The structure and chemistry of nanoparticles and polymers are interesting for applications in electronics and sensors. However, because they are outside of the standard material set typically used for these applications, widespread use of these materials has not yet been realized. This is due in part to the limited ability of traditional manufacturing processes to adapt to these unique materials. As a result, several alternative manufacturing methods have been developed, including nanoimprint lithography, gravure printing, inkjet printing, and screen printing, among many others. However, these current processes are not able to simultaneously produce patterns with high resolution and high dimensional fidelity, rapidly, over large areas, and in a completely additive manner.
In this work, a novel template-based manufacturing process for patterning nanoparticles and polymers is developed. This process uses vapor permeable polymers as templates for patterning nanoparticle or polymer inks, consisting of the solutes dissolved in a carrier solvent. Briefly, a template is filled with clean solvent and an evaporation-driven flow is used to fill the templates with ink. Continued evaporation is used to completely remove the solvent from the ink, leaving only solidified solute and therefore preventing reflow of material once the template is removed. This allows thepatterned features to retain the same resolution and dimensional fidelity ofthe original template. The process is also completely additive, eliminating the need for an etching step to remove any residual layer, and can be used to pattern over large areas. Finally, the process is such that many different types of materials can be patterned within the same template in a single processing step, enabling rapid and low cost creation of complex devices with a limited number of processing steps.
Mathematical modeling and experimental analysis are used to confirm the principles of operation and demonstrate the viability of the manufacturing process. Various nanoparticles including gold, silver, zinc oxide, and iron oxide, and polymers including cellulose acetate, chitosan, poly(methylmethacrylate), poly(vinylidene fluoride), and acrylonitrile butadiene styrene are patterned on various substrates, including silicon, polyimide, and glass. The proposed mechanism of operation is confirmed by comparing experimentally observed nanoparticle fluid flow in the templates to the developed mathematical model.
The template materials, being the critical components of the manufacturing process, are then examined. Two materials, poly(dimethylsiloxane)(PDMS) and poly(4-methyl-2-pentyne) (PMP), are used for creating templates. It is shown that, while PDMS is a simple prototyping material that is easily used to create microscale features, much higher resolutions and faster patterning is possible using PMP. This is due to the higher vapor permeability and Young’s modulus of the PMP as compared to the PDMS. Using the PMP templates, a patterning resolution of less than 350 nm is achieved.
Further manufacturing viability is demonstrated by converting the stamp-and-repeat process into a continuous, roll-to-roll process. A simple proto-type roller system is created utilizing patterned, vapor permeable PDMS-aramid fiber or PMP-PDMS-aramid fiber composite belts. Using such a system, simple patterns are created having patterning fidelity similar to that obtained with the stamp-and-repeat process.
Finally, two applications of nanoparticles are demonstrated using the proposed manufacturing system. First, low-temperature metallization is performed on a polymer substrate using gold nanoparticles. The particles arepatterned and sintered into conductive traces at a temperature of only 220◦C due to the small size and therefore low melting temperature of the particles. Additionally, an ultraviolet light sensor is created using zinc oxide nanoparticles by aligning patterns of the nanoparticles to previously patterned gold electrodes on a silicon dioxide substrate.
May 31, 2012
Demko, M. T. (2012). High Resolution Additive Patterning of Nanoparticles and Polymers Enabled by Vapor Permeable Polymer Templates. United States: University of California, Berkeley.