Fabrication and characterisation of carbon-based devices

Thin film material properties and measurement characterisation techniques are crucial for the development of micro-electromechanical systems (MEMS) devices. Furthermore, as the technology scales down from microtechnology towards nanotechnology, nanoscale materials such as carbon nanotubes (CNTs) are required in electronic devices to overcome the limitations encountered by conventional materials at the nanoscale. The integration of CNTs into micro-electronics and material applications is expected to provide a wide range of new applications. The work presented in this thesis has contributed to the development of thin film material characterisation through research on the thermal conductivity measurement and the control of the residual stress of thin film materials used commonly in MEMS devices. In addition, the use of CNTs in micro-electronics and as filler reinforcement in composite materials applications have been investigated, leading to low resistivity CNTs interconnects and CNTs-Polyimide (PI) composites based resistive humidity sensors. In the first part of this thesis, the thermal conductivity of conductive thin films as well as the control of the residual stress arising from fabrication process in PI micro-cantilevers have been studied. A MEMS device has been developed for the thermal conductivity characterisation of conductive thin films showing good agreement with thermal conductivity of bulk material. Low energy Ar+ ion bombardment in a plasma has been used to control the residual stress present in PI cantilevers. Appropriate ion energy and exposure time have led to stress relaxation of the beams resulting in a straight PI cantilever beam. In the second part of this thesis, low resistivity CNTs interconnects have been developed using both dielectrophoresis (DEP) and Focused Ion Beam (FIB) techniques. An investigation of the effects of CNT concentration, applied voltage and frequency on the CNTs alignment between Al and Ti electrodes has resulted in the lowering of the CNTs’ resistance. The deposition of Pt contact using FIB at the CNTs-metal electrodes interface has been found to decrease the high contact resistances of the devices by four and two orders of magnitude for Al and Ti electrodes respectively. The last part of this thesis focuses on the preparation of CNTs-PI composite materials, its characterisation and its application as resistive humidity sensor. The integration of CNTs inside the PI matrix has resulted in enhancing significantly the electrical and mechanical properties of the composites. In particular, a DEP technique employed to induce CNTs alignment inside the PI matrix during curing has been attributed to play an important role in improving the composite properties and lowering the percolation threshold. In addition, the fabrication and testing of CNTs-PI resistive humidity sensors have been carried out. The sensing performance of the devices have shown to be dependent highly on the CNT concentration. Finally, the alignment of CNTs by DEP has improved the sensing properties of CNTs-PI humidity sensors and confirmed that the change of resistance in response to humidity is governed by the change of the CNTs’ resistances due to charge transfer from the water molecules to the CNTs

Solvent‐Driven Biomimetic Soft Sensors and Actuators

Abstract The emergence of soft actuators that exhibit large, complex, programmable, and reversible shape deformation is of fundamental interest having potential applications in optics, medicals, and robotics fields. However, existing soft actuators are generally driven by only few given external stimuli such as temperature, humidity, or light which limit their interactions with their surroundings. Here, biomimetic soft actuators that respond to a variety of solvent vapors via programmable motion studied by Finite Element Modeling (FEM) are presented. A versatile micromachining process is used to fabricate these biomimetic soft actuators able to bend, curve, and twist in different manners according to their designs mimicking stamen, seed pots, and petals of Bauhinia variegate and Dendrobium orchids. The kinetic parameters of the transient response and recovery actuation are taken as the input feature in principal component analysis (PCA) to discriminate analyte molecules. Finally, to broaden the accessible 3D motions and thus functions of these smart actuators, an origami approach is employed to provide further flexibility and novel controlled structural changes in continuum structures such as snake‐like soft actuators, walkers, and grippers

Preparation of Carbon Nanotubes (CNTs)-SU8 composite for piezo-resistive gauges application

International audienc

Highly piezoresistive hybrid MEMS sensors

International audienc

Formulation of piezoresistive composites and their integration in organic MEMS resonators

International audienc

Multilayer transducer for highly efficient initiation of time-resolved Brillouin scattering

Structures made of a metallic film deposited on a substrate are conventionally used as opto-acoustic transducers for picosecond ultrasonic experiments where detection in the time domain of the Brillouin scattering in a transparent sample is sought. In this paper, we substitute the metallic film for a periodic stack of nanometric layers made of gold and lithium fluoride to increase the amplitude, at the Brillouin frequency shift, of the strain generated by the photo-thermal effect. A model is used to analyze the generated strain amplification with the volume fraction and with the total thickness of this structure and to evaluate the gain in terms of sample dynamic reflectivity changes. Amplification by a factor of 20 is measured when using the composite structure with respect to signals detected with a transducer made of a single gold layer

Effect of Additive in Fullerene and Non-Fullerene Acceptor Organic Solar Cells

International audienc

Colloid Polym Sci

Fluorinated Electroactive Polymers (FEPs) are emerging as one of the most prominent classes of insulating materials found in organic electronic devices.Despite their broad application, those materials have fixed electronic properties that are difficult to be tuned in order to achieve optimal performance in different applications. This mini-review highlights the need for tailoring the electronic properties of FEPs and explores the different approaches our group has proposed as solutions to such problem. Those include strategies to obtain stable dielectric properties and thus stable OFET performance over a broad range of temperature, as well as strategies to make FEPs directly compatible with photolithography, which is the most widely used fabrication technique by the semiconductor industry. Last, a general strategy to introduce different functional groups on FEPs is presented, allowing the introduction of altogether new properties to those polymers.“Plate-forme de l’Université de Bordeaux pour l’organique électronique imprimable : de la molécule aux dispositifs et systèmes intégrés - valorisation et commercialisation

Organic MicroElectroMechanical Systems

National audienc

MEMS Resonators Activities at the IMS

National audienc