Styrenic polymers as gate dielectrics for pentacene field-effect transistors

Abstract

The effect of the chemical structure of the dielectric layer in organic thin-film transistors was examined by evaporating pentacene onto five different styrenic polymer dielectrics: poly(styrene), poly(4-hydroxystyrene), poly(4-methylstyrene), poly(4-vinylpyridine), and poly(2-vinylnaphthalene). We find that the polymer has a significant effect, with measured field-effect mobilities ranging from between 0.1 and 1cm2∕Vs. This variation appears uncorrelated with either the polymer suface morphology or the observed pentacene crystallite size. The distribution of mobility, threshold voltage, on/off ratio, and subthreshold swing observed for each of the polymer dielectrics is presented.

Thin Film Growth of Pentacene on Polymeric Dielectrics: Unexpected Changes in the Evolution of Surface Morphology with Substrate

“…In Figure 13, we plot the rms roughness of the pentacene thin films (determined from AFM) vs the surface energy of the underlying substrate for all three E i investigated. These results represent those considered above in Figures 4,7,9,and 11, and the nominal thin film thickness in all cases was ∼9 ML (all within 8.63−9.69 ML). Here, for SiO 2 , we make use of the average value reported for the surface energy from two studies, 31,32 and the value for PEI is a minimum.…”

“…We also show as individual points the values for the rms surface roughness found from AFM. As may be seen, there is good agreement between the final roughness predicted by the model and that measured directly by AFM (in all cases the deviation is <6%), as discussed in connection with Figures 4,7,9,and 11. We also note that a plot of these data for E i = 4.7 or 7.0 eV looks very similar (discounting the result on PMMA at E i = 7.0 eV).…”

“…In one study a systematic variation of the chemical structure of styrenic polymers did not reveal any clear correlations between thin film structure and electrical properties, even for cases where the electrical mobility varied by nearly an order of magnitude. 11 In other work, 12,13 however, investigating a similar set of styrenic polymers, but also poly(methylmethacrylate) (PMMA) 12 and polyvinyl alcohol (PVA), 13 a connection between thin film morphology ("grain size") and electrical mobility was reported, where there apparently exists a minimum grain size to achieve superior electronic properties. In this work, perhaps the most compelling identification was the importance of mobility of the polymeric chains at the dielectric surface, as gauged by the glass transition temperature.…”

Field effect in epitaxial graphene on a silicon carbide substrate

“…Polystyrene was chosen because it is non-polar and therefore does not cause hysteresis in currentvoltage measurements, ensuring accurate field effect mobility extraction. 12,13,15 Although the field effect mobility achieved here is among the highest so far reported in epitaxial graphene, 16 it is more than one order of magnitude lower than measured in exfoliated graphene. This discrepancy is tentatively attributed to the rough morphology of the graphene layer, rather than being intrinsic to epitaxial graphene, since high Hall mobility has been measured by others in small patterned features of epitaxial graphene, although at cryogenic temperatures.…”

Pentacene Nanostructures on Surface‐Hydrophobicity‐Controlled Polymer/SiO2 Bilayer Gate‐Dielectrics

“…[10,16] The dielectric surface has also been tuned by depositing a secondary polymer film onto a primary inorganic gate dielectric, because a polymeric dielectric by itself requires a very thick layer to achieve low gate leakage. [17] In contrast to SAM-treated SiO 2 dielectrics, one key advantage of polymer-coated gate dielectrics is that polymeric film deposition is not limited by SAM-inorganic coupling, which determines surface epitaxy and the coverage of SAMs. [18] Accordingly, many investigations have focused on simply processible bilayer dielectric strategies to enhance field-effect mobility, [19][20][21][22] yet the effect of both SAM-treated and polymer-coated dielectric surface properties on crystalline nanostructures and device performance of thermally evaporated semiconductors is seldom discussed.…”