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Influence of Emitter Width and Emitter-Base Distance on the Current Gain in 4H-SiC Power BJTs
KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.
KTH, Skolan för informations- och kommunikationsteknik (ICT), Integrerade komponenter och kretsar.ORCID-id: 0000-0001-6459-749X
Vise andre og tillknytning
2010 (engelsk)Inngår i: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 57, nr 10, s. 2664-2670Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The influence of the emitter-base geometry on the current gain has been investigated by means of measurements and simulations. Particular attention has been placed on the emitter width and on the distance between the emitter edge and the base contact. When the emitter width is decreased from 40 to 8 mu m, the current gain is reduced by 20%, whereas when the distance between the base contact and the emitter edge is decreased from 5 to 2 mu m, the current gain is reduced by 10%. Simulations have been used to investigate the reasons for the current gain reduction. The reduction of the emitter width induces two mechanisms of current gain reduction: earlier forward biasing of the base-collector junction and higher recombination in the emitter region. Both mechanisms result from the higher current density flowing under the emitter region. Placing the base contact very close to the emitter edge increases the base current by increasing the gradient of the electron concentration toward the base contact. The effect of increasing the base doping in the extrinsic region has been simulated, and the results demonstrate that the current gain can be improved if a high doping concentration in the range of 5 x 10(18) cm(-3) is used.

sted, utgiver, år, opplag, sider
2010. Vol. 57, nr 10, s. 2664-2670
Emneord [en]
Bipolar junction transistor (BJT), current gain, emitter-base distance, emitter width, silicon carbide (SiC), simulations
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-29823DOI: 10.1109/TED.2010.2061854ISI: 000283346500040Scopus ID: 2-s2.0-77956993929OAI: oai:DiVA.org:kth-29823DiVA, id: diva2:398298
Merknad
QC 20110217Tilgjengelig fra: 2011-02-17 Laget: 2011-02-17 Sist oppdatert: 2017-12-11bibliografisk kontrollert
Inngår i avhandling
1. Simulation and Characterization of Silicon Carbide Power Bipolar Junction Transistors
Åpne denne publikasjonen i ny fane eller vindu >>Simulation and Characterization of Silicon Carbide Power Bipolar Junction Transistors
2012 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Stockholm: KTH Royal Institute of Technology, 2012. s. xiv, 82
Serie
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2012:08
Emneord
silicon carbide, power device, BJT, diode, simulation, characterization, current gain, on-resistance, breakdown voltage, forward voltage drop, degradation
HSV kategori
Forskningsprogram
SRA - Informations- och kommunikationsteknik
Identifikatorer
urn:nbn:se:kth:diva-95320 (URN)978-91-7501-365-7 (ISBN)
Disputas
2012-06-08, C1, Electrum, KTH-ICT, Isafjordsgatan 26, Kista, 10:00 (engelsk)
Opponent
Veileder
Merknad
QC 20120522Tilgjengelig fra: 2012-05-22 Laget: 2012-05-22 Sist oppdatert: 2012-05-22bibliografisk kontrollert

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