Micromachined resonators of high Q-factor based on atomic layer deposited alumina

In this paper, atomic layer deposited (ALD) alumina (Al2O3) has been demonstrated as the structural material for a micro-resonator for the first time. An electrostatically actuated micro-bridge made of chromium (Cr) coated ALD Al2O3 was used as a resonator. The resonator was formed by simple wet- and dry-etching processes. The static displacement profile of the micro-resonator under electrostatic load was measured by an optical interferometer. A model of a pinned–pinned beam with axial stress of 250 MPa was used to fit the measured data. Two techniques based on scanning electron microscope (SEM) and atomic force microscope (AFM) were developed to characterize the resonant frequencies of different modes and quality factor of the resonator. The measured resonant frequencies match well with the calculated values with residual stress of 258 MPa, providing additional insight into resonator model and ALD alumina material properties. The developed techniques can be applied to further size reduction of devices made with ALD methods.