A theoretical study of transconductance characteristics (gm − Vgs profile) of AlGaN/GaN high electron mobility transistors (HEMTs) with a graded AlGaN layer is given in this paper. The calculations were made using a self-consistent solution of the Schrödinger-Poisson equations and an AlGaN/GaN HEMTs numerical device model. Transconductance characteristics of the devices are discussed while the thickness and Al composition of the graded AlGaN layer are optimized. It is found that graded AlGaN layer structure can tailor device’s gm − Vgs profile by improving polar optical phonon mobility and interface roughness mobility. Good agreement is obtained between the theoretical calculations and experimental measurements over the full range of applied gate bias.

The development of power electronics in the field of transportations (automotive, aeronautics) requires the use of power semiconductor devices providing protection and diagnostic functions. In the case of series protections power semiconductor devices which provide protection may operate in shortcircuit and act as a current limiting device. This mode of operations is very constraining due to the large dissipation of power. In these particular conditions of operation, electro-thermal models of power semiconductor devices are of key importance in order to optimize their thermal design and increase their reliability. The development of such an electro-thermal model for power MOSFET transistors based on the coupling between two computation softwares (Matlab and Cast3M) is described in this paper. The 2D electro-thermal model is able to predict (i) the temperature distribution on chip surface well as in the volume under short-circuit operations, (ii) the effect of the temperature on the distribution of the current flowing within the die and (iii) the effects of the ageing of the metallization layer on the current density and the temperature. In this paper, the electrical and thermal models are described as well as the implemented coupling scheme.

In this paper, terminal capacitances of a normally-on SiCED-JFET are measured, analyzed and simulated. All these capacitances are measured using an auto-balanced (guarded) capacitance test-bench that leads to the standard 3-terminal model capacitors CGS, CDS and CGD. This test bench is developed to measure each capacitance individually, without any mutual influence. 2D finite-element simulations are used to show that the capacitance CGD cannot be modeled by a standard planar junction model. This is due to the influence of two dimensional effects around the buried layer P+. A new analytical model of CGD is proposed. A good agreement is obtained between simulations and measurements of the different capacitances.

In this paper porous silicon (PS) has been prepared by electrochemical etching technique and then ZnO thin film deposition on PS by spray pyrolysis method, the study of AFM show improve the structural stability of the PS substrate with crystalline growth of ZnO thin film. PL spectra explained a blue-shifting in PS layer come from oxidation the surface of PS after coating with ZnO film, Raman measurement show quantum confinement in PS layers with decreasing in variation mode of ZnO film, and the J-V characteristic show increasing in resistivity of Al/ZnO/PS/c-Si/Al due to increasing in depletion layer junction compere with PS layer.

In this work, the correlation between BEMA model and FTIR analysis was employed to investigate the chemical composition of silicon oxynitride (SiOxNy) films deposited by low pressure chemical vapour deposition (LPCVD) technique at temperature of 850 °C from nitrous oxide N2O, ammonia NH3 and dichlorosilane SiH2Cl2. Different stoichiometries were obtained for different values of relative gas flow ratio NH3/N2O while keeping the SiH2Cl2 flow constant. The optical properties were studied using spectroscopic ellipsometry. Apart from films thickness, their refractive index as well as their SiO2 and Si3N4 volume fractions were deduced using the Bruggeman effective medium approximation (BEMA) model. It was found that the refractive index increases from 1.45 to 1.60 with increasing nitrogen incorporation. The Fourier Transform Infrared spectroscopy was carried out to study the evolution of chemical bonding of LPCVD SiOxNy films. In order to improve the qualitative analysis of their Si-N and Si-O vibrational modes, a correlation between Fourier transform infrared and spectroscopic ellipsometry measurements was established. A shift of infrared peaks position with the increase of relative gas flow ratio is observed. Furthermore, the calculated areas of absorption bands were used to estimate the SiOxNy stoichiometry. This quantitative analysis was proved with an adequate method in the literature. We found a decrease of x values from 1.94 to 1.26 and an increase of y from 0.04 to 0.49, when the NH3/N2O gas flow ratio increases. This behavior was explained by the increase of nitrogen content as well as the decrease of oxygen content in the SiOxNy film.

In this article, a simple method was proposed for determining the thermal effusivity of defects using pulsed thermography. This method is complementary to other methods such as those that implement periodic thermal stresses for identification of the thermal properties of materials, or which use specific photothermal analysis or extended. Theoretically, this technique is based on solving the heat equation in the case of an isotropic solid heated by a delta Dirac pulse. The application conditions of this new technique have been studied by numerical simulations. A finite element modeling has been performed in the case of a steel sample which may contain geometry defects filled in by air, resin, oil, wax or water. The analysis of surface temperature distribution of the infected samples by the proposed method allowed to determine the thermal effusivity of defects. The experimental measurements have confirmed the importance and simplicity of this method in the characterization of defects using pulsed thermography. The results show the possibility of approaching, at an acceptable error, the defect thermal effusivity.

This paper analyzes surface waves (SW) supported by a biaxial metamaterial layer placed between two semi-infinite isotropic media. The metamaterial fabricated by periodic alternating semiconductor and dielectric layers and subjected to an external magnetic field. The magnetic field is applied parallel to the layers. We consider such structure in the long-wave limit so that we apply the effective medium theory to describe the electrodynamic properties. The necessary conditions of SW existence were found in terms of anisotropy of the structure. The dependences of penetration depth and attenuation constant (AC) of SW on the external magnetic field and thicknesses of the layers were examined analytically and numerically.

A magnetoelectric theoretical model combing piezoelectric and piezomagnetic parts about the longitudinal vibration was proposed for the laminate composite based on equivalent circuit. The model shows that the magnetoelectric voltage is relative to the thickness ratio, total thickness, frequency and loss. A simple laminate magnetoelectric composite was prepared by bonding a nickel plate and a multilayer piezoelectric vibrator together for the experimental research. The multilayer vibrator enjoys high capacitance, large effective area and low thickness, leading to a high magnetic field sensitivity of 1 mOe at the magnetoelectric field coefficient of 2.58 V/cmOe in the simple composite with nickel thickness of 0.2 mm. The model fits the resonance frequency well with the experimental results. Numerical calculation well predicates the magnetoelectric experimental behaviors, presenting a magnetoelectric maximum at about the thickness ratio 0.3 between the nickel plate and multilayer vibrators. This approach provides a method for the magnetoelectric application.

In this paper, a measurement of the total amount of liquid metal created by an electric arc in air is made for copper anodes and cathodes. This amount is compared with usual erosion for the same experimental conditions for various values of the electrode gap (3–10 mm). It appears that the amount of liquid is ten times greater than the erosion for copper cathodes and may be fifty times greater for copper anodes. A method using experimental results and a numerical simulation of the thermal phenomena occurring in the electrode during the arc heating is then used to assess the characteristics of the power flux brought by the electric arc to the copper electrodes. It was found that about 80% of the energy received by the electrodes was conducted in the solid phase and that about 20% of this energy was used to melt or vaporize the electrode material. The power surface density brought to the electrodes was found in the range 4.6 × 108–1.9 × 109 W/m2 for the cathode and in the range 6.4 × 108–1.1 × 1010 W/m2 for the anode.

Design of integrated power converters needs prototype-less approaches. Specific simulations are required for investigation and validation process. Simulation relies on active and passive device models. Models of planar devices, for instance, are still not available in power simulator tools. There is, thus, a specific limitation during the simulation process of integrated power systems. The paper focuses on the development of a physically-based planar inductor model and its validation inside a power converter during transient switching. The planar inductor model remains a complex device to model, particularly when the skin, the proximity and the parasitic capacitances effects are taken into account. Heterogeneous simulation scheme, including circuit and device models, is successfully implemented in VHDL-AMS language and simulated in Simplorer platform. The mixed simulation results has been favorably tested and compared with practical measurements. It is found that the multi-domain simulation results and measurements data are in close agreement.

A simple and rapid analysis and design method is proposed for a coreless permanent magnet machine (CPMM) using a hexagonal winding (HW). The HW, which combines a rectangular winding (RTW) and rhombic winding (RBW), can compensate for the disadvantages and maximize the advantages of the RTW and RBW. The CPMM is typically analyzed using complex differential equations or a timeconsuming finite element analysis (FEA). To address this problem, a relatively simpler and less timeconsuming analysis method is proposed by using a lumped equivalent magnetic circuit (LEMC) model. Furthermore, an effect of winding angle on a motor performance is analyzed via precise inspection of the relationship between the variables of the HW and the characteristics of motor. The validity and usefulness of the proposed method are verified via FEA and experiment.

We prove that combinations of small eccentricity, ovality and/or triangularity in the rotor and stator can produce complex whirling motions of an unbalanced rotor in large synchronous generators. It is concluded which structures of shape deviations that are more harmful, in the sense of producing complex whirling motions, than others. For each such structure, we derive simplified equations of motions from which we conclude analytically the relation between shape deviations and mass unbalance that yield non-smooth whirling motions. Finally we discuss validity of our results in the sense of modeling of the unbalanced magnetic pull force.