Study On LTCC Materials With High Dielectric Constant Based On La₂O₃-B₂O₃ Glass-ceramics

Low temperature co-fired ceramics（LTCC）technology is the excellent packaging technology to realize the integration and modularization of the electronic components,which is widely used in the remote sensing,communication systems,and aerospace.The passive components such as resistance,capacitance and inductance can be embedded in the substrate to achieve high density integrated packaging.At present,compared with the LTCC substrate materials with low dielectric constant,the LTCC materials with high dielectric constant for embedded capacitance are still scarce.It is difficult to achieve the low sintering temperature and high dielectric properties at the same time.The main objective of this study is to reduce the sintering temperature of 0.5(Ca_0.7Nd_0.2)Ti O₃-0.5(Li_0.5Nd_0.5)Ti O₃（CNT-LNT）ceramic by involving La₂O₃-B₂O₃ glass-ceramics as the sintering aids without damaging the dielectric properties seriously,which is of great significance to promote the development of LTCC technology.In this paper,the glass formation range,thermophysical properties,phase composition and crystallization characteristics of La₂O₃-B₂O₃ glass-ceramics with different Group IIA oxides（Mg O,Ca O,Ba O）are studied.It is proved that the crystal phases can improve the quality factor（Q?f）of the sample.The addition of Group IIA oxides can not only reduce the glass transition temperature and softening temperature,but also increase the crystallization temperature of glass-ceramics.Moreover,The Group II A oxides with smaller atomic coefficient have higher crystallization temperature and larger sintering temperature range.The addition of Ti O₂ can improve the crystallization characteristics and broaden the sintering temperature range of the LBM glass-ceramics.The LBB4（?T=127℃）、LBC3（?T=138℃）、LBM6（?T=149℃）、LBMT2（?T=201℃）glass-ceramics with better performance and different sintering temperature ranges are selected as the sintering aids to prepare the glass-ceramics/ceramic composites respectively.（1-x）(Ca_0.7Nd_0.2)Ti O₃-x(Li_0.5Nd_0.5)Ti O₃（（1-x）CNT-x LNT）ceramics were prepared by solid sintering method.The phase composition,microstructure and dielectric properties of（1-x）CNT-x LNT ceramics were studied.The results indicate that the crystal structure of（1-x）CNT-x LNT ceramics is orthogonal perovskite.With the value of x increasing,the dielectric constant increases first and then decreases,and the quality factor decreases gradually.The dielectric properties of 0.5CNT-0.5LNT ceramic sintered at1200℃are better（ε_r=127,Q??=2792 GHz,τ_f=91 ppm/℃）.La₂O₃-B₂O₃ glass-ceramics with different sintering temperature ranges are used as the sintering aids to lower the sintering temperature of 0.5CNT-0.5LNT ceramics.The sintering densification process,phase composition and dielectric properties of the glass-ceramics/ceramics are studied.The results show that the LBMT2 glass-ceramics with the largest sintering temperature range have the best sintering properties.Finally,the influence of the content of LBMT2glass-ceramics on the density,phase composition,microstructure and dielectric properties of 0.5CNT-0.5LNT/LBMT2 composites are studied.The results show that LBMT2 glass-ceramics have a good wettability to 0.5CNT-0.5LNT ceramics.The microstructure of the composite has the characteristics of liquid phase sintering.The diffusion of Nd³⁺and La³⁺between glass-ceramics and ceramic is beneficial to promote the densification process and the enhance the bonding strength at the interface.The increase of glass-ceramics content is beneficial to the densification process and reduces the sintering temperature of the material effectively.But excessive residual glass will damage the dielectric properties of composites.The 0.5CNT-0.5LNT ceramic composite with 10 wt%LBMT2 glass-ceramics sintered at 960℃exhibits good dielectric properties ofε_r=80.96,Q??=1900GHz andτ_f=67 ppm/℃.It indicates that 0.5CNT-0.5LNT ceramic/LBMT2 glass-ceramics composites have a good potential application prospect in microwave LTCC materials.