New Materials and Methods for Nanoimprint Patterning of Inorganic Materials for Devices

New Materials and Methods for Nanoimprint Patterning of Inorganic Materials for Devices

I. R. Howell, F. Dundar, W. Li, Y. Zhou, and J. J. Watkins

Polymer Science and Engineering Department
Center for Hierarchical Manufacturing

University of Massachusetts

Amherst, MA 01003

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We are developing new materials and approaches for direct imprint patterning of crystalline metal oxides for a variety of applications. Typically a patterned polymer master stamp is used to imprint a resist containing high concentrations of crystalline nanoparticles dispersed in solvent and/or sol-gel precursors to a desired inorganic phase. In the absence of the sol-gel precursor in the inks, patterning relies on solvent removal through the master. In contrast, the use of low concentrations of precursor in inkscontaining high concentrations of nanoparticles enables patterning assisted by UV exposure or heat and provides a broader process window and rapid imprint times. In all cases, high aspect ratio nanostructures (3:1) and sub-100 nm features are easily realized. We examine the relationship between film properties and the relative concentration of crystalline nanoparticle and precursor in the ink. In the absence of precursor, the as imprinted structures exhibit little shrinkage (less than 5% under some conditions) upon thermal annealing and/or calcination. By contrast, use of the sol-gel precursor as the imprint resists in the absence of the nanoparticles can lead feature size reductions of 80% or more. We find inks containing low concentrations of sol-gel precursor provide the optimal results yielding rapid thermal patterning processes, low shrinkage and high film density. Residual layer free direct imprinting (no etching) was achieved in some of the systems by choosing the resist with the appropriate surface energy to ensure dewetting at stamp-substrate interface. The technique was further extended to stack the nanostructures by deploying a layer-by-layer imprint strategy.

Here we will provide several examples of patterned materials and their applications. These include 3-D photonic band gap materials prepared by patterning of crystalline TiO2 grid structures, patterned ITO films for optical applications, high surface area ZnO electrodes for biosensors and robust ZrO2 surfaces for application as anti-fouling and anti-bacterial coatings. The method is scalable and can produce large area device quality nanostructures in a rapid fashion at a low cost.

Figure 1.3-D ZnO composite electrodes for applications in high surface area sensors (left), square hole array patterns in ITO for optical applications (middle) and patterned ZrO2films for applications in anti-fouling and anti-bacterial coatings (right).