Simultaneous Modification of Bottom‐Contact Electrode and Dielectric Surfaces for Organic Thin‐Film Transistors Through Single‐Component Spin‐Cast Monolayers

Abstract An efficient process is developed by spin‐coating a single‐component, self‐assembled monolayer (SAM) to simultaneously modify the bottom‐contact electrode and dielectric surfaces of organic thin‐film transistors (OTFTs). This effi cient interface modifi cation is achieved using n ‐alkyl phosphonic acid based SAMs to prime silver bottom‐contacts and hafnium oxide (HfO 2 ) dielectrics in low‐voltage OTFTs. Surface characterization using near edge X‐ray absorption fi ne structure (NEXAFS) spectroscopy, X‐ray photoelectron spectroscopy (XPS), attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry suggest this process yields structurally well‐defi ned phosphonate SAMs on both metal and oxide surfaces. Rational selection of the alkyl length of the SAM leads to greatly enhanced performance for both n ‐channel (C 60 ) and p‐channel (pentacene) based OTFTs. Specifi cally, SAMs of n ‐octylphos‐phonic acid (OPA) provide both low‐contact resistance at the bottom‐contact electrodes and excellent interfacial properties for compact semiconductor grain growth with high carrier mobilities. OTFTs based on OPA modifi ed silver electrode/HfO 2 dielectric bottom‐contact structures can be operated using < 3V with low contact resistance (down to 700 Ohm‐cm), low subthreshold swing (as low as 75 mV dec −1 ), high on/off current ratios of 107, and charge carrier mobilities as high as 4.6 and 0.8 cm 2 V −1 s −1 , for C60 and pentacene, respectively. These results demonstrate that this is a simple and efficient process for improving the performance of bottom‐contact OTFTs.