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Influence of the base contact on the electrical characteristics of SiC BJTs
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.ORCID iD: 0000-0001-8108-2631
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.ORCID iD: 0000-0002-5845-3032
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2007 (English)In: 19th International Symposium on Power Semiconductor Devices and ICs, ISPSD'07: Jeju Island; 27 May 2007 through 31 May 2007, 2007, 153-156 p.Conference paper, Published paper (Refereed)
Abstract [en]

In this paper, we have investigated how the specific on-resistance and common emitter current gain of SiC BJTs depend on the base contact resistance. The on-state characteristics of SiC BJTs were investigated before and after base contact annealing at different temperatures. The common emitter current gain and specific on-resistance was improved by 23 % and 300 % compared to the values of before base contact annealing, respectively. Large area SiC BJTs (active area 0.0324 cm(2)), have been measured up to 34 A collector current in pulsed mode showing a gain of 35, and a specific on-resistance of 2 8.79 m Omega center dot cm(2)

Place, publisher, year, edition, pages
2007. 153-156 p.
Series
International Symposium on Power Semiconductor Devices and ICs, ISSN 1063-6854
Keyword [en]
silicon carbide; bipolar junction transistor; current gain; contact resistance; specific on-resistance
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-7935DOI: 10.1109/ISPSD.2007.4294955ISI: 000249645200039Scopus ID: 2-s2.0-36148982672ISBN: 978-1-4244-1095-8 (print)OAI: oai:DiVA.org:kth-7935DiVA: diva2:13118
Note
QC 20100819Available from: 2008-01-30 Created: 2008-01-30 Last updated: 2010-08-19Bibliographically approved
In thesis
1. Fabrication and Characterization of Silicon Carbide Power Bipolar Junction Transistors
Open this publication in new window or tab >>Fabrication and Characterization of Silicon Carbide Power Bipolar Junction Transistors
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Silicon carbide bipolar junction transistors (BJTs) are attractive power switching devices because of the unique material properties of SiC with high breakdown electric field, high thermal conductivity and high saturated drift velocity of electrons. The SiC BJT has potential for very low specific on-resistances and this together with high temperature operation makes it very suitable for applications with high power densities. For SiC BJTs the common emitter current gain (β), the specific on-resistance (RSP_ON), and the breakdown voltage are important to optimize for competition with silicon based power devices. In this thesis, power SiC BJTs with high current gain β ≈ 60 , low on-resistance RSP_ON ≈ 5 mΩcm2, and high breakdown voltage BVCEO ≈ 1200 V have been demonstrated. The 1200 V SiC BJT that has been demonstrated has about 80 % lower on-state power losses compared to a typical 1200 V Si IGBT chip.

A continuous epitaxial growth of the base-emitter layers has been used to reduce interface defects and thus improve the current gain. A significant influence of surface recombination on the current gain was identified by comparing the experiments with device simulations. In order to reduce the surface recombination, different passivation layers were investigated in SiC BJTs, and thermal oxidation in N2O ambient was identified as an efficient passivation method to increase the current gain.

To obtain a low contact resistance, especially to the p-type base contact, is one critical issue to fabricate SiC power BJTs with low on-resistance. Low temperature anneal (~ 800 oC) of a p-type Ni/Ti/Al contact on 4H-SiC has been demonstrated. The contact resistivity on the ion implanted base region of the BJT was 1.3 × 10-4 Ωcm2 after annealing. The Ni/Ti/Al p-type ohmic contact was adapted to 4H-SiC BJTs fabrication indicating that the base contact plays a role for achieving a low on-resistance of SiC BJTs.

To achieve a high breakdown voltage, optimized junction termination is important in a power device. A guard ring assisted Junction Termination Extension (JTE) structure was used to improve the breakdown voltage of the SiC BJTs. The highest breakdown voltage of the fabricated SiC BJTs was obtained for devices with guard ring assisted JTE using the base contact implant step for a simultaneous formation of guard rings.

As a new approach to fabricate SiC BJTs, epitaxial regrowth of an extrinsic base layer was demonstrated. SiC BJTs without any ion implantation were successfully demonstrated using epitaxial regrowth of a highly doped p-type region and an etched JTE using the epitaxial base. A maximum current gain of 42 was measured for a 1.8 mm × 1.8 mm BJT with a stable and reproducible open base breakdown voltage of 1800 V.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. xvi, 74 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2008:01
Keyword
silicon carbide, power device, BJT, current gain, specific on resistance (RSP_ON), breakdown voltage, forward voltage drop, surface recombination, ohmic contact.
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-4623 (URN)
Public defence
2008-02-15, Sal E, Forum, Isafjordsgatan 39, Kista, Stockholm, 10:15
Opponent
Supervisors
Note
QC 20100819Available from: 2008-01-30 Created: 2008-01-30 Last updated: 2010-08-19Bibliographically approved

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Zetterling, Carl-Mikael

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