Special attention has been paid in this work to use all possible means to measure an intrinsic quality factor (Q) for silicon beam resonators realized on SOI wafers. Specifically, this work points to the energy dissipation into the support; a model is given and a high insulating system for clamped–clamped and clamped-free configurations has been studied, preserving the resonating element from support damping. Finite element analysis on these structures evidences values of Qsupport higher than 107. Out-of-plane and in-plane vibration Q values up to 1.0 × 105 have been measured under a high vacuum using, respectively, laser Doppler vibrometry and stroboscopic optical microscopy combined with image processing. The results have shown good agreement with thermoelastic theory. However, the observed agreement on the resonator dimension dependences is limited to quality factors lower than 3.0 × 104. Beyond these values, a physical limitation is evidenced in both cases (in-plane and out-of-plane) which does not match with the surface and clamping models listed. The role of the SOI wafer's oxide layer is discussed as a possible source of dissipation.

Vacuum encapsulation is required for various microsensors to improve their performances. In the case of wafer level vacuum encapsulation, dedicated techniques must be developed to measure the background pressure in the bonded cavities. In this paper we investigated ex situ measurement techniques based on the measurement by interference microscopy of the deformation and vibrations of the caps as function of an external pressure. Because these techniques detect the equality between external and internal pressure, they do not require any modelling nor prior calibration. Application to wafer level encapsulations fabricated by goldsilicon eutectic wafer bonding demonstrates that a detection limit in the 10 À2 -10 À1 mbar range can be reached for millimetre size caps.

The high specific surface of porous silicon and its high reactivity makes this material a good candidate for chemical sensors based on electrical or electromechanical devices. In this paper, several processes are presented to realize free-standing porous silicon microstructures (membranes and cantilever beams). Good resonance quality factors were measured (Q = 110 and 760 respectively) demonstrating that porous silicon is a suitable material for resonant chemical sensors.