Quantum capacitance

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

A Compact Virtual-Source Model for Carbon Nanotube Field-Effect Transistors in the Sub-10-nm Regime-Part I Intrinsic Elements

Abstract: We presents a data-calibrated compact model of carbon nanotube (CNT) field-effect transistors (CNFETs) based on the virtual-source (VS) approach, describing the intrinsic current-voltage and charge-voltage characteristics. The features of the model include: (i) carrier VS velocity extracted from experimental devices with gate lengths down to 15 nm; (ii) carrier effective mobility and velocity depending on the CNT diameter; (iii) short channel effect such as inverse subthreshold slope degradation and drain-induced barrier lowering depending on the device dimensions; (iv) small-signal capacitances including the CNT quantum capacitance effect to account for the decreasing gate capacitance at high gate bias. The CNFET model captures dimensional scaling effects and is suitable for technology benchmarking and performance projection at the sub-10-nm technology nodes.

Quantum capacitance and density of states of graphene

Abstract: We report on measurements of the quantum capacitance in graphene as a function of charge carrier density. A resonant LC-circuit giving high sensitivity to small capacitance changes is employed. The density of states, which is directly proportional to the quantum capacitance, is found to be significantly larger than zero at and around the charge neutrality point. This finding is interpreted to be a result of potential fluctuations with amplitudes of the order of 100 meV in good agreement with scanning single-electron transistor measurements on bulk graphene and transport studies on nanoribbons.

Assessment of silicon MOS and carbon nanotube FET performance limits using a general theory of ballistic transistors

Abstract: A simple model for ballistic nanotransistors, which extends previous work by treating both the charge control and the quantum capacitance limits of MOSFET-like transistors, is presented. We apply this new model to MOSFET-like carbon nanotube FETs (CNTFETs) and to MOSFETs at the scaling limit. The device physics for operation at ballistic and quantum capacitance limits are explored. Based on the analysis of recently reported CNTFETs, we compare CNTFETs to MOSFETs. The potential performance advantages over Si that might be achieved at the scaling limit are established by using the new model.

Boron Nitride–Graphene Nanocapacitor and the Origins of Anomalous Size-Dependent Increase of Capacitance

Abstract: Conventional wisdom suggests that decreasing dimensions of dielectric materials (e.g., thickness of a film) should yield increasing capacitance. However, the quantum capacitance and the so-called “dead-layer” effect often conspire to decrease the capacitance of extremely small nanostructures, which is in sharp contrast to what is expected from classical electrostatics. Very recently, first-principles studies have predicted that a nanocapacitor made of graphene and hexagonal boron nitride (h-BN) films can achieve superior capacitor properties. In this work, we fabricate the thinnest possible nanocapacitor system, essentially consisting of only monolayer materials: h-BN with graphene electrodes. We experimentally demonstrate an increase of the h-BN films’ permittivity in different stack structures combined with graphene. We find a significant increase in capacitance below a thickness of ∼5 nm, more than 100% of what is predicted by classical electrostatics. Detailed quantum mechanical calculations suggest t...

First-Principles-Inspired Design Strategies for Graphene-Based Supercapacitor Electrodes

Abstract: Using density-functional theory calculations on a variety of model surfaces, we demonstrate that the low theoretical quantum capacitance of graphene-based electrodes can be significantly improved by altering local structural and morphological features. Common point defects, dopants, strain, and surface rippling are considered, as well as differences between locally single-layer and multilayer configurations. Local curvature is particularly effective at improving quantum capacitance, as is the inclusion of certain point defects and substitutional dopants at sufficiently high concentrations. We also show that single-layer graphene exhibits poor screening behavior of the double-layer potential when compared with multilayer samples, which suggests that higher area-specific capacitance can be obtained with samples a few layers thick. Overall, our results demonstrate the viability of local structural engineering as a tool to optimize graphene derivatives for use as supercapacitor electrodes, potentially increas...