Vertical thermal actuators for micro-opto-electro-mechanical systems

This paper presents novel micro-opto-electro-mechanical (MOEM) applications employing vertical thermal actuators. The high force and large deflection of backbent vertical thermal actuators are useful in many applications, particularly when a single large deflection is required for device setup. For example, backbending two actuators driven in parallel flips a 250 mu m square mirror to 45 degrees off the substrate. The actuators can then be driven to permit scanning over 45 degrees. In another example, 3 backbent actuators are used to position an electrostatically actuated optical beam steering mirror 10 mu m off the substrate thereby increasing the maximum steering angle by a factor of 5. Critical to applications like these is predictable and repeatable operation of the actuators. The actuators are comprised of a polysilicon cantilever bar mechanically coupled to two expansion arms. If sufficient current is driven through the expansion arms they deform, bowing upward. Upon removal of the drive current the expansion arms shrink, backbending the actuator by pulling the tip of the actuator upward. Test actuators of three different sizes were carefully backbent. After backbending, the deflection of each actuator was measured on an interferometric microscope with +/- 5 nm precision. Although nonlinear, the relationship of backbending deflection to drive power is well behaved, and repeatable.