Dielectric films with nanometer thickness play a central role in the performances of field effect transistors (FETs). In this article, a new class of organic gate dielectric based on the electrochemical grafting of diazonium salts on metallic electrodes is investigated. The versatile diazonium salt strategy is a local and room-temperature process that provides robustness and performances. Moreover, this process produces ultrathin (4-8 nm) and smooth films. To prove their efficiency as gate dielectric, they were integrated in MoS2-FETs gate stacks. The devices display excellent switching behavior for reduced gate bias swing (down to 1V) and suppressed hysteresis thank to the highly hydrophobic nature of the fluorinated grafted film. Furthermore, the devices exhibit steep subthreshold slopes (as low as 110 mV/decade), demonstrating excellent gate coupling.
 Electrografted Fluorinated Organic Ultrathin Film as Efficient Gate Dielectric in MoS2 Transistors
H. Casademont, L. Fillaud, X. Lefevre, B. Jousselme, V. Derycke, J. Phys. Chem. C (2016), in press - link
Fig: (left) SEM image of an exfoliated MoS2 flake bridging on top of a gold electrode grafted with a very thin and hydrophobic organic film, (right) transfer and output characteristics. VLG correspond to the bias applied on the local gate (grafted) electrode. VGG is the back-gate bias used to n-doped the access areas near the source and drain contacts.
We are presently extending this study to CVD-based monolayer MoS2 and to flexible devices.