DE1415457A1 - Resistance with high temperature coefficient - Google Patents

Description

Addition to the patent. (amtl.AZ.P 14 15 406. x 4;

The invention relates to a system consisting of ferroelectric crystallite grains sintered together and made to conduct interference ceramic resistor with. high temperature coefficient its total resistance value.

In the manufacture of such resistors, it has been found that they often have an undesirable voltage dependency of the resistance value. In order to eliminate this voltage dependency or to a level that is no longer disruptive to reduce, was already in the main patent. ... ... (patent application P 14 15 406j PA 58/2313) proposed that the contacts be applied to the material essentially without a barrier layer of the resistance value. It was further suggested to use a base metal, in particular aluminum or zinc, for contacting.

In further experiments the connection between ■ varistor effect, i.e. the voltage dependence of the "resistance value,

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and the type of contacting metal used. " It has been shown that the freedom from blocking of the contact depends heavily on the type of contacting metal.

A substantially non-blocking contact is possible if the contacting metal is able to use the Ceramic containing 4-valent metal oxide of the ferroelectric Reduce base material. This applies to all metals "for which the enthalpy of formation of their oxide at least is about the same or only slightly smaller than the difference in the enthalpies of formation of the trivalent and tetravalent oxides of the 4-valent metal in the ferroelectric base material.

According to the invention, a ceramic resistor is therefore proposed, "in which a metal is applied to the ceramic semiconductor material for contacting, which in the 4-valued ceramics contained. Metal oxide of ferroelectric Able to reduce the base material by reducing the enthalpy of formation of an oxide of the contact metal at least is about the same or only slightly smaller than the difference in the enthalpies of formation of the trivalent and tetravalent oxides of the im ferroelectric base material of tetravalent metal.

It is assumed that this reduction leads to overdoping in the surface area, so that a barrier height can no longer be formed. "·"'■' ■ - ■ ** "■ y-

The enthalpy of formation of the oxide of this metal was used as a measure of the reducing power of the contacting metal. If this enthalpy of formation is greater (more negative) than that of the transition from the 3-valent to the 4-valent oxide of the metal that is l-valued in the ferroelectric base material, thus a reduction from tetravalent to "trivalent oxide" is complete this contacting metal possible,

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In the following, using an exemplary embodiment, the Experimental results are discussed.

The ceramic resistor consists, for example, of a barium titanate-based one built-up semiconductor ceramic. The electrical conductivity is achieved by doping with antimony oxide (SbgO,) achieved. Ceramic disks became part of the experiments used, which were vapor-coated with aluminum on one side, in order to ensure non-blocking contact on this side achieve. The samples were so placed in an electrolytic cell used that only the side was exposed to the electrolyte, which was not covered with aluminum. The layer thickness of the deposited metal was about 5 to 10 µm. The resistance ratio was used as a parameter for the varistor effect used for the measuring voltages 0.2 and 5 V (R 0.2 V / R 5 V) .. The fundamental differences of the varista effect in different metals changes .also a change in the resistance dimensions or the Doping, nothing * It was also the composition of the Electrolyte in the deposition of the same metal varies without seeing; a major impact on the Varistor effect showed ·.

In. 'ig;! * T .. is (-.bezogen jeweiIs · on 1i atomic oxygen..) the enthalpy of formation of the metal oxides AE plotted against the varistor (R V 0.2 / R 5 V). Instead of formation ^ H ^ IU should be applied more precisely the free Bildungsenthalpi "arising out of, through Berücksichtigung-; _N entropy ergiht * This correction of formation is, but höelTstens 3 calories / Hol and falls therefore. _; does not matter.

of the transition from Tl ₀ O ^ to 210 after

_{5 of} the equation "2TiO ₂ 5Ti ₃ O ₃ + t / 2 O ₂ is ^ iB = 62.3 kCal

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It can be seen from the diagram in FIG. 1 that at a contact metal whose enthalpy of oxide formation is greater (more negative) than about 55 kCal / mol is already a considerable one Reduction of the varistor effect occurs and that with metals whose oxide formation enthalpy is greater (more negative) than about 60 kCal / mol, a substantially barrier-free contact can be achieved. In the thermodynamic realm of existence of the 5ip ^ 3 there is practically no varistor effect on. On the other hand, it becomes very strong in the area in which no reduction in TiOp is possible.

The diagram also shows that the varistor effect silver is about a power of ten higher than comparable metals such as palladium.

The present results show that one can assume that the barium titanate is superficially reduced during contacting and thus becomes highly conductive, so that no Locking effect can occur more. Accordingly, attempts were made to reduce in other ways. On the surface the ceramic was first electrolytically deposited hydrogen and immediately afterwards copper was deposited, which otherwise has a strong varistor effect. In this pail, however, a lock-free contact was formed.

The test results show that there is a reduction in the surface area a lockable contact allows and that all Metals that are able to convert tetravalent titanium to trivalent Reducing titanium results in a practically non-blocking contact.

Fig. 2 shows an embodiment of a resistor according to the invention. 1 is the -from ferroelectric crystal-

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liten sintered rod-shaped resistance body, which in particular made of a barium titanate-based semiconductor ceramics. The end faces 2 and 3 of the resistor body are provided with, for example, an electrolytically deposited metal coating 4 and 5, for example made of iron exists, whose enthalpy of oxide formation is about -64 kCal / mol and is therefore greater (more negative) than the enthalpy of formation the transition from tetravalent to trivalent titanium dioxide, causing a reduction in the ceramic surface will. The power supply can now be attached directly to the metal rails or a metal cap can be used be pressed in the manner of resistance contact over the ends of the semiconductor body, which is mechanically fixed sits on the resistor body and which is directly soldered to the corresponding metal layer. aside from that the metal layers can also be produced by vapor deposition.

In 3 ig. 3, the resistance is plotted as the ordinate and the voltage _s as the abscissa, both on a logarithmic scale. Curve 1 shows the resistance profile of a resistance body contacted, for example, with iron without blocking. There is practically no varistor effect. The curve 2 represents the resistance profile of a resistance body contacted with copper. The formation of senthalpy of the copper oxide _m is about 38 kcal / mol. In accordance with the above, curve 2 shows a strong voltage dependency of the resistance.

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Claims (2)

Claims 1. From sintered together ferroelectric made conductive Crystallite grains of existing ceramic resistor with a high temperature coefficient Total resistance value, "at which to achieve negligible small voltage dependence of the total resistance value, the contacts are essentially non-blocking applied to the material of the resistor are, according to patent (Patentanmeldg. P 14 15 406. 4J PA 58/2313), characterized in that the ceramic Semiconductor material a metal is applied for contacting, which is contained in the ceramic The tetravalent metal oxide of the ferroelectric base material is able to reduce by the formation enthaipie of an oxide of the contact metal is at least approximately equal to or only slightly smaller than the difference the enthalpies of formation of the trivalent and tetravalent oxides des in ferroelectric base material · tetravalent metal. 2. Resistor according to claim 1 with a titanium-lasting ferroelektrisehen base material, characterized in that a contact metal is applied, whose negative enthalpy of oxide formation greater than about 55 kCal / mol, -in particular is greater than 60 kcal / mol. UUQ documents i V-. _Λ -.-. . «- ■ o ^"'u - s Ai .. ^ njngsgesr.v. 809805/0708