| 1. |
- Buono, Benedetto, et al.
(författare)
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Current Gain Degradation in 4H-SiC Power BJTs
- 2011
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Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 679-680, s. 702-705
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Tidskriftsartikel (refereegranskat)abstract
- SiC airs are very attractive for high power application, but long term stability is still problematic and it could prohibit commercial production of these devices. The aim of this paper is to investigate the current gain degradation in BJTs with no significant degradation of the on-resistance. Electrical measurements and simulations have been used to characterize the behavior of the BJT during the stress test. Current gain degradation occurs, the gain drops from 58 before stress to 43 after 40 hours, and, moreover, the knee current shows fluctuations in its value during the first 20 hours. Current gain degradation has been attributed to increased interface traps or reduced lifetime in the base-emitter region or small stacking faults in the base-emitter region, while fluctuations of the knee current might be due to stacking faults in the collector region.
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| 2. |
- Buono, Benedetto, et al.
(författare)
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Influence of Emitter Width and Emitter-Base Distance on the Current Gain in 4H-SiC Power BJTs
- 2010
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Ingår i: IEEE Transactions on Electron Devices. - 0018-9383 .- 1557-9646. ; 57:10, s. 2664-2670
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Buono, Benedetto, et al.
(författare)
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Investigation of Current Gain Degradation in 4H-SiC Power BJTs
- 2012
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Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 717-720, s. 1131-1134
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Tidskriftsartikel (refereegranskat)abstract
- The current gain degradation of 4H-SiC BJTs with no significant drift of the on-resistance is investigated. Electrical stress on devices with different emitter widths suggests that the device design can influence the degradation behavior. Analysis of the base current extrapolated from the Gummel plot indicates that the reduction of the carrier lifetime in the base region could be the cause for the degradation of the gain. However, analysis of the base current of the base-emitter diode shows that the degradation of the passivation layer could also influence the reduction of the current gain.
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| 4. |
- Buono, Benedetto, et al.
(författare)
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Modeling and Characterization of Current Gain Versus Temperature in 4H-SiC Power BJTs
- 2010
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Ingår i: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9383 .- 1557-9646. ; 57:3, s. 704-711
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Tidskriftsartikel (refereegranskat)abstract
- Accurate physical modeling has been developed to describe the current gain of silicon carbide (SiC) power bipolar junction transistors (BJTs), and the results have been compared with measurements. Interface traps between SiC and SiO2 have been used to model the surface recombination by changing the trap profile, capture cross section, and concentration. The best agreement with measurement is obtained using one single energy level at 1 eV above the valence band, a capture cross section of 1 x 10(-15) cm(2), and a trap concentration of 2 x 10(12) cm(-2). Simulations have been performed at different temperatures to validate the model and characterize the temperature behavior of SiC BJTs. An analysis of the carrier concentration at different collector currents has been performed in order to describe the mechanisms of the current gain fall-off at a high collector current both at room temperature and high temperatures. At room temperature, high injection in the base ( which has a doping concentration of 3 x 10(17) cm(-3)) and forward biasing of the base-collector junction occur simultaneously, causing an abrupt drop of the current gain. At higher temperatures, high injection in the base is alleviated by the higher ionization degree of the aluminum dopants, and then forward biasing of the base-collector junction is the acting mechanism for the current gain fall-off. Forward biasing of the base-collector junction can also explain the reduction of the knee current with increasing temperature by means of the negative temperature dependence of the mobility.
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| 5. |
- Buono, Benedetto, et al.
(författare)
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Modeling and Characterization of the ON-Resistance in 4H-SiC Power BJTs
- 2011
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Ingår i: IEEE Transactions on Electron Devices. - 0018-9383 .- 1557-9646. ; 58:7, s. 2081-2087
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Buono, Benedetto, et al.
(författare)
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Simulations of Open Emitter Breakdown Voltage in SiC BJTs with non Implanted JTE
- 2009
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Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 615-617, s. 841-844
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Tidskriftsartikel (refereegranskat)abstract
- Ion implantation for selective doping of SiC is problematic due to damage generation during the process and low activation of dopants. In SiC bipolar junction transistor (BJT) the junction termination extension (JTE) can be formed without ion implantation using instead a controlled etching into the epitaxial base. This etched JTE is advantageous because it eliminates ion implantation induced damage and the need for high temperature annealing. However, the dose, which is controlled by the etched base thickness and doping concentration, plays a crucial role. In order to find the optimum parameters, device simulations of different etched base thicknesses have been performed using the software Sentaurus Device. A surface passivation layer consisting of silicon dioxide, considering interface traps and fixed trapped charge, has been included in the analysis by simulations. Moreover a comparison with measured data for fabricated SiC BJTs has been performed.
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| 7. |
- Buono, Benedetto, et al.
(författare)
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Temperature Modeling and Characterization of the Current Gain in 4H-SiC Power BJTs
- 2010
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Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 645-648, s. 1061-1064
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Tidskriftsartikel (refereegranskat)abstract
- The current gain of 4H-SiC BJTs has been modeled using interface traps between SIC and SiO2 to describe surface recombination, by a positive temperature dependence of the carrier lifetime in the base region and by bandgap narrowing in the emitter region. The interface traps have been modeled by one single level at 1 eV above the valence band, with capture cross section of 1 x 10(-15) cm(2) and concentration of 2 x 10(12) cm(-2). The temperature behavior of SiC BJTs has been simulated and the results have been compared with measurements. An analysis of the carrier concentration has been performed in order to describe the mechanisms for fall-off of the current gain at high collector current. At room temperature high injection in the base and forward biasing of the base-collector junction occur simultaneously causing an abrupt drop of the current gain. At higher temperatures high injection in the base is alleviated by the higher ionization degree of the aluminum dopants, and then forward biasing of the base-collector junction is the only acting mechanism for the current gain fall-off at high collector current. This mechanism and the negative temperature dependence of the carrier mobility can also explain the reduction of the knee current for gain fall-off with increasing temperature. Simulations with different emitter widths have been also performed and analyzed to characterize the emitter size effect. Higher current density caused by reducing the emitter width introduces higher carrier recombination in the emitter region, leading to a reduction of the current gain.
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| 8. |
- Cho, H., et al.
(författare)
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Ultradeep, low-damage dry etching of SiC
- 2000
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 76:6, s. 739-741
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Tidskriftsartikel (refereegranskat)abstract
- The Schottky barrier height (Phi(B)) and reverse breakdown voltage (V-B) of Au/n-SiC diodes were used to examine the effect of inductively coupled plasma SF6/O-2 discharges on the near-surface electrical properties of SiC. For low ion energies (less than or equal to 60 eV) in the discharge, there is minimal change in Phi(B) and V-B, but both parameters degrade at higher energies. Highly anisotropic features typical of through-wafer via holes were formed in SiC using an Al mask.
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| 9. |
- Dahlquist, Fanny, et al.
(författare)
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2.8 kV, forward drop JBS diode with low leakage
- 2000
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Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 338-342, s. 1179-1182
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Tidskriftsartikel (refereegranskat)abstract
- High voltage Schottky-, Junction Barrier Schottky (JBS)- and PiN-diodes with an implanted JTE termination have been fabricated on the same 4H-SiC wafer. Blocking voltages of 2.5-2.8 kV were reached for JBS and PiN diodes while the Schottky diodes reach about 2.0 kV. It is shown that the JBS design increases the blocking voltage effectively compared to the Schottky device with less than 10% increase in on-state static losses. Also, a comparison of static losses to a PiN diode gives a decrease of 40% for the JBS. The leakage current is also lowered by two decades compared to the Schottky device at its blocking voltage. Temperature measurements show that the low leakage current is maintained up to at least 225 °C.
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| 10. |
- Dahlquist, Fanny, et al.
(författare)
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Junction barrier Schottky diodes in 4H-SiC and 6H-SiC
- 1998
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Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 264-268:PART 2, s. 1061-1064
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Tidskriftsartikel (refereegranskat)abstract
- The Junction Barrier Schottky (JBS) diode in silicon carbide is a promising candidate for a low-leakage power rectifier for high switching frequencies and elevated temperature operation. It has the advantage of a low forward voltage drop while keeping a low leakage current at high blocking voltage. JBS devices have been fabricated in 4H SiC and 6H SiC and then electrically characterised in comparison with pn and Schottky diodes on the same wafer. The JBS devices reached blocking voltages up to 1.0 kV at a leakage current density of 13 ÎŒA/cm2 and the forward conduction was limited by an on-resistance close to the theoretical value.
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