Design, Fabrication and Evaluation of High Speed Microscale Shape Memory Alloy Actuator

Abstract

We designed, fabricated, and evaluated a shape memory alloy-based microscale actuator. To achieve complex shape fabrication and an in situ mechanical characterization, a manipulation and characterization platform equipped with high-resolution nanopositioners (with multiple degrees of freedom) and a micro-force sensor was developed. The challenges inherent in precise and accurate fabrication of samples with complex geometry were overcome so that the platform can be used for mechanical property characterization with an in situ method in the high vacuum chamber of a focused ion beam (FIB) system. Using the developed platform, diamond-shaped frame structures 1–1.5 μm in thickness were manufactured using an FIB milling process with a shape memory alloy (SMA). The behavior of these structures under mechanical deformation and changes in thermal conditions was investigated with respect to use as a driving force for a high-speed microscale actuator. Thermal energy was delivered by an optical method, including ion beam irradiation and laser irradiation. Because this method does not require any wiring, unlike other heating methods such as Joule heating, we could realize the fabricated SMA structure without any structural interruptions that could negatively affect the fast actuation motion. As an application, a microscale actuator is proposed. Due to the scale effect, a microscale linear motion actuator can vibrate at over 500 Hz with laser-induced heating. The reaction force and response speed were investigated according to changes in the laser switching speed and power. Additionally, a gripper having a negative Poissons ratio structure could grab small objects and deliver an objective by triggering the shape memory effect. We expect the proposed actuators to contribute to the development of micro- and nanoscale devices for microscale investigations and medical purposes.