High‐dielectric‐constant hafnium silicate insulator for low‐voltage pentacene field‐effect transistors

We prepared HfSiO x on a heavily doped n‐type silicon wafer by sputtering of a HfSi (50:50 at%) target using Ar:N 2 :O 2 as carrier gas. The HfSiO x layer thus prepared was characterized by XPS, XRD, STEM and C – F measurements, indicating that the layer mainly consisted of 100 nm thick amorphous HfSiO 5 with a dielectric constant ϵ r = 7.7. The leakage current density was 1 nA/cm 2 at an electric field of 2 MV/cm. We first fabricated top‐contact pentacene FETs using the high dielectric constant hafnium silicate as an insulator, coupled with a polymer microfiber‐based channel patterning technique. The pentacene FET showed well‐saturated output characteristics at low driving voltages, i.e. V D = –10 V and V G = –10 V, and hole mobility of 0.02 cm 2 /V s and on/off current ratio of 2600. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)