Active solid-state devices (e.g. – transistors – solid-state diode – Regenerative type switching device – With means to control triggering
Patent
1998-11-20
2000-05-23
Guay, John
Active solid-state devices (e.g., transistors, solid-state diode
Regenerative type switching device
With means to control triggering
257157, 257158, 257166, 257115, H01L 2974
Patent
active
060668644
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a thyristor and specifically to a light-triggerable power thyristor.
A thyristor already ignites before the static trigger voltage U.sub.BO is reached when the time change dU/dt of the voltage U applied between its terminals exceeds a specific maximum value for the respective thyristor. This misignition that may lead to the destruction of the thyristor under certain circumstances is caused by the build-up of the space-charge zone at the p-base
-base junction and the shift current I.sub.d =C.sub.d dU/dt (C.sub.d : voltage-dependent space charge capacitance of the pn-junction) resulting therefrom that intensifies the blocking current. The dU/dt strength of a thyristor can be substantially improved with the assistance of cathode-emitter shorts, since a majority of the capacitative shift current I.sub.d in the semiconductor body no longer flows over the pn-junction of the cathode side but directly from the base to the cathode. The critical value of the voltage steepness of correspondingly constructed thyristors typically amounts to several 1000 V/.mu.s.
2. Description of Related Art
Power thyristors must be provided with emitter shorts in order to meet the demands with respect to the dU/dt loadability. Emitter shorts, however, divert a part of the gate current directly to the cathode, which has a disadvantageous effect on the trigger sensitivity of the thyristor. Among the things proposed for solving this problem is to optimize the structure of the gate, to compensate the change in potential of the base of the cathode side caused by the capacitative current I.sub.d and to increase the optical trigger sensitivity of the thyristor with a plurality of "amplifying gate" stages connected following one another (see, for example, the reference to Paul D. Taylor, "Thyristor Design and Realization", John Wiley & Sons (1987), pp. 133-141, and the reference IEEE Transactions on Electron Devices, Vol. ED-30, No. 7, July 1983, pp. 816-824.
SUMMARY OF THE INVENTION
The subject matter os the invention is, in particular, a light-triggerable and BOD-(break-over diode) protected thyristor with integrated dU/dt protection. The thyristor should be constructed such that, given a high dU/dt load in trigger direction, it does not ignite in uncontrolled fashion in the region of the cathode surface or of the edge termination. A thyristor with the features recited in patent claim 1 has this property. The dependent claims are directed to advantageous developments and improvements of the thyristor.
Dependent on the type of ignition (electrical or optical drive, dU/dt triggering), the trigger behavior of a thyristor is decisively influenced by the sheet resistivity of the base of the cathode side. The invention utilizes this property in order to displace the trigger event caused by too high a dU/dt load into the central region of the thyristor. Since the volume affected by the triggering always lies within the region limited by the first auxiliary thyristor, the plasma--as in the case of a controlled ignition--can propagate large-area and uniformly in radial direction without having the current density reach critical values.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is explained below with reference to the drawing. Show are:
FIG. 1 shows the ignition structure of a BOD-protected, light-triggerable thyristor in crossection;
FIG. 2 is a partially cut away perspective view which shows the BOD structure of the thyristor in crossection;
FIGS. 3a, 3b, 3c, and 3d, are side sectional views of the semiconductor body of the thyristor after implementation of some steps of the method for manufacturing an annular zone of increased resistance in the base of the cathode side.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The light-triggerable thyristor that is shown in crossection in FIG. 1 and is equipped with a BOD (Breakover diode) structure has a rotationally balanced structure with respect to the axis 4 residing perpendicular on the
REFERENCES:
patent: 4908687 (1990-03-01), Temple
patent: 5204273 (1993-04-01), Kuhnert et al.
European Patent Office, Patent Abstracts of Japan, Publication No. 59220970, Publication Date Dec. 12, 1984.
European Patent Office, Patent Abstracts of Japan, Publication No. 07122728, Publication Date Dec. 5, 1995.
Thyristor Design and Realization, John Wiley & Sons, Paul D. Taylor, pp. 151-153 (1987).
IEEE Transactions on Electron Devices, vol. Ed 30, No. 7, Jul. 1983, "Controlled Turn-On Thyristors", Victor A.K. Temple.
Pfirsch Frank
Ruff Martin
Schulze Hans-Joachim
Guay John
Siemens Aktiengesellschaft
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