Individual contact resistance in random network carbon nanotube thin-film transistors considering asymmetric properties

Abstract

Owing to their excellent electrical and mechanical properties, carbon nanotube thin-film transistors (CNT-TFTs) have emerged as promising candidates for high-performance TFTs. In particular, the long mean free path and quasi-ballistic transport characteristics of charge carriers in CNT make the contact properties a critical factor in device performance. As a result, significant research has been conducted on extracting the contact resistance in CNT-TFTs. However, previous studies have not sufficiently accounted for the asymmetric characteristics of CNT-TFTs. Since CNT-TFTs fabricated using solution-based processes inherently exhibit asymmetric properties, considering the effective gate bias, which reflects the voltage drop across individual contact resistances, is important when analyzing the device characteristics. In this work, we propose a method for accurately extracting individual contact resistances that accounts for these effects in CNT-TFTs. This approach is independent of the contact resistance method (CRM), applicable to large-area devices, and enables accurate threshold voltage extraction under asymmetric contact conditions. We also compare the resistances extracted using the proposed method with those obtained via a method that does not consider the voltage drop across individual contact resistances to analyze the impact of the voltage drop. Finally, using the extracted individual contact resistances, we eliminate the mobility degradation effects caused by the contact resistances and extract the intrinsic mobility. We expect that the proposed technique will serve as a robust approach for accurate characterization, modeling, and simulation of CNT-TFTs and their associated circuits, as it reliably extracts individual contact resistances across various semiconducting CNT purities.