Patterned shape memory alloy films

Abstract

The uniaxial stress field in shape memory alloy (SMA) films patterned into thin strips increases the transformation induced deflection of SMA/Si cantilever bimorphs in comparison to cantilevers with planar films. In the single phase temperature ranges T > Af, Ms and T < As, Mf (Af-austenite finish, As-austenite start, Mf-martensite finish and Ms-martensite start temperatures), where the deflection is controlled by the thermoelastic stress, the change reflects the difference between the uniaxial and biaxial stress states. In the temperature regimes As < T < Af, Mf < T < Ms, the martensitic microstructures created by uni- vs. biaxial stress fields are responsible for the difference of the cantilever deflection.