Experimental Repeatability of a Thermal Actuator for Nanopositioning

Microactuators are increasingly being applied to nanometer-accurate position control. The purpose of this paper is to investigate the feasibility of using the thermomechanical in-plane microactuator (TIM) in nanopositioning applications. The TIM is a class of thermal actuators in which electric current flows through thin beams which are arranged in a chevron pattern. The beam angle and end constraints amplify the thermal expansion to achieve a larger output displacement. As a fully compliant mechanism, the TIM has potential for superb accuracy because it does not experience friction or backlash. Repeatability tests are conducted with two different TIM configurations. Both are fabricated from polycrystalline silicon by surface micromachining. The first configuration is actuated 33 times with an open loop current of 4 mA. The steady-state displacements are measured from scanning electron micrographs. The average displacement is 222 nm and the standard deviation is 8.4 nm, which results in a 95% precision interval of ±17 nm. The second configuration is cycled 31 times with 10 mA and an average displacement of 697 nm. The standard deviation is 6.8 nm and the 95% precision interval is ±14 nm. The open-loop repeatabilities observed in these tests indicate that the TIM is suitable for nanopositioning, and even better performance is anticipated with the implementation of feedback control.