A temperature-dependent model for the complex dielectric function of GaAs

In this work, we discuss a temperature-dependent model for the complex dielectric function for GaAs valid for the temperature range 31°C ≤ T ≤ 634°C. We describe our model, which is an extension of the critical point parabolic band method. This is a phenomenological method which is based on the physical processes occurring in the semiconductor, and has been previously demonstrated for composition-dependent models of the dielectric function for lattice-matched materials systems. We demonstrate the quality of the model in fitting optical data for individual temperatures, and compare our results to other established models. The data used for each fitting ranges from 1.25 to 4.5 eV. Using results obtained from the individual fits, we generate a temperature-dependent model that is valid for the range of temperatures given above. Also, we show how this model can be used to accurately determine the temperature (±2.3°C) of a material whose dielectric response has been obtained but was not included when generating the model.     

Thin-film recording media

Thin-film magnetic recording media are reviewed in this paper. Although the magnetic materials and deposition processes are necessarily discussed, this paper is intended to review film media from a broader perspective than is usually found in the literature. Therefore, the subjects of applications, magnetic properties pertinent to recording, materials and processes, and reliability receive balanced attention. Moreover, within the materials and processes section and the reliability section, the topics of substrate preparation, overcoats, and mechanical and chemical stability are addressed as issues which are as important as the magnetic properties themselves. Rather than grouping film media according to the type of deposition process used (sputtered, plated, etc.) as is often done, media are grouped according to the type of magnetic anisotropies exploited and whether they are metallic or not. This classification better reflects the recording performance observed in the various film media.     

The Standard Model of the Heterostructure for Microwave Devices

A methodology of the selection of the initial materials, architecture and synthesis of heterostructures based on domestic materials and technologies as applied to specific types of microwave components needs to be developed. As the nomenclature expands, the requirements on energy consumption, overall dimensions and weight, frequency range, noise, values of working temperatures, and other characteristics of microwave components have significantly increased. Specific examples of power amplifiers for various applications (wireless communication systems and location systems) are considered. It is shown that in order to implement such developments, it is necessary to apply modern methods of multilevel computer modeling using various methods of optimization and widely use the tested technical solutions. The final result of this development is the creation of a set of basic physical models of the heterostructures, including those based on the solution of optimized problems by choosing the initial material, substrate material, layer composition, their sequences, layer thicknesses, impurity contents, and their distribution by the layer thickness. All this makes it possible to form an acceptable level of mechanical stresses and high values of the electrophysical characteristics in the heterostructure. The initial data set in the form of a library of basic models of the heterostructures will make it possible to significantly accelerate the development of various microwave components and optoelectronic components in the system of instrument and technological design and improve the characteristics of the devices and economic rates.     

Soft-magnetic fluxguide materials

This paper reviews the research done on soft-magnetic fluxguide materials for use in sandwich heads and in thin-film recording heads for digital magnetic recording. After dealing with the basic principles of magnetic recording, the requirements on modern soft-magnetic materials are discussed. The roles of magnetic anistropy and magnetostriction in relation to permeability are discussed. Next, we review the recent advances in soft-magnetic materials processing, in particular for amorphous cobalt (CoNbZr) and nanocrystalline iron alloys, such as FeMX, with M being group IVa-Va metals such as Zr, Hf, Nb, Ta, etc., and X being N and O.     

New frequency-dependent parametric modeling of dielectric materials

The recent increase in the use of electromagnetic (EM) waves raises more and more concern about the impact of EM radiation. Dielectric properties of materials are important indications of the depth of EM propagation and dispersion. This led to substantial research on the parametric modeling of dielectric properties of materials. In this paper, such modeling of material is studied for frequencies up to 100 GHz. The new model proposed was developed to describe the variation of dielectric properties of dielectricity as a function of frequency using experimental results on dielectric dispersion. Approximate modeling of electrical parameters can be very useful in that it allows the engineer to avoid complex equations of conventional models. Specifically, this work analyzes the dielectric properties of human parts, water, soil and vegetation. The new model is proposed for those materials. The theoretical background on those materials was investigated and simulation results on complex permittivity, the attenuation and phase constants of wave, of each of those materials were performed to assess the accuracy of the new approximate model. This model has further enabled conclusions in terms of measurable biophysical parameters.     

Analysis of finite-differencing errors to determine cell size when modeling ferrites and other lossy electric and magnetic materials using FDTD

The focus of this paper is the modeling of materials that have both significant electric and magnetic losses, such as ferrites, using finite-difference time domain (FDTD). The primary contribution is identifying appropriate cell sizes when modeling these types of materials. It is shown that finite-differencing errors increase in lossy media compared to lossless media when sampling at the same number of cells per wavelength. Losses in a medium are defined by the ratio of the attenuation constant, /spl alpha/, to the phase constant, /spl beta/, since that ratio accounts for all losses, whether they be electric or magnetic. In addition to a detailed finite-differencing error analysis, a simple approximation is given for selecting a cell size in a lossy material that will give the same finite-differencing error as ten cells per wavelength in a lossless material. This paper also presents a means for deriving pure real constitutive parameters from complex constitutive parameters. Being able to make such calculations is useful in cases where complex constitutive parameters are given for a material, and the FDTD model being used only accepts pure real constitutive parameters, as is the case for several contemporary models. Comparisons of theoretical and FDTD-modeled reflection and transmission show that the derived, real constitutive parameters are valid.     

Modeling of GaN optoelectronic devices and strain-inducedpiezoelectric effects

Modeling of nitride-based LEDs and laser diodes requires a fast modular tool for numerical simulation and analysis. It is required that the modeling tool reflects the primary physical processes of current injection, quantum well (QW) bound-state dynamics, QW capture, radiative, and nonradiative transitions. The model must also have the flexibility to incorporate secondary physical effects, such as induced piezoelectric strain fields due to lattice mismatch and spontaneous polarization fields. A 1-D model with a phenomenological well-capture process, similar to that developed by Tessler and Eisenstein, has been implemented. The radiative processes are calculated from first principles, and the material band structures are computed using k·p theory. The model also features the incorporation of such effects as thermionic emission at heterojunctions. Shockley-Read-Hall recombination, piezoelectric strain fields, and self-consistent calculation of the QW bound states with dynamic device operation. The set of equations underlying the model is presented, with particular emphasis on the approximations used to achieve the previously stated goals. A sample structure is analyzed, and representative physical parameters are plotted. The model is then used to analyze the effects of incorporation of the strain-induced piezoelectric fields generated by lattice mismatch and the spontaneous polarization fields. It is shown that these built-in fields can accurately account for the blue-shift phenomena observed in a number of different GaN LEDs     

Frameworks for direct bonding

The spontaneous formation of a direct bond between materials — a phenomenon sometimes encountered in mechanics and optics — was considered inconvenient at first. It was some time before the advantages of the possibility of realizing direct bonds were realized: direct bonds obviated the need for intermediate adhesive layers. A good deal of research had to be done into the required pretreatment of the material parts and the aftertreatment for bond tightening before direct bonding could be used as a technology.Geometrical, mechanical, chemical and physical properties of the materials involved all play a part in the formation of a direct bond; they are collectively referred to as the physiognomic properties. This chapter will describe a number of examples demonstrating the wide variety of materials (both inorganic and organic) that can be directly bonded, after which some magnetic, electric and electromagnetic advantages of directly bonded, electromagnetically active materials will be briefly outlined.     

Magnetooptics: A thermomagnetic recording technology

Erasable magnetooptic (MO) recording is viewed as a possible successor to electromagnetic recording that is used today in high-performance disk drives for mainframe computers, hard disks, and floppy disks for personal computers and magnetic tape drives. A large number of rare earth-transition metal alloys have been investigated for use as the magnetic recording material. The properties of the films are very sensitive to the film deposition processing parameters. Accelerated life tests show that there are magnetooptic materials that do have all of the necessary properties and stability for use in computer digital storage.     

Low-Frequency Shielding Effectiveness of Nonuniform Enclosures

This paper presents a quasi-static approximate solution to the magnetic shielding of several nonuniform enclosures using the integral form of Maxwell's equations and insight gained from other approaches. The solution is called quasi-static as the assumptions made are from physical arguments based on low-frequency cases where the enclosure size is much less than a wavelength. The integral form of Maxwell's equations is used to obtain a first order correction to the static solution to obtain induced currents in the time-varying case. A cylindrical shell immersed in an axial magnetic field is used to illustrate the method, which is then extended to derive a formula for a similarly excited rectangular enclosure. These shields are seen to behave like a low-pass filter. Although the enclosure dimensions are small compared to the wavelength, the skin depth effects in the walls cannot be neglected even for relatively thin material as usually encountered in an enclosure. These skin effects are included in the analysis and experimental checks performed on a variety of enclosure sizes and materials, excited by a Helmholtz coil show agreement within two decibels over the 4-octave frequency range examined. No one can say whether this method offers a better solution to the shielding problem, as all solutions are approximate, but the author attempts to present an alternative formulation that aids in understanding the physical processes involved in the shielding effectiveness of an enclosure and fills some of the gaps between the plane-wave analysis and circuit approaches presently used.     

Combined use of finite-state machines and petri nets for modelling communicating processes

In order to model and verify systems of concurrent processes (such as those involved in communication protocols), finite-state machines and Petri nets can be used as local and global models, respectively. The problem of composing a set of communicating finite-state machines into a single global Petri net is considered in the letter with special attention to the case of more than two processes.     

Evolution of Models and Algorithms for Calculating the Parameters of Technological Processes to Obtain Materials for Micro- and Nanoelectronics

The results of creating a system of models and algorithms for calculating the parameters of technological processes for obtaining materials of micro- and nanoelectronics and designing equipment are considered. It is shown that the distinctive feature of the teaching methods for special technological courses in electronic engineering materials is the construction of courses by analogy with the technological processes for obtaining materials for electronics: from a bulk single crystal to instrumental structures, whose dimensions do not currently exceed several tens of nanometers. A scientific model approach to the solution of technological problems was formed in the study of heat and mass transfer processes, which together with the processes of interaction in liquids and gas, taking heterogeneous reactions into account, are the theoretical basis of the technology of electronic engineering materials. The possibilities of physical and mathematical modeling are compared. Approaches to create mathematical models of the growth processes of single crystals of semiconductors, epitaxial layers, and heterostructures are considered and the possibilities of their practical use are determined. It is determined that the ideas proposed by V.V. Krapukhin at the initial stages of training specialists in the field of the technology of electronic material and developed by his students identified the possibility of training several generations of qualified specialists.     

Electromagnetic Scattering From Arbitrarily Shaped Dielectric Bodies Using Paired Pulse Vector Basis Functions and Method of Moments

A pair of orthogonal pulse vector basis functions is demonstrated for the calculation of electromagnetic scattering from arbitrarily-shaped material bodies. The basis functions are intended for use with triangular surface patch modeling applied to a method of moments (MoM) solution. For modeling the behavior of dielectric materials, several authors have used the same set of basis functions to represent equivalent electric and magnetic surface currents. This practice can result in zero-valued or very small diagonal terms in the moment matrix and an unstable numerical solution. To provide a more stable solution, we have developed orthogonally placed, pulse basis vectors: one for the electric surface current and one for the magnetic surface current. This combination ensures strongly diagonal moment matrices. The basis functions are suitable for electric field integral equation (EFIE), magnetic field integral equation (HFIE), and combined field formulations. In this work, we describe the implementations for EFIE and HFIE formulations and show example results for canonical figures.      

Heat Assisted Magnetic Recording

Heat-assisted magnetic recording is a promising approach for enabling large increases in the storage density of hard disk drives. A laser is used to momentarily heat the recording area of the medium to reduce its coercivity below that of the applied magnetic field from the recording head. In such a system, the recording materials have a very high magnetic anisotropy, which is essential for the thermal stability of the magnetization of the extremely small grains in the medium. This technology involves new recording physics, new approaches to near field optics, a recording head that integrates optics and magnetics, new recording materials, lubricants that can withstand extremely high temperatures, and new approaches to the recording channel design. This paper surveys the challenges for this technology and the progress that has been made in addressing them.      

Prediction of cure induced warpage of micro-electronic products

Prediction of residual stresses in micro-electronic devises is an important issue. Virtual prototyping is used to minimize residual stresses in order to prevent failure or malfunction of electronic products.Already during encapsulation stresses build up due to polymerization induced shrinkage of the molding compound. Differences in coefficient of thermal expansion of the involved materials cause additional stresses during cooling down from molding to ambient temperature. Since industry is availed by reliable prediction methods, detailed material models are required. In electronic packaging, mechanical properties of most of the involved materials have constant mechanical properties. However, the viscoelastic properties of the encapsulation material depends highly on temperature and degree of cure. Reliable predictions of residual stresses require simulation models which take into account the effect of temperature and conversion level.In this paper, properties of molding compound are discussed which are relevant for the prediction of warpage of micro-electronics products. The models for the individual properties are combined to one single model suitable for finite element simulations. The numerical implementation in finite element code is not standard and is done by using user-subroutines.Validation experiments are performed in order to verify the developed material model which is done by measuring and predicting the warpage of a mold map. A Topography and Deformation Measurement (TDM) device is used to measure the deformations at elevated temperatures in a non-intrusive way such that the developed material model could be validated in a broad range of temperature.Finally, simulations are carried out with simplified material models of molding compound. The results of these simulations are compared with results obtained with the cure dependent viscoelastic model and real warpage data. From these comparisons it is concluded that for reliable prediction of warpage, the cure dependent viscoelastic model is has to be used.     

Photorefractive optics in three-dimensional digital memory

To exceed the capacity limitation of the surface-recording method of current optical data storage, the third dimension is introduced with photorefractive materials. Photorefractive materials are suitable for three-dimensional data storage in conjunction with nonlinear optical systems such as the two-photon absorption process of the material for recording and the confocal laser-scanning system for reading. I will describe the systems and the materials for three-dimensional digital memory with the experimental results for read-only memory with photopolymer, erasable memory with a lithium niobate crystal and rewritable memory with photochromic organic materials. The comparison between photorefractive digital three-dimensional memory with conventional holographic three-dimensional memory and near-field memory is also discussed in terms of dynamic range, noise, recording density, and accessibility     

Automatic generation of accurate low-order models for magnetic devices

A method to automatically create low order state-space models for magnetic devices is set forth. The method begins with geometrical and materials data from which the finite element analysis (FEA) is used to build a high order state-space model. It is shown that this model contains far more state variables than are necessary to achieve the nearly the same results in the frequency band of interest. It is shown that the full-order model can be reduced methodically without additional physical assumptions. The reduction method is applicable directly to magnetically linear systems, but applies to a wide range of power electronics applications and can be a basis for future nonlinear device modeling. The method reduced an example inductor model from 882 state variables to two. To confirm correct model derivation, the full-order model is checked against and agrees with experimental data to the extent that the FEA and materials data are accurate. The reduced-order model agrees very well with the full-order model, particularly in computing impedance.     

电子陶瓷薄膜动压悬浮流延的动力学特性分析

为了解决电子陶瓷薄膜的高精密与超薄化流延问题将硬磁盘存储系统中磁头相对磁盘的动压悬浮运动理论运用于电子陶瓷流延过程中,建立了动压悬浮流延法,并给出了流延头相对流延辊子的动静态物理模型.根据该模型所确立的动力学方程式,对其流延过程的动力学特性进行了计算机仿真,获得了系统各参数对流延系统稳定性的影响规律,并利用仿真结果得到实现系统动压悬浮的合理参数,确保了系统的稳定性。