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Modeling and Characterization of the ON-Resistance in 4H-SiC Power BJTs
KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.ORCID iD: 0000-0001-6459-749X
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2011 (English)In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 58, no 7, 2081-2087 p.Article in journal (Refereed) Published
Abstract [en]

The ON-resistance of silicon carbide bipolar transistors is characterized and simulated. Output characteristics are compared at different base currents and different temperatures in order to validate the physical model parameters. A good agreement is obtained, and the key factors, which limit the improvement of R-ON, are identified. Surface recombination and material quality play an important role in improving device performances, but the device design is also crucial. Based on simulation results, a design that can enhance the conductivity modulation in the lowly doped drift region is proposed. By increasing the base doping in the extrinsic region, it is possible to meet the requirements of having low voltage drop, high current density, and satisfactory forced current gain. According to simulation results, if the doping is 5 x 10(18) cm(-3), it is possible to conduct 200 A/cm(2) at V-CE = 1 V by having a forced current gain of about 8, which represents a large improvement, compared with the simulated value of only one in the standard design.

Place, publisher, year, edition, pages
2011. Vol. 58, no 7, 2081-2087 p.
Keyword [en]
Bipolar junction transistor (BJT), extrinsic base, forced current gain, ON-resistance, 4H-silicon carbide (SiC)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-36242DOI: 10.1109/TED.2011.2141141ISI: 000291952900034Scopus ID: 2-s2.0-79959514175OAI: oai:DiVA.org:kth-36242DiVA: diva2:430590
Note
QC 20110711Available from: 2011-07-11 Created: 2011-07-11 Last updated: 2017-12-11Bibliographically approved
In thesis
1. Simulation and Characterization of Silicon Carbide Power Bipolar Junction Transistors
Open this publication in new window or tab >>Simulation and Characterization of Silicon Carbide Power Bipolar Junction Transistors
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The superior characteristics of silicon carbide, compared with silicon, have suggested considering this material for the next generation of power semiconductor devices. Among the different power switches, the bipolar junction transistor (BJT) can provide a very low forward voltage drop, a high current capability and a fast switching speed. However, in order to compete on the market, it is crucial to a have high current gain and a breakdown voltage close to ideal. Moreover, the absence of conductivity modulation and long-term stability has to be solved.

In this thesis, these topics are investigated comparing simulations and measurements. Initially, an efficient etched JTE has been simulated and fabricated. In agreement with the simulations, the fabricated diodes exhibit the highest BV of around 4.3 kV when a two-zone JTE is implemented. Furthermore, the simulations and measurements demonstrate a good agreement between the electric field distribution inside the device and the optical luminescence measured at breakdown.

Additionally, an accurate model to simulate the forward characteristics of 4H-SiC BJTs is presented. In order to validate the model, the simulated current gains are compared with measurements at different temperatures and different base-emitter geometries. Moreover, the simulations and measurements of the on-resistance are compared at different base currents and different temperatures. This comparison, coupled with a detailed analysis of the carrier concentration inside the BJT, indicates that internal forward biasing of the base-collector junction limits the BJT to operate at high current density and low forward voltage drop simultaneously. In agreement with the measurements, a design with a highly-doped extrinsic base is proposed to alleviate this problem.

In addition to the static characteristics, the comparison of measured and simulated switching waveforms demonstrates that the SiC BJT can provide fast switching speed when it acts as a unipolar device. This is crucial to have low power losses during transient.

Finally, the long-term stability is investigated. It is observed that the electrical stress of the base-emitter diode produces current gain degradation; however, the degradation mechanisms are still unclear. In fact, the analysis of the measured Gummel plot suggests that the reduction of the carrier lifetime in the base-emitter region might be only one of the causes of this degradation. In addition, the current gain degradation due to ionizing radiation is investigated comparing the simulations and measurements. The simulations suggest that the creation of positive charge in the passivation layer can increase the base current; this increase is also observed in the electrical measurements.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. xiv, 82 p.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2012:08
Keyword
silicon carbide, power device, BJT, diode, simulation, characterization, current gain, on-resistance, breakdown voltage, forward voltage drop, degradation
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
SRA - ICT
Identifiers
urn:nbn:se:kth:diva-95320 (URN)978-91-7501-365-7 (ISBN)
Public defence
2012-06-08, C1, Electrum, KTH-ICT, Isafjordsgatan 26, Kista, 10:00 (English)
Opponent
Supervisors
Note
QC 20120522Available from: 2012-05-22 Created: 2012-05-22 Last updated: 2012-05-22Bibliographically approved

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Malm, Bengt GunnarZetterling, Carl-Mikael

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