Outgassing characterization of MEMS thin film packaging materials

Abstract

In the field of MEMS packaging technology the pressure limit inside the cavity is a crucial parameter. As the cavity size becomes smaller and smaller the vacuum is mainly affected by the outgassing of the materials used in the fabrication process. A full characterization of this phenomenon for oxides that can be integrated as encapsulation layer is presented in this study. A combination of dynamic outgassing, Residual Gas Analysis (RGA) and thermodynamic simulations is involved to fully investigate the material outgassing behavior. The temperature and the nature of released gases are evaluated indicating the optimal annealing or other cleaning process before the sealing of cavities. Moreover the combination of these oxides with a getter material is analyzed. The affinity between carbon dioxide, nitrogen, hydrogen and the getter material is demonstrated as well as its non-reactivity with hydrocarbons. The pressure inside the cavity can be efficiently decreased by integrating this pumping material. Therefore a selection of materials and new fabrication processes can be considered using those results.

Temperature-Dependent in Situ Studies of Volatile Molecule Trapping in Low-Temperature-Activated Zr Alloy-Based Getters

“…22 Considering a hermetically sealed cavity (i.e., no leakage), material outgassing would be the only source of pressure increase within MEMS cavities. 27 The material is generally sputter deposited on the cap wafer for wafer-level packaging prior to wafer bonding. 22 However, the material remains inactive due to the formation of an oxide layer on the surface upon exposure to ambient conditions.…”

“…Bulk getters were developed for vacuum chambers or cavities that are incompatible with the continuous evaporation of materials and cannot withstand the high annealing temperatures at which flashed getters are sublimated (>1000 °C). ,, Bulk getters are often integrated in vacuum packaged MEMS devices for maintaining proper operating conditions for the lifetime of the device (10+ years). , The vacuum requirement varies depending on the application and ranges between 10 –4 and 225 Torr . Considering a hermetically sealed cavity (i.e., no leakage), material outgassing would be the only source of pressure increase within MEMS cavities . The material is generally sputter deposited on the cap wafer for wafer-level packaging prior to wafer bonding .…”

Development of a Reliable High-Performance WLP for a SAW Device

“…The SAW devices are also sealed with a stiff cap structure using wafer-to-wafer or chip-to-wafer bonding technologies. The cap layer made of glass or polymer film with via interconnects were formed to contact the external circuits and the chip’s pads [ 15 , 16 ]. Partially limiting the interdigital transducer (IDT) regions while leaving the SAW devices’ IOs available is more cost-effective.…”