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Low-forward-voltage-drop 4H-SiC BJTs without base contact implantation
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.ORCID iD: 0000-0001-8108-2631
KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.ORCID iD: 0000-0002-5845-3032
2008 (English)In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 55, no 8, 1907-1911 p.Article in journal (Refereed) Published
Abstract [en]

Bipolar junction transistors (BJTs) of 4H-SiC, with a low collector--emitter forward voltage drop YCE, have been fabricated without base contact implantation. A comparison of BJTs on the same wafer with and without base contact implantation shows less than 10% higher VcE for the BJTs without base contact implantation. Omitting the base contact implantation eliminates high concentrations of implantation-induced defects that act as recombination centers. This is advantageous because it allows a shorter distance Wp+ between the emitter edge and the base contact, without affecting the current gain when no base contact implantation is used. The BJTs without contact implantation show a constant current gain as Wp+ was reduced from 3 to I pm, whereas the gain decreased by 45% for the BJTs with base contact implantation for the same reduction of Wp+. A key to the successful fabrication of low-forward-voltage-drop SiC BJTs without base contact implantation is the formation of low-resistivity Ni/Ti/Al ohmic contacts to the base. The contact resistivity on the base region (N-A approximate to 4 x 10(17) cm(-3)) was measured with linear transmission line method structures to PC = 1.9 X 10(-3) Omega cm(2), whereas the contact resistivity with the base contact implantation was PC = 1.3 x 10-4 Omega cm(2), both after rapid thermal processing annealing at 800 degrees C.

Place, publisher, year, edition, pages
2008. Vol. 55, no 8, 1907-1911 p.
Keyword [en]
bipolar junction transistor (BJT), emitter injection efficiency, forward voltage drop, ohmic contact, 4H-silicon carbide, ohmic contacts, al/ti
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-17722DOI: 10.1109/ted.2008.926641ISI: 000257950300020Scopus ID: 2-s2.0-49249099302OAI: oai:DiVA.org:kth-17722DiVA: diva2:335767
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically 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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