Impact of the Contact Thickness on the Contact Resistance of Coplanar Bottom‐Contact Organic Thin‐Film Transistors

The contact resistance of organic thin‐film transistors (TFTs) fabricated in the inverted coplanar (bottom‐gate, bottom‐contact) device architecture has been predicted to depend on the thickness of the source and drain contacts. To investigate this dependence experimentally, organic TFTs with a contact thickness ranging from 6 to 50 nm are fabricated and their contact resistance is measured using the transmission line method (TLM). Gold is used as the contact metal, and the contacts are functionalized with a chemisorbed monolayer of pentafluorobenzenethiol (PFBT). As the semiconductor, the vacuum‐deposited small‐molecule material 2,9‐diphenyl‐dinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene (DPh‐DNTT) is employed. A trend toward smaller contact resistances is observed when the contact thickness is increased from 6 to 25 nm, and the contact resistance appears to saturate at a value of ≈100 Ωcm once the contact thickness exceeds a value of ≈30 nm. For the most part, this is consistent with results from simulations presented in the literature.