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 (Tg) and softening temperature (TS) 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 (x 10-6/ degrees C) and 4.23 to 4.73 (x 10-6/ degrees 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 degrees 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.