Investigation On Ferroelectric/Ferromagnetic Composite Materials And Device For Low Temperature Cofired Ceramic Technology

With the development of imformation and communication technologies, even higher requirements are put forward for materials, designment and integration technology when the further improvement has been made in the miniaturization, lightening, and multifunction of the systems. Facing the challenges, the composite materials are more advantageous in function integration. Having both capacitive and inductive properties, ferroelectric/ferromagnetic composite materials provide not only more choices for the integration of capacitive part and inductive part in the electronic devices, but also more methods for the designment of novel devices or functional units. Meanwhile, the low temperature cofired ceramic (LTCC) technology is gradually becoming the main way of passive integration because of its excellent thermal mechanical reliability, electronic and interconnection properties. Combination of ferroelectric/ferromagnetic composite materials and LTCC technology will help not only to resolve the problem that performance parameters seriation of LTCC materials is not implemented, but also avoid mismatch in cofiring by using a ferroelectric/ferromagnetic composite material instead of two kind of materials with capacitive and inductive properties, respectively.The low temperature sintering and properties research of two kinds of ferroelectric/ferromagnetic composites?BaTiO₃ (BTO)/ NiCuZn Ferrite (NCZF) and Bi₄Ti₃O₁₂ (BIT)/ NiCuZn Ferrite (NCZF) are carried out in this paper. At first, the densification of BTO/NCZF composite with low BTO content has been realized using 2wt% Bi₂O₃ by solid state reaction below 950o?. An analytical model has been builded on basis of the performance comparison between BTO/NCZF and CaTiO₃/NCZF with same mass ratio of dielectric phase to ferrite phase. It can predict the dielectric and magnetic properties of low fired ceramic composites. Meanwhile, influence of sintering temperature and dielectric phase content on the magnetizing processes has been investigated. Secondly, the BTO/NCZF composites have been successfully prepared by three kinds of methods (soft chemical method, Bi₂O₃-Li2CO3-V2O5 doping and low melting point glass fluxing method) at 900o?. It can be found that the BTO powder prepared by sol-gel method is benefit to reduce the dielectric loss of the system, but unable to improve the permittivity of the composites. Furthermore, the fine BTO powder is more favorable for the decrease of gap parameter than the powder with relatively larger grain size, and results in higher permeability. When the composites are prepared by Bi₂O₃-Li2CO3-V2O5 doping, good dielectric properties (??=28³1 at the frequency range of 1MHz¹GHz, tan?<0.02 at the frequency range of 1¹27MHz) can be abtained with mass ratio of BTO to ferrite 1:5. At this time,??=12¹4, and cut-off frequency is 488MHz. When keeping the above ratio unchanged, influence of B2O3-Bi₂O₃-SiO2-ZnO (BBSZ) glass adding amount on the electromagnetic properties of the composites has been investigated. The BTO/NCZF/BBSZ composite with good performance (??=13, cut-off frequency 585MHz,??=26) has been chosen for fabricating a LTCC low-pass filter which has 3dB cut-off frequency at 66.3MHz, and 20dB out band rejection at 145MHz. Moreover, variation of properties with composition in the BTO/NCZF composites prepared by different methods has been analysed by the above model. At last, low melting point Bi₄Ti₃O₁₂ (BIT) ferroelectric ceramic has been used to instead of BTO in the two-phase system. The magnetic and dielectric properties of low fired NCZF doped with BIT has been analysed. Adding appropriate amount of BIT can not only effectively improve the ferrite grain growth, but also be benefit for the improvement of dielectric properties. Then, influence of BIT content on the electromagnetic properties of the BIT/NCZF composites has been investigated.