Polymeric helices with submicron dimensions for MEMS devices (Invited Paper)

Polymer helices with submicron dimensions have been fabricated from a variety of isotropic and liquid crystalline polymers with storage moduli ranging from 38MPa to 1.9GPa (measured at 1Hz, room temperature). These helices are made using a double templating process, in which a thin film comprised of independent helical structures deposited using glancing angle deposition (GLAD) acts as the master. In our process the 'positive' structure of the master is copied into a polymer 'negative', which then itself acts as a template for the final film of polymer helices. Liquid crystalline polymers are of particular interest for use in MEMS because highly ordered liquid crystalline polymers can be actuated by exposing them to a stimulus (such as heat) that causes a decrease in order, leading to a reversible, macroscopic change in shape. The phase behavior, optical properties, and mechanical properties of planar aligned monoacrylate liquid crystalline polymers with varying crosslinker content are investigated, in order to determine the composition that will yield the largest deformations upon heating. We find that films with the lowest crosslinker content investigated (2.5%) undergo the largest reduction in birefringence as they are heated, corresponding to a loss in order. However, we also observe that the films with the highest crosslinker content investigated (10%) undergo the largest physical deformation upon heating. SEM images illustrating the deformation of liquid crystalline polymer helices as they are heated are also presented.