Separation of bias stress degradation between insulator and semiconductor carrier trapping in organic thin-film transistors

Organic thin-film transistors (OTFTs) are studied intensively for realizing practical applications of flexible or large-area circuits, but rapid degradation of OTFTs due to stress voltage or reaction with water vapor or oxygen in the air limits their lifetime. In order to analyze the cause of rapid bias-stress degradation, we propose a method that separates the cause of threshold voltage (V_th) shift into insulator carrier trapping (ICT) and semiconductor carrier trapping components. The experimental results show that the ICT components account for nearly 50% of the total V_th shift in n-type OTFTs, while the ICT-induced V_th shifts is about 20% of the total V_th shift in p-type OTFTs regardless of the insulator materials: SAM or parylene. The experimental results suggest that the short lifetime of the n-type OTFTs with SAM-based insulator is caused by the instability of the SAM-based insulator due to ICT. In addition, the instability of the p-type OTFTs with SAM-based insulator is discussed based on measurement, and as a result, capacitance shift due to ICT may also affect the degradation of highly biased p-type OTFTs. (author)