Dielectric composition and electronic component

Abstract

To provide a novel dielectric composition with high density even when fired at relatively low temperature.SOLUTION: A dielectric composition comprises: tantalum and at least one of barium and strontium as main components; and calcium and silicon as minor components.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a dielectric composition and an electronic component. [Background technology]

[0002] For example, as shown in Patent Document 1, a dielectric composition that does not contain lead or alkali metals and has a high relative dielectric constant has been developed.

[0003] However, new dielectric compositions that are being developed have the problem that high-density dielectrics cannot be obtained unless they are fired at high temperatures. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-103671 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above circumstances, and has as its object to provide a novel dielectric composition that has a high density even when fired at a relatively low temperature. [Means for solving the problem]

[0006] The dielectric composition according to the present invention contains, as a main component, at least one of barium and strontium, and tantalum, Contains calcium and silicon as secondary ingredients.

[0007] The dielectric composition according to the present invention has a high density and a high relative dielectric constant even when fired at a relatively low temperature. The reasons for this are thought to be as follows.

[0008] The inclusion of calcium and silicon as minor components in the dielectric composition of the present invention is believed to facilitate the movement of elements constituting the main component via the minor components. As a result, it is believed that the density can be improved even when the dielectric composition is fired at a relatively low temperature. Furthermore, the relative dielectric constant can also be improved.

[0009] The main component preferably contains strontium.

[0010] This makes it possible to increase the density and the relative dielectric constant of the dielectric composition even when the composition is fired at a relatively low temperature.

[0011] The main components preferably include barium and strontium.

[0012] This makes it possible to increase the density and the relative dielectric constant of the dielectric composition even when the composition is fired at a relatively low temperature.

[0013] The auxiliary component preferably further contains barium.

[0014] This makes it possible to increase the density and the relative dielectric constant of the dielectric composition even when the composition is fired at a relatively low temperature.

[0015] When the total amount of the dielectric composition is 100 parts by mass, The total content of calcium and silicon is preferably 0.5 to 10 parts by mass in terms of oxides when the valence of calcium is divalent and the valence of silicon is tetravalent.

[0016] The main component is {Ba x Sr (1-x)} m Ta4O 12 where x is preferably 0.75 or less. This results in a higher relative permittivity and a higher density. Furthermore, the resistivity is higher and the dielectric loss is lower.

[0017] It is preferable that m is 1.8 to 2.2, which leads to a higher relative permittivity, higher density and resistivity, and lower dielectric loss.

[0018] The crystal system of the main component is preferably a tetragonal system.

[0019] The dielectric composition according to the present invention is preferably substantially free of niobium, alkali metals and lead.

[0020] Moreover, an electronic device according to the present invention comprises the above-mentioned dielectric composition. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 1 is a schematic cross-sectional view of a multilayer ceramic capacitor according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] < Multilayer ceramic capacitors > FIG. 1 shows a multilayer ceramic capacitor 1 as an example of an electronic component according to this embodiment. The multilayer ceramic capacitor 1 has an element body 10 configured by alternately stacking dielectric layers 2 and internal electrode layers 3. A pair of external electrodes 4 is formed on both ends of the element body 10, and is electrically connected to the internal electrode layers 3 alternately arranged inside the element body 10. There are no particular restrictions on the shape of the element body 10, but it is usually a rectangular parallelepiped. There are also no particular restrictions on the dimensions of the element body 10, and the dimensions may be appropriate depending on the application.

[0023] < Dielectric layer > The dielectric layer 2 is made of a dielectric composition according to this embodiment, which will be described later.

[0024] The thickness per layer of the dielectric layer 2 (interlayer thickness) is not particularly limited and can be set according to the desired characteristics, application, etc. Usually, the interlayer thickness is preferably 30 μm or less, more preferably 15 μm or less, and even more preferably 10 μm or less.

[0025] < internal electrode layer > In this embodiment, the internal electrode layers 3 are stacked so that their ends are alternately exposed on the surfaces of two opposing end faces of the element body 10 .

[0026] The conductive material contained in the internal electrode layer 3 is not particularly limited. Examples of noble metals used as conductive materials include palladium, platinum, and silver-palladium alloys. Examples of base metals used as conductive materials include nickel, nickel-based alloys, copper, and copper-based alloys. Note that nickel, nickel-based alloys, copper, or copper-based alloys may contain trace components such as phosphorus and / or sulfur in an amount of about 0.1 mass % or less. The internal electrode layer 3 may also be formed using a commercially available electrode paste. The thickness of the internal electrode layer 3 may be determined appropriately depending on the application, etc.

[0027] < external electrode > There are no particular restrictions on the conductive material contained in the external electrodes 4. For example, known conductive materials such as nickel, copper, tin, silver, palladium, platinum, gold, or alloys of these, conductive resins, etc. may be used. The thickness of the external electrodes 4 may be determined appropriately depending on the application, etc.

[0028] < Dielectric composition > The dielectric composition constituting the dielectric layer 2 according to this embodiment contains at least one of barium and strontium, and tantalum as main components.

[0029] The main component of the dielectric composition according to this embodiment preferably contains strontium, and more preferably contains both strontium and barium.

[0030] The main component of the dielectric composition according to this embodiment is {Ba x Sr (1-x)} m Ta4O 12 It is expressed as:

[0031] It is preferable that x is 0.75 or less.

[0032] m is preferably 1.8 to 2.2, and more preferably 1.9 to 2.1.

[0033] The crystal system of the main component of the dielectric composition according to this embodiment is not particularly limited, but is preferably a tetragonal or orthorhombic system, and more preferably a tetragonal system.

[0034] The main component is a component that occupies 80 to 100 parts by mol, preferably 90 to 100 parts by mol, when the elements other than oxygen contained in the dielectric composition are taken as 100 parts by mol.

[0035] Furthermore, the dielectric composition according to this embodiment is substantially free of niobium, alkali metals, and lead. "Substantially free of niobium, alkali metals, and lead" means that the total amount of "niobium, alkali metals, and lead" is 10 parts by mol or less, and preferably 5 parts by mol or less, when the total amount of elements other than oxygen contained in the dielectric composition is 100 parts by mol.

[0036] The dielectric composition according to this embodiment contains calcium and silicon as minor components, and preferably further contains barium as a minor component.

[0037] When the total amount of the dielectric composition is taken as 100 parts by mass, in this embodiment, the total amount of calcium and silicon contained in the dielectric composition is preferably 0.5 to 10 parts by mass, and more preferably 1 to 5 parts by mass, in terms of oxide, when the valence of calcium is divalent and the valence of silicon is tetravalent.

[0038] The ratio of the amount (moles) of calcium contained in the dielectric composition to the amount (moles) of silicon contained in the dielectric composition according to this embodiment is preferably 0.12 to 1.1, and more preferably 0.22 to 0.88.

[0039] The dielectric composition according to this embodiment may contain vanadium, titanium, aluminum, magnesium, manganese, chromium, rare earth elements, and the like in addition to the above-mentioned main and sub-components.

[0040] < Manufacturing method for multilayer ceramic capacitors > Next, an example of a method for manufacturing the multilayer ceramic capacitor 1 shown in FIG. 1 will be described.

[0041] In this embodiment, powders of the main components and powders of the subcomponents that constitute the dielectric composition are prepared. The method for producing the main component powder is not particularly limited, but it can be produced by a solid-phase reaction method such as calcination. The raw materials for the elements that constitute the main component powder or the subcomponent powder are not particularly limited, and oxides of the respective elements can be used. In addition, various compounds that can produce oxides of the respective elements by firing can be used.

[0042] In this embodiment, barium may be contained as a secondary component. The inclusion of barium in the powder of the secondary component makes it easier for barium to be present at grain boundaries. The ratio of the amount (moles) of barium contained in the secondary component to the amount (moles) of silicon contained in the secondary component (hereinafter referred to as "Ba / Si") is preferably 0.12 to 1.1, and more preferably 0.22 to 0.88.

[0043] The raw materials for the main component powder and the subcomponent powder are weighed in a predetermined ratio and then wet-mixed for a predetermined time using a ball mill or the like. The mixed powder is dried and then heat-treated in the air at a temperature of 700 to 1300°C to obtain calcined powders of the main component and the subcomponent. The calcined powder may also be pulverized for a predetermined time using a ball mill or the like.

[0044] Next, a paste for producing a green chip is prepared. The calcined powder of the main component and the subcomponent is kneaded with a solvent to form a paste for the dielectric layer. Known binders and solvents may be used.

[0045] The dielectric layer paste may contain additives such as a plasticizer and a dispersant, if necessary.

[0046] The internal electrode layer paste is obtained by kneading the above-mentioned raw materials of the conductive material, a binder, and a solvent. Known binders and solvents may be used. The internal electrode layer paste may contain additives such as co-materials and plasticizers as necessary.

[0047] The external electrode paste can be prepared in the same manner as the internal electrode layer paste.

[0048] Using each of the obtained pastes, green sheets and internal electrode patterns are formed, and these are laminated to obtain a green chip.

[0049] The obtained green chip is subjected to a binder removal treatment as required. The binder removal treatment conditions are, for example, a holding temperature of preferably 200 to 350°C.

[0050] After the binder removal process, the green chip is fired to obtain the element body 10. In this embodiment, the atmosphere during firing is not particularly limited, and the firing may be performed in air or in a reducing atmosphere. In this embodiment, the holding temperature during firing is, for example, 1250 to 1455°C.

[0051] After firing, the obtained element body 10 is subjected to a reoxidation treatment (annealing) as necessary. The annealing conditions are preferably, for example, such that the oxygen partial pressure during annealing is higher than the oxygen partial pressure during firing, and the holding temperature is 1150°C or lower.

[0052] The dielectric composition constituting the dielectric layer 2 of the element body 10 obtained as described above is the dielectric composition described above. The end faces of this element body 10 are polished, and an external electrode paste is applied and baked to form the external electrodes 4. Then, if necessary, a coating layer is formed on the surface of the external electrodes 4 by plating or the like.

[0053] In this manner, the multilayer ceramic capacitor 1 according to this embodiment is manufactured.

[0054] In this embodiment, since the dielectric composition contains calcium and silicon as minor components, the dielectric composition can have a high density even when fired and sintered at a relatively low temperature. The reasons for this are thought to be as follows.

[0055] It is believed that the inclusion of calcium and silicon as minor components in the dielectric composition of this embodiment facilitates the movement of elements constituting the main component via the minor components. As a result, it is believed that the density of the dielectric composition of this embodiment can be improved even when fired at a relatively low temperature. In addition, the relative dielectric constant can also be improved.

[0056] Furthermore, it is believed that the inclusion of barium as a minor component facilitates the movement of elements constituting the main component via the minor component, which is believed to result in improved density and dielectric constant even when fired at a relatively low temperature.

[0057] Furthermore, according to this embodiment, by containing tantalum and at least one selected from barium and strontium as main components, it is possible to obtain a dielectric composition having a constant and high relative dielectric constant over a wide temperature range. Specifically, the dielectric composition according to this embodiment can exhibit a relative dielectric constant of 35 or more in the temperature range of -55 to 150°C, and a relative dielectric constant of 33 or more in the temperature range of -70 to 180°C.

[0058] Furthermore, with the dielectric composition according to this embodiment, the capacitance change rate can be kept within ±22% in the temperature range of −55 to 150° C., with the reference temperature set to 25° C., thereby satisfying the X8S characteristics. Furthermore, with the reference temperature set to 25° C., the capacitance change rate can be kept within ±22% in the temperature range of −70 to 180° C.

[0059] Furthermore, according to this embodiment, it is possible to obtain a dielectric composition that is substantially free of niobium, alkali metals, and lead, and that exhibits high density, high relative dielectric constant, low dielectric loss, and high resistivity.

[0060] Dielectric compositions exhibiting a high relative dielectric constant include (Sr,Ba)Nb2O6, which is mainly composed of niobium, (Na,K)NbO3, which contains alkali metals, and Pb(Zr,Ti)O3, which contains lead.

[0061] The dielectric composition according to this embodiment, which contains tantalum and is substantially free of niobium, tends to exhibit a higher dielectric constant, lower dielectric loss, and higher resistivity than conventional dielectric compositions that are free of tantalum and contain niobium, possibly because oxygen defects are less likely to occur in tantalum oxide than in niobium oxide.

[0062] Dielectric properties are characteristics that are assumed to be those of an insulator. Therefore, a dielectric composition is required to have high resistance so that it does not become a semiconductor or a conductor. As mentioned above, tantalum oxide is less likely to develop oxygen defects than niobium oxide. In other words, the change in valence is controlled. For this reason, even when tantalum oxide is subjected to reduction firing in order to be co-fired with a base metal, the valence is less likely to change, and the decrease in resistivity is suppressed, which is thought to enable high resistivity to be exhibited over a wide temperature range. For the same reason, it is also thought that tantalum oxide can exhibit low dielectric loss.

[0063] Furthermore, since the dielectric composition according to this embodiment does not substantially contain alkali metals, it is possible to prevent deviation in the composition of the dielectric composition and contamination of the furnace due to evaporation of alkali metals.

[0064] Furthermore, although the use of lead is restricted by the RoHS (Restriction of Hazardous Substances Directive) and the like, the dielectric composition according to this embodiment does not substantially contain lead.

[0065] Although the embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and it goes without saying that the present invention can be embodied in various different forms without departing from the spirit of the present invention.

[0066] In the above-described embodiment, the electronic component according to the present invention is described as a multilayer ceramic capacitor. However, the electronic component according to the present invention is not limited to a multilayer ceramic capacitor, and may be any electronic component having the above-described dielectric composition.

[0067] For example, it may be a single-plate ceramic capacitor in which a pair of electrodes is formed on a single-layer dielectric substrate made of the above-mentioned dielectric composition.

[0068] Furthermore, the electronic component according to the present invention may be a filter, a diplexer, a resonator, an oscillator, an antenna, or the like, in addition to a capacitor. [Example]

[0069] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to the following examples.

[0070] [ Experiment 1 ] < Sample numbers 1-3, 11-13, 21-23, 31-33, 41-44, 51-54 > Powders of barium carbonate, strontium carbonate, and tantalum oxide were prepared as starting materials for the main components of the dielectric composition. The prepared starting materials for the main components were weighed so that the compositions of the main components after firing would be as shown in Tables 1 to 3.

[0071] Furthermore, raw material powders of each of the minor components shown in Tables 1 to 3 were prepared as starting materials for the minor components of the dielectric composition. The prepared starting materials for the minor components were weighed so that the contents of the minor components after firing would be as shown in Tables 1 to 3. Note that the "content of the minor components" refers to the "content in oxide equivalent of the elements constituting the minor components when the total amount of the dielectric composition is 100 parts by mass." In this case, the valences were calculated by assuming that barium, calcium, silicon, and magnesium were divalent, respectively.

[0072] Specifically, calcium carbonate and silicon oxide were prepared as starting materials for the minor components in Sample Nos. 2, 12, and 22. In Sample Nos. 2, 12, and 22, the ratio of the amount (moles) of calcium contained in the minor component to the amount (moles) of silicon contained in the minor component (hereinafter referred to as "Ca / Si") was 0.42.

[0073] Furthermore, barium carbonate, calcium carbonate, and silicon oxide were prepared as starting materials for the subcomponents in sample numbers 3, 13, and 23. In sample numbers 3, 13, and 23, Ba / Si was set to 0.58, and Ca / Si was set to 0.42.

[0074] Next, the weighed powders were wet mixed in a ball mill using ion-exchanged water as a dispersion medium, and the mixture was dried to obtain a mixed raw material powder. The mixed raw material powder was then heat-treated in air at a holding temperature of 900°C for 2 hours to obtain calcined powders of the main and subcomponents.

[0075] The calcined powder of the main component and the subcomponent thus obtained was wet-pulverized in a ball mill using ion-exchanged water as a dispersion medium, and then dried to obtain a dielectric material.

[0076] To 100 parts by mass of the obtained dielectric raw material, 10 parts by mass of an aqueous solution containing 6 parts by mass of polyvinyl alcohol resin as a binder was added and granulated to obtain a granulated powder.

[0077] The obtained granulated powder was poured into a φ12 mm die and subjected to a pressure of 0.6 ton / cm2 The material is pre-press molded at a pressure of 1.2 ton / cm. 2 The mixture was pressed under a pressure of 1000 to obtain a disk-shaped green compact.

[0078] Next, the obtained green molded body was subjected to a binder removal treatment, firing, and annealing under the following conditions to obtain a device body.

[0079] The binder removal treatment conditions were as follows: holding temperature: 400°C, temperature holding time: 2 hours, atmosphere: air.

[0080] The firing conditions were: holding temperature: 1340°C, temperature holding time: 2 hours, atmosphere: humidified N2 + H2 mixed gas (oxygen partial pressure 10 -12 A wetter was used to humidify the atmospheric gas during firing.

[0081] The annealing conditions were: holding temperature: 1050°C, temperature holding time: 2 hours, atmospheric gas: humidified N2 gas (oxygen partial pressure: 10 -7 A wetter was used to moisten the atmospheric gas during annealing.

[0082] The density and relative dielectric constant of the obtained sintered body (dielectric composition) were examined by the following method. To measure the relative dielectric constant, an In-Ga electrode was applied to the above-mentioned dielectric composition (sintered body) to obtain a disk-shaped ceramic capacitor sample (capacitor sample).

[0083] < density > The density of the dielectric composition was measured as follows. First, the volume V of the dielectric composition was calculated. Next, the mass m of the disk-shaped dielectric composition was measured, and the density of the dielectric composition was obtained by calculating m / V. The results are shown in Tables 1 to 3.

[0084] < relative permittivity > A signal with a frequency of 1 kHz and an input signal level (measurement voltage) of 1 Vrms was input to the capacitor sample using a digital LCR meter (4284A manufactured by YHP) at room temperature (20°C) to measure the capacitance C. The relative dielectric constant was then calculated based on the thickness of the sintered body, the effective electrode area, and the capacitance C obtained as a result of the measurement. The results are shown in Tables 1 to 3.

[0085] [Table 1]

[0086] [Table 2]

[0087] [Table 3]

[0088] From Table 1, it was confirmed that when calcium and silicon were contained as secondary components (sample numbers 2, 3, 12, 13, 22, and 23), the density and relative dielectric constant were higher than in other cases (sample numbers 1, 11, 21, and 31 to 33).

[0089] From Table 2, it was confirmed that when the calcium and silicon contents were 0.5 to 10 parts by mass in terms of oxides (sample numbers 12, 41 to 44), high density and high dielectric constant were obtained, and when the calcium and silicon contents were 1 to 5 parts by mass in terms of oxides (sample numbers 12, 42 and 43), even higher density and higher dielectric constant were obtained.

[0090] From Table 3, it was confirmed that when Ca / Si was 0.12 to 1.1 (sample numbers 12 and 51 to 54), high density and high dielectric constant were obtained, and when Ca / Si was 0.22 to 0.88 (sample numbers 12, 52 and 53), even higher density and higher dielectric constant were obtained.

[0091] In this example, since silicon and calcium are not contained in addition to the minor components, "when Ca / Si is 0.12 to 1.1" (sample numbers 12 and 51 to 54) means "when the ratio of the amount of calcium (moles) contained in the dielectric composition to the amount of silicon (moles) contained in the dielectric composition is 0.12 to 1.1" (sample numbers 12, 51 to 54). Similarly, "when Ca / Si is 0.22 to 0.88" (sample numbers 12, 52, and 53) means "when the ratio of the amount of calcium (moles) contained in the dielectric composition to the amount of silicon (moles) contained in the dielectric composition is 0.22 to 0.88" (sample numbers 12, 52, and 53).

[0092] [ Experiment 2 ] < Sample numbers 61 to 63, 71, and 72 > For sample numbers 61 to 63, 71 and 72, dielectric compositions were obtained in the same manner as in Experiment 1, except that the components and amounts of the starting materials for the dielectric compositions were as follows, and the density and dielectric constant were examined. The density and dielectric constant of each sample are shown in Tables 4 and 5.

[0093] That is, in Experiment 2, powders of barium carbonate, strontium carbonate, and tantalum oxide were prepared as starting materials for the main components of the dielectric composition. x Sr (1-x)} m Ta4O 12 The starting materials for the main components were weighed out so that the compositions shown in Table 4 or Table 5 were obtained.

[0094] The accessory components were calcium and silicon, with Ca / Si being 0.42. When the total amount of the dielectric composition was 100 parts by mass, the content of the accessory components was 3 parts by mass in terms of oxides.

[0095] [Table 4]

[0096] [Table 5]

[0097] From Tables 4 and 5, the main components are {Ba x Sr (1-x)} m Ta4O 12 It was confirmed that when x was 0.75 or less (sample numbers 12, 22, 61 to 63) and when m was 1.90 to 2.10 (sample numbers 12, 71 and 72), high density and high relative dielectric constant were obtained. [Explanation of symbols]

[0098] 1. Multilayer ceramic capacitor 10... Element body 2... Dielectric layer 3… Internal electrode layer 4… External electrode

Claims

1. Contains at least one of barium and strontium, and tantalum as main components, A dielectric composition containing calcium and silicon as minor components, The main component includes strontium, The main component is represented by {BaxSr(1-x)}mTa4O12, x is equal to or less than 0.75; m is 1.8 to 2.2, When the total amount of the dielectric composition is 100 parts by mass, The total amount of calcium and silicon contained in the dielectric composition is 0.5 to 10 parts by mass in terms of oxide when the valence of calcium is assumed to be divalent and the valence of silicon is assumed to be tetravalent, A dielectric composition, wherein the ratio of the amount of calcium contained in said dielectric composition to the amount of silicon contained in said dielectric composition is 0.12 to 1.

1.

2. 2. The dielectric composition of claim 1, wherein the main components include barium and strontium.

3. 3. The dielectric composition according to claim 1, wherein the auxiliary component further comprises barium.

4. An electronic component comprising the dielectric composition according to any one of claims 1 to 3.

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