Sprague Electric Company

Mra Laboratories, Inc.

Galeb H Maher

Samir G Maher

Sidney D Ross

Clinton E Hutchins

Veerabhadrarao Bheemineni

James M Wilson

Susan E Stefanik

Susan E Corah

A dielectric ceramic powder and multilayer ceramic capacitors made from the powders are disclosed. A dielectric start powder mixture includes at least ninety weight percent essentially pure barium titanate powder having an average particle size of from 0.2 to 1.2 microns; from 0.2 to 2.5 weight percent of barium lithium borosilicate; from 0.1 to 0.3 weight percent of MnCO ; 0.4 to 1.50 weight percent Nb  or a niobate compound, or a molar equivalent of Ta O or a tantalum compound as a grain growth inhibitor; and, 0.4 to 1.2 weight percent of gadolinium oxide (Gd O ). The start powder mixture is calcined and then sintered in an open zirconia setter at from 950&deg; C. to 1,025&deg; C. to produce a dielectric ceramic body that satisfies X7R capacitor performance characteristics; that includes no hazardous heavy metal oxides; and, that may include silver-palladium electrodes having 85 weight percent or more of silver.

High dielectric constant very low fired X7R ceramic capacitor, and powder for making

The invention includes a dielectric ceramic powder mixture comprising at least ninety weight percent essentially pure barium titanate powder having an average particle size of from 0.2 to 1.2 microns; from 0.2 to 2.5 weight percent of barium lithium borosilicate flux; from 0.1 to 0.3 weight percent of MnCO ; a grain growth inhibitor such as niobium oxide or other niobate compound; and, 0.4 to 1.2 weight percent of an additive selected from the group consisting of a rare earth oxide, yttrium oxide, a combination of rare earth oxides, and a combination of yttrium oxide and rare earth oxides, such that ions of the additive(s) have an average ionic radius of about 0.97 angstroms. The dielectric ceramic powder provides a start powder for making very low firing multilayer ceramic capacitors satisfying X7R performance requirements.

In a start powder mixture of magnesium zinc titanate and a barium lithium boro-silicate flux, it is discovered that the addition of lithium to the flux enables the manufacture of multilayer ceramic capacitors using the powder mixture, that perform to the COG standard including an accelerated life test. This addition of lithium also makes possible the sintering to maturity of COG multilayer capacitors at temperatures as low as 950&deg; C., which in turn allows the use of silver-palladium alloy buried electrodes of high silver and low palladium content which in turn lead to higher capacitor Q and lower manufacturing costs.

Magnesium zinc titanate powder with a barium boron lithium silicate flux and a multilayer ceramic COG capacitor made therefrom

Temperature compensating capacitors and dielectric ceramic powder compositions therefor are disclosed, based upon a dual-component barium borate and zinc silicate sintering flux. The precursor dielectric ceramic powders can include (1&minus;m) BaTiO,&plus;(m) CaZrO,(BTCZ composition), with m ranging from 20 mole percent to 35 mole percent, xBaO.yTiO,.zRE,O,(rare earth composition), (RE being a rare earth metal), with x ranging from 0 m % to 30 m %, y ranging from 45 m % to 95 m %, and z ranging from 5 m % to 50 m %, or a combination of the BTCZ and rare earth composition in varying weight percents. The effective range of B,O,in the barium borate ranges from 0.029 w % to 2.75 w % of the total dielectric composition, whereas the effective range of SiO,in the zinc silicate ranges from 0.08 w % to 1.42 w % of the total dielectric composition.

Capacitor and dielectric ceramic powder based upon a barium borate and zinc silicate dual-component sintering flux

Multilayer capacitors with have been made including a cadmium silicate flux by firing in a closed crucible at about 1100.degree. C. to provide a high K and smooth X7R coefficient of K with temperature, but tend to acquire a low insulation resistance in a high temperature life test under voltage. This problem was solved heretofore by the added step of a post-sinter anneal. However, the anneal step adds cost and further complexity to the manufacturing process. Through a number of experiments it has been discovered that by the addition of a very small and critical quantity of a calcium compound such as calcium carbonate or calcium niobate to the start ceramic powder that the unwanted anneal step may be eliminated while maintaining a high insulation resistance in an accelerated life test and with only a very small reduction of dielectric constant or smoothness with temperature

High dielectric constant X7R ceramic capacitor, and powder for making

A ceramic powder mixture is made by combining from 96 to 98 mole percent of precursors of a stoichiometric barium zirconate titanate (BZT) wherein zirconium amounts to from 13.5 to 15.0 mole percent, and adding from 0.5 to 1.5 mole percent niobium or lanthanum, from 1.2 to 2.6 weight percent of a cadmium silicate sintering flux, essentially no lead, and from zero to 2 mole % of an alkaline earth metal to obtain in the powder mixture a ratio (A/B) of the large cations (A) to the small cations (B) in the range from 1.024 to 1.035. The mixture is calcined to obtain a powder comprised of agglomerates of essentially identical composition within the ranges given above. This powder of agglomerates may then be formed into a compact body that is sintered and fired to maturity at 1100.degree. C. to produce a mature dielectric ceramic body meeting the Y5V standard and having a dielectric constant greater than 10,000 at the Curie temperature.

Method for making a BaTiO.sub.3 powder mixture the powder mixture and

Disc and monolithic (multilayer) ceramic capacitors having a fine grained barium titanate body exhibit a high dielectric constant and a smooth (X7R) temperature coefficient of capacitance. The start ceramic materials for making such capacitors are predominantly spherical barium titanate powder particles of average particle size less than 0.7 micron and of narrow particle size distribution. The barium titanate is mixed with around 2 weight percent of a the cadmium silicate flux, 3Cd.SiO.sub.2, serving as a reactivity and sintering promoting agent; and about one weight percent of a reactivity and sintering inhibitor agent, Nb.sub.2 O.sub.5. After preparing a green body of this mixture, the body is sintered at about 1100.degree. C. A powder mixture for manufacture of such capacitors includes mixing powders of the three above-described materials, mildly sintering the powder mixture and if necessary comminuting the calcine to produce a ceramic powder of agglomerates of the start powders, each agglomerate having the same composition as did the precursor mixture. Low firing monolithic ceramic capacitors have been made with 70% Ag 30% Pd buried electrodes and with ten microns thick active ceramic dielectric layers having a dielectric constant (K) of 4800 and a temperature coefficient well within the X7R range.

Fine grained BaTiO.sub.3 powder mixture and method for making

Disc and multilayer ceramic capacitors having a fine grained barium titanate body having been sintered at less than 1100.degree. C. exhibit a high dielectric constant and a smooth (X7R) temperature coefficient of capacitance. Such capacitors are made by mixing barium titanate powder of less than 0.6 micron average particle size, with around 2 weight percent of a silicate flux serving as a reactivity and sintering promoter and one weight percent Nb.sub.2 O.sub.5 serving as a reactivity and sintering inhibitor. After preparing a green body of this mixture, the body is sintered at about 1100.degree. C. In the case of making a multilayer monolithic capacitor, the buried electrodes contain no more than 30 weight percent palladium, and adjacent pairs of the buried electrodes have been spaced apart as close as 5 microns in capacitors of this fine grained high dielectric constant X7R ceramic leading to very high packing density.

Capacitor with fine grained BaTiO.sub.3 body and method for making

Dried emulsion of precursors for ceramic additives are added to paints containing fine particle ceramic materials for use in ceramic capacitors. The precursors are converted into the desired additives in the paints during the sintering of the capacitor bodies.

Dried emulsion ceramic process

A ceramic includes a dielectric ceramic body that is made by mixing powders of two barium titanate compositions of widely disparate Curie temperature with a minor quantity of a borate flux and a sintering-inhibitor such as titania or bismuth oxide. A body is formed of this start powders mixture. Upon sintering to maturity at about 1100.degree. C., the capacitor body becomes only partially co-reacted and has a dielectric constant around 2000 that varies no more than about 15% over a board operating temperature range. These properties are not a strong function of sintering conditions leading to good control at manufacturing.

Process for manufacturing a ceramic body having multiple barium-titanate

The average chemical composition of a reaction band at the interface adjacent co-sintered layers of barium titanate and a low K magnesium zinc titanate is found to be Mg.sub.0.5 Ba.sub.0.25 Zn.sub.0.25 TiO.sub.3. That magnesium barium zinc titanate is further shown to be compatible physically and chemically with barium titanate when the two are made adjacent in the green state and are themselves subsequently co-sintered. The preferred structure for use as a printed-wiring substrate capable of containing surface and buried capacitors and resistors, is a stack having a barium titanate layer sandwiched between two magnesium barium zinc titanate layers. The ratio of the dielectric constants (K) of the two materials exceeds 100. Thus, there is the possibility for making large value capacitors buried in the barium titanate while there is little capacitance and cross-talk between conductors in the outer low K material layers.

Magnesium titanate ceramic and dual dielectric substrate using same

A green ceramic cake is formed comprised of a center layer of fine-ceramic particles sandwiched between two outer layers of relatively coarse-ceramic particles. However, the chemical compositions of the center and outer layers are all essentially the same. The center layer contains a stack of spaced-apart film-patterns of electroding ink. This cake is separated into many individual green monolithic-ceramic capacitors each with electrodes extending conventionally to opposite ends thereof. These capacitors are sintered to mature the ceramic, and conductive terminations are formed at the opposite ends contacting the buried electrodes. The finer start powder of the center layer is relatively expensive, but the resulting fine grain homogenous grain structure there in the finished capacitor permits closely spaced buried electrodes and generally a higher quality dielectric due to greater density and more homogenous composition than is achieved in the cheaper outer layer material.

Monolithic compound-ceramic capacitor

Water soluble precursors of ceramic compounds are emulsified in an organic fluid containing an organic surfactant. The emulsion is subsequently mildly heated at a pressure of about 0.05 atmospheres to remove the free water from the emulsion droplets. The resulting sludge consists of particles deriving from the dehydrated emulsion droplets. These particles may only be bound by the surfactant, all or most of the original organic fluid having been boiling off under low pressure. This sludge is then heated in a standard air atmosphere to char the surfactant, which char is to maintain the separation between the dried droplet-derived particles to prevent forming sintered or fused agglomerates thereof. With continued heating the transient char is subsequently burned off and the particles are calcined to controllably and simply produce a fine ceramic powder of spherical particles having a narrow size distribution and an average size in the particularly useful range of 0.1 micron to 1.0 micron.

Emulsion-char method for making fine ceramic powders

A ceramic capacitor has a lead lanthanum titanate zirconate dielectric body including less than 1 weight % of an intergranular phase of a borate flux. Cadmium and/or zinc borate fluxes are found to be superior providing both efficient sintering and efficient gettering of the free lead that escapes the PLZT crystals during sintering so that a post anneal step to drive out the residual semiconducting lead oxide after sintering is no longer required to obtain high breakdown voltages and good accelerated life test results.

Capacitor with dielectric of PLZT and an intergranular borate

A laminar electrical component has at least one ceramic dielectric layer of from 85 to 100 mole percent magnesium orthoborate (Mg.sub.3 B.sub.2 O.sub.6) which has a low dielectric constant and a high Q. A monolithic ceramic capacitor may have a predominantly magnesium orthoborate body with lithium oxide as a flux so that sintering may be as low as 850.degree. C. and in a reducing atmosphere accommodating buried copper electrodes. A predominantly Mg.sub.3 B.sub.2 O.sub.6 multi-level printed wiring substrate of low dielectric constant can include tightly adhered layers of a high dielectric constant ceramic for making buried high capacity filter capacitors, and can also include cofired base metal conductors.

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North Adams, MA, United States of America

Galeb H Maher