Chemical capacitance proposed for manganite-based ceramics

The measured value of effective electric permittivity \varepsilon_{eff} of several compounds, e.g., (BiNa)(MnNb)O_{3}, (BiPb)(MnNb)O_{3}, and BiMnO_{3} increases from a value \approx 10-100 at the low temperature range (100-300 K) up to the high value reaching the value 10^5 at high temperature range, e.g., 500-800 K. Such features suggest the manifestation of thermally activated space charge carriers, which effect the measured capacitance. The measured high-value effective permittivity of several manganite compounds can be ascribed to the chemical capacitance C_{\mu}=e^2\partial N_{i}/\partial \mu_{i} expressed in terms of the chemical potential \mu. The chemical capacitance C_{\mu}^{(cb)} = e^2 n_{C}/k_{B}T depends on temperature when the conduction electrons with density n_{C} = N_{C} \exp(\mu_{n}- E_{C})/k_{B}T are considered. The experimental results obtained for the manganite compounds, at high temperature range, are discussed in the framework of the chemical capacitance model. However, the measured capacitance dependence on geometrical factors is analysed for BiMnO_{3} indicating that the non-homogeneous electrostatic capacitor model is valid in 300-500 K range.Comment: 10 pages, 7 figure

Quantum capacitance and density of states of graphene

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

The effect of electron dielectric response on the quantum capacitance of graphene in a strong magnetic field

The quantum capacitance of graphene can be negative when the graphene is placed in a strong magnetic field, which is a clear experimental signature of positional correlations between electrons. Here we show that the quantum capacitance of graphene is also strongly affected by its dielectric polarizability, which in a magnetic field is wave vector-dependent. We study this effect both theoretically and experimentally. We develop a theory and numerical procedure for accounting for the graphene dielectric response, and we present measurements of the quantum capacitance of high-quality graphene capacitors on boron nitride. Theory and experiment are found to be in good agreement.Comment: 8+ pages, 6 figure

Design and simulation of zipping variable capacitors

Variable capacitors are essential for building tunable RF systems. We present here the design and simulation of novel zipping variable capacitors with a high permittivity dielectric layer. Two modelling techniques are presented: finite element simulation and variational analysis. A capacitance ratio greater than 40 can be obtained for a 100µm x 25µm device which has a high permittivity dielectric layer (εr = 200). By shaping either the top electrode beam or the bottom electrode, continuously variable capacitance is achieved at low bias voltages

Influence of the spatial distribution of border traps in the capacitance frequency dispersion of Al2O3/InGaAs

In this paper, the capacitance frequency dispersion in strong accumulation of capacitance voltage curves has been studied for different high-k dielectric layers in MOS stacks. By studying experimental data at low (77 K) and room temperature (300 K), in oxides with different density of defects, it was possible reflect the spatial distribution of the defects in the capacitance frequency dispersion. The experimental data show that while at room temperature, the capacitance dispersion is dominated by the exchange of carriers from the semiconductor into oxide traps far away from the interface, at low temperature the oxide traps near the Al2O3/InGaAs interface are responsible for the frequency dispersion. The results indicate that the capacitance dispersion in strong accumulation reflect the spatial distribution of traps within the oxide, and that dielectric/semiconductor conduction band offset is a critical parameter for determining the capacitance dispersion for Al2O3/InGaAs based gate stacks.Fil: Palumbo, Félix Roberto Mario. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional; ArgentinaFil: Aguirre, Fernando Leonel. Universidad Tecnológica Nacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Pazos, Sebastián Matías. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Krylov, Igor. Technion - Israel Institute of Technology; IsraelFil: Winter, Roy. Technion - Israel Institute of Technology; IsraelFil: Eizenberg, Moshe. Technion - Israel Institute of Technology; Israe