| 1. |
- Buchholt, Kristina, et al.
(författare)
-
Growth and characterization of epitaxial Ti3GeC2 thin films on 4H-SiC(0001)
- 2012
-
Ingår i: Journal of Crystal Growth. - : Elsevier. - 0022-0248 .- 1873-5002. ; 343:1, s. 133-137
-
Tidskriftsartikel (refereegranskat)abstract
- Epitaxial Ti3GeC2 thin films were deposited on 4 degrees off-cut 4H-SiC(0001) using magnetron sputtering from high purity Ti, C, and Ge targets. Scanning electron microscopy and helium ion microscopy show that the Ti3GeC2 films grow by lateral step-flow with {11 (2) over bar0} faceting on the SiC surface. Using elastic recoil detection analysis, atomic force microscopy, and X-Ray diffraction the films were found to be substoichiometric in Ge with the presence of small Ge particles at the surface of the film.
|
|
| 2. |
- Buchholt, Kristina, et al.
(författare)
-
Ohmic contact properties of magnetron sputtered Ti3SiC2 on n- and p-type 4H-silicon carbide
- 2011
-
Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 98:4, s. 042108-
-
Tidskriftsartikel (refereegranskat)abstract
- Epitaxial Ti3SiC2 (0001) thin film contacts were grown on doped 4H-SiC (0001) using magnetron sputtering in an ultra high vacuum system. The specific contact resistance was investigated using linear transmission line measurements. Rapid thermal annealing at 950 degrees C for 1 min of as-deposited films yielded ohmic contacts to n-type SiC with contact resistances in the order of 10(-4) Omega cm(2). Transmission electron microscopy shows that the interface between Ti3SiC2 and n-type SiC is atomically sharp with evidence of interfacial ordering after annealing. (c) 2011 American Institute of Physics.
|
|
| 3. |
- Buono, Benedetto, et al.
(författare)
-
Current Gain Degradation in 4H-SiC Power BJTs
- 2011
-
Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 679-680, s. 702-705
-
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.
|
|
| 4. |
- Buono, Benedetto, et al.
(författare)
-
Influence of Emitter Width and Emitter-Base Distance on the Current Gain in 4H-SiC Power BJTs
- 2010
-
Ingår i: IEEE Transactions on Electron Devices. - 0018-9383 .- 1557-9646. ; 57:10, s. 2664-2670
-
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.
|
|
| 5. |
- Buono, Benedetto, et al.
(författare)
-
Investigation of Current Gain Degradation in 4H-SiC Power BJTs
- 2012
-
Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 717-720, s. 1131-1134
-
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.
|
|
| 6. |
- Buono, Benedetto, et al.
(författare)
-
Modeling and Characterization of Current Gain Versus Temperature in 4H-SiC Power BJTs
- 2010
-
Ingår i: IEEE Transactions on Electron Devices. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9383 .- 1557-9646. ; 57:3, s. 704-711
-
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.
|
|
| 7. |
- Buono, Benedetto, et al.
(författare)
-
Modeling and Characterization of the ON-Resistance in 4H-SiC Power BJTs
- 2011
-
Ingår i: IEEE Transactions on Electron Devices. - 0018-9383 .- 1557-9646. ; 58:7, s. 2081-2087
-
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.
|
|
| 8. |
- Buono, Benedetto
(författare)
-
Simulation and Characterization of Silicon Carbide Power Bipolar Junction Transistors
- 2012
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
|
|
| 9. |
- Buono, Benedetto, et al.
(författare)
-
Temperature Modeling and Characterization of the Current Gain in 4H-SiC Power BJTs
- 2010
-
Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 645-648, s. 1061-1064
-
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.
|
|
| 10. |
- Domeij, David, et al.
(författare)
-
Inequality Trends in Sweden 1978-2004
- 2010
-
Ingår i: Review of economic dynamics. - : Elsevier BV. - 1094-2025 .- 1096-6099. ; 13:1, s. 179-208
-
Tidskriftsartikel (refereegranskat)abstract
- We document a clear increase in Swedish earnings inequality in the early 1990s, andthat much of this increase was generated by movements in and out of the labor market.Inequality in disposable income and earnings net of taxes and transfers also increased,but much less than the increased inequality in pre-government earnings. These di¤er-ent developments are most likely explained by the generous Swedish welfare system.Consistent with these observations, we see no clear trend in consumption inequality.We also estimate stochastic processes for household earnings. A simple random-walkprocess captures much of the life-cycle dynamics. But we .nd clear evidence that thetrue earnings process is not a random walk. We demonstrate that some estimationmethods result in severe upward bias in the estimated volatility of permanent shocksif serial correlation in temporary shocks is ignored.Our estimation results show that the increase in earnings inequality is almost entirelydriven by an increase in residualearnings inequality. Moreover, this increase wasmostly generated by an increased volatility of persistent shocks.
|
|
| 11. |
- Domeij, Martin, et al.
(författare)
-
2.2 kV SiC BJTs with low V(CESAT) fast switching and short-circuit capability
- 2010
-
Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2009, PTS 1 AND 2. ; , s. 1033-1036
-
Konferensbidrag (refereegranskat)abstract
- This paper reports large active area (15 mm(2)) 4H-SiC BJTS with a low V(CESAT)=0.6 V at 1(C)=20 A (J(C)=133 A/cm(2)) and an open-base breakdown voltage BV(CEO)=2.3 kV at T=25 degrees C. The corresponding room temperature specific on-resistance R(SP.ON)=4.5 m Omega cm(2) is to the authors knowledge the lowest reported value for a large area SiC BJT blocking more than 2 kV. The onstate and blocking characteristics were analyzed by device simulation and found to be in good agreement with measurements. Fast switching with VcE rise- and fall-times in the range of 20-30 ns was demonstrated for a 6 A 1200 V rated SiC BJT. It was concluded that high dynamic base currents are essential for fast switching to charge the BJT parasitic base-collector capacitance. In addition, 10 mu s short-circuit capability with V(CE)=800 V was shown for the 1200 V BJT.
|
|
| 12. |
- Farese, Luca, et al.
(författare)
-
Experimental Study of Degradation in 4H-SiC BJTs by Means of Electrical Characterization and Electroluminescence
- 2010
-
Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2009. ; , s. 1037-1040
-
Konferensbidrag (refereegranskat)abstract
- SiC power bipolar junction transistors (BJTs), for high voltage applications, have been studied under elevated temperature and electrical stress conditions. Electroluminescence has been used to capture effects of defect motion and growth, in complete transistor structures, leading to a quantifiable degradation in the electrical performance. The observed degradation of current gain (beta) and on-resistance (RON) was relatively modest and saturated after a limited stress time, resulting in stable device performance. The characteristic wavelength (450 nm) of the electroluminescence, or light emission, in the visual and near infrared (NIR) range, coupled to the shape of the defects indicates that basal plane dislocations and stacking faults are involved.
|
|
| 13. |
- Ghandi, Reza, et al.
(författare)
-
Experimental evaluation of different passivation layers on the performance of 3kV 4H-SiC BJTs
- 2010
-
Ingår i: Materials Science Forum. - 0255-5476 .- 1662-9752. ; 645-648:Part 1-2, s. 661-664
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, the electrical performance in terms of maximum current gain, ON-resistance and blocking capability has been compared for 4H-SiC BJTs passivated with different surface passivation layers. Variation in BJT performance has been correlated to densities of interface traps and fixed oxide charge, as evaluated through MOS capacitors. Six different methods were used to fabricate SiO2 surface passivation on BJT samples from the same wafer. The highest current gain was obtained for PECVD deposited SiO2 which was annealed in N2O ambient at 1100 degrees C during 3 hours. Variations in breakdown voltage for different surface passivations were also found, and this is attributed to differences in fixed oxide charge that can affect the optimum dose of the high voltage JTE termination.
|
|
| 14. |
- Ghandi, Reza
(författare)
-
Fabrication Technology for Efficient High Power Silicon Carbide Bipolar Junction Transistors
- 2011
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The superior characteristics of Silicon Carbide as a wide band gap semiconductor have motivated many industrial and non-industrial research groups to consider SiC for the next generations of high power semiconductor devices. The SiC Bipolar Junction Transistor (BJT) is one candidate for high power applications due to its low on-state power loss and fast switching capability. However, to compete with other switching devices such as Field Effect Transistors (FETs) or IGBTs, it is necessary for a power SiC BJT to provide a high current gain to reduce the power required from the drive circuit. In this thesis implantation free 4H-SiC BJTs with linearly graded base layer have been demonstrated with common-emitter current gain of 50 and open-base breakdown voltage of 2700 V. Also an efficient junction termination extension (JTE) with 80% of theoretical parallel-plane breakdown voltage was analyzed by fabrication of high voltage PiN diodes to achieve an optimum dose of remaining JTE charge. Surface passivation of 4H-SiC BJT is an essential factor for efficient power BJTs. Therefore different passivation techniques were compared and showed that around 60% higher maximum current gain can be achieved by a newsurface passivation layer with low interface trap density that consists of PECVD oxide followed by post-deposition oxide anneal in N2O ambient. This surface passivation along with doublezone JTE were used for fabrication of high power BJTs that result in successful demonstration of 2800 V breakdown voltage for small area (0.3 × 0.3 mm) and large area (1.8 × 1.8 mm) BJTs with a maximum dc current gain of 55 and 52, respectively. The small area BJT showed RON = 4mΩcm2, while for the large are BJT RON = 6.8 mΩcm2. Finally, a Darlington transistor with a maximum current gain of 2900 at room temperature and 640 at 200 °C is reported. The high current gain of the Darlington transistor is achieved by optimum design for the ratio of the active area of the driver BJT to the output BJT.
|
|
| 15. |
- Ghandi, Reza, et al.
(författare)
-
High current-gain implantation-free 4H-SiC Monolithic Darlington Transistor
- 2011
-
Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 32:2, s. 188-190
-
Tidskriftsartikel (refereegranskat)abstract
- An implantation-free 4H-SiC Darlington transistor with high current gain of 2900 ( JC= \970A/cm2) and VCE) = 6V) at room temperature is reported. The device demonstrates a record maximum current gain of 640 at 200 hC, offering an attractive solution for high-temperature applications. The monolithic Darlington device exhibits an open-base breakdown voltage of 1 kV that is less than the optimum bulk breakdown due to isolation trench between the driver and the output bipolar junction transistor. On the same wafer, a monolithic Darlington pair with a nonisolated base layer was also fabricated. At room temperature, this device shows a maximum current gain of 1000 and an open-base breakdown voltage of 2.8 kV, which is 75% of the parallel-plane breakdown voltage
|
|
| 16. |
- Ghandi, Reza, et al.
(författare)
-
High Voltage (2.8 kV) Implantation-free 4H-SiC BJTs with Long-TermStability of the Current Gain
- 2011
-
Ingår i: IEEE Transactions on Electron Devices. - 0018-9383 .- 1557-9646. ; 58:8, s. 2665-2669
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, implantation-free 4H-SiC BJTs with high breakdown of 2800 V have been fabricated utilizing acontrolled two-step etched junction termination extension (JTE). The small area devices show a maximum dc current gainof 55 at Ic=0.33 A (JC=825 A/cm2) and VCESAT = 1.05 V at Ic = 0.107 A that corresponds to a low ON-resistance of 4mΩ·cm2. The large area device have a maximum dc current gain of 52 at Ic = 9.36 A (JC=289 A/cm2) and VCESAT = 1.14 Vat Ic = 5 A that corresponds to an ON-resistance of 6.8 mΩ·cm2. Also these devices demonstrate a negative temperaturecoefficient of the current gain (β=26 at 200°C) and a positive temperature coefficient of the ON-resistance (RON = 10.2mΩ·cm2 at 200°C). The small area BJT shows no bipolar degradation and low current gain degradation after 150 Hrs stressof the base-emitter diode with current level of 0.2A (JE=500 A/cm2). Also, large area BJT shows a VCE fall time of 18 nsduring turn-on and a VCE rise time of 10 ns during turn-off for 400 V switching characteristics.
|
|
| 17. |
- Ghandi, Reza, et al.
(författare)
-
High Voltage, Low On-resistance 4H-SiC BJTs with Improved Junction Termination Extension
- 2011
-
Ingår i: Materials Science Forum. - : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 679-680, s. 706-709
-
Tidskriftsartikel (refereegranskat)abstract
- In this work, implantation-free 4H-SiC bipolar transistors with two-zone etched-JTE and improved surface passivation are fabricated. This design provides a stable open-base breakdown voltage of 2.8 kV which is about 75% of the parallel plane breakdown voltage. The small area devices shows a maximum dc current gain of 55 at Ic=0.33 A (J(C)=825 A/cm(2)) and V-CESAT = 1.05 V at Ic = 0.107 A that corresponds to a low ON-resistance of 4 m Omega.cm(2). The large area device shows a maximum dc current gain of 52 at Ic = 9.36 A (J(C)=312 A/cm(2)) and V-CESAT = 1.14 V at Ic = 5 A that corresponds to an ON-resistance of 6.8 m Omega.cm(2). Also these devices demonstrate a negative temperature coefficient of the current gain (beta=26 at 200 degrees C) and positive temperature coefficient of the ON-resistance (R-ON = 10.2 m Omega.cm(2)).
|
|
| 18. |
- Ghandi, Reza, et al.
(författare)
-
Influence of crystal orientation on the current gain in 4H-SiC BJTs
- 2010
-
Ingår i: Device Research Conference - Conference Digest, DRC. - 9781424478705 ; , s. 131-132
-
Konferensbidrag (refereegranskat)abstract
- The 4H-SiC bipolar junction transistors (BJT) are considered as efficient high power switching devices due to the ability of obtaining very low specific on-resistance compared to FET based devices. However, one drawback with the present high voltage BJTs is the relatively low current gain. To reduce the power required by the drive circuit, it is important to increase the common-emitter current gain ( #x03B2;). 4H-SiC (0001) Si-face has become a favorable plane for vertical power BJTs with epitaxial layers that shows higher mobility along the c-axis and provides higher current gain. Furthermore, important progress on improving the current gain focused on the quality of surface passivation at the SiC/SiO2 interface has been reported during previous years. Higher quality of passivation can provide less interface traps and thereby minimizes the surface recombination current. Conventionally, vertical 4H-SiC BJTs are fabricated along the [11_00] direction on (0001) Si-face. However due to anisotropic properties of 4H-SiC, different orientations on Si-face can also affect the base current of the BJT through variation of mobility and interface traps density distribution along each direction. In this work, single-finger small area BJTs are fabricated on (0001) Si-face along [12_10], [011_0], [112_0] and [11_00] directions. This design can provide various orientations of BJTs that corresponds to an angular range between 0 to 180 degrees relative to conventional [11_00] direction. The goal was to find a correlation between different crystallographic orientation, mobility and interface traps density distribution through transistor characteristics and finally comparison with simulation. Fig.1 shows a cross section and top view of fabricated BJTs. The n+ emitter epi-layer is 1.35 #x03BC;m nitrogen doped to 6 #x00D7;1018 cm-3 and capped by 200-nm-thick 2 #x00D7;1019 cm-3 layer. The base epi-layer is 650 nm Al-d- - oped with concentration of 4.3 #x00D7;1017 cm-3. The drift n- epilayer is 20 #x03BC;m thick and doped to 6 #x00D7;1015 cm-3. Inductively coupled plasma (ICP) etching with an oxide mask was used to form emitter and base mesas. Fig.2 is a comparison of the maximum current gain with different orientations normalized to the maximum current gain along [11_00] before surface passivation and contact metallization. The results indicate that the maximum current gain is orientation-dependent and has a maximum for BJTs with the emitter edge aligned to the [112_0] direction. The variation effect of planar mobility and interface traps concentration on the current gain is simulated based on the previous work and is illustrated in Fig.3. The simulation shows that interface oxide charges has more influence on the current gain compared to the mobility and higher current gain is attributed to lower oxide interface charges. The orientation dependence of the transistor parameters such as maximum current gain after passivation and the base resistance will be evaluated and compared with simulation.
|
|
| 19. |
- Ghandi, Reza, et al.
(författare)
-
Removal of Crystal Orientation Effects on the Current Gain of 4H-SiC BJTs Using Surface Passivation
- 2011
-
Ingår i: IEEE Electron Device Letters. - : IEEE. - 0741-3106 .- 1558-0563. ; 32:5, s. 596-598
-
Tidskriftsartikel (refereegranskat)abstract
- In this letter, the dependence of current gain and base resistance on crystal orientations for single-finger 4H-SiC bipolar junction transistors ( BJTs) is analyzed. Statistical evaluation techniques were also applied to study the effect of surface passivation and mobility on the performance of the devices. It is shown that BJTs with an emitter edge aligned to the [1 (2) under bar 10] direction shows a lower current gain before surface passivation and higher base resistance after contact formation compared with other investigated crystal directions. However, the devices show a similar current gain independent of the crystal orientation after surface passivation.
|
|
| 20. |
- Ghandi, Reza, et al.
(författare)
-
Surface-passivation effects on the performance of 4H-SiC BJTs
- 2011
-
Ingår i: IEEE Transactions on Electron Devices. - 0018-9383 .- 1557-9646. ; 58, s. 259-265
-
Tidskriftsartikel (refereegranskat)abstract
- In this brief, the electrical performance in terms of maximum current gain and breakdown voltage is compared experimentally and by device simulation for 4H-SiC BJTs passivated with different surface-passivation layers. Variation in bipolar junction transistor (BJT) performance has been correlated to densities of interface traps and fixed oxide charge, as evaluated through MOS capacitors. Six different methods were used to fabricate SiO2 surface passivation on BJT samples from the same wafer. The highest current gain was obtained for plasma-deposited SiO2 which was annealed in N2O ambient at 1100 °C for 3 h. Variations in breakdown voltage for different surface passivations were also found, and this was attributed to differences in fixed oxide charge that can affect the optimum dose of the high-voltage junction-termination extension (JTE). The dependence of breakdown voltage on the dose was also evaluated through nonimplanted BJTs with etched JTE.
|
|
| 21. |
- Hallén, Anders, et al.
(författare)
-
Low-Temperature Annealing of Radiation-Induced Degradation in 4H-SiC Bipolar Junction Transistors
- 2010
-
Ingår i: IEEE Electron Device Letters. - 0741-3106 .- 1558-0563. ; 31:7, s. 707-709
-
Tidskriftsartikel (refereegranskat)abstract
- Radiation hardness is tested for 4H-SiC n-p-n bipolar junction transistors designed for 1200-V breakdown voltage by implanting MeV protons and carbon ions at different doses and energies. The current gain is found to be a very sensitive parameter, and a fluence as low as 1 x 107 cm(-2) of 10 MeV C-12 can be clearly detected in the forward-output characteristics, I-C(V-CE). At this low dose, no influence of ion radiation is seen in the open-collector characteristics, I-B(V-EB), or the reverse bias leakage and breakdown properties. Moreover, by annealing the implanted devices at 420 degrees C for 30 min, a complete recovery of the electrical characteristics is accomplished.
|
|
| 22. |
- Konstantinov, A., et al.
(författare)
-
Operation of Silicon Carbide BJTs Free from Bipolar Degradation
- 2010
-
Ingår i: SILICON CARBIDE AND RELATED MATERIALS 2009, PTS 1 AND 2. ; , s. 1057-1060
-
Konferensbidrag (refereegranskat)abstract
- The mechanisms of bipolar degradation in silicon carbide BJTs are investigated and identified. Bipolar degradation occurs as result of stacking fault (SF) growth within the low-doped collector region. A stacking fault blocks vertical current transport through the collector, driving the defective region into saturation. This results in considerable drop of emitter current gain if the BJT is run at a reasonably low collector-emitter bias. The base region does not play any significant role in bipolar degradation. Long-term stress tests have shown full stability of large-area high-power BJTs under minority carrier injection conditions provided the devices are fabricated using low Basal Plane Dislocation (BPD) material. However, an approximately 20% current gain compression is observed for the first 30-60 hours of burn-in under common emitter operation, which is related to instability of surface recombination in the passive base region.
|
|
| 23. |
- Lanni, Luigia, et al.
(författare)
-
Bipolar Integrated OR-NOR Gate in 4H-SiC
- 2011
-
Ingår i: Proceedings of International Conference on Silicon Carbibe and Related Materials 2011.
-
Konferensbidrag (refereegranskat)
|
|
| 24. |
|
|
| 25. |
- Usman, Muhammad, et al.
(författare)
-
Effect of 3.0 MeV helium implantation on electrical characteristics of 4H-SiC BJTs
- 2010
-
Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T140, s. 014012-
-
Tidskriftsartikel (refereegranskat)abstract
- Degradation of 4H-SiC power bipolar junction transistors (BJTs) under the influence of a high-energy helium ion beam was studied. Epitaxially grown npn BJTs were implanted with 3.0 MeV helium in the fluence range of 10(10)-10(11) cm(-2). The devices were characterized by their current-voltage (I-V) behaviour before and after the implantation, and the results showed a clear degradation of the output characteristics of the devices. Annealing these implanted devices increased the interface traps between passivation oxide and the semiconductor, resulting in an increase of base current in the low-voltage operation range.
|
|
| 26. |
- Östling, Mikael, et al.
(författare)
-
SiC bipolar power transistors : Design and technology issues for ultimate performance
- 2010
-
Ingår i: 2010 MRS Spring Meeting. - 9781605112237 ; , s. 175-186
-
Konferensbidrag (refereegranskat)abstract
- Silicon carbide (SiC) semiconductor devices for high power are becoming more mature and are now commercially available as discrete devices. Schottky diodes have been on the market since a few years but also bipolar junction transistors (BJTs), JFETs and MOSFETs are now reaching the market. The interest is rapidly growing for these devices in high power and high temperature applications. The BJTs have low conduction losses, fast switching capability, operate in normally-off mode, have high radiation hardness, and can handle high power density.This paper will review the current state of the art in active switching device performance with special emphasis on BJTs. Device performance has been demonstrated over a wide temperature interval. A very important feature in high power switch applications is the low on-resistance of a device. Better material quality and epi processes suppress the amount of basal plane dislocations to avoid stacking fault formation generated during high current injection. This has long been a concern for bipolar SiC devices but several research reports and long term reliability measurements of pn-junctions show that the bipolar degradation problem can be solved by a fine-tuned epitaxial technique. A discussion on surface passivation control is included. Finally, an example of a power switching module is given also demonstrating the excellent paralleling capability of BJTs.
|
|
