A loss mechanism study of a very high Q silicon micromechanical oscillator -: art. no. 023524

The room-temperature quality factors of silicon micromechanical oscillators have been investigated by scanning laser vibrometry. One of the flexural modes has very little attachment loss to its environment, which enables us to study internal loss mechanisms. After several consecutive annealing steps up to 800 degreesC, the quality factor Q has increased from 8x10(4) to 6.0x10(5). However, the Q decays to 1.4x10(5) over six months in air. We conclude that near-surface lattice defects caused by reactive-ion etching and surface adsorbates are the main source of internal loss while surface adsorbates are responsible for the time dependence. We also discuss the thermoelastic limit in terms of Zener's theory and flexural modal components of thin plates with vibratory volume change, and compare it with our results.