Active solid-state devices (e.g. – transistors – solid-state diode – Specified wide band gap semiconductor material other than... – Diamond or silicon carbide
Reexamination Certificate
2000-02-08
2004-03-09
Nadav, Ori (Department: 2811)
Active solid-state devices (e.g., transistors, solid-state diode
Specified wide band gap semiconductor material other than...
Diamond or silicon carbide
C257S147000, C257S148000
Reexamination Certificate
active
06703642
ABSTRACT:
This invention relates to an improvement in the design of high power, high temperature switches, more specifically, SiC gate turn off (GTO) thyristors. Conventional SiC GTO thyristors typically have a drift region made of p-type rather than n-type material adjacent to an n-type region with gate contacts. Conventional SiC GTO thyristor structures also typically have a thin highly doped p-type buffer layer below the relatively thick, low level p-type drift region. This is known as an asymmetrical GTO (gate turn-off) thyristor structure. Thyristors typically use complementary dopants for the drift region and the gated base region to create a pn junction between the two regions (i.e., if the drift region is p-type then the gated base region is n-type and vice versa.)
Examples of various conventional SiC GTO thyristors can be found in U.S. Pat. No. 5,831,289 to A. K. Agarwal, entitled “Silicon carbide gate turn-off thyristor arrangement;” U.S. Pat. No. 5,539,217 to J. A. Edmond, J. W. Palmour entitled, “Silicon carbide thyristor;” M. E. Levinshtein, J. W. Palmour, S. L. Rumyanetsev, and R. Singh, “Turnon process in 4H-SiC Thyristors,”
IEEE Trans. Elect. Dev
. Vol 44, p. 1177, 1997; K. Xie, J. H. Zhao, J. R. Flemish, T. Burke, W. R. Buchwald, G. Lorenzo, and H. Singh, “A high current and high temperature 6H-SiC thyristor,”
IEEE Elect. Dev. Lett
., vol. 17, p 142, 1996; P. B. Shah and K. A. Jones, “Two-dimensional numerical investigation of the impact of material-parameter uncertainty on the steady-state performnance of passivated 4H-SiC thyristors,”
J Appl. Phys
., vol. 84, p. 4625, 1998; J. B. Casady, A. K. Agarwal, S. Seshadri, R. R. Siergiej, L. B. Rowland, M. F. Macmillan, D. C. Sheridan, P. A. Sanger, and C. D. Brandt., “4H SiC power devices for use in power electronic motor control,”
Solid State Electronics
, vol. 42, p. 2165, 1998; and A. K. Agarwal, J. B. Casady, L. B. Rowland, S. Seshadri, R. R. Siergiej, W. F. Valek, and C. D. Brandt, “700 V Asymmetrical 4H-SiC Gate Turn-Off Thyristors (GTO),
IEEE Elect. Dev. Lett
., vol. 18, p. 518, 1997.
BACKGROUND
Silicon GTO thyristors have been commercially available since the 1960s. However they are not able to operate at the high temperatures that silicon carbide GTO thyristors can. Also silicon carbide GTO thyristors should be able to block larger voltages in the off-state, and conduct higher current densities in the on state than silicon GTO thyristors. These are the reasons for making GTO thyristors out of silicon carbide. However, because of material issues, the optimum structure for silicon GTO thyristors cannot be used for silicon carbide GTO thyristors . Thus, new designs are needed.
SiC GTO thyristors have only recently come of age because of the difficulty in producing good SiC. They are, for the most part, still only being used experimentally. A very intense effort is, however, underway in research laboratories throughout the world to improve the quality of SiC and the performance of SiC GTO thyristors. Ordinary silicon GTO thyristors are widely used in high power conditioning circuits, in high voltage DC systems, and in traction circuits. Other applications include motor control, power factor control, and other power conditioning circuits. Such systems are finding increased military applications and will be found in future electric or hybrid electric tanks, electric helicopters, and other vehicles used by the Army.
A thyristor is made up of layers of alternately doped n-type and p-type material. N-type and p-type refer to the majority carriers that are present in the region. In an n-type region “electrons” are the majority carriers of charge, and in a p-type region “holes” (the absence of electrons) are the majority carriers of charge. To make a region n-type, additional nitrogen atoms or “impurities” (donors, N
D
) are typically added to the SiC crystal. To make a region p-type, aluminum impurities (acceptors, N
A
) are typically added to the SiC crystal. The alternating semiconductor layers of the thyristor, in effect, make up two three-layer combinations where each is equivalent to a bipolar junction transistor. When the sum of the forward current gain across the two three layer combinations is greater than one, the thyristor will latch on and current will flow from anode to cathode. The thyristor will stay on until the anode to cathode current is interrupted.
The GTO thyristor has been a particularly successful design since it overcomes the problem of switching off anode to cathode current. A GTO thyristor can be switched on by a gate current of one polarity and switched off by a gate current of the opposite polarity. Known SiC GTO thyristors, are multi-layer pnpn devices. They have limited turn-off gain and turn-off speed and voltage blocking performance is limited as well.
OBJECTS OF THE INVENTION AND SUMMARY
Accordingly, it is a primary object of the present invention to provide a SiC GTO thyristor that has improved performance characteristics such as turn-off gain and turn off speed and voltage blocking and at the same time be highly reliable and inexpensive to manufacture and produce.
The foregoing objects are achieved, at least in part by a silicon carbide gate-turn-off thyristor that includes a p-type anode region, a n-type gated base region positioned beneath the anode region, a n-type drift region positioned beneath the gated base region and doped to a lower concentration of donors than that of the gated base region, a p-type buffer region positioned beneath the n-type drift region and doped with acceptors to a concentration whose magnitude lies between the doping concentration of the anode region and the drift region, and an n-type substrate positioned beneath the drift region. In another aspect of the invention of this application, a silicon or silicon carbide gate-turn-off thyristor includes a GTO thyristor structure with a thick buffer layer having a high, free-carrier recombination rate.
REFERENCES:
patent: 5132767 (1992-07-01), Ogura et al.
patent: 5831289 (1998-11-01), Agarwal
patent: 6274892 (2001-08-01), Kub et al.
patent: 4-130773 (1992-05-01), None
4H-SiC Gate Turn-Off Thyristor Designs for Very High Power Control, P.B. Shad, B.R. Geil, K.A. Jones, T.E. Griffin & M.A. Derenge International Conference on Silicon Carbide and Related Materials —99.
two-dimensional Numerical Investigation of the Impact of Material-Parameter Uncertainty on the Steady-State Performance of Passivated 4H-SiC Thyristors, Journal of Applied Physics, vol. 84, No. 9, Oct. 15, 1998.
Punchthrough Type GTO with Buffer Layer and Homogeneous Low Efficiency Anode Structure, S.Eicher, F. Bauer, A. Weber, H.R. Zeller and W. Fichtner, IEEE 1996.
4H-SIC Power Devices For Use In Power Electronic Motor Control, J.B. Casady, A.K. Agarwal, S. Seshadri, R.R. Siergielj, L. B. Rowland, M.F. MacMilland, D.C. Sheridan & P.A. Sanger, Solid-State Electronics, vol. 42, No. 12, pp. 2165-2176, 1998.
Turn-On Process in 4H-SiC Thyristors, IEEE Transactions on Electro Devices, vol. 44 No. 7/97, Michael E. Levinshtein, John W. Palmour, Sergey L. Rumyanetsev & Ranbir Singh.
Design Considerations for p-I-n Thyristor Structures, IEEE Transactions on Power Electronics, vol. 7 No. 2, 4/92, Ranadeep Dutta & Allen Rothwarf.
700-V Asymmetrical 4H-SiC Gate Turn-Off Thyristors (GTO's), A.K. Agarwal, Jeffrey B. Casady, L. B. Rowland, S. Seshadri, R.R. Siegiej, W.F. Valek & C.D. Brandt, IEEE vol. 18 No. 11 11/97.
Characterization of 4H-SiC Gate Turn-Off Thyristor, Lihui Cao, Binghui Li, Jianh. Zhao, Solid-State Electronics 44 (2000) pp 347-352.
Kelly Mark D.
Nadav Ori
Stolarun Edward L.
The United States of America as represented by the Secretary of
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