MG-TA BASED DIELECTRIC CERAMIC FOR MULTI-LAYER CERAMIC CAPACITOR AND LOW-TEMPERATURE PREPARATION METHOD THEREOF

Abstract

A Mg—Ta based dielectric ceramic for multi-layer ceramic capacitor (MLCC) and a low-temperature preparation method thereof are provided. By providing a glass additive with high matching with a Mg—Ta ceramic, a modifier A.sup.+1.sub.2CO.sub.3—B.sup.2+O—C.sup.3+.sub.2O.sub.3—SiO.sub.2 (A=Li, K; B=MnO, CuO, BaO; C=B, Al) is intruded in to a main material MgO—Ta.sub.2O.sub.5, which can significantly reduce the sintering temperature and provide a negative temperature coefficient of dielectric constant of −100±30 ppm/° C., and reduce the deterioration factors of loss caused by an additive for sintering, and prepare a dielectric material applied to RF MLCC with low loss, low cost and good process stability.

Claims

1. A magnesium-tantalum (Mg—Ta) based dielectric ceramic for multi-layer ceramic capacitor, comprising a ceramic material and a modifier; wherein a chemical formula of the ceramic material is MgTa.sub.2O.sub.6; a formula of the modifier is A.sub.2CO.sub.3—BO—C.sub.2O.sub.3—SiO.sub.2 with a mass ratio of 31:17:36:16, A.sub.2CO.sub.3 consists of 20 wt. % of Li.sub.2CO.sub.3 and 11 wt. % of K.sub.2CO.sub.3; BO consists of 2 wt. % BaO, 5 wt. % of MnO and 10 wt. % of CuO; and C.sub.2O.sub.3 consists of 30 wt. % of B.sub.2O.sub.3 and 6 wt. % of Al.sub.2O.sub.3; a formula of the Mg—Ta based dielectric ceramic is MgTa.sub.2O.sub.6+2 wt. % of the modifier, the Mg—Ta based dielectric ceramic is prepared by a solid-state method, a main crystal phase of the Mg—Ta based dielectric ceramic is MgTa.sub.2O.sub.6 phase with a Trirutile structure; under a sintering temperature of 1150 degrees Celsius (° C.), a dielectric constant of the Mg—Ta based dielectric ceramic is 26.87, a dielectric loss of the Mg—Ta based dielectric ceramic is 1.71×10.sup.−4, and a value of a quality factor Q×f of the Mg—Ta based dielectric ceramic is 44398 GHz; and a temperature coefficient τ.sub.ε of the dielectric constant is stable and meets M2G temperature characteristics of (−55° C.: τ.sub.ε=−118 parts per million (ppm)/° C.; 85° C.: τ.sub.ε=−110 ppm/° C.); the Mg—Ta based dielectric ceramic for multi-layer ceramic capacitor is prepared through the following steps: step 1, mixing raw powders of magnesium oxide (MgO) and Ta.sub.2O.sub.5 according to the chemical formula MgTa.sub.2O.sub.6 to obtain a mixed powder; step 2, putting the mixed powder prepared in step 1 into a ball milling tank, using zirconium balls and deionized water as a grinding medium and performing planet ball milling for 4-6 hours according to a mass ratio of the mixed powder:the zirconium balls:the deionized water of 1:4-5:2-4 to obtain a mixed slurry, drying the mixed slurry in an oven after the planet ball milling and then sieving with a 60-100 mesh sieve to obtain a sieved powder; and sintering the sieved powder in an atmosphere of 900-1000° C. for 3-5 hours to obtain MgTa.sub.2O.sub.6; step 3, mixing raw powders of Li.sub.2CO.sub.3, K.sub.2CO.sub.3, BaO, MnO, CuO, B.sub.2O.sub.3, Al.sub.2O.sub.3, and SiO.sub.2 according a mass ratio of Li.sub.2CO.sub.3:K.sub.2CO.sub.3:BaO:MnO:CuO:B.sub.2O.sub.3:Al.sub.2O.sub.3:SiO.sub.2 of 20:11:2:5:10:30:6:16 to obtain a second mixed powder; using the zirconium balls and alcohol as a grinding medium and performing planet ball milling for 6-8 hours according to a mass ratio of the second mixed powder:the zirconium balls:the alcohol of 1:4-5:4-6 to obtain a ball-milled material, sintering the ball-milled material at a temperature of 600-650° C. for 3-6 hours after drying the ball-milled material and then heating to a temperature of 1450-1550° C. for melting for 3-5 hours to obtain a melted material, pouring the melted material into the deionized water for cooling to obtain a cooled material, and grinding the cooled material to a uniform power as the modifier; step 4, mixing the modifier prepared in step 3 into MgTa.sub.2O.sub.6 prepared in step 2 according to the formula of the Mg—Ta based dielectric ceramic MgTa.sub.2O.sub.6+2 wt. % to obtain a third mixed power, performing planetary ball milling for 3-5 hours according to a mass ratio of the third mixed powder:the zirconium balls:the deionized water of 1:4-5:3-5 to obtain a second ball-milled material, and adding a polyvinyl alcohol solution, as a binder, into the second ball-milled material after drying the second ball-milled material to perform granulation to obtain a granular material; and step 5: performing press-molding on the granular material prepared in step 4, heating at a heating rate of 2-5° C./minutes (min) and discharging glue at 600-650° C. for 3-5 hours, and then heating at the same heating rate to a temperature of 1150° C. and keeping the temperature for 4-6 hours, thereby obtaining a modified MgTa.sub.2O.sub.6 dielectric ceramic material.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0020] FIG. 1 illustrates a schematic diagram of an X-ray diffraction (XRD) pattern according to an embodiment 6 of the disclosure.

[0021] FIG. 2 illustrates a schematic diagram of scanning electron microscope (SEM) according to the embodiment 6 of the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

[0022] The disclosure will be further described in detail with the attached drawings and embodiments.

[0023] A method for preparing a Mg—Ta based dielectric ceramic for multi-layer ceramic capacitor is provided and includes the following steps: step 1, mixing raw powders of magnesium oxide (MgO) and Ta.sub.2O.sub.5 according to the chemical formula MgTa.sub.2O.sub.6 to obtain a mixed powder; [0024] step 2, putting the mixed powder prepared in step 1 into a ball milling tank, using zirconium balls and deionized water as a grinding medium and performing planet ball milling for 6 hours according to a mass ratio of the mixed powder:the zirconium balls:the deionized water of 1:5:4 to obtain a mixed slurry, drying the mixed slurry in an oven after the planet ball milling and then sieving with a 100 mesh sieve to obtain a sieved powder; and sintering the sieved powder in an atmosphere of 1000° C. for 5 hours to obtain MgTa.sub.2O.sub.6; [0025] step 3, mixing raw powders of Li.sub.2CO.sub.3, K.sub.2CO.sub.3 BaO, MnO, CuO, B.sub.2O.sub.3, Al.sub.2O.sub.3, and SiO.sub.2 according a mass ratio of Li.sub.2CO.sub.3:K.sub.2CO.sub.3:BaO:MnO:CuO:B.sub.2O.sub.3:Al.sub.2O.sub.3:SiO.sub.2 of 20:11:2:5:10:30:6:16 to obtain a second mixed powder; using the zirconium balls and alcohol as a grinding medium and performing planet ball milling for 6 hours according to a mass ratio of the second mixed powder:the zirconium balls:the alcohol of 1:5:4 to obtain a ball-milled material, sintering the ball-milled material at a temperature of 600° C. for 5 hours after drying the ball-milled material and then heating to a temperature of 1500° C. for melting for 4 hours to obtain a melted material, pouring the melted material into the deionized water for cooling to obtain a cooled material, and grinding the cooled material to a uniform power as the modifier; [0026] step 4, mixing the modifier (also referred to as glass additive) prepared in step 3 into MgTa.sub.2O.sub.6 (also preferred to as pre-fired material) prepared in step 2 according to the formula of the Mg—Ta based dielectric ceramic MgTa.sub.2O.sub.6+x wt. % to obtain a third mixed power, x is 1 or 2, performing planetary ball milling for 5 hours according to a mass ratio of the third mixed powder:the zirconium balls:the deionized water of 1:5:4 to obtain a second ball-milled material, and adding an 8 wt. % of polyvinyl alcohol solution, as a binder, into the second ball-milled material after drying the second ball-milled material to perform granulation to obtain a ceramic raw material; and [0027] step 5: performing press-molding on the ceramic raw material prepared in step 4, heating at a heating rate of 5° C./min and discharging glue at 650° C. for 4 hours, and then heating at the same heating rate to a temperature of 1050-1150° C. and keeping the temperature for 6 hours, thereby obtaining a modified MgTa.sub.2O.sub.6 dielectric ceramic material.

[0028] In order to better illustrate the effect of the disclosure, six embodiment samples are made according to the above steps. FIG. 1 is the XRD pattern of an embodiment 6. After searching, the phase composition of the ceramic corresponds to the standard card of MgTa.sub.2O.sub.6, i.e. joint committee on powder diffraction standards (JCPDS) card with No. 32-0631, no second phase diffraction peak is found in the system at this time, which indicates that ion substitution will not change the crystal structure at this doping amount, and this type of ceramic belongs to the MgTa.sub.2O.sub.6 structure.

[0029] FIG. 2 is a SEM topography diagram of the embodiment 6. As can be seen from FIG. 2, the grain size is small, and there are fewer pores.

[0030] The composition and microwave dielectric properties of the embodiments are shown in Table 1 and Table 2 as follows.

[0031] Table 1 shows the components of each embodiment sample.

TABLE-US-00001 Embodiment number 1 2 3 4 5 6 Mass of MgO 8.358 8.358 8.358 8.358 8.358 8.358 each Ta.sub.2O.sub.5 91.642 91.642 91.642 91.642 91.642 91.642 component Li.sub.2CO.sub.3 0.200 0.200 0.200 0.400 0.400 0.400 K.sub.2CO.sub.3 0.110 0.110 0.110 0.220 0.220 0.220 BaO 0.020 0.020 0.020 0.040 0.040 0.040 MnO 0.050 0.050 0.050 0.100 0.100 0.100 CuO 0.100 0.100 0.100 0.200 0.200 0.200 B.sub.2O.sub.3 0.300 0.300 0.300 0.600 0.600 0.600 Al.sub.2O.sub.3 0.060 0.060 0.060 0.120 0.120 0.120 SiO.sub.2 0.160 0.160 0.160 0.320 0.320 0.320 Sintering temperature 1050 1100 1150 1050 1100 1150 (° C.)

[0032] Table 2 shows the dielectric properties of each embodiment sample.

TABLE-US-00002 Embodiment dielectric tanδ Q × f τ.sub.∈ (ppm/° C.) number constant ∈.sub.r (10.sup.−4) (GHz) −55° C. 85° C. 1 21.33 3.09 25793 −94 −98 2 24.69 2.25 33956 −107 −115 3 27.81 1.88 40521 −114 −105 4 20.38 4.89 16587 −80 −88 5 25.17 1.82 42665 −103 −112 6 26.87 1.71 44398 −118 −110

[0033] From the data shown in Table 1 and Table 2, it can be seen that in the embodiment 6, when the sintering temperature is 1150° C., the dielectric constant and Q×f value of the modified MgTa.sub.2O.sub.6 dielectric ceramic material get the best values: ε.sub.r=26.87, tan δ=1.71×10.sup.−4, Q×f=44398 GHz, and τ.sub.ε is in a range of −118 ppm/° C. to −110 ppm/° C. Compared with literature reports in the related art, the sintering temperature is greatly reduced and the dielectric loss is kept low, at the same time, the temperature coefficient of dielectric constant is relatively stable in the range of −55° C. to 85° C., the modified dielectric ceramic material is suitable for industrial application.