Manufacturing issues of thin film NiTi microwrapper

Manufacturing issues related to a thin film NiTi shape memory alloy (SMA) m icroactuator (i.e. microwrapper) have been investigated using both wet and dry etching techniques. Results show that wet etching the amorphous film pr oduces a cleaner pattern than the crystallized film. Transformation tempera tures are not affected by the pre-exposure of the NiTi film to air before c rystallization. However, this process produces breakage in the NiTi film at sacrificial layer steps. This is believed to be due to residual stresses d eveloped between the film and substrate during sputtering. The film breakag e is overcome by dry etching the film with an ion-milling technique. Curvat ure in the microwrapper arms is induced using either a bi-layer material (i .e. polyimide and NiTi) or a functionally gradated NiTi film. Results show that when heated the microwrapper arms flatten due to shape memory effect a nd curl up to form a cage-like structure when cooled. (C) 2001 Elsevier Sci ence B.V. All rights reserved.