Showing papers on "Capacitance published in 1968"

Variational Method for the Analysis of Microstrip-Like Transmission Lines

Abstract: A theoretical method is presented by which microstrip-like transmission lines can be analyzed. These transmission lines are characterized by conducting strips, large ground planes, multi-dielectric-layer insulation, and planar geometry. The method is essentially based on a variational calculation of the line capacitance in the Fourier-transformed domain and on the charge density distribution as a trial function. A shielded double-layer microstrip line is analyzed by this method. Derived formulas for this structure are also applicable to simpler structures: a double-layer microstrip line, a shielded microstrip line, and a microstrip line. The calculated values of the line capacitance and the guide wavelength are compared with the measured values where possible. Oxide-layer effects on a silicon microstrip line and shielding effects on a sapphire microstrip line are also discussed based on this theory. The limitations and possible applications of this method are described.

Four‐Electrode Null Techniques for Impedance Measurement with High Resolution

Abstract: At low frequencies, the normally difficult measurement of the dielectric properties of conducting materials is severely compromised by electrode polarization. This problem at the electrode‐sample interface arises from the modulation of the normal dc boundary potential by the passage of alternating current. A solution, permitting a conductance resolution of 1:105 for frequencies between 10 cps and 1 kc, is to use a second noncurrent‐carrying pair of electrodes to measure the voltage across the sample and to employ a null technique for obtaining the required precision. Several four‐electrode null techniques are proposed, each having certain relative merits. In all cases the resolution in capacitance is shown to be governed by a combination of the resolution in conductance, the sample properties, and the frequency of the measurement.

Effects of deep impurities on n + p junction reverse-biased small-signal capacitance

Abstract: The a.c. small signal capacitance of a reverse-biased n+p junction containing deep impurities is analyzed. Expressions are obtained that govern the frequency and temperature dependence of the capacitance. The capacitance decreases considerably above a certain frequency if the deep level in the lightly doped side is incompletely compensated, but the frequency dependence is relatively small when the shallow level density exceeds the deep level density. The break point on a log C vs. log frequency plot depends strongly on trap depth, trap density, temperature, majority carrier lifetime, and reverse bias. Measurements on indium-doped silicon n+π-junctions near 77°K agree satisfactorily with theory.

Method for determining the state of charge of nickel cadmium batteries by measuring the farad capacitance thereof

Abstract: Method for predicting the capacity of nickel-cadmium batteries with a standard reference curve that indicates battery capacitance as a function of the state-of-charge of a given nickel-cadmium battery type wherein the standard reference curve is used with the measurement of the capacitance of any battery of the given type to indicate the state-of-charge of the battery.

Low-temperature hysteresis effects in metal-oxide-silicon capacitors caused by surface-state trapping

Abstract: At low temperatures, charge exchange in all surface states except those close to the band edges can occur only by capture of free carriers because emission rates become very slow. If means are provided to supply minority carriers (either from an extended inversion layer or in a gate-controlled diode), pronounced charge-trapping effects can be observed. A ledge in the C-V characteristic is identified as being due to the charging of almost all surface states within the forbidden gap at a surface potential dependent on surface-state density, capture cross section and voltage sweep rate. Capture cross sections at low temperatures can be estimated from the onset of the ledge. When the C-V curves are traced from accumulation to inversion the capacitance drops below the equilibrium minimum value into depletion and increases rapidly when inversion is reached. This "hook" is caused by a barrier against minority carrier flow at the boundary of the MOS capacitor. The barrier disappears when sufficient voltage is applied to charge the surface states in the boundary region.

Calculation of Characteristic Admittances and Coupling Coefficients for Strip Transmission Lines

Abstract: An integral equation technique is presented which may be used to efficiently compute the Maxwellian capacitance matrix, i.e., the coefficients of capacitance and inductance, for any system of zero-thickness strip conductors located parallel to and between two ground planes, The TEM characteristic admittances for various operating modes and the coupling coefficients can then be obtained from the elements of this matrix. A single computer program based upon this technique can be used to compute the capacitance matrix for any particular strip line configuration desired and would thus be especially valuable to the design engineer who would like to quickly obtain accurate design curves for a previously unstudied configuration of ship conductors. This procedure gives much more accurate results in but a fraction of the computer time required when the more common finite difference equation approach is used, and it avoids the necessity for a separate mathematical analysis for each new strip line configuration, as would be required when using a conformal mapping technique. Illustrative results are given for several different strip-line configurations.

An Absolute Determination of Resistance Based on a Calculable Standard of Capacitance

Abstract: A determination of the NSL unit of resistance based on standards of length and frequency has been made. A cylindrical cross-capacitor, for which the change in capacitance for a measured change in length may be calculated very precisely, is used to calibrate a number of small fixed capacitors (1/6 or 1/4 pF). AC bridge techniques are used to build up to 10 nF and also to measure the resistance of a 10 kΩ resistor in terms of this capacitance and a measured frequency (ω = 104). DC measurements are used to relate the 10 kΩ resistor to the Laboratory's 1 Ω standard resistors. The estimated uncertainty in the measurements is 2 in 107 but the accuracy of the determination is limited to ± 7 in 107 because of the uncertainty in the speed of light. Mean values, derived from a number of determinations, and corresponding to the times of the BIPM international comparisons, are Jan. 1964 ΩNSL = 1 Ω - 3.58 μΩ Feb. 1967 ΩNSL = 1 Ω - 3.80 μΩ. The standard deviation of a series of determinations was 0.06 μΩ.

Evaluation of doping profiles from capacitance measurements

Abstract: Approximate CV curves are calculated for a number of typical doping profiles near a semiconductor p — n junction. These calculated curves can be used for the evaluation of doping profiles from experimentally determined CV curves. This evaluation of doping profiles from measured CV curves alone is never unambiguous. It is shown that it is often possible to reach a decision regarding the real profile, if additional information concerning the semiconductor material and the process of preparation of the junction is available.

Capacitance of Junctions on Gold‐Doped Silicon

Abstract: The capacitance of p+—n junctions and Schottky barriers on gold‐doped, n‐type silicon has been measured as a function of applied bias and time in the temperature range 205°‐255°K. The gold‐diffusion temperature was 1000°C. The time dependence of the capacitance has been examined on the basis of a model which assumes that the gold acceptor level has the same charge as in the bulk for some distance λ(t) from the edge of the depletion region. The analysis yields a value for the density of neutral acceptors in the depletion region of 1.1×1016 cm‐3, indicating that en»ep for the gold center. The energy associated with the capacitance time constant is 0.545±0.005 eV and the capture cross section σn is calculated to be 2.9×10‐15 cm2 at 250°K. Of a more general nature, a simple procedure is described for determining the contribution of slow‐responding deep levels to the capacitance of abrupt p—n junctions. This involves a plot of dV/d(1/C2) vs C, a relationship which was essentially derived by Goodman.

MOS field effect transistors formed by gate masked ion implantation

Abstract: MOS enhancement mode field effect transistors with a circular geometry and with drains offset from the gate by distances from 0.1 mil to 0.9 mil were implanted with boron ions to fill in the offset region and thus achieve perfect alignment (i.e., no overlap) between gate and drain. The energies used were 50 to 100 keV and a 4000 A-thick aluminum gate acted as a mask to prevent ions from penetrating into the channel region. The best junctions were obtained with 100-keV ions, with the sheet resistances being typically 4000 ω/□ for the implanted region. This additional drain resistance was quite small compared to the channel resistance of the devices and so was not objectionable. Ordinary diffused MOSFET's were included on the same wafers for comparison with the ion implanted MOSFET's. It was found that the differences in noise, leakage, and drain breakdown voltage were not serious. The chief advantage of the ion implanted MOSFET is the extremely low feedback capacitance due to the lack of gate-drain overlap, but this advantage is difficult to exploit in a conventional package because of the package capacitance. However, a significant difference was noted in switching characteristics between diffused and ion implanted MOSFET's mounted on TO-18 headers.

The temperature coefficient of capacitance

Abstract: The temperature coefficient of capacitance (TCC) of most insulators is dominated by five components. The theoretical analysis of these components is outlined and it is shown that, for given ranges of permittivity, the analysis can be greatly simplified. This simplified treatment is shown to apply to widely different types of compound. Since TCC depends on permittivity, the permittivity of a variety of materials has been rationalized by reference to their `I' factor, which is defined as mean atomic number per cubic angstrom.

Voltage variable capacitor tuning: A review

Abstract: This paper discusses the history, device theory, characteristics, applications, and future trends of voltage varible capacitor tuning. All equations are stated in terms of two general exponents of power law functions, namely the impurity distribution proportional to xmand the differential capacitance proportional to (V + V 0 )-n. The role of these exponents is shown in the device theory, the temperature drift, linearity in a VCO, and the cross modulation in an FM modulator. Important results from many papers and reports are cited to reinforce the ideas presented. Throughout the review, the desirability of the exponent n = 2 is reiterated.

Capacitance Observations of Landau Levels in Surface Quantization

Abstract: Capacitance observations of Landau levels in a two-dimensional electron gas induced in the inversion layer on a (100) surface of $p$-type silicon are reported. Evidence for surface quantization and the associated lifting of the spin and valley degeneracy are presented. An observed increase in the carrier threshold with increasing magnetic field is shown to be further evidence of surface quantization.

Capacitance Measurements on Au–GaAs Schottky Barriers

Abstract: Dark capacitance measurements have been made on Au–GaAs Schottky barriers using boat‐grown, oxygen‐doped n‐type GaAs with room‐temperature carrier concentrations from 2×1013 to 4×1016 cm−3. The voltage and time dependence of the capacitance was analyzed using a modified version of Goodman's model for traps in depletion layers. The results yield a concentration of the dominant active trap of 1–4×1016 cm−3 in all the crystals examined. From the variation in the time dependence of the capacitance in the range 275°–365°K, the energy for the emission of an electron from this trap is 0.90±0.02 eV. Other aspects of the capacitance data locate this trap at around 0.7 eV below the conduction band, which is the energy previously assigned. Another, faster time‐dependence observed in the higher‐resistivity material was investigated in the range 225°–255°K. The activation energy associated with the latter time dependence is found to be 0.7 eV. The behavior of the capacitance at high reverse bias is explained in terms of electron capture by the dominant trap as the current increases due to impact ionization.

A Low Walk, High Resolution Timing System for Silicon Detectors

Abstract: Utilizing times of flight on the order of a nanosecond for heavy particle identification with silicon detectors, it is desirable to reliably distinguish time differences of approximately 100 picoseconds or less. In addition, the required timing circuitry must not substantially deteriorate amplitude resolution capability. In the system designed for this purpose the detector charge is first collected on the capacitance of the detector and fast, low noise, preamplifier and is later transferred to the charge sensitive preamplifier. The fast signal is processed to obtain good time resolution and low walk. The system has a FWHM time resolution of 40 picoseconds, referred to 5.8 MeV deposited in a 100 pF silicon detector. An actual peak width from 3 MeV deposited in an 80 pF silicon by He3 particles was 165 psec FWHM, which is about twice that expected if more optimum pulse shaping had been employed. The instrumental walk for a 100 to 1 amplitude range is less than 150 picoseconds, and is approximately 100 picoseconds for a 30 to 1 range. The noise added to the slow system is equal to that caused by an additional 17 pF of capacitance at its input, plus an overall increase of 5% or less for commonly used slow pulse shaping.

Potential distribution and capacitance of abrupt heterojunctions

Abstract: The transition region analysis of an abrupt heterojunction is extended to include the effects of mobile carriers‘ charge in the space charge regions. Deviations from the depletion model are obtained when the wide band-gap semiconductor is heavier-doped-This is due to a non-negligible potential drop across the narrow band-gap semiconductor at an isotype (i.e. n-n or p-p) heterojunction, and to an inversion layer at the interface in the same semiconductor at an anisotype (i.e. p-n or n-p) heterojunction. The C−2 versus V plots are acceptable, straight lines having slopes in agreement with the depletion model predictions, but the intercept voltages differ. A constant electric dipole at the interface causes a similar effect.

Freeze‐out characteristics of the mos varactor

Abstract: Experimental MOS C(V) data are obtained in the temperature range over which majority carriers are substantially frozen out (40° − 70°K). These are compared with calculated curves and other calculated curves are presented to show the effect of impurity concentration and compensation. The C(V) curves are characterized by a secondary minimum in capacitance near the flat band bias.

Thermal Imaging Using Pyroelectric Detectors

Abstract: The pyroelectric detector is a new radiation detector that employs the temperature sensitivity of electrostatic polarization as the sensing principle. Electrically, the detector behaves as a capacitance on which a charge appears when thermally irradiated. This detector has a number of features that make its use attractive for thermal imaging. It does not require cooling, and no biasing voltage is needed. Being electrically capacitative, the noise decreases with frequency, and consequently it has a useful signal/noise ratio at frequencies far above that corresponding to its thermal time constant. Also, these characteristics suppress 1/f type amplifier noise and permit good performance at very low frequencies. A new thermal imaging device or thermograph has been developed to exploit these properties. This is a scanning radiometer that scans a 10 degrees x 10 degrees field in 30 sec with a 0.1 degrees x 0.1 degrees instantaneous element, thus giving 10,000 picture elements. It uses a 7.6-cm diam germanium objective lens and has a noise equivalent temperature of 0.1 degrees C. The thermal image is presented as either a black to white tonal picture or a color picture on Polaroid film. Examples of its use for nondestructive testing purposes are given.

A Solid‐State Electrochemical Cell Based on Ion Conductive Ceramics

Abstract: A solid‐state electrochemical cell has been devised using a ceramic ion conducting electrolyte and ceramic electrodes which are simultaneously ion and electron conducting. Charge/discharge of the cell occurs without chemical phase change and the reaction of the cell to an electric current is therefore capacitive. The origin of the capacitance is discussed in terms of the crystal structure of the ceramic used and the transient electrical characteristics described in terms of diffusion theory. Possible applications are suggested.

The electrical characteristics of nZnSe—pGe heterodiodes†

Abstract: The forward and reverse current-voltage characteristics and reverse-biased capacitance are described for the nZnSo-p+ Ge emitter-base diodes of heterojunction transistors The forward diode current flow involves essentially electron injection into the Go together with loss-mechanisms of recombination of injected electrons through interface states and, probably, electron capture into ZnSo traps followed by tunnelling into interface states In the junctions that have been fabricated, the current-voltage characteristics are dominated by the high resistivity bulk ZnSo in series with the junction, resulting in space-charge-limited flow The reverse junction characteristics demonstrate semi-saturation, avalanche multiplication, and negative resistance The junction capacitance is strongly frequency dependent duo to the presence of relatively deep traps, and both abrupt and linearly graded junctions have boon observed, depending on the growth technique

Reverse‐Biased Gallium Phosphide Diodes as High‐Frequency Light Modulators

Abstract: Reverse‐biased gallium phosphide diodes have been successfully operated as high‐frequency intensity and phase modulators of light at room temperature. The high‐frequency modulation is fundamentally limited by the series resistance and the capacitance of the diodes. Cutoff frequencies as high as 7 GHz have been measured. Diode capacitance, typically less than 7 pF at the operating point, and driver impedance determine the broad‐band characteristic. Intensity modulation measurements have been performed up to 500 MHz. The power consumption per MHz bandwidth for 40% intensity modulation was 2.7 mW for a diode only 0.7 mm long. A diode of 1.5 mm length used as a phase modulator needed only 1.5 mW of power per MHz bandwidth for a modulation index of 1 rad at a wavelength of 0.633 μ. This latter value corresponds to an intensity modulation depth of over 80%.

Dominant Surface Electronic Properties of SiO2‐Passivated Ge Surfaces as a Function of Various Annealing Treatments

Abstract: The metal‐oxide‐semiconductor (MOS), capacitance vs applied voltage (C‐V) measurement technique was used to investigate SiO2‐passivated Ge surfaces as a function of high‐temperature annealing treatments in H2, O2, N2, and H2O. Capacitance measurements were made at high frequencies (100 MHz) and/or reduced temperatures (145°, 77°K) to eliminate the capacitive contribution of fast surface states to the ac signal. Since the surface states did equilibrate with the superimposed applied dc voltage, is was possible to determine surface‐state type, energy, and densityfrom voltage shifts in the C‐V traces. Hydrogen annealing at 600°C or above introduces a high density (>1013/cm2) of fast acceptor states. These states are located at the center of the Ge energy gap. In addition, hydrogen annealing at 700°–800°C introduces acceptors close to the valence band or fixed negative charge. Most of these hydrogen‐induced states are removed by annealing in oxygen or water vapor at 230°–440°C. At the same time the oxygen or w...

A Transformer-Ratio-Arm Bridge for Measuring Large Capacitors Above 100 Volts

Abstract: A high-voltage bridge suitable for measuring capacitance ratios up to a million to one is described. The high ratio is realized by cascading a two-stage current transformer to a bridge based on the current comparator principle. Circuits that compensate for the lead impedances of large capacitors are presented. The bridge is direct reading in the capacitance ratio and the dissipation factor and the uncertainties for both components are less than 10 parts per million (ppm).

Surface-diffused transistor with isolated field plate

Abstract: A surface-diffused transistor exhibiting high stability and low collector capacitance includes a metallic field plate buried within an insulating film which covers the active major wafer surface thereof and passivates a surface-adjacent collector junction. Metal field plate is fixed to a negative potential and prevents inversion of a surface-adjacent region of the P-type semiconductor, thereby preventing surface leakage and increased capacitance.

On the solution of poisson equation for an isotype heterojunction under zero-current condition

Abstract: A theory of the transition capacitance of an isotype heterojunction has been developed by solving the Poisson equation for the transition region under zero current condition. The main assumption made is the abruptness approximation that all the physical parameters such as energy band gap, electron affinity, dielectric constant pertaining to one semiconductor remain unchanged right up to the interface and then abruptly change over to those pertaining to the other semiconductor. The theory emerges as a natural generalization of the metal-semiconductor contact where the smaller gap semiconductor takes the role of the metal. The expression for the transition capacitance obtained goes over into the usual expression for the transition capacitance of a metal-semiconductor contact under proper limiting conditions. It is found that, although there is no sharp edge to the transition region and in theory it extends throughout the bulk, the total space charge is actually confined to within a few lengths (ϵkT/8πq 2 )N D ) 1 2 of the junction, where ϵ is the dielectric constant, ND is the donor concentration and the symbols q, k, T have the usual meaning.