Title:  Organic Field-effect Transistors on Novel Renewable Substrates

Committee:

Dr. Bernard Kippelen, ECE, Chair , Advisor

Dr. Oliver Brand, ECE

Dr. Saibal Mukhopadhyay, ECE

Dr. Gee-Kung Chang, ECE

Dr. Samuel Graham, ME

Abstract: 

The objective of the proposed research is to develop high-performance organic field-effect transistors (OFETs) on novel renewable substrates that are environmental friendly. To achieve this goal, the first task in the preliminary research was to fabricate top-gate OFETs with a spin-coated TIPS-pentacene/PTAA blend as a semiconductor layer and CYTOP/Al2O3 as a bilayer gate dielectric layer on cellulose nanocrystal (CNC)/glycerol substrates, which can be dissolved in water at room temperature. To avoid damages of CNC/glycerol during the solution porcess, we deposited a barrier layer of ALD-grown Al2O3 on top of CNC/glycerol to compare OFETs on bare CNC/glycerol with the barrier layer on CNC/glycerol. The mobility of OFETs on CNC/glycerol with the barrier layer was at the range of 0.1 to 1 cm2/Vs that was comparable to that of OFETs on plastic substrates, and the stability was much greater than that of OFETs on bare CNC/glycerol. The second task was to use CYTOP/NL as the gate dielectric layer to achieve better environmental stability. OFETs fabricated on glass substrates with CYTOP/NL gate dielectric also had comparable electrical characteristics and sustained in water at 95 ˚C for several tens of minutes meanwhile OFETs with CYTOP/Al2O3 only last for less than 3 minutes. The third task was to reduce the contact resistance of OFETs by depositing a layer of Mo(tfd)3 on top of the source and drain electrodes to reduce the energy barrier between the organic semiconductor layer and sour/drain electrodes, and the contact resistance significantly decreased to 25% of the original contact resistance. The fourth and the last task was to fabricate OFETs on paper with a buffer layer, a modified gate dielectric layer, and reduced contact resistance that we learned from previous tasks. These OFETs can have comparable performance as they were fabricated on glass substrates. Operational and bending tests were done on these OFETs, and no obvious degradation was observed after these tests. By demonstrating comparable device performance and operational stability, this work displays the potential of flexible electronics on environmental friendly substrates.