Engineering Environmentally Friendly Dielectrics for use in Capacitors and Thin Film Transistors
Creators: name: Tousignant, Mathieu
Publisher: name: Université d'Ottawa / University of Ottawa
Year: 2023
Subjects: Green dielectric
Organic electronics
Sustainable electronics
Polymer dielectrics
Bilayer dielectrics

description: Electronic devices are used for tasks such as keeping people connected, figuring out the contents of a package or detecting impurities in the air. The use of electronic sensors in short life cycle products has also begun to increase with the field of smart packaging. For example, RFID tags are used everyday in sorting facilities to identify packages and then discarded when the packaging is thrown away. Every year the world generates millions of tons of E-waste and most of it is exported, incinerated, or put in landfills. To mitigate the impact of electronics on the environment, it is essential that the next generation of disposable electronic devices are fabricated using environmentally friendly materials. For these materials to be considered for high throughput fabrication they need to be solution processable and biodegradable, all while having the necessary mechanical and electrical properties. This thesis focuses on the development of novel environmentally friendly dielectrics that can be used in capacitors and thin film transistors. A common environmentally friendly and biodegradable material used as a polymer dielectric is poly(vinyl alcohol) (PVA). Although PVA has a high capacitance it also has its drawbacks. Being mostly processed from aqueous solutions it is hard to form uniform thin films of PVA and it is sensitive to moisture which changes its capacitance. PVA is also a polar material which can cause charge trapping at the semiconductor/dielectric interface when used as a dielectric in the fabrication of organic thin film transistors (OTFTs). In this thesis we use different strategies such as blending dielectrics and stacking them to help improve the performance of PVA as a dielectric in OTFTs. In the first study, I demonstrate how low weight percentages of cellulose nanocrystals can be used to increase the viscosity of PVA without negatively impacting its dielectric properties. This led to better film uniformity and a larger number of functioning OTFTs. The second study focused on using a toluene diisocyanate terminated polycaprolactone (TPCL) polymer as a low-k barrier between PVA and the semiconductor. The TPCL led to an increase in OTFT performance and a large reduction in moisture sensitivity. For the third study, I improved the shelf life of the TPCL materials by replacing the toluene diisocyanate end units with UV crosslinking end units. The UV end units were protected unlike the TPCL end units allowing the polymer to remain stable under ambient conditions. The UV-PCL demonstrates similar resistance to moisture and dielectric properties to TPCL while being more stable and easier to use in traditional printing processes. My last study, investigates the use of a poly(lactic acid) (PLA) layer as a third layer in the TPCL/PVA/PLA dielectric system. The PLA layer acted as an intermediate between the substrate and PVA increasing the adhesion of PVA. Further the PLA layer improved OTFT performance and allowed for n-type single walled carbon nanotube transistors under ambient conditions. Finally, this work has demonstrated ways to improve the performance of PVA so that it can be used as an environmentally friendly dielectric in thin film, flexible and printed electronic applications.