Polyimide nanostructures fabricated by nanoimprint lithography and its applications

Polyimides have attractive thermal, mechanical and electrical properties, and have found applications in fields ranging from spacecraft to microelectronics and optoelectronics. Patterning polyimide at nanoscale would open the window for many new applications. In this work, we developed three approaches to pattern polyimide using nanoimprint lithography (NIL): imprint at its uncured soft state and cure it afterwards; imprint another low Tg polymer, then transfer the pattern into polyimide by RIE; and direct imprint into polyimide at temperature higher than its Tg. Polyimide gratings with 200 mn period and 110 nm line-width were successfully fabricated by all the three approaches. Each approach has its advantages and disadvantages. The first method is relatively simple and fast, but some residual solvent and water may cause outgassing when subjected to temperature well above 200 degrees C for prolonged time. The second approach is more complicated, while the third approach needs very high temperature. Two applications of the nanostructured polyintide are demonstrated: as a flexible mould to structure PMMA by NIL and as a template for chemical sensor based on surface enhanced Raman spectroscopy (SERS). Both applications have taken advantage of polyimide's high temperature stability and excellent mechanical properties, and cannot be realized by other common thermoplastic polymers. We believe that NIL is an efficient technique to pattern polyimide with high throughput and low cost. (c) 2006 Elsevier B.V. All rights reserved.