ABSTRACT
36In this chapter, we have studied the systematic effects of different polymeric dielectric layers on the operational and environmental stability of CuPc based organic field-effect transistors (OFETs). Hydrophilic poly(vinylalcohol) (PVA) and hydrophobic poly-(methylmethacrylate) (PMMA) polymers were used as organic dielectric materials in addition to the anodized alumina layer. PVA, PMMA, and PVA/PMMA single and bilayers are used as dielectric materials. We have studied the performance and stability of the devices under vacuum and ambient air conditions. PVA based devices are highly sensitive to polar ambient gases and degrade very easily. In order to overcome that we have used PMMA layer together with the PVA layer as bilayer combination. The hysteresis and bias-stress stability were studied under both the conditions. The variation of drain current under bias-stress was explained by the modified stretched exponential function by introducing dipole polarization relaxation term. The possible mechanism for the stability of the device was explained by proposing a model for the polarization of hydroxyl groups present in PVA layer under vacuum and humidity conditions. We demonstrated how the systematic exploration of the engineered dielectrics could provide a meaningful step toward optimizing the organic semiconductor/dielectric interface, thereby implementing highly ambient stable and high-performance OFETs.
