Enhanced 3-D folding of silicon microstructures via thermal shrinkage of a composite organic/inorganic bilayer

Although 3-D out-of-plane structures based on the thermal shrinkage of polyimide-filled V-grooves have already been demonstrated, for large bending angles, this method typically requires several V-grooves and high curing temperatures, which are real-estate consuming and can damage temperature-sensitive components. In this paper, we show that the addition of an inorganic layer (called the boosting layer) beneath the V-grooves can significantly enlarge the bending angle without requiring more V-grooves or higher curing temperatures. For example, a 2-[micro]m-thick Si[O.sub.2] boosting layer can raise the bending angle of a single V-groove joint by a factor of seven. In addition, the boosting layer removes the requirement for a V-groove and permits the use of straight-wall dry-etched grooves, hence allowing a sharper curvature in a smaller area. Index Terms--Bilayer, self-assembly, thermal actuator, 3-D MEMS.