Non-resonant 2-D piezoelectric MEMS optical scanner actuated by Nb doped PZT thin film

This paper reports a non-resonant 2-D piezoelectric MEMS scanner actuated by a Nb doped PZT (PNZT) thin film for endoscopic optical coherence tomography (E-OCT) application. The unimorph actuator with the PNZT film shows more than twice as large displacement as that with a non-doped PZT films, and is suitable for large angle non-resonance scan, which was difficult for conventional non-resonant piezoelectric scanners. We designed a gimbal-less scanner with folded L-shape actuators enabling two-axis scan motion of a 1 mm × 1 mm mirror within a compact device size of 2.2 mm × 2.7 mm. The fabricated MEMS scanner with PNZT actuators showed an optical scan angle of 18.6° for both scan axes at a drive voltage of 40 Vpp in non-resonance mode. This scan angle is more than 1.7 times larger than that of the scanner with PZT actuators, and is high enough to achieve a clinically useful scan area of 1 mm × 0.7 mm at 3 mm working distance in a side-imaging probe. The resonance frequency of the scanner was greater than 1.37 kHz, which was sufficiently high for non-sinusoidal actuation up to 50 Hz in OCT imaging. The scanner was driven by 25 Hz triangle waves and 50 Hz sawtooth waves through a low pass filter for linear OCT imaging at 50 lines per second.