Study Of Dielectric Materials For BaTiO₃ Based Mlcc Required By X9R

Based on desirable performance-cost behavior,multilayer ceramic capacitors,especially Ni-BaTiO₃ base metal multilayer ceramic capacitors（BME-MLCC）,have been widely used in various microelectronic devices.With the application of this kind of devices in more and more fields,the devices with even better electrical performances are required.Applications,such as certain defense and automotive electronics,require highly the capacitors that could be used at relatively higher temperatures,leading to the development of MLCC devices with ultra-thin layers while higher capacitance and better stability in wider temperature range.In this work,the dielectric that maintains reasonable capacitance stability up to 200℃ was successfully prepared by solid phase method using BaTiO₃ powder as matrix material.First,nano-scale bismuth titanate sodium powders with high Curie temperature and composite perovskite structure were prepared by solid-state method,then x BT-（1-x）BNT ferroelectric ceramics with relatively high Curie temperature were successfully synthesized.A series of studies on the effect of BNT addition on the Curie temperature of x BT（1-x）BNT solid solution was carried out.It is found that the sample of 0.9BT-0.1BNT shows Curie temperature of 190℃.Microstructure of BTBNT ceramics was characterized by using SEM,TEM,and XRD,respectively.It has been revealed that x BT（1-x）BNT is solid solution of tetragonal perovskite structure with ferroelectric domain at room temperature.The capacitance stability of BT-BNT ceramics in the temperature range from-55℃ to 200℃ has been significantly improved by adding 2.0 mol% Nb₂O₅ into 0.9 BT-0.1BNT solid solution,which meets the requirement for EIA X9R.mixrostructure and microchemistry investigation at nano-scale by TEM/STEM/EDS revealed that the dopant Nb distributs inhomegenesly within the ceramic grains.Nb is mainly located in the area next to grain boundary,and it is most likely free of Nb inside ceramic grain.Such Nb distribution in BTBNT grain is responsible for the formation of "core-shell" structure.In addition,the influence of dopants,such as MgO,Mg CO₃,Dy₂O₃,and Ho₂O₃,on the dielectric properties and microstructure of 0.9BT-0.1BNT-Nb based ceramics was also investigated.It has been showed that the MgO doping accelerates the Nb diffusion inside the whole grains.Most likely Nb is present whole grain,resulted in the disappearance of "core-shell" structure.The dielectric with MgO dopant won’t meet the EIA X9R requirements.However,"core-shell" structure is well maintained in 0.9BT-0.1BNT-Nb based ceramics with dopants,such as Mg CO3,Dy2O3,and Ho2O3.The capacitance-temperture stability is well meets the EIA X9R requirements.