No. 1 (2004)
Published:
2004-03-30
ARTICLES FROM THIS ISSUE
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Silicon everywhere
Abstract
The paper discusses the ubiquity of silicon and its compounds in the geo-chemical structure of the Earth. The dominant role of mineral oxidized compounds of silicon as the building material of the primordial magma, metamorphic and sedimentary rocks is also shown. The reader`s attention is also attracted to the numerous varieties of silicon compounds valued for their intrinsic beauty. Finally, methods of silicon production for electronics purposes are briefly addressed.
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Silicon microelectronics: where we have come from and where we are heading
Abstract
The paper briefly presents the history of microelectronics and the limitations of its further progress, as well as possible solutions. The discussion includes the consequences of the reduction of gate-stack capacitance and difficulties associated with supply-voltage scaling, minimization of parasitic resistance, increased channel doping and small size. Novel device architectures (e.g. SON, double-gate transistor) and the advantages of silicon-germanium are considered, too.
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Critical modeling issues of SiGe semiconductor devices
Abstract
We present the state-of-the-art in simulation of silicon-germanium (SiGe) semiconductor devices. The work includes a detailed comparison of device simulators and current transport models. Among the critical modeling issues addressed in the paper, special attention is focused on the description of the anisotropic majority/minority electron mobility in strained SiGe grown on Si. We use a direct approach to obtain scattering parameters S-parameters and other derived figures of merit of SiGe heterojunction bipolar transistors (HBTs) by means of small-signal AC-analysis. Results from two-dimensional hydrodynamic simulations of SiGe HBTs are presented in good agreement with measured data. The examples are chosen to demonstrate technologically important issues which can be addressed and solved by device simulation.
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Recent developments in vertical MOSFETs and SiGe HBTs
Abstract
There is a well recognised need to introduce new materials and device architectures to Si technology to achieve the objectives set by the international roadmap. This paper summarises our work in two areas: vertical MOSFETs, which can allow increased current drive per unit area of Si chip and SiGe HBT`s in silicon-on-insulator technology, which bring together and promise to extend the very high frequency performance of SiGe HBT`s with SOI-CMOS.
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Modeling SiGe-base HBT using APSYS 2000 - a 2D simulator
Abstract
The paper is devoted to optimization of SiGe-base HBT with respect to operation speed by means of numerical simulation. The influence of design parameters on fT is studied.
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Scattering mechanisms in MOS/SOI devices with ultrathin semiconductor layers
Abstract
Main scattering mechanisms affecting electron transport in MOS/SOI devices are considered within the quantum-mechanical approach. Electron mobility components (i.e., phonon, Coulomb and interface roughness limited mobilities) are calculated for ultrathin symmetrical DG SOI transistor, employing the relaxation time approximation, and the effective electron mobility is obtained showing possible mobility increase relative to the conventional MOSFET in the range of the active semiconductor layer thickness of about 3 nm.
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High-field current transport and charge trapping in buried oxide of SOI materials under high-field electron injection
Abstract
Mechanisms of the charge transfer, the charge trapping, and the generation of positive charge during the high-field electron injection into buried oxide of silicon-on-insulator structures fabricated by different technologies are analyzed based on the data obtained from current-voltage, injection current-time, and capacitance-voltage characteristics together with SIMS data. Electron injection both from the Si film and the Si substrate is considered. The possibility of using the trap-assisted electron tunneling mechanisms to explain the high-field charge transfer through the buried oxides of UNIBOND and SIMOX SOI materials is considered. It is shown that considerable positive charge is accumulated near the buried oxide/substrate interface independently from the direction of the injection (from the film or from the silicon substrate) for UNIBOND and SIMOX SOI structures. Thermal stability of the charge trapped in the buried oxides is studied at temperatures ranging from 20 to 400OC. The theory is compared with the experimental data to find out the mechanisms of the generation of positive charge in UNIBOND and SIMOX buried oxides.
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Ultrathin oxynitride films for CMOS technology
Abstract
In this work, a review of possible methods of oxynitride film formation will be given. These are different combinations of methods applying high-temperature oxidation and nitridation, as well as ion implantation and deposition techniques. The layers obtained using these methods differ, among other aspects in: nitrogen content, its profile across the ultrathin layer, ... etc., which have considerable impact on device properties, such as leakage current, channel mobility, device stability and its reliability. Unlike high-temperature processes, which (understood as a single process step) usually do not allow the control of the nitrogen content at the silicon-oxynitride layer interface, different types of deposition techniques allow certain freedom in this respect. However, deposition techniques have been believed for many years not to be suitable for such a responsible task as the formation of gate dielectrics in MOS devices. Nowadays, this belief seems unjustified. On the contrary, these methods often allow the formation of the layers not only with a uniquely high content of nitrogen but also a very unusual nitrogen profile, both at exceptionally low temperatures. This advantage is invaluable in the times of tight restrictions imposed on the thermal budget (especially for high performance devices). Certain specific features of these methods also allow unique solutions in certain technologies (leading to simplifications of the manufacturing process and/or higher performance and reliability), such as dual gate technology for system-on-chip (SOC) manufacturing.
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Closed-form 2D modeling of sub-100 nm MOSFETs in the subthreshold regime
Abstract
Closed-form 2D modeling of deep-submicron and sub-100 nm MOSFETs is explored using a conformal mapping technique where the 2D Poisson equation in the depletion regions is separated into a 1D long-channel case and a 2D Laplace equation. The 1D solution defines the boundary potential values for the Laplacian, which in turn provides a 2D correction of the channel potential. The model has been tested for classical MOSFETs with gate lengths in the range 200-250 nm, and for a super-steep retrograde MOSFET with a gate length of 70 nm. With a minimal parameter set, the present modeling reproduces both qualitatively and quantitatively the experimental data obtained for such devices.
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New approach to power semiconductor devices modeling
Abstract
The main problems occurring during high power device modeling are discussed in this paper. Unipolar and bipolar device properties are compared and the problems concerning high time-constant values related to the diffusion phenomena in the large base are explained. Traditional and novel concepts of power device simulation are presented. In order to make accurate and modern semiconductor device models widely accessible, a website has been designed and made available to Internet users http://www.dmcs.p.lodz.pl/dmcs-spice, allowing them to perform simulations of electronic circuits containing high power semiconductor devices. In this software, a new distributed model of power diode has been included. Together with the existing VDMOS macromodel library, the presented approach can facilitate the design process of power circuits. In the future, distributed models of IGBT, BJT and thyristor will be added.
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Process and device requirements for mixed-signal integrated circuits in broadband networking
Abstract
The paper describes the present status of the broadband wireline infrastructure consisting of the backbone core, metro rings, access network, local and storage area networks. Examples of various mixed-signal integrated circuits are described. Based on these considerations required process and device performance is extrapolated.
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Evolution and recent advances in RF/microwave transistors
Abstract
Most applications for radio frequency/microwave (thereafter called RF) transistors had been military oriented in the early 1980s. Recently, this has been changed drastically due to the explosive growth of the markets for civil wireless communication systems. This paper gives an overview on the evolution, current status, and future trend of transistors used in RF electronic systems. Important background, development and major milestones leading to modern RF transistors are presented. The concept of heterostructure, a feature frequently used in RF transistors, is discussed. The different transistor types and their figures of merit are then addressed. Finally an outlook of expected future developments and applications of RF transistors is given.
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Photonic crystal fibre characterisation with the method of lines
Abstract
Photonic crystal fibres are longitudinally uniform fibres in which in lateral directions periodic refractive index changes occur. Two basically different light guiding mechanisms occur in crystal fibres: index guiding and bandgap guiding. In the paper different modelling methods have been evaluated when applied to photonic crystal fibres. In particular, the method of lines has been shown to be effective and reliable for both classes of photonic crystal fibres. High accuracy results for optical field distribution and dispersion characteristics in a photonic crystal fibre have been achieved with the method of lines.
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Sensitivity of microwave radiometers with square - law and linear detectors
Abstract
Stochastic analysis of modulation microwave radiometers with square - law and linear detectors is presented in the paper. Assuming ideal detector characteristics it is shown that in typical applications, i.e., in very low power measurements, a type of detector used is of no influence on total radiometer sensitivity. Other aspects of use of a particular detector are also presented.
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Multifrequency microwave thermograph for biomedical applications
Abstract
This paper presents problems related to thermal radiation of human bodies in microwave range in aspect of diagnosis of breast carcinoma. A mathematical model of thermal radiation transfer through tissues is introduced and methods of measurement of temperature, depth and size of a heat source, by means of multifrequency microwave thermography are described. Theoretical considerations are supplemented by presentation of experimental results.
