High performance organic field-effect transistors using high-Κ dielectrics grown by atomic layer deposition (ALD)

We report on high performance field-effect transistors fabricated with pentacene as an active material and Al₂O₃ as a gate dielectric material grown by atomic layer deposition (ALD). These transistors were operated in enhancement mode with a zero turn-on voltage and exhibited a low threshold voltage (< -10 V) as well as a low subthreshold slope (< 1 V/decade) and an on/off current ratio larger than 10⁶. Hole mobility values of 1.5 ± 0.2 cm²/Vs were obtained when using heavily n-doped silicon (n⁺-Si) as gate electrodes and substrates. Atomic force microscopy (AFM) images of pentacene films on Al₂O₃ treated with octadecyltrichlorosilane (OTS) revealed well-ordered island formation, and X-ray diffraction patterns showed characteristics of a "thin film" phase. Compared with thermally-grown SiO₂, Al₂O₃ gate insulators have lower surface trap density and higher capacitance density, to which the high performance of pentacene field-effect transistors can be attributed.