Organic field effect transistors based on multilayer films via Molecular Layer Epitaxy

A Self-Assembly oriented technique from the vapor-phase, Molecular Layer Epitaxy (MLE), was utilized for the buildup of organic multilayers as the active channel in organic field effect transistors (OFET). Carrier gas-assisted chemical vapor deposition (CVD) of 1,4,5,8-naphthalene-tetracarboxylic- dianhydride (NTCDA) and an aliphatic spacer are used in a pulsed mode for the covalent attachment of a single monolayer at a time resulting in an ordered dense multilayer film. The MLE approach uses a template layer to promote coupling between the substrate and the precursors deposited from the vapor phase. Interlayer epitaxy is governed by self-limiting vapor-phase condensation reactions while intra-layer ordering is achieved via horizontal π-stacking. Resulting multilayers were characterized by means of contact angle, variable angle spectroscopic ellipsometry (VASE), AFM, absorbance in the UV-vis.-NIR and FTIR. Multilayer structures are also built on a silicon substrate with predefined gold electrodes, using a self assembled template layer on the electrodes and on the thin gate oxide, thus allowing for the buildup of a multilayer structure covering both the electrodes and the channel area while enhancing the nature of the contact between the multilayer and the source and drain electrodes. Resulting OFET devices show n-type conductivity with a mobility of 0.031 cm² V^-1 s^-1 for a 6mn thickness MLE film, thus justifying the utilization of the technique in OFETs research and applications.