Although a lot of micromechanical mirror devices are already available, there is still a lack of devices for measurement applications with large reflective plains and static deflection in the range of <-10° to >10° in analog mode. In our approach, aluminum nitride (AlN) deposited by reactive sputtering is used as torsional spring material. In contrast to crystalline and amorphous materials such as silicon or silica, the nanocrystallinity of AlN inhibits the propagation of cracks. Material tests show high mechanical strength and linear elastic behavior. Fatigue of the hinges couldn’t be observed so far. Those material attributes enable the fabrication of thin and compliant springs. Aside from the geometric parameters, spring stiffness can be tuned by the mechanical film stress during deposition. To reach highly dynamic mirror deflection, electrostatic actuation is used. Measurement results show an analog mechanical deflection range of ±11.7°. Using the pull-in, a digital rotation angle of about ±21° is achieved. These results match well with simulations. The mirror plain is stiffened by a bulk silicon layer. The samples have a mirror plate of 1.2 x 1.0 mm²suspended by 20 or 30 μm wide, 350 μm long and 0.4 μm thin stacked AlN (300 nm) /Al (100 nm) torsional springs.

Date Published: 13 March 2013
PDF: 9 pages
Proc. SPIE 8616, MOEMS and Miniaturized Systems XII, 86160E (13 March 2013); doi: 10.1117/12.2002288

Published in SPIE Proceedings Vol. 8616:
MOEMS and Miniaturized Systems XII
Wibool Piyawattanametha; Yong-Hwa Park, Editor(s)