Influence of target design on the damage threshold for optically powered MEMS thermal actuators

• Published in: Sensors and actuators. A. Physical. 2007-03, Vol.134 (2), p.538-543
• Main Authors: Phinney, Leslie M., Serrano, Justin R.
• Format: Article
• Language: English
• Subjects: Laser heating; Optical actuation; Polycrystalline silicon; Surface micromachined MEMS
• ISSN: 0924-4247; 1873-3069
• DOI: 10.1016/j.sna.2006.06.021

Bent-beam, polycrystalline silicon MEMS thermal actuators were optically powered using laser illumination. The actuators were designed with a target suspended between angled legs that expand creating displacement and force when the target is heated by a laser. The laser power threshold for immediate damage and extent of the damage exhibited a strong dependence on the target design. The optically powered thermal actuators were fabricated using a five-layer surface micromachining process from combinations of 2.25 μm thick polysilicon layers (poly3 and poly4) and a 2.0 μm thick sacrificial layer. The target compositions listed in decreasing order of laser damage threshold are: the poly3–poly4 laminate targets, the poly3–poly4 targets with an intermediate 2.0 μm thick oxide layer, the poly3–poly4 targets with a 2.0 μm thick air gap, and the poly4 only targets. The laser damage thresholds for the poly3–poly4 targets with connecting posts and an air gap increases with increasing post size, which allows for better thermal transport from the irradiated poly4 layer to the underlying poly3 layer. The laser damage thresholds ranged from a maximum of 475 mW for an oval poly3–poly4 laminate actuator target to a minimum of 190 mW for a circular poly4 only actuator target.