Actuation and internal friction of torsional nanomechanical silicon resonators

We report on the actuation and mechanical properties of silicon resonators with nanometer-scale supporting rods operating in the 3-20 MHz range. The s ymmetrically designed paddles can be excited both in their flexural and tor sional modes of motion. Fabrication imperfections as small as 10-20 nm prov ide enough asymmetry to allow such torsional excitation. We also report on internal friction studies in these systems. Thin Al overlayers contribute t o the room temperature internal losses, as quality factor drops From 3300 t o 380 for 160 Angstrom thick film. A temperature dependence of internal Fri ction has a broad peak in the T = 160 - 190 K range, and attributed to the Debye relaxation and thermally activated friction mechanisms. Analysis show s that the peak shifts to higher temperatures with increasing resonator fre quency. (C) 2000 American Vacuum Society. [S0734-211X(00)00206-7].