D.C. and high-frequency characteristics of built-in channel MOS-FETs

This paper analyses the d.c. and small-signal a.c. characteristics of MOS-FETs with a built-in conducting channel that can either be completely depleted or enhanced in conductivity by carrier accumulation. The effects of the substrate resistivity are considered for low, moderate and high doping concentrations. It is shown that only when the channel thickness is much smaller than the oxide thickness the device saturation characteristics can be approximated by a square function of the gate voltage. Results of small-signal calculations are presented for both generalized and specific device structures which depict the gate voltage dependence of the gate and substrate transconductance and the input capacitance parameters for both depletion and accumulation mode of operations.A small signal equivalent network model is proposed which can be used for the calculation of high-frequency device limitations.     

A new approach to diffraction analysis of conductor grids. I.Parallel-polarized incident plane waves

Diffraction analysis is presented for infinite planar conducting-cylinder grids illuminated by normally incident (parallel-polarized) plane waves, the electric fields of which are parallel to the cylinder axes. The Green's function kernel integral equations are used for the induced currents, which are based on the equivalent waveguide theory and solved for the currents by the moment method. This is a universal analysis approach, applicable to infinite planar grids made of conducting cylinders of arbitrary cross section, uniform or periodic, dense or sparse, single layer or multilayer     

有限元法与矩量法结合分析背腔天线的辐射特性

采用有限元法与矩量法相结合分析有限导体面上背腔天线的辐射特性。计算中采用一种有效的积分方程及矢量权函数的形式来保证计算精度。在前处理中采用ＡｕｔｏＣＡＤ中的实体造型技术,对目标可方便地进行离散的局部加密,计算机存储空间及计算量明显下降,使本文方法成为对背腔天线辐射总是中有效方法,文中计算了有限导体面上同轴腔及同轴馈电圆形腔的辐射特性,并与已发表的结果进行比较,验证了本文算法的有效性。     

Percolation‐Controlled Metal/Polyelectrolyte Complexed Films for All‐Solution‐Processable Electrical Conductors

The use of solution‐processable electrically conducting films is imperative for realizing next‐generation flexible and wearable devices in a large‐scale and economically viable way. However, the conventional approach of simply complexing metallic nanoparticles with a polymeric medium leads to a tradeoff between electrical conductivity and material properties. To address this issue, in this study, a novel strategy is presented for fabricating all‐solution‐processable conducting films by means of metal/polyelectrolyte complexation to achieve controlled electrical percolation; this simultaneously imparts superior electrical conductivity and good mechanical properties. A polymeric matrix comprised of polyelectrolyte multilayers is first formed using layer‐by‐layer assembly, and then Ag nanoparticles are gradually synthesized and gradationally distributed inside the polymeric matrix by means of a subsequent procedure of repeated cationic exchange and reduction. During this process, electrical percolation between Ag nanoparticles and networking of electrical pathways is facilitated in the surface region of the complexed film, providing outstanding electrical conductivity only one order of magnitude less than that of metallic Ag. At the same time, the polymer‐rich underlying region imparts strong, yet compliant, binding characteristics to the upper Ag‐containing conducting region while allowing highly flexible mechanical deformations of bending and folding, which consequently makes the system outperform existing materials.     

High frequency capacitance-voltage and conductance-voltage characteristics of d.c. sputter deposited a-carbon/silicon MIS structures

Dark and illuminated C–V and G–V characteristics of A1/a-carbon/silicon MIS structures have been measured in the frequency range of 10 kHz to 10 MHz. The a-carbon passivating layer is prepared by d.c. sputtering of a graphite target in Ar gas. There is no evidence of Fermi level pinning, and surface carrier inversion is clearly demonstrated. Electrical instabilities are noted and briefly discussed. The high frequency electrical behavior seems to be dominated by states in the dielectric rather than states at the interface. a-carbon appears to be a promising dielectric material for use in silicon solid state electronics.     

Avalanche noise in GaAs m.e.s.f.e.t.s

Instabilities in the d.c. characteristics of GaAs m.e.s.f.e.t.s for drain to source voltages greater than 4 V. believed to be due to reloading of traps in the interface between active layer and bulk material, or gunn-domain formation, seem to have their origin in avalanche breakdown of the back diode under the drain contact. Microplasma switching, vertical to the active layer, strongly modulates the drain current producing large broadband noise power.     

Resolution of electrooptic light valves

The voltage distribution in an electrooptic light-valve structure, consisting of an isotropic dielectric layer and a dielectrically anisotropic longitudinal electrooptic crystal sandwiched between conducting electrodes, has been analyzed in detail for the case where a spatial modulation in the charge density is introduced at the interface. The sensitivity of this sandwich structure is then defined as the reciprocal of the charge density necessary to produce the half-wave voltage across the electrooptic material. Several devices reported in the literature are then compared on a uniform plot of sensitivity versus spatial modulation frequency. The theoretical curves indicate graphically that, though the material characteristics alone determine the high-spatial-frequency sensitivity, the layer thicknesses drastically affect the low-spatial-frequency sensitivity. Since the electrooptic material and the isotropic dielectric material are usually chosen because certain characteristics (photoconductivity, optical perfection, low half-wave voltage, etc.) make them uniquely suited for a particular device, the major additional choice available in the design of the electrooptic light valve is this tradeoff of sensitivity for spatial bandwidth.     

Continuous roll to roll nanoimprinting of inherently conducting polyaniline

Roll to roll printing has been used recently to produce organic electronics. In future, the high speed manufacturing methods offer a way to integrate electronic functions on consumer products and packages. The minimum feature sizes achieved with roll to roll printing processes, such as gravure or flexography printing, are in the range of tens of microns. Roll to roll nanoimprinting enables a way to produce submicron features at high speed. In this work we have investigated roll to roll manufacturing of submicron structures of conducting polymer using a custom made laboratory scale nanoimprinting machine. The machine combines a gravure printing unit and a nanoimprinting unit. The units can be used consecutively to pattern the web in a single pass. We present results obtained using the gravure unit to print inherently conducting polymer layer on the substrate web, followed by pattering the polymer layer using the nanoimprinting unit. Using this approach we have realised submicron features in inherently conductive polyaniline-dodecylbenzenesulfonic acid (PANI-DBSA) film.     

Conductivity modulation enhanced lateral IGBT with SiO2 shielded layer anode by SIMOX technology on SOI substrate

A new lateral insulated-gate bipolar transistor (LIGBT) with a SiO2 shielded layer anode on SOI substrate is proposed and discussed.Compared to the conventional LIGBT,the proposed device offers an enhanced conductivity modulation effect due to the SiO2 shielded layer anode structure which can be formed by SIMOX technology.Simulation results show that,for the proposed LIGBT,during the conducting state,the electron-hole plasma concentrations in the n-drift region are several times larger than those of the conventional LIGBT; the conducting current is up to 37% larger than that of the conventional one.The enhanced conductivity modulation effect by SiO2 shielded layer anode does not sacrifice other characteristics of the device,such as breakdown and switching,but is compatible with other optimized technologies.     

Analysis of multiconductor transmission lines of arbitrary crosssection in multilayered uniaxial media

A mixed-potential electric field integral equation is formulated and applied in conjunction with the method of moments to analyze a transmission-line system consisting of multiple conducting strips of arbitrary cross section embedded in a stratified medium with or without top and/or bottom ground planes. Each layer of the medium is possibly uniaxially anisotropic, with its optical axis perpendicular to the dielectric interfaces. Computed dispersion curves and modal currents are presented and, when possible, are compared with data available in the literature     

The Effects of Moisture in Low‐Voltage Organic Field‐Effect Transistors Gated with a Hydrous Solid Electrolyte

The concept of using ion conducting membranes (50–150 μm thick) for gating low‐voltage (1 V) organic field‐effect transistors (OFETs) is attractive due to its low‐cost and large‐area manufacturing capabilities. Furthermore, the membranes can be tailor‐made to be ion conducting in any desired way or pattern. For the electrolyte gated OFETs in general, the key to low‐voltage operation is the electrolyte “insulator” (the membrane) that provides a high effective capacitance due to ionic polarization within the insulator. Hydrous ion conducting membranes are easy to process and readily available. However, the role of the water in combination with the polymeric semiconductor has not yet been fully clarified. In this work electrical and optical techniques are utilized to carefully monitor the electrolyte/semiconductor interface in an ion conducting membrane based OFET. The main findings are that 1) moisture plays a major part in the transistor operation and careful control of both the ambient atmosphere and the potential differences between the electrodes are required for stable and consistent device behavior, 2) the obtained maximum effective capacitance (5 μF cm^?2) of the membrane suggests that the electric double layer is distributed over a broad region within the polyelectrolyte, and 3) electromodulation spectroscopy combined with current–voltage characteristics provide a method to determine the threshold gate voltage from an electrostatic field‐effect doping to a region of (irreversible) electrochemical perturbation of the polymeric semiconductor.     

Single electron charging and single electron tunneling in sub-micron AlGaAs/GaAs double barrier transistor structures

Transport phenomena in a specially optimized vertical asymmetric sub-micron Al_0.28Ga_0.72As/GaAs double barrier structure with modulation-doped barriers is investigated by applying a bias to a special Schottky side gate, which allows the effective area of the conducting channel to be finely “tuned”. For a sufficiently small device, the electrical properties of the controllable quantum dot bounded by well defined heterostructure barriers and an adjustable side wall potential are expected to be governed by single electron charging, and single electron resonant tunneling. Single electron transistor (SET) operation is possible because the number of electrons in the dot, n, can be varied one-by-one with the side gate. The drain current flowing through the conducting channel in response to a small drain voltage is strongly modulated by the gate voltage close to “pinch-off” as n approaches zero, and oscillations in the drain current persist up to about 25 K. A gate modulated zero current region of Coulomb blockade, step-like features, and resonances exhibiting negative differential resistance are clearly observed at low bias. Although this technology is very promising for the realization of SET operation at temperatures well above 4.2 K, the temperature dependence of the Coulomb blockade is an important limitation. We describe the evolution of the conductance oscillations and the degradation of Coulomb blockade with temperature from 0.3 K up to 25 K, and propose that co-tunneling in a small system containing just a “few” electrons in which the zero-dimensional energy level spacing is significant and comparable to the Coulomb charging energy is important, and is likely to be more complex than that documented for large planar dot structures containing “many” electrons.     

Electrical characterization of dielectrically isolated siliconsubstrates containing buried metallic layers

Dielectrically isolated substrates containing buried highly conducting WSi₂ layers are characterized for the first time using MOS capacitors. The active silicon layer is approximately 3 μm thick with a buried WSi₂ layer adjacent to the isolation layer. The buried metal forms the back contact of the capacitor and excellent MOS characteristics are observed. Minority carrier lifetimes in excess of 200 μs were measured indicating the suitability of these substrates for use in device manufacture     

D.C. characteristics of silicon p-n junctions at avalanche breakdown including selfheating

The computation of the d.c. characteristics of a silicon p-n junction at breakdown is described in this paper. In the analysis, the effect of the dissipated electric power on the junction temperature is taken into account. The influences of the thermal resistance, the ambient temperature and the low-voltage reverse current on the d.c. characteristics at breakdown are shown. A formula describing the differential resistance of a junction at breakdown is derived. The temperature coefficients of voltage and current for the d.c. characteristics under consideration are derived as well. The coordinates of the points at which these coefficients change the sign are calculated and the influence of the thermal resistance, the ambient temperature and the low-voltage reverse current on the coordinates of these points is discussed.     

Evaluation of perfectly matched layer mesh terminations infinite-element bioelectromagnetic scattering computations

There has been considerable interest in and development of perfectly matched layer (PML) mesh terminations for electromagnetic scattering problems. For the most part, PML performance has been characterized on benchmarks which involve scattering from perfectly conducting objects. In this paper, we evaluate a recent PML implementation for node-based finite-element formulations using a prototype problem which is relevant to bioelectromagnetic computations. Variables under consideration include the layer material properties, layer thickness, and layer distance from the biological body. The results demonstrate that distance from the body is the strongest determinant of solution accuracy with increasing errors occurring with increasing frequency at a fixed distance, although average solution variations of less than 10% are observed in most cases where layers are located at a distance of at least 1.5 times the smallest body dimension. In addition, the PML need only consist of two to three layers in order to reduce solution variations resulting from layer thickness, and this thickness requirement is largely independent of layer distance from the body. This is in contrast to results from perfectly conducting scatterers where six to eight or more layers have been recommended. Further, the computed solutions are not a strong function of the layer material property and this parameter can easily be determined from a simple analytical decay formula without compromising PML performance. These findings are encouraging from a computational economy perspective and they suggest that the PML concept is an excellent choice for finite-element mesh truncation in bioelectromagnetic computations     

Effect of a d.c. electric field parallel to the depletion layer on the microwave oscillations in a p-i-n IMPATT diode

High frequency properties of a p-i-n IMPATT diode have been analysed when an additional d.c. electric field parallel to the area of the junction and perpendicular to the high electric field caused by reverse biasing the device is established in the space charge layer. The transit time required by the carriers to cross the depletion layer is increased due to the increase in the path length caused by the change in the direction of the resultant field while the velocity of the carriers remain saturated. It is found that the frequency for maximum negative resistance decreases with the increase of the additional d.c. electric field.     

Two-dimensional analysis of double-gate m.o.s. transistor

The principles of a new form of cascode m.o.s. device are discussed. A method of analysis for the derivation of d.c. characteristics is provided. Theoretical results have been validated by comparison with those of a practical device.     

Normally-off m.e.s.f.e.t. with fast switching behaviour

Normally-off m.c.s.f.e.t.s, fabricated on an insulating GaAs substrate with a vapour-phase-grown double layer (n?/n), showed a d.c. characteristic with a good saturation range and a switching response of 35 ps risetime.     

The magnetically coated conducting surface as a dual conductor andits application to antennas and microwaves

An electric conducting surface coated with a thin, lossy magnetic layer has been both theoretically and experimentally observed to be equivalent to a surface that is conducting to both electric and magnetic fields of plane waves at near-grazing incidence angles. This dual conductivity phenomenon has been utilized to design horn antennas for desired performance characteristics such as symmetric beams, low sidelobes, and low cross polarization. The effects of this surface are in many ways similar to those of the corrugated conducting surface. However, this coated surface appears to have a broader spectrum of applications in other antennas and microwave devices because of its apparent dual (electric and magnetic) conductivity