FEM simulation approach to investigate electro-thermal behavior of power transistors in 3-D

A simulation approach is presented which can be used to investigate electro-thermal behavior of power transistors in variety of operating conditions. The approach is discussed in detail and demonstrated using ANSYS simulator. The power transistor is considered as a distributed voltage controlled resistor consisting of many in parallel connected cells. Because every cell has individual gate- and drain-source voltage, 3-D effects depending on geometric configuration and used materials can be observed. This is shown on a simple power transistor model for three principal electrical operating points: below TCP (temperature compensated point), at TCP and above TCP. Additionally, a mix-mode operating point is showed. The simulation results show 3-D effect of current density distribution as a function of the operating points. The results showed very good agreement with the prediction from the theory and already published results achieved by 3-D modeling approaches

ANSYS based 3D electro-thermal simulations for the evaluation of power MOSFETs robustness

Electro-thermal simulators are useful tools for introducing design and technology improvements during the design process of power MOSFET transistors. They are also helpful to predict the device behavior when operating under extreme electrical and temperature conditions and thus to predict its thermal robustness. Such simulators have to correctly take into account interactions between electrical and thermal behavior. In this paper we propose a new method to perform electro-thermal simulations of power MOSFETs using ANSYS simulator. The electrical and the thermal problem are fully coupled and iteratively solved using the FEM method. By means of a test chip, simulations and comparison with measurement have been performed in order to validate the simulation approach

Comments on species divergence in the genus Sphaerium (Bivalvia) and phylogenetic affinities of Sphaerium nucleus and S. corneum var. mamillanum based on karyotypes and sequences of 16S and ITS1 rDNA

Chromosome, 16S and ITS1 rDNA sequence analyses were used to obtain reliable diagnostic characters and to clarify phylogenetic relationships of sphaeriid bivalves of the genus Sphaerium. The species studied were found to be diploid, with modal number 2n = 28 in S. nucleus and 2n = 30 in S. corneum var. mamillanum. Small, biarmed, C- negative B chromosomes were found in all studied populations of both species. Karyological and molecular markers revealed no differences between S. corneum s. str. and S. corneum var. mamillanum. No intraspecific differences were found in the basic karyotype of S. nucleus. Molecular analyses, however, uncovered three genetically distinct ITS1 lineages: one comprised of samples from Lithuania, Slovakia, and Russia, another from Czech, and a third from Ukraine. Additionally to known 16S haplotype from Ukraine, three new 16S haplotypes of S. nucleus were detected: one in the samples from Lithuania and Russia, one in Slovakian and one in Czech population. In the ITS1 phylogenetic tree, all branches of S. nucleus clustered in one clade. In the 16S phylogenetic tree, however, the haplotype of Czech S. nucleus formed a separate branch, distant from three other haplotypes of S. nucleus. Molecular results indicate that in the context of the Evolutionary Species Concept the S. nucleus morphospecies may represent a complex of separate taxa, however referring on the Biological Species Concept the genetic lineages could represent the intraspecific variability