Design and performance of a double hot arm polysilicon thermal actuator

Abstract

This paper presents a new polysilicon actuator design. In a typical thermally-driven actuator, the hot arm is thinner than the cold arm, so the electrical resistance of the hot arm is higher. When electric current passes through the device (both the hot and cold arms), the hot arm is heated to a higher temperature than the cold arm. This temperature increase causes the hot arm to expand in length, thus forcing the tip of the device to rotate about a flexure. The new thermal actuator design eliminates the parasitic electrical resistance of the cold arm through the use of an additional hot arm. The second hot arm results in an improvement in electrical efficiency by providing an active return current pass. Also, the rotating cold arm can have a thinner flexure than the flexure in a traditional device because it does not have to pass an electric current. The thinner flexure results in an improvement in mechanical efficiency. This paper compares single and double hot arm thermallydriven actuator designs, and demonstrates various devices constructed with the new thermal actuator design. Deflection and force measurements of both actuators as a function of applied electrical current are presented. Keywords: MEMS, Polysilicon, Actuator, Motor, Mirror.