A novel fabrication and wafer level hermetic sealing method for SOI-MEMS devices using SOI cap wafers

This paper presents a novel and inherently simple all-silicon fabrication and hermetic packaging method developed for SOI-MEMS devices, enabling lead transfer using vertical feedthroughs formed on an SOI cap wafer. The processes of the SOI cap wafer and the SOI-MEMS wafer require a total of five inherently-simple mask steps, providing a combined process and packaging yield as high as 95%. The hermetic encapsulation is achieved by Au-Si eutectic bonding at 400°C. The package pressure is measured as 1 Torr without any getter activation, and the package is proved to remain hermetic even after various temperature cycling tests. The shear strength of the fabricated chips is measured to be above 15 MPa, indicating a mechanically strong bonding.