Active solid-state devices (e.g. – transistors – solid-state diode – Regenerative type switching device
Reexamination Certificate
2002-04-05
2004-04-27
Mai, Son L. (Department: 2818)
Active solid-state devices (e.g., transistors, solid-state diode
Regenerative type switching device
C257S111000, C257S131000, C257S139000, C257S143000, C257S144000, C257S152000, C257S153000
Reexamination Certificate
active
06727526
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a thyristor having the following construction; in a body made of differently doped semiconductor material which has an electrode serving as cathode and also an electrode serving as anode, there are formed
a cathodal emitter of a first conduction type
a cathodal base of a second conduction type,
an anodal base of the first conduction type,
an anodal emitter of the second conduction type and
at least one driver stage for amplifying a control current fed into the cathodal base,
the driver stage has a further emitter of the first conduction type, which is formed in the cathodal base and is isolated from the cathodal emitter, and also a metallization layer which makes contact both with the cathodal base and with the further emitter.
A thyristor of the aforementioned type is disclosed by H. Mitlehner, J. Sack, H.-J-Schulze: “High Voltage Thyristor for HVDC Transmission and Static VAR Compensators”, Proceedings of PESC, Kyoto, 1988, S. 934, or by WO 98/34282 (97P1089). In this known thyristor, the cathodal emitter of the first conduction type is formed by an n
+
-doped region of the wafer-type body composed of semiconductor material in the form of silicon, said region adjoining a main area of said body.
The cathodal base of the second conduction type is defined by a p-doped region of the body, which region adjoins the n
+
-doped region and, together with this region, forms an np junction.
The anodal base of the first conduction type is defined by an n
−
-doped region and an n
+
-doped region of the body which adjoin one another and of which the n
−
-doped region adjoins the p-doped region of the cathodal base and, together with this region, forms a pn junction.
The anodal emitter of the second conduction type is defined by a p
+
-doped region of the body, which region, on the one hand, adjoins the n
+
-doped region of the anodal base and, together with this region, forms an np junction and, on the other hand, adjoins the main area of the body which is remote from the first main area.
Cathode short circuits are formed in the cathodal emitter of the thyristor, which cathode short circuits connect the cathodal base and the cathode to one another and ensure that, even in the event of a large dU/dt loading of a few 1000 volts/&mgr;s, the thyristor does not already trigger in an uncontrolled manner before the static breakover voltage is reached.
In order to suppress the influence of a leakage current on a transistor gain factor &agr;
pnp
of the thyristor, which factor, below the cathode of the thyristor, is defined by the cathodal base, the anodal base and the anodal emitter, with a low leakage current density, a plurality of anode short circuits are formed in the anodal emitter, which anode short circuits connect the anodal base and the anode to one another.
The further emitter of the single driver stage (“amplifying gate”) is defined by an n
+
-doped region which adjoins the first main area of the body but is spatially separate from the n
+
-doped region of the cathodal emitter and is formed in the p-doped region of the cathodal base and, together with this region, forms an np junction.
The p-doped region of the cathodal base likewise adjoins the first main area of the body laterally beside the n
+
-doped region of the further emitter. The metallization layer is applied on this first main area and makes contact both with the p-doped region of the cathodal base and with the n
+
-doped region of the further emitter.
Instead of only one such driver stage, there may be two or more of them present (see, for example, FIG. 5 of the first document mentioned above).
The control current fed into the p-doped region of the cathodal base is generated at a location beside the n
+
-doped further emitter of the driver stage at which the p-doped region of the cathodal base adjoins the first main area of the body in a manner free from the metallization layer of the driver stage.
The control current can be generated with the aid of a triggering contact and/or a light-sensitive structure which are/is formed at said location at the first main area of the body.
In particular, the thyristor is formed such that it is rotationally symmetrical with regard to an axis perpendicular to the two main areas of the body. The location for feeding in the control current lies in a central partial region—surrounding the axis—of the first main area of the wafer-type body.
The driver stage is arranged radially with respect to the axis between the central partial region and the cathode of the thyristor.
Moreover, the known thyristor is an asymmetrical thyristor having a stop zone of the first conduction type which is formed by the n
+
-doped region of the anodal base. This stop zone has the effect that the breakover triggering of the thyristor is constrained not by an avalanche breakdown (avalanche effect) but rather by the so-called “punch-through” effect, i.e. by the expansion of the space charge zone of the reverse-biased pn junction between the cathodal base and the anodal base as far as the forward-biased np junction between the anodal base and the anodal emitter in the body made of semiconductor material.
The asymmetrical thyristor disclosed in the first document mentioned above has the special feature that it is connected in series with a diode and, together with this diode, forms a tandem thyristor which is an alternative to a tandem thyristor comprising two symmetrical thyristors connected in series.
The thyristor disclosed by WO 98/34282 has the special feature that the n
+
-doped stop zone is doped more weakly in a region lying below the central partial region than in the laterally adjoining region. This special feature has the advantage that the breakover voltage of the thyristor does not depend on the temperature or depends on the temperature only to an insignificant extent. In this case, moreover, there is the advantage that a stop zone which has a comparatively more weakly doped region besides a more highly doped region can be fabricated simply and cost-effectively, for example by means of “masked” implantation.
H.-J. Schulze, M. Ruff, B. Baur, F. Pfirsch, H. Kabza, U. Kellner, P. Voss: “Light Triggered 8 kV Thyristor with a New Type of Integrated Breakover Diode”, Proceedings of PCIM, Maui, 1996, pages 465-472, disclose realizing, in symmetrically blocking thyristors, a higher carrier lifetime in an amplifying gate structure situated in the central region of the thyristor than in the region below the cathode of the first main area of the body made of semiconductor material.
The invention is based on the object of providing a thyristor which can be loaded with a voltage surge within the recovery time without, in the process, the thyristor being destroyed by current splitting which usually occurs in the region of the body made of semiconductor material which lies below the cathode of the thyristor.
SUMMARY OF THE INVENTION
This solution provides a thyristor having the following construction: in a body made of differently doped semiconductor material which has an electrode serving as cathode and also an electrode serving as anode, there are formed
a cathodal emitter of a first conduction type
a cathodal base of a second conduction type,
an anodal base of the first conduction type,
an anodal emitter of the second conduction type and
at least one driver stage for amplifying a control current fed into the cathodal base,
the driver stage has a further emitter of the first conduction type, which is formed in the cathodal base and is isolated from the cathodal emitter, and also a metallization layer which makes contact both with the cathodal base and with the further emitter,
a transistor gain factor &agr;′
npn
of the at least one driver stage, which factor is defined, below the metallization layer of said driver stage, by the further emitter, the cathodal base and the anodal base, is greater than a transistor gain factor &agr;
npn
of the thyristor, which factor is defined, below the cat
Niedernostheide Franz Josef
Schulze Hans-Joachim
Feiereisen Henry M.
Mai Son L.
Siemens Aktiengesellschaft
Tran Mai-Huong
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