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

Abstract

Pentacene organic TFTs (OTFTs) using high-k Nd 2 O 3 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 Nd 2 O 3 gate dielectric shows an obvious improvement in carrier mobility compared with its counterpart with pure Nd 2 O 3 as gate dielectric. Moreover, for the lower temperature of 200 °C, the OTFT with both niobium and nitrogen dopings in the Nd 2 O 3 gate dielectric achieves further improvement with a small threshold voltage of −0.79 V and a high carrier mobility of 2.24 cm 2 /V·s. AFM and XPS reveal that the nitrogen doping, like the niobium doping, can reduce the hygroscopicity of Nd 2 O 3 , 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. •For pentacene OTFTs, Nb incorporation in Nd oxide as gate dielectric can reduce its hygroscopicity, leading to a smoother dielectric surface, larger pentacene grains, fewer interface traps and resultant improved performance. •Furthermore with N inclusion in NdNbO, high-performance OTFT can be achieved by using lower-temperature oxide annealing. •Besides passivation effect of nitrogen to further reduce hygroscopicity and oxygen vacancies, results show that nitrogen helps suppress formation of the dielectric/Si-gate interlayer, thus enhancing gate screening effect on the remote phonon scattering to improve carrier mobility.