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Deepak
Professor,
 Materials Science and Engineering,
 Indian Institute of Technology-Kanpur ,
 Work Phone: (512) 2597353,
 Email: saboo[at]iitk.ac.in

Manish Shankar’s Thesis

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Thesis  Topic:
Fabrication of Nano-Scale Organic Thin Film Transistor Using Focused Ion Beam
The thesis was aimed at fabrication of organic thin film transistors (OTFTs) with channel length in the order of conjugation length of organic supramolecules. The supramolecules were chosen from the existing literature having suitable redox gradient for a directed wire-like transport. Among these supramolecules, the covalently linked porphyrin-fullerene based systems undergo long-lived charge separation with high quantum yield on photo-excitation, a characteristics useful for photovoltaic applications. The intrinsic properties and self-assembly of these molecules on the electrodes are still need to be explored in deep for use in commercially viable photovoltaic applications. Different orientations of self-assembly of organic molecules on metal electrodes were considered and appropriate device designs for their electrical characterization was proposed. Among various patterning techniques, focused ion beam serve as most attractive option for fabrication of large number of OTFTs in lesser time and efforts.
In this thesis, we were able to successfully fabricate large number of OTFTs in 150-300nm range by using Focused Ion beam milling and standardized the process for the same. Remarkably, we were able to pattern I-shaped patterns with bridge width less than 10 micrometer just by using optical lithography. Widely researched pentacene was used to check the quality of transistors formed. Various tests of morphological and electrical characterization were done to ensure the quality of OTFTs formed. We were also able to explore problems related to FIB milling and propose reasonable solutions for future improvement in the fabrication process.