Papers by Author: G. Amaratunga

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Authors: Gheorghe Brezeanu, M. Badila, Phillippe Godignon, José Millan, F. Udrea, Andrej Mihaila, G. Amaratunga
Authors: S.J. Rashid, C. Mark Johnson, F. Udrea, Andrej Mihaila, G. Amaratunga, Rajesh Kumar Malhan
Abstract: A novel high temperature wire bondless packaging technique is numerically investigated in this paper. Extraction of device effective resistivity with temperature from numerical characteristics of 1.2kV 4H-SiC MOSFETs at a current density of 400A/cm2 have demonstrated a T−2 temperature dependence. Electro-thermal finite element analysis (FEA) of 1.2kV 4H-SiC MOSFETs sandwiched between two etched direct-bonded-copper substrate tiles has been performed. The thermal resistance of the ceramic sandwich package shows a 75% reduction in thermal resistance compared to conventional wire bonded assemblies. Mechanical analysis of the assembly has been used to investigate the residual stresses in the SiC dies at room temperature, which are then alleviated at higher temperatures during device operation. Mismatch of the expansion coefficients of the auxiliary materials in the assembly result in elevated stresses at full load operation, however these are well below the tensile strength of the respective materials and hence do not compromise the mechanical integrity of the package.
Authors: Gheorghe Brezeanu, M. Brezeanu, F. Udrea, G. Amaratunga, C. Boianceanu, M. Badila, Konstantinos Zekentes, Adi Visoreanu
Abstract: A classical implementation of the field plate technique is the oxide ramp termination. This paper presents for the first time a comparison between SiC and diamond Schottky barrier diodes (SBD) using this termination. The influences of the ramp angle and oxide thickness on the diodes electrical performance are investigated for both punch-through (PT) and non punch-through (nPT) structures. The efficiency of the termination is also evaluated.
Authors: Andrej Mihaila, F. Udrea, S.J. Rashid, G. Amaratunga, Mitsuhiro Kataoka, Yuuichi Takeuchi, Rajesh Kumar Malhan
Abstract: An investigation concerning suitable termination techniques for 4H-SiC trench JFETs is presented. Field plates, p+ floating rings and junction termination extension techniques are used to terminate 1.2kV class PiN diodes. The fabricated PiN diodes evaluated here have a similar design to trench JFETs. Therefore, the conclusions for PiN diodes can be applied to JFET structures as well. Numerical simulations are also used to illustrate the effect of the terminations on the diodes’ blocking mode behaviour.
Authors: S.J. Rashid, Andrej Mihaila, F. Udrea, Rajesh Kumar Malhan, G. Amaratunga
Authors: Cyril Buttay, C. Mark Johnson, Jeremy Rashid, F. Udrea, G. Amaratunga, Peter Tappin, Nicolas G. Wright, Peter Ireland, Takeo Yamamoto, Yuuichi Takeuchi, Rajesh Kumar Malhan
Abstract: In this paper a novel approach to the design and fabrication of a high temperature inverter module for hybrid electrical vehicles is presented. Firstly, SiC power electronic devices are considered in place of the conventional Si devices. Use of SiC raises the maximum practical operating junction temperature to well over 200°C, giving much greater thermal headroom between the chips and the coolant. In the first fabrication, a SiC Schottky barrier diode (SBD) replaces the Si pin diode and is paired with a Si-IGBT. Secondly, doublesided cooling is employed, in which the semiconductor chips are sandwiched between two substrate tiles. The tiles provide electrical connections to the top and the bottom of the chips, thus replacing the conventional wire bonded interconnect. Each tile assembly supports two IGBTs and two SBDs in a half-bridge configuration. Both sides of the assembly are cooled directly using a high-performance liquid impingement system. Specific features of the design ensure that thermo-mechanical stresses are controlled so as to achieve long thermal cycling life. A prototype 10 kW inverter module is described incorporating three half-bridge sandwich assemblies, gate drives, dc-link capacitance and two heat-exchangers. This achieves a volumetric power density of 30W/cm3.
Authors: Gheorghe Brezeanu, F. Udrea, G. Amaratunga, Andrej Mihaila, Phillippe Godignon, José Millan, M. Badila
Authors: Gheorghe Brezeanu, C. Boianceanu, M. Brezeanu, Andrej Mihaila, F. Udrea, G. Amaratunga
Abstract: The behavior of the MOS switch and of two cascode configurations are evaluated, by using OR-CAD simulations, and the resulting data are comparatively presented. By analytical and numerical investigations, the superior performance of the multiple cascode circuit is demonstrated.
Authors: K.H. Ang, I. Alexandrou, N.D. Mathur, R. Lacerda, I.Y.Y. Bu, G. Amaratunga, S. Haq
Abstract: An electric arc discharge in de-ionised water between a solid graphite cathode and an anode made by compressing Ni and C containing powders in a mass ratio of Ni:C = 7:3 was used here to prepare carbon encapsulated Ni nanoparticles in the form of powder suspended in water. The morphology of the produced material was analysed using high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The magnetic properties of the samples were determined using a Princeton vibrating sample magnetometer (VSM). Collection of the powder produced from different depths in the water container has proved to be an effective method for obtaining samples with narrow particle size distribution. Further material purification by dry NH4 plasma etching was used to remove the amorphous carbon content of the samples. XRD and HRTEM analysis showed that the material synthesized is fcc Ni particles with mean particle size ranging from 14 to 30 nm encapsulated in 2 to 5 graphitic cages. The data suggests that the process reported has the ability to mass-produce carbon encapsulated ferromagnetic nanoparticles with desired particle size distribution, and hence with controlled size-dependent magnetic properties.
Authors: Andrej Mihaila, F. Udrea, Gheorghe Brezeanu, R. Azar, G. Amaratunga
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