Active solid-state devices (e.g. – transistors – solid-state diode – Regenerative type switching device
Reexamination Certificate
1999-07-22
2001-08-07
Abraham, Fetsum (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Regenerative type switching device
C257S139000, C257S143000, C257S144000, C257S147000, C257S149000, C257S152000, C257S153000
Reexamination Certificate
active
06271545
ABSTRACT:
BACKGROUND OF THE INVENTION
Both the blocking voltage as well as the sweep voltage (blocking voltage after which the thyristor switches into the conductive condition) of a thyristor exhibit a pronounced temperature behavior. Thus, the blocking and the sweep voltage initially continuously increase with the temperature, reach a maximum, in order to ultimately drop to comparatively low values. Whereas the influence of the positive temperature coefficient of the avalanche coefficients characterizing the electron multiplication by impact ionization predominates at low and moderate temperatures, the drop of the blocking and sweep voltage at higher temperatures T≧100° C. can be attributed to the dominance of the positive temperature coefficient of the transistor current gain &agr;
pnp
as a result of the greatly increasing blocking current. The temperature dependency of the blocking and sweep voltage has an especially disturbing influence in highly inhibiting thyristors that exhibit a protection against overhead ignition integrated in the semiconductor body. Given these thyristors, the blocking and the sweep voltage can change by up to 15% in the relevant temperature range (5° C.-120° C.). For example, the sweep voltage thus rises from U
BO
=8.0 kV to values U
BO
≈9.2 kV when the thyristor heats from T=23° C. to T=90° C. during operation.
The user must take this effect into account with a more complicated wiring of the thyristor. The manufacturer of the component, by contrast, is compelled to keep the scatter of the parameters (basic doping of the Si substrate, dopant profiles, contour of the edge termination, etc.) that influence the blocking or respectively, sweep voltage extremely low. The product becomes substantially more expensive due to the high technological outlay given simultaneously reduced yield that accompanies this.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an asymmetrical thyristor whose sweep voltage is not dependent on the temperature or only insignificantly dependent on the temperature. This is achieved by a lateral non-uniform distribution of the dopant in the stop zone of the anode-side base. A stop zone having a comparatively lightly doped central region and a more highly doped outside region can be simply and cost-beneficially manufactured (“masked” implementation).
In general terms the present invention is an asymmetrical thyristor having a semiconductor body provided with a first electrode serving as cathode and with a second electrode serving as anode, whereby the semiconductor body has a plurality of differently doped regions. The doping and position of the regions are prescribed such that the regions form a cathode-side emitter of a first conductivity type, a cathode-side base of a second conductivity type, an anode-side base of the first conductivity type and an anode-side emitter of the second conductivity type. A stop zone of the first conductivity type is located in the anode-side base. The stop zone has a central region lying under a trigger contact or under a light-sensitive structure and a region laterally adjoining thereto. The stop zone is more lightly doped in the central region than in the laterally adjoining region. The anode-side emitter is provided with anode shorts.
Advantageous developments of the present invention are as follows.
The doping of the central region and of the laterally adjoining region of the stop zone are selected such that the space charge zone of the p-junction separating the cathode-side and the anode-side base reaches the anode-side pn-junction only in the central region of the semiconductor body given a predetermined value of the difference between cathode and anode potential.
The metallization arranged on a cathode-side principal surface of the semiconductor body contacts both the cathode-side base as well as an auxiliary emitter of the first conductivity type embedded into the cathode-side base.
The laterally non-uniform distribution of the dopant concentration in the stop zone is effected in that a dopant in the central region of the stop zone is implanted in a dose lower by a factor of 100-5000 than in the laterally adjoining region. In one embodiment the dose of the dopant in the central region of the stop zone is in a range of 0.3-2·10
12
cm
−2
.
REFERENCES:
patent: 4642669 (1987-02-01), Roggwiller et al.
patent: 4689647 (1987-08-01), Nakagawa et al.
patent: 4717947 (1988-01-01), Matsuda et al.
patent: 5352910 (1994-10-01), Muraoka et al.
patent: 5644149 (1997-07-01), Streit
patent: 0108961 (1984-05-01), None
Patent Abstracts of Japan, vol. 011, No. 33 (E-476), Jan. 30, 1987, & JP 61 202465, Sep. 08, 1986, Toshiba Corp., Y. Takashi, “Thyristor with Overvoltage Protecting Function”, pp. 357-363 (English Abstract attached).
Mitlehner, H. et al, “High Voltage Thyristor for HVDC Transmission and Static Var Compensators”, IEEE (1988), pp. 934-939.
Abraham Fetsum
Schiff & Hardin & Waite
Siemens Aktiengesellschaft
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