Investigation of Void-free Chip-to-Chip Bonding Methods for CMOS-MEMS Compatibility

A thin bonding interface that is void-free and composed of materials with low attenuation is needed to achieve GHz bulk acoustic wave signal transmission for analog computing accelerators. The presence of voids in the bonding interface would have significant attenuation of acoustic transmission, which often results in complete reflection of the acoustic signal. Thus, we aimed to develop a bonding process via heterogeneous integration involving MEMS and CMOS components, with a total absence of air bubbles between the bonded surfaces in the ambient air process. This paper presents the use of various methods including preform and thermocompression bonding to facilitate void-free bonding, enabling low attenuation for acoustic transmission through the sample and die-attach layers. From the results, it was found that TCB between Au and AuSn surface resulted in the least loss of signal.