Basic Research On Technology And Application Of LTCC YIG Micro And Millimeter Wave Composite

Low temperature co-fire sintering ceramics?LTCC?technology as a modern material,device and system in packaging technology?SIP?is changing the processing methods and preparation processes of electronic information hardware systems of our time.The micro-systemization of SIP will inevitably lead to the further development of miniaturization,integration,multi-function,high speed,low power consumption and low cost,and is leading the revolution of a new generation of high-frequency microwave communication devices.The RF-microwave-millimeter band low-temperature co-fired ferrite magnet material has become the material of concern for this international revolution,and it is also the technical bottleneck in the application.Nowadays,many materials are applied to LTCC technology,but the low-temperature co-firing technology of low-loss microwave/millimeter-wave yttrium iron garnet ferrite powder materials has not been solved and applied internationally.The reason is that the ultra-high sintering temperature?1450°C?is so high compare to the requirement of LTCC process?below 960°C?.Too low sintering temperature makes the internal structure of YIG ferrite loose,and the void ratio is too high,which seriously affects the performance of YIG ferrite.In particular,the soft magnetic properties and the gyromagnetic properties such as saturation magnetization,coercive force and ferromagnetic resonance line width are very dependent on the uniform density of the microstructure of the ferrite material.Therefore,how to achieve solid phase sintering YIG ferrite dense and good performance below 960°C,so that it can be applied to LTCC technology to prepare microwave devices such as new generation circulators,which has become a very difficult research topic in the world.It's also a serious challenge to us.This dissertation is working on this scientific issue,as follows:First,the effect of changing the sintering environment on YIG ferrite was explored.We used BBSZ?H₃BO₃-Bi₂O₃-SiO₂-ZnO?glass phase sintering agent as a dopant to synthesize YIG ferrite material by solid phase method to investigate the effect of sintering environment on sintering and grain growth of YIG ferrite.It was found that the addition of BBSZ can effectively lower the sintering temperature,and a sintered mature ferrite can be obtained within a temperature drop range of 200°C.The addition of an appropriate amount of BBSZ can reduce the porosity of the sample,promote grain growth and fusion,and obtain better performance.However,beyond this temperature range,the power of the sample to reduce the porosity and promote the growth of the crystal grains is seriously insufficient,and the demand for low temperature lowering is not satisfied at all.If too much BBSZ is added,although the crystal grains can be sufficiently grown,the performance is seriously deteriorated,and it is not worth the loss.According to this series of experiments,we conclude that changing the sintering environment can improve the sintering of ferrite materials to a certain extent,but it cannot meet the cooling requirements of 500°C at all,and the external helium conditions cannot fundamentally solve this sintering problem.Therefore,fundamentally overcoming the sintering problem requires changing the intrinsic conditions and reaction paths from the intrinsic energy angle.At the same time,we explored the role of BBSZ in the sintering process and provided research ideas for the next experiment.Secondly,according to the internal conditions,the low melting point oxide Bi₂O₃was used to replace the high melting point oxide Y₂O₃,and the mature YIG ferrite powder material was successfully sintered.The microstructure and the change of performance under low temperature sintering conditions were systematically studied.The experimental results show that Y³⁺ions in Bi:YIG can effectively reduce the sintering temperature.The Bi ion completely enters the center position of the dodecahedral sublattice,which can change the lattice constant and make the crystal morphology of the grain uniform and dense at a lower temperature,promote grain growth and have a small porosity.And the performance of the sample has been greatly improved.The ferrite sample sintered at 950°C obtained the best parameters when the substitution amount of Bi ion was 0.9,that is,Y_2.1Bi_0.9Fe₅O₁₂,the saturation magnetization?Ms?reached 15.2emu/g,and the coercive force decreased to about 41 Oe,the ferromagnetic resonance linewidth FMR is reduced to about 254 Oe.This series of experiments has played an innovative role in the cooling and sintering of YIG ferrite,enabling YIG to be applied to the LTCC circulator in the X-band or higher frequency band,which proves its application value and points out the direction for further improvement of performance.Then,based on this,the content of Fe in the ferrite substituted by Bi is changed,and the sintering of the ferrite powder is further optimized.The experimental results show that proper iron deficiency can improve the low-temperature sintering performance of ferrite,which is beneficial to grain growth,densification and porosity reduction,and improve magnetic properties and gyromagnetic properties.Under the condition of sintering at 950°C,when the iron deficiency reaches 4%,that is,Y_2.1Bi_0.9Fe_?5-x?O_?12-1.5x?,x=0.2,better performance can be obtained,and the sample is uniform and dense.The grain size is large,the saturation magnetization rises to 27.5 emu/g,the coercive force decreases to 23.8 Oe,and the ferromagnetic resonance line width decreases to 180 Oe.According to this result,YIG has a very broad application prospect in LTCC technology.In this experiment,the reason why Bi-substituted YIG sintering changed the reaction path to reduce the sintering temperature was also analyzed from the viewpoint of energy change.The process and tendency of sub-lattice magnetic moment generation during grain growth were analyzed by the change of saturation magnetization.Then,continue to optimize the performance of Bi-substituted YIG ferrite,set different sintering curves by changing the temperature point at the time of holding,and multi-step sintering to explore the effect of sintering environment on low-temperature sintering of Bi-substituted YIG.The experimental results show that multiple oscillation sintering is beneficial to optimize the sintering process of ferrite,making the grain growth more uniformly and densifily,and the grain size is larger.At the same time,better performance is achieved.Eight-step sintering gives the best gyromagnetic properties,and the ferromagnetic resonance linewidth is reduced from 254 Oe to 232 Oe.However,too many sintering steps lead to a decrease in saturation magnetization.This experiment also explores the variation of temperature oscillations on grain boundaries.Low-temperature sintering of yttrium iron garnet?below 960°C?and ultra-low gyromagnetic loss??H<200 Oe?are two big problems around the world.In this dissertation,the low-temperature sintered LTCF samples with the best performance are obtained from the internal conditions,environmental conditions,BBSZ combustion and Bi₂O₃ substitution,distribution sintering and other reaction pathways.The application of polycrystalline yttrium iron garnet in LTCC integrated devices is obtained.The foundation is laid to form an X-band yttrium iron garnet material with independent property rights.