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SiC VJFETs are excellent candidates for reliable high-power/temperature switching as they only use pn junctions in the active device area where the high-electric fields occur. VJFETs do not suffer from forward voltage degradation, exhibit excellent short-circuit performance, and operate at 300◦C. 0.19 cm2 1200 V normally-on and 0.15 cm2 low-voltage normally-off VJFETs were fabricated.
The 1200-V VJFET outputs 53 A with a forward drain voltage drop of 2V and a specific onstate resistance of 5.4mΩcm2. The low-voltage VJFET outputs 28 A with a forward drain voltage drop of 3.3 V and a specific onstate resistance of 15mΩcm2.
The 1200-V VJFET outputs 53 A with a forward drain voltage drop of 2V and a specific onstate resistance of 5.4mΩcm2. The low-voltage VJFET outputs 28 A with a forward drain voltage drop of 3.3 V and a specific onstate resistance of 15mΩcm2.
The 1200-V SiC VJFET was connected in the cascode configuration with two Si MOSFETs and with a low-voltage SiC VJFET to form normally-off power switches. At a forward drain voltage drop of 2.2V, the SiC/MOSFETs cascode switch outputs 33 A. The all-SiC cascode switch outputs 24 A at a voltage drop of 4.7 V.
INTRODUCTION
Wideband gap semiconductors like silicon carbide (SiC) and the III-IV nitrides are currently being developed for high-power/temperature applications. Silicon carbide (SiC)is ideally suited for power-conditioning applications due to its high saturated drift velocity, its mechanical strength, its excellent thermal conductivity, and its high critical field strength. For power devices, the tenfold increase in critical field strength of SiC relative to Si allows high-voltage blocking layers to be fabricated significantly thinner than those of comparable Si devices. This reduces device onstate resistance, and the associated conduction and switching losses, while maintaining the same high-voltage blocking capability. Figure 1 shows the theoretical specific onstate resistance of blocking regions designed for certain breakdown voltages in Si and 4H-SiC, under optimum punchthrough conditions [1].
The specific onstate resistance of 4H-SiC is approximately 400 times lower than that of Si at a given breakdown voltage. This allows for high current operation at relatively low-forward voltage drop. In addition, the wide band gap of SiC allows operation at high temperatures where conventional Si devices fail. Forward voltage drop versus current density of Northrop Grumman’s all-SiC vertical junction field effect transistor- (VJFET-) based cascode switch, and those of commercial Si MOSFET, Si IGBT, and Si CoolMOS switches are shown in Figure 2. The SiC switch has a lower voltage drop at a given current density, even at the elevated temperature of 150◦C. The low-loss and the high-temperature operational capabilities of SiC devices can potentially eliminate the costly cooling systems present in today’s Si based power electronics. Presently, several SiC devices are being developed for 600 V (1200V rating) power switching applications.
SiC MOS-based devices show promise as normally-off power switches but suffer from low-MOS mobility and native oxide issues that limit reliable operation to below 175◦C [2]. Furthermore, several temperature-dependant factors result in a decrease of the SiC MOSFET threshold voltage with temperature. This may lead to unwanted MOSFET turnon at temperatures over 200◦C. The SiC bipolar junction transistor is another normallyoff power switching candidate. However, as with all SiC bipolar devices, its long term performance deteriorates due to forward bias voltage degradation [3]. Also, the BJT is a current controlled device that can require substantial base drive current [4].
The SiC VJFET is a very promising candidate for highpower/temperature switching as it only uses pn junctions in the active device area, where the high-electric fields
occur, and can therefore fully exploit the high-temperature properties of SiC in a gate voltage controlled switching device. VJFETs for high voltage applications are typically normally-on devices, and an all-SiC normally-off power switch can be implemented by combining a high-voltage normally-on VJFET with a low-voltage normally-off VJFET in the cascode configuration.
In this paper, we review the reliability and high temperature characteristics of 1.25 × 10−3 cm2 area unipolar ionimplanted SiC VJFETs. Subsequently, we present the forward current and locking voltage characteristics of 0.19 cm2 area 1200 V normally-on and 0.15 cm2 area low-voltage normally-off SiC VJFETs. The 0.19 cm2 1200-V VJFETs have been connected in the cascode configuration with SiMOSFETs and 0.15 cm2 low-voltage SiC VJFETs to form
normally-off power switches.
CONCLUSION
The SiC VJFET is a very promising candidate for reliable high-power/temperature switching as it only uses pn junctions in the active device area where the high-electric fields occur. VJFETs do not suffer from forward voltagedegradation, and exhibit holdoff times higher than those
of their Si counterparts in short circuit testing. The VJFET based all-SiC normally-off cascode switch’s internal diode has exhibited a very fast 100 nanoseconds reverse recovery time, eliminating the need for antiparallel diodes in power switching circuits. VJFETs were successfully operated at 300◦C junction temperature. The measured reduction in onstate current is in good agreement with the theoretical reduction in SiC electron mobility.
To meet the current handling requirements of modern power conditioning systems, 1200 V normally-on VJFETs of 0.19 cm2 and low-voltage normally-off VJFETs of 0.15 cm2 areas were fabricated. At a gate bias of 2.5V, the 1200-V VJFET outputs 53 A with a forward drain voltage drop of 2V and a specific onstate resistance of 5.4mΩcm2. The lowvoltage VJFET’s drain current is 28 A, at a gate bias of 2.5V, with a forward drain voltage drop of 3.3V and a specific onstate resistance of 15mΩcm2.
A 1200-V SiC VJFET was connected in the cascode configuration with two commercial Si MOSFETs to form a normally-off power switch. At aMOSFET gate-to-source bias of 15V, the cascode switch outputs 33 A at a forward drain voltage drop of 2.2V. To fully exploit the high-temperature capability of SiC in a normally-off power switch, a 0.15 cm2 low-voltage normally-off SiC VJFET was connected with a 0.19cm2 1200-V normally-on VJFET in the cascode configuration. At a forward drain voltage drop of 4.7V, the all-SiC cascode switch outputs 24 A at 2.5V cascode gate bias. Operating the 1200 V normally-on SiC VJFET as a switch in an inherently safe gate-drive circuit eliminates the need for a low-voltage normally-off SiC VJFET cascode component, and enables high-current/high-gain operation with low voltage drop and low onstate resistance.
REFERENCES
[1] J. A. Cooper Jr., M. R. Melloch, R. Singh, A. Agarwal, and J. W. Palmour, “Status and prospects for SiC power MOSFETs,” IEEE Transactions on Electron Devices, vol. 49, no. 4, pp. 658– 664, 2002.
[2] S. Krishnaswami, M. Das, B. Hull, et al., “Gate oxide reliability of 4H-SiC MOS devices,” in Proceedings of the 43rd Annual International Reliability Physics Symposium (IRPS ’05), pp.
592–593, San Jose, Calif, USA, April 2005.
[3] A. Agarwal, S. Krishnaswami, J. Richmond, et al., “Influence of basal plane dislocation induced stacking faults on the current gain in SiC BJTs,” Materials Science Forum, vol. 527–529, part 2, pp. 1409–1412, 2006.
[4] S. Krishnaswami, A. Agarwal, S.-H. Ryu, et al., “1000-V, 30- A 4H-SiC BJTs with high current gain,” IEEE Electron Device Letters, vol. 26, no. 3, pp. 175–177, 2005.
[5] V. Veliadis, M. McCoy, T. McNutt, et al., “Fabrication of a robust high-performance floating guard ring edge termination for power silicon carbide vertical junction field effecttransistors,” in Proceedings of the International Conference on Compound Semiconductor Manufacturing Technology (CS MANTECH ’07), pp. 217–220, Hilton Austin, Tex, USA, May 2007.
[6] V. Veliadis, L.-S. Chen, E. Stewart, et al., “2.1 mΩcm2, 1.6 kV 4H-silicon carbide VJFET for power applications,” in Proceedings of the International Semiconductor Device Research Symposium (ISDRS ’005), pp. 166–167, Bethesda, Md, USA, December 2005.
[7] V. Veliadis, L. S. Chen, M. McCoy, et al., “High-yield silicon carbide vertical junction field effect transistor manufacturing for RF and power applications,” in Proceedings of the International Conference on Compound Semiconductor Manufacturing Technology (CS MANTECH ’06), pp. 219–222, Vancouver, Canada, April 2006.
[8] V. Veliadis, M. McCoy, L. S. Chen, et al., “Silicon carbide vertical junction field effect transistors for RF applications: processing, DC testing, and yields,” in Proceedings of the IEEE
Lester Eastman Conference on High Performance Devices, p. 77, Ithaca, NY, USA, August 2006.
[9] V. Veliadis, T. McNutt, E. Stewart, M. McCoy, H. Hearne, and C. Clarke, “Recent progress in 300◦C silicon carbide JFET technology for power conditioning in electric vehicles,” in Proceedings of the 7th International All Electric Combat Vehicle Conference (AECV ’07), Stockholm, Sweden, June 2007, paper FCXST-07060711-545141-1.
[10] T. McNutt, V. Veliadis, E. Stewart, et al., “Silicon carbide JFET cascode switch for power conditioning applications,” in Proceedings of the IEEE Vehicle Power and Propulsion Conference (VPPC ’05), pp. 574–581, Chicago, Ill, USA, September 2005.
[11] T. McNutt, J. Reichl, H. Hearne, et al., “Demonstration of high-voltage SiC VJFET cascode in a half-bridge inverter,” Materials Science Forum, vol. 556-557, pp. 979–982, 2007.
[12] P. Friedrichs, “Charge controlled silicon carbide switching devices,” in Materials Research Society Symposium Proceedings (MRS ’04), vol. 815, pp. 255–266, San Francisco, Calif, USA,
May 2004, paper J3.1.
[13] H. F. Hamann, A. Weger, J. A. Lacey, et al., “Hotspot-limited microprocessors: direct temperature and power distribution measurements,” IEEE Journal of Solid-State Circuits, vol. 42, no. 1, pp. 56–64, 2007.
[14] R. Kelley and M. S. Mazzola, “SiC JFET gate driver design for use in DC/DC converters,” in Proceedings of the 21st Annual IEEE Applied Power Electronics Conference and Exposition
(APEC ’06), vol. 2006, pp. 179–182, Dallas, Tex, USA, March 2006.
[15] A. B. Lostetter, Arkansas Power Electronics International Inc., private communication, 2007.
[16] B. Weis, M. Braun, and P. Friedrichs, “Turn-off and short circuit behaviour of 4H SiC JFETs,” in Proceedings of the 36th IAS Annual Meeting on Industry Applications Conference, vol. 1, pp. 365–369, Chicago, Ill, USA, September-October 2001.
INTRODUCTION
Wideband gap semiconductors like silicon carbide (SiC) and the III-IV nitrides are currently being developed for high-power/temperature applications. Silicon carbide (SiC)is ideally suited for power-conditioning applications due to its high saturated drift velocity, its mechanical strength, its excellent thermal conductivity, and its high critical field strength. For power devices, the tenfold increase in critical field strength of SiC relative to Si allows high-voltage blocking layers to be fabricated significantly thinner than those of comparable Si devices. This reduces device onstate resistance, and the associated conduction and switching losses, while maintaining the same high-voltage blocking capability. Figure 1 shows the theoretical specific onstate resistance of blocking regions designed for certain breakdown voltages in Si and 4H-SiC, under optimum punchthrough conditions [1].
The specific onstate resistance of 4H-SiC is approximately 400 times lower than that of Si at a given breakdown voltage. This allows for high current operation at relatively low-forward voltage drop. In addition, the wide band gap of SiC allows operation at high temperatures where conventional Si devices fail. Forward voltage drop versus current density of Northrop Grumman’s all-SiC vertical junction field effect transistor- (VJFET-) based cascode switch, and those of commercial Si MOSFET, Si IGBT, and Si CoolMOS switches are shown in Figure 2. The SiC switch has a lower voltage drop at a given current density, even at the elevated temperature of 150◦C. The low-loss and the high-temperature operational capabilities of SiC devices can potentially eliminate the costly cooling systems present in today’s Si based power electronics. Presently, several SiC devices are being developed for 600 V (1200V rating) power switching applications.
SiC MOS-based devices show promise as normally-off power switches but suffer from low-MOS mobility and native oxide issues that limit reliable operation to below 175◦C [2]. Furthermore, several temperature-dependant factors result in a decrease of the SiC MOSFET threshold voltage with temperature. This may lead to unwanted MOSFET turnon at temperatures over 200◦C. The SiC bipolar junction transistor is another normallyoff power switching candidate. However, as with all SiC bipolar devices, its long term performance deteriorates due to forward bias voltage degradation [3]. Also, the BJT is a current controlled device that can require substantial base drive current [4].
The SiC VJFET is a very promising candidate for highpower/temperature switching as it only uses pn junctions in the active device area, where the high-electric fields
occur, and can therefore fully exploit the high-temperature properties of SiC in a gate voltage controlled switching device. VJFETs for high voltage applications are typically normally-on devices, and an all-SiC normally-off power switch can be implemented by combining a high-voltage normally-on VJFET with a low-voltage normally-off VJFET in the cascode configuration.
In this paper, we review the reliability and high temperature characteristics of 1.25 × 10−3 cm2 area unipolar ionimplanted SiC VJFETs. Subsequently, we present the forward current and locking voltage characteristics of 0.19 cm2 area 1200 V normally-on and 0.15 cm2 area low-voltage normally-off SiC VJFETs. The 0.19 cm2 1200-V VJFETs have been connected in the cascode configuration with SiMOSFETs and 0.15 cm2 low-voltage SiC VJFETs to form
normally-off power switches.
CONCLUSION
The SiC VJFET is a very promising candidate for reliable high-power/temperature switching as it only uses pn junctions in the active device area where the high-electric fields occur. VJFETs do not suffer from forward voltagedegradation, and exhibit holdoff times higher than those
of their Si counterparts in short circuit testing. The VJFET based all-SiC normally-off cascode switch’s internal diode has exhibited a very fast 100 nanoseconds reverse recovery time, eliminating the need for antiparallel diodes in power switching circuits. VJFETs were successfully operated at 300◦C junction temperature. The measured reduction in onstate current is in good agreement with the theoretical reduction in SiC electron mobility.
To meet the current handling requirements of modern power conditioning systems, 1200 V normally-on VJFETs of 0.19 cm2 and low-voltage normally-off VJFETs of 0.15 cm2 areas were fabricated. At a gate bias of 2.5V, the 1200-V VJFET outputs 53 A with a forward drain voltage drop of 2V and a specific onstate resistance of 5.4mΩcm2. The lowvoltage VJFET’s drain current is 28 A, at a gate bias of 2.5V, with a forward drain voltage drop of 3.3V and a specific onstate resistance of 15mΩcm2.
A 1200-V SiC VJFET was connected in the cascode configuration with two commercial Si MOSFETs to form a normally-off power switch. At aMOSFET gate-to-source bias of 15V, the cascode switch outputs 33 A at a forward drain voltage drop of 2.2V. To fully exploit the high-temperature capability of SiC in a normally-off power switch, a 0.15 cm2 low-voltage normally-off SiC VJFET was connected with a 0.19cm2 1200-V normally-on VJFET in the cascode configuration. At a forward drain voltage drop of 4.7V, the all-SiC cascode switch outputs 24 A at 2.5V cascode gate bias. Operating the 1200 V normally-on SiC VJFET as a switch in an inherently safe gate-drive circuit eliminates the need for a low-voltage normally-off SiC VJFET cascode component, and enables high-current/high-gain operation with low voltage drop and low onstate resistance.
REFERENCES
[1] J. A. Cooper Jr., M. R. Melloch, R. Singh, A. Agarwal, and J. W. Palmour, “Status and prospects for SiC power MOSFETs,” IEEE Transactions on Electron Devices, vol. 49, no. 4, pp. 658– 664, 2002.
[2] S. Krishnaswami, M. Das, B. Hull, et al., “Gate oxide reliability of 4H-SiC MOS devices,” in Proceedings of the 43rd Annual International Reliability Physics Symposium (IRPS ’05), pp.
592–593, San Jose, Calif, USA, April 2005.
[3] A. Agarwal, S. Krishnaswami, J. Richmond, et al., “Influence of basal plane dislocation induced stacking faults on the current gain in SiC BJTs,” Materials Science Forum, vol. 527–529, part 2, pp. 1409–1412, 2006.
[4] S. Krishnaswami, A. Agarwal, S.-H. Ryu, et al., “1000-V, 30- A 4H-SiC BJTs with high current gain,” IEEE Electron Device Letters, vol. 26, no. 3, pp. 175–177, 2005.
[5] V. Veliadis, M. McCoy, T. McNutt, et al., “Fabrication of a robust high-performance floating guard ring edge termination for power silicon carbide vertical junction field effecttransistors,” in Proceedings of the International Conference on Compound Semiconductor Manufacturing Technology (CS MANTECH ’07), pp. 217–220, Hilton Austin, Tex, USA, May 2007.
[6] V. Veliadis, L.-S. Chen, E. Stewart, et al., “2.1 mΩcm2, 1.6 kV 4H-silicon carbide VJFET for power applications,” in Proceedings of the International Semiconductor Device Research Symposium (ISDRS ’005), pp. 166–167, Bethesda, Md, USA, December 2005.
[7] V. Veliadis, L. S. Chen, M. McCoy, et al., “High-yield silicon carbide vertical junction field effect transistor manufacturing for RF and power applications,” in Proceedings of the International Conference on Compound Semiconductor Manufacturing Technology (CS MANTECH ’06), pp. 219–222, Vancouver, Canada, April 2006.
[8] V. Veliadis, M. McCoy, L. S. Chen, et al., “Silicon carbide vertical junction field effect transistors for RF applications: processing, DC testing, and yields,” in Proceedings of the IEEE
Lester Eastman Conference on High Performance Devices, p. 77, Ithaca, NY, USA, August 2006.
[9] V. Veliadis, T. McNutt, E. Stewart, M. McCoy, H. Hearne, and C. Clarke, “Recent progress in 300◦C silicon carbide JFET technology for power conditioning in electric vehicles,” in Proceedings of the 7th International All Electric Combat Vehicle Conference (AECV ’07), Stockholm, Sweden, June 2007, paper FCXST-07060711-545141-1.
[10] T. McNutt, V. Veliadis, E. Stewart, et al., “Silicon carbide JFET cascode switch for power conditioning applications,” in Proceedings of the IEEE Vehicle Power and Propulsion Conference (VPPC ’05), pp. 574–581, Chicago, Ill, USA, September 2005.
[11] T. McNutt, J. Reichl, H. Hearne, et al., “Demonstration of high-voltage SiC VJFET cascode in a half-bridge inverter,” Materials Science Forum, vol. 556-557, pp. 979–982, 2007.
[12] P. Friedrichs, “Charge controlled silicon carbide switching devices,” in Materials Research Society Symposium Proceedings (MRS ’04), vol. 815, pp. 255–266, San Francisco, Calif, USA,
May 2004, paper J3.1.
[13] H. F. Hamann, A. Weger, J. A. Lacey, et al., “Hotspot-limited microprocessors: direct temperature and power distribution measurements,” IEEE Journal of Solid-State Circuits, vol. 42, no. 1, pp. 56–64, 2007.
[14] R. Kelley and M. S. Mazzola, “SiC JFET gate driver design for use in DC/DC converters,” in Proceedings of the 21st Annual IEEE Applied Power Electronics Conference and Exposition
(APEC ’06), vol. 2006, pp. 179–182, Dallas, Tex, USA, March 2006.
[15] A. B. Lostetter, Arkansas Power Electronics International Inc., private communication, 2007.
[16] B. Weis, M. Braun, and P. Friedrichs, “Turn-off and short circuit behaviour of 4H SiC JFETs,” in Proceedings of the 36th IAS Annual Meeting on Industry Applications Conference, vol. 1, pp. 365–369, Chicago, Ill, USA, September-October 2001.
By : Victor Veliadis, Ty McNutt, Megan Snook, Harold Hearne, Paul Potyraj,
Jeremy Junghans, and Charles Scozzie2
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