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2. Theory of superjunction devices

Author

Kang, Hyemin and Udrea, Florin

Subjects
621.31, Power device, MOSFETs, Superjunction, Analytic model, Figures of Merit, Dynamic, Capacitance
Abstract

Since the first ideal specific resistance model by Fujihira in 1997 and the first commercial superjunction MOSFET by Infineon technology in 1998, the technology and the understanding of superjunction devices have been gradually progressed. Although Fujihira’s ideal model was developed to estimate the specific on-state resistance at a given cell pitch as a function of the breakdown voltage, the model does not work for sub micro cell pitches because it does not consider the parasitic junction field effect transistor (JFET) presented in the superjunction. Fujihira’s model assumes the limit of the minimum cell pitch, by saying that the specific resistance can be decreased indefinitely with decreasing the cell pitch. In 2018, the first universal model for the specific on-state resistance of a superjunction MOSFET including the parasitic JFET effect was derived by H. Kang and F. Udrea. This model employs the classical JFET theory into the superjunction structure and clearly presents the true limit of the cell pitch of superjunction MOSFETs, as well as the specific resistance for different semiconductor materials. The classical JFET theory can be also applied to various superjunction structures and the detailed derivation process is described in Chapter 2. In Chapter 3, an advance device structure, three-dimensional (3-D) superjunction MOSFET, is introduced. To understand the superior performance of 3-D superjunction MOSFET, radial Poisson equation is employed. From theses mathematical calculation, it can be clearly seen that the 3-D superjunction is able to decrease the specific on-state resistance by half of the 2-D. In Chapter 4, based on the depletion process of superjunction during the switching, the inner circuit models for capacitance are provided. From the inner circuit models, typical capacitance curves with respect to the applied bias are drawn and they are expressed in terms of material parameters.

Published
2020
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29. Effects of nitrate and sulfate on the performance and bacterial community structure of membrane-less single-chamber air-cathode microbial fuel cells.

Author

Seo, Yoonjoo, Kang, Hyemin, Chang, Sumin, Lee, Yun-Yeong, and Cho, Kyung-Suk

Subjects
*BACTERIAL communities, *PHYSIOLOGICAL effects of nitrates, *ARTIFICIAL membranes, *MICROBIAL fuel cells, *WASTEWATER treatment, *CHEMICAL oxygen demand
Abstract

Membrane-less, single-chamber, air-cathode, microbial fuel cells (ML-SC MFCs) have attracted attention as being suitable for wastewater treatment. In this study, the effects of nitrate and sulfate on the performance of ML-SC MFCs and their bacterial structures were evaluated. The maximum power density increased after nitrate addition from 8.6 mW·m−2to 14.0 mW·m−2, while it decreased after sulfate addition from 11.5 mW·m−2to 7.7 mW·m−2. The chemical oxygen demand removal efficiencies remained at more than 90% regardless of the nitrate or sulfate additions. The nitrate was removed completely (93.0%) in the ML-SC MFC, while the sulfate removal efficiency was relatively low (17.6%).Clostridium(23.1%),Petrimonas(20.0%), and unclassifiedRhodocyclaceae(6.2%) were dominant on the anode before the addition of nitrate or sulfate. After the addition of nitrate,Clostridiumwas still the most dominant on the anode (23.6%), butPetrimonassignificantly decreased (6.0%) and unclassifiedRhodocyclaceaeincreased (17.1%). After the addition of sulfate, the amount ofClostridiumalmost doubled in the composition on the anode (43.2%), whilePetrimonasdecreased (5.5%). The bacterial community on the cathode was similar to that on the anode after the addition of nitrate. However,Desulfovibriowas remarkably dominant on the cathode (32.9%) after the addition of sulfate. These results promote a deeper understanding of the effects of nitrate or sulfate on the ML-SC MFCs' performance and their bacterial community. [ABSTRACT FROM AUTHOR]

Published
2018
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35. Photocatalytic effect of thermal atomic layer deposition of TiO2 on stainless steel

Author

Kang, Hyemin, Lee, Chang-Soo, Kim, Do-Young, Kim, Jungwon, Choi, Wonyong, and Kim, Hyungjun

Subjects
*PHOTOCATALYSIS, *THERMAL analysis, *TITANIUM dioxide, *STAINLESS steel, *MOLECULAR structure, *THICKNESS measurement, *THIN films, *CRYSTAL growth
Abstract

Abstract: The thermal atomic layer deposition (Th-ALD) of TiO2 films on stainless steel for use as a photocatalyst was investigated and compared to plasma-enhanced ALD (PE-ALD) using the same precursor. Th-ALD TiO2 films were deposited on stainless steel using a Ti(NMe2)4 [tetrakis(dimethylamido) Ti, TDMAT] precursor. The microstructure of the Th-ALD TiO2 films was greatly dependent on the growth temperature as an amorphous structure was obtained at 200°C and a polycrystalline structure was achieved at temperatures above 300°C. From the contact angle measurement of water, the crystalline TiO2 films exhibited super-hydrophilicity after UV irradiation. The anatase phase of both the Th- and PE-ALD TiO2 films grown on stainless steel showed higher photocatalytic abilities than the rutile phase grown at 400°C. In addition, the anatase PE-ALD TiO2 film demonstrated a higher photocatalytic efficiency than the Th-ALD films. The photocatalytic efficiency of the Th-ALD TiO2 films was investigated as a function of film thickness and it was found that the efficiency was saturated above a film thickness of 120nm. [Copyright &y& Elsevier]

Published
2011
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