Interface formation and thin film deposition for molecular and organic electronics

Organic materials are playing an increasing role in modern microelectronic devices-beyond their traditional role as photoresists. Emerging applications such as low-? dielectrics, semiconductors and components in molecular electronics demand excellent control of the interface between organic and inorganic materials. To date, almost all work concerning the formation of inorganic-on-organic structures on pre-existing organic layers has involved elemental evaporation of metal thin films. An alternative approach has been examined via the reaction of an organo-transition metal complex, tetrakis(dimethylamido)titanium, Ti[N(CH3)2]4, with self-assembled monolayers (SAMs) terminated by -OH, -NH2 and -CH3 groups, using X-ray photoelectron spectroscopy (XPS). This is the first detailed study which clearly correlates the reactivity of Ti[N(CH3)2]4 with the functionality and density of molecules in a self-assembled monolayer. Extent of reaction, stoichiometry at the interface, ligand loss and decomposition have also been investigated in this study. A second area of research has involved the formation of organic-on-inorganic structures. Supersonic molecular beams have been employed as sources for deposition of thin films of pentacene, an organic semiconductor, on bare SiO2 and SiO2 modified with hexamethyldisilazane (HMDS). Organic materials are often bound by rather weak dispersion (van der Waals) forces and crystallize in different phases, separated in total energy by a few kBT. Consequently, considerable promise exists in the use of these energy tunable molecular beams for the deposition of organic thin films. Experiments have provided significant insight into fundamental phenomena involved in nucleation in the monolayer regime, and both the kinetics of thin film deposition and the microstructure in the multilayer regime, evidenced by results from ellipsometry and atomic force microscopy (AFM). Promising performance characteristics have been obtained for organic thin film transistors (OTFTs) fabricated from these pentacene films which can be correlated to film microstructure. Finally, modification of the dielectric surface with hexamethyldisilazane (HMDS) has been found to strongly influence nucleation and greatly enhance OTFT performance, possibly due to reduced charge trapping at the semiconductor-dielectric interface.This work was supported by the Cornell Center for Materials Research (CCMR), a Materials Research Science and Engineering Center of the National Science Foundation (DMR-0079992). Additional support was also provided by a Nanoscale Interdisciplinary Research Team on Inorganic-Organic Interfaces (NSF-ECS-0210693) and the Semiconductor Research Corporation via the Center for Advanced Interconnect Systems Technologies (SRC task 995.011)