A high force low area MEMS thermal actuator

This paper presents a new type of MEMS (micro-electromechanical systems) actuator consisting of an array of inplane micro-fabricated thermal buckle-beam actuators. The technology used in MEMS actuators is typically magnetic, electrostatic or thermal. Magnetic actuators may require special materials in the fabrication process while electrostatic actuators typically require high voltages, large chip areas and produce very low forces. Thermal actuators have seen some use in MEMS applications, the most popular being the pseudo-bimorph that relies on differential expansion of a cold and hot arm to cause it to bend in-plane (parallel to the substrate). These thermal actuators typically generate on the order of a few micro-Newtons each but can be combined for larger forces by linking with small tendons. A disadvantage of this type of actuator is that it moves in an are where most desired movements are linear. Also, when combined in an array, the linking tendons consume much of the energy in bending them. Also, arrays of these can still occupy a fairly large chip area. The electro-thermal actuator described here resembles a chevron where an array of buckle-beams are packed close together and link two common anchored arms with a movable third arm. Arrays can be made within a single released micromachined layer and generate many mN of force. Additional actuators can be arrayed with no coupling penalty and occupy much less area that an equivalent pseudo-bimorph actuator. Preliminary tests indicate that a 450 x 120 mu m array consumes 240 mW of power, deflection up to 14 mu m and can produce many milli-Newtons. A chip of actuator geometry variations and different applications has been fabricated and tested.