Multiphysic modeling and design of carbon nanotubes based variable capacitors for microwave applications

This paper describes the multiphysic methodology developed to design carbon nanotubes (CNT) based variable capacitor (varactor). Instead of using classical RF-MEMS design methodologies; we take into account the real shape of the CNT, its nanoscale dimensions and its real capacitance to ground. A capacitance-based numerical algorithm has then been developed in order to predict the pull-in voltage and the RF-capacitance of the CNT-based varactor. This software, which has been validated by measurements on various devices, has been used to design varactor device for which 20V of actuation voltage has been predicted. We finally extend the numerical modeling to describe the electromagnetical behavior of the devices. The RF performances has also been efficiently predicted and the varactor (in parallel configuration) exhibits predicted losses of 0.3 dB at 5 GHz and quality factor of 22at 5 GHz, which is relevant for high quality reconfigurable circuits requirements where as the expected sub-microsecond switching time range opens the door to real time tunability.