Preparation And Dielectric Properties Of Low Dielectric Constant MLCC Materials Magnesium Melilite （Ca₂MgSi₂O₇）

Rapid developments of modern electronic information technology toward high frequency, high stability and low loss have create a high demand for multi-layer ceramic capacitors, or MLCC, which are key components of communication circuit. To fulfill these requirements, the dielectric ceramic materials with low dielectric constant, low dielectric losses, near-zero temperature coefficient and low cost has become one of the hot research topic.Ca2MgSi2O7with a tetragonal structure exhibits good chemical and thermal stability, which was extensively studied in the fields of biomaterial and light-emitting material. However, the dielectric properties and potential application in MLCC has not yet been reported. In this research, the structure and dielectric properties of Ca2MgSi2O7was studied and modified by substitution and the introduction of second phases and sintering aids. The relationship between sintering properties, phase composition, microstructure and dielectric properties were revealed. Ceramic materials of low sintering temperature, low dielectric loss, low temperature coefficient of capacitance (TCC) and chemical compatibility with Ag/Pd electrode were developed, which suggested promising materials for NPO MLCC application.1. Undoped and ZnO-doped Ca2MgSi2O7ceramics were prepared via solid state method. It was found that pure Ca2MgSi2O7phase was hard to get by solid state route, and it was always accompanied by a small amount of S1O2phase. The ceramic sintered at1300℃shows optimum dielectric properties of εr=7.87, tanδ=0.0025, TCC between-34-35ppm/℃. Pure Ca2MgSi2C7ceramics revealed high sintering temperature, low density, large dielectric loss and big TCC values. With the doping of ZnO, Mg-site was substitute by Zn2+, and the sintering temperature was slightly lowered. But the dielectric performance was not obviously enhanced due to the appearance of CaSiO3second phase.2. The thermal stability of Ca2MgSi2O7ceramics was significantly improved by adding negative-TCC CaTiO3. CaTiO3dispersed in the ceramic matrix as second phase. With8.5wt%CaTiO3addition, the best performance of TCC, between-35-lppm/℃, was achieved. But the addition of CaTiO3hindered the sintering performance.3. The sintering temperature of Ca2MgSi2O7-CaTiO3composite ceramic was lowered by adding Bi2O3or Bi2O3-B2C3sintering aids. The sintering behavior, phase component and microstructure was investigated to reveal the mechanisms to lower sintering temperature. With5wt%Bi2O3added, the ceramic sintered at1190℃shows good dielectric properties of εr=12.65, tanδ<10-4, TCC between-34-35ppm/℃. By adding Bi2O3-B2O3, well densified microwave ceramics with uniform grains could be obtained even underl100℃. Typically, optimum dielectric microwave of εr=12.53, tanδ <10-4, TCC between-26.35-29.52ppm/℃was achieved for5wt%Bi2O3-2wt%B2O3adding samples sintered at1100℃for4h. The Ca2MgSi2O7-8.5wt%CaTiO3-5wt%Bi2O3-2wt%B2O3composite ceramic was compatible with70Ag/30Pd electrodes.