Sub-micron Patterning of ZnO-PMMA Hybrid Films

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Virginia Tech


Sub-micron patterning is fundamental to the fabrication of numerous devices Traditional commercial manufacturing methods either lack the resolution needed to attain the appropriate size or are prohibitively expensive due to low throughput or the necessity of expensive equipment. Imprint lithography is a rapid, inexpensive alternative to making sub-micron features that can be tailored to work with a variety of materials. Imprint lithography, while traditionally used with pure polymers has been tailored to be used with nanoparticle-polymer hybrid films. This work has achieved high-fidelity pattern transfer onto polymer-nanoparticle hybrid films with feature sizes as small as 250 nm.

The polymer-nanoparticle hybrid was fabricated by creating a liquid suspension of functionalized ZnO nanoparticles and poly(methyl methacrylate) (PMMA) in a solvent. The ZnO particles were functionalized by adding nonanoic acid in order to facilitate the dispersion of the particles in a non-polar solvent. This suspension was spread onto substrate, imprinted with a patterned stamp, allowed to dry, and was demolded. The final result was features ranging from 250 nm to 1 μm in size with good fidelity as determined by the accuracy of the feature replication and the surface roughness of the overall sample. The effect of the ZnO content as well as the method of combining the suspension components on the feature fidelity was studied. In general, it was found that feature fidelity is acceptable up to a dry-film composition of 15 vol% ZnO and that feature sizes above 500 nm were more tolerant of higher solids loading.

The same imprint lithography method was also used to pattern a polymer-derived SiOC glass. The SiOC was shown to be have interesting shrinkage properties where the feature-level linear shrinkage was up to 5% more than that of the bulk. The features were shown to be stable during pyrolysis up to 1000°C and stable at operating temperatures up to 1000°C.

A constant number Monte Carlo simulation was used to describe the suspension behavior to confirm the empirical results from the physical experiments. The effects of Van der Waals forces, steric stabilization, depletion flocculation, as well as the physical impediment of entangled polymer chains were considered. A similar agglomeration behavior was shown in the simulations compared to the physical experiments.

This thesis shows that polymer-nanoparticle hybrid films are a compatible material for imprint lithography using appropriate suspension parameters. This is very important for a variety of applications and devices. Using imprint lithography to make these devices makes them cheaper and more accessible to the commercial market and can make a large number of theoretical devices a reality.



Imprint Lithography, Submicron Patterning, ZnO Nanoparticles, Poly(methyl methacrylate), Constant Number Monte Carlo, Polymer-derived SiOC