Micro-interconnection technology suitable for RF-NEMS varactors elaboration

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.