Investigation of ZnO-B2O3-SiO2 glass and its application for joining AlN ceramic

In this paper, we designed two series of the ZnO-B₂O₃-SiO₂ (ZBS) glass to explore their applicability for joining AlN ceramic. The density, flexural strength, structure, characteristic temperature, coefficient of thermal expansion (CTE) and crystallization behavior of the ZBS glass with varying ZnO and B₂O₃ content were systematically studied. The results show that as B₂O₃ content increase, the glass network is disrupted with the transition from three-dimensional shelf-like structure [BO₄] to two-dimensional layers [BO₃], increasing the number of the broken bonds, while an increase in ZnO results in a more compact glass network structure. We also found that both glass transition temperature (T_g) and softening temperature (T_S) exhibit a declining trend with the increase in B₂O₃ and ZnO. Zn₂SiO₄ and ZnAl₂O₄, began to precipitate after heat treatments in all the samples except 60ZnO-30B₂O₃–10SiO₂ (abbreviated as B30), where the diffraction peaks do not appear in Zn₂SiO₄ but in Zn₄B₆O₁₃. Notably, Zn₂SiO₄ is the main phase for most samples while the main phase of B30 sample is ZnAl₂O₄. The CTE increases from 4.6 to 5.03 (× 10^–6/ °C) and 4.23 to 4.73 (× 10^–6/ °C) with an increase of B₂O₃ and ZnO content, respectively. Among these, the CTE of B30 sample is compatible with that of AlN ceramic substrate. The optimal shear strength, 60.32±10.26 MPa, was achieved with B30 samples at 750 °C. The high strength was attributed to the interfacial reaction that leads to strong chemical bonding and the uniform distribution of the ZnAl₂O₄ in the interlayer, which reinforces the strength of the interlayer itself.