Low-temperature sintering ZTA ceramics with CuO–TiO₂–Nb₂O₅ composite oxide sintering aids for LTCC applications

Zirconia-toughened alumina (ZTA) ceramics have attracted much attention as electronic package substrate materials because of their excellent mechanical properties and chemical stability. The high sintering temperatures of ZTA ceramics restrict their multilayer co-firing with copper electrodes for low-temperature co-fired ceramic (LTCC) applications. To achieve a balance between good properties and low sintering temperatures, this work proposes CuO–TiO₂–Nb₂O₅ (CTN) composite oxide sintering aids for ZTA ceramics to obtain a novel glass-free LTCC material. A low-temperature densification mechanism based on multiphase synergy and interfacial reactions is revealed. The results show that the sintering temperature of ZTA ceramics doped with 5 wt% CTN can be significantly reduced to 1050 °C, resulting in high thermal conductivity (18.7 W/(m·K)), high bending strength (405 MPa), and low dielectric loss (9.97×10⁻⁴@11.97 GHz). The co-firing compatibility with a multilayer copper inner electrode is also demonstrated. This work overcomes the traditional trade-off between low-temperature sintering and high performance in glass-free LTCC materials and provides a new strategy for the design and development of multilayer ceramic substrates with copper inner electrodes.