Patterning Organic Electronics Based on Nanoimprint Lithography

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

Optical direct-write nanolithography based on self-assembled resist

Holographic display is being developed for next generation mobile phones. However, manufacturing of miniature gratings for the holographic projectors cost a few thousand dollars today, not making the concept practical for commercial purposes. In this thesis, we discuss the feasibility of self-assembled nanoparticles to manufacture holographic gratings cost-effectively and at the nanoscale. Using our approach, the gratings can be manufactured at the scale of 20nm and the cost per chip is expected to cost a few dollars.^ In this thesis, a hydrophobic SAM was used to modify the surface of silicon. Direct-write UV laser lithography was used for photothermal patterning and obtain a hydrophobic-hydrophilic pattern. Experimental and numerical analysis of the patterning technique was done to investigate a possibility photothermal patterning mechanism. Lastly, the patterned substrate was functionalized with gold nanoparticle SAM to show the feasibility of producing the holographic gratings

Direct-Write Ion Beam Lithography

Patterning with a focused ion beam (FIB) is an extremely versatile fabrication process that can be used to create microscale and nanoscale designs on the surface of practically any solid sample material. Based on the type of ion-sample interaction utilized, FIB-based manufacturing can be both subtractive and additive, even in the same processing step. Indeed, the capability of easily creating three-dimensional patterns and shaping objects by milling and deposition is probably the most recognized feature of ion beam lithography (IBL) and micromachining. However, there exist several other techniques, such as ion implantation- and ion damage-based patterning and surface functionalization types of processes that have emerged as valuable additions to the nanofabrication toolkit and that are less widely known. While fabrication throughput, in general, is arguably low due to the serial nature of the direct-writing process, speed is not necessarily a problem in these IBL applications that work with small ion doses. Here we provide a comprehensive review of ion beam lithography in general and a practical guide to the individual IBL techniques developed to date. Special attention is given to applications in nanofabrication