A bi-axial vacuum-packaged piezoelectric MEMS mirror for smart headlights

This paper presents a 2D MEMS mirror for smart headlights, combing high-Q vacuum package with AR (Anti Reflecting)-coating, piezoelectric driving and Lissajous scanning. While the vacuum package protects the MEMS device and the AR-coating suppresses parasite reflections from the glass lid, the AlN-based piezoelectric actuators are robust against shock and vibration in harsh environment, comparing to fragile capacitive finger structures. This gimbal-less MEMS mirror with a large circular aperture (diameter = 5.5 mm) utilizes Lissajous scanning possessing two perpendicular torsion modes with frequencies of fx = 2.26 kHz, fy = 2.30 kHz fulfilling high light density and large total optical scanning angles of 55°, 30° at ± 40 VAC. A 2D projection of 50° x 20° was realized, where the angle loss comparing to the 1D testing arose from pincushion distortion, whose effect was severely reduced by the redesign run. Due to the great long-term stability of AlN and protection of vacuum packages, the MEMS mirror also shows a good reliability. This paper will describe and discuss the design, fabrication and characterization results of this MEMS mirror.