Perovskite type composite adjustable capacitor for LTCC (Low Temperature Co-Fired Ceramic) and preparation method

Abstract

The invention discloses a perovskite type composite adjustable capacitor for LTCC and a preparation method, and belongs to the technical field of passive electronic devices. The preparation method comprises the following steps: S1, mixing and ball-milling barium strontium titanate ceramic powder, bismuth magnesium niobate ceramic powder, an organic solvent, a binder, a plasticizer and a dispersant to prepare tape casting slurry; s2, preparing a ceramic green body film through tape casting; s3, one side of the ceramic green body film is coated with an electrode, staggered lamination is carried out, and a ceramic block is obtained; and S4, isostatic pressing treatment, cutting forming, glue discharging and high-temperature sintering are carried out, finally silver paste coating is carried out, heat treatment is carried out, and the composite material is obtained. The BST-BMN composite ceramic is used as a core dielectric material to prepare the MLCC, the dynamic regulation and control of the dielectric property of the device can be realized, the applicability of the device under complex working conditions is greatly expanded, the dielectric loss is relatively low, the temperature stability is relatively good, and the reliability of the MLCC is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of passive electronic devices, and in particular to a perovskite-type composite adjustable capacitor for LTCC and a preparation method thereof. Background Art

[0002] As RF systems evolve toward miniaturization and integration, tunable capacitors, essential components for key circuits such as tunable filters, antennas, and phase shifters, are facing urgent demand for high capacitance and compact size. Multilayer ceramic capacitors (MLCCs), widely used chip components in electronic devices, rely heavily on the choice of ceramic dielectric materials. These materials not only isolate electrodes and regulate electric fields, but also directly impact key performance characteristics such as temperature stability and dielectric tunability.

[0003] Barium strontium titanate (BST) ceramics, thanks to their high dielectric constant, low loss tangent, and excellent high-frequency and high-temperature stability, exhibit outstanding structural stability and electrical performance after high-temperature sintering. Bismuth magnesium niobate (BMN) ceramic materials also have excellent dielectric properties. Their high dielectric constant, extremely low loss tangent, and outstanding temperature stability and heat resistance enable them to perform outstandingly in high-frequency and high-temperature working environments.

[0004] Although MLCCs are currently widely used in the electronics field, they still lack tunability in dynamic operating environments, making it difficult to meet the adaptive needs of different circuit conditions. Therefore, developing a composite ceramic system with tunable dielectric properties for MLCCs that can dynamically adjust capacitance performance according to actual application requirements is of great significance for promoting the development of electronic devices towards higher integration and greater adaptability. Summary of the Invention

[0005] In order to solve the above technical problems, the purpose of the present invention is to provide a perovskite composite tunable capacitor for LTCC and a preparation method to solve the problems such as the lack of tunability of existing MLCC in dynamic working environment and difficulty in meeting the adaptive requirements of different circuit conditions.

[0006] The technical solution of the present invention to solve the above technical problems is as follows:

[0007] The first object of the present invention is to provide a method for preparing a perovskite composite tunable capacitor for LTCC, comprising the following steps:

[0008] S1: barium strontium titanate ceramic powder, bismuth magnesium niobate ceramic powder, organic solvent, binder, plasticizer and dispersant are mixed and ball-milled to prepare a tape casting slurry;

[0009] S2: Using the tape casting slurry obtained in S1 as a raw material, a ceramic green film is prepared as a dielectric layer by a tape casting method;

[0010] S3: coating one side of the ceramic green film obtained in S2 with an electrode as a metal electrode layer, and then performing staggered lamination to obtain a ceramic block;

[0011] S4: The ceramic blocks obtained in S3 are first subjected to isostatic pressing, then cut into shape, subjected to binder removal and high-temperature sintering, and finally coated with silver paste and subjected to heat treatment to obtain the product.

[0012] Furthermore, the barium strontium titanate ceramic powder in S1 is prepared by the following method:

[0013] First, barium carbonate, strontium carbonate and titanium dioxide are evenly mixed to obtain a precursor powder, and then the precursor powder is mixed with a ball milling solvent for the first ball milling, followed by the first vacuum drying and pre-calcining treatment, and finally the second ball milling, the second vacuum drying and grinding and sieving are performed to obtain barium strontium titanate ceramic powder.

[0014] Furthermore, the chemical formula of the barium strontium titanate ceramic powder is Ba 1-x Sr x TiO3, wherein x = 0.1-0.5;

[0015] The mass ratio of precursor powder to ball milling solvent is (0.8-1.2): (0.8-1.2);

[0016] The first ball milling time is 20-50h, and the ball milling speed is 300-320rpm;

[0017] The temperature of the first vacuum drying is 60-100°C and the time is 10-15h;

[0018] The pre-sintering treatment conditions are: heating to 1100-1300℃ at a heating rate of 1-10℃ / min, keeping at this temperature for 1-3h and then cooling with the furnace;

[0019] The second ball milling time is 20-30h, and the ball milling speed is 300-320rpm;

[0020] The temperature of the second vacuum drying is 60-100°C and the time is 10-15h.

[0021] Preferably, the chemical formula of the barium strontium titanate ceramic powder is Ba 1-x Sr x TiO3, where x = 0.2;

[0022] The mass ratio of precursor powder to ball milling solvent is 1:1;

[0023] The first ball milling time was 32 h, and the ball milling speed was 310 rpm;

[0024] The first vacuum drying temperature was 80 °C and the time was 12 h;

[0025] The pre-sintering conditions were as follows: heating to 1200°C at a heating rate of 5°C / min, holding for 2 h, and then cooling in the furnace;

[0026] The second ball milling time was 24 h, and the ball milling speed was 310 rpm;

[0027] The second vacuum drying temperature was 80°C and the time was 2 h.

[0028] Furthermore, barium carbonate, strontium carbonate and titanium dioxide are mixed according to the stoichiometric ratio of the chemical formula of barium strontium titanate ceramic powder, wherein barium carbonate is additionally added in an amount of 3% by mass of the total raw materials.

[0029] Furthermore, the ball milling solvent is anhydrous ethanol or deionized water with a resistivity of ≥18 MΩ·cm.

[0030] Furthermore, the ball mill uses agate grinding balls with three levels of particle size (diameters of 3 mm, 6 mm, and 9 mm, respectively), which are filled in a volume ratio of 1:2:3.

[0031] The beneficial effect of adopting the above further technical solution is: adopting this parameter combination for ball milling can significantly improve the ball milling efficiency of the powder, ensuring that D can be obtained after ball milling. 50 Slurry with particle size ≤200nm and uniform distribution.

[0032] Furthermore, the sieve used for grinding and sieving is 100 mesh.

[0033] Furthermore, the bismuth magnesium niobate ceramic powder in S1 is prepared by the following method:

[0034] Bismuth oxide, magnesium oxide and niobium oxide are firstly mixed uniformly to obtain a precursor powder, and then the precursor powder is mixed with a ball milling solvent for the first ball milling, followed by the first vacuum drying and pre-calcining treatment, and finally the second ball milling, the second vacuum drying and grinding and sieving are performed to obtain bismuth magnesium niobate ceramic powder.

[0035] The beneficial effects of adopting the above-mentioned further technical solution are: the preparation method of the present invention for preparing bismuth magnesium niobate ceramic powder can ensure the stability of the performance of the final product, and the use of a lower pre-firing temperature than the traditional method is conducive to controlling grain growth, and the obtained powder has excellent sintering activity and is suitable for preparing high-performance MLCC devices.

[0036] Furthermore, the chemical formula of the bismuth magnesium niobate ceramic powder is Bi 1.5 MgNb1.5 O7;

[0037] The mass ratio of precursor powder to ball milling solvent is (0.8-1.2): (0.8-1.2);

[0038] The first ball milling time is 20-50h, and the ball milling speed is 300-320rpm;

[0039] The temperature of the first vacuum drying is 60-100°C and the time is 10-15h;

[0040] The pre-sintering treatment conditions are: heating to 800-900℃ at a heating rate of 1-10℃ / min, keeping at this temperature for 2-4h and then cooling with the furnace;

[0041] The second ball milling time is 20-30h, and the ball milling speed is 300-320rpm;

[0042] The temperature of the second vacuum drying is 60-100°C and the time is 10-15h.

[0043] Preferably, the mass ratio of the precursor powder to the ball milling solvent is 1:1;

[0044] The first ball milling time was 32 h, and the ball milling speed was 310 rpm;

[0045] The first vacuum drying temperature was 80 °C and the time was 12 h;

[0046] The pre-sintering conditions are as follows: heating to 850°C at a heating rate of 5°C / min, keeping at this temperature for 3h and then cooling in the furnace;

[0047] The second ball milling time was 24 h, and the ball milling speed was 310 rpm;

[0048] The second vacuum drying temperature was 80°C and the time was 12 h.

[0049] Furthermore, the raw materials are weighed and mixed according to the stoichiometric ratio of the chemical formula of the bismuth magnesium niobate ceramic powder.

[0050] Furthermore, the ball milling solvent is anhydrous ethanol or deionized water with a resistivity of ≥18 MΩ·cm.

[0051] Furthermore, the ball mill uses agate grinding balls with three-level particle size ratios (diameters of 3 mm, 6 mm, and 9 mm, respectively), which are filled in a volume ratio of 1:2:3.

[0052] The beneficial effect of adopting the above further technical solution is: adopting this parameter combination for ball milling can significantly improve the ball milling efficiency of the powder, ensuring that D can be obtained after ball milling. 50 Slurry with particle size ≤200nm and uniform particle size distribution.

[0053] Furthermore, the sieve used for grinding and sieving is 100 mesh.

[0054] Furthermore, the weight proportions of the raw materials used in the tape casting slurry in S1 are: 90-100 parts of strontium barium titanate ceramic powder, 2-10 parts of bismuth magnesium niobate ceramic powder, 40-50 parts of organic solvent, 8-10 parts of binder, 8-10 parts of plasticizer and 0.5-1 part of dispersant;

[0055] The ball milling speed is 50-100 rpm and the time is 40-60 h.

[0056] Furthermore, the organic solvent is a mixed solvent consisting of anhydrous ethanol and toluene in a volume ratio of 60:40.

[0057] Furthermore, the binder is polyvinyl butyral (PVB); the plasticizer is dioctyl phthalate (DOP); and the dispersant is polyacrylamide.

[0058] Furthermore, the thickness of the ceramic green film in S2 is 30-35 μm.

[0059] Furthermore, the tape casting in S2 adopts a doctor blade tape casting process, and the slurry is cast on a polyester film substrate at a single speed of 0.1-1m / min, a doctor blade gap of 45-55μm, a drying temperature of 23-27°C, and an ambient humidity of less than 40%RH.

[0060] The beneficial effect of adopting the above further technical solution is that the dimensional accuracy can be kept within ±0.5% by adopting the above tape casting process for processing.

[0061] Furthermore, the ceramic block in S3 has a structure in which dielectric layers and metal electrode layers are alternately arranged, and the topmost layer and the bottommost layer are both dielectric layers.

[0062] Furthermore, in S3, an 80-90 mesh screen is used for electrode coating, the electrode slurry is a Pt electrode, and after coating, the electrode is dried at 90-100° C. for 5-10 minutes.

[0063] Furthermore, the staggered stacking is performed using a lamination process, maintained at a pressure of 10-20 MPa and a temperature of 45-55° C. for 20-40 seconds.

[0064] Furthermore, after staggered lamination, the interlayer bonding strength is ensured to be above 1.5 MPa.

[0065] Preferably, the number of dielectric layers is 9.

[0066] Furthermore, the pressure of the medium static pressure treatment in S4 is 20-60 MPa, the temperature is 70-75° C., and the time is 20-40 min.

[0067] The beneficial effect of adopting the above further technical solution is that, through isostatic pressing, the green density can reach 60-65% of the theoretical density, while maintaining the dimensional accuracy within ±0.5%.

[0068] Furthermore, the binder removal conditions in S4 are as follows: heating to 300-500°C at a heating rate of 1-3°C / min in an air atmosphere and keeping the temperature for 2-3h;

[0069] The high-temperature sintering conditions are as follows: heating to 900-1200°C at a heating rate of 1-10°C / min in a protective gas atmosphere and holding for 0.5-2h;

[0070] The heat treatment temperature is 800-900°C and the time is 10-20 minutes.

[0071] Preferably, the binder removal conditions in S4 are: heating to 400° C. at a heating rate of 1° C. / min in an air atmosphere and keeping the temperature for 2.5 hours;

[0072] The high-temperature sintering conditions were as follows: heating to 1000°C at a heating rate of 5°C / min in a protective gas atmosphere and holding at that temperature for 0.75h;

[0073] The heat treatment temperature is 800-900°C and the time is 10-20 minutes.

[0074] Furthermore, the thickness of the Ag terminal electrode obtained by coating the silver paste in S4 is 1-5 μm.

[0075] Furthermore, a good ohmic contact is formed by heat treatment, and the contact resistance is ≤10mΩ.

[0076] The second object of the present invention is to provide a perovskite composite tunable capacitor for LTCC, which is prepared by the above-mentioned preparation method.

[0077] Furthermore, the perovskite composite tunable capacitor used for LTCC has a structure in which dielectric layers and electrode layers are alternately stacked, the bottom layer and the top layer are both dielectric layers, and the number of dielectric layers is greater than or equal to 2.

[0078] The present invention has the following beneficial effects:

[0079] The present invention uses BST-BMN composite ceramics as the core dielectric material and prepares MLCCs through a multilayer structure design of alternating ceramic dielectric layers and metal electrode layers. By applying external electric fields of varying intensities, the device's dielectric properties can be dynamically controlled, allowing it to flexibly adjust operating parameters according to actual application scenarios. This unique electric field response characteristic greatly expands the device's applicability under complex working conditions and provides modern electronic systems with superior performance adjustment capabilities. The BST-BMN composite ceramic system enables MLCCs to have lower dielectric loss and better temperature stability at lower sintering temperatures, thereby improving their reliability. In addition, the lead-free BST-BMN composite ceramic material used in the present invention is more in line with the development needs of electronic devices for environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Figure 1 XRD patterns of the ceramic thick films and MLCC samples obtained in Examples 6-10;

[0081] Figure 2 XRD patterns of BST ceramic powders with different ratios in the test examples;

[0082] Figure 3 SEM characterization images of MLCC samples prepared in Example 2 and Comparative Example 2, wherein (a) is a microscopic morphology image of the MLCC sample prepared in Example 2, (b) is a microscopic morphology image of the grains of the MLCC sample prepared in Example 2, and (c) is a microscopic morphology image of the MLCC sample prepared in Comparative Example 2;

[0083] Figure 4 The temperature characteristic diagram of the electrical performance of the MLCC samples prepared in Examples 1-3, where (a) is the dielectric constant and (b) is the dielectric loss;

[0084] Figure 5 Dielectric tuning rates of MLCC samples prepared for Examples 1-3 and Comparative Example 3, where (a) is for Examples 1-3 and (b) is for Comparative Example 1;

[0085] Figure 6 The figure shows the change of dielectric tuning rate of MLCC samples prepared in Examples 1-3 with temperature. DETAILED DESCRIPTION

[0086] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples are only used to explain the present invention and are not intended to limit the scope of the invention. In the embodiments, if specific conditions are not specified, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0087] Example 1:

[0088] A method for preparing a perovskite-type composite tunable capacitor for LTCC, comprising the following steps:

[0089] (1) Preparation of barium strontium titanate ceramic powder

[0090] According to Ba 0.8 Sr 0.2 Barium carbonate (Ba2CO3, purity ≥99%), strontium carbonate (SrCO3, purity ≥99.95%) and titanium dioxide (TiO2, purity ≥99%) are weighed in a stoichiometric ratio of TiO3, mixed evenly, and 3% of the total powder weight of barium carbonate is additionally added to obtain a barium strontium titanate ceramic precursor powder;

[0091] The barium strontium titanate ceramic precursor powder was mixed with anhydrous ethanol at a mass ratio of 1:1 to prepare a slurry. Agate grinding balls with three-grade particle size ratios (diameters of 3 mm, 6 mm, and 9 mm) were added and loaded at a volume ratio of 1:2:3. The volume ratio of the slurry to the agate balls was 1:2. The mixture was wet-milled in a planetary ball mill at a speed of 310 rpm for 32 h.

[0092] The ball-milled slurry was placed in a vacuum drying oven at 80°C for 12 hours, sieved after grinding, and then pre-sintered in a box furnace at a heating rate of 5°C / min to 1200°C. After holding the temperature for 2 hours, the slurry was cooled in the furnace to obtain a ceramic block.

[0093] The obtained ceramic block was ball-milled again and mixed with anhydrous ethanol at a mass ratio of 1:1 to prepare a slurry. Agate grinding balls with three-grade particle size ratios (diameters of 3 mm, 6 mm, and 9 mm) were added and loaded at a volume ratio of 1:2:3. The volume ratio of slurry to agate balls was 2:1. The slurry was wet-milled in a planetary ball mill for 24 h at a ball milling speed of 310 rpm.

[0094] The ball-milled product was vacuum-dried at 80°C for 12 h, manually ground with a zirconia mortar, and passed through a 100-mesh sieve to obtain barium strontium titanate ceramic powder BST with uniform particle size distribution.

[0095] (2) Preparation of bismuth magnesium niobate ceramic powder

[0096] According to Bi 1.5 MgNb 1.5 Bismuth oxide (Bi2O3, purity ≥99%), magnesium oxide (MgO, purity ≥99.95%) and niobium oxide (Nb2O5, purity ≥99%) are weighed in a stoichiometric ratio of 1:1 to 2:1 and mixed to obtain a bismuth magnesium niobate ceramic precursor powder.

[0097] The bismuth magnesium niobate ceramic precursor powder and anhydrous ethanol were mixed uniformly in a mass ratio of 1:1 to prepare a slurry. Agate grinding balls with three-grade particle size ratios (diameters of 3 mm, 6 mm, and 9 mm) were added and loaded in a volume ratio of 1:2:3. The volume ratio of the slurry to the agate balls was 1:2. The mixture was wet-milled in a planetary ball mill for 32 hours at a speed of 310 rpm.

[0098] The ball-milled slurry was placed in a vacuum drying oven at 80°C for 12 hours, sieved after grinding, and then pre-sintered in a box furnace at a heating rate of 5°C / min to 850°C. After holding the temperature for 2 hours, the slurry was cooled in the furnace to obtain a ceramic block.

[0099] The obtained ceramic block was ball-milled again and mixed with anhydrous ethanol at a mass ratio of 1:1 to prepare a slurry. Agate grinding balls with three-grade particle size ratios (diameters of 3 mm, 6 mm, and 9 mm) were added and loaded at a volume ratio of 1:2:3. The volume ratio of slurry to agate balls was 2:1. The slurry was wet-milled in a planetary ball mill for 24 h at a ball milling speed of 310 rpm.

[0100] The ball-milled product was vacuum-dried at 80°C for 12 h, manually ground with a zirconia mortar, and passed through a 100-mesh sieve to obtain bismuth magnesium niobate ceramic powder BMN with uniform particle size distribution.

[0101] (3) Preparation of tape casting slurry

[0102] The raw materials were evenly mixed according to the following weight fractions: 97.5 parts of BST ceramic powder, 2.5 parts of BMN ceramic powder, 45 parts of organic solvent (obtained by mixing anhydrous ethanol and toluene in a volume ratio of 60:40), 9 parts of binder (polyvinyl butyral), 9.14 parts of plasticizer (dioctyl phthalate) and 0.7 parts of dispersant (polyacrylamide); the mixed raw materials were ball milled in a horizontal rolling ball mill at a speed of 60 rpm for 52 hours to finally obtain a casting slurry with suitable viscosity and rheological properties.

[0103] (4) Preparation of MLCC green components

[0104] Using a doctor blade process, the casting slurry obtained in step (3) was cast onto a polyester film substrate at a speed of 0.5 m / min. By precisely controlling the doctor blade gap (50 μm) and the drying temperature (25°C), a ceramic green film with a thickness of 32.5 μm was produced. The ambient humidity was maintained below 40% RH during the casting process to ensure that the film layer had excellent surface flatness and thickness uniformity.

[0105] One side of the obtained ceramic thick film was coated with an electrode by a screen printer using an 80-mesh screen. The electrode slurry was Pt electrode and dried at 95°C for 7.5 minutes. After completion, the film was staggered and laminated using a lamination process at a pressure of 14 MPa and a temperature of 50°C for 30 seconds to obtain a ceramic block having a dielectric layer / (metal electrode layer / dielectric layer) n, wherein the number of dielectric layers was 9.

[0106] The ceramic blocks were subjected to isostatic pressing at a pressure of 40 MPa, a temperature of 72.5°C, and a time of 30 min.

[0107] After isostatic pressing, the MLCC green body is cut according to the electrode pattern.

[0108] (5) Preparation of perovskite composite tunable capacitors for LTCC

[0109] The MLCC green body obtained in step (4) was placed in a high-temperature sintering furnace and heated to 1000°C at a heating rate of 5°C / min in an inert gas atmosphere for 0.75h, followed by cooling to room temperature. The sintered sample was coated with silver paste on the electrode areas at both ends by screen printing, with the Ag end electrode thickness of 3μm. After heat treatment at 850°C for 15min, ohmic contact was formed to obtain a perovskite composite adjustable capacitor for LTCC.

[0110] Example 2:

[0111] A method for preparing a perovskite-type composite tunable capacitor for LTCC, comprising the following steps:

[0112] The preparation method is the same as that of Example 1, except that the weight proportions of BST ceramic powder and BMN ceramic powder in step (3) are changed to 95 parts and 5 parts, respectively.

[0113] Example 3:

[0114] A method for preparing a perovskite-type composite tunable capacitor for LTCC, comprising the following steps:

[0115] The preparation method is the same as that of Example 1, except that the weight proportions of BST ceramic powder and BMN ceramic powder in step (3) are changed to 92.5 parts and 7.5 parts, respectively.

[0116] Example 4:

[0117] A method for preparing a perovskite-type composite tunable capacitor for LTCC, comprising the following steps:

[0118] The preparation method is the same as that of Example 1, except that the temperature of high-temperature sintering in step (5) is changed from 1000°C to 900°C.

[0119] Example 5:

[0120] A method for preparing a perovskite-type composite tunable capacitor for LTCC, comprising the following steps:

[0121] The preparation method is the same as that of Example 1, except that the temperature of high-temperature sintering in step (5) is changed from 1000°C to 1100°C.

[0122] Example 6:

[0123] A method for preparing a perovskite-type composite tunable capacitor for LTCC, comprising the following steps:

[0124] The preparation method is the same as that of Example 1, except that the high-temperature sintering temperature in step (5) is changed from 1000° C. to 1100° C., and the holding time is changed to 1 h.

[0125] Example 7:

[0126] A method for preparing a perovskite-type composite tunable capacitor for LTCC, comprising the following steps:

[0127] The preparation method is the same as that of Example 1, except that the high-temperature sintering temperature in step (5) is changed from 1000° C. to 1050° C., and the holding time is changed to 1.5 h.

[0128] Example 8:

[0129] A method for preparing a perovskite-type composite tunable capacitor for LTCC, comprising the following steps:

[0130] The preparation method is the same as that of Example 1, except that the temperature of high-temperature sintering in step (5) is changed from 1000° C. to 1050° C., and the holding time is changed to 1 h.

[0131] Example 9:

[0132] A method for preparing a perovskite-type composite tunable capacitor for LTCC, comprising the following steps:

[0133] The preparation method is the same as that of Example 1, except that the high-temperature sintering temperature in step (5) is changed from 1000° C. to 1020° C., and the holding time is changed to 1.5 h.

[0134] Example 10:

[0135] A method for preparing a perovskite-type composite tunable capacitor for LTCC, comprising the following steps:

[0136] The preparation method is the same as that of Example 1, except that the high-temperature sintering temperature in step (5) is changed from 1000°C to 1020°C, and the holding time is changed to 1 hour.

[0137] Comparative Example 1:

[0138] A method for preparing a perovskite-type composite tunable capacitor for LTCC, comprising the following steps:

[0139] The preparation method is the same as that of Example 1, except that in step (3) of this comparative example, no BMN ceramic powder is added, and the weight proportion of BST ceramic powder is changed to 100 parts.

[0140] Comparative Example 2:

[0141] A method for preparing a perovskite-type composite tunable capacitor for LTCC, comprising the following steps:

[0142] The preparation method is the same as that of Example 1, except that the weight proportions of BST ceramic powder and BMN ceramic powder in step (3) are changed to 80 parts and 20 parts, respectively.

[0143] Comparative Example 3:

[0144] A method for preparing a perovskite-type composite tunable capacitor for LTCC, comprising the following steps:

[0145] The preparation method is the same as that of Example 1, except that in step (3) of this comparative example, no BST ceramic powder is added, and the weight proportion of BMN ceramic powder is changed to 100 parts.

[0146] Test example:

[0147] (1) X-ray diffraction experiments were performed on BST ceramic powders obtained by different raw material ratios using the method of Example 1 and ceramic thick films and MLCC samples obtained by different sintering temperatures and times in Examples 6-10. The experimental results are as follows: Figure 1 and Figure 2 shown.

[0148] Depend on Figure 1 It can be seen that all samples have a perovskite phase and a cubic pyrochlore structure, and their XRD spectra are consistent with the standard cubic pyrochlore BZN (PDF#54-0971). As the sintering temperature increases, bismuth elements evaporate from the bismuth magnesium niobate ceramic, causing the A site to be occupied by more magnesium ions, resulting in unit cell shrinkage. This change is reflected in the (222) main peak of the thick film ceramic sample gradually shifting to higher angles. In addition, compared with the thick film sample, the XRD spectrum of the MLCC sample shows a weak impurity phase peak in the range of 31° to 32°. Figure 2Figure 2 shows the XRD patterns of the BST ceramic powders used in the examples. All BST ceramic powder samples exhibit a typical perovskite structure. During the powder mixing process, barium, due to its large relative atomic mass, tends to accumulate at the bottom of the ball mill, resulting in a shift in the (110) main peak. Furthermore, MLCC samples from different batches exhibit distinct perovskite phase characteristics.

[0149] (2) The MLCC samples prepared in Example 2 and Comparative Example 2 were characterized by micromorphology. The experimental results are shown in Figure 2. Figure 3 shown.

[0150] in Figure 3 Figure (a) shows the overall microscopic morphology of Example 2 after sintering, specifically showing an 8-layer (dielectric layer / metal electrode layer) structure, where the thickness of the metal conductive layer is about 4 μm and the thickness of the dielectric layer is about 30 μm. Other embodiments have similar structures. Figure 3 Figure (b) shows the microstructural characteristics of the dielectric layer, where a densified grain morphology can be observed, the porosity inside the ceramic is low, the material density is high, and the grain size is uniformly increased. This phenomenon confirms that the BST-BMN composite ceramic system in Example 2 has good sintering performance. It is particularly noteworthy that the introduction of BMN ceramic powder effectively reduces the sintering temperature of the system. This feature provides an important advantage for subsequent process optimization: it allows the internal electrode material to be replaced from expensive Pt electrodes to lower-cost base metal electrodes, thereby creating conditions for large-scale low-cost production. Figure 3 Figure (c) shows the interface morphology of Comparative Example 2. When the content of BMN ceramic powder in the dielectric thick film is further increased, the internal stress of the dielectric layer is too large and cannot be released during the sintering process, resulting in the fragmentation of the dielectric layer and the inability to form an MLCC structure. This shows that blindly increasing the doping content of BMN cannot improve the dielectric properties of MLCC.

[0151] (3) The dielectric temperature spectrum characteristics of the MLCC samples prepared in Examples 1-3 were characterized, and the characterization results are shown in Figure (4).

[0152] All MLCC samples in the examples showed the typical ferroelectric phase transition characteristics in which the dielectric constant first increased and then decreased with temperature, confirming that the BMN content has a significant regulatory effect on the phase transition behavior of the material. Among them, Example 2 showed the best comprehensive performance: its Curie temperature was the highest (77°C), and the maximum dielectric constant (about 5600) was obtained at the phase transition point; and as the BMN content deviated from the optimal ratio, the peak value of the dielectric constant decreased significantly. These results show that by precisely controlling the content of BMN ceramic powder, the temperature stability of the dielectric properties of MLCC can be effectively optimized. Figure 4As shown in Figure (b), the dielectric loss of all samples exhibits typical temperature dependence characteristics: as the temperature increases, the dielectric loss first gradually increases, then drops sharply when the Curie temperature is reached, and then turns to a slow increase. It is worth noting that samples with different components show obvious performance differences: the rate of change of the dielectric loss of the Example 2 sample with increasing temperature is the most significant, showing a steep growth curve; in contrast, the Example 3 sample shows a relatively flat dielectric loss-temperature change characteristic. This difference is closely related to the polarization mechanism transition behavior of different components at high temperatures.

[0153] (4) The dielectric properties of the MLCC samples prepared in Examples 1-3 and Comparative Examples 1 and 3 were characterized under an applied electric field at a test frequency of 100 kHz. The experimental results are shown in FIG. Figure 5 and as shown in Table 1.

[0154] Table 1 Dielectric properties of different embodiments and comparative examples (@100kHz)

[0155]

[0156]

[0157] like Figure 5 As shown in Figure (a), the MLCC samples obtained in Examples 1-3 of the present invention exhibited significantly different dielectric response behaviors under the action of an external electric field, and all exhibited excellent dielectric properties. Among them, Example 1 exhibited the most excellent electric field regulation performance, and its dielectric constant showed a significant nonlinear change trend with the increase of the external electric field intensity. The maximum dielectric tuning rate was calculated (up to 85%, @100kV / cm). This excellent adjustability is mainly due to the strong inhomogeneous polarization field and rich domain wall motion formed in the material. However, it is worth noting that the voltage resistance of this sample is relatively poor, and the breakdown field strength only reaches 100kV / cm, which may be due to the high concentration of mobile charge carriers and a large number of grain boundary defects. Figure 5 Figure (b) shows the change in dielectric constant of Comparative Example 3 with applied voltage. Compared with the Example, the dielectric constant of Comparative Example 3 is smaller, and under the same applied electric field strength, it shows a smaller dielectric strip slope of only 10%. This shows that compared with Comparative Example 3, the dielectric tuning rate and dielectric constant of the Example show a more obvious advantage. According to Table 1, although the dielectric tuning rate of Comparative Example 1 is more outstanding, its higher dielectric loss rate restricts its further application. Compared with the comparative example, Example 2 has more application prospects.

[0158] (5) The characteristic curve of dielectric tunability of MLCC samples prepared in Examples 1-3 was measured under the conditions of 100kHz and 15kV / cm. The experimental results are as follows: Figure 6shown.

[0159] like Figure 6 As shown, at 30°C, Example 2 exhibits a dielectric tunability of 47%, which is significantly higher than the other comparison samples. As the temperature increases, the dielectric tunability of all samples shows a trend of first increasing and then decreasing, and reaches a maximum value near the Curie temperature (TC), which is consistent with the phase transition behavior of typical ferroelectric materials. It is worth noting that Example 2 not only has a higher initial dielectric tunability, but also has better temperature stability: in the high temperature region, its performance decay rate is significantly lower than that of other samples. This difference is mainly due to the higher TC value of Example 1 and the optimized BMN ceramic doping process. The experimental results show that by precisely controlling the BMN doping content, the stable operating temperature range of the dielectric tunability of MLCC devices can be effectively broadened, which has important guiding significance for practical applications.

[0160] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a perovskite composite tunable capacitor for LTCC, characterized in that: The following steps are involved: S1: barium strontium titanate ceramic powder, bismuth magnesium niobate ceramic powder, organic solvent, binder, plasticizer and dispersant are mixed and ball-milled to prepare a tape casting slurry; S2: Using the tape casting slurry obtained in S1 as a raw material, a ceramic green film is prepared as a dielectric layer by a tape casting method; S3: coating one side of the ceramic green film obtained in S2 with an electrode as a metal electrode layer, and then performing staggered lamination to obtain a ceramic block; S4: The ceramic blocks obtained in S3 are first subjected to isostatic pressing, then cut into shape, subjected to binder removal and high-temperature sintering, and finally coated with silver paste and subjected to heat treatment to obtain the product.

2. The method for preparing a perovskite composite tunable capacitor for LTCC according to claim 1, wherein: The barium strontium titanate ceramic powder in S1 is prepared by the following method: First, barium carbonate, strontium carbonate and titanium dioxide are evenly mixed to obtain a precursor powder, and then the precursor powder is mixed with a ball milling solvent for the first ball milling, followed by the first vacuum drying and pre-calcining treatment, and finally the second ball milling, the second vacuum drying and grinding and sieving are performed to obtain barium strontium titanate ceramic powder.

3. The method for preparing a perovskite composite tunable capacitor for LTCC according to claim 2, wherein: The chemical formula of the barium strontium titanate ceramic powder is Ba 1-x Sr x TiO3, wherein x = 0.1-0.5; The mass ratio of the precursor powder to the ball milling solvent is (0.8-1.2): (0.8-1.2); The first ball milling time is 20-50h, and the ball milling speed is 300-320rpm; The first vacuum drying is carried out at a temperature of 60-100°C for 10-15 hours; The pre-sintering treatment conditions are: heating to 1100-1300°C at a heating rate of 1-10°C / min, keeping the temperature for 1-3 hours and then cooling with the furnace; The second ball milling time is 20-30h, and the ball milling speed is 300-320rpm; The temperature of the second vacuum drying is 60-100° C. and the time is 10-15 hours.

4. The method for preparing a perovskite composite tunable capacitor for LTCC according to claim 1, wherein: The bismuth magnesium niobate ceramic powder in S1 is prepared by the following method: Bismuth oxide, magnesium oxide and niobium oxide are firstly mixed uniformly to obtain a precursor powder, and then the precursor powder is mixed with a ball milling solvent for the first ball milling, followed by the first vacuum drying and pre-calcining treatment, and finally the second ball milling, the second vacuum drying and grinding and sieving are performed to obtain bismuth magnesium niobate ceramic powder.

5. The method for preparing a perovskite composite tunable capacitor for LTCC according to claim 4, wherein: The chemical formula of the bismuth magnesium niobate ceramic powder is Bi 1.5 MgNb 1.5 O7; The mass ratio of the precursor powder to the ball milling solvent is (0.8-1.2): (0.8-1.2); The first ball milling time is 20-50h, and the ball milling speed is 300-320rpm; The first vacuum drying is carried out at a temperature of 60-100°C for 10-15 hours; The pre-sintering treatment conditions are: heating to 800-900°C at a heating rate of 1-10°C / min, keeping at this temperature for 2-4 hours and then cooling in the furnace; The second ball milling time is 20-30h, and the ball milling speed is 300-320rpm; The temperature of the second vacuum drying is 60-100° C. and the time is 10-15 hours.

6. The method for preparing a perovskite composite tunable capacitor for LTCC according to claim 1, wherein: The weight proportions of the raw materials used in the tape casting slurry in S1 are: 90-100 parts of strontium barium titanate ceramic powder, 2-10 parts of bismuth magnesium niobate ceramic powder, 40-50 parts of organic solvent, 8-10 parts of binder, 8-10 parts of plasticizer and 0.5-1 part of dispersant; The ball milling speed is 50-100 rpm and the time is 40-60 h.

7. The method for preparing a perovskite composite tunable capacitor for LTCC according to claim 1, wherein: The thickness of the ceramic green film in S2 is 30-35 μm.

8. The method for preparing a perovskite composite tunable capacitor for LTCC according to claim 1, wherein: The ceramic block in S3 is a structure in which dielectric layers and metal electrode layers are alternately arranged, and the topmost layer and the bottommost layer are both dielectric layers.

9. The method for preparing a perovskite composite tunable capacitor for LTCC according to claim 1, wherein: The binder removal conditions in S4 are: heating to 300-500°C at a heating rate of 1-3°C / min in an air atmosphere and keeping the temperature for 2-3 hours; The high-temperature sintering conditions are as follows: heating to 900-1200°C at a heating rate of 1-10°C / min in a protective gas atmosphere and holding for 0.5-2h; The heat treatment temperature is 800-900°C and the time is 10-20 minutes.

10. A perovskite composite tunable capacitor for LTCC, characterized in that: The method is prepared according to any one of claims 1 to 9.

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