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This work presents a flexible polyimide-based capacitive tactile sensing array with sub-millimeter spatial resolution. The sensor is conceived to be embedded in a multimodal artificial finger to detect and classify the texture morphology of an object’s surface. The proposed tactile sensor comprises a $16\times 16$ array of capacitive sensing units. Each unit is composed of a parallel square electrode pairs ( $340~ {\mu }\text{m}\,\,\times 340~ {\mu }\text{m}$ ) separated by a compressible air cavity and embedded into a flexible polyimide substrate. Standard MEMS microfabrication techniques were used to develop the sensor. The polyimide device was covered with a thin compressible PDMS layer to tune the normal pressure sensitivity and dynamic range (225–430 ${\mu }\text{m}$ thin PDMS layer resulting in 0.23–0.14 fF/kPa). The detection of the surface morphologies of a regular grating stamp for different orientation and a small metallic nut placed on the sensor is demonstrated, showing a 420 ${\mu }\text{m}$ spatial resolution. The proposed sensor represents a novel capacitive tactile sensing device with a sub-mm resolution of human fingertip sensitivity.

Large-area and dense arrays of nanometric scale structures are commonly fabricated for several applications. The characterisation of sub-micron structures (below 1 μm) at a large scale as well as the related data analysis are challenging tasks. Here, we present a method to address the image acquisition, the data extraction and the data analysis, applied to the evaluation of the uniformity of nanometric structures in a silicon master. Automated routines for both high and low magnification Scanning Electron Microscope (SEM) imaging have been successfully developed. SEM images have been automatically acquired by scripting routines, which collect large amounts of images of the nanometric structures covering multiple regions of the wafer in a few hours. Geometric parameters of the nanometric structures such as diameter, period and height have been extracted from the raw images using the developed image processing scripts. Finally, the data extracted from more than 4800 images acquired with three different characterisation scripts (1600 images for each study) have been analysed and plotted according to their position in the wafer.

This paper describes a specific route for the complete integration of a novel planar thermoelectric microgenerator (μTEG) that can operate under environmental conditions using commercial miniaturized heat exchangers. The proposed heat exchanger integration process is compatible with the fragility of planar micromachined silicon structures. The main structure of the μTEG is built around a micromachined silicon platform defined by silicon microfabrication technologies. Different silicon-based materials, such as bottom-up grown silicon and silicon-germanium nanowire arrays as well as top-down fabricated silicon microbeams are used as thermoelectric materials. μTEGs with those materials are characterized both before and after heat exchanger integration. The presence of the heat exchanger increases the μTEG performance significantly and power densities around 40 μW cm−2 are obtained when placed on a heat source at 100 °C and exposed under natural convection to a surrounding ambient at room temperature

Multisite neural probes are a fundamental tool to study brain function. Hybrid silicon/polymer neural probes combine rigid silicon and flexible polymer parts into one single device and allow, for example, the precise integration of complex probe geometries, such as multishank designs, with flexible biocompatible cabling. Despite these advantages and benefiting from highly reproducible fabrication methods on both silicon and polymer substrates, they have not been widely available. This paper presents the development, fabrication, characterization, and in vivo electrophysiological assessment of a hybrid multisite multishank silicon probe with a monolithically integrated polyimide flexible interconnect cable. The fabrication process was optimized at wafer level, and several neural probes with 64 gold electrode sites equally distributed along 8 shanks with an integrated 8 µm thick highly flexible polyimide interconnect cable were produced. The monolithic integration of the polyimide cable in the same fabrication process removed the necessity of the postfabrication bonding of the cable to the probe. This is the highest electrode site density and thinnest flexible cable ever reported for a hybrid silicon/polymer probe. Additionally, to avoid the time-consuming bonding of the probe to definitive packaging, the flexible cable was designed to terminate in a connector pad that can mate with commercial zero-insertion force (ZIF) connectors for electronics interfacing. This allows great experimental flexibility because interchangeable packaging can be used according to experimental demands. High-density distributed in vivo electrophysiological recordings were obtained from the hybrid neural probes with low intrinsic noise and high signal-to-noise ratio (SNR)., This work has been funded by: national funds through the Foundation for Science and Technology (FCT)—projects UIDB/50026/2020 and UIDP/50026/2020; the projects NORTE-01-0145- FEDER-000013 (“PersonalizedNOS—New avenues for the development of personalized medical interventions for neurological, oncologic and surgical disorders”) and NORTE-01-0145-FEDER-000023 (“FROnTHERA—Frontiers of technology for theranostics of cancer, metabolic and neurodegenerative diseases”), supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (ERDF); ICVS Scientific Microscopy Platform, member of the national infrastructure PPBI— Portuguese Platform of Bioimaging (PPBI-POCI-01-0145-FEDER-022122); FCT project PTDC/MEDNEU/ 28073/2017 (POCI-01-0145-FEDER-028073); and The Branco Weiss fellowship—Society in Science, (ETH Zurich).

Multisite neural probes are a fundamental tool to study brain function. Hybrid silicon/polymer neural probes, in particular, allow the integration of complex probe geometries, such as multi-shank designs, with flexible biocompatible cabling. Despite these advantages and benefiting from the highly reproducible fabrication methods on both silicon and polymer substrates, they have not been widely available. This paper presents the development, fabrication, characterization, and in vivo electrophysiological assessment of a hybrid multisite multi-shank silicon probe with a monolithically integrated polyimide flexible interconnect cable. The fabrication process was optimized on wafer level and several neural probes with 64 gold electrode sites equally distributed along 8 shanks with an integrated 8 μm-thick highly flexible polyimide interconnect cable were produce. To avoid the time-consuming bonding of the probe to definitive packaging, the flexible cable was designed to terminate in a connector pad that can mate with commercial zero-insertion force (ZIF) connectors for electronics interfacing. This allows great experimental flexibility since interchangeable packaging can be used according to experimental demands. High-density distributed in vivo electrophysiological recordings were obtained from the hybrid neural probes with low intrinsic noise and high signal-to-noise ratio (SNR).

The gas sensing properties of germanium (Ge) monocrystalline nanowires (NWs) at temperatures up to 100 °C have been demonstrated for the first time. The devices have been fabricated based on an energy efficient and site-specific vapor-liquid-solid growth of NW meshes on top of microhotplates, which contain a buried heater and top electrodes. The devices have been investigated for the detection of oxygen, nitrogen dioxide and carbon monoxide gases, showing the important effect played by pre-adsorbed surface oxygen in the response to the different gases. The Ge NW-based devices exhibit p-type conductivity and show high selectivity in their response towards water vapor. Water vapor interaction is not dependent on the presence of oxygen and the adsorption leads to electron donation in the Ge nanowires. TEM analysis of the NWs proves that they are covered by a thin, outer germanium oxide layer, which is stable and does not grow upon exposure to these gases and operation temperatures up to 100 °C. The presence of this oxide layer plays a key role in the sensing mechanisms.

Thermoelectric micro/nanogenerators (µTEGs) are potential candidates as energy harvesters to power IoT sensors. This study reports on a thermoelectric micro/nanogenerator with a planar architecture built by silicon micromachining technologies that uses silicon-germanium (SiGe) nanowire (NW) arrays as thermoelectric material. The growth of bottom-up NW arrays by means of Chemical Vapour Deposition - Vapour Liquid Solid growth (CVD-VLS) and their monolithic integration into prefabricated microplatforms are presented. It is shown that SiGe NWs based µTEGs can harvest 7.1 μW/cm2 without any additional heat exchanger, when there is a waste heat source available at a temperature of 200 °C. Since the required power density for many sensing applications is in the range of 10–100 μW/cm2 the results obtained in this work are close to meet expectations.

A thermoelectric microgenerator based on multiple silicon nanowire arrays is fabricated and its performance evaluated for different convection regimes. Mature silicon microfabrication technology is used to fabricate the device structure. As a post-process, a bottom-up approach is used to grow silicon nanowires by a VLS-CVD mechanism. The thermal design of the microgenerator features a thermally isolated silicon platform which is connected to the bulk silicon rim through several arrays of silicon nanowires. Simulations are carried out to evaluate the need of an external heat sink to improve the thermal gradient seen by the nanowires and the power output of the microgenerator. Results show a significant improvement with a heat sink raising the thermal gradient from 3 K to approximately 100 K when the external temperature gradient is 300 K. Experimental measurements with different convection regimes also show a radical improvement on the power output comparing natural convection and two different forced convection regimes. The first forced convection regime is a broad airflow from a commercial CPU fan placed on top of the device, while the second (air jet forced convection) uses a syringe to focus the airflow from the compressed air line to the platform. The maximum output power for a natural convection regime is 2.2 nW for a hotplate temperature of 200 °C, while the air jet forced convection regime generates up to 700 nW, which correspond to 35 µW/cm2 considering a device footprint of 2 mm2.

Omnidirectional absorption is important to non-tracking systems designed for the harvesting of solar energy. Presently, we examine both experimentally and numerically the broadband absorption under oblique illumination driven by deep sidewall subwavelength structures (DSSS) in silicon nanopillar arrays (DSSS arrays). Specifically, we target DSSS geometries that are a built-in side effect of the top-down cyclic Bosch dry etch process employed to realize high aspect ratio silicon nanopillar (NP) arrays. We numerically compare the DSSS array with an optically-optimized straight-sidewall nanopillar array (SSNP array) under oblique illumination. We show how the presence of DSSS generates a higher absorptivity particularly for the spectral range >600 nm, induces the formation of absorptivity peaks at the near-infrared spectral range, and overall provides an enhanced omnidirectional broadband absorption. We experimentally show that the specular reflectivity and the total reflectivity of silicon DSSS arrays that were fabricated using a top-down Bosch dry etch process is significantly lower compared with that of the corresponding SSNP arrays. Specifically, we show a decrement in the broadband specular reflection of up to 30% for certain angles of illumination, and about 13% decrement in the total reflectivity.

Light trapping and the broadband absorption of the solar radiation are significant to a plethora of absorption-based photonic devices. Specifically, efficient broadband absorption was recently demonstrated with arrays of subwavelength structures. The current study examines both numerically and experimentally light trapping driven by deep sidewall subwavelength structures (DSSS) in silicon nanopillar (NP) arrays (DSSS arrays). Particularly, the focus is on DSSS geometries that are an inherent outcome of the top-down dry etch approach used in arrays of high aspect ratio NPs due to the periodical operationality of the Bosch dry etch method. ~10% enhancement in the broadband absorption of DSSS arrays compared with NP arrays is demonstrated numerically, as well as the generation of near-IR absorptivity peaks of ~25% for DSSS arrays. Importantly, it is shown that the introduction of DSSS systematically blue-shifts the absorptivity peaks of the NP arrays and in this manner a deterministic light trapping is possible. Finally, decrements of ~40% in direct reflectivity and ~7% in diffused reflectivity in DSSS arrays realized on silicon wafers is demonstrated experimentally.

Silicon nanopillar (NP) arrays are known to exhibit efficient light trapping and broadband absorption of solar radiation. In this study, we consider the effect of deep subwavelength sidewall scalloping (DSSS) on the broadband absorption of the arrays. Practically, the formation of DSSS is a side effect of top-down dry etching of NP arrays of several microns height. We use finite-difference time-domain electromagnetic calculations to show that the presence of DSSS can result in efficient excitation of optical modes in both the arrays and the underlying substrates. We demonstrate a broadband absorption enhancement of >10% in a DSSS-NP array with an underlying substrate. Finally, we use device calculations to examine the effect of DSSS on the electrical performance of a photovoltaic cell, as the main concern is the degradation of the open-circuit voltage due to surface recombination (DSSS results in higher surface-to-volume ratio). We show that the effect of DSSS on open-circuit voltage is negligible. Finally, deep-subwavelength sidewall features offer a new, interesting photon management strategy towards absorption enhancement.

Ordered dense arrays of p -type Si nanowires produced with a VLS method have been surveyed as a new active material to produce all-Si thermoelectri c energy harvester s. The thermoelectri c properties of th e meta-material consisting of bundles of thousands of 10 Πm long Si nanowires (with a mean diameter of 100 nm ) were measured making use of an integrated self-test element (heater/thermometer) that allow s an accurate control of the temperature gradient in the silicon micromachined structure used to assemble the thermocouple s. The measured Seebeck coefficient S and thermal conductivity k together with the resistivity reported in literature for similar boron doped Si nanowires suggest a ZT figure of merit at ambient temperature between 0.30 and 0.93, showing that proposed nanowire arrays can be a promising candidate for enhancing Si thermoelectric properties. © 2014 Elsevier Ltd. All rights reserved. Selection and peer -review under responsibility of Conference Committee members of the 12th European Conference on Thermoelectrics .

This work presents current achievements on the fabrication and characterization of an all-Si based planar thermoelectric microgenerator. Ordered dense arrays of Vapor-Liquid-Solid (VLS) grown p-type Si nanowires (Si NWs) are integrated in predefined thermally isolated microstructures as nanostructured thermoelectric active material. Optimizations in device processing and architecture that improved both thermal and electrical performances of the microgenerator resulted in a 70 fold increase in power output. Furthermore, the performance of microgenerators with Si NWs is compared to that of microgenerators with micron-sized Si beams as active material. Additionally, a 60 fold improvement in power output is observed by placing a cold-finger on top of the thermally isolated microstructure to demonstrate the effect of a heat exchanger, which is currently being implemented on the microgenerator.

Energy autonomy keeps being one of the most desired enabling functionalities in the context of off-grid applications, such as continuous monitoring scenarios and distributed intelligence paradigms (Internet of Things, Trillion Sensors). SiNERGY, a European project (GA n° 604169) coordinated by IMB-CNM (CSIC) has focused on silicon and silicon friendly materials and technologies to explore energy harvesting and storage concepts for powering microsensors nodes. Harvesting energy, tapping into environmentally available sources may be a good solution to overcome the use of primary batteries. 10–100 microwatts per square centimeter power densities seem appropriate for many such applications. Specific thermoelectric and piezoelectric developments are reviewed.

This paper reports a novel and straightforward approach to the development of a compact micro direct methanol fuel cell. The device consists of a hybrid polymer membrane as a feasible microintegrable electrolyte to be used together with silicon current collectors. These current collectors consist in microfabricated silicon chips that incorporate a fine electrode grid. The membrane combines two polymers with different functionalities, Nafion® as a proton conducting material and PDMS as a flexible mechanical support. The compatibility of this membrane with MEMS fabrication processes lies in the acknowledged bonding capabilities of the PDMS polymer to materials typically used in microsystems technologies—such as silicon, silicon dioxide and glass—as well as its ability to withstand variations of the Nafion® volume. The compatibility of all the components with microfabrication processes will permit the application of batch fabrication techniques for the whole device, so contributing to a significant lowering of the fabrication costs.

Micro and nanotechnologies are called to play a key role in the fabrication of small and low cost sensors with excellent performance enabling new continuous monitoring scenarios and distributed intelligence paradigms (Internet of Things, Trillion Sensors). Harvesting devices providing energy autonomy to those large numbers of microsensors will be essential. In those scenarios where waste heat sources are present, thermoelectricity will be the obvious choice. However, miniaturization of state of the art thermoelectric modules is not easy with the current technologies used for their fabrication. Micro and nanotechnologies offer an interesting alternative considering that silicon in nanowire form is a material with a promising thermoelectric figure of merit. This paper presents two approaches for the integration of large numbers of silicon nanowires in a cost-effective and practical way using only micromachining and thin-film processes compatible with silicon technologies. Both approaches lead to automated physical and electrical integration of medium-high density stacked arrays of crystalline or polycrystalline silicon nanowires with arbitrary length (tens to hundreds microns) and diameters below 100 nm.

A miniaturized Planar Field Asymmetric Ion Mobility Spectrometer (P-FAIMS) has been simulated in N 2 at ambient pressure using COMSOL Multiphysics software. Micro-IMS is based on ion gas-phase separation due to the dependence of ion mobility with electric field. Ions are selected by a DC voltage characteristic of each kind of ion. The average kinetic behaviour of ions in high electric fields conditions is well known but not the chemical reactions and physical collisions related with. The aim of this work is the modelling of the average kinetic behaviour of different kind of ions in a P-FAIMS taking into account the main factors involved in their movement. Three different compounds, with high impact on security applications, have been studied: an explosive 2,4,6-trinitrotouluene (TNT−H) − , a volatile organic compound Ac 2 H + and a chemical warfare agent simulant DMMPH + that emulates gas sarin. Displacement simulations along the P-FAIMS of theirs vapour phase ions have been done at different values of drift electric field amplitude to gas number density ( E / N ) ratio. Ions were selected between the ones present in the literature that covers the previous applications and the ones with more reliable experimental data of the main parameters involved in the definition of ions mobility needed for their analysis. Results show that simulations of ions behaviour in a P-FAIMS are possible with COMSOL Multiphysics software and that the time and intensity at which ions are detected are in good agreement with an experimental data in the literature.

The potential use of a micromachined thermopile based sensor device for analyzing natural gas is explored. The sensor consists of a thermally isolated hotplate, which is heated by the application of a sequence of programmed voltages to an integrated heater. Once the hotplate reaches a stationary temperature, the thermopile provides a signal proportional to the hotplate temperature. These signals are processed in order to determine different natural gas properties. Sensor response is mainly dependent on the thermal conductivity of the surrounding gas at different temperatures. Seven predicted properties (normal density, superior heating value, Wobbe index and the concentrations of methane, ethane, carbon dioxide and nitrogen) are calibrated against sensor signals by using multivariate regression, in particular partial least squares. Experimental data have been used for calibration and validation. Results show property prediction capability with reasonable accuracy except for prediction of carbon dioxide concentration. A detailed uncertainty analysis is provided to better understand the metrological limits of the system. These results imply for the first time the possibility of designing unprecedented low-cost natural gas analyzers. The concept may be extended to other constrained gas mixtures ( e.g. of a known number of components) to enable low-cost multicomponent gas analyzers.

A novel micromachined thermal infrared emitter using a heavily boron doped silicon slab as radiating element is presented. The fabrication process has been designed to allow the integration of such infrared emitters with an array of thermopile infrared detectors, with the aim of achieving an integrated non-dispersive infrared microspectrometer. A first set of infrared emitters with a common size for the doped silicon radiating slab (1,100 × 300 × 8 μm3) has been successfully fabricated and characterized. The working temperature of the Joule-heated radiating slabs has been controlled by means of DC and pulsed electrical signals, achieving temperatures well beyond 700°C. The thermal time constant measured in pulsed operation, around 50 ms, is adequate to enable the direct electrical modulation of the emitted radiation up to a frequency of 5 Hz while maintaining the full modulation depth. The temperature distribution in the radiating elements has been analyzed using two different thermal imaging methods.

Special suspended micro-platforms have been designed as a part of silicon compatible planar thermoelectric microgenerators. Bottom-up grown silicon nanowires are going to bridge in the future such platforms to the surrounding silicon bulk rim. They will act as thermoelectric material thus configuring an all-silicon thermoelectric device. In the new platform design other additional bridging elements (usually auxiliary support silicon beams) are substituted by low conductance thin film dielectric membranes in order to maximize the temperature difference developed between both areas. These membranes follow a sieve-like design that allows fabricating them with a short additional wet anisotropic etch step. © Published under licence by IOP Publishing Ltd.

Silicon nanowires have been implemented in microfabricated structures to develop planar thermoelectric microgenerators (μTEGs) monolithically integrated in silicon to convert heat flow from thermal gradients naturally present in the environment into electrical energy. The compatibility of typical microfabrication technologies and the vapor–liquid–solid (VLS) mechanism employed for silicon nanowire growth has been evaluated. Low-thermal-mass suspended structures have been designed, simulated, and microfabricated on silicon-on-insulator substrates to passively generate thermal gradients and operate as microgenerators using silicon nanowires as thermoelectric material. Both electrical measurements to evaluate the connectivity of the nanowires and thermoreflectance imaging to determine the heat transfer along the device have been employed.

A micro Planar high-Field Asymmetric waveform Ion Mobility Spectrometer (P-FAIMS) operating at ambient pressure and temperature has been simulated using COMSOL Multiphysics software. P-FAIMS is based on ion gas-phase separation due to the dependence of ion mobility with electric field. Ions are selected by a DC voltage characteristic of each ion kind. Physics of ion behaviour in high electric fields conditions is well known but not the chemistry behind ion reactions and kinetics. The aim of this work is the modelling of different kind of ions in a P-FAIMS having account of the main factors involved in their movement in the drift tube. Simulations of vapour phase ions of three compounds have been studied for different values of drift electric field amplitude to gas number density (E/N) ratio: protonated water clusters H+(H2O) n and $${{\rm O}_{2}^{-}({\rm H}_{2}{\rm O})_{n}}$$ ions obtained in air, and a chemical warfare agent simulant DMMPH+ that emulates gas sarin. Ions were selected due to simulation needs of experimental data of the main quantities involved in the definition of ions mobilities. Results show that simulations of ions behaviour in a P-FAIMS are possible with COMSOL Multiphysics software and that the time and intensity at which ions are detected are in good agreement with experimental data from literature.

A non-specific non dispersive infrared (NDIR) micro-optical gas detection system is presented. The system is based on a monolithic filter microarray (up to 16 non substance oriented elements) that is attached by flip-chip onto a matching microarray of thermopiles, configuring a compact CMOS compatible optical detector. The system aims to combine the stability of infrared optical devices and the versatility of electronic-nose approaches. The transmission spectra of the filters, multi-peaked and of broad band nature, are not oriented to any specific substance detection, and multivariate regression techniques are used to predict gas type and concentrations from the voltage pattern generated by the thermopile array. The ability of the system for substance discrimination has been proved by means of qualitative volatile identification (ethanol, isopropanol and acetone) and quantitative tests have been performed with CH 4 and CO 2 mixtures.

This paper reports on the enhancements introduced into the ITC-irst RF MEMS multi-user fabrication process, which have been assessed by means of the electromechanical characterization of a set of test structures consisting of low actuation voltage capacitive switches. A simple quasistatic CV measurement has been used to extract the switch capacitance in both the on and off states (C"o"n and C"o"f"f) and the voltage needed for the actuation of the different designs. The devices under test use folded serpentine springs and large area actuation electrodes to decrease the pull-in voltage. The spring constant of the suspensions is used to control the actuation voltage of the different designs with a slight increase of the overall size and without affecting the switching performance at higher frequencies. The introduction of a floating metal layer into the flow of the fabrication process has allowed a great increase in the off state capacitances, getting C"o"f"f/C"o"n ratios up to 10 times greater than the ones obtained for the same structures without this feature.

The present study investigates the main electrical transport mechanism in V2O5 thin films deposited by RF magnetron sputtering on the basis of the Mott's small polaron hopping model. The material under test was obtained at room temperature from a V2O5 target and then oxidized at high temperature under air atmosphere to obtain the desired V2O5 phase. The dependence of the electrical conductivity of the V2O5 thin films with temperature was analyzed using the Mott's small polarons hopping transport model under the Schnakenberg form. Model results suggest a polaron binding energy WH = 0.1682 eV, with a structural disorder energy WD = 0.2241 eV and an optical phonon frequency ν0 = 0.468 × 1013s- 1. These results are in agreement with data reported in literature for single crystal V2O5. However, the carrier mobility μ = 1.5019 × 10- 5 cm2/Vs computed in the non-adiabatic regime is significantly smaller than that of the single crystal, suggesting a strong electron-phonon coupling in the V2O5 thin films obtained with the proposed deposition method. Fil: Giannetta, Hernan. Instituto Nacional de Tecnología Industrial. Centro de Micro y Nanoelectrónica del Bicentenario; Argentina. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte; Argentina Fil: Calaza, Carlos. Consejo Superior de Investigaciones Científicas; España Fil: Lamas, Diego Germán. Universidad Nacional del Comahue. Facultad de Ingeniería; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto de Investigaciones Científicas y Técnicas de las Fuerzas Armadas; Argentina Fil: Fonseca, Luis. Consejo Superior de Investigaciones Científicas; España Fil: Fraigi, Liliana. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Norte; Argentina. Instituto Nacional de Tecnología Industrial. Centro de Micro y Nanoelectrónica del Bicentenario; Argentina

Silicon nanowires present outstanding properties for electronics, energy, and environmental monitoring applications. However, their integration into microelectromechanical systems (MEMS) is a major issue so far due to low compatibility with mainstream technology, which complicates patterning and controlled morphology. This work addresses the growth of 〈111〉 aligned silicon nanowire arrays fully integrated into standard MEMS processing by means of the chemical vapor deposition–vapor liquid solid method (CVD–VLS) using silane as a precursor. A reinterpretation of the galvanic displacement method is presented for selectively depositing gold nanoparticles of controlled size and shape. Moreover, a comprehensive analysis of the effects of synthesis temperature and pressure on the growth rate and alignment of nanowires is presented for the most common silicon precursor, i.e., silane. Compared with previously reported protocols, the redefined galvanic displacement together with a silane-based CVD–VLS growth methodology provides a more standard and low-temperature (, Nanotechnology, 26 (19)

Proceedings Volume 9517, Smart Sensors, Actuators, and MEMS VII; and Cyber Physical Systems; 95172C (2015).-- Event: SPIE Microtechnologies, 2015, Barcelona, Spain., Silicon nanowires thermoelectric properties are much better than those of silicon bulk. Taking advantage of silicon microfabrication techniques and compatibilizing the device fabrication with the CVD-VLS silicon nanowire growth, we present a thermoelectric microgenerator based on silicon nanowire arrays with interdigitated structures which enhance the power density compared to previous designs presented by the authors. The proposed design features a thermally isolated silicon platform on the silicon device layer of an SOI silicon wafer. This silicon platform has vertical walls exposing planes where gold nanoparticles are deposited by galvanic displacement. These gold nanoparticles act as seeds for the silicon nanowires. The growth takes place in a CVD with silane precursor, and uses the Vapor-Solid-Liquid synthesis. Once the silicon nanowires are grown, they connect the silicon platform with the silicon bulk. The proposed thermoelectric generator is unileg, which means that only one type of semiconductor is used, and the second connection is made through a metal. In addition, to improve the thermal isolation of the silicon platform, multiple trenches of silicon nanowire arrays are used, up to a maximum of nine. After packaging the device with nanowires, we are able to measure the Seebeck voltage and the power obtained with different operation modes: harvesting mode, where the bottom device is heated up, and the silicon platform is cooled down by natural or forced convection, and test mode, where a heater integrated on the silicon platform is used to produce a thermal gradient., This work has been supported by FP7–NMP–2013–SMALL–7, SiNERGY (Silicon Friendly Materials and Device Solutions for Microenergy Applications) Project, Contract n. 604169. One of the authors (C.C.) acknowledges a Ramón y Cajal research grant., Sí, Publisher's version

Internet of Things and Trillion Sensors are buzzwords illustrating the path towards the next grand paradigm: Smart Everywhere. In many of those realizations long term autonomy of sensor systems is a must to tackle different societal challenges and innovation scenarios. Microenergy autonomy solutions based on energy harvesting offer a promising way in which, KETS mediated, silicon technology and silicon friendly materials may play a decisive role., This work was supported by FP7- NMP-2013-SMALL-7, SiNERGY (Silicon Friendly Materials and Device Solutions for Microenergy Applications), Contract n. 604169

This paper reports the design, fabrication and assessment of a low-cost uncooled infrared imager that has been conceived as a general purpose system to be used in a wide range of infrared applications. The imager has been fabricated using the AMS 0.8 μm CYE CMOS process together with a compatible front-side bulk micromachining post-process provided by the CMP service of the TIMA laboratory. The adopted fabrication approach does not involve any lithography step, material deposition or particular etch-stop technique after the CMOS process, so that the imager cost is almost equal to the CMOS chip cost. The infrared imager is composed of a focal plane array (FPA) with 16 × 16 thermopile pixels, which are monolithically integrated with the addressing and readout electronics. Each pixel consists of a thermally isolated micromachined membrane suspended by two arms that contain the polysilicon/aluminium thermocouples of the embedded thermopile sensor. The pixel membrane also includes a heating resistor intended to implement a self-test function that allows an electrical test of the FPA without need of specific infrared equipment. Since the voltage levels generated by the thermopile pixels are in the range of a few μV the readout channel consists of a low-noise voltage amplifier with a high variable gain that can be tuned for different operation conditions. The readout circuit makes use of the chopper principle and the correlated double sampling technique to reduce the noise floor and the amplifier offset levels. Optical measurements performed with the fabricated prototypes have shown a pixel responsivity of 15.0 V/W, a noise equivalent power of 1.37 nW and a normalized detectivity of 1.05 × 107 cm Hz1/2 W−1, values that are in line with current state of the art. The readout channel features a maximum gain of 85 dB with a 4.3 kHz bandwidth and an equivalent input noise of 22 nV/Hz1/2. An infrared imager based on the FPA has been build and thermal imaging has been demonstrated.

A tuneable Fabry-Perot interferometer fabricated with a tailored surface micromachining process is presented in this work. The device based on a movable flat micromirror driven by electrostatic actuation, is intended for gas sensing applications and operates in the medium-infrared spectral range. The electrostatic actuation features of the proposed structure are presented showing that a flat and parallel displacement of the mobile mirror is obtained. The characterization of the optical transmittance of the structure shows that this displacement allows covering a range of the transmitted spectra between 3.5 and 5.0 μm.

The thermal characterization capabilities of an AFM have been applied to a fragile bulk micromachined device, showing its advantages over other contact and non-contact thermal probing techniques. This technique has proved its suitability to obtain very spatially accurate temperature distribution of this kind of devices. This thermal information has been obtained for a micromachined thermopile designed for gas sensing purposes. In this way, a good understanding of the thermoelectrical response of this device has been obtained, allowing to analyze the thermal effect of the geometric design parameters and helping to their optimization.

In this work we have studied the feasibility of integrating an infrared filter and an infrared detector by means of a flip-chip technique. This filter and detector combination should be the heart of a future gas detection cell based on infrared absorption. In our case the filter is a surface micromachined Fabry-Perot interferometer, and the infrared detector is a bulk micromachined thermopile. The flip-chip technique is an elegant solution to assure the optical micro-alignment of both devices and allows the electrical contact needed to actuate active optical filters.

Electrostatically driven moving micromirrors are proposed in this work for the fabrication of a tuneable Fabry–Perot interferometer. The device is intended for a gas sensing application, and operates in the medium infrared spectral range. In order to achieve high filter selectivity and to reduce the loss of transmitted light it is of utmost importance that the mirrors are kept parallel after release and during device actuation. Surface micromachined polysilicon mirrors have been selected for this application. This technology provides an accurate control of the air gap between mirrors. The internal homogeneous stress and stress gradient states of the polysilicon films have a great influence on mirror deflection upon release. The micromachining process developed to obtain flat-surface micromirrors with an accurate air gap, by reducing the stress-induced polysilicon deflection and building thick oxide sacrificial layers is described in this work.

A model of a miniaturized non-dispersive infrared (NDIR) gas analysis system, aiming to predict the final system specifications, is presented. It comprises the different elements of the NDIR detector, including a surface micromachined Fabry-Perot tunable filter. These models have been used to estimate the response of the NDIR system to different gas mixtures. Multivariate regression methods like partial least squares allow recovering the true sample composition from the IR absorption spectra measured with the NDIR system, despite the limited selectivity of the filter. Combining model and data processing permits to predict the effect on the final system specification of design parameters. Here, we compare the effect of the technology used for the filter on the system errors.

Aerosol Assisted Chemical Vapor Deposition (AACVD) induced via localized heating microsensor platforms is used to directly deposit tungsten oxide nanostructures from tungsten hexacarbonyl [W(CO)6] precursor. Results demonstrate the viability to grow and confine either nanoparticle-like or quasi-one-dimensional-like structures on microsensor devices by using the self-heating capability of the sensor platforms. The microsensors fabricated using this method show appreciable responses to toluene, with sensors based on films composed of nanoneedles and nanotubes having almost two-fold higher responses than sensors based on films composed of nanoparticles.

One-dimensional (1D) nanowire structures have been shown to be promising candidates for enhancing the thermoelectric properties of semiconductor materials. This is also true for (abundant and technologically enabling) silicon, which in bulk form behaves poorly in the thermoelectric domain. This paper goes beyond single nanowire characterization and reports on the integration into MEMS structures of multiple dense arrays of well-oriented, size-controlled and electrically connected silicon nanowires (Si NWs). By combining generic top-down and bottom-up processes in the micro and the nano domain, a route for all-silicon planar thermoelectric microgenerators can then be envisaged using a rather simple technology.

Low-dimensional structures have been shown to be promising candidates for enhancing the thermoelectric properties of semiconductors, paving the way for integration of thermoelectric generators into silicon microtechnology. With this aim, dense arrays of well-oriented and size-controlled silicon nanowires (Si NWs) obtained by the chemical vapor deposition (CVD)-vapor-liquid-solid (VLS) mechanism have been implemented into microfabricated structures to develop planar unileg thermoelectric microgenerators (μTEGs). Different low-thermal-mass suspended structures have been designed and microfabricated on silicon-on-insulator (SOI) substrates to operate as microthermoelements using p-type Si NW arrays as the thermoelectric material. To obtain nanowire arrays with effective lengths larger than normally attained by the VLS technique, structures composed of multiple ordered arrays consecutively bridged by transversal microspacers have been fabricated. The successive linkage of multiple Si NW arrays enabled the development of larger temperature differences while preserving good electrical contact. This gives rise to small internal thermoelement resistances, enhancing the performance of the devices as energy harvesters. © 2013 TMS., This investigation has been supported by the Spanish Ministry of Economy and Competitiveness (TEC-2008-03255-E and TEC-2010-20844-E) and the Generalitat de Catalunya [Advanced Materials for Energy Network (XaRMAE), 2009-SGR-440]. A. Tarancón and C. Calaza would like to acknowledge the financial support of the Ramón y Cajal postdoc-toral program of the Spanish Ministry of Economy and Competitiveness. M. Salleras would like to acknowledge the JAE-Doc contract with CSIC cofinanced by the European Social Fund (FSE). D. Dávila would like to acknowledge the financial support granted by the Spanish MAEC-AECID fellowship program.

This work reports the efforts to optimize the output power achieved with all-silicon thermoelectric microgenerators based on MEMS fabrication technology and silicon nanowires as active material. Recent improvements introduced in both the fabrication process and the device design are described, and a set of experimental results obtained with both device types (new vs. old design/process) are provided to assess the impact of the different modifications on thermal and electrical performance, as well as in the overall harvested power.

One-dimensional (1D) nanowire structures have been shown to be promising candidates for enhancing the thermoelectric properties of semiconductor materials. This paper goes beyond single nanowire characterization and reports on the implementation of multiple electrically connected dense arrays of well-oriented and size-controlled silicon nanowires (Si NWs) grown by the CVD-VLS mechanism into microfabricated structures to develop thermoelectric microgenerators (οTEGs). Low thermal mass suspended silicon structures have been designed and microfabricated to naturally generate thermal gradients in planar microthermoelements. The hot and cold parts of the device are linked with horizontal arrays of Si NWs growth by a single bottom-up process. In order to improve the performance of the device as energy harvester, the successive linkage of multiple Si NW arrays has been developed to generate larger temperature differences while preserving a good electrical contact that allows keeping small internal thermoelement resistances. The fabricated thermoelements have shown Seebeck voltages up to 60mV and generated power densities up to 1.44mW/cm 2 for ΔT=300°C and, working as energy harvesters, a maximum Seebeck voltage of 4.4mV and a generated power density of 9οW/cm 2 for ΔT=27°C (across the nanowires) in a single thermoelement. The fabricated microgenerator, taking advantage of the simple planar geometry and compatibility with silicon technology, provides an alternative to the state-of-the-art οTEGs based on non-integrable and scarce V-VI semiconductor materials and a promising energy harvester for advanced micro/nanosystems. © 2012 Elsevier Ltd., The research at IREC was supported by European Regional Development Founds (ERDF, FEDER Programa Competitivitat de Catalunya 2007–2013). Moreover, this investigation has been supported by the Spanish Ministry of Economy and Competitiveness (TEC-2008-03255-E and TEC-2010-20844-E) and the “Generalitat de Catalunya” (Advanced Materials for Energy Network (XaRMAE), 2009-SGR-440). A. Tarancón and C. Calaza would like to thank the financial support of the Ramón y Cajal postdoctoral program of the Spanish Ministry of Economy and Competitiveness. M. Salleras would like to acknowledge the JAE-Doc contract with CSIC co-financed by the European Social Fund (FSE). D. Dávila would like to thank the financial support granted by the Spanish MAEC-AECID fellowship program.

A generic purpose, compact and affordable instrument for the chemical analysis of liquid samples based on the non dispersive infrared (NDIR) scheme is presented. It comprises a detector module built from two matching arrays of CMOS compatible thermopiles and non-specific infrared filters (Fabry-Perot resonators). Each filter provides a set of transmission peaks distributed along the midinfrared spectral range instead of a single transmission peak associated to a specific wavelength, so that each channel collects information concerning the absorption at several wavelengths, and the whole array produces a pattern with information regarding the sample absorption in the entire midinfrared range. Strictly speaking, this instrument does not operate as a spectrometer (measuring the sample absorption as a function of wavelength), but it is an affordable alternative that makes available patterns with enclosed spectroscopic information.

A compact natural gas analyzer prototype is presented which incorporates several advanced features. In first place a very recently reported MEMS sensing technology for properties determination of natural gas mixtures is implemented. Besides, the prototype is a very complete smart instrument incorporating fault detection, self-identification to a network and measurement quality metrics (self validation or SEVA), provided by the combination of the IEEE-1451 and BS-7986 smart sensor standards. Experimental measurements are presented for calibration and validation of the device, with a remarkable uncertainty for the determination of Superior Calorific Value (SCV) of 1.1%. The instrument demonstrates the advanced fault detection possibilities implemented and its enhanced connectivity features granted by IEEE-1451.2 The approach demonstrates the feasibility of compact, low-cost, and smart natural gas analyzers using a single MEMS microsensor and advanced smart sensor standards.

Metal oxide nanowires are used for their integration in gas nanosensors. These semiconducting nanowires are deposited onto suspended sensing platforms and are electrically contacted (a single nanowire in each substrate) by means of electron beam induced deposition inside a FIB dual beam system. The platforms are equipped with a buried integrated resistor that permits their heating, allowing to tune the reaction of the gas species with the surface of the nanowire, thus controlling the response. These low power consumption nanosensor prototypes exhibit good responses to toxic gases, like CO, NOx and O3, making them suitable for environmental monitoring.