Browsing by Author "Borchert, James W."

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Open Access
A critical outlook for the pursuit of lower contact resistance in organic transistors
(2021) Borchert, James W.; Weitz, R. Thomas; Ludwigs, Sabine; Klauk, Hagen
To take full advantage of recent and anticipated improvements in the performance of organic semiconductors employed in organic transistors, the high contact resistance arising at the interfaces between the organic semiconductor and the source and drain contacts must be reduced significantly. To date, only a small portion of the accumulated research on organic thin‐film transistors (TFTs) has reported channel‐width‐normalized contact resistances below 100 Ωcm, well above what is regularly demonstrated in transistors based on inorganic semiconductors. A closer look at these cases and the relevant literature strongly suggests that the most significant factor leading to the lowest contact resistances in organic TFTs so far has been the control of the thin‐film morphology of the organic semiconductor. By contrast, approaches aimed at increasing the charge‐carrier density and/or reducing the intrinsic Schottky barrier height have so far played a relatively minor role in achieving the lowest contact resistances. Herein, the possible explanations for these observations are explored, including the prevalence of Fermi‐level pinning and the difficulties in forming optimized interfaces with organic semiconductors. An overview of the research on these topics is provided, and potential device‐engineering solutions are discussed based on recent advancements in the theoretical and experimental work on both organic and inorganic semiconductors.
Open Access
On the minimization of contact resistance in organic thin-film transistors
(2020) Borchert, James W.; Ludwigs, Sabine (Prof. Dr.)
Organic semiconductors have been implemented in a variety of electronic devices ranging from organic light-emitting diodes, organic photovoltaic devices, and organic transistors. In all of these devices, the efficient injection and/or extraction of charges across interfaces with conducting contacts is an essential requirement for device performance. The high contact resistance in organic transistors, which limits their usefulness in high-frequency electronics applications, has been a particularly challenging problem to solve. The contact resistance can depend strongly on various parameters, including the transistor architecture and the mismatch between the contact work function and the transport levels of the organic semiconductor. In this work, it is shown that using a thin gate-dielectric layer (around 5 nm) in a thin-film transistor (TFT) in combination with contacts modified using a chemisorbed monolayer to tune the contact-semiconductor interface properties yields record-low contact resistance in organic transistors (as small as 10 Ωcm). This approach was then extended to small-scale TFTs and circuits leading to additional record results in the dynamic performance, including voltage-normalized transit frequency of 7 MHz/V. Finally, strong evidence is shown that Fermi-level pinning limits the effectiveness of tuning the contact work function with chemisorbed monolayers to improve the contact resistance further.