Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
  • H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors
  • H01C7/1006—Thick film varistors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
  • H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors
  • H01C7/102—Varistor boundary, e.g. surface layers
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
  • H01C7/10—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material voltage responsive, i.e. varistors
  • H01C7/105—Varistor cores
  • H01C7/108—Metal oxide
  • H01C7/112—ZnO type
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C17/00—Apparatus or processes specially adapted for manufacturing resistors
  • H01C17/06—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base
  • H01C17/065—Apparatus or processes specially adapted for manufacturing resistors adapted for coating resistive material on a base by thick film techniques, e.g. serigraphy
  • H01C17/06506—Precursor compositions therefor, e.g. pastes, inks, glass frits
  • H01C17/06513—Precursor compositions therefor, e.g. pastes, inks, glass frits characterised by the resistive component
  • H01C17/06533—Precursor compositions therefor, e.g. pastes, inks, glass frits characterised by the resistive component composed of oxides
  • H01C17/06546—Oxides of zinc or cadmium
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01C—RESISTORS
  • H01C7/00—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material
  • H01C7/18—Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered semi-conducting material with or without insulating material comprising a plurality of layers stacked between terminals

Definitions

• the present invention relates to a multilayer varistor.
• the present invention also relates to a method for producing a multilayer varistor.
• Multilayer varistors are used as effective protective elements against temporary overvoltages (such as ESD - "Electrostatic Discharge”; electrostatic discharge) .
• ESD electrostatic Discharge
• electrostatic discharge electrostatic discharge
• the material used for multilayer varistors consists of doped zinc oxide (ZnO).
• ZnO doped zinc oxide
• the series and parallel connection of the individual barrier layers results in the capacity - but also the Breakdown voltage of the active area. Since the breakdown voltage is specified in the design of the component, this also results in the capacitance of the active area.
• the DK of the ZnO ceramic is largely coupled with the breakdown voltage and therefore cannot be used as a degree of freedom to lower the capacitance.
• the stray capacitance of the ceramic component outside the active volume also contributes to the capacitance of a varistor.
• the proportion of the stray capacitance in the total capacitance increases more and more and thus limits the achievable effect by a design with a minimal overlapping area of the electrodes. Therefore, in order to efficiently reduce the capacitance of a varistor, it is necessary to reduce this stray capacitance as much as possible.
• the document JP 3735151 B2 describes a method in which the outermost areas of the ceramic are chemically modified after sintering. During an additional heat treatment, lithium or sodium is diffused into the surface of the ceramic body. Doping with acceptors reduces the leakage current and the dielectric constant of the outermost layer. The capacitance of the multilayer varistor can be significantly reduced in this way. The disadvantage of this method is that this subsequent modification requires considerable effort. Further heat treatment would also be required to apply an additional layer of glass on the outside, which is extremely difficult due to the high diffusion rates of sodium and lithium.
• the document JP H-113809 A describes a multilayer varistor consisting of an insulating support layer with a low dielectric constant, onto which the actual varistor ceramic is laminated.
• the carrier layer itself is also made from a ceramic with a low dielectric constant using the layer process.
• a disadvantage of this multilayer varistor is the costly production of the same: instead of a uniform ceramic, two different ceramics with very different properties are required. This can be due to a different marriage Mixed composition can be achieved, resulting in a weak bond between the carrier layer and the varistor ceramic.
• the document DE 10 2018 116 221 A1 describes a multi-layer varistor that consists of two chemically very different materials that differ in the ZnO grain size after the sintering process.
• the aim of this construction of a multilayer varistor is to keep the current flow in the component away from thermo-mechanical weak points and thus increase the impulse strength of the protective element.
• the focus here is not on the effect of the chemically very different materials, which are both used in the active area, for example, on the capacitance of the multilayer varistor.
• the document DE 10 2017 105 673 A1 describes the combination of two different ZnO ceramics in order to increase the pulse strength of the component.
• the two materials must be bonded to the electrodes in order to show the effect.
• the effects in near-surface areas as well as the impact on capacity are not addressed.
• the object of the present invention is to describe a multilayer varistor and a method for producing a multilayer varistor which solve the above problems. This object is achieved by a multilayer varistor and a method for producing a multilayer varistor according to the independent claims.
• a multilayer varistor has a ceramic body.
• the ceramic body has a plurality of layers.
• a plurality of internal electrodes are formed in the ceramic body.
• the inner electrodes have, for example, silver, palladium, platinum or an alloy of these metals.
• the ceramic body has an active area.
• the ceramic body also has an inactive area.
• the areas between the different inner electrodes of different polarity, which are decisive for the current flow between the same, are to be understood as the active area.
• the areas in the ceramic body of the multilayer varistor that do not (or not significantly) contribute to the flow of current between the differently contacted internal electrodes are referred to as the inactive area.
• the ceramic body has an area close to the surface.
• the area close to the surface in each case borders on an upper side and an underside of the multilayer varistor.
• the area close to the surface only has minimal electrical conductivity.
• the area close to the surface is designed to be essentially electrically insulating.
• the area close to the surface comprises a cover layer and/or an isolation zone of the multilayer varistor.
• the ceramic body has at least a first or primary ceramic material on .
• the multi-layer varistor has exactly a first or primary ceramic material on .
• the Ceramic body at least one second or modified ceramic material.
• the main component of the two ceramic materials is zinc oxide (ZnO).
• the two ceramic materials are based on ZnO.
• the first and the second ceramic material differ in a concentration of monovalent elements X + or elements with a stable oxidation state +1.
• X+ is selected from Li + , Na + , K + or Ag + .
• the monovalent elements preferably have a low diffusion constant.
• the multilayer varistor is manufactured by a method which will be described later in detail.
• the second or modified ceramic material is doped with the monovalent elements.
• the second ceramic material is doped with potassium oxide.
• the first or primary ceramic material may be free from doping with monovalent elements. Alternatively, however, the first ceramic material can also be slightly doped with monovalent elements.
• the dopants that distinguish the ceramic materials occur in low concentrations. Due to the doping with monovalent elements, the electrical properties of the second/modified ceramic material differ greatly from those of the first/primary ceramic material. However, chemically there is no significant difference between the ceramic materials. Notably, the two materials are otherwise nearly identical.
• Ceramic material has a lower dielectric constant as the first or primary ceramic material.
• a multilayer varistor with a reduced stray capacitance and consequently a reduced total capacitance can thus be provided.
• the highest concentration of monovalent elements X + is in the area close to the surface.
• the lowest concentration of monovalent elements X + is in the active region.
• the concentration of monovalent elements consequently decreases, starting from the surface towards the inner area/active area of the multilayer varistor. Accordingly, the value for the dielectric constant increases, starting from the surface towards the interior of the multilayer varistor. This reduces the stray capacitance of the varistor. The total capacitance of the varistor is consequently effectively reduced.
• the ceramic materials differ chemically from one another by ⁇ 1%.
• the ceramic materials are nearly identical chemically. This means that both materials can be excellently processed together.
• the layers of modified materials can be sintered together without defects. A particularly reliable multilayer varistor is thus made available.
• the dielectric constants sr of the first and second ceramic material differ from one another by a factor of >5.
• the stray capacitance of the varistor can consequently be significantly reduced in a simple manner by the only slight doping with monovalent elements.
• the first/primary ceramic material is arranged in the active area.
• the second/modified ceramic material forms an insulating cover layer of the ceramic body.
• the second ceramic material is arranged on the top and on the bottom of the multilayer varistor. Consequently, the multi-layer varistor has an insulating cover layer or low-dielectric cladding on . The stray capacitance of the multilayer varistor is thus significantly reduced in comparison to conventional multilayer varistors.
• the ceramic materials differ from one another in the concentration of monovalent elements X + by a maximum of 50 ppm ⁇ Ac(X + ) ⁇ 5000 ppm.
• Ac denotes the maximum concentration difference that occurs between the active area and the area near the surface.
• the concentration of acceptors in the second ceramic material is at most between 50 ppm and 5000 ppm higher than in the first ceramic material.
• the ceramic materials of the multilayer varistor preferably differ from one another by 100 ppm ⁇ Ac(X + ) ⁇ 1000 ppm.
• the concentration of monovalent elements X + in the active area is preferably ⁇ 100 ppm, preferably ⁇ 50 ppm.
• the first ceramic material is consequently almost free from monovalent elements.
• the proportion of monovalent elements is due in particular to their diffusion from the second ceramic material during production of the multilayer varistor.
• the cover layers can therefore be dimensioned with sufficiently high thicknesses, as a result of which the shielding effect is enhanced.
• the ceramic body has at least three ceramic materials.
• the ceramic body has the first/primary ceramic material, the second/modified ceramic material and a third/modified ceramic material.
• the ceramic body can also have more than three ceramic materials.
• the ceramic body can also have a fourth or modified ceramic material.
• the third ceramic material is interposed between the first ceramic material and the second ceramic material.
• the third ceramic material is arranged in the inactive area and in particular in the area close to the surface of the multilayer varistor.
• the third ceramic material forms a near-surface insulation zone.
• the three ceramic materials differ chemically by ⁇ 1%.
• the three ceramic materials differ in the concentration of monovalent elements.
• the first ceramic material active area
• the second ceramic material outer insulating cover layer
• the third material near-surface isolation zone
• the concentration of monovalents decreases
• a thickness of the second and/or the third ceramic material is adapted to a diffusion behavior of the monovalent element.
• the thickness is chosen such that there is as little diffusion of the acceptors into the active region as possible.
• the thickness of the cover layers is thus adapted to the diffusion constant of the monovalent element.
• the thickness reduces as the diffusion constant increases. Due to the reduced diffusion, a defined concentration gradient of monovalent elements occurs and, associated with this, a defined gradient of the electrical properties, above all the dielectric constant.
• the thickness of the second and third ceramic material is based on the overall height of the component and its internal structure.
• the design principle is that the effectiveness increases the higher the proportion of the second and third ceramic material in the inactive cover layers. On the other hand, this increases the risk that the monovalent element can diffuse into the active area during sintering. For example, a safety distance of 100 pm can be useful. In other words, after the last printed laminate, there are still another 100 ⁇ m from the first ceramic material as “diffusion buffer”. But also a smaller one
• a method for producing a multilayer varistor is described.
• the multilayer varistor described above is preferably produced by the method. All properties that are disclosed in relation to the multilayer varistor or the method are also disclosed correspondingly in relation to the respective other aspect and vice versa, even if the respective property is not explicitly mentioned in the context of the respective aspect.
• the procedure consists of the following steps :
• the ceramic powders essentially contain ZnO.
• the second ceramic powder is doped, in particular slightly doped, with monovalent elements X + , for example Li + , Na + , K + or Ag + .
• the first ceramic powder may be free from monovalent element doping or may have a small amount of monovalent element doping.
• the concentration of monovalent elements in the first ceramic powder is many times lower than the concentration of monovalent elements in the second ceramic powder.
• the dopant has a low diffusion constant.
• a doping with potassium for example K2O, KC4H5O6 or K2C03
• potassium for example K2O, KC4H5O6 or K2C03
• the latter is characterized in that - due to a high Melting point and a high decomposition temperature - few losses occur during sintering.
• Li or Na can also be used as doping. Na and Li are hardly or not at all susceptible to peroxide formation in air and the melting points of the metals are very high. The losses during sintering can thus be kept low.
• the dopant only occurs in a low concentration.
• the ceramic powders differ in the concentration of monovalent elements X + by 50 ppm ⁇ Ac (X + ) ⁇ 5000 ppm.
• Ac denotes the maximum concentration difference that occurs between an active area and an area close to the surface of the finished multilayer varistor.
• a third ceramic powder can additionally be provided for the production of a third ceramic material.
• the concentration of monovalent elements X + in the third ceramic powder is lower than in the second ceramic powder but higher than in the first ceramic powder.
• the third ceramic powder therefore has an average concentration of monovalent elements.
• green tapes with the lowest or medium concentration of monovalent elements can be printed with metal paste to form Faraday or guard electrodes .
• the green films are stacked in such a way that the second ceramic material forms a cover layer of the multilayer varistor. If a third ceramic material is present, the green sheets are stacked in such a way that the green sheets made of the third ceramic material are arranged between the green sheets made of the first and the third ceramic material.
• the green sheets are in particular stacked in such a way that a defined concentration gradient of monovalent elements X + is formed, with the concentration decreasing starting from the second ceramic material (cover layer) down to the first ceramic material (active area).
• the green sheets are preferably sintered at 1100° C.
• the outer electrodes can be single-layered (CN type) or multi-layered.
• the component Before electroplating, the component must be provided with a protective layer (glazing).
• the modified ceramic materials are of particular importance in the process. Since the modified ceramic materials are to be manufactured using the same process as the primary ceramic material, and the various ceramic materials are to be processed together in the stacking, laminating and sintering steps, it is important that the mechanical and thermal properties of the materials are well matched are . At the same time, the electrical properties have to be adapted to the very different requirements.
• FIG. 1 shows a sectional view of a multilayer varistor according to a first exemplary embodiment
• FIG. 2 shows a sectional view of a multilayer varistor according to a further exemplary embodiment
• FIG. 3 shows a sectional view of a multilayer varistor according to the third exemplary embodiment.
• FIG. 1 shows a first embodiment of a multilayer varistor 1 .
• the multilayer varistor 1 has a ceramic body 2 .
• a large number of internal electrodes 5 are formed in the ceramic body 2 .
• Figure 1 are only two internal electrodes 5 shown.
• the multilayer varistor 1 can have more than two internal electrodes 5 .
• the inner electrodes 5 have silver, palladium, platinum or an alloy of these metals.
• the inner electrodes 5 are arranged alternately and overlap in an inner area of the multilayer varistor 1 .
• the overlapping area forms an active area 3 of the multilayer varistor 1 .
• the multilayer varistor 1 also has a region 4 close to the surface.
• the region 4 close to the surface has only minimal electrical conductivity.
• the region 4 close to the surface borders on an upper side 1a and an underside 1b of the multilayer varistor 1, as can be seen in FIG.
• the near-surface area 4 has a top layer or. an isolation area of the multi-layer varistor 1 .
• the multilayer varistor 1 also has two outer electrodes 9 .
• the multilayer varistor 1 can also have more than two outer electrodes 9 .
• the outer electrodes 9 are electrically connected to the inner electrodes 5 for electrical contacting of the multilayer varistor 1 .
• the external electrodes 9 are formed on side faces of the multilayer varistor 1 . Furthermore, the external electrodes 9 are also formed on parts of the bottom 1b and the top 1a of the multilayer varistor 1 .
• the outer electrodes are constructed in one layer.
• the outer electrodes 9 can also have a multilayer structure (not shown explicitly).
• the respective outer electrode 9 preferably has a first or inner layer for contacting the inner electrodes 9 .
• the first layer preferably comprises silver.
• the respective outer electrode 9 has a second or middle layer as a diffusion barrier.
• the second layer preferably comprises nickel.
• the respective outer electrode 9 has a third or outer layer, which enables the multilayer varistor 1 to be soldered to printed circuit boards.
• the third layer preferably comprises tin.
• the varistor 1 must be provided with a protective layer (preferably glass) before electroplating.
• a further protective layer (electroplating protection, for example glass) is applied (not explicitly shown) to the upper side 1a and the lower side 1b (ie over the second ceramic material 7 described below).
• This glass layer chemically insulates the ceramic body 2 and thus increases the durability of the varistor 1 .
• the ceramic body 2 has two ceramic materials or Varistor ceramics 6 , 7 on .
• a first or primary ceramic material 6 is formed in an inner portion of multilayer varistor 1 .
• the active area 3 has the first ceramic material 6 .
• a second or Modified ceramic material 7 is formed in an edge area of multilayer varistor 1 .
• the second ceramic material is arranged in the area 4 close to the surface and thus essentially in the inactive area. In addition to the second ceramic material 7, the inaccurate tive area but also a part of the first ceramic material 6, as can be seen from Figure 1.
• the ceramic materials 6, 7 contain ZnO.
• ZnO is the main component of the ceramic materials 6, 7.
• the ceramic materials 6, 7 may contain a varistor-forming oxide such as bismuth oxide or a rare earth oxide (e.g. praseodymium oxide) and other oxides which improve the varistor properties.
• the ceramic materials 6, 7 are chemically almost identical. In particular, the ceramic materials 6, 7 correspond chemically to >99%. However, the ceramic materials 6, 7 have a different dielectric constant ⁇ o* ⁇ r or dielectric constant s r . In particular, the dielectric constants ⁇ o* ⁇ r or dielectric constants s r of the ceramic materials 6, 7 differ from one another by a factor of >5. The dielectric constant of the first ceramic material 6 - and thus in the active region 3 - is greater than the dielectric constant of the second ceramic material 7 - and thus in the region 4 near the surface.
• the ceramic materials 6, 7 differ in the concentration of monovalent elements X + (X + stands for Li + , Na + , K + or Ag + ).
• the ceramic materials differ from each other by a maximum of 50 ppm ⁇ Ac (X + ) ⁇ 5000 ppm.
• Ac denotes the maximum concentration difference that occurs between the active area 3 and the area 4 near the surface.
• concentration is monovalent Elements in the near-surface area 4 are 100 ppm to 1000 ppm higher than in the active area 3 .
• the monovalent elements Li + , Na + , K + , Ag + act as "acceptor doping" in the semiconducting ZnO . Therefore, the above doping can be applied to all ZnO-based varistor ceramics (regardless of the recipe).
• the ceramic materials 6, 7 must be doped with acceptors that have relatively low diffusion constants. Furthermore, the dopants in which the ceramic materials 6, 7 differ must occur in low concentrations.
• the concentration X + in the active region 3 (concentration of monovalent elements in the first ceramic material 6) is at a low level (X + ⁇ 100 ppm). In other words, the concentration of monovalent elements X + in the active area 3 is significantly lower than in the inactive area or . in the near-surface area 4 .
• a low concentration of monovalent elements X + is associated with a large (or larger) dielectric constant. Consequently, the active region 3 has a higher dielectric constant/dielectric constant than the region 4 close to the surface. An increase in the concentration of monovalent elements X + causes the dielectric constant to decrease. Overall, a significant reduction in the dielectric constant is achieved even with small amounts of monovalent elements added.
• the two ceramic materials 6, 7 are combined in such a way that the highest concentration of monovalent Elements X + in the near-surface region 4 and the lowest concentration in the active region 3 is present.
• the second ceramic material 7 thus serves as an insulating cover layer with acceptor doping and a low dielectric constant. Starting from the area 4 close to the surface, the concentration decreases step by step in the direction of the active area 3 (concentration gradient). This significantly reduces the parasitic capacitance/stray capacitance of the multilayer varistor 1 .
• FIG. 2 shows a second embodiment of a multilayer varistor 1 .
• the internal electrodes 5 and external electrodes 9 reference is made to the description in connection with FIG.
• the multilayer varistor in this exemplary embodiment has three ceramic materials/varistor ceramics 6, 7, 8 with different concentrations of monovalent elements X + .
• the second and third ceramic material (modified ceramic materials) 7 , 8 is arranged in the region 4 near the surface.
• the third ceramic material 8 is arranged between the first and the second ceramic material 6 , 7 .
• the first ceramic material 6 has a low concentration of monovalent elements.
• the first ceramic material 6 has a high dielectric constant.
• the second ceramic material 7 has a higher concentration of monovalent elements than the first ceramic material 6 .
• the concentration of monovalent elements in the third ceramic material 8 is between those of the first ceramic material 6 and the second ceramic material 7 .
• the first ceramic material 6 has the lowest concentration of monovalent elements and the second ceramic material 7 has the highest concentration of monovalent elements.
• the third ceramic material 8 has a medium concentration. This creates a concentration gradient.
• the concentration of the acceptors in the second and third ceramic material 7 , 8 is for example between 50 ppm and 5000 ppm higher than in the active ceramic layer (first or primary ceramic material 6 ).
• the second and third ceramic materials 7, 8 serve as an insulating cover layer and. Isolation zone with acceptor doping and low dielectric constant.
• FIG. 3 shows a third embodiment of a multilayer varistor 1 .
• the internal electrodes 5 in this exemplary embodiment are arranged in a tip-to-tip position. The area between the tips of the internal electrodes 5 forms the active area 3 of the multilayer varistor 1 .
• the multilayer varistor 1 has metallic protective or Faraday electrodes 10, which increase the protective function of the multilayer varistor 1 against electrostatic discharges.
• the multilayer varistor 1 in this exemplary embodiment has three ceramic materials 6, 7, 8 with different concentrations of monovalent elements X + .
• the Faraday electrodes 10 contribute to preventing the diffusion between the ceramic materials 6,7,8. Due to the reduced diffusion, a defined concentration gradient arises and, associated with this, a defined gradient of the electrical properties, above all the dielectric constant.
• the thicknesses of the cover layers are chosen so that the least possible diffusion of the acceptors into the active region 3 occurs.
• a respective extension of the second ceramic material 7 or of the third ceramic material 8 perpendicular to a main extension of the multilayer varistor 1 is understood as the thickness of the cover layers.
• the concentration of the acceptors in the second and third ceramic material 7, 8 is between 50 ppm and 5000 ppm (preferably between 100 ppm and 1000 ppm) higher than in the active ceramic layer (first ceramic material 6).
• the second and third ceramic materials 7, 8 serve as an insulating cover layer with acceptor doping and a low dielectric constant.
• the particular advantage of this invention is that the electrical properties of the modified varistor ceramic 7, 8 (second or third ceramic material 7, 8) differ greatly from those of the original varistor ceramic (first or primary res ceramic material 6 ) differ without the materials being chemically significantly different from each other . Therefore the materials are otherwise almost identical and can be processed without any problems.
• a method for producing a multilayer varistor 1 in particular a multilayer varistor according to one of the above exemplary embodiments, is described below.
• the procedure consists of the following steps :
• the ceramic powders are chemically 1 99 % identical.
• the ceramic powders essentially contain ZnO as the base material. Table 1 shows a possible composition of the base material of the ceramic powder. Of course, other compositions are also conceivable, with ZnO being the main component of the ceramic material in each case.
• Table 1 Composition of the base material of the ceramic powder. * ) Cross-contamination and entry through process: typically 1- 10 ppm potassium
• the ceramic powders differ in the concentration of monovalent elements X + .
• the ceramic powders differ in the concentration X + by 50 ppm ⁇ Ac(X+) ⁇ 5000 ppm.
• the first or Primary ceramic powder has the lowest concentration of acceptors/monovalent elements.
• the concentration of monovalent elements X + in the first ceramic powder is preferably ⁇ 100 ppm.
• the second ceramic powder has the highest concentration of acceptors/monovalent elements.
• the third ceramic powder has an intermediate/intermediate concentration of acceptors/monovalent elements.
• a second step B green films are formed from the ceramic powders.
• the powders are first ground, spray-dried and decarburized.
• the decarburized powders are slurried with organic binders and dispersants and then drawn into green sheets.
• the foils are cut to size.
• part of the green films is partially printed with a metal paste (preferably silver and/or palladium) to form the internal electrodes 5 .
• a metal paste preferably silver and/or palladium
• a further metal paste (preferably silver and/or palladium) can also be printed onto part of the green foils in order to form protective electrodes 10 (see FIG. 3).
• this metal paste is on the green sheets with the lowest and / or the. average concentration of monovalent elements (FIG. 3).
• step D the stacking of printed and unprinted green films takes place.
• the stacking takes place in such a way that the final multilayer varistor 1 has a defined concentration gradient of monovalent elements X + , the concentration decreasing starting from the second ceramic material 7 via the third ceramic material 8 ( FIGS. 2 and 3 ) to the first ceramic material 6 .
• the green films are laminated, decarburized and sintered.
• the sintering temperature is preferably 1100° C.
• the method produces a multilayer varistor 1 which has a very low stray capacitance and therefore a low capacitance.
• the modified varistor ceramic (second or third ceramic material 7, 8) is treated in production in the same way as the original/primary varistor ceramic (first ceramic material 6), since the materials differ only slightly chemically. Therefore, the powder, slip and foil properties of the materials are very similar and can be processed in the same way. The same applies to the processing of the foils into laminates and the finishing of the components (cutting, decarburization, sintering). Since the elements, such as potassium, in which the materials differ from each other have only a small difference in concentration (concentration gradient), diffusion thereof into the active volume can be neglected even during sintering. Therefore, the cover layers can be dimensioned with sufficiently high thicknesses, which increases the shielding effect.
• the capacities of the disks were measured at 1 V and 1 kHz (see Table 2).
• compositions with a reduced dielectric constant were provided which were suitable for testing the invention on the multilayer varistor.
• the composition of the first ceramic powder corresponded to the base material (see Table 1).
• the second ceramic powder was additionally doped with 1,000 ppm of potassium.
• the third ceramic powder was additionally doped with 1000 ppm potassium and 1000 ppm lanthanum.
• the powder mixtures produced in this way were ground, spray-dried and decarburized.
• the decarburized powders were ganic binder and dispersant and drawn into films.
• the foils were cut to size, printed with palladium paste, stacked and cut into multilayer components.
• the simplest design (see FIG. 1) of a 1206 ML varistor with 2 internal electrodes (120 micron electrode spacing and 0.8 mm 2 overlap area) was selected for testing. Three types of devices were produced with the three types of ceramic sheets.
• the core of the second type of component consisted of the base material with a covering layer of the second ceramic (with increased potassium concentration).
• the core of the third type of component consisted of the base material with a covering layer of the third ceramic (with increased potassium concentration and lanthanum-doped).
• the components produced in this way were each sintered at 1100°C.
• the micrographs showed that the cover layers were sintered with the core layer without any defects (no cracks, etc.).
• the components with outer electrodes made of a layer of silver were metallized and burned in.
• the capacitances of the components were measured at 1 V and 1 MHz.
• the first type of component (reference type) had a capacitance of 17.713.1 pF.
• the second type of device (top layer with increased potassium concentration) had a capacitance of 13.211.3 pF. This corresponds to a reduction in capacity of 25%.
• the third type of device (cap layer with increased potassium concentration and doped with lanthanum) had a capacitance from 11.1 ⁇ 2.4 pF to . This corresponds to a reduction in capacity of 37%. It was thus possible to show that even the simplest type of application of the invention leads to a significant reduction in the overall capacitance of the multilayer varistor.
• the current/voltage characteristic of the components was measured with increasing static currents in the range from 10 nA to 1 mA.
• the first type of component (reference type) showed a varistor voltage at 1 mA of 21591144 V with 1 .
• the second type of device had a varistor voltage at 1 mA of 22101172 V mnr 1 . This corresponds to a change in the varistor voltage of only 2%.
• the third type of device had a varistor voltage at 1 mA of 22731183 V mnr 1 . This corresponds to a 5% change in the varistor voltage.

Landscapes

• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Manufacturing & Machinery (AREA)
• Thermistors And Varistors (AREA)
• Apparatuses And Processes For Manufacturing Resistors (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=77179996

Family Applications (1)

Country Status (6)

Family Cites Families (19)

• 2020
  • 2020-08-26 DE DE102020122299.8A patent/DE102020122299B3/de active Active
• 2021
  • 2021-07-26 US US17/638,635 patent/US11901100B2/en active Active
  • 2021-07-26 EP EP21749584.5A patent/EP4205148A1/de active Pending
  • 2021-07-26 WO PCT/EP2021/070804 patent/WO2022042971A1/de unknown
  • 2021-07-26 JP JP2022512767A patent/JP2022552069A/ja active Pending
  • 2021-07-26 CN CN202180005146.3A patent/CN114521274A/zh active Pending
• 2024
  • 2024-01-23 JP JP2024008292A patent/JP2024045288A/ja active Pending

Also Published As

Similar Documents

Legal Events