N. F. de Rooij

École Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland

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Publications (765)503.63 Total impact

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    Full-text · Article · Feb 2016
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    ABSTRACT: We propose an autonomous battery-less wireless sensor node that combines on a single printed circuit board an ultra-wideband (UWB) transmitter and its printed antenna, together with a piezoelectric cantilever and a solar cell array to harvest vibrations and light energy, respectively. The co-design of the solar cell array with the printed UWB antenna allows a prototype size of only 85 × 35 mm2, i.e., less than 65% of a credit card size. Low-cost is achieved by using inexpensive FR4 dual-layer substrate, standard-ceramic capacitors, and low-cost harvesters. The vibrational energy scavenger is fabricated at the wafer scale based on commercially available bulk polycrystalline Lead Zirconate Titanate (PZT), and the solar cells are fabricated by depositing amorphous-Si on 0.5 mm thick glass substrate. The cold-startup time of the demonstrator is about 42 min under indoor-ambient light conditions, and about 34 min under 700 mg vibrations at a frequency of 100 Hz. Once started, the sensor requires only 12.6 μW to allow a transmission rate of one temperature sensor readout every 34 s, thanks to the UWB transmitter that consumes only 206 pJ per pulse and a custom protocol with a reduced overhead.
    No preview · Article · Jan 2016 · Sensors and Actuators A Physical
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    ABSTRACT: We report on printed strain sensors on several meters long PET fibers for integration in textile at large scale. The sensors are made by locally inkjet printing capacitive transducers on cylindrical PET fibers used in industrial textiles. Sensor measurements were performed for strains up to 1%. 10 meters long functionalized PET fibers were woven with metallic interconnect fibers using large scale industrial weaving machine and resulted in a 1 m2 smart textile demonstrator. Applications are foreseen in predictive maintenance of industrial textiles and in the automotive industry.
    No preview · Article · Dec 2015 · Procedia Engineering
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    ABSTRACT: We report on the development of a metal oxide (MOx) sensor prepared by inkjet printing technology onto polyimide foil. Gold electrodes and a gold heater were printed on each side of the substrate, respectively. SnO2 based ink was developed by sol-gel method and printed onto the electrodes. A final annealing at 400°C compatible with the polymeric transducers allows to synthetize the SnO2 film. Electrical measurements were carried out to characterize the response of fully printed sensor under different gases. The device was operated at a temperature between 200 and 300°C using the integrated heater. The sensor exhibited responses to carbon monoxide and nitrogen dioxide, under dry and wet air.
    No preview · Article · Dec 2015 · Procedia Engineering
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    M. Camara · M. Rieu · P. Breuil · C. Pijolat · D. Briand · N.F. de Rooij
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    ABSTRACT: This paper presents the design and implementation of a foil gas preconcentrator (FGP) on polyimide (PI) substrate. One novelty of the paper is that our device is made on flexible foil by using printing whereas all preconcentrators seen in literature are mainly based on rigid substrates and are micro-machined using cleanroom processes. Printing allows the additive and localized deposition of materials at low temperature on large area and can be applied to both the patterning of the heating element and the integration of the gas absorbent material. The benefits are the easy and flexible processing of cost-effective and lightweight preconcentrators for a variety of target gases. The tubular shape of the FGP is obtained by rolling up and sealing the inkjet printed gold hotplate on foil, which is then filled with the gas absorbent material (Carbopack B and Tenax). The diameter of the inlet/outlet of FGP is adjustable leading to high flow rates, up to 1.5 L/min, much larger than their silicon counterpart. The concept was validated using two target gases (Benzene and Acetophenone) at concentrations down to 250 ppb.
    Full-text · Article · Dec 2015 · Procedia Engineering
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    ABSTRACT: 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.
    Full-text · Article · Aug 2015 · Biomedical Microdevices
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    ABSTRACT: We present a microfabricated alkali vapor cell equipped with an anti-relaxation wall coating. The anti-relaxation coating used is octadecyltrichlorosilane and the cell was sealed by thin-film indium-bonding at a low temperature of 140 °C. The cell body is made of silicon and Pyrex and features a double-chamber design. Depolarizing properties due to liquid Rb droplets are avoided by confining the Rb droplets to one chamber only. Optical and microwave spectroscopy performed on this wall-coated cell are used to evaluate the cell's relaxation properties and a potential gas contamination. Double-resonance signals obtained from the cell show an intrinsic linewidth that is significantly lower than the linewidth that would be expected in case the cell had no wall coating but only contained a buffer-gas contamination on the level measured by optical spectroscopy. Combined with further experimental evidence this proves the presence of a working anti-relaxation wall coating in the cell. Such cells are of interest for applications in miniature atomic clocks, magnetometers, and other quantum sensors.
    Full-text · Article · Jul 2014 · Applied Physics Letters
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    ABSTRACT: We have experimentally studied the variation in electrical resistance of flexible platinum lines patterned on polyimide foil when they are subjected to circular bending constraints. The lines were patterned by means of standard photolithography and sputtering deposition. Two different photolithography masks were used for comparative evaluation: an un-expensive transparency mask and a standard chromium mask. Measurements of the temperature coefficient of resistance (TCR) and time stability of the resistance have been acquired for lines bent down to 1.25 mm radius of curvature on a customized bending setup, showing good reliability results. The robustness of the lines has been also assessed by registering their change in resistance while bending at different radii of curvature. The lines showed reliability issues for radii of curvature below 1.25 mm, presenting a resistance variation of 19% for transparency mask-fabricated lines and 9% for chromium mask-fabricated lines. The worse reliability performances of transparency mask lines, compared to the chromium mask ones, was found to be due to their imperfect edges, which promoted the formation and propagation of cracks during bending. The results of the experiments in this work permitted to compare the performances of flexible conductive lines with different geometry and fabricated with two different masks, establishing quantitative and qualitative bending limits for their appropriate operation in flexible electronics systems.
    Full-text · Article · Jul 2014 · Microelectronics Reliability
  • P. Janphuang · R. Lockhart · N. Uffer · D. Briand · N.F. de Rooij
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    ABSTRACT: We present a complete wafer level microfabrication process for the production of unimorph MEMS energy harvesters based on thinned bulk piezoelectric ceramic, lead zirconate titanate (PZT), sheets. This process eliminates the need for individual bonding of PZT pieces and proof masses at the chip level while still benefitting from the excellent properties of bulk PZT. With the process presented in this paper, 20 piezoelectric energy harvesters have been fabricated in parallel at the wafer level by bonding a single bulk (PZT) sheet onto a silicon-on-insulator (SOI) wafer using a low-temperature process and structuring the bonded stack with standard microfabrication techniques including thinning of the bulk PZT sheet using mechanical grinding as well as electrodeposition to deposit a thick nickel proof mass on the tip of each cantilever. A single fabricated harvester with an effective volume of 47.82 mm3 is capable of generating a normalized power density of 3346 μW cm−3 g−2 with an average power of 1.6 μW under an excitation of 0.1 g (1 g = 9.81 m s−2) at a resonant frequency of 100 Hz through an optimal resistive load of 11.8 kΩ. Thinned bulk PZT exhibits high power and a useable voltage while maintaining a low optimal resistive load, demonstrating the potential of high performance piezoelectric MEMS energy harvesters using bulk PZT sheets fabricated at the wafer level.
    No preview · Article · Apr 2014 · Sensors and Actuators A Physical
  • M. Camara · F. James · P. Breuil · C. Pijolat · D. Briand · N.F. de Rooij
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    ABSTRACT: Over the past decade, different designs of micro gas preconcentrators (µ-GP) have been proposed in literature for targeting diverse applications from medical diagnostic to explosives detection [1,2,3, 4]. The common point of all these developments is that the design of the µGP is driven by its future use. Therefore, we address here the technical aspect of the development of μGP for meeting the requirement of both pollution monitoring and explosives detection applications. In this paper, we have proposed four different designs of silicon μGP optimized from fluidic and thermal simulations but also from experimental results in regards to the chosen application. Beside the choice of the adsorbent material and the experimental parameters, the efficiency of a μGP is closed related to its shape and size. In General the μGP needs to be small enough to fit with fast desorption heating rate requiring a low thermal mass device and not too much small for allowing high flow rates during the adsorption and thus reducing the duration of preconcentration cycle
    No preview · Conference Paper · Mar 2014
  • F. Molina-Lopez · D. Briand · N.F. de Rooij
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    ABSTRACT: In this work we present a novel strategy to fabricate printed comb electrodes devices with decreased size by the introduction of a thin dielectric layer between the two combs. The electrical insulation of the two polarities prevents short-cuts occurring because of printing defects. In this way, the yield of the process increases as well as its resolution by decreasing significantly the gap between the electrodes. An analytical model is proposed and evaluated, confirming the capability of the method to enhance the nominal capacitance value of comb electrodes capacitors with reduced area. The validation of the proposed method has been performed by fabricating transducers made of inkjet printed silver combed electrodes with a parylene-C dielectric interlayer. The whole process takes place at low temperature, being compatible with the utilized PET substrate. Finally, the potential of such devices for sensing applications with improved performances was demonstrated by inkjet coating the transducers with a humidity sensing layer and characterizing their response for the capacitive detection of relative humidity.
    No preview · Article · Dec 2013 · Sensors and Actuators B Chemical
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    ABSTRACT: This paper presents the fabrication and characterization of multilayer PVDF resonant micro-vibrational energy harvesters designed to withstand environments in which high levels of acceleration are present. The multilayer cantilevers are fabricated by combining two folded PVDF stacks into a multilayered, bimorph structure. This acts to increase the overall capacitance of the harvester, a problem that plaques PVDF cantilevers as a result of its low dielectric constant. Moderate powers (7 μW) are produced from the cantilevers even at high acceleration levels (20 g) due to the limited piezoelectric coefficient of PVDF; however, as a result of the high tensile strength and low elastic modulus of PVDF, the cantilevers are able to survive extremely high accelerations (> 4000 g) without breakage - a critical problem for harvesters based on brittle piezoelectric materials and substrates.
    No preview · Article · Dec 2013 · Journal of Physics Conference Series
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    ABSTRACT: This paper presents experimentally-verified multiphysics finite element model of a wideband vibration energy harvester with impact coupling, which operates on the principle of frequency up-conversion: under low-frequency harmonic base excitation a cantilever-type resonator (with resonant frequency of 18.8 Hz) impacts a high-frequency piezoelectric cantilever, which starts freely vibrate at its resonant frequency of 374 Hz. Such input frequency amplification enables efficient power generation under low-frequency ambient excitations. The model was implemented in COMSOL and the contact between the cantilevers was formulated by using a nonlinear viscoelastic model. Reported results of dynamical and electrical testing of the fabricated vibration energy harvester confirm the accuracy of the model as well as reveal some operational characteristics of the device under varying impact and excitation conditions.
    No preview · Article · Dec 2013 · Journal of Physics Conference Series
  • N. Besse · A. P. Pisano · N. F. de Rooij
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    ABSTRACT: Thin circular piezoelectric energy harvester diaphragms undergoing large deflection in a harsh liquid environment are investigated in this paper. A material set combining AlN as transducer, SiC as electronics, Mo as wiring and Si as holder is considered. A highly accurate analytical model, which presents less than 5% error compared to FEM simulations in COMSOL, is first developed to study thoroughly flat diaphragms. Consequently, etching the wafer and adding a corrugation are proposed to reduce both the stress concentration at the edge and the influence of residual stress on the device behavior, respectively. Both ideas are predicted to increase the power density compared to the standard flat case by at least a factor of 5 to 10.
    No preview · Article · Dec 2013 · Journal of Physics Conference Series
  • P. Janphuang · R. Lockhart · S. Henein · D. Briand · N. F. de Rooij
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    ABSTRACT: This paper demonstrates a novel methodology using a rotational flywheel to determine the energy conversion efficiency of the impact based piezoelectric energy harvesters. The influence of the impact speed and additional proof mass on the efficiency is presented here. In order to convert low frequency mechanical oscillations into usable electrical energy, a piezoelectric harvester is coupled to a rotating gear wheel driven by flywheel. The efficiency is determined from the ratio of the electrical energy generated by the harvester to the mechanical energy dissipated by the flywheel. The experimental results reveal that free vibrations of the harvester after plucking contribute significantly to the efficiency. The efficiency and output energy can be greatly improved by adding a proof mass to the harvester. Under certain conditions, the piezoelectric harvesters have an impact energy conversion efficiency of 1.2%.
    No preview · Article · Dec 2013 · Journal of Physics Conference Series
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    F. Molina-Lopez · T. Kinkeldei · D. Briand · G. Troster · N.F. de Rooij
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    ABSTRACT: Interdigitated electrodes are common structures in the fields of microelectronics and MEMS. Recent developments in flexible electronics compel an understanding of such structures under bending constraints. In this work, the behavior of interdigitated micro-electrodes when subjected to circular bending has been theoretically and experimentally studied through changes in capacitance. An analytical model has been developed to calculate the expected variation in capacitance of such structures while undergoing outward and inward bending along the direction perpendicular to the electrodes. The model combines conformal mapping techniques to account for the electric field redistribution and fundamental aspects of solid mechanics in order to define the geometrical deformation of the electrodes while bending. To experimentally verify our theoretical predictions, several interdigitated electrode structures with different geometries were fabricated on polymeric substrates by means of photolithography. The samples, placed in a customized bending setup, were bent to controlled radii of curvature while measuring their capacitance. A maximum variation in capacitance of less than 3% was observed at a minimum radius of curvature of 2.5 mm for all the devices tested with very thin electrodes whereas changes of up to 7% were found on stiffer, plated electrodes. Larger or smaller variations would be possible, in theory, by adjusting the geometry of the device. This work establishes a useful predictive tool for the design and evaluation of truly flexible/bendable electronics consisting of interdigitated structures, allowing one to tune the bending influence on the capacitance value through geometrical design.
    Full-text · Article · Nov 2013 · Journal of Applied Physics
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    ABSTRACT: We have been performing pioneer work on lithographic based ultra-low power platinum (Pt) micro-hotplates on polyimide for metal-oxide gas sensors on which SnO2-based material used as sensing layer has been deposited by drop coating [1]. Following this development, we opted for printing processes which present many advantages compared to lithography. The outcome of the printing process is cost-effective and flexible hotplates devices that can be processed using large area manufacturing techniques. Here we report on fully printed micro-hotplates on flexible polymeric substrate for gas sensors. These printed devices are realized by inkjet printing silver nanoparticles in combination with a lamination process of an interlayer dielectric.
    No preview · Conference Paper · Jul 2013
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    R Straessle · Y Pétremand · D Briand · M Dadras · N F de Rooij
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    ABSTRACT: This paper reports on low-temperature and hermetic thin-film indium bonding for wafer-level encapsulation and packaging of delicate and temperature sensitive devices. This indium-bonding technology enables bonding of surface materials commonly used in MEMS technology. The temperature is kept below 140 °C for all process steps and no surface treatment is applied before and during bonding. This bonding technology allows hermetic sealing at 140 °C with a leak rate below 4 × 10−12 mbar l s−1 at room temperature. The tensile strength of the bonds up to 25 MPa goes along with a very high yield.
    Full-text · Article · Jun 2013 · Journal of Micromechanics and Microengineering
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    ABSTRACT: 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.
    Full-text · Conference Paper · Jun 2013
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    ABSTRACT: We present an insulated conductive atomic force microscope (AFM) probe with Au tip. The probe is based on a previously reported PtxSiy-tip AFM probe. After the fabrication of the PtxSiy-tip probe, a homogeneous gold cluster layer was grown exclusively on the conductive tip apex by feedback controlled electrochemical deposition of Au in a HAuCl4 based electrolyte. The size of the gold clusters was around 2 similar to 5 nm in diameter. A controlled deposition of approximately 10 nm-thick gold layer was successfully achieved. A typical tip radius of curvature was 40 nm. A potential application of this probe is simultaneous characterization of mechanical and electrical properties of molecules.
    No preview · Article · Mar 2013 · ECS Transactions

Publication Stats

7k Citations
503.63 Total Impact Points


  • 2009-2016
    • École Polytechnique Fédérale de Lausanne
      • • Sensors, Actuators and Microsystems Laboratory
      • • Institute of Microengineering
      Lausanne, Vaud, Switzerland
  • 2012
    • Universität Luzern
      Luzern, Lucerne, Switzerland
  • 2000-2012
    • Centre Suisse d'Electronique et de Microtechnique
      • Centre Suisse d’Electronique et de Microtechnique SA (CSEM)
      Neuenburg, Neuchâtel, Switzerland
  • 1988-2009
    • Université de Neuchâtel
      • Laboratoire Temps-Fréquence (LTF)
      Neuenburg, Neuchâtel, Switzerland
  • 1999
    • Universität Basel
      Bâle, Basel-City, Switzerland
  • 1998
    • Sumitomo Heavy Industries, Ltd
      Edo, Tōkyō, Japan
  • 1996-1998
    • Eawag: Das Wasserforschungs-Institut des ETH-Bereichs
      Duebendorf, Zurich, Switzerland
  • 1989
    • University of Geneva
      • Faculty of Medicine
      Genève, Geneva, Switzerland
  • 1987
    • Massachusetts Institute of Technology
      Cambridge, Massachusetts, United States
  • 1977-1980
    • Universiteit Twente
      • Department of Electrical Engineering
      Enschede, Overijssel, Netherlands