Patterning Organic Electronics Based on Nanoimprint Lithography



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The objective of this work is to investigate a high-resolution patterning method based on nanoimprint lithography (NIL) for the fabrication of organic electronics. First, a high-resolution, nondestructive method was developed to pattern organic semiconductors. In this approach, a sacrificial template made of amorphous fluorinated polymer (Teflon-AF) was first patterned by NIL. Poly(3-hexylthiophene) (P3HT), a organic semiconductor, was then spin-coated on the Teflon-AF template. Removing the sacrificial template by a fluorinated solvent achieved high-resolution P3HT patterns. P3HT lines and squares of various sizes (0.35 micron to tens of microns) were obtained by this method. This process of removing the sacrificial template is fully compatible with organic semiconductors. This technique was then used to fabricate passive-matrix organic light-emitting diode (PMOLED) arrays for flat-panel display applications.

Fabrication of a self-aligned bottom gate electrode for organic metal semiconductor field effect transistor (OMESFET) was also developed. This self-aligned gate allows the transistor to have a potential to operate in the high frequency. Owing to the lack of an insulating layer, OMESFET can also work in a relatively low voltage range compared to other organic field effect transistors with an insulating layer. This work also demonstrates its capability of patterning alternating self-aligned metals at the nanoscale.

This research also developed a low-cost and time-saving technique to create nanostructures by transferring nanoscale polymeric sidewalls into a substrate. This polymer sidewall transfer lithographic technique can be used for generating nanostructures without advanced electron-beam lithography. Potential applications include the fabrication of nanoimprint molds with high-resolution patterns for applications in nanofluidics and nanophotonics. The polymeric sidewall is a vertically spreading layer deposited by spin-coating a polymer solution on a vertical template. Varying processing parameters such as the solution concentration or the spin-coating speed, changes the sidewall dimension, which, after pattern transfer, also changes the structure dimension on the substrate. High-resolution trenches of about 15 nm have been achieved after transferring straight-line sidewalls into the substrate. Other than straight-line sidewall patterns, this method also fabricated ring-shaped patterns including circles, squares, and concentric squares.

Finally, a new structure of organic solar cells (OSCs) was investigated for increasing the solar power conversion efficiency. Although the experimental result did not meet the theoretical expectation, reasonable modifications of the device structure will be tested to achieve the goal in the future.