Transfer Printing and Stacking of Patterned Negative Index Materials

In this paper we show the fabrication of stacked Fishnet and Swiss cross samples using Nanoimprint Lithography (NIL) and their optical properties measured by transmission/reflection. Fishnet and Swiss cross samples consist of two patterned gold gratings separated by a MgO or MgF2 layer to provide resonances for the electric and magnetic field such that negative refraction occured. Few approaches have been done to achieve 3D negative index materials (NIM), which will be an important step towards the application in practical devices like perfect lenses and cloaking devices. The usual reported fabrication techniques are often restricted to small area and/or consist of different and often complicated process steps. The stacking method we will present using NIL is a very fast technique to achieve 3D materials. First single layers of Negative Index Material (NIM) structures are fabricated on Si substrate using a two layer lift-off system. Afterwards the single layers are peeled off by using a UVcurable hybrid polymer as “glue”. Performing this process several times on top of each other leads to stacked NIM layers. The stacking process can be performed onto quartz, borofloat or also flexible substrates taking only few minutes. This process works for Split Ring Resonators (SRR) as well as for double gold layer structures like Fishnet and Swiss cross patterns. The Fishnet layers have been characterized using transmission and reflection measurements and the investigation using ellipsometry under oblique incident is ongoing. The retrieved μ and e give negative n around 1.8 μm for the fishnet samples and 1.4 μm for the swiss cross samples. The achieved alignment accuracy for NIL fabricated samples is around 50 nm.