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
NEMS.
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 SiO2 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.
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