noise level down to about 1 fA/Hz1/2 during operation with the ion filter at the maximum voltage and frequency. The FAIMS system was characterized by detecting different standard chemical compounds. Additionally, we investigated the use of a synchronous modulation/demodulation technique to improve the signal-to-noise ratio in FAIMS measurements. In particular, we implemented the modulation of the compensation voltage with the synchronous demodulation of the ion current. The analysis of the measurements at low concentration levels led to an extrapolated limit of detection for acetone of 10 ppt with an averaging time of 1 s.

Self-assembly is a key coordination mechanism for large multi-unit systems and a powerful bottom-up technology for micro/nanofabrication. Controlled self-assembly and dynamic reconfiguration of large ensembles of microscopic particles can effectively bridge these domains to build innovative systems. In this perspective, we present SelfSys, a novel platform for the automated control of the fluidic self-assembly of microparticles. SelfSys centers around a water-filled microfluidic chamber whose agitation modes, induced by a coupled ultrasonic actuator, drive the assembly. Microparticle dynamics is imaged, tracked and analyzed in real-time by an integrated software framework, which in turn algorithmically controls the agitation modes of the microchamber. The closed control loop is fully automated and can direct the stochastic assembly of microparticle clusters of preset dimension. Control issues specific to SelfSys implementation are discussed, and its potential applications presented. The SelfSys platform embodies at microscale the automated self-assembly control paradigm we first demonstrated in an earlier platform.

We have developed a micromachined flow cell consisting of a flow channel integrated with micropipettes. The flow cell is used in combination with an optical trap setup (optical tweezers) to study mechanical and structural properties of /spl lambda/-DNA molecules. The flow cell was realized using silicon micromachining including the so-called buried channel technology to fabricate the micropipettes, the wet etching of glass to create the flow channel, and the powder blasting of glass to make the fluid connections. The volume of the flow cell is 2 /spl mu/l. The pipettes have a length of 130 /spl mu/m, a width of 5-10 /spl mu/m, a round opening of 1 /spl mu/m and can be processed with different shapes. Using this flow cell we stretched single molecules (/spl lambda/-DNA) showing typical force-extension curves also found with conventional techniques. These pipettes can be also used for drug delivery, for injection of small gas bubbles into a liquid flow to monitor the streamlines, and for the mixing of liquids to study diffusion effects. The paper describes the design, the fabrication and testing of the flow cell.

We present a 3D shadow mask technique for patterned modification of an area that is deeply recessed from the top surface with a large topographical step. The silicon shadow mask is micromachined such that it fits in a self-aligned fashion into the removed area of the device wafer and thus approaches the apertures close to the surface. Furthermore, owing to self-alignment between shadow and target, the lateral overlay precision is improved. The use of this technique is demonstrated for direct evaporation of metal patterns 10×50 μm 2 in size on the backside of a membrane of a bimorph-actuated device that is recessed by 500 μm. The same pattern dimensions were achieved in positive and negative resist by exposing it through the shadow mask aperture. We also show an application that uses a different type of shadow mask for the evaporation of an array of 25-μm wide metal wires across a step of 120 μm with no loss of dimension control. Full-wafer processing with the reusable shadow mask is demonstrated.

New types of piezoresistive cantilevers for torque magnetometry have been microfabricated and tested. The design is optimized to detect the flexion and torsion of the cantilever corresponding to a torque in two directions, which is induced by a microscopic magnetic sample mounted on the lever surrounded by an external magnetic field. The high sensitivity (up to ≈10 −14 N m) of the device is achieved by its special geometrical design featuring cantilever legs with only 3-μm-wide beams. The microfabrication process makes use of silicon-on-insulator wafers for precise etch-stop of a novel deep-trench etch process from the backside to fabricate the individual chips. One cantilever version has an integrated metal loop for absolute calibration of the sensor within 1%. The loop can also be used to actuate the lever mechanically. Owing to their small dimension and mass, the new devices feature ultrahigh sensitivity combined with short response time, which allows the characterization of microscopic magnetic samples with very high resolution.

We describe a new O-ring setup for wet-etching processes of microelectromechanical systems (MEMS) . Our new low-cost approach using siloxane-based seal rings entails the single-side etching of silicon and silicon dioxide using potassium hydroxide and buffered hydrofluoric acid, respectively. With this approach, the wafer is not immersed into the etching solution, but only the side to be etched is in contact with the solution, hence the previously fabricated device elements on the other side of the wafer are not damaged. In one process for etching silicon the etch solution is heated by an infrared lamp. We describe the fabrication of various cantilever-based sensors, such as arrays of 0.8-um thick levers for a chemical/electronic nose, and 5-um-thick silicon cantilevers having piezoresistive sensors. Our technique has gooduniformity and process control and, in addition, eliminates mechanical stress on the fragile wafers incurred by wafer chucks, which are required for the conventional immersion approach. It has improved process yield and reduces the waste of chemicals.

Detailed investigations of the limits of a new negative-tone near-UV resist (IBM SU-8) have been performed. SU-8 is an epoxy-based resist designed specifically for ultrathick, high-aspect-ratio MEMS-type applications. We have demonstrated that with single-layer coatings, thicknesses of more than 500 μm can be achieved reproducibly. Thicker resist layers can be made by applying multiple coatings, and we have achieved exposures in 1200 μm thick, double-coated SU-8 resist layers. We have found that the aspect ratio for near-UV (400 nm) exposed and developed structures can be greater than 18 and remains constant in the thickness range between 80 and 1200 μm. Vertical sidewall profiles result in good dimensional control over the entire resist thickness. To our knowledge, this is the highest aspect ratio reported for near-UV exposures and the given range of resist thicknesses. These results will open up new possibilities for low-cost LIGA-type processes for MEMS applications. The application potential of SU-8 is demonstrated by several examples of devices and structures fabricated by electroplating and photoplastic techniques. The latter is especially interesting as SU-8 has attractive mechanical properties.

In this article an integrated force sensor based on a stress-sensing MOS transistor is introduced for applications in scanning force microscopy (SFM) . The sensor configuration will be described, and theoretical and experimental investigations of the sensitivity will be presented. With the fabrication process, consisting of a standard CMOS process and post-processing (conventional silicon bulk micromachining), cantilevers with MOS transistors integrated at the base for deflection detection have been fabricated. The cantilevers typically have a spring constant of 1 N m-1, are 400 to 950 um in length and have a mechanical resonance frequency between 6.2 and 35 kHz. It is found that the stress sensitivity of the MOS transistor changes with the gate voltage, while being independent of the drain voltage. The cantilevers have successfully been used for SFM imaging in both contact mode and dynamic mode (tapping mode). These cantilevers together with integrated circuits are expected to be well suited for mass production because of their CMOS processing compatibility.

Selective Ga + ion implantation and miring by focused ion beam exposure and subsequent wet chemical etching is used to fabricate micro/nanomechanical elements in Si. Freestanding elements with a ~ 30 nm membrane thickness are made by controlled selective underetching between unexposed and exposed areas. Ultrahigh-frequency cantilever beams have been made with resonances in the tens of MHz range. Using a U-shaped beam cross section, mechanical stiffness could be increased 100-fold, which in turn increased the beam resonance frequency to several hundreds of MHz. The direct-write patterning/milling technique was used to fabricate various arbitrary shapes with vertical sidewalls such as submicrometer-sized containers, cups, and other nanomechanical devices.

This paper presents a novel in-liquid method to manipulate and micro-assemble MEMS in 3D by means of holographic optical trapping and hydrophobic interaction. Up to eight traps can be simultaneously generated with a trapping stiffness of 5 pN/mu m each. SU8 cylinders (10 mu m diameter, 10 mu m- 40 mu m height) were used as test MEMS, which could be translated with a speed of 6 mu m/s and rotated at 30 rpm. All forces were calibrated by video tracking the Brownian motion of the trapped MEMS and applying Boltzmann statistics. Selected surfaces of the MEMS parts were rendered hydrophobic and used as assembly sites. Using this approach it was possible to permanently assemble SU8 cylinders.

The possibilities of sub-micron patterning by means of microstencils using pulsed laser deposition were investigated. Stencils with circular and elliptical patterns were used, with pore sizes ranging from 1 mum down to 500 nm. Strontium titanate (SrTiO3), silicon (Si) and self-assembled monolayers on gold were used as substrate materials, whereas nickel (Ni), nickel oxide (NiO) and gold (Au) have been deposited. The results show that the chosen deposition setup makes an easy and fast way for high-quality pattern creation.

We present and characterize an organic?inorganic hybrid sol?gel material, phenyl-bridged polysilsesquioxane (ph-PSQ), for use as a new high resolution resist for electron beam lithography (EBL). The resist has a unique characteristic as the only positive tone silica-based resist available for EBL. Exploring the processing parameters has revealed that it is possible to switch the behaviour from negative to positive tone by application of a post-exposure bake (PEB). Based on the results from micro-FTIR spectroscopy, a description of the tone switching mechanisms is proposed. The negative tone behaviour is explained by the etch rate difference between silanol groups and cross-linked silica, present in unexposed and in exposed areas of the films, respectively. In the case of positive tone, after a PEB, the etch rate difference between a thermally densified cross-linked silica network and cage-like silica structures allows us to reveal the pattern. Contrast and sensitivity are estimated under different processing conditions, and the significant parameters for line edge roughness minimization are pointed out. Dense patterns down to 25?nm half-pitch and isolated structures down to 30?nm are demonstrated, exploiting the positive tone, and dense patterns down to 60?nm half-pitch are demonstrated in the negative tone. Etching selectivities in fluorinated gases for ph-PSQ nanostructures on silicon substrates are 1?9 for the positive tone and 1?12 for the negative tone.

Rhodamine B and Alexa Fluor 430 fluorophores have been used as doping agents for xerogel waveguides defined over an antiresonant (ARROW) filter. This configuration has a significant level of integration, since it merges the waveguide, the light emitter and the filter in a single photonic element. Different technologies have been combined for their implementation, namely soft lithography, standard silicon-based technology and silicon bulk micromachining. The spectral response of 15-mm long waveguides without fluorophore is first analyzed as a function of the waveguide width. Here, it has been observed how the xerogel used has a high transparency in the visible spectra, having only significant absorption at the wavelength where the ARROW filter is in resonance. In a second step, identical waveguides but doped with two different concentrations of Rhodamine B and Alexa Fluor 430 are studied. In addition to the effect of the filter, fluorophore-doped xerogel waveguides show losses close to -2 dB (equivalent to 2 dB of light emission). In addition, it has been observed how an increase of the fluorophore concentration within the xerogel matrix does not provide with a emission increase, but saturation or even a decrease of this magnitude due to self-absorption. Finally, the total losses of the proposed waveguides are analyzed as a function of their width, obtaining losses close to 5 dB for waveguide widths higher than 50 µm.

A monocrystalline silicon lever with an integrated silicon tip for a force/friction microscope was realized. Theoretical studies have been carried out to find the shape and dimensioning according to the mechanical system requirements. Moreover, sharp tips with a high aspect ratio could be demonstrated.

International audience; In this paper, we study the localized deposition of ZnO micro and nanostructures deposited by non-reactive rf-magnetron sputtering through a stencil mask on ultra-thin (10 nm) SiO2 layers containing a single plane of silicon nanocrystals (NCs), synthetized by ultra-low energy ion implantation followed by thermal annealing. The localized ZnO-deposited areas are reproducing the exact stencil mask patterns. A resistivity of around 5×10−3 Ω cm is measured on ZnO layer. The as-deposited ZnO material is 97% transparent above the wavelength at 400 nm. ZnO nanostructures can thus be used as transparent electrodes for Si NCs embedded in the gate-oxide of MOS devices.

A monocrystalline silicon lever with an integrated silicon tip for a Force/Friction Microscope was realized. Theoretical studies have been carried out to find the shape and dimensioning according to the mechanical system requirements. Moreover, sharp tips with a high aspect ratio could be demonstrated.

We describe a resistless proximal probe-based lithography technique, which enables the direct patterning of complex and submicron-sized structures of various materials. The method is based on a combination of scanning probe microscopy and the shadow masking technique, whereby structures are locally deposited through pinhole-like apertures situated in the proximity of a cantilever tip. Predefined excursions of the sample lead to the direct fabrication of arbitrary structures on the surface. Complex patterns such as rings and intersecting lines with linewidths well below 0.1 μm are presented.

In this paper we report on the effect of the environment on the SiO2/pentacene interface. Two batches of bottom-contact pentacene thin-film transistors have been fabricated with a 100 nm thick SiO2 as dielectric. Considerable shifts of the threshold voltages have been observed for the TFTs whose dielectric surface has been exposed to air for long periods of storage before depositing the pentacene layer. Based on reports from other research groups in the field, we consider that long exposure of the SiO2 to air may have the same effect on the SiO2-pentace interface as short but more aggressive oxygen plasma treatment.

We propose an original approach called a "stencil-masked ion implantation process" for performing a spatially localized synthesis of a limited number of Si nanocrystals within a thin SiO2 layer. In this process, the SiO2 layer is irradiated with 1 keV silicon ions through a stencil mask containing apertures (from 100 nm to 2 mu m), and subsequently thermally annealed to create Si nanocrystals. Scanning electron microscopy images show that the implanted areas mimic the mask geometry. Energy-filtered transmission electron microscopy and photoluminescence spectroscopy studies confirm that only the implanted areas are Si nanocrystal rich and fight emitting. The smaller nanocrystal size detected near the edges of the implanted areas is attributed to dose reduction effects. This feature leads to a blueshift of the PL energy. Electrical properties of the structures produced are investigated using Al gate MOS capacitors. Room temperature I-V and I-t characteristics exhibit discrete current peaks that are associated with single-electron charging of the nanocrystals and electrostatic interaction of the trapped charges with the tunnelling current. (C) 2007 Elsevier Ltd. All rights reserved.

A fully integrated nanoelectromechanical system (NEMS) resonator together with a compact built-in complementary metal-oxide-semiconductor (CMOS) interfacing circuitry is presented. The proposed low-power second generation current conveyor circuit allows measuring the mechanical frequency response of the nanocantilever structure in the megahertz range. Detailed experimental results at different DC biasing conditions and pressure levels are presented for a real mixed electromechanical system integrated through a combination of in-house standard CMOS technology and nanodevice post-processing based on nanostencil lithography. The proposed readout circuit can be adapted to operate the nanocantilever in closed loop as a stand-alone oscillator.