Damien Thuau

Rapid Prototyping of Chemical Microsensors Based on Molecularly Imprinted Polymers Synthesized by Two-Photon Stereolithography

Two-photon stereolithography is used for rapid prototyping of submicrometre molecularly imprinted polymer-based 3D structures. The structures are evaluated as chemical sensing elements and their specific recognition properties for target molecules are confirmed. The 3D design capability is exploited and highlighted through the fabrication of an all-organic molecularly imprinted polymeric microelectromechanical sensor.

Piezoelectric polymer gated OFET: Cutting-edge electro-mechanical transducer for organic MEMS-based sensors

The growth of micro electro-mechanical system (MEMS) based sensors on the electronic market is forecast to be invigorated soon by the development of a new branch of MEMS-based sensors made of organic materials. Organic MEMS have the potential to revolutionize sensor products due to their light weight, low-cost and mechanical flexibility. However, their sensitivity and stability in comparison to inorganic MEMS-based sensors have been the major concerns. In the present work, an organic MEMS sensor with a cutting-edge electro-mechanical transducer based on an active organic field effect transistor (OFET) has been demonstrated. Using poly(vinylidenefluoride/trifluoroethylene) (P(VDF-TrFE)) piezoelectric polymer as active gate dielectric in the transistor mounted on a polymeric micro-cantilever, unique electro-mechanical properties were observed. Such an advanced scheme enables highly efficient integrated electro-mechanical transduction for physical and chemical sensing applications. Record relative sensitivity over 600 in the low strain regime (<0.3%) was demonstrated, which represents a key-step for the development of highly sensitive all organic MEMS-based sensors.

Advanced thermo-mechanical characterization of organic materials by piezoresistive organic resonators

We present the piezoresistive transduction of an all-organic microelectromechanical system (MEMS) based resonant sensor fabricated through a low-cost and highly versatile process. The MEMS resonator consists of a U-shaped cantilever beam resonator made of a thin layer of a piezoresistive nanocomposite (SU/8 epoxy resin filled with industrially produced carbon nanotubes, or CNTs) deposited on flexible substrates such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and paper. The structures have been fabricated using a commercially available vinyl cutting machine. External piezoelectric actuation has been used to drive the devices into resonance while integrated piezoresistive transduction has been chosen as the resonance sensing approach. The achieved measurements validate the concept of dynamic piezoresistive-transduced organic MEMS. The sensitivity to temperature is comparable with that of state-of-the-art inorganic temperature sensors, thus confirming the high accuracy level of the new resonators. As an example of a sensing application, the present MEMS sensors are employed as microdynamical mechanical analyzers enabling the rapid, low-cost and accurate characterization of the viscoelastic properties of organic materials.

The role of H-bonds in the solid state organization of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) structures: bis(hydroxy-hexyl)-BTBT, as a functional derivative offering efficient air stable organic field effect transistors (OFETs)

The study of a [1]benzothieno[3,2-b][1]benzothiophene (BTBT) derivative decorated with hexyl chains functionalized with hydroxyl end groups is reported. A rapid and inexpensive functionalization of the BTBT in positions 2 and 7 has been developed. This compound is able to self-organize into a lamellar structure through σ–π stacking and van der Waals interactions but also through hydrogen bonding interactions. The hydrogen-bonded network controls the interlamellar region in terms of organization and stability. The liquid-crystal phase and structural changes observed by DSC have been characterized using an original approach combining FTIR and powder XRD measurements as a function of temperature. Thermally evaporated diol based OFETs exhibited good mobilities of up to 0.17 cm2 V−1 s−1 measured under an inert atmosphere but also in ambient air. The diol derivative is considered to be a very promising platform for the design of new functionalized BTBT.

All inkjet-printed piezoelectric electronic devices: energy generators, sensors and actuators

Inkjet printing is considered to be a key technology in the field of flexible electronics due to its capability to deposit different types of materials in a controlled and defined manner. However, inkjet printing of functional materials such as the fluorinated piezoelectric copolymer P(VDF–TrFE) still remains a challenge. In this regard, a piezoelectric ink was formulated in a narrow viscosity range compatible with the specific print head used in this work. Characterization of the dielectric, ferroelectric and piezoelectric properties along with the morphology and crystallinity of the film showed excellent agreement with traditional solution processed thin films. Consequently, inkjet printed P(VDF–TrFE) layers were subsequently integrated as a functional layer into entirely inkjet printed flexible electronics devices such as energy harvesters, sensors and actuators contributing to the development of flexible electronic applications.

Development of Analytical Models of T- and U-shaped Cantilever-based MEMS Devices for Sensing and Energy Harvesting Applications

Dynamic-mode cantilever-based structures supporting end masses are frequently used as MEMS/NEMS devices in application areas as diverse as chemical/biosensing, atomic force microscopy, and energy harvesting. This paper presents a new analytical solution for the free vibration of a cantilever with a rigid end mass of finite size. The effects of both translational and rotational inertia as well as horizontal eccentricity of the end mass are incorporated into the model. This model is general regarding the end-mass distribution/geometry and is validated here for the commonly encountered geometries of T- and U-shaped cantilevers. Comparisons with 3D FEA simulations and experiments on silicon and organic MEMS are quite encouraging. The new solution gives insight into device behavior, provides an efficient tool for preliminary design, and may be extended in a straightforward manner to account for inherent energy dissipation in the case of organic-based cantilevers.

Unusual electromechanical response in rubrene single crystals

Organic semiconductors are intensively studied as promising materials for the realisation of low-cost flexible electronic devices. The flexibility requirement implies either performance stability towards deformation, or conversely, detectable response to the deformation itself. The knowledge of the electromechanical response of organic semiconductors to external stresses is therefore not only interesting from a fundamental point of view, but also necessary for the development of real world applications. To this end, in this work we predict and measure the variation of charge carrier mobility in rubrene single crystals as a function of mechanical strain, applied selectively along the crystal axes. We find that strain induces simultaneous mobility changes along all three axes, and that in some cases the response is higher along directions orthogonal to the mechanical deformation. These variations cannot be explained by the modulation of intermolecular distances, but only by a more complex molecular reorganisation, which is particularly enhanced, in terms of response, by π-stacking and herringbone stacking. This microscopic knowledge of the relation between structural and mobility variations is essential for the interpretation of electromechanical measurements for crystalline organic semiconductors, and for the rational design of electronic devices.

Engineering polymer MEMS using combined microfluidic pervaporation and micro-molding

In view of the extensive increase of flexible devices and wearable electronics, the development of polymer micro-electro-mechanical systems (MEMS) is becoming more and more important since their potential to meet the multiple needs for sensing applications in flexible electronics is now clearly established. Nevertheless, polymer micromachining for MEMS applications is not yet as mature as its silicon counterpart, and innovative microfabrication techniques are still expected. We show in the present work an emerging and versatile microfabrication method to produce arbitrary organic, spatially resolved multilayer micro-structures, starting from dilute inks, and with possibly a large choice of materials. This approach consists in extending classical microfluidic pervaporation combined with MIcro-Molding In Capillaries. To illustrate the potential of this technique, bilayer polymer double-clamped resonators with integrated piezoresistive readout have been fabricated, characterized, and applied to humidity sensing. The present work opens new opportunities for the conception and integration of polymers in MEMS.MEMS: Versatile technique paves the way for new flexible devicesAn innovative and versatile technique for fabricating micro electromechanical systems (MEMS) from polymers opens the door to new sensing technologies for use in flexible devices. Owing to their low cost, flexibility, and biocompatibility, polymer and composite materials are attracting considerable attention as an alternative to silicon-based MEMS for biological applications, and energy and sensing technologies. Current manufacturing processes for polymer-based MEMS, however, still lag behind those for silicon. Now, Damien Thuau and colleagues from the University of Bordeaux in France have used classical microfluidic pervaporation combined with micro-molding to produce multilayer polymeric micro-structures. The technique could be used for creating micro-structuration from almost any type of materials, starting from dilute colloidal dispersions to polymer solutions, and paves the way for new applications, including bio-sensors, mechanical energy harvesters, and actuators

Integrated Electromechanical Transduction Schemes for Polymer MEMS Sensors

Polymer Micro ElectroMechanical Systems (MEMS) have the potential to constitute a powerful alternative to silicon-based MEMS devices for sensing applications. Although the use of commercial photoresists as structural material in polymer MEMS has been widely reported, the integration of functional polymer materials as electromechanical transducers has not yet received the same amount of interest. In this context, we report on the design and fabrication of different electromechanical schemes based on polymeric materials ensuring different transduction functions. Piezoresistive transduction made of carbon nanotube-based nanocomposites with a gauge factor of 200 was embedded within U-shaped polymeric cantilevers operating either in static or dynamic modes. Flexible resonators with integrated piezoelectric transduction were also realized and used as efficient viscosity sensors. Finally, piezoelectric-based organic field effect transistor (OFET) electromechanical transduction exhibiting a record sensitivity of over 600 was integrated into polymer cantilevers and used as highly sensitive strain and humidity sensors. Such advances in integrated electromechanical transduction schemes should favor the development of novel all-polymer MEMS devices for flexible and wearable applications in the future.

Giant electro-mechanical transduction in all-organic MEMS for physical and chemical sensors

This paper reports an organic MEMS sensor with a cutting-edge electro-mechanical transducer based on an active organic field effect transistor (OFET). The strategy lies in the integration of a piezoelectric Poly (VinyliDene Fluoride/TriFluoroEthylene) (P(VDF/TrFE)) copolymer as active gate dielectric layer in an OFET device mounted on a polymer micro-cantilever. The charges generated by the piezoelectric layer due to surface strain are converted and amplified into drain current. Such an advanced scheme enables highly efficient integrated electromechanical transduction with record relative sensitivity ((ΔID/IDS)/ε) over 600 in the low strain regime, constituting a key-step for the development of highly sensitive MEMS sensors.