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 degrees C, and 4.3 MPa. In addition, the deposition temperature affected the bonding strength. Particularly, the film deposited at 200 degrees 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.