Premium
Influence of Thiol Self‐Assembled Monolayer Processing on Bottom‐Contact Thin‐Film Transistors Based on n‐Type Organic Semiconductors
Author(s) -
Youn Jangdae,
Dholakia Geetha R.,
Huang Hui,
Hennek Jonnathan W.,
Facchetti Antonio,
Marks Tobin J.
Publication year - 2012
Publication title -
advanced functional materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 6.069
H-Index - 322
eISSN - 1616-3028
pISSN - 1616-301X
DOI - 10.1002/adfm.201102312
Subject(s) - materials science , thin film transistor , monolayer , contact resistance , semiconductor , nanotechnology , contact angle , organic semiconductor , optoelectronics , scanning tunneling microscope , transistor , thin film , layer (electronics) , composite material , electrical engineering , engineering , voltage
The performance of bottom‐contact thin‐film transistor (TFT) structures lags behind that of top‐contact structures owing to the far greater contact resistance. The major sources of the contact resistance in bottom‐contact TFTs are believed to reflect a combination of non‐optimal semiconductor growth morphology on the metallic contact surface and the limited available charge injection area versus top‐contact geometries. As a part of an effort to understand the sources of high charge injection barriers in n‐channel TFTs, the influence of thiol metal contact treatment on the molecular‐level structures of such interfaces is investigated using hexamethyldisilazane (HMDS)‐treated SiO 2 gate dielectrics. The focus is on the self‐assembled monolayer (SAM) contact surface treatment methods for bottom‐contact TFTs based on two archetypical n‐type semiconductors, α,ω‐diperfluorohexylquarterthiophene (DFH‐4T) and N , N ′bis(n‐octyl)‐dicyanoperylene‐3,4:9,10‐bis(dicarboximide) (PDI‐8CN 2 ). TFT performance can be greatly enhanced, to the level of the top contact device performance in terms of mobility, on/off ratio, and contact resistance. To analyze the molecular‐level film structural changes arising from the contact surface treatment, surface morphologies are characterized by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). The high‐resolution STM images show that the growth orientation of the semiconductor molecules at the gold/SAM/semiconductor interface preserves the molecular long axis orientation along the substrate normal. As a result, the film microstructure is well‐organized for charge transport in the interfacial region.