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International audience; This paper presents the optimization of a micro gas preconcentrator (μ-GP) system applied to atmospheric pollution monitoring, with the help of a complete modeling of the preconcentration cycle. Two different approaches based on kinetic equations are used to illustrate the behavior of the micro gas preconcentrator for given experimental conditions. The need for high adsorption flow and heating rate and for low desorption flow and detection volume is demonstrated in this paper. Preliminary to this optimization, the preconcentration factor is discussed and a definition is proposed.

Erworben im Rahmen der Schweizer Nationallizenzen (http://www.nationallizenzen.ch), This work presents a planar, longitudinal mode ultrasonic scalpel microfabricated from monocrystalline silicon wafers. Silicon was selected as the material for the ultrasonic horn due to its high speed of sound and thermal conductivity as well as its low density compared to commonly used titanium based alloys. Combined with a relatively high Young's modulus, a lighter, more efficient design for the ultrasonic scalpel can be implemented which, due to silicon batch manufacturing, can be fabricated at a lower cost. Transverse displacement of the piezoelectric actuators is coupled into the planar silicon structure and amplified by its horn-like geometry. Using finite element modeling and experimental displacement and velocity data as well as cutting tests, key design parameters have been identified that directly influence the power efficiency and robustness of the device as well as its ease of controllability when driven in resonance. Designs in which the full- and half-wave transverse modes of the transducer are matched or not matched to the natural frequencies of the piezoelectric actuators have been evaluated. The performance of the Si micromachined scalpels has been found to be comparable to existing commercial titanium based ultrasonic scalpels used in surgical operations for efficient dissection of tissue as well as coaptation and coagulation of tissue for hemostasis. Tip displacements (peak-to-peak) of the scalpels in the range of 10-50 μm with velocities ranging from 4 to 11 m/s have been achieved. The frequency of operation is in the range of 50-100 kHz depending on the transverse operating mode and the length of the scalpel. The cutting ability of the micromachined scalpels has been successfully demonstrated on chicken tissue.

We have performed thermal measurements and electrothermal simulations (finite element modelling) with the aim of optimizing the power consumption and the temperature distribution of micro-hotplates for gas-sensing applications. A silicon island was added underneath the membrane of the micro-hotplate to improve the temperature distribution of drop-coated metal-oxide gas sensors and to thermally isolate MOSFET gas sensors. The temperature distribution over the sensing area and the power consumption depend on the silicon island thickness, which was optimized for both applications using the software MEMCAD from Microcosm Technologies. In the optimization process, we considered the thermal conductivity of silicon and dielectric membrane, the operating temperature, the geometry and the area of the heater, and the processing of the silicon island. The thickness of the silicon island was optimized to ensure a good temperature distribution over the gas-sensing area for metal-oxide and MOSFET gas sensors with specific geometry.

Flexible high-voltage thin-film transistors (HVTFTs) operating at more than 1 kV are integrated with compliant dielectric elastomer actuators (DEA) to create a flexible array of 16 independent actuators. To allow for high-voltage operation, the HVTFT implements a zinc-tin oxide channel, a thick dielectric stack, and an offset gate. At a source-drain bias of 1 kV, the HVTFT has a 20 µA on-current at a gate voltage bias of 30 V. Their electrical characteristics enable the switching of DEAs which require drive voltages of over 1 kV, making control of an array simpler in comparison to the use of external high-voltage switching. These HVTFTs are integrated in a flexible haptic display consisting of a 4 × 4 matrix of DEAs and HVTFTs. Using a single 1.4 kV supply, each DEA is independently switched by its associated HVTFT, requiring only a 30 V gate voltage for full DEA deflection. The 4 × 4 display operates well even when bent to a 5 mm radius of curvature. By enabling DEA switching at low voltages, flexible metal-oxide HVTFTs enable complex flexible systems with dozens to hundreds of independent DEAs for applications in haptics, Braille displays, and soft robotics.

In this paper we report the detection of explosive compounds using a miniaturized gas preconcentrator (μGP) made of porous silicon (PS) filled in with Carbopack B as an adsorbent material. The μGP includes also a platinum heater patterned at the backside and fluidic connectors sealed on the glass cover. Our μGP is designed and optimized through fluidic and thermal simulations for meeting the requirements of trace explosives detection. The thermal mass of the device was minimized while the flow rate was maximized for a reduced cycle time. A detection limit below 200ppb of 2, 4-dinitrotoluene (DNT) was demonstrated with our Carbopack-PS μGP. © 2014 The Authors. Published by Elsevier Ltd.

Here we describe a novel ChemFET sensor array that utilises carbon black composite polymers for the detection of organic vapours. Three vapour-sensitive composite polymers have been used as the gate materials of FET devices. A shift in the threshold voltage to toluene is observed with a linear dependence to concentration (Henry’s law) and a voltage sensitivity of up to 2.8 μV/ppm. The effects of humidity and temperature have also been examined and the magnitude of the response shows little dependence to humidity but an exponential fall with increasing temperature. We believe that this reduction in response is primarily due to a modification in the bulk solubility of the polymer. The shift in device threshold voltage may be caused by a change in the work function of the polymer composite, a swelling effect or a charge transfer effect. A generalised linear model is proposed here for the response of a ChemFET to an organic vapour at different humdities.

Reference EPFL-ARTICLE-172617doi:10.1166/sl.2010.1279View record in Web of Science Record created on 2011-12-16, modified on 2016-08-09

This paper reports on the design, fabrication, and characterization of the first low-power consumption MOSFET gas sensor, The novel MOSFET array gas sensor has been fabricated using anisotropic bulk silicon micromachining. A heating resistor, a diode used as temperature sensor, and four MOSFETs are located in a silicon island suspended by a dielectric membrane. The membrane has a low thermal conductivity coefficient and, therefore, thermally isolates the electronic components from the chip frame. This low thermal mass device allows the reduction of the power consumption to a value of 90 mW for an array of four MOSFETs at an operating temperature of 170/spl deg/C. Three of the MOSFETs have their gate covered with thin catalytic metals and are used as gas sensors. The fourth one has a standard gate covered with nitride and could act as a reference. The sensor was tested under different gaseous atmospheres and has shown good gas sensitivities to hydrogen and ammonia. The low-power MOSFET array gas sensor presented is suitable for applications in portable gas sensor instruments, electronic noses, and automobiles.

Note: 243 Reference SAMLAB-ARTICLE-2000-004 Record created on 2009-05-12, modified on 2016-08-08

This works describes the fabrication process of an array of printed MEMS microbridges on polymeric foil, performed in only four easy steps. Each functional material was deposited exclusively by inkjet-printing technique, compatible with large-area fabrication. The array occupies an area of 2 mm x 2 mm and consists of 80 individual microbridges of 120 mu m x 80 mu m size each. When connecting all the bridges in parallel, the array displays a total capacitance value of 1.5 pF. The potential of the fabricated array has been demonstrated by employing it as a swelling-based capacitive humidity sensor where the polymeric substrate acts directly as the sensing layer.

This paper presents the design of a dual-mode (direct/differential) switched-capacitor (SC) interface system for an inkjet-printed capacitive sensor. The proposed system consists of a single-stage SC capacitance-to-voltage (C2V) converter and a 10-bit successive approximation register (SAR) ADC. The specifications of C2V are optimized at system level, emphasizing the C2V operation followed by the data converter. Cascade amplification is avoided to simplify the front-end. Both reference capacitor and feedback capacitor are calibrated to match the required value with 25 fF step. Correlated double sampling (CDS) technique attenuates the DC offset and flicker noise. Gain-boosting amplifier is adopted to improve linearity with low feedback factor. The 10-bit capacitive cascaded-binary-weighted (CBW) digital to analog converter (DAC) makes up the charge redistribution converter and achieves a balance between area, power and accuracy. Self-timing SAR logic uses extra half cycle and relaxes the settling time of pre-amplifiers. The entire interface system operates at 46 kHz sampling rate with 62 uW power consumption. Post layout simulation results show 3.5 mLSB integral non-linearity (INL) at the output of C2V and 9.9 bit ENOB of ADC. The active core area is 0.6mm2.

In this work we report on a self-standing parallel-plate capacitive humidity sensor on a thin dry photoresist film with integrated resistive temperature sensor and heater on each electrode, respectively. The simple concept proposes dry photoresist film as substrate but also as dielectric humidity sensing layer. The characteristics of the temperature sensor (TCR ~900 ppmK-1), resistive heater (0.65 °C/mW) and humidity sensor (response time ~230 seconds, sensitivity ~23 fF / 1%R.H) were measured and are reported. FEM simulations were used to visualize the temperature distribution generated by the integrated heater.

This paper shows the high performance of low-temperature thin-film indium bonding in terms of reliability, temperature stability, and leak rates. The bonding was performed at low temperatures between 60°C and 140°C, avoiding flux or any other pretreatment of the surface (e.g. formic acid). Through patterning of the indium and the applied pressure, the indium is squeezed out of its oxide shell and forms a strong, 1-2 μm-thick bond. Materials, designs of the bond rings, and bonding parameters have been varied and compared according to the tensile strength of the bonds which lie between 10 and 25 MPa. Leak rate measurements were performed with samples bonded at 140 °C and at 60 °C and both show high hermeticity. No leak could be detected with samples bonded at 140 °C and stored at 125°C for 5 weeks.

We report on the design, fabrication and characterization of polymeric printed micro-hotplates for gas sensing applications. The micro-hotplates sensing platforms have been realized by inkjet-printing. The silver nanoparticles-based heater and the interdigitated electrodes were both printed with a dielectric interlayer of laminated dry photoresist between them. The devices were completed with the deposition of a polyaniline sensing layer doped with polymeric acids, which when operated at 80°C, resulted in sensitive and reliable resistive ammonia sensor fabricated on flexible foil.

Platinum TSVs compatible with harsh-environment post-processing were fabricated on an SOI wafer. This study was part of a larger project for the development of a SWCNT resonator, 3D-integrated, in a “via-first” approach, with its driving electronics. After their passivation, they are compatible with the harsh-environment post-processes necessary for the fabrication of the SWCNT resonator: the growth of CNT at a high temperature of 850 °C in an oxidizing environment, and their release in concentrated HF solution. The TSV metallization formed a stable ohmic contact with the silicon device layer on which the CNT resonator will be standing. We present RF (radio frequency) simulations correlated with RF measurements of the Pt-TSVs from 0.3 to 5 GHz. A reflection coefficient of -20 dB and transmission coefficient of -4 dB were measured at 5 GHz.

The scanning thermal microscope (SThM) has become a versatile tool for local surface temperature mapping or measuring thermal properties of solid materials. In this article, we present recent improvements in a SThM system, based on a micro-wire thermocouple probe associated with a quartz tuning fork for contact strength detection. Some results obtained on an electrothermal micro-hotplate device, operated in active and passive modes, allow demonstrating its performance as a coupled force detection and thermal measurement system.

A low-temperature sealing technique for micro-fabricated alkali vapor cells for chip-scale atomic clock applications is developed and evaluated. A thin-film indium bonding technique was used for sealing the cells at temperatures of

A scanning thermal microscope working in passive mode using a micronic thermocouple probe is presented as a quantitative technique. We show that actual surface temperature distributions of microsystems are measurable under conditions for which most of usual techniques cannot operate. The quantitative aspect relies on the necessity of an appropriate calibration procedure which takes into account of the probe-to-sample thermal interaction prior to any measurement. Besides this consideration that should be treated for any thermal contact probing system, the main advantages of our thermal microscope deal with the temperature available range, the insensitivity to the surface optical parameters, the possibility to image DC, and AC temperature components up to 1 kHz typically and a resolution limit related to near-field behavior. (C) 2013 AIP Publishing LLC.

This chapter reviews micromachined semiconductor gas sensors. First, this chapter briefly discusses the history of this technology. It then addresses the microhotplates' concept that has led to the development of different types of micromachined gas sensor devices. The different realizations of micromachined semiconductor gas sensors are presented: thin- and thick-film metal oxide, field effect, and those using complementary metal oxide semiconductors and silicon on insulator technologies. Recent developments on gas-sensitive nanostructures integrated on micromachined transducers and semiconductor gas sensors on polymeric foil and their printing are highlighted. Finally, the industrialization of micromachined gas sensors is addressed.

Power generating soft triboelectric based shoe insole fully elastomeric and compatible with large-scale fabrication technique has been developed. During the process, film casting and stencil printing techniques were implemented to deposit/pattern elastomeric and soft/flexible materials, such as, polydimethylsiloxane (PDMS) and polyurethane (PU). Carbon- based elastomeric materials were used as electrodes, which were also film casted. The developed triboelectric generator (TENG) was capable of harnessing electrical power effectively from mechanical deformation of the system during walking or running activities. The performance of the device was tested for walking with frequency of 0.9±0.2 Hz. The power (rms value) of 0.25 mW was achieved for load resistance of 100 MΩ,, which corresponded to the power density (rms value) of 1.9 μW/cm2.

This work reports on the design, fabrication and characterization of an inkjet-printed multisensing platform on flexible polymeric substrates integrated into a printed semi-passive high frequency radio frequency identification (HF RFID) smart label. The printed platform was integrated after fabrication to the main RFID carrier, which contained an NFC RFID chip, a microprocessor, a readout frontend and a screen-printed circuitry and antenna. The multisensing platform has channels for capacitive vapor detection (i.e. humidity), two channels for resistive-based vapor detection (i.e. ammonia) with heating capability, and one resistive channel for temperature detection (RTD). A modular approach was employed where the sensing platform was integrated to the base RFID label carrier using foil-to-foil integration techniques compatible with large area fabrication. Besides wireless communication, the semi-passive label possesses data logging and the possibility of measuring all the sensors simultaneously through a direct readout circuitry. In addition to individual sensor characterization, the full functionality of the smart label was successfully demonstrated by measuring different temperature, humidity and ammonia levels.

Piezoelectric harvesters are considered an alternative power source for applications that can support low to medium data rate transmissions in wireless sensor networks where ambient vibrations can provide microwatts to milliwatts of power. In this paper, we report the design and performance of a proof-of-concept (POC) autonomous sensor-node prototype including: an in-house piezoelectric harvester; a power management unit (PMU) made of discrete components; and an in-house ultra-wide band impulse radio (UWB-IR) transmitter. The piezoelectric harvester provides 54µW at 3.3V rms at 450 milli-g and resonant frequency of 160 Hz. In these conditions, it was observed that the sensor node is capable of sending 1 burst of 100 pulses every 110 seconds consuming an average of 8.2µW, which is much less than the generated energy. The POC sensor node using kinetics energy harvester shows energy autonomy, thus opening range of possibilities for sub 100µW energy harvesting wireless sensor nodes.

Small fully inkjet-printed gas sensors based on capacitive parallel-plate (PP) structures have been realized on flexible plastic foil and characterized. A gas sensing layer was inkjet-printed between inkjet-printed bottom and top silver electrodes. Compared with comb electrode (CE) geometries, PP structures drastically reduce the developing complexity of gas sensors on polymeric foil, avoiding the substrate parasitic signal. Furthermore, the use of porous inkjet-printed metal makes the patterning of complex grids on the top electrode unnecessary, since such porosity permits the analyte to flow into the sensing layer. This low demanding patterning resolution facilitates the miniaturization of the inkjet-printed sensors, introducing significant improvements in their sensing performances, such as sensitivity or response time. The printed sensing devices were characterized against pulses of relative humidity (R.H.) and their performances were analyzed.

This work presents a light and powerful silicon based ultrasonic micro-cutter. In order to achieve high cutting efficiency as well as good controllability when driven by commercially available control systems, important design parameters haven been identified. They have been verified by FEM-simulation as well as experiments via laser Doppler vibrometer measurements and cutting tests. The samples have been manufactured cost-effectively by microfabrication batch processing and their cutting ability has been successfully demonstrated on chicken tissue, while driven in a typical frequency range from 50 kHz to 100 kHz, generating tip displacements up to 36 μmpp.

The residual stress and buckling patterns of free-standing 8?mol.% yttria-stabilized-zirconia (8YSZ) membranes prepared by pulsed laser deposition and microfabrication techniques on silicon substrates are investigated by wafer curvature, light microscopy, white light interferometry, and nanoindentation. The 300?nm thin 8YSZ membranes (390?mu m?x?390?mu m) deposited at 25?degrees C are almost flat after free-etching, whereas deposition at 700?degrees C yields strongly buckled membranes with a compressive stress of 1,100?+/-?150?MPa and an out-of-plane-displacement of 6.5?mu m. These latter membranes are mechanically stable during thermal cycling up to 500?degrees C. Numerical simulations of the buckling shape using the RayleighRitz-method and a Young's modulus of 200?GPa are in good agreement with the experimental data. The simulated buckling patterns are used to extract the local stress distribution within the free-standing membrane which consists of tensile and compressive stress regions that are below the failure stresses. This is important regarding the application in, e.g., microsolid oxide fuel cell membranes which must be thermomechanically stable during microfabrication and device operation.

We report on the realization and evaluation of micro-fabricated alkali vapor cells using a thin-film indium bonding technique. Optical and double-resonance spectroscopy performed on the cells demonstrates their suitability for atomic clock applications. Long-term measurements show a stable pressure inside the cells and therefore an excellent hermeticity of the bonding over several months. The low bonding process temperature of ≤ 140°C combined with good bond strength makes this method a promising candidate for realizing micro-fabricated alkali cells with anti-relaxation wall-coatings.

We present a study of our in-house made tetracontane wall-coated 87Rb vapour cells for rubidium atomic clock applications. Evolution of the double-resonance (DR) signal during the so-called ripening process of these cells is measured and interpreted. Intrinsic properties of the coated cells post ripening are presented. Intrinsic linewidths below 70 Hz, and moderate temperature coefficients (1.5 × 10−10 /K) are promising cell properties in view of highly compact and miniature atomic clocks.

Inkjet printed interdigitated transducers have been produced on flexible substrates and optimized for gas sensing applications by improving the sintering conditions and employing additional passivation procedures, like electroplating with Ni or whole transducer passivation through Parylene-C coating. The results of the performed investigations showed that the transducers printed with Ag ink can be used, as prepared, in capacitive gas sensing structures up to 70% relative humidity only. Higher humidity levels resulted in irreversible shifts of the nominal capacitance and conductance of the transducers. This drawback could be eliminated by the already addressed passivation procedures or upgraded sintering. The gas sensor structures based on the passivated printed transducers displayed good stability and sensing performance, demonstrating that fully printed and flexible capacitive gas sensors are feasible

This paper reports a study on the dynamics of foil-based functional component self-alignment onto patterned test substrates and its demonstration when integrating a flexible sensor onto a printed circuitry. We investigate the dependence of alignment time and final precision of stacking of mm- and cm-sized foil dies on a number of system parameters, such as amount of assembly medium dispensed on target positions, size and weight of assembling dies and their initial misalignment. Using water as a medium for direct self-alignment, mm- and cm-sized square-shaped pre-marked foil dies were aligned with accuracy down to 30 μm and smaller, which reflects a high precision relatively to their lateral dimensions on patterned marked carriers. High-speed camera stage and image recognition tools were used for analyzing rapid capillary-driven self-alignment processes of marked foil dies. It is shown that there is a definite range of initial misalignment values allowing dies to align with high accuracy and yield within the same time window, whereas both under smaller and larger initial offsets, i.e. with dies correspondingly too close or too far from their target positions, yield and alignment precision is significantly lower. The high-alignment accuracy of mm- to cm-sized functional foils was demonstrated by means of the integration of an interdigitated electrodes (IDE) capacitive sensor to a flexible polymeric substrate. Additionally, high-yield electrical interconnection was performed using anisotropic conductive adhesives (ACA). The latter opens the perspective of efficiently assembling interesting new systems such as separately manufactured sensors, paper batteries and RFIDs components through the direct capillary-driven self-alignment approach and ACA electrical interconnection.

This paper presents a low-complexity and low temperature (85°C) fabrication process for vibration energy harvesters. The process employs lamination steps to transfer thinned PZT thick sheets onto flexible polymeric substrates, using dry film photoresist. The influence of geometrical parameters on the device performance were assessed by FEM simulations (using COMSOL) and supported by experiments. Optimization of the output power was performed by modifying the neutral plane within the device and by using a localized seismic mass at the tip, which has resulted in an output power of 30 μW at 52 Hz and an acceleration of 1g. Finally, a low-complexity and fully polymeric package is proposed, which together with the harvester process are compatible with large area fabrication methods.

We present a review of Microsystems-based technologies for the miniaturization of gas detection systems with a focus on air quality monitoring. On one hand, compared to sensors technologies, an approach based on microanalytical instruments can fulfill some of the requirements linked to the detection at the trace level of some pollutants with improved selectivity. On the other hand, the detection system becomes more complex at a higher cost which can result in a limited deployment. Some of the Microsystems components to be highlighted in this communication include micromachined gas preconcentrators, gas chromatographs, and infrared spectrometers. Several performing individual components have been reported in the last decade but several issues still remain at the system integration level to get commercially viable and robust products on the market.

We present a low-temperature indium hermetic bonding technique on wafer level without using flux, active atmosphere or other pretreatment of the indium. Its simplicity and low temperatures allow encapsulation of sensitive MEMS devices. Bonding stronger than 18 MPa was accomplished with temperatures never exceeding 140 degrees C. Leak rate measurements revealed leak rate below 2.5 x 10(-12) atm cc/s. This bonding technique is then applied to fabricate rubidium vapor-cells for chip-scale atomic clocks (CSAC). Saturated absorption spectroscopy performed two and five months after fabrication confirms less than 1 mbar of gas contamination, and the retrieved clock signal demonstrates the suitability of the cell for clock applications.

We report on inkjet printing of silver nanoparticles on paper for the design of resistive temperature and capacitive humidity sensors. Temperature and humidity have shown to have an influence on the electrical and mechanical properties of the Ag printed structures on paper. The passivation of the paper substrate and the Ag structures with parylene was investigated to reduce these effects and improve the stability of the structures. The lines were printed with an average thickness of 0.8 μm and a resistivity of 30 μΩ•cm. The Ag thermometer coated with parylene showed a good linearity with a TCR of 0.0011°C-1, while the capacitive humidity sensor exhibited an exponential response. This study foresees the possibility of using paper as substrate with inkjet printing of materials for the design of low-cost environmental sensors.

This paper presents the optimization of a micro gas preconcentrator based on a micro-channel in porous and non-porous silicon filled with an adequate adsorbent. This micro gas preconcentrator is both applicable in the fields of atmospheric pollution monitoring (Volatil organic compounds VOCs) and explosives detection (nitroaromatic compounds). Different designs of micro-devices and adsorbent materials have been investigated since these two parameters are of importance in the performances of the micro-device. The optimization of the device and its operation were driven by its future application in outdoor environments. Parameters such as the preconcentration factor, cycle time and the influence of the humidity were considered along the optimization process. As a result of this study, a preconcentrator with a total cycle time of 10 min and the use of single wall carbon nanotubes (SWCNTs) as adsorbent exhibits a good preconcentration factor for VOCs with a limited influence of the humidity. The benefits of using porous silicon to modify the gas desorption kinetics are also investigated. 2011 Elsevier B.V. All rights reserved.

Abstruct- We investigate in this work the perlbrmance of two conligurations of room temperature bolometers dedicated to THz applications. Fabrication processes, noise level, sensitivity and resolution characterizations ùre presented. Results emphasize the cllicicncy of the proposed approach.

Titanium nitride (TiN) has been investigated as a heater material for microhotplates and microreactors. TiN is available in many CMOS processes, unlike many other microheater materials. In addition, TiN has a very high melting point (2950 ◦C) meaning that it is stable up to higher temperatures than platinum (Pt) and polysilicon. For the first time, TiN is tested inside a conventional membrane of LPCVD silicon nitride (SiN). Two types of sputtered TiN are considered: high stress and low stress. Their performance is compared with that of e-beam evaporated Pt. The maximum average temperature of TiN heaters is 11% higher than those of Pt, and reaches over 700 ◦C. Failure of the TiN heaters is due to rupture of the membrane. Failure of the Pt heater is due to electro-stress migration. For high-stress TiN, the temperature coefficient of resistance is almost constant and close to that of Pt, making the material very suitable for temperature sensing. In the case of low-stress TiN the temperature coefficient of resistance (TCR) becomes nonlinear and changes sign. The large differences between the materials are explained by the grain structure. The different grain structures are related to the sputtering parameters according to the Thornton model.

Anodically bonded Pyrex-/Metal double stack were investigated for applications in the sensor encapsulation field. The use of metals can increase the robustness of the packaging and eliminate the use of glue. Titanium anodically bonded to glass can lead to biocompatible systems The anodic bonding of metallic sheets of Invar, Kovar, Alloy 42 and titanium to ion-containing glasses, Pyrex and Foturan, was evaluated in terms of samples preparation, bonding parameters, and bonding characteristics. At a bonding temperature below 300 °C, the stress induced to Pyrex was smaller when the Invar was used, however, a weak bonding was obtained at the lowest bonding temperatures investigated. In comparison with Invar and Alloy 42 bonded to Pyrex, Kovar induced a smaller stress for bonding temperatures higher than 350 °C. For bonding temperatures in between 300 and 350 °C, a similar value of stress was obtained for Kovar and Alloy 42 bonded to Pyrex as well as a high bonding strength. A post-annealing step at a temperature of and higher than the bonding temperature was shown to decrease the bonding stress and can be used to improve the bonding strength of samples bonded at low temperature. Kovar and Alloy 42 bonded to Pyrex at temperatures of and higher than 250 °C were tight to liquid at a pressure of 1.5 bars. In the case of titanium, Pyrex and Foturan were successfully bonded to titanium thin films and sheets, respectively. A proper selection of metals and bonding parameters led to levels of residual stress, strength and tightness that make anodic bonding of metals to glass a suitable technique for the assembling and packaging of microsystems, for instance piezoresistive silicon sensors and microfluidic devices.

Screen-printing technology is widely used in the field of gas sensors and can also be used to fabricate electrodes for solid oxide fuel cell (SOFC). The compatibility of this technique with micro-hotplate is studied to produce micro sensors and micro SOFC. For sensors application, development of inks containing precursor of sensing element allows to decrease annealing temperature and to improve adhesion. For SOFC development, we investigated a new type of device named single-chamber fuel cell (SCFC) for which the fuel and the oxygen are mixed and in contact with both the anode and cathode. Such devices were firstly built at a millimeter scale using LSM for cathode, YSZ for electrolyte and Ni-YSZ cermet for anode. Two types of configuration were studied: SCFC developed on YSZ support with screen-printed electrodes, and SCFC entirely manufactured by screen-printing on a inert ceramic substrate made of alumina. Although weak power densities were measured, around 1 mW/cm2, the feasibility of SCFC was confirmed. Then, preliminary results concerning LSM cathode deposition on micro-hotplate were obtained. LSM layers annealed up to 800 °C resist well to temperature cycling but exhibit low conductivity. © 2006 Elsevier B.V. All rights reserved.

In this communication, we report on the integration of metal-oxide gas sensors on polymeric micro-hotplates made on polyimide and silicon substrates. Low-power consumption micro-hotplates with platinum electrodes and heaters were fabricated on polyimide membranes. Their thermal behavior was optimized using temperature probing at the micro-scale level coupled with thermal simulations. Tin oxide thick films were successfully integrated on these polyimide micro-hotplates using the drop coating technique. The annealing process of the tin oxide drops on the polyimide substrate was investigated and gas measurements are presented. Compared to the polyimide hotplates on silicon substrates, the hotplates made on polyimide sheets are simpler to process and more robust, and therefore, they are more suitable for the integration of metal-oxide films. Finally, a wafer level packaging technique using multiple polyimide layers was developed and led to a polymeric platform for metal oxide sensors. The technology is also promising for the integration of polyimide humidity sensors, of resistive and capacitive gas-sensitive polymeric films to realise fully flexible gas sensor arrays. © 2007 Elsevier B.V. All rights reserved.

Special high temperature micro-hotplates were investigated for their potential use as a technology platform for miniaturized solid oxide fuel cells (SOFCs). To evaluate the compatibility of these hotplates with typical SOFC materials and processing techniques, spray pyrolysis was used for the deposition of an SOFC cathode material (La0.6Sr0.4Co0.2Fe0.8O3, LSCF) onto the micro-hotplate. The resulting microstructures and the electrical conductivity of the thin film (thickness ∼500 nm) were characterized. Post-deposition annealing in external furnaces as well as using the integrated heater of the micro-hotplate confirmed that these micro-hotplates are suitable for a maximum operation temperature of 800 °C and a long-term operation at 600 °C. Very fast heating and cooling rates of several 100 °C min-1 were achieved using the micro-hotplate as a heater, allowing fast processing and aging tests. Bending of the micro-hotplate was found to be critical to the integrity of the thin film, which coats the micro-hotplate. Bending might be reduced using other membrane materials. These membranes are potential components for a micro-SOFC in which the integrated heater is used for start-up operation of the fuel cell. © 2007 Elsevier B.V. All rights reserved.

International audience; This paper presents the development of a gas preconcentrator based on a micro-channel in porous silicon filled with carbon nanopowders by a micro-fluidic process. The particularity of this device is its applicability in the fields of atmospheric pollution monitoring by targeting VOCS (volatiles organic compounds). Various designs of micro-devices have been investigated and a special focus has been dedicated to the carbon adsorbent. The optimization of the device and its operation were driven by its future application in outdoor environments. The benefits of using porous silicon to ease the fixing of the carbon absorbent in micro-channels and to modify the gas desorption kinetic are also investigated. Results on a device based on a carbon adsorbent powder filled in a porous silicon micro-channel for benzene preconcentration are reported.

A polymeric-based colorimetric gas sensor with its associated electronics targeting ammonia detection at low-cost and low-power is presented. The gas sensitive layer was inkjet printed on a plastic foil used as an optical waveguide. The planar configuration of the sensor makes it compatible with large scale fabrication techniques, such as roll-to-roll processes. Its power consumption and noise level were measured. The sensor exhibited a good sensitivity to ammonia with a theoretical limit of detection of 104 ppb in a constant operation mode. The power consumption was reduced to the sub-mW range when operating in pulsed mode. It foresees applications in the field of wireless systems, for environmental and safety monitoring.

We report on the design and fabrication of ultra-low power metal-oxide (MOX) gas sensors on plastic foils envisioning their fabrication at large scale and low cost. A complete sensor solution is presented including its packaging at the foil level and the driving/readout circuitry. The latter allowed the sensor to operate in pulsed temperature mode to reduce the power consumption in the sub-mW range. Gas measurements under CO, CH 4 and NO 2 have proven the proper operation of the sensor. These devices are being developed targeting wireless applications.

International audience; This communication reports on the design of ultra-low power micro-hotplates on polyimide (PI) substrate based on thermal simulations and characterization. The goal of this study was, by establishing a simulation model for very small scale heating elements, to decrease the power consumption of PI micro-hotplates to few mWs to make them suitable for very low-power applications. To this end, the mean heat transfer coefficients in air of the devices were extracted by finite element simulations combined with very precise thermographic measurements. A simulation model was implemented to investigate both the influence of the hotplates' downscaling and the bulk micromaching of the polyimide substrate to lower their power consumptions. Simulations were in very good agreement to the experimental results. The main parameters influencing significantly the power consumption at such dimensions were identified and guidelines have been established allowing the design of very small (15×15 μm2) and ultra-low power heating elements (6 mW at 300°C). These very low-power heating structures could allow the realization of flexible sensors (gas, flow, wind) for applications in autonomous wireless sensors networks or RFID applications and make them compatible with large scale production on foil such as roll to roll or printing processes.

Since local thermal probing has become a major tool for studying transport phenomena at micro- and nanoscale levels, the fundamental aspect of the interaction between the tip of the probe and the sample has remained the key point on which any quantitative measurement relies. In this paper we present results on thermal resistances involved in the contact mechanism of a microthermocouple cantilever probe that is used to scan the surface of a microhotplate at different levels of temperature. We point out the potential of such an active microsystem as an efficient calibration tool for near-field thermal probes. Copyright © 2008 by ASME.

This communication reports on the application of a silicon micromachined lamellar grating interferometer in a Fourier transform infrared (FTIR) spectrometer for the detection of gases in the IR region. The goal of this work was the evaluation of the gas detection capability of a silicon micromachined FTIR spectrometer in close relation to potential applications. The research was focused on the measurements of specific gases in the NIR region in order to determine the limit of detection and the selectivity that could be obtained using such a micro-spectrometer. The performed gas measurements showed the proof of principle of the micro FTIR gas analyser, and identified the need to expand the spectral range of the system towards the middle infrared radiation (MIR). Work performed on a micro FTIR gas analyzer operating in the MIR region with the spectrometer combined with other miniaturized components (IR source and White cell) is also reported.

In this work, the novel fabrication and characterization of elastomeric piezoelectric nanocomposites are explored. Fabrication methods explored herein utilize ball milled barium titanate powder dispersions, along with double walled carbon nanotubes which are dispersed in toluene though the use of an ultrasonic probe. Test devices are then constructed with electrodes made from evaporated gold on polyimide foils and protective dielectrics of pristine PDMS. Two different device construction methods are explored utilizing both direct contact bonding and plasma bonding of the active composite layers to the dielectric/electrode. Test samples are evaluated through the use of a dedicated Berlincourt type piezoelectric d33 meter. © Published under licence by IOP Publishing Ltd.

In this communication, we present the fabrication and the characterisation of micro-heating elements made on polyimide (PI) sheets and on spin coated polyimide membranes. Different types of polyimide and heater materials were investigated to realise micro-hotplates for gas-sensing and thermal actuating applications. The effects of the type of polyimide used and of the different annealing performed on the mechanical and electrical properties of the metallic heaters were characterised. Using an optimised combination of materials and processes, flexible micro-hotplates on polyimide sheets and on polyimide membranes on silicon were realised and their thermal properties evaluated. Platinum and aluminium micro-heating elements on polyimide exhibited promising characteristics for their integration in low-power gas sensors and thermal actuators.