Fabrication Of A Ghz Band Surface Acoustic Wave Filter By Uv-Nanoimprint With An Hsq Stamp

A GHz band surface acoustic wave (SAW) filter was fabricated by UV-nanoimprint lithography (UV-NIL). The key techniques to produce a SAW filter include stamp and interdigital transducer (IDT) fabrication. For the stamp, high-aspect-ratio (AR) hydrogen silsesquioxane (HSQ)/ITO/glass stamps were first exposed by low e-beam dose. Adequate post-exposure bake, tetramethylammoniumhydroxide concentration, and etch time were utilized to pattern the HSQ stamps with a perfect vertical sidewall. HSQ/ITO/glass IDT stamps with widths in the range 46-168 nm were fabricated. The stamps were then cured with a novel step-like heating cycle as hard-bake. The modified HSQ stamps have a high hardness of 19 GPa. The HSQ/ITO/glass layered structure shows 80% transmittance at 365 nm UV light. Afterward, the IDT patterns were transferred on UV-curable resist/lithium niobate (LiNbO(3)) by UV-NIL at room temperature and low pressure. After removing the residual layer, Al/Ti films were deposited on UV-curable resist/LiNbO(3). IDTs with widths in the range 62-219 nm and thickness of 20 nm could be obtained by following a lift-off process. The center frequency of 4.3-8.6 GHz and insertion loss of -14.1 to -61.7 dB of the SAW filters were measured by a network analyzer HP 8510C. The reactive ion etching step for residual layer elimination has significant implication for the electrical characterization of a SAW filter. The thorough removal of the residual layer not only ensures a clean interface between IDTs and LiNbO(3) for SAW filters with minimum insertion loss, but also keeps intact IDT patterns for small center frequency shift.