tesi R. Miscioscia.pdf - EleA@UniSA

50 State of the Art
o Self-assembled monolayers (SAM)
o Multilayers (SAMT)
• Hybrid materials
2.5.1 Surface treatments on SiO2 and other relevant
dielectrics
SiO2 is traditionally one of the most widely used gate
insulators in VLSI electronics and it has particularly important in the
category of inorganic dielectrics. It has been also used in the world of
OE (Organic Electronics) for the realization of bottom-gate
topologies with gate of monocrystalline silicon normally used as
benchmark gate in the study of single channel materials.
However, this oxide, in particular when grown by thermal
oxidation (high thermal budget) from a slice of crystalline silicon,
cannot be a relevant player for the in OE applications because of its
obvious processing limitations. Furthermore, there are many organic
materials that exhibit dielectric constant higher than 3.9 (εr of SiO2)
and lower dielectric losses which encourages the application of
polymeric materials in the fabrication of gate dielectric layers.
Nevertheless, there are contributions in literature on the
interface between silicon oxide and the channel through appropriate
surface treatments [32] especially by HMDS (Hexamethyldisilazane),
OTS (Octadecyltrichlorosilane) and other Fluoroalkyltriclorosilanes
obtaining an improvement of the transport of charge.
This improvement is attributable to the fact that these
treatments cause a change in surface energy of the interface and force
a preferential orientation of the molecules in the channel.
As reported by prof. Kobayashi and Coworkers [33], it is
possible to increase several orders of magnitude both the mobility of
p-type transistors made by pentacene (C22H14) and mobility of n-type
fullerene-based OTFTs (C60) by silicon oxide interfaces treatment.
Those two kinds of semiconductors have been employed
because they represented the state of the art in performances and well
reproducible and studied results.