Nanoimprint-induced orientation of localized wrinkles with SU-8

With thermal processing of multilayer systems' prevention of wrinkling is challenging, but when wrinkling results in well-controlled patterns, this self-forming process is interesting for a lot of applications, in particular, when mechanically stable and transparent materials are involved. The authors use the widely used negative tone photoresist SU-8; the hard top layer is realized by vacuum ultraviolet-treatment. Applicability of the established wrinkling theories to this SU-8 system is verified. The control of wrinkling is provided by masked lithography and nanoimprint. In combination, these two techniques allow controlling the wrinkling area and, moreover, are capable of inducing anisotropy to the wrinkling pattern. An analytical calculation of the anisotropy is presented and compared to experimental results. The calculation is based on the bending stiffness of two orthogonal directions. Two types of imprinted line-structures are investigated, normal and inverted V-grooves. Wrinkling amplitudes and anisotropies found are in good accordance with theoretical results.