scispace - formally typeset
Search or ask a question

Showing papers on "Capacitance published in 2002"


Journal ArticleDOI
TL;DR: Several of the extraction methods currently used to determine the value of threshold voltage from the measured drain current versus gate voltage transfer characteristics, focusing specially on single-crystal bulk MOSFETs are reviewed.

813 citations



Journal ArticleDOI
TL;DR: In this paper, the authors discussed and experimentally verified how to lower the operating voltage that drives liquid droplets by the principle of electrowetting on dielectric (EWOD).
Abstract: This article discusses and experimentally verifies how to lower the operating voltage that drives liquid droplets by the principle of electrowetting on dielectric (EWOD). A significant contact angle change (120°→80°) is desired to reliably pump the droplet in microchannels for applications such as lab-on-a-chip or micrototal analysis systems. Typically, much higher voltages (>100 V) are used to change the wettability of an electrolyte droplet on a dielectric layer compared with a conductive layer. The required voltage can be reduced by increasing the dielectric constant and decreasing the thickness of the dielectric layer, thus increasing the capacitance of the insulating layer. This dependence of applied voltage on dielectric thickness is confirmed through EWOD experiments for three different dielectric materials of varying thickness: Amorphous fluoropolymer (Teflon® AF, Dupont), silicon dioxide (SiO2) and parylene. The dependence on the dielectric constant is confirmed with two different dielectric mate...

681 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present a technique to directly excite Luttinger liquid collective modes in carbon nanotubes at gigahertz frequencies by modeling the nanotube as a nano-transmission line with distributed kinetic and magnetic inductance as well as distributed quantum and electrostatic capacitance.
Abstract: Presents a technique to directly excite Luttinger liquid collective modes in carbon nanotubes at gigahertz frequencies. By modeling the nanotube as a nano-transmission line with distributed kinetic and magnetic inductance as well as distributed quantum and electrostatic capacitance, we calculate the complex frequency-dependent impedance for a variety of measurement geometries. Exciting voltage waves on the nano-transmission line is equivalent to directly exciting the yet-to-be observed one-dimensional plasmons, the low energy excitation of a Luttinger liquid. Our technique has already been applied to two-dimensional plasmons and should work well for one-dimensional plasmons. Tubes of length 100 microns must be grown for gigahertz resonance frequencies. Ohmic contact is not necessary with our technique; capacitive contacts can work. Our modeling has applications in potentially terahertz nanotube transistors and RF nanospintronics.

617 citations


Journal ArticleDOI
01 Apr 2002-Carbon
TL;DR: In this article, the influence of carbon-oxygen complexes on the performance of polyacrylonitrile-based activated carbon fabric capacitors was explored, and it was found that most of the oxygen functional groups created from the oxygen treatment were the carbonyl or quinone type.

570 citations


Journal ArticleDOI
TL;DR: In this article, polyaniline doped with HCl and LiPF6 (Pani-LiPF6) is used as the active electrode material of symmetric redox supercapacitors.

519 citations


Journal ArticleDOI
TL;DR: In this article, a nanocomposite electrode of single-walled carbon nanotube (SWNT) and polypyrrole (Ppy) is fabricated to improve the specific capacitance of the supercapacitor.
Abstract: A nanocomposite electrode of single-walled carbon nanotube (SWNT) and polypyrrole (Ppy) is fabricated to improve the specific capacitance of the supercapacitor. The individual nanotubes and nanoparticles are uniformly coated with Ppy by in situ chemical polymerization of pyrrole. To characterize the SWNT-Ppy nanocomposite electrodes, a charge-discharge cycling test for measuring specific capacitance, cyclic voltammetry, and an ac impedance test are executed. The SWNT-Ppy nanocomposite electrode shows much higher specific capacitance than pure Ppy and as-grown SWNT electrodes, due to the uniformly coated Ppy on the SWNTs. The effects of the conducting agent added in the nanocomposite electrodes on specific capacitance and internal resistance of supercapacitors are also investigated. © 2002 The Electrochemical Society. All rights reserved.

420 citations


Journal ArticleDOI
TL;DR: In this paper, a novel nanostructure polymer-ceramic composite with a very high dielectric constant (er ∼110, a new record for the highest reported er value of a nanocomposite) was developed.
Abstract: Embedded capacitor technology can increase silicon packing efficiency, improve electrical performance, and reduce assembly cost compared with traditional discrete capacitor technology. Developing a suitable material that satisfies electrical, reliability, and processing requirements is one of the major challenges of incorporating capacitors into a printed wiring board (PWB). Polymer–ceramic composites have been of great interest as embedded capacitor material because they combine the processability of polymers with the high dielectric constant of ceramics. A novel nanostructure polymer–ceramic composite with a very high dielectric constant (er ∼110, a new record for the highest reported er value of a nanocomposite) was developed in this work. A high dielectric constant is obtained by increasing the dielectric constant of the epoxy matrix (er >6) and using the combination of lead magnesium niobate–lead titanate (PMN–PT)/BaTiO3 as the ceramic filler. This nanocomposite has a low curing temperature (<200°C); thus, it is multichip-module laminate (MCM-L) process-compatible. An embedded capacitor prototype with a capacitance density of 50 nF/cm2 was manufactured using this nanocomposite and spin-coating technology. The effect of the composite microstructure on the effective dielectric constant was studied. This novel nanocomposite can be used for integral capacitors in PWBs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1084–1090, 2002

329 citations


Journal ArticleDOI
TL;DR: In this article, the feasibility of integrating a high-permittivity gate dielectric material zirconium oxide into the MOS capacitors fabricated on pure germanium substrates was demonstrated.
Abstract: For the first time, we have successfully demonstrated the feasibility of integrating a high-permittivity (/spl kappa/) gate dielectric material zirconium oxide into the MOS capacitors fabricated on pure germanium substrates. The entire fabrication process was essentially performed at room temperature with the exception of a 410/spl deg/C forming gas anneal. After processing steps intended to remove the germanium native oxide interlayer between the zirconium oxide dielectric and germanium substrate, an excellent capacitance-based equivalent SiO/sub 2/ thickness (EOT) on the order of 5-8 /spl Aring/ and capacitance-voltage (C-V) characteristics with hysteresis of 16 mV have been achieved. Additionally, excellent device yield and uniformity were possible using this low thermal budget process.

324 citations


Journal ArticleDOI
TL;DR: In this article, the electron transport and recombination in several nanoporous titanium dioxide films have been studied as a function of the applied potential, using the electrochemical impedance technique, and the model provided a satisfactory description of the spectra in widely different conditions of conductivity of the TiO2 phase.
Abstract: Processes in the dark of electron transport and recombination in several nanoporous titanium dioxide films have been studied as a function of the applied potential, using the electrochemical impedance technique. Contact and bulk characteristics have been identified, decoupled, and interpreted, applying a transmission line model that identifies the following elements: (i) the capacitance of the interface between the exposed surface of the substrate and the electrolyte, (ii) the electron transport resistance, (iii) the charge-transfer resistance distributed in the TiO2/electrolyte interface, and (iv) a distributed capacitive element related to charging the porous matrix. The model provides a satisfactory description of the spectra in widely different conditions of conductivity of the TiO2 phase. The electron conductivity has been determined as a function of applied potential and coincides for the different samples under study. Classical electrochemical frameworks of transport and interfacial charge transfe...

286 citations


Journal ArticleDOI
TL;DR: In this paper, it was shown that the charge storage in cobalt oxide was similar to that of nickel oxide, although their capacitances were different, and the material was shown to be inferior to nickel hydroxide/oxide when used as a positive electrode, it was seen to be superior as a negative.

Journal ArticleDOI
TL;DR: Unprecedented resolution of electrochemically observed quantized double layer (QDL) charging is described with use of reduced solution temperatures and with an annealing procedure that produces hexanethiolate monolayer protected gold clusters (C6 MPCs) with a high level of monodispersity in charging capacitance, C(CLU).
Abstract: We describe unprecedented resolution of electrochemically observed quantized double layer (QDL) charging, attained with use of reduced solution temperatures and with an annealing procedure that produces hexanethiolate monolayer protected gold clusters (C6 MPCs) with a high level of monodispersity in charging capacitance, C(CLU). The spacing DeltaV = e/C(CLU) on the electrochemical potential axis between one electron changes in the electronic charge of nanoscopic metal particles is determined by their effective capacitance C(CLU). The high monodispersity of the C6 MPCs with Au(140) cores facilitates (a) detailed rotated disk and cyclic voltammetric measurements, (b) simulation of QDL waveshapes based on assumed reversible, multivalent redox-like behavior, (c) determination of nanoparticle diffusion rates, and (d) observation of as many as 13 changes in the MPC charge state, from MPC(6-) to MPC(7+). The single electron QDL charging peaks are quite evenly spaced (DeltaV constant) at potentials near the MPC potential of zero charge, but are irregularly spaced at more positive and negative potentials. The irregular spacing is difficult to rationalize with classical double layer capacitance ideas and is proposed to arise from a correspondingly structured (e.g., not smooth) density of electronic states of the nanoparticle core, resulting from its small HOMO/LUMO gap and incipiently molecule-like behavior.

Journal ArticleDOI
TL;DR: In this paper, a hybrid capacitor in neutral KCl aqueous electrolyte, which consists of amorphous manganese oxide (a-MnO 2.nH 2 O) as a cathode and activated carbon as an anode, was reported.
Abstract: This study reports a hybrid capacitor in neutral KCI aqueous electrolyte, which consists of amorphous manganese oxide (a-MnO 2 .nH 2 O) as a cathode and activated carbon as an anode. The electrochemical performance of the hybrid capacitor is characterized by cyclic voltammetry and a dc charge/discharge test. The hybrid capacitor shows ideal capacitor behavior with an extended operating voltage of 2 V. The extended operating voltage is preferentially attributed to having asymmetric electrodes with different stable voltage windows and good electrochemical stability in neutral KCl aqueous electrolyte. According to the extended operating voltage, the energy density of the hybrid capacitor at a current density of 0.25 A/g, was found to be 28.8 Wh/kg which is comparable to that of an amorphous ruthenium oxide capacitor (26.7 Wh/kg). The hybrid capacitor also shows no degradation of capacitance during 100 cycles except an initial loss of 7% within a few cycles.

Journal ArticleDOI
TL;DR: In this article, two sets of SnO 2 -based supercapacitors were synthesized and characterized, and a surface-grafting technique was introduced to delay grain coarsening, giving rise to a maximum capacitance in 1M KOH (aq) of 16 −F g −1 (or 64 −F cm −3 ).

Journal ArticleDOI
TL;DR: Theoretical limits for the capacitance density of integrated capacitors with combined lateral and vertical field components are derived in this article, and the limits are used to investigate the efficiency of various capacitive structures such as lateral flux and quasifractal capacitors.
Abstract: Theoretical limits for the capacitance density of integrated capacitors with combined lateral and vertical field components are derived. These limits are used to investigate the efficiency of various capacitive structures such as lateral flux and quasifractal capacitors. This study leads to two new capacitor structures with high lateral-field efficiencies. These new capacitors demonstrate larger capacities, superior matching properties, tighter tolerances, and higher self-resonance frequencies than the standard horizontal parallel plate and previously reported lateral-field capacitors, while maintaining comparable quality factors. These superior qualities are verified by simulation and experimental results.

Journal ArticleDOI
TL;DR: In this paper, composite electrodes for supercapacitors are prepared via chemical polymerization of pyrrole (Py) on the surface of a porous graphite fiber matrix, and capacitance properties are investigated with cyclic voltammetry (CV), ac impedance spectroscopy and charge-discharge tests.

Journal ArticleDOI
TL;DR: In this article, an equivalent circuit analysis on a mixed conductor electrode/solid oxide electrolyte system was performed on a dense film of La 0.6 Sr 0.4 CoO 3-δ deposited on a sintered plate of Ce 0.9 Gd 0.1 O 1.95 by a laser ablation method.
Abstract: Equivalent circuit analysis was undertaken on a mixed conductor electrode/solid oxide electrolyte system. In a limited case where surface reaction is the predominant rate-controlling process, the equivalent circuit was simplified to parallel connection of a resistor (surface reaction resistance) and a capacitor (chemical capacitance due to oxygen nonstoichiometry). Equilibrium oxygen vacancy concentration was correlated with the chemical capacitance. The model was applied to a dense film of La 0.6 Sr 0.4 CoO 3-δ deposited on a sintered plate of Ce 0.9 Gd 0.1 O 1.95 by a laser ablation method. Frequency response of the electrochemical impedance was measured under dc bias at 873-1073 K in O 2 -Ar gas mixtures. The observed capacitance was extremely large, e.g., around 0.1 to I F cm -2 for the 1.5 μm thick film. The oxygen vacancy concentration in the film was calculated from the capacitance and compared with the literature data measured by thermogravimetry. The film was found to show smaller oxygen nonstoichiometry. The enthalpy for oxygen vacancy formation in the film was about 40 kJ mol -1 larger than the bulk.

Journal ArticleDOI
TL;DR: In this article, the authors show that the distribution of R and C elements in a porous electrode structure leads to a decline of energy-density with operating power-density as current drain is increased.

Journal ArticleDOI
Jong Hyeok Park1, O Ok Park1
TL;DR: In this article, the performance of a polyaniline-activated carbon, hybrid electrochemical capacitor was evaluated by using a constant charge-discharge test, and a specific capacitance of 380 F g−1 was obtained.

Journal ArticleDOI
Jong Hyeok Park1, O Ok Park1, Kyung Hee Shin, Chang Soo Jin, Jong Huy Kim 
TL;DR: In this paper, a hybrid type pseudocapacitor/electric double layer capacitor (EDLC) was investigated and its electrochemical properties were investigated, and stable charge/discharge behaviors were observed with much higher specific capacitance values of 530 F/g compared with that of EDLC.
Abstract: In order to enhance energy density, a hybrid type pseudocapacitor/electric double layer capacitor (EDLC) was considered and its electrochemical properties were investigated. At various current densities, stable charge/discharge behaviors were observed with much higher specific capacitance values of 530 F/g compared with that of EDLC (230 F/g), by introducing as a cathode material. By using the modified cathode of a /activated carbon composite electrode, the specific capacitance was less sensitive to charge/discharge current density exhibiting stable power characteristics. © 2001 The Electrochemical Society. All rights reserved.

Patent
Masao Murade1
17 Dec 2002
TL;DR: An active matrix driven electro-optical device, such as a liquid crystal device, enabled to add sufficient storage capacitance to pixel electrodes and decrease the diameter of contact holes connecting with pixel electrodes even when a fine pixel pitch is employed.
Abstract: An active matrix driven electro-optical device, such as a liquid crystal device, enabled to add sufficient storage capacitance to pixel electrodes and decrease the diameter of contact holes connecting with pixel electrodes even when a fine pixel pitch is employed. The liquid crystal device has TFTs, data lines, scanning lines, storage capacitor lines, and pixel electrodes provided on a TFT array substrate. Each of the pixel electrodes is electrically connected to one of the TFTs by two contact holes through a barrier layer. A part of a semiconductor layer and each of the capacitor lines sandwich a first dielectric film and constitute a first storage capacitor, while a part of the barrier layer and each of the capacitor lines sandwich a second dielectric film and constitute a second storage capacitor.

Journal ArticleDOI
Soshi Shiraishi1, Hideyuki Kurihara1, K Okabe1, Denisa Hulicova1, Asao Oya1 
TL;DR: The double layer capacitance of highly pure single-walled carbon nanotubes (SWCNTs) prepared by the HiPco(TM) process was measured in 1.0 mol dm(-3) LiClO4/propylene carbonate solution.

Patent
07 May 2002
TL;DR: In this article, a Faraday shield is electrically isolated from the earth and the capacitance of the variable capacitor is determined to be such a value that the voltage at the two ends of the antenna may be equal in absolute values and inverted to reduce the partial removal of the wall after the plasma ignition.
Abstract: A plasma is generated by feeding an antenna with radio-frequency electric power generated by a radio-frequency power source, and one end of the antenna is grounded to the earth through a capacitor of variable capacitance. A Faraday shield is electrically isolated from the earth, and the capacitance of the variable capacitor is determined to be such a value that the voltage at the two ends of the antenna may be equal in absolute values and inverted to reduce the partial removal of the wall after the plasma ignition. At the time of igniting the plasma, the capacitance of the capacitor is adjusted to a larger or smaller value than that minimizing the damage of the wall.

Journal ArticleDOI
TL;DR: In this article, two different approaches are introduced to control charge in the actuator by means of current driving, and theoretical equations derived for each method show that full range of travel can be achieved without voltage penalty.
Abstract: When a voltage source drives an electrostatic parallel plate actuator, the well-known pull-in instability limits the range of displacement to 1/3 of the gap. Different strategies have been reported to overcome this limitation. More recently, experimental results have been presented using a capacitor in series with the actuator. Nevertheless, this strategy requires higher voltage than the pull-in voltage value to achieve full range of travel. In order to reduce the operating voltage, a switched-capacitor configuration has been also proposed. In this paper, two different approaches are introduced to control charge in the actuator by means of current driving. Theoretical equations derived for each method show that full range of travel can be achieved without voltage penalty. Both approaches are based on the use of current pulses injecting the required amount of charge to fix the position of the movable plate. Experimental measurements, showing that displacement beyond the pull-in point can be achieved, are in good agreement with the theoretical and the predicted simulated behavior.

Journal ArticleDOI
TL;DR: In this article, a polyaniline (PANI) coated supercapacitor was applied to stainless-steel (SS) electrodes to obtain a capacitance of about 450 F over a long cycle-life.

Journal ArticleDOI
Juan Bisquert1
TL;DR: In this paper, the authors developed a new framework for the interpretation of impedance or capacitance spectroscopy of ion insertion processes in thin film electrodes, with a particular emphasis in electrochromic materials.

Patent
05 Mar 2002
TL;DR: In this paper, a force sensor for sensing a touch force applied to a touch surface is described, which includes a first element (106) including an elastic element and a first capacitive surface, the elastic element including at least part of the first capacitor plate; and a second element (105) including a second capacitor plate (114) opposed to the first capacitance plate.
Abstract: A force sensor for sensing a touch force applied to a touch surface (103a) is disclosed. The force sensor includes: a first element (106) including an elastic element and a first capacitor plate having a first capacitive surface, the elastic element including at least part of the first capacitor plate; and a second element (105) including a second capacitor plate (114) opposed to the first capacitor plate; wherein transmission of at least part of the touch force through the elastic element (106) contributes to a change in capacitance between the first capacitor plate (106) and the second capacitor plate (114). The elastic element (106) and the first capacitor plate may be integral. Other force sensors and methods for manufacturing said force sensors are also disclosed. Touch location devices suitable for use with the disclosed force sensors are also disclosed.

Patent
22 Jan 2002
TL;DR: In this article, a peritoneal dialysis system is presented, where the pump having the capacitance sensor fluidly connects to a patient. But the sensor is used to measure the volume of dialysate supplied to and drained from the patient.
Abstract: A fluid volumetric pumping system has a fluid pump and capacitor plates disposed around a pump chamber of the fluid pump. The capacitance between the capacitor plates changes as the volume of fluid in the pump chamber changes. An electrical circuit measures a change in the capacitance between the plates and outputs a signal indicative of the volume of fluid in the pump chamber. The pump having the capacitance sensor of the present invention fluidly connects to a patient. In an embodiment, a peritoneal dialysis system provides dialysate to the patient via the pump, and the capacitance sensor measures the volume of dialysate supplied to and drained from a peritoneal cavity of the patient.

Journal ArticleDOI
TL;DR: In this paper, the capacitances of nanocrystalline ZnO and TiO2 electrodes were compared by using potential step chronoamperometry to compare the capacitance of the metal oxide electrodes.
Abstract: Potential step chronoamperometry is employed to compare the capacitances of nanocrystalline ZnO and TiO2 electrodes. These capacitance data are complemented by transient optical absorption studies of charge recombination following adsorption of molecular sensitizer dyes to these metal oxide electrodes. Both measurements are conducted as a function of electrochemical bias applied to the metal oxide film in a three-electrode photoelectrochemical cell. For both metal oxides, a power law dependence was observed between the half times for charge recombination (t50%) and the metal oxide electron density n determined from integration of the capacitance data, t50% ∝ n-1/α, where α = 0.27 and 0.30 ± 0.05 for ZnO and TiO2, respectively. A numerical model for the recombination dynamics based upon a random walk of electrons between localized sub-bandgap states is found to be in good agreement with experimental observations for both metal oxides. At negative applied potentials, the film capacitance, and therefore elec...

Patent
09 Jul 2002
TL;DR: In this article, a compressible variable capacitance sensor for determining the presence, size, position, and type of an object such as a human body part includes two flexible conductor elements separated by a nonconductive compressible element.
Abstract: A compressible variable capacitance sensor for determining the presence, size, position, and type of an object such as a human body part includes two flexible conductor elements separated by a non-conductive compressible element. The capacitance of the capacitance sensor changes as a function of force applied by an object on the capacitance sensor. A controller senses the capacitance of the capacitance sensor and controls a device accordingly. The device may be a movable closed opening such as a window in which the controller controls the window as a function of the monitored capacitance to prevent pinching of the object. The device may also be a seat in which the controller determines the characteristics of the seat occupant based on the monitored capacitance.