<title>Loss mechanisms in MEMS oscillators</title>

Abstract

Micro electro-mechanical systems (MEMS) devices are being developed for a broad range of applications. In most cases, the sensitivity of the final device is a function of the intrinsic dissipation of mechanical energy, or Q-1. We use laser Doppler vibrometery (LDV) and finite element modeling to examine and quantify a variety of different dissipation mechanisms that are important for the room temperature operation of MEMS oscillator devices. In this work we examine dissipation mechanisms that include phonon-phonon scattering, thermoelastic dissipation, acoustic radiation, viscous drag and attachment loss. We examine three different systems experimentally and analytically to demonstrate that different loss mechanisms are dominant in each case at room temperature. Full-field LDV measurements are used to show that resonant reflectors are responding as predicted by finite element modeling and reduce the torque that the oscillator imposes on its foundation. This result shows that the attachment loss can be mitigated with the use of resonant reflectors and by careful design and fabrication. However, this reduction in the attachment loss does not reduce the Q-1 at room temperature for this device. From this we conclude that for these oscillators, attachment loss is not an important dissipation mechanism at room temperature, and the loss is due to some other intrinsic mechanisms mentioned above. We find that at pressure greater than 1O-2 Ton acoustic radiation dominates for our MEMS paddle oscillators, while for a diamond oscillator, 10-3 Ton is the low-pressure for when radiation damping is dominant.