Quantum capacitance

About: Quantum capacitance is a research topic. Over the lifetime, 954 publications have been published within this topic receiving 24165 citations.

Theoretical investigation of quantum capacitance in armchair-edge graphene nanoribbons

Abstract: Graphene nanoribbons (GNRs) are considered as a prospective material for the next generation of nanoelectroic devices. One of the important properties of GNRs in determining the performance of such devices is capacitance; in particular, the quantum capacitance when the device size approaches in the scale of nanometer. This work presents a comprehensive investigation of the bandgap structure and the classical and quantum capacitance in armchair-edge GNRs (A-GNRs) using semi-analytical method. The method is simple and more realistic considering edge effects of A-GNRs. The results show that the edge effects have significant influence in defining the bandgap which is a necessary input in the accurate analyses of capacitance. The classical capacitance is completely determined by the device geometry and a dielectric constant of the medium. The quantum capacitance is obtained considering edge effects and discussed for both degenerate (high gate voltage) and nondegenerate (low gate voltage) regime. It is demonstrated that the total capacitance is equivalent to the classical capacitance in nondegenerate regime, whereas in degenerate regime, quantum capacitance dominates over the classical capacitance. Such detail analysis of GNRs considering a realistic model would be useful for the optimized design of GNR based nanoelectronic devices.

Effects of Parasitics and Interface Traps on Ballistic Nanowire FET in the Ultimate Quantum Capacitance Limit

Abstract: In this paper, we focus on the performance of a nanowire field-effect transistor in the ultimate quantum capacitance limit (UQCL) (where only one subband is occupied) in the presence of interface traps (Dit), parasitic capacitance (CL), and source/drain series resistance (Rs, d), using a ballistic transport model and compare the performance with its classical capacitance limit (CCL) counterpart. We discuss four different aspects relevant to the present scenario, namely: 1) gate capacitance; 2) drain-current saturation; 3) subthreshold slope; and 4) scaling performance. To gain physical insights into these effects, we also develop a set of semianalytical equations. The key observations are as follows: 1) A strongly energy-quantized nanowire shows nonmonotonic multiple-peak C-V characteristics due to discrete contributions from individual subbands; 2) the ballistic drain current saturates better in the UQCL than in the CCL, both in the presence and absence of Dit and Rs, d; 3) the subthreshold slope does not suffer any relative degradation in the UQCL compared to the CCL, even with Dit and Rs, d; 4) the UQCL scaling outperforms the CCL in the ideal condition; and 5) the UQCL scaling is more immune to Rs, d, but the presence of Dit and CL significantly degrades the scaling advantages in the UQCL.

Origin of the anomalous size-dependent increase of capacitance in boron nitride–graphene nanocapacitors

Abstract: The anomalous size-dependent increase in capacitance in boron nitride–graphene nanocapacitors is a puzzle that has been initially attributed to the negative quantum capacitance exhibited by this particular materials system. However, we show in this work that the anomalous nanocapacitance of this system is not due to quantum effects but has pure electrostatic origin and can be explained by a parallel-plate (square) nanocapacitor model filled with a dielectric film characterized by a size/thickness-dependent relative permittivity. The model presented here is in excellent agreement with the experimentally measured capacitance values of recently fabricated graphene and hexagonal boron nitride nanocapacitors. The results obtained seem to suggest that the size-dependent increase of capacitance in the above-mentioned family of nanocapacitors can be explained by classical finite-size geometric electrostatic effects.

Gate capacitance optimization for arrays of carbon nanotube field-effect transistors

Abstract: In this paper, three different gate electrode configurations of CNFETs are studied by calculating the capacitance per tube of carbon nanotube arrays. We then show, that an optimal design point can be found a practical configuration.