Shell-type micromechanical resonators operating in radio frequency range were fabricated utilizing mechanical stress that is built into polysilicon thin films. Significant increase of the resonant frequency (in comparison with flat, plate-type resonators of the same size) and the rich variety of vibrating modes demonstrate great potential for "2.5-Dimensional" MEMS structures. A finite curvature of the shell also provides a mechanism for driving resonators by coupling in plane stress with out of plane deflection. By modulating the intensity of a low power laser beam (P~10μWatts) focused on the resonator we introduced a time-variable, in-plane, thermomechanical stress. This stress modulation resulted in experimentally observed, large amplitude, out-of-plane, vibrations for a dome-type resonator.
A double laser beam experimental setup was constructed where mechanical motion of a shell-type resonator was actuated by a modulated, sharply focused Ar<sup>+ </sup>ion (blue) laser beam and detected by a red HeNe laser using an interferometric setup. A positive feedback loop was implemented by amplifying the red laser signal (related to the oscillator deflection) and applying it to modulate the blue (driving) laser beam. Stable self-sustained vibrations were observed providing that the feedback gain was high enough. Employing a frequency selective amplifier in the feedback loop allowed excitation of different modes of vibrations. Fine frequency tuning was realized by adjusting the CW component of either lasers' intensity or a phase shift in the feedback loop. Frequency stability better than 1 ppm (10<sup>-6</sup>) at 9 MHz was demonstrated for self-sustained vibrations for certain modes of the dome-shaped oscillators.