Patent
1983-09-15
1986-07-08
James, Andrew J.
357 13, 357 52, 357 86, 357 34, 357 43, 357 53, H01L 2702
Patent
active
045996385
DESCRIPTION:
BRIEF SUMMARY
STATE OF THE ART
The invention relates to a planar semiconductor structure having a main surface of a specific conductivity type, at least one annular zone produced by diffusion into the main surface, a passivation layer, and a cover electrode. Semiconductor structures of this kind are already known. However, they have the disadvantage that electrical fields affecting them from outside, such as are produced by the polarisation of cover lacquers during high-voltage and high-temperature operation, can cause the degradation of blocking characteristics, or that the breakdown voltage can be affected only by varying the thickness of the passivation layer within certain limits but cannot be varied after the metallizing coating is applied.
ADVANTAGES OF THE INVENTION
Briefly, the semiconductor structure according to the invention and having an annular zone acting as a stop-ring and a cover electrode, with an adjustable potential, extending over the stop-ring has the advantage over the prior art that the space charge zone forming around the first zone during operation is confined inside the annular zone acting as a stop ring and is shielded from external electrical fields beneath the cover electrode, and that, furthermore, the breakdown voltage at the first p-n junction is variable within wide limits. Claim 2 affords a particularly simple possible realization of the adjustment of this breakdown voltage with the aid of a voltage divider. Particularly advantageous further developments of the subject of claims 1 and 2 are disclosed in the further dependent claims 3-12.
DRAWING
Exemplary embodiments of the semiconductor structure according to the invention are shown in the drawing and described in greater detail in the ensuing description. Shown are:
FIG. 1, a section through a planar semiconductor structure according to the invention, having an external ohmic voltage divider for adjusting the breakdown voltage at the first p-n junction;
FIG. 2, the breakdown voltage U.sub.Br at the first p-n junction in accordance with the divider ratio of this external voltage divider;
FIG. 3, a plan view on a semiconductor structure according to the invention, in which the ohmic voltage divider is monolithically integrated;
FIG. 4, a section taken along the line A--A' of FIG. 3;
FIG. 5, a plan view on a portion of a semiconductor structure according to the invention, in which the ohmic voltage divider is partially replaced by a chain of Zener diodes; and
FIG. 6, a section taken along the line B--B' of FIG. 5.
DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
The intention is that a planar p-n junction 12 be protected by means of a metal electrode 15 above the insulator 13 such that the blocking behavior cannot be affected in an undesirable manner by external influences (such as substances with polar groups, alkali ions, metal flakes and the like).
FIG. 1 shows an exemplary embodiment in schematic form. The semiconductor chip 10 comprises n.sup.- -conductive silicon; the insulator 13 is of thermally grown silicon dioxide. The metal electrode 15 overlaps the p zone 11 and an n.sup.+ zone 14, which in an n-p-n transistor can be introduced by diffusion simultaneously with the emitter. The n.sup.+ -conductive emitter zone of the n-p-n transistor is not shown in FIG. 1, however, so the structure of FIG. 1 must be conceived of as a Zener diode. The attainable breakdown voltage is dependent not only on the basic doping of the silicon but also, substantially, on the thickness of the oxide layer 13 and on the potential of the electrode 15.
FIG. 2 shows the dependency of the breakdown voltage as a function of the divider ratio R.sub.1 : R of an external voltage divider 16. U.sub.1 is the breakdown voltage obtained if the cover electrode 15 is connected directly to the p zone 11. In the present exemple, it is markedly lower than the breakdown voltage that is attainable without a cover electrode 15. It is equal to the voltage upon the depletion breakdown of a corresponding metal oxide semiconductor structure. U.sub.2 is the breakdown voltage up
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James Andrew J.
Mintel William
Robert & Bosch GmbH
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