Thermomechanical behavior of bulk NiTi shape-memory-alloy microactuators based on bimorph actuation

Abstract

Shape-memory-alloy (SMA) has attracted considerable attention in recent years as a smart and efficient material, due to its unique properties. SMA microactuators became one of the potential solutions for unresolved issues in microelectromechanical systems (MEMS). This paper presents a thermomechanical behavior analysis of bimorph SMA structure and studies the effect of varying the SMA layer thickness, the type of stress layer and its thickness, and the processing temperature on the displacement of the microactuator. Furthermore, the analyzed results were verified by experimental work, where the fabrication of the SMA microactuators followed the standards of the MEMS fabrication process. SiO2, Si3N4 and Poly-Si were used as stress layers. The fabrication results showed that the bimorph SMA structure achieved maximum displacement when SiO2 was used. The SMA structure with dimensions of 10 mm (length) × 2 mm (width) × 80 µm (thickness), had maximum displacement of 804 µm when 4.1 µm of SiO2 layer was deposited at a temperature of 400 °C.