Improved carrier mobility of pentacene organic TFTs by suppressed oxide growth at remote interface using nitrogen doping in high-k NdNbO dielectric

Pentacene organic TFTs (OTFTs) using high-k Nd₂O₃ doped with niobium and/or nitrogen as gate dielectric have been fabricated with gate-dielectric annealing at 200 °C and 400 °C. For 400 °C, the OTFT with only niobium doping in the Nd₂O₃ gate dielectric shows an obvious improvement in carrier mobility compared with its counterpart with pure Nd₂O₃ as gate dielectric. Moreover, for the lower temperature of 200 °C, the OTFT with both niobium and nitrogen dopings in the Nd₂O₃ gate dielectric achieves further improvement with a small threshold voltage of −0.79 V and a high carrier mobility of 2.24 cm²/V·s. AFM and XPS reveal that the nitrogen doping, like the niobium doping, can reduce the hygroscopicity of Nd₂O₃, leading to a smoother surface of dielectric and thus larger overlying pentacene grains for reducing the scatterings of surface roughness and grain boundary respectively. Besides, highest mobility is achieved for the NdNbON gate dielectric without the best film quality because with nitrogen doping and lower-temperature annealing, a thinner interlayer between the gate dielectric and the Si gate is formed to enhance the electrostatic coupling between them, thus suppressing the phonon scattering on channel carriers caused by the thermal oscillation of the atoms inside the gate dielectric.