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Title: Organic Thin-Film Transistors with Low Voltage Operation and High Operation Stability
Committee:
Dr. Kippelen, Advisor
Dr. Ansari, Chair
Dr. Naeemi
Abstract: The objective of the proposed research is to solve two main technological hurdles for organic thin-film transistors (OTFTs) to be commercialized, which are poor operational stability and high operating voltage. Possible solutions for the two problems have been suggested in this proposal. The first solution is using a thin bottom bilayer gate dielectric which is composed of amorphous fluoropolymer CYTOP and high-k metal oxide (HfO2). The thickness of the bilayer can be reduced down to 17 nm. This gate dielectric provided operating voltage as low as -1 V, and because of the aging mechanism of the bilayer gate dielectric, the fabricated OTFT showed only 0.1 V of threshold voltage shift after applying DC bias stress for 24 hours. The second solution was analyzing the intrinsic contact resistance of OTFTs. A quantitative model for the intrinsic contact resistance was designed using Y-function method and transmission line method. The model was applied to OTFTs which have the bottom bilayer gate dielectrics with a wide range of gate capacitance density (36.6 nF/cm2 to 231.7 nF/cm2). Applying the method and analyzing the intrinsic contact resistance, bilayers with a high gate dielectric capacitance as high as 231.7 nF/cm2 can yield low contact resistance values smaller than 1 kΩcm. This result can indicate higher gate capacitance density can provide lower contact resistance values. For the future works, p-doping using phosphomolybdic acid (PMA) to the channel of OTFTs can be applied in order to reduce the contact resistance further. Also, analysis for the aging mechanism under DC bias stress is needed. This analysis can be done by measuring gate-to-source current of OTFTs with various thickness values of the CYTOP and the high-k dielectrics.
