Active solid-state devices (e.g. – transistors – solid-state diode – Bipolar transistor structure – Plural non-isolated transistor structures in same structure
Patent
1993-06-11
1995-09-12
Limanek, Robert P.
Active solid-state devices (e.g., transistors, solid-state diode
Bipolar transistor structure
Plural non-isolated transistor structures in same structure
257572, 257491, 257488, H01L 29861
Patent
active
054499496
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a monolithic integrated semiconductor device.
Semiconductor devices are known that, in order to limit the breakdown voltage of transistors, especially Darlington transistors, have an oxide-separated metal cover electrode above the space charge region that is connected by means of a voltage divider to a certain potential between the base and the collector. The breakdown voltage is determined substantially by the voltage potential of the cover electrode and by the thickness of the oxide.
U.S. Pat. No. 4,618,875, FLOHRS, discloses this kind of Darlington transistor circuit, in which the cover electrode is formed on the surface of the substrate and extends across two spaced-apart zones of opposite doping. The maximum attainable breakdown voltage is equivalent to the voltage value resulting from the sum of the enhancement breakdown voltage and depletion breakdown voltage. However, it must be taken into account that the thermal oxides typically used in planar processes cannot be made arbitrarily thick, so that the maximum attainable voltage with such a device is limited.
ADVANTAGES OF THE INVENTION
A monolithic integrated semiconductor device has the advantage over the prior art that the breakdown voltages are dependent only on the depletion breakdown voltage and on the divider ratio of the voltage divider, which is connected by its pickup to the cover electrode and determines the voltage potential thereof. In an n-p-n transistor, the cover electrode no longer completely covers the collector zone but instead covers only a junction region of the low-n-doped collector zone and the peripheral region of an adjacent highly n-doped zone. In an n-p-n transistor, the cover electrode does not reach as far as the p-doped base zone. Conversely, in a p-n-p transistor, it is precisely the junction region of the base zone that is covered by the cover electrode, which in this case does not extend as far as the spaced-apart p-doped zone.
In a further feature of the invention, the p-n junction between the high-impedance collector zone and the p-doped base zone, in a semiconductor device formed as a transistor, can also be passivated by means of a second cover electrode. The second cover electrode is identical to the base metallizing coating of the transistor. However, it is also possible to connect this second cover electrode to emitter potential; in any case, it must be assured that the two cover electrodes are electrically separated, so that no enhancement breakdown can occur. In this version as well, the maximum attainable breakdown voltage is dependent only on the depletion breakdown voltage and on the voltage divider ratio of the voltage divider to whose pickup the first cover electrode, remote from the base zone, is connected.
The voltage potential for the cover electrode is preferably adjusted by means of a monolithically integrated voltage divider. The embodiment of such a voltage divider is known from both European Patent 179 099 and U.S. Pat. No. 4,695,867.
To achieve a temperature compensation of the breakdown voltage, the resistors forming the voltage divider may be formed of unequally highly doped silicon.
The divider resistors can be integrated very easily in the form of strip-shaped zones that except for connection points are covered with a passivation layer. At the connection points, the necessary bonding, such as to the pickup of the voltage divider, can be done by applying a metal layer.
Advantageous further features of the invention are defined by the dependent claims.
DRAWINGS
The invention will be described in further detail below in terms of one conventional semiconductor device, and additional versions according to the invention.
Shown are:
FIG. 1, a conventional semiconductor device;
FIG. 2, a first device according to the invention, having a cover electrode that covers an n--n junction;
FIG. 3, a device according to the invention with an additional base cover electrode, in an n-p-n transistor;
FIG. 4, the dependency of the breakdown voltage of a
REFERENCES:
patent: 4618875 (1986-10-01), Flohrs
patent: 4695867 (1987-09-01), Flohrs et al.
patent: 4916494 (1990-04-01), Flohrs et al.
C. G. Jambotkar, "Spaced Field Plate for Increasing Planar Junction Breakdown Voltage," IBM Technical Disclosure Bulletin, vol. 19, No. 2, pp. 478-479, Jul. 1976, Armonk, N.Y.
Flohrs Peter
Goerlach Alfred
Michel Hartmut
Haroy David B.
Limanek Robert P.
Robert & Bosch GmbH
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