During the past decade, soft lithography has developed into a versatile technique for fabricating chemically micro- and nanostructured surfaces. Techniques known collectively as soft lithography make use of polymer stamps, which are much softer than silicon based molds or masks and therefore allow getting in conformal contact with uneven / structured surfaces. Commonly, these techniques are easy to perform, they use low cost materials, and can be usually carried out at normal lab conditions. At the same time many of these techniques are biocompatible and capable to generate feature sizes smaller 100nm. Typically, many soft lithography techniques combine bottom up strategies like self assembly of ink molecules with top down lithography approaches for the fabrication of the polymer stamp. We have been using these techniques for the assembly of junctions for molecular electronics and for local addressing of cell binding ligands.
Patterning of surfaces in the nanometer range is a key issue in both nanoscience and nanotechnology. Nanoimprint Lithography (NIL) has been an emerging technology for future nanofabrication since it was introduced. NIL is considered to be an alternative to Optical Lithography (OL) and Electron Beam Lithography (EBL) by combining the advantages of high resolution, low costs and high throughput. In UV NIL (Scheme), a liquid precursor is applied to the substrate as resist. A structured and UV transparent mold is pressed into the resist layer forcing the fluid to flow into the cavities. In the next step, the monomeric molecules in the precursor cross-link by exposure to UV light to form a cured polymeric film. Afterwards the mold can be released and the wafer can be further processed. At our institute, sub 20 nm and sub 50 nm patterning resolution were achieved by UV NIL based on rigid and soft polymer molds, respectively.
Nanoimprint Lithography is used as versatile technique to apply chemical patterns to surfaces or to locally deposit biomolecules in electronic junctions. One application with biological background is the patterning of cell adhesion protein for cell guiding. Therefore, we developed strategies to place the fragile binding ligands from solution with sub micron resolution.
Furthermore, NIL processes are increasingly included as an affordable technique for the fabrication of nanosized electronic devices, see Scalable Molecular Junctions.
Microcontact printing (µCP) has become the most commonly used soft lithography method since it is easy to perform and can be used for many applications, as for instance biotechnology, molecular and plastic electronics, and sensorics.
Microcontact printing uses a structured polymer stamp to transfer locally inks from a stamp to the surface of a target substrate. µCP facilitates printing of a broad variety of inks as for instance proteins, organic molecules, and even solids. We aim to reduce feature sizes of transferred patterns substantially below 100nm. Local addressing of adhesion ligands with ultimate resolution supports realization of device bound neuron networks.