AlN Piezoelectric Micromirror Enables 4-DOF Motion, IEEE Xplore Says
An aluminum nitride-based piezoelectric micromirror achieves four-degree-of-freedom motion, combining tip, tilt, piston displacements, and mirror curvature tuning within a single compact device, IEEE Xplore reported. All of these motions are generated by piezoelectric actuation. This design has promising applications in various compact optical systems.
Design Specifications and Performance Metrics
The micromirror features an optical aperture of 1.0 square millimeter on its mirror plate. Under a DC bias voltage of plus or minus 50 volts, the mirror’s radius of curvature adjusts from 10.98 to 12.28 inverse millimeters. Testing identified the first three resonant modes at 1.680 kilohertz for piston motion, 2.611 kilohertz for tip motion, and 2.660 kilohertz for tilt motion. Driven by a voltage of 40 volts peak-to-peak, the device achieves an optical scanning angle of 13.0 degrees for tilt at 2.660 kilohertz and a vertical displacement of 48 micrometers for piston motion at 1.680 kilohertz.
Overcoming Limitations in Compact Optical Systems
Traditional optical setups require separate subsystems for zooming, angular scanning, and phase modulation, which complicates miniaturization efforts. Fortunately, microelectromechanical system technology provides an effective solution for miniaturization, and optical scanners fabricated by this technology have been widely used in many applications. While microelectromechanical system technology offers alternatives, most existing micromirrors remain restricted to two-degrees-of-freedom angular scanning without piston movement or focal length tuning.
Prior developments attempted to close these functional gaps. In 2019, Inagaki et al. demonstrated a self-deformable varifocal micromirror for a focus-tunable single-axis scanner. Later in 2024, Sasaki et al. introduced a piezoelectrically actuated micromirror integrating a two-axis scanning function alongside a varifocal capability, though that device lacked piston displacement functionality. Other researchers, including Morrison et al., combined tip, tilt, piston, and varifocal modes into an electrothermally actuated mirror design, but faced constraints involving smaller mirror plate diameters, negative impacts on reflectivity from release holes, and fabrication complexity.
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