Indirect bonding of MgO wafers based on intercalation crystallisation of amorphous MgO film

Breakthroughs in high-temperature sensors require the achievement of a high bonding strength using a single wafer material to overcome thermal expansion mismatch. In this context, to improve the bonding strength of MgO (100)/MgO (100) wafers, an indirect bonding method based on inserting an amorphous MgO film at the interface is proposed herein. Notably, this method increased the bonding strength from 7 to 10.7 MPa without the introduction of other materials. Grazing incidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM) results showed that the films crystallised to MgO (100) under the thermocompression bonding parameters of vacuum, 1200 °C, and 4.3 MPa. In addition, the deposition temperature affected the bonding strength. Particularly, the film deposited at 200 °C exhibited the best improvement effect, while those deposited at other temperatures were suboptimal. This method avoids bonding failure caused by a sharp difference in thermal expansion between materials at high temperatures. Consequently, this method provides a key technology to improve the high-temperature resistance of MEMS devices using MgO wafer bonding.