Local Capacitance Measurements Research Articles

Electrically-functionalised nanoindenter dedicated to local capacitive measurements: Experimental set-up and data-processing procedure for quantitative analysis

In this work, we report the experimental development and the application of a new characterisation tool combining mechanical testing and dielectric characterisation. The experimental set-up is essentially a nanoindentation head functionalised for capacitive measurements. First the experimental procedure for the characterisation of dielectric thin films is given: detailed set-up description, procedure for the capacitance-vs-voltage (C-V) measurements, stray capacitance. Secondly, a complete data-processing method is proposed to perform the quantitative analysis of capacitance data. To this end, a fully analytical model has been developed, able to relate the C-V curves to the system characteristics (set-up geometry and specimen properties) without any fitting parameter. Finally dielectric films with different thicknesses and relative permittivities have been tested to validate both the characterisation tool and the data-processing method. The analytical model has been used to predict the permittivity of each dielectric thin film. The extracted data have been compared to data obtained from a calibrated macro-scale technique and showed remarkable agreement. One of the strengths of the data-processing method is to eliminate the stray capacitance which usually disturbs local capacitance measurements. Even though the effect of mechanical load is not investigated in the present study, the experimental proof-of-principle is shown and the data-processing method is validated. This work opens prospects for local and quantitative dielectric characterisations under mechanical loads. It should also fill a gap between quantitative characterisations at macro-scales and spatially highly-resolved characterisations at nano-scale.

Inside Back Cover: Differentiation between Single‐ and Double‐Stranded DNA through Local Capacitance Measurements (ChemElectroChem 6/2016)

Inside Back Cover: Differentiation between Single‐ and Double‐Stranded DNA through Local Capacitance Measurements (ChemElectroChem 6/2016)

Differentiation between Single‐ and Double‐Stranded DNA through Local Capacitance Measurements

AbstractLocal differentiation of single‐stranded (ss) and double‐stranded (ds) DNA in microarrays by using electrochemical techniques has gained increasing interest. We propose a method for distinguishing areas on gold electrodes modified with ssDNA and dsDNA based on the difference in their local capacitance. The local capacitance is visualized by means of scanning electrochemical impedance microscopy and alternating‐current scanning electrochemical microscopy.

Capacitive sensing of local bond layer thickness and coverage in thermal interface materials

An instrumentation technique is developed using embedded capacitive sensors to measure the thickness and evenness of coverage of a thin layer of dielectric thermal interface material (TIM) between two substrates. The technique requires an array of sensors embedded into one substrate, with an electrically conductive opposing substrate. Local capacitance measurements are sensitive to both local bond layer thickness and local voiding. We propose a means for using an array of capacitance measurements to interpret both bond layer thickness and local voiding at every sensor location. An algorithm is developed which reveals both characteristics from a single set of capacitance measurements. Experiments are conducted with thermal grease layers of different bond layer thicknesses and void distributions using a prototype system constructed on printed circuit boards. The thickness and void distribution are successfully mapped across the bond layer using the algorithm developed. The technique offers a sensing approach for in situ instrumentation of layers of thermal grease in a thermal test vehicle.

Influence of substrate dielectric permittivity on local capacitive behavior in graphene

Graphene deposited on silicon dioxide (DG-SiO2) and high-κ dielectric strontium titanate (DG-STO) are investigated for electrostatic properties by local capacitance measurements carried out with Scanning Capacitance Spectroscopy (SCS). The quantum capacitance associated with 2DEG in graphene showed significant increase for DG-STO as a function of Fermi level (EF) as compared to that for DG-SiO2. The quantum capacitance, being a fundamental property of graphene 2DEG, is not expected to vary with substrate dielectric properties in the absence of any interaction. However, the observed increase in quantum capacitance in our case is predominantly due to the enhanced effectively biased area in DG-STO. We suggest that this effect is a consequence of better dielectric screening of commonly observed charged impurities, on graphene and/or at the graphene/substrate interface, by the use of high permittivity substrate.

1/f noise and slow relaxations in glasses

Recently we have shown that slow relaxations in the electron glass system can be understood in terms of the spectrum of a matrix describing the relaxation of the system close to a metastable state. The model focused on the electron glass system, but its generality was demonstrated on various other examples. Here, we study the noise spectrum in the same framework. We obtain a remarkable relation between the spectrum of relaxation rates $\lambda$ described by the distribution function $P(\lambda) \sim 1/\lambda$ and the $1/f$ noise in the fluctuating occupancies of the localized electronic sites. This noise can be observed using local capacitance measurements. We confirm our analytic results using numerics, and also show how the Onsager symmetry is fulfilled in the system.

1/f noise and slow relaxations in glasses

AbstractRecently we have shown that slow relaxations in the electron glass system can be understood in terms of the spectrum of a matrix describing the relaxation of the system close to a metastable state. The model focused on the electron glass system, but its generality was demonstrated on various other examples. Here, we study the noise spectrum in the same framework. We obtain a remarkable relation between the spectrum of relaxation rates λ described by the distribution function P (λ) ∼ 1/λ and the 1/f noise in the fluctuating occupancies of the localized electronic sites. This noise can be observed using local capacitance measurements. We confirm our analytic results using numerics, and also show how the Onsager symmetry is fulfilled in the system.

Local capacitance measurements on InAs dot-covered GaAs surfaces by scanning capacitance microscopy

Capacitance images responsible for surface depletion were observed on an InAs dot-covered GaAs surface by scanning capacitance microscopy. We performed local capacitance versus bias voltage measurements on quantum dots (QDs) and a wetting layer (WL) as well as conductance versus bias voltage (G–V) measurements. Both results indicate that the surface depletion is more suppressed beneath the QDs than under the WL. In addition, the conventional thermionic equation theory fitted to the measured G–V curves shows that the interface barrier height between the GaAs and the InAs QD increases as the QD size is reduced. We ascribe this result to the influence of the surrounding WL, whose surface Fermi level is strongly pinned at the midgap of the n-GaAs.

A capacitive displacement monitor system for the delphi microvertex detector

Abstract We describe the design of a Displacement Monitor System relying on local capacitance measurements. This system controls the relative position of the Delphi microstrip Vertex Detector at LEP. Results from the first months of data taking are presented. They show displacements are effectively monitored with the expected micron precision.