Small-signal Voltage Research Articles

Direct current characterization of depletion-mode 6HSiC MOSFETs from 294 to 723 K

6HSiC depletion-mode, n-channel MOSFETs were analyzed across the temperature range of 295–723 K. Effective channel mobilities ranged from 94 cm 2V −1·s −1 at 296K to about 20 cm 2V −1·s −1 in the five devices measured. Small-signal voltage gain ranged from 5 V/V to 20 V/V in the five devices tested, and was essentially constant for all devices up to 723 K. Thermally-activated leakage across the 450 Å thick gate oxide (SiO 2) was identified as the primary cause of device failure from 673 to 773 K. The mechanisms responsible for the leakage across SiO 2 were identified as Fowler-Nordheim tunneling at bias levels greater than about 650 kV cm −1, while low-field leakage was a result of trap-assisted tunneling in combination with other mechanisms such as Poole-Frenkel or thermionic emission. Measured source-drain to body ( pn junction) leakage was thermally activated with an activation energy of approximately 972 meV.

Integration Aspects and Electrical Properties of SrBi2Ta2O9 for Non-Volatile Memory Applications

AbstractHighlights and solutions to some of the challenges involved in integrating SrBi2Ta2O9 (SBT) capacitors with Pt electrodes on silicon wafers for non-volatile memory applications are discussed. These include the diffusion of Bi through the Pt bottom electrode during firing, capacitor patterning, and process damage that results from hydrogen containing atmospheres.Next, studies of the temperature dependence of many of the important electrical properties of SBT are presented. These include the remanent polarization (2Pr), the non-volatile polarization (Pnv), and the coercive field (Ec) all of which are studied as functions of the pulse amplitude; fatigue resistance of 2Pr and Pnv; the retention; the small signal capacitance versus voltage behavior; and the current versus voltage behavior. These studies demonstrate that SBT looks very promising for ferroelectric non-volatile memories over the consumer application range (0 to 70 °C).

Small-signal and transient behaviour of a two-module DC-DC converter using mutually coupled output filter inductors

Small-signal characteristics and output voltage transients of a voltage-mode controlled two-module DC-to-DC converter feeding a common resistive load are investigated. The parallel-input/series-output converter system works in the continuous current conduction mode (CCM), and uses magnetic coupling between the separate output filler inductors to reduce converter size and weight. A damping circuit can be designed to ensure that the natural frequencies of the output filter are well damped and adequate stability margins are achieved. The converter model is implemented using ‘MATLAB‘ and results are varified against ‘PSPICE’ simulations.

Conditions under which Na +channels can Boost conduction of small graded potentials

It has recently become apparent that in the dendrites or short axons of some neurons, voltage-dependent sodium channels are used not to generate action potentials but to modulate graded potentials; graded potentials carry far more information than do action potentials. A model axon (or dendrite) is described in which sodium channels with kinetics described by equations of the Hodgkin-Huxley type boost conduction of small voltage signals. For a sodium channel density beyond a certain minimum there exists an optimal potential, depolarized with respect to the resting potential, at which there is no steady-state decrement along the axon. For an axon not longer than about 0.7 length constants, small, steady-state deviations from this optimal potential imposed at one end of the axon appear amplified in a graded and stable way at the other end. A small pulse of potential is propagated with amplification and more rapidly than in an axon with a passive membrane. Compared to passive propagation, there will be an improvement in signal-to-noise ratio at the synapse; the axon also acts as a selective frequency filter. The same axon is capable of conducting an action potential.

DC small signal symbolic analysis of large analog integrated circuits

This paper presents a new methodology and its implementation (AnalogSifter) for DC small signal fully symbolic analysis of large analog integrated circuits. Our new sifting approach consists of six algorithms designed to relax the circuit size limitation of previously known methods. We show fully symbolic analysis results for much larger circuits than have ever been reported. Very compact symbolic expressions for the DC small signal voltage gains of the 741 and 725 operational amplifiers were obtained in less than 40 CPU seconds on a SUN SPARCstation 2, and the simplified results were numerically within 12% of the exact values. The output is expressed in terms of products of sums which can give the user insight into the behavior of the circuit. The overall time complexity is superquadratic with respect to the number of nodes. The implementation can output simplified symbolic expressions for any desired DC small signal transfer function, including input resistances, output resistances, as well as current and voltage gains. It also provides simplified symbolic expressions for noise analysis, sensitivity analysis, and power supply rejection ratio.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Classification of voltage problems in electric power systems

In this paper sufficient mathematical and operating conditions are defined for distinguishing between voltage problems with insignificant frequency changes and voltage problems accompanied by frequency instabilities. With this as the main classification, additional conditions are introduced under which voltage related problems are either of a steady state character, or they evolve as the mid-/long-term phenomena only (in contrast to very fast, transient stability type phenomena). Within the first class (insignificant frequency changes) two distinct groups of voltage problems could arise, the most common of which is the existence of post-contigency voltage outside of operating limits. The other group of voltage problems within the first class is reflected in a small signal instability of an existing load flow solution. Assuming that a post-contingency load flow solution exists, mathematical and operating conditions are reviewed under which these problems occur. New conditions are established for preventing the second group of voltage problems from this class, i.e. small signal voltage instabilities. As a result, voltage related problems in this class are guaranteed to be, at worst, mid-/long-term type phenomena. Within the second class (accompanied by frequency instabilities), two groups of voltage-related problems occur. The first group is reflected in persistent but bounded terminal voltage oscillations, primarily contributed by the unstable mode associated with the rotor angle. The second group is characterized by unbounded changes of terminal voltages, primarily contributed by the unstable mode in field-flux voltage E q ′. In this paper, conditions are derived under which persistent but bounded voltage oscillations take place, as opposed to unbounded changes of state representing voltage dynamics, such as field-flux voltage E q ′ of the machine and its terminal voltage V t.

Modelling of GaAs MESFET output conductance and transconductance frequency dispersion

Abstract The output conductance and transconductance frequency dispersion phenomena of a GaAs MESFET have been modelled. A non-uniform temperature distribution between the substrate and surface channel is accounted for. Experimental data are used to justify the accuracy of the present model. Good agreement between the model prediction and measurement has been obtained. The output conductance and transconductance frequency dispersion has a significant impact in determining the small-signal voltage gain of a MESFET amplifier.

Analysis of the small-signal voltage decay technique in the characterization of Si concentrator solar cells

Detailed analyses of the small-signal voltage decay (SSVD) method of lifetime measurement have been performed. The main difficulty in voltage decay techniques is that the boundary conditions at the junction are coupled. A solution to the time-dependent diffusion equations has been obtained using the quasi-static emitter (QSE) approximation. Assuming a power-law emitter doping profile, a solution to the coupled diffusion equations has also been obtained using a dynamical approach without the QSE approximation. The extent to which effects such as emitter recombination and bandgap narrowing affect the SSVD lifetime has been examined using this solution. The SSVD technique has been applied in investigating the variation of minority-carrier recombination rates in the emitter, base, and back surface of concentrator solar cells with illumination intensities. The experimentally observed degradation in SSVD lifetime with increasing illumination intensity has been accounted for quantitatively. >

Performance and reliability design issues for deep-submicrometer MOSFETs

Device design constraints, such as threshold voltage variation due to short-channel and drain-induced-barrier-lowering effects, off-state leakage current due to punchthrough and gate-induced drain leakage, hot-carrier effects such as hot-electron degradation and avalanche breakdown, and time-dependent dielectric breakdown, are examined. The current-driving capability, ring-oscillator switching speed, and small-signal voltage gain are examined. The impact that each of these factors has on the allowable choice of MOSFET channel length, oxide thickness, and power supply voltage is examined. Based on experimental results, a set of design curves, using a set of typical performance and reliability criteria, is presented for deep-submicrometer nonlightly doped drain (non-LDD) n-channel devices. From these curves, the relative importance of each particular performance/reliability mechanism for a given technology and design criteria can be determined. Because the performance and reliability issues addressed are also relevant to other MOSFET technologies, the design guidelines can also be extended to other technologies, including p-channel and LDD devices.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A 5-ns 1-Mb ECL BiCMOS SRAM

A 1-Mword*1-b ECL (emitter coupled logic) 10 K I/O (input/output) compatible SRAM (static random-access memory) with 5-ns typical address access time has been developed using double-level poly-Si, double-level metal, 0.8- mu m BiCMOS technology. To achieve 5-ns address access time, high-speed X-address decoding circuits with wired-OR predecoders and ECL-to-CMOS voltage-level converters with partial address decoding function and sensing circuits with small differential signal voltage swing were developed. The die and memory cell sizes are 16.8 mm*6.7 mm and 8.5 mu m*5.3 mu m, respectively. The active power is 1 W at 100-MHz operation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modeling of frequency and temperature effects in GaAs MESFETs

The small-signal conductance and large-signal I-V characteristics of conventional 1- mu m recessed-gate GaAs depletion-mode MESFET devices have been investigated. The small-signal saturation-region output conductance g/sub ds/ of a conventional GaAs MESFET is dependent on both frequency and temperature. These dependencies present serious difficulties in the design of many GaAs integrated circuits, since the small-signal voltage gain in analog circuits and the propagation delay in digital circuits depend on g/sub ds/, and no accurate simulation model is available. A semiempirical model for the frequency-dependent parameters in GaAs depletion-mode MESFETs is presented. An analytical formulation of temperature dependence is also included by an extension of the basic Curtice model. The resulting model is significantly more accurate than other models, which have not previously incorporated frequency- and temperature-dependent effects.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dc and ac transport in molecular-beam-epitaxy-grown metal/ZnSe/GaAs heterojunction structures

The room-temperature electrical transport properties of ZnSe epilayers grown above the critical layer thickness on n+-GaAs substrates by molecular-beam epitaxy have been studied. dc current versus voltage and small-signal ac admittance versus voltage and frequency measurements were made on Schottky contacts (Au or Hg). A novel method of analysis is presented which, extending a previous model to include the three-dimensional effects of current spreading as a function of frequency, allows the ZnSe epilayer resistivity to be obtained. Combining this with the doping concentration obtained from analysis of the C-V characteristics, the ZnSe mobility may be calculated. Mobilities thus measured compare well with our own and other workers’ published Hall mobility data on similar samples, as well as with theoretical calculations. We believe that our results represent a unique and detailed characterization of an epilayer heterostructure on a highly conducting substrate.

A family of high-swing CMOS operational amplifiers

A family of high-swing CMOS operational amplifiers has been developed to maximize the available dynamic range with low supply voltages. Complementary differential pairs are used to achieve an almost rail-to-rail input common-mode voltage range. High linearity is obtained by summing currents so that the small-signal differential-mode voltage gain is constant over the entire input common-mode range. With a 5.0-V power supply, the total harmonic distortion is typically only 1% in a unity-gain configuration with a 4.5-V/sub p-p/ signal. The measured DC offset voltages versus input common-mode range track between the conventional and high-swing versions. These measurements suggest that the commonly feared crossover distortion may not be a problem when the current summation high-swing topology is used. The measured step response characteristics were excellent and exhibited no signs of phase mismatch crossover distortion for high-frequency signals. >

The influence of interface states upon the admittance of metal-semiconductor diodes

The effects of interface states upon the electrical properties of metal-semiconductor diodes are investigated with the purpose of casting some light on current interpretations of capacitance and conductance measurements. The predominance of majority-carrier mechanisms in the ideal diode is quantitatively reassessed. Several kinds of interface state are considered, accounting as well for states in equilibrium with the semiconductor as for states in equilibrium with the metal. Electrostatic and kinetic effects lead to three types of admittance that are evaluated and compared under a small signal voltage superimposed on a forward bias. The major contribution arises from the reaction of interface charge variations with the diode conductance and depletion width. Corresponding conductances and capacitances are analysed as a function of the energy distribution of states, bias voltage, frequency and temperature. Densities about 1013 eV-1 cm-2 or higher and the existence of several types of states lead to non-linear effects as a function of the density of states and even to negative differential capacitance when recombining centres are concerned. Some fundamental and technological implications are discussed.

Determination of 2-D Electron-gas carrier mobility in short gate-length MODFET's by direct elimination of parasitic resistance effects

Two-dimensional (2-D) electron-gas carrier mobiliy in 1µm gate-length modulation-doped FET's has been determined as a function of the gate bias voltage. The measurement technique utilizes a small-signal gate voltage excitation and probes the true channel conductance by directly eliminating the source and drain series resistance effects. The mobility is extracted by combining the channel conductance data with the CV data and its variation with gate bias voltage is indicative of the variation of the effectiveness of screening of the ionized impurities and the quality of the MBE-grown GaAs buffer layer.

Piezoelectric Actuator for Scanning Tunneling Microscopy

A piezoelectric element possessing a function of three-dimensional actuation for scanning tunneling microscopy is proposed. The characteristics at low frequency are accurately measured by using Talystep. The piezoelectric element responds to small voltage signals with a high resolution of the order of 0.1 nm. The z-axis displacement accompanied by x- and y-axis actuations can be completely compensated by feedback of actuation signals. In order to confirm the actuation properties, specimen scanning in scanning electron microscope is successfully attemped by using the three-dimensional piezoelectric element in place of electron beam scanning by deflection coils.

Josephson-junction mixer analysis using frequency-conversion and noise-correlation matrices

A complete characterization and optimization have been carried out for an externally pumped Josephson-junction mixer. A noise-driven nonlinear pump equation is first solved in the time domain on a computer in order to obtain a conversion matrix and noise-correlation matrix for the small-signal current and voltage. A set of linear circuit equations formed by the matrices is then solved in the frequency domain for the mixer noise temperature and conversion efficiency. Finally, optimization is made with respect to circuit, bias, and junction parameters to find the ultimate theoretical performance.

An electrochemical transistor using a solid electrolyte

Transistor action has been observed at elevated temperatures (800 °C) with a structure composed of two ceramic ZrO2 electrochemical cells separated by an enclosed volume. One cell emits O2 from an ambient atmosphere into the volume (base region) where it is collected and returned to the ambient by the opposing cell. Electrical operation can be understood in terms of the current limitation presented by the Pt cathode of the collector cell. Small signal voltage, current, and power amplification are observed with a frequency response limited by the double-layer capacity of the collector. This approach to transistor action should be applicable to other solid-electrolyte systems.

Cross-modulation figure of merit for transistor amplifier stages

This article concerns itself with comparison of transistor amplifier configurations in relation to their cross-modulation distortion characteristics. Only the base-emitter junction nonlinearity is considered, since this nonlinearity is considered to be the most significant contributor to cross-modulation distortion. For this case investigations have shown that since cross modulation occurs because of a third-order nonlinearity, the cross-modulation distortion is therefore proportional to the square of the interfering voltage which appears across the base-emitter junction. In this article the cross modulation of the transistor stage is analyzed from its equivalent circuit rather than from the theoretical device characteristics, It is assumed that the transistor stage gain and input impedance remain relatively constant with small signal voltage excursions. Using these hypotheses, a figure of merit factor is derived for comparison of transistor and transistor amplifier configurations with respect to their cross-modulation distortion characteristics. This figure of merit factor is then used to compare the relative cross-modulation susceptibility of the common collector, common emitter, and common base configurations. All three configurations are compared in the hypothetical voltage-generator and short-circuit load case. The derivation of the equations is shown in Appendix I. For this case it is shown that the three configurations have equal figures of merit. The latter two configurations are then analyzed and compared for the more practical matched input and matched output (maximum power transfer) case. Familiar formulas for transistor gain and input impedance in the low-frequency equivalent model are used for this analysis. Derivations of the equations are shown in Appendix II. The effect of feedback on the cross-modulation figure of merit is then analyzed using both degenerative and regenerative types of feedback. It is then shown that by use of the analysis of the low-frequency model, together with the analyses of the effects of feedback, a high-frequency analysis of cross-modulation figure of merit can be made. This analysis is most applicable to wide-band VHF amplifiers, such as used in Community Antenna Television trunk cascades. A convenient means for analysing cross modulation in the more complicated high-frequency circuit is thus described. Other types of stages, such as push-pull and parallel outputs, are also discussed in regards to the defined cross-modulation figure of merit. A set of conclusions concerning the defined cross-modulation figure of merit is then reached.

Precision Measurement with the Total-Feedback Electrometer

The total-feedback electrometer finds frequent application in biomedical instrumentation. Three methods of using this electrometer: measurement of feedback current, measurement of feedback voltage, and a null method, are described and compared from the viewpoint of convenience and precision. The theory of the total-feedback electrometer, relevant to measurement precision, together with formulae for use with the feedback voltage method, are given. It is emphasized that the precision measurement of feedback voltage on a digital voltmeter provides a rapid and convenient method of reading data from a total-feedback electrometer, and is capable of a precision of about 0·1% for a single reading. Determination of electrometer gain as a function of signal voltage gives the basic information needed to correct for the error inherent in the small input signal voltage.