Research On The Multi-layer Ceramic Capacitors Of Bismuth Magnesium Niobate Materials

Tunable capacitors made from tunable dielectric materials offer numerous benefits,including high reliability,fast tuning rates,and compact size,which significantly improve system integration.Ba_0.6Sr_0.4TiO₃（BST）is currently the most widely researched dielectric tunable material.However,the ferroelectric hysteresis effect of ferroelectric materials can increase the dielectric loss of BST,limiting its practical application.In contrast,Bi_1.5MgNb_1.5O₇（BMN）is a non-ferroelectric material with a cubic pyrochlore structure,has a moderate dielectric constant（～170）,high dielectric tunability（>50%）,and extremely low dielectric loss（<0.001）.BMN is an excellent candidate for the development of tunable devices,particularly for multilayer ceramic capacitors（MLCCs）,which currently have the highest output and utilization rate among electronic devices.The incorporation of dielectric tunability into MLCCs can further enhance their suitability for high-integration electronic systems by increasing system bandwidth and efficiency.This study focuses on the development of BMN-based MLCCs,including the preparation process and investigation of their dielectric properties.BMN thick films were prepared via casting,and BMN-MLCCs were subsequently fabricated via multilayer stacking.The key findings and conclusions of this study are outlined below.1.BMN thick films were fabricated using the organic tape-casting method and the effects of different process parameters,including binder type,solvent content,and tape-casting temperature,were analyzed with respect to the ceramic microstructure and dielectric properties.By precisely controlling the preparation conditions and optimizing the fabrication process,BMN thick film ceramics were successfully produced with a dielectric constant of 176,a loss of 0.0007 and a dielectric tunability nr of 6.3%under an electric field of 330 kV/cm were successfully prepared.BMN ceramics were subjected to high frequency dielectric property measurements at Ku-band using the waveguide method.Results indicate a decrease in the dielectric constant to 75-84 and an increase in the dielectric loss to 0.06-0.16 in the 12-20 GHz frequency range.2.Tunable MLCCs with Ag0.7/Pd0.3 as the inner electrode were prepared,and it was demonstrated through XPS and XRD tests that the Ag-based electrode materials do not react with BMN ceramic.However,interdiffusion occurs between Ag0.7/Pd0.3 and the dielectric at the interface during the co-firing process due to thermal atomic movement.The diffusion of Mg/Nb from the dielectric layer into the electrode generates a heterophase Mg₅Nb₄O₁₅,which enhances the temperature stability and dielectric constant of the ceramic.The maximum dielectric constant of BMN-MLCC,at 216,corresponds to a low loss of 0.00036,τ_εof-249.94 ppm/°C,and a relative dielectric tunability n_rof 10.8%.3.The frequency response of the BMN-MLCC was investigated,revealing that the MLCC’s performance remains consistent at lower frequencies.The dielectric constant exhibits negligible frequency dependence,while the loss experiences significant fluctuations that are primarily attributed to conduction loss arising from internal metal electrodes.As the test frequency surpasses approximately 2 MHz and approaches the MLCC’s self-resonant frequency,the MLCC shifts from a capacitive to an inductive state.