US 3188535 A
Description (OCR text may contain errors)
June 8, 1965 D w ALRAVEN ETAL-. 4 3,188,535 SEMI-CONDUCTOR ELECTRODE SYSTEM HAVING AT LEAST ONE ALUMINIUM-CONTAINING ELECTRODE Filed Aug. 24. 1960 zap Han /nea AGENT United States Patent 4 Claims. or. 317-234 The invention relates to a semi-conductor electrode system, such as a diode, transistor or photo-electric cell, having a semi-conductor body and at least one aluminumcontaining electrode on this body, a resilient contact member being brought into compression contact with the electrode.
It is known to use such a compression contact, since it has turned out to be difficult to connect a wire by soldering to such an electrode the surface of which in general is covered with an aluminum oxide film.
It has appeared that in such a contact formed by spring pressure, fluctuations may occur in the resistance which may cause undesired fluctuations in the current, for example in the case of a diode biased with a constant voltage in the forward direction.
According to the invention, the contact member is covered, at least on the side facing the electrode, with .a layer consisting of a soft metal. A soft metal is to be understood to mean herein a metal or an alloy softer than the electrode material at a temperature between room temperature and the lowest temperature at which the electrode material forms a melt.
It was surprisingly found that when using such a layer in a compression contact, an electrical connection of a constant low resistance can be obtained with the alloying electrode. This contradicts the expectation that the commonly used hard material of the spring contact would improve the electrical connection by damaging the oxide layer, whereas the soft metal would protect this oxide layer against injury.
The layer preferably consists at least partially of tin, indium, lead, bismuth, cadmium and/or gallium. Its thickness preferably exceeds 10a; for practical purposes a thickness of at least 50 is preferred. The maximum thickness is determined by the maximum heightwhich the electrode projects above the surface of the semiconductor body. For practical purposes preferably layer thicknesses up to 200 are chosen.
For the manufacture of the electrode system according to the invention, a current pulse is applied through the contact preferably after compressing the contact member. This current pulse should be stronger than the current to be expected in normal operation.
In order to further improve the contact and to increase its mechanical strength preferably after the treatment with the current pulse, the layer is made softer by heating whereby the alloyed electrode is pressed deeper into the layer.
In order that the invention may be readily carried into effect, it will now be described, by way of example,
with reference to the accompanying drawing, the figure :of which shows a vertical sectional view of a crystal diode.
In the figure, 1 is a disc of n-silicon soldered to the end of a filamentary current conductor 3 fused in a glass envelope 2. On the body 1 a rectifying, aluminum containing electrode 4 is melted. In the glass envelope 2 a second filamentary current conductor 5 is fused, which conductor is provided with a resilient contact member in the form of a bent strip 6 of a manganese-nickel alloy which is provided with a layer or coating 7 consisting of one of the above preferred compositions, e.g. tin, indium, lead, bismuth, cadmium or an alloy of two or more of these metals, to which also some gallium may be added, and having a thickness of for example 150 The resilient strip 6 thereby presses 5 against the electrode 4 by means of the layer 7.
'During the manufacture of the crystal diode, after providing the pressure contact between the contact member 6 and the electrode 4, a current pulse was applied through the diode, for example by connecting it to a 10 source of direct voltage of 40 v. in the forward direction for 0.4 second. Then the layer 7 was made softer by slightly heating, for example above 100 C. for at least about 30 sec., as a result of which the electrode penetrated further into the thin layer on account of the pressure exerted by the resilient contact member. After cooling, a mechanical, rigid contact was obtained between the electrode 4 and the resilient contact member.
It appeared that the thus obtained diodes never caused any substantially disturbing fluctuations in the current when biased with a constant voltage in the forward direction.
The soft metal applied to the resilient contact member 6 cannot be used for the entire contact member 6, because it does not possess appreciable resilience and thus could not provide a pressure contact to the aluminum electrode. The resilient member 6 is made of spring-like hard metal, such as manganese-nickel or any other suitable composition well known in the art.
The invention is not limited to the diode shown in the drawing. Nor is it restricted to crystal diodes but it also relates to other semi-conductor electrode systems, for example transistors or photoelectric cells, having aluminum-containing electrodes and resilient contact members connected to them, in which also for these systems troublesome occurrence of fluctuations of the contact resistances could be prevented by using the invention.
What is claimed is:
1. A semiconductor device comprising a semiconductive body, an electrode containing aluminum on said body, a resilient contact member having a portion in pressure engagement with and making electrical connec tion to said electrode, and a layer of a soft metal coated on the said portion engaging the electrode, said layer having a thickness between about 10 and 200 microns.
2.-A semiconnductor device as set forth in claim 1 wherein the soft metal includes at least one element selected from the group consisting of tin, indium, lead, bismuth, cadmium and gallium.
3. A silicon semiconductor device comprising a semiconductive body, an electrode comprising aluminum fused to said body, a hard metal resilient contact member having an end portion in pressure engagement with said electrode, and a layer of a soft metal selected from the group consisting of tin, indium, lead, bismuth, cadmium, gallium and alloys thereof coated on said end portion engaging said electrode, said layer having a thickness between 10 and 200 microns.
4. A device as set forth in claim 3 wherein the electrode is partially embedded in the soft metal layer.
References Cited by the Examiner UNITED STATES PATENTS DAVID J. GALVIN, Primary Examiner. JAMES D. KALLAM, Examiner.