High permittivity dielectrics for poly(3-alkylthiophene) field-effect transistor devices

In an attempt to disentangle the effects of permittivity and surface energy of the gate insulator (expressed by its dielectric constant k and water contact angle, respectively) on the performance of organic field-effect transistors (FETs), we fabricated top- and bottom-gate FET architectures with poly(3-alkylthiophenes) (P3ATs) of different side-chain lengths, using a range of gate dielectrics. We find that this class of semiconductor, including the short butyl-(C4–) substituted derivative, is significantly less susceptible to the often detrimental effects that high-k dielectrics can have on the performance of many organic FETs. For bottom gate devices we identify the surface energy of the gate dielectric to predominantly dictate the device mobility.

(a) Transfer characteristics of poly(3-hexylthiophene) (P3HT) devices fabricated with three different gate insulators: Si3N4, SiO2 and HMDS-treated SiO2 (respectively, dotted, dashed and solid line), (b and c) saturated mobility deduced for P3BT, P3HT and P3DDT bottom-gate bottom-contact devices plotted against (b) the dielectric constant of the three insulators used to fabricate such bottom-gate FETs and (c) their water contact angle.Figure optionsDownload as PowerPoint slideHighlights
► High permittivity insensitivity for semiconducting polymers with short alkyl side chains.
► Consistent dependence of mobility on dielectric surface energy despite different dielectric constant dielectrics.
► Utilization of high permittivity dielectrics for increased charge density.