We report on the development and characterization of a simple two-terminal non-volatile graphene switch. After
an initial electroforming step during which Joule heating leads to the formation of a nano-gap impeding the
current flow, the devices can be switched reversibly between two well-separated resistance states. To do so,
either voltage sweeps or pulses can be used, with the condition that V<sub>SET</sub> < V<sub>RESET</sub> , where SET is the process
decreasing the resistance and RESET the process increasing the resistance. We achieve reversible switching on
more than 100 cycles with resistance ratio values of 10<sup>4</sup>. This approach of graphene memory is competitive
as compared to other graphene approaches such as redox of graphene oxide, or electro-mechanical switches
with suspended graphene. We suggest a switching model based on a planar electro-mechanical switch, whereby
electrostatic, elastic and friction forces are competing to switch devices ON and OFF, and the stability in the
ON state is achieved by the formation of covalent bonds between the two stretched sides of the graphene,
hence bridging the nano-gap. Developing a planar electro-mechanical switch enables to obtain the advantages of
electro-mechanical switches while avoiding most of their drawbacks.
Graphene has been given great attention to overcome current physical limits in electronic devices and its synthesis routes
are developing rapidly. However, graphene film manufacturing is still hindered by either low throughput or low material
quality. Here, we present a low temperature PE-CVD assisted graphene growth process on nickel thin films deposited on silicon oxide. Furthermore, our process leads to the formation of two separated graphene films, one at the nickel surface and the other at the Ni/SiO2 interface. A mixture of methane and hydrogen was employed as carbon precursor and activated by DC plasma. We found that the number of graphene layers on top of nickel can be controlled by carbon exposure time, from 1 to around 10 layers. Further annealing process of samples allowed us to achieve improved graphene films by the dissolution and segregation-crystallization process.
We successfully synthesized organized Carbon nanotubes (CNTs) and Silicon Nanowires (SiNWs) arrays using LPAA.
This approach can yield very dense assemblies of nano-objects with a planar-type organization compatible with existing
tools inherited from advanced microelectronic processes and adapted to electronic devices as field effect transistors,
interconnects, sensors, etc. CNTs/SiNWs were grown using Hot-filament Chemical Vapor Deposition (HFCVD) within
lateral-type porous anodic alumina. We demonstrate that the pulsed electrodeposition of metal nanoparticles to be further
used as catalysts inside the membranes requires specific thinning and pore widening process to remove the alumina
barrier layer located at the bottom of the pores. The growth of CNTs was found to strongly depend on the
electrodeposition conditions as well as on the CVD parameters. In addition, we found that introducing atomic hydrogen
(generated using a hot-wire) as etching agent was essential to prevent parasitic carbon/silicon deposition on the surface
of PAA or on the wall of pores and to improve CNTs/NWs growth. Such organized CNTs/SiNWs arrays are very
promising as advanced microelectronic devices and their potentiality for photosensing applications were investigated.
In this paper we demonstrate the efficiency of porous anodic alumina (PAA) to confine the growth of silicon
nanowires (SiNWs). High-density arrays of parallel, straight and organized SiNWs have been realized, by Hot Wire
Chemical Vapor Deposition (HW-CVD) growth process inside PAA templates with electrodeposited copper as catalyst.
The PAA was made by the anodization of an aluminium layer, followed by the catalysts electrodeposition at the bottom
of the pores. Subsequently, SiNWs were grown in a modified HW-CVD reactor with SiH<sub>4</sub> as the precursor gas. The
morphology and the structure of the wires have been investigated by SEM and TEM, and their collective electrical
behavior has been characterized with a 2-probes device.
Since it was isolated in 2004, graphene, the first known 2D crystal, is the object of a growing interest, due to the range of its possible applications as well as its intrinsic properties. From large scale electronics and photovoltaics to spintronics and fundamental quantum phenomena, graphene films have attracted a large community of researchers. But bringing graphene to industrial applications will require a reliable, low cost and easily scalable synthesis process. In this paper we present a new growth process based on plasma enhanced chemical vapor deposition. Furthermore, we show that, when the substrate is an oxidized silicon wafer covered by a nickel thin film, graphene is formed not only on top of the nickel film, but also at the interface with the supporting SiO<sub>2</sub> layer. The films grown using this method were characterized using classical methods (Raman spectroscopy, AFM, SEM) and their conductivity is found to be close to those reported by others.
This publication deals with the design of carbon nanotubes (CNT) based nano-electromechanical system (NEMS)
consisting in a variable capacitor working at microwave frequencies. This device is based on an array of moveable CNT
cantilever electrostatically actuated over a ground plane (figure 1 and 2). To design this component, a time-efficient
numerical algorithm for the prediction of CNT electromechanical behavior has been developed. This numerical tool
permits to calculate the pull-in voltage and flexion of the CNT's tip for various devices' parameters like CNT's diameter
and length, initial air gap (g) ... Our software also takes into account the Van der Waals (VdW) forces and the fringing
field effects. The results demonstrate that, unlike for RF-MEMS, fringing field effects are preponderant for CNT-based
This paper also discusses on the accuracy of the developed software. In order to validate our prediction, we used
finite element simulation software : COMSOL® and experimental results found in literature and compare them to our
prediction. Results prove that we obtain, for a decrease of the simulation time by two orders of magnitude, a maximum
error on the pull-in voltage of 7% for various kinds of structures and dimensions.
These results were finally used for the design of NEMS demonstrators. The microwave behavior of the varactors,
over a large range of frequency, is presented. Simulations with 3D finite-element-method electromagnetic software were
performed to optimize the structure and predict its microwave performances, which conclude the design of our
microwave carbon nanotubes (CNT) based nano-electromechanical system (NEMS) variable capacitor.
This paper deals with the development of a micro-interconnection technology suitable for the elaboration of RF-NEMS
(Nano-ElectroMechanical Systems) varactors. It aims to present an extension of RF MEMS concept into nano-scale domain
by using multi-walled carbon nanotubes (MWCNT) as movable part instead of micrometric membranes into reconfigurable
passive circuits for microwave applications.
For such a study, horizontal configuration of the NEMS varactors has been chosen and is commented. The technology is
established to fulfill several constraints, technological and microwave ones.
As far as technological requirements are concerned, specific attentions and tests have been carried out to satisfy:
• Possible and later industrialization. No e-beam technique has been selected for RF NEMS varactor elaboration.
Lateral MWCNT growth performed on a Ni catalyst layer, sandwiched between two SiO<sub>2</sub> layers, showed
feasibility of suspended MWCNT beam.
• High thermal budget, induced by the MWCNT growth by CVD (Chemical Vapor Deposition), at least to 600°C.
All the dielectric and metallic layers, required to interlink the nano world with the micrometric measurements one,
have been studied accordingly. Consequently, the order of the technological steps has been identified.
About microwave and actuation specifications (targeted close to 25V), the minimization of losses and actuation voltage
implies large layer's thicknesses compared to the CNT diameter.
Several specific technological issues are presented in this paper, taking care of both technological and microwave
compatibility to go toward RF NEMS varactor's elaboration.
We present some early results on the controlled growth of carbon nanotubes inside lateral porous
alumina templates. Such lateral templates provide an easy way of organizing nano-objects in the
plane of their supporting substrate, with potential densities of more than 100/μm, thus paving the
way for the realization of dense circuits. Here we discuss the growth conditions inside the lateral
pores of the templates, with the aim of avoiding the parasitic deposition of amorphous carbon. Our
organization method should also apply to other nanostructures such as semiconductor nanowires.
We present here, a novel approach for the membrane-based synthesis, also called template synthesis of arrays of nanomaterials with monodispersed geometrical features. The basic principle is to grow or generate the desired material inside the pores of a nanoporous alumina membrane. The pores of are synthesised parallel to the surface of the substrate by performing the anodic oxidation of an aluminium thin film laterally, i.e. parallel to the surface of the substrate, instead of perpendicular as usually done. We obtain highly regular and ordered pore arrays, with a minimum pore size in the range of ~3 to 4 nm, which to the best of our knowledge is the smallest reported to date for anodic alumina membranes. After anodic oxidation, the pores of the lateral alumina membranes have been electrochemically “filled” with Te nanowires. Such porous alumina structures may allow to control the in-plane organisation of arrays of template-grown nanowires and carbon nanotubes for reproducible device fabrication.