Patent Application
20140098455
This application claims the priority of Korean Patent Application No. 10-2012-0110786 filed on Oct. 5, 2012, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a dielectric composition having excellent dielectric properties and electrical properties and a multilayer ceramic electronic component manufactured using the same.
2. Description of the Related Art
A perovskite powder, a ferroelectric ceramic material, has been used as a raw material of electronic components, such as a multilayer ceramic capacitor (MLCC), a ceramic filter, a piezoelectric element, a ferroelectric memory, a thermistor, a varistor, and the like.
Barium titanate (BaTiO3) is a high dielectric material having a perovskite structure, and has been used as a dielectric material for a multilayer ceramic capacitor.
Today, with the trend for slimness, compactness, high capacitance, high reliability, and the like, in electronic components, a ferroelectric particle is required to have a small size as well as an excellent dielectric constant and reliability.
If the particle diameter of a barium titanate powder, a main component of a dielectric layer, is large, surface roughness of the dielectric layer may be increased, and thus, a short circuit ratio may be increased and insulation resistance may be defective.
For this reason, as a main component of the dielectric layer, the barium titanate powder is required to be finely-granulated.
However, as a barium titanate powder is finely granulated and the dielectric layer of a multilayer ceramic electronic component is thinner, a reduction in capacitance, short circuit defects, reliability defects, and the like, may occur.
For this reason, the development of multilayer ceramic electronic components securing a dielectric constant in a dielectric layer and having excellent reliability is still in demand.
An aspect of the present invention provides a dielectric composition having excellent dielectric properties and electrical properties and a multilayer ceramic electronic component manufactured using the same.
According to an aspect of the present invention, there is provided a dielectric composition, including: dielectric grains having a perovskite structure represented by ABO3, a portion of the dielectric grains having a core-shell structure, wherein dielectric grains having an average length of a core equal to or less than 250 nm and a ratio of the average length of the core to an average length of the dielectric grain below 0.8 may be 50% or more of the portion of dielectric grains having a core-shell structure.
The portion of the dielectric grains having the core-shell structure may be less than 80% of all of the dielectric grains.
The A may include one or more selected from a group consisting of barium (Ba), strontium (Sr), lead (Pb), and calcium (Ca).
The B may include one or more selected from a group consisting of titanium (Ti) and zirconium (Zr).
In the core-shell structure, a content of rare earth elements included in a shell may be 0.4 to 4.0 at % based on 100 at % of a B-site ion.
The rare earth elements may include one or more selected from a group consisting of scandium (Sc), yttrium (Y), lanthanum (La), actinium (Ac), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and ruthenium (Ru).
The dielectric grains may include one or more selected from a group consisting of BamTiO3(0.995≦m≦1.010), (Ba1-xCax)m(Ti1-yZry)O3(0.995≦m≦1.010, 0≦x≦0.10, 0<y≦0.20), and Bam(Ti1-xZrx)O3(0.995≦m≦1.010, x≦0.10); and BamTiO3(0.995≦m≦1.010), (Ba1-xCax)m(Ti1-yZry)O3(0.995≦m≦1.010, 0≦x≦0.10, 0<y≦0.20), and Bam(Ti1-xZrx)O3 (0.995≦m≦1.010, x≦0.10), in which one or more rare earth elements are partially dissolved.
According to another aspect of the present invention, there is provided a multilayer ceramic electronic component, including: a ceramic body including dielectric layers each having an average thickness of 0.48 μm or less; and internal electrodes disposed to face each other with the dielectric layer therebetween within the ceramic body, wherein the dielectric layer may include a dielectric composition including dielectric grains having a perovskite structure represented by ABO3, and a portion of the dielectric grains may have a core-shell structure, dielectric grains having an average length of a core equal to or less than 250 nm and a ratio of the average length of the core to an average length of the dielectric grain below 0.8 being 50% or more of the portion of dielectric grains having a core-shell structure.
The portion of the dielectric grains having the core-shell structure may be less than 80% of all of the dielectric grains.
The A may include one or more selected from a group consisting of barium (Ba), strontium (Sr), lead (Pb), and calcium (Ca).
The B may include one or more selected from a group consisting of titanium (Ti) and zirconium (Zr).
In the core-shell structure, a content of rare earth elements included in a shell may be 0.4 to 4.0 at % based on 100 at % of a B-site ion.
The rare earth elements may include one or more selected from a group consisting of scandium (Sc), yttrium (Y), lanthanum (La), actinium (Ac), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and ruthenium (Ru).
The dielectric grains may include one or more selected from a group consisting of BamTiO3(0.995≦m≦1.010), (Ba1-xCax)m(Ti1-yZry)O3(0.995≦m≦1.010, 0≦x≦0.10, 0<y≦0.20), and Bam(Ti1-xZrx)O3(0.995≦m≦1.010, x≦0.10); and BamTiO3(0.995≦m≦1.010), (Ba1-xCax)m(Ti1-yZry)O3 (0.995≦m≦1.010, 0≦x≦0.10, 0<y≦0.20), and Bam(Ti1-xZrx)O3 (0.995≦m≦1.010, x≦0.10), in which one or more rare earth elements are partially dissolved.
The dielectric layer may have a dielectric constant of 4000 or greater.
The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, the shapes and dimensions of elements may be exaggerated for clarity, and the same reference numerals will be used throughout to designate the same or like elements.
Referring to
Hereinafter, the dielectric composition according to the embodiment of the present invention will be described in detail.
According to the embodiment of the present invention, the dielectric composition may include the dielectric grains 10 having a perovskite structure represented by ABO3.
In addition, the A may include one or more selected from the group consisting of barium (Ba), strontium (Sr), lead (Pb), and calcium (Ca), but is not limited thereto.
As the B, any material that can be situated in site B in the perovskite structure may be used, but is not particularly limited thereto, and examples thereof may include one or more selected from the group consisting of titanium (Ti) and zirconium (Zr).
The dielectric grain may include one or more selected from the group consisting of BamTiO3(0.995≦m≦1.010), (Ba1-xCax)m(Ti1-yZry)O3(0.995≦m≦1.010, 0≦x≦0.10, 0<≦0.20), and Bam(Ti1-xZrx)O3(0.995≦m≦1.010, x≦0.10); and BamTiO3(0.995≦m≦1.010), (Ba1-xCax)m(Ti1-yZry)O3(0.995≦m≦1.010, 0≦x≦0.10, 0<y≦0.20), and Bam(Ti1-xZrx)O3 (0.995≦m≦1.010, x≦0.10), in which one or more rare earth elements are partially dissolved, but is not limited thereto.
Generally, as the dielectric grains included in the dielectric composition are finely-granulated and a dielectric layer of a multilayer ceramic electronic component manufactured using the dielectric grains has a reduced thickness, short circuit defects, reliability defects, and the like, may occur.
Moreover, it is difficult to perform dispersion at the time of preparing slurry using a fine-granulated dielectric powder, which may cause reliability degradation in the multilayer ceramic electronic component manufactured by using the dielectric composition.
In order to overcome deterioration in reliability, a dielectric grain having rare earth elements completely dissolved therein and a perovskite structure oxide as a base material may be preferably used.
That is, in order to solve short circuit defects, reliability defects, and the like, due to the dielectric layer of the multilayer ceramic electronic component having a reduced thickness, it is necessary to control the content of rare earth elements in the dielectric grain having a perovskite structure.
In addition, in order to solve short circuit defects, reliability defects, and the like, due to the dielectric layer of the multilayer ceramic electronic component having a reduced thickness, it is necessary to control the length of the core in the dielectric grain having a core-shell structure.
According to the embodiment of the present invention, a portion of the dielectric grains 10 may include the core 1 and the shell 2 and have a core-shell structure, wherein dielectric grains having the average length (Lc) of the core 1 equal to or less than 250 nm and a ratio of the average length (Lc) of the core 1 to the average length (Lg) of the dielectric grain 10 below 0.8 may be 50% or more of the portion of dielectric grains having a core-shell structure.
A portion of the dielectric grains 10 may have a core-shell structure, and may be, is are not particularly limited to, for example, less than 80% of all of the dielectric grains 10.
The dielectric grain 10 having a core-shell structure may be defined by a dielectric grain in which another grain seems to be present, after ion-milling and chemically etching a multilayer ceramic capacitor to be described later and then measuring the multilayer ceramic capacitor at a magnification of 50,000× in a field emission scanning electron microscope (FE-SEM) under conditions of 2 kV.
In the portion of the dielectric grains 10 having a core-shell structure, dielectric grains having the average length Lc of the core 1 equal to or less than 250 nm and the ratio of the average length Lc of the core 1 to the average length Lg of the dielectric grain 10 below 0.8 may be 50% or more of the portion of dielectric grains having a core-shell structure.
With respect to the ratio of the average length (Lc) of the core 1 to the average length (Lg) of the dielectric grain 10, the average length (Lc) of the core 1 may be defined as a length of another grain observed within the dielectric grain 10 and the average length (Lg) of the dielectric grain 10 may be a length thereof, in a length direction passing through a center C of the grain in the dielectric grain 10 having a core-shell structure.
When the average length (Lc) of the core 1, the ratio of the average length (Lc) of the core 1 to the average length (Lg) of the dielectric grain 10, and the ratio conditions of the dielectric grain satisfying the above conditions are satisfied, sufficient capacitance can be secured and reliability can be improved.
Whereas, if the average length (Lc) of the core 1 is above 250 nm, the shell 2 may not be sufficiently formed, and thus, it may be difficult to improve capacitance and reliability.
In addition, in a portion of the dielectric grains 10 having a core-shell structure, if dielectric grains having a ratio of the average length (Lc) of the core 1 to the average length (Lg) of the dielectric grain 10 below 0.8 are less than 50% of the portion of dielectric grains having the core-shell structure, it is difficult to realize sufficient reliability.
Meanwhile, according to the embodiment of the present invention, when an imaginary line is drawn in a direction from the center C of the dielectric grain 10 having a core-shell structure to a grain boundary b thereof, the content of rare earth elements in a region corresponding to 0.75 to 0.95% of the dielectric grain 10 from the center C thereof may be 0.4 to 4.0 at o, based on 100 at % of a B-site ion.
The content of rare earth elements may be a content thereof in a region corresponding to 0.75 to 0.95% of the dielectric grain 10 from the center C of the dielectric grain 10 when an imaginary line is drawn in the direction from the center C of the dielectric grain 10 to the grain boundary b thereof.
The imaginary line drawn in the direction from the center C of the dielectric grain 10 to the grain boundary b thereof is not particularly limited thereto, and for example, the imaginary line may be drawn from the center C of the dielectric grain 10 to the grain boundary b thereof in which the shell is thickest.
By controlling the content of rare earth elements to satisfy 0.4 to 4.0 at o, based on 100 at % of the B-site ion, short circuit defects, reliability defects, and the like, of the multilayer ceramic electronic component manufactured by using the dielectric composition including the dielectric grain can be solved.
If the content of rare earth elements is below 0.4 at %, based on 100 at % of the B-site ion, the dielectric grain 10 has a core-shell structure the same as a core-shell structure of a dielectric grain according to the related art, which may be ineffective in improvements in reliability.
Meanwhile, if the content of rare earth elements is above 4.0 at %, based on 100 at % of the B-site ion, a desired high dielectric constant may not be obtained.
The rare earth elements may not be particularly limited, and may include one or more selected from the group consisting of scandium (Sc), yttrium (Y), lanthanum (La), actinium (Ac), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and ruthenium (Ru), for example.
The dielectric grain of the dielectric composition according to the embodiment of the present invention may be produced by the following method.
The perovskite powder is powder having a structure of ABO3. In the embodiment of the present invention, a metal oxide is an element source corresponding to site B and a metal salt is an element source corresponding to site A.
First, a perovskite particle nucleus may be formed by mixing the metal salt and the metal oxide.
The metal oxide may be one or more selected from the group consisting of titanium (Ti) and zirconium (Zr).
Titania and zirconia are very easily hydrolysable, and thus, if they are mixed with pure water without additional additive, hydrous titanium or hydrous zirconium may be precipitated in a gel form.
The hydrous metal oxide may be washed to remove impurities therefrom.
More specifically, the hydrous metal oxide is filtered by pressure, to remove a residual solution, and then filtered while being washed with pure water, to remove impurities present on a particle surface.
Next, pure water and acid or a base may be added to the hydrous metal oxide.
The pure water may be put into hydrous metal oxide powder obtained after filtering, and then the mixture was stirred by a high-viscosity stirrer at a temperature of 0° C. to 60° C. for 0.1 to 72 hours, thereby preparing a hydrous metal oxide slurry.
Acid or a base may be added to the prepared slurry. Here, the acid or base may be used as a peptizing agent, and may be added in 0.00001 to 0.2 moles, based on the content of hydrous metal oxide.
The acid is not particularly limited as long as it is commonly used, and examples thereof may include hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid, formic acid, acetic acid, polycarboxylic acid, and the like, which may be used alone or in combination of at least two thereof.
The base is not particularly limited as long as it is commonly used, and examples thereof may include tetramethyl ammonium hydroxide, tetra ethyl ammonium hydroxide, and the like, which may be used alone or in combination of at least two thereof.
The metal salt may be barium hydroxide or a combination of a rare earth salt and barium hydroxide.
The rare earth salt may be scandium (Sc), yttrium (Y), lanthanum (La), actinium (Ac), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), ruthenium (Ru) or the like, but are not limited thereto.
The forming of the perovskite particle nucleus may performed at 60° C. to 150° C.
Next, the perovskite particle nucleus is input into a hydrothermal reactor and subjected to hydrothermal treatment, such that the perovskite particle nucleus may be grown in the hydrothermal reactor.
Next, an aqueous metal salt solution is inputted into the hydrothermal reactor by using a high-pressure pump, to prepare a mixture liquid. The mixture liquid is heated to obtain a dielectric grain having a perovskite structure represented by ABO3.
The aqueous metal salt solution is not particularly limited, and may be, for example, one or more selected from the group consisting of nitrate and acetate.
Referring to
Hereinafter, the multilayer ceramic electronic component according to the embodiment of the present invention, particularly, the multilayer ceramic capacitor, will be described, but the present invention is not limited thereto.
In the multilayer ceramic capacitor according to the embodiment of the present invention, “length direction”, “width direction”, and “thickness direction” will be defined as the ‘L’ direction, the ‘W’ direction, and the ‘T’ direction, of
According to the embodiment of the present invention, a raw material for forming the dielectric layer 11 is not particularly limited as long as sufficient capacitance can be obtained thereby. For example, the raw material may be a barium titanate (BaTiO3) powder.
The multilayer ceramic capacitor manufactured by using the barium titanate (BaTiO3) powder has a high room-temperature dielectric constant and excellent insulation resistance and withstand voltage characteristics, and thus, reliability thereof can be improved.
The dielectric layer 11 may include a dielectric composition including dielectric grains 10 having a perovskite structure represented by ABO3, and a portion of the dielectric grains may have a core-shell structure, wherein dielectric grains having an average length of a core equal to or less than 250 nm and a ratio of the average length of the core to an average length of the dielectric grain below 0.8 may be 50% or more of the portion of dielectric grains having a core-shell structure, such that the multilayer ceramic capacitor has a high room-temperature dielectric constant and excellent insulation resistance and withstand voltage characteristics, and thus, reliability thereof can be improved.
In addition, the multilayer ceramic capacitor according to the embodiment of the present invention may include the dielectric grain in which when an imaginary line is drawn in a direction from the center C of the dielectric grain to the grain boundary b thereof, the content of rare earth elements in a region corresponding to 0.75 to 0.95% of the dielectric grain from the center C thereof may be 0.4 to 4.0 at o, based on 100 at % of the B-site ion, such that the multilayer ceramic capacitor has a high room-temperature dielectric constant and excellent insulation resistance and withstand voltage characteristics, and thus, reliability thereof can be improved.
As a material for forming the dielectric layer 11, various ceramic additives, organic solvents, plasticizers, binders, dispersants, or the like may be added to powder, such as the barium titanate (BaTiO3) powder, depending on the objects of the present invention.
The average thickness of the dielectric layer 11 may be, but is not particularly limited to, for example, 0.48 μm or less.
The dielectric composition according to the embodiment of the present invention has better effects when the average thickness of the dielectric layer 11 is 0.48 μm or less. That is, the multilayer ceramic capacitor manufactured by using the dielectric composition has excellent reliability when the average thickness of the dielectric layer is 0.48 μm or less.
The dielectric constant of the dielectric layer 11 may be, but is not particularly limited to, for example, 4000 or greater.
The other features of the present embodiment overlap the features of the dielectric grain according to the aforementioned embodiment of the present invention, and thus, descriptions thereof will be omitted.
A material for forming the first and second internal electrodes 21 and 22 is not particularly limited. For example, they may be formed by using a conductive paste made of one or more of silver (Ag), lead (Pb), platinum (Pt), nickel (Ni) and copper (Cu).
The multilayer ceramic capacitor according to the embodiment of the present invention may further include a first external electrode 31 electrically connected to the first internal electrode 21 and a second external electrode 32 electrically connected to the second internal electrode 22.
The first and second external electrodes 31 and 32 may be electrically connected to the respective first and second internal electrodes 21 and 22 so as to form capacitance, and the second external electrode 32 may be connected to a potential different from that of the first external electrode 31.
A material for forming the first and second external electrodes 31 and 32 is not particularly limited as long as the first and second external electrodes 31 and 32 can be electrically connected to the first and second internal electrodes 21 and 22 so as to form capacitance, and may include one or more selected from the group consisting of copper (Cu), nickel (Ni), silver (Ag), and silver-palladium (Ag—Pd).
Hereafter, the present invention will be described in detail with reference to examples, but is not limited thereto.
Examples of the present invention were manufactured by using a dielectric composition including dielectric grains having a perovskite structure represented by ABO3, a portion of the dielectric grains having a core-shell structure, wherein dielectric grains having an average length of a core equal to or less than 250 nm and a ratio of the average length of the core to an average length of the dielectric grain below 0.8 are 50% or more of the portion of dielectric grains having a core-shell structure.
In addition, the examples of the present invention were manufactured by using a dielectric composition, including a dielectric composition including a dielectric grain having a perovskite structure represented by ABO3, in which, when an imaginary line is drawn in a direction from a center of the dielectric grain to a grain boundary thereof, a content of rare earth elements in a region corresponding to 0.75 to 0.95% of the dielectric grain from the center thereof may be 0.4 to 4.0 at %, based on 100 at % of a B-site ion.
Comparative Examples were manufactured by preparing a dielectric composition including a dielectric grain having the same composition as that of the examples of the present invention, except that numeral ranges were outside of the foregoing numeral ranges of the present invention.
Table 1 below shows results in which reliability evaluation was compared according to core-shell grain fractions and the fractions of dielectric grains in which a ratio of the average length of the core to the average length of the dielectric grain is below 0.8.
The reliability evaluation was measured at 1 kHz and 0.5V by using an LCR meter, after the dielectric composition was heated and then one hour had elapsed. Reliability evaluation was performed by counting the number of defective samples among 40 samples under the conditions of 130° C., 8V, and 4 hours.
It can be seen from Table 1 above that each of Samples 2, 3, 5, 6, and 8 was a multilayer ceramic capacitor manufactured by using a dielectric grain satisfying the numeral range of the present invention, and reliability thereof was excellent.
Whereas, it can be seen that each of Samples 1, 4, and 7 was outside of the numeral range of the present invention, and had defects in terms of reliability.
Table 2 below shows results in which capacitance and dielectric loss were compared according to the content of rare earth elements in a different position of the dielectric grain.
The capacitance and the dielectric loss were measured at 1 kHz and 0.5V by using an LCR meter, after the dielectric composition was heated and then one hour had elapsed. Reliability evaluation was performed by counting the number of defective samples among 40 samples under the conditions of 130° C., 8V, and 4 hours.
Capacitances of the samples were measured, and the samples were determined to be good or bad based on 2.68 as a minimum capacitance.
It can be seen from Table 2 above that each of Samples 9, 10, 14-16, and 20 was a multilayer ceramic capacitor manufactured by using a dielectric grain satisfying the numerical range of the present invention, and capacitance thereof was high and reliability thereof was excellent.
Whereas, it can be seen that each of Samples 11-13, 17-19, and 21 was outside of the numeral range of the present invention, and had defects in capacitance or reliability, or both capacitance and reliability.
As set forth above, according to the embodiments of the present invention, the multilayer ceramic electronic component manufactured using the dielectric composition can have excellent reliability and secure a high dielectric constant.
While the present invention has been shown and described in connection with the embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2012-0110786 | Oct 2012 | KR | national |
