Creating Single-Crystalline β-CaSiO₃ for High-Performance Dielectric Packaging Substrate

β-CaSiO₃ based glass-ceramics are among the most reliable materials for electronic packaging. However, developing a CaSiO₃ glass-ceramic substrate with both high strength (>230 MPa) and low dielectric constant (<5) remains challenging due to its polycrystalline nature. The present work has succeeded in synthesizing single-crystalline β-CaSiO₃ for a high-performance glass-ceramic substrate. This is accomplished by introducing Al³⁺ into the CaO-B₂O₃-SiO₂ glass system, and by optimizing the sintering condition. Al³⁺ doping facilitates a heterogeneous network structure that energetically favors the precipitation of polycrystalline particles, including nanosized β-CaSiO₃ crystals and sub-nanosized α-CaSiO₃ crystals. As the sintering temperature increases, the nano α-CaSiO₃ crystals (2-10 nm) are gradually absorbed by the β-CaSiO₃ crystals. Through atomic rearrangement, α-CaSiO₃ crystals transform into micrometer-sized single crystal β-CaSiO₃ (1-2 µm) with layered structure. The low temperature co-fired β-CaSiO₃ glass-ceramics exhibit exceptional properties, including a low dielectric constant of 4.04, a low dielectric loss of 3.15 × 10^-3 at 15 GHz, and a high flexural strength of 256 MPa. This work provides a new strategy for fabricating high-performance single-crystalline glass-ceramics for electronic packaging and other applications.