X7R type multilayer ceramic capacitor dielectric material and preparation method thereof

Abstract

The invention relates to an X7R type multilayer ceramic capacitor dielectric material and a preparation method thereof. The X7R type multilayer ceramic capacitor dielectric material is composed of a main component and auxiliary components, wherein the main component is a compound which is represented by a general formula ABO3 and has a perovskite type crystal structure, the first auxiliary component is at least one of Nb2O5 or MoO3, the second auxiliary component is an oxide of a rare earth element Re, the third auxiliary component is an oxide of Mg, and the fourth auxiliary component is an oxide of Si; relative to 1mol of ABO3 main component, the total addition amount a of Nb or Mo element is more than 0 and less than or equal to 0.1% mol, the addition amount b of Re element is more than or equal to 1.2 and less than or equal to 3.0% mol, the addition amount c of Mg element is more than or equal to 1.5 and less than or equal to 3.0% mol, and the addition amount d of Si element is more than or equal to 0.8 and less than or equal to 1.2% mol; a, b, c and d are located in a range surrounded by specific points in a ternary phase diagram formed by a + b, c and d.

Description

Technical Field

[0001] This invention belongs to the field of electronic component ceramic materials technology, specifically relating to an X7R type multilayer ceramic capacitor dielectric material and its preparation method. Background Technology

[0002] Multilayer ceramic capacitors (MLCCs) are passive chip components formed by stacking ceramic dielectric films with printed internal electrodes in a staggered manner using multilayer ceramic technology, co-firing them at high temperature to form a ceramic chip, and then sealing metal terminals at both ends of the chip. MLCCs are basic components in circuits used for oscillation, tuning, noise bypassing, power supply filtering, and energy storage. They have advantages such as high capacitance, low dielectric loss, good frequency characteristics, high breakdown strength, small size, long life, and low cost, and are widely used in smart terminals, automotive electronics, 5G communications, and aerospace.

[0003] The equivalent circuit of an MLCC (Multi-Layer Ceramic Capacitor) is multiple simple parallel-plate capacitors connected in parallel. Its capacitance is directly proportional to the overlap area of ​​the internal electrodes, the number of dielectric layers, and the relative permittivity of the dielectric material, and inversely proportional to the thickness of a single dielectric layer. In recent years, with the trend towards thinner and lighter smartphones and the increasing richness and continuous upgrading of terminal device functions, MLCCs have been driven towards miniaturization and higher capacitance. The most effective technical approach to achieving miniaturization and higher capacitance is to increase the dielectric constant of the dielectric material, reduce the dielectric film thickness, and increase the number of layers. Thinning the dielectric layer of an MLCC not only increases the capacitance of a single layer but also reduces the volume, increasing the space for increasing the number of layers. Currently, the most advanced MLCC technology can achieve a single dielectric layer thickness of 1 μm. To ensure the reliability of MLCCs, a single dielectric layer must contain at least three grains in the thickness direction. Therefore, the grain size must be controlled below 350 nm while ensuring density. At the same time, high dielectric constant dielectric materials can achieve higher capacitance with the same dielectric thickness, which requires maintaining a high dielectric constant while controlling the grain size.

[0004] Currently, the challenge of widely used barium titanate-based MLCC dielectric materials lies in the fact that high dielectric constant, small grain size, high reliability, and a wide stable temperature range are often mutually exclusive. The key to solving this problem is controlling the formation of the core-shell structure in barium titanate ceramics. In addition, to match the current mainstream nickel metal internal electrode co-firing process, MLCC dielectric materials are also required to have excellent reduction resistance under reducing atmosphere sintering conditions. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide an X7R type multilayer ceramic capacitor dielectric material with small grain size, high dielectric constant, and co-fired with nickel metal internal electrodes under a reducing atmosphere, as well as a method for preparing the same.

[0006] In a first aspect, the present invention provides an X7R type multilayer ceramic capacitor dielectric material, wherein the X7R type multilayer ceramic capacitor dielectric material is composed of a main component and a secondary component; The main component is a compound with a perovskite-type crystal structure represented by the general formula ABO3; wherein, A is Ba alone or Ba and at least one selected from Ca or Sr, and B is Ti alone or Ti and Zr. The first secondary component is at least one of Nb₂O₅ or MoO₃; wherein, relative to 1 mol of ABO₃ main component, the total amount of Nb or Mo added, a, is 0 < a ≤ 0.1% mol, preferably 0.05% ≤ a ≤ 0.1% mol; The second component is an oxide of the rare earth element Re; wherein, relative to 1 mol of the ABO3 main component, the amount of Re added, b, is 1.2 ≤ b ≤ 3.0% mol, preferably 1.6 ≤ b ≤ 2.6% mol; The third component is Mg oxide; wherein, relative to 1 mol of ABO3 main component, the amount of Mg added, c, is 1.5 ≤ c ≤ 3.0% mol, preferably 2.0 ≤ c ≤ 2.5% mol; The fourth sub-component is an oxide of Si; wherein, relative to 1 mol of the main ABO3 component, the amount of Si element added, d, is 0.8 ≤ d ≤ 1.2% mol, preferably 0.9 ≤ d ≤ 1.1% mol; The addition amounts a, b, c, and d of the first, second, third, and fourth sub-components in the dielectric material of the X7R type multilayer ceramic capacitor are located within the range enclosed by points (0.32, 0.46, 0.22), (0.34, 0.50, 0.16), (0.47, 0.38, 0.15), and (0.38, 0.40, 0.22) in the ternary phase diagram formed by a+b, c, and d.

[0007] Preferably, Re is selected from at least one of Y, Dy, Ho, Tb, Gd, Sc, Er, Tm, Yb, and Lu, and is preferably Dy or Y.

[0008] Preferably, a, b, c, and d are located within the range enclosed by points (0.32, 0.46, 0.22), (0.34, 0.50, 0.16), (0.37, 0.45, 0.18), (0.41, 0.39, 0.20), and (0.38, 0.40, 0.22) in the ternary phase diagram formed by a+b, c, and d.

[0009] Preferably, the dielectric material of the X7R type multilayer ceramic capacitor further includes a fifth sub-component; wherein the fifth sub-component is an oxide of Mn; the amount of Mn added, e, relative to 1 mol of the ABO3 main component is 0.3 ≤ e ≤ 1.0% mol, preferably 0.4 ≤ e ≤ 0.6% mol.

[0010] Preferably, the dielectric material of the X7R type multilayer ceramic capacitor further includes a sixth sub-component; wherein the sixth sub-component is an oxide of Ba; wherein, relative to 1 mol of the main ABO3 component, the amount of Ba element added f is 0.4 ≤ f ≤ 2.0% mol, preferably 0.5 ≤ f ≤ 1.0% mol.

[0011] Preferably, the average particle size of the main component ABO3 compound in the dielectric material of the X7R type multilayer ceramic capacitor is 100-350 nm, and more preferably 150-250 nm.

[0012] Preferably, the average particle size of each component of the secondary component of the X7R type multilayer ceramic capacitor dielectric material is less than or equal to 1 / 2 of the average particle size of the main component, and more preferably less than or equal to 1 / 3 of the average particle size of the main component.

[0013] Secondly, the present invention provides a method for preparing the dielectric material of the above-mentioned X7R type multilayer ceramic capacitor, the method comprising the following steps: (1) The main component ABO3 compound was prepared by solid-phase method or liquid-phase method including hydrothermal synthesis, oxalate method, alkoxide method and sol-gel method; (2) Take the oxides of each of the secondary components in the dielectric material of the X7R type multilayer ceramic capacitor or the precursor compounds that can be converted into the oxides of the secondary components by firing. (3) Mix the main components and secondary components in the X7R type multilayer ceramic capacitor dielectric material according to the ratio of the main components and secondary components to obtain the X7R type multilayer ceramic capacitor dielectric material.

[0014] Preferably, the precursor compound includes carbonates, oxalates, hydroxides, and organometallic compounds.

[0015] Beneficial effects This invention uses ABO3 perovskite-type compounds with small particle size as the main component. By adjusting the amount and relative ratio of high-valence donor elements Nb or Mo, amphoteric rare earth elements, acceptor elements Mg and Si, it can ensure a high dielectric constant while possessing excellent dielectric temperature characteristics. Furthermore, by adjusting the amount and relative ratio of rare earth elements and MgO, the dielectric constant and capacitance temperature characteristics can be effectively controlled. Attached Figure Description

[0016] Figure 1 This is a schematic diagram showing the distribution of the amounts of Nb or Mo, Re, Mg, and Si added in the sample prepared in Example 1, in a ternary phase diagram consisting of a+b, c, and d. Figure 2 This is a schematic diagram showing the change in the volumetric temperature change rate of the material in the sample prepared in Example 1 as a function of the amount of Re added. Figure 3 This is a schematic diagram showing the distribution of the amounts of Nb or Mo, Re, Mg, and Si added in the sample prepared in Example 2, in a ternary phase diagram composed of a+b, c, and d. Detailed Implementation

[0017] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0018] First, this invention provides an X7R type multilayer ceramic capacitor dielectric material. The X7R type multilayer ceramic capacitor dielectric material is composed of a main component and secondary components.

[0019] In some embodiments, the main component is a compound with a perovskite-type crystal structure represented by the general formula ABO3; wherein A can be Ba alone or Ba with at least one selected from Ca or Sr, and B can be Ti alone or Ti with Zr. Preferably, the main component ABO3 is barium titanate or calcium barium titanate.

[0020] In some embodiments, the first secondary component of the dielectric material of the X7R type multilayer ceramic capacitor can be at least one of Nb₂O₅ or MoO₃. Specifically, the total amount of Nb or Mo added, 'a', relative to 1 mol of ABO₃ main component can be 0 < a ≤ 0.1% mol, preferably 0.05% ≤ a ≤ 0.1% mol. The Nb₂O₅ and MoO₃ in the secondary components of this invention act as donor dopant, which can suppress grain growth and promote core-shell structure formation, contributing to improved dielectric constant, enhanced dielectric properties above the Curie temperature, and increased reliability.

[0021] In some embodiments, the second secondary component of the X7R type multilayer ceramic capacitor dielectric material can be an oxide of the rare earth element Re. The Re can be selected from at least one of Y, Dy, Ho, Tb, Gd, Sc, Er, Tm, Yb, and Lu, preferably Dy or Y. The amount of Re added, b, relative to 1 mol of the ABO3 main component can be 1.2 ≤ b ≤ 3.0% mol, preferably 1.6 ≤ b ≤ 2.6% mol. The rare earth elements in the secondary component of this invention can occupy Ba and Ti sites depending on the Ba / Ti ratio of the material, playing different donor and acceptor regulatory roles, thereby significantly improving the material's resistance to reduction and reliability.

[0022] In some embodiments, the third secondary component of the X7R type multilayer ceramic capacitor dielectric material can be Mg oxide. Specifically, the amount of Mg added, c, relative to 1 mol of ABO3 main component can be 1.5 ≤ c ≤ 3.0% mol, preferably 2.0 ≤ c ≤ 2.5% mol. In this invention, MgO in the secondary component acts as an acceptor dopant, forming a shell on the BaTiO3 surface at a relatively low reaction temperature. Simultaneously, a second phase is generated and enriched at the grain boundaries to inhibit grain growth, forming a typical core-shell structure.

[0023] In some embodiments, the fourth secondary component of the X7R type multilayer ceramic capacitor dielectric material can be an oxide of Si. Specifically, relative to 1 mol of the ABO3 main component, the amount of Si added, d, can be 0.8 ≤ d ≤ 1.2% mol, preferably 0.9 ≤ d ≤ 1.1% mol. The SiO2 in the secondary component of this invention can form a liquid phase to promote the uniform distribution of the added elements and simultaneously enhance high-temperature voltage resistance.

[0024] In some embodiments, the amounts a, b, c, and d of the first, second, third, and fourth sub-components in the X7R-type multilayer ceramic capacitor dielectric material can be located within the range enclosed by points (0.32, 0.46, 0.22), (0.34, 0.50, 0.16), (0.47, 0.38, 0.15), and (0.38, 0.40, 0.22) in the ternary phase diagram formed by a+b, c, and d, preferably within the range enclosed by points (0.32, 0.46, 0.22), (0.34, 0.50, 0.16), (0.37, 0.45, 0.18), (0.41, 0.39, 0.20), and (0.38, 0.40, 0.22). In this case, the dielectric constant of the X7R-type multilayer ceramic capacitor dielectric material of the present invention can reach over 3000.

[0025] To improve the dielectric constant, this invention introduces the first secondary components Nb and Mo. Since both Nb / Mo and the rare earth element Re act as donor dopants, the addition amounts of Nb / Mo and rare earth elements are combined and calculated as a+b in the ternary phase diagram. If only the addition amounts of rare earth, Mg, and Si are considered in the ternary phase diagram, excessive Nb / Mo addition will lead to an imbalance between donor and acceptor valences, thus affecting the final performance.

[0026] In some embodiments, the fifth secondary component of the dielectric material of the X7R type multilayer ceramic capacitor can be an oxide of Mn. Specifically, the amount of Mn added, e, relative to 1 mol of the ABO3 main component, can be 0.3 ≤ e ≤ 1.0% mol, preferably 0.4 ≤ e ≤ 0.6% mol. The Mn element in the secondary component of this invention is mainly used to improve the insulation resistance and reliability of the ceramic capacitor.

[0027] In some embodiments, the sixth sub-component of the dielectric material of the X7R type multilayer ceramic capacitor can be an oxide of Ba. Specifically, the amount of Ba added, f, relative to 1 mol of the ABO3 main component, can be 0.4 ≤ f ≤ 2.0% mol, preferably 0.5 ≤ f ≤ 1.0% mol.

[0028] In some embodiments, the average particle size of the main component ABO3 compound in the dielectric material of the X7R type multilayer ceramic capacitor can be 100-350 nm, preferably 150-250 nm.

[0029] In some embodiments, the average particle size of each component of the secondary component in the X7R type multilayer ceramic capacitor dielectric material is less than or equal to 1 / 2 of the average particle size of the main component, preferably less than or equal to 1 / 3 of the average particle size of the main component. Using smaller particle size secondary component particles can achieve the effect of uniform mixing and encapsulation with the main component.

[0030] In summary, this invention uses small-particle-size ABO3 perovskite compounds as the main component. By adjusting the amount and relative ratio of high-valence donor elements Nb or Mo, amphoteric rare earth element Re, acceptor element Mg, and Si, it achieves both a high dielectric constant and excellent dielectric temperature characteristics. Furthermore, by adjusting the amount of rare earth element Re2O3 and the relative ratio of MgO to Re2O3, the dielectric constant and capacitance temperature characteristics can be effectively controlled, thus meeting the X7R characteristic requirements while maintaining a high dielectric constant. The amount of SiO2 added affects the distribution of Nb / Mo, rare earth element Re, and Mg around the main component BT particles, and therefore needs to be controlled within a reasonable range. This invention innovatively provides an intuitive correspondence using a ternary phase diagram of the above four component addition amounts a+b, c, and d, and further narrows down the range to show the region with a dielectric constant greater than 3000.

[0031] It should also be noted that, generally, if BT particles of 350 nm or 400 nm or larger (i.e., the main component in this patent) are selected, it is easier to obtain X7R materials with higher dielectric constants. However, the technical problem to be solved by this invention is mainly to maintain good temperature characteristics and high dielectric constants even with small particle sizes, and more importantly, to maintain high dielectric constants (>3000) even with grain sizes of 200 nm or smaller. To achieve the above objective, it is necessary to select small-diameter main component particles and to quickly determine the relative addition amounts of different by-components corresponding to regions with high dielectric constants using a ternary phase diagram.

[0032] The following is an exemplary description of a method for preparing the dielectric material of the X7R type multilayer ceramic capacitor provided by the present invention. The preparation method may include the following steps: (1) The main component ABO3 compound was prepared by solid-phase method or liquid-phase method including hydrothermal synthesis, oxalate method, alkoxide method and sol-gel method; (2) Take the oxides of each secondary component in the dielectric material of the X7R type multilayer ceramic capacitor or the precursor compounds that can be converted into the oxides of the secondary components through firing; wherein, the precursor compounds may include carbonates, oxalates, hydroxides, and organometallic compounds; (3) Mix the main components and secondary components in the X7R type multilayer ceramic capacitor dielectric material according to the ratio of the main components and secondary components to obtain the X7R type multilayer ceramic capacitor dielectric material.

[0033] The dielectric material obtained by the preparation method provided by this invention, after being formed by a casting process, produces ceramic sheets whose dielectric constant and capacitance temperature characteristics both meet the X7R index requirements.

[0034] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art.

[0035] Example 1

[0036] The method for preparing the dielectric material of the X7R type multilayer ceramic capacitor provided in this embodiment includes the following steps: (1) The ABO3 powder used as the main component is BaTiO3 powder with an average particle size of 200 nm; the first secondary component is Nb2O5 powder with an average particle size of 100 nm or MoO3 powder with an average particle size of 50 nm; the second secondary component is Dy2O3 powder with an average particle size of 40 nm or Y2O3 powder with an average particle size of 30 nm or Yb2O3 powder with an average particle size of 40 nm; the third secondary component is MgO powder with an average particle size of 50 nm; the fourth secondary component is SiO2 powder with an average particle size of 30 nm; the fifth secondary component is MnO2 powder with an average particle size of 50 nm; and the sixth secondary component is BaCO3 powder with an average particle size of 20 nm. (2) For 100 mol parts of BaTiO3 powder, the molar parts of each secondary component are shown in Table 1. After converting the molar ratio of the corresponding main component and secondary component into weight, weigh each raw material powder prepared above. After mixing each raw material powder, use anhydrous ethanol as solvent and perform planetary ball milling for 6 hours using a wet process. After drying and sieving, obtain the X7R type multilayer ceramic capacitor dielectric material.

[0037] The multilayer ceramic capacitor dielectric material prepared above was granulated by adding 3.6 wt% PVA as a binder, and then pressed into discs with a diameter of 13 mm. The discs were then debonded by holding them at 500°C in air for 2 hours. The debonded discs were then sintered in an atmosphere furnace at a heating rate of 10°C / min to 1280°C and held for 1 hour. They were then annealed by cooling to 900°C at a rate of 5°C / min and holding for 2 hours. The sintering atmosphere consisted of a humidified nitrogen / hydrogen mixture with an oxygen partial pressure of 10. -6 Pa; the annealing process is carried out under humidified nitrogen with an oxygen partial pressure of 0.1 Pa; then, the upper and lower surfaces of the ceramic disc sintered in the above atmosphere are polished with sandpaper, cleaned and dried, and silver electrodes are uniformly coated on both sides of the disc. After firing, dielectric properties are tested.

[0038] The room temperature capacitance, loss, and capacitance-temperature curve were all obtained using a Keysight E4990A. The dielectric constant was calculated from the measured capacitance value using the formula: ε=(C·d) / (ε0·S), where C is the capacitance, ε0 is the vacuum dielectric constant, d is the thickness of the ceramic disc, and S is the electrode area covered by the ceramic disc.

[0039] Table 1: *For comparison

[0040] Figure 1This is a schematic diagram showing the distribution of the amounts of Nb or Mo, Re, Mg, and Si elements (a, b, c, d) in the sample prepared in Example 1 within a ternary phase diagram consisting of a + b, c, and d. (From Table 1 and...) Figure 1 As can be seen, when the addition amounts of each byproduct a, b, c, d, e, and f in samples 1 to 29 are all within the range of this invention, and a, b, c, and d are located within the range enclosed by the four points (0.32, 0.46, 0.22), (0.34, 0.50, 0.16), (0.47, 0.38, 0.15), and (0.38, 0.40, 0.22) in the ternary phase diagram formed by a+b, c, and d, the capacitance... The temperature characteristics all meet the X7R index requirements; when a, b, c, and d are located within the range enclosed by the five points (0.32, 0.46, 0.22), (0.34, 0.50, 0.16), (0.37, 0.45, 0.18), (0.41, 0.39, 0.20), and (0.38, 0.40, 0.22) in the ternary phase diagram formed by a+b, c, and d, the dielectric constant of each sample can reach over 3000.

[0041] The Nb₂O₅ and MoO₃ in the by-components of this invention act as donor dopant, which can suppress grain growth and promote the formation of core-shell structures, as well as improve the dielectric temperature characteristics above the Curie temperature and enhance reliability. The total amount of Nb or Mo added to the comparative example samples 1* to 4* in Table 1 is not within the scope of this invention, therefore their capacitance-temperature characteristics do not meet the X7R index requirements.

[0042] The rare earth elements in the by-products of this invention can occupy Ba and Ti sites depending on the Ba / Ti ratio of the material, playing different donor and acceptor regulatory roles, thereby significantly improving the material's reduction resistance and reliability. As shown in Table 1, the addition of different rare earth elements Dy, Y, Yb, or multiple rare earth elements, as long as the amount added (b) is within the range of this invention, can achieve similar effects. However, the amount of rare earth elements (b) added in the comparative example samples 5* to 7* in Table 1 is not within the range of this invention; therefore, their capacitance-temperature characteristics do not meet the X7R index requirements.

[0043] In this invention, MgO, as an acceptor dopant, can form a shell on the surface of BaTiO3 at a relatively low reaction temperature. Simultaneously, a second phase is generated and enriched at the grain boundaries to inhibit grain growth, forming a typical core-shell structure. The amount of Mg added (c) in comparative example sample number 8* in Table 1 is outside the range of this invention; therefore, its capacitance-temperature characteristics do not meet the X7R specification requirements.

[0044] The SiO2 in the by-product of this invention can form a liquid phase to promote the uniform distribution of the added elements and enhance the high-temperature voltage resistance characteristics. The amount of Si added, d, in the comparative example samples 9* and 10* in Table 1 is not within the range of this invention, therefore their capacitance temperature characteristics do not meet the X7R index requirements.

[0045] In this invention, adjusting the amount and relative proportion of high-valence donor elements Nb / Mo and Re, acceptor element Mg, and co-solvent Si is key to controlling the dielectric constant and temperature characteristics. In Table 1, the amounts of each byproduct (a, b, c, d, e, f) in the comparative example samples 11* to 15* are all within the range of this invention. However, a, b, c, and d are not within the range enclosed by the four points (0.32, 0.46, 0.22), (0.34, 0.50, 0.16), (0.47, 0.38, 0.15), and (0.38, 0.40, 0.22) in the ternary phase diagram formed by a+b, c, and d. Therefore, their capacitance-temperature characteristics do not meet the X7R specification requirements.

[0046] By adjusting the amount of rare earth element Y2O3 added and the relative addition ratio of MgO to Y2O3, the dielectric constant and capacitance temperature characteristics can be effectively controlled. Figure 2 This is a schematic diagram illustrating the change in capacitance temperature rate of the material in the sample prepared in Example 1 as a function of the amount of Re added. As can be seen from the figure, with the increase of Y₂O₃ addition, the capacitance temperature rate at 125℃ is -14.4 (#12), -8.2 (#17), and -5.2 (#21), respectively, showing a significant improvement.

[0047] Example 2

[0048] The preparation method of the X7R type multilayer ceramic capacitor dielectric material provided in this embodiment is the same as that in Embodiment 1, the main difference being that: the ABO3 powder used as the main component is selected as BaTiO3 powder with an average particle size of 300nm; the molar proportions of each secondary component corresponding to 100mol of BaTiO3 powder are shown in Table 2.

[0049] Table 2:

[0050] Ceramic disc samples numbered 30 to 61 were prepared under the same conditions as in Example 1, and the dielectric properties were tested in the same way as in Example 1.

[0051] Figure 3 This is a schematic diagram showing the distribution of the amounts of Nb or Mo, Re, Mg, and Si elements (a, b, c, d) in the sample prepared in Example 2 within a ternary phase diagram consisting of a + b, c, and d. (From Table 2 and...) Figure 3It can be seen that when the addition amounts of each byproduct a, b, c, d, e, and f in samples 30-61 are all within the range of this invention, and a, b, c, and d are located within the range enclosed by the four points (0.32, 0.46, 0.22), (0.34, 0.50, 0.16), (0.47, 0.38, 0.15), and (0.38, 0.40, 0.22) in the ternary phase diagram formed by a+b, c, and d, the capacitance... The temperature characteristics all meet the X7R index requirements; and when a, b, c, and d are located within the range enclosed by the five points (0.32, 0.46, 0.22), (0.34, 0.50, 0.16), (0.37, 0.45, 0.18), (0.41, 0.39, 0.20), and (0.38, 0.40, 0.22) in the ternary phase diagram formed by a+b, c, and d, the dielectric constant of each sample can reach over 3000.

[0052] Below, the corresponding sample numbers shown in Table 3 of Examples 1 and 2 were selected, ceramic sheets were prepared by tape casting process, and dielectric properties were tested.

[0053] The content of the multilayer ceramic capacitor dielectric powder described in this invention in the casting slurry is 48-51 wt%. The solvent is a 1:1 mixture of ethyl acetate and anhydrous ethanol, with a solvent volume of 43-46 wt%. Furthermore, to improve the tensile strength, flexibility, and smoothness of the green ceramic tape, a dispersant, binder, and plasticizer are added in a total amount of 3-7 wt%. The casting slurry is mixed and degassed by ball milling for 24 hours before casting. The thickness of a single layer of green ceramic tape is 9.5-10.5 μm, and 33 layers are stacked together. Then, it is cut into 10×10 mm sheets. These sheets are held at 450°C in air for 2 hours to remove the binder, then heated to 1260 or 1280°C in an atmosphere furnace at a heating rate of 10°C / min and held for 1 hour for sintering. Finally, the temperature is lowered to 900°C at a rate of 5°C / min and held for 2 hours for annealing. The sintering process is carried out under a humidified nitrogen / hydrogen mixture with an oxygen partial pressure of 10. -6 Pa. The annealing process was carried out under humidified nitrogen atmosphere with an oxygen partial pressure of 0.1 Pa. Silver electrodes were uniformly coated on both sides of the cast film sintered in the above atmosphere, and dielectric properties were tested after firing.

[0054] Table 3:

[0055] As can be seen from Table 3, different sample numbers were selected where the average particle size of BaTiO3 powder and the amount of each auxiliary component (a, b, c, d, e, f) were all within the scope of this invention. The room temperature dielectric constant of the cast sheets was significantly improved compared with that of ceramic discs, and the capacitance temperature characteristics still met the X7R index requirements.

[0056] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A dielectric material for an X7R type multilayer ceramic capacitor, characterized in that, The dielectric material of the X7R type multilayer ceramic capacitor is composed of a main component and a secondary component; The main component is a compound with a perovskite-type crystal structure represented by the general formula ABO3; wherein, A is Ba alone or Ba and at least one selected from Ca or Sr, and B is Ti alone or Ti and Zr. The first secondary component is at least one of Nb₂O₅ or MoO₃; wherein, relative to 1 mol of ABO₃ main component, the total amount of Nb or Mo added, a, is 0 < a ≤ 0.1% mol, preferably 0.05% ≤ a ≤ 0.1% mol; The second component is an oxide of the rare earth element Re; wherein, relative to 1 mol of the ABO3 main component, the amount of Re added, b, is 1.2 ≤ b ≤ 3.0% mol, preferably 1.6 ≤ b ≤ 2.6% mol; The third component is Mg oxide; wherein, relative to 1 mol of ABO3 main component, the amount of Mg added, c, is 1.5 ≤ c ≤ 3.0% mol, preferably 2.0 ≤ c ≤ 2.5% mol; The fourth sub-component is an oxide of Si; wherein, relative to 1 mol of the main ABO3 component, the amount of Si element added, d, is 0.8 ≤ d ≤ 1.2% mol, preferably 0.9 ≤ d ≤ 1.1% mol; The addition amounts a, b, c, and d of the first, second, third, and fourth sub-components in the dielectric material of the X7R type multilayer ceramic capacitor are located within the range enclosed by points (0.32, 0.46, 0.22), (0.34, 0.50, 0.16), (0.47, 0.38, 0.15), and (0.38, 0.40, 0.22) in the ternary phase diagram formed by a+b, c, and d.

2. The dielectric material of the X7R type multilayer ceramic capacitor according to claim 1, characterized in that, The Re is selected from at least one of Y, Dy, Ho, Tb, Gd, Sc, Er, Tm, Yb, and Lu, preferably Dy or Y.

3. The dielectric material of the X7R type multilayer ceramic capacitor according to claim 1 or 2, characterized in that, a, b, c, and d are located within the range enclosed by points (0.32, 0.46, 0.22), (0.34, 0.50, 0.16), (0.37, 0.45, 0.18), (0.41, 0.39, 0.20), and (0.38, 0.40, 0.22) in the ternary phase diagram formed by a+b, c, and d.

4. The dielectric material of the X7R type multilayer ceramic capacitor according to any one of claims 1-3, characterized in that, The dielectric material of the X7R type multilayer ceramic capacitor further includes a fifth sub-component; wherein, the fifth sub-component is an oxide of Mn; relative to 1 mol of the main ABO3 component, the amount of Mn element added, e, is 0.3 ≤ e ≤ 1.0% mol, preferably 0.4 ≤ e ≤ 0.6% mol.

5. The dielectric material of the X7R type multilayer ceramic capacitor according to any one of claims 1-4, characterized in that, The dielectric material of the X7R type multilayer ceramic capacitor further includes a sixth sub-component; wherein the sixth sub-component is an oxide of Ba; wherein, relative to 1 mol of the main ABO3 component, the amount of Ba element added f is 0.4 ≤ f ≤ 2.0% mol, preferably 0.5 ≤ f ≤ 1.0% mol.

6. The dielectric material of the X7R type multilayer ceramic capacitor according to any one of claims 1-5, characterized in that, The ABO3 compound, the main component of the dielectric material of the X7R type multilayer ceramic capacitor, has an average particle size of 100–350 nm, preferably 150–250 nm.

7. The dielectric material of the X7R type multilayer ceramic capacitor according to any one of claims 1-6, characterized in that, The average particle size of each component of the dielectric material of the X7R type multilayer ceramic capacitor is less than or equal to 1 / 2 of the average particle size of the main component, preferably less than or equal to 1 / 3 of the average particle size of the main component.

8. A method for preparing the dielectric material of an X7R type multilayer ceramic capacitor according to any one of claims 1-7, characterized in that, The preparation method includes the following steps: (1) The main component ABO3 compound was prepared by solid-phase method or liquid-phase method including hydrothermal synthesis, oxalate method, alkoxide method and sol-gel method; (2) Take the oxides of each of the secondary components in the dielectric material of the X7R type multilayer ceramic capacitor or the precursor compounds that can be converted into the oxides of the secondary components by firing. (3) Mix the main components and secondary components in the X7R type multilayer ceramic capacitor dielectric material according to the ratio of the main components and secondary components to obtain the X7R type multilayer ceramic capacitor dielectric material.

9. The preparation method according to claim 8, characterized in that, The precursor compounds include carbonates, oxalates, hydroxides, and organometallic compounds.

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