Three-dimensional characterization of OTFT on modified hydrophobic flexible polymeric substrate by low energy Cs+ ion sputtering

• Published in: Applied surface science Vol. 448; pp. 628 - 635
• Main Authors: Tortora, Luca, Urbini, Marco, Fabbri, Andrea, Branchini, Paolo, Mariucci, Luigi, Rapisarda, Matteo, Barra, Mario, Chiarella, Fabio, Cassinese, Antonio, Di Capua, Francesco, Aloisio, Alberto
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-08-2018
• Subjects: Depth profiling; Organic electronics; OTFT; PCA; ToF-SIMS; ToF-SIMS; Depth profiling; OTFT; Organic electronics; PCA
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2018.04.097

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•Non passivated flexible OTFTs were studied through ToF-SIMS.•Two hybrid interfaces were succesfully characterized in a single run.•The hydrophobic treatment was detected and mapped in the multilayer structure.•Multivariate analysis applied to 3D ToF-SIMS datasets revealed chemical treatments.
Here, electron-transporting semiconducting organic channels made of N,N′-1H, 1H-perfluorobutyl dicyanoperylenecarboxydiimmide (PDIF-CN2) molecules were thermally evaporated on flexible polyethylene-naphtalate (PEN) plastic substrates equipped with gold (Au) electrodes. This multilayer structure represents the basic component for the fabrication of staggered top-gate n-type organic thin-film transistors (OTFTs) to be completed with the addition of a polymeric dielectric layer and an aluminum gate electrode. PEN substrate was treated with hexamethyldisilazane (HMDS) in order to make it more hydrophobic. Indeed, the hydrophobized surface of the plastic substrate was shown to induce a more ordered supramolecular structure of the semiconductor layer during the evaporation process. The hybrid organic/inorganic formally trilayer non-passivated OTFT structure was successfully profiled in a single run through ToF-SIMS depth profiling experiments with low energy cesium ions. High mass molecular fragment ions were obtained and used as indicators of interfaces, leading to an increase of information on molecular specificity. The HMDS surface modification was clearly detected and spatially located. Finally, a chemometric approach was also adopted to evaluate depth profiling data. In particular, principal component analysis (PCA) and K-means algorithm were tested as innovative method for the identification of molecular fragments useful for the OTFT multi-layer structure characterization and the determination of the number of OTFT layers, respectively.