A tip-tilt-piston micromirror with a double S-shaped unimorph piezoelectric actuator

This paper presents the design, fabrication and characterization of a tip-tilt-piston (TTP) piezoelectric micromirror. A unique double S-shaped unimorph piezoelectric (dSUP) actuator design is employed. The dSUP actuator design can generate large vertical displacement. With four such actuators symmetrically located on the four sides of the mirror plate, both tip and tilt as well as piston motion can be realized. Lead zirconate titanate (PZT) is used due to its high piezoelectric coefficient and it is fabricated with a sol-gel method. The Zr/Ti ratio of the PZT material is 53/47. The dSUP actuators consist of Pt/Ti/PZT/Pt/Ti/SiO₂ multilayers. The thickness of the PZT layer is 0.7 μm. The 1.1 mm × 1.1 mm mirror plate is backed by a 50 μm-thick single-crystal silicon layer to ensure the flatness. Backside deep silicon etching and front-side isotropic silicon undercut are used to release the device. Experiments show that the resonant frequency of the tip-tilt scan modes is 3.5 kHz. 27 μm vertical displacement was observed under 5 V DC driving of one pair of opposite actuator and the scan angle can achieve 9.65° under sine wave resonant driving at 2 V amplitude on one pair of opposite actuator.