Poly(3-hexylthiophene) field-effect transistors with high dielectric constant gate insulator

Abstract

High dielectric constant $\text{(k=41)}$ titanium oxide $({\mathrm{TiO}}_2)$ was used as the gate insulator in field-effect transistors (FETs) with regioregular poly(3-hexylthiophene) (RR-P3HT) as the electronically active semiconductor. Good FET characteristics were obtained with saturation at low drive voltages (≈−2 V) and with carrier mobilities of ${\text{1.3×10}}^{\text{−2}}\hspace{0.17em}{\mathrm{cm}}^2/\mathrm{V s}.$ Deposition of a thin layer of ${\mathrm{SiO}}_2$ (thicknesses of 3 and 17 nm) on top of the ${\mathrm{TiO}}_2$ (97 nm) gate insulator resulted in a reduced effective dielectric constant ${\mathrm{(k}}_{\mathrm{eff}}\text{=31}$ for 3 nm of ${\mathrm{SiO}}_2$ and $k_{\mathrm{eff}}\text{=19}$ for 17 nm ${\mathrm{SiO}}_2\mathrm{),}$ but with significant improvement in the FET characteristics; the field-effect mobility increased to ${\text{5.4×10}}^{\text{−2}}\hspace{0.17em}{\mathrm{cm}}^2/\mathrm{V s},$ the on/off ratio increased from ${10}^2$ to ${\text{6×10}}^4,$ and the leakage current decreased by a factor of approximately ${10}^2.$ The importance of the thin ${\mathrm{SiO}}_2$ layer was confirmed using aluminum oxide $({\mathrm{Al}}_2{\mathrm{O}}_3)$ $\text{(k=8.4)}$ as the gate insulator in RR-P3HT FETs.