Q-factor enhancement for MEMS devices: The role of the getter film

The need to reach the highest possible values of the Q-factor is one of the most important issues of resonant MEMS in order to make high-performance sensors. The Q-factor is strongly influenced by the internal environment of the MEMS packaging, by total pressure, gas composition and eventually by the presence of a getter film that is able to chemically absorb active gasses under vacuum or in inert gas. Getter technical solution for wafer to wafer hermetically bonded MEMS systems is PaGeWafer, a silicon or glass wafer with patterned getter film, few microns thick. MEMS hermetically bonded devices such as gyroscopes, accelerometers, pressure and flow sensors, IR sensors, RF-MEMS and optical mirrors requires getter thin film solutions at wafer level to work properly. In this paper, first the theoretical evaluation of Q-factor of a MEMS resonant structure in presence of a getter film is investigated and compared to the results of a Residual Gas Analysis of the same MEMS res onant structure and with the conventional measurement of Q-factor. Using getter thin film technology, total pressures from 1 mbar down to 10-4 mbar with corresponding extremely high Q-factor have been achieved in MEMS resonant structures. We were therefore able to confirm that getter film can provide high Q-values, stability of sensor signal (phase stability), performances stability during the lifetime, removal of dangerous gases like H2 and H 2O, reduction of mass-loading effect accounting for drift in resonant frequency in hermetically sealed MEMS resonant structures.