(Invited) Wafer-Bonding for MEMS – Status and Trends

Abstract

The current sensor portfolio at Bosch is covering a large variety of different MEMS-based sensor products for automotive and consumer applications. Most of them use wafer-bonding as capping-technology on wafer-level. The basic features that wafer bonding technologies for MEMS must fulfil for a successful wafer-level packaging process are hermeticity, high bond strength and high temperature stability. Glass-frit and anodic bonding are well and long-term established standard technologies used for hermetic packaging of MEMS on wafer-level. But both technologies require comparatively large chip sizes that are not compatible with the requirements for miniaturization and cost reduction of new consumer sensors. Therefore metallic bonding processes like eutectic bonding with aluminium-germanium were used for current sensor generations. One step further is the realization of hermetic encapsulation and electrical interconnection, if an ASIC wafer serves as a functionalized cap. Cu-Cu thermo-compression and Cu/Sn SLID bonding are promising techniques that are of high interest for MEMS products of the future.