Wafer level vacuum packaging with Al-Ge bonding for MEMS

Wafer level vacuum packaging (WLVP) is essential for MEMS devices packaging. Devices such as Infra-red (IR) bolometer, resonator, inertial sensors and pressure sensors all requires vacuum environment to perform at the optimal condition. The vacuum environment requirement for these sensors ranges from 300mTorr to 10mTorr. In order to achieve this level of vacuum we have implemented eutectic Al-Ge bonding on a wafer scale packaging. In the preliminary work we have achieved ∼100mTorr vacuum level. This result is repeatable at full wafer level and it is verified with a pirani vacuum indicator. For pirani device, the vacuum level is reflected by the resistance change (R%) when voltage is sweep from 0∼10V. Based on a reference curve previously calibrated, we can accurately determine the vacuum level encapsulated in the micro-environment the MEMS devices are being sealed.