Fabrication of photonic crystals for applications in the visible range by Nanoimprint Lithography

► Fabrication of photonic crystals for applications in the visible range (minimal structure size 80 nm) using Nanoimprint Lithography. ► Photonic crystals were integrated in waveguides. ► Simultaneous replication of feature sizes ranging from 80 nm to 50 μm with high structure fidelity. ► Photonic Band Gap was measured and favorably compared to simulation. The integration of photonic crystals into optical circuits is a decisive factor for further development of photonic crystal applications. The feasibility of these applications depends on fabrication technologies suitable for mass production. In this work, we used Nanoimprint Lithography (NIL) for the fabrication of photonic crystal structures for applications in the visible range. The photonic crystals were integrated into waveguides in order to characterize the created system. The waveguides have dimensions of up to 50 μm whereas the holes in the photonic crystals have dimensions of 80 nm. Due to parameter optimization photonic crystal structures and the corresponding waveguides could be replicated with high accuracy. For the fabrication of the photonic crystal structures a Si substrate with an oxide and a nitride layer was used. A poly-methyl-methacrylate (PMMA) layer was spincoated onto this substrate. A stamp containing the negative structures was fabricated using Electron Beam Lithography (EBL). This stamp was used for imprinting the structures into the PMMA layer. The structures were than transferred into the nitride layer using reactive ion etching (RIE). The underlying oxide layer was used as a sacrificial layer to achieve a nitride membrane. The fabricated structures were characterized by measuring the transmission spectra. The results were compared favorably to a simulation and a photonic band gap (PBG) in the range of 670 nm to 780 nm has been observed.