This paper presents the development of Al-Ge eutectic bonding for wafer level chip scale packaging of MEMS sensors. Al is sputtered on the MEMS wafer while an AUTi/Ge stack is sputtered on the cap wafer. The bonding temperature and bonding time are 43UC and 30min, respectively. A CMOS compatible Ti/Ni stack was deposited as getter on the cap wafer to maintain the vacuum level inside the cavity. A silicon pirani gauge was used as hermeticity indicator to evaluate the vacuum level of the bonding. The operational dynamic range of the pirani gauge is 100mTorr-76Torr. The experimental results over three wafers show that the achieved vacuum level of the bonding is less than 200mTorr with yield more than 90%; 1000 rapid
thermal cycles from -50°C to 150°C with 1 hour for each cycle were conducted, and the related vacuum level were recorded at 150th, 400th, 650th, 800th, 1000th cycle. The normalized vacuum degradation percentage are about 1.6%, 2.05%, 2.25%, 2.54%, 2.78%, 2.82%, respectively. The results also show the vacuum level trends to be stable from the 650th cycle.
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