Basic Device Parameters Research Articles

Readout improvement in large area a-SiC:H-based image sensors

We suggest to enhance the performance of image acquisition systems based on large area amorphous silicon-based sensors by optimizing the readout parameters such as the intensity and cross-section of scanner beam, acquisition time and bias conditions. The sensor responsivity and signal-to-noise ratio is related to basic parameters such as image intensity, scanner intensity and sensor bias. The influence of bias voltage, scanner beam spot size and wavelength and scanning speed on the sensor output characteristics are evaluated. It was shown that the sensor resolution is related to the basic device parameters and, in practice, limited by the acquisition time and scanning beam properties. The scanning beam spot size limits the resolution due to the overlapping of dark and illuminated zones leading to a blurring effect on the final image and a consequent degradation in the resolution. The sensor response is limited by the external load, which for fast scanning speed should be kept small.

Physics Design Guidelines for Estimating Plasma Performance in a Burning Plasma Experiment (FIRE)

The physics design guidelines for a next step, high-field tokamak, burning plasma experiment (FIRE, Fusion Ignition Research Experiment) have been developed as an update of the ITER Physics Basis (IPB). The plasma performance attainable in FIRE (or any next-step device) is affected by many physics issues, including energy confinement, L-to-H-mode power transition thresholds, MHD stability/beta limit, density limit, helium accumulation/removal, impurity content, sawtooth effects, etc. Design basis and guidelines are provided in each of these areas, along with sensitivities and/or uncertainties involved. The overall basic device parameters and features for FIRE (R = 2 m, a = 0.525 m, κ95 ~ 1.8, δ95 ~ 0.4, q95 > 3, B = 10-12 T, I = 6.45-7.7 MA, Pfus ~ 100-200 MW, Q ~ 5-10) are consistent with these guidelines and uncertainties if the potential design upgrade option (12 T, 8 MA) is considered as part of the main design option.

Image Acquisition Using Non-Pixeled Amorphous Silicon Based Sensors

AbstractWe suggest to enhance the performance of image acquisition systems based on large area amorphous silicon based sensors by optimizing the readout parameters such as the intensity and cross-section of scanner beam, acquisition time and bias conditions. The main output device characteristics as image responsivity, signal to noise ratio and spatial resolution were analyzed in open circuit, short circuit and photodiode modes. The result show that the highest signal to noise ratio and best dark to bright ratio can be achieved in short circuit mode.It was shown that the sensor resolution is related to the basic device parameters and, in practice, limited by the acquisition time and scanning beam properties. The scanning beam spot size limits the resolution due to the overlapping of dark and illuminated zones leading to a blurring effect on the final image and a consequent degradation in the resolution.

Frequency optimization of pseudomorphic modulation-doped field-effect transistor (AlGaAs/InGaAs) for microwave and millimeter-wave applications

The results of an analysis based on the solution of the 2-D Poisson equation are presented to investigate the dependence of the small-signal parameters on biasing conditions. The switching parameters are calculated simply from the charge variations, and it is found that the characteristics depend only on the basic device parameters and terminal voltages. The high value of ft proves the utility of the model in the design of low-power MMICs. A maximum frequency of 101.42 GHz at 0.25 μm is obtained, and the results show close agreement with the experimental data, thereby proving the validity of the proposed model. © 2000 John Wiley & Sons, Inc. Microwave Opt Technol Lett 25: 377–383, 2000.

Microscopic theory of hot-carrier relaxation in semiconductor-based quantum-cascade lasers

A microscopic analysis of basic nonequilibrium phenomena in unipolar quantum devices is presented. In particular, energy-relaxation processes governing the hot-carrier dynamics in the active region of GaAs-based quantum-cascade lasers are investigated by means of a generalized ensemble Monte Carlo simulation. Such analysis is essential in determining the validity range and limitations of purely macroscopic models with respect to basic device parameters, like injection current and temperature.

Random telegraph signal currents and low-frequency noise in junction field effect transistors

The detailed study of random telegraph signal (RTS) currents and low-frequency (LF) noise in semiconductor devices in recent years has confirmed their cause and effect relationship. In this paper we describe the physical mechanisms responsible for RTS currents in any device. The methods for calculating the amplitudes and characteristic times of the RTS currents produced by traps with known electrical characteristics and locations are described. The noise spectra in junction field effect transistors (JFET's) resulting from traps in the silicon or the oxide are derived as a function of basic device parameters, operating conditions and temperature. Experimental results verifying the predictions of the models are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Prediction of second breakdown power

Semiconductor device damage due to electrostatic discharge often results from second breakdown, an abrupt increase in current with a drop in voltage. Thus there is a clear need to be able to predict and screen for second breakdown of semiconductors from the basic device parameters. A computer analysis shows that diode areas, widths, and doping levels are required to predict second breakdown powers. These three parameters can be obtained from low-power reverse and forward current-voltage static characteristics. A new disclosure is that the forward-biased silicon diode shows a transition from a quadratic to linear current dependence upon voltage at moderate currents. The diode width can be obtained from the transition voltage.

The turnoff transient of the bipolar-mode field-effect transistor

A model of the turnoff transient of the field-effect transistor, operated in the bipolar mode (BMFET), is developed. It is shown that the transient consists of two parts pertaining to the two-carrier and to the one-carrier operations of the device, respectively, the former being much slower than the latter. The model allows the prediction of the switching transient from the basic device parameters; thus, it allows an understanding of the underlying physics of BMFET operation and why the BMFET is faster than other bipolar devices. The mode has also been found to be in good quantitative agreement with experiments, and thus it is a useful tool for the design of the BMFET.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Back side reflection influence on quantum efficiency of photovoltaic devices

A method is proposed for calculation of the quantum efficiency of photovoltaic devices, which takes into account the back side reflection and corresponding surface recombination rates. The applied technique enables simple theoretical prediction of basic photovoltaic device parameters.

Squeezed-state generation using a Josephson parametric amplifier

Josephson-junction parametric amplifiers are promising candidates as sources of squeezed microwave radiation. Here, an analysis of one such amplifier, a radio-frequency superconducting quantum interference device operated in either the three-photon or the four-photon mode, is presented. Expressions for the amount of squeezing that could be obtained from such a device are derived in terms of the basic device parameters.

Design of Microwave GaAs MESFET's for Broad-Band Low-Noise Amplifiers

As a basis for designing GaAs MESFET's for broad-band low-noise amplifiers, the fundamental relationships between basic device parameters, and two-port noise parameters are investigated in a semiempirical manner. A set of four noise parameters are shown as simple functions of equivalent circuit elements of a GaAs MESFET. Each element is then expressed in a simple analytical form with the geometrical and material parameters of this device. Thus practical expressions for the four noise parameters are developed in terms of the geometrical and material parameters. Among the four noise parameters, the minimum noise figure F/sub min/, and equivalent noise resistance R/sub n/, are considered crucial for broad-band Iow-noise amplifiers. A low R/sub n/ corresponds to less sensitivity to input rnismatch, and can be obtained with a short heavily doped thin active channel. Such a high channel doping-to-thickness (N/a) ratio has a potential of producing high power gain, but is contradictory to obtaining a low F/min/. Therefore, a compromise in choosing N and a is necessary for best overall amplifier performance. Four numerical examples are given to show optimization processes.

Short-channel C-MOS/SOS technology

Design, fabrication, and characterization of Si-gate short-channel C-MOS/SOS devices with channel length ranging from 1 to 3 µm are presented. Basic device parameters and their interrelations are discussed and illustrated in detail. Extremely-high-speed and low-power capability has been demonstrated for short-channel devices operating from a 5-V supply voltage. The process reproducibility and circuit performance point to the suitability of short-channel C-MOS/SOS technology for VLSI applications.

High-frequency network properties of MOS transistors including the substrate resistivity effects

The small-signal differential equations describing the intrinsic high-frequency characteristics of MOS transistors are derived under three basic modes of signal application: gate excitation, substrate excitation, and combined gate-substrate excitation. These equations are shown to be analogous to those of a double RC transmission line having a uniformly distributed common resistance but two separate capacitances distributed nonuniformly. High-frequency device admittances are calculated in terms of those of the analog RC transmission line using the method of "piecewise" uniformity for the capacitance distributions. Useful expressions are derived for the various Y-parameters which are explicitly related to the more readily measurable low-frequency input capacitance and transconductance parameters which, in turn, are related to the basic device physical parameters. The admittance expressions clearly indicate the influence of the substrate resistivity both on the forward transfer admittance magnitudes at low and high frequencies and on the input conductance at high frequencies. The intrinsic Y-parameters are combined with the associated extrinsic RC networks and presented in the form of equivalent circuits. Results of UHF admittance measurements on representative n-channel devices are given which support the overall validity of the proposed equivalent circuit models.

Calculation of Electrical and Radiation Storage Time in Transistors

The conventional viewpoint of saturation in junction transistors, from a device point of view, considers the excess minority carriers in the base region. A different viewpoint considers the majority carriers in the base. The important elements then are the number of these carriers stored in the transistor and whether they are stored in the active base region, the extrinsic base region, the collector body, or the epitaxial layer. The storage of carriers in the active base region plays a relatively minor role in the storage effect for most modern transistors because of the small volume of semiconductor material involved. In alloy, diffused, and epitaxial transistors the storage of carriers (electrons in a PNP transistor) is shown to be in the last three regions named above, respectively; in none of these transistor types is the storage region identifiable as the active base region. This new viewpoint leads to well-accepted storage-time expressions for alloy and diffused transistors and to new storage-time expressions for epitaxial transistors. Detailed calculations of the primary photocurrent have been made for three practical transistor construction types that relate this current to basic device parameters and to the electrical storage time. In addition, the radiation storage time has been calculated in terms of the electrical storage time for epitaxial transistors. Examples of these calculations are given and the results presented.

Theoretical and Experimental Analysis of the Ferromagnetic Explosively Shocked Current Pulse Generator

To most effectively utilize the potential capability of the ferromagnetic explosively actuated current generator one must understand the effect of variation of parameters upon the device output into a given load. This report presents theories of operation of the device, an approximate theoretical analysis of the effect of variation of the basic circuit and device parameters and a comparison of theory with experimental results. Theoretical and experimental data are presented and compared for peak current versus circuit load inductance, device load coil turns, and magnetic core width (for a fixed thickness). There is a gratifying similarity between theoretically predicted and experimentally determined data. Guiding criteria are given for an optimum ferromagnetic current pulse generator system.