Semi-conducting carbon nanotube as variable capacitor

Abstract

This paper proposes a novel, one-part, variable capacitor, using semi-conducting carbon nanotube (CNT). This variable capacitor works based on the change in the electronic structure of CNTs under applied voltage and deformations. Positive and negative charges are stored at both ends of a non-zero band gap nanotube which works as metallic electrodes in parallel plate capacitors. Also the neutral strip in the middle acts as the dielectric part of a conventional capacitor under the influence of an external electric field. Mechanical strains on carbon nanotube change its band gap energy and thus the length of neutral strip and charged regions. The lengths of these parts are primarily dependent on the nanotube chirality, deformation mode and applied voltage. This way, different parts of a conventional cantilever, parallel plate or bridge capacitor are reduced to a one part semi-conducting CNT capacitor. Analytical calculations based on classical electrostatics and density of states (DOS) relations are employed to investigate the effect of CNTs geometry, applied voltage and deformations on capacitive features. The proposed CNT-variable-capacitor can be useful for nano-electromechanical systems (NEMS), including displacement measurement sensors and tunable capacitor in integrated circuits.