Microwave dielectric properties of Ca _0.7Nd _0.2TiO ₃ ceramic-filled CaO–B ₂O ₃–SiO ₂ glass for LTCC applications

Abstract

The effects of the Ca _0.7Nd _0.2TiO ₃ ceramic addition on the crystallization, densification, and dielectric properties of CaO–B ₂O ₃–SiO ₂–(Al ₂O ₃) glass (C1: CaO–B ₂O ₃–SiO ₂ glass and C1A03: CaO–B ₂O ₃–SiO ₂–Al ₂O ₃ glass) for low-temperature co-fired ceramic (LTCC) applications are investigated. The cristobalite phase crystallized from C1 glass was inhibited by adding Al ₂O ₃. During sintering, Ca _0.7Nd _0.2TiO ₃ ceramic reacted with CaO–B ₂O ₃–SiO ₂–(Al ₂O ₃) glass to form the sphene (CaTiSiO ₅) phase. The amount of sphene phase increases with increasing sintering temperature. By adding 50–60 wt% C1 or C1A03 glass, Ca _0.7Nd _0.2TiO ₃ can be densified at 850–900 °C. The relative dielectric constants for Ca _0.7Nd _0.2TiO ₃ added with C1 and C1A03 glasses were all 20–23. Ca _0.7Nd _0.2TiO ₃ added with C1 glass exhibited a lower dielectric constant than C1A03 glass due to cristobalite phase formation. For Ca _0.7Nd _0.2TiO ₃ ceramics added with 50 wt% glass, the variation in Q × f value presented the same trend as the sphene formation amount variation. The best Q × f value of 2380 GHz was achieved for Ca _0.7Nd _0.2TiO ₃ ceramics added with 50 wt% C1A03 glass sintered at 900 °C due to the dense structure and greater amount of sphene. Ca _0.7Nd _0.2TiO ₃ ceramics added with 50 wt% C1A03 glass sintered at 900 °C exhibited a dielectric constant of 22.8 and Q × f value of 2380 GHz, which are suitable for microwave LTCC applications.