Characterization of LiF/CuO-Codoped BaTiO 3 for Embedded Capacitors

Sintering additives for BaTiO 3 were studied in order to facilitate the use of BaTiO 3 as a material for embedded decoupling capacitors in high-density multilayered low-temperature cofired ceramic (LTCC) modules for mobile communication systems and three-dimensional (3D) printing modules. Among the studied additives, the CuO/LiF mixture was the most promising sintering additive for cofiring BaTiO 3 with a commercial low-permittivity ( ε r ) LTCC sheet (MLS-22, NEG Co.). The temperature dependence of the dielectric properties of BaTiO 3 was successfully controlled by adjusting the CuO/LiF amount and ratio and the sintering temperature. BaTiO 3 codoped with 10 wt.% LiF/CuO (1:1 ratio) and sintered at 860°C for 30 min showed 95% sintering density. The room-temperature permittivity ( ε r ) of LiF/CuO-codoped BaTiO 3 was 1620 at 1 MHz, and the temperature coefficient of capacitance satisfied the X5R specification. After cofiring this LiF/CuO-codoped BaTiO 3 ceramic with an MLS-22 sheet at 860°C, there was no crack formation at the layer boundary. Also a chemical compatibility test revealed that there were no severe reactions between the LiF/CuO-codoped BaTiO 3 and an Ag electrode.