Split-Frame Gimbaled Two-Dimensional MEMS Scanner for Miniature Dual-Axis Confocal Microendoscopes Fabricated by Front-Side Processing

In this paper, we introduce a 2-D microelectromechanical systems scanner for 3.2-mm-diameter dual-axis confocal microendoscopes, fabricated exclusively by front-side processing. Compared to conventional bulk micromachining that incorporates back-side etching, the front-side process is simple and thus enables high device yield. By eliminating the back-side etch window, the process yields compact and robust structures that facilitate handling and packaging. An important component of our front- side fabrication is a low-power deep reactive ion etching (DRIE) process that avoids the heating problems associated with standard DRIE. Reducing the RF etch coil power from 2400 to 1500 W leads to elimination of the spring disconnection problem caused by heat-induced aggressive local etching. In our scanner, the outer frame of the gimbal is split and noncontinuous to allow the scanner to be diced along the very edge of the scanning mirror in order to minimize the chip size (1.8 mm × 1.8 mm). The maximum optical deflection angles in static mode are ±5.5° and ±3.8° for the outer and inner axes, respectively. In dynamic operation, the optical deflection angles are ±11.8° at 1.18 kHz for the outer axis and ±8.8° at 2.76 kHz for the inner axis.