The Development Of Multilayer Ceramic Capacitors For Pulse Power Application

In the application fields of high pulse power, such as oil prospecting, ignition system, electromagnetic emissions and so on, ceramic dielectric material has considerable prospects because of its high pulse power, short charging time, high charge and discharge efficiency and long cycle life. But compared to lithium ion batteries and super capacitors, the energy storage density of multilayer ceramic capacitor（MLCC） is quite low, starting from the energy storage density formula of linear dielectric material, by maintaining a high dielectric constant, improvement of the dielectric breakdown voltage is the main way to increase the energy storage density. This article chooses rutile TiO₂ which has the highest dielectric constant in the one class of ceramics as raw materials. The dielectric properties of TiO₂-based dielectrics have been studied from two aspects including material modification and device fabrication for pulse discharge applications.Oxygen vacancies existing in rutile TiO₂ will degenerate dielectric properties, due to the unchanged oxygen partial pressure, the concentration of oxygen defects didn’t decrease even sintered in pure oxygen atmosphere. However, bivalent manganese（Mn） doping can reduce the loss of the conductance and the polarization of the TiO₂. The sample of 0.05mol% Mn doped TiO₂ sintered in 1050℃ for 9 hours maintained stability of the dielectric constant and loss less than 0.01 in the frequency range from 100Hz-1MHz. At room temperature, samples of Mn doping TiO₂ had dielectric constant of 125, breakdown electric field of 38.07 kV/mm, calculated energy storage density of 0.81 J/cm3.BaO-B₂O₃-Al₂O₃-SiO2 alkali-free glass were prepared using both solid state sintering and sol-gel method. Multiple process of ball-milling and pre-sintering can improve the uniformity of the glass coated ceramic particles prepared by solid state sintering. Mn doped TiO₂ coated alkali-free glass prepared by sol-gel method could further improve the breakdown voltage, the composite dielectrics remained stable dielectric constant and loss less than 0.005 in the frequency range from 100Hz-1MHz. In the temperature range 298 k to 473 k, the capacitance drift less than 10%, the sample with 15wt% glass content can achieve the energy storage density of 1.43 J/cm3, which was 1.76 times than sample’s of Mn doped TiO₂（0.81 J/cm3）, and from the polarization curves, energy conversion efficiency of Mn doping TiO₂ with alkali-free glass addition was close to 0.95.TiO₂-based MLCC were prepared by LTCC（Low Temperature Co-Fired Ceramic） technique. Through the insulation resistance test, almost all of the #1 MLCC（ 25 μm thickness） didn’t have capacitance characteristics, and the resistance of #2 MLCC（ 50 μm thickness） could reach the MΩ level. The resistivity of #2 MLCC was lower than the rutile TiO₂ sample’s under the same sintering conditions. Combined with the SEM figures of cross section of MLCC, the failure might be caused by two main reasons: firstly, the poor quality of cast films leaded to permeation of internal electrode paste into dielectric layers to decrease effective thickness; secondly, the palladium/silver ions diffused into the lattice of TiO₂ by sintering driving force, the presence of the metal ions increased the electrical conductivity of the dielectric layers.