Planar CMOS-Compatible Fusion-Bonded Silica Vacuum Packages

We present a vacuum packaging process based on standard fused silica wafer bonding combined with laser-assisted simultaneous localized fusion bonding and dicing technology. Direct bonding of fused silica wafer stacks results in an optically transparent package without introducing intermediate bonding layers. The temperature inside the package is maintained lower than 400 °C during the fabrication process to preserve CMOS compatibility. To characterize the vacuum level inside the package, white light interferometery is introduced to observe the surface topography of the package. Simulation and experimental results indicate that the vacuum level inside the package is at or below 1 Torr. Such fused silica vacuum and hermetic packages have many favorable features such as vacuum for encapsulating resonating devices, optical transparency for packaging MOEMS, biocompatibility and hermeticity for implantation applications, and transparency at radio frequencies for encapsulating electronics for wireless power and signal transmission.