Research On Giant Dielectric/Ferrite Magnetoelectric Composite Materials And Components In Radio Frequency Domain

The revolutions in information technology guide the development of electronic components to LTCC, and new magnetoelectric composites have become a research focus at present and in the near future. If we can find a new magnetoelectric composite, which possesses an acceptable dielectric constant and permeability in the same frequency range, and also has a low loss tangent, then the design and process of the new LTCC components will become more simply and the performance will be better. New giant dielectric material CaCu₃Ti₄O₁₂ (CCTO) is known to be a more promising dielectric phase candidate material in magnetoelectric composites. Because it shows a high and temperature-independent dielectric constant value of 104 over a wide temperature range from 100 to 600 K, and its sintering temperature is relatively low ( 1100?). Therefore, in this dissertation, the investigations were first focus on the serial problem existing in dielectric phase material CCTO of magnetoelectric composite materials. On the basis of the above results, the magnetic phase material NiCuZn ferrite was used to composite with CCTO, and the magnetic and dielectric properties of CCTO/NiCuZn ferrite composite materials were studied. Finally, the LTCC low pass chip filters were fabricated using ourself-research ferrite-dielectric composite materials. The concrete contents are as following:Firstly, the influences of point defects on the dielectric relaxation of dielectric phase material CCTO had been investigated by substituting Ti⁴⁺ with Nb⁵⁺ and analyzing the dielectric properties of the surface and the interior of a 10 mm thickness columned ceramic. The results showed that the low frequency dielectric relaxation is related to the electrode-sample contact and the surface layers effects. In order to further explore the interior structure and mechanism of CCTO, the influences of dc bias voltage on the dielectric behaviors of dielectric phase material CCTO had been investigated. A model containing two n-type semiconductor MOSs connected in series were presented to explain the dielectric behaviors at low and high frequency under dc bias voltage. This result confirmed the contribution of the surface layers to the ceramic dielectric constant. Then, in order to improve the dielectric properties of dielectric phase material CCTO, the effects of Li-doped and low melting glass BBSZ on the dielectric properties of CCTO ceramics had been investigated. The results showed that the dielectric constant of Li-doped CCTO ceramics could keep on 10⁵ order of magnitude, meanwhile, its dielectric loss reduced to 0.06. However, the addition of BBSZ could make the sintering temperature of CCTO decrease 50?and its dielectric loss reduced to 0.05, while the dielectric constant of >2500 still remained.Secondly, CCTO/NiCuZn ferrite composite materials were synthesized for the first time. The effect of composition on the sintering properties, crystalline-phase structure, microstructure, magnetic and dielectric properties of the new ferrite-dielectric composite materials had been investigated systematically. To realize low temperature sintering of the composite materials and by a comprehensive evaluation of both magnetic and dielectric properties, we chose the composition of 85wt% NiCuZn ferrite/15wt% CCTO and 80wt% NiCuZn ferrite/20 wt% CCTO in here. Then, Bi2O3 or BBSZ glass were considered as an alternative additive and its effect on sintering behavior, magnetic and dielectric properties of CCTO/NiCuZn ferrite composite materials were studied, respectively. The results showed that the density of all BBSZ-doped samples sintered at 900?had reached 95% of theoretical density. The dielectric constant and permeability of composites showed weak frequency dependence in a frequency range from 1 MHz to 30 MHz. At 10 MHz, as the BBSZ content increased from 0 to 3 wt%, the permeability?of composites increased from 13.2 to 47.9, and the magnetic loss tan??decreased from 0.022 to 0.017. Meanwhile, the resonant frequency of composites decreased from 10⁹ Hz to 3.2×10⁸ Hz. Correspondingly, the dielectric constant?of composites increased from 9.2 to 16, and the dielectric loss tan??decreased from 0.069 to 0.012. The excellent whole performances of composites are expected to be able to promote practical applications.Finally, the 30 MHz LTCC low pass filter were designed and fabricated using ourself-research ferrite-dielectric composite materials for the first time. The measuring results showed that the 3 dB cut-off frequency of the low pass filter was 29 MHz, and the out band rejection at 100 MHz reached 22.6 dB. The results meet the requirements of performance indexes in the design of filter, and also verify the availability of ourself-research magnetoelectric composite materials. It is helpful to solve the problem of co-fired match between dissimilar materials.