Morphological and eletrical studies of new bi-functional SAM molecules for realization of organic floating gate memories

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Floating gate memories are standard architectures to generate low-power consuming, non-volatile memories (NVM) on the base of mono crystalline silicon layer (layer thickness 7-10 nm) [1]. In 2007 these electronic devices have accessed the mass market with 13.9 Bill. US$. In the final quart of 2009 there will be 60% of Laptops equipped with this shock resistant and power-saving technology (iSupply), demonstrating the huge success of this technical approach. Simple concepts of organic non-volatile memories (NVM) are of enormous interest due to their potential application in low-cost flexible electronics, e.g. to individualize radio frequency identification tags (RFID-tags) or to program variable information on smart cards. In these low-end applications the memory technology is not driven by high storage densities rather than simple processing, robust functionality and high reliability. Thus, the goal of new organic NVMs is not in competition to the well established high storage density NVMs based on silicon platforms, but to capture new application fields due to their basic attribute, to be placed on flexible substrates like plastics or paper [2], [3], [4], [5]. The goal of this project is the realization and investigation of electrically programmable molecular gate dielectric layer for organic thin film transistors (OTFTs), which can be reversibly charged and discharged and remain these digital states even the electrical field is removed. The dielectric systems are created from a mixed monolayer of special molecules on a patterned and activated A!-gate approaching and simplifying the classical memory multi-layer stack as known from silicon technology (barrier oxide - floated gate - tunnel oxide) on a molecular level by self-assembling organic molecules. Design, synthesis and self-assembling of bi-functional molecules, which are able to reversible charge storage and thereby controlling the transistor threshold voltage (thus the drain current at a given voltage) will offer a new approach in low-power molecular scale electronics with new functionality. The electrical properties of self-assembled monolayers (SAMs) based on these new molecules will be investigated in capacitors and low-voltage transistors at air and ambient conditions (threshold voltage, hysteresis, leakage current). SAMs based on these bi-functional molecules as well as mixed SAMs (bi- and mon-functional molecules) are of interest. Furthermore, floating gate devices are investigated due to their reversibility functionality, retention time, switching voltage and switching speed. Temperature dependent investigations on the stability of charges should provide information according to charging mechanisms and deletion processes (Fowler-Nordheim tunnelling, hot carrier injection). A new technique will be introduced to investigate the surface of high isolating layers at nano scale resolution (by detection of hydrophobic/hydrophilic areas). AFM measurements in aqueous environment can reveal the ordering of SAM layers concerning formation of domains and substructures and furthermore of phase behaviour of mixed SAM layers (phase separation, mixtures). This morphological characterisation method closes the gap between molecular modelling, molecule synthesis and the electrical performance of molecular electronics and is an essential method to correlate electrical properties to morphological SAM properties. Furthermore a basic understanding In SAM formation is expected - in particular on surfaces of relevance!