Showing papers on "Capacitance published in 1996"

A silicon nanocrystals based memory

Abstract: A new memory structure using threshold shifting from charge stored in nanocrystals of silicon (≊5nm in size) is described. The devices utilize direct tunneling and storage of electrons in the nanocrystals. The limited size and capacitance of the nanocrystals limit the numbers of stored electrons. Coulomb blockade effects may be important in these structures but are not necessary for their operation. The threshold shifts of 0.2–0.4 V with read and write times less than 100’s of a nanosecond at operating voltages below 2.5 V have been obtained experimentally. The retention times are measured in days and weeks, and the structures have been operated in an excess of 109 cycles without degradation in performance. This nanomemory exhibits characteristics necessary for high density and low power.

Determination of defect distributions from admittance measurements and application to Cu(In,Ga)Se2 based heterojunctions

Abstract: A method to deduce energy distributions of defects in the band gap of a semiconductor by measuring the complex admittance of a junction is proposed. It consists of calculating the derivative of the junction capacitance with respect to the angular frequency of the ac signal corrected by a factor taking into account the band bending and the drop of the ac signal over the space charge region of the junction. Numerical modeling demonstrates that defect distributions in energy can be reconstructed by this method with high accuracy. Defect distributions of polycrystalline Cu(In,Ga)Se2 thin films are determined by this method from temperature dependent admittance measurements on heterojunctions of Cu(In,Ga)Se2 with ZnO that are used as efficient thin film solar cells.

Materials for electrochemical capacitors: Theoretical and experimental constraints

Abstract: Electrochemical capacitors, also called supercapacitors, are unique devices exhibiting 20 to 200 times greater capacitance than conventional capacitors. The large capacitance exhibited by these systems has been demonstrated to arise from a combination of the double-layer capacitance and pseudocapacitance associated with surface redox-type reactions. The purpose of this review is to survey the published data of available electrode materials possessing high specific double-layer or pseudocapacitance and examine their reported performance data in relation to their theoretical expectations.

Pressure sensitive scrollbar feature

Abstract: A proximity sensor system includes a sensor matrix array having a characteristic capacitance on horizontal and vertical conductors connected to sensor pads. The capacitance changes as a function of the proximity of an object or objects to the sensor matrix. The change in capacitance of each node in both the X and Y directions of the matrix due to the approach of an object is converted to a set of voltages in the X and Y directions. These voltages are processed by circuitry to develop electrical signals representative of the centroid of the profile of the object, i.e, its position in the X and Y dimensions. Noise reduction and background level setting techniques inherently available in the architecture are employed.

Accuracy of electron counting using a 7‐junction electron pump

Abstract: We have operated a 7‐junction electron pump as an electron counter with an error per pumped electron of 15 parts in 109 and an average hold time of 600 s. The accuracy and hold time are sufficient to enable a new fundamental standard of capacitance. We compare the measured accuracy of the pump as a function of pumping speed and temperature with theoretical predictions based on a model which includes stray capacitance.

Electric surgical apparatus

Abstract: PURPOSE: To utilize an electrosurgical apparatus for electric surgical treatment, particularly for tissue cutting, by increasing an output voltage. CONSTITUTION: In an electrosurgical apparatus for drying and cutting a tissue, an electric surgical generator has a negative charge capacitance CL and output inductor L connected in series. The capacitance contains an electrode unit and a cable connected with a generator output 12A. The inductor forms a resonant circuit connected in series. Frequency of the resonant circuit connected in series is typically 1.5f, wherein f is operating frequency. The capacitor is included between conductors and bonded with them. By the conductors, a bipolar electrode 20E is connected with the generator in order to increase negative charge capacitance CL.

Impedance Spectroscopy of Undoped BaTiO3 Ceramics

Abstract: The electrical properties of ceramic BaTiO3 were investigated by ac impedance spectroscopy over the ranges 25°-330°C and 0.03 Hz-1 MHz. Results are compared with those obtained from fixed-frequency measurements, at 1 kHz and 100 kHz. Fixed-frequency Curie-Weiss plots show deviations from linearity at temperatures well above tc. The ac measurements show that grain boundary impedances influence Curie-Weiss plots in two ways: at high temperatures, they increasingly dominate the fixed-frequency permittivities; at lower temperatures, closer to Tc, the high-frequency permittivity contains a contribution from grain boundary effects. Methods for extraction of bulk and grain boundary capacitances from permittivity and electric modulus complex plane plots are discussed. The importance of selecting the appropriate equivalent circuit to model the impedance response is stressed. A constriction impedance model for the grain boundary in BaTiO3 ceramics is proposed: the grain boundary capacitance is neither temperature-independent, nor shows Curie-Weiss behavior. The grain boundary is ferroelectric, similar to the grains, but its impedance is modified by either air gaps or high-impedance electrical inhomogeneity in the region of the necks between grains; the activation energy of the constriction grain boundary impedance differs from that of the bulk, suggesting differences in defect states or impurity levels.

A review of reconstruction techniques for capacitance tomography

Abstract: Capacitance tomography has been used to image several processes, such as liquid/gas pipe flow, oil/water/gas gravity separation, pneumatic conveying, fluidized beds and flame combustion. The nature of the capacitance sensors is such that reconstruction algorithms well developed for medical tomography are not applicable. The main problem is that the relationship between the measured quantity (capacitance) and the parameter of interest (distribution of the dielectric constant) is nonlinear. Furthermore, it is impossible to establish an explicit expression which relates the dielectric constant distribution to the measured capacitance. Also it should be pointed out that the number of measurements in capacitance tomography is small (typically less than 100) compared to medical tomography. For these reasons the first tested algorithm in capacitance tomography was based on the crude back projection algorithm. This algorithm has over the years been enhanced for use with a capacitance tomograph. In addition other techniques, such as various iterative methods, algorithms based on artificial neural networks and `look-up' tables have been developed and tested. This paper outlines the working principles for the different techniques and presents the main results.

Hardware design of electrical capacitance tomography systems

Abstract: Electrical capacitance tomography (ECT) was one of the techniques which were firstly developed for process tomography (PT) Two types of capacitance measuring circuits are the most suitable for the use in ECT systems - the charge/discharge circuit and the AC-based circuit - because of their immunity to stray capacitance Since the standing capacitances involved are relatively large and the capacitance changes to be measured are very small, the standing values need to be cancelled by DC offset compensation or AC feedback compensation Alternatively, the capacitances can be measured by high-accuracy self-balancing circuits without standing value compensation In this paper different designs of sensing electronics for ECT systems are presented and the advantages and disadvantages compared

Analysis and design of a DC voltage-controlled static VAr compensator using quad-series voltage-source inverters

Abstract: This paper presents a DC voltage-controlled static VAr compensator (SVC) using quad-series voltage-source non-PWM inverters. The SVC consists of four three-phase voltage-source inverters having a common DC capacitor and four three-phase transformers, the primary windings of which are connected in series with each other. Although each inverter outputs a square wave voltage, the synthesized AC voltage of the SVC has a 24-step waveshape. This results not only in a great reduction of harmonic currents and DC voltage ripples but also in less switching and snubbing losses. This paper develops the analysis of the transient response and the resonance between the AC reactors and the DC capacitor, with the focus on practical use. Experimental results obtained from a 10-kVA laboratory system are shown to agree well with the analytical results, thus verifying the analysis and leading to the design of DC capacitance value.

VBIC95, the vertical bipolar inter-company model

Abstract: This paper details the VBIC95 bipolar junction transistor (BJT) model. The model was developed as an industry standard replacement for the SPICE Gummel-Poon (SGP) model, to improve deficiencies of the SGP model that have become apparent over time because of the advances in BJT process technology. VBIC95 is still based on the Gummel-Poon formulation, and thus can degenerate to be similar to the familiar SGP model. However, it includes improved modeling of the Early effect, quasi-saturation, substrate and oxide parasitics, avalanche multiplication, and temperature behavior that can be invoked selectively based on model parameter values.

Insulated-gate semiconductor device

Abstract: PURPOSE: To obtain an insulated-gate semiconductor device of a structure, wherein an excess voltage at the time of switching is made low and at the same time, the whole application system comprising a snubber circuit can be constituted compact. CONSTITUTION: An insulated-gate semiconductor device has gate trenches 36, which are respectively provided with a gate electrode 38 via a gate insulating film 37, and an emitter trench 39 arranged with an emitter electrode 40 via a silicon oxide layer 41 and a main current path is provided with a capacitor capacitance by using the layer 41 provided in the trench 39. Accordingly, the insulated-gate semiconductor device of a structure, wherein a surge voltage, which is accompanied by the wiring inductance of a snubber circuit, can be effectively made low and an application system comprising the snubber circuit can be miniaturized, can be formed.

Size dependence of the characteristics of Si single-electron transistors on SIMOX substrates

Abstract: A Si single-electron transistor (SET) was fabricated by converting a one-dimensional (1-D) Si wire on a SIMOX substrate into a small Si island with a tunneling barrier at each end by means of pattern-dependent oxidation. Since the size of the Si island became as small as around 10 nm owing to this novel technique, the total capacitance of the SET was reduced to a value of the order of 1 aF, which guaranteed the conductance oscillation of the SET even at room temperature. Furthermore, a linear relation between the designed wire length and the gate capacitance of SET's was obtained, which clearly indicates that the single island was actually formed in the middle of the one dimensional Si wire. These results were achieved owing to the highly reproducible fabrication process based on pattern dependent oxidation of SIMOX-Si layers.

Dynamic admittance of mesoscopic conductors : discrete-potential model

Abstract: We present a discussion of the low-frequency admittance of mesoscopic conductors in close analogy with the scattering approach to dc conductance. The mesoscopic conductor is coupled via contacts and gates to a macroscopic circuit which contains ac-current sources or ac-voltage sources. We find the admittance matrix which relates the currents at the contacts of the mesoscopic sample and of nearby gates to the voltages at these contacts. The problem is solved in two steps: we first evaluate the currents at the sample contacts in response to the oscillating voltages at the contacts, keeping the internal electrostatic potential fixed. In a second stage an internal response due to the potential induced by the injected charges is evaluated. The self-consistent calculation is carried out for the simple limit in which each conductor is characterized by a single induced potential. Our discussion treats the conductor and the gates on equal footing. Since our approach includes all conductors on which induced fields can change the charge distribution, the admittance of the total response is current conserving, and the current response depends only on ac-voltage differences. We apply our approach to a mesoscopic capacitor for which each capacitor plate is coupled via a lead to an electron reservoir. We find an electrochemical capacitance with density-of-state contributions in series with the geometrical capacitance. The dissipative part of the admittance is governed by a charge-relaxation resistance which is a consequence of the dynamics of the charge pileup on the capacitor plates. We specialize on a geometry displaying an Aharonov-Bohm effect only at nonzero frequencies. For a double barrier with a well coupled capacitively to a gate the low-frequency admittance terms may have either sign, reflecting either a capacitive or a kinetic-inductive behavior. The validity of a second-quantization-current-operator expression which neglects spatial information is examined for perfect leads in both the frequency and the magnetic-field domain. \textcopyright{} 1996 The American Physical Society.

Threshold voltage, field effect mobility, and gate-to-channel capacitance in polysilicon TFTs

Abstract: Based on experimental and theoretical studies of n- and p-channel polysilicon thin film transistors with gate W/L ratios from 0.3 to 3.3, we have demonstrated that the threshold voltage extracted from gate to channel capacitance data results in field effect mobility parameters which are independent of device geometry. The parameters extracted using this V/sub t/ allow us to reproduce the I-V characteristics of the n- and p channel TFTs over wide ranges of bias voltages and gate sizes. The C/sub gc/-V/sub GS/ characteristics of polysilicon TFTs are strongly affected by the trapping and de-trapping of carriers. As a result, the measured C/sub gc/ characteristic is a function of measurement frequency and gate length. However, we demonstrate that to the first order, the frequency dispersion of the C/sub gc/ curve can be related to the effective carrier transit time determined using the V/sub GS/ dependent field effect mobility.

Recent developments and industrial/research applications of capacitance tomography

Abstract: In this paper the general principles of capacitance tomography are explained. Recent developments in the design of the primary sensor, the sensor electronics and the reconstruction are shown as well as future trends identified. Industrial and research applications of capacitance tomography are given.

An on-chip, attofarad interconnect charge-based capacitance measurement (CBCM) technique

Abstract: In this paper, a sensitive and simple technique for parasitic interconnect capacitance measurement with 0.0l fF or 10 aF sensitivity is presented. This on-chip technique is based upon an efficient test structure design. No reference capacitor is needed. The measurement itself is also simple; only a DC current meter is required. We have applied this technique to extract various interconnect geometry capacitances, including the capacitance of a single Metal 2 over Metal 1 crossing, for an industrial double metal process.

Apparatus for determining and recording injection doses in syringes using electrical capacitance measurements

Abstract: An apparatus for electrically determining and recording the dose of an agent delivered with a syringe of the type having a barrel for holding the agent and a plunger for expelling the agent. The syringe includes a capacitive element having first and second conducting surfaces arranged such that the capacitance of the capacitive element varies in dependence upon the dose of agent contained in the barrel. An input terminal and an output terminal located on the outside of the syringe are electrically connected to the first and second conducting surfaces, respectively. The apparatus produces a voltage difference across the terminals, thereby charging the capacitive element. A capacitance meter measures the capacitance and a microprocessor calculates the dose from the measured capacitance. The calculated dose is recorded by a digital memory unit.

Modeling and extraction of interconnect capacitances for multilayer VLSI circuits

Abstract: We report an accurate and practical method of estimating interconnect capacitances for a given circuit layout. The method allows extraction of the complete circuit level capacitances at each node in the circuit. The layout geometry is reduced into base elements that consist of different vertical profiles at each node in the layout. Accurate analytical models are developed for calculating capacitances of multilayer structures using a 2D capacitance simulator TDTL. These models are then transformed into 3D geometry. The resulting model capacitance values are found to be within 10% of both the measured data and 3D simulations of structures that are prevalent in typical VLSI chips. The models and their coefficients for different vertical profiles are stored in the capacitance extraction tool CUP, which is coupled to the layout extractor HILEX. As each base element has a unique vertical profile, the corresponding capacitance can easily be calculated for each node that is then written out to a circuit netlist. The comparisons of the models with the measured data, as well as 3D simulations results, are also discussed.

Low Frequency Admittance of a Quantum Point Contact.

Abstract: We present a current and charge conserving theory for the low frequency admittance of a quantum point contact. We derive expressions for the electrochemical capacitance and the displacement current. The latter is determined by the emittance which equals the capacitance only in the limit of vanishing transmission. With the opening of channels the capacitance and the emittance decrease in a steplike manner in synchronism with the conductance steps. For vanishing reflection, the capacitance vanishes and the emittance is negative.

Pressure sensor diagnostics in a process transmitter

Abstract: A transmitter in a process control system includes diagnostic circuitry for determining condition of a pressure sensor. The pressure sensor includes a pressure responsive structure and a capacitor coupled to the pressure responsive structure whereby capacitance of the capacitor varies in response to process pressure. Measurement circuitry determines capacitance which is transmitted over a process control loop using output circuitry. The diagnostic circuitry is coupled to the pressure sensor and provides a diagnostic input to the pressure sensor. The diagnostic input causes a change in the capacitance which is monitored to determine condition of the pressure sensor.

Design of novel thin-film piezoelectric accelerometer

Abstract: A novel piezoelectric thin-film accelerometer has been designed and its performance has been analysed. The piezoelectric thin film (PZT for example) is delineated into an array of pads to reduce the sensor capacitance. By filling the cavity around the PZT pads either with a polymer or a gas with controlled pressure, damping can be controlled. The piezoelectric thin-film material (i.e., pads) is clamped between a seismic mass and a base plate (silicon substrate). During acceleration in the axial direction the seismic mass exerts a force on the piezoelectric layer, resulting in the generation of a charge due to the piezoelectric effect. The induced charge is independent of the dimensions of the piezoelectric layer and hence of its tolerances. The generated charge is directly sensed by a charge-sensitive preamplifier that is implemented by CMOS technology on a tiny silicon chip. In principle, the proposed thin-film accelerometer can be integrated with the electronic readout and can be extended into an array of accelerometers. The dynamic response is presented and the trade-offs between several design considerations are discussed. For a specific design, a sensor sensitivity of 320 mV g(-1) and lower and upper cut-off frequencies of, respectively, 1 Hz and 0.2 MHz have been calculated. By using differential sensing, the proposed thin-film accelerometer can be further developed to include compensation for temperature and pyroelectric effects. In addition, self-test features based on the application of electrostatic forces are feasible but require more sophisticated signal processing.

Capacitance anomaly near the metal—non-metal transition in Cr—hydrogenated amorphous Si—V thin-film devices

Abstract: We present experimental results that show a metal—non-metal (MNM) transition occurring in hydrogenated amorphous Si (a-Si: H) analogue memory devices as a function of temperature. The dc resistance of the devices undergoes a continuous change in the range 65–100 K from semiconductor-like behaviour to metallic behaviour, as the temperature increases. The ac conductivity, measured over the frequency range 1–3·1 × 107 Hz, shows an anomalous change as the temperature is varied over the MNM transition. Ac characteristics were modelled using multicomponent RC and RL equivalent circuits below and above the MNM transition region respectively. It is found that the capacitance increases markedly when the temperature approaches the MNM transition from the semiconductor side. Near the transition temperature this capacitance disappears, and the equivalent circuit now requires an inductive component together with a resistance which has a positive temperature coefficient of resistance equivalent to that of the ...