Multilayer Component and Process for Producing Multilayer Component

Abstract

A multilayer component and a mathod for producing a multilayer component are disclosed. In an embodiment the multilayer component includes a ceramic main element being a varistor ceramic and at least one metal structure, wherein the metal structure is cosintered, and wherein the main element is doped with a material of the metal structure in such a way that a diffusion of the material from the metal structure into the main element during a sintering operation is reduced.

Claims

1-15. (canceled)

16. A multilayer component comprising: a ceramic main element being a varistor ceramic; and at least one metal structure, wherein the metal structure is cosintered, and wherein the main element is doped with a material of the metal structure in such a way that a diffusion of the material from the metal structure into the main element during a sintering operation is reduced.

17. The multilayer component according to claim 16, wherein the main element is doped with 0.1 to 1 mol per cent of a chemical compound of the material of the metal structure.

18. The multilayer component according to claim 16, wherein the main element comprises ZnO.

19. The multilayer component according to claim 16, wherein the main element comprises bismuth oxide, praseodymium oxide or antimony oxide.

20. The multilayer component according to claim 16, wherein the main element comprises one or more of the materials Co.sub.3O.sub.4, Mn.sub.2O.sub.3, SiO.sub.2, Cr.sub.2O.sub.3, B.sub.2O.sub.3, Al.sub.2O.sub.3 or NiO.

21. The multilayer component according to claim 16, wherein the main element has the composition: ≧90 mol % of ZnO, from 0.5 to 5 mol % of Sb.sub.2O.sub.3 or Bi.sub.2O.sub.3, from 0.05 to 2 mol % of Co.sub.3O.sub.4, Mn.sub.2O.sub.3, SiO.sub.2 and/or Cr.sub.2O.sub.3, <0.1 mol % of B.sub.2O.sub.3, Al.sub.2O.sub.3 and/or NiO.

22. The multilayer component according to claim 16 wherein the main element is a ceramic sintered with an aid of liquid phases.

23. The multilayer component according to claim 16, wherein the metal structure comprises at least one internal electrode, at least one external metallization and/or at least one via.

24. The multilayer component according to claim 16, wherein the metal structure is doped with at least one material of the ceramic main element.

25. The multilayer component according to claim 16, wherein a thickness or lateral extension of the metal structure is less than or equal to 1.5 μm.

26. The multilayer component according to claim 16, wherein the metal structure comprises silver.

27. The multilayer component according to claim 26, wherein the metal structure comprises 99% of silver.

28. The multilayer component according to claim 16, wherein the doping material comprises silver oxide or silver carbonate.

29. The multilayer component according to claim 16, wherein the metal structure comprises palladium.)

16. The multilayer component according to claim 16, wherein the doping material comprises a palladium compound.

31. The multilayer component according to claim 16 further comprising at least one passivating layer, wherein the passivating layer is cosintered, and wherein the passivating layer comprises a glass including a filler material or a ceramic.

32. The multilayer component according to claim 31, wherein the passivating layer is doped with at least one material of the metal structure and the doping is greater than or equal to a saturation concentration of the material in the passivating layer.

33. A method for producing a multilayer component, the method comprising: arranging layers comprising a ceramic composition and layers comprising an electrode paste alternately on top of one another to form a stack of layers, wherein the ceramic composition is doped with at least one material of the electrode paste; and sintering the stack of layers to provide ceramic layers with internal electrodes arranged in between.

34. The method according to claim 33, wherein the ceramic composition is doped with 0.1 to 1 mol per cent of the material of the electrode paste.

35. The method according to claim 33, wherein the electrode paste comprises silver, and wherein the electrode paste is doped with at least one material of the ceramic composition and the ceramic composition is doped with silver oxide or silver carbonate.

36. The method according to claim 33, further comprising: applying an insulating layer on at least one upper side of the ceramic composition, wherein the insulating layer is doped with at least one material of the electrode paste and at least one material of the ceramic composition, wherein the insulating layer is applied before sintering.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The invention will be illustrated below with the aid of illustrative embodiments and the associated figures.

[0037] The drawings described below are not to be interpreted as true to scale. Rather, individual dimensions can be shown larger, smaller or even distorted to give better depiction.

[0038] Elements which are identical or perform the same function are denoted by the same reference numerals.

[0039] FIG. 1 schematically shows a multilayer component in cross section,

[0040] FIG. 2 shows the multilayer component of FIG. 1 in plan view,

[0041] FIG. 3 schematically shows a multilayer component in cross section,

[0042] FIG. 4 schematically shows a multilayer component in cross section,

[0043] FIG. 5 shows the multilayer component of FIG. 4 in plan view,

[0044] FIG. 6A shows an image of an actual multilayer component according to the prior art,

[0045] FIG. 6B shows an image of an actual multilayer component according to the invention, and

[0046] FIG. 7 shows an image of an actual multilayer component according to the invention.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0047] FIG. 1 schematically shows a multilayer component in cross section.

[0048] The multilayer component 1 is a varistor multilayer component. The multilayer component 1 comprises a ceramic main element 2. The main element 2 consists of a plurality of layers. The multilayer component 1 comprises metal structures. In particular, internal electrodes 3 are arranged between the layers of the main element 2 in this illustrative embodiment. Internal electrodes 3 and ceramic main element 2 are sintered together (cosintered) in order to obtain the finished multilayer component 1.

[0049] The main element 2 is a zinc oxide (ZnO) varistor in this illustrative embodiment. In particular, the main element 2 comprises about 95 mol per cent of ZnO. Sb.sub.2O.sub.3, Bi.sub.2O.sub.3 can be present as further material of the main element, for example, in the range from 0.5 to 5 mol per cent. Furthermore, the main element 2 can comprise Co.sub.3O.sub.4, Mn.sub.2O.sub.3, SiO.sub.2, Cr.sub.2O.sub.3, for example, in the range from 0.05 to 0.2 mol per cent. Furthermore, materials such as B.sub.2O.sub.3, Al.sub.2O.sub.3 and NiO can be present in concentrations of less than 0.1 mol per cent. The ceramic further comprises a sintering aid, for example, bismuth oxide.

[0050] The internal electrodes 3 comprise a metal. In particular, the internal electrodes 3 comprise silver (Ag). The internal electrodes preferably comprise more than 90 per cent by weight of silver, for example, 95 or 98 or 99 per cent by weight. As an alternative to silver, the internal electrodes 3 can comprise a different metal, for example, palladium. In this case, the internal electrodes 3 preferably comprise essentially palladium.

[0051] The internal electrodes 3 are made particularly thin. In particular, the internal electrodes 3 have a thickness of less than or equal to 1.5 μm, for example, 1.4 μm or 1.2 μm or 1.0 μm. The thickness of the internal electrodes 3 is preferably selected so that it is just sufficient to withstand a sintering process. The only small thickness of the internal electrodes 3 significantly reduces the risk of delamination in which the electrode layer becomes detached from the ceramic material of the main element 2, making the component 1 unstable. Furthermore, an electrode layer having a small thickness has the advantage that a volume of the component 1 can be utilized better for an equal function.

[0052] The main element 2 further comprises electrode material as material. In particular, the main element 2 is doped with a chemical compound of the metal of the internal electrodes 3. The ceramic material of the main element 2 is preferably doped with silver oxide or silver carbonate. As an alternative, the main element can also be doped with a palladium compound when the internal electrodes 3 correspondingly comprise palladium. For example, the main element is doped with a proportion of from 0.1 to 1 mol per cent of the chemical compound of the metal of the internal electrodes 3.

[0053] As a result of the doping of the ceramic material of the main element 2 with electrode material, diffusion of the material of the internal electrodes 3 into the ceramic volume during a sintering operation can be controlled or avoided. In particular, the proportion of electrode material in the ceramic can produce a diffusion equilibrium which prevents diffusion of electrode metal into the ceramic during sintering. The influence of the internal electrodes 3 on the ceramic properties can thus be reduced.

[0054] After sintering of ceramic main element 2 and internal electrodes 3, a passivating layer 4 is applied to the multilayer component 1 in this illustrative embodiment. The passivating layer 4 is applied to a surface or outside of the main element 2. In particular, the passivating layer 4 covers the entire surface of the main element 2. The passivating layer 4 protects the main element 2 against external influences. The passivating layer 4 can, for example, comprise glass having a filler material or a ceramic. The passivating layer 4 can comprise a varistor ceramic.

[0055] Furthermore, the multilayer component 1 has external metallizations 5 for electrical connection of the multilayer component 1. The external metallizations 5 are arranged on opposite side faces of the component 1. The external metallizations 5 preferably comprise the same material as the internal electrodes 3. For example, the external metallizations 5 comprise silver.

[0056] The external metallizations 5 are arranged on the passivating layer 4. The external metallizations 5 are, in this illustrative embodiment, likewise applied after the sintering operation. FIG. 2 shows the passivating layer 4 applied after sintering and also the external metallizations 5 in plan view.

[0057] FIG. 3 schematically shows a multilayer component according to a further illustrative embodiment.

[0058] In contrast to the multilayer component described in connection with FIGS. 1 and 2, the passivating layer 4 is sintered together with the main element 2 and the internal electrodes 3 in the multilayer component 1 shown in Figure 3. For this purpose, the passivating layer 4 is applied to the main element 2 before sintering. The passivating layer 4 is applied to the entire surface of the main element 2 or only to subregions of the surface of the main element 2.

[0059] In order to cosinter the passivating layer 4, the material of the passivating layer 4 is doped with electrode material. The passivating layer 4 is preferably doped with silver. Here, the silver doping can be the same as or greater than the saturation value of silver in the passivating layer 4 because there is no longer any electrically active region in the passivating layer 4. Degradation of the metal structures (internal electrodes 3) during sintering can be prevented by the doping of the passivating layer 4.

[0060] FIG. 4 schematically shows a multilayer component according to a further illustrative embodiment.

[0061] In this illustrative embodiment, the multilayer component 1 comprises a ceramic main element 2, with the main element 2 being configured as ZnO substrate or support element.

[0062] Metal structures are arranged in the main element 2. In particular, internal electrodes 3 and vias 6 are arranged in the main element 2. While the internal electrodes 3 run horizontally through the main element 2, the vias 6 are arranged perpendicular to the internal electrodes 3. Internal electrodes 3, vias 6 and ceramic main element 2 are cosintered in order to obtain the finished multilayer component 1.

[0063] The internal electrodes 3 and vias 6 comprise a metal. The internal electrodes 3 and vias 6 preferably comprise silver. As an alternative, the internal electrodes 3 and vias 6 can also comprise palladium, as described above. As described above in connection with the illustrative embodiment shown in FIGS. 1 and 2, the metal structures (internal electrodes 3, vias 6) are made particularly thin. The internal electrodes 3 have a thickness of less than or equal to 1.5 μm, for example, 1.0 μm or 1.2 μm. The vias 6 also have only a small lateral extension.

[0064] The main element 2 further comprises material of the metal structures as material. This prevents diffusion of electrode material into the main element 2 during the sintering operation. Furthermore, reference is made to what has been said in connection with FIGS. 1 and 2.

[0065] Like the multilayer component 1 of FIGS. 1 and 2, the multilayer component 1 of FIG. 4 has a passivating layer 4 and also external metallizations 5. Passivating layer 4 and external metallizations 5 are, in this illustrative embodiment, applied after the sintering operation. Figure 5 shows the passivating layer 4 applied after sintering and also the external metallizations 5 in plan view.

[0066] Passivating layer 4 and external metallization 5 can also be cosintered, as has been described above in connection with the preceding figures. In this case, sufficient doping of the passivating layer 4 with the material of the metal structures is necessary.

[0067] The process for producing a multilayer component is described by way of example below. In particular, a process for producing a multilayer component which comprises metal structures comprising essentially silver is described. As an alternative, a multilayer component which comprises metal structures comprising essentially palladium or an alloy of palladium and silver can also be produced by a corresponding process.

[0068] To produce varistors having a multilayer structure, green ceramic sheets are firstly produced from the dielectric ceramic components. As described above, the ceramic sheets can comprise the following constituents: [0069] ZnO in an amount of about 95 mol per cent; [0070] doping with Sb.sub.2O.sub.3, Bi.sub.2O.sub.3 in the range from 0.5 to 5 mol per cent; [0071] doping with Co.sub.3O.sub.4, Mn.sub.2O.sub.3, SiO.sub.2, Cr.sub.2O.sub.3 in the range from 0.05 to 2 mol per cent; [0072] doping with B.sub.2O.sub.3, Al.sub.2O.sub.3 and NiO in concentrations of less than 0.1 mol per cent.

[0073] Furthermore, the ceramic has to be of such a nature that it can be sintered with high quality at below the melting point of the material of the metal structures (preferably silver). For this reason, a liquid phase which exists even at low temperatures is required during sintering. This is ensured by a liquid phase such as bismuth oxide. The ceramic is consequently based on zinc oxide doped with bismuth oxide. The doping with bismuth oxide generally increases the diffusion of silver from the internal electrodes 3, but this is prevented by doping of the ceramic with silver.

[0074] The ceramic is, in particular, doped with silver oxide or silver carbonate. The doping is selected so that the ceramic is saturated with silver even before sintering. The saturation leads to the ceramic no longer being able to take up any silver during the sintering operation. As a result, no loss of material occurs from the metal structure (here: internal electrodes 3) during sintering. Due to the doping of the ceramic sheets with silver oxide/silver carbonate, the ceramic formulation can also comprise a relatively large amount of sintering aid such as bismuth oxide, for example, to reduce the porosity.

[0075] Finally, the ceramic also comprises an organic binder preparation.

[0076] The internal electrodes 3 are applied to these ceramic sheets by coating the green ceramic with a metallizing paste in the electrode pattern. These metallized green films are stacked. As metallizing paste or electrode paste for internal electrodes, use is made of a paste which comprises essentially silver as metallic component.

[0077] The green body is subsequently sintered, with the binder, in particular its organic constituents, being volatilized. The sintering temperature is matched to the material of the internal electrodes 3. In the case of the Ag internal electrodes, the sintering temperature is preferably less than 1000° C., particularly preferably less than 960° C. The sintering temperature is, for example, 900° C.

[0078] The diffusion of electrode material into the ceramic during sintering thus displays the following behaviour: at a sintering temperature of 900° C. and a silver concentration of more than 0.1 mol per cent in the ceramic sheets, the diffusion constant is 7.Math.10.sup.−11 cm.sup.2/s. At a sintering temperature of 900° C. and a silver concentration of less than 0.1 mol per cent in the ceramic sheets, the diffusion constant is 3.Math.10.sup.−8 cm.sup.2/s.

[0079] As a result of the doping of the ceramic, the silver content in the ceramic is independent of sintering, the formulation of the ceramic or the shape and quantity of the metal structures. This leads to the ceramic always having constant properties both in respect of the thermal properties (thermal expansion, shrinkage) and in respect of the electrical properties (capacity, V-I curve, robustness).

[0080] According to the illustrative embodiment shown in Figure 3, the passivating layer 4 can also be cosintered. In this case, the passivating layer 4 is applied to an outside or surface of the ceramic sheets before sintering. In the case of cosintering with the passivating material, the latter also has to be doped with silver so that no silver can diffuse into the passivating layer 4 during sintering. Here, the doping can be higher than the saturation value of the passivating material.

[0081] In a further illustrative embodiment which is not shown, the external metallization 5 can also be cosintered. In this case, the external metallization 5 is applied to an outside or surface of the ceramic sheets or to the passivation before sintering. The external metallization 5 comprises essentially silver. The diffusion of silver is prevented by the doping of the ceramic sheets with silver (and in the case of cosintering of the passivation, also by the silver doping therein).

[0082] According to the illustrative embodiment shown in Figure 4, the main element 2 can be used as substrate or support element after sintering. Figure 7 shows an image of an actual multilayer component. In this case, further metal structures (vias 6) can be introduced into the green body before sintering and subsequently be jointly sintered. The further metal structures likewise comprise essential silver. The diffusion of silver is prevented by the doping of the ceramic sheets with silver (and in the case of cosintering of the passivation, also by the silver doping therein).

[0083] FIG. 6B shows an image of an actual multilayer component according to the invention. The regular profile of the internal electrodes 3 is conspicuous here. In particular, it can be seen that no loss of material from the internal electrodes 3 has taken place during the sintering operation. This is in contrast to multilayer components according to the prior art in which the ceramic body has not been doped with the electrode material (silver) (see FIG. 6A).

[0084] The description of the subjects and processes indicated here is not restricted to the individual specific embodiments. Rather, the features of the individual embodiments can, in so far as it is technically feasible, be combined with one another in any way.