Patent Publication Number: US-2023145935-A1

Title: Modified NiO-Ta2O5-based Microwave Dielectric Ceramic Material Sintered at Low Temperature and Its Preparation Method

Description:
TECHNICAL FIELD 
     The present invention belongs to the field of electronic ceramics and its manufacturing, and relates to a modified NiO-Ta 2 O 5 -based microwave dielectric ceramic material sintered at low temperature and its preparation method. 
     BACKGROUND 
     With the development of mobile communication in the direction of high frequency, the importance of electronic components such as dielectric filters, dielectric resonator antennas, dielectric waveguides, etc. is highlighted, while microwave dielectric ceramics can play a functional role in the range of 300 MHz~300 GHz, and are the key basic materials widely used to prepare the above electronic components at present. 
     Traditional microwave equipment is heavy and expensive. With the development of communication industry, it is required that the space occupied by circuit system should be as small as possible. As a new type of three-dimensional integrated packaging and interconnection technology, low-temperature co-fired ceramic(LTCC) technology provides a reliable solution for preparing ceramic modules or integrated circuits with embedded electrodes because of it can meet the high-frequency application. Therefore, developing ceramic systems applied to LTCC technology has become the focus of research in this field. 
     The microwave dielectric properties of NiO-Ta 2 O 5  ceramic material with tetragonal Tri-rutile crystal structure at 1400° C. are: ε r  = 25, Q×f = 31200 GHz, T f  = 26 ppm/°C, but it can’t be co-fired with Ag or Cu electrodes in LTCC technology due to too high sintering temperature (co-firing with Ag electrodes should not exceed 950° C.; Co-firing with Cu electrode should not exceed 1000° C. and be carried out in reducing atmosphere), and the temperature coefficient T f  of resonance frequency is also large (T f  value between 10 ppm/°C means excellent temperature stability). Up to now, there is no exploration of low-temperature sintering of NiO-Ta 2 O 5  ceramics. Therefore, it is urgent to reduce the sintering temperature of NiO-Ta 2 O 5 -basedceramics and maintain the microwave dielectric properties. 
     SUMMARY 
     In view of the above problems or deficiencies, in order to solve the problem that the existing NiO-Ta 2 O 5  ceramics can’t be co-fired with Ag or Cu electrodes in LTCC technology due to high sintering temperature, the present invention provides a low-temperature sintering modified NiO-Ta 2 O 5 -based microwave dielectric ceramic material and its preparation method, which realizes low-temperature sintering while maintaining excellent microwave dielectric properties. Its temperature is stable, and it can be widely used in LTCC technical field. 
     The invention provides a modified NiO-Ta 2 O 5 -based microwave dielectric ceramic material sintered at low temperature, and the general chemical formula of it is:
     (1.587y-0.198xy)ZnO-(2.597y-0.324xy)CuO-(1-x)NiO-(1.855y-0.23 1xy)B 2 O 3 -3xSnO 2 -(1-x)Ta 2 O 5 -(0.284y-0.035 x   y )V 2 O 5 ; wherein 0.1≤x≤0.2; and 0.03≤y≤0.09; and prepared by solid-phase method; and the crystal type is NiTa 2 O 6  structure;   the sintering temperature of the microwave dielectric ceramic material is 875-950° C., and the microwave dielectric ceramic material is pre-sintered in the atmosphere environment of 850-900° C.; in addition, the dielectric constant is 17~21, the quality factor Q×f value is 14,000-23,000 GHz, and the temperature coefficient of resonance frequency is 5~10 ppm/°C.   

     Preferably, when x=0.15 and y=0.06, the dielectric constant of the material is 20.2 at the sintering temperature of 925° C., the quality factor Q×f value is 22417 GHz, and the temperature coefficient of resonant frequency is 8.7ppm/°C, which can be used in the LTCC technical field. 
     The preparation method of the modified NiO-Ta 2 O 5 -based microwave dielectric ceramic material sintered at low temperature comprises the following steps: 
     step 1, mix ZnO, CuO, NiO, B 2 O 3 , SnO 2 , Ta 2 O 5  and V 2 O 5  powder according to the general chemical formula: (1.587y-0.198xy)ZnO-(2.597y-0.324xy)CuO-(1-x)NiO-(1.855y-0.231xy)B 2 O 3 -3 xSnO 2 -(1-x)Ta 2 O 5 -(0.284y-0.035xy)V 2 O 5 ;(x = 0.1 ~ 0.2y=0.03~0.09);   step 2: put the powder mixed in step 1 into a ball milling tank, and perform ball milling with zirconia balls and deionized water according to the mass ratio of powder: zirconia balls: deionized water of 1:5-7:3-5, perform the planetary ball milling for 6-8 hours, take it out, dry it in an oven at 80-120° C., sieve it with a 40-60 mesh sieve, and pre-sinter it in an atmosphere environment environment at 850-900° C. for 3~5 hours;   step 3: perform ball milling on the powder pre-sintered in step 2 again according to the mass ratio of powder: zirconium balls: deionized water of 1:4-6:1-3, and perform planetary ball milling and mixing for 3-6 hours, take it out and dry, and add polyvinyl alcohol solution into the obtained powder for granulation;   step 4, press and mold the ceramic raw material prepared in step 3, discharge the glue at 600-650° C., and then sinter in the atmosphere environment environment at 875-950° C. for 4-6 hours to obtain the modified NiO-Ta 2 O 5 -based microwave dielectric ceramic material sintered at low temperature.   

     The invention is different from the technology reported in the prior field, that is, by adding oxides such as CuO, V 2 O 5 , B 2 O 3  and the like into the pre-sintered NiO-Ta 2 O 5  material as sintering aids, the purpose of sintering into ceramic at low-temperature is achieved under the action of liquid phase. Instead, it is guided by ion doping modification, which not only takes into account the substitution of ions with similar radius to realize the preparation of solid solution ceramics, such as Zn 2+  replacing Ni 2+  ions, V 5+  replacing Ta 5+  ions, and (Ni1/3Ta2/3)  4+  composite ions being replaced by Sn4+, and the synergistic effect among different ions can improve the comprehensive microwave dielectric properties; At the same time, the selected doped oxide still has the property of low melting point, so the purpose of improving the main crystalline phase of NiO-Ta 2 O 5  synthesized at a lower temperature can be achieved, and the sintering temperature can be reduced while the ceramic material maintains excellent microwave dielectric properties. 
     The present invention provides a modified NiO-Ta 2 O 5 -based ceramic material sintered at low temperature, and its chemical general formula is (1.587y-0.198xy)ZnO-(2.597y-0.324xy)CuO-(1-x)NiO-(1.855y-0.231xy)B 2 O 3 -3 xSnO 2 -(1-x)Ta 2 O 5 -(0.284y-0.035xy)V2O5. By adjusting the molar content of each raw material, the NiO-Ta 2 O 5 -based ceramic material with low-temperature sintering, stable temperature and excellent microwave dielectric properties is directly synthesized at one time, which can be widely used in LTCC technical field. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    shows X-ray diffraction (XRD) pattern of ceramic sample corresponding to embodiment 3; 
         FIG.  2    shows a morphology diagram of the ceramic sample corresponding to the embodiment 3 under a scanning electron microscope (SEM). 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will be further explained in detail below with reference to the figures and embodiments. 
     step 1, mix ZnO, CuO, NiO, B 2 O 3 , SnO 2 , Ta 2 O 5  and V 2 O 5  powder in molar ratio according to the general chemical formula: (1.587y-0.198xy)ZnO-(2.597y-0.324xy)CuO-(1-x)NiO-(1.855y-0.231xy)B 2 O 3 -3 xSnO 2 -(1-x)Ta 2 O 5 -(0.284y-0.035xy)V 2 O 5 ;(x = 0.1 ~ 0.2y=0.03~0.09);   step 2, put the powder weighted in step 1 into a ball milling tank, and perform planetary ball milling with zirconia balls and deionized water according to the mass ratio of powder: zirconia balls: deionized water of 1:6:3 for 6 hours, take it out, dry it in an oven at 100° C., sieve it with a 60 mesh sieve, and pre-sinter it in an atmosphere environment environment at 900° C. for 3 hours;   step 3, perform the second ball milling on the pre-sintered powder, and perform planetary ball milling according to the mass ratio of powder: zirconia balls: deionized water of 1:6:2, for 4 hours, take it out and dry, and add polyvinyl alcohol solution into the obtained powder for granulation;   step 4, put the granulated powder into a mold of φ12 and form it into a cylinder by dry-pressing under pressure of 20 MPa. Then, keep the cylinder block at 650° C. for 2 hours to remove the binder, and then raise it to 875° C. ~ 950° C. for 4 hours. Finally, the modified NiO-Ta 2 O 5 -based microwave dielectric ceramic material under the condition of low-temperature sintering is prepared. The molar ratios of its chemical formulas are: ZnO-CuO-NiO-B2O3-SnO2-Ta2O5-V2O5(3.7: 6.1: 33.7: 4.3: 17.8: 33.7: 0.7 mol %).   

     In order to better illustrate the effect of the present invention, four embodiments are made according to the above steps.  FIG.  1    shows the X-ray diffraction (XRD) pattern of ceramic sample corresponding to embodiment 3. After searching, the phase composition of ceramics corresponds to the standard card JCPDS card No.32-0702 of NiTa 2 O 6 . At this time, no second phase diffraction peak is found in the system, which means that this type of ceramics belongs to the solid solution with NiTa 2 O 6  structure. 
       FIG.  2    is the morphology diagram of the ceramic sample corresponding to the embodiment 3 under a scanning electron microscope (SEM). It can be seen that the grain growth of the ceramic sample is sufficient, and the grain boundary is clearly visible, indicating that its low-temperature sintering characteristics are good, but the microscopic pores still exist at this time. 
     Components and microwave dielectric properties of each embodiment are as follows:   
     Table 1 shows the components of the sample groups of each embodiment.    
     Table 2 shows the microwave dielectric properties of the samples of each embodiment. 
     From the data shown in Table 1 and Table 2, it can be seen that when x = 0.15 and y = 0.06, the sintering temperature is in the range of 875 ~ 925° C., the dielectric constant and Q×f value of modified NiO-Ta 2 O 5 -based ceramic materials first increase and then decrease, and the best values are obtained at 925° C.: ε r = 20.2, tanδ = 4.1× 10 -4 , Q×F = 22417 GHz,  Tf = 8. 7 ppm/°C. And compared with the existing literature reports, the sintering temperature is greatly reduced, while excellent temperature stability and microwave dielectric properties are maintained, which can be widely used in LTCC technical field.