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Pentacene organic thin-film transistors (OTFTs) using high-k Nd x Nb (1Àx) O gate dielectric with different Nb contents (x ¼ 1, 0.950, 0.908, and 0.877) are fabricated. The best OTFT has x ¼ 0.950, achieving a high carrier mobility of 1.95 cm 2 V À1 s À1 , small threshold voltage of À1.57 V, small sub-threshold swing of 0.13 V dec À1 , and small hysteresis of 0.13 V. Atomic force microscopy and X-ray photoelectron spectroscopy measurements reveal that the Nb doping can suppress the hygroscopicity of Nd oxide to produce a smoother dielectric surface, on which larger pentacene grains are grown to result in higher carrier mobility. The hysteresis of the OTFTs is attributed to donor-like traps associated with the hydroxide formed in Nd 2 O 3 after absorbing moisture and also acceptor-like traps (in the form of oxygen vacancies) induced by Nb incorporation.

When processed at a low temperature of 200 °C, organic thin-film transistors (OTFTs) with pentacene channel adopting high-k Neodymium-Titanium oxynitride mixtures (NdTiON) with various Ti contents as gate dielectrics are fabricated. The Ti content in the NdTiON is varied by co-sputtering a Ti target at 0 W, 10 W, 20 W and 30 W, respectively, while fixing the sputtering power of an Nd target at 45 W. High-performance OTFT is obtained for the 20 W-sputtered Ti, including a small threshold voltage of −0.71 V and high carrier mobility of 1.70 cm2/V·s. The mobility improvement for the optimal Ti content can be attributed to smoother dielectric surface and resultant larger overlying pentacene grains as reflected by Atomic Force Microscopy measurements. Moreover, this sample with the optimal Ti content shows much higher mobility than its counterpart processed at a higher temperature of 400 °C (0.8 cm2/V·s) because it has a thinner gate-dielectric/gate-electrode interlayer for stronger screening on the remote phonon scattering by the gate electrode. In addition, a high dielectric constant of around 10 is obtained for the NdTiON gate dielectric that contributes to a threshold voltage smaller than 1 V for the pentacene OTFT, implying the high potential of the Nd-Ti oxynitride in future high-performance organic devices.

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