Parametric Investigation on laser annealing of polyimide on improving the characteristics of NiTi SMA-based bimorph towards the development of microactuators

Abstract

Laser annealing of polyimide enhances the characteristics such as actuation and substrate-to-film adhesion of the NiTi shape memory alloy (SMA) bimorph. This work investigated the laser annealing of Kapton polyimide with 355 nm Nd: YAG laser for varying fluence and % line overlap (% LO). The laser annealing has enhanced the crystallinity of the polyimide surface below the laser fluence of 1630 mJ/cm2. Furthermore, annealing at 500 mJ/cm2 fluence at 90% LO and 1630 mJ/cm2 at 50% LO and 70% LO yielded low contact angles of 58.1° ± 3.6°, 42.7° ± 1.5°, and 57.5° ± 2.1°, respectively. The deposited film adhesion has significantly improved for annealing at 1630 mJ/cm2 at 70% LO. The bimorph fabricated on the mentioned substrates has produced higher tip displacement than the pristine substrate in the electrical actuation study. The maximum increment in tip displacement of the NiTi SMA bimorph was 1.5 mm in samples with annealed substrate compared to the as-fabricated bimorph. Moreover, the laser-annealed bimorph has shown the capability of enhanced tip displacement even with a loading of 45 mg. © 2023 Elsevier B.V.